GTR-181 Table of Contents

William F. Laudenslayer, Jr., Patrick J. Shea,

Bradley E. Valentine, C. Phillip Weatherspoon,

and Thomas E. Lisle Technical Coordinators

Contents 

Table of Contents 156 K

Preface and Acknowledgements 136 K

Publication Information 264 K

Importance of Dead and Downed Wood

Dead Wood: From Forester's Bane to Environmental Boon 172 K

Jack Ward Thomas

Decaying Wood: An Overview of Its Status and Ecology in the 

United Kingdom and Continental Europe 172 K

Jill Butler, Keith Alexander, and Ted Green

Importance to Aquatic Systems

Dead Dynamics in Stream Ecosystems 3.7 MB

Robert J. Naiman, Estelle V. Ballan, Krista K. Bartz, 

Robert E. Bilby, and Joshua J. Latterell

Effects of Wildfire on In-Channel Woody Debris in the Eastern 

Sierra Nevada, California 2.4 MB< BR> 

Neil H. Berg, David Azuma, and Ann Carlson

Influence of Bank Afforestation and Snag Angle -of-fall on 

Riparian Large Woody Debris Recruitment 152 K

Don C. Bragg and Jeffrey L. Kershner

Modeling the Delivery of Large Wood to Streams with Light 

Detection and Ranging (LIDAR) Data 512 K 

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GTR-181 Table of Contents

William Cody Fleece

How Much Dead Wood in Stream Channels is Enough? 444 K

Thomas E. Lisle

Importance to Invertebrates

An Investigation of the Insect Fauna Associated with Coarse 

Woody Debris of Pinus ponderosa and Abies concolor in 

Northeastern California 228 K

Ethan Koenigs, Patrick J. Shea, Robert Borys, and 

Michael L. Haverty

A Preliminary Study of Ant Diversity and of Ant Dependence on 

Dead Wood in Central Interior British Columbia 192 K

B. Staffan Lindgren and A. M. MacIsaac

Effects of Ecosystem Restoration Treatments on Cavity-nesting 

Birds, Their Habitat, and Their Insectivorous Prey in Firemaintained -Forests of Southeastern British Columbia 228 K

Marlene Machmer

The Role of Coarse Woody Debris in Southeastern Pine Forests: 

Preliminary Results from a Large-scale Experiment 220 K

Timothy S. McCay, James L. Hanula, Susan C. Loeb, 

Steven M. Lohr, James W. McMinn, and Brett D. WrightMiley

Girdled versus Bark Beetle-created Ponderosa Pine Snags: 

Utilization by Cavity-dependent Species and Differences in 

Decay Rate and Insect Diversity 180 K

Patrick J. Shea, William F. Laudenslayer, Jr., George 

Ferrell, and Robert Borys

The Role of Disturbance in Creating Dead Wood: Insect 

Defoliation and Tree Mortality in Northeastern Oregon 324 K

Andrew Youngblood and Boyd E. Wickman

Importance to Vertebrates

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GTR-181 Table of Contents

The Value of Coarse Woody Debris to Vertebrates in the Pacific 

Northwest 168 K

Evelyn L. Bull

Are There Snags in the System? Comparing Cavity Use among 

Nesting Birds in "Snag-rich" and "Snag-poor" Eastside Pine 

Forests 216 K

Steve Zack, T. Luke George, and William F. 

Laudenslayer, Jr.

Distribution Patterns of Birds Associated with Snags in Natural 

and Managed Eastern Boreal Forests 252 K

Pierre Drapeau, Antoine Nappi, Jean François Giroux, 

Alain Leduc, and Jean-Pierre Savard

Habitat Preferences of Primary Cavity Excavators in 

Washington's East Cascades 984 K

Kenneth R. Bevis and Sandra K. Martin

Cavity-nesting Bird Use of Snags in Eastside Pine Forests of 

Northeastern California 228 K

William F. Laudenslayer, Jr.

Woodpecker Foraging and the Successional Decay of Ponderosa 

Pine 252 K

Kerry L. Farris, Edward O. Garton, Patricia J. Heglund, 

Steve Zack, and Patrick J. Shea

Forest Age and Relative Abundance of Pileated Woodpeckers on 

Southeastern Vancouver Island 232 K

Carol L. Hartwig, Donald S. Eastman, and Alton S. 

Harestad

The Pileated Woodpecker as a Keystone Habitat Modifier in the 

Pacific Northwest 260 K

Keith B. Aubry and Catherine M. Raley

Characteristics and Dynamics of Cavity Nest Trees in Southern 

British Columbia 228 K

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GTR-181 Table of Contents

Christoph Steeger and Jakob A. Dulisse

How Dead Trees Sustain Live Organisms in Western Forests 324 

K

Fred L. Bunnell, Isabelle Houde, Barb Johnston, and Elke 

Wind

Summer and Fall Use of Logging Residue Piles by Female Shorttailed Weasels 260 K

Kimberly A. Lisgo, Fred L. Bunnell, and Alton S. 

Harestad

Dead Wood and the Richness of Small Terrestrial Vertebrates in 

Southwestern Oregon 248 K

Chris C. Maguire

Stag Retention and Use by Arboreal Marsupials in Eucalypt 

Forests in Southeast Queensland, Australia: Implications for 

Management 196 K

Damien Moloney, Kevin Wormington, and Stephen 

DeStefano

Importance to Soils and Other Forest 

Resources

Fire as a Coarse Filter for Snags and Logs 508 K

James K. Agee

Assemblages of Vascular Plants on Logs and Stumps within 28-

year-old Aspen-dominated Boreal Forests 300 K

Philip Lee and Kelly Sturgess

The Nutritional Significance of Coarse Woody Debris in Three 

Rocky Mountain Coniferous Forests 272 K

Cindy E. Prescott and Raija Laiho

The Effects of Microsite (Logs versus Ground Surface) on the 

Presence of Forest Floor Biota in a Second-growth Hardwood 

Forest 188 K

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GTR-181 Table of Contents

Charlotte Pyle and Michelle M. Brown

Demographics and Dynamics of Dead 

Wood

Overview of Agents and Patterns of Mortality and Resulting 

Coarse Woody Debris Recruitment in Western Forests 620 K

Brytten E. Steed and Michael R. Wagner 

Comparing Deterioration and Ecosystem Function of Decayresistant and Decay-susceptible Species of Dead Trees 744 K

Paul E. Hennon, Michael H. McClellan, and Patricia 

Palkovic

Influence of Fire on the Dynamics of Dead Woody Material in 

Forests of California and Southwestern Oregon 224 K

Carl N. Skinner

Demographics and Dynamics in Coastal 

Mesic Forests

Simulation of Stream Wood Source Distance for Small Streams 

in the Western Cascades, Oregon 244 K

Mark A. Meleason, Stanley V. Gregory, and John Bolte

Standing Dead Tree Dynamics Extracted from Growth and Yield 

Permanent Sample Plots in British Columbia 200 K

Jeff Stone, John Parminter, and Joe Braz

Dead Wood and Fire Relationships in Southwestern Oregon 

Western Hemlock Forests 168 K

Diane E. White, Thomas Atzet, Patricia A. Martinez, and 

Lisa A. McCrimmon

The Number and Composition of Snags in the Pine-Spruce 

Stands of the Bialowieza National Park, Poland 160 K

Wieslaw Walankiewicz

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Demographics and Dynamics in the 

Cascades Forests

A Coarse Wood Dynamics Model for the Western Cascades 244 

K

Kim Mellen and Alan Ager

Snag Recruitment in Subalpine Forests of the North Cascades, 

Washington State 176 K

Paul T. Flanagan, Penelope Morgan, and Richard L. 

Everett

DecAID: A Decaying Wood Advisory Model for Oregon and 

Washington 272 K

Kim Mellen, Bruce G. Marcot, Janet L. Ohmann, Karen L. 

Waddell, Elizabeth A. Willhite, Bruce B. Hostetler, Susan 

A. Livingston, and Cay Ogden

Regional Patterns of Dead Wood in Forested Habitats of Oregon 

and Washington 996 K

Janet L. Ohmann and Karen L. Waddell

The DecAID Advisory Model: Wildlife Component 1.4 MB

Bruce G. Marcot, Kim Mellen, Susan A. Livingston, and 

Cay Ogden

Demographics and Dynamics in Sierra 

Nevada Forests

Dead Branches and Other Wildlife Resources on California 

Black Oak (Quercus kelloggii) 296 K

Barrett A. Garrison, Robin L. Wachs, Terry A. Giles, and 

Matthew L. Triggs

Demography of Snags in Eastside Pine Forests of California 228 

K

F. Michael Landram, William F. Laudenslayer, Jr., 

Thomas Atzet

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GTR-181 Table of Contents

Assessing the Effect of Fire Regime on Coarse Woody 

Debris 248 K

Pamela Wright, Mark Harmon, and Fred Swanson

Demographics and Dynamics in Rocky 

Mountain Forests

Mortality as a Source of Coarse Woody Debris in Managed 

Stands 2.3 MB

Carl E. Fie dler and Todd A. Morgan

Snags and Down Wood in the Interior Columbia Basin 

Ecosystem Management Project 316 K

Jerome J. Korol, Miles A. Hemstrom, Wendel J. Hann, 

and Rebecca A. Gravenmier

Assessment of the Line Transect Method: An Examination of the 

Spatial Patterns of Down and Standing Dead Wood 284 K

Duncan C. Lutes

Management of Dead Wood

Forest Management and the Dead Wood Resource in Ponderosa 

Pine Forests: Effects on Small Mammal 256 K

Carol L. Chambers

Dying and Dead Hardwoods: Their Implications to 

Management 4.5 MB

Fred L. Bunnell, Elke Wind, and Ralph Wells

Diameters and Heights of Trees with Cavities: Their Implications 

to Management 1.6 MB

Fred L. Bunnell, Elke Wind, Mark Boyland, and Isabelle 

Houde

How Should We Spatially Distribute Dying and Dead 

Wood? 248 K

Fred L. Bunnell, Mark Boyland, and Elke Wind

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GTR-181 Table of Contents

Evaluating the Effects of Partial Cutting on Wildlife Trees and 

Coarse Woody Debris 332 K

Susan K. Stevenson and Dagmar G. Keisker

Created Snag Monitoring on the Willamette National Forest 204 

K

Pat Boleyn, Eric Wold, and Ken Byford

The Efficacy of Inoculating Fungi into Conifer Trees to Promote 

Cavity Excavation by Woodpeckers in Managed Forests in 

Western Washington 416 K

Martin J. Huss, James C. Bednarz, David M. Juliano, and 

Daniel E. Varland

Characteristics of Log Resources in Northeastern Oregon: Case 

Studies of Four Management Treatments 228 K

Torolf R. Torgerse

Samping Methods for Snags and Large Trees Important to 

Wildlife 124 K

Lisa J. Bate, Edward O. Garton, and Michael J. Wisdom

Accuracy and Efficiency of Methods to Sample Logs for Wildlife 

Research and Management 156 K

Lisa J. Bate, Torolf R. Torgersen, Edward O. Garton, and 

Michael J. Wisdom

Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife 

Habitat Components: Preliminary Results and a Method for 

Monitoring 252 K

Tammy Randall-Parker and Richard Miller

Selection of Fire-created Snags at Two Spatial Scales by Cavitynesting Birds 288 K

Victoria Saab, Ree Brannon, Jonathan Dudley, Larry 

Donohoo, Dave Vanderzanden, Vicky Johnson, and Henry 

Lachowski

Dead Tree Management in British Columbia 196 K

Jeff Stone, John Parminter, Andr ̃ Arsenault, Todd 

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GTR-181 Table of Contents

Manning, Nancy Densmore, Gerry Davis, and Andy 

MacKinnon

British Columbia's Dangerous Tree Assessment Process 384 K

Todd Manning, Peter Bradford, Cary White, David Rowe, 

Nancy Densmore, and Stewart Guy

Managing Coarse Woody Debris in British Columbia's Forests: A 

Cultural Shift for Professional Foresters? 168 K

André Arsenault

Water, Wildlife, Recreation, Timber... Coarse Woody 

Debris? 92 K

John R. Mount

Creating and Maintaining Wildlife, Insect, and Fish Habitat 

Structures in Dead Wood 188 K

Timothy K. Brown

Perspectives and Approaches to 

Management

An Ecological Functional Basis for Managing Dead Wood Decay 

Elements for Wildlife 792 K

Bruce G. Marco

A Case Study of Habitat Conservation Plans and the Protection 

of Snags and Coarse Woody Debris on Industrial Forest Lands 

 396 K

Lorin L. Hicks and Henning C. Stabins

Management of Dead Wood: Perspectives of a State Forestry 

Agency 140 K

Christopher P. Rowney

Moving Towards a New Paradigm for Woody Detritus 

Management 280 K

Mark E. Harmon

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Symposium Synthesis

Dead Wood Management Issues and Opportunities: Future 

Directions 96 K

Ann M. Bartuska

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Proceedings of the Symposium on the 

Ecology and Management of Dead Wood 

in Western Forests 

November 2-4, 1999 Reno, Nevada 

William F. Laudenslayer, Jr., Patrick J. Shea, Bradley E. 

Valentine, C. Phillip Weatherspoon, and Thomas E. Lisle 

Technical Coordinators 

Contents 

Preface and Acknowledgments .................................................ix 

Importance of Dead and Downed Wood....................................1 

Dead Wood: From Forester’s Bane to Environmental Boon...................3

Jack Ward Thomas 

Decaying Wood: An Overview of Its Status and Ecology 

in the United Kingdom and Continental Europe ..........................11 

Jill Butler, Keith Alexander, and Ted Green 

Importance to Aquatic Systems.................................................21 

Dead Wood Dynamics in Stream Ecosystems .......................................23 

Robert J. Naiman, Estelle V. Balian, Krista K. Bartz, 

Robert E. Bilby, and Joshua J. Latterell 

Effects of Wildfire on In-Channel Woody Debris in the 

Eastern Sierra Nevada, California...............................................49 

Neil H. Berg, David Azuma, and Ann Carlson 

Influence of Bank Afforestation and Snag Angle-of-fall 

on Riparian Large Woody Debris Recruitment............................65 

Don C. Bragg and Jeffrey L. Kershner 

Modeling the Delivery of Large Wood to Streams with 

Light Detection and Ranging (LIDAR) Data ................................71 

William Cody Fleece 

How Much Dead Wood in Stream Channels Is Enough? .......................85 

Thomas E. Lisle 

Pacific Southwest 

Research Station 

USDA Forest Service 

General Technical 

Report 

PSW-GTR-181 

August 2002
ii USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

Importance to Invertebrates....................................................... 95 

An Investigation of the Insect Fauna Associated with Coarse 

Woody Debris of Pinus ponderosa and Abies concolor 

in Northeastern California ........................................................... 97 

Ethan Koenigs, Patrick J. Shea, 

Robert Borys, and Michael I. Haverty 

A Preliminary Study of Ant Diversity and of Ant Dependence 

on Dead Wood in Central Interior British Columbia .................... 111 

B. Staffan Lindgren and A. M. MacIsaac 

Effects of Ecosystem Restoration Treatments on Cavity-nesting Birds, 

Their Habitat, and Their Insectivorous Prey in Fire-maintained 

Forests of Southeastern British Columbia .................................. 121 

Marlene Machmer 

The Role of Coarse Woody Debris in Southeastern Pine Forests: 

Preliminary Results from a Large-scale Experiment................... 135 

Timothy S. McCay, James L. Hanula, Susan C. Loeb, 

Steven M. Lohr, James W. McMinn, and Brett D. Wright-Miley 

Girdled versus Bark Beetle-created Ponderosa Pine Snags: 

Utilization by Cavity-dependent Species and Differences 

in Decay Rate and Insect Diversity ............................................. 145 

Patrick J. Shea, William F. Laudenslayer, Jr., 

George Ferrell, and Robert Borys

The Role of Disturbance in Creating Dead Wood: Insect Defoliation 

and Tree Mortality in Northeastern Oregon ................................ 155 

Andrew Youngblood and Boyd E. Wickman 

Importance to Vertebrates ......................................................... 169 

The Value of Coarse Woody Debris to Vertebrates in the 

Pacific Northwest ........................................................................ 171 

Evelyn L. Bull 

Are There Snags in the System? Comparing Cavity Use 

among Nesting Birds in “Snag-rich” and “Snag-poor” 

Eastside Pine Forests................................................................. 179 

Steve Zack, T. Luke George, and William F. Laudenslayer, Jr. 

Distribution Patterns of Birds Associated with Snags in 

Natural and Managed Eastern Boreal Forests............................ 193 

Pierre Drapeau, Antoine Nappi, Jean François Giroux, 

Alain Leduc, and Jean-Pierre Savard 

Habitat Preferences of Primary Cavity Excavators 

 in Washington’s East Cascades ................................................. 207 

Kenneth R. Bevis and Sandra K. Martin 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. iii 

Cavity-nesting Bird Use of Snags in Eastside Pine Forests 

of Northeastern California ...........................................................223 

William F. Laudenslayer, Jr. 

Woodpecker Foraging and the Successional Decay of 

Ponderosa Pine...........................................................................237 

Kerry L. Farris, Edward O. Garton, Patricia J. Heglund, 

Steve Zack, and Patrick J. Shea 

Forest Age and Relative Abundance of Pileated Woodpeckers 

on Southeastern Vancouver Island .............................................247 

Carol L. Hartwig, Donald S. Eastman, and Alton S. Harestad 

The Pileated Woodpecker as a Keystone Habitat Modifier 

in the Pacific Northwest...............................................................257 

Keith B. Aubry and Catherine M. Raley 

Characteristics and Dynamics of Cavity Nest Trees in 

Southern British Columbia ..........................................................275 

Christoph Steeger and Jakob A. Dulisse 

How Dead Trees Sustain Live Organisms in Western Forests...............291 

Fred L. Bunnell, Isabelle Houde, Barb Johnston, 

and Elke Wind 

Summer and Fall Use of Logging Residue Piles by Female 

Short-tailed Weasels ...................................................................319 

Kimberly A. Lisgo, Fred L. Bunnell, and Alton S. Harestad 

Dead Wood and the Richness of Small Terrestrial Vertebrates 

in Southwestern Oregon .............................................................331 

Chris C. Maguire 

Stag Retention and Use by Arboreal Marsupials in Eucalypt 

Forests in Southeast Queensland, Australia: Implications 

for Management ..........................................................................347 

Damien Moloney, Kevin Wormington, and Stephen DeStefano 

Importance to Soils and Other Forest Resources....................357 

Fire as a Coarse Filter for Snags and Logs ............................................359 

James K. Agee 

Assemblages of Vascular Plants on Logs and Stumps 

within 28-year-old Aspen-dominated Boreal Forests ..................369 

Philip Lee and Kelly Sturgess 

The Nutritional Significance of Coarse Woody Debris in 

Three Rocky Mountain Coniferous Forests.................................381 

Cindy E. Prescott and Raija Laiho 
iv USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

The Effects of Microsite (Logs versus Ground Surface) on the 

Presence of Forest Floor Biota in a Second-growth 

Hardwood Forest ........................................................................ 393 

Charlotte Pyle and Michelle M. Brown 

Demographics and Dynamics of Dead Wood........................... 405 

Overview of Agents and Patterns of Mortality and Resulting 

Coarse Woody Debris Recruitment in Western Forests ............. 407 

Brytten E. Steed and Michael R. Wagner 

Comparing Deterioration and Ecosystem Function of 

Decay-resistant and Decay-susceptible Species 

of Dead Trees ............................................................................. 435 

Paul E. Hennon, Michael H. McClellan, 

and Patricia Palkovic 

Influence of Fire on the Dynamics of Dead Woody Material 

in Forests of California and Southwestern Oregon ..................... 445 

Carl N. Skinner 

Demographics and Dynamics in Coastal Mesic Forests......... 455 

Simulation of Stream Wood Source Distance for Small Streams 

in the Western Cascades, Oregon.............................................. 457 

Mark A. Meleason, Stanley V. Gregory, and John Bolte 

Standing Dead Tree Dynamics Extracted from Growth and 

Yield Permanent Sample Plots in British Columbia .................... 467 

Jeff Stone, John Parminter, and Joe Braz 

Dead Wood and Fire Relationships in Southwestern Oregon 

Western Hemlock Forests........................................................... 479 

Diane E. White, Thomas Atzet, Patricia A. Martinez, 

and Lisa A. McCrimmon 

The Number and Composition of Snags in the Pine-Spruce 

Stands of the Bialowieza National Park, Poland......................... 489 

Wieslaw Walankiewicz 

Demographics and Dynamics in the Cascades Forests.......... 501 

A Coarse Wood Dynamics Model for the Western Cascades ................ 503 

Kim Mellen and Alan Ager 

Snag Recruitment in Subalpine Forests of the North Cascades, 

Washington State........................................................................ 517 

Paul T. Flanagan, Penelope Morgan, and Richard L. Everett 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. v 

DecAID: A Decaying Wood Advisory Model for Oregon 

and Washington ..........................................................................527 

Kim Mellen, Bruce G. Marcot, Janet L. Ohmann, 

Karen L. Waddell, Elizabeth A. Willhite, Bruce B. Hostetler, 

Susan A. Livingston, and Cay Ogden

Regional Patterns of Dead Wood in Forested Habitats of 

Oregon and Washington .............................................................535 

Janet L. Ohmann and Karen L. Waddell 

The DecAID Advisory Model: Wildlife Component..................................561 

Bruce G. Marcot, Kim Mellen, Susan A. Livingston, 

and Cay Ogden 

Demographics and Dynamics in Sierra Nevada Forests .........591 

Dead Branches and Other Wildlife Resources on California 

Black Oak (Quercus kelloggii).....................................................593 

Barrett A. Garrison, Robin L. Wachs, Terry A. Giles, 

and Matthew L. Triggs 

Demography of Snags in Eastside Pine Forests of California ................605 

F. Michael Landram, William F. Laudenslayer, Jr., 

Thomas Atzet 

Assessing the Effect of Fire Regime on Coarse Woody Debris..............621 

Pamela Wright, Mark Harmon, and Fred Swanson 

Demographics and Dynamics in Rocky Mountain Forests......635 

Mortality as a Source of Coarse Woody Debris in 

 Managed Stands.........................................................................637 

Carl E. Fiedler and Todd A. Morgan 

Snags and Down Wood in the Interior Columbia Basin 

Ecosystem Management Project ................................................649 

Jerome J. Korol, Miles A. Hemstrom, Wendel J. Hann, 

and Rebecca A. Gravenmier 

Assessment of the Line Transect Method: An Examination of the 

Spatial Patterns of Down and Standing Dead Wood ..................665 

Duncan C. Lutes 

Management of Dead Wood .......................................................677 

Forest Management and the Dead Wood Resource in Ponderosa 

 Pine Forests: Effects on Small Mammals ....................................679 

Carol L. Chambers 
vi USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

Dying and Dead Hardwoods: Their Implications to Management........... 695 

Fred L. Bunnell, Elke Wind, and Ralph Wells 

Diameters and Heights of Trees with Cavities: Their Implications 

to Management ........................................................................... 717 

Fred L. Bunnell, Elke Wind, Mark Boyland, 

and Isabelle Houde 

How Should We Spatially Distribute Dying and Dead Wood? ................ 739 

Fred L. Bunnell, Mark Boyland, and Elke Wind 

Evaluating the Effects of Partial Cutting on Wildlife Trees 

and Coarse Woody Debris.......................................................... 753 

Susan K. Stevenson and Dagmar G. Keisker 

Created Snag Monitoring on the Willamette National Forest.................. 765 

Pat Boleyn, Eric Wold, and Ken Byford 

The Efficacy of Inoculating Fungi into Conifer Trees to Promote 

Cavity Excavation by Woodpeckers in Managed Forests 

in Western Washington............................................................... 777 

Martin J. Huss, James C. Bednarz, David M. Juliano, 

and Daniel E. Varland 

Characteristics of Log Resources in Northeastern Oregon: 

Case Studies of Four Management Treatments ......................... 795 

Torolf R. Torgersen 

Samping Methods for Snags and Large Trees Important to Wildlife ...... 811 

Lisa J. Bate, Edward O. Garton, and Michael J. Wisdom 

Accuracy and Efficiency of Methods to Sample Logs for Wildlife 

Research and Management........................................................ 817 

Lisa J. Bate, Torolf R. Torgersen, Edward O. Garton, 

and Michael J. Wisdom 

Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife 

Habitat Components: Preliminary Results and a Method 

for Monitoring.............................................................................. 823 

Tammy Randall-Parker and Richard Miller 

Selection of Fire-created Snags at Two Spatial Scales 

by Cavity-nesting Birds ............................................................... 835 

Victoria Saab, Ree Brannon, Jonathan Dudley, 

Larry Donohoo, Dave Vanderzanden, Vicky Johnson, 

and Henry Lachowski 

Dead Tree Management in British Columbia.......................................... 849 

Jeff Stone, John Parminter, André Arsenault, 

Todd Manning, Nancy Densmore, Gerry Davis, 

and Andy MacKinnon 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. vii

British Columbia’s Dangerous Tree Assessment Process......................863 

Todd Manning, Peter Bradford, Cary White, David Rowe, 

 Nancy Densmore, and Stewart Guy 

Managing Coarse Woody Debris in British Columbia’s Forests: 

A Cultural Shift for Professional Foresters? ................................869 

André Arsenault 

Water, Wildlife, Recreation, Timber... Coarse Woody Debris? ..............879 

John R. Mount 

Creating and Maintaining Wildlife, Insect, and Fish Habitat 

Structures in Dead Wood ............................................................883 

Timothy K. Brown 

Perspectives and Approaches to Management........................893 

An Ecological Functional Basis for Managing Dead Wood 

Decay Elements for Wildlife ........................................................895 

Bruce G. Marcot 

A Case Study of Habitat Conservation Plans and the 

 Protection of Snags and Coarse Woody Debris 

 on Industrial Forest Lands ..........................................................911 

Lorin L. Hicks and Henning C. Stabins 

Management of Dead Wood: Perspectives of a State 

 Forestry Agency..........................................................................923 

Christopher P. Rowney 

Moving towards a New Paradigm for Woody Detritus 

Management ...............................................................................929 

Mark E. Harmon 

Symposium Synthesis ................................................................945 

Dead Wood Management Issues and Opportunities: 

Future Directions.........................................................................947 

Ann M. Bartuska 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. ix 

Preface 

Forest structure, especially snag and down log abundance and their spatial and 

temporal variation, can play a major role in the suitability of habitat for wildlife. 

Indeed, for some species, these attributes can be more influential than successional 

stage or topographic variables. Besides silviculture and timber harvest per se, other 

timberland management such as mechanical site preparation, broadcast burning, and 

fire prevention/suppression can directly or indirectly affect the quantity, quality, and 

dynamics of dead wood resources. 

In 1997 and 1998, as a biologist for the California Department of Forestry and 

Fire Protection, I was asked to review and comment on the adequacy of proposed 

“Sustained Yield Plans” (SYP). Under the California Forest Practice Rules, owners 

of large areas of timberland were required to include in these plans a description of 

not only how they intended to generate maximum sustained production of high 

quality timber products but also how they would provide for fish, wildlife, and 

beneficial uses of water. These plans were intended to guide management of these 

lands with a 100-year planning horizon. Subsequent to the approval of an SYP, 

individual timber harvests tiered to them would likely undergo less environmental 

scrutiny and lighter analysis of potential cumulative impacts and mitigation. The 

combination of extensive areas and long time horizons of these proposals heightened 

the need for scientifically based review and modification, as necessary. 

An early SYP submittal I reviewed from one of the large timberland owners, 

who exercised intensive management, prompted me to study proposed standards 

related to snags and down logs. Proposals for standards and the application of 

standards for regulations for forest management should be based on the best scientific 

information available, using professional judgment only to fill in holes. Additionally, 

under California law, standards based on the relationships of fish and wildlife species 

presence or abundance to management-sensitive variables carry more weight than do 

standards based on “reference conditions.” I was familiar with many scientific studies 

on the values of snags (standing dead trees) to wildlife, especially primary and 

secondary cavity nesting birds. A number of suggested management 

recommendations and approaches had been well compiled in such places as Jack 

Ward Thomas’ 1979 milestone Wildlife Habitats in Managed Forests―the Blue 

Mountains of Oregon and Washington and Davis and others’ (1983) Snag Habitat 

Management. These documents provided good biological information and 

conceptual, logic-driven models that have formed the basis for subsequent modeling 

efforts. With the concern about the status of anadromous salmonids growing over the 

last decade or two, the knowledge base for the relationship of wood in streams with 

fish habitat value has been expanding and some guidelines have been developed. 

However, as far as I knew, the relationships and modeling of down logs on the forest 

floor were far less well considered. Wanting to provide a solid review and 

recommendation, I struggled with the paucity of region-specific information on the 

relationships of wildlife to all forms of dead wood, but felt very uncomfortable with 

the paucity of down log information. Thus these were some of the motivations behind 

the genesis of the idea for a symposium to synthesize past efforts and pull together 

current research on this important topic. 
Preface 

x USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

I spoke with several people about the idea, and everyone thought it would be a 

valuable contribution to both the resources involved as well as to the resource 

managers and scientists. Bill Laudenslayer of the USDA Forest Service was anxious 

to participate on the Technical Steering Committee and helped me identify others 

who might also have the expertise and connections to make it happen. The Steering 

Committee was formed, and consisted of Patrick Shea, Phillip Weatherspoon, Bill 

Laudenslayer, and Brett Harvey (Research Entomologist, Fire Ecologist, Wildlife 

Ecologist, and Fisheries Ecologist, respectively, Pacific Southwest Research Station 

[PSW], Forest Service); Gary Nakamura (Extension Forester, University of 

California Cooperative Extension); Dan Williams (Professor of Biology, California 

State University, Stanislaus); Lowell Diller (Biologist, Simpson Timber Company), 

and Don Owen and Brad Valentine (Entomologist and Biologist, respectively, 

California Department of Forestry and Fire Protection). This group met several times 

in Redding, California, to plan the symposium, despite the long distances necessary 

for some of us to travel in order to convene a meeting. 

The desire of the Technical Steering Committee was to structure the symposium 

to promote understanding about the importance of dead wood resources in western 

forests, the processes that form and remove dead wood from forests, and application 

of management to the dead wood resource that could enable the development of 

scientifically-credible management recommendations. To that end, we grouped the 

sessions by these topics: the importance of dead wood to the forests’ resources 

(aquatic systems, invertebrates, vertebrates, and soils); the dynamics and demography 

of dead wood in different forest systems; perspectives on dead wood management, 

and finally; guidelines for and ideas about dead wood management. To round out the 

information, we added preview and synthesis sessions. 

The Steering Committee discussed several issues relative to the scope of the 

symposium. Which of the natural resources fields should we target for contributed 

papers and attendance, and would focusing on one field preclude participation by 

another? Would advertising the meeting as one directed at snags or wood in streams 

overwhelm and perhaps discourage submissions on down logs in terrestrial 

situations? Should we omit snags, since there is a more extensive history and 

probably current research focus on them, relative to logs? We decided to be broadbased, because we thought that focusing only on logs in the terrestrial ecosystem 

would result in too few submittals and perhaps miss the vital association between 

snags and logs. Another issue was the geographic scope. The entire Steering 

Committee resided in California, and one of the primary sponsoring institutions―the 

Western Section of The Wildlife Society―covers California and Nevada. However, 

we concluded that forest ecosystems across western North America were sufficiently 

similar that the concepts derived in one would be transferable to another; that the 

Steering Committee’s personal contacts were wide enough that we could target 

invitations to provide valuable information attractive to a wide audience; and that 

especially with electronic communications a wide audience could be reached with 

symposium notices. The Steering Committee’s decisions proved to be fruitful. The 

response to the “Call for Papers” underscored the timeliness of the topic for a 

symposium. The numerous submittals within the topic and geographic range 

necessitated concurrent sessions and interest was widespread with enquiries from 

Canada, Mexico, Australia, Europe, Russia, and Africa. 

A very important foundation for developing a quality symposium is to invite 

selected speakers who can attract and energize the participants. Perhaps more 
Preface 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. xi 

important is that the invited speakers lend credibility to the symposium owing to their 

recognized expertise on the subject matter. The speakers we invited―Ann Bartuska, 

Robert Bilby, Evelyn Bull, Efren Cazares, Mark Harmon, Michael Haverty, Becki 

Heath, Paul Hennon, Lorin Hicks, Bruce Marcot, Robert Naiman, Catherine Parks, 

Christopher Rowney, Carl Skinner, Jack Ward Thomas, and Michael Wagner―

fulfilled their roles well. Without their interest and participation, the symposium 

would have not been the high quality event that it turned out to be. 

The Steering Committee could not accomplish all the work itself. We identified 

and invited other knowledgeable and capable people to act as Session Chairs. We 

asked the Session Chairs to not only introduce speakers and their presentations but 

also to run their sessions like tyrants keeping the talks on time and thus facilitating 

the concurrent session structure of the symposium. Far more than that, we asked 

Session Chairs to solicit papers for their sessions, and to review some of the 

manuscripts and make recommendations to the Editorial Committee regarding the 

quality of manuscripts for the proceedings. The Steering Committee would like to 

thank James Agee, Bruce Bingham, Lowell Diller, Carl Fiedler, Mark Harmon, 

Michael Haverty, Bruce Hostetler, Bill Laudenslayer, Thomas Lisle, Bruce Marcot, 

Don Own, Patrick Shea, Torolf Torgersen, Bradley Valentine, Phillip Weatherspoon, 

and Dan Williams for gladly assuming the extended range of Session Chair’s chores. 

The authors responded immediately and thoughtfully to the “Call for Papers” 

and followed well the manuscript guidelines, making the Editorial Committee’s job 

that much easier. The Steering Committee placed another burden on authors that is 

not common in other symposia. Authors were required to have their manuscript 

“peer-reviewed” by two people knowledgeable in the field associated with their topic 

before submitting it to the Session Chairs or the Steering Committee. At least one of 

their reviewers had to be someone who was unrelated to their project. Finally, all 

technical manuscripts were reviewed by the Editorial Committee to meet publishing 

standards, and the PSW editorial staff provided style editing after the technical 

editing was completed. Technical manuscripts thus received at least three, and some 

received four, reviews prior to being included in the proceedings. Non-technical 

papers (literature reviews, perspectives, symposium introduction, and synthesis) did 

not undergo “peer review,” but were reviewed editorially for style and content. 

Bill Hull, then Executive Secretary for the Western Section of The Wildlife 

Society, relieved the Steering Committee of some of the logistical burden of staging a 

major event such as this. He negotiated and coordinated all the intricate details with 

the facility that hosted the conference. In addition, he managed the registration 

operations for the conference. He found the Atlantis Casino Resort in Reno, Nevada, 

to be a hospitable facility with which to work. 

Four of the original Steering Committee members stayed on after the 

symposium to finish the task of publishing the proceedings. This “Editorial 

Committee”―Phillip Weatherspoon, Patrick Shea, Bradley Valentine, and Bill 

Laudenslayer―continued to meet and to communicate, to review manuscripts, and to 

prepare them for publishing. We soon realized that our group lacked the expertise to 

review hydrologic and aquatic manuscripts; thus, we invited Tom Lisle to participate 

on our Editorial Committee―a role that he graciously accepted. Bill Laudenslayer 

assumed the yeoman’s job of chairing the Editorial Committee, one that we all wish 

to acknowledge. 

Bradley E. Valentine, Technical Coordinator 
Preface 

xii USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Acknowledgments 

The symposium would never have happened without the support of the 

organizations represented on the Steering Committee: Simpson Timber Company; 

California State University, Stanislaus; California Department of Forestry and Fire 

Protection; and the Pacific Southwest Research Station, USDA Forest Service. We 

also thank the Western Section of The Wildlife Society for assuming the up-front risk 

and providing the staffing support to make the “Symposium on the Ecology and 

Management of Dead Wood in Western Forests” an extraordinary success. Finally, 

without all of the participants, presenters, audience, and readers of these proceedings, 

there would not have been any reason to organize this symposium and prepare the 

proceedings. 

We thank the symposium attendees, speakers and authors, and session chairs for 

their interest and contributions that provided the reason for publishing this volume. 

We greatly appreciate the work of Bill Hull for his considerable contributions to the 

arrangements and the operations of the symposium. We also thank all of the 

reviewers of the individual papers who contributed to and improved each paper. The 

formatting of manuscripts by Nydia Whimberly, Sandy Hicks, and Leticia Vidrio was 

essential to completing the proceedings, and we greatly appreciate their 

contributions. We also greatly appreciate the work of Martha Shibata, who designed 

the proceedings cover. Finally, we owe a great debt to Laurie Dunn, who edited every 

paper to ensure that they read smoothly and met the formatting standards, managed 

the work flow process, and prepared the final page layout of the manuscripts for the 

proceedings. Thanks to you all! 

William F. Laudenslayer, Jr. 

Patrick J. Shea 

Bradley E. Valentine 

C. Phillip Weatherspoon 

Thomas E. Lisle 

Technical Coordinators 

References 

Davis, J. W.; Goodwin, G. A.; Ockenfels, R. A., technical coordinators. 1983. Snag habitat 

management: proceedings of the symposium. Gen. Tech. Rep. RM-99. Fort Collins, 

CO: Rocky Mountain Forest and Range Experiment Station, Forest Service, U.S. 

Department of Agriculture; 226 p. 

Thomas, Jack Ward, technical editor. 1979. Wildlife habitats in managed forests—the Blue 

Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: U.S. 

Department of Agriculture; 512 p. 
Publisher

Albany, California 

Mailing address:

P.O. Box 245 

Berkeley, CA 

94701-0245 

(510) 559-6300 

http://www.psw.fs.fed.us 

August 2002 

Pacific Southwest Research Station 

Forest Service 

U.S. Department of Agriculture 

Abstract 

Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, 

C. Phillip; Lisle, Thomas E., technical coordinators. 2002. Proceedings of the 

symposium on the ecology and management of dead wood in western forests. 

1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: 

Pacific Southwest Research Station, Forest Service, U.S. Department of 

Agriculture; 949 p. 

Dead trees, both snags (standing dead trees) and logs (downed dead trees), are critical 

elements of healthy and productive forests. The “Symposium on the Ecology and 

Management of Dead Wood in Western Forests” was convened to bring together forest 

researchers and managers to share the current state of knowledge relative to the values 

and interactions of dead wood to and in a functioning forest. Topics covered include 

the value of dead wood organisms in both terrestrial and aquatic habitats, the dynamics 

of dead wood, and ecological, industrial, and State and Federal land management 

agency perspectives. This information is immensely valuable to researchers and 

managers working with or managing dead wood in a variety of ecosystems. 

Retrieval Terms: cavity-dependent species, dead and down wood, dead wood 

distribution, dead wood value, debris flows, logs, snags, tree mortality 

Technical Coordinators 

William F. Laudenslayer, Jr. is Research Wildlife Ecologist, Pacific Southwest 

Research Station, USDA Forest Service, 2081 E. Sierra Ave. Fresno, CA 93720 

(e-mail: blaudenslayer@fs.fed.us). 

Patrick J. Shea is Research Entomologist (Emeritus), Pacific Southwest Research 

Station, USDA Forest Service, 1107 Kennedy Place, Suite 8, Davis, CA 95616 

(e-mail: pjshea@davis.com). 

Bradley E. Valentine is Staff Environmental Scientist, California Department of Fish 

& Game, P.O. Box 47, Yountville, CA 94599 (e-mail: bvalentine@dfg.ca.gov). 

(Formerly: Senior Biologist, California Department of Forestry and Fire Protection, 

135 Ridgway Ave., Santa Rosa, CA 95404.) 

C. Phillip Weatherspoon is Research Forester (Emeritus), Pacific Southwest Research 

Station, USDA Forest Service, 2400 Washington Ave., Redding, CA 96001 (e-mail: 

pweatherspoon@fs.fed.us). 

Thomas E. Lisle is Research Hydrologist, Pacific Southwest Research Station, USDA 

Forest Service, 1700 Bayview Dr., Arcata, CA 95521 (e-mail: tlisle@fs.fed.us). 
Importance of Dead and Downed Wood

1
Dead Wood: From Forester’s Bane to 

Environmental Boon1 

Jack Ward Thomas2 

Abstract 

Forest managers are increasingly aware of the significance of Aldo Leopold’s admonition that 

“to keep every cog and wheel is the first rule of intelligent tinkering.” Dead wood, standing 

and down, is one of those “cogs and wheels.” This was recognized in the 1970s and triggered 

additional research and evaluation of management action related to dead wood in managed 

forests. Much of this new information will be discussed at this conference. What will remain 

at the close is the essential need for synthesis of this new knowledge from research and 

management experience into a useable form for managers. This is the remaining challenge. 

Introduction 

When Patrick Shea approached me about giving this keynote address, I asked if 

he had thought about what comedian Jay Leno could do with a “government” 

conference on “dead wood.” I accepted only after checking to see if the Office of 

Personnel Management was a co-sponsor. Then I began to consider why a retiree had 

been asked to deliver the keynote address and decided to quit thinking about such 

things. I remembered what my old friend and mentor Les Pengelly said when I 

congratulated him on a great keynote address at a conference on mule deer 

management: “Just remember what is happening when you are frequently selected to 

give keynote addresses. Your friends and colleagues remember you fondly, but know 

that you are really out of the game.” Thank you for the honor and remembering me. 

Dead Wood as the Bane of Forestry 

There are a number of us in the room who can remember, in the early stages of 

our careers, when dead wood in any form was considered the bane of foresters who 

had been trained to focus on the most efficient commercial production of wood and 

wood fiber. Snags (standing dead trees) were considered a safety hazard to woodland 

workers and a potential source of spreading sparks that ignited spot fires. Down 

woody material was considered “fuel” that facilitated the spread of fire, a haven for 

vertebrate pests that hampered reforestation, and unsightly (Maser and others 1979). 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4 1999, Reno, Nevada. 2

 Chief Emeritus, USDA Forest Service; Boone and Crockett Professor of Wildlife Conservation, School 

of Forestry, University of Montana, Missoula, Montana 59812 (e-mail: jwt@forestry.umt.edu) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 3 
Dead Wood: From Forester’s Bane to Environmental Boon—Thomas 

The Times They Are A’Changin’ 

Like the verse from the old Bob Dylan song, “The times they are a’changin’.” 

At this conference, we are gathered to discuss the ecological role of dead wood in our 

dynamic search for means of attaining sustainable forest management. 

Let me begin with a quote from Aldo Leopold (1953): 

The land is one organism. Its parts, like our own parts, compete with 

each other and cooperate with each other. The competitions are as much a 

part of the inner workings as the cooperations. You can regulate them 

cautiously but not abolish them.... If the biota, in the course of eons, has 

built something we like but do not understand, then who but a fool would 

discard seemingly useless parts? To keep every cog and wheel is the first 

rule of intelligent tinkering (p. 146-147). 

I often ponder why Aldo Leopold’s admonition about keeping “cogs and 

wheels” is widely quoted and how often we are surprised at the consequences, both 

ecological and political, when it is ignored. By now, we should have learned that all 

the segments of a “naturally” functioning ecosystem play some role in that system 

whether or not we understand all the relationships. And we should have learned by 

now that biological systems are significantly simplified at some peril to the 

maintenance of that system. 

System Simplification Implies Risk 

Obviously, gross simplification of naturally occurring ecosystems has produced 

the means whereby dramatically increasing human populations could be supported. 

In some cases, such as in Western Europe, the U.S., and Canada, this has led to a lifestyle of the common people that would have been deemed impossible only one 

generation earlier. Today, however, experience is beginning to accumulate that such 

simplification may carry the seeds of diminution of productivity over the longer term. 

The consideration of dead wood as one part of the essential functioning of 

forested ecosystems (including all of its component parts—biotic and abiotic) can be 

most instructive. We should keep in mind during these deliberations that dead wood 

is only one of many attributes of the forested ecosystems of the world. However, the 

discussion will undoubtedly elaborate Paul Ehrlich’s corollary to Aldo Leopold’s 

admonition about saving cogs and wheels. It is the “why” to the first rule of 

intelligent tinkering—“all things are connected and there are consequences to all 

manipulations of biological systems” (Ehrlich and Roughgarden 1987). 

Recognizing the Importance of Dead Wood: Better Late

Than Never 

In retrospect, it is amazing that forest managers did not realize that dead wood 

was a critical habitat component—for vertebrate and invertebrate wildlife and for the 

forest itself. Elton (1966) succinctly described the role of dead wood as a critical 

habitat component: 

When one walks through the rather dull and tidy woodlands...that 

result from modern forestry practices, it is difficult to believe that dying 

and dead wood provides one of the two or three greatest resources for 

4 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
Dead Wood: From Forester’s Bane to Environmental Boon—Thomas 

animal species in a natural forest, and that if fallen timber and slightly 

decayed trees are removed the whole system is gravely impoverished of 

perhaps more than a fifth of its fauna (p. 279). 

By using the example of Wyndam Wood in England, Elton (1966) described the 

number of species that might be related to dead wood as habitat: “Indexes of the 

Ecological Survey contain 456 species of animals (including invertebrates)... living 

in wood or under bark where decay has begun or already gone far. Another 518 

species are known to occur in this habitat elsewhere in Britain....” (p. 279). 

By the 1970s, researchers and forest managers were becoming increasingly 

aware of the role of dead wood in the ecology of the managed forest. The important 

implications of decomposing woody debris in mineral cycling, nutrient 

immobilization (Fogel and Cromack 1977, MacMillan and others 1977), and nitrogen 

fixation (Cornaby and Waide 1973) had been put forward. Logs were recognized as 

frequently serving as substrates for fungal hyphae, rhizomorphs, and sporocarps 

(Ausmus and others 1975, Cromack and others 1975). Harvey and others (1976) had 

demonstrated the role of decaying logs as sites for colonization of ectomychorrhizal 

fungi that aided in the survival of several species of trees. Mychorrhizal fungi had 

been shown to aid processes of nitrogen fixation (MacMillan and others 1977). 

Cromack and others (1975), Maser and others (1978), Miller and Halls (1969), and 

Trappe and Maser (1976) had identified fungi associated with dead wood as an 

important food source for both vertebrate and invertebrate wildlife. Earlier, Graham 

(1925), Kimmey and Furniss (1943), and Savely (1939) had noted that decaying logs 

provided varying attributes of wildlife habitat, depending on the state of decay. 

Researchers, most of whom were associated with the USDA Forest Service 

research unit at La Grande, Oregon, began multi-disciplinary cooperative studies in 

the late 1970s to further expand knowledge about mortality factors associated with 

the western spruce budworm (Choristoneura occidentalis) (Campbell and others 

1983, Campbell and Torgerson 1982, Torgerson and Campbell 1982). They identified 

and quantified the major effects of insectivorous birds (most of whom were 

secondary cavity nesters) and foliage-foraging predaceous ants as regulators in the 

dynamics of low-level budworm populations. There were 13 species of ants (11 of 

which were associated with dead wood) identified as predators on the budworm 

(Genus Camponotus and Formica) (Torgerson and others 1990). 

Bull and others (1992) determined that a major portion of the diet of pileated 

woodpeckers (Dryocopus pileatus) were the same species that were major predators 

on spruce budworm. Torgerson and Bull (1995) collaborated in the characterization 

of logs that were habitat for ants and used by pileated woodpeckers for foraging. 

They found that budworm outbreaks occur about every 40 years (Swetnam and 

others 1995). After trees are killed, some become snag-habitat for woodpeckers, 

secondary cavity nesting insectivorous birds, and ant predators of the budworm. The 

snags become down logs, which then become the home for colonies of ants and 

forage for woodpeckers. Ants and birds are dominant regulatory forces on budworm 

populations at low population levels. Decaying wood simultaneously plays a role in 

nutrient cycling. Outbreaks eventually occur, tree mortality results, and the cycle 

begins anew (Torgerson, pers. comm.). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 5 
Dead Wood: From Forester’s Bane to Environmental Boon—Thomas 

Everything Is Connected to Everything Else 

At this meeting, we will discuss the role of dead wood in forested ecosystems, 

including its role in associated aquatic systems. We will examine at least some of the 

connections between dead wood and “everything else” in the healthy forest, and this 

is only the beginning of knowledge. As Aldo Leopold (1953) stated: “The 

outstanding scientific discovery of the twentieth century is... the complexity of the 

land organism. Only those who know the most about it can appreciate how little we 

know about it...” (p. 146). 

Yet, it is clear that there can be no respite from our tinkering with natural 

systems. As with all our fellow creatures, human populations must exploit the 

environment in order to live. There is no question about that. The question, then, 

becomes one of how such exploitation occurs. The challenge of the new millenium 

for natural resource managers is the question of how we can exploit our environment 

and maintain its productivity and health (defined as the capacity for renewal)—not 

only for the short term but also for the centuries. That is what the buzzwords such as 

“sustainability,” “ecosystem management,” and “forest health” mean. At least for the 

foreseeable future, this will be a challenge because of the increasing human 

population. 

The Growing Need for Synthesis and Re-synthesis 

In this conference, we will address a small piece of the concerns of how forest 

managers can combine the objective of meeting people’s needs and, simultaneously, 

maintain forest health. The journey of learning and understanding more and adjusting 

management will be a continual feedback loop that will require constant adjustments 

in management. This is inevitable and should be accepted as part of routine business. 

I predict there will be, at the end of our deliberations, a sense of confusion 

among the managers in attendance about the information and insights presented here. 

Managers will probably be overwhelmed with the various bits of new information, 

insights into the role of dead wood in forested ecosystems, and the various 

suggestions for the management of the dead wood component. That inevitable 

confusion will require synthesis of the myriad pieces of information into some useful, 

and defensible, form for the use of managers. And, who will do that chore? It seems 

likely, if past is indeed prologue, that the essential synthesis will be “blowing in the 

wind,” as the individual presenters retreat into their specialized niches in research 

organizations. 

Synthesis: It Has Been Done Before 

It does not have to turn out that way. I hope that before this conference ends an 

ad hoc team has been formed that is pledged to the synthesis of the material 

presented here, and material that can be found elsewhere, into a useful treatise on the 

subject of the role and management of dead wood in managed forests. This can be 

done. It has been done before, beginning with some chapters entitled “Snags” 

(Thomas and others 1979) and “Dead and Down Woody Material” (Maser and others 

1979) in the document Wildlife Habitats in Managed Forests—The Blue Mountains 

of Oregon and Washington (Thomas 1979). 

6 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
Dead Wood: From Forester’s Bane to Environmental Boon—Thomas 

Synthesis: Not for the Faint of Heart 

It took nerve to go forward with the synthesis of the extant information (which 

was sparse compared to what will be presented at this conference), make informed 

“guesses” when detailed understanding based on “hard data” was lacking, and then 

make suggestions to management. Frankly, it will take nerve to take the next step. 

Synthesis and management guides are not for the faint of heart. In this action lies the 

bridge from creation of knowledge and pontification to responsibility. 

There was some applause and some criticism. One critic criticized us in a 

meeting with the accusation that we had “guessed” at some critical points. I conceded 

that he was correct, but that we offered no apologies. The “guesses” (we preferred the 

descriptive term of “informed opinion”) were clearly identified as such. But, if 

nothing else, we had put forward a number of hypotheses that he and a number of 

other researchers—including ourselves—were chasing. In the meantime, we had 

certainly brought attention to the need to consider dead wood in forest management. 

Changes could be made in response to better research-based data when such was 

available. I am certain that we will see a great deal of that improved knowledge at 

this conference. 

We considered that 71 species of birds and 51 mammals (122 out of 378 

vertebrate species in the Blue Mountains—32 percent) depended to some degree on 

snags as a habitat component. When we further considered that snags were becoming 

ever more scarce under the forest management regimes in place, it was clear that 

there was a problem developing (Thomas and others 1979). That problem could take 

the form of an impending collision with the Endangered Species Act of 1973. Or, 

more likely, there was a problem that was related to the purpose of that Act (“to 

provide a means whereby the ecosystems upon which endangered and threatened 

species depend may be conserved” [Endangered Species Act of 1973, Sec. 2 (b) (1)]). 

This was likewise true of down woody material. We believed that 5 amphibians, 

9 reptiles, 116 birds, and 49 mammals (179 out of 378 vertebrate species—47 

percent) made some use of logs and other down woody materials (Maser and others 

1979). 

Synthesis: The Two Choices Are “Too Soon” and “Too 

Late” 

We were criticized by some of our colleagues who maintained that we were 

“premature” in our findings and in our recommendations for management. We 

looked those colleagues squarely in the eye and announced that, in our minds, we had 

two choices—“too soon” or “too late.” We opted for the former and challenged 

managers to test the hypotheses and develop a deeper understanding of the role of 

dead wood in the forests. Our view was summed up in the following statement from 

Thomas (1979): 

Perhaps the greatest challenge that faces professionals engaged in 

forest research and management is the organization of knowledge and 

insights into forms that can be readily applied. To say we don’t know 

enough is to take refuge behind a half-truth and ignore the fact that 

decisions will be made regardless of the amount of information available. 

In my opinion it is far better to examine available knowledge, combine it 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 7 
Dead Wood: From Forester’s Bane to Environmental Boon—Thomas 

with expert opinion on how the system operates, and make predictions 

about the consequences of alternative management actions. 

Synthesis? Just Do It 

This is the challenge I present to you today. Do not walk away from this 

conference content with a publication of dozens of additional pieces of disjunct 

information and recommendations. That leaves the job half-done. Surely, in this 

audience is a team just waiting to be formed that can and will produce a summary 

treatise on the role of dead wood in managed forests that will help guide managers as 

they struggle toward sustainable forestry. If not, I suggest that we may just have 

wasted our time and produced one more publication to add to a thousand others on 

library shelves where it will reside until someone seeks synthesis. Through 

experience, I have found that pontification is far less risky, and far easier, than 

assumption of responsibility. But, in the exercise of responsibility lies the ability to 

make change and be accountable. Take the responsibility. 

It has been done before, 20 years ago, with much less information than exists 

today, and it made a difference. This conference will significantly reinforce the base 

of information and understanding. 

Now is the time. The need is apparent. There is more and better information than 

ever before. All that is required is courage, some “street smarts,” the will, hard work, 

credibility, and the guts to put reputations on the line. My final plea is do it, just do it. 

References 

Ausmus, Beverly S.; Dodson, Gladys J.; Todd, Don G. 1975. Microbial-invertebrate 

interactions: The mechanism of wood decomposition. Ecological Society of America 

Bulletin 56(2): 42. 

Bull, E. L.; Beckwith, R. C.; Holthausen, R. S. 1992. Arthropod diet of pileated 

woodpeckers in northeastern Oregon. Northwest Naturalist 73: 42-45. 

Campbell, R. W.; Torgerson, T. R. 1982. Some effects of predaceous ants on western 

spruce budworm in north central Washington. Environmental Entomology 11(1): 

111-114. 

Campbell, Robert W.; Torgerson, Torolf R.; Srivastava, Nilima. 1983. A suggested role for 

predaceous birds and ants in the population dynamics of the western spruce 

budworm. Forest. Science 29(4): 779-790. 

Cornaby, Barney W.; Waide, Jack B. 1973. Nitrogen fixation in decaying chestnut logs. 

Plant and Soil 39(2): 445-448. 

Cromack, Kermit, Jr., Todd, Robert L.; Monk, Carl D. 1975. Patterns of Basidiomycete 

nutrient accumulation in conifer and deciduous forest litter. Soil Biol. Biochem.7(4-

5): 265-268. 

Ehrlich, Paul R.; Roughgarden, J. 1987. The science of ecology. New York: Macmillian; 710 

p. 

Elton, Charles Sutherland.1966. Dying and dead wood. In: The patterns of animal 

communities. New York: John Wiley and Sons, Inc.; 279-305. 

8 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
Dead Wood: From Forester’s Bane to Environmental Boon—Thomas 

Fogel, Robert; Cromack, Kermit, Jr. 1977. Effect of habitat and substrate quality on 

Douglas-fir litter decomposition in western Oregon. Canadian Journal Botany 55(12): 

1632-1640. 

Graham, S. A. 1925. The felled tree trunk as an ecological unit. Ecology 6(4): 397-411. 

Harvey, A. E.; Larsen, M. J.; Jurgenson, M. F. 1976. Distribution of ectomycorrhizae in a 

mature Douglas-fir/larch forest soil in western Montana. Forest Science 22(4): 393-

398. 

Kimmey, J. W.; Furniss, R. L. 1943. Deterioration of fire-killed Douglas-fir. USDA Tech. 

Bull. 851, Washington, DC; 61 p. 

Leopold, Aldo. 1953. Round river. Edited by Luna B. Leopold. New York: Oxford 

University Press; 173 p. 

MacMillan, P.; Means, J.; Hawk, G. M.; Cromack, K., Jr.; Fogel, R. 1977. Log 

decomposition in an old-growth Douglas-fir forest. Northwest Science Assocication 

Program and Abstracts of papers for the 50th annual meeting; 13 p. 

Maser, Chris; Trappe, James M.; Nussbaum, Ronald A. 1978. Fungal-small mammal 

interrelationships with emphasis on Oregon coniferous forests. Ecology 59(6): 799-

809. 

Maser, Chris, Ralph G. Anderson, Kermit Cromack, Jr., Jerry T. Williams, and Robert E. 

Martin. 1979. Dead and down woody material. In: Wildlife habitats in managed 

forests―the Blue Mountains of Oregon and Washington. Agric. Handb. No. 556. 

Washington, DC: U.S. Department of Agriculture; 78-95. 

Miller, Howard A.; Halls, Lowell K. 1969. Fleshy fungi commonly eaten by southern 

wildlife. USDA Forest Service Res. Paper SO-49. New Orleans, LA: Southern Forest 

Experiment Station; 28 p. 

Savely, Harvey Epperson, Jr. 1939. Ecological relations of certain animals in dead pine 

and oak logs. Ecological Monographs 9(3): 321-385. 

Swetnam, Thomas W.; Wickman, Boyd E.; Paul, H. Gene; Baisan, Christopher H. 1995. 

Historical patterns of western spruce budworm and Douglas-fir tussock moth 

outbreaks in the northern Blue Mountains, Oregon, since A.D. 1700. Res. Paper 

PNW-RP-484. Portland, OR: Pacific Northwest Experiment Station, USDA Forest 

Service; 27 p. 

Thomas, Jack Ward, editor. 1979. Wildlife habitats in managed forests―the Blue 

Mountains of Oregon and Washington. Agric. Handb. No. 553. Washington, DC: 

U.S. Department of Agriculture; 512 p. 

Thomas, Jack Ward; Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: 

Wildlife habitats in managed forests―the Blue Mountains of Oregon and Washington. 

Agric. Handb. No. 553. Washington, DC: U.S. Department of Agriculture; 60-77. 

Trappe, James M.; Maser, Chris. 1976. Germination of spores of Glomus macrocarpus

(Endogonaceae) after passage through a rodent digestive tract. Mycologia 68(2): 

433-436. 

Torgerson, T. R.; Campbell, R. W. 1982. Some effects of avian predators on the western 

spruce budworm in north central Washington. Environmental Entomology 11(2): 

429-431. 

Torgerson, Torolf R.; Mason, Richard R.; Campbell, Robert W. 1990. Predation by birds 

and ants on two forest insect pests in the Pacific Northwest. In: Morrison, M. L.; 

Ralph C. J. Avian foraging: theory, methodology, and applications. 

Verner, J.; Jehl, J. R. Jr. Studies in avian biology 13:14-19. Cooper Ornithological Society. 

Lawrence, Kansas: Allen Press. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 9 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 11 

Decaying Wood: An Overview of Its Status 

and Ecology in the United Kingdom and 

Continental Europe1

Jill Butler,2 Keith Alexander,3 and Ted Green4

Abstract 

Decaying wood habitats are rare in Europe because of centuries of forestry and agricultural 

practices. Where there has been continuous woodland cover and within it an unbroken 

presence of old trees, the decaying wood communities are exceptional. The main woodland 

management systems operating in Europe are explained and how they influence the decaying 

wood component and associated wildlife. Priorities for conservation in a European context are 

outlined and selections of important old-growth sites are provided. 

Introduction 

Dead, or perhaps more accurately, decaying wood and much of the wildlife 

associated with it has become very rare in Europe. Any form of agriculture or 

forestry diverts natural resources from wildlife towards human activity (Fry and 

Lonsdale 1991), and our history is one in which timber and woody material have 

been removed from our woodlands. In traditional systems man would have utilized 

nearly every piece of wood. Today, dead trees are still cleared to make way for new 

tree crops; sanitation felling and burning is still practiced to protect lowland 

broadleaved forestry crops from a misguided perception of infection (Winter 1993); 

and a tidiness mentality overrides all. Mechanized operations encourage more 

intensive exploitation of timber produce and drive earlier and earlier returns on 

capital expenditure, reducing the age of standing tree crops and at the same time 

increasing the scope of sanitation and tidiness activities. 

Intensive land use over the centuries and especially in the past 50 years has led 

to massive loss of a whole range of semi-natural habitats, and those that remain have 

become ever more isolated. Only a maximum of 10 percent of the land surface of 

most of Europe today remains in some more or less “semi-natural” condition 

(Speight 1987). In the United Kingdom (UK) nearly 50 percent of ancient woodland 

has been lost since 1947 (Fry and Lonsdale 1991). Between 1979 and 1990 there was 

a 14 percent loss of vegetation species richness in woodlandthe highest for any 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Woodland Conservation Consultant, Windrush, Spade Oak Reach, Bourne End, SL8 5RQ, UK (e-mail: 

jillbutler@woodland-trust.org.uk) 

3

 Saproxylic Invertebrate Consultant, National Trust, 33 Sheep Street, Cirencester, GL7 1RQ, UK (email: XEAKXA@grpwse.ntrust.org.uk) 

4

 Ecological Consultant, 22 Reeve Road, Holyport, Maidenhead, SL6 2LS, UK (e-mail: Ted.Green@ 

care4free.net.uk) 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

12 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

habitat in the UK (Department of the Environment 1994). Because dead wood within 

existing semi-natural woodland is poorly represented, relic decaying wood 

communities have become more isolated than most. 

Because the situation became more alarming, the Council of Europe (1988) 

adopted a recommendation on the protection of saproxylic organisms and their 

biotopes. This highlights that Europe is beginning to understand the importance of 

the decaying wood ecosystem. Since the 1990s, there has been a gradual change and 

the protection of decaying wood habitat is now cited as an environmental concern in 

forestry policy and procedures in many European countries. 

Ancient Woodland 

Ancient woodland is woodland that has existed since at least the 16th century on 

the same site, although it may have been managed throughout the centuries. Less than 

2 percent of the land area of Britain is ancient woodland and mainly comprises small 

areas separated from each other by intensively managed landscapes; more than 8 out 

of 10 woodlands are less than 20 ha (50 acres). In many of these ancient woods there 

has always been woodland cover of one type or another that retains a continuity of 

habitat structure similar to the wild wood or virgin forest, which developed after the 

last ice age around 7,500 years ago. This continuity of woodland cover provides a 

habitat and biodiversity that is irreplaceable. However, in many cases the woodland 

often comprises young stands of trees. In ancient woods containing old trees and 

where there has been a continuous presence of old trees on the site, i.e., old-growth 

woodland, additional assemblages of rare wood-decaying species can be found. 

Wood Pasture 

Wood pastures are extensively grazed, open-structured woodlands that allow the 

regeneration of open grown trees, especially shade intolerant species. Trees in these 

open conditions have a much shorter, stockier stature as they achieve a full canopy 

without needing great height. As they age they become hollow, and the canopy may 

reduce further. Often there has been a tradition of pollarding the treesregular 

cutting of the trees at head height or higher on rotationfor a renewable source of 

wood that has been very beneficial for the creation of decaying heartwood. The old 

trees are very important for decaying wood communities. Wood pastures are very 

vulnerable to intensification of use—changes that increase productivity of grass and 

overgrazing, which results in trees that are severely affected by high chemical inputs 

from fertilizers, pesticides and animal drugs, compaction, and water logging 

(Alexander and others 1996, Read 2000). This more open type of habitat is also 

particularly vulnerable to external influences, such as spray drift and air pollution 

from surrounding intensive grazing and arable production systems. British wood 

pastures and parkland are more common than in mainland northwest Europe probably 

because there has been a continuity of land ownership by the aristocracy who used 

wood pasture and parkland for deer hunting. 

Coppice Woodland 

By the Middle Ages, the typical management for coppice resulted in widely 

spaced trees that grew to maturity. Because of frequent harvest on short rotations of 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 13 

the wood resource through the centuries, this woodland is most likely to have low 

quantities and a limited dead and decaying wood structure. However, old coppice 

stools, which survive and increase in size and age through many harvesting cycles, 

provide continuity of dead wood habitat. The old stools are known to be especially 

valuable for saproxylic hoverflies and other Diptera that favor decay in moist 

situations. 

High Forest 

By 1980, 75 percent of UK broadleaved woodland was managed as high forest 

(Hart 1994). Although accumulation of decaying wood in unmanaged woodland may 

amount to 50-200 cu m per hectare, in conventional high forest managed systems it 

may well be as low as 1-5 cu m per ha, and the variety of the dead wood resource 

tends to be much diminished by such management (Ferris-Kaan and others 1993). 

Many European countries are increasing the areas of minimum intervention 

woodlandthat are largely untouched by people except to combat unwanted human 

influences. This should allow decaying wood levels to rise within them once again. 

Wet Woodland 

Wet woodland, such as Atlantic or oceanic woodland—which is characterized 

by cool, wet climate with few temperature extremes or woodland with wet features 

such as springs, streams, or rivers—can be especially important. This habitat supports 

humidity-demanding dead and decaying wood species, which are now very rare in 

Europe, and many of those that remain have been badly degraded by overgrazing 

(Hodgetts 1996). 

Comparisons with Continental Europe 

In much of continental Europe, forests generally are young high forest stands of 

trees, as wood is still a major source of fuel for local communities; whereas in 

Britain, coal, natural gas, and nuclear fuels have provided significant alternatives for 

centuries. The UK has more old trees in ancient woodland, wood pasture sites, and 

traditional agricultural landscapes than most other northern European countries 

(Green 1994). These ancient sites with existing old trees and shrubs contain 

characteristic dead and decaying wood communities, especially fungi, lichens and 

invertebrates. Because some of the trees can be more than 1,000 years old and many 

more than 500 years old, only a small number of generations have spanned the period 

between the last Ice Age and today (Key, pers. comm.). 

Decaying Wood and Its Wildlife 

Dead wood has a limited existence: it decays and is ultimately recycled. 

Conservation of wood decay communities requires conservation of a diverse age 

structure of living trees to senility and death because the living tissues generate the 

wood, which will ultimately decay. A continuity of different wood decay habitats in 

individual trees, above- and belowground and a variety of standing and fallen wood 

in different environments in woodland is therefore necessary to ensure sustainable 

wood decay communities. 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

14 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The most important wood decay resources are large, old, standing, living and 

dying trees that develop columns of decay in the dead heartwood or center of the tree. 

Fungi are fundamental to the decay process. 

Fungi 

“A tree (or woodland) without fungi is like a stage without actors. For, 

throughout its life a tree generates a mobile wooden framework upon and within 

which literally countless fungi enact diverse ecological roles. Whereas some fungi 

bring resources to the tree others degrade and recycle its products” (Rayner 1996). 

In Europe, “fungi do not figure in the usual brief for wildlife or habitat 

conservation. No voice has been raised on their behalf. They, however,... stoke the 

power plant of the forest. The more substantial the vegetation, the greater the variety 

of fungi for its degradation” (Corner 1994). 

In the UK the role and importance of fungi in the wood decay system and in 

habitats generally is only starting to be recognized. Despite their importance at the 

center of woodland ecology, they have been largely overlooked and dismissed. Very 

old trees are exceptionally valuable for fungi, and the fact that the trees have reached 

an advanced age at all may be largely due to their relationship with fungi. 

White rotted heartwood and brown rotted heartwood are produced as a result of 

non-pathogenic fungi digesting the principle wood components–lignin or cellulose, 

respectively. It is this decay process that creates the succession of decaying wood 

habitats that other species can exploit. Various other fungi can decompose or 

naturally prune the aerial parts of the trees in site; however, frequently different soilinhabiting, decomposition fungi colonize the wood when it falls to the ground. 

Belowground fungi are also present colonizing roots. Finally, the fungal mycelium or 

fruit bodies themselves can provide specialist habitats for another community of 

invertebrates. The natural process of breakdown of dead wood releases valuable 

nutrients, which then can be recycled often via mycorrhizal fungi to living parts of 

the tree. 

Invertebrates 

About 6 percent of the entire British invertebrate fauna breed in or feed 

exclusively on other species that breed in decaying wood (Alexander 1999). This 

translates into 1,700 species with different lifestyles, since each species has very 

particular requirements. Very few invertebrates possess the necessary gut enzymes to 

break down the principle components of woodcellulose and ligninso most rely 

on fungi and other micro-organisms to convert them into something more edible. 

In both brown and white heart rot, the end product is black wood mulch, which 

accumulates in the bottom of the hollow trunk as the fungi work into the upper trunk 

and main boughs. Fifteen percent of Britain’s rarest insects, listed in the British Red 

Data Book (Shirt 1987), develop in this medium of relatively constant temperature 

and humidity, protected from the outside world by the surrounding living trunk 

tissuesfor example, the click beetles Lacon querceus and Ampedus cardinalis. 

Specialist invertebrates also exploit the communities in and on the bark, including the 

epiphytic lichens. 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 15 

Lichens 

The most well-known epiphytic lower plant community is the Lobarion 

pulmonariae. Lobarion-rich parkland, with its well spaced ancient trees and a 

continuity of old trees, is of extreme importance for these and other lower plants; 

they are quantitatively richer and qualitatively different, holding a considerable 

number of epiphytic species confined, or nearly so, to such habitats (Rose 1991). 

Although lichens may not be confined to the largest or oldest trees, the presence of 

ancient trees in the area is the feature most strongly associated with lichen-rich 

stands. The Lobarion pulmonariae would be the climax epiphytic community in 

lowland Europe, but it has largely disappeared because of tree felling and pollution 

(Hodgetts 1996). 

Lichens are key indicator species, demonstrating continuity of old trees on a site 

that is also well suited for fungi and saproxylic invertebrates. 

Mammals and Birds 

Some of the UK’s most charismatic animals—woodpeckers, owls and batsare 

associated with decaying wood habitat. These animals find opportunities for cavity 

nest sites in the dead wood and a wealth of invertebrate life in the food chain. Many 

are under severe threat in Western Europesuch as the Eurasian flying squirrel 

(Pteromys volans) and white backed woodpecker (Dendrocopos leucotos)

(Spiridinov and Virkkala 1997)due to the intensification of forestry practices and 

the effectiveness of sanitation felling. 

Identifying Good Dead Wood Habitat: Demonstrating 

Continuity 

Indexes of ecological continuity have been developed for lichens (Rose 1976) 

and saproxylic beetle fauna (Alexander 1988, Fowles and others 1999). Fungi 

representative of late stage successional habitats can provide further examples, 

although no index has yet been developed. 

These indexes demonstrate that our priority is to perpetuate the continuity of 

wood decay habitats comprising old trees (both living and dead standing trees) on 

primary or ancient woodland sites. 

Management for Decaying Wood in Europe 

The wildwood of lowland Europe, in which wood-decaying communities were 

more frequent than today, comprised a mosaic of open sunlit glades, dappled by 

different densities of tree cover and dense high forest. It seems likely that there was a 

high proportion of woodland glades comprising low tree cover and dappled shade 

over extensive areas (Vera 1998). The glades would have been created initially by the 

role of fungi (Green 1996), sometimes in association with phytophagous insects and 

perhaps enlarged by other forces of wind, snow, fire, and erosion (Peterken 1996). 

However, in the UK the influence of fire and erosion is negligible (Rackham 1986). 

Once created they would have been kept open by browsing animals, many of which 

have long since disappeared from our woodlands (Dobson and Crawley 1994). 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

16 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The priority in Europe is to identify and select areas of ancient old-growth or 

relic forest (Harding and Alexander 1994) and then maintain and perpetuate the 

continuity of old trees present on them. To perpetuate wood pastures, it is necessary 

to retain the remaining trees as long as possible, minimize damaging activities in 

their vicinityfor example, deep ploughing under the canopy of the treesand 

promote the establishment of new stands of open-grown trees adjacent to existing 

stands or in close proximity (Alexander and others 1996). 

It is also necessary to protect and enhance decaying wood in our semi-natural 

high forests and coppice woodlands by retaining far more variety and quantity of 

decaying wood habitats and especially to retain far more standing decaying trees of 

all ages. On these sites all fallen dead wood needs to be retained and “tidiness” 

discouraged. Equally as important is to ensure a sustainable provision of all types of 

decaying wood through the next millennium by retaining enough trees in each stand 

to become the decaying wood of the future. 

The worst of all possible management scenarios is to burn the decaying wood 

(Green 1994, 1996). Along the Atlantic coast of northwest Europe, fire is not a 

natural part of the ecosystem of broadleaved woodlands. As decaying wood habitat is 

recycled by a succession of specialized species within the community, fire would 

seriously compromise natural processes. 

Climate change and the isolation of habitats by intensification of land use will 

continue to have marked impacts on islands of biodiversity unless species 

populations have opportunities to develop and expand. Although there is all too little 

knowledge of the rate with which communities can expand and recover given 

suitable habitat directly connected or nearby to it, it is clearly a priority to identify the 

remaining vestiges of habitat that have a well differentiated fauna or flora of 

saproxylic organisms; manage them effectively; and buffer, extend, and ultimately 

work towards connectivity between them. 

A Selection of the Most Important Decaying Wood Sites 

in Europe 

• The New ForestA remarkable area of wood pasture and the largest of its 

type in southern England. 

• The North CotswoldsA large area of traditional agricultural landscape with 

ash (Fraxinus excelsior) pollards in southern England. This area is 

remarkable for its richness of saproxylic fungi and invertebrates that is only 

slowly being recognized. 

• The Lake DistrictAn extensive landscape of pollard trees with exceptional 

epiphytic communities in northern England. 

• Windsor Great ParkA high number of very large, old oak (Quercus robur)

trees near London in southern England, some of which are over 1,000 years 

old, in a variety of environments from minimum intervention high forest, 

wood pasture and parkland, and intensive arable cultivation. 

This is perhaps the largest concentration of very old oak trees in the world in 

association with one of the highest indexes of continuity of saproxylic beetles 

and fungi in the UK. 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 17 

• Fontainbleau ForestSmall areas of minimum intervention woodland in the 

midst of a large commercial and recreation forest by European standards, 

located southeast of Paris, France. 

• Bialowieza National ParkThe largest area of minimum intervention forest 

in Europe, 10,502 ha with some remnant old growth areas, located in eastern 

Poland. 

• Island of VilmFormer pasture woodland with no clearcutting since the 16th

century. Nature reserve with old oak (Quercus robur) and beech (Fagus 

sylvatica) trees, located near the island of Ruegen, northeastern Germany. 

• Bjärka-SäbyLarger oak (Quercus robur) woodland meadows now pastured 

by cattle, located South of Linköping, southeastern Sweden. 

Glossary 

Ancient woodland: Woodland that has existed continuously on the site since AD 

1600 and has been cut only for under wood or timber production. 

Semi-natural ancient woodland: Stands of ancient woodland comprised of 

mainly native species growing where their presence is apparently natural and not 

obviously planted. 

Ancient replanted woodland: Ancient woodland sites with obviously planted 

woodland of a broadleaved, mixed or coniferous type. 

Old-growth forest: [UK] Stands with more than 200 years’ growth (Peterken 

1996). Rose (1992) stresses the importance of continuity of trees older than 200 

years. 

Wood pastures and parkland: Historic land management systems that represent 

vegetation structure rather than a plant community and increasingly thought to mimic 

the structure of the natural forest before human activity. Typically this structure 

consists of large open-grown or high forest trees (often pollards) at various densities, 

in a matrix of grazed grassland, heath land and/or woodland floras. 

Coppice: Trees cut regularly near the ground usually in rotation to produce a 

supply of small wood of small diameter for poles, stakes, and firewood. Usually 

grown with scattered trees allowed to grow to maturity without being cut back. 

Pollards: Trees cut regularly at 2.5-4.0 m above ground level. At this point new 

shoots grow to provide a supply of small wood. The advantage of pollarding is that 

the land under the trees can be used at the same time as pasture for animals or stock 

without the danger of the animals eating the new shoots. 

Native species: Trees and shrubs that colonized Britain unaided by human 

activity before the land bridge with mainland Europe was broken. 

Exotic species: Trees and shrubs introduced into the UK by human activity in 

increasing numbers after 1600. 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

18 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

References 

Alexander, K. N. A. 1988: The development of an index of ecological continuity for 

deadwood associated beetles. In: Welch R. C., compiler: Insect indicators of ancient 

woodland. Antenna 12: 69-70. 

Alexander, K, 1994. The use of freshly downed timber by insects following the 1987 

storm. In: Kirby K. J.; Buckley G. P., eds. Ecological responses to the 1987 Great Storm 

in the woods of southeast England. English Nature Science No. 23: 134-150. 

Alexander, K. N. A. 1999. The invertebrates of Britain’s wood pastures. British Wildlife 

Vol 11(2): 108-117. 

Alexander, K. N. A. 1999. The top British sites for the specialist saproxylic beetle fauna 

of historic woodlands and pasture woodlands. [Personal communication]. 

Alexander, K. N. A.; Green, E. E.; Key, R. 1996. The management of over mature tree 

populations for nature conservation—the basic guidelines. In: Read, H. J., ed. 

Pollard and veteran tree management II. Corporation of London; 122-135. 

Corner, E. J. H. 1994. Address to the British Mycological Society. 29 March 1994. 

Department of the Environment. 1994. Biodiversity: the UK action plan. HMSO Cm 2428. 

Dobson, A.; Crawley, M. 1994. Pathogens and the structure of plant communities. Tree 

9(10). 

Ferris-Kaan, R.; Lonsdale, D.; Winter, T. 1993. The conservation management of 

deadwood in forests. Research Information Note 241. Research Division, Forestry 

Authority. 

Fowles, A. P.; Alexander, K. N. A.; Key, R. S. 1999. The saproxylic quality index: 

evaluating wooded habitats for the conservation of dead wood coleoptera. 

Coleopterist 8: 121-140. 

Green, E. E. 1994. Remember the wood and forget the matches. Wildlife [Sussex] Vol. 

114. 

Green, E. E. 1996. Deadwood for wildlife. Enact 4(1). 

Green, E. E. 1996. Pollarding—origins and some practical hints. British Wildlife 8(2). 

Harding, P. T.; Alexander, K. N. A. 1994. The use of saproxylic invertebrates in the 

selection and evaluation of areas of relic forest in pasture-woodlands. British Journal 

of Entomology and Natural History 7(Suppl. 1): 21-26. 

Hart, C. 1994. Practical forestry for the agent and surveyor. Alan Sutton. 

Hodgetts, N. G. 1996. The conservation of lower plants in woodland. Peterborough: JNCC. 

Lonsdale, D.; Fry, R. 1991. Habitat conservation for insectsa neglected green issue. The 

Amateur Entomologist 21. 

Peterken, G. F. 1996. Natural woodland. Cambridge University Press. 

Rackham, O. 1986. The history of the British Countryside. London: JM Dent. 

Rayner, A. D. M., 1993 The fundamental importance of fungi in woodlands. British 

Wildlife 5: 205-215. 

Rayner, A. D. M. 1996. The tree as a fungal community. In: Read, H. J., ed. Pollard and 

veteran tree management II. Corporation of London; 6-9. 

Read, H. J. 2000. Veteran trees: a guide to good management. English Nature. 
Decaying Wood Status and Ecology in the United Kingdom—Butler, Alexander, and Green 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 19 

Rose, F. 1976. Lichenological indicators of age and environmental continuity in 

woodlands. In: Brown. D. H.; Hawksworth, D. L.; Bailey, R. H., eds. Lichenology: 

progress and problems. Academic Press. 

Rose, F. 1991. The importance of old trees, including pollards, for lichen and bryophyte 

epiphytes. In: Read, H. J., ed. Pollard and veteran tree management. Corporation of 

London. 

Rose, F. 1992. Temperate forest management: its effects on bryophytes and lichen floras 

and habitats. In: Bates, J. W.; Farmer, A. M., eds. Bryophytes and lichens in a changing 

environment; 211-233. 

Rose, F. 1993. Ancient British woodlands and their epiphytes. British Wildlife 5: 83-93. 

Rose, F. 1999. Indicators of Ancient Woodland. British Wildlife 10: 241-251. 

Shirt, D. B., ed, 1987. British red data books: 2. Insects. Peterborough: Nature Conservancy 

Council. 

Speight, M. 1987. Saproxylic invertebrates and their Conservation. Council of Europe. 

Steering Committee for the conservation and management of the environment and 

natural habitats (CPDE). 

Spiridinov, J.; Virkkala, R. 1997. White backed woodpecker. In: Hagenmeijer, W. J. M.; 

Blair, M. J. The EBCC atlas of European breeding birdstheir distribution and 

abundance. European Bird Census Council. T. and A.D. Poyser Ltd. 

UK Biodiversity Group. 1998. Tranche 2 action plans. Terrestrial and freshwater 

habitats. Peterborough: English Nature. 

Winter, T. 1993. Dead woodis it a threat to commercial forestry? In: Kirby, K. J.; Drake, 

C. M., eds. Dead wood matters: the ecology and conservation of saproxylic invertebrates 

in Britain. English Nature Science No.7. 

Vera, F. 1998. Large herbivores and the management of natural landscapes–oak and 

hazel as metaphors for diversity. Planta Europa: 293–300. 
Importance to Aquatic Systems

21
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 65 

Influence of Bank Afforestation and Snag 

Angle-of-fall on Riparian Large Woody 

Debris Recruitment1

Don C. Bragg2 and Jeffrey L. Kershner3

Abstract 

A riparian large woody debris (LWD) recruitment simulator (Coarse Woody Debris [CWD]) 

was used to test the impact of bank afforestation and snag fall direction on delivery trends. 

Combining all cumulative LWD recruitment across bank afforestation levels averaged 77.1 

cubic meters per 100 meter reach (both banks forested) compared to 49.3 cubic meters per 

100 meter reach (one side timbered). Both bank afforestation and snag fall patterns generated 

significant differences in riparian LWD delivery, but there was no noticeable interaction. 

Scenarios with only one bank forested delivered 15 to 50 percent less LWD than their two 

bank counterparts. Snag fall patterns also produced statistically different LWD recruitment, 

with some registering only 35 to 52 percent of the most productive fall patterns. These results 

suggest testing the assumptions of random snag fall from two forested banks before modeling 

riparian LWD recruitment. 

Introduction 

Large woody debris (LWD) recruitment is critical to healthy riparian ecosystems 

(Bisson and others 1987, Dolloff 1994, Kershner 1997), making its recovery a 

primary goal of streamside management (Berg 1995, Kershner 1997). Surprisingly 

little work has been attempted on long-term recruitment dynamics, as research has 

concentrated on the quantification of riparian LWD and its ecological role. However, 

a growing interest in computer modeling of riparian LWD recruitment has prompted 

the development of some simulators in recent years (e.g., Bragg and others 2000, 

Murphy and Koski 1989, Rainville and others 1985, Van Sickle and Gregory 1990). 

While creating a new riparian LWD recruitment model, we became concerned 

about some traditional assumptions. For instance, most efforts have presumed that 

both banks are equally forested. Although this may be true in mesic regions, some 

semi-arid areas have limited forest on some banks. Modelers have also assumed 

random snag fall without testing this premise. Random tree fall patterns can occur 

when failure is not influenced by either disturbances or geomorphology (Maser and 

Trappe 1984, Robison and Beschta 1990, Van Sickle and Gregory 1990). Although 

most riparian LWD simulations have applied this pattern, other distinct 

 

1 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Graduate Research Assistant, Department of Forest Resources and Ecology Center, Utah State 

University, Logan, UT 84322. Current address: Research Forester, Southern Research Station, USDA 

Forest Service, P.O. Box 3516 UAM, Monticello, AR 71656 (e-mail: dbragg@fs.fed.us) 3 Fish Ecologist, USDA Forest Service, Fish Ecology Unit and Department of Fisheries and Wildlife, 

Utah State University, Logan, UT 84322-5210 (e-mail: kershner@cc.usu.edu) 
Riparian Large Woody Debris Recruitment—Bragg and Kershner 

66 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

configurations are possible (Alexander and Buell 1955, Bragg and others 2000, 

Grizzel and Wolff 1998, Schmid and others 1985, Veblen 1986). Another biasing 

factor, tree lean, plays only a limited role in riparian LWD delivery (Hairston-Strang 

and Adams 1998). We decided to test the influence of different bank afforestation 

and angle-of-snag-fall patterns on riparian LWD delivery to the stream using 

computer simulation, which we hoped would improve the long-term prediction of 

riparian LWD recruitment. 

Methods 

Project Design and Assumptions 

The riparian LWD recruitment simulator Coarse Woody Debris (CWD, version 

1.4) was used to predict bankfull channel delivery. CWD is a post-processor to the 

Forest Vegetation Simulator (FVS) (Wykoff and others 1982). We will only briefly 

describe the most salient features of the models’ interplay (Bragg and others 2000). 

FVS establishes, grows, and kills all simulated trees, while CWD drives LWD 

formation and channel recruitment. CWD takes dead trees, places them within the 

riparian zone, selects an angle-of-fall from a predetermined distribution, fells and 

breaks the snag, and assigns which pieces are recruited to the channel. Both 

disturbance-related and self-thinning mortality can be emulated (Bragg 2000). CWD 

randomly assigns tree locations in relation to the channel. Because the angle-of-fall 

pattern set by the user is fixed for the whole riparian forest, biased fall directions 

should be carefully designed to ensure consistency with local conditions. Depending 

on the need, CWD allocated the trees to one or two banks. This effort assumed LWD 

was greater than 10 centimeters in diameter and more than 1 meter long and was 

“recruited” to the bankfull channel if it extended at least 1 meter into this zone. 

Modeled Stream Description 

Dry Lake Creek, a second order stream about 60 km northeast of Jackson, 

Wyoming, on the Bridger-Teton National Forest, was exclusively used for these 

simulations. Along the sampled reach, Dry Lake Creek had a mean bankfull width of 

5.5 meters, an average gradient of 3.5 percent, a mean elevation of 2,565 meters, and 

drained an upstream basin of 1,033 hectares (Bragg and others 2000). Riparian LWD 

volumes within this reach of Dry Lake Creek averaged 8.6 cubic meters per 100 

meter (Bragg and others 2000). The predominantly Engelmann spruce (Picea 

engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa [Hook.] Nutt.) 

forests along Dry Lake Creek averaged approximately 33 square meters per hectare 

of live basal area. Both banks along this particular reach were wooded, but for 

demonstration purposes, half of the simulations considered only one side was 

forested. A bankfull width of 5.5 meters and a streamside forest depth of 38 meters 

for each bank were also assumed. All simulations covered 300 years. 

Statistical Design and Analysis 

In this study, we tested five different snag fall patterns: (1) random (RND); (2) 

the tri-modal CWD default (DEF); (3) snags falling primarily towards the channel 

(TWRD); (4) a fall pattern quartering towards the channel (QRT); and (5) snag 
Riparian Large Woody Debris Recruitment—Bragg and Kershner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 67 

failure largely paralleling the channel (PRL) under two bank afforestation conditions 

(one [O] or both [B] forested) (table 1).

Table 1—Treatment codes, descriptions, and predicted riparian LWD recruitment by bank 

afforestation and snag fall pattern.

Treatment 

code 

Description Cumulative Standard 

 volume deviation 

2 banks forested ---- m3

 per 100 m reach ---- 

BRND Random pattern 79.7 3.74 

BDEF Tri-modal (CWD default) pattern 78.4 5.18 

BTWRD Fall direction towards the channel 90.7 6.87 

BQRT Fall direction quartering towards channel 77.6 5.44 

BPRL Fall direction parallel to the channel 59.0 2.85 

Pooled Average of all 2 bank treatments 77.1 11.41 

 

1 bank forested 

ORND Random pattern 39.9 3.80 

ODEF Tri-modal (CWD default) pattern 38.4 2.60 

OTWRD Fall direction towards the channel 76.6 2.00 

OQRT Fall direction quartering towards channel 64.0 4.59 

OPRL Fall direction parallel to the channel 27.5 2.16 

Pooled Average of all 1 bank treatments 49.3 20.27 

Because of the stochasticity in some CWD subroutines, 10 replicates were run 

for each snag fall pattern. Total LWD recruitment (in cubic meters per 100 meter 

reach) over the simulation period was compared to determine the cumulative 

significance of bank afforestation and snag fall patterns. Because of untransformable 

heterogeneity of variance and non-normal data distributions, the nonparametric twofactor extension of the Kruskal-Wallis (K-W) analysis of variance test and a multiple 

comparison using rank scores were used to identify treatment effects (Zar 1984). 

Results 

Both bank afforestation and snag fall direction significantly (P < 0.05) affected 

cumulative LWD recruitment to Dry Lake Creek, but there was no significant 

interaction between the two (table 1). Recruitment was always lower from streams 

with one forested bank: when averaged across snag fall patterns, having both banks 

forested delivered 77.1 cubic meters per 100 meter reach (standard deviation [SD] = 

11.41), while one forested bank treatments averaged 49.3 cubic meters per 100 meter 

reach (SD = 20.27). 

With only one bank forested, random (ORND), default (ODEF), and OPRL snag 

failure patterns yielded almost 50 percent less LWD recruitment than the same 

patterns (BRND, BDEF, and BPRL) when both banks were forested. Of these 

treatments, only the BPRL versus OPRL comparison proved statistically 

insignificant. OTWRD and OQRT declined only 15 to 20 percent from BTWRD and 

BQRT. However, consistently lower LWD delivery from only one forested bank 

resulted in the rejection of the null hypothesis of no effect of bank afforestation. 
Riparian Large Woody Debris Recruitment—Bragg and Kershner 

68 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The tree fall pattern predominantly towards the channel (TWRD) produced the 

most LWD recruitment (regardless of bank afforestation), while the patterns 

paralleling the channel (PRL) yielded the least (table 1). Even though BTWRD did 

not noticeably differ from BQRT, BDEF, and BRND when both banks were forested, 

it was significantly greater than BPRL. BTWRD (P < 0.05) and BRND (P < 0.10) 

also contributed more LWD to the channel than BPRL. OTWRD yielded more LWD 

than OPRL, ODEF, and ORND (35 percent, 50 percent, and 52 percent of OTWRD’s 

cumulative LWD total, respectively), while OQRT provided more (P < 0.10) than 

OPRL. The ORND, ODEF, and OPRL treatments did not differ statistically. 

Discussion 

Although these bank afforestation and snag fall patterns are greatly simplified, 

their influence on LWD recruitment is statistically and ecologically meaningful. 

Random or tri-modal (i.e., CWD default) patterns produced intermediate levels of 

recruitment, while fall patterns biased strongly in particular directions resulted in 

either greater or lesser delivery, depending on bank afforestation and the predominant 

snag failure direction. 

With only one forested bank, both the magnitude and the absolute volume of 

LWD recruited were substantially decreased (table 1). Three of the simulated 

patterns (ORND, ODEF, and OPRL) yielded about 50 percent less debris than their 

well-forested counterparts. Rather than uniformly decreasing by half the LWD 

recruitment totals, the biased patterns tending towards the channel (OTWRD and 

OQRT) experienced a decrease of only 15 to 20 percent, suggesting that snags falling 

along the major axis are the most important component of riparian LWD recruitment. 

Conclusions 

This research showed that bank afforestation and snag angle-of-fall significantly 

influenced riparian LWD recruitment. Unfortunately, very few simulation studies 

have accounted for the impact of streamside forest coverage and snag fall when 

predicting long-term woody debris dynamics. With both banks forested, a greater 

volume of LWD was delivered over the simulation period, while snag failure patterns 

biased towards the stream outproduced random or other patterns not favoring the 

channel. Snag angle-of-fall became critical when only one side was forested and a 

strong unidirectional control (e.g., prevailing winds) was present. 

Acknowledgments 

We would like to recognize the following people: Dave Roberts (Utah State 

University [USU]); Mark Novak (Bridger-Teton National Forest [BTNF]), Kurt 

Nelson (BTNF), Bob Hildebrand (USU), John Shaw (USU), Andy Dolloff, Marty 

Spetich, and Bernie Parresol (all of the Southern Research Station, USDA Forest 

Service), and several anonymous reviewers. The Fish Ecology Unit of the Forest 

Service and the USU Departments of Fisheries and Wildlife and Forest Resources 

and the Ecology Center provided financial and logistical support. 
Riparian Large Woody Debris Recruitment—Bragg and Kershner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 69 

References 

Alexander, R. R.; Buell, J. H. 1955. Determining the direction of destructive winds in a 

Rocky Mountain timber stand. Journal of Forestry 53: 19-23. 

Berg, D. R. 1995. Riparian silvicultural system design and assessment in the Pacific 

Northwest Cascade Mountains, USA. Ecological Applications 5: 87-96. 

Bisson, P. A.; Bilby, R. E.; Bryant, M. D.; Dolloff, C. A.; Grette, G. B.; House, R. A.; 

Murphy, M. L.; Koski, K. V.; Sedell, J. R. 1987. Large woody debris in forested 

streams in the Pacific Northwest: past, present, and future. In: Salo, E. O.; Cundy, 

T. W., editors. Streamside management: forestry and fishery interactions. Seattle, WA: 

University of Washington Press; 143-190. 

Bragg, D. C. 2000. Simulating catastrophic and individualistic large woody debris 

recruitment for a small riparian system. Ecology 81: 1383-1394. 

Bragg, D. C.; Kershner, J. L.; Roberts, D. W. 2000. Modeling large woody debris in 

riparian mixed conifer forests and small streams of the central Rocky Mountains.

Gen. Tech. Rep. RMRS-55. Ogden, UT: Rocky Mountain Research Station, Forest 

Service, U.S. Department of Agriculture; 36 p. 

Dolloff, C. A. 1994. Large woody debris—the common denominator for integrated 

environmental management of forest streams. In: Cairns, J.; Crawford, T. V.; 

Salwasser, H., editors. Implementing integrated environmental management. 

Blacksburg, VA: Virginia Polytechnic Institute and State University; 93-108. 

Grizzel, J. D.; Wolff, N. 1998. Occurrence of windthrow in forest buffer strips and its 

effect on small streams in northwest Washington. Northwest Science 72: 214-223. 

Hairston-Strang, A. B.; Adams, P. W. 1998. Potential large woody debris sources in 

riparian buffers after harvesting in Oregon, USA. Forest Ecology and Management 

112: 67-77. 

Kershner, J. L. 1997. Setting riparian/aquatic restoration objectives within a watershed

context. Restoration Ecology 5: 15-24. 

Maser, C.; Trappe, J. M. 1984. The seen and unseen world of the fallen tree. Gen. Tech. 

Rep. PNW-164. Portland, OR: Pacific Northwest Forest Experiment Station, Forest 

Service, U.S. Department of Agriculture; 56 p. 

Murphy, M. L.; Koski, K. V. 1989. Input and deletion of woody debris in Alaska streams 

and implications for streamside management. North American Journal of Fisheries 

Management 9: 427-436. 

Rainville, R. P.; Rainville, S. C.; Lider, E. L. 1985. Riparian silvicultural strategies for fish

habitat emphasis. Washington, D.C., Proceedings, 1985 Society of American Foresters 

annual convention; 186-196. 

Robison, E. G.; Beschta, R. L. 1990. Identifying trees in riparian areas that can provide 

coarse woody debris to streams. Forest Science 36: 790-801. 

Schmid, J. M.; Mata, S. A; McCambridge, W. F. 1985. Natural falling of beetle-killed

ponderosa pine. Res. Note RM-131. Fort Collins, CO: Rocky Mountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Van Sickle, J.; Gregory, S. V. 1990. Modeling inputs of large woody debris to streams 

from falling trees. Canadian Journal of Forest Research 20: 1593-1601. 

Veblen, T. T. 1986. Treefalls and the coexistence of conifers in subalpine forests of the 

central Rockies. Ecology 67: 644-649. 
Riparian Large Woody Debris Recruitment—Bragg and Kershner 

70 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Wykoff, W. R.; Crookston, N. L.; Stage, A. R. 1982. User’s guide to the stand prognosis

model. Gen. Tech. Rep. INT-133. Ogden, UT: Intermountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 112 p. 

Zar, J. H. 1984. Biostatistical analysis. 2nd ed. Engelwood Cliffs, NJ: Prentice-Hall; 718 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 71 

Modeling the Delivery of Large Wood to 

Streams with Light Detection and Ranging 

(LIDAR) Data1

William Cody Fleece2

Abstract 

A remote sensing technology called Light Detection and Ranging (LIDAR) was used to assess 

the characteristics of streamside forest structure and predict the delivery of wood to over 55 

stream kilometers in a 28-square kilometer study area. The LIDAR data correlated with 

canopy height (R2

 = 0.65) and stand average basal area (R2 = 0.45). The model predicted that 

83 percent of wood delivered to streams originated within 20 meters of the channel and that 

95 percent came from within 30 meters of the channel. 

Introduction 

Modeling the rate of large wood delivery to streams over large areas is not 

practical because the forest structure information required is frequently unavailable. 

Recent advances in remote sensing technology can now provide resource managers 

with the ability to characterize the structure of streamside vegetation and model the 

loading of wood to streams. The objective of this study was to use Light Detection 

and Ranging (LIDAR) data to model the delivery of wood to streams within the study 

area. This was accomplished by first transforming raw point elevation measurements 

to gridded surfaces. These surfaces were then compared to ground-based forest 

structure information in order to determine if the LIDAR data accurately 

characterized forest structure. The LIDAR data was used for two of three variables 

needed in a wood delivery model. 

Large wood is an integral part of many stream ecosystems in the Pacific 

Northwest. A wide variety of organisms have life histories associated with wood 

located in the active channel. It is a substrate for photosynthetic organisms such as 

green algae, cyanobacteria, diatoms, liverworts, mosses, and trees (Harmon and 

others 1986). Large woody debris jams often create low velocity lateral habitats, 

which provide resources and refugia for juvenile fish (Moore and Gregory 1989). 

Streams with large pieces of wood in the active channel better retain dissolved and 

particulate carbon than those without large wood (Bilby 1981, Bilby and Likens 

1980). In addition to the chemical and biological interactions mentioned above, large 

wood is a key factor in determining the geomorphic response of a stream to the 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Staff Aquatic Ecologist, Entrix Inc., 590 Ygnacio Valley Blvd., Suite 200, Walnut Creek, CA 94596 

(e-mail: CFleece@entrix.com) 
LIDAR and Wood Delivery to Streams—Fleece 

72 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

physical disturbances that shape the channel. There is a positive relationship between 

pool volume and the amount of large wood in the channel (Carlson and others 1990). 

Energy dissipation of streamflow caused by the presence of wood dams causes the 

formation of upstream gravel bars (Lisle 1986). 

Most large wood delivered to streams originates in the streamside vegetation. In 

fact approximately 80 percent of the wood in western Oregon Cascades streams was 

delivered from within 20 m of the active channel (McDade and others 1989, Van 

Sickle and Gregory 1990). Murphy and Koski (1989) reached similar conclusions for 

some Alaskan streams, but the distance of origin was less than that reported in the 

previously mentioned studies. Difference in tree height is the likely cause of this 

disparity. 

Timber harvesting adjacent to streams has, in many cases depleted the source of 

large wood pieces. Consequently many of these streams now have fewer large pieces 

than streams with undisturbed riparian stands (Bilby and Ward 1991). In some cases 

the harvested stands supply a greater number of wood pieces. These pieces, however, 

are smaller and highly mobile compared to downed wood in the streams of oldgrowth forests (Evans and others 1993, McHenry and others 1998). 

Estimating the delivery of wood to streams by means described in traditional 

methods requires detailed information on stand structure (i.e., the height of every tree 

and its distance from the stream) (Minor 1997, Van Sickle and Gregory 1990). 

Alternatively, loading may be estimated by surveying a stream over a period of years 

and recording wood inputs (McDade and others 1989). This information is not 

readily available for many forested streams. In cases where the required information 

is available, it is often limited to very small spatial extents. This study seeks to 

determine whether a remote sensing technology called Light Detection and Ranging 

(LIDAR) can provide information necessary to predict wood delivery to streams over 

a wider spatial extent than is practical with ground-based methods. 

Study Area 

This study was conducted in the McDonald-Dunn State Research Forest 

(McDonald-Dunn Forest) near Corvallis, Oregon (fig. 1). The McDonald-Dunn 

Forest is located in the Valley Foothills subecoregion of the Willamette Valley 

ecoregion. The Valley Foothills range in elevation from 10 to 1,500 feet and receive 

40 to 60 inches of rain per year (Pater and others 1997). 

The McDonald Forest comprises approximately 48 square kilometers and within 

its boundaries are more than 30 different tree species, including Abies grandis, 

Pseudotsuga menziesi, and Quercus garryana. The majority of stands in the 

McDonald-Dunn Forest are either coniferous or a coniferous/hardwood mixture. 

Only 13 of 179 stands are greater than 200 years old, and the median stand age is 

roughly 60 years. The LIDAR flight line and the 28 square kilometer study area 

include portions of the McDonald-Dunn Forest as well as some privately owned land. 

Approximately 55-kilometers of stream occur within the study area, most of which 

are first-order and second-order streams. The largest stream, Soap Creek, is fourthorder and lies on the eastern boundary of the study area. 
LIDAR and Wood Delivery to Streams—Fleece 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 73 

Figure 1―The study area in the McDonald-Dunn State Research Forest near 

Corvallis, Oregon.

LIDAR Technology 

LIDAR is a remote sensing technology capable of characterizing a variety of 

vegetation structure metrics. Studies have shown LIDAR capable of accurately 

measuring mean canopy height (Magnussen and Boudevyn 1998, Naesset 1997), 

timber volume (Naesset 1997, Nilsson 1996), basal area (Lefsky and others 1997, 

Means and others 1999), and biomass (Lefsky and others 1999, Nelson 1997). 

LIDAR is also used for characterizing topography (Garvin 1996). LIDAR technology 

is based upon the general principle that a portion(s) of an emitted laser pulse will 

reflect to its source. Because the travel rate of a pulse is constant (i.e., the speed of 

light), concurrently emitted pulses with different return times must have differing 

travel distances. Portions of these pulses reflect back to a sensor on the airplane. 

Because the position and orientation of the sensor is known for each emitted pulse, 

every returning signal has a unique set of three-dimensional coordinates. 

The LIDAR unit used for this study is a scanning system. Approximately 15,000 

pulses per second were emitted in a sinusoidal pattern (fig. 2) from an airplane at an 

altitude of 2,000 m. The footprint, or size of the laser pulse upon reaching the earth, 

was approximately 0.5 m in diameter. The spacing between pulses over bare earth 

was approximately 6 m, and the width of each scan was approximately 4,500 m. 

Because the same pulse can generate several returning signals, the distance between 

points, in the horizontal plane is often less than 6 m. Multiple returns are generated 

when some portion of a laser pulse is intercepted by a reflective surface and returned 

to the airborne sensor. The uninterrupted portion of the pulse can generate additional 

return signals if reflective surfaces are encountered.
LIDAR and Wood Delivery to Streams—Fleece 

74 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 2―Airborne laser scanner. 

Methods 

The objective of this study is to use LIDAR data to model the delivery of wood 

to streams within the study area. To accomplish this, LIDAR was first transformed to 

gridded surfaces representing the ground and canopy surface. These surfaces were 

then compared to ground-based forest structure information in order to determine if 

LIDAR accurately characterized forest structure. LIDAR was then used to derive two 

of three variables in a probabilistic wood delivery model. 

Airborne Data Collection 

Airborne data were collected in October 1998. The number of returning signals 

was highly variable. A single returning signal was most common. Second and third 

returns were also very common but respectively less frequent. Fourth or fifth returns 

were captured in rare instances. 

Number of return signals for study area: 

 Signal return order No. of signals 

 1st 992,208 

 2nd 200,611 

 3rd 27,784 

 4th 2,068 

5th 89 

 Y 

 X 

OBJ 
LIDAR and Wood Delivery to Streams—Fleece 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 75 

One explanation for the decreasing number of signals with return order is 

technological. There was a limit on the speed at which return signals were 

assimilated. The scanning equipment is capable of capturing only one signal every 

0.2 nanoseconds. Once a signal was recorded, additional capture was precluded for a 

time that equated to approximately 5 m of travel distance. Therefore, only vegetation 

greater than 5 m in height can generate multiple returns from a single pulse. 

Ground Data Collection 

Two ground-based data sets were used in this study. The first was a set of 

ground plots, and the second was a stand-level aggregation of ground plot data. The 

ground plot data used in this study were collected as part of an ongoing forest 

inventory at the McDonald-Dunn Forest. Data collection occurred between July 1997 

and February 1998. All sample plots have a variable radius. Tree size and distance 

from a reference center point determine the radius of these plots. All trees equal to or 

greater than 20-centimeters in diameter at breast height (DBH) and located within 6.1 

m of the plot center were automatically included in the sample. Large trees located 

beyond the 6.1 meter threshold were included in the sample if the DBH was 

sufficiently large. Either prisms or relaskops were used to identify trees for inclusion 

in the sample (Oregon State University 1999). Among the recorded measurements 

were DBH and tree heights. Tree heights were recorded for all living and dead trees 

within the plot. 

The stand data used in this study were derived from the ground plot data and 

digital orthophotographs. Ground plots with similar characteristics (e.g., height, age) 

were grouped together and stand boundaries were digitized around those clusters 

based on the features observed in the photographs. These groupings contain the 

attribute summaries of information collected at the plot level including, but not 

limited to, basal area. Since not every ground plot was sampled every year, where 

current stand information was missing, a growth and yield model called ORGANON 

was used to simulate the growth of individual trees from the last period of record to 

the present date. The return interval for sampling an individual ground plot is 

typically less than 10 years but can vary from 1 to 15 years. 

Airborne Data Transformation 

Each LIDAR return signal contains a unique three-dimensional coordinate. 

Ground elevation return signals were separated from return signals generated by the 

vegetation via a proprietary processing algorithm (Renslow, pers. comm.). Generally 

described, this process works as follows: 1) last return signals are separated from 

non-first return signals, 2) a Triangulated Irregular Network surface (TIN) is created 

from these points, 3) points obviously above the ground were removed on the basis of 

visual inspection, 4) the process is repeated until all points above the ground were 

removed. Digital orthophoto stereo pairs were used to verify the categorization of 

these signals. Triangulated Irregular Network surfaces (TINs) were computed from 

the x, y, and z coordinates of the ground and first return LIDAR point files. A TIN is 

a set of non-overlapping, adjacent triangles intersecting the points with threedimensional coordinates (fig. 3). The TINs in this study were used to generate 

gridded surfaces called lattices. Lattices are similar to TINs in that the mesh points 

contain elevation information. The spacing and resolution of these two data models, 

however, is very different. The mesh points of a TIN contain information from the 
LIDAR and Wood Delivery to Streams—Fleece 

76 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

original point files. Mesh points do not exist between the original raw point locations. 

In the conversion from TIN to lattice, mesh points are created at regular intervals. 

Interpolation is used to calculate the mesh point elevation where the distance between 

original points is greater than the resolution of the created lattice. The principle 

advantage of a lattice over a TIN is that calculations can be performed on lattices, 

whereas this capability is not available for TINs. After creation of the lattices, the 

ground elevation surface was subtracted from the first return elevation surface. The 

result of this calculation was a new lattice for which each cell contained a canopy 

height value. The cell size for each of these surfaces is approximately 1.5 m. 

Figure 3―Data model structure. 

Thirty-two ground plots in a 929-hectare section of the southwestern portion of 

the study area were selected and compared to the canopy height grid. This section of 

the study area was selected because it contained the full range of forest structure 

characteristics, from very old to very young. Ground plots located adjacent to roads 

or clear cuts were excluded from the analysis because of uncertainties regarding the 

geographic location of the plot’s GIS data set. The heights of individual trees in each 

ground plot were averaged, and the values were plotted against the laser-derived 

canopy height (fig. 4).

The rate of large wood delivery, to streams, predicted by the model in this study 

was compared to wood delivery rates observed in the Western Cascades ecoregion 

(Lienkaemper and Swanson 1987). Five hundred-year-old conifer forests surrounded 

the streams in the Cascade study. The Cascade sites are higher in elevation and 

receive more precipitation than the McDonald-Dunn Forest. Differing environmental 

conditions may influence the result of any comparison. However, these forests 

(especially the older forests) have structural similarities that may make a comparison 

useful. Many of the tree species such as Douglas-fir (Pseudotsuga menziesii) are 

common to both study areas. Trees in the Cascade sites are likely to be larger than 

trees in the McDonald Forest, resulting in larger source areas. 

Lienkaemper and Swanson (1986) recorded the number of trees entering five 

streams over a period of 7 to 9 years. From this information I calculated the number 

of trees entering the stream per hectare of source area over a 5-year period. I assume 

that all the trees entering the Cascade streams had origins less than 35 m from the 

channel (McDade and others 1989). This may be a conservative estimate considering 

that McDade (1988) observed evidence of trees falling into streams from distances 

greater than 60 m. 
LIDAR and Wood Delivery to Streams—Fleece 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 77 

Figure 4―Ground plot height vs. laser height.

The Wood Model 

Unlike most wood delivery models, data used in this study are not tree specific. 

LIDAR data do not provide information about individual trees. Instead, LIDAR 

defines a surface(s) that approximates tree height. The resolution of each of these 

surfaces is approximately 1.5 m. Therefore, the model in this study describes the 

probability that a given cell will deliver wood to a stream. Delivery of wood to 

streams is characterized by the equation: 

Wd = Ps D Rf (1) 

The delivery of wood to a stream is represented by (Wd) and is expressed as the 

number of trees falling in a stream per hectare over a 5-year period. Ps equals the 

probability that a tree will fall in a stream given the height of the tree and its distance 

from the stream. D is a relative measure of tree density and is unit-less. Rf, the rate of 

tree fall, equals the average number of trees that fell per hectare over a 5-year period. 

Probability of Falling in a Stream 

The probability of a tree falling in a stream is a function of tree height and 

distance from the stream. It is assumed that the direction of tree fall is random. The 

probability of a given grid cell contributing wood to a stream (Ps) is based on the 

trigonometric function: 

Ps = (arccosine ( z / h ) ) / 180 (2) 

in which the variable z equals the perpendicular distance to the stream and h equals 

the height of a given cell. A geographic information system (GIS) was used to obtain 

both variables for this equation. Using GIS, a grid was created to compute the 

shortest perpendicular distance to a given segment of the stream network. It was not 

possible to calculate the distance to two streams. Therefore, it is necessary to assume 

that when a tree falls it always falls in the nearest stream. A visual assessment of the 

study area showed that only a small number of canopy height grid cells could 

y = 0.78x - 0.09

R2

 = 0.65

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Mean height ground plot (m)

Laser height (m) 
LIDAR and Wood Delivery to Streams—Fleece 

78 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

potentially contribute to two streams (i.e., near confluences); thus, this was not 

expected to affect the model results. 

 

Density 

Density in the wood delivery models (Minor 1997, Van Sickle and Gregory 

1990) is the number of trees per unit area. In this study an alternative approach was 

taken because of the inability to discern individual trees with this LIDAR data set. I 

hypothesized that a relationship between the density of LIDAR return signals, per 

unit area, and forest density might exist. 

Because first return signals are so numerous (one flight line of approximately 6-

miles in length contained more than 5-million first return points) and because even 

clearcuts generate first returns, these points were eliminated from the density 

analysis. A grid was created to represent the density of non-first return points per unit 

area. The point density computation counted every LIDAR point within a 0.4-hecare 

area (equivalent to a circle 36m in diameter). The results of this analysis were 

converted to points per hectare that were then compared to stand averages for basal 

area (fig. 5). Basal area was used here as a relative measure of density. I then used the 

relationship observed in figure 5 and equation 3 to assign the stand average basal area 

to every grid cell in the study area. 

Basal Area = ( ln ( dnst-grd / 36.594 )) / 0.0248 (3) 

This equation yielded the basal area in square meters per hectare. The fraction of 

basal area (BA) per cell was calculated as: 

 D = ( BA m2

 / ha ) * ( 1 ha / 10,000 m2) (4) 

This value was used as density in the total loading calculation. 

y = 36.594e 0.0248x

R2 = 0.4487

0

50

100

150

200

250

0 10 20 30 40 50 60 70

Stand average basal area (m2

/hectare)

Non-first return signals per

hectare

Figure 5―Basal area vs. non-first return signals. 
LIDAR and Wood Delivery to Streams—Fleece 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 79 

Rate of Fall 

No direct estimate of tree fall was available for this study. Van Sickle and 

Gregory (1990) used mortality as a rough approximation of the probability of tree 

fall. ORGANON, a model designed to predict the growth of individual trees in a 

stand, is also capable of estimating mortality for all trees less than 109-centimeters in 

diameter. I assume for this study that the probability of tree fall equals mortality, thus 

no trees were snags after mortality. ORGANON and input files for every stand in the 

McDonald Forest are available at the Web site: http://www.cof.orst.edu/resfor/ 

mcdonald/purpose.sht. 

The data from 30 stands within the study area were randomly selected as input 

files for ORGANON. The model is designed to run with greater than 50 trees per 

stand. Twenty of the initial 30 stands did not meet this requirement and were 

discarded. Growth over a 25-year period was calculated for each of the remaining 

input files: 

Stand No. Mortality 1 

61103 56.049 

60802 56.148 

 60513 81.259 

 60811 111.901 

 70501 133.457 

 60402 198.346 

 60403 209.580 

 51101 259.951 

 51001 325.062 

 60901 334.272 

Average/25 yrs. 176.603 

Average/5yrs. 35.321

1 Number of trees/hectare for 25-year period. 

The average mortality of all 10 stands was calculated for a 5-year period and 

applied uniformly across the study area as an approximation for the rate of fall (Rf). A 

uniform Rf was used in the wood delivery model, though it is recognized that 

mortality is highly variable and site specific. The 5-year time period was chosen 

because the results of this model will be compared to data collected in the western 

Cascade Mountains over a similar time interval. 

Results 

The cumulative frequency of wood delivered to streams, as a function of 

distance from the stream, is a value commonly reported in wood delivery studies 

(McDade 1988, McDade and others 1989, Minor 1997, Van Sickle and Gregory 

1990). This study found that 83 percent of the predicted wood delivered to streams 

came from within 20 m of the channel, and 95 percent came from within 30 m of the 
LIDAR and Wood Delivery to Streams—Fleece 

80 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

channel (fig. 6). Murphy and Koski (1989) found that 99 percent of the wood in 

southeast Alaska came from within 30 m of the channel. McDade (1988) reported 

that roughly 90 percent of wood delivery to streams in 29 old growth forests in 

Oregon and Washington originated within 30 m of the stream. It is not surprising that 

the cumulative frequency distribution curves presented in this study report greater 

cumulative percentages from shorter distances than those reported in McDade (1988) 

because the stands in the McDonald-Dunn Forest, on average, are much shorter. Only 

thirteen of 179 stands studied were greater than 200 years old. The median age of the 

stands within the study area was approximately 60 years. 

The model in this study also predicted the rate at which large wood enters 

streams. These predictions were compared to values reported by Lienkaemper and 

Swanson (1987). Predictions from the McDonald-Dunn Forest closely match those of 

the H.J. Andrews Research Forest (table 1). The values for Lookout Creek may be 

lower than expected due to the presence of a road in the source area. The value 

reported for the McDonald-Dunn Forest is the mean of the entire study area. Further 

investigation of loading rates from specific stream segments and from various stand 

structure types is needed. 

Figure 6―Wood recruitment as a function of distance from the stream for the entire 

study area. 

Tables 1―Loading Rate Comparison between H.J. Andrews Research Forest and 

McDonald-Dunn Forest. 

Location No. of 

years 

Reach 

length 

Width1 Area 

(ha) 

No. of 

trees 

added 

Trees/ha Trees/ha 

5-yr. 

period 

ws-92 8 170 70 1.19 6 5.0420 3.1513 

ws-22 8 146 70 1.022 4 3.9139 2.4462 

Mack Creek2 9 332 70 2.324 10 4.3029 2.3905 

Upper Lookout2 9 483 70 3.381 12 3.5492 1.9718 

Lower Lookout2 7 350 70 2.45 6 2.4490 1.7493 

McDonald-Dunn 

Forest3 

 3.0035 

1 Assumed source-area based from McDade and others 1989. 2 Numbers derived from values reported in Lienkaemper and Swanson 1986. 2 Average for entire study area. 

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80

Distance from stream (m)

Cumulative % of wood delivered
LIDAR and Wood Delivery to Streams—Fleece 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 81 

Discussion 

The ORGANON mortality values used in this study were not spatially explicit. 

ORGANON calculated mortality values for a wide range of age classes. With the aid 

of height regression equations, mortality could be applied variably across the 

landscape based on the canopy height observed in each grid cell. This approach 

might be warranted because Headman and others (1996) found that loading rates 

varied with stand age, indicating that mortality is lowest for moderately aged stands. 

Further, this study utilized only a small portion of the total number of stands. As 

illustrated, mortality varies from stand to stand. Mortality values could potentially be 

associated with the geographic location of each stand. Because this approach would 

not be practical in remote areas with little stand data, it was not pursued in this study. 

The delivery rate value reported in this study was a mean for all 55 stream 

kilometers. The delivery rates reported in the Lienkaemper and Swanson (1987) 

study were for comparatively short stream reaches of a few 100 meters. Most of the 

stands in the McDonald-Dunn Forest are much younger and shorter than those 

studied at the H.J. Andrews Forest. Although these results are encouraging, further 

evaluation of model predictions for shorter stream reaches in the McDonald-Dunn 

Forest is warranted. 

Conclusion 

A strong correlation was observed between the ground plot forest structure 

metrics and laser derived canopy height. A relationship was also observed between 

the stand average basal area and the number on non-first return LIDAR points. The 

cumulative frequency distribution curve and the wood delivery rate predicted by this 

model are consistent with the conceptual frameworks established in other studies. 

Additional research is needed to refine the ability of this technology to assess the 

wood delivery potential of streamside forests, but initial results are promising. 

Although the scope of the modeling in this study was limited to wood delivery, 

LIDAR technology shows great potential as a tool in the study of stream ecosystems. 

Some potential applications are stream shading studies, litterfall modeling, 

quantification of the area of streamside forests that can potentially deliver wood to 

streams, and a number of topographic applications. Because LIDAR data can be 

collected over such large areas, it shows great promise as a watershed assessment 

tool. 

Acknowledgments 

I thank Aileen Buckley, Stan Gregory, and Tom Lisle for comments that greatly 

improved this manuscript. I also appreciate Bill Huber’s assistance with some of the 

spatial calculations used in this study. Debbie Johnson and Janet Ross graciously 

provided the ground-based forest structure measurements, and Mike Renslow shared 

the airborne laser data. 
LIDAR and Wood Delivery to Streams—Fleece 

82 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

References 

Bilby, Robert E.; Likens, Gene E. 1980. Importance of organic debris dams in the 

structure and function of stream ecosystems. Ecology 61(5): 1107-1113. 

Bilby, Robert E. 1981. Role of organic debris dams in regulating the export of dissolved 

and particulate matter from a forest watershed. Ecology 62(5): 1234-1243. 

Bilby, Robert E.; Ward, James W. 1991. Characteristics and function of large woody 

debris in streams draining old-growth, clear-cut, and second-growth forests in 

southwestern Washington. Canadian Journal of Fisheries and Aquatic Science 48: 

2499-2508. 

Carlson, J. Y.; Andrus, C. W.; Froehlich, H. A. 1990. Woody debris, channel features, and 

macroinvertebrates of streams with logged and undisturbed riparian timber in 

Northeastern Oregon, U.S.A. Canadian Journal of Fisheries and Aquatic Sciences 47: 

1103-1111. 

Evans, Brent F.; Townsend, Colin R.; Crowl, Todd A. 1993. Distribution and abundance of 

coarse woody debris in some southern New Zealand streams from contrasting 

forest catchments. New Zealand Journal of Marine and Freshwater Research 27: 227-

239. 

Garvin, James B. 1996. Topographic characterization and monitoring of volcanoes via 

airborne laser altimetry. In: McGuire, W. J.; Jones, A. P.; Neuberg, J., eds. Volcano 

instability on the Earth and Other Planets, Geological Society Special Publications No. 

110: 137-152. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromac, K. Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in temperate 

ecosystems. Advances in Ecological Research 15:133-302. 

Headman, Craig W.; Van Lear, David H.; Swank, Wayne T. 1996. In-stream large woody 

debris loading and riparian forest seral stage associations in the southern 

Appalachian Mountains. Canadian Journal of Forest Research 26: 1218-1227. 

Lefsky, Michael; Cohen, W. B.; Acker, S. A.; Spies, T. A.; Parker, G. G.; Harding, D. 1997. 

LIDAR remote sensing of forest canopy structure and related biophysical 

parameters at the H.J. Andrews experimental forest, Oregon, USA. In: Greer, J. D., 

ed. Natural resources management using remote sensing and GIS. Washington DC: 

American Society of Photogrammetry and Remote Sensing. 

Lefsky, Michael A.; Harding, D.; Cohen, W. B.; Parker, G.; Shugart, H. H. 1999. Surface 

LIDAR remote sensing of basal area and biomass in deciduous forests of eastern 

Maryland, USA. Remote Sensing of Environment 67: 83-98. 

Lienkaemper, G. W.; Swanson, F. J. 1986. Dynamics of large woody debris in streams in 

old-growth Douglas-fir forests. Canadian Journal of Forest Research 17: 150-156. 

Lisle, Thomas E. 1986. Stabilization of a gravel channel by large streamside obstructions 

and bedrock bends, Jacoby Creek, northwestern California. Geological Society of 

America Bulletin 97: 999-1011. 

Magnussen, S.; Boudewyn, P. 1998. Derivations of stand heights from airborne laser 

scanner data with canopy-based quantile estimators. Canadian Journal of Forest 

Research 28: 1016-1031. 

McDade, M. H. 1988. The source area for coarse woody debris in small streams in 

western Oregon and Washington; 69 p. M.S. thesis. 
LIDAR and Wood Delivery to Streams—Fleece 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 83 

McDade, M. H.; Swanson, F. J.; McKee, W. A.; Franklin, J. F.; Van Sickle, J. 1989. Source 

distances for coarse woody debris entering small streams in western Oregon and 

Washington. Canadian Journal of Forest Research 20: 326-330. 

McHenry, Michael L.; Schott, Eric; Conrad, Robert H.; and Grette, Glenn B. 1998. Changes 

in the quantity and characteristics of large woody debris in streams of the Olympic 

Peninsula, Washington, U.S.A. (1982-1993). Canadian Journal of Fisheries and 

Aquatic Sciences 55: 1395-1407. 

Means, Joseph E.; Acker, Steven A.; Harding, D. J.; Blair; B. J.; Lefsky, Michael A.; Cohen, 

Warren B.; Harmon, M. E.; McKee, W. Arthur. 1999. Use of large-footprint scanning 

airborne LIDAR to estimate forest stand characteristics in the western Cascades of 

Oregon. Remote Sensing of the Environment. 67: 298-308 

Minor, Kathleen P. 1997. Estimating large woody debris recruitment from adjacent 

riparian areas. Corvallis: Oregon State University; 34 p. M.S. thesis. 

Moore K. M. S.; Gregory, S. V. 1988. Response of young-of-the-year cutthroat trout to 

manipulation of habitat structure in a small stream. Transactions of the American 

Fisheries Society 117: 162-170. 

Murphy, Michael L.; Koski, K. V. 1989. Input and depletion of woody debris in Alaska 

streams and implications for streamside management. North American Journal of 

Fisheries Management 9: 427-436. 

Naesset, Erik. 1996. Determination of mean tree height of forest stands using airborne 

laser scanner data. Photogrammetry & Remote Sensing 52: 49-56. 

Naesset, Erik. 1997. Estimating timber volume of forest stands using airborne laser 

scanner data. Remote Sensing of Environment 61: 246-253. 

Nelson, Ross. 1997. Modeling forest canopy heights: The effects of canopy shape. Remote 

Sensing of Environment 60: 327-334. 

Nelson, Ross; Oderwald, Richard; Gregoire, Timothy G. 1997. Seperating the ground and 

airborne laser sampling phases to estimate tropical forest basal area, volume, and 

biomass. Remote Sensing of Environment 60: 311-326. 

Nilsson, Mats. 1996. Estimation of Tree heights and stand volume using an airborne 

LIDAR system. Remote Sensing of Environment 56: 1-7. 

Oregon State University, College of Forestry. 1999. Research forests inventory manual. 

Corvallis, OR. 

Pater, D. E.; Bryce, S. A.; Thorsen, T. D.; Kagan, J.; Chappell, C.; Omernik, J. M.; Azevedo, 

S. H.; Woods, A. J. 1997. Ecoregions of western Washington and Oregon. 

1:1,350,000. United States Environmental Protection Agency. 

Van Sickle, John; Gregory, Stanley V. 1990. Modeling inputs of large woody debris to 

streams from falling trees. Canadian Journal of Forest Research 20: 1593-1601. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 85 

How Much Dead Wood in Stream Channels 

Is Enough?1 

Thomas E. Lisle2

Abstract 

Private forest managers often seek guidelines on how much dead wood should be retained in 

streams in order to adequately fulfill ecosystem functions. There are three approaches to 

answering this question for a particular reach of channel. The first approach uses an 

understanding of ecologic functions of dead wood in streams to determine the amount needed 

to fulfill ecologic and geomorphic functions. This approach fails because the complexities of 

sizes, shapes, and arrangements of dead wood in a variety of lotic ecosystems overwhelm any 

scientific specification of target loadings. Another approach uses reference loadings to 

evaluate departures in amounts of dead wood in streams from reference amounts in unaltered 

systems. A precise threshold cannot be defined using this approach because dead wood 

volumes are highly variable, even within pristine channels in similar settings, and 

distributions for managed and pristine channels overlap. A third approach constructs a wood 

budget by evaluating past, present, and projected supplies in streams and riparian areas. This 

is a cumulative-effects analysis that shifts the focus from channels to riparian forests. In 

combination, the three approaches provide the best information to determine how much wood 

is enough, but they do not offer simple, formulaic prescriptions. The demands for performing 

the necessary analyses before harvesting riparian wood suggest that management of riparian 

forests will continue to be guided most often by general prescriptions. 

Introduction 

A primary goal of managing riparian forests is to maintain sufficient dead wood 

in stream channels so that it fully performs its natural geomorphic and ecologic 

functions. Much is at stake in balancing the economic and ecologic values of riparian 

wood. Today, most land managers appreciate the value of dead wood in large fishbearing channels, although less is known or appreciated about its value in low-order, 

intermittent tributaries. This gap is critical because first- and second-order channels 

comprise a large portion of the drainage network; in sixth-order drainage networks, 

for example, such low-order channels account for roughly two-thirds of the total 

channel length. The economic value of riparian wood can be evaluated from the 

market, although the profit realized by a timberland owner is uncertain, due in part to 

evolving regulations. The ecological value cannot be evaluated as precisely because 

of the complexity and variability of riparian conditions and processes supporting the 

functions of dead wood in aquatic ecosystems. How do we weigh the economic and 

ecologic contribution of riparian wood and manage riparian forests under some 

inevitable uncertainties? 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Hydrologist, Pacific Southwest Research Station, USDA Forest Service, 1700 Bayview 

Drive, Arcata, CA 95521 (e-mail: tel7001@axe.Humboldt.edu) 
How Much Dead Wood Is Enough—Lisle 

86 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

In the 1994 Northwest Forest Plan (FEMAT 1993), Federal agencies managing 

forests in the Pacific Northwest pled ignorance of natural processes and gave 

guidelines for setting aside riparian reserves in which direct pathways of watershed 

products (water, sediment, wood, heat, and nutrients) to aquatic ecosystems would 

not be disturbed by human activities until those pathways were analyzed and 

understood (e.g., watershed analysis; FEMAT 1993). Although the implementation of 

these guidelines remains controversial, this strategy greatly simplifies management 

decisions in riparian reserves once they are designated. In contrast, many private 

forest owners press to limit the size of buffer strips and continue entering riparian 

forests to harvest timber. Extracting riparian wood without significantly impacting 

lotic ecosystems requires more active management strategies and motivates better 

understanding of the dynamics and functions of dead wood and other functions of 

riparian forests for aquatic ecosystems. The private forester might phrase the problem 

as: “How much wood should I retain in order to satisfy the ecologic functions that 

society demands?” 

This question can be analyzed by using three approaches: 

1. Ecologic functions: Determine the amount of dead wood in streams needed 

to fulfill vital functions, e.g., maintaining habitat for a sensitive species. 

2. Reference loadings: Determine desired amounts of dead wood in streams 

from amounts in unaltered systems. 

3. Wood budgets: Determine desired amounts in streams and riparian sources 

by constructing a wood budget to evaluate past, present, and projected 

supplies. 

In this paper, I evaluate these approaches and present a new compilation of data on 

dead wood volumes in California and Oregon. 

Approach 1: Ecological Functions of Dead Wood

The great variety of functions of dead wood in lotic ecosystems is summarized 

elsewhere (Harmon and others 1986, Sedell and others 1988), and I will mention only 

a few here for the sake of discussion. In general, lotic communities have evolved 

with natural and variable supplies of watershed products, including large quantities of 

wood in forested streams. Dead wood is commonly the most important source of 

structure in forest streams. It also affects the routing of other watershed products, 

particularly sediment, and their influence on ecosystems. By concentrating and 

dispersing hydraulic forces, dead wood can greatly diversify physical conditions in 

streams and provide habitats for various species and age classes in aquatic 

communities. 

A salient characteristic of dead wood in channels is its variability in terms of 

supply, longevity, and function. The diameter of dead wood is commonly larger than 

bed particles by an order of magnitude or more and comparable in scale to channel 

depth; wood length is comparable to channel width. Thus, single pieces can locally 

control channel morphology. Consequently, the myriad of sizes and shapes of dead 

wood can create a myriad of channel forms at the reach scale, depending on the 

arrangement of the wood and the background geomorphic and hydrologic conditions 

of the channel. One must be careful not to discount the variety of functions of dead 

wood in aquatic and riparian ecosystems. Nevertheless, the population of dead wood 
How Much Dead Wood Is Enough—Lisle 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 87 

as distributed naturally in channels is highly inefficient in performing some easily 

recognizable functions for habitat. On the one hand, a single piece can strategically 

lodge along a channel thalweg at the outside bank of an incipient bend and thereby 

scour a deep pool. But more wood is likely to hang up on a bar or flood plain and 

interact with the flow only during flood stages. Thus, the influence of a single piece 

can vary widely as it moves downstream. 

Moreover, dead wood in channels tends to be concentrated. Common wood 

input processes—wind storms, wildfire, landslides, and debris flows—quickly deliver 

large amounts of wood at points in the channel network. Even if inputs are 

widespread, fluvially transported wood tends to aggregate (Braudrick and others 

1997). Although deposited aggregates (debris jams) can strongly affect channels, the 

obvious influence of individual pieces diminishes quickly with growth of the 

aggregate. 

I do not mean to imply that there is plenty of wood to spare in streams, but that 

it is impossible to practically and scientifically specify how much is enough. The 

diversity of size and arrangement of wood and the diversity of channels makes it 

futile to say how a given amount of dead wood will result in particular habitat 

conditions. Effects are complex and stochastic. On the one hand, channels without 

dead wood or other forms of structure can quickly evolve to very simple forms. 

Moderately sized channels with gradients of about 1 to 4 percent are particularly 

prone to simplify, because they have a weak tendency to form bars and pools without 

exogenous structure (Montgomery and Buffington 1997). These conditions typify 

fish-bearing streams in managed forests in the west. On the other hand, the typically 

large volumes of dead wood in pristine forest channels contribute to diverse habitats. 

There is no scientifically defensible, site-specific way to determine what smaller 

amounts would adequately perform the same functions. For channels in intensively 

managed private forests, where is the middle ground? This type of uncertainty was 

the motive in the Northwest Forest Plan for setting aside riparian reserves with strong 

limitations on entry. 

By using approach 1 alone, we are presently incapable of resolving the issue of 

how much wood is enough. Approach 1 motivates further research and conscientious, 

site-specific management of streams. By exploring the functions of dead wood in 

aquatic ecosystems, it provides a scientific basis for managing forest streams. 

However, it offers no simple prescriptions for the broader, regulatory arena. 

 

Approach 2: Reference Values of Dead Wood Loading

Another approach to determining how much dead wood is enough is to compare 

volumes and sizes in a given channel to those in comparable channels that serve as 

references. Given that aquatic communities evolved long before intensive forest- and 

waterway management began, pristine channels offer the obvious reference 

condition. Management within the range of pristine conditions provides a level of 

confidence that natural communities will persist. Although this reference may not 

always be attainable under management, it provides a standard to measure departures 

from natural conditions. To apply this approach, we need to know how the volume 

and size of dead wood varies between regions and within a region, and how 

management affects those variations. 
How Much Dead Wood Is Enough—Lisle 

88 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Let us consider dead wood volumes first. I compiled frequency distributions of 

in-channel volumes of dead wood (m3

 per ha of bankfull channel area) in unmanaged 

forests in different climatic regions of California and Oregon (fig. 1). Distributions in 

each region were compiled from a small sample of 9 to 12 reaches that were at least 

200 m in length. The channels are second- to fourth-order; drainage areas range from 

50 to 3,000 ha. Because these reaches were not selected randomly, they do not 

represent an unbiased sample of pristine conditions. Despite these limitations, the 

data show some expected trends. There are wide differences between regions. For 

example, the median loading for old-growth redwood is about 1,000 m3

/ha, while 

median loading for mixed conifers in the northern Sierra Nevada is only 30 m3

/ha. 

This indicates that reference (or pristine) loadings for one region must not be applied 

to another. There are also wide variations within regions; the difference between 

minimum and maximum loadings is well over tenfold in each region. 

Figure 1—Cumulative frequency distributions of volumes of dead wood in pristine 

channels in four forest types: Oregon Cascades and Klamath Mountains (Harmon 

and others 1986); coastal redwood (Keller and Tally 1979); and Sierra Nevada (Berg 

and others 1998). Number of channels in the sample are given in parentheses. Study 

reaches are at least 200 m long. 
How Much Dead Wood Is Enough—Lisle 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 89 

Within coastal redwood forests, management has clearly reduced dead wood 

volumes in streams. Channels flowing through managed redwood forests contain two 

to five times less wood than old-growth channels for a given cumulative percentage 

(fig. 2). A history of logging, log running, salvage, and stream cleaning has 

apparently created a deficit of wood in channels. However, as is common with 

environmental parameters, distributions for managed and unmanaged channels 

overlap. Although there is a clear departure of managed channels from pristine 

conditions, a comparison of frequency distributions is not very useful for prescribing 

target loadings for individual channels. For example, using a “natural-range-ofvariability” criterion could suggest that loadings of 200 m3

/ha in managed channels 

would meet “natural” conditions since such low loadings are represented in at least 

one old-growth channel. However, such a prescription would tend to increase the 

wood deficit on a regional scale, because improvement would be prescribed only for 

the 20 percent of managed channels having the lowest loading. On the other hand, a 

prescription of the median old-growth loading (1,000 m3

/ha) might substantially 

decrease the regional deficit, but would be unachievable in most managed channels 

since one-half of the old-growth channels (nearly all in reserves) would already be 

“in violation.” A single-valued prescription for woody debris loading, even in the 

same forest type, is therefore unworkable. 

Figure 2—Cumulative frequency distributions of volumes of dead wood in channels 

in managed (Knopp 1993) and old-growth (Keller and Tally 1979) coastal redwoods. 

Number of channels in the sample are given in parentheses. Study reaches are at 

least 200 m long. 
How Much Dead Wood Is Enough—Lisle 

90 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Differences in wood size between pristine and managed streams are probably 

also pronounced. As large, old-growth dead wood in managed streams decreases 

through decay, salvage, cleaning, and mobilization, it is replaced by smaller wood 

from managed stands. The size difference is important because big wood lasts longer 

and affects channels more strongly. The difference is exemplified in a comparison of 

frequency distributions of the volume of individual pieces of dead wood in two thirdorder, coastal redwood channels having similar drainage areas: Little Lost Man Creek 

(Keller and Tally 1979), an old-growth channel, and North Fork Caspar Creek, a 

second-growth channel (fig. 3). Old-growth wood in Caspar Creek was nearly 

eliminated by splash-dam operations at the turn of the century, and second-growth 

forests have since supplied wood without human intervention (Napolitano 1998). For 

this analysis, the lower bound of piece size was set at 0.4 m3

. The frequency of small 

sizes (0.4-0.8 m3

) is similar, but frequencies diverge rapidly for larger sizes. The 

second-growth channel clearly has smaller wood. 

Figure 3—Cumulative frequency distributions of volumes of individual pieces of dead 

wood in two coastal redwood streams: North Fork Caspar Creek (second-growth) 

and Little Lost Man Creek (old-growth; Keller and Tally 1979). 
How Much Dead Wood Is Enough—Lisle 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 91 

Although approach 2 fails to prescribe uniform target loadings (and sizes), some 

general goals and directions for regional management for dead wood in aquatic 

ecosystems are clearly suggested. First, there is an apparent regional deficit in dead 

wood loadings that is probably affecting species such as coho salmon that benefit 

from wood-formed habitats. This could motivate regional goals to improve protection 

of in-channel and riparian supplies of wood. Second, the wide variation and overlap 

between wood loadings in managed and pristine streams suggest that site-specific 

analyses are needed to achieve these goals if riparian wood is to be harvested. 

Approach 3: Dead Wood Budgets 

One of the shortcomings of approaches 1 and 2 is that even if we knew how 

much wood in streams is enough, we would also have to know how to manage 

riparian forests to achieve that loading. Approach 3 widens the focus to wood 

supplies in riparian forests. Wood in streams is evaluated in context of the potential 

of the riparian forest to furnish adequate wood to the channel, given historical inputs 

and outputs that have culminated in the present loading. Then, current and projected 

trends can be evaluated under alternative management. By accounting for local 

variations in wood loading, approach 3 is the site-specific alternative to approach 2. 

Implicit in the analysis is the consideration of size as well as volume of wood. 

Approach 3 is essentially a cumulative effects analysis accomplished by constructing 

a wood budget (Surfleet and Ziemer 1996, Swanson and others 1982) to answer three 

questions: 

• What accounts for present wood loading, and more specifically, how much 

has land use affected riparian sources and input and output mechanisms 

since intensive land use began? 

• What is the trend in wood loading given the present and future potential of 

the existing riparian forest to contribute wood to the stream? 

• How will management alternatives affect future loadings? 

Although historic values for volumes of wood lost or gained usually cannot be 

determined precisely, enough can be learned of past events and conditions to roughly 

evaluate departures from natural loadings. This may be adequate to inform managers 

which alternative land use plans would be appropriate, given present and projected 

trends in wood supplies. For example, if there has been a history of wood depletion 

from log runs in the nineteenth century in a particular stream, followed by aggressive 

stream cleaning in the 1980s, then there would be added incentive to maintain 

recovering supplies in managed riparian stands. Wind throw from narrow buffer 

strips might provide short-term increases in wood, but early cashing-in of remaining 

wood supplies could perpetuate the deficit in future decades. 

Wood size as well as volume must be considered in a wood budget. Sustainable 

supplies of old-growth wood are gone from most managed streams. In its absence, 

the effectiveness of smaller size classes of available wood to replace the functions of 

old-growth wood needs to be evaluated (approach 1). Perhaps some minimum 

effective size can be used to categorize size classes in a wood budget. Longevity is 

another important consideration. 

A wood budget (approach 3), along with knowledge of the role of wood in that 

particular channel (approach 1) and its loading compared to that in other channels in 
How Much Dead Wood Is Enough—Lisle 

92 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

the same forest type (approach 2), provide the best information to weigh land use 

alternatives. It correctly sets the stage for regulatory debate by shifting the focus on 

how much wood is enough from channels to the riparian zone. However, it does not 

provide a standard formula for making such a determination, but instead informs the 

debate. 

Conclusions 

Dead wood in streams in the Pacific Northwest is being managed in the context 

of conflicting interests of protecting sensitive salmonid populations and tapping 

riparian wood supplies for timber. This motivates the question: “How much dead 

wood in forest streams is enough?” Federal agencies in the Northwest Forest Plan 

effectively skirted this question in favor of salmonids by designating riparian reserves 

that, among other provisions, were intended to fully protect riparian supplies of dead 

wood for streams. The Federal provisions, applied over a wide area to important 

protected species, set an undeniable precedent. If not met on State and private land, 

an alternative strategy is needed: If habitat is to be adequately protected as riparian 

wood is harvested, then detailed, site-by-site analyses of dead wood and other habitat 

variables must be performed. I suggest that three kinds of information are needed for 

such analyses: the role of dead wood in forest streams and watersheds; relative 

volumes and sizes of dead wood in managed and reference streams in the same forest 

type; historical and projected conditions, events, and processes that control wood 

supply and longevity in riparian forests and streams. Together, they provide the best 

information to guide land-management decisions. However, analyses must be sitespecific. Simple, effective, standardized prescriptions, formulas, or procedures 

requiring little understanding are not obviously forthcoming. 

One cost of intensive management of riparian forests is to support site-specific 

analyses that could justify harvesting riparian wood. Adequate wood-based, 

cumulative effects analyses are unlikely to be done because first, such analyses 

would be costly and their conclusions contestable under the inevitable uncertainties 

outlined in this paper; and second, considering the widespread depletion of dead 

wood from streams in managed forests, these analyses are not likely to support 

harvesting much wood from riparian forests. Given this, general prescriptions of 

riparian preserves are likely to remain the primary approach to managing dead wood 

in streams. In the meantime, continued research into the three approaches should 

better inform general prescriptions and improve site-specific analyses. In particular, 

approach 1 provides the scientific basis for determining how much wood is enough; 

approach 3 leads to how this can be achieved. 

Acknowledgments 

I thank Bret Harvey and Robert Ziemer for reviewing the paper and Sue Hilton for 

compiling frequency distributions of wood size. 

References 

Berg, N.; Carlson, A.; Azuma, D. 1998. Function and dynamics of woody debris in stream 

reaches in the central Sierra Nevada, California. Canadian Journal Fisheries and 

Aquatic Science 55: 1807-1820.
How Much Dead Wood Is Enough—Lisle 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 93 

Braudrick, C. A.; Grant, G. E.; Ishikawa, Y.; Ikeda, H. 1997. Dynamics of wood transport 

in streams: A flume experiment. Earth Surface Processes and Landforms 22: 669-

683. 

Forest Ecosystem Management Assessment Team (FEMAT). 1993. Forest ecosystem

management: An ecological, economic, and social assessment. Washington, DC: 

U.S. Government Printing Office. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, Jr., K.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15: 133-302. 

Keller, E. A.; Tally, T. 1979. Effects of large organic debris on channel form and fluvial 

processes in the coastal redwood environment. In: Williams, G. P.; Rhodes, D. D., 

editors. Adjustments of the fluvial system. Binghamton, NY: Kendall/Hall; 169-197. 

Knopp, C. 1993. Testing indices of cold water fish habitat. Santa Rosa, CA: North Coast 

Regional Water Quality Control Board; 56 p. 

Montgomery, D. R.; Buffington, J. M. 1997. Channel-reach morphology in mountain 

drainage basins. GSA Bulletin 109(5): 596-611. 

Napolitano, M. B. 1998. Persistence of historical logging impacts on channel form in

mainstem North Fork Caspar Creek. In: Ziemer, R. R., editor. Conference on 

coastal watersheds: The Caspar Creek Story. Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; 97-102. 

Sedell, J. R.; Bisson, P. A.; Swanson, F. J.; Gregory, S. V. 1988. What we know about large 

trees that fall into streams and rivers. In: Maser, C.; Tarrant, R. F.; Trappe, J. M.; 

Franklin, J. F., editors. From the forest to the sea: A story of fallen trees. Gen. Tech. 

Rep. PNW-GTR-229. Portland: OR. USDA Forest Service; 47-81. 

 Surfleet, C. G.; Ziemer, R. R. 1996. Effects of forest harvesting on large organic debris in 

coastal streams. In: LeBlanc, J., editor. Coast redwood forest ecology and 

management; Arcata, CA: Humboldt State University; 134-136. 

Swanson, F. J.; Fredriksen, R. L.; McCorison, F. M. 1982. Material transfer in a western 

Oregon forested watershed. In: Edmonds, R. L., editor. Analysis of coniferous 

forest ecosystems in the western United States. Stroudsburg, PA: Hutchinson Ross 

Publishing Company; 233-266. 
Importance to Invertebrates

95
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 97 

An Investigation of the Insect Fauna 

Associated with Coarse Woody Debris of 

Pinus ponderosa and Abies concolor in 

Northeastern California1 

Ethan Koenigs,2 Patrick J. Shea,2 Robert Borys,3 and Michael I. 

Haverty4 

Abstract 

This study was initiated to determine the diversity and community structure of 

macroarthropods found in the coarse woody debris (CWD) of a pine/fir dominated forest. The 

USDA Forest Service has placed increased emphasis on understanding ecosystem processes 

that support long-term sustainability and biological diversity. Our study site was located in 

northeast California just west of the town of Tenant in the Klamath National Forest, 

Goosenest Adaptive Management Area (GAMA). We surveyed the arthropod fauna entering 

and emerging from CWD with three trap types: an acrylic pane trap with a water filled 

collection basin; a collar trap that wraps around a portion of a fallen log; and a solid plastic 

cylinder placed over stumps. Only data from the collar traps with the specimens identified to 

high taxonomic levels are reported in this paper. Equal numbers of traps were placed on white 

fir (Abies concolor) and ponderosa pine (Pinus ponderosa). Three stages of log 

decomposition, recently dead to soft but structurally intact, were sampled from each tree 

species. The insects from all traps were sorted to order, except for the Coleoptera, which were 

sorted to family or species level. The most numerous insects belong to the Order Diptera, 

followed by Coleoptera and Hymenoptera. Staphylinidae were the most numerous 

coleopterans, excluding the earliest decay stage in both tree species, where the Scolytidae 

were dominant. Termites, commonly found in CWD, were absent from all traps in all years. 

Introduction

Much of the information on coarse woody debris (CWD) to date has focused on 

its importance as nutrient storage and as wildlife habitat (Bull and others 1997, Maser 

and others 1988). While mentioning the invertebrates associated with CWD and their 

potential importance in the decay process, few studies have attempted to elucidate the 

role they play. This study was designed to collect background information about 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. Contribution #5 of the 

Goosenest Adaptive Management Area Research Project, Pacific Southwest Research Station, USDA 

Forest Service. 

2

 Biological Technician and Principal Research Entomologist (Emeritus Scientist), respectively, Pacific 

Southwest Research Station, USDA Forest Service, 1107 Kennedy Place, Suite 8, Davis, CA 95616 (email: pjshea@davis.com) 

3

 Entomologist, Pacific Southwest Research Station, USDA Forest Service, 2480 Carson Rd, Placerville, 

CA 95667 (e-mail: rborys@fs.fed.us) 

4

 Chief Research Entomologist, Pacific Southwest Research Station, USDA Forest Service, PO Box 245, 

Berkeley, CA 94701 (e-mail: mhaverty@fs.fed.us) 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

98 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

insect diversity in this habitat type with the hope of providing methodologies and 

basic taxonomic data in the form of presence/absence and relative abundance for 

future research. Zhong and Showalter (1989) suggested that the rate of log 

decomposition could be influenced by the sequence of insect colonization and the 

micro flora brought in by these insects. Understanding the sequence of colonization is 

one of the first steps in understanding the role insects play in the decomposition 

process. Our long-term goals are to determine the diversity of insects associated with 

CWD; to assess the roles of various groups of insects found in CWD; and to provide 

analysis of various management strategies with regard to CWD inhabiting insects. 

Additionally, most of the work on CWD to date has focused on the damp, 

coastal and western cascade forests of Oregon and Washington. Spies and others 

(1998), noted that to get a broader picture of the many roles of CWD, the range of 

sites needs to be expanded. This study in northern California should provide relevant 

information for many California forests. 

There has been great attention in recent decades in preserving and maintaining 

our increasingly rare old-growth forests. Documents such as the Sierra Nevada 

Ecosystem Project, Final Report to Congress, exemplify this concern (Science Team 

1996). We have recognized that these ecologically rich areas are critical to wildlife 

and that there is much to learn from them about maintaining sustainable forestry. To 

that end, some old-growth stands have been set aside in the form of National Parks 

and wilderness areas. Because of the mandate for sustainable forestry, management 

strategies will likely see a shift toward restoration. We do not want to de-emphasize 

the importance of preserves, for which there will always be a need, but restoration 

also holds great promise of regaining the diversity of wild lands. It offers us a chance 

to put into practice the lessons learned from natural areas by applying them to timber 

producing stands. 

This project is part of a large, multidisciplinary ecosystem study on the 

Goosenest Adaptive Management Area (GAMA), northeast of Mount Shasta. The 

goal of the GAMA is to test methods of accelerating and restoring ponderosa pine 

old-growth characteristics through selective management. This study is being carried 

out on 20, 100-acre plots, which are being silviculturally managed to produce four 

treatments. These treatments include pine dominance with fire as a management tool; 

pine dominance with mechanical thinning; retain only large diameter trees regardless 

of species by mechanical thinning; control, or no silvicultural treatment. After these 

treatments have been initiated, the plots will be monitored for years to come, 

assessing the affects of each treatment on multiple parameters (wildlife, forest 

structure, fire effects, forest health, etc.). At present, our CWD insect emergence 

trapping has been conducted in areas near the study plots because of site availability 

and eastside pine/fir type mix suitability. 

One aspect of old-growth is structural diversity. This refers to the forest canopy 

and the forest floor as well. A structurally diverse forest will have a variety of woody 

material at the soil surface providing habitat, nutrient recycling, and moisture to the 

forest. Once the plots have been created, we will be involved in monitoring the 

insects utilizing the CWD. 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 99 

Study Site

The study site is located in northeastern California on the Goosenest Ranger 

district of the Klamath National Forest. The site is located on land designated as the 

GAMA. The landscape is characterized as rolling volcanic topography, typical of the 

Cascade province with elevations between 1,270 and 2,600 meters. The relatively dry 

climate reflects the topographic influence of the coastal mountains and the main 

thrust of the Cascades to the west. Most of the area receives 25-100 cm of 

precipitation that falls in the form of snow, with some summer thunderstorm rain 

contributing to the total (USDA 1996). As a result, the eastside ponderosa pine 

community dominates much of the GAMA. The area of study occurs in the transition 

zone between the eastside pine type and the coastal Douglas-fir (Pseudotsuga 

menziesii) type. This zone is dominated by a mixture of ponderosa pine (Pinus 

ponderosa) and white fir (Abies concolor).

Materials and Methods

Three types of traps were used in this investigation, but only data from the collar 

traps are presented here. To capture insects emerging from prostrate logs, traps were 

fashioned from a double layer of 95 percent shade cloth. The shade cloth was custom 

fit to cover 1-meter sections of logs of varying diameters. To ensure a relatively tight 

fit over the irregularities of the log and provide room for insects to travel under the 

shade cloth, the cloth was fitted over 10-cm-thick strips of medium density foam at 

both ends. Velcro strips were used to attach the shade cloth to the foam, to make for 

easy removal of the trap from the log. The foam strips were set 1 meter apart on the 

log and attached to the log with aluminum nails. Then the shade cloth could be laid 

across the foam, providing a space between the log and the cloth. The only source of 

light that insects could phototropically respond to was a glass mason jar fitted to the 

shade cloth on one side of the log. Emerging insects were attracted to the light and 

entered the jar containing a small insecticide impregnated chip containing 2,2-

Dichlorovinyl dimethyl phosphate (DDVP). The insecticide kills the emerging 

insects before they can do damage to each other and make identification difficult or 

impossible. 

To sample the insect fauna emerging from stumps, a modified 118- or 190-liter 

plastic garbage can was placed over the stumps, dependent on stump diameter. A 

medium hole was cut in the upper side of each can so that a transparent plastic funnel 

could be attached, large end toward the can. The funnel served as the only source of 

light inside the can, provided the only exit from the plastic can, and “funneled” the 

insects into a clear plastic collection cup. To prevent insects from leaving the cup or 

doing damage to each other, a similar insecticide impregnated chip, DDVP, was 

placed in the cup. In an attempt to lower the temperature inside the can, two square 

holes were cut in the side of the can and covered with shade cloth. This would allow 

some air movement inside the can to moderate temperatures without letting in much 

light. 

To capture and sample insects from the surrounding environment, a clear acrylic 

sheet (pane trap), 0.5 cm thick by 80 cm long and 60 cm high, was placed against a 

down log bolted to upright aluminum brackets inserted into the ground. An acrylic 

collection tray, the same length as the pane trap, 14 cm wide and 10 cm high, was 

attached to the base of the pane and filled with soapy water to collect insects as they 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

100 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

fell. A wire screen was placed over the collection tray to prevent birds and small 

mammals from removing insects from the traps. 

Experimental Design 

There were several specific objectives of this study. First, we wanted to develop 

effective sampling methods to detect insects utilizing stumps and fallen logs of 

various diameters. Then we hoped to compare the insect fauna found in white fir to 

that found in ponderosa pine. Finally, we wanted to compare the insect fauna across 3 

decay stages, representing a continuum from recently dead to fairly decayed but 

maintaining shape. In the first year, 1997, our priority was to establish the 

effectiveness of the trapping technique. Because of this, the number and placement of 

traps was different than during the two succeeding years. In 1997, 54 emergence 

traps were deployed on a total of 18 logs, 3 traps per log. Of the 18 logs, 9 were 

ponderosa pine and 9 were white fir. Within each tree species, three trees in each of 

three decay classes (see below) were sampled. In 1998 and 1999, our trapping 

procedure changed after examining the 1997 data. To better compensate for variation, 

more trees (replicates) were sampled in each decay class. A total of 108 traps were 

deployed on 54 logs. With this arrangement, there were nine replications of each 

decay class for each species of tree. Thus, each trap covered a 1-meter section of log 

and with two traps per log, resulted in 18 meters of log being sampled from each 

decay class. This is twice the amount sampled in 1997 (3 logs x 3 traps/log x 1 

meter/trap = 9 meters). 

A total of 18 stump emergence traps were used in 1997, following the same 

pattern of three replications for each decay class in each species of tree. Because of 

the paucity of insects collected from these traps in 1997, the total number of traps 

was tripled to 54 in 1998, resulting in nine replications of each decay class for each 

tree species. 

A total of 54 pane traps were used in 1997. Thirty-six traps were placed two per 

log on logs that contained collar traps. Another 18 pane traps were placed 

independently within the study area against down logs not containing color traps as 

controls. In 1998 and 1999, the amount of pane traps used was reduced to 18. One 

trap per log repeated three times for each decay class within both species. The large 

numbers of insects collected from the pane traps in 1997 precluded the use of as 

many traps in the following 2 years. 

Decay Classes 

The decay stage of each log was determined by using a set of modified 

parameters described by Maser and others (1979). Many investigators have used this 

classification system, likely due to the simple approach it uses to grade logs. In this 

system there are five decay classes based primarily on visual characteristics of the 

log. Class one has intact bark with intact texture. The log is round, twigs are present 

and the log is elevated on support points from broken branch stubs. Class two has 

intact bark with intact to partially soft texture. The log is round, twigs are absent and 

the log is elevated on support points or sagging slightly. Class three has partial or 

trace bark intact due to sloughing, with a texture of hard, large woody pieces. The log 

is round, twigs are absent and the log is sagging or portions on ground. Class four has 

bark absent with a texture of small, soft blocky wood pieces. The log is round to oval 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 101 

with portions of log on ground. Class five has bark absent with soft, powdery texture. 

The log is oval and on ground. We limited our survey of insects to the first three 

decay classes, in which most insect activity occurs (Harmon and others 1987). In 

classes four and five the log is becoming so soft that its quality as habitat for gallery 

forming insects decreases and the nutritive quality of the wood itself is also greatly 

diminished. At this point, decomposition is likely completed by fungi and microbes. 

Stump Traps 

The stump traps were deployed at the same time as the emergence traps. Three 

diameter classes were used and distributed between both ponderosa pine and white 

fir. The diameter classes were 20-24.5 cm, 29.5-30.5 cm, and 35.5-38 cm. Similar to 

the log emergence traps, 3 decay classes were selected: 1) xylem hard and bark 

tightly attached; 2) bark beginning to separate; 3) bark beginning to fall away and 

xylem becoming soft. Each combination was replicated three times resulting in 54 

stumps being studied each of 2 years. At the beginning of each year the plastic 

buckets were placed over a stump, and dirt was shoveled around the base to seal and 

secure the bucket from being wind blown. 

Results and Discussion 

After trapping on such a large scale for 3 years, a tremendous amount of data 

has been gathered. The job of analyzing all of this data is ongoing. The purpose of 

this paper is not a rigorous analysis in detail of this study. Instead, our purpose is to 

summarize our findings by highlighting interesting trends indicated by the numbers 

of insects in broad taxonomic categories. Only the data from the emergence traps 

placed on logs will be considered in this paper. Samples were sorted and counted, 

then categorized at the ordinal level. We have identified most of the Coleoptera to the 

family level; some beetles were further identified to genus. We are currently working 

on species level identifications of these families. Finer taxonomic distinctions are 

beginning to show subtle differences in the faunal composition of each decay class 

and between tree species. 

 

Log Emergence Traps 

The log emergence traps were quite successful in capturing emerging insects. 

We have been satisfied with the design despite some persistent difficulties that seem 

to come with any field study. The biggest obstacle has been coping with the small 

mammal population, which naturally finds this new resource interesting, if not 

accommodating. Chipmunks (Tamias spp.), mice and voles (Peromyscus and 

Microtus spp.), shrews (Sorex spp.), and squirrels (Spermophilus spp.) have all found 

some use of the traps across both log species and all decay classes, to our constant 

frustration. Many attempts to keep them from damaging the traps have been, at best, 

only partially successful. We have become resigned to accepting some level of 

damage and dealing with it during each sample interval. This has surely influenced 

the results to some degree, mostly by allowing insects to escape collection due to the 

physical damage to the trap. With the large number of traps deployed (1998, 1999), 

our sample size should be able to account for this effect. 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

102 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

a

1

10

100

1000

10000

Insect Orders

1997 380 3 162 117 219 9 1 1 7

1998 631 8 125 353 2041 16 4 5 39

1999 398 1 180 584 2140 39 8 7 14

Coleoptera Hemiptera Hymenoptera Formicidae Diptera Orthoptera Lepidoptera Neuroptera Diplopoda

b

1

10

100

1000

10000

Insect Orders

1997 124 6 151 54 246 11 4 1 10

1998 639 3 388 451 7059 33 5 9 13

1999 541 1 422 314 2936 26 5 1 46

Coleoptera Hemiptera Hymenoptera Formicidae Diptera Orthoptera Lepidoptera Neuroptera Diplopoda

 

(Figure 1 continued on next page) 

No. Specimens Trapped No. Specimens Trapped 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 103 

(Figure 1 continued) 

c

1

10

100

1000

10000

Insect Orders

1997 94 4 112 63 459 10 1 1 3

1998 708 5 418 544 5407 31 1 8 14

1999 600 2 552 437 3511 45 6 3 43

Coleoptera Hemiptera Hymenopter

a Formicidae Diptera Orthoptera Lepidoptera Neuroptera Diplopoda

Figure 1—Total number of insects from taxa emerging from ponderosa pine logs by 

decay class and year (logarithmic scale). a = decay class 1, b = decay class 2, c = 

decay class 3. 

In reviewing the summary data (figs. 1a-c) from the collar traps, several patterns 

are evident. First, for those insects emerging from ponderosa pine, there is a 

remarkable similarity in the abundance of each insect order emerging from logs in all 

three decay classes. This holds true for both white fir and ponderosa pine. Note that 

the logarithmic scale was used because of the large quantities of Diptera and much 

smaller quantities of many other orders. The Family Formicidae in the Order 

Hymenoptera, is treated separately from other Hymenoptera throughout the 

taxonomic analysis of the data due to the large numbers captured in the emergence 

traps. Second, the major insect taxa in this habitat are the Diptera, Coleoptera, 

Formicidae, and other Hymenoptera. Third, there is little difference in the number of 

representatives from the higher-level taxonomic groups between each tree species. 

This is not too surprising given that the similarity of the resource should attract 

members of the same guild. However, we do expect to see increasing differences in 

the composition of each guild at finer levels of taxonomy. Biochemical differences in 

the tissues of these two tree species will likely select for organisms specifically 

adapted to exploiting the respective resource. This is especially true at early stages of 

decomposition when the presence of various defensive compounds (terpenes and 

phenolics) is at its greatest. 

The relative abundance of some taxa differed between tree species at each decay 

class (table 1). The most striking difference is with both tree species within decay 

class one, where the primary and secondary beetles (Dendroctonus in Pinus and 

Pseudohylesinus in Abies) are rated as abundant, but are absent in the other two No. Specimens Trapped 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

104 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

decay classes. The other interesting difference is that weevils (Family Curculionidae) 

in decay class two of ponderosa pine are abundant, yet are rare or common in the 

other two decay classes of ponderosa pine and all three decay classes of white fir. 

Table 1—Relative abundance of taxa between tree species for each decay class collected 

during 1997-1999. 

Orders/Families WF11 PP1 Difference2 WF2 PP2 Difference WF3 PP3 Difference 

Coleoptera 

 Dendroctonus N3 A XX4 N N N N 

 Pseudohyles. A R XX N N N N 

 Hylur./ Hylast. R R X R R R R 

 Gnathotricus A C X R N X N N 

 Ptiliidae C R X C R X C C 

 Cantharidae R R R C X R R 

 Cerambycidae R R C C R R 

 Buprestidae R R R R R R 

 Histeridae C R X C R X R R 

 Staphylinidae A A A A A A 

 Carabidae C C C C C C 

 Curculionidae C C R A XX C C 

 Elateridae C C C C C C 

 Tenebrionidae C C R R C R X 

 Throscidae C C C C C C 

 Leiodidae C C C C C A X 

 Leptodiridae C R X R C X R C X 

 Pselaphidae R R R R R R 

 Nitidulidae R C X C C C C 

 Melyridae R R R R R R 

 Melandryidae R C X C C R C X 

 Mycetophagidae R R R R R R 

Other Orders A C X C C C C 

 Hemiptera R R R R R R 

 Hymenoptera A A A A A A 

 Formicidae A A A A A A 

 Diptera A A A A A A 

 Orthoptera C C C C C C 

 Lepidoptera R R R R R R 

 Neuroptera R R R R R R 

 Diplopoda C C C C C C 

Differences 12 7 4 

1 WF = White fir, PP = Ponderosa pine, 1, 2, and 3 are decay stages 

2

 Difference denotes the change in relative abundance between each decay class 3

 Abundance categories: N = none, R = rare 1-25, C = common 26-150, A = abundant >150 4

 X = a change of 1 category; XX = a change of more than one category. 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 105 

The numbers of Diptera emerging from all of the logs was surprising. Finer 

taxonomic analysis has not been done on these, but we suspect most belong to 

fungivorous taxa. The number of Diptera collected from logs over 3 years illustrates 

the large annual fluctuation in populations (tables 2a-2b). We believe these likely are 

a result of weather differences. Relative to 1999, in 1998 there were many more 

dipterans emerging from all of the logs, except decay class 1 of ponderosa pine (table 

3). There appears to be more dipteran use of ponderosa pine compared to fir. In 1999, 

this difference is seen in all 3 decay classes, with ponderosa pine having considerably 

higher numbers of dipterans in each case. The 1998 data shows a clear difference in 

class 2, a less substantial difference in class 3, and a reversal in class 1. 

Table 2a—Collections from each decay class of log emergence traps in Pinus ponderosa, 

1997-1999. 

Order1/ Pinus ponderosa Class 1 Pinus ponderosa Class 2 Pinus ponderosa Class 3 

Family 97 98 99 Total 97 98 99 Total 97 98 99 Total 

Diplopoda 7 39 14 60 10 13 46 69 3 14 43 60 

Hemiptera 3 8 0 11 6 3 1 10 4 5 2 11 

Hymenoptera 162 125 180 467 151 388 422 961 112 418 552 1,082 

 Formicidae 117 353 584 1,054 54 451 314 819 63 544 437 1,044 

Diptera 219 2,041 2,140 4,400 246 7,059 2,936 10,241 459 5,407 3,511 9,377 

Orthoptera 9 16 39 64 11 33 26 70 10 31 45 86 

Lepidoptera 0 4 8 12 4 5 5 14 1 0 6 7 

Neuroptera 0 5 7 12 0 9 0 9 0 8 3 11 

Coleoptera 380 631 398 1,409 124 639 541 1,304 94 708 600 1,402 

 Scolytidae 209 165 0 374 2 0 0 2 0 9 0 9 

 Ptiliidae 5 4 9 10 2 12 81 13 94 

 Cantharidae 0 0 15 15 0 1 26 27 0 5 9 14 

 Cerambycidae 7 10 6 23 3 15 11 29 0 1 6 7 

 Buprestidae 0 2 0 2 1 0 3 4 0 1 0 1 

 Histeridae 2 8 2 12 0 1 2 3 2 5 5 12 

 Staphylinidae 61 130 94 285 10 140 78 228 15 166 130 311 

 Carabidae 1 40 23 64 9 28 36 73 4 72 45 121 

 Curculionidae 16 53 11 80 37 149 103 289 10 78 5 93 

 Elateridae 28 61 55 144 32 70 48 150 15 55 63 133 

 Tenebrionidae 1 15 26 42 0 1 11 12 1 4 12 17 

 Throscidae 3 33 53 89 1 4 25 30 2 12 21 35 

 Leiodidae 0 25 14 39 1 49 41 91 5 99 107 211 

 Leptodiridae 2 1 15 18 4 10 17 31 1 25 28 54 

 Pselaphidae 10 4 14 6 2 8 13 3 16 

 Nitidulidae 22 29 51 28 25 53 7 19 26 

 Melyridae 4 8 5 17 2 4 2 8 0 10 1 11 

 Melandryidae 46 1 10 57 22 22 71 115 39 14 74 127 

 Mycetophagidae 0 1 1 2 2 4 2 2 4 

Other 42 31 73 99 36 135 49 57 106 

1

 Insect orders are bold and families are not bold. 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

106 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 2b—Collections from each decay class of log emergence traps in Abies concolor, 

1997-1999. 

Order1/ Abies concolor Class 1 Abies concolor Class 2 Abies concolor Class 3 

Family 97 98 99 Total 97 98 99 Total 97 98 99 Total 

Diplopoda 9 21 29 59 3 9 26 38 2 13 35 50 

Hemiptera 1 3 8 12 3 16 6 25 3 7 0 10 

Hymenoptera* 268 264 187 719 265 229 185 679 207 278 144 629 

Formicidae 145 477 402 1,024 197 596 738 1531 138 507 464 1,109 

Diptera 385 3,424 1,195 5,004 218 3,791 1,853 5,862 431 4,408 1,683 6,522 

Orthoptera 9 23 32 64 16 12 19 47 5 9 24 38 

Lepidoptera 3 7 13 23 5 7 9 21 4 3 2 9 

Neuroptera 2 2 8 12 1 4 2 7 2 2 2 6 

Coleoptera 2,229 1,826 439 4,494 113 465 471 1049 145 476 264 885 

Scolytidae 2,153 759 5 2,917 2 0 0 2 1 0 0 1 

Ptiliidae 39 3 42 49 10 59 64 3 67 

Cantharidae 6 2 8 5 12 17 14 11 25 

Cerambycidae 2 1 5 8 12 7 8 27 3 1 6 10 

Buprestidae 1 3 1 5 2 0 2 4 11 0 1 12 

Histeridae 1 23 9 33 10 23 15 48 0 8 3 11 

Staphylinidae 16 166 71 253 15 189 97 301 36 183 39 258 

Carabidae 11 21 13 45 9 22 31 62 16 19 17 52 

Curculionidae 4 22 2 28 5 8 2 15 6 23 5 34 

Elateridae 27 39 26 92 33 18 47 98 22 34 25 81 

Tenebrionidae 14 12 28 4 7 7 18 24 5 1 

Throscidae 4 46 82 132 8 7 33 48 11 13 10 34 

Leiodidae 0 58 17 75 2 32 57 91 0 51 17 68 

Leptodiridae 2 4 29 35 1 2 16 19 4 4 13 21 

Pselaphidae 14 2 16 13 1 14 4 0 4 

Nitidulidae 11 12 23 28 84 112 19 84 103 

Melyridae 0 3 7 10 0 1 5 6 0 4 3 7 

Melandryidae 4 5 9 5 25 30 1 3 4 

Mycetophagidae 0 1 1 3 2 5 1 2 3 

Other 6 593 135 734 10 46 17 73 11 28 21 60 

1

 Insect orders are bold and families are not bold. 

Table 3—Diptera from log emergence collar traps from 1997-1999. 

Year Decay 

class 24-Jun 7-Jul 21-Jul 4-Aug 19-Aug 3-Sep 16-Sep Class Totals 

Pinus ponderosa

 1 21 21 38 27 48 40 24 219 

 1997 2 21 39 24 45 54 44 19 246 

 3 106 88 64 101 34 48 18 459 

 1 305 279 335 455 667 194 2,041 

 1998 2 2,984 1,247 720 1,374 734 404 7,059 

 3 791 1,745 892 1,084 895 341 5,407 

 1 758 427 104 288 208 355 2,140 

 1999 2 997 455 283 441 290 470 2,936 

 3 1,027 518 494 564 451 457 3,511 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 107 

Year Decay 

class 24-Jun 7-Jul 21-Jul 4-Aug 19-Aug 3-Sep 16-Sep Class 

Totals 

Abies concolor

 1 86 45 21 51 40 110 32 385 

 1997 2 43 14 33 35 35 43 15 218 

 3 35 44 144 114 26 53 15 431 

 1 842 632 942 532 476 327 3,424 

 1998 2 848 706 694 1,034 509 283 3,791 

 3 1,327 1,230 647 701 503 268 4,408 

 1 305 254 133 182 113 208 1,195 

 1999 2 397 463 174 358 264 197 1,853 

 3 454 290 159 279 207 294 1,683 

Beetles, ants, and termites are commonly associated with woody material on the 

forest floor. Surprisingly, there were no termites collected from stumps or logs. The 

sample size was increased after the first year from 9 to 54 logs; yet even with the 

larger sample size, termites were still absent from the collections in 1998 and 1999. 

Collections from the pane traps indicated that the termites, Zootermopsis nevadensis

were flying in the area (1998 data), yet none were captured in emergence traps. 

Perhaps the degree of decay of the logs and stumps was not advanced to the degree 

that mature, alate-producing colonies inhabited the logs. Furthermore, Zootermopsis 

colonies are much more common in ponderosa pine that co-occurs with white fir 

(Thorne and others 1993). 

Hymenopterans were always abundant in the log and stump collections; most of 

these were Formicidae (tables 2a-2b). The majority of these ants were Camponotus 

spp. foragers, which were probably attempting to remove the insects in the collection 

jars. Occasionally, large flights of alates were collected from the stump traps, usually 

toward the end of summer. There were substantial numbers of other hymenopterans 

emerging from the logs. These consisted largely of members of the superfamilies 

Ichneumonoidea and Chalcidoidea and were probably parasitoids of the numerous 

Diptera and Coleoptera inhabiting the decomposing logs. 

The abundance of Coleoptera families collected from logs of Abies and Pinus

differed (fig. 2). Several of the commonly collected families of Coleoptera are used to 

illustrate distinctions in the faunal composition of these two species of trees. In 

addition, decay classes produced different capture rates for some families. The most 

striking is in the Curculionidae, which are much more abundant in each decay class 

of the pine compared to fir. Within the pine, decay class 2 has considerably more 

(289 >> 80, 93) curculionids than classes 1 and 3. This also appears to be the case for 

Melandryidae. 

Among the Coleoptera emerging from the logs, the biggest surprise was the 

scarcity of the classic wood-boring beetles, Cerambycidae and Buprestidae. In 

ponderosa pine, the most cerambycids were collected from decay classes 1 and 2 

where there were 3-year totals of 23 and 29 beetles, respectively (table 2a). 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

108 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

a

0

50

100

150

200

250

300

350

Coleoptera Families

Pinus

Decay Class 1 57 51 285 80 144

Decay Class 2 115 53 228 289 150

Decay Class 3 127 26 311 93 133

Melandridae Nitidulidae Staphilinidae Curculionidae Elateridae

b

0

50

100

150

200

250

300

350

Coleoptera Families

Decay Class 1 9 23 253 28 92

Decay Class 2 30 112 301 15 98

Decay Class 3 4 103 258 34 81

Melandridae Nitidulidae Staphilinidae Curculionidae Elateridae

Figure 2—Total number of beetles collected from (a) ponderosa pine and (b) white fir 

for selected families of Coleoptera in each of three decay classes over 3 years. 

Conclusions 

We had some difficulty with the system used to classify the logs based on decay. 

The criteria can be quite subjective and making clear distinctions between classes 2 

and 3 was sometimes difficult. This reflects our application of an artificial No. Specimens Trapped in Pinus No. Specimens Trapped in Abies
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 109 

categorization scheme on a process that operates as a continuum. That is, the classes 

do not delineate distinct units in nature. Logs and stumps, at a stage in the decay 

process near a class break, are ambiguously assigned. A less subjective classification 

system would be useful. Perhaps an instrument could be developed that designates 

the stage of decay based on the softness of the wood. 

There is still a considerable amount of data to be assembled, summarized, and 

analyzed. In addition to the obvious analysis, concerning biological diversity— 

especially at fine taxonomic levels—there remains analysis of the flight periodicity of 

the various orders. Fortunately, we collected the log, stump, and pane traps on a 

regular basis from approximately June until the end of September of each year. This 

will allow us to describe the periods of flight activity for each of the major groups. 

This data could be valuable to other researchers who want to investigate these groups 

in more detail. 

Finally, the decay of CWD is a long and complex process that involves different 

groups of organisms playing different roles. The process is set on a trajectory from 

the time a tree is killed, often by the primary beetles, to the time the chemical 

constituents are returned to the soil as soil nutrient. In addition to the role that various 

insect groups play in the decay process, it should be emphasized that they also 

function as prey items to various vertebrate organisms. The important role of insects 

as prey is poorly understood and should gain more attention. 

References 

Bull, E. L.; Parks, C. G.; Torgersen, T. R. 1997. Trees and logs important to wildlife in the 

Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. Portland, OR: 

Pacific Northwest Research Station, Forest Service, United States Department of 

Agriculture; 55 p. 

Harmon. M. E. 1986. Long-term experiments on log decomposition at the H. J. Andrews 

Experimental forest. Portland, OR: Pacific Northwest Research Station, Forest Service, 

United States Department of Agriculture; 1 p. 

Harmon. M. E.; Cromack, K.; Smith, B. G. 1987. Coarse woody debris in mixed-conifer 

forests. Sequoia National Park, California. Canadian Journal of Forest Research 17: 

1265-1272. 

Maser, C.; Anderson, R. G.; Cromack, K.; Williams, J.; Martin, R. E. 1979. Dead and down 

woody material. In: Thomas, J. W., ed. Wildlife habitats in managed forests—the Blue 

Mountains of Oregon and Washington. Agric. Handb. 553. Washington DC: U.S. 

Department of Agriculture, Forest Service; 78-90. 

Maser, C.; Tarrant, R. F.; Trappe, J. M.; Franklin, J. F., technical editors. 1988. From the 

forest to the sea: a story of fallen trees. Portland, OR: Pacific Northwest Research 

Station, Forest Service, United States Department of Agriculture; 3 p. 

Scholwater, T. D.; Caldwell, B. A.; Carpenter, S. B.; Griffiths, R. P.; Harmon, M.E.; Ingram, 

E. R.; Kelsy, R. G.; Lattin, J. D.; Moldenke, A. R. 1992. Decomposition of fallen trees: 

Effects of initial conditions and heterotrophic colonization rates. In: Singh, K. P.; 

Singh, J. S., editors. Tropical ecosystem, ecology and management. New Delhi, India: 

Wiley Eastern, Ltd.; 373-383. 

Science Team. 1996. Sierra Nevada Ecosystem Project (SNEP). Status of the Sierra 

Nevada. Vol. 1. Assessment summaries and management strategies. Wildland 

Resources Center Report No. 36. Davis, CA: University of California; 205 p. 
Insect Fauna Reared from Coarse Woody Debris in California—Koenigs, Shea, Borys, and Haverty 

110 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Spies, T. A.; Franklin, J. F.; Thomas, T. B. 1988. Coarse woody debris in Douglas-fir 

forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Thorne, B. L.; Haverty, M. I.; Page, M.; Nutting, W. L. 1993. Distribution and 

biogeography of the North American termite genus Zootermopsis (Isoptera: 

Termopsidae). Annals of the Entomological Society of America 86: 532-544. 

Zhong, H.; Schowalter; T. D. 1989. Conifer bole utilization of wood-boring beetles in 

western Oregon. Canadian Journal of Forest Research 19: 943-947. 

United States Department of Agriculture. 1996. Goosenest Adaptive Management Area 

(GAMA). Macdoel, CA: Ecosystem Analysis, Goosenest Ranger District, Klamath 

National Forest. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 111 

A Preliminary Study of Ant Diversity and of 

Ant Dependence on Dead Wood in Central 

Interior British Columbia1

B. Staffan Lindgren2 and A. M. MacIsaac2

Abstract 

Nineteen species of ants in three subfamilies and seven genera were found during a 

preliminary survey near Prince George, British Columbia. Ant diversity was low to moderate, 

with up to 7 species collected within areas of less than 1 ha in size. Wood was the preferred 

nest substrate for the majority of species, with 12 of the species utilizing wood in more than 

69 percent of the collections. The nests of three to four species frequently shared logs or 

stumps. 

Introduction 

Ants are known to be ecologically significant invertebrates in many ecosystems 

(Hölldobler and Wilson 1990). They positively affect physical and chemical soil 

properties, plant and animal distribution, and forest health. Some species (e.g., 

carpenter ants [Camponotus spp.]) attain direct pest status because they may cause 

serious structural damage in buildings. Other species invade homes, and some cause 

indirect damage to plants by tending aphids and scale insects. Ants serve as important 

food for many vertebrates, including woodpeckers (Torgersen and Bull 1995) and 

both grizzly and black bears (Kansas and others 1989, Raine and Kansas 1990). For 

example, Raine and Kansas (1990) found that "The ant season was found to occur 

from mid-June to mid- to late July, when berries began to ripen. Ants and ant larvae 

were the main food items observed to be eaten by bears during this season. Bears 

searched for ants in old logs and under stones" (p. 299). In terms of biomass, ants 

often dominate in warm temperate and tropical ecosystems, but become increasingly 

less important with increasing latitude. For example, Francoeur (1983) found only 

four species at the tree line in Quebec. 

Ants have been poorly studied in the sub-boreal forests of central British 

Columbia (BC). Few collections are available, and the species that occur there can 

only be deduced by puzzling together data from adjacent regions. In a recent 

synthesis of what is known about the ant fauna in BC (Naumann and others 1999), 

only one species, Formica podzolica Francoeur, is represented by collections near 

Prince George (table 1), where our study is conducted. Francoeur (1997) found 19 

species in the Yukon, the majority of which are also present in BC. It is also possible 

 

1

An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Associate Professor and Research Technician, respectively, College of Science and Management, 

University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada V2N 4Z9, 

(e-mail addresses: lindgren@unbc.ca and macisaac@unbc.ca) 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

112 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

that transcontinental species not listed in table 1, but listed by Francoeur (1997) as 

being present in the Yukon, occur in north-central BC. However, no records exist. 

The number of species in the north-central part of BC is uncertain, because Buckell 

(1932), from which most of the northern information in table 1 is derived, does not 

specify locales. Instead, he indicates wide geographic regions, e.g., the Chilcotin, 

which spans several biogeoclimatic zones (Meidinger and Pojar 1991). In other 

words, many ant species that occur in the southern parts of the Chilcotin or Cariboo 

regions are unlikely to occur in the Prince George area. 

Table 1Ant species listed as occurring in north central British Columbia, or that can 

reasonably be expected to occur there. Data based on Naumann and others (1999) and 

Francoeur (1997). 

Subfamily Locality/range Reference 

Species 

Myrmicinae

Myrmica alaskensis Cordillera Francoeur 1983 

Myrmica incompleta Lac LaHache RBCM1

Myrmica lobicornis Arizona-Alaska Smith 1979 

Myrmica brevispinosa Chilcotin, Cariboo, 

Alaska 

Buckell 1932 

Nielsen 1987 

Aphaenogaster subterranea Chilcotin Buckell 1932 

Solenopsis molesta Throughout BC Buckell 1932 

Leptothorax muscorum Arizona-Alaska Smith 1979 

Leptothorax retractus Yukon Francoeur 1997 

Dolichoderinae

Tapinoma sessile Chilcotin Buckell 1932 

Formicinae

Camponotus herculeanus Chilcotin Buckell 1932 

Camponotus modoc Chilcotin Buckell 1932 

Camponotus noveboracensis Chilcotin Buckell 1932 

Camponotus vicinus Chilcotin Buckell 1932 

Lasius alienus 70 Mile House RBCM 

Lasius flavus Chilcotin Buckell 1932 

Lasius pallitarsis Lac La Hache RBCM 

Formica lasioides Chilcotin Buckell 1932 

Formica neogagates Chilcotin Buckell 1932 

Formica fusca Chilcotin, Cariboo Buckell 1932 

Formica neoclara Lac LaHache RBCM 

Formica neorufibarbis Barkerville 

Liard Hot Springs 

Buckell 1932 

Francoeur 1973 

Formica podzolica Prince George UBC2

Formica subpolita Chilcotin Buckell 1932 

Formica dakotensis New Mexico-Alaska Smith 1979 

Formica obscuripes Chilcotin Buckell 1932 

Formica oreas Chilcotin Buckell 1932 

Formica aserva Lac LaHache RBCM 

Polyergus breviceps Chilcotin Buckell 1932 1 Royal British Columbia Museum, Victoria, B.C. 

2

 Spencer Museum, University of British Columbia, Vancouver, B.C. 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 113 

Ants utilize various substrates for nesting, including dead wood. Hölldobler and 

Wilson (1994) note that ants nest preferentially under flat rocks in cooler climates, 

because these have low specific heat when dry, and thus heat up faster than the 

surrounding soil. Similarly, the large thatch mounds of many species in the Formica 

rufa group are beneficial in cold climates (Hölldobler and Wilson 1994). Wheeler 

and Wheeler (1986) provide a list of ants in Nevada, indicating typical nest 

substrates. Of 177 species, only 15 regularly utilize dead wood substrates for nesting, 

and another two species nest under wood or other substrates. Most nest under rocks, 

or build nests directly in exposed soil, which is prevalent in the drier biomes of 

Nevada (Wheeler and Wheeler 1986). Of the 17 species listed as utilizing wood, 10 

are listed in table 1, i.e., they are likely to occur in central BC. Of 82 species of ants 

occurring in North Dakota, Wheeler and Wheeler (1963) listed 29 that nest in wood, 

and an additional 9 species that nest in soil under wood, i.e., almost half of the 

species regularly utilize wood for their nests. 

In the relatively wet sub-boreal forests, typical of the area around Prince George, 

exposed rocks are rare but dead wood of all sizes and ages is plentiful, both in natural 

stands and in stands with a history of harvesting. Thus, it is reasonable to hypothesize 

that dead wood constitutes an important nest substrate for many ant species. The 

objectives of this study are: 1) to conduct a survey of ant species in the Prince George 

area, 2) to determine to what extent wood is utilized as a nest substrate, and if 

specific substrate attributes are associated with particular species of ants, and 3) to 

estimate ant abundance. This paper reports on preliminary findings from data 

collected in 1999. No formal measurements of ant abundance were made at this 

preliminary stage due to limitations in time and resources. Thus, ant abundance in 

this paper is only reported subjectively. 

Materials and Methods 

The study was conducted in the area around Prince George in central BC. The 

area is in the sub-boreal spruce biogeoclimatic zone, which is dominated by 

lodgepole pine (Pinus contorta var. latifolia Dougl. ex Loud) and hybrid spruce 

(Picea glauca x engelmanni (Parry) Engelmann) forests (Meidinger and Pojar 1991). 

Species Survey 

Ants were collected from a variety of environments, including urban sites within 

the city of Prince George. Since the objective was to obtain and identify as many 

species as possible, we included ants from traps and collections of unrelated studies 

conducted from 1997 to 1999 in the same area, ants from the nest survey (see below), 

and stray ants that were encountered. Ants were tentatively identified to species by 

using the keys of Francoeur (1973), Hansen and Akre (1985), Naumann and others 

(1999), and Wheeler and Wheeler (1963, 1977, 1986). In cases where identification 

to species was not possible, ants were designated a morphospecies number. 

Specimens were then sent to experts for identification. Dr. André Francoeur 

(Directeur, Centre de données sur la biodiversité du Québec, Chicoutimi, Québec) 

(Myrmica, Leptothorax) and W. B. Preston (946 McMillan Ave., Winnipeg, 

Manitoba) (all other genera) identified these to species. 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

114 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Nest Survey 

The nest survey was restricted to lodgepole pine stands at this preliminary stage 

of the study, but will eventually be expanded to include all forest types. Thus, 

collections were done in lodgepole pine stands approximately 15–100 years old 

located west and southwest of Prince George. Twenty to thirty worker ants were 

collected from nests by hand. Reproductives were collected when available. 

Depending on the species, individuals were picked directly from the nest, or a portion 

of the nest substrate was transferred to a white plastic bucket, from which the ants 

could be transferred to small vials containing 70 percent ethanol. The most 

aggressive species were transferred again by tipping the bucket and directing the ants 

to run out over the edge into a small container containing soapy water, from which 

they could easily be collected after a few minutes. Each nest was assigned a field 

number, and in the majority of cases the substrate was photographed. The nest 

substrate was measured, and the integrity and general condition of the wood noted. 

Results and Discussion 

Species Survey 

Species identification of ants is difficult because of a lack of reference 

collections and the fact that most of the available keys are either out of print and 

unavailable (e.g., Creighton 1950), or are restricted to the ant fauna of specific 

regions (Wheeler and Wheeler 1963, 1986). A manuscript version of the key in 

Naumann and others 1999, which is specific to ants in BC, was valuable in that 

distribution records for the province could be consulted (table 1). However, since 

most collections have been done in southern BC, even these records were of limited 

use. Existing keys for the genera Myrmica and Leptothorax (Subfamily Myrmicinae) 

are unreliable, and these genera are under revision (Francoeur 1997). The names used 

follow Bolton (1995). 

Based on our preliminary survey, we found 19 species of ants in 7 genera that 

occur in the area (table 2). Of these Manica invidia Wheeler (= mutica Emery), 

Myrmica fracticornis Forel (= detritinodis Emery), Lasius subumbratus Viereck, 

Formica hewitti Wheeler, F. argentea Wheeler, and F. obscuriventris Mayr were not 

expected to occur in the area surveyed based on available information (table 1). In 

other words, 31.6 percent of the species we found in this preliminary survey had not 

been collected previously in north central British Columbia. Diversity can be 

moderate locally, e.g., Lindgren (personal observation) has found seven species 

occurring in and around the yard of his personal residence (an area of about 0.25 ha) 

in the city of Prince George. Normally, we found four to six species in any one area, 

often with three or more species sharing nest resources, or at least nesting in close 

proximity to each other. 

Nest Survey 

Subfamily Myrmicinae 

We found that wood was utilized by ants to a high degree for nesting. In an 

unrelated study in 1998, we found that small nests of Myrmica incompleta

(Provancher), M. alaskensis Wheeler and M. fracticornis Forel were common under 

the bark of lodgepole pine stumps, which were only 12 months old and still had 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 115 

active bark beetle infestations. Of 24 records of these three Myrmica species located 

in this study, more than 75 percent were found in wood (table 2). In most cases they 

were found in the mature forest. 

Table 2Species list of ants collected in the Prince George area, May–August, 1999, and 

information of their use and characteristics of wood for nesting. 

Subfamily Use of 

wood 

(pct) 

Length 

range (cm) 

Diameter 

range 

(cm) 

Predominant 

consistency of 

wood 

N 

 Species 

Myrmicinae 

Myrmica alaskensis 100 17-900 10-59 Rotten 6 

Myrmica brevispinosa 25 38 10 Rotten 4 

Myrmica fracticornis 83.3 3-120 4-8 Very rotten 6 

Myrmica incompleta 75 15-1300 10-50 Rotten 12 

Manica invidia 0 – – – 1 

Leptothorax muscorum 91.7 10-1300 5-25 Rotten 12 

Dolichoderinae 

 Tapinoma sessile 50 17-700 10-59 Solid 6 

Formicinae 

Camponotus herculeanus 100 50-800 10-50 Solid 10 

Camponotus modoc 100 50 500 Solid 1 

Lasius pallitarsis 73.3 15-350 8-53 Very rotten 15 

Lasius subumbratus 0 – – – 1 

Formica lasioides n/a – – – 1 

Formica obscuripes

 

01

 – – – 3 

Formica obscuriventris 50 300 30 Rotten 2 

Formica argentea 50 20-100 16-46 Rotten 10 

Formica fusca 100 33-150 20-77 Variable 3 

Formica hewitti 100 36 6 Rotten 22

Formica neorufibarbis 100 250 15 Heartrot 1 

Formica aserva 91.7 10-900 10-77 Rotten 12 1 Pine needle thatch mounds.

2 Measurement missing from a log.

In 11 of the 24 records, the nests were found in logs also occupied by other ant 

species, and in 6 of those records these were nests of Formica spp. or Camponotus 

herculeanus (Linnaeus). One nest of Myrmica brevispinosa Wheeler was found in 

wood in an open area at the edge of a ca. 15-year old stand of lodgepole pine, but this 

species appears to be more likely to nest in the soil. We never found this species in 

the mature forest. 

Nests of Leptothorax muscorum Nylander (=canadensis Provancher) were 

particularly common in wood occupied by other species. The nests of these minute 

ants were found in a variety of situations, but were often close to the surface of the 

wood, where it was dry and relatively firm. Nests were also found in very small 

pieces (10 x 15 cm in one case) of wood on the ground, where other species were not 

present. Nests of these ants were easily found by looking for fine excavating dust, 

which would accumulate under or in crevices on the wood containing an active nest. 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

116 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Subfamily Formicinae 

Camponotus herculeanus was the only species of carpenter ant we encountered 

in the pine forests, and it was always found in relatively large pieces of wood, i.e., 

stumps or down logs. This is similar to what was found for C. modoc Wheeler in 

Oregon (Torgersen and Bull 1995). Although we found evidence of C. herculeanus

nests in standing live trees, we did not collect from these, since collecting would have 

required cutting the trees down. The nests were usually not evident until the wood 

was broken open, since carpenter ants frequently pack excavated wood in tunnels and 

galleries (Sanders 1964). Majors of C. herculeanus are quite impressive in size, but 

this is a very timid species. When a nest was opened, the ants would rush about 

trying to save their brood, but were extremely reluctant to attack. In fact, groups of 

workers were frequently found cowering in chambers as they tried to escape the 

intruders. C. herculeanus occurred mainly in shaded locations, e.g., in mature stands. 

Unlike C. modoc, which Torgersen and Bull (1995) found to apparently avoid 

lodgepole pine, C. herculeanus used this species frequently. C. modoc was found 

during the species survey in a Douglas-fir stand, situated on the ridge at the top of a 

south-facing slope, but was never encountered elsewhere. 

In exposed areas, carpenter ants were replaced by Formica aserva Forel 

(=subnuda Emery). These aggressive ants were particularly prevalent in stumps, 

where their presence was usually quite evident due to the bustling activity of the ants 

themselves, excavating dust, and accumulations of thatching materials around the 

base of the nest. Disturbance of the nest brought about an immediate response of a 

large numbers of ants, which never hesitated to attack. Based on our preliminary 

observations, these ants favored low stumps and down logs with limited decay. F. 

aserva workers were at times observed carrying prey or tending aphids. It is the ants 

in the Formica rufa and F. sanguinea groups, along with the carpenter ants, that may 

contain the majority of potentially beneficial ants (Youngs and Campbell 1984), both 

by physically breaking down wood and as predators (although see Sanders and Pang 

1992). 

In one mature lodgepole pine stand within the city of Prince George, we found 

numerous large thatch mounds of Formica obscuripes Forel. The nests appeared to 

be polycalic, i.e., small accessory thatch mounds were in close proximity to the two 

large mounds from which we collected the ants. The largest dome had a base of 200 x 

250 cm and was about 100 cm tall. This attractive species was also extremely 

aggressive when defending nests. We could not determine if nests were initiated in 

wood, since this would have meant destroying the mounds 

Ants in the Formica fusca group, primarily F. argentea, F. hewitti, and F. fusca

Linnaeus also commonly used wood (table 2). F. argentea were found in soil nests in 

seven of ten cases. These soil mounds can be quite large, e.g., we found one nest 

covering more than 4 m2

 with a height of about 30 cm at its apex. Thus, this species 

is potentially important in terms of soil processes in the area surveyed, as are other 

species in the F. fusca group (Wiken and others 1976). In one of two cases where we 

dug up the nest, we found a rotten piece of wood at the center of a nest, indicating 

that the nest had been founded in wood. Both F. hewitti, and F. fusca nests were 

found in wood. These species were relatively aggressive, but in small nests workers 

usually tried to hide, rather than defend the nest. 

Lasius pallitarsis (Provancher) was the only species in this genus encountered 

during the nest survey. In forest environments we found this small species in very 

wet, rotten wood more or less buried in the soil. Small-diameter stumps were a 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 117 

particularly favored habitat. In several cases, the nest substrate was shared with 

Myrmica species. Nests were found in mature, as well as young pine forests, but we 

also found nests of these versatile ants under rocks and other objects in open fields. 

This is consistent with the information in Naumann and others 1999. 

Subfamily Dolichoderinae 

The only species in this genus was the ubiquitous Tapinoma sessile (Say). This 

diminutive, but aggressive, species showed no preference for nest substrate, 

consistent with its ability to inhabit virtually any habitat (Wheeler and Wheeler 

1963). 

Abundance 

Although no quantitative assessment of ant abundance was made, we judged 

ants to be numerous locally, particularly in open areas. Thus, they may be presumed 

to be an important component of the arthropod fauna in the area studied. The relative 

abundance of most of the species encountered in our study appeared to be favored by 

the presence of woody debris. A quantitative assessment of the relationship between 

the abundance of ants and woody debris needs to be done to establish whether or not 

this is true. 

Conclusion 

Because little is known about the ecology of most of the species present in the 

sub-boreal forests of interior BC, it is difficult to assess in what ways ants contribute 

to ecosystem function. Some species of ants are highly significant as predators of 

forest defoliators, and as a primary food source for woodpeckers (Torgersen and Bull 

1995). Further studies on the ecological roles of ants in sub-boreal forests are needed 

to determine their relative importance. It is clear from our preliminary study that 

woody debris constitutes an important habitat component for ants. For some species, 

the availability of woody nest substrates may limit nest founding success, and 

ultimately populations of ants. Additional information is required on the ecological 

significance of ants in sub-boreal forests, and the characteristics of wood associated 

with the nests of different species. Such information would ensure that beneficial 

species of ants could be promoted by providing suitable nest habitats in a manner 

similar to what is being done for cavity nesting birds. We intend to continue with the 

species inventory, and to conduct research on the ecological roles of ants in subboreal forests. 

Acknowledgments 

We thank K. Naumann and J. Heron for constructive comments on the 

manuscript, and W. B. Preston and A. Francoeur for identifying specimens and for 

advice and encouragement. This research was funded by Operating Grant 

OGP0194765, Natural Sciences and Engineering Research Council of Canada. 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

118 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

References 

Bolton, B. 1995. A new general catalogue of the ants of the world. Cambridge, MA: 

Harvard University Press; 504 p. 

Buckell, E. R. 1932. A list of the ants of British Columbia. Proceedings of the 

Entomological Society of British Columbia 29: 22-25. 

Creighton, W. S. 1950. The ants of North America. Bulletin of the Museum of Comparative 

Zoology 104: 1-585. 

Francoeur, A.; Maldague, M. 1966. Classification des micromilieux de nidification des 

Fourmis. Le Naturaliste Canadien 93: 473-478. 

Francoeur, A. 1973. Rèvision taxonomique des espèces nèarctiques du groupe fusca, 

genre Formica (Formicidae, Hymenoptera). Memoires du Société Entomologique du 

Québec 3: 1-316. 

Francoeur, A. 1983. The ant fauna near the tree-line in northern Québec (Formicidae, 

Hymenoptera). Nordicana 47: 177-180. 

Francoeur, A. 1997. Ants of the Yukon. In: Danks, H. V.; Downes, J. A., eds. Insects of the 

Yukon. Ottawa: Biological survey of Canada (terrestrial arthropods); 901-910. 

Hansen, L. D.; Akre, R. D. 1985. Biology of carpenter ants in Washington State 

(Hymenoptera: Formicidae: Camponotus). Melanderia 43: 1-61. 

Hölldobler, B.; Wilson, E. O. 1990. The ants. Cambridge, MA: Harvard University Press; 

732 p. 

Hölldobler, B.; Wilson, E. O. 1994. Journey to the ants. Cambridge, MA: The Belknap Press 

of the Harvard University Press; 228 p. 

Meidinger, D.; Pojar, J. 1991. Ecosystems of British Columbia. Victoria, BC: Ministry of 

Forests: Special Report Series Number 6; 330 p. 

Kansas, J. L.; Achuff, P. L.; Raine, R. M. 1989. A food habits model for grizzly bear 

habitat evaluation in Banff, Jasper, Kootenay and Yoho national parks. Final 

Report. Beak Associates Cons. Ltd. for Canada Parks. 

Naumann, K.; Preston, W. B.; Ayre, G. L. 1999. An annotated checklist of the ants 

(Hymenoptera: Formicidae) of British Columbia. Journal of the Entomological 

Society of British Columbia 96: 29-68. 

Nielsen, M. G. 1987. The ant fauna (Hymenoptera: Formicidae) in northern and interior 

Alaska. A survey along the trans-Alaskan pipeline and a few highways.

Entomological News 98: 74-88. 

Raine, R. M.; Kansas, J. L. 1990. Black bear seasonal food habits and distribution by 

elevation in Banff National Park, Alberta. International Conference Bear Research 

and Management 8: 297-304. 

Sanders, C. J. 1964. The biology of carpenter ants in New Brunswick. The Canadian 

Entomologist 96: 894-909. 

Sanders, C. J.; Pang, A. 1992. Carpenter ants as predators of spruce budworm in the 

boreal forests of northwestern Ontario. The Canadian Entomologist 124: 1093-1100. 

Smith, D. R. 1979. Superfamily Formicoidea. In: Krombein, K. V.; Hurd, Jr., P. D.; Smith, 

D. R.; Burks, B. D., eds. Catalog of Hymenoptera in America North of Mexico. Volume 

2. Apocrita (Aculeata). Washington, DC: Smithsonian Institution Press; 1323-1467. 

Torgersen, T. R.; Bull, E. L. 1995. Down logs as habitat for forest-dwelling ants–the 

primary prey of pileated woodpeckers in northeastern Oregon. Northwest Science 

69: 294-303. 
Ant Diversity and Dependence on Dead Wood—Lindgren and MacIsaac 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 119 

Wheeler, G. C.; Wheeler, J. 1963. The ants of North Dakota. Grand Forks, ND: University 

of North Dakota Press; 326 p. 

Wheeler, G. C.; Wheeler, J. 1977. North Dakota ants updated. Reno, NV: Desert Research 

Institute, University of Nevada System; 27 p. 

Wheeler, G. C.; Wheeler, J. 1986. The ants of Nevada. Los Angeles, CA: Natural History 

Museum of Los Angeles County; 138 p. 

Wiken, E. B.; Broersma, K,; Lavkulich, L. M.; Farstad, L. 1976. Biosynthetic alteration in a 

British Columbia soil by ants (Formica fusca Linné). Soil Science Society of America 

Journal 40: 422-426. 

Youngs, L. C.; Campbell, R. W. 1984. Ants preying on pupae of the western spruce 

budworm, Choristoneura occidentalis (Lepidoptera: Tortricidae), in eastern Oregon 

and western Montana. The Canadian Entomologist 116: 1665-1669. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 121 

Effects of Ecosystem Restoration 

Treatments on Cavity-nesting Birds, Their 

Habitat, and Their Insectivorous Prey in 

Fire-maintained Forests of Southeastern 

British Columbia1

Marlene Machmer2 

Abstract 

Long-term fire suppression and cessation of aboriginal burning has resulted in forest ingrowth 

and associated structural and functional changes to dry, fire-maintained forests of 

southeastern British Columbia. In this experimental study, effects of ecosystem restoration 

treatments (prescribed fire, partial harvesting, prescribed fire and partial harvesting, and 

untreated controls) on cavity-nesting birds, their habitat, and their insectivorous prey were 

investigated. Pre- and post-treatment data on the nesting density of cavity-nesters, the 

availability of wildlife trees, the foraging intensity of woodpeckers, and the relative 

abundance and species diversity of insects each breeding season were gathered, beginning in 

1996. Preliminary results (1996 to 1998) indicate that harvested treatments were associated 

with a decline in the nesting density and species richness of cavity nesters over the short term; 

snag densities decreased in harvested and burned treatments; the number of trees per hectare 

with fresh woodpecker foraging sign did not differ significantly comparing pre- and posttreatment; and large increases in the relative abundance of selected insect species in some 

families were apparent in the treated units. Insect response was most pronounced in the burn 

only treatment, followed by the harvest and burn, and the harvest only treatments. 

Management implications for future ecosystem restoration efforts are discussed. 

Introduction 

In the Rocky Mountain Trench and adjoining side valleys of southeastern British 

Columbia, an estimated 250,000 ha of land within the ponderosa pine (PP) and 

interior Douglas-fir (IDF) biogeoclimatic zones is classified as Natural Disturbance 

Type 4 (NDT4). Before 1900, these forests were characterized by “frequent, standmaintaining fires” resulting in open park-like conditions with widely-spaced large old 

trees, sparse regeneration, and low incidence of insects and diseases (Arno and others 

1995, Covington and Moore 1994, Daigle 1996, Gayton 1996). Systematic and longterm fire suppression and cessation of aboriginal burning has eliminated fire from 

these forests. This has stimulated forest ingrowth and encroachment, with associated 

reductions in ungulate forage quantity and quality, increased risk of stand 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Senior Biologist, Pandion Ecological Research, 732 Park Street, Nelson, British Columbia, Canada 

V1L 2G9 (e-mail: mmachmer@netidea.com) 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

122 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

replacement fires, and major forest insect and disease outbreaks. Recent operational 

trials have used mechanical treatments (e.g., partial cutting, slashing pruning) and 

prescribed fire in an attempt to restore the fire-maintained character of these forests 

(Gayton and others 1995, Hawe and DeLong 1998, White 1997). Once stands have 

been thinned and fuels have cured, prescribed burning can be carried without the risk 

of catastrophic fire, while providing some revenue from sawlogs and pulp. Effects of 

restoration treatments on wildlife communities have not been well documented in an 

experimental context (Finch and others 1997, Saab and Dudley 1997). 

This study focuses on cavity-nesting birds—birds that are dependent on standing 

dead and defective live trees for nesting, roosting and feeding (Bull and others 1997, 

Raphael and White 1984, Steeger and others 1996). In dry, fire-maintained forests, 

the proportion of cavity-nesting species is comparatively high relative to other forestdwelling vertebrates (Bunnell 1995). Burns create fire-scorched or killed trees, which 

are attractive to a host of wood, bark, and cambium-dwelling insects (Amman and 

Ryan 1991, Fellin 1980, Furniss and Carolin 1977, Samuelsson and others 1994). 

These insects form the prey base for many cavity-nesting species (Machmer and 

Steeger 1995). I hypothesized that the temporal and spatial occurrence of burns 

would have a strong influence on the population dynamics of this wildlife guild. 

The objectives of this study are to investigate the individual and combined 

effects of ecosystem restoration treatments on the nesting abundance and species 

richness of cavity nesters, the availability of wildlife tree habitat, the foraging 

intensity of woodpeckers, and the relative abundance and species richness of woodassociated insects. In this paper, preliminary (1996 to 1998) results are reported, and 

some management implications for future restoration treatments are discussed. 

Study Area and Design 

The study is being conducted in the Ta Ta Creek range unit (49°46’N, 

115°46’W) located 45 km north of Cranbrook in the Rocky Mountain Trench of 

southeastern British Columbia. The study area is in a flat valley bottom (850 to 900 

meter elevation) and consists of moderately dense to semi-open multi-storied stands 

of 90- to 100-year-old Douglas-fir (Pseudotsuga menziesii) and ponderosa pine 

(Pinus ponderosa). Small pockets of lodgepole pine (P. contorta) and trembling 

aspen (Populus tremuloides) are found in draws and wetter sites. Fire has been 

excluded from these for an estimated 60 years. 

Three treatments (25 ha burn only; 40 ha harvest and burn; and 40 ha harvest 

only) and two control areas (one located adjacent to and a second located 3.5 km 

away from the treatment units) were tested without replication during operational 

trials. A uniform “shelterwood with reserves” silvicultural system was used for 

harvest treatments with the following objectives for post-harvest target densities: 26-

36 stems ha-1 (sph) of layer 1a (20-65 cm dbh) healthy, well-formed 

veteran/dominant ponderosa pine and Douglas-fir; 5-20 sph of layer 1b (15-20 cm 

dbh) ponderosa pine and Douglas-fir; 10-20 sph of layer 2 (10-15 cm dbh) ponderosa 

pine and Douglas-fir; and 50-60 sph of layer 3 (3-5 cm dbh) ponderosa pine. Postharvest slashing of small sub-merchantable stems was conducted in the harvest and 

burn treatment to ensure sufficient fuel to carry the fire. Burning treatments involved 

low-intensity prescribed fire with the following specific objectives: eliminate 75 and 

25 percent of trees in the < 5 and < 15 cm diameter at breast height (dbh) classes, 

respectively; limit mortality of trees > 30 cm dbh to < 10 percent; prune all trees to a 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 123 

height of 2 m; and reduce ground fuels <10 cm and > 20 cm diameter by 50-75 and 

5-10 percent, respectively. Harvesting was completed in February of 1997, and 

burning was conducted during April of 1998. Resulting stands differed visibly in 

terms of large stem densities and associated stand structure: post-treatment (1999) 

densities of trees > 10 cm dbh averaged 160, 48 and 161 sph in the burn only, harvest 

and burn and harvest only treatments, respectively, while densities of smaller stems 

were relatively comparable among treated areas. 

Methods 

We established 20 ha core sampling areas in each of the five treatment units 

during spring of 1996. These areas were monitored pre- and post-treatment during the 

1996 to 1999 breeding seasons. 

Cavity Nest Inventory 

From early May to late June, we systematically searched the sampling areas for 

the presence of cavity-nesting species (both primary cavity excavators and secondary 

cavity users) and cavities in trees. We considered a nest active if parents were 

observed incubating, tending a brood, feeding young, or if young were heard 

vocalizing within the cavity. Two observers visited each of the five treatment units 

weekly on a regular rotation for 7 weeks (70 observer-days/season). We monitored 

nests weekly to determine their status and fate (i.e., success or failure), and calculated 

cavity nest densities for each treatment, excluding pairs that failed prior to 

confirming incubation. 

Wildlife Tree Inventory 

We assessed the number and characteristics of all standing live healthy trees, 

dead trees, and wildlife trees (i.e., dead trees, live defective trees, and live trees with 

evidence of foraging sign) > 10 cm dbh in stratified random plots of 11.28 m radius 

before (1996) and after (1998) treatment. Tree characteristics included tree species, 

dbh, height, decay class (British Columbia Wildlife Tree Committee 1997), and 

presence of particular tree defects and disturbance agents. A total of 100 plots (20 

plots per treatment unit) were sampled in late June of each year. 

Woodpecker Foraging Inventory 

We assessed all trees (no diameter limit) in the random plots for evidence of 

fresh woodpecker foraging activity before (1996) and after (1998) treatment. Freshly 

“woodpeckered” bark characterized by newly exposed wood was readily 

distinguished from old foraging sign that appears discolored. We classified foraging 

sign as scaling, excavations, or sapsucking. This method is conservative in that it 

excludes foraging that does not leave quantifiable sign, such as gleaning of insects 

from bark or foliage. To assist with the interpretation of foraging sign data, we made 

opportunistic observations on foraging woodpeckers during surveys in the sampling 

areas. 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

124 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Insect Trapping 

We used Lindgren multiple-funnel traps (baited with an ethanol-releasing device 

and containing a Vapona pest strip)3

 to assess the abundance and diversity of arboreal 

beetles and other insects likely to serve as prey items for woodpeckers and other 

cavity-nesting species. Four traps were suspended (between trees with collection cups 

at 0.5 to 1.0 meter above ground level) in each treatment unit from late April to early 

September. Catches were collected every 3 weeks and stored in plastic bags at -10°C. 

Later, insects were sorted to family, identified to species or genus, and tallied. Insect 

analyses are still in progress and only preliminary; 1996—1998 results are presented 

here. 

Results 

Cavity Nest Density and Species Richness 

We found a total of 10 cavity-nesting species breeding in the study area: hairy 

(Picoides villosus) and pileated woodpeckers (Dryocopus pileatus), northern flicker 

(Colaptes auratus), white- (Sitta carolinensis) and red-breasted nuthatches (S. 

canadensis), black-capped (Parus atricapillus) and mountain chickadees (P.

gambeli), mountain bluebird (Sialia currucoides), red squirrel (Tamiasciurus 

hudsonicus), and northern flying squirrel (Glaucomys sabrinus). Pre-treatment (1996) 

cavity nest densities ranged from 2 to 10 nests per 20 ha treatment unit (0.1 to 0.5 

nests per ha; fig. 1). After harvest treatments were completed in 1997, nest densities 

in the harvest and burn and harvest only treatments decreased by 50 percent. Those in 

the burn only treatment (still untreated in 1997) increased by 50 percent, relative to 

pre-treatment. Nest densities in adjacent and distant controls increased and decreased 

respectively, during this period. After burning treatments were completed in 1998, 

nest densities remained 50 percent lower than pre-treatment in the harvest only, and 

were either comparable to or higher than pre-treatment in all other units. Of the posttreatment cavity nests found in the harvested treatments, 50 percent in the harvest 

only (1997 and 1998) and 33 percent in the harvest and burn (1998 only) were 

located in wildlife tree patch-reserves, rather than in harvested portions of the treated 

units. These reserves comprised only 4.2 percent of the total area harvested, yet they 

supported up to half the breeding cavity nesters. Although sample sizes are low and 

statistical comparisons are not possible due to lack of replication, these results 

suggest that over the short term the harvest only treatment was associated with a 

decrease in cavity nest densities. 

Pre-treatment species richness of cavity nesters was low, ranging from two to 

four species per treatment unit (fig. 2). Following harvest in 1997, nesting species 

richness decreased in both harvested treatments, but remained constant in the 

adjacent control, and increased in the burn only and distant control. After burning 

was completed in April of 1998, cavity nesting species richness was 50 percent lower 

in the harvest only and higher in all other units, relative to pre-treatment. These 

trends also suggest a short term decrease in cavity-nesting species richness associated 

with the harvest only treatment. 

 

3

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 125 

Figure 1―Number of active cavity nests per 20 ha treatment unit by year (1996 to 

1998) and treatment type in the Ta Ta Creek operational trial, southeastern British 

Columbia. Note that 1996 was a pre-treatment, 1998 was a post-treatment year, and 

1997 was pre-treatment for burning and post-treatment for harvesting activities. 

Figure 2―Number of cavity-nesting species per 20 ha treatment unit by year (1996 

to1998) and treatment type in the Ta Ta Creek operational trial, southeastern British 

Columbia. Note that 1996 was a pre-treatment, 1998 was a post-treatment year, and 

1997 was pre-treatment for burning and post-treatment for harvesting activities. 

The mountain bluebird was the only species to nest in a treated area (burn 

only) after treatment that was not breeding there before treatment. Conversely, the 

northern flying squirrel and white-breasted nuthatch did not breed in treated units 

(harvest only and burn only, respectively) once treatments were completed, although 

they were nesting there before. 

0

3

6

9

12

burn only harvest & burn harvest only adjacent control distant control

Treatment Type 

No. cavity nests/20 ha 

1996 1997 1998

0

2

4

6

8

burn only harvest & burn harvest only adjacent control distant control

Treatment Type 

No. cavity-nesting species 

1996 1997 1998
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

126 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Availability of Wildlife Trees 

The harvest and burn and harvest only treatments showed reductions in basal 

area of 60.6 and 66.4 percent, respectively, as determined during a companion study 

monitoring vegetation response to treatments (Penniket & Associates 1998). As 

expected, total densities of trees measuring > 10 cm dbh differed significantly 

between years and among treatments (fig. 3). In particular, the two harvested 

treatments showed significant post-treatment declines (two-way Anova: F = 11.2, df 

= 1, P = 0.001 for year; F = 3.66, df = 4, P = 0.05 for treatment; F = 3.69, df = 4, P = 

0.006 for treatment × year). 

Snag densities ranged from 2.5 to 12.5 snags per hectare in the treatment units in 

1996 compared with 0.1 to 15.0 snags per ha in 1998 (fig. 3). All three treated units 

had lower snag densities post-treatment, i.e., decreases of 97 percent in the burn only, 

98 percent in the harvest and burn and 50 percent in the harvest only, while densities 

in adjacent and distant controls were 48 percent lower and 50 percent higher, 

respectively, relative to pre-treatment. Differences among treatments and between 

years were not statistically significant (two-way Anova: F = 0.718, df = 4, P < 0.581 

for treatment; F = 1.13, df = 1, P = 0.289 for year; F = 0.732, df = 4, P = 0.571 for 

treatment × year). 

Figure 3―Densities (stems ha-1) of wildlife trees, snags, and all trees (> 10 cm dbh) 

by treatment type in 1996 (pre-treatment) and 1998 (post-treatment). 

Pre- and post-treatment, the densities of wildlife trees were significantly lower 

in 1998, but differences among treatments and interactions between treatment and 

year were not (two-way Anova: F = 20.4, df = 1, P < 0.0001 for year; F = 2.03, df = 

4, P = 0.092 for treatment; F = 2.00, df = 4, P = 0.097 for treatment × year). The 

significant year-effect is related to the way wildlife trees were defined (i.e., dead 

0

20

40

60

burn only harvest & burn harvest only adjacent

control

distant control

Mean stems/ha

pre-treatment (1996) post-treatment (1998) 

 Wildlife Trees 

0

4

8

12

16

burn only harvest & burn harvest only adjacent

control

distant control

Mean stems/ha

 Snags 

0

200

400

600

burn only harvest & burn harvest only adjacent

control

distant control

Treatm ent Type

Mean stems/ha 

Total trees >10 dbh
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 127 

trees, live defective trees, and live trees with evidence of foraging sign or other 

wildlife use), and reflects the significantly lower level of woodpecker foraging 

activity found on trees in the overall study area in 1998 (see below). 

Woodpecker Foraging Intensity 

Woodpecker scaling and excavations accounted for approximately 80 and 20 

percent, respectively, of foraging observations in both years (81.4 scaling and 18.6 

percent excavations in 1996 compared with 79.3 scaling and 20.7 percent excavations 

in 1998). The number of trees with fresh woodpecker foraging sign in the treatment 

units ranged from 5 to 22.5 trees/ha in 1996 and 2.5 to 15 trees/ha in 1998 (fig. 4).

Differences between years were significant; however, treatment effects and 

interactions between treatment and year were not (Two-way anova: F = 4.69, df = 1, 

P < 0.0317 for year; F = 0.444, df = 4, P = 0.777 for treatment; F = 0.444, df = 4, P = 

0.777 for treatment × year). Woodpecker foraging activity on trees was lower in the 

winter, spring, and early summer preceding our June 1998 observations than in the 

corresponding seasons prior to 1996. These differences were not treatment related 

and may be linked to abiotic factors (e.g., temperature, snow pack) affecting the 

entire study area. 

Figure 4―Density (stems ha-1) of trees with fresh woodpecker foraging sign by 

treatment type in 1996 (pre-treatment) and 1998 (post-treatment). 

Abundance and Diversity of Insects 

Pre-treatment insect diversity and abundance was similar across treatment units, 

with a total of 1,919 individuals, 84 species, 57 genera, and 25 families represented 

in trap catches (Wilson 1999). After treatments were completed in 1998, 10,642 

individuals representing 98 species, 68 genera, and 26 families were tallied in 

catches. Relative to controls, all three treated units showed large (>100 percent) posttreatment (1998) increases in abundance of selected species in the following families: 

0

5

10

15

20

25

burn only harvest &

burn

harvest only adjacent

control

distant

control

Treatment Type

Mean stems/ha 

pre-treatment (1996) post-treatment (1998)
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

128 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Buprestidae, Cerambycidae, Cleridae, Hymenoptera, Nitulidae, Oedemeridae, 

Salpingidae, Scolytidae and Trogositidae. Increases in species abundance, especially 

Hylastes spp., Hylurgops spp., Dendroctonus valens, Asemum nitidum, and Rhagium

inquisitor, were greatest in the burn only treatment. Relative to controls, total 

numbers of insects captured were 170, 54, and 45 percent higher in the burn only, 

harvest and burn and harvest only treatments, respectively. Increases in posttreatment insect species diversity were also apparent in the families Buprestidae (flatheaded wood borers), Cerambycidae (round-headed wood borers) and Scolytidae 

(bark beetles). The latter families inhabit dead and dying wood and are associated 

with forest disturbances (Furniss and Carolin 1977). Preliminary results suggest that 

insect response to restoration treatments is quite species-specific, but that selected 

species increased dramatically, with responses most pronounced in the burn only 

treatment, followed by the harvest and burn and harvest only. 

Discussion 

Overall, species composition of breeding cavity nesters found in this study was 

similar to that in nearby Idaho Douglas-fir forests (Medin 1985), although nest 

densities reported here are considerably lower. Lack of replication prevented me 

from detecting treatment effects; however, preliminary results do suggest that 

harvesting (either through greater disturbance and/or direct effects on the landscape) 

was associated with a decline in cavity nest densities and species richness. The whitebreasted nuthatch was the only species to breed at a site pre-treatment and then 

vacate after treatment, while continuing to nest in controls. This response is 

consistent with Hejl and others (1995) who reported that in the Southwest, this 

species was less abundant in clearcut and partial cut ponderosa pine stands relative to 

unharvested forests. 

Several species, such as red-breasted nuthatch, mountain chickadee, and red 

squirrel present in the harvested areas shifted into untreated wildlife tree patches to 

nest after harvest treatments were completed. Overall, 40 percent of post-treatment 

cavity nests were located in wildlife tree patches, compared with only 10 percent pretreatment. These shifts imply that for some species, untreated patch reserves provide 

preferred habitat relative to partially logged areas. My findings are consistent with 

studies demonstrating that red-breasted nuthatches and mountain chickadees are more 

abundant in unharvested forest than in partial cuts (Medin 1985, Szaro and Balda 

1979, Waterhouse and Dawson 1998) or in clearcut stands (Hejl 1994, Hejl and 

others 1995). Both species have been shown to use residual patches. Their detection 

rates in patches are comparable to those in contiguous forest and greater than in 

adjacent logged areas (Gyug and Bennett 1995, Seip and Parker 1997). Similarly, red 

squirrel populations tend to be highest in mature to old unmanaged forests (Carey 

1995), and Klenner (1998) demonstrated that partial cutting treatments involving 20-

50 percent volume removal are associated with moderate declines, although this 

species does use patches of residual snags and green trees. 

Shifts of cavity nesters into wildlife tree patches suggest that declines in nest 

density and species richness were partially offset through patch retention. Patches 

represented only 4.2 percent of the total area harvested in this operational trial. This 

is 0.3 percent less than area-based retention requirements still in effect (Province of 

British Columbia 1999). A greater level of patch retention (or a lighter level of 

treatment) could potentially minimize impacts of harvesting on the resident cavity-
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 129 

nesting guild. Retention should be based on pre-treatment surveys to delineate the 

most valuable wildlife tree habitat, rather than operational ease. 

I did not detect short-term effects of burning treatments on cavity nest densities 

or species richness, with the exception of some anecdotal shifts in species 

composition. This lack of effect is consistent with lesser severity of the burn 

treatment on stand structure and with other studies investigating effects of prescribed 

fire on breeding birds in pine forests (Bock and Bock 1983, Finch and others 1997, 

Horton and Mannan 1988). After treatment in 1998, mountain bluebirds moved into 

the burn only to breed, whereas northern flying squirrels, which bred there in 1997, 

vacated in 1998. Mountain bluebirds are closely associated with early post-fire 

conditions (Finch and others 1997, Hutto 1995), and Bock and Bock (1983) found a 

greater abundance of this species in burns when compared with unburned forests. 

Conversely, northern flying squirrels are more abundant in mature to old forests 

(Carey 1995, Klenner 1998, McDonald 1995). Thus, this species may have been 

displaced in my study owing to reduced habitat suitability or short term disturbance 

directly associated with prescribed burning. We did not detect the Lewis’s 

woodpecker (Melanerpes lewis) in our study area from 1996 to 1998. In 1999, this 

species was observed incidentally for the first time, which is consistent with its 

reported association with early post-fire habitats (Hutto 1995, Saab and Rich 1997). 

Snag densities differed in pre- and post-treatment settings. Specifically, snag 

densities were 97, 98, and 50 percent lower in the burn only, harvest and burn and 

harvest only, respectively. In the two harvested treatments, snags were removed to 

comply with occupational health and safety regulations (Workers’ Compensation 

Board of British Columbia 1998). At the time of the harvest, the regulations required 

that all snags in reach of work areas be felled during harvesting operations, unless 

buffered in wildlife tree patches or surrounded by no-work zones. Snag densities in 

the burn only treatment were very low prior to treatment (approximately 3.8 sph). 

However, I observed several smaller (< 30 cm dbh) fallen burnt snags with advanced 

decay and previously active nests in late April of 1998 after the burn. These fallen 

snags were most likely destabilized by prescribed fire, and similar declines in snag 

density have been documented for other prescribed burns: 56 percent decrease by 

Gaines and others (1958); 35-48 percent decrease by Gordon (1996); and 45 percent 

decrease by Horton and Mannon (1988). In 1999, it became apparent that prescribed 

burning killed many smaller (<15 cm dbh) trees in the two burned treatments (82.5 

and 87.3 percent reduction in mean layer 4 sph in the burn only and harvest and burn, 

respectively; Penniket & Associates Ltd. 1998). These smaller trees were intensively 

used for foraging by woodpeckers in 1999, but were too small to provide suitable 

cavity nesting habitat (Machmer 2000). 

The increased abundance and diversity of insects found in the burn only (and to 

a lesser extent in the harvest and burn and harvest only) is consistent with other 

studies that have reported a greater abundance of buprestid and cerambicid beetle 

larvae in recent fire-killed and/or harvested trees (Amman and Ryan 1991, Evans 

1964, Fellin 1980). I anticipate an increase in woodpecker foraging activity on trees 

in burned areas in future years, as pupae and larvae of the elevated 1998 insect 

populations become available prey. Monitoring at this site will continue for another 1 

to 2 years. 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

130 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Management Implications 

Successful management of the cavity-nesting bird community during broadscale application of ecosystem restoration treatments will require a multi-faceted 

approach that satisfies the diverse requirements of various guild members. Recently 

revised occupational health and safety regulations in British Columbia (Workers’ 

Compensation Board of British Columbia 1998) permit retention of dead trees in all 

forestry operations, provided they do not pose a hazard to forest workers. To promote 

populations of cavity nesters that are associated with semi-open stands (e.g., redbreasted nuthatch, mountain chickadee, northern flying squirrel) during restoration 

treatments, I recommend that managers attempt to achieve a patchy rather than 

uniform treatment severity during mechanical treatments, and that wildlife tree 

patches be established in all areas planned for restoration treatment. Consideration 

should be given to exceeding current area-based retention requirements (Province of 

British Columbia 1999) in an attempt to approach historical stand conditions and 

minimize the likelihood of adverse impacts on the cavity-nesting guild. Furthermore, 

patch-reserves should be delineated based on pre-treatment surveys to identify 

patches with features of highest demonstrated value to cavity nesters, such as dead 

trees with broken tops, evidence of internal decay and/or previous cavity use in the 

largest available diameter classes (Bull and others 1997, Steeger and Dulisse 2002). 

To address the needs of species associated with open habitats, such as Lewis’s 

woodpecker and mountain bluebird, an abundance of high value dead trees should be 

retained as individuals or clumps in the main portion of treatment areas. The latter 

should represent a range of decay classes favoring the largest diameter stems, which 

have the greatest longevity during fire and satisfy the requirements of the most 

species (Finch and others 1997, Raphael and White 1984). 

To minimize loss of snags during prescribed fire treatment, constructing fire 

lines around them (Gordon 1996) and/or using fire retardant to protect these habitat 

features should be considered. 

Preliminary insect responses to the treatments suggest that enhancement of food 

supplies for cavity nesters associated with burning may be greater for partial cutting 

in combination with burning than for partial cutting alone. If further monitoring 

substantiates this difference, then consideration should be given to the establishment 

of “burn only” patch-reserves within areas planned for “harvest and burn” restoration 

treatment. After treatment, these patch-reserves would contain a higher density of 

standing dead trees charred by fire to support dependent insect populations that serve 

as prey for cavity nesters. 

Acknowledgments 

Billie Gowans, Maryann McDonaugh, Paula Rodriguez, and Carl Savignac 

participated in the field data collection. Ian Wilson conducted insect analyses and 

provided a preliminary summary of results. Torolf Torgerson, Chris Steeger, and 

William Laudenslayer reviewed and improved earlier versions of the manuscript. 

Funding for this project was provided by the Forest Renewal British Columbia 

Research Program and administered by the Science Council of British Columbia. 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 131 

References 

Amman, Gene D.; Ryan, Kevin D. 1991. Insect infestation of fire-injured trees in the 

greater Yellowstone area. Res. Note INT-398. Ogden, UT: Intermountain Research 

Station, Forest Service, U.S. Department of Agriculture; 9 p. 

Arno, Stephen F.; Scott, Joe H.; Hartwell, Michael G. 1995. Age-class structure of oldgrowth ponderosa pine/Douglas-fir stands and its relationship to fire. Res. Rep. 

INT-481. Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department 

of Agriculture; 25 p. 

Bock, C. E.; Bock, J. H. 1983. Responses of birds and deer mice to prescribed burning in 

ponderosa pine. Journal of Wildlife Management 47: 836-840. 

British Columbia Wildlife Tree Committee. 1997. Wildlife/danger tree assessor’s course 

workbook. 5th edition. Manning, Todd; Guy, Stewart; Bradford, Peter, editors. Victoria, 

British Columbia: B.C. Ministry of Forests, B.C. Ministry of Environment and Workers’ 

Compensation Board of B.C. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Bunnell, Fred R. 1995. Forest-dwelling vertebrate faunas and natural fire regimes in 

British Columbia: patterns and implications for conservation. Conservation Biology 

9: 636-644. 

Carey, A. B. 1995. Sciurids in the Pacific Northwest: managed and old-growth forests.

Ecological Applications 5: 648-661. 

Covington, W. Wallace; Moore, Margaret M. 1994. Southwestern ponderosa pine forest 

structure. J. of Forestry 29: 39-47. 

Daigle, Patrick. 1996. Fire in the dry interior forests of British Columbia. Extension Note 

8, British Columbia Ministry of Forests Research Program, Victoria, B.C.; 5 p. 

Evans, W. G. 1964. Infra-red receptors in Melanophilia acuminata DeGeer. Nature 

(London) 202: 211. 

Fellin, D. G. 1980. A review of some interactions between harvesting, residue 

management, fire, forest insects and diseases. In: Proceedings of the symposium on 

environmental consequences of timber harvesting in Rocky Mountain coniferous forests. 

Gen. Tech. Rep. INT-90. Ogden, UT: Intermountain Research Station, Forest Service, 

U.S. Department of Agriculture; 335-414. 

Finch, Deborah M.; Ganey, Joseph L.; Yong, Wang; Kimball, Rebecca T.; Sallabanks, R. 

1997. Effects and interactions of fire, logging, and grazing. In: Songbird ecology in 

southwestern ponderosa pine forests: a literature review. Gen. Tech. Rep. RM-GTR-292. 

Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 103-136. 

Furniss, R. L.; Carolin. V. M. 1977. Western forest insects. Miscellaneous Publication No. 

1339, Forest Service, U.S. Department of Agriculture; 654 p. 

Gaines, E. M.; Kallander, H. R.; Wagner, J. A. 1958. Controlled burning in southwestern 

ponderosa pine: results from the Blue Mountains plots, Fort Apache Indian 

Reservation. Journal of Forests 56: 323-327. 

Gayton, Don. 1996. Fire-maintained ecosystems and the effects of forest ingrowth.

December 1996 Research Summary. Nelson Forest Region, British Columbia Ministry 

of Forests, Nelson, B.C.; 4 p. 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

132 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Gayton, Don; Braumandl, Tom; Stewart, Rick. 1995. Ecosystem maintenance burning 

evaluation and research pilot project. Nelson Forest Region, British Columbia 

Ministry of Forests, Nelson, B.C.; 31 p. 

Gordon, J. V. 1996. Effects of prescribed fire on snags and logs in northern Arizona 

ponderosa pine forests. Flagstaff, Arizona: University of Northern Arizona; 55 p. M.S. 

thesis. 

Gyug, Les W.; Bennett, Stephen P. 1995. Bird use of wildlife tree patches 25 years after 

clearcutting. In: Bradford, Peter; Manning, Todd; L’Anson, Bill, editors. Proceedings 

of a workshop on wildlife trees and stand-level biodiversity, 1994 October 17-18; 

Victoria, British Columbia. B.C., Ministry of Forests and B.C. Ministry of Environment, 

Victoria, B.C.; 15-34. 

Hawe, Angela; DeLong Debbie. 1998. Partial cutting and controlled fire to restore oldgrowth forest conditions in the East Kootenay Trench. In: Vyse, Alan; Hollstedt, 

Chris; Huggard, Dave, editors. Proceedings of the workshop on managing the dry 

Douglas-fir forests of the southern interior; 1997 April 29-30, B.C. Ministry of Forests 

Research Program, Kamloops, British Columbia; 29-36. 

Hejl, Sallie J. 1994. Human-induced changes in bird populations in coniferous forests in 

western North America during the last 100 years. In: Jehl, J. R.; Johnson, N. K., 

editors. A century of avifaunal change in western North America. Studies in Avian 

Biology No. 15: 232-246. 

Hejl, S. J.; Hutto, R. L.; Preston, C. R.; Finch, D. M. 1995. Effects of silvicultural 

treatments in the Rocky Mountains. In: Martin, T. E.; Finch, D. M., editors. Ecology 

and management of neotropical migratory birds. Oxford, UK: Oxford University Press; 

55-84. 

Horton, S. P.; Mannan, R. W. 1988. Effects of prescribed fire on snags and cavity-nesting 

birds in southeastern Arizona pine forests. Wildlife Society Bulletin 16: 37-44. 

Hutto, Richard L. 1995. Composition of bird communities following stand-replacement 

fires in northern Rocky Mountain conifer forests. Conservation Biology 9: 1041-

1058. 

Klenner, Walt. 1998. Effects of experimental harvesting treatments on the demography 

and behaviour of sciurids at Opax Mountain. In: Vyse, Alan; Hollstedt, Chris; 

Huggard, Dave, editors. Proceedings of the workshop on managing the dry Douglas-fir 

forests of the southern interior; 1997 April 29-30, B.C. Ministry of Forests Research 

Program, Kamloops, British Columbia; 264-276. 

McDonald, L. 1995. Relationships between northern flyinh squirrels and stand age and 

structure in aspen mixedwood forests in Alberta. In: Stelfox, J. B., editor. 

Relationships between stand age, stand structure, and biodiversity in Aspen mixedwood 

forests in Alberta. Edmonton, Alberta: Alberta Environmental Service and Canadian 

Forest Service; 227-240. 

Machmer, Marlene M.; Steeger, Christoph. 1995. The ecological roles of wildlife tree users 

in forest ecosystems. Victoria, British Columbia: B.C. Ministry of Forests, Land 

Management Handbook 35; 54 p. 

Machmer, Marlene M. 2000. The ecological role of fire for cavity nesting birds.

Unpublished final technical report prepared for Forest Renewal British Columbia, 

Burnaby, B.C.; 55 p. 

Medin, Dean A. 1985. Breeding bird responses to diameter-cut logging in west-central 

Idaho. Res. Paper INT-355. Ogden, UT: Intermountain Research Station, Forest 

Service, U.S. Department of Agriculture; 12 p. 
Effects of Restoration Treatments on Cavity-nesting Birds—Machmer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 133 

Penniket & Associates Ltd. 1998. East Kootenay Trench restoration treatments 

monitoring project: general workplan and establishment report for the TaTa 

Creek site. Unpublished report prepared for the Rocky Mountain Trench Natural 

Resources Society and Forest Renewal British Columbia, Burnaby, B.C.; 40 p. 

Province of British Columbia. 1999. Landscape unit planning guide. Victoria, British 

Columbia: B.C. Ministry of Forests and B.C. Ministry of Environment, Lands and Parks; 

101 p. 

Raphael, Martin G.; White, M. 1984. Use of snags by cavity-nesting birds in the Sierra 

Nevada. Wildlife Monograph 86: 1-66. 

Saab, Victoria; Dudley, Jonathon. 1997. Bird responses to stand-replacement fire and 

salvage logging in ponderosa pine/Douglas-fir forests of southwestern Idaho.

Unpublished progress report. Boise, ID: Intermountain Research Station, Forest Service, 

U.S. Department of Agriculture; 1-34. 

Saab, Victoria A.; Rich, Terrell, D. 1997. Large-scale conservation assessment for 

neotropical migratory land birds in the interior Columbia River basin. Gen. Tech. 

Rep. PNW-GTR-399. Portland, OR: Pacific Northwest Research Station, Forest Service, 

U.S. Department of Agriculture; 56 p. 

Samuelsson, J.; Gustafsson, L.; Ingelög, T. 1994. Dying and dead trees: a review of their 

importance for biodiversity. Uppsala, Sweden: Swedish National Environmental 

Protection Agency Report No. 4306, Swedish Threatened Species Unit. 

Seip, Dale; Parker, Ken. 1997. Use of wildlife tree patches by forest birds in the subboreal spruce (SBS) zone. Forest Research Note PG-08. Prince George, British 

Columbia, Prince George Forest Region, Forest Resources and Practices Team; 6 p.

Steeger, Christoph; Dulisse, Jakob. 2002. Characteristics and dynamics of cavity nest trees 

in southern British Columbia. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Steeger, Christoph; Machmer, Marlene M.; Walters, Eric. 1996. Ecology and management 

of woodpeckers and wildlife trees in British Columbia. Canadian Wildlife Service, 

Pacific Wildlife Research Centre, Delta, British Columbia; 28 p. 

Szaro, Robert C.; Balda, Russell P. 1979. Effects of harvesting ponderosa pine on nongame 

bird populations. Res. Paper RM-212. Fort Collins, CO: Rocky Mountain Forest and 

Range Research Station, Forest Service, U.S. Department of Agriculture; 8 p. 

Waterhouse, Michaela J; Dawson, Rick. 1998. Bird communities in interior Douglas-fir 

forests in the Cariboo forest region. In: Proceedings of a workshop on managing the 

dry Douglas-fir forests of the southern interior; 1997 April 29-30, B.C. Ministry of 

Forests Research Program, Kamloops, British Columbia; 90-112. 

White, D. 1997. Rocky Mountain trench ecosystem restoration: interim report. Enhanced 

Forest Management Pilot Project Summary, Rep. No. 5. British Columbia Ministry of 

Forests, Invermere Forest District, Invermere, B.C.; 4 p. 

Wilson, Ian. 1999. Analyses of funnel trap catches at the TaTa Creek underburn trial, 

1998. Unpublished report. Vernon, British Columbia: Phero Tech Inc.; 6 p. 

Workers’ Compensation Board of British Columbia. 1998. Occupational health and safety 

regulation: industry/activity specific requirements; parts 20-33. Vancouver, British 

Columbia: Workers’ Compensation Board of British Columbia. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 135 

The Role of Coarse Woody Debris in 

Southeastern Pine Forests: Preliminary 

Results from a Large-scale Experiment1

Timothy S. McCay,2 James L. Hanula,3 Susan C. Loeb,4 Steven M. 

Lohr,5 James W. McMinn,3 and Brett D. Wright-Miley6

Abstract 

We initiated a long-term experiment involving manipulation of coarse woody debris (CWD) 

at the Savannah River National Environmental Research Park in the upper Coastal Plain of 

South Carolina. Each of four 9.3-ha plots in each of four blocks was subject to one of the 

following treatments: removal of all snags and fallen logs, removal of fallen logs only, felling 

and girdling to simulate a catastrophic pulse of CWD, and control. Removal treatments were 

applied in 1996, and the felling or snag-creation treatment will be applied in 2000-2001. 

Monitoring of invertebrate, herptile, avian, and mammalian assemblages and CWD dynamics 

began immediately after CWD removal and continues through the present. Removal 

treatments resulted in a fivefold to tenfold reduction in CWD abundance. To date, significant 

differences among treatments have only been detected for a few animal taxa. However, 

preliminary results underscore the benefits of large-scale experiments. This experiment 

allowed unambiguous tests of hypotheses regarding the effect of CWD abundance on fauna. 

Coupled with studies of habitat use and trophic interactions, the experimental approach may 

result in stronger inferences regarding the function of CWD than results obtained through 

natural history observation or uncontrolled correlative studies. 

Introduction 

Coarse woody debris (CWD) includes standing or fallen dead wood and 

decomposing root systems. Several studies have generally supported the conclusion 

that CWD provides an important resource for many animals and plants. However, 

these studies have often been based on data collected under uncontrolled conditions 

(Harmon and others 1986). Uncontrolled studies of the effects of CWD on animals 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Assistant Professor, Biology Department, Colgate University, 13 Oak Drive, Hamilton, NY 13346 (email: tmccay@mail.colgate.edu) 

3

 Research Entomologist and Project Leader, respectively, Southern Research Station, USDA Forest 

Service, 320 Green Street, Athens, GA 30602 (e-mail: Hanula_James/srs_athens@fs.fed.us and 

McMinn_James/srs_athens@fs.fed.us) 4

 Research Ecologist, Southern Research Station, USDA Forest Service, Department of Forest 

Resources, Clemson University, Clemson, SC 29634 (e-mail: sloeb@clemson.edu) 5

 Wildlife Biologist, South Carolina Department of Natural Resources, Sandhills Research and 

Education Center, P.O. Box 23205, Columbia, SC 23205 (e-mail: slohr@clemson.edu) 6

 Forestry Technician, Savannah River Natural Resource Management and Research Institute, USDA 

Forest Service, P.O. Box 710, New Ellenton, SC 29809 (e-mail addresses: WrightMiley_Brett/r8_savannahriver@fs.fed.us) 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

136 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

are susceptible to confounding factors because the same conditions leading to CWD 

abundance (e.g., wind storms) often lead to increased vegetative growth. Changes in 

vegetation may positively affect populations of animals through increased cover and 

food availability. Controlled experiments are, therefore, necessary to produce 

unambiguous conclusions regarding the effects of woody debris within an ecosystem. 

The amount and role of CWD markedly vary among forested ecosystems. The 

amount and role of CWD in old-growth conifer forests of the Pacific Northwest have 

been intensively studied, but few studies of CWD in southeastern pine forests exist 

(McMinn and Crossley 1996a). In general, southeastern pine forests are younger than 

western conifer forests, with tree species that exhibit smaller maximum sizes and 

shorter life spans than western species. With shorter rotations, often for pulpwood 

production, managed southeastern forests have low amounts and small pieces of 

CWD. Typical volumes of CWD in managed forests of the Southeast are poorly 

known, but mean volume of CWD in natural pine forests on public land in Georgia is 

estimated at < 20 m3 ha-1 (McMinn and Hardt 1996). By contrast, some of the highest 

recorded mean CWD volumes are in old-growth Douglas-fir forests of western 

Oregon (502 m3 ha-1; Spies and Cline 1988). 

Dead wood also decomposes more quickly in southeastern than northwestern 

forests because of the humid, warm climate of the Southeast (Barber and Van Lear 

1984, Harmon and others 1986). Rapid decay, shorter rotations, and smaller trees 

combine to produce very different CWD characteristics in the Southeast compared to 

the Pacific Northwest. Consequently, we expect that the role of CWD as a resource 

for fauna also differs between the two regions. Because managed southern pine 

forests typically have low structural and vegetative diversity, coarse woody debris 

may be particularly important as a refuge and food substrate for animals in this 

environment. 

Woody debris is an ecosystem component amenable to management (McMinn 

and Crossley 1996a). Indeed, forest management practices lead to changes in the 

abundance of CWD―planned or not. A workshop entitled “Biodiversity and Coarse 

Woody Debris in Southern Forests,” held in Athens, Georgia, in 1994 underscored 

the potential negative consequences of failure to understand the role of CWD in 

southeastern forests. Understanding the role of CWD in managed loblolly pine (Pinus 

taeda) forests in the Southeast is particularly important because of the predominance 

of this forest type in the landscape (Schultz 1997). Currently, there are insufficient 

data to allow specific management recommendations for CWD in managed 

southeastern pine forests (McMinn and Crossley 1996b). 

The purpose of this paper is to present the preliminary results of a manipulative 

experiment into the role of CWD in southeastern forests. This study is a unique 

interdisciplinary examination of the importance of dead wood to the biotic 

community in a largely unstudied environment. 

Methods 

We initiated an experiment to better understand the importance of CWD to 

fauna in loblolly-pine plantations of the southeastern Coastal Plain. This experiment 

has been underway since summer 1996, with annual re-treatment of plots. Retreatment of plots and monitoring of woody debris and fauna are planned through 

2007. 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 137 

Study Area 

This research was conducted at the Savannah River National Environmental 

Research Park (SRNERP), a 78,000-ha nuclear production facility managed by the 

United States Department of Energy. The SRNERP is located in Aiken, Barnwell, 

and Allendale Counties, South Carolina (33°0-25'N, 81°25-50'W). The study area lies 

in the upper portion of the Coastal Plain Physiographic Province (Fenneman 1938) 

and is bounded on the west by the Savannah River. Vegetation communities of the 

SRNERP range along topographic and moisture gradients from freshwater wetlands 

to xeric sandhills (Workman and McLeod 1990). Pine plantations dominate a 

majority of the SRNERP; loblolly pine is the most abundant species. 

Experimental Design 

The study was designed as a randomized complete block with four treatments 

replicated in four blocks. Blocks were four forest stands chosen subject to the 

following criteria: forested with approximately 45-year-old loblolly pine plantations; 

≥ 76 m from nearest wetland, road, and power line; and able to accommodate four 

square 9.3-ha plots. Finally, accessibility was considered to allow installation and 

frequent checking of various traps. Within each stand, we established four square 9.3-

ha plots. Each plot consisted of a 6-ha core area used for CWD and faunal surveys, 

surrounded by a 3.3-ha buffer area subject to the same treatment as the core area. 

Buffer areas were largely unused for surveys to avoid the influence of edge effects. 

Timber harvesting was prohibited within 61 m of plots. 

Within each stand, each of the four plots was randomly assigned to one of the 

following treatments: removal of all snags and fallen logs, removal of fallen logs 

only, felling and girdling to simulate a catastrophic pulse of debris, and control. We 

defined CWD as dead woody material ≥ 10 cm in diameter and ≥ 60 cm in length. 

Removals were conducted by a private crew under USDA Forest Service supervision 

in July/August 1996, February 1997, February/March 1998, and February/March 

1999. Annual removals are planned during the winter of each year of the study. The 

catastrophic treatment, which will result in the addition of fallen logs and snags, is 

planned for the winter of 2000-2001. We are currently planning the specific 

management action involved in the catastrophic treatment. Choices include cutting 

trees to mimic wind breakage, pulling trees down to create tip-up mounds, and 

girdling trees to create snags. Activities would mimic natural blow-down events or 

beetle attacks. Preliminary proposals call for the felling of 60-90 m3 ha-1 (340-360 

stems ha-1), which is roughly 10 times the current CWD load. 

All plots had been thinned between 1991 and 1996. Plots were thinned as 

necessary in 1996 to achieve a standing basal area of 13.8–20.8 m2 ha-1. All plots will 

be thinned at about 10-year intervals throughout the study. Most of the experimental 

areas had been intentionally burned between 1990 and 1996, although some areas had 

not been burned since 1972. In the winter of 1999-2000 all plots will be burned to 

normalize plots with respect to this important factor. Thereafter, plots will be burned 

at about 5-year intervals. 

Two grids of equally spaced markers have been used to orient investigators 

within the plots. A large-scale 7-by-7 grid, with 50-m spacing, has been used for the 

monitoring of birds. A small-scale 8-by-8 grid, with 20-m spacing, has aided in 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

138 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

studies of small mammals, invertebrates, reptiles, and amphibians. Monitoring of 

woody debris has also been referenced to the 7-by-7 grid. 

Monitoring of Woody Debris 

Inventories of fallen logs and snags were completed during the late spring and 

early summer of 1997-1999 on all plots. All fallen logs and snags were tagged with a 

unique number. Species or genus, length, sound class (range 1-3 based on wood 

integrity), and bark presence (percent) were measured for all CWD. When possible, 

cause of mortality (e.g., lightning) was noted. Number of cavities, diameter at breast 

height (DBH), and standing integrity (degree to which branches and trunk remain 

intact) were recorded for snags. Mid-point diameter, degree of ground contact, and 

shape (round, elliptical, or flat) were recorded for fallen logs. Surveys have been 

conducted annually to measure recruitment of CWD and note changes in the 

decomposition of previously marked debris. 

Population Responses 

Arthropods are being monitored with crawl traps (Hanula and New 1996) and 

burlap bands on tree boles. Pitfalls are used to capture arthropods on the ground. 

Crawl traps and burlap bands aid in determining whether CWD is important in 

maintaining arthropod resources on trees, which are a common foraging habitat for a 

variety of birds. Fifteen crawl traps per plot are open continuously and samples are 

collected monthly. Fifteen burlap bands per plot are monitored monthly. Arthropods 

crawling on the ground are sampled with 15 pitfalls placed throughout each plot and 

operated for 1 week every other month. 

Sampling of amphibians, reptiles, and insectivorous small mammals is being 

conducted at 3 of the 4 experimental stands, for a total of 12 plots. These animals are 

monitored using a series of pitfall-drift-fence arrays and snake traps. We are using 

four Y-shaped arrays (Kirkland and Sheppard 1994) and one X-shaped array 

(Campbell and Christman 1982) at each plot. Aluminum flashing is used as drift 

fencing. Interspersed along drift-fence spans are pitfall traps (19-l buckets) and snake 

traps. All traps are opened and checked daily during a 14-day period in each of 

winter, summer, and autumn, and a 28-day period in spring. Because frogs and 

salamanders have been observed to breed within temporary pools within or near 

certain plots, we have restricted our analyses to adults. 

Small rodents and some larger mammals are being sampled with box-style traps 

at three of the four experimental stands. At each station in the 8 × 8 grid, one 

Sherman live trap (7.5 × 9.0 × 25.5 cm) is placed on the ground and one Sherman 

live trap is placed on the nearest (≤ 5 m) tree trunk. Traps on trees are placed in 

wooden sleeves attached to the tree approximately 1.5 m above the ground. Mosbytype wooden box traps (19 × 19 × 61 cm) are placed on the ground at selected 

stations. Trapping sessions are conducted every other month and include nine 

consecutive nights of trapping during the new- to quarter-moon phases. 

Birds have been sampled using spot-mapping and nest searches during the 

breeding season (May to July; Bibby and others 1992) and transect surveys during 

winter (December to February; Kolb 1965). Both morning and afternoon surveys 

were conducted during the breeding seasons of 1997 and 1998. Transect surveys 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 139 

were conducted during the winters of 1997-1998 and 1998-1999 (Lohr 1999). In 

addition to determining population responses, Shannon’s measure of diversity (H′; 

Ludwig and Reynolds 1988) also was calculated for bird assemblages at each study 

plot. 

Study of Habitat Use 

Use of woody debris by cotton mice (Peromyscus gossypinus) was examined in 

1997 and 1998 using radio-telemetry and fluorescent-powder tracking (McCay 

2000). Locations of mice were noted at night when mice were active, and during the 

day when mice were inactive. Observations were made in areas where CWD was not 

manipulated. 

Preliminary Results 

Sampling and analyses are ongoing. Nevertheless, preliminary results 

underscore many benefits of large-scale experiments in the study of CWD. Our 

results also illustrate some problems common in ecological field studies. 

Woody Debris Loading 

Treatments involving removal of fallen CWD resulted in a greater than tenfold 

decrease in the density and volume of fallen logs (table 1). The treatment involving 

removal of snags also was successful, reducing snag density by 75 percent and snag 

volume by 90 percent. There were few differences in the size distribution, decay 

class, or species composition of CWD among treatments. However, CWD at removal 

plots was more decayed than at non-removal plots because of the difficulty of 

removing very decayed logs. Starting with the 1999 removal, very decayed logs 

located in removal plots will be raked apart if they cannot be removed. 

Table 1―Mean density (No./ha) and estimated volume (m3

/ha) of coarse woody debris at 

plots in one of four treatments: removal of all woody debris (ALL); removal of fallen logs, but 

not snags (DOW); catastrophic felling (CAT); and control (CON) in 1998. The catastrophic 

treatment will be implemented in 2000; thus, neither control nor catastrophic plots had been 

manipulated in 1998.1

 

 Down woody 

debris 

Standing woody 

debris 

Treatment N Density Volume Density Volume 

ALL 4 6.3 A 0.35 A 2.1 0.22 

DOW 4 8.4 A 0.39 A 8.4 2.18 

CAT 4 98.9 B 7.87 B 8.1 2.19 

CON 4 94.4 B 6.45 B 8.2 2.04 

 1 Means not followed by the same letter were different at α = 0.05 (Fisher’s least- 

 significant-difference test). 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

140 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Population Response 

We have presently identified arthropods collected in pitfalls for 1 year after 

initial CWD removal. We captured an average (± SE) of 703 (± 175.6) beetles per 

plot in control plots and 350 (± 149.4) beetles per plot in removal plots. Flies 

(control, 165.0 ± 40.1; removal, 91.3 ± 46.8) and spiders (control, 532.5 ± 130.9; 

removal, 296.0 ± 86.6) showed similar trends. Despite these relatively large 

differences in higher taxonomic categories, only a few families of arthropods were 

significantly affected by CWD removal. Pitfall captures of ground beetles 

(Carabidae; control, 134.0 ± 21.3; removal, 58.5 ± 13.3; p < 0.03), silken fungus 

beetles (Cryptophagidae; control, 192.0 ± 62.1; removal, 30.0 ± 26.5; p < 0.07), and 

bark-gnawing beetles (Trogositidae; control, 19.0 ± 6.2; removal, 1.5 ± 0.5; p < 0.06) 

were lower in the CWD removal than in the non-removal plots. 

Studies of amphibians, reptiles, and insectivorous mammals have presently 

demonstrated no treatment effects (table 2). However, mean capture rates of most 

groups were greater at plots without log removal than plots from which logs were 

removed. There was relatively strong spatial and temporal variation in these data, 

which reduced our ability to detect treatment differences (i.e., statistical power, Sokal 

and Rohlf 1981). Additional sampling should increase our ability to detect an effect 

of log removal on these forest-floor vertebrates.

Among rodents, only southern flying squirrels (Glaucomys volans) varied 

significantly in abundance among treatments (F = 6.18, df = 3,8, P = 0.02; table 3).

Relative abundance of flying squirrels was highest in plots from which dead trees had 

been removed. Because this species commonly nests in tree cavities, we were 

surprised by this result. Presently, it is unclear whether differences in flying squirrel 

captures reflect treatment effects, pre-existing plot differences, or differences in 

sampling ability related to snag removal. 

A previous study on the SRNERP demonstrated that increased abundance of 

CWD was associated with increased abundance of cotton mice and that cotton rat 

(Sigmodon hispidus) populations may also be positively affected by large amounts of 

CWD (Loeb 1999). Although there were no significant differences in captures of 

cotton mice or cotton rats (table 3), both species appeared to be slightly more 

abundant in plots where no CWD removal had occurred. Again, spatial and temporal 

variation may have reduced statistical power to detect differences. 

The number of breeding territories of woodpeckers and of all birds combined 

was lower on plots from which snags were removed than control plots (table 4). In 

particular, removal of snags affected red-headed woodpeckers (Melanerpes 

erythrocephalus), red-bellied woodpeckers (Melanerpes carolinus), and Carolina 

wrens (Thryothorus ludovicianus). Breeding bird diversity also was highest on 

control (H' = 2.72) and lowest on all removal (H' = 2.01) plots (P < 0.05). 

Abundance of weak excavators and secondary cavity-nesters, as well as birds that 

nest in vegetation, was not markedly affected by treatments. Likewise, CWD removal 

apparently had no effect on the bird community during winter (Lohr 1999). 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 141 

Table 2―Mean number of captures per 14-day sampling period of taxa of forest-floor 

vertebrates at 3 replicates receiving 1 of 4 treatments: removal of all woody debris (ALL), 

removal of fallen logs (DOW), catastrophic felling (CAT), and control (CON).1

 

 Removal plots Non-removal plots 

Taxon ALL DOW CAT CON F-value 

Shrews 2.93 2.60 3.33 3.87 0.41 

Frogs and toads 60.87 53.00 74.87 77.67 0.33 

Salamanders 7.13 5.33 8.73 6.93 0.21 

All amphibians 68.00 58.37 83.60 84.60 0.32 

Lizards 7.53 6.27 5.20 5.93 0.34 

Snakes 1.53 1.40 1.00 2.53 1.44 

All reptiles 9.07 7.73 6.20 8.53 0.42 

1

 F-value for tests of the hypothesis in which means did not differ (df = 3,6) is also included. The 

hypothesis was not rejected for any group at α = 0.05. 

Table 3―Mean number of captures per 1000 trap nights (± 1 SE) of common species of 

rodents at 3 replicates receiving 1 of 4 treatments: removal of all woody debris (ALL), 

removal of fallen logs (DOW), catastrophic felling (not implemented to date; CAT), and 

control (CON).1

 

Species ALL DOW CAT CON 

Southern flying squirrel 

(Glaucomys volans)

29.10 ± 1.92 A 17.87 ± 0.89 B 21.97 ± 2.88 AB 24.28 ± 1.22 AB 

Cotton mouse 

(Peromyscus gossypinus) 

15.92 ± 3.50 A 13.49 ± 3.82 A 17.83 ± 4.19 A 16.82 ± 6.16 A 

Golden mouse 

(Ochrotomys nuttali) 

0.77 ± 0.35 A 1.30 ± 0.89 A 0.61 ± 0.31 A 1.71 ± 1.59 A 

Old-field mouse 

(Peromyscus polionotus) 

1.17 ± 0.96 A 0.05 ± 0.05 A 0.25 ± 0.18 A 0.54 ± 0.30 A 

Fox squirrel 

(Sciurus niger) 

1.14 ± 0.44 A 0.93 ± 0.53 A 1.28 ± 0.81 A 0.34 ± 0.81 A 

Cotton rat 

(Sigmodon hispidus) 

0.03 ± 0.03 A 0.17 ± 0.17 A 0.66 ± 0.39 A 1.14 ± 0.62 A 

All 25.33 ± 3.87 A 19.17 ± 4.25 A 24.35 ± 3.74 A 26.41 ± 5.27 A 

1

 Means not followed by the same letter were significantly different (α = 0.05; Fisher’s Least Significant 

Difference Test). 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

142 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 4―Mean number of breeding territories for breeding-bird guilds at plots receiving one 

of three treatments: removal of all woody debris (ALL), removal of fallen logs (DOW), and 

control (CON) during 1997 and 1998.1

 

Breeding-bird Guild ALL DOW CON 

Woodpeckers 1.4 A 3.5 A 4.5 B 

Secondary cavity-nesters 1.8 A 2.2 A 4.8 A 

Understory nesters 5.1 A 5.5 A 7.1 A 

Midstory and canopy nesters 9.9 A 11.7 A 12.4 A 

All breeding birds 20.1 A 23.5 AB 27.5 B 

1

Means not followed by the same letter were significantly different 

(α = 0.05; Fisher’s Least Significant Difference Test). 

Study of Habitat Use 

Cotton mice selectively used decomposing root systems during the day and 

fallen logs at night (McCay 2000). One hundred out of 108 unique daytime den sites 

of cotton mice were associated with some form of CWD, usually decomposing root 

systems. Because other den sites used by cotton mice elsewhere (e.g., burrows of 

large vertebrates; Frank and Layne 1992) are not abundant in managed loblolly 

stands, there were probably few alternatives to decomposing root systems. Analysis 

of powder trails demonstrated the selective inclusion of fallen logs in the pathways of 

mice, perhaps because logs are useful in navigation (McCay 2000). 

Discussion and Conclusion 

Animals responding to CWD manipulation during the first few years of this 

study were those for which CWD is probably a critical resource (e.g., cavity-nesting 

birds). Reduction in the volume of CWD in forest stands, especially stands with low 

ambient amounts of CWD, probably changes the quality of the environment for most 

animals in subtle ways. Thus, detecting the effects of CWD manipulation in 

southeastern pine forests may require several years of observation. Because 

population responses reflect differences present in the first few years after 

manipulation of CWD, they provide conservative depictions of the long-term 

importance of CWD in pine ecosystems of the Southeast. 

The size of plots used in this study was many times larger than the size of home 

ranges of most insects, many birds (Gill 1994), and most small mammals (e.g., cotton 

mouse; Wolfe and Linzey 1977). Thus, this experiment permits inferences 

concerning demographic responses of these species. In contrast, most studies of the 

effects of CWD on animals have only permitted inferences regarding microhabitat 

use (e.g., Planz and Kirkland 1992). Nevertheless, even the large plot size used in this 

study was too small to test population-level responses of highly mobile species, such 

as the fox squirrel. 

The large size of plots in this study precluded the establishment of more than 

four replicates within each treatment. Furthermore, the effort that was required to 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 143 

sample animals within these large areas precluded the use of all four replicates for the 

study of some groups (e.g., small mammals). Low replication, coupled with expected 

temporal and spatial variability, reduced our ability to detect all but the most drastic 

changes in animal populations during the first few years of study. Over time, 

however, we expect our ability to detect treatment effects to increase as differences 

become larger. 

Acknowledgments 

Funding and support were provided by the Department of Energy-Savannah 

River Operations office through the Forest Service Savannah River Station and 

Forest Service Southern Research Station under Interagency Agreement DE-IA09-

76SR00056. John Blake made this research possible through his vision, 

encouragement, and support in all stages of the project. W. Mark Ford and E. Olsen 

aided in site selection and project initiation. Thanks to Mary Howard and the fire 

crew of the SRI for management of the study plots and early CWD monitoring. 

Thomas A. Waldrop and W. Mark Ford provided helpful reviews of the manuscript. 

References 

Barber, B. L.; Van Lear, D. H. 1984. Weight loss and nutrient dynamics in decomposing 

woody loblolly pine slash. Soil Science of America Journal 48: 906-910. 

Bibby, C. J.; Burgess, N. D.; Hill, D. A. 1992. Bird census techniques. San Diego, 

California: Academic Press; 257 p. 

Campbell, H. W.; Christman, S. P. 1982. Field techniques for herpetofaunal community 

analysis. In: Scott, N. J., Jr., ed. Herpetological communities. Wildl. Res. Rep. 13. Fish 

and Wildlife Service, U.S. Department of Interior; 193-200. 

Fenneman, N. M. 1938. Physiography of the eastern United States. New York: MacGraw 

Hill Box Co., Inc.; 179 p. 

Frank, P. A.; Layne, J. N. 1992. Nest and daytime refugia of cotton mice (Peromyscus 

gossypinus) and golden mice (Ochrotomys nuttali) in south-central Florida. 

American Midland Naturalist 127: 21-30. 

Gill, F. B. 1994. Ornithology. 2d ed. New York: W. H. Freeman and Company; 766 p. 

Hanula, J. L.; New, K. C. P. 1996. A trap for capturing arthropods crawling up tree boles. 

Res. Note SRS-RN-3. Aiken, SC: Savannah River Station, Forest Service, U.S. 

Department of Agriculture. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Swanon, F. J.; Sollins, P.; Gregory, S. V.; 

Lattin, J. D.; Anderson, H. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, 

G. W.; Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15:133-302. 

Kirkland, G. L., Jr.; Sheppard, P. K. 1994. Proposed standard protocol for sampling small 

mammal communities. In: Merritt, J. F.; Kirkland, G. L., Jr.; Rose, R. K., eds. 

Advances in the biology of shrews. Spec. Publ. 18. Pittsburgh, PA: Carnegie Museum of 

Natural History; 277-283. 

Kolb, H. 1965. The Audubon winter bird-population study. Audubon Field Notes 19: 432-

434. 

Loeb, S. C. 1999. Small mammal responses to coarse woody debris in a southeastern pine 

forest. Journal of Mammalogy 80: 460-471. 
Coarse Woody Debris in Southeastern Pine Forests—McCay, Hanula, Loeb, Lohr, McMinn, and 

Wright-Miley 

144 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Lohr, S. 1999. The effects of coarse woody debris and vegetation structure on bird 

communities of loblolly pine (Pinus taeda) forests at the Savannah River Site.

Clemson, South Carolina: Clemson University; 38 p. M.S. thesis. 

Ludwig, J. A.; Reynolds, J. F. 1988. Statistical ecology: a primer on methods and 

computing. New York: John Wiley and Sons; 337 p. 

McCay, T. S. 2000. The use of woody debris by cotton mice (Peromyscus gossypinus) in a 

southeastern pine forest. Journal of Mammalogy 81: 527-535. 

McMinn, J. W.; Crossley, D. A., Jr. 1996a. Preface. In: McMinn, J. W.; Crossley, D. A., Jr., 

eds. Biodiversity and coarse woody debris in southern forests. Proceedings of the 

workshop on coarse woody debris in southern forests: effects on biodiversity. Gen. 

Tech. Rep. SE-94. Asheville, NC: Southern Research Station, Forest Service, U.S. 

Department of Agriculture; iii. 

McMinn, J. W.; Crossley, D. A., Jr. 1996b. Workshop summary and recommendations. In: 

McMinn, J. W.; Crossley, D. A., Jr., eds. Biodiversity and coarse woody debris in 

southern forests. Proceedings of the workshop on coarse woody debris in southern 

forests: effects on biodiversity. Gen. Tech. Rep. SE-94. Asheville, NC: Southern 

Research Station, Forest Service, U.S. Department of Agriculture; 144. 

McMinn, J. W.; Hardt, R. A. 1996. Accumulation of coarse woody debris in southern 

forests. In: McMinn, J. W.; Crossley, D. A., Jr., eds. Biodiversity and coarse woody 

debris in southern forests. Proceedings of the workshop on coarse woody debris in 

southern forests: effects on biodiversity. Gen. Tech. Rep. SE-94. Asheville, NC: 

Southern Research Station, Forest Service, U.S. Department of Agriculture; 1-9. 

Planz, J. V.; Kirkland, G. L., Jr. 1992. Use of woody ground litter as a substrate for travel 

by the white-footed mouse, Peromyscus leucopus. Canadian Field-Naturalist 106: 118-

121. 

Schultz, R. P. 1997. Loblolly pine: ecology and culture of loblolly pine. Agricultural 

Handbook, Forest Service, U.S. Department of Agriculture. 

Sokal, R. R.; Rohlf, F. J. 1981. Biometry: the principles and practice of statistics in 

biological research. 3d ed. New York: W. H. Freeman and Company; 887 p. 

Spies, T. A.; Cline, S. P. 1988. Coarse woody debris in forests and plantations of coastal 

Oregon. In: Maser, C.; Tarrant, R. F.; Trappe, J. M.; Franklin, J. F., tech. eds. From the 

forest to the sea: a story of fallen trees. Gen. Tech. Rep. PNW-GTR-229. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 5-

23. 

Wolfe, J. L.; Linzey, A. V. 1977. Peromyscus gossypinus. Mammalian Species 70: 1-5. 

Workman, S. W.; McLeod, K. W. 1990. Vegetation of the Savannah River Site: major 

community types. National Environmental Research Park Program SRO-NERP-19. 

Aiken, SC; Savannah River Ecology Laboratory; 137 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 145 

Girdled versus Bark Beetle-created 

Ponderosa Pine Snags: Utilization by 

Cavity-dependent Species and Differences 

in Decay Rate and Insect Diversity1

Patrick J. Shea,2 William F. Laudenslayer Jr.,3 George Ferrell,4 and 

Robert Borys5

Abstract 

Snags are a natural component of forest ecosystems and provide a variety of functions and 

values to forests and their constituents. Snags provide important feeding substrates, nesting 

sites, and habitat for a variety of invertebrates and vertebrates, and many of these functions 

continue after the snag eventually falls and becomes a log (coarse woody debris). Some forest 

landscapes are thought to be “snag deficient” for wildlife needs because of the direct action of 

forest managers or because of natural events such as winter storms or fire. Therefore, it is not 

unusual for forest managers to desire to create snags by various means. In this study we 

compared snags created by mechanical girdling (chainsaw) and bark beetle (western pine 

beetle aggregation pheromone) attack to determine acceptability and suitability to cavity 

dependent species, tree decomposition characteristics, and insect diversity. After 6 years we 

have found differences in the rate of deterioration (tree fading rates, branchlet retention, bole 

failure, top breakage, bark sloughing), woodpecker feeding activity, cavity excavation, and 

insect diversity. Our data indicate that bark beetle-killed trees provide a more biologically rich 

snag that is both suitable and acceptable to cavity dependent species. 

Introduction 

Snags are a natural component of ecosystems that have a variety of values to 

sustainable forest ecosystems. Snags provide important feeding substrates, nesting 

sites, and habitat for a variety of invertebrates and vertebrates, and these functions 

continue long after the snag eventually falls and becomes course woody debris 

(Laudenslayer 1997, Thomas and others 1979). Historically, snags have been 

removed from the forest to meet a variety of objectives, including timber production, 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. Contribution #11 of the Blacks 

Mountain Ecological Research Project, Pacific Southwest Research Station, USDA Forest Service. 2

 Principal Research Entomologist (Emeritus Scientist), Pacific Southwest Research Station, USDA 

Forest Service, 1107 Kennedy Place, Suite 8, Davis, Ca 95616 (e-mail: pjshea@davis.com) 3

 Research Wildlife Biologist, Pacific Southwest Research Station, USDA Forest Service, 2081 E. Sierra 

Ave., Fresno, CA 93710 (e-mail: blaudenslayer@fs.fed.us) 

4

 Research Entomologist (retired), Pacific Southwest Research Station, USDA Forest Service, 2400 

Washington Ave., Redding CA 96001 

5

 Entomologist, Pacific Southwest Research Station, USDA Forest Service, 2480 Carson Rd., 

Placerville, CA 95667 (e-mail: rborys@fs.fed.us) 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

146 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

removal of hazardous trees, and to reduce the potential of crown fires. Currently, 

snags in many areas appear to be in low numbers for wildlife use, and managers may 

need to create snags to meet management objectives. Methods for stressing trees to 

kill them for this purpose have been the subject of several studies (Bull and others 

1981, Bull and Partridge 1986, Conner and others 1981, Parks and others 1996). 

Some of these methods can be expensive and hazardous (topping trees with 

chainsaws and explosives) (Lewis 1998) or could be environmentally problematic 

(application of chemical herbicides). Less understood, however, are factors, many of 

them episodic (i.e., fire and insects), affecting the process of snag creation and 

longevity (Morrison and Raphael 1993). 

Prime among these factors, in addition to the nature of the stress causing death, 

is the physiological condition of the tree when the stress occurs. Among the factors 

influencing tree stress are tree condition, tree size (age), and the season at which the 

stress occurs. Together, these factors probably determine in large part the particular 

sequence of decay-promoting organisms (i.e., insects and fungi) invading the tree as 

it is dying and afterward. This invasion sequence likely has a strong influence on how 

quickly the tree dies, how long the resulting snags stand erect, and those 

characteristics affecting its suitability and acceptability for use by wildlife. It is thus 

important to understand the process of snag creation, and the factors affecting it, in 

both artificially and naturally created snags. In this experiment we examined some of 

these processes. 

To the extent possible, processes used to create snags should mimic natural 

processes to ensure resulting snags are ecologically optimal. In other words, these 

snags should contribute to a fully functional forest rather than simply meeting snag 

standards for wildlife. However, technical factors, such as safety and cost, are also 

important. Two likely methods for creation of snags are girdling and baiting with 

bark beetle pheromones. Bark beetle pheromones are chemical messengers between 

conspecifics that create a mass attack on an individual tree for the purpose of killing 

it (Bedard and Wood 1974). Commercially available pheromones that are speciesspecific can be deployed in an economic and safe manner that creates a mass attack 

on a target tree (Browne 1978, Byers 1989). Resulting tree death can be rapid and is 

followed by an apparently natural sequence of secondary insects, fungi, other 

arthropods, and vertebrates. This method thus closely mimics natural tree killing by 

bark beetles. 

Mechanical girdling, while technically acceptable, does not closely mimic 

natural tree death. Girdled trees may not die promptly or at all. Snags created by 

girdling may be structurally weakened and fall sooner (Bull and Partridge 1986). In 

California, neither method has been adequately investigated in the large diameter 

trees favored by woodpeckers as nesting sites (Landram and others 2002, 

Laudenslayer 1997). 

This study investigates processes of snag formation in trees killed by girdling or 

with bark beetle pheromones with the goal of developing methods that are both 

technically and ecologically optimal. Specifically, the objectives were to compare the 

differences between girdled and bark beetle-killed trees relative to the use by cavitydependent species, decomposition rate, and diversity of insect fauna. We were also 

interested in whether season of death or diameter of tree had an influence on these 

variables. 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 147 

Methods 

This study was conducted at the Blacks Mountain Experimental Forest (BMEF) 

located within the Eagle Lake District of the Lassen National Forest in northeastern 

California. It was an adjunct study to an interdisciplinary research program also sited 

within BMEF. This large, long-term research program compares the effects of 

treatment combinations that include, vegetation structure, livestock grazing, and 

prescribed fire on forest ecosystem structure and function. BMEF lies ~60 km 

northwest of Susanville, California, in the eastside pine type. This forest type is 

representative of a forest assemblage that extends north from Baja California into 

central British Columbia and is characterized by temperature extremes, low average 

annual precipitation, and episodic fire. Growing sites tend to be uniform in slope and 

exposure. The forests of eastside pine are growing on volcanic soils characteristic of 

the region. BMEF includes a relatively large acreage of old-growth pine forests that, 

except for fire exclusion, have not been extensively altered. 

Except as noted, experimental trees consisted of 48 ponderosa pine (Pinus 

ponderosa Laws), 24 in each of two diameter classes (38-64 and >76 cm dbh). Eight 

(4 in each dbh class) trees, each no less than 100 m from other groups, will constitute 

an experimental plot or block. The six plots were selected on the basis of having a 

high stand complement of ponderosa pine with adequate representation of the 

diameter classes defined above. Half of the trees within each dbh class on each plot 

were assigned at random to one of the following treatments: 

• Girdling: Two girdling chainsaw cuts, 20 cm apart, and 5 cm into the 

sapwood were made 61 cm above ground level. Bark and phloem were 

removed between the chainsaw cuts to prevent healing. 

• Pheromone-baiting: A pheromone dispenser obtained from Phero Tech Inc., 

containing the western pine beetle (Dendroctonus brevicomis Leconte) 

aggregation pheromone, was fixed to the bole of each tree at 2 m above the 

ground. The western pine beetle aggregation pheromone dispenser contains 

specific amounts of exo-brevicomin, frontalin, and myrcene. Baits were 

placed during times of western pine beetle flight that was determined by 

baited monitoring traps placed in the general vicinity. 

Half of the trees in each of the above treatment combinations on each plot were 

assigned at random to spring (June 1993) and half to fall (September 1993) treatment 

periods. Thus, there will be one tree with each snag creation method by dbh by time 

of treatment combination. 

Pheromone treated trees were monitored every 2 to 3 weeks after bait placement 

to assess the progress of mass attack by western pine beetle. All trees in all treatment 

combinations were visited every month post-treatment (except during the winter) to 

assess fading rates (foliage color changed) during the first year and then twice yearly 

thereafter. Pheromone baited trees were judged to be successfully attacked by 

western pine beetle when more than 50 red pitch tubes could be counted in the lower 

4 m of the bole. Pheromone baits were then removed. 

One, two, three and five years after baiting and girdling, each tree was visited to 

assess the amount of secondary insect and woodpecker activity. Insect activity was 

monitored by Lindgren funnel traps hung on pulleys next to the bole of the tree at 

three heights (dbh, 6 m, and 12 m). Insects from these traps were collected 

approximately every 2 weeks from June to September from 1993 to 1997. They were 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

148 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

identified to either order or family, counted, and selected specimens were mounted 

for future reference. In 1995 each tree was also assessed for emergence of secondary 

insects. This was done by counting and characterizing the shape and size of 

emergence holes (Furniss and Carolin 1977) on the surface of the bole that fell within 

a 30 X 30 cm template. The template was placed at dbh and 4 m above the ground. 

The circumference of the bole at each height was divided as closely as possible to 12-

inch segments, and the site of sampling was randomly selected. 

Flaking of bark by woodpeckers is used to extract prey items from within the 

bark and is defined as pieces of bark being chipped away from the bole. Flaked areas 

can be readily recognized by the discolored area of the bark. The bark surface 

remains relatively flat in contrast to feeding holes drilled by a different woodpecker 

feeding activity. Drilling is defined as woodpecker action that actually drills a hole 

through the bark to the xylem tissue to access prey. The hole is wider at the surface 

and narrows as it reaches the xylem. The surface of the drilled hole is ragged and 

uneven. Chips from both methods accumulate around the base of the tree. During 

surveys the presence or absence of the two woodpecker feeding activities on the 

experimental trees was recorded. 

Beginning in the fall of 1994 and each year thereafter, all trees were visually 

inspected for the presence of nesting cavities. Full cavities are defined as an almost 

perfectly round excavation in the bole of study trees with perceptible depth to the 

hole. A cavity start is defined as a full cavity where the excavation has little depth but 

does reach the xylem tissue. Observers used various types of binoculars to make 

these inspections. 

In 1999 in addition to rating the type and degree of woodpecker activity, 

observers also assessed tree decomposition characteristics. The amount and location 

of bark sloughing was noted as well as whether there was top breakage. Sloughing of 

the bark is defined as the bark separated from the xylem and either falling away from 

the bole or sliding apart. Either action exposed the xylem tissue. Finally, each study 

tree was observed for the presence or absence of branchlets. These are defined as the 

outmost woody tissue on each branch. These data were taken in 1999. 

We are in the sixth year of this continuous study and much data has been 

collected. In this paper we only present a portion of the data collected, mostly in the 

form of qualitative observations. 

Results and Discussion

Three years into this study there appeared to be no difference between springand fall-treated trees for any variable tested; therefore, the treatments of interest 

became method of snag creation and diameter class. There was no significant 

difference in mean tree diameter for each of the two classes between the methods 

used to create snags (table 1). All the ponderosa pine trees baited with western pine 

beetle aggregation pheromone were successfully attacked by western pine beetle and 

no additional adjacent trees were attacked. One tree within the pheromone 

baited/small diameter treatment group failed to be attacked because it was 

misidentified as a ponderosa pine when in fact it was a Jeffrey pine (Pinus jeffreryi

Grev. and Balf.). Consequently this tree was not considered as part of the experiment. 

Bark-beetle killed trees faded rapidly whereas girdled trees showed no sign of needle 

fade for 23 months. Those trees baited with pheromones in July of 1993 turned 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 149 

yellow or straw colored by August/September of the same year, whereas those trees 

baited in September began to fade in late-June/early-July 1994. 

Secondary insects including adult members of the family Buprestidae (primarily 

Melanophila spp.), Cerambycidae (in particular Ergates spp and Monochamus spp.), 

Elateridae, and Bostrichidae were captured in the Lindgren funnel traps from both 

girdled and pheromone-baited trees. However, the numbers of insects captured from 

girdled and pheromone-baited trees were considerably different. An example of the 

difference in numbers of emerging woodboring insects collected from the two 

treatment groups is presented in table 2. By September 1995, over 2 years after 

treatment, the number of emergence holes counted in the 12 large diameter 

pheromone-baited trees were approximately 16 to 20 times greater than occurred on 

those trees that were girdled. This same relationship, albeit with a somewhat smaller 

difference, also occurred on the small diameter trees for both snag creation methods. 

Colonization by red turpentine beetle (RTB) Dendroctonus valens LeConte on both 

treatment groups also appeared to be different. Typically RTB attacks occur at the 

base of trees and usually follow colonization by western pine beetle or other primary 

Dendroctonus attacks. They also are quite common in trees of sufficient diameter that 

have been injured by fire (Furniss and Carolin 1977). Experimental ponderosa pine 

baited with pheromone averaged 74.6 attacks by RTB compared to 23.6 attacks on 

the girdled trees. 

Tree decomposition appeared to be quite different for some variables, depending 

on whether the snag tree was girdled or killed by bark beetles. Of the 24 trees in the 

girdled treatment, three trees have fallen. Two of the trees belong to the small 

diameter group and the remaining tree was a large diameter tree. Two of these trees 

(one in each of the diameter groups) were uprooted and one tree broke at 0.6 m above 

ground level. In the pheromone-baited treatment four trees have fallen: two within 

the small diameter group and two in the large diameter treatment. One tree (small 

diameter) was uprooted and three trees broke at 1.5 (small diameter), 10.6, and 15.5 

m (both large diameter) above ground level. We consider the latter trees as viable 

snags as evidence by the occurrence of cavities in each. Girdled trees showed a lower 

percentage of bark sloughing and a higher percentage of branchlets still present than 

pheromone-baited trees 6 years after treatment (table 3). Neither observation is 

surprising considering that the girdled trees did not begin to fade or show outward 

signs of mortality (i.e., fading) until 23 months after girdling. 

Table 1Mean (+/-sem) diameter at breast height and range for all ponderosa pine trees in 

girdled/pheromon- baited/diameter/treatment combinations.1 

Treatments N Mean (+/-sem) Range 

Girdled 

Small diameter 12 18.90(0.83)a 15.1 – 24.0 

Large diameter 12 40.80(2.73)b 30.1 – 62.4 

Pheromone 

Small diameter 12 19.14(0.76) a 15.6 – 24.4 

Large diameter 12 37.31(1.98)b 30.1 – 51.6 

1

Means followed by the same letter are not different from each other at alpha=0.05 by one-way ANOVA 

using Bonferroni mean separation test. 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

150 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 2 Number of emergence holes made by secondary insects from girdled and bark 

beetle-killed ponderosa pine trees 2 years after treatment, 1995. The number is the sum of the 

holes counted in a 30.4 cm X 30.4 cm template, one at breast height (DBH) and the other at 

approximately 4 m above the ground. 

Girdled large diameter Baited large diameter 

Tree No. DHB 4 m Tree No. DBH 4m 

5 0 0 6 1 12 

11 0 0 8 8 14 

14 0 0 13 2 11 

15 0 0 16 0 8 

21 0 0 22 14 21 

24 0 0 23 3 7 

29 2 6 31 4 3 

30 2 6 32 7 8 

38 0 0 37 2 12 

40 0 0 39 17 13 

45 0 0 46 4 3 

48 0 0 47 19 1 

 

Mean .33 1.0 6.75 10.91 

+/- sem 0.22 0.67 1.87 1.43 

Table 3Percent of trees in each treatment group according to tree decomposition 

characteristics, woodpecker activity, and presence/absence of cavities, 1999, 6 years after 

treatment.1

Treatment GSD GLD PSD PLD 

Bark sloughing 18 9 66 66 

Presence of branchlets 100 100 40 50 

Flaking 0 0 100 100 

Drilling 58 75 66 100 

Cavity starts 0 0 33 33 

Cavities 0 0 44 44 

1

GSD – Girdled, small diameter; GLD – Girdled, large diameter; 

PSD – Pheromone, small diameter; PLD – Pheromone, large diameter. 

Trees killed by colonization by western pine beetle clearly showed considerably 

more woodpecker activity than girdled trees (table 3). Whereas 100 percent of the 

trees baited with western pine beetle pheromones showed evidence of the flaking 

feeding behavior, none of the girdled trees had evidence of this behavior (table 3).

All trees baited with pheromones in the spring of 1993 had woodpecker feeding 

activity (flaking) by September of that year. For those trees baited in the fall of 1993 

all showed woodpecker activity by July of 1994. It seems reasonable to assume that 

the flaking feeding behavior is aimed at capturing pre-emergent western pine beetle 

adults. It is characteristic of this bark beetle to turn out into the outer bark in the early 

larval stage, where it continues development, pupates, and rests as a callow adult 

prior to emergence (Furniss and Caroline 1977, Miller and Keen 1960, Stark and 

Dahlsten 1970). Thus, these insect stages would be readily available to foraging 

woodpeckers flaking or scaling. The precise method by which woodpeckers find 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 151 

these areas of dense prey is unknown. Several of the authors (PJS, WFL, RB) have 

observed numerous occasions where large areas of the bark of lodgepole pine have 

been removed down to the xylem tissue by woodpeckers in search of mountain pine 

beetle (Dendroctonus ponderosa Hopk.) larvae, pupae and callow adults. 

Drilling is the other feeding behavior recorded to measure woodpecker feeding 

activity. The percentage of trees showing this type of feeding activity varied across 

all treatment groups (table 3). It should be noted however that 100 percent of the 

large diameter trees that were baited with pheromones had feeding behavior 

characterized as drilling. We point out also that the number of holes drilled by 

woodpeckers varied greatly across treatments. Those trees killed by western pine 

beetle, regardless of diameter class, showed considerably more drilled holes than the 

trees that were girdled. Of the 12 trees in the girdled/small diameter treatment group 

that showed evidence of woodpecker drilling, seven trees had two to seven holes 

each. In the girdled/large diameter treatment, 10 of the 12 trees showing evidence of 

woodpecker drilling had one to nine holes each. In contrast none of trees in 

pheromone baited treatments (small and large diameter classes) had fewer than 15 

drilled holes in any tree. Several (8) pheromone baited/large diameter trees had > 350 

woodpecker holes, whereas no tree in the girdled treatment group had in excess of 60 

holes. 

The construction of cavities in snags is the definitive answer to whether snags, 

artificially created or not, are acceptable and suitable to cavity-dependent species. In 

this study the data as of 1999 strongly suggests that bark beetle-killed ponderosa pine 

offer those characteristics that are acceptable and suitable to these vertebrates. Six 

years after pheromone-baiting, 44 percent of the trees in both diameter classes had 

full cavities compared to no cavities in the girdled treatment groups (table 3).

Further, an additional 33 percent of the pheromone-baited snags had cavity starts, 

while no cavity starts where found in the girdled snags (table 3). In those pheromonebaited snags that had cavities, the number of cavities in any particular tree ranged 

from one to eight. Those trees that had multiple cavities were always found in the 

large diameter class, and a high proportion (62 percent) of the cavities were found in 

the upper 50 percent of the bole. 

It is apparent that not all snags/trees are suitable for wildlife. The results of this 

study differ somewhat from others (Bull and Partridge 1986, Bull and others 1981, 

Chambers and others 1997, Conner and others 1981, Parks and others 1996) that 

investigated various means of creating viable snags needed by cavity-dependent 

species. The percent of cavity construction was higher in the bark beetle-killed trees; 

none of the girdled trees were used by woodpeckers as sites for cavities as was seen 

in previous studies. However, even in this study many questions remain. For 

instance, do secondary insects, particularly woodborers, carry inoculum for sapwood 

and heart rots into the tree that make a particular site favorable for cavity excavation? 

In the process of using bark beetle-killed trees as feeding sites, do woodpeckers 

become favorably inclined to use these as cavity trees? Unfortunately, little 

information exists to answer these questions and many others. Research and 

monitoring are needed to evaluate wildlife use of created snags both at the individual 

snag/tree and landscape levels. 

When selecting a particular method of creating snags in snag deficient areas, 

land managers must consider a number of factors. Whether the particular method 

creates a snag that the targeted wildlife will use is crucial. We point out that snags 

created by bark beetle colonization serve multiple objectives. First, these snags serve 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

152 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

as feeding sites from the time they are colonized by a particular bark beetle species, 

and then for a number of years after this event as secondary beetles cycle through the 

snag. Second, they serve as suitable sites for cavity excavation that are used by a 

number of different cavity-dependent species. 

Lewis (1998) points out that safety and economics are other factors that land 

managers must consider when selecting a method to create wildlife snags. He 

suggests that blasting and saw-topping are both extremely dangerous, in addition to 

being costly, compared to basal and crown girdling and fungal inoculation. The use 

of bark beetle pheromones is quite inexpensive. Western pine beetle pheromones cost 

approximately $8.00/unit and can be used several times if stored properly, and no 

machinery is needed as with girdling. The most obvious concern about the use of 

bark beetle pheromones is whether or not their use could create unwanted bark beetle 

mortality. Although the probability of starting a bark beetle epidemic (local or 

otherwise) with their use is remote, common sense should be used. If local 

populations are sparse and stand and tree conditions are thrifty, there is little risk in 

using bark beetle pheromones. In this study no collateral mortality was associated 

with either pheromone baiting or girdling. Conversely, if local populations of bark 

beetles are rising or locally epidemic because of droughty conditions or other 

predisposing conditions, this method of creating snags should be used with great 

care. 

Finally, whatever method is used to create wildlife snags to meet standards and 

guides concerning snag densities, the resulting snags must be suitable and acceptable 

to the wildlife species of concern. 

References 

Bedard, William D.; Wood, David L. 1974. Bark beetlesthe western pine beetle. In: 

Birch, Martin C., ed. Pheromones. Sec. 22.8. Frontiers of biology, Vol 32, North 

Holland Amsterdam; 441-449. 

Browne, Lloyd E. 1978. A trapping system for the western pine beetle using attractive 

pheromones. Journal of Chemical Ecology 4(3): 261-275. 

Bull, Evelyn L.; Partridge, Arthur D.; Williams, W. G. 1981. Creating snags with 

explosives. Res. Note PNW-393. USDA Forest Service; 4 p. 

Bull, Evelyn L.; Partridge, Arthur D. 1986. Methods of killing trees for use by cavitynesters. Wildlife Society Bulletin 14: 142-146. 

Byers, John A. 1989. Chemical ecology of bark beetles. Experientia 45: 271-283. 

Chambers, Carol L.; Carrigan, Tara; Sabin, Thomas E.; Tappeiner, John; McComb, William 

C. 1997. Use of artifically created Douglas-fir snags by cavity nesting birds. Western 

Journal of Applied Forestry 12: 93-97. 

Conner Richard N.; Dickson, J. G.; Locke, B. A. 1981. Herbicide-killed trees infected by 

fungi: potential cavity sites for woodpeckers. Wildlife Society Bulletin 9(4): 308-310. 

Furniss, Rober L.; Carolin, Val M. 1977. Western forest insects. Miscellaneous Publication 

No. 1339. U.S. Department of Agriculture Forest Service; 654 p. 

Landram; F. Michael; Laudenslayer, William F., Jr.; Atzet, Thomas. 2002. Demography of 

snags in eastside pine forests of California. In: Laudenslayer, William F., Jr.; Shea, 

Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 
Creation of Snags and Their Use by Insects and Woodpeckers—Shea, Laudenslayer, Ferrell, and 

Borys 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 153 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume].

Laudenslayer, William, F. Jr. 1997. Dead, dying, and diseased trees and their values to 

wildlife. In: Dams, D.; Rios, J. E., eds. Proceedings, 45th animal damage meeting of the 

California Forest Pest Council, November 13-14, 1996. Sacramento, CA: California 

Dept of Forestry and Fire Protection; 9-14. 

Lewis, Jeffrey C. 1998. Creating snags and wildlife trees in commercial forest landscapes.

Western Journal of Applied Forestry 13(3) 97-101. 

Miller, John M.; Keen, Frank P. 1960. Biology and control of the western pine beetle. 

USDA Forest Service Miscellaneous Publication 800; 381 p. 

Morrison, Michael; Raphael, Martin G. 1993. Modeling the dynamics of snags. Ecological 

Appliations 3: 322-330. 

Parks, Catherine G.; Bull, Evelyn L.; Filip, Greg M. 1996. Using artificially inoculated 

decay fungi to create wildlife habitat. In: Bradford, P.; Manning, Todd; l’Anson, Bill, 

eds. Wildlife tree/stand-level biodiversity workshop proc B.C. Min. of forestry Victoria, 

B.C.; 87-89. 

Stark, Ronald W.; Dahlsten, Donald L. 1970. Studies on the population dynamics of the 

western pine beetle, Dendroctonus brevicomis LeConte. University of California, 

Agricultural Science Publication; 174 p. 

Thomas, Jack W.; Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: 

Thomas, J. W., tech. ed. Wildlife habitats in managed forests: the Blue Mountains of 

Oregon and Washington. Agric. Handb. 533. USDA Forest Service; 60-77. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 155 

The Role of Disturbance in Creating Dead 

Wood: Insect Defoliation and Tree Mortality 

in Northeastern Oregon1

Andrew Youngblood2 and Boyd E. Wickman3

Abstract 

Knowledge of natural disturbance factors that influence ecosystems over large temporal and 

spatial scales is essential for understanding interactions among ecosystem processes. Repeated 

assessment of forest stand structure after disturbance events may aid in identifying ecosystem 

processes and components affected by disturbance that are not readily apparent until long 

after the disturbance event. In northeastern Oregon, conifer defoliation by phytophagous 

insects occurs over large temporal and spatial scales and often leads to tree mortality. The 

current composition and stand structure in mixed conifer stands were documented after two 

such disturbances: stands 23 years after defoliation by Douglas-fir tussock moth (Orgyia 

pseudotsugata McD.) in the Wenaha-Tucannon Wilderness, and stands 12 years after 

defoliation by the western spruce budworm (Choristoneura occidentalis Freeman) in the 

Starkey Experimental Forest. Assessment of these areas includes the density of snags, the 

density and size of down logs, and the change in associated vegetation. The research suggests 

that similar patterns of stand dynamics, including tree mortality and eventual conversion of 

standing dead to down logs, along with new seedling establishment, can result from 

defoliation events with vastly differing durations. This work provides valuable insights into 

the role of large insect outbreaks and the dynamics of dead wood in these mixed conifer 

stands. 

Introduction 

Knowledge of natural stand-replacement disturbances over large temporal and 

spatial scales is essential for understanding the interactions among ecosystem 

processes, such as nutrient cycling, plant competition and community development, 

and wildlife habitat and population dynamics. In the Blue Mountains of northeastern 

Oregon and southeastern Washington, natural stand-replacement disturbances in 

mixed conifer stands of grand fir (Abies grandis [Dougl. ex D. Don] Lindl.), 

Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco), Engelmann spruce (Picea 

engelmannii Parry ex Engelm.), and western larch (Larix occidentalis Nutt.) 

primarily occur as either wildfire (Agee 1993) or insect herbivory (Hessburg and 

others 1994, Wickman 1992). The largest Douglas-fir tussock moth (Orgyia 

pseudotsugata McD.) outbreak on record occurred in this area between 1972 and 

1974, resulting in about 3,240 km2

 of defoliation (Brookes and Campbell 1978, 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Silviculturist, Pacific Northwest Research Station, USDA Forest Service, 1401 Gekeler Lane, 

LaGrande, OR 97850 (e-mail: ayoungblood@fs.fed.us) 

3

 Research Entomologist (Emeritus), Pacific Northwest Research Station, USDA Forest Service, 1401 

Gekeler Lane, LaGrande, OR 97850; current address Deschutes National Forest, USDA Forest Service, 

1645 Highway 20 East, Bend, OR 97701. 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

156 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Graham and others 1975, USDA 1978). Grand fir and Douglas-fir that were stripped 

of foliage for more than 90 percent of their crown length died (Wickman 1978). 

Patches of dead trees were scattered throughout the outbreak area. Federal and State 

land managers and private landowners initiated chemical control programs to reduce 

larval densities and salvage harvesting of timber to reduce fuels and capture tree 

volume. In the early 1980s, a western spruce budworm (Choristoneura occidentalis

Freeman) outbreak began in northeastern Oregon. Stands throughout eastern Oregon 

and eastern Washington eventually were infested, resulting in about 28,300 km2 of 

defoliation (USDA Forest Service 1988). Again, salvage harvesting of timber and 

aerial spray programs occurred throughout the two states. 

Studying the long-term effects of natural disturbances such as Douglas-fir 

tussock moth or western spruce budworm outbreaks requires assessment of stand 

dynamics over several decades. It also requires assessment of stands that remain 

relatively undisturbed by human activities or management. After the recent Douglasfir tussock moth and western spruce budworm outbreaks, managers were increasingly 

concerned about long-term ecological effects, especially the changes in stand 

structure and the accumulation of dead and down wood that may increase fire hazard. 

Many opportunities to evaluate long-term changes, however, were compromised by 

management activities, including harvesting and aerial spraying. Two areas in 

northeastern Oregon in which natural processes were not altered by management 

activities were recognized at the onset of the respective outbreaks and thus provide an 

opportunity for long-term assessment. A study site at Grizzly Bear Ridge, in the 

Wenaha-Tucannon Wilderness Area, Umatilla National Forest, was established in 

1972 during the early phase of the Douglas-fir tussock moth outbreak. A similar site 

at Bally Mountain, in the Starkey Experimental Forest, Wallowa-Whitman National 

Forest, was established in 1983 at the beginning of the western spruce budworm 

outbreak. Both sites have a multi-century history of insect-caused defoliation 

(Swetnam and others 1995). The original study objectives at both sites were to assess 

host tree mortality and damage such as top-kill and growth loss, and stand dynamics 

and compositional changes including natural regeneration. The stands were examined 

annually for 10 years after the outbreaks. 

Tree mortality after Douglas-fir tussock moth defoliation occurred over a 5-year 

period from 1973 to 1977 at the Grizzly Bear Ridge site. Tree mortality after western 

spruce budworm defoliation occurred over an 8-year period from 1984 to 1992 at the 

Bally Mountain site. Stands at both sites had similar extreme post-outbreak tree 

mortality, ranging from 40 to 90 percent tree mortality (Wickman and others 1986).4

Ten years after the onset of the outbreak, natural regeneration was assessed at Grizzly 

Bear Ridge. About 1,230 new seedlings per hectare were counted, of which 60 

percent were grand fir (Wickman and others 1986). Wickman and others (1986) 

suggested that, in the absence of fire, the stand structure would be conducive to 

supporting the next Douglas-fir tussock moth outbreak in 70 to 90 years. 

With increasing recognition of the importance of snags and logs for wildlife 

habitat (Bull and others 1997, Maser and others 1979) and ecosystem processes, such 

as the role of nonsymbiotic nitrogen fixation in nutrient cycling, coarse woody debris 

in ectomycorrhizae relations, and long-term carbon storage (Harvey and others 1987, 

Jurgensen and others 1992), we expanded the original study objectives to include 

assessment of the dead wood component. In 1995, we re-examined stand structure at 

 

4

 Unpublished data on file at the Pacific Northwest Research Station, LaGrande, Oreg. 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 157 

the Grizzly Bear Ridge site, focusing on natural regeneration, snag and log 

distribution, and plant community composition. This represented a 23-year 

postoutbreak assessment of stand conditions. In 1997, we re-examined stand structure 

at Bally Mountain, focusing on establishment of natural regeneration and snag and 

log distribution. This represented a 12-year postoutbreak assessment of stand 

conditions. 

In this paper, we describe stand conditions at both Grizzly Bear Ridge and Bally 

Mountain, emphasizing the dead wood component. We believe these results have 

relevancy as individual case studies of typical Blue Mountain mixed-conifer stands 

subjected to extreme defoliation after which natural processes of mortality and down 

wood recruitment were allowed to proceed unhindered by management activities. 

Study Area and Methods 

Stand structure after Douglas-fir tussock moth defoliation was examined on 

Grizzly Bear Ridge in the Wenaha-Tucannon Wilderness (fig. 1). The study site 

(latitude 45o

 59' 45", longitude 117o 44' 30") is on a gentle south-facing slope and 

broad plateau at about 1,280 m elevation, above steep Wenaha River canyon 

“breaks.” At the onset of the last Douglas-fir tussock moth outbreak, these stands 

were composed of mature grand fir and Douglas-fir as well as minor amounts of 

western larch and ponderosa pine, totaling about 830 trees per hectare and 58 m2

 per 

hectare of basal area. Ten years after the outbreak, the live residual overstory 

consisted of about 370 trees per hectare and 23 m2

 per hectare of basal area 

(Wickman and others 1986). The study area conforms to the grand fir/twinflower 

plant association as described by Johnson and Clausnitzer (1992). 

Washington

Oregon

La Grande

Blue Mountains

Washington

Oregon

Walla Walla

Elgin

Hwy 86

I-84

Hwy 11

Kilometers

Grizzly

Bear

Ridge

Bally Mountain

Figure 1—Grizzly Bear Ridge and Bally Mountain study areas for assessing longterm changes in stand structure after severe insect-caused defoliation, northeastern 

Oregon. 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

158 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Assessment of stand structure in 1995 was made by using the same sample grid 

used in 1972 to assess tree mortality and top-kill (Wickman 1978) and later used to 

document natural regeneration (Wickman and others 1986). Thirty-four circular 

sample plots, each 81 m2

 (1/50 acre) in size, were systematically located at 30-m 

intervals along eight transects in two stands. Diameter at breast height (1.37 m high) 

was measured on all live overstory trees previously tagged, and additional mortality 

from the assessment in 1986 was noted. All down logs with large-end diameters at 

least 7.6 cm within the same sample plot were measured for total length to the nearest 

foot and mid-length diameter to the nearest inch. External and internal wood 

condition of each log was assessed by using a hatchet to chop into the log at intervals 

along its length and estimate the percent sound material based on wood hardness, 

moisture content, and color, and presence of bark (Torgersen and Bull 1995). Heights 

of all seedlings within a 16-m2

 circular subplot centered on the 81-m2 circular plot 

were measured with a height pole to the nearest inch. Total overstory canopy 

coverage and canopy coverage of all vascular plants by species were ocularly 

estimated on the same 81-m2

 circular plot. 

Stand structure after western spruce budworm defoliation was examined on 

Bally Mountain in the Starkey Experimental Forest (fig. 1). The study site (latitude 

45 o 17' 30", longitude 118 o 36' 30") is on a gentle east-facing slope at about 1,417 m 

elevation. At the onset of the western spruce budworm outbreak in 1983, this stand 

was composed of 77-year-old grand fir, 165-year-old Douglas-fir and 132-year-old 

western larch, with minor amounts of ponderosa and lodgepole pine (Pinus contorta

Doug. ex Loud), totaling about 400 trees per hectare and about 27 m2

 per hectare of 

basal area.5

 Grand fir represented almost 80 percent of the density and basal area. The 

study area most closely conforms to the grand fir/twinflower plant association as 

described by Johnson and Clausnitzer (1992). 

Stand structure was assessed at Bally Mountain in 1997 with a sample grid 

similar to that used at Grizzly Bear Ridge. Seventy-five circular sample plots, each 

200 m2

 (1/20 acre) in size, were systematically located at about 30-m intervals 

throughout a single stand. Diameter at breast height was measured on all live 

overstory trees previously tagged, and additional mortality from the assessment in 

1993 was noted. Because mortality at Bally Mountain was more recent than at 

Grizzly Bear Ridge, and more of the dead stems remained standing, we did not 

measure logs directly. Instead, we assumed all broken sections of snags in the plot 

would fall as logs into the plot, and no sections of snags from outside the plot would 

fall into the plot. Quantity and size of logs on the ground was estimated by 

calculating the dimensions of tree boles no longer standing. We measured the height 

at which snags were broken on all snags with breaks above breast height by using a 

survey laser. All seedlings within the same plot were counted by species. Because the 

Bally Mountain site was adjacent to open areas that were grazed by cattle and the 

understory vegetation was frequently disturbed, we opted not to assess species 

composition of associated vegetation. 

We summarized the data by species at both sites to estimate density, basal area, 

and diameter class distribution of live and dead stems, and density of logs. For Bally 

Mountain, we calculated total tree height based on diameter at breast height by using 

the Lundqvest function with specific parameters for each tree species (Moore and 

others 1996). We then used the USDA Forest Service’s (1999) computer program 

 

5

 Unpublished data on file at the Pacific Northwest Research Station, LaGrande, Oreg. 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 159 

NATVOL to estimate the diameter at the top of broken snags and the length and 

volume of both the standing and down (log) portions. These estimates were based on 

measured breast-height diameter and snag height and calculated total tree height, 

using equations for taper and volume within NATVOL by species derived from more 

than 14,000 trees. For both sites, we calculated the mass of logs, assuming a constant 

0.256 kg per m3

 (20 pounds per foot3). Because the amount of cover provided by logs 

for small vertebrates is related to size of the logs, we calculated the cover as a 

percentage of total area based on mid-length diameter and total log length at Grizzly 

Bear Ridge and large end-diameter and total length at Bally Mountain, and assumed 

no overlap of pieces. Finally, associated vegetation at Grizzly Bear Ridge was 

summarized by constancy (the percentage of sample plots containing that species) 

and the mean cover (average of the observed cover values where present). 

Results 

Live Tree Structure 

Residual live trees with overstory canopies occurred on 74 percent of the plots 

and provided about 44 percent canopy cover at Grizzly Bear Ridge. Total live tree 

density was about 2,290 trees per hectare and total basal area was about 30 m2

 per 

hectare (table 1). Most of the live stems and basal area was grand fir. More than 65 

percent of the live stems at Grizzly Bear Ridge were grand fir seedlings and saplings 

that contributed little to the total basal area (table 2). Average height of natural 

regeneration (mean and standard error in cm) was 46.6 ± 12.08 for ponderosa pine, 

41.6 ± 12.34 for grand fir, 20.9 ± 6.70 for Douglas-fir, 26.2 ± 144.21 for western 

larch, and 7.2 ± 25.59 for Engelmann spruce. 

Live tree density at Bally Mountain was about 560 trees per hectare, of which 

almost 50 percent was western larch and 30 percent was grand fir (table 1). Total 

basal area was 2 m2

 per hectare. More than 85 percent of the live trees were seedlings 

and saplings less than 1.37 m tall (table 2). Regenerated species included ponderosa 

pine, grand fir, Douglas-fir, western larch, and lodgepole pine. 

 

Dead Tree Structure 

At Grizzly Bear Ridge, there were 109 stems per hectare standing dead, of 

which 67 percent was grand fir and 20 percent was western larch (table 1). Almost 21 

m2

 per hectare in basal area of dead trees remained; about 75 percent of this was dead 

grand fir (table 1). Almost 30 percent of the standing dead was grand fir with breast 

height diameters greater than 50 cm (table 2). The largest standing dead grand fir had 

a diameter of 87 cm. Although infrequently represented, dead ponderosa pine had 

diameters greater than 80 cm. 

Bally Mountain had the same density of standing dead (109 stems per hectare); 

almost 90 percent of these were grand fir (table 1). Total basal area of dead was 

almost 8 m2

 per hectare and was dominated by grand fir. Grand fir that were dead had 

diameters that ranged from 6 to 74 cm; about 13 percent were greater than 50 cm 

(table 2). There were 28 dead stems per hectare with tops broken above breast height; 

more than 80 percent of these were grand fir. Height of the break ranged from 1.5 to 

15.8 m (mean ± standard error = 7.1 ± 0.83) for grand fir, 1.7 to 24.4 m (7.0 ± 3.52) 

for Douglas-fir, and 5.4 to 24.3 m (14.8 ± 9.45) for western larch. 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

160 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 1—Average density and basal area of standing live and dead trees (mean and standard 

error) at Grizzly Bear Ridge and Bally Mountain, northeastern Oregon. 

Number of trees1

 Basal area2

Mean SE Mean SE 

Grizzly Bear Ridge

Live stems: 

Pipo3 152.6 33.01 --4 -- 

Abgr 1780.6 482.28 24.6

0

 5.383 

Psme 243.5 74.04 -- -- 

Laoc 58.1 18.98 4.75 2.051 

Pien 58.1 41.15 0.31 0.311 

 Total 2292.9 506.82 29.6

6

 5.600 

Dead stems: 

Pipo 7.3 5.06 4.07 2.839 

Abgr 72.7 20.28 15.4

6

 5.126 

Laoc 21.8 15.18 0.97 0.615 

Hardwood 3.6 3.63 0.04 0.042 

Unknown 3.6 3.63 0.26 0.265 

 Total 109.0 32.48 20.8

1

 7.430 

 

Bally Mountain

Live stems: 

Pipo 30.7 5.61 0.22 0.149 

Abgr 168.7 40.63 0.60 0.361 

Psme 90.7 19.63 0.16 0.159 

Laoc 266.7 47.33 1.00 0.354 

Pico 6.0 2.50 0.01 0.012 

Pien 0.7 0.67 0.00 0.000 

 Total 563.3 74.67 2.00 0.532 

Dead stems: 

Abgr 96.0 9.28 6.82 0.851 

Psme 10.7 2.73 0.77 0.335 

Laoc 2.7 1.31 0.30 0.202 

 Total 109.3 10.60 7.89 0.930 1

 Stems ha-1

2

 m2 ha-1

3 Species codes: Pipo, Pinus ponderosa; Abgr, Abies grandis; Psme, Pseudotsuga menziesii; Laoc, Larix 

occidentalis; Pico, Pinus contorta; Pien, Picea engelmannii 4 – = negligible amount 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 161 

Table 2—Cumulative frequency distribution of live and dead stems by diameter class and 

species at Grizzly Bear Ridge and Bally Mountain, northeastern Oregon. 

 Pipo1

 Abgr Psme Laoc Pico Pien Other 

Grizzly Bear Ridge

Live: 

< bh2

 6.7 65.6 10.6 0.9 0 2.4 0 

0.0 - 9.93

 0 1.9 0 0 0 0 0 

10.0 - 19.9 0 3.8 0 0 0 0 0 

20.0 - 29.9 0 2.4 0 0.3 0 0 0 

30.0 - 39.9 0 1.3 0 0.6 0 0.2 0 

40.0 - 49.9 0 0.9 0 0.3 0 0 0 

> 50 0 1.7 0 0.3 0 0 0 

Dead: 

< bh 0 0 0 0 0 0 0 

0.0 - 9.9 0 3.3 0 3.3 0 0 0 

10.0 - 19.9 0 6.7 0 3.3 0 0 3.3 

20.0 - 29.9 0 10.0 0 6.7 0 0 0 

30.0 - 39.9 0 16.7 0 6.7 0 0 3.3 

40.0 - 49.9 0 0 0 0 0 0 0 

> 50.0 6.7 29.9 0 0 0 0 0 

 

Bally Mountain

Live: 

< bh 4.7 27.1 13.6 39.3 0.5 0 0 

0.0 - 9.9 0.2 2.4 2.4 6.3 0.5 0 0 

10.0 - 19.9 0.1 0 0 0.2 0.1 0 0 

20.0 - 29.9 0 0 0 0 0 0 0 

30.0 - 39.9 0.1 0 0 0.7 0 0 0 

40.0 - 49.9 0.1 0.1 0 0.2 0 0 0 

> 50 0.1 0.2 0.1 0.6 0 0 0 

Dead: 

< bh 0 0 0 0 0 0 0 

0.0 - 9.9 0 9.8 1.2 0 0 0 0 

10.0 - 19.9 0 28.1 2.4 0 0 1.2 0 

20.0 - 29.9 0 0 0 0 0 0 0 

30.0 - 39.9 0 26.2 3.7 0 0 0 0 

40.0 - 49.9 0 10.4 1.2 0 0 0 0 

> 50.0 0 13.4 1.2 0 0 1.2 0 1

 Species codes: Pipo, Pinus ponderosa; Abgr, Abies grandis; Psme, Pseudotsuga menziesii; Laoc, Larix

occidentalis; Pico, Pinus contorta; Pien, Picea engelmannii 2

 Breast height (1.37 m tall) 

3

 Diameter class in centimeters 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

162 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Logs 

We measured 210 logs at Grizzly Bear Ridge. Logs ranged in length from 0.6 to 

10.1 m (mean ± standard error = 5.0 ± 0.20). Density was 763 logs per hectare, of 

which 55 percent were identified as grand fir, 14 percent were western larch, almost 

2 percent were ponderosa pine, and 28 percent could not be identified to species 

(table 3). These logs totaled approximately 400 m3

 per hectare in volume, 3,800 m 

per hectare of linear log length, and 128,800 kg per hectare of mass. Slightly more 

than 11 percent of the ground was covered by logs. Most of the logs exhibited 

various indicators of advanced decomposition; 70 percent of all the logs were 

considered 30 percent sound or less and about 14 percent of the logs were considered 

at least 80 percent sound. Grand fir logs and those unidentified to species generally 

were less sound, and western larch and ponderosa pine logs were generally more 

sound. 

Table 3—Stem characteristics (mean and standard error) of logs by species at Grizzly Bear 

Ridge and Bally Mountain, northeastern Oregon. 

Number 

(Stems ha-1) 

Volume 

(m3 ha-1) 

Length 

(m ha-1) 

Mass 

(kg ha-1) 

Cover 

(Percent) 

Mean SE Mean SE Mean SE Mean SE Mean SE 

 

Grizzly Bear Ridge

Pipo1 14.5 8.67 17.4 13.26 64.2 38.97 5582.9 4247.81 0.3 .24 

Abgr 425.2 53.50 211.3 49.09 2104.2 325.97 67704.5 15726.72 6.2 1.08 

Laoc 105.4 27.67 37.2 14.23 650.9 175.31 11925.1 4558.83 1.4 .40 

Unknown 218.0 29.99 136.0 60.61 963.6 153.71 43564.8 19418.96 3.2 .88 

 Total 763.1 75.13 402.0 76.27 3783.0 404.36 128777.4 22433.49 11.2 1.40 

Bally Mountain 

Abgr 51.3 6.64 63.5 27.03 844.1 112.07 20354.6 8659.69 1.3 0.31 

Psme 6.7 2.19 2.2 1.09 86.4 30.63 694.9 349.71 0.1 .03 

Laoc 1.3 .94 .02 .17 10.8 8.13 67.2 56.04 --2

 -- 

Pico 0.7 .67 -- .01 5.3 5.32 -- 4.48 -- -- 

 Total 60.0 8.54 65.9 27.02 946.6 128.37 21134.2 8656.87 1.4 .31 

1 Species codes: Abgr, Abies grandis; Psme, Pseudotsuga menziesii; Laoc, Larix occidentalis; Pico, 

Pinus contorta; Pipo, Pinus ponderosa 2

 = negligible. 

We calculated log characteristics for Bally Mountain based on 48 observed 

broken snags. Logs were between 4.9 and 50.6 m in length (mean ± standard error = 

15.8 ± 0.80). Density was 60 logs per hectare, of which more than 85 percent were 

grand fir (table 3). Density of Douglas-fir, western larch and lodgepole pine logs was 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 163 

low. Almost all of the log volume (65.9 m3 per hectare), linear log length (almost 950 

m per hectare), and mass (about 21,130 kg per hectare) was from grand fir. Only 1.4 

percent of the ground was covered with logs. Large-end diameter of logs at Bally 

Mountain ranged from 7.1 to 152.4 cm; about 42 percent were less than 15.2 cm (6 

inches), 34 percent were between 15.2 and 30.2 cm (6.0 to 11.9 inches), 19 percent 

were between 30.5 and 50.5 cm (12 and 19.9 inches), and 4 percent were larger than 

51 cm (20 inches). 

Associated Vegetation 

We identified 49 species of shrubs, forbs, and graminoids in the diverse 

understory at Grizzly Bear Ridge. Common shrubs included Symphoricarpos albus

(L.) Blake, Spiraea betulifolia Pall., Rosa species, Vaccinium membranaceum

Dougl., and Linnaea borealis L. (table 4). Common forbs were Osmorhiza species, 

Galium triflorum L., Adenocaulon bicolor Hook., and the fern Pteridium aquilinum 

(L.) Kuhn. Calamagrostis rubescens Buckl. was the most common grass. 

Table 4—Constancy and average cover of important plants at Grizzly 

Bear Ridge site, northeastern Oregon. 

Constancy Mean cover

 Percent 

Shrubs: 

Acer glabrum 26 11 

Amelanchier alnifolia 29 8 

Berberis repens 12 4 

Ceanothus velutinus 9 1 

Holodiscus discolor 15 5 

Linnaea borealis 44 31 

Lonicera ciliosa 9 5 

Lonicera utahensis 41 14 

Ribes lacustre 21 7 

Ribes viscosissimum 38 7 

Rosa nutkana/R. woodsii 59 21 

Rubus idaeus 3 1 

Rubus parviflorus 29 13 

Salix scouleriana 9 7 

Sambucus cerulea 3 1 

Spiraea betulifolia 59 11 

Symphoricarpos albus 71 32 

Vaccinium membranaceum 53 22 

Forbs: 

Achillea millefolium 6 15 

Adenocaulon bicolor 32 23 

Arnica cordifolia 32 5 

Chimaphila umbellata 15 1 

Clintonia uniflora 12 9 

Disporum trachycarpum 3 1 

Galium triflorum 47 14 

Goodyera oblongifolia 3 1 

Hedysarum boreale 9 10 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

164 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Constancy Mean cover

 Percent 

Hieracium albiflorum 3 1 

Mitella pentandra 6 28 

Osmorhiza chilensis/O. occidentalis 56 8 

Pedicularis racemosa 12 1 

Pteridium aquilinum 29 48 

Smilacina stellata 26 5 

Thalictrum occidentale 15 1 

Trifolium longipes 18 20 

Valeriana sitchensis 29 15 

Graminoids: 

Bromus carinatus 9 12 

Calamagrostis rubescens 35 10 

Carex geyeri 18 3 

Carex rossii 12 3 

Elymus glaucus 21 4 

Discussion 

Although currently dominated by grand fir, Grizzly Bear Ridge and Bally 

Mountain represent relatively dry, mid-elevation sites throughout the Blue Mountains 

of northeastern Oregon and southeastern Washington on which mixtures of conifers 

develop as a result of past disturbances. Under historical fire regimes, these sites 

were dominated by seral species such as ponderosa pine, western larch, and 

occasionally Douglas-fir that arose from infrequent stand-replacement fires and were 

maintained by frequent, low intensity, underburning (Agee 1993, Agee 1994, 

Hessburg and others 1994). Grand fir rarely dominated in these stands; thin bark and 

low-growing canopies were easily consumed by frequent wildfires that maintained 

these sites in open, park-like stands. The presence of wildfire was not uniform across 

the landscape, however, leading to a wide range in fire return intervals. As ponderosa 

pine and Douglas-fir matured and perhaps became stressed by climatic conditions, 

other disturbances such as root diseases, mechanical injuries such as lightning strikes, 

or insects may have caused mortality (Hessburg and others 1994). Douglas-fir 

tussock moth and western spruce budworm defoliation occurred in these mixed 

conifer stands periodically, especially as cohorts of grand fir and Douglas-fir reached 

into the mid- and upper canopy. Landscape-scale outbreaks probably occurred when 

less frequent wildfire allowed development of relatively uniform mid-canopy strata 

composed of grand fir and Douglas-fir. Dendrochronology records indicated outbreak 

episodes of similar periodicity dating back to the 1700s (Wickman and others 1993). 

Outbreaks likely were smaller in extent than the most recent outbreaks because the 

food base (primarily grand fir and Douglas-fir) was discontinuous (Hessburg and 

others 1994). 

With the advent of fire suppression efforts shortly after the turn of the century, 

sites throughout the Blue Mountains like Grizzly Bear Ridge and Bally Mountain 

have undergone dramatic shifts in structure and composition. Fire exclusion allowed 

more shade-tolerant species such as grand fir and Douglas-fir to become established 

and to develop into dominant positions in the stand canopies. In addition, seral 

ponderosa pine and western larch were harvested to meet a growing demand for clear 

lumber for home construction, railroad ties, and shipping boxes for agricultural 

products (Oliver and others 1994, Wickman 1992). Scattered cut stumps at Bally 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 165 

Mountain suggest past harvesting of individual stems four to five decades ago. 

Increased densities of grand fir and Douglas-fir provided a more uniformly 

distributed food base for insects and led to severe outbreaks of Douglas-fir tussock 

moth and western spruce budworm. At the onset of the Douglas-fir tussock moth 

outbreak, stands at Grizzly Bear Ridge probably were composed of multiple cohorts 

of grand fir and Douglas-fir in the overstory and understory, with remnant ponderosa 

pine and western larch extending above the upper continuous canopy. Our estimate of 

pre-outbreak density and basal area (about 830 trees and about 58 m2

 per hectare) 

suggests that these stands exceeded accepted guidelines of stocking levels for 

managed stands (Cochran and others 1994). Stocking levels at Bally Mountain were 

lower, presumably because some harvesting had occurred in prior decades, and only 

a single cohort of grand fir existed. 

Our work at Grizzly Bear Ridge and Bally Mountain suggests that similar 

patterns of stand dynamics can result from defoliation events that have vastly 

different durations (2 or 3 years for Douglas-fir tussock moth and 8 to 10 years for 

western spruce budworm). In these two areas, severe Douglas-fir tussock moth and 

western spruce budworm defoliation of 40 to 90 percent of the crown weakened trees 

presumably stressed by competition for growing space and moisture. Fir engraver 

beetle (Scolytus ventralis LeConte) and Douglas-fir beetle (Dendroctonus 

pseudotsugae Hopkins) and perhaps root diseases then followed at Grizzly Bear 

Ridge, eventually resulting in up to 75 percent mortality in grand fir and Douglas-fir 

(Wright and others 1984). We noted little additional mortality in our recent 

reassessment. In both areas, grand fir mortality exists as both standing dead snags and 

down logs. Our reassessment of structure at Grizzly Bear Ridge indicated over 70 

stems per hectare were dead grand fir that remain standing 23 years after the onset of 

defoliation and mortality. We have no means of quantifying actual fall rates, but our 

observations of log wood condition suggest that the dead grand fir that remain 

standing likely are soft snags that will fall within a decade. Species composition of 

natural regeneration mirrors the live overstory composition at both locations; 

ponderosa pine, Douglas-fir, western larch, and Engelmann spruce remain in the 

overstory and occur as seedlings at Grizzly Bear Ridge, and ponderosa pine, 

Douglas-fir, western larch, and lodgepole pine remain in the overstory and occur as 

seedlings at Bally Mountain. We made no attempt to differentiate seedling cohorts by 

age at Grizzly Bear Ridge, although grand fir seedlings established before the 

outbreak and grand fir seedlings established immediately after the outbreak existed in 

about equal numbers 10 years after the outbreak (Wickman and others 1986). Our 

seedling height measurements indicated relatively rapid growth for the shadeintolerant ponderosa pine, and relatively slow growth for shade-tolerant Douglas-fir, 

and Engelmann spruce. Mean grand fir seedling height (about 47 cm) probably 

represents a mixture of two cohorts. Grand fir regeneration was abundant at both 

Grizzly Bear Ridge and Bally Mountain, setting the stage for the next defoliation 

event. 

Although our description of logs is within normal ranges for similar sites in the 

Blue Mountains,6

 we urge caution in extrapolation. Our census at Grizzly Bear Ridge 

was based on relatively small plots and involved counting all logs with large-end 

diameters at least 7.6 cm. Stand composition at the time of the Douglas-fir tussock 

moth outbreak suggests that these stands were advanced in age with multiple cohorts 

of grand fir. Scattered hardwoods presumed to be aspen (Populus tremuloides

 

6

 Unpublished data on file at the Pacific Northwest Research Station, LaGrande, Oreg. 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

166 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

[Michx.]), ponderosa pine, and western larch previously in the overstory had died. 

Thus, aspen, ponderosa pine, western larch, and grand fir logs already lay on the 

forest floor before the outbreak. Our census of logs at Grizzly Bear Ridge represents 

total accumulation of logs since the last stand-replacement fire. In contrast, our 

census at Bally Mountain was an indirect estimate of log density, based on estimated 

volume absent in standing snags. This method accounts only for the volume added to 

the forest floor since the western spruce budworm outbreak and thus underestimates 

total log resources. Differences in these two methods also account for differences in 

average log length. Perhaps the most significant aspect of the log survey was the 

large number of logs at Grizzly Bear Ridge that exhibited indicators of advanced 

decomposition. Measured logs were all aboveground, intact, and belonged to log 

structural class 1 and 2 (Bull and others 1997), yet a majority of the logs were 

characterized as 30 percent sound or less. This probably represents a high incidence 

of stem decay after defoliation-caused mortality. Relatively uniform height of broken 

grand fir snags at Bally Mountain also was a result of stem decay in combination 

with local storm patterns. Difference between species was expected because of 

different bole and dead crown architecture. Our sample size, however, prevented a 

rigorous test of this hypothesis. 

Our work suggests that dead wood recruitment after a defoliator outbreak 

follows a pattern of relatively slow recruitment of snags and logs over a long period 

of time. This slow recruitment of dead wood probably provides a longer-term and 

more stable environment for many species of wildlife dependent on dying and dead 

wood compared to more rapid turnover of snags and logs after stand-replacement 

wildfire. 

We described existing associated vegetation at Grizzly Bear Ridge to help 

characterize the site and to help identify successional pathways after disturbance. In 

general, plots at Grizzly Bear Ridge contained numerous species we believe are 

indicative of past disturbance, especially shade intolerant species such as Holodiscus 

discolor (Pursh) Maxim., Lonicera utahensis S. Wats., Symphoricarpos albus, 

Adenocaulon bicolor, Hedysarum boreale Nutt., Valeriana sitchensis Bong., Bromus 

carinatus Hook. and Arn., and Elymus glaucus Buckl. Surprisingly, the fern 

Pteridium aquilinum became well established and persistent. Collectively, this 

species composition describes a lush, early-successional community that might 

develop after complete overstory removal with little ground disturbance. Few of 

these plant species would persist after a wildfire. Diversity of shrubs and forbs was 

greater than would be expected after a stand-replacement fire (Johnson 1998) or in 

mature stands (Johnson and Clausnitzer 1992). 

Our case studies at Grizzly Bear Ridge and Bally Mountain have provided 

unique opportunities to follow stand dynamics after severe insect defoliation and 

point to the effect of insect defoliation on long-term maintenance of dead wood 

resources. Despite annual visits during the first decade and frequent visits through 23 

years at Grizzly Bear Ridge, our picture of stand dynamics in mixed conifer 

ecosystems in the Blue Mountains remains incomplete. A large number of stems 

remain standing at both sites; these stems will continue to fall as stem decay, wind, 

and cavity-forming wildlife species function to weaken the boles. Further work is 

needed to quantify fall rates by species and to quantify log dynamics after similar 

insect outbreaks. Seedlings will continue to grow, eventually developing a full 

canopy of susceptible host type. And in the absence of wildfire, both Grizzly Bear 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 167 

Ridge and Bally Mountain will likely support a major insect outbreak, leading to 

defoliation and stand mortality. 

Acknowledgments 

Special thanks are extended to our field support during the re-examination of 

these two sites, including H. Gene Paul, Gail Wickman, Dick Woodfin, Larry 

Carpender, and Kerry Metlen. Cilla Coe prepared the map. Helpful reviews of an 

earlier draft were provided by Dave Powell, Richard Mason, Jim McIver, and Don 

Scott. 

References 

Agee, James K. 1993. Fire ecology of the Pacific Northwest forests. Washington, DC: 

Island Press; 493 p. 

Agee, James K. 1994. Fire and weather disturbances in terrestrial ecosystems of the 

eastern Cascades. Gen. Tech. Rep. PNW-GTR-320. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 52 p. 

Brookes, Martha H.; Campbell, Robert W., editors. 1978. The Douglas-fir tussock moth: a 

synthesis. Science and Education Agency Tech. Bull. 1585. Washington, DC: Forest 

Service, Department of Agriculture; 331 p. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia Basin. Gen. Tech. Rep. PNW-GTR-391. Portland, 

OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p 

Cochran, P. H.; Geist, J. M.; Clemens, D. L.; Clausnitzer, Rodrick R.; Powell, David C. 1994. 

Suggested stocking levels for forest stands in northeastern Oregon and 

southeastern Washington. Res. Note PNW-RN-513. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 21 p. 

Graham, David A.; Mounts, Jack; Almas, Dewey. 1975. 1974 cooperative Douglas-fir 

tussock moth control project. Portland, OR: Pacific Northwest Region, Forest Service, 

Department of Agriculture; 74 p. 

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J.; Graham, R. T. 1987. Relationships among 

soil microsite, ectomycorrhizae, and natural conifer regeneration of old-growth 

forests in western Montana. Canadian Journal Forestry Research 17: 58-62. 

Hessburg, Paul F.; Mitchell, Russel G.; Filip, Gregory M. 1994. Historical and current roles 

of insects and pathogens in eastern Oregon and Washington forested landscapes. 

Gen. Tech. Rep. PNW-GTR-327. Portland, OR: Pacific Northwest Research Station, 

Forest Service, U.S. Department of Agriculture; 72 p. 

Johnson, Charles Grier, Jr. 1998. Vegetation response after wildfires in National Forests of 

northeastern Oregon. R6-NR-ECOL-TP-06-98. Portland, OR: Pacific Northwest 

Region, Forest Service, U.S. Department of Agriculture; 127 p. (plus appendices). 

Johnson, Charles Grier, Jr.; Clausnitzer, Rodrick R. 1992. Plant associations of the Blue and 

Ochoco Mountains. R6-ERW-TP-036-92. Portland, OR: Wallowa-Whitman National 

Forest, Pacific Northwest Region, U.S. Department of Agriculture; 164 p. (plus 

appendices). 
Dead Wood after Insect Defoliation in Northeastern Oregon—Youngblood and Wickman 

168 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Jurgensen, M. F.; Graham, R. T.; Larsen, M. J.; Harvey, A. H. 1992. Clear-cutting, woody 

residue removal, and nonsymbiotic nitrogen fixation in forest soils of the Inland 

Pacific Northwest. Canadian Journal Forestry Research 22: 1172-1178. 

Maser, Chris; Anderson, Ralph G; Cromack Kermit, Jr.; Williams, Jerry T.; Martin, Robert E. 

1979. Dead and down woody material. In: Thomas, Jack Ward, technical editor. 

Wildlife habitats in managed forests: the Blue Mountains of Oregon and Washington. 

Agric. Handb. 553. Washington, DC: Forest Service, U.S. Department of Agriculture: 

78-95. 

Moore, James A.; Zhang, Lianjun; Stuch, Dean. 1996. Height-diameter equations for ten 

tree species in the inland empire. Western Journal of Applied Forestry 11: 132-137. 

Oliver, Chadwick D.; Irwin, Larry L; Knapp, Walter H. 1994. Eastside forest management 

practices: historical overview, extent of their applications, and their effects on 

sustainablility of ecosystems. Gen Tech. Rep. PNW-GTR-324. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 73 p. 

Swetnam, T. W.; Wickman, B. E.; Paul, H. G.; Baisan, C. H. 1995. Historical patterns of 

western spruce budworm and Douglas-fir tussock moth outbreaks in the northern 

Blue Mountains, Oregon, since A.D. 1700. Res. Paper PNW-RP-484. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 27 

p. 

Torgersen, Torolf R.; Bull, Evelyn L. 1995. Down logs as habitat for forest-dwelling ants–

the primary prey of pileated woodpeckers in northeastern Oregon. Northwest 

Science 69: 294-303. 

USDA 1978. Douglas-fir tussock moth program accomplishments report. Agriculture 

Information Bulletin No. 417. Washington, DC: Combined Forest Pest Research and 

Development Program; 20 p. 

USDA Forest Service. 1988. Western spruce budworm in Oregon and Washington 

during 1988. Environmental assessment. Unnumbered report. Portland, OR: Pacific 

Northwest Region; 67 p. (plus appendixes). 

USDA Forest Service. 1999. NATVOL: National volume program. Version beta 2.0. Ft. 

Collins, CO: Forest Management Service Center, Forest Service. 

Wickman, Boyd E. 1978. Tree mortality and top-kill related to defoliation by the 

Douglas-fir tussock moth in the Blue Mountains outbreak. Res. Paper RP-PNW-233. 

Portland, OR: Pacific Northwest Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture; 47 p. 

Wickman, Boyd E. 1992. Forest health in the Blue Mountains: the influence of insects 

and diseases. Gen Tech. Rep. PNW-GTR-295. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 15 p. 

Wickman, B. E.; Seidel, K. W.; Starr, G. Lynn. 1986. Natural regeneration 10 years after a 

Douglas-fir tussock moth outbreak in northeastern Oregon. Res. Paper PNW-RP370. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department 

of Agriculture; 15 p. 

Wickman, B. E.; Mason, R. R.; Swetnam, T. W. 1993. Searching for long-term patterns of 

forest insect outbreaks. In: Leather, S. R.; Walters, K. F. A.; Mill, N. J.; Watt, A. D., 

eds. Individuals, populations and patterns in ecology. Andover, Hampshire, UK: 

Intercept Ltd; 251-261. 

Wright, L. C.; Berryman, A. A.; Wickman, B. E. 1984. Abundance of the fir engraver, 

Scolytus ventralis, and the Douglas-fir beetle, Dendroctonus pseudotsugae, following 

tree defoliation by the Douglas-fir tussock moth, Orgyia pseudotsugata. Canadian 

Entomologist 116: 293-305. 
Importance to Vertebrates

169
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 171 

The Value of Coarse Woody Debris to 

Vertebrates in the Pacific Northwest1

Evelyn L. Bull2

Abstract 

Many species of birds, mammals, amphibians, and reptiles use coarse woody debris (i.e., 

standing and downed dead wood) for nesting, roosting, foraging, and shelter. Woodpeckers 

depend on decayed wood to excavate nest and roost cavities in standing trees. Secondary 

cavity nesters then claim the abandoned cavities for their nesting or roosting. Many of the 

woodpeckers and secondary cavity nesters use dead wood to forage on forest insects, 

including bark beetles and defoliators. Characteristics that affect the type and extent of 

vertebrate use of dead wood include the physical orientation, size, decay state, tree species, 

and overall abundance. Some species of heartwood decaying fungi create hollow chambers in 

living trees, which eventually die to become hollow, standing dead trees. Standing trees with 

hollow chambers are used by Vaux’s swifts (Chaetura vauxi) for nesting and roosting, 

pileated woodpeckers (Dryocopus pileatus) for roosting, black bears (Ursus americanus) for 

overwintering, American martens (Martes americana) for denning and resting, and many 

other species of small mammals for shelter. Once the trees fall, many of the same species 

continue to use the hollow structures, except the avian species. Solid logs provide cover or 

travel lanes for small mammals. Accumulations of logs stacked on top of each other provide 

important habitat in the open spaces formed under the snow where martens and small 

mammals spend much of the winter. Large-diameter logs are used extensively by pileated 

woodpeckers and black bears for foraging on carpenter ants. Extensively decayed logs 

provide habitat for amphibians and reptiles. 

Introduction 

Coarse woody debris, which is defined as standing dead trees and downed trees 

(i.e., logs) and large branches, is a critical element of healthy, productive, and 

biologically diverse forests. Coarse woody debris provides habitat for many 

vertebrate species, including birds, mammals, amphibians, and reptiles. Thomas 

(1979) identified 179 vertebrate species that use coarse woody debris in the Blue 

Mountains of Oregon and Washington, which represents 57 percent of the vertebrate 

species breeding there. For those species using standing dead trees, birds dominate 

the list by number of species, although many mammals and some reptiles and 

amphibians use cavities as well as other structural features of dead trees. In the Blue 

Mountains, 39 bird and 23 mammal species use standing dead trees for nesting and 

shelter (Thomas 1979). Bunnell and others (1997) found that about 25 percent of the 

vertebrate species in British Columbia used cavities. Harmon and others (1986) state 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Wildlife Biologist, Pacific Northwest Research Station, USDA Forest Service, 1401 Gekeler 

Lane, La Grande, OR 97850 (e-mail address: ebull@fs.fed.us) 
The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest—Bull 

172 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

that cavity-nesting birds account for 9-39 percent and 8-62 percent of the total bird 

species in deciduous and coniferous forests, respectively. 

Coarse woody debris is formed in a variety of ways. Trees can be killed by fire, 

insects, decay fungi, flooding, drought, and windthrow. The means by which a tree is 

killed influences the manner in which it decays, how long the tree will stand, and the 

rate of deterioration. A strong relationship exists between the kind of decay in a tree 

and what species can use it, particularly for nesting and foraging. The degree of 

decay can be translated into structural classes of standing dead trees and downed 

trees (Bull and others 1997), which may be useful in categorizing the dead wood 

resources. 

In addition to decay, characteristics that affect the type and extent of vertebrate 

use of coarse woody debris include physical orientation (vertical or horizontal), size 

(diameter and length), species of wood, and overall abundance of material (Harmon 

and others 1986). The majority of species that use snags are birds and bats, while the 

majority of species using downed trees include small mammals, amphibians, and 

reptiles. The importance of different characteristics of coarse woody debris will be 

discussed for the following groups of vertebrates: birds, mammals, amphibians, and 

reptiles. 

Birds 

Woodpeckers, termed primary cavity excavators, excavate the cavities they use 

for nesting and roosting. Species using vacated existing cavities are termed secondary 

cavity nesters. Woodpeckers usually excavate their nest cavities in decayed wood in 

dead trees because most woodpeckers lack the adaptations (bill structure, cushion in 

brain, muscle structure) needed to excavate in sound wood. The pileated woodpecker 

(Dryocopus pileatus) is the strongest excavator and can excavate cavities in sound 

wood, while weaker excavators like the Lewis’s woodpecker (Melanerpes lewis)

require advanced decay before they can excavate a cavity. A woodpecker’s 

preference for a particular tree species for nesting is largely influenced by the specific 

decay characteristics that occur in that tree species. Live trees can function as dead 

trees if portions of the wood (e.g., dead tops or large dead branches) contain decay as 

a result of wounding, lightning, or other injuries. Loose bark on dead trees may also 

provide nesting crevices for brown creepers (Certhia americana) and some 

secondary nesting birds. 

Hollow trees are a unique structural feature in forests. The heartwood in these 

trees is decayed by heart-rot fungi while the tree is alive (Bull and others 1997). 

Ninety-five percent of pileated woodpecker roost sites in northeastern Oregon were 

in hollow trees, and 5 percent were in vacated nest cavities (Bull and others 1992). 

Pileated woodpeckers excavate entrance holes in these trees to access the hollow 

chamber. Once an entrance to the hollow chamber has been made, other species like 

the northern flicker (Colaptes auratus) also use these trees for roosting. The great 

depth of some of these hollow chambers makes them unsuitable for nesting by most 

birds, except the Vaux’s swift (Chaetura vauxi), which is dependent on these hollow 

trees for nesting in forest communities. All 21 swift nest trees located in northeastern 

Oregon were in hollow grand fir (Abies grandis). Swift nest trees averaged 67.5 cm 

d.b.h. and 25 m tall with an internal hollow chamber that averaged 28 cm in diameter 

and 5.7 m deep (Bull and Collins 1993). 
The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest—Bull 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 173 

In a recent study, I placed swift nest boxes (3 m deep and 30-cm square) in trees 

to simulate hollow trees in three categories of stands: stands of old forest multi-strata 

(multi-cohort, multi-strata stands with large old trees) in grand fir forest types, 

regeneration cuts in grand fir types, and mature stands of ponderosa pine. Thirty 

percent of the bird boxes in old forest multi-strata stands were used by swifts for 

nesting. Other use included roosting by pileated woodpeckers and northern flickers 

and nesting by flying squirrels (Glaucomys sabrinus) and red squirrels (Tamiasciurus 

hudsonicus).

Size of dead tree can be critical for nesting for some species. Woodpeckers must 

select a dead tree that is large enough to accommodate the cavity they excavate at a 

height at which they prefer to nest. Typically, the larger diameter dead trees can 

accommodate a greater variety of species and stand longer than smaller diameter 

snags. The larger woodpecker species are particularly important because they create 

larger cavities that can be used by larger secondary cavity nesters, like the northern 

saw-whet owl (Aegolius acadicus).

Many woodpecker species forage extensively on invertebrates found in dying 

and dead trees and logs. Woodpecker foraging may effectively reduce populations of 

some bark beetles (Steeger and others 1998). In northeastern Oregon, 38 percent of 

pileated woodpecker foraging was on dead trees, and 38 percent was on logs; 

carpenter (Camponotus spp.) and red forest (Formica spp.) ants were the primary 

prey based on analysis of woodpecker scats. Logs preferred for foraging by the 

pileated woodpeckers were decayed Douglas-fir (Pseudotsuga menseizii) or western 

larch (Larix occidentalis) larger than 38 cm in diameter (Bull and Holthausen 1993). 

Foraging on logs occurs primarily in snow-free months when logs are accessible. 

Northern flickers forage on logs with a high incidence of decay. Black-backed 

(Picoides arcticus) and three-toed woodpeckers (Picoides tridactylus) also forage on 

bark beetles (Scolytidae) and secondary insects (Cerambycidae and Buprestidae) in 

logs. Foraging by vertebrates on logs probably peaks toward the middle or late stages 

of decay when logs are softer and invertebrates and fungal fruiting bodies are more 

common (Harmon and others 1986). 

Although isolated dead trees and logs are used for nesting and foraging, 

concentrations of dead trees and logs provide better cover and more opportunities for 

use. Some woodpeckers, like the pileated woodpecker, frequently nest in the same 

vicinity but use different trees each year. Woodpecker nests in isolated dead trees 

may be more vulnerable to predators than nests in a cluster of dead trees where 

predators would have to search more dead trees and other vacated cavities. 

 Some cavity users may be associated with natural disturbances like fire. Hutto 

(1995) reported that black-backed woodpeckers seemed to be largely restricted to 

standing dead trees created by stand-replacement fires in Montana. In southwestern 

Idaho, Saab and Dudley (1998) found high densities of black-backed and Lewis’s 

woodpeckers in stand-replacement fires in ponderosa pine (Pinus ponderosa),

although nesting black-backed woodpeckers in northeastern Oregon were not 

restricted to stands with fire (Bull and others 1986). 

Some of the cavity-nesting birds like the pileated and white-headed 

woodpeckers (Picoides albolarvatus), Vaux’s swifts, and flammulated owls (Otus 

flammeolus) are associated with stands with large-diameter trees because of their 

reliance on large trees and other structural attributes of these forests. 
The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest—Bull 

174 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Mammals 

Dead wood, both standing and down, is important to mammals for cover, 

denning, and resting. The cavities created by woodpeckers are readily used by red 

squirrels, flying squirrels, bushy-tailed woodrats (Neotoma cinerea), and some bats. 

Larger cavities in decayed heartwood are used by American martens (Martes 

americana), fishers (Martes pennanti), bobcats (Lynx rufus), and black bears for 

denning and shelter. The function of logs depends largely on the extent of decay, 

their size, and abundance. Logs lacking decay are typically used for cover and 

runways. As logs decay and the bark loosens, small mammals can burrow into the 

wood under the bark. 

Research in the last two decades has identified the value of cavities in snags for 

roosting bats. Maternity colonies of silver-haired bats (Lasionycteris noctivagans)

normally are located in cavities in trees during the summer, although males and 

nonreproductive females may roost alone in cracks in trees and under bark (Mattson 

and others 1996, Betts 1998). In northeastern Oregon, trees with cavities that were 

used by roosting bats were taller, less decayed, and farther from adjacent trees than a 

sample of available trees; this selection presumably took advantage of the absorption 

of solar radiation and retention of heat in the trees (Betts 1998). Silver-haired bats are 

dependent on trees, typically roosting in narrow crevices in tree trunks or under the 

bark in large trees in Canada (Barclay and others 1988, Nagorsen and Brigham 

1993). In southern interior British Columbia, big brown bats (Eptesicus fuscus)

roosted in hollow cavities in large-diameter ponderosa pine snags (Brigham 1991). 

Vonhof and Barclay (1996) found that four species of tree-roosting bats (E. fuscus, L. 

noctivagans, Myotis evotis, and M. volans) preferred roosts in tall trees associated 

with lower canopy closure. Of 21 roosts, 14 were beneath loose bark, 5 were in 

cavities excavated by woodpeckers, and 2 were in natural cavities. 

Long-legged bats (Myotis volans) in the central Oregon Cascades roosted in 

large Douglas-fir snags averaging 97 cm dbh and 38 m high (Ormsbee and McComb 

1998). Bats in California roosted in basal hollows in old-growth redwood stands 

(Sequoia sempervirens) in both contiguous forests and in small isolated remnant 

patches (Zielinski and Gellman 1999). 

Hollow standing trees, both live and dead, and hollow logs are used extensively 

by black bears, American martens, fishers, bushy-tailed woodrats, and flying and red 

squirrels. Hollow trees with either a top-entry or base-entry comprised 22 percent of 

165 black bear dens in northeastern Oregon; 12 percent of the dens were in hollow 

logs (Bull and others 2000). Top-entry den trees averaged 114 cm dbh, while baseentry trees averaged 108 cm dbh. The majority of hollow trees and logs were grand 

fir, with Indian paint fungus (Echinodontium tinctorium) being the primary agent 

responsible for creating the hollow chambers in these trees. 

Hollow trees and logs are particularly important habitat for American martens in 

northeastern Oregon where 23 percent of 1,184 rest sites of martens were in trees 

with cavities (mostly hollow trees) (Bull and Heater 2000). Seventy-three percent of 

natal dens were in hollow trees, while 58 percent and 21 percent of maternal (postnatal) dens were in hollow logs and hollow trees, respectively. These hollow 

structures provided dry, warm, and secure sites that were inaccessible to most 

predators. 

Many carnivores are associated with dead wood. Logs provide cover for 

mountain lions (Felix concolor) at diurnal bed sites and at natal and maternal den 
The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest—Bull 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 175 

sites (J. Akenson, pers. comm.). Wolverines (Gulo gulo) may require coarse woody 

debris in some habitats for denning (MacKinnon 1998). Lynx (Lynx lynx) require 

mature forests for denning and a high density of logs (Koehler 1990). Logs and 

stumps may be the most important component of lynx denning habitat because they 

provide cover for kittens (Koehler and Brittell 1990). Accumulations of logs under 

snow are used extensively by American martens for hunting and for shelter (Buskirk 

and Powell 1994). These accumulations of logs are also used by red squirrels for their 

middens during the winter. 

Abundance of small mammals is associated with log cover. On the Olympic 

Peninsula, abundance of deer mice (Peromyscus maniculatus), red-backed voles 

(Clethrionomys spp.), Trowbridge’s shrews (Sorex trowbridgii), and shrew-moles 

(Neurotrichus gibbsii) increased with coarse woody debris in coniferous stands 

(Carey and Johnson 1995). Red squirrels are abundant in older aspen stands (Roy and 

others 1995) and use snags and large trees for nesting and cover and use fungi and 

lichens growing on coarse woody debris as food. 

Red-backed voles use logs extensively for cover and food, eating mostly fungi 

and truffles, many of which are associated with logs (Ure and Maser 1982). The 

mean number of captures of this species was positively correlated with mean log 

diameter and size of log overhang (Hayes and Cross 1987). The larger logs probably 

provide more protective cover from predators than the smaller ones for traveling 

voles. In southwestern Oregon, locations of radio-tagged red-backed voles coincided 

with downed logs 98 percent of the time, even though only 7 percent of the study 

area was covered with logs. In addition, red-backed voles used logs in the later stages 

of decay significantly more often than logs in the earlier stages of decay (Tallman 

and Mills 1994). 

Amphibians and Reptiles 

At least 16 species of salamanders are associated with forests in Oregon 

(Bunnell and others 1997). More specifically, three species of predatory salamanders 

(Batrachoseps wrighti, Ensatina eschscholtzi, and Aneides ferreus) deposit eggs 

within logs in coniferous forests in western Oregon, as well as foraging on most 

invertebrate species found in those logs (Maser and Trappe 1984, Harmon and others 

1986). Clouded salamanders (Aneides ferreus) are found in large coarse woody 

debris with loose bark, and their populations are positively correlated with stand age 

(Aubry and Hall 1991). Ensatinas (Ensatina eschscholtzii) are associated with 

decayed coarse woody debris (Bury and others 1991). Species diversity and 

abundance among the herpetofauna differed among different forest structures in the 

Oregon and Washington Cascades (Bury and Corn 1988) and in southwestern Oregon 

and northwestern California (Welsh and Lind 1988). 

Conclusions 

Although a great deal has been learned about the importance of dead wood to 

wildlife and ecosystems in the last two decades, there are still information gaps. The 

influence of fire, insects, and disease on creating and removing (fire) dead wood 

across landscapes needs intensive research to understand the dynamics of this 

ecological component in western forests. Additional information is needed on the 

density and types of dead trees and their relationships to the density and types of live 
The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest—Bull 

176 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

trees also present that will provide habitat (particularly for foraging) for viable 

populations of primary and secondary cavity nesters. The best methods for creating 

dead trees is still an important issue in restoration efforts. Artificially creating hollow 

trees is as yet not possible, although experiments using inoculation of decay fungi are 

ongoing. 

Limited information on the density and kind of logs is available for many areas, 

and few studies have addressed the density required to provide habitat for viable 

populations of small mammals and herpetofauna. Many management plans do not 

adequately address density of logs, particularly on a landscape level. There continue 

to be conflicts in management agencies between retaining logs and lowering fuel 

levels to reduce the risk and extent of wildfire. If maintaining viable populations of 

species that require high densities of logs (like pileated woodpeckers and American 

martens) is an important management goal, an integration of managing the risk of 

wildlfire, the habitat requirements of these species, and the ecological processes 

resulting from fire is needed. 

Acknowledgments 

Arlene Blumton, Jane Hayes, Catherine Parks, and Torolf Torgersen reviewed 

an earlier draft of the manuscript. 

References 

Aubry, Keith B.; Hall, Patricia A. 1991. Terrestrial amphibian communities in the 

southern Washington Cascade Range. In Ruggiero, Leonard F.; Aubry, Keith B.; 

Carey, Andrew B.; Huff, Mark H., technical coordinators. Wildlife and vegetation of 

unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 327-338. 

Barclay, Robert M. R.; Faure, Paul A.; Farr, Daniel R. 1988. Roosting behavior and roost 

selection by migrating silver-haired bats (Lasionycteris noctivagans). Journal of 

Mammalogy 69: 821-825. 

Betts, Burr J. 1998. Roosts used by maternity colonies of silver-haired bats in 

northeastern Oregon. Journal of Mammalogy 79: 643-650. 

Brigham, R. Mark. 1991. Flexibility in foraging and roosting behavior by the big brown 

bat (Eptesicus fuscus). Canadian Journal of Zoology 69:117-121. 

Bull, Evelyn L.; Akenson, James J.; Henjum, Mark G. 2000. Characteristics of black bear 

dens in trees and logs in northeastern Oregon. Northwestern Naturalist 81: 148-153. 

Bull, Evelyn L.; Collins, Charles T. 1993. Vaux’s swift (Chaetura vauxi). In: Poole, A.; Gill, 

R., editors. The birds of North America, No. 77. Philadelphia: the Academy of Natural 

Sciences; Washington, DC: The American Ornithologists’ Union. 

Bull, Evelyn L.; Heater, Thad W. 2000. Resting and denning sites of American martens in 

northeastern Oregon. Northwest Science 74: 179-185. 

Bull, Evelyn L.; Holthausen, Richard S. 1993. Habitat use and management of pileated 

woodpeckers in northeastern Oregon. Journal of Wildlife Management 57: 335-345. 

Bull, Evelyn. L.; Holthausen, Richard S.; Henjum, Mark G. 1992. Roost trees used by 

pileated woodpeckers in northeastern Oregon. Journal Wildlife Management 56: 786-

793. 
The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest—Bull 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 177 

Bull, Evelyn L.; Parks, Catherine, G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the Interior Columbia River basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Bull, Evelyn L.; Peterson, Steven R.; Thomas, Jack Ward. 1986. Resource partitioning 

among woodpeckers in northeastern Oregon. Res. Note PNW-444. Portland, OR: 

Pacific Northwest Research Station, U.S. Department of Agriculture; 19 p. 

Bunnell, Fred L.; Kremsater, Laurie L.; Wells, Ralph W. 1997. Likely consequences of 

forest management on terrestrial, forest-dwelling vertebrates in Oregon. Report M7 of the Center for Applied Conservation Biology, University of British Columbia, 

Vancouver, B.C., Canada. 

Bury, R. Bruce; Corn, Paul Stephen.1988. Douglas-fir forests in Oregon and Washington 

Cascades: relation of the herpetofauna to stand age and moisture. In: Szaro, R. C.; 

Severson, K. E.; Patton, D. R., technical editors. Proceedings of the symposium on 

management of amphibians, reptiles, and small mammals in North America; 1988 July 

17-21; Flagstaff, AZ. Gen. Tech. Rep. RM-166. Rocky Mountain Research Station, 

Forest Service, U.S. Department of Agriculture; 11-22. 

Bury, R. Bruce; Corn, Paul Stephen; Aubry Keith B. 1991. Regional patterns of terrestrial 

amphibian communities in Oregon and Washington. In: Ruggiero, Leonard F.; 

Aubry, Keith B.; Carey, Andrew B.; Huff, Mark H., technical coordinators. Wildlife and 

vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 341-350. 

Buskirk, Steven W.; Powell, R. A. 1994. Habitat ecology of fishers and American martens. 

In: Buskirk, Steven W.; Harestad, Alton S.; Raphael, Martin G.; Powell, Roger A., 

editors. Martens, sables, and fishers biology and conservation. Ithaca, NY: Cornell 

University Press; 283-296. 

Carey, Andrew. B.; Johnson, Murray L. 1995. Small mammals in managed, naturally 

young, and old-growth forests. Ecological Applications 5: 336-352. 

Hagan, John M.; Grove, Stacie L.1999. Coarse woody debris. Journal of Forestry Jan: 6-11. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V. 1986. Ecology of 

coarse woody debris in temperate ecosystems. Advances in Ecological Research 15: 

133-302. 

Hayes, John P.; Cross, Stephen P. 1987. Characteristics of logs used by western redbacked voles, Clethrionomys californicus, and deer mice, Peromyscus maniculatus. 

Canadian Field-Naturalist 101: 543-546. 

Hutto, Richard L. 1995. Composition of bird communities following stand-replacement 

fires in northern Rocky Mountain (U.S.A.) conifer forests. Conservation Biology 

9(5): 1041-1058. 

Koehler, Gary M. 1990. Population and habitat characteristics of lynx and snowshoe 

hares in north central Washington. Canadian Journal of Zoology 68: 845-851. 

Koehler, Gary M.; Brittell, J. David. 1990. Managing spruce-fir habitat for lynx and 

snowshoe hares. Journal of Forestry Oct: 10-14. 

MacKinnon, Andy. 1998. Biodiversity and old-growth forests. In: Voller, Joan; Harrison, 

Scott, editors. Conservation Biology Principles for Forested Landscapes. Vancouver, 

BC: UBC Press; 146-184. 

Maser, Chris; Trappe, James M., technical editors.1984. The seen and unseen world of the 

fallen tree. Gen. Tech. Rep. PNW-164. Portland, OR: Pacific Northwest Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture. 
The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest—Bull 

178 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Mattson, Todd A.; Buskirk, Steven W.; Stanton, Nancy L. 1996. Roost sites of the silverhaired bat (Lasionycteris noctivagans) in the Black Hills, South Dakota. Great Basin 

Naturalist 56: 247-253. 

Nagorsen, David W.; Brigham, R.Mark. 1993. Bats of British Columbia. Vancouver, BC: 

UBC Press. 

Ormsbee, Patricia C.; McComb, William C. 1998. Selection of day roosts by female longlegged myotis in the central Oregon Cascade Range. Journal of Wildlife Management 

62: 596-603. 

Roy, L. D.; Stelfox, J.B.; Nolan, J.W. 1995. Relationships between mammal biodiversity 

and stand age and structure in aspen mixed wood forests in Alberta. In: Stelfox, J. 

B., editor. Relationships between stand age, stand structure, and biodiversity in aspen 

mixed wood forests in Alberta. Jointly published by Alberta Environmental Centre, 

Vegreville, Alta, and Canadian Forest Service, Edmonton, Alta; 159-189 

Saab, Victoria A.; Dudley, Jonathan G. 1998. Responses of cavity-nesting birds to standreplacement fire and salvage logging of ponderosa pine/Douglas-fir forests of 

southwestern Idaho. Res. Paper RMRS-11, Fort Collins, CO: Rocky Mountain 

Research Station, Forest Service, U.S. Department of Agriculture; 17 p. 

Steeger, C; Machmer, M. M.; Gowans, B. 1998. Impact of insectivores birds on bark 

beetles: a literature review. Pandion Ecological Research Ltd., P.O. Box 26, Ymir B.C. 

V0G 2K0. 

Tallman, David; Mills, L. Scott. 1994. Use of logs within home ranges of California redbacked voles on a remanant of forest. Journal of Mammalogy 75: 97-101. 

Thomas, Jack Ward. 1979. Wildlife habitats in managed forests: the Blue Mountains of 

Oregon and Washington. Agric. Handb. No. 553. Washington., DC: Forest Service, 

U.S. Department of Agriculture; 512 p. 

Ure, Douglas C;. Maser, Chris. 1982. Mycophagy of red-backed voles in Oregon and 

Washington. Canadian Journal of Zoology 60: 3307-3315. 

Vonhof, Maarten J.; Barclay, Robert M. R. 1996. Roost-site selection and roosting ecology 

of forest-swelling bats in southern British Columbia. Canadian Journal of Zoology 

74: 1797-1805. 

Welsh, Hartwell H.; Lind, Amy J. 1988. Old growth forests and the distribution of the 

terrestrial herpetofauna. In: Szaro, R. C.; Severson, K. E.; Patton, D. R., technical 

editors. Proceedings of the symposium on management of amphibians, reptiles, and 

small mammals in North America; 1988 July 17-21; Flagstaff, AZ. Gen. Tech. Rep. 

RM-166. Rocky Mountain Research Station, Forest Service, U.S. Department of 

Agriculture; 439-458. 

Zielinski, William J.; Gellman Steven T. 1999. Bat use of remnant old-growth redwood 

stands. Conservation Biology 13: 160-167. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 179 

Are There Snags in the System? Comparing 

Cavity Use among Nesting Birds in “Snagrich” and “Snag-poor” Eastside Pine 

Forests1 

Steve Zack,2 T. Luke George,3

 and William F. Laudenslayer, Jr.4

Abstract 

We compared the density of snags, snags with cavities, and cavity-nesting bird use at two 

sites in northern California: Blacks Mountain Experimental Forest, a site with large trees and 

large snags because of protection from logging, contrasted with the Goosenest Adaptive 

Management Area, where a century of logging left this forest with few large trees and snags. 

Indeed, there was a threefold difference between sites in total snags, and a fifteenfold 

difference in cavity-nesting bird use. However, we feel finding a “snags per acre” prescription 

is inadequate, as tree size, rate of snag generation, and mode of tree death have been disrupted 

this past century. We argue that understanding the interactions between fire, bark beetles, 

woodpecker foraging and excavating, sapwood decay organisms, snag “demography,” and 

cavity-nesting species ecological requirements apart from simply cavities are required in place 

of simply counting snags in landscapes. 

Introduction 

The habitat structure and ecological processes for our western coniferous forests 

have changed dramatically in the past century primarily because of extensive logging 

and fire suppression. The forests of today often are denser, have a larger component 

of shade tolerant species, and have fewer large, older trees (Bonnicksen 2000, 

Covington and Moore 1994). This is particularly true of eastside pine forests of 

California and Oregon, dominated by ponderosa pine (Pinus ponderosa) and Jeffrey 

pine (P. jeffreyi) (Covington and Moore 1994, Laudenslayer and Darr 1990). 

The density of large snag trees and the processes of their creation have been 

greatly altered as well. Logging and salvage logging have reduced densities of 

potential and actual snags from many landscapes. The suppression of fire has 

suppressed the naturally prevalent mode of snag generation (Horton and Mannan 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. Contribution #12 of the Blacks 

Mountain Ecological Research Project, Pacific Southwest Research Station, USDA Forest Service. 2

 Conservation Scientist, North America Program, Wildlife Conservation Society, 185th Street and 

Southern Blvd., Bronx, NY 10460, (current address: 1746 NW Hartwell Place, Portland, OR 97229); 

and Adjunct Professor, Wildlife Department, Humboldt State University, Arcata, CA 95521 (e-mail: 

SteveZack@msn.com) 

3

 Associate Professor, Wildlife Department, Humboldt State University, Arcata, CA 95521. 4

 Research Wildlife Ecologist, Pacific Southwest Research Station, USDA Forest Service, 2081 E. 

Sierra Ave., Fresno, CA 93710 (e-mail: blaudenslayer@fs.fed.us) 
Are There Snags in the System?—Zack, George, Laudenslayer 

180 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

1988). Understanding these changes in the world of snags in forests is important 

because snags with cavities are essential to wildlife populations. Snags with cavities 

are needed as nesting sites for many species of birds and are used by other wildlife 

(Bu1l 1983, Cline and others 1980, Ganey 1999, Mannan and others 1980, Miller and 

Miller 1980, Moorman and others 1999, Raphael and White 1984, Scott 1978). The 

issue of snag management, and prescribing adequate “snags per acre” for wildlife in 

forests, has been and continues to be a major focus of forest management (Brawn and 

Balda 1988, Brawn and others 1987, Bull and others 1997, Ganey 1999, Horton and 

Mannan 1988, Martin and Eadie 1999, McClellan and Frissell 1975, McComb and 

others 1986, Morrison and others 1986, Ohmann and others 1994, Raphael and White 

1984, Ross and Niwa 1997, Scott 1979, Schreiber and deCalesta 1992, Thomas and 

others 1979, Zarnowitz and Manuwal 1985). 

We have been studying wildlife-forest relationships at two sites in northern 

California (Zack and others 1999). The eastside pine forests at the Goosenest 

Adaptive Management Area in the Klamath National Forest are more or less 

“typical” in that they have been logged and fire suppressed this past century, 

resulting in a dense forest with few large tree and few snags. In contrast, the eastside 

pine forests of the Blacks Mountain Experimental Forest in the Lassen National 

Forest, particularly those in the Research Natural Areas, have not been extensively 

logged (but have been fire suppressed), and so contain many large pine trees and 

snags (Oliver and Powers 1998). 

In this paper, we compare the abundance of snags and snag cavity use at these 

sites from data collected in 1999, and discuss the implications of our results for 

eastside pine forest management and wildlife. We also present data on bark beetle 

and woodpecker foraging patterns in relation to snags and cavity prevalence. 

Methods 

This study was conducted at two sites in northern California: the Blacks 

Mountain Experimental Forest (BMEF), in the Lassen National Forest, northeast of 

Lassen National Park, and at the Goosenest Adaptive Management Area (GAMA), 

Klamath National Forest, east of Mount Shasta. These sites are currently part of 

large-scale experimental research intent on restoring, and evaluating responses to, 

late successional forest structures (and contrasting treatments with controls) in 

eastside pine forests (Oliver and Powers 1998, Zack, and others 1999). 

For this study, we wished to evaluate the snag densities in plots not subjected to 

experimental manipulation. Thus, at BMEF we opted to evaluate snag density at 

three of four of the existing Research Natural Areas (RNAs) that are part of our study 

plots. These RNAs had no prior logging history and an 80+ years of history of fire 

suppression. One RNA―RNA C―was subject to a prescribed fire in 1997. At 

GAMA, we randomly chose three plots from the 14 plots that, in 1999, had not yet 

been logged or had a prescribed fire treatment as part of our experimental study there. 

The three RNAs at BMEF comprised a total of 284 acres (ca. 115 ha.), while all 

plots at GAMA are exactly 100 acres in size so the total there was 300 acres (about 

40.5 ha.) (table 1). All plots at both sites are gridded with spikes and uniquely 

numbered caps at 100-m intervals. 

At each plot at both GAMA and BMEF we mapped and individually tagged 

(with numbered round aluminum tags nailed on the north side of the snag at dbh 
Are There Snags in the System?—Zack, George, Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 181 

height) all snags 20 cm dbh or greater and at least 1 m tall. A given tree was 

considered a snag if it was dead or clearly dying. Dying trees were detected by the 

color change in all leaves. In most all cases, the leaf color change was obvious and 

ranged from yellow to red to brown. 

Table 1―Total snags and acreage at Blacks Mountain Experimental Forest (BMEF) and at 

the Goosenest Adaptive Management Area (GAMA) sites for those plots assessed Research 

Natural Areas (RNAs) at BMEF and plot numbers at GAMA. Also noted are the total numbers 

of “yellow” pine snags (Pinus ponderosa and P. jeffreyi at BMEF, P. ponderosa only at 

GAMA) for these eastside pine sites. 

Acres Snags S/Acre1

 Pines2 P S/Ac3 Percent pine4

BMEF 

RNA C 126 389 3.09 259 2.06 66.58 

RNA B 91 723 7.95 358 3.93 49.52 

RNA D 67 700 10.45 318 4.75 45.43 

TOTAL 284 1,812 6.38 935 3.29 51.60 

 

GAMA 

Plot 4 100 181 1.81 46 0.46 25.41 

Plot 10 100 245 2.45 72 0.72 29.39 

Plot 13 100 186 1.86 24 0.24 12.90 

TOTAL 300 612 2.04 142 0.47 23.20 

1

 Snags per acre 

2

 Total Pinus pine snags 3

 Pine snags per acre 

4

 Percent of all snags that are pine. 

For each snag, we recorded the following information (snag evaluation methods 

developed by Farris and others 2002): the site (BMEF or GAMA), the plot number or 

name, the tag number applied to the snag, and the tree species of each snag 

encountered. For each snag, we measured the diameter at breast height (dbh) in cm 

and the height to the nearest decimeter (measured with use of clinometers). The 

condition of the top of the snag (intact, broken, or with multiple leaders) and the 

color of remaining leaves was recorded. The degree of branching was estimated 

(from one to four degrees of branching). The percent bark remaining to the nearest 10 

percent was recorded for each snag. Bark integrity was judged to be either tight or 

loose by examination. 

The following data were obtained to evaluate the previous history of beetle 

infestation and woodpecker foraging response. These variables were judged primarily 

on the snag from diameter-at-breast-height to about 4 meters height. We evaluated 

and categorized the number of pitch tubes seen, the number of beetle (primarily 

Dendroctonus) exit tubes observed, the number of fungal bodies on the snag 

observed (primarily Cryptoporus), and finally the number of woodpecker foraging 

sites seen. Each variable was scored into one of five categories: 0 detected, 1-10, 10-

20, 20-30, or 30+ detected. 

If the snag had bird-excavated cavities, the number was noted. We also noted if 

the cavity was likely drilled by a woodpecker or by a nuthatch (Sitta spp.), which was 

determined by the size of the hole. 
Are There Snags in the System?—Zack, George, Laudenslayer 

182 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

To determine if a given cavity was in use by a breeding bird, we monitored the 

snag for about 10-minute periods during the breeding season of 1999, as possible. We 

also used a “Tree-Peeper” extensively. The “Tree-Peeper” is a cavity-examining tool 

equipped with a small camera lens and light (at BMEF) or with an infrared camera (at 

GAMA) mounted on a telescoping set of PVC tubing. A small screen for cavity 

viewing is at the base of the apparatus. The “Tree-Peeper” was able to access almost 

all cavities up to about 15 m. We believe we detected almost all cavity use by 

breeding birds in 1999 on our snag plots with these methods in combination, with the 

likely exception of early season failed nesting efforts. In no case did we examine a 

cavity thought to have no breeding by the “Tree-Peeper” and find evidence of 

breeding. 

Results 

As expected, there were far more snags at BMEF than at GAMA (table 1).

There are more than three times as many snags (6.38/acre vs. 2.04/acre, respectively) 

of all tree species at BMEF compared to GAMA overall, and the density of Pinus

snags represents a sevenfold difference between the sites (3.29 snags/acre at BMEF, 

0.47 at GAMA, table 1). More than 50 percent of the snags at BMEF were Pinus, 

while less than 25 percent were Pinus at GAMA. 

There were also dramatic differences in the density of cavities available for 

cavity-nesting species between the two sites. We counted 0.90 snags with 

cavities/acre at BMEF compared to 0.42/acre at GAMA, and the total cavities/acre 

difference was even more pronounced (2.38 vs. 0.56, respectively; table 2).

Table 2―Snag densities with cavities and cavities per acre at BMEF and GAMA. 

Total snags Snags with cavities Snags with cavities per 

acre 

Cavities per 

acres 

BMEF 1,812 257 0.90 2.38 

GAMA 612 125 0.42 0.56 

We portray the percent of trees with cavities by species for each site in table 3. 

At BMEF, Pinus species have cavities more often than either white fir (Abies 

concolor) or incense-cedar (Calocedrus decurrens). At GAMA, although P. 

ponderosa has a higher percentage of snags with cavities than the other conifers, the 

difference between it and white fir is far less pronounced than at BMEF. The 

proportion of snags designated as “unknown” species is higher at GAMA; we 

presume most of those snags are indeed very decayed Pinus that our crews couldn’t 

discern. 
Are There Snags in the System?—Zack, George, Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 183 

Table 3―Snags with and without cavities arranged by species. “Yellow” Pinus include P. 

ponderosa and P. jeffreyi.

BMEF Snags without 

cavities 

Snags with 

cavities 

Percent of snags with 

cavities 

Abies concolor 651 48 6.87 

Calocedrus decurrens 99 7 6.60 

Yellow Pinus spp. 746 189 20.21 

Unknown 239 13 5.16 

 

GAMA 

Abies concolor 362 81 18.28 

Calocedrus decurrens 1 0 0.00 

Pinus lambertiana 13 1 7.14 

Pinus ponderosa 97 30 23.62 

Unknown 15 11 42.31 

The use of snags by cavity-nesting bird species was dramatically different 

between the sites. Thirty-one cavity-nesting pairs from 10 species were detected at 

BMEF, while only one pair each of two species were detected at GAMA (table 4).

Red-breasted nuthatches (Sitta canadensis) (seven pairs), northern flickers (Colaptes 

auratus) (six), and mountain chickadees (Poecile gambeli) (five) were the more 

commonly encountered nesting species at BMEF. Other species included whitebreasted nuthatches (S. carolinensis) (three pairs found), Williamson’s sapsuckers 

(Sphyrapicus thyroideus) (two), and single nesting pairs of American kestrel (Falco 

sparvarius), white-headed woodpecker (Picoides albolarvatus), black-backed 

woodpecker (P. arcticus), and brown creeper (Certhia americana). Two nuthatch and 

one woodpecker species nested but were not identified to species with certainty, and 

one other cavity-nesting species was not identified at all, but the nest had eggs. Only 

one nesting pair each of mountain chickadees and red-breasted nuthatch were found 

at GAMA. This fifteenfold difference is much greater than any measure of snags or 

cavities reported above. Overall, nesting use as a function of available cavities was 

surprisingly low (about 12 percent of snags with cavities used at BMEF and only 2 

percent at GAMA; table 4).

Table 4―Number of bird pairs nesting, total number of bird species nesting, and 

relationships to the number of snags and cavities at BMEF and GAMA sites. 

Total 

individual 

nests 

Total number 

of bird species 

nesting 

Nests per 

snag 

Nests per snag 

with at least 

one cavity 

Nests per total 

available 

cavities 

BMEF 31 10 0.017 0.12 0.05 

GAMA 2 2 0.003 0.02 0.01 
Are There Snags in the System?—Zack, George, Laudenslayer 

184 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

There was a tendency for cavity-nesting birds to use snags of larger size than 

snags with cavities overall, and further for cavity-bearing snags to be larger than 

snags without cavities (with size based on dbh) at BMEF (fig. 1). A similar pattern of 

snags with cavities being larger overall than snags without cavities occurred at 

GAMA as well (fig. 2). At both sites (BMEF and GAMA), the majority of snags are 

in the most decayed category (decay measured as percent bark remaining) (fig. 3).

There are weak tendencies of bark beetle activity and whether the snag has 

cavities (table 5). Recognizing that almost all “0 exit tube” entries come from snags 

that have no bark and thus the details of bark beetle activity are lost, we found that at 

both BMEF and GAMA the highest percentage of snags with cavities were those that 

had the highest counts (31+ exit tubes). More compelling is the fact that 23 out of 28 

snags that had the highest beetle exit tube counts had cavity-nesting birds at BMEF. 

Further, 20/28 snags that had nesting birds had the highest category of woodpecker 

foraging (31+ woodpecker foraging excavations) on the bark. 

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

20-39 40-59 60-79 80-99 100-119 120-139 140+

%

Snags w/o

cavities

Snags with cavities

Nesting use by birds

dbh classes (cm)

BMEF

Figure 1―Percent representation of snags without cavities (black bars), snags with 

cavities (white bars), and snags with cavity-nesting birds (gray bars) as a function of 

dbh size classes at BMEF. percent 
Are There Snags in the System?—Zack, George, Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 185 

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

20-39 40-59 60-79 80-99 100-119 120-139 140+

GAMA

Snags w/o

cavities

Snags with cavities

%

dbh classes (cm)

Figure 2―Percent representation of snags without cavities (black bars) and snags 

with cavities (white bars) at GAMA (cavity-nesting birds [N=2] not represented). 

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

Fading Leaves 85-100% Bark 50-80% Bark 20-45% Bark <20% Bark

%

BMEF

GAMA

Figure 3―Percent representation of snags in various categories of decay (portrayed 

as the percent bark remaining) at BMEF (black bars) and at GAMA (white bars). percent percent 
Are There Snags in the System?—Zack, George, Laudenslayer 

186 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 5―The relationship between beetle exit tubes detected on a snag and the occurrence of 

cavities on the snag for BMEF and GAMA. 

BMEF Total snags Snags with cavities Percent of snags with 

cavities 

0 exit tubes1 7 7 50.00 

1-10 exit tubes 27 4 12.90 

11-20 exit tubes 42 7 14.29 

21-30 exit tubes 56 11 16.42 

31+ exit tubes 624 177 22.10 

 

GAMA 

0 exit tubes1

 12 8 40.00 

1-10 exit tubes 9 3 25.00 

11-20 exit tubes 28 5 15.15 

21-30 exit tubes 37 8 17.78 

31+ exit tubes 24 10 29.41 

1 The “0 exit tubes” category includes snags with no remaining bark, thus no possibility of detecting exit 

tubes. 

Discussion 

We initiated this study to begin to quantify what would seem to be 

straightforward relationships of “snags per acre” and wildlife use. As we previously 

noted, quantifying and implementing this relationship is an essential element of forest 

management for wildlife. 

For our study, we quantified cavity-nesting bird use of cavities. The use of the 

“Tree Peeper” would allow us to detect nocturnal small mammal use (none were 

detected in cavities). As expected, we found strong differences in both snags and 

cavity-nesting birds between our two sites. At the Blacks Mountain Experimental 

Forest (BMEF), with a history of little logging and thus large stands of large 

ponderosa and Jeffrey pine, we found snags at three times the density compared to 

our Goosenest Adaptive Management Area (GAMA) site, a site with a long history 

of logging and thus few large trees. The cavity-nesting bird density was even more 

pronounced, as BMEF had 15 times the nesting pairs as GAMA (31 vs. 2 breeding 

birds in cavity nests, respectively). 

These main results, however, do not afford us a start in enumerating a “snags per 

acre” prescription in eastside pine forests for several reasons. First and foremost, the 

majority of Pinus snags in the landscape do not have cavities, so simply counting 

“snags per acre” dramatically underestimates the potential density of cavities for 

wildlife. In our study, three-fourths or more of yellow pine snags did not have 

cavities, and this disparity was true for all snag species (table 3). The seeming 

“requirement” of sapwood decay in yellow pine snags in order for woodpeckers to 

excavate cavities requires further study. Snag numbers differed dramatically between 

sites, and so did nesting bird response, but at both sites there were many available 

cavities unused. 

We feel that forest managers may well be asking a misleading question. “Snags 

per acre” requirements implicitly assume an equilibrium condition and reflect only 

one ecological requirement for a given cavity-nesting species. Our subsequent 
Are There Snags in the System?—Zack, George, Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 187 

discussion will address these concerns and indicate the direction our research is 

taking as a result. 

First, the vanishingly few cavity nesters detected on our GAMA plots is 

remarkable and suggests strongly that a consideration of foraging habitat and other 

ecological requirements must be part of the “snags per acre” management 

considerations. This is an important, but somewhat daunting proposition, as potential 

cavity-nesting species are diverse, and each species likely has very different foraging 

ecologies, as well as other differences in habitat requirements. There were an 

abundant number of unused cavities at both sites (about 88 percent of the cavitybearing snags were unused at BMEF and 98 percent at GAMA, derived from table 

4), suggesting that cavity availability is not driving the differences between sites. 

However, we have no measure of cavity “quality.” Thus, we cannot know if unused 

cavities were for some reason unusable by birds. Their interiors may have been too 

decayed, or previous use by nesting birds may have fouled the nest environs. 

The size of snags does differ between sites, with BMEF having an apparent 

abundant population of large snags, while GAMA has very few large snags (compare 

the distributions of snag dbh sizes and proportions in figs. 2, 3). As cavity nesters at 

BMEF used larger snags on average (fig. 2), it is possible that one explanation for the 

dramatic difference in cavity-nesting birds between sites is the presence of large 

snags available for nesting at BMEF, and their paucity at GAMA, even though 

excavated cavities are apparently abundant at both. This assertion cannot be a 

complete explanation, however, because there is wide variation in the height of 

cavities used (fig. 2) at BMEF and in other studies (Bu1l 1983, Cline and others 

1980, Ganey 1999, Laudenslayer this volume, Mannan and others 1980, Miller and 

Miller 1980, Moorman and others 1999, Raphael and White 1984, Scott 1978). 

Nonetheless, the loss of large trees due to logging in eastside pine and other forests, 

over the past century has major implications for cavity-nesting birds. 

A consideration of snag “demography” is also important (Bull 1983, Cline and 

others 1980, Harmon 1982, Huggard 1999, Keen 1955, Moorman and others 1999), 

as snags do not stand forever in forests, and in eastside pine they may, on the 

average, fall 8 years after tree death (Landram and others 2002). In our study, the 

majority of standing snags are very decayed (i.e., have less than 20 percent of their 

bark remaining; fig. 3). This suggests an uneven recruitment of trees into snags, such 

that it seems possible that the density of snags in our forests is declining. Clearly, 

forest managers must have a sense of snag recruitment in relationship to snag fall, 

and the patterns and processes that underlie them, when addressing wildlife needs. 

Our results suggest an intriguing connection with biological activity early in the 

decay process of snags, its relation to a snag’s eventual capacity to have cavities, and 

whether those cavities have nesting birds using them. Our collaborations (Farris and 

others 2002, Shea and others 2002) suggest that for ponderosa pine, the key to snags 

containing cavities may lie in the understanding how and if sapwood decay 

organisms are part of the decay process. In ponderosa pine, it is the sapwood (Rayner 

and Boddy 1988), not heartwood as in most other conifers, that is the tissue 

excavated by woodpeckers into nesting cavities. Experimental comparisons between 

pheromone-baited killed ponderosa pines and girdled pines (Shea and others 2002) 

reveal that far more cavities have been excavated in trees that were experimentally 

killed by bark beetles. Those results, and our correlations reported here, suggest that 

it might be that the action of bark beetle infestation and woodpecker foraging 

response increases the probability that sapwood decay organisms are part of the 
Are There Snags in the System?—Zack, George, Laudenslayer 

188 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

decay process, increasing the likelihood that a given snag may later be capable of 

cavity excavation. As only about 20-24 percent of our pine snags at both sites had 

cavities (table 3), it seems possible that sapwood decay does not occur in the majority 

of decaying snags. 

It is also important to remember that the coupling of fire and bark beetle attack 

has been dramatically disrupted in the century of fire suppression. In the context of 

snag ecology, the historical prevalence of frequent, low intensity fires in eastside pine 

has been altered to infrequent, high intensity fires (Agee 1993, Skinner and Chang 

1996), which changes how trees respond (survive or succumb) to fire (see Jackson 

and others 1999). Our understanding of bark beetles, their natural forest ecology, and 

rates of infestation (e.g., Christiansen and others 1987, Goyer and others, 1988, Ross 

and Niwa 1997) is likely incomplete because we rarely have observed the coupling of 

bark beetle activities in natural fire regimes. Certainly, the response to fires by 

woodpeckers (Blackford 1955, Koplin 1969) and how that was likely central to their 

life histories has been dramatically disrupted. These issues are interrelated and were 

likely historically intertwined in generating historical “snags per acre” levels lost in 

the past century. 

We view the understanding of these complexities to be of primary importance in 

forest management for wildlife. Our ongoing collaborative research is focused on 

efforts to reconstruct historic forest structure and fire regimes in eastside pine, 

evaluate the wildlife and bark beetle responses to prescribed fire, and understand the 

interactive ecology of snag decay (including bark beetles, woodpeckers, and sapwood 

decay onset) as it relates to the possibility of cavity excavation. We feel it crucial to 

understand snags not as entities for simple enumeration (a “snags per acre” 

prescription), but as the result of complex interactions in dynamic forests. We hope 

this research pathway affords us a view of how snags develop and proliferate in the 

eastside pine forest system.

Acknowledgments 

Our research was supported by funds from the Pacific Southwest Research 

Station, USDA Forest Service. The Goosenest District of the Klamath National 

Forest provided housing and vehicles, the Lassen National Forest also provided 

vehicles. Paul Radley, Jessica Steffen, Kathleen Bentler, Jean Claude 

Razafimahaimodison, Kevin Pietrzak, Kristie Nelson, Elizabeth Ailes, and Greg Gray 

examined all the snags for us and didn’t tell us how monotonous it was until after the 

field season. We also thank Kathy Harkensen, Kerry Farris, Patrick Shea and other 

members of our interdisciplinary teams at BMEF and GAMA for logistic support and 

wide-ranging discussions. 

References 

Agee, James K. 1993. Fire ecology of Pacific Northwest forests. Washington, DC: Island 

Press; 493 p. 

Blackford, John L. 1955. Woodpecker concentration in burned forest. The Condor 57: 28-

30. 
Are There Snags in the System?—Zack, George, Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 189 

Brawn, J. D.; Boeklen, W. J.; Balda, R. P. 1987. Investigations of density interactions 

among breeding birds in ponderosa pine forests: correlative and experimental 

evidence. Oecologia 72: 348-357. 

Brawn, Jeffrey D.; Balda, Russell P. 1988. Population biology of cavity nesters in northern 

Arizona: do nest sites limit breeding densities? The Condor 90: 61-71. 

Bull, E. L. 1983. Longevity of snags and their use by woodpeckers. In: Davis, J. W.; 

Goodwin, G. A.; Ockenfels, R. A., eds. Snag habitat management symposium. 1980 

June 7-9; Flagstaff, AZ.: Gen. Tech. Rep. RM-GTR-99. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 64-67. 

Bull, E. L.; Parks, C. G.; Torgersen, T. R. 1997. Trees and logs important to wildlife in the 

Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture: 55 

p. 

Christiansen, Erik; Waring, Richard H.; Berryman, Alan. 1987. Resistance of conifers to 

bark beetle attack: searching for general relationships. Forest Ecology and 

Management 22: 89-106. 

Cline, Steven P.; Berg, Alan B.; Wight, Howard M. 1980. Snag characteristics and 

dynamics in Douglas-fir forests, western Oregon. Journal of Wildlife Management 

44: 733-786. 

Covington, W. W.; Moore, M. M. 1994. Southwestern ponderosa forest structure, changes 

since Euro-American settlement. Journal of Forestry (January) 39-47.\ 

Farris, Kerry L.; Garton, Edward O.; Heglund, Patricia J.; Zack, Steve; Shea, Patrick J. 2002. 

Woodpecker foraging and the successional decay of ponderosa pine. In: 

Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. 

Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the symposium on the 

ecology and management of dead wood in western forests. 1999 November 2-4; Reno, 

NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; [this volume]. 

Ganey, Joseph L. 1999. Snag density and composition of snag populations on two 

National Forests in northern Arizona. Forest Ecology and Management 117: 169-178. 

Goyer, Richard A.; Wagner, Michael R.; Schowalter, Timothy D. 1998. Current and 

proposed technologies for bark beetle management. Journal of Forestry 95: 29-33. 

Harmon, Mark E. 1982. Decomposition of standing dead trees in the Southern 

Appalachian Mountains. Oecologia 52: 214-215. 

Harrod, Richy J.; McRae, Bradner H.; Hartl, William E. 1999. Historical stand 

reconstruction in ponderosa pine forests to guide silvicultural prescriptions. Forest 

Ecology and Management 114: 433-446. 

Horton, Scott P.; Mannan, R. William. 1988. Effects of prescribed fire on snags and cavitynesting bird in southeastern Arizona pine forests. Wildlife Society Bulletin 16: 37-

44. 

Huggard, David J. 1999. Static life-table analysis of fall rates of subalpine fir snags. 

Ecological Applications 9: 1009-1016. 

Jackson, James F.; Adams, Dean C.; Jackson, Ursula B. 1999. Allometry of constitutive 

defense: a model and comparative test with tree bark and fire regime. American 

Naturalist 153: 614-632. 

Keen, F. P. 1955. The rate of natural falling of beetle-killed ponderosa pine snags. Journal 

of Forestry 53: 720-723. 
Are There Snags in the System?—Zack, George, Laudenslayer 

190 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Koplin, James R. 1969. The numerical response of woodpeckers to insect prey in a 

subalpine forest in Colorado. Condor 71: 436-438. 

Landram, F. Michael; Laudenslayer, William F., Jr.; Atzet, Thomas. 2002. Demography of 

snags in eastside pine forests of California. In: Laudenslayer, William F., Jr.; Shea, 

Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Mannan, R. William; Meslow, E. Charles; Wight. Howard W. 1980. Use of snags by birds in 

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44: 787-797. 

Martin, Kathy; Eadie, John M. 1999. Nest webs: a community-wide approach to the 

management and conservation of cavity-nesting forest birds. Forest Ecology and 

Management 115: 243-257. 

Mast, Joy Nystrom; Fule, Peter Z.; Moore, Margaret M.; Covington, W. Wallace; Waltz, Amy 

E. M. 1999. Restoration of presettlement age structure of an Arizona ponderosa 

pine forest. Ecological Applications 9: 228-239. 

McClellan, B. Riley; Frissell, Sidney S. 1975. Identifying forest snags useful for holenesting birds. Journal of Forestry 73: 414-417. 

McComb, William C.; Bonney, Stephen A.; Sheffield, Raymen M.; Cost, Noel D. 1986. Snag 

resources in Florida – are they sufficient for average populations of primary cavitynesters? Wildlife Society Bulletin 14: 40-48. 

Miller, E.; Miller, D. R. 1980. Snag use by birds. In: Degraaf, R. M., ed. Management for 

non-game birds. Gen. Tech. Rep. INT-GTR-86. Ogden, UT: Intermountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 337-356. 

Moorman, Christopher E.; Russell, Kevin R.; Sabin, Guy R.; Guynn, David C. Jr. 1999. Snag 

dynamics and cavity occurrence in the South Carolina Piedmont. Forest Ecology 

and Management 118: 37-48. 

Morrison, Michael L.; Dedon, Mark F.; Raphael; Martin G.; Yoder-Williams, Michael P. 

1986. Snag requirements of cavity-nesting birds: are USDA Forest Service 

guidelines being met? Western Journal of Applied Forestry 1: 38-40. 

Ohmann, Janet L.; McComb, William C.; Zumrawi, Abdel Azim. 1994. Snag abundance for 

primary cavity-nesting birds on nonfederal forest lands in Oregon and 

Washington. Wildlife Society Bulletin 22:607-620. 

Oliver, W. W.; Powers, R. F. 1998. Blacks Mountain, California: interdisciplinary field 

research in ponderosa pine. Journal of Forestry 96: 4-9. 

Raphael, Martin G.; White, Marshall. 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada. Wildlife Monographs 86: 1-66. 

Rayner, A. D. M.; Boddy, L. 1988. Fungal decomposition of wood: its biology and ecology. 

New York: John Wiley and Sons; 587 p. 

Ross, Darrell W.; Niwa, Ghrisine G. 1997. Using aggregation and antiaggregation 

pheromones of the Douglas-fir beetle to produce snags for wildlife habitat. Western 

Journal of Applied Forestry 12: 52-54. 

Schepps, Jake; Lohr, Steve; Martin, Thomas E. 1999. Does tree hardness influence nest-tree 

selection by primary cavity nesters? The Auk 116: 658-665. 

Schreiber, B.; deCalesta, D.S. 1992. The relationship between cavity-nesting birds and 

snags on clearcuts in western Oregon. Forest Ecology and Management 50: 299-316. 
Are There Snags in the System?—Zack, George, Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 191 

Scott, Virgil E. 1978. Characteristics of ponderosa pine snags used by cavity-nesting 

birds in Arizona. Journal of Forestry 76: 26-28. 

Scott, Virgil E. 1979. Bird response to snag removal in ponderosa pine. Journal of Forestry 

77: 26-28. 

Shea, Patrick; Laudenslayer, William F., Jr.; Ferrell, George; Borys, Robert. 2002. Girdled 

versus bark beetle-created ponderosa pine snags: utilization by cavity-dependent 

species and differences in decay rate and insect diversity. In: Laudenslayer, William 

F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas 

E., technical coordinators. Proceedings of the symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; [this volume]. 

Skinner, C. N.; Chang, C.-R. 1996. Fire regimes, past and present. In: Sierra Nevada 

ecosystem project: Final report to Congress, Vol. II. Assessments and scientific basis for 

management options. Davis, CA: University of California, Davis. 

Thomas, J. W.; Anderson, R. G.; Maser, C.; Bull, E. L. 1979. Snags. In: Thomas, J. W., ed. 

Wildlife habitats in managed forests: the Blue Mountains of Oregon and Washington. 

Agric. Handb. 553. Washington, DC: U.S. Department of Agriculture; 60-77. 

Zack, Steve; Laudenslayer, W. F.; George, T. L.; Skinner, C.; Oliver, W. 1999. A prospectus 

on restoring late successional forest structure to eastside in ecosystems through 

large-scale, interdisciplinary research. In: Cook, J. E.; Oswald, B.P., compilers. First 

Biennial North American Forest Ecology Workshop. Forest Ecology Working Group, 

Society of American Foresters; 343-355. 

Zarnowitz, Jill E.; Manuwal, David A. 1985. The effects of forest management on cavitynesting birds in northwestern Washington. Journal of Wildlife Management 49: 255-

263. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 193 

Distribution Patterns of Birds Associated 

with Snags in Natural and Managed Eastern 

Boreal Forests1

Pierre Drapeau,2 Antoine Nappi,2 Jean-François Giroux,2 Alain 

Leduc,2 and Jean-Pierre Savard3

Abstract 

In boreal forests, several bird species use standing dead trees for feeding or nesting and 

depend on them for their survival. Studies on wildlife use of snags have shown that their 

availability is greatly influenced by the age of the forest and the type of perturbation (natural 

versus anthropogenic). Accordingly, cavity-nesting birds seem largely affected by these 

changes in availability of snags. In North American boreal forests, relationships between birds 

and dead wood availability have predominantly been documented in western forests. The 

dynamics of dead wood and the distribution patterns of birds associated with this habitat 

feature remain largely unknown in eastern black spruce forests. Distribution patterns of birds 

associated with dead wood were documented in the eastern black spruce forest of 

northwestern Quebec, Canada. Study areas were composed of four forest landscapes (50-100 

km2

) that were naturally disturbed by different fire events (1 year, 20 years, 100 years and > 

200 years) and two logged landscapes (20 years, 80 years). Birds were surveyed by point 

counts. Overall, 348 point counts were distributed over the six forest landscapes. Vegetation 

plots centered at each point count were used to sample live trees and dead wood. In naturally 

disturbed forest landscapes, species richness and abundance cavity-nesting birds reached a 

peak in early post-fire and in mature forest landscapes. Standing dead wood availability and 

abundance patterns of cavity-nesting birds were significantly less in 20-year-old managed 

forests landscapes than in those of naturally disturbed forests landscapes. This pattern was 

persistent in mature forests comparisons between 80-year-old horse-logged second-growth 

forests and mature forests of post-fire origin. Our results suggest that old-growth forests in 

this portion of the eastern black-spruce forest ecosystem do not play a key role for cavitynesting birds. Mature and over-mature stands are, however, key habitats for many species of 

secondary cavity nesters, whereas early post-fire stands are key habitats for primary cavitynesting birds and represent the main source of recruitment for standing dead wood in this 

ecosystem. Changes in silvicultural practices designed to maintain specific structure of overmature stands (increased partial cutting) may provide a means for maintaining cavity-nesting 

birds at the landscape scale. Intensification of salvage cutting in early post-fire landscapes is 

another serious concern in black spruce forests. Reduction in the overall availability of dead 

wood through such forest practice may affect populations of some primary cavity nesters that 

are restricted to this specific forest type. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Professor, Graduate Student, Professor, and Research Scientist, respectively, Groupe de Recherche en 

Écologie Forestière Interuniversitaire, Département de Sciences Biologiques, Université du Québec à 

Montréal, C.P. 8888, succ. Centre-ville, Montréal, Québec, Canada, H3C 3P8 (e-mail address: 

drapeau.pierre@uqam.ca). 

3

 Research Scientist, Canadian Wildlife Service, Quebec Region, C.P. 10100, 1141 route de l’Église, 

Ste-Foy, Québec, Canada G1V 4H5.
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

194 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Introduction 

In the boreal forest ecosystem, large-scale natural disturbances, especially fires, 

have historically played a major role in determining the structure of boreal forest 

landscapes (Anglestam 1996, Bergeron 1991, Johnson 1992, Van Wagner 1978). In 

the last 40 years, however, commercial timber management has become the prevalent 

perturbation in many parts of the boreal forest (Anglestam 1996, Enoksson and others 

1995, Franklin and Forman 1987, Spies and others 1994). Although forest 

management may show some similarities with natural disturbances (fire and insect 

outbreaks) to which organisms are adapted, there are important differences between 

these two types of disturbances. Cutting rates are generally shorter than natural 

disturbance cycles (Gauthier and others 1996, Spies and others 1994) and more 

severe in terms of live trees and coarse woody debris that remain after logging (Spies 

and others 1994). Hence, in industrial forest landscapes, concerns regarding the issue 

of biodiversity have identified two important aspects: changes in the age structure of 

forests, and whether managed forests successfully substitute for unmanaged forests 

for maintaining biodiversity (Franklin 1993, Hansen and others 1991, Hejl and others 

1995)—particularly in their capacity to maintain key environmental attributes such as 

coarse woody debris. 

Until now, most knowledge on forest ecosystems biodiversity and how it relates 

to key habitats such as over-mature and old-growth stand types or key stand attributes 

such as density and quality of standing dead wood and fallen logs has mainly come 

from studies conducted in the Pacific Northwest forest (Hansen and others 1991, 

1995a,b; Lamberson and others 1992; McGarrigle and McComb 1995; Spies and 

others 1988). Recommendations and management guidelines for sustainable forestry 

in this biome are not necessarily applicable in the eastern boreal forest. Moreover, as 

noticed by Freedman and others (1994), the status of forest types (by age-class) in 

eastern Canada and their contribution to biodiversity across landscapes remains 

poorly documented. Comprehensive efforts to assess the state of forest types and 

their contribution to biodiversity in the eastern boreal forest are critical. Coincident 

with these efforts, the question of how well managed forests substitute for natural 

forests is linked to quantitative field investigations that focus on whether key 

differences exist in biodiversity patterns between managed forests and naturally 

disturbed forests, and on how critical these differences are to the maintenance of 

regional biodiversity. For instance, in the eastern boreal black spruce forest, 

comparatively little information exists on responses of birds associated with dead 

wood. Does the general pattern of increased structural complexity of the forest as it is 

aging still hold for landscapes dominated by black spruce stands? Do the quantity and 

quality of dead wood show the same patterns of variation with forest age that has 

been documented in western coniferous forests? How do birds respond to changes in 

dead wood availability across time? Even though it is well recognized that standing 

dead wood is far less abundant in forests that were logged than they are in forests that 

regenerate from fire, what is the magnitude of differences in density of snags and in 

bird species’ abundance? To tackle these issues, ecological investigations must 

incorporate both stand and landscape level approaches (Freedman and others 1994, 

Hejl and others 1995, Thompson and others 1995). 

In this paper, we document distribution patterns of birds associated with snags in 

the eastern black spruce forest of northwestern Quebec, Canada. We examine 

abundance patterns across broad gradients in forest age and management history in 

four forest landscapes (50-100 km2

) that were naturally disturbed by different fire 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 195 

events (1 year, 20 years, 100 years and > 200 years) and in two timber harvested 

landscapes (20 years, 80 years). The first objective of this study is to document and 

explain the distribution patterns of birds associated with standing dead wood in 

naturally disturbed forest landscapes. The second objective is to evaluate some of the 

effects of forest management on this avian guild by comparing bird patterns and 

standing dead wood availability between natural and managed forest landscapes. 

Study Area 

The study was undertaken in the eastern black spruce forest in the northwestern 

part of the Abitibi region in Québec (49°13’17” to 49°51’05”; 78°38’35” to 

79°23’13”) and in the Abitibi Lake Model Forest (49°03’33” to 49°42’20”; 

80°09’03” to 80°38’35”) in Ontario (fig. 1). These regions are part of the northern 

Clay Belt, a broad physiographic unit characterized by lacustrine deposits from the 

proglacial lakes Barlow and Ojibway (Vincent and Hardy 1977). Clay soils are 

predominant in the region, the topography is relatively flat, and the forest mosaic is 

dominated by stands of black spruce (Picea mariana). Jack pine (Pinus banksiana) is 

dominant on drier sites such as outwash deposits, old beaches, and eskers (Rowe 

1972). 

Figure 1—Location of the study area in the Quebec-Ontario eastern boreal black 

spruce forest. 

Even though industrial forestry is increasingly shaping the present forest 

landscape, a large proportion of the forest cover is under a natural disturbance 

regime. Dendrochronological reconstructions of fire events indicate that natural fire 

frequency has decreased in the last 150 years (Bergeron and others 1998, 1999b). 

This decrease is responsible for the presence of large tracks of over-mature and oldgrowth forests in the study region. For the Quebec section of our study area, 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

196 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

industrial timber harvesting was initiated in the early 1970s, whereas even-aged 

management is the dominant silvicultural system with clearcutting as the main 

forestry practice. In Ontario, some areas have been horse-logged in the 1920s. As in 

many other regions of the Canadian boreal forest, clearcutting is followed by planting 

and seeding in 20 percent of the area, whereas 80 percent of logged areas are under 

natural regeneration (Haddon 1997). 

Methods 

Study Design 

Our study sites were within an area where a large (25,000 km2) fire history 

reconstruction project has been ongoing between the 48th and the 50th degrees of 

latitude along a south-north transect (Bergeron and others 1999b). A stand initiation 

map at the scale of 1:250,000 was constructed using either archives and aerial 

photographs (some dating from the 1930s) to delineate fires during the 20th century, 

or dendrochronology records of cored trees for older fires. We used forest cover 

maps and the fire history reconstruction map by Bergeron and others (2001) to 

delineate six forest landscapes (100 to 250 km2

) that originated from different fire 

events (1 year, 20 years, 100 years and > 200 years) or logging events (20 years 

clear-cut and 80 years horse-logged). The forest cover maps and aerial photographs 

(for horse-logged forests) allowed us to identify the location of timber harvested 

areas, the time when they were harvested, and the location of access roads. 

In each landscape, sampling stations were grouped by line transects to maximize 

time spent sampling, minimize time traveling between sites, and include inter-stand 

heterogeneity of forest mosaics. Four to six stations were located along line transects 

1.2 to 2.5 km long. Line transects were separated by at least 1 km. Distance between 

stations varied from 350 to 450 m ensuring independence between stations (Bibby 

and others 1992). Each station was within a relatively homogeneous black spruce 

forest type. Overall, 348 sampling stations along 80 line transects provided extensive 

coverage of the study area. 

Bird Sampling 

The point count method was used to sample bird populations at each sampling 

station (Blondel and others 1970, 1981, Ralph and others 1995). Sampling was 

initiated at dawn and was conducted until 9:00 (EST). Data on bird species 

occurrence and abundance were recorded within a fixed radius of 75 m and over an 

unlimited distance around each station. Sampling stations were visited twice during 

the breeding season of 1997 and 1998: once in the first half and once in the second 

half of June. On each visit, birds (seen or heard) were recorded at 5-min intervals for 

a 20-min period. The sampling sequence varied so that each station was visited once 

at dawn and once later in the morning to maximize detection probabilities of each 

species present. 

Sampling procedure adopted in this study with regard to the number of visits, 

the spacing of visits during the breeding season, the hourly periods appropriate for 

sampling, and count duration were based on a methodological study on the efficiency 

of the point count method in characterizing bird communities (Drapeau and others 

1999a). The maximum count on either one of the two visits was used to estimate the 

relative abundance of each species at each station. Bird censuses were conducted in 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 197 

comparable weather conditions, under clear and partly cloudy sky, and when wind 

speed generally did not exceed 8 km per hour. Counts were interrupted when wind 

speed exceeded 16 km per hour and when raining. Each sampling station was visited 

in only 1 of the 2 years. 

Habitat Variables 

Habitat measurements were centered on the bird sampling station. From midJuly to mid-August of each year, features of vegetation structure and composition of 

live trees and dead wood were measured at each sampling station within a single 

triangular plot of 40 m per side covering a sampled area of 700 m2

. For dead wood, 

measures of both standing dead wood and fallen logs were recorded in each plot. In 

this paper, emphasis is put on relationships between birds and standing dead wood. 

Hence, only methods for snags are presented. 

Diameter at breast height (DBH) was recorded for all standing dead trees (snags) 

> 1.3 m tall in all plots. For each snag, decay stage was recorded using three 

variables: crown condition, bark, and wood condition. Crown condition was 

estimated by using the following classes: (1) all foliage, twigs and branches present; 

(2) some or all foliage lost, possibly some twigs lost, all branches usually present, 

possible broken top; (3) no foliage, up to 50 percent of twigs lost, most branches 

present, possible broken top; (4) no foliage, up to 50 percent of branches lost, top 

usually broken; (5) most branches gone, some sound branch stubs remain, top 

broken; (6) no branches, some sound and rotting branch stubs, top broken; and (7) no 

branches, minimum of rotting branch stubs, top broken. 

Bark retention was determined using the following classes: (1) all bark present, 

(2) 1-5 percent bark lost, (3) 5-25 percent bark lost, (4) 26-50 percent bark lost, (5) 

51-75 percent bark lost, and (6) >76 percent bark lost. Wood condition was assessed 

as follows: (1) no decay, (2) probable limited internal decay and wood essentially 

hard, limited decay, (3) wood mostly hard but decay spreading, soft wood present (4) 

balance of hard and soft wood (5) more soft wood than hard wood, (6) no more hard 

wood, and (7) hollow shell. Wildlife tree use, i.e., feeding activities (small holes 

and/or bark flaking) and nesting activities (nesting cavities) were also recorded for 

each of snag. These marks were identified to the bird species when possible. 

Data Analyses 

To assess the overall stage of decay of standing dead wood, we used principal 

components analysis (PCA) (Legendre and Legendre 1998) to derive a single 

component variable that best describes the decomposition stage of each snag and that 

can provide a quantitative value of the mean stage of decay of snags in each sampling 

station. The first principal component accounted for 69 percent of the variance of the 

set of decay variables. PCA1 was partitioned into three equidistant classes of decay 

that will be used in further analyses. 

Comparisons among landscapes were conducted for species groups, such as (1) 

all cavity-nesting birds, (2) primary, and (3) secondary cavity-nesters. Species were 

grouped on the basis of their ability to excavate trees or to use holes excavated by 

other species. Relationships between these species groups and forest landscape types 

were determined using Kruskal-Wallis tests (Sokal and Rohlf 1981). 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

198 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Differences between forest landscapes in mean availability (basal area) and 

decay stages of snags were evaluated using Kruskal-Wallis tests. For all significant 

Kruskal-Wallis tests, a Student-Newman-Keuls’s (SNK) pairwise comparison 

procedure was used a posteriori to determine which landscapes showed significant 

differences. All analysis were performed using SAS (SAS Institute Inc. 1990). The 

significance level of each test was 0.05. Even though we counted birds with both 

limited (75 m radius) and unlimited distance (> 75 m) count points, data analyses 

were performed only with birds registered within 75 m of sampling stations centers. 

Results 

Habitat Distribution of Birds at the Guild Level 

Overall, 94 species were detected across the 348 sampling stations. Half of these 

species were uncommon; 52 were detected in more than 5 percent of the sampling 

stations. Across landscapes the ratio of species associated with standing dead wood 

for nesting and feeding (hereafter cavity-nesting birds, CNB) peaked at 15 percent. 

Along the gradient of time since fire, CNB’s reached a peak in early post-fire forests 

and in the mature forest landscape (fig. 2). The ratio of primary cavity nesters 

(PCNB) was highest in the early post-fire landscape, whereas the ratio of secondary 

cavity nesters (SCNB) peaked in the mature forest landscape, but was also important 

in old-growth forests. PCNB birds were absent in the old-growth forest landscape. 

Figure 2—Distribution of cavity-nesting birds (CNB), primary cavity nesters (PCNB) 

and secondary cavity nesters (SCNB) in four natural landscapes that cover a time 

since fire gradient from early post-fire to old-growth forest types in the eastern boreal 

black spruce forest in Abitibi, Québec. For each category of birds, significant 

differences (P < 0.05) for mean values (± 1 SE) between landscapes are indicated by 

different letters. 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 199 

Changes in Standing Dead Wood over Time since Fire 

Significant differences in standing dead wood availability were observed among 

forest landscapes (fig. 3). Availability of snags was highest in the 1-year post-burned 

forest landscape and was lowest in the old-growth forest landscape (fig. 3).

Landscapes burned 20 years and 100 years (mature forests) were similar with 

intermediate values. 

Figure 3—Changes in availability of standing dead wood in relation to forest 

landscapes’ time since last fire in the eastern boreal black spruce forest in Abitibi, 

Québec. Significant differences (P < 0.05) for mean values (± 1 SE) among 

landscapes are indicated by different letters. 

The decomposition stage of snags varied significantly among forest landscapes 

(Kruskal-Wallis: χ2

 = 27.7, df = 3, P = 0.001 ). The majority of standing dead trees 

were scarcely decayed in the early post-fire landscape, whereas the 20-year burned 

landscape showed the highest proportion of highly decayed snags (fig. 4). Decay 

stages of dead trees were similar between the mature and the old-growth forest 

landscapes. In these landscapes, the largest proportion of standing dead trees were in 

the intermediate decay class (fig. 4).

Birds and Dead Wood in Managed Forests 

Comparisons between managed and natural forest landscapes were conducted 

for two time periods: 20 years after disturbance and 80 to 100 years after disturbance. 

Mean basal areas of snags > 5 cm were significantly higher in both 20 and 100 year 

post-burned landscapes than in logged forests (fig. 5a). The proportion of birds 

associated to snags was also higher in post-burned landscapes than in their logged 

counterpart for both time periods (20 years and > 80 years after disturbance). The 

only comparison that showed no significant difference was with the proportion of 

primary cavity nesters in the 20-year-old logged and burned landscapes (fig. 5b). 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

200 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 4—Decay stage of standing dead wood in relation to forest landscapes’ time 

since last fire in the eastern boreal black spruce forest in Abitibi, Québec. Decay 

classes (Dec 1= weakly decayed, Dec 2= intermediate, Dec 3= highly decayed) were 

derived using scores on the first axis of a PCA conducted on the set of decay 

variables for standing dead trees. 

Discussion 

Old-growth forests are usually considered key habitats for wildlife due to the 

overall increase in complexity of forest structure, amount of dead wood, and 

increases in live and dead tree diameter (Probst and others 1992, Raphael and White 

1984). Our results show that in the black spruce forest, this age-class type does not 

have the same importance in the distribution of birds associated with dead wood than 

what has been suggested by other studies. For instance, no primary cavity-nesting 

birds were detected in the old-growth forest landscape, and the importance of 

secondary cavity-nesting birds in these forests was mainly related to Winter Wren’s 

(Troglodytes troglodytes) abundance, which in our study area was widespread across 

the age-class gradient sampled (Drapeau and others 1999b). Coincident with these 

results, data on the mean basal area of snags was at its lowest in the old-growth forest 

landscape. Thus, snag availability was significantly reduced in old-growth forests, in 

particular for the larger snags (>15 cm dbh) that are significantly more likely to show 

evidence of feeding and nesting use by birds (Hutto 1995, Nappi 2000) than are 

smaller trees. This may explain why primary nesting birds were absent in the oldgrowth landscape. Our results suggest that old-growth forests in this portion of the 

boreal forest ecosystem may not play a key role for cavity-nesting birds. This is 

contrary to Shieck and others (1995) findings on the importance of old-growth stands 

for birds that nest in tree cavities in aspen-dominated boreal forests in Alberta. The 

importance of old-growth forests for birds may change depending on forest 

ecosystem or geographic area. In a recent review on silviculture and Rocky Mountain 

forest birds, Hejl and others (1995) found that assigning species as old-growth 

associates is not an easy task. They also found that even though some species were 

more abundant in some old-growth forests of the Rocky Mountains, none of these 

species were consistently more abundant in all old-growth forests among the studies 

they compared. 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 201 

Figure 5—Distribution of (a) standing dead wood and (b) cavity-nesting birds in postlogged and post-burned forests in the eastern boreal black spruce forest in Abitibi, 

Québec. Significant differences (P < 0.05) between means (± 1 SE) for combinations 

of age-related harvested and naturally disturbed landscapes are indicated by 

different letters. 

Comparisons among all four natural forest landscapes showed highest 

occurrence of primary cavity nesters (woodpeckers) and secondary cavity nesters in 

recently-burned forests and mature to over-mature stands, respectively. In early postfire forests some species, like the black-backed woodpecker (Picoides arcticus), were 

not only more abundant but were restricted in their habitat distribution (Nappi 2000). 

Distribution of this woodpecker species in eastern boreal forests is thus consistent 

with Hutto’s (1995) and Saab and others (1998) results in northern Rocky Mountain 

coniferous forests. Across their range, black-backed woodpeckers seem to be 

specialists of recently burned forests. The abundance of secondary cavity nesters 

reached its peak in mature to over-mature forests possibly because this age-class had 

a higher density of large live trees (> 20 cm) with few large snags, which may 

provide the combination of habitat characteristics that is important for species like 

the red-breasted nuthatch (Sitta canadensis), the brown creeper (Certhia americana),

and the boreal chickadee (Poecile hudsonicus). Ratio CNB/All Species 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

202 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Quantity and quality of standing dead trees also indicate that early post-fire 

forests are key habitats for snag recruitment. This is not surprising in boreal systems 

where trees killed by fire is clearly a major source of dead wood. The importance of 

recently burned forests in our study area is, however, exacerbated by the fact that, in 

contrast to other forest ecosystems, the basal area or snags did not increase in our 

old-growth forests but was significantly less than in mature forests (Clark and others 

1998, Tyrrell and Crow 1994). 

Comparisons between logged and burned forest landscapes suggest that even 

though the availability of snags is low in natural landscapes at these time periods (20 

and 100 years), clearcutting is not only significantly reducing the amount of snags 

but also the proportion of cavity-nesting birds. Secondary cavity nesters are 

particularly reduced in these forest age-classes. Retention of snags and living trees in 

black spruce forests during timber operations should be given more attention in 

future managed landscapes. 

Management Implications 

Although forest management’s main objective is to perpetuate forests not to 

convert them to other land uses as with other human disturbances (Hejl and others 

1995), it may nevertheless alter the composition and structure of forest mosaics and 

hence biodiversity in the long term. In eastern boreal mixed-wood forests, large-scale 

conversion of mature forests from mixed-wood to deciduous cover due to the impacts 

of industrial logging on vegetation regeneration (Carleton and McLellan 1994) 

coupled with short timber rotations (Spies and others 1994, Gauthier and others 

1996) may jeopardize the ecological integrity of bird communities (Drapeau and 

others 2000). In the black spruce forest, even though tree species composition will 

not be affected by short rotations, changes in the structural complexity are expected, 

notably in the overall decrease of over-mature and old-growth forests (Bergeron and 

others 1999a). Although our results are not consistent with those of other studies as 

for the importance of old-growth forests for cavity-nesting birds, they nevertheless 

raise concerns on the future of mature and over-mature stands that are key habitats 

for many species of secondary cavity nesters. For our study area, Bergeron and others 

(1999a) have showed that the natural forest stand age distribution follows a negative 

exponential with over 23 percent of the stands in intermediate stage (between 100–

200 years). Hence, even though old-growth forests are not as important for birds as 

they are in other forest biomes, the dramatic reduction in the proportion of 

intermediate-aged seral stages in black spruce forests under normal rotations may 

pose a serious threat to bird communities. 

Changes in bird communities we observed may be attenuated, provided that 

current forestry practices are modified in managed forest landscapes. The use of 

silvicultural practices designed to maintain specific structure of intermediate-aged 

stands may provide a means for maintaining species of secondary cavity nesters. For 

instance, diversified forest practices including partial cutting and careful logging that 

simulates the natural evolution of over-mature black spruce stands could be used to 

maintain an equivalent proportion of forests stands that retain intermediate-aged 

stand characteristics across the landscape (Bergeron and others 1999a). 

Finally, given the major contribution of recently burned forests, both as a key 

habitat for primary cavity-nesting birds and as the main source of recruitment for 

dead wood, the intensification of salvage cutting raises serious concerns in black 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 203 

spruce forests. It not only may compromise the maintenance of viable populations for 

species that require this specific forest type, but it may reduce the overall availability 

of dead wood to wildlife across current and future landscapes. 

Acknowledgments 

This research was supported by the National Centers for Excellence on 

Sustainable Forest Management, the Quebec Ministry of Natural Resources, the 

Canadian Wildlife Service (Quebec region), and the Lake Abitibi Model Forest. We 

thank Réjean Deschênes, Daniel Brongo, Simon Bérubé, Emmanuel Milot, François 

Gagnon and Julie Fortin for their assistance during fieldwork. Marc-André Villard 

and Yves Bergeron made helpful suggestions on previous versions of the manuscript. 

References 

Anglestam, Per A. 1996. The ghost of forest past—natural disturbance regimes as a basis 

for reconstruction of biologically diverse forests in Europe. In: DeGraaf, R. M.; 

Miller, R. I., editors. Conservation of faunal diversity in forested landscapes. New York, 

NY: Chapman and Hall; 287-337. 

Bergeron, Yves. 1991. The influence of island and mainland lakeshore landscapes on the 

boreal forest fire regimes. Ecology 72: 1980-1992. 

Bergeron, Yves; Gauthier, S., Kafka, V., Lefort, P., Lesieur, D. 2001. Natural fire frequency 

for the eastern Canadian boreal forest: consequences for sustainable forestry.

Canadian Journal of Forrest Research 31: 384-391. 

Bergeron, Yves; Richard, P. J. H.; Carcaillet, C.; Gauthier, S.; Flannigan, M.; Prairie, Y. T. 

1998. Variability in fire frequency and forest composition in Canada's southeastern 

boreal forest: a challenge for sustainable forest management. Conservation Ecology 

[serial online] 12. Article available at: http://www.consecol.org/vol2/iss2/art6. 

Bergeron, Yves; Harvey, B.; Leduc, A.; Gauthier, S. 1999a. Forest management guidelines 

based on natural disturbance dynamics: stand- and forest-level considerations.

Forestry Chronicle 75: 1-6. 

Bergeron, Yves; Gauthier, S.; Carcaillet, C.; Flannigan, M.; Richard, P. J. H. 1999b. 

Reconstruction of recent and Holocene fire chronologies and associated changes in 

forest composition: a basis for forest landscape management. Scientific Report # 

1999-16. Edmonton, Alberta: Network of Centres of Excellence. Sustainable Forest 

management network. University of Alberta. 

Bibby, Colin, J., Burgess, N. D.; Hill, D. A. 1992. Bird census techniques. Academic Press. 

San Diego, California. 

Blondel, Jacques; Ferry, C.; Frochot, B. 1970. La méthode des indices ponctuels 

d’abondance (I.P.A.) ou des relevés d’avifaune par “stations d’écoute.” Alauda 38: 

55-71. 

Blondel, Jacques; Ferry, C.; Frochot B. 1981. Point counts with unlimited distance. Studies 

in Avian Biology 6: 414-420. 

Carleton, Terence, J.; McLellan, P. 1994. Woody vegetation responses to fire versus clearcutting logging: A comparative survey in the central Canadian boreal forest.

Ecoscience 1: 141-152. 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

204 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Clark, Donald, F.; Kneeshaw, D. D.; Burton, P. J.; Antos, J. A. 1998. Coarse woody debris 

in sub-boreal spruce forests of west-central British Columbia. Canadian Journal of 

Forest Research 28: 284-290. 

Drapeau, Pierre; Leduc, A.; McNeil, R. 1999a. Refining the use of point counts at the scale 

of individual points in studies of bird-habitat relationships. Journal of Avian Biology 

30: 367-382. 

Drapeau, Pierre; Bergeron, Y.; Harvey, B. 1999b. Key factors in the maintenance of 

biodiversity in the boreal forest at local and landscape scales. In: Veeman, T. S.; 

Smith, D. W.; Purdy, B. G.; Salkie, F. J.; Larkin, G. A., editors. Edmonton: Alberta SFM 

Network Conference 1999; 52-57. 

Drapeau, Pierre; Leduc, A.; Giroux, J.-F.; Savard, J.-P.; Bergeron, Y.; Vickery, W. L. 2000. 

Landscape-scale disturbances and changes in bird communities of boreal mixedwood forests. Ecological Monographs 70: 423-444. 

Edenius, Lars; Elmberg, J. 1996. Landscape level effects of modern forestry on bird 

communities in North Swedish boreal forests. Landscape Ecology 11: 325-338. 

Enoksson, Bodil; Anglestam, P.; Larsson, K. 1995. Deciduous forest and resident birds: the 

problem of fragmentation within coniferous forest landscape. Landscape Ecology 

10: 267-275. 

Franklin, Jerry F.; Forman, R. T. 1987. Creating landscape patterns by forest cutting: 

ecological consequences and principles. Landscape Ecology 1: 5-18. 

Franklin, Jerry F. 1993. Preserving biodiversity: species, ecosystems, or landscapes. 

Ecological Applications 3: 202-205. 

Freedman, Bill; Woodley, S.; Loo, J. 1994. Forestry practices and biodiversity, with 

particular reference to the Maritime Provinces of eastern Canada. Environmental 

Review 2: 33-77. 

Gauthier, Sylvie; Leduc, A.; Bergeron, Y. 1996. Forest dynamics modeling under natural 

fire cycles: a tool to define natural mosaic diversity for forest management. 

Environmental Monitoring and Assessment 39: 417-434. 

Haddon, Brian. 1997. The status of forest regeneration in Canada. Forestry Chronicle 73: 

586-589. 

Hansen, Andrew J.; Spies, T. A.; Swanson, F. J.; Ohmann, J. L. 1991. Conserving 

biodiversity in managed forests, lessons from natural forests. BioScience 41: 382-

392. 

Hansen, Andrew J.; Garman, S. L.; Weigand, J. F.; Urban, D. L.; McComb, W. C.; Raphael, 

M. G. 1995. Alternative silvicultural regimes in the Pacific Northwest: simulations 

of ecological and economic effects. Ecological Applications 5: 535-569. 

Hansen Andrew J.; McComb, W. C.; Vega, R.; Raphael, M. G.; Hunter, M. 1995. Bird 

habitat relationships in natural and managed forests in the West Cascades of 

Oregon. Ecological Applications 5: 555-569. 

Hejl, Sally J.; Hutto, R. L.; Preston, C. R.; Finch, D. M. 1995. Effects of silvicultural 

treatments in the Rocky Mountains. In: Martin, T. E.; Finch, D. M., editors. Ecology 

and management of neotropical migratory birds: a synthesis and review of critical issues. 

New York, NY: Oxford University Press; 220-244.

Hutto, Richard L. 1995. Composition of bird communities following stand-replacement 

fires in northern Rocky Mountain (USA) conifer forests. Conservation Biology 9: 

1041-1058. 

Johnson, Edward A. 1992. Fire and vegetation dynamics: studies from the North 

American boreal forests. Cambridge studies in Ecology, Cambridge University Press. 
Cavity-Nesting Birds in Eastern Boreal Forests—Drapeau, Nappi, Giroux, Leduc, and Savard 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 205 

Lamberson, Roland H.; McKelvey, F.; Noon, B. R.; Voss, C. 1992. A dynamic analysis of 

Northern Spotted Owl viability in a fragmented forest landscape. Conservation 

Biology 6: 505-512. 

Legendre, Pierre; Legendre, L. 1998. Numerical ecology. 2nd English edition. Amsterdam: 

Elsevier Science BV; xv + 853 pages. 

McGarigal, Kevin; McComb, W. C. 1995. Relationships between landscape structure and 

breeding birds in the Oregon coast range. Ecological Monographs 65: 235-260. 

Nappi, Antoine. 2000. Distribution des pics et utilisation des arbres morts dans les forêts 

soumises aux perturbations naturelles en pessière à mousses. Université du Québec à 

Montréal; 62 pages. M.Sc. thesis. 

Probst, J. R.; Rakstad, D. S.; Rugg, D. J. 1992. Breeding bird communities in regenerating 

and mature broadleaf forests in the USA Lake States. Forest Ecology and 

Management 49: 43-60. 

Ralph, C. John; Sauer, J. R.; Droege, S., eds. 1995. Monitoring bird populations by point 

counts. Gen. Tech. Rep. PSW–GTR–149. Albany, CA: Pacific Southwest Research 

Station, Forest Service, U.S. Department of Agriculture. 

Raphael, Martin G.; White, M. 1984. Use of snags by cavity-nesting birds in the Sierra 

Nevada. Wildlife Monographs 86: 1-66. 

Rowe, J. Stan. 1972. Forest regions of Canada. Environment Canada, Ottawa. 

SAS Institute, Inc. 1990. SAS/STAT user’s guide version 6. 4th edition. SAS Institute, Inc., 

Cary, North Carolina. 

Schieck, Jim; Nietfield, M.; Stelfox, J. B. 1995. Differences in bird species richness and 

abundance among three successional stages of aspen-dominated boreal forests. 

Canadian Journal of Zoology 73: 1417-1431. 

Spies, Thomas A.; Franklin, J. F.; Thomas, T. B. 1988. Coarse woody debris in Douglas-fir 

forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Spies, Thomas A.; Ripple, W. J.; Bradshaw, G. A. 1994. Dynamics and pattern of a 

managed coniferous forest landscape in Oregon. Ecological Applications 4: 555-568. 

Saab, Victoria A.; Dudley, J. G. 1998. Responses of cavity-nesting birds to standreplacement fire and salvage logging in ponderasa pine/Douglas-fir forests of 

southwestern Idaho. Res. Paper RMRS-RP-11. Fort Collins, CO: Rocky Mountain 

Research Station, USDA Forest Service. 

Sokal, Robert R.; Rohlf, F. J. 1981. Biometry, 2nd edition. San Francisco, CA: Freeman. 

Thompson, Frank R., III.; Probst, G. R.; Raphael, M. G. 1995. Impacts of silviculture: 

overview and management recommendations. In: Martin, T. E.; Finch, D. M., editors. 

Ecology and management of neotropical migratory birds: a synthesis and review of 

critical issues. New York: Oxford University Press; 201-219.

Tyrrell, Lucy E.; Crow, T. R. 1994. Structural characteristics of old-growth hemlockhardwood forests in relation to age. Ecology 75: 370-386. 

Van Wagner, C .E. 1978. Age-class distribution and the forest fire cycle. Canadian Journal 

of Forest Research 8: 431-460. 

Vincent, J. L.; Hardy, L. 1977. L’évolution et l’extinction des grands lacs glaciaires 

Barlow et Ojibway en territoire québécois. Géographie Physique et Quaternaire 31: 

357-372. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 207 

Habitat Preferences of Primary Cavity 

Excavators in Washington’s East Cascades1

Kenneth R. Bevis2 and Sandra K. Martin3

Abstract

Primary cavity excavator (PCE) bird densities and habitat preferences in relation to forest 

management treatments and snag characteristics were investigated in grand fir forests of 

eastern Washington. PCE birds selected large diameter, broken top snags for feeding and 

nesting. They selected western larch and Douglas-fir for feeding excavations and ponderosa 

pine and Douglas-fir for nest cavity snags. Grand fir were also utilized as available on 

managed plots. Soft snags with advanced wood decay were particularly important for nest 

sites. Species composition of PCE birds varied significantly in different forest management 

treatments, with unique species groups associated with unmanaged and heavily managed sites. 

Total population densities of PCE birds were most closely associated with snag density, 

particularly large diameter snags (> 25 cm DBH). 

 

Introduction

Dead wood, particularly standing dead trees (snags) or down logs, is important 

habitat for many species in forest ecosystems. Primary cavity excavator (PCE) birds, 

best represented by woodpeckers, use this dead wood extensively. These species 

excavate hollow cavities in tree stems, usually in dead and decayed wood, as a part of 

regular nesting and courtship behavior. These cavities are critical for life history 

needs of other species of birds and mammals, known as secondary cavity users. Thus, 

PCE birds can be considered “keystone species” in forest ecosystems, because many 

other species of forest wildlife are dependent on them for cavities (Wilson 1992). 

Characterizing snags selected by PCE birds in any given forest type can provide 

important basic information for biologists and land managers. This information was 

unavailable for grand fir (Abies grandis) stands in Washington’s East Cascades, a 

major vegetation type in this region, prior to the initiation of our project. 

Previous research suggests that important attributes of snags selected by PCE 

birds in coniferous forests of the western United States include large diameters, 

advanced decay, and broken tops (Raphael and White 1984, Zarnowitz and Manuwal 

1985). Snag abundance has been hypothesized as a limiting factor for PCE 

populations. A model for predicting “potential population” levels of cavity 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Area Habitat Biologist, Washington Department of Fish and Wildlife, 1701 S. 24th Ave., Yakima, WA 

98902 (e-mail: beviskrb@dfw.wa.gov) 

3

 Executive Editor, Women in Natural Resources, Department of Fish and Wildlife Resources, 

University of Idaho, Moscow ID 83844-1136. 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

208 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

excavating birds based upon numbers of available snags and nesting territory sizes 

(Thomas and others 1979) has been used extensively as a forest management 

guideline in the Pacific Northwest. This model assumes a direct relationship between 

PCE bird and snag abundance. Our study examined the relationship between snags 

and PCE bird densities in grand fir forests. 

Questions we sought to answer with our study included: 1) What are the 

characteristics of snags selected by PCE birds for feeding and nest cavity excavation? 

2) How does PCE species composition and abundance differ among forest 

management treatments? 3) What habitat variables best predict the abundance of PCE 

birds across a series of forest management treatments? 

Methods 

The research was conducted 6 km south of Cle Elum, Washington, in and 

adjacent to the central portions of the Taneum Creek basin (fig. 1). Lands in the study 

area are owned and managed either by the USDA Forest Service or the Plum Creek 

Timber Company. Forest conditions in this basin range from recent clearcuts to lateseral mixed-conifer stands. 

Figure 1―Study location. 

Forest Management Treatments 

Three plots—Gooseberry, North Fork, and South Fork—were characterized as 

unmanaged forest habitats. There was no evidence or record of historic logging 

activity on these sites. Unmanaged stands had heterogeneous overstories of large 

Douglas-fir and western larch, with understories of predominantly grand fir. Patches 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 209 

of even-aged co-dominant lodgepole pine and Douglas-fir also occurred. These areas 

were structurally heterogenous due to past fires and other natural disturbances. 

Two plots, Taneum and Tillman, were characterized as dense shelterwood 

habitats where recent logging removed most of the dominant overstory trees and 

thinned the remaining co-dominant trees between 1983 and 1987. Canopy closure 

remained high. The residual stand consisted of predominantly Douglas-fir, in a 

moderately dense stand with high canopy closure. These stands were considerably 

denser than typical shelterwood treatments. 

Two plots, Frosty and Currant, were characterized as seed tree habitats where 

only a few dispersed, large Douglas-fir or western larch trees were retained after 

harvest. At the time of this study, the planted understory trees (Douglas-fir and larch) 

were less than 1 m tall, and the shrub layer was poorly developed. Grazing by 

domestic sheep had minimized the shrub and herbaceous layers as well. These plots 

were also logged between 1983 and 1987. 

Plot Description 

Six 15 ha and one 12 ha rectangular plots were established and sampled for 

habitat characteristics and PCE birds in 1991 and 1992. The 12 ha plot (Tillman) was 

the best available replicate of the dense shelterwood treatment. Plots were located in 

interior portions of large, homogenous blocks of habitat, at least 50 m from 

substantially different adjacent habitats. A 50 x 50 m grid was established on each 

plot to facilitate bird and habitat measurements. 

Plots were verified as occurring within Abies grandis vegetation associations by 

using the guide, Forested Plant Associations for the Wenatchee National Forest

(Williams and Smith 1990). All plots had a predominantly north aspect and occupied 

mid- to upper slope positions. All plots possessed moderate slopes and were within 

350 m elevation to each other. One habitat point was measured on each ha of each 

study plot. Nine habitat parameters were measured on each habitat point: slope, 

aspect, canopy closure, live tree basal area, live tree density, snag density, live tree 

and snag species composition, snags selected for feeding and/or nest cavity 

excavation, and down wood. Slope and aspect were measured with clinometer and 

compass, respectively. Canopy closure was taken with a spherical densiometer. Live 

tree basal area was measured with a relaskop or prism. Live tree density and species 

composition were taken using the point quarter method (Brewer and McCann 1982) 

at each habitat point. Down wood was tallied using a (Brown 1974) point intercept 

method to the estimate the approximate tons/acre of dead wood. 

All snags were tallied on 20 x 200 m (1 acre) strips within the larger rectangular 

study plots, at a rate of 16 percent of the total plot area. These strips were 

systematically located along bird transect lines on the 50 m plot grid. A snag was 

defined as a standing dead tree with a minimum diameter breast height (DBH) of 10 

cm and a minimum total height of 2 m. This definition was based on minimum nest 

tree diameters and heights for chickadees, the smallest excavator species group 

observed in the study area (Thomas and others 1979). Recorded for each snag were 

tree species, DBH, total height, decay class, presence of feeding excavations, 

presence of nest cavities, and presence of broken tops. Decay Class was recorded 

using a system developed by Cline and others (1977) using five stages, or Classes, of 

dead wood decay. Decay Class 5 was eliminated in 1992 surveys and subsequent 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

210 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

analyses after 1991 data indicated that very few snags were described in this 

category. Heavily decayed (Class 5) snags were then described as Class 4. Diameter 

classes for snag densities were derived from minimum nest tree diameters required 

for three dominant PCE bird species occurring on this study area: mountain 

chickadee, hairy woodpecker, and pileated woodpecker (Thomas and others 1979). 

Feeding excavations were considered present when the surface of the snag had 

obvious shallow holes chipped into it by woodpeckers (Mannan and others 1980, 

Swallow and others 1988). Nest and roost cavity excavations were identified by the 

presence of much larger circular or oval openings excavated by PCE birds (Horton 

and Mannan 1988, Mannan and others 1980). We increased the sample size for snags 

with visible nest cavities by measuring cavity excavated snags and active PCE nests 

from similar forest habitats within and adjacent to the study plots. No snag included 

in the data set was more than 150 m from a plot, or in a substantially different habitat 

from the nearby plot. 

Data on PCE bird abundance and species composition was collected on 100 m 

wide fixed-width transects (Manuwal and Carey 1991) by the first author and a field 

assistant working alone on each survey. Surveys began before 7 a.m. and were 

completed by 9 a.m. Time spent on each survey was standardized. Bird censuses 

occurred in June-July 1991 and May-July 1992. Results were pooled from both years 

for analyses. 

Data were analyzed with Statistical Analysis System (SAS) software. DBH and 

height of snags with and without excavations were compared using T-tests. Decay 

class, species, and broken top selection were investigated using X2

 and KolmogorovSmirnof tests. Selection for individual categories was examined with two category X2

tests with Yate's correction (Sokal and Rolf 1969). Species composition of PCE birds 

was examined using Duncan’s multiple range test, which identifies significant 

groupings among categorical data. Multiple regression analyses were used to 

determine which habitat variables were the strongest predictors of bird densities. 

Results 

PCE Bird Species Observed and Plot Characteristics 

Ten species of PCE birds were observed on the study plots (table 1). Redbreasted nuthatch, chestnut-backed chickadee, mountain chickadee, and northern 

flicker were the most abundant species observed. Three-toed woodpeckers were 

detected only in unmanaged stands. 

Basal area and canopy closure varied by treatment, with some significant 

variation (ANOVA results p=.05) within treatments. Live tree densities varied 

between treatments, with highest densities on the unmanaged plots. Dense 

shelterwoods had larger trees removed by logging, but maintained high densities of 

smaller trees and seed tree plots had few live trees (table 2). Six plots had Douglas-fir 

as the dominant live tree species. On the unmanaged Gooseberry plot, grand fir was 

the dominant species. Snag density varied across the plots, with the highest densities 

occurring on two unmanaged plots. The dense shelterwoods and one unmanaged plot 

had intermediate snag densities. The seed tree plots had the lowest snag densities 

(table 3). 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 211 

Snag Habitat Selection by PCE birds 

Snag selection by PCE birds for feeding and cavity excavation was investigated 

by analyzing the total sample of 1,638 snags and appropriate subsets. Five snag 

attributes were analyzed: DBH, height, Decay Class, snag species, and presence or 

absence of a broken top. Additionally, 40 snags containing active PCE nests were 

measured and compared with selection characteristics of snags with cavity 

excavations but without known active nests. 

Table 1―Primary cavity excavator bird species observed on study plots. 

Common name Abbreviation Scientific name 

Red breasted nuthatch RBNU Sitta canadensis 

Chestnut-backed chickadee CHCH Poecita rufescens 

Mountain chickadee MOCH Poecita gambeli 

Pileated woodpecker PIWO Dryocopus pileatus 

Hairy woodpecker HAWO Picoides villosus 

Black-backed woodpecker BLWO Picoides arcticus 

Three-toed woodpecker TTWO Picoides tridactylus 

Red-naped sapsucker RNSA Syphrapicus nuchalis 

Williamson’s sapsucker WISA Syphrapicus thyroideus 

Northern flicker NOFL Colaptes auratus 

Table 2―Live tree plot characteristics. 

Treatment and plot1

 Mean Live tree Live tree density 

 Pct canopy Basal area M2/ha > 25 cm DBH/ ha 

Unmg 

Goo 89.3 17.6 179.9 

SFk 77.6 12.9 175.3 

NFk 86.2 18.3 277.8 

Dshr 

Tan 64.6 9.9 119.1 

Til 75.0 14.6 214.4 

Seed 

Fro 8.0 .9 6.7 

Cur 2.2 .3 4.9 

1

 Treatment: Unmg = Unmanaged, Dshr = Dense Shelterwood, Seed = Seed Tree 

Plot names: Goo = Gooseberry, SFk = South Fork, NFk = North Fork, Tan = Taneum, Til = Tillman, 

Fro = Frosty, Cur = Currant 

Table 3―Snag density/ha by diameter class. 

Treatment 

and plot1

Density/ha by diameter classes (cm DBH) 

 10-25 25-50 >50+ >25 total >10 

Unmg 

Goo 88.5 48.5 20.6 69.1 157.6 

SFk 113.9 42.4 9.5 51.8 165.8 

NFk 78.2 19.7 2.0 21.8 100.0 

Dshr 

Tan 58.0 20.2 .8 20.6 77.7 

Til 67.9 15.4 1.0 16.5 84.4 

Seed 

Fro 14.4 2.9 3.7 6.6 21.0 

Cur 5.8 3.3 3.7 7.0 12.7 

1

 Treatment: Unmg = Unmanaged, Dshr = Dense Shelterwood, Seed = Seed Tree; see table 2 for plots. 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

212 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Characteristics of Feeding Snags 

The mean DBH for 677 feeding snags (ave. = 29.3 cm, p < .0001) was 

significantly larger than mean DBH of snags without feeding excavations (n = 775, 

ave. = 16.7 cm; T-test, p < .0001). Feeding snags were also significantly taller (ave. = 

14.3 m) than non-excavated snags (ave. = 11.7 m; T-test, p < .0001). 

Selection of tree species used for feeding snags was found when utilized snags 

were compared to the total snag sample. Grand fir (Χ2

, p = .05) and lodgepole pine 

(Χ2

, p < .005) were selected against, while selection for Western larch (Χ2, p < .005) 

was found. Douglas-fir and ponderosa pine were neutral for feeding selection. 

Broken top snags were significantly selected for feeding (Χ2

, p < .005). Preferred 

characteristics of feeding snags therefore were: large DBH (>25 cm), tall (> 10 m) 

western larch snag, , with a broken top. 

Characteristics of Cavity Snags 

It was not known what PCE bird species were responsible for excavating the 

observed cavities. Mean diameters of cavity and non-cavity snags were compared. 

Mean diameters of cavity snags (n = 239, ave. = 47.9 cm) were significantly larger 

than that of non-selected snags (n = 1,399, ave. = 21.9 cm; T-test, p < .001) (table 4).

Heights of cavity snags (ave. = 9.8 m) were significantly shorter than height of snags 

without cavities (ave. = 13.0 m; T-test, p < .0001). 

Cline (1977) used a 5 class system to describe relative decay state: Class 1—a 

recently dead, hard snag with fine needles and branches remaining; Class 2—a hard 

snag with most of the bark remaining and fine branches gone; Class 3—early decay 

phase soft snag, with wood difficult to break by hand and bark sloughing; Class 4— 

advanced decay with bark blocky and wood easily hand broken; and Class 5— 

advanced decay with wood extremely soft and nearly humus. 

Snags in Decay Class 1 were significantly selected against for cavity excavation 

in all forest management treatments (p < .005) and when compared to all snags (p < 

.005). Decay Class 2 was selected against when compared with total snags (p < .05). 

Snags in Decay Class 3 were significantly selected for cavity snags well above their 

availability on all treatments and when compared with total snags (p < .005). Class 4 

snags were neutral in selection for total snags, but indicated selection on the dense 

shelterwood treatment (table 5).

Broken top snags were significantly selected as cavity snags on unmanaged 

plots and within the total snag population. On all managed plots, however, selection 

of broken top snags was not significant, likely because of the large proportion of 

snags existing on managed plots that were broken mid-stem. 

Different tree species produce snags with different characteristics, affecting use 

for cavity excavation by PCE birds. Douglas-fir was the most consistently selected 

species of cavity snag; selection for this species was significant in the unmanaged 

treatment plots (p < .005) and for all available snags (p < .005). Ponderosa pine was 

selected for cavity excavation on the unmanaged plots (the only treatment where this 

species occurred) and for total snags. Western larch and lodgepole pine were selected 

against for cavity snags. Grand fir was neutral in selection when compared with total 

snag frequency. This suggests that grand fir is not preferred when other species are 

available, but is utilized when more preferred species are not present. Species 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 213 

selection for cavity snags was neutral in dense shelterwood and seed tree treatments 

(table 6). 

Table 4―DBH of cavity and non-cavity snags with T-test results. 

 Cavity 

Treatment and plot1 Cavity Non-cavity 

 Mean 

 n n DBH (cm) DBH P>[T] 

Unmg 

Goo 56 354 53.3 24.9 .0001 

SFk 53 388 51.9 21.7 .0001 

NFk 45 235 40.0 19.3 .0001 

Dshr 

Tan 19 188 33.1 19.6 .0015 

Til 13 159 32.8 20.3 .0144 

Seed 

Fro 29 49 57.4 24.3 .0000 

Cur 24 26 50.2 31.8 .0011 

 

Total snags 239 1,399 47.9 21.9 .0001 

1

 Treatment: Unmg = Unmanaged, Dshr = Dense Shelterwood, Seed = Seed Tree 

Plot names: Goo = Gooseberry, SFk = South Fork, NFk = North Fork, Tan = Taneum, Til = Tillman, 

Fro = Frosty, Cur = Currant 

Table 5―Decay class of cavity and non-cavity snags.1

Treatment Decay 1 Decay 2 Decay 3 Decay 4 

Unmn2 x* x +* 0 

DShltr x* 0 +* + 

Seed x* 0 +* 0 

Total snags x* x* +* 0 

1

Results from 2 category X2 tests; @ p=.05, + = Selected for, 

x = Selected against, 0 = no selection; 

* = significant at <.005 

2

 Unmn = Unmanaged, Dshltr = Dense Shelterwood 

Table 6―Tree species selection for cavity snags.1

Treatment ABGR2

 LAOC PICO PIPO PSME 

 

Unmn3 x x* x* +* +* 

DShltr 0 0 . . 0 

Seed 0 0 . . 0 

Total snags 0 x* x* +* +* 

1

 p=.05, + = Selected for, x = Selected against, 0 = no selection; 

* = significant at <.005 

2

 ABGR = Grand fir, LAOC = W. larch, PICO = lodgepole pine, PIPO = ponderos pine, PSME = 

Douglas-fir 

3

 Unmn =Unmanaged , DShltr = Dense Shelterwood 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

214 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Active PCE Nests 

Active nest trees were significantly larger in diameter (n = 40, ave. = 56.9 cm) 

than cavity snags (n = 239, ave. = 47.9 cm; T-test, p < .001). Active nest trees were 

also significantly taller than cavity snags (active nest trees ave. = 13.8 m, cavity 

snags ave. = 9.8 m; T-test, p < .05). Nest trees used by Williamson’s sapsuckers had 

the largest diameter (n = 4, ave. = 92.1 cm). Nest trees used by the two species with 

the largest number of observed nests, northern flicker and red-breasted nuthatch, had 

similar diameters at 53.4 (n = 14) and 56.8 cm (n = 13), respectively. Northern 

flickers used the shortest nest snags; they consistently were found nesting in broken 

off, well-rotted snags in the managed forest treatments. Broken tops were found on 

73 percent of active nests and 83 percent of cavity snags. 

Fifteen percent of active nests were in either live trees or Decay Class 1 snags. 

Twenty percent of active nests were in Decay Class 2, and no nests were found in 

Decay Class 4. Sixty-five percent of active nests were in Decay Class 3 snags, a 

category previously shown as selected for excavation. 

Fifty percent of active nests were in Douglas-fir, a species also found to be 

significantly selected for cavity excavation. Thirty-five percent of active nests were 

in grand fir, a species not significantly selected in cavity snags. The active nests in 

grand fir were mostly northern flicker nests on the seed tree plots, where large 

diameter, broken-topped, Decay Class 3, grand fir snags were available and well used 

by flickers. Western larch nest sites were primarily those of Williamson's sapsuckers, 

in live trees. No nests were found in lodgepole pine, a species also not selected as 

cavity snags. Three nests were found in ponderosa pine, in areas with low abundance 

of this snag species. The hypothesis that ponderosa pine is a preferred cavity species 

is also supported by the significant selection for ponderosa pine for cavity snags 

Preferred characteristics of nest snags identified in this study were: large diameter 

(>50 cm), medium height (> 9 m), Decay Class 3, Douglas-fir, or ponderosa pine 

with a broken top. 

Relative frequencies of tree species selected for cavity excavation were similar 

for those for known nest sites. Grand fir, Western larch, ponderosa pine and Douglasfir comprised all observed nests, and similarly comprised all cavity snags. A slightly 

higher percent of observed nests were in Grand fir (32 percent) than for cavity snags 

(28 percent), and a slightly higher percent of cavity snags (57 percent) were in 

Douglas fir than for known nests (50 percent). Western larch had exactly the same 

percent of observed nests as cavity snags (10 percent). 

PCE Densities and Species Composition

The highest PCE species transect counts during this study were, in descending 

order: red-breasted nuthatch, mountain and chestnut-backed chickadee, hairy 

woodpecker and northern flicker (table 7). Total PCE plot densities decreased from 

highest levels in unmanaged stands, to intermediate levels in dense shelterwoods, to 

lowest levels on seed tree plots. Species composition was also significantly different 

among management treatments (table 8). The species group identified for unmanaged 

plots, was dominated by small excavators: red-breasted nuthatch, mountain chickadee 

and chestnut-backed chickadee. Highest red-breasted nuthatch counts were found on 

the Gooseberry and South Fork plots, which were unmanaged stands with large trees 

and high snag densities. The species group found on unmanaged plots also included 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 215 

three-toed and black-backed woodpeckers, species known to be associated with fires, 

high snag densities, and recently killed trees (Bock 1974, Herr 1992). 

The species compositions of birds found on unmanaged and seed tree plots were 

distinctive, while the species composition of birds on the dense shelterwood plots 

were an intermediate mix between the other two treatment types (Duncan’s Multiple 

Range Test, table 8). Hairy woodpeckers were counted most often on a dense 

shelterwood plot (Taneum), but occurred in all treatment types. Other species found 

on dense shelterwood plots included those found on unmanaged forest plots (redbreasted nuthatch, chickadees, pileated and hairy woodpeckers), and a small number 

of birds also found on the seed tree plots (red-naped and Williamson’s sapsucker, and 

northern flicker). The PCE group found on seed tree plots included the largest 

proportion of a single species on any treatment, northern flicker. Red-naped and 

Williamson’s sapsuckers were observed most often on seed tree plots, but were still 

uncommon. 

Table 7―Average density/15 ha by bird species by treatment.1

1 See table 1 for bird species abbreviations. 2 TCH= Total chickadees, mountain and chestnut-backed combined. 3

 Unmg = Unmanaged, DShr = Dense Shelterwood 

Table 8―Bird species composition shift summarized by treatment.1 

 Treatment 

PCE species Unmanaged Shelterwood Seed tree 

RBNU2

 X X 

TCH X X * 

PIWO X X 

HAWO X X X 

TTWO X 

BLWO X * * 

RNSA * * 

WISA * X 

NOFL X 

1 X = major component; * = minor component 

2 See table 1 for bird species abbreviations.

PCE Bird Densities and Habitat Variables 

Relationships of PCE bird densities by species with habitat variables were 

investigated using stepwise multiple regression analyses. A close correlation was 

found showing density of red-breasted nuthatches best predicted by snag densities in 

the 25-50 cm diameter class (R2

 = .94). Total chickadee densities were also best 

predicted by snag densities in the same diameter class (R2

 = .83). In both cases, 

Treatment RBNU TCH2 PIWO HAWO TTWO BLWO RNSA WISA NOFL Total 

 

Unmg3 9.87 6.00 .20 .94 .21 .43 0 0 .16 17.84 

DShr 4.50 3.54 .20 1.10 0 .06 .06 .14 .34 9.97 

Seed .04 .30 0 .69 0 .08 .11 .50 4.04 5.77 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

216 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

greater densities of these small PCE birds were found in habitats with greater 

densities of snags. No habitat variables significantly predicted densities of hairy 

woodpeckers. Similarly, no significant relationships were distinguished for densities 

of pileated woodpecker, three-toed woodpecker, black-backed woodpecker or rednaped sapsucker, likely due to small sample sizes for these birds. Williamson’s 

sapsucker and northern flicker densities varied significantly and inversely with 

canopy closure in regression analyses (R2

 = .96, and R2 = .91, respectively). Total 

PCE bird abundance was best predicted by snag density >25 cm DBH (R2

 = .93). 

Discussion 

Snag Selection 

Observed feeding snags, cavity snags and observed nests shared many 

characteristics. All were larger diameter and in advanced decay states, often with 

broken tops. Larger diameter snags may be needed to meet the thermal and 

mechanical needs dictated by the size of the PCE birds (Thomas and others 1979). 

Most excavated cavities and nests occurred in broken off snags, likely due to the 

increased opportunity for introduction of various stem rots, thus facilitating 

excavation. Many excavated cavities were observed within a few meters of the break 

off point on the tree stem. Because of the variability introduced by these broken tops, 

height is a poor measure of suitability of snags for PCE birds, other than to help 

determine acceptable minimums and target heights for snag viability in management. 

These results strongly suggest that larger snags may be critical to PCE birds. 

Decay Class indicated time since death of the tree and affected characteristics 

important to PCE birds. Snags in Decay Class 1 were recently dead and probably had 

not been dead long enough to develop substantial insect populations or accumulated 

evidence of PCE feeding. Class 2 snags probably had active insect populations 

available for PCE birds. By the time a snag reached Class 3, enough time had elapsed 

for such activity and evidence to accumulate; hence, significant selection for this 

Decay Class was found. Snags in Class 4 were very decayed, often with large areas 

of missing bark, with evidence of PCE bird use obscured by the effects of decay. 

Decay class 3 snags showed the highest abundance of feeding evidence, but this was 

probably the result of accumulation over time, and does not demonstrate an 

immediate feeding preference for decay class. Because of the cumulative nature of 

feeding evidence on snags, analysis of feeding selection in decay class was 

inconclusive. 

Snags in Decay Class 3 were significantly selected for cavity excavation on all 

plots, treatments, and for total snags. In addition, 65 percent of observed active nests 

were in Decay Class 3 snags. Snags in earlier Decay Classes were likely not softened 

enough by decay to facilitate excavation. Some excavation occurred in Class 2 snags 

(20 percent of nests), usually in portions of the stem with decay. 

As expected, similar tree species were selected for cavity snags and observed 

nests, with Douglas-fir and ponderosa pine preferred. Western larch was selected for 

feeding snags but not for cavity snags. This may have been due to the smaller 

average diameter for most western larch present on the study sites, which may have 

been insufficient for cavity excavation. Lodgepole pine was not selected for any 

excavations, and this is consistent with the literature, implying that this species, may 

not be a good choice for retention if PCE birds are an objective. Grand fir was neutral 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 217 

for feeding selection, but was sometimes used for cavities. Grand fir wood appears to 

decay more quickly than other species, perhaps supplying a less durable substrate for 

nest cavities. Our data, however, suggest considerable PCE bird use of grand fir on 

the east side of the Cascades. The role of grand fir as a component of PCE habitat 

needs further investigation. 

We found that snags are used by PCE birds for feeding in earlier decay states 

than those snags chosen for nesting. Habitat needs of PCE birds, therefore, 

encompass snags in all stages of decay. Additionally, because decay progresses 

through time, live and declining trees must be maintained after timber harvests as 

replacement snags. Results from this study support the work of many others in 

identifying snags in more advanced decay classes as particularly valuable habitat 

elements for PCE birds (Conner and others 1976, Madsen 1985, Raphael and White 

1984). The need for snags with advanced decay means that snag management is a 

long-term endeavor, requiring protection of existing snags and an adequate supply of 

all diameter “legacy” snag recruits to be maintained over time. 

The significant selection by PCE birds for broken tops may be explained by a 

preference for snags with more decay, and perhaps increased insect activity. Broken 

top snags probably collect precipitation moisture directly into their stems, thus 

improving fungal growth conditions and allowing the broader introduction of woodsoftening fungi. 

Active nests were found in significantly larger stems than cavity snags, lending 

support to the conclusion that PCE birds prefer large snags for nest cavity sites. 

Known nest snags were also found to be significantly taller than cavity snags in this 

study. The minimum height of an observed nest tree in this study was 2.1 m, which is 

similar to the minimum height of snags (2 m) recommended by Thomas and others 

(1979). This minimum, however, constitutes a poor management guideline. The 

influence of decay, rather than height, is likely the most important factor regarding 

cavity site location by PCE birds. Height is only relevant as a management (i.e., 

safety) factor. 

The active nest sample effectively acted as a control group to compare with 

measured cavity snags, adding considerable meaning to the data set. The most 

numerous observed nests were those of red-breasted nuthatches and northern flickers. 

Nuthatch nests were found predominantly in large diameter, highly rotted stems in 

unmanaged stands with high densities of large trees and snags. Flicker nests were 

located exclusively in seed tree areas, where large DBH, short stubs (residuals from 

the mature, pre-logged stand) were likely retained because they posed no safety 

hazard to logging operations. Northern flicker nests were found mostly in largediameter, broken-top, well-decayed grand fir snags. These two species were the most 

different in habitats used in this study, yet their nest snag characteristics were very 

similar. This suggests that the characteristics of snags preferred by PCE birds are 

consistent across habitat types. 

PCE Bird Density and Abundance 

Red-breasted nuthatch densities were most closely predicted in the regression 

analyses by density of snags between 25 and 50 cm DBH (R2

 = .94). Habitat with 

high densities of snags of this diameter category was most prevalent in unmanaged 

forest. Basal area was the second predictor for red-breasted nuthatch density in our 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

218 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

study, suggesting a preference for denser forests. These plots also had the highest 

abundance of large diameter trees. Other researchers have found that red-breasted 

Nuthatches prefer older forest stands with larger stems and high structural diversity 

(Adams and Morrison 1993, Mannan and Meslow 1984). Timber harvest, which 

simplifies stand structure, opens the canopy, and removes large stems and dead 

wood, undoubtedly reduces habitat quality for red-breasted nuthatches. 

Chickadees nest and feed in dead, rotting wood, and utilize thick forest and 

brushy areas in northwestern coniferous forests (Thomas and others 1979). Our study 

reinforced this finding, as we documented decreased abundance of chickadees in 

dense shelterwood plots, compared to unmanaged forest, and lowest abundance in 

seed tree plots. Chickadees are also likely to be negatively impacted by timber 

harvest in the central Cascades, which reduces forest complexity and snag density. 

Black-backed and three-toed woodpeckers were observed in highest densities on 

the North Fork and South Fork plots, areas with high densities of relatively small 

snags (tables 3, 8). The literature also reports that these woodpeckers nest in smaller 

snags than many other PCE birds (McClelland and others 1979, Thomas and others 

1979). The four nests occupied by these species in this study were in smaller snags 

(diameter range 26.7 to 34.4 cm dbh, n = 4), suggesting that these two species may be 

able to utilize younger stands. 

Pileated woodpeckers were counted on all unmanaged plots and on both 

shelterwood plots, but in low densities (table 8). These birds are known to have large 

territories, estimated between 200 and 689 ha (494 to 1,650 acres) for similar habitat 

types in the Blue Mountains of Oregon (Bull and Holthausen 1993). These 

woodpeckers were not tallied on the seed tree plots where canopy closure, tree 

density, and snag density were all relatively low. Heavy timber harvest probably 

negatively effects this species, but their presence on the dense shelterwood plots in 

our study suggests that active forest management that retains adequate dead wood for 

feeding, nesting, and roosting needs, may result in habitat that remains suitable for 

pileated woodpeckers. 

Williamson’s and red-naped sapsuckers were found more frequently on the more 

open plots in our study, perhaps as a reflection of increased visibility, rather than 

higher densities. Previous work (Madsen 1985, Raphael and White 1984) found 

Williamson’s sapsucker nest sites to occur largely in areas of dense snags and high 

basal area. Our result may suggest that sapsucker breeding territories are determined 

by the presence of adequate suitable structures, such as large diameter western larch, 

rather than forest density. 

Northern flickers prefer habitats where open ground for feeding and snags for 

nest sites occur together (Ehrlich and others 1988). Flicker densities were most 

closely predicted by canopy closure in this study (R2

= .82), showing a distinct 

preference for open, meadow-edge habitat types, represented in this study by seed 

tree plots. Their breeding presence, however, is probably limited by the availability 

of suitable snags. Seed tree plots with snags present may represent nearly optimal 

habitat for breeding northern flickers, based upon their density as the third highest for 

any species by treatment in this study (table 7). Western bluebirds and Kestrels 

commonly utilized old cavities, most likely excavated by flickers, on the seed tree 

plots. 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 219 

Methods 

The bird count method utilized in this study may have resulted in undercounts of 

birds in the unmanaged and dense shelterwood habitats due to the quiet nature of 

woodpeckers during the latter portion of the breeding season when many of our 

transects were measured. In addition, observer bias in distance estimation can be a 

significant problem that affects results in bird surveys that we employed. In future 

PCE studies or monitoring, we recommend using simple transect or point counts, 

thus minimizing distance estimates. We also recommend use of as few highly trained 

observers as possible conducting all surveys, to eliminate intra-observer bias. Two 

different field assistants in 2 years complicated results on this study, particularly in 

reference to chickadee identification. PCE bird monitoring and research should 

include red-breasted nuthatches. We observed these birds excavating cavities in soft 

wood, and their calls are quite distinctive. If possible, surveys should occur earlier in 

the breeding season, beginning in April and ending in early June. This would more 

closely coincide with territorial displays. Nest searches should occur in June and 

early July, when young are readying to fledge, and nests are easiest to find. 

Treatment Effects 

Treatments were not always uniform, and therefore effects were not entirely 

clearly evident. Approximately the same PCE bird species composition was found in 

the dense shelterwood plots as the unmanaged plots, but PCE birds were less 

abundant in the dense shelterwoods (table 7). While the life requirements of the PCE 

species were apparently met in the shelterwoods, some habitat limitation resulted in 

lower population density. It is possible that these shelterwoods are population sinks. 

It is noteworthy that the North Fork plot, although characterized as unmanaged 

forest, had snag densities more similar to the dense shelterwoods than the other 

unmanaged plots (table 3). PCE species composition and abundance measured on the 

North Fork plot were also more similar to those recorded on the dense shelterwood 

plots. These data support the hypothesis that snag abundance is likely a key habitat 

component supporting PCE density. Hairy woodpecker occurrence in all treatment 

types supports their description by several authors as habitat generalists (Mannan and 

Meslow 1984, Thomas and others 1979). The seed tree treatments held low numbers 

of all PCE bird species, except for northern flickers, suggesting that these highly 

managed areas were currently unsuitable habitat for most forest PCE species. 

PCE Populations and Habitat 

A strong relationship found in the regression analysis was between total birds 

and snag density > 25 cm (R2

 = .94). Therefore, density of large snags may be the 

most important habitat component affecting PCE bird abundance in grand fir forests 

in eastern Washington. Our study supports conclusions of similar research (Raphael 

and White 1984, Zarnowitz and Manuwal 1985). The maintenance of adequate 

densities of larger snags, with a continuum of decay conditions present at all times, is 

undoubtedly a significant factor in sustaining populations of PCE birds. 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

220 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Preferred Snag Characteristics and Management 

Recommendations 

Preferred species for PCE feeding snags are western larch and Douglas-fir and 

preferred species for cavity snags are Douglas-fir and ponderosa pine. Grand fir is 

also utilized, but may not be a preferred species. Snags should be maintained in all 

Decay Classes, particularly in Classes 2 and 3. Snags and green recruitment trees 

should be retained in the larger diameter classes (minimum of >35 cm (14 in) DBH) 

to provide a continuous supply of snags over time. This DBH is based upon the 

minimum nest snag utilized by hairy woodpeckers and northern flickers on this study. 

Minimum snag height should be 5 m (15 ft), based upon the observed minimum 

height of snag used by hairy woodpeckers. This is recommended as a management 

guideline rather than the minimum diameters and heights (25 cm and 2 m) 

determined by chickadees and used by many land management agencies. We 

maintain that snags should be managed for larger diameters and heights than 

currently practiced to provide the best chance of population viability for the host of 

cavity dependent species. Large diameter western larch should be retained in forest 

management because of the importance of these trees for Williamson’s sapsuckers. 

Maintaining high snag densities alone will not provide quality habitat for PCE 

birds. Snags with specific characteristics (Decay Class, broken tops, and species) 

must also be maintained. The importance of decay trajectories to habitat use by PCE 

species remains a rich area for future research. In addition, target bird species 

compositions and territory sizes should be considered in PCE management. 

Despite the well-documented fact that snags are important components of forest 

ecosystems, they are often removed from forest stands during timber harvest, forest 

management activities, and for fuel wood. Cutting of the largest snags (especially 

Douglas-fir and Western larch) for firewood is a common practice throughout the 

Northwest, but contributes to habitat degradation for all cavity species. Snags are also 

cut for hazard reduction at parks and public facilities. Quality wildlife trees are often 

removed during logging that could have been maintained through planning and 

forethought. Protection of existing high quality snags and maintenance of adequate 

recruitment trees must become more widely recognized as key tools for forest 

biodiversity preservation, and elevated to common practice. This would promote 

healthy populations of cavity nesting birds and associated species across the forested 

landscape over time. 

References 

Adams, E. M.; Morrison, M. L. 1993. Effects of forest stand structure and composition on 

red-breasted nuthatches and brown creepers. Journal of Wildlife Management 57(3): 

616-629. 

Bock, C. E. 1974. Geographic ecology and evolution of three-toed woodpecker. American 

Midland Naturalist 92(2): 397-405. 

Brewer, R.; McCann, M. T. 1982. Laboratories and field manual of ecology. Saunders New 

York: College Publ.; 269 p. 

Brown, J. K. 1974. Handbook for inventorying downed woody material. Gen. Tech. Rep. 

INT-16. Ogden, UT: USDA Forest Service; 26 p. 

Bull, E. L.; Holthausen, R. S. 1993. Habitat use and management of pileated woodpeckers 

in northeastern Oregon. Journal of Wildlife Management 57(2): 335-345. 
Habitat Preferences of Primary Cavity Excavators in Washington's East Cascades—Bevis and 

Martin 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 221 

Cline, S. P.; Berg, A. B.; Wight, H. M. 1977. Snag characteristics and dynamics in 

Douglas-fir forests, Western Oregon. Journal of Wildlife Management 44: 773-786. 

Conner, R. N.; Miller, O. K.; Adkisson, C. S. 1976. Woodpecker dependence on trees 

infected by fungal heart rots. Wilson Bulletin 88: 575-581. 

Ehrlich, P. R.; Dobkin, D. S.; Wheye, D. 1988. The birder’s handbook. New York: Fireside 

Book; 785 p. 

Herr, D. S. 1992. Locating three-toed woodpeckers. Oregon Birds 18(1): 24-25 

Horton S. P.; Mannan, R. W. 1988. Effects of prescribed fire on snags and cavity nesting 

birds in southeastern Arizona pine forests. Wildlife Society Bulletin. 16: 37-44. 

Madsen, S. 1985. Habitat use by cavity nesting birds in the Okanogan National Forest, 

Washington. University of Washington; M.S. thesis. 

Mannan, R. W.; Meslow, E. C. 1984. Bird populations and vegetation characteristics in 

managed and old growth forests, northeastern Oregon. Journal of Wildlife 

Management 48: 1219-1238. 

Mannan, R. W.; Meslow, E. C.; Wight, H. M. 1980. Use of snags in Douglas-fir forests, 

western Oregon. Journal of Wildlife Management 44: 787-797. 

Manuwal, D. A.; Carey, A. B. 1991. Methods for measuring populations of small diurnal 

forest birds. Gen. Tech. Rep. PNW-GTR-275. USDA Forest Service, Pacific Northwest 

Research Station; 23 p. 

McClelland, B. R.; Frissell, S. S.; Fishcher, W. C.; Halvorson, C. H. 1979. Habitat 

management for hole nesting birds in forests of western larch and Douglas-fir. 

Journal of Forestry 77: 480-483. 

Raphael, M. G.; White, M. 1984. Use of snags by cavity nesting birds in the Sierra 

Nevada. Wildlife Monographs 86: 1-66. 

Sokal, R. R.; Rohlf, J. 1969. Biometry. W. H. Freeman and Co.; 776 p. 

Swallow, S. K.; Gutierrez, R. J.; Howard, R. A. 1988. Snag preferences of woodpeckers 

foraging in a northeastern hardwood forest. Wilson Bulletin 100(2): 236-246. 

Thomas, J. W., editor. 1979. Wildlife habitats in managed forests: the Blue Mountains of 

Oregon and Washington. Agric. Handb. 553 Washington, DC: USDA Forest Service; 

511 p. 

Williams, C. K.; Smith, B. G. 1990. Forested plant associations of the Wenatchee National 

Forest. Wenatchee, WA: Wen. Nat. Forest; 211 p. 

Wilson, E. O. 1992. The diversity of life. Cambridge, MA: Belnap Press of Harvard 

University; 424 p. 

Zarnowitz, J. E.; Manuwal, D. A. 1985. The effects of forest management on cavity nesting 

birds in northwestern Washington. Journal of Wildlife Management 49 (1): 255-263. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 223 

Cavity-nesting Bird Use of Snags in 

Eastside Pine Forests of Northeastern 

California1 

William F. Laudenslayer, Jr.2

Abstract 

Relationships between snags (standing dead trees) and cavity-nesting birds were examined in 

the breeding seasons of 1989, 1990, 1991 on the Modoc and Lassen National Forests and 

Lassen Volcanic National Park, California. Transects, that differed by snag density, were 

randomly placed in eastside pine habitat patches dominated by either ponderosa (Pinus 

ponderosa) or Jeffrey pine (P. jeffreyi). Snags with active nests had greater diameters and 

were taller than random alternative snags; both differences were significant (P > 0.05). Snags 

with historical nest cavities generally were of larger diameter than snags without historical 

nest cavities. Despite the heavier nesting use of larger snags, many large snags, with similar 

visual deterioration characteristics, showed no indication of historical nesting use. 

Introduction 

Snags (standing dead trees) are an important component of forests and play a 

crucial role in the continuation of soil fertility as well as perpetuation of species that 

depend on snags for parts of their life histories (e.g., snag associated insects, 

substrates for vertebrate nesting, and roosting cavities) (Bull and others 1997, 

Machmer and Steeger 1995, Parks and others 1997). Some bird species, because of 

their need for cavities in which to nest (i.e., natural cavities, existing excavated 

cavities, or suitable conditions for the excavation of new cavities), find suitable 

nesting substrate in snags or live trees with patches of decay or cavities resulting 

from limb breakage. Some 85 species of North American birds, not to mention 

numerous other vertebrates and invertebrates, construct nests in snags, or nest in 

natural cavities, or previously excavated holes in snags (Scott and others 1977). 

Availability of nest sites may limit the numbers of cavity-nesting species. 

Snag size, especially diameter, and to a lesser extent height, are also thought to 

be important characteristics related to bird usage. Generally, larger diameter snags 

are used in preference to smaller diameter snags (Bull 1975, Cunningham and others 

1980, Mannan and others 1980, McClelland and Frissell 1975, Milne and Hejl 1989, 

Raphael and White 1984, Scott 1978, Scott and Oldemeyer 1983). To the contrary, 

Hay and Guntert (1983) concluded that smaller snags are preferred by some species 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Wildlife Ecologist, Pacific Southwest Research Station, USDA Forest Service, 2081 E. 

Sierra Ave., Fresno, CA 93710 (e-mail: blaudenslayer@fs.fed.us) 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

224 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

for purposes other than nesting. Many authors consider the presence of snags to be 

essential for the continued presence of cavity-nesting birds. 

The eastside pine forest of California is characterized by relatively open stands 

of pine with relatively few snags compared to other western forests. Preliminary 

surveys of this forest in 1988 indicated that very large portions of the Modoc and 

Lassen National Forests had well under one snag to the acre. The paucity of snags is 

related to the lower tree densities inherent in these stands as well as past management 

activities. In the late 1980s, the USDA Forest Service became concerned about the 

effects of this perceived current and future snag deficit on cavity-nesting birds. 

To gain a better understanding of the effects of snag densities on cavity-nesting 

birds, a study was designed to examine the relations between snag numbers and 

numbers of cavity-nesting birds. The study also collected information on the 

characteristics of snags used by these nesting birds. This paper contrasts the 

characteristics of snags used by actively nesting birds with the characteristics of 

snags available in close proximity but not used; and it will contrast the characteristics 

of snags used currently with those used by nesting birds in the past. 

Methods 

Study Areas 

The 24 study areas are located in eastside pine forests of Modoc, Lassen, and 

Shasta Counties, California. These forests are dominated by ponderosa pine (Pinus 

ponderosa), Jeffrey pine (P. jeffreyi) in some locations, and white fir (Abies 

concolor) with smaller amounts of incense cedar (Calocedrus decurrens), western 

juniper (Juniperus occidentalis), California black oak (Quercus kelloggii), and 

lodgepole pine (P. contorta). Dominant shrubs include big sagebrush (Artemisia 

tridentata), bitterbrush (Purshia tridentata), and mahala mat (Ceanothus prostratus);

with lesser amounts of Nevada manzanita (Arctostaphylos nevadensis), curl-leaf 

mountain-mahogany (Cercocarpus ledifolius), and silver sagebrush (Artemisia cana). 

Study Design 

Snag densities were estimated for approximately 1,000 land management 

polygons on the Modoc and Lassen National Forests, and suitable areas within 

Lassen Volcanic National Park. Study areas were randomly selected from the pool of 

potential study areas in seven snag density classes: 0, >0 to <0.20, >0.20 to 0.40, 

>0.40 to <0.61, >0.61 to <0.81, >0.81 to <1.21, and >1.21/hectare. All of the lesser 

snag density classes had sufficient numbers of potential study areas from which to 

randomly draw the study areas. For the two densest snag density classes, all areas 

found with such densities were used in the study. One 100 x 500 m long strip transect 

was placed randomly within each of the 24 selected study areas; the bounds of these 

areas were used as the basis of all subsequent work. 

Active Nests 

From 1989 through 1991, each transect was searched for nests, especially of 

cavity-nesting birds. Nests were located by following birds back to their nests, 

visually examining potential nest holes for indication of recent excavation, and 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 225 

watching and listening for nesting activity (e.g., carrying nesting material, food 

delivery, hearing the sounds of young birds). 

At active nests, information was collected on tree or snag species, diameter at 

breast height (DBH), total height, nest height, nest hole diameter, compass direction 

the nest hole faces, and whether the nest was constructed in living or dead portions of 

the tree. For each active nest tree, the nearest random alternative snag or live tree, 

without an active nest, was also identified. Information collected from this snag or 

tree was species, DBH, height. If either the nest snag or alternative site was a snag 

included in the snag inventory, the snag number was also recorded linking the nest or 

alternative site to the snag characteristics data collected under snags. 

Historic Nest Holes 

All snags with diameters in excess of 15 cm were permanently marked, mapped, 

and information including species, diameter, height, percent bark remaining, and 

number of nest holes were taken on 23 of the 24 study plots in 1989. On one plot, the 

number of small snags (<25 cm in diameter) was so great that information was taken 

only on those snags with diameters in excess of 25 cm. 

Analysis 

Primary and secondary cavity-nesting bird species found nesting in the study 

areas were red-breasted sapsucker (Sphyrapicus ruber), Williamson’s sapsucker 

(Sphyrapicus thyroideus), hairy woodpecker (Picoides villosus), white-headed 

woodpecker (Picoides albolarvatus), black-backed woodpecker (Picoides arcticus),

northern flicker (Colaptes auratus), pileated woodpecker (Dryocopus pileatus), tree 

swallow (Tachycineta bicolor), mountain chickadee (Poecile gamblei), red-breasted 

nuthatch (Sitta canadensis), white-breasted nuthatch (Sitta carolinensis), pygmy 

nuthatch (Sitta pygmaea), brown creeper (Certhia americana), house wren 

(Troglodytes aedon), and mountain bluebird (Sialia currucoides). 

Comparisons of individual species were based on the four with the greatest 

number of nests found: hairy woodpecker, mountain chickadee, red-breasted 

nuthatch, and pygmy nuthatch. Characteristics of snags with active nests were 

compared to alternative nest snags using t-tests and box plots. Information on 

historical nest holes and nesting snags (of snags >15 inches in DBH) was taken from 

data collected in 1990. 

Results 

Active Nests 

Over the 3-year bird study period, 110 active nests of cavity-nesting birds were 

located. All but four of these nests were in ponderosa or Jeffrey pines. The majority 

of nests were of hairy woodpecker (17), mountain chickadee (12), red-breasted 

nuthatch (11), and pygmy nuthatch (16). 

On occasion, live trees were used for nesting and most of the cavity-nesting bird 

species took advantage of such sites. Eight nests (7 percent of total) were found in 

live trees; these sites include the dead tops of large diameter pine trees, a crack in the 

bole of a large tree, other damaged areas where the bark was lost, and a dead limb in 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

226 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

a western juniper. Half of the live tree nests were on transects with more than 0.4 

snags greater than 38 cm in diameter during the bird study time period (see Landram 

and others 2002 for a discussion of snag demography on these study areas). 

Mean DBH of snags used for nesting were in excess of 70 cm for the four birds 

of interest (fig. 1). The smallest diameter used by all four species was approximately 

40 cm. Although the smallest diameters used by each species approximated 40 cm, 

the largest diameters were quite variable ranging from <100 (mountain chickadee) to 

approximately 180 cm (red-breasted nuthatch). 

Figure 1—Mean diameters (cm) of nesting snags used by hairy woodpecker (HaWo - 

n = 17), mountain chickadee (MoCh - n =10), red-breasted nuthatch (RbNu - n = 11), 

and pygmy nuthatch (PyNu - n = 16) + 1 standard error and values for the largest and 

smallest nest tree diameter. 

Heights of snags used for nesting ranged from less than 5 m (mountain 

chickadee) to more than 45 m (red-breasted nuthatch) (fig. 2). The shortest trees used 

by each species was between 7 and 9 m in height except for mountain chickadee—

one nest at 3 m and two at essentially 0 m (both in downed logs). Tallest trees used 

approached the maximum available. Despite this variation in the ranges in nest tree 

height by species, mean heights of nest trees selected by each species were not very 

different with the exception of hairy woodpecker, which generally used shorter trees 

than the other three species. 

Nest heights were quite variable: hairy woodpecker nests generally were higher 

than the other three species, and mountain chickadee nests generally were lower than 

the other three species (fig. 3). Range of nest heights was from about 2 m for all 

except mountain chickadee to 20 m and above. Several mountain chickadee nests 

were in logs nearly at ground level. 

Trees selected for nesting differed significantly in diameter (fig. 4) (t-value = 

6.774; df = 106; P-value <0.0001) and height (fig. 5) (t-value = 2.916; df = 106; Pvalue = 0.0043) from the nearest randomly selected trees. 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 227 

Figure 2—Mean heights (m) of nesting snags used by hairy woodpecker (HaWo - n 

= 17), mountain chickadee (MoCh - n =10), red-breasted nuthatch (RbNu - n = 11), 

and pygmy nuthatch (PyNu - n = 16) + 1 standard error and values for the tallest and 

shortest nest trees. 

Figure 3—Mean nest heights (m) of hairy woodpecker (HaWo - n = 17), mountain 

chickadee (MoCh - n =10), red-breasted nuthatch (RbNu - n = 11), and pygmy 

nuthatch (PyNu - n = 16) + 1 standard error and values for the highest and lowest 

nest locations. 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

228 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 4—Comparison of nest snag diameters (cm) to diameters of alternative snags 

(n = 107). The box plots display the 10th, 25th, 50th, 75th and 90th percentiles of 

each variable. 

Figure 5—Comparison of nest snag heights (m) to heights of alternative snags (n = 

107). The box plots display the 10th, 25th, 50th, 75th and 90th percentiles of each 

variable. 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 229 

Historic Nest Holes 

In 1989, a total of 1,459 snags of 9 snag species were found on the 24-5 ha study 

plots (table 1). Nest holes were not found in any of the California black oak, incense 

cedar, lodgepole pine, red fir, or western juniper snags on any study plot. Of the tree 

species with nest holes, Jeffrey pine, ponderosa pine, and white fir, only about 15 

percent of the snags of each species had at least one nest hole (fig. 6). For the fourth 

category, unknown pine (Jeffrey or ponderosa pine but too deteriorated to determine 

which species), some 35 percent of the snags had at least one nest hole. Snags with 

more than eight nest holes were very rare and found only in Jeffrey and ponderosa 

pines. 

For the four taxa of snags with nest holes, as snag diameter increased, generally 

a higher proportion of snags had nest holes (fig. 7). Almost none of the snags in the 

0-30 cm diameter class had nest holes regardless of species but between 10 (white 

fir) and 100 percent (unknown pine) of the >120 cm diameter class had nest holes. 

Numbers of nest holes relative to the numbers of snags increase as diameter 

class increases (fig. 8). Except for white fir, snags in larger diameter classes generally 

had greater numbers of nest holes than did snags in smaller diameter classes. 

Table 1—Numbers of snags present by snag species across all 24-5 ha study plots in 1989. 

Snag species No. of snags 

California black oak 4 

Incense cedar 27 

Jeffrey pine 843 

Lodgepole pine 30 

Unknown pine 35 

Ponderosa pine 269 

Red fir 1 

Western juniper 66 

White fir 184 

Total 1,459 

Figure 6—Percentages of snags with historic nest holes, for the snag species that 

possessed more than one nest hole, ranging from 0 nest holes to more than 8. 

Jeffrey pine = JePi (n = 843), ponderosa pine = PoPi (n = 269), unknown pine = Unk 

Pi (n = 35), white fir = WhFi (n = 183). Both JePi and PoPi have snags with >8 nest 

holes per snag, but the percentages are too low (0.1 and 0.7 percent respectively) to 

be illustrated in the figure. 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

230 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 7—Percentages of snags by diameter class with historic nest holes, for the 

snag species with more than one nest hole, that had nest holes compared to those 

without any nest holes. Jeffrey pine = JePi (n = 843), ponderosa pine = PoPi (n = 

269), unknown pine = Unk Pi (n = 35), white fir = WhFi (n = 183). 

Figure 8—Numbers of snags by diameter classes with nest holes, for the snag 

species with more than one nest hole, compared to the number of nest holes in each 

diameter class. Jeffrey pine = JePi (n = 843), ponderosa pine = PoPi (n = 269), 

unknown pine = Unk Pi (n = 35), white fir = WhFi (n = 183). 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 231 

Discussion 

Active Nests 

All four bird species nested in trees, generally dead or in the dead sections of 

live trees, that were greater than 40 cm DBH and with heights of nest trees that 

generally exceeded 10 m. The smallest diameter trees used approximate the lower 

limits of snag diameters found in many snag guidelines (e.g., Studinski and Ross 

1986). The majority of the nests were in trees substantially larger in diameter than 40 

cm DBH. Hairy woodpeckers often used shorter trees than the other species, but the 

majority of nests of all species were in trees in excess of 20 m in height. The heights 

of the nests, somewhat dependent on the height of the trees, was perhaps more 

variable than either the diameters or heights of trees selected for nesting. Hairy 

woodpeckers, despite selecting shorter trees on the average, tended to place their 

nests higher in the trees than the other species. 

The assemblage of cavity-nesting birds generally placed their nests in trees 

larger in diameter and taller than randomly selected alternative trees found in the 

study areas. The difference in diameters was greater than the difference in heights, 

suggesting that tree diameter may be the more important variable driving nest tree 

selection. Another explanation is that tree diameters are more stable than tree heights, 

as tree height often becomes shorter as trees decay, whereas once the bark is lost tree 

diameters do not change measurably. 

The selection of larger trees for nesting by cavity-nesting birds in California 

eastside pine forests reflects what is known from other forests and is well 

documented in the literature (e.g., Bull 1978, Cunningham and others 1980, 

Gutzwiller and Anderson 1986, Gutzwiller and Anderson 1987, Mannan and others 

1980, Mannan and Meslow 1984, McClelland and Frissell 1975, Raphael and White 

1984, Rosenberg and others 1988, Swallow and others 1988). Larger trees are 

generally preferred over smaller trees for most cavity-nesting species. 

Ponderosa and Jeffrey pines are the tree taxa most used for nesting in this study. 

These eastside pine forests are dominated by ponderosa or Jeffrey pine with other 

species of trees relatively uncommon. The pines were generally of larger diameter 

than the other tree species. 

Sapwood decay in ponderosa pine, and perhaps Jeffrey pine also, tends to be 

rapid and the decayed sapwood is easily excavated in cavity construction (Parks and 

others 1997). Thus, the entire cross-section of potential nest trees may not be suitable 

for excavation, and trees larger in diameter than the nominal guidelines suggest may 

be necessary for nesting birds. For the larger-bodied species, larger diameter trees 

may even be more desirable. 

Historic Nest Holes 

When the study was initiated, nearly 1,500 snags were available for nesting. The 

numbers of snags per plot varied considerably from 0 on several plots to as many as 

several hundred in a few cases. The vast majority of snags did not contain any nest 

holes, and only a very few snags had more than two-nest holes. Some 10-15 percent 

of the ponderosa and Jeffrey pine and white fir snags had nest holes; and 25 percent 

of the unknown pine species snags had nest holes. Although many ponderosa and 

Jeffrey pine and white fir snags had not decayed to a state that would permit 

excavation of nest holes (i.e., obvious separation of the bark from the bole or loss of 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

232 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

large portions of the bark, absence of needles and branchlets), the majority of 

unknown pine species snags had aged to a point where one might expect the birds to 

be able to excavate a nesting cavity. These pine snags had decayed to a state where 

they could no longer be classified into either ponderosa or Jeffrey pine using our field 

methods. However, even in these rather well decayed trees, a large number of snags 

did not have any nest holes. This suggests that a rather large number of the snags in 

this study were not suitable or capable for excavation of nest holes or that birds select 

snags for locating nest holes on criteria not readily apparent from the visual 

characteristics of the snags. 

Zack and others (2002) reported that the majority of snags at Blacks Mountain 

Experimental Forest and Goosenest Adaptive Management Area did not have any 

cavities. However, more snags at Blacks Mountain had cavities than at Goosenest.

Welsh and Capen (1992) also noted that relatively large numbers of apparently 

suitable nest trees were not used as nesting sites and also found that the number of 

excavated cavities per cavity trees were relatively low. Experimental evidence related 

to this question is not conclusive. Differences in habitat characteristics may influence 

the findings from snag and cavity studies. Waters and others (1990) reported that nest 

sites are not limiting to the secondary cavity-nesting bird community in an oak-pine 

woodland. However, Brawn and Balda (1988) showed that nest sites can be limiting 

for secondary cavity nesters in a ponderosa pine forest. 

Birds apparently do not randomly choose snags in which to excavate a nest. The 

larger the diameter of the snag, the more probable it is to have had nest holes 

excavated in it. This is particularly apparent in ponderosa and Jeffrey pine, and 

unknown pine snags and, as indicated earlier, may be related to the portions of the 

trees where the decay takes place. 

Management Implications 

Snags with large diameters and heights (e.g., greater than 25 inches in diameter) 

have been identified as very important to many of the cavity-nesting bird species. 

Such snags can only be derived from large trees that have been given the time to 

grow large. Because of the commercial value of large trees, they appear to be in short 

supply across large landscapes in eastside pine forests. To best provide habitat for 

these cavity-nesting species, larger parcels of land should be managed to provide 

trees of a variety of sizes and permit some of the largest trees to become snags. 

Management guidelines for specific snag densities are difficult to propose 

because the capability of the land to produce snags, especially large ones, is so 

variable, the snag resource is highly dynamic both in space and time, and many snags 

do not appear to be used as nesting substrate, suggesting that some snags may be 

surplus (as far as bird nesting is concerned). Balda (1975), as well as many others 

since, has proposed methods for estimating how many snags are needed by specific 

bird species. Application of those methods could form a baseline for specifying snag 

densities. However, snag numbers are probably related to the capability of particular 

sites to produce and sustain snags through time and related to site-specific variables, 

such as the number of large trees existing per acre, the lifespans of the large trees, 

and the mean standing duration of large snags. Snag numbers are also related to the 

historical consequences and causes of mortality (e.g., fire, insect attack) and their 

effects on the residual of large live trees that will eventually become snags. Thus, 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 233 

regardless of guidelines proposed, they will need to be tailored to specific landscape 

capabilities and conditions at the project scale. 

Snags are dynamic “entities” on dynamic landscapes that emerge and fall at 

different rates, depending on a variety of conditions related to cause of mortality and 

site characteristics. As such, land managers cannot be expected to understand or 

manage the decay trajectories of each snag. Despite the uncertainties involved in snag 

management, snag condition, hardness or softness, or simply the age of the snag may 

be useful criteria for choosing snags for removal or retention. Generally, it seems that 

the longer a snag stands, the more opportunity it has to be used to excavate a cavity 

or provide an existing cavity for a secondary cavity nester to use. Old snags are 

usually not commercially valuable, and land managers should attempt to retain those 

that do not pose a substantial safety or fire risk. Specific snag objectives might then 

be based on retention of hard snags. 

The removal of hazard trees and reduction of fuels can also reduce snag 

numbers substantially, especially in well roaded areas like northeastern California. It 

is often necessary to reduce hazards and reduce fuels, but removal of entire snags in 

many cases is not justified. Topping trees rather than total removal is an option that 

will maintain some, perhaps the majority, of the snag value yet reduce the hazards 

inherent in standing snags. Snag topping, as done on the Modoc National Forest 

(sawing off the tops; Studinski, pers. comm.) and at Yosemite National Park (pulling 

out the tops; Mattos, pers. comm.), may also permit snags to persist for a longer time. 

However, it is not yet known if such methods extend snag life, and it is not known 

how cavity-nesting species respond to such treated snags. 

If there are fewer snags on landscapes of interest than desired, snags can be 

created by a variety of methods (see Shea and others 2002 for a discussion on snag 

creation methods and results). Depending on the agent used to create snags, such 

trees can provide habitat for cavity-nesting birds as well as other organisms. Even 

retaining stumps, cut as high as possible, will still retain some of the snag values for 

cavity-nesting birds. However, Morrison and others (1983) recommend that high-cut 

stumps be employed only when absolutely necessary for safety considerations. 

Information about the relationships of cavity-nesting birds with snag 

characteristics can be used to craft management approaches to the conservation of the 

snag resource and cavity-nesting birds. However, managers must not predicate their 

management strategies only on providing nesting substrates. These birds require a 

continual sequencing of snags into their habitats for foraging as well as for nesting. In 

addition, cavity-nesting birds are not the only organisms that prefer or perhaps 

require dying and dead trees for their survival; a myriad of other organisms, 

including fungi, invertebrates, and other vertebrates, are also associated with these 

trees. Simply managing for the birds’ needs may not fulfill the requirements of other 

species that may actually be more essential to the processes in the forest, such as the 

recycling of wood. 

Acknowledgments 

The advice and ideas of James A. Baldwin, Barry R. Noon, David A. Sharpnack, 

and Jared Verner were incorporated into the design and methods of the study. Sandra 

Arnold, George Banuelos, Craig DeMartini, Erin Deneke, Mary Flores, Sheila Kee, 

Bo Larsen, David Lee, Britta Muiznieks, John Sterling, and Ellen VanGelder served 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

234 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

as field observers for portions of the study. Thoughts of Jon Arnold, Alan Berryman, 

Robert Borys, Al Denniston, Gary Eberlein, Kerry Farris, George Ferrell, George 

Gittings, R.J. Laacke, Pat Shea, George Steger, George Studinski and Steve Zack all 

contributed to this paper. Review comments by Don Behrens, Dean Carrier, Sandy 

Hicks, Brad Valentine, and Steve Zack were greatly appreciated and incorporated. 

References 

Balda, Russell P. 1975. The relationship of secondary cavity nesters to snag densities in 

western coniferous forests. Wildlife Habitat Technical Bulletin No. 1. Albuquerque, 

NM: Southwestern Region, Forest Service, U.S. Department of Agriculture; 37 p. 

Brawn, Jeffrey D.; Balda, Russell P. 1988. Population biology of cavity nesters in northern 

Arizona: do nest sites limit breeding densities? The Condor 90: 61-71. 

Bull, Evelyn L. 1975. Habitat utilization of the pileated woodpecker, Blue Mountains, 

Oregon. Corvallis: Oregon State University; 58 p. M.S. thesis. 

Bull, Evelyn L. 1978. Specialized habitat requirements of birds: snag management, old 

growth, and riparian habitat. In: DeGraaf, Richard M., technical coordinator. 

Proceedings of the workshop on nongame bird habitat management in the coniferous 

forests of the western United States. Gen. Tech. Rep. PNW-64. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 74-82. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 53 p. 

Cunningham, James B.; Balda, Russell P.; Gaud, William S. 1980. Selection and use of 

snags by secondary cavity-nesting birds of the ponderosa pine forests. Res. Paper 

RM-222. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. 

Department of Agriculture; 15 p. 

Gutzwiller, Kevin J.; Anderson, Stanley H. 1986. Trees used simultaneously and 

sequentially by breeding cavity-nesting birds. Great Basin Naturalist 46: 358-360.

Gutzwiller, Kevin J.; Anderson, Stanley H. 1987. Multiscale associations between cavitynesting birds and features of Wyoming streamside woodlands. The Condor 89: 534-

548. 

Hay, Douglas B.; Guntert, Marcel. 1983. Seasonal selection of tree cavities by pygmy 

nuthatches based on cavity characteristics. In: Davis, Jerry W.; Goodwin, Gregory 

A.; Ockenfels, Richard A., technical coordinators. Snag habitat management: 

proceedings of the symposium. Gen. Tech. Rep. RM-99. Fort Collins, CO: Rocky 

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 117-120. 

Landram, F. Michael; Laudenslayer, William F., Jr.; Atzet, Thomas. 2002. Demography of 

snags in eastside pine forests of California. In: Laudenslayer, William F., Jr.; Shea, 

Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Machmer, Marlene M.; Steeger, Christoph. 1995. The ecological roles of wildlife tree users 

in forest ecosystems. Land Management Handbook 35. Victoria, BC: Ministry of 

Forests Research Program, Province of British Columbia; 54 p. 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 235 

Mannan, R.William; Meslow, E. Charles. 1984. Bird populations and vegetation 

characteristics in managed and old-growth forests, northeastern Oregon. Journal of 

Wildlife Management 48: 1219-1238. 

Mannan, R. William; Meslow, E. Charles; Wight, Howard M. 1980. Use of snags by birds in 

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44: 787-797. 

McClelland, B. Riley; Frissell, Sidney S. 1975. Identifying forest snags useful for holenesting birds. Journal of Forestry 73: 414-417. 

Milne, Kathleen A.; Hejl, Sallie J. 1989. Nest-site characteristics of white-headed 

woodpeckers. Journal of Wildlife Management 53: 50-55. 

Morrison, Michael L.; Raphael, Martin G.; Heald, Robert C. 1983. The use of high-cut 

stumps by cavity-nesting birds. In: Davis, Jerry W.; Goodwin, Gregory A.; Richard A. 

Ockenfels, technical coordinators. Snag habitat management: proceedings of the 

symposium. Gen. Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture; 73-79. 

Parks, Catherine G.; Bull, Evelyn L.; Torgersen, Torolf R. 1997. Field guide for the 

identification of snags and logs in the Interior Columbia River Basin. Gen. Tech. 

Rep. PNW-GTR-390. Portland, OR: Pacific Northwest Research Station, Forest Service, 

U.S. Department of Agriculture; 40 p. 

Raphael, Martin G.; White, Marshall. 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada, California. Wildlife Monographs No. 86. 

Rosenberg, Daniel K.; Fraser, James D.; Stauffer, Dean R. 1988. Use and characteristics of 

snags in young and old forest stands in southwest Virginia. Forest Science 34(1): 

224-228. 

Scott, Virgil E. 1978. Characteristics of ponderosa pine snags used by cavity-nesting 

birds in Arizona. Journal of Forestry 76: 26-28. 

Scott, Virgil E.; Oldemeyer, John L. 1983. Cavity-nesting bird requirements and responses 

to snag cutting. In: Davis, Jerry W.; Goodwin, Gregory A.; Ockenfels, Richard A., 

technical coordinators. Snag habitat management: proceedings of the symposium. Gen. 

Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, 

U.S. Department of Agriculture; 19-23. 

Scott, Virgil E.; Evans, Keith E.; Patton, David R.; Stone, Charles P. 1977. Cavity-nesting 

birds of North American forests. Agricultural Handbook 511. Washington, DC: U.S. 

Department of Agriculture; 112 p. 

Shea, Patrick; Laudenslayer, William F., Jr.; Ferrell, George; Borys, Robert. 2002. Girdled 

versus bark beetle-created ponderosa pine snags: utilization by cavity-dependent 

species and differences in decay rate and insect diversity. In: Laudenslayer, William 

F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas 

E., technical coordinators. Proceedings of the symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; [this volume]. 

Studinski, George; Ross, Michael. 1986. Modoc National Forest snags: analysis of the 

management situation. Forest Report. Alturas, CA: Modoc National Forest, Forest 

Service, U.S. Department of Agriculture. 

Swallow, Stephen K.; Howard, Ronald A., Jr.; Gutierrez, R.J. 1988. Snag preferences of 

woodpeckers foraging in a northeastern hardwood forest. Wilson Bulletin 100(2): 

236-246. 

Waters, Jeffrey R.; Noon, Barry R.; Verner, Jared. 1990. Lack of nest site limitation in a 

cavity-nesting bird community. Journal of Wildlife Management 54(2): 239-245. 
Nesting Bird Use of Snags in Eastside Pine Forests—Laudenslayer 

236 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Welsh, Christopher J.E.; Capen, David E. 1992. Availability of nesting sites as a limit to 

woodpecker populations. Forest Ecology and Management 48: 31-41. 

Zack, Steve; George, T. Luke; Laudenslayer, William F., Jr. 2002. Are there snags in the 

system? Comparing cavity use among nesting birds in “snag-rich” and “snag-poor” 

eastside pine forests. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, 

Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. 

Proceedings of the symposium on the ecology and management of dead wood in western 

forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: 

Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 

[this volume]. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 237 

Woodpecker Foraging and the 

Successional Decay of Ponderosa Pine1

 

Kerry L. Farris,2,6 Edward O. Garton,2 Patricia J. Heglund,3 Steve 

Zack,4 and Patrick J. Shea5 

Abstract 

In 1998 we initiated a long-term study investigating the relationships between woodpecker 

foraging and snag decay processes in interior ponderosa pine forest communities located in 

Oregon and California. We describe temporal changes in snag structure and quantify both 

woodpecker foraging activity and relative sapwood decay in 144 ponderosa pine snags, 

ranging in age from 1 to 9 years (time since death). Preliminary results indicate that temporal 

changes in snag characteristics were reflective of both inherent insect activity and 

woodpecker foraging quality. Statistical analysis revealed no significant difference in 

cumulative woodpecker foraging abundance as snags aged, indicating that woodpecker 

foraging activity occurred primarily in the younger aged snags. Additionally, there was no 

correlation between woodpecker foraging intensity and relative sapwood decay. These results 

offer insights into the interactive biology of bark beetles, woodpeckers, and fungi in the 

decomposition of ponderosa pine. 

Introduction 

Woodpecker foraging and nesting ecology is closely tied to insect infestations 

and tree decomposition stages. Foraging woodpeckers tend to select trees and snags 

containing high levels of bark and wood boring insects (Baldwin 1960, Kroll and 

Fleet 1979, Otvos 1965), whereas nesting woodpeckers generally require pockets of 

older, decayed wood that permit nest excavation (Bull 1983, Bull and others 1997, 

Conner and others 1976, Harris 1983). In fact, Conner and others (1976) and Miller 

and Miller (1980) suggested that some form of wood decay is a prerequisite for nest 

excavation by most species of woodpecker. While the characteristics of snags utilized 

by woodpeckers for nesting have been studied widely, relatively little is known about 

structures associated with foraging (Bull and others 1997, Conner and others 1994, 

Steeger and others 1996). Moreover, the potential influences of foraging 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. Contribution #13 of the Blacks 

Mountain Ecological Research Project, Pacific Southwest Research Station, USDA Forest Service. 2 Graduate Research Assistant and Professor of Wildlife Ecology, respectively, Department of Fish and 

Wildlife Resources, University of Idaho, Moscow, ID 83844-1136 (e-mail: ogarton@uidaho.edu) 3 Wildlife Biologist, U.S. Fish and Wildlife Service―Refuges, 1011 East Tudor Road, Anchorage, AK 

99503-2212 (e-mail: patricia_heglund@fws.gov) 

4 Conservation Scientist, Wildlife Conservation Society, North America Program, 1746 NW Hartwell 

Place, Portland, OR 97229 (e-mail: szack@wcs.org) 

5 Research Entomologist, Pacific Southwest Research Station, USDA Forest Service, 1107 Kennedy 

Place, Suite 8, Davis, CA 95616 (e-mail: pjshea@davis.com) 6 Associate Conservation Ecologist, Wildlife Conservation Society, North American Program, 2814 E. 

Waverly St. #2, Tucson, AZ 85716 (e-mail: kfarris@wcs.org) 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

238 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

woodpeckers on snag decomposition characteristics, and therefore subsequent nest 

site quality, have gone largely unexplored. 

In the interior ponderosa pine forests of the western United States, woodpeckers 

are commonly associated with dead or dying trees where they feed upon bark and 

wood boring beetles. In their search for prey, they puncture bark surfaces and 

fragment the underlying wood, thereby altering local microhabitat conditions. Otvos 

(1979) suggested that such behavior may actually expedite the process of snag decay 

by creating vectors for the colonization of wood decay organisms. Additionally, 

Conner and others (1994) observed that hardwood snags which received relatively 

more foraging activity by woodpeckers tended to have higher incidences of decayed 

wood. Considering that most species of woodpecker in North America require some 

form of wood decay for nest excavation, potential interrelationships between foraging 

activities and the spread of decay fungi in snags are intriguing. 

Because organisms that promote sapwood decay tend to rapidly colonize dying 

conifers (Harmon and others 1986, Mercer 1982, Rayner and Boddy 1988), early 

patterns of snag utilization are likely central to understanding the relationship 

between woodpecker use and subsequent decay dynamics. Several researchers have 

reported concentrated foraging activity by some woodpecker species within the first 

few years of tree death (Bull 1983, Bull and others 1986, Murphy and Lehnhausen 

1998, Steeger and others 1996). However, few have quantified foraging intensity 

across a spectrum of decay classes, or elucidated the relationships between foraging 

woodpeckers and subsequent snag decay dynamics. 

Addressing such ecological questions requires the use of large populations of 

known age snags. Consequently, researchers often rely on snags produced in 

naturally occurring perturbations such as wildfires, insect outbreaks, or windthrow 

events, but this may prove problematic in many cases because the exact time and 

mode of death may be attributed to several underlying sources. Because the 

biological decay activity of a tree is directly related to both the timing and cause of 

its demise, it is easy to envision how controlling these two variables can greatly aid 

in the reduction of long term error. In this study, we made use of an experimental 

population of snags intentionally infested with bark beetles (using pheromone baits) 

as part of a separate, long-term entomological study. As a result, the exact date and 

mode of mortality were known, which narrowed the range of possible decay 

pathways and permitted us to better examine the effects of foraging woodpeckers on 

subsequent snag decay processes. 

The purpose of this research was to investigate the dynamic relationship of 

foraging woodpeckers and ponderosa pine decay. Specifically, we wanted to identify 

the structural changes in ponderosa pine throughout the decay sequence, determine 

the decomposition stages used most intensely by foraging woodpeckers, and examine 

the effect of these foraging activities on sapwood decomposition. 

Study Area and Methods 

The study was conducted on three National Forests in the Cascade Range: the 

Lassen located in northeastern California and the Ochoco and Deschutes National 

Forests in central Oregon (fig. 1). Interior ponderosa pine (Pinus ponderosa var. 

ponderosa) was the dominant species at all three locations. The Oregon sites had a 

minor component of both Douglas-fir (Pseudotsuga menziesii) and white fir (Abies 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 239 

concolor var. lowiana), while the higher elevations of the Lassen site contained a 

large component of Jeffrey pine (Pinus jeffreyi), with scattered inclusions of white fir 

and incense-cedar (Libocedrus decurrens). Elevations ranged from 2,275 meters on 

the Ochoco National Forest to 2,730 meters on the Lassen National Forest. Resident 

woodpecker species of interest included the white-headed (Picoides albolarvatus), 

downy (P. pubescens) three-toed (P. tridactylus), black-backed (P. arcticus), hairy 

(P. villosus), and pileated woodpeckers (Dryocopus pileatus). Other woodpecker 

species (i.e., northern flicker [Colaptes auratus] and three species of Sphyrapicus

sapsuckers) were also present, but do not typically feed on decaying pines. 

Figure 1—The three snag data collection areas in central Oregon and northeastern 

California. 

Methods 

Because snag decomposition is a slow and variable process, charting structural 

and biological changes directly requires very long periods of time. One recognized 

alternative is to use a chronosequence of snags with known dates of origin for 

reconstructing temporal patterns of decay. Between the three forests, we developed a 

chronosequence consisting of 144 snags ranging in age from 1 to 9 years. Snags on 

the Ochoco and Deschutes sites were created by bark beetles responding to 

pheromone baits in 1998 and 1997, respectively. Snags on the Lassen site were 

sampled from two separate populations. Half were baited with bark beetle pheromone 

in 1993 and the remainder were sampled from a large population of naturally 

occurring snags with known ages. All 144 snags, which ranged from 40 to 130 

centimeters in diameter, were sampled between 1 June and 31 August 1999. 

To document structural and biological changes in the snags across the 

chronosequence, seven age-dependant variables were visually recorded. These 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

240 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

included: foliage color (green, lime green, yellow, red), foliage retention (expressed 

as percent of needles remaining), bark retention (expressed as percent remaining), 

bark integrity (tight or loose, as indicated when the bark was punctured), presence of 

woodpecker nest cavities, presence of bark beetle pitch tubes, and type and quantity 

of beetle exit holes. Because the phenology of beetles foraging on ponderosa pine 

follows a distinct chronology, the size and shape of holes left in the bark when 

beetles exit the snag are indicative of particular families, and are therefore useful 

indicators of decay progression (Patrick J. Shea, pers. comm.). Using this 

information, we were able to classify and quantify exit holes of three taxonomic 

families in chronological order of tree infestation: Scolytidae (“primary” invaders), 

Buprestidae (“secondary” invaders), and Cerambycidae (“secondary” invaders). 

To compare woodpecker foraging activity across snag ages, we developed a 

foraging intensity index based on the cumulative number of foraging excavations per 

square meter. Foraging intensity was quantified on each snag using a 30x spotting 

scope and counting all visible foraging excavations from a distance of 30 meters on a 

randomly selected azimuth. Counts were cumulative and did not distinguish between 

current season and previous years’ foraging evidence. The surface area surveyed was 

calculated and divided into the number of observed foraging “hits,” resulting in a 

standardized index of foraging hits per square meter of snag surface. 

As a relative indicator of sapwood softness, we used a six-joule Proceq Pilodyn 

wood tester (Crown 1978, Sprague and others 1983). The Pilodyn compresses a 

spring loaded steel pin into the sapwood with a constant force, measuring penetration 

depth in millimeters. On each snag, at a height of 1.3 meters, we removed a square 

piece of bark measuring 4 centimeters2

 at each of the four cardinal directions. This 

permitted the Pilodyn direct access into the sapwood, which was measured with the 

Pilodyn three times at each exposed site to compute an average penetration in 

millimeters for 12 strikes per snag. Before bark removal, we quantified woodpecker 

foraging within the immediate area by counting foraging hits in a 15x15 centimeter 

area. 

Because snags were sampled from two differing sources (bark beetle killed and 

unknown mortality causes) and considering that the mode of tree death likely 

influences subsequent woodpecker foraging activity and decay dynamics, we divided 

the data into two subsets, based on mortality agent, prior to analysis. We used simple 

linear regression to evaluate the relationships between woodpecker foraging, and 

both snag age and sapwood softness. 

Results 

Visual decay characteristics changed directionally with increasing snag age 

along the chronosequence (table 1). In general, foliage color tended to turn from dark 

green to lime or yellow within the first year and was red by year 2. Needle retention 

dropped to an average of 85 percent within the first year and 14 percent by year 2. By 

year 3 all snags had completely lost their foliage. Bark retention was 100 percent 

until year 4, then fell to between 90 and 95 percent for the remainder of age classes. 

However, 50 percent of the sampled snags had loose or sloughing bark by year 4 and 

all snags had loose bark by age 6. 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 241 

Table 1—Structural decay characteristics of 144 ponderosa pine snags across 10 

age classes in the central and southern Cascades of Oregon and northeastern 

California, 1999.

Snag Mean/std. dev. age class Percent of age class exhibiting described feature 

Age Foliage Pct needles Pct bark Loose Pitch Exit holes Nest 

Class Color1 Remaining Remaining Bark Tubes Scolytidae Buprestidae Cerambycidae Cavities 

0 Green 100/0 100/0 0 0 0 0 0 0 

1 Lime 85/23 100/0 0 97 93 71 0 0 

2 Red 13.5/24 100/0 0 92 100 90 23 0 

3 n/a 0/0 100/0 50 75 100 100 100 50 

4 n/a 0/0 95/5 71 75 100 100 100 50 

5 n/a 0/0 90/7 75 50 100 100 100 50 

6 n/a 0/0 90/19 100 50 100 100 100 71 

7 n/a 0/0 90/0 100 50 100 100 100 100 

8 n/a 0/0 90/14 100 50 100 100 100 100 

9 n/a 0/0 90/29 100 13 100 100 100 100 1 Color means calculated using 1 = green, 2 = lime, 3 = yellow, 4 = orange, and 5 = red. 

The presence of beetle pitch tubes, which indicates either past or present beetle 

infestation, was highest during the first year, with 97 percent of sampled snags 

exhibiting tubes. This proportion gradually decreased over time, with only 13 percent 

of the snags having old tubes remaining by age 9. Ninety-three percent of 1-year-old 

snags exhibited exit holes created by members of the family Scolytidae, and this 

figure increased to 100 percent by the second year. Secondary beetles of the families 

Buprestidae and Cerambycidae emerged during the first and second years, 

respectively. Ninety percent of 1-year-old snags had Buprestid exits, but no visual 

evidence of Cerambycid emergence. By the second year, 100 percent of the snags 

showed signs of Buprestid emergence, while Cerambycid beetles emerged from only 

23 percent of the snags. By the third year, 100 percent of the snags showed evidence 

of both beetle families. Nest cavities showed up in 50 percent of the snags by the 

third year, 71 percent by year 6, and all snags had cavities by year 7. 

Initial linear regression analysis revealed no significant increase in woodpecker 

foraging intensity between beetle killed snags and those with unknown causes of 

mortality. Additionally, because t-test comparisons revealed similar slopes for each 

set (p = 0.001), the two data sets were combined for all subsequent analyses. Further 

regression analysis on the entire set of snags yielded similar results, with no increase 

in woodpecker foraging intensity as snags aged (fig. 2). The slope of the regression 

line did not significantly differ from zero (p < 0.0001), indicating that most 

woodpecker foraging activity took place in the early stages of decay. Sapwood 

softness was not linearly related to the amount of woodpecker foraging (fig. 3). 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

242 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

R2 = 0.008

0

10

20

30

40

50

0 4 8 12 16

Foraging Intensity (hits/15 cm2)

Pilodyn Penetration (mm)

R

2

 = 0.0000

-20

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8 9 10

Snag Age

Fora

gin

g Intensit

y (hits/m2

)

 

Figure 2—Linear regression analysis of cumulative woodpecker foraging intensity 

and snag age from 144 snags sampled on the Deschutes and Ochoco Forests in 

central Oregon and the Lassen National Forest in northeastern California, 1999. 

Dashed lines indicate 95 percent confidence intervals. 

Figure 3—Linear regression analysis of woodpecker foraging intensity and sapwood 

softness as indicated by pilodyn penetration measured from 144 snags sampled on 

the Deschutes and Ochoco Forests in central Oregon and the Lassen National Forest 

in northeastern California, 1999. Dashed lines indicate 95 percent confidence 

intervals. 

Snag Age 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 243 

Discussion 

The decay characteristics exhibited in this snag population show similarities 

with those described by other authors (Bull 1983, Raphael and Morrison 1987, 

Steeger and others 1996). However, we discretely defined snag decay characteristics 

to better reflect their value to foraging woodpeckers. For example, the commonly 

used decay classifications put forth by Thomas and others (1979) and Steeger and 

others (1996) broadly categorize snags on the basis of bark retention, needle, twig, 

and branch presence. Although these classifications are useful for defining suitable 

nest substrates, they probably do not reflect the more subtle changes in woodpecker 

foraging value resulting from early fluctuations in arthropod populations. We found 

that needleless snags were generally only 3 years old and would fit into decay 

category 1 (first category under “dead”), using established classification systems 

(Bull and others 1997, Steeger and others 1996, Thomas and others 1979). However, 

examination of beetle phenology data from our study areas (using exit holes as 

guidelines) suggests that most 3-year-old snags are probably past the peak of bark 

and wood boring beetle activity, and therefore less likely to be used by foraging 

woodpeckers. Consequently, a highly valuable foraging stage may be masked by 

current classifications. Maintaining high quality woodpecker foraging habitat may 

require modifications of current snag classifications to account for early stages of 

snag decay. 

Woodpeckers in the study areas appear to concentrate their foraging activity 

within the first few years of tree death. This period coincides with the densest 

populations of bark and wood boring beetles, as evidenced by the appearance of 

beetle exit holes. These findings agree with what is currently known about the diets 

of Picoides woodpeckers that specialize on bark and wood boring beetles (Otvos 

1965, 1970, 1979). Similar temporal foraging patterns have been documented in the 

literature (Bull 1983, Bull and others 1986, Parks 1999, Steeger and others 1996), 

especially in areas of epidemic beetle outbreaks (Amman 1984, Baldwin 1960, Kroll 

and Fleet 1979, Otvos 1965), or as a response to a localized perturbation such as 

windthrow (Wickman 1965) and fire (Murphy and Lehnhausen 1998). 

Although these data appear to reinforce the notion that foraging woodpeckers 

concentrate their use on younger snags, it is based on a chronosequence of snag 

decay. Substituting space (in the sense of different geographical areas or individual 

snags) for time requires an inherent assumption regarding the temporal pattern of the 

foraging activity. When we sampled older snags, we assumed that the visible 

foraging sign took place in the early stages of the tree’s demise. This may be a 

reasonably safe assumption considering the rapid, abundant, response of both beetles 

and woodpeckers to a dying tree. In general, the activities of both groups within the 

early stages of tree death is so intense, it numerically overwhelms further evidence of 

subsequent beetle-woodpecker activities. However, because each individual snag was 

not followed yearly from death, we cannot unequivocally determine at what point 

along the decay sequence the foraging took place. To gain accurate insight into the 

relationships between foraging woodpeckers and snag decay, it is critical to have a 

long term data set in which each snag is followed and woodpecker foraging is 

quantified yearly from the time of death. We hope to rectify this problem over time 

as our data set grows, but until then these results should be interpreted accordingly. 

Finally, these data did not reveal any pattern between the intensity of 

woodpecker foraging and the relative degree of sapwood decay. There could be 

several explanations for this particular finding, two of which relate to the use of the 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

244 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Pilodyn as a sampling tool, and one that has to do with woodpecker foraging ecology. 

First, in addition to the effects of climate, aspect, and microhabitat differences, live 

trees compartmentalize invading bacteria and fungi, thus isolating these organisms to 

localized areas, creating a patchy mosaic of sound and decayed wood (Shigo 1984). 

Our survey methods were only designed to measure sapwood decay in one small 

localized, radial area, but as demonstrated by Shigo (1984), wood decay is spatially 

variable in nature, thereby making our measures with the Pilodyn a hit or miss 

procedure. This is evidenced by the often highly variable Pilodyn readings even 

within a small, 1 cm2

 area. Although one measure may have hit sound wood, another 

just a few millimeters away might have produced a clearly decayed reading. Our 

selected method of decay quantification was somewhat limited considering this finescale variability. 

A second possible reason for our inability to detect a relationship between 

woodpecker foraging intensity and sapwood decay could be explained by a 

phenomenon known as “case hardening.” Mercer (1982) noted that the outer 3-4 

centimeters of sapwood is frequently harder than more interior points due to 

weathering and drying of the snag surface. The Pilodyn had a maximum extension of 

40 millimeters. Consequently, it may not even have been penetrating the truly soft 

areas of the wood. It is clear that the Pilodyn has limitations for this purpose, yet 

several researchers have found Pilodyn measures comparable to those of specific 

gravity (Conner and others 1994, Sprague and others 1983) and wood density (Crown 

1978). We are currently exploring various options to better detect and quantify 

relative sapwood decay on a more universal scale. 

Finally, we believe that the foraging ecology of woodpeckers could have a 

marked effect on the dynamics of wood decomposition, thus affecting our ability to 

accurately quantify an interrelationship. Methods of food procurement differ between 

woodpecker species and could play a role in whether the wood is exposed to decay 

fungi. For example, several species of woodpecker are thought to predominantly 

“scale” for primary bark beetles, while others “excavate” for secondary wood boring 

beetles. Scaling behavior involves striking the bark at an angle to “scale” away the 

outer surfaces. This behavior rarely penetrates the wood, its purpose being to exploit 

food resources just under the bark’s surface. In contrast, excavation involves creating 

large holes into the bark and wood (usually in pursuit of wood boring organisms) 

which significantly alters the microhabitat of the sapwood. It is easy to envision how 

this excavation behavior might facilitate more rapid fungal colonization by providing 

greater access points into the snag’s interior. 

Because particular species of woodpecker are thought to specialize in certain 

foraging behaviors, interspecific population dynamics in the area of an individual 

snag could alter the rates of sapwood fungal invasion. For example, the three-toed 

woodpecker generally forages using the scaling technique (Bull and others 1986, 

Murphy and Lehnhausen 1998), whereas species such as the hairy and black-backed 

woodpeckers are relatively stronger excavators (Bull and others 1986). If a given area 

had relatively larger populations of “scaling” species, then decay rates could be less 

pronounced due to the relatively minor substrate manipulations created by this 

foraging strategy. 

These preliminary results offer some insights into the dynamic relationship of 

woodpecker foraging and ponderosa pine decay, yet our sampling methods need 

refinement to more accurately quantify the potential effect of foraging woodpeckers 

on snag decay processes. In particular, a better method of quantifying sapwood decay 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 245 

is needed. We are currently engaged in exploring these methodological issues and 

hope to further investigate the interactive biology of bark beetles, woodpeckers, and 

fungi in the decomposition of ponderosa pine. 

References 

Amman, G. D. 1984. Mountain pine beetle (Coleoptera: Scolytidae) mortality in three 

types of infestations. Environmental Entomology 13: 184-191. 

Baldwin, P. H. 1960. Overwintering of woodpeckers in bark-beetle infested spruce-fir 

forests in Colorado. 12th International ornithological congressional proceedings. 1958. 

Helsinki; 71-84. 

Bull, E. L. 1983. Longevity of snags and their use by woodpeckers. In: Davis, J. W.; 

Goodwin, G. A.; Ockenfels, R. A., eds. Snag habitat management symposium. 1980 

June 7-9; Flagstaff, AZ. Gen. Tech. Rep. RM-GTR-99. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 64-67. 

Bull, E. L.; Peterson, S. R.; Thomas, J. W. 1986. Resource partitioning among 

woodpeckers in northeastern Oregon. Gen. Tech. Rep. PNW-GTR-444. Portland, OR; 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 19 

p. 

Bull, E. L.; Parks, C. G.; Torgersen, T. R. 1997. Trees and logs important to wildlife in the 

Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. Portland, OR; 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 55 

p. 

Conner, R. N.; Jones, S. D.; Jones, G. D. 1994. Snag condition and woodpecker foraging 

ecology in a bottomland hardwood forest. Wilson Bulletin 106(2): 242-257. 

Conner, R. N.; Miller, O. K., Jr.; Adkisson, C. S. 1976. Woodpecker dependence on trees 

infected by fungal heart rots. Wilson Bulletin 88: 575-581. 

Crown, D. J. 1978. Comparison of the Pilodyn and Torsiometer methods for the rapid 

assessment of wood density in living trees. New Zealand Journal of Forest Science 

8(3): 384-391. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedill, J. R.; Lienkaemper, G. W.; 

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. In: Macfadyen, A.; Ford, E. D., eds. Advances in ecological 

research. Vol. 15. Academic Press; 133-302. 

Harris, R. D. 1983. Decay characteristics of pileated woodpecker nest trees. In: Davis, J. 

W.; Goodwin, G. A.; Ockenfels, R. A., eds. Snag habitat management symposium. 1980 

June 7-9; Flagstaff, AZ. Gen. Tech. Rep. RM-GTR-99. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 125-129. 

Kroll, J. J; Fleet, R. R. 1979. Impact of woodpecker predation on over-wintering withintree populations of the southern pine beetle (Dendroctonus frontalis). In: Dickson, J. 

G.; Conner, R. N.; Fleet, R. R.; Jackson, J. A.; Kroll, J. C. eds. New York: Academic 

Press; 269-82. 

Mercer, P. C. 1982. Basidiomycete decay of standing trees. In: Frankland, J. C.; Hedger, J. 

N.; Swift, M. J., eds. Decomposer basidiomycetes. British Mycological Society 

Symposium #4. New York: Cambridge University Press; 143-160. 
Woodpecker Foraging and Snag Decay—Farris, Garton, Heglund, Zack, and Shea 

246 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Miller, E.; Miller, D. R. 1980. Snag use by birds. In: DeGraaf, R. M., ed. Management for 

non-game birds. Gen. Tech. Rep. INT-GTR-86. Ogden, UT: Intermountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 337-356. 

Murphy, E. C.; Lehnhausen, W. A. 1998. Density and foraging ecology of woodpeckers 

following a stand-replacement fire. Journal of Wildlife Management 62(4): 1359-

1372. 

Otvos, I. S. 1965. Studies of avian predators of Dendroctonus brevicomis Leconte 

(Coleptera: Scolvtidae), with special reference to Picidae. Canadian Entomologist 97: 

1184-1199. 

Otvos, I. S. 1970. Avian predation of the western pine beetle. In: Stark, R.; Dahlsten, D., 

eds. Studies of the population dynamics of the western pine beetle, Dendroctonus 

brevicomis Leconte (Coleoptera: Scolytidae). Berkeley: University of California Press; 

119-127. 

Otvos, I. S. 1979. The effects of insectivorous bird activities in forest ecosystems: an 

evaluation. In: Dickson, J. G.; Conner, R. N.; Fleet, R. R.; Jackson, J. A.; Kroll, J. C., 

eds. New York: Academic Press; 341-74. 

Parks, C. A.; Conklin, D. A.; Bednar, L.; Maffei, H. 1999. Woodpecker use and fall rates of 

snags created by killing ponderosa pine infected with dwarf mistletoe. Res. Paper 

PNW-RP-515. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 11 p. 

Raphael, M. G; Morrison, M. L. 1987. Decay and dynamics of snags in the Sierra Nevada, 

California. Forest Science 33(3): 774-783. 

Rayner, A. D. M.; Boddy, L. 1988. Fungal decomposition of wood: its biology and ecology. 

New York: John Wiley and Sons; 587 p. 

Shigo, A. L. 1984. Compartmentalization: a conceptual framework for understanding 

how trees grow and defend themselves. Annual Review of Phytopathology 22: 189-

214. 

Sprague, J. R.; Talbert, J. T.; Jett, J. B.; Bryant, R. L. 1983. Utility of the Pilodyn in 

selection for mature wood specific gravity in loblolly pine. Forest Science 29(4): 696-

701. 

Steeger, C.; Machmer, M.; Walters, E. 1996. Ecology and management of woodpeckers 

and wildlife trees in British Columbia. B.C. Ministry of Forests, Fraser River Action 

Plan; 23 p. 

Thomas, J. W.; Anderson, R. G.; Maser, C.; Bull, E. L. 1979. Snags. In: Thomas, J. W., ed. 

Wildlife habitats in managed forests: the Blue Mountains of Oregon and 

Washington. U.S. Department of Agriculture Handbook 553. Washington, D.C.; 60-77. 

Wickman, B. E. 1965. Black-backed three-toed woodpecker, Picoides arcticus, predation 

on Monochamus oregonensis (Coleoptera: Cerambycidae). Pan-Pacific Entomologist 

41(3): 162-164. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 247 

Forest Age and Relative Abundance of 

Pileated Woodpeckers on Southeastern 

Vancouver Island1

Carol L. Hartwig,2 Donald S. Eastman,3 and Alton S. Harestad4

Abstract

We estimated relative abundance of the pileated woodpeckers (Dryocopus pileatus) at four 

sites in the Coastal Western Hemlock Biogeoclimatic zone, on southeastern Vancouver Island 

during 1996-1997. The number of pileated woodpecker calls was correlated with age and 

structure of forests. Pileated woodpeckers did not use intensively managed forests < 80 years 

old that had low densities of dead wood (large snags and logs). They were most abundant in 

forests that had greater densities of dead wood and where 51 percent of the area was covered 

by >140-year-old stands. However, their abundance in these forests did not differ significantly 

from that in early seral forests (49 percent > 80-year-old stands) or old forests (70 percent > 

140-year-old stands). 

Introduction 

The pileated woodpecker (Dryocopus pileatus) is an important species in forests 

of North America because, as a primary cavity nester, it creates habitat opportunities 

for secondary cavity nesters. It is the largest extant woodpecker species in North 

America and, because of its size, excavates large cavities. Hence, many species 

benefit from its nesting and roosting activities (Bunnell and others 2002). Loss of 

structural elements (e.g., logs, snags, and trees with broken tops, scars, decay, or 

damage) has the most significant impact on pileated woodpecker habitat; forest 

fragmentation likely reduces population density and makes pileated woodpeckers 

vulnerable to predation as they fly between forest fragments (Bull and Jackson 1995). 

We estimated relative abundance of pileated woodpeckers in relation to habitat 

types and stand characteristics in the Coastal Western Hemlock Biogeoclimatic zone 

on southeastern Vancouver Island. For our study, we define relative abundance as the 

number of responses (the number of pileated woodpeckers calling or drumming in 

response to a recording) received per call station within an area. Relative abundance 

can be used to infer the quality of the habitat for species, and differences in the 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Partner, Ecodomain Consulting, 934 Khenipsen Road, Duncan, British Columbia, Canada, V9L 5L3, 

(e-mail: chartwig@shaw.ca) 

3

 Faculty Coordinator, Restoration of Natural Systems Program, School of Environmental Studies, 

University of Victoria, Box 1700, Victoria, British Columbia, Canada, V8W 2Y2 (e-mail: 

deastman@uvic.ca) 

4

 Associate Professor, Department of Biological Sciences, Simon Fraser University, 8888 University 

Way, Burnaby, British Columbia, Canada, V5A 1S6 (e-mail: harestad@sfu.ca) 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

248 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

abundance of bird species often reflect the availability of resources to them 

(Schoener 1968). 

Our objectives were to estimate relative abundance of pileated woodpeckers in 

different seral stages and structure classes of forest stands and examine associations 

between habitat features and abundance of pileated woodpeckers. We hypothesized 

that the relative abundance of pileated woodpeckers increases as age of forest 

increases and as the amount of forest harvesting decreases. We also expected that 

landscapes with greater quantities of dead or decayed large forest structures (i.e., 

snags, defective trees, and logs) will have a greater abundance of pileated 

woodpeckers. 

Methods 

Study Area

We selected our study area on southeastern Vancouver Island because it has a 

population of pileated woodpeckers (determined from historical records [Campell 

and others 1990] and from pilot surveys), a range of forest conditions, and because 

commercial timber harvesting occurs in the region. Forest management for timber in 

each site ranged from 100 percent logged and 60-80 percent spaced in the early seral 

study site, 40 percent logged and 39 percent spaced in the mid-seral study site, 20 

percent logged and 4 percent spaced in the mature study site, and 22 percent logged 

and 5 percent spaced in the mature/old study site. The study area is located within the 

Very Dry Maritime Coastal Western Hemlock Biogeoclimatic subzone (CWHxm) 

(Anonymous 1993). It has warm, dry summers and moist, mild winters (Green and 

Klinka 1994). Forests in the CWHxm subzone are coniferous, dominated by 

Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and 

minor amounts of western red-cedar (Thuja plicata), but some deciduous species 

such as red alder (Alnus rubra) and bigleaf maple (Acer macrophyllum) occur (Green 

and Klinka 1994). 

Field Methods 

We established four 1,450-ha study sites. Each study site encompassed an area 

equal to the home ranges of approximately two to three breeding pairs of pileated 

woodpeckers. Home range size was estimated to be 478 ha for individuals after 

young fledged in coastal western hemlock climax forests dominated by Douglas-fir 

(Mellen and others 1992). The four sites represented four landscapes that differed in 

seral stage and forest structure. The Hillridge site was a homogeneous, early seral 

forest with few snags and medium numbers of large logs remaining after cutting of 

the primary forest (tables 1, 2). Niagara was a mid-seral forest with abundant 

remnant large snags and logs. Sooke was a mixed forest with early and mid-seral 

forests and mature/old forests with abundant remnant large snags and logs. Rithet 

represented most closely an unlogged mature/old seral forest with abundant snags 

and a modest number of logs. 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 249 

Table 1—Percentage of forest stand age classes in four pileated woodpecker study sites on 

southeastern Vancouver Island. 

Study site 

Early seral 

< 60 years 

Mid-seral 

61-100 

Mature 

101-140 

Mature/old 

>140 

Non-forest 

Hillridge 73 27 0 0 0 

Niagara 47 22 14 13 5 

Sooke 26 9 0 51 13 

Rithet 22 5 3 70 1 

Table 2―Mean (± SE) or percent frequency of forest characteristics of four pileated 

woodpecker study sites on southeastern Vancouver Island, 1996-1997.

 Study sites (n = plots) 

Characteristic Hillridge (10) Niagara (19) Sooke (20) Rithet (10) P 

Coarse woody debris (m3 ha-1) 75 (± 19) 176 (± 33) 213 (± 39) 114 (± 34) 10.11 

Snag or defective tree basal 

area (m2

ha-1) 0.7 (± 0.2) 4.3 (± 1.3) 7.1 (± 1.4) 11.9(± 2.5) 1<0.01 

Stem density (stems ha-1) 1,810 (± 818) 688 (± 154) 355 (± 110) 760 (± 130) 1

<0.01 

Structural stage (pct) 2

<0.01 

Shrub 0 26 0 0 

Pole/sapling 30 37 5 0 

Young forest 70 21 30 10 

Mature forest 0 16 40 60 

Old forest 0 0 25 30 

Successional stage (pct) 2

<0.01 

Pioneer or young seral 70 58 5 0 

Mature or overmature seral 10 21 15 10 

Young climatic climax 20 10.5 20 10 

Maturing climax, maturing 

climatic climax and disclimax 0 10.5 60 80 

Disturbance (pct) 2

<0.01 

Logging, thinning, or spacing 100 84 40 0 

Fire, wind, or edge 0 16 25 70 

None 0 0 35 30 

Elevation (m) 387 (± 21) 518 (± 13) 371 (± 33) 537 (± 42) 1

<0.01 

1

Kruskal-Wallis comparison among four study sites. 2

Chi-square test between two young study sites (Hillridge and Niagara pooled) and two older study sites 

(Sooke and Rithet pooled). 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

250 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Transects and call stations were systematically located in each study site to 

ensure even coverage. Four or five transects about 4 km long were placed along an 

east-west line 800 m apart. Call stations were located every 400 m along those 

transects, giving approximately 40 call stations in each study site. We avoided 

placing transects along known habitat gradients that might influence bird abundance 

(e.g., a riparian corridor) and thereby bias the sampling procedure (Ralph and others 

1995). 

Call-playback Survey 

Call-playback surveys were used to estimate the relative abundance of pileated 

woodpeckers in two of the study sites during mating season (March 1996) and in all 

four study sites during nesting (May to June 1996 and 1997) and post-fledging 

seasons (July to August 1996 and 1997). We defined relative abundance as the 

response rate, or the number of responses (the number of pileated woodpeckers 

calling or drumming in response to a recording) divided by the number of call 

stations. 

At each call station, a taped recording of pileated woodpecker calls and 

territorial drums was played at 30-s intervals using a 3-volt cassette player amplified 

by a battery-powered, hand-held 12-volt sound horn (Radio Shack Genexxa).5

 We 

used a pileated woodpecker call-playback survey methodology following protocols 

from British Columbia (Anonymous 1996a) and the USDA Forest Service’s Pacific 

Northwest Research Station (Raley and Aubry 1993). Upon arriving at a call station, 

two field assistants would listen quietly and wait for 60-s while looking in all 

directions. If there was no call, or drum, or observation of a pileated woodpecker, 

then the entire recording of four calls and four drums was played, followed by a 5-

min wait. If there was a call, drum or observation, during the initial 60-s wait or 

during the recording, the recording was stopped while observers watched and 

listened. Mid-transect responses and second responses at call stations were recorded 

but not included in the final data set. Mid-call station responses were disregarded 

because call-playback can stimulate pileated woodpeckers to follow observers or to 

call repeatedly. Records of second birds were eliminated to standardize the surveys as 

counts of potential pairs instead of counts of individual birds. 

Surveys were conducted in good weather, neither on windy days (enough wind 

to cause leaves and twigs to be in motion: Beaufort scale 3) nor rainy days (steady 

rain), to maintain standard conditions for audibility and allow comparisons among 

surveys. We reduced observer bias by training field assistants and rotating assistants 

among transects. The survey period was divided into mating, nesting, and postfledging seasons, based on observed pileated woodpecker behavior during the study, 

and on studies in British Columbia, Oregon, and Washington (Aubry and Raley, pers. 

comm.; Bull and Jackson 1995; Campbell and others 1990). 

We examined how responses per call station and variability changed as number 

of call stations increased during a survey to determine the optimum sampling effort 

needed to estimate the relative abundance of pileated woodpecker. All the analyzed 

responses were randomized to remove seasonal and daily biases. 

 

5

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 251 

Habitat Characteristics 

To quantify habitat characteristics of study sites, 0.4-ha habitat circular plots 

(35.7-m radius) were established along 4 or 5 call-back transects in each study site: 

10 plots each in Hillridge and Rithet, 19 plots in Niagara, and 20 plots in Sooke. 

Heterogeneous study sites were sampled at twice the effort of more homogeneous 

study sites. Information about each habitat plot was recorded using the Ecosystem 

Field Form and procedures of Ministry of Forests and Ministry of Environment 

(Anonymous 1996b, Luttmerding and others 1990). The variables used for analysis 

included volume of coarse woody debris, basal area of snags and defective trees, tree 

stems per hectare, structural stage, successional stage, disturbance type, and 

elevation. Coarse woody debris was defined as fallen trees or pieces of such trees ≥

20 cm in diameter that were not self-supporting (fallen or suspended). Snags and 

defective trees were defined as dead trees ≥ 20 cm in diameter at breast height (dbh) 

and trees ≥ 20 cm dbh with broken tops, scars, decay, or damage, respectively. Stem 

density was estimated for each plot by counting all stems > 3 m tall within a 5.64-m 

radius circle in the center of each plot, and then multiplying by 100. 

Geographical information system (GIS) data (area of study sites, forest 

coverages, elevation, and aspect) about the sites were compiled from digital data 

prepared in 1991 and 1994 from aerial photographic interpretation and fieldwork 

conducted in 1986 and 1988. These data were updated to include changes in forest 

management activities and improvements in inventory classifications according to 

standards of the Ministry of Forests Inventory Branch. 

Statistical Analysis 

Data from call-playback surveys were analysed for statistical significance by 

using a logistic regression model. This model was appropriate because response data 

(whether a pileated woodpecker responded or not) were binary. Because all habitat 

data were non-normal, a non-parametric Kruskal-Wallis test was used to test for the 

differences in the dispersion of ratio habitat data from groups of more than two 

samples by ranking the data (Norušis 1998, Zar 1996). A Mann-Whitney U-test was 

used for ratio data to determine the differences between the dispersion of two groups 

(Sokal and Rohlf 1981, Zar 1996). For nominal habitat data, a Chi-square cross 

tabulation was used to test for the hypothesis of independence of the rows and 

columns of a contingency table (Norušis 1998, Siegel and Castellan 1988, Zar 1996). 

The level of significance utilized for table-wide comparisons was α = 0.05. A 

Bonferroni correction was used for multiple comparison tests. 

Results 

Determination of Adequate Sample Size 

The optimum sampling effort was determined from the three sites: Niagara, 

Sooke and Rithet (fig. 1). As the number of call stations reached 15 to 20 in habitats 

at the three study sites on southeastern Vancouver Island, the response rate and 

standard deviation stabilized. The steady decline of variability in mean response rate 

over cumulative number of call stations demonstrated that our sampling effort of ≥ 

37 call stations per study area was sufficient to determine relative abundance of 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

252 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

pileated woodpeckers. The sampling effort is probably optimal at 15-20 call stations 

for this type of forest in this biogeoclimatic zone. 

Figure 1―Mean response per call station using randomized data from 13 surveys in 

three pileated woodpecker study sites (Niagara, Sooke, Rithet) on southeastern 

Vancouver Island, 1996-1997. 

Relative Abundance 

A total of 16 call-playback surveys were conducted over two summers in 1996 

and 1997. The lowest number of responses occurred in Hillridge: no responses in the 

nesting season and one response in the post-fledging season (fig. 2). Niagara and 

Sooke had greater mean responses per call station than Hillridge. Rithet was not 

significantly different than Hillridge, Niagara, or Sooke. Hillridge and Rithet were 

not surveyed during mating season due to logistical complications (snow).

The relative abundance of pileated woodpecker differed significantly overall 

among the study sites and differed significantly between some study sites: 

Effect or contrast of variables: P 

All sites: average effect 0.01 

Hillridge-Niagara <0.01 

Hillridge-Sooke <0.01 

Hillridge-Rithet 0.01 

Niagara-Sooke 0.19 

Niagara-Rithet 0.82 

Sooke-Rithet 0.18 

All seasons: average effect 0.17

Mating season-nesting season 0.14 

Mating season-post-fledging season 0.06 

Nesting season-post-fledging season 0.52 

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

Cumulative number of call statio

Mean response per call station ( +-S.D. )

Mean

Standard

deviation

 Mean response 

Cumulative number of call stations 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 253 

Thus, the likelihood of receiving a response of a pileated woodpecker to a 

transmitted call differed among sites; overall, the effect of site was significant (P = 

0.01). Hillridge had the lowest relative abundance, in particular, during the nesting 

season when pileated woodpeckers were not detected during call-playback surveys. 

The likelihood of receiving a response in Hillridge was significantly lower than in the 

other study sites. Niagara and Rithet were the least different in abundance. 

Sooke had the highest mean response rate of any study site for all three seasons. 

However, there was no significant difference in relative abundance of pileated 

woodpeckers between Sooke and Niagara. Niagara and Rithet also did not differ 

significantly. The effect of season on the likelihood of receiving a response of a 

pileated woodpecker was not significant (P = 0.17). 

N = 82 40 37 86 39 83 84 83 109 41

Rithet

Sooke

Niagara

Hillridge

Response rate ( +-S.E.)

0.2

0.2

0.1

0.1

0.1

00.0

0-.1

Season

Mating

Nesting

Post-fledging

Figure 2Relative abundance of pileated woodpecker at four study sites on 

southeastern Vancouver Island during three seasons, 1996-1997. Study sites are 

arranged from earliest to latest seral stage from left to right, n = number of call 

stations. 

Habitat Characteristics of Study Sites 

The study sites differed significantly for all habitat characteristics except coarse 

woody debris (table 2). Coarse woody debris, however, was greater at Niagara and 

Sooke than at Hillridge and Rithet. Significant differences occurred for amount of 

snag and defective tree basal area, number of stems, structural stages, successional 

stage, disturbance, and elevation. The following tabulation gives the P values for 

these comparisons between areas:

P values for habitat characteristics 

Between site comparisons Basal area Stem density 

Hillridge-Niagara 0.286 0.040 

Hillridge-Sooke <0.001 0.002 

Hillridge-Rithet <0.001 0.247 

Niagara-Sooke 0.057 0.065 

Niagara-Rithet 0.002 0.429 

Sooke-Rithet 0.035 0.017 

n= 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

254 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Although the statistical significance of differences among sites varied with 

individual habitat features, the four study sites can be characterized as follows. 

Hillridge consisted of pole/sapling and young forest structural stages, typical of 

mainly early seral forest. It had low amounts of coarse woody debris, a low basal area 

of snags, and it had the highest density of tree stems. The entire area was disturbed 

by logging, thinning, and spacing. Niagara was composed of several structural stages: 

shrub, pole/sapling, and young forest with a smaller amount of mature forest. Niagara 

had more seral stages than Hillridge and the coarse woody debris and basal area were 

greater than at Hillridge. The Niagara study site was disturbed by logging, thinning, 

or spacing. 

Sooke had young forest, mature forest, and old forest structural stages but also 

had older seral stages. Amount of coarse woody debris and basal area of snags were 

greater than Hillridge or Niagara. Disturbance from logging was less than at Hillridge 

or Niagara sites. Rithet had structural stages similar to those at Sooke but with more 

mature and old structural stages and older seral stages. Amount of coarse woody 

debris was less than Niagara or Sooke, although the basal area of snags was greater 

than at other sites. The amount of disturbance was much less because none of the 

area was logged, thinned, or spaced. 

Discussion 

Our examination of the relative abundance of pileated woodpeckers in different 

seral stages has shown that there is not a direct correspondence between relative 

abundance and forest age. This occurs because both forest age and the quality of 

forest in terms of older wooden structures, both live and dead, appear to determine 

abundance of pileated woodpeckers. There was no significant difference in relative 

abundance of pileated woodpeckers among seasons, although relative abundance 

tended to increase in all study sites from nesting to post-fledging seasons probably 

because of the recruitment of juveniles. We accepted our hypothesis that landscapes 

with a significantly higher abundance of pileated woodpeckers have greater 

quantities of mature forest structures (snags, defective trees, logs). 

The uniform young forest at Hillridge, < 80 years old, was not used by pileated 

woodpeckers during the nesting season and was used minimally during the postfledging season. This low abundance may indicate that nesting sites were not 

available either within or close to Hillridge. The low abundance of pileated 

woodpeckers may also reflect that second-growth forests harvested before 80 years 

and then the cut blocks burned would likely lose old wooden structures important to 

pileated woodpecker, particularly for nesting. In Douglas-fir and western hemlock 

forests of western Oregon, the density of pileated woodpeckers was greater in forests 

> 80 years old than in forests < 80 years old (Nelson 1988). This suggests that 

intensive forest harvest that removes most residual old structures, could significantly 

reduce the relative abundance of pileated woodpecker for up to at least 80 years. 

Mannan (1984) found that pileated woodpeckers did not use forests < 40 years old 

for foraging and did not use forests < 70 years old for nesting. 

There was no significant difference between the abundance of pileated 

woodpeckers in the mainly early- and mid-seral forest at Niagara and in the older 

forests at Sooke and Rithet. This may indicate that pileated woodpecker has some 

habitat flexibility in age of forest and in quality of that forest as expressed by residual 

old structures. This flexibility, however, should not be construed to mean that any 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 255 

early seral forest is acceptable habitat to pileated woodpeckers. All three study sites 

contained contiguous or residual patches of old forests or old forest structures. 

Without these late seral remnants, we expect that the abundance of pileated 

woodpeckers would differ among sites. On southern Vancouver Island, pileated 

woodpeckers do not require contiguous older forest, and their abundance is not 

significantly reduced in a mixed seral forest with abundant residual old wooden 

structures and patches of old forest (Hartwig 1999). 

Although not statistically different than Niagara and Rithet, the relative 

abundance of pileated woodpeckers was highest in Sooke, the study site with the 

greatest amounts of dead wood. This suggests that the combination of large amounts 

of coarse woody debris, high basal areas of snags and defective trees, and low 

densities of stems were the most attractive habitat features to pileated woodpeckers. 

The relative abundance of pileated woodpeckers at the Rithet study site 

decreased during the post-fledging season despite that its relative abundance during 

the nesting season was similar to Sooke’s. The high basal areas of snags and 

defective trees may have provided suitable nesting sites, but the low amounts of 

coarse woody debris may indicate poorer foraging habitat. 

Acknowledgments 

Funding for this project was provided by the Habitat Conservation Trust Fund 

and the King-Platt Fellowship. Technical and logistical support were provided by 

Capital Region Water District, British Columbia (BC) Wildlife Branch, BC Resource 

Stewardship Branch, TimberWest Forest Ltd., Pacific Forestry Center, Department of 

National Defence, Capital Region District Parks, and BC Parks. We thank Richard L. 

Bonar and Eric L. Walters for reviewing the manuscript. 

References 

Anonymous. 1993. Biogeoclimatic units of the Vancouver Forest Region, Southern 

Vancouver Island and Sunshine Coast. Ministry of Forests. Victoria: Province of 

British Columbia; map sheet 5 of 6. 

Anonymous. 1996a. Standardized inventory methodologies for components of British 

Columbia’s biodiversity: woodpeckers. Victoria: Wildlife Branch, Ministry of 

Environment, Lands and Parks; 53 p. 

Anonymous. 1996b. Field manual for describing terrestrial ecosystem. Ministry of Forests 

and Ministry of Environment. Victoria: Province of British Columbia; 108 p. 

Bull, Evelyn L.; Jackson, Jerome A. 1995. Pileated woodpecker (Drocopus pileatus). In: 

Poole, Alan; Gill, Frank B., eds. The birds of North America No. 148. Washington, DC: 

The Academy of Natural Sciences, Philadelphia, Pennsylvania, and the American 

Ornithologists’ Union; 1-24. 

Bunnell, Fred L.; Wind, Elke; Boyland, Mark; Houde, Isabelle. 2002. Diameters and heights 

of trees with cavities: their implications to management. In: Laudenslayer, William 

F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas 

E., technical coordinators. Proceedings of the symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; [this volume]. 
Abundance of Pileated Woodpeckers on Vancouver Island—Hartwig, Eastman, and Harestad 

256 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Campbell, R. Wayne; Dawe, Neil K.; McTaggart-Cowan, Ian; Cooper, John M.; Kaiser, Gary 

W.; McNall, Michael C.E. 1990. The birds of British Columbia, Volume 1, 

Nonpasserines. Victoria, BC: Royal British Columbia Museum; 514 p. 

Green, Robert N.; Klinka, Karel. 1994. A field guide to site identification and 

interpretation for the Vancouver Forest Region. Victoria, BC: Ministry of Forests; 

285 p. 

Hartwig, Carol L. 1999. Effect of forest age, structural elements, and prey density on the 

relative abundance of pileated woodpecker (Dryocopus pileatus) on southeastern 

Vancouver Island. Victoria: University of Victoria; 162 p. M.Sc. thesis. 

Luttmerding, Herb A.; Demarchi, Dennis A.; Lea, Edward C.; Meidinger Del V.; Vold, Terje 

1990. Describing ecosystems in the field. 2d ed. Victoria: Ministry of Environment, 

Lands and Parks and Ministry of Forests; 213 p. 

Mannan, R.William. 1984. Summer area requirements of pileated woodpeckers in 

western Oregon. Wildlife Society Bulletin 12: 265-268. 

Mellen, T. Kim; Meslow, E. Charles; Mannan, R. William. 1992. Summertime home range 

and habitat use of pileated woodpeckers in western Oregon. Journal of Wildlife 

Management 56(1): 96-103. 

Nelson, S. Kim. 1988. Habitat use and densities of cavity-nesting birds in the Oregon 

Coast Ranges. Corvallis: Oregon State University; 75 p. M.Sc. thesis. 

Norušis, Marija J. 1998. Guide to data analysis. Upper Saddle River, NJ: Prentice Hall; 563 

p. 

Raley, Catherine M.; Aubry, Keith B. 1993. Protocol for pileated woodpecker call surveys 

and nest searches. Olympia, WA: Pacific Northwest Research Station, Forest Service, 

U.S. Department of Agriculture; 7 p. 

Ralph, C. John; Drogue, Sam; Saucer, John R. 1995. Managing and monitoring birds using 

point counts: standards and applications. In: Ralph, C. J.; Saucer, J. R.; Drogue, S., 

eds. Monitoring bird populations by point counts. Gen. Tech. Rep., PSW-GTR-149. 

Albany, CA: Pacific Southwest Region, Forest Service, U.S. Department of Agriculture; 

161-168. 

Schoener, Robert W. 1968. Sizes of feeding territories among birds. Ecology 49(1): 123-

141. 

 Siegel, Sidney; Castellan N. John, Jr. 1988. Nonparametric statistics for the behavioral 

sciences. New York: McGraw-Hill Book Company; 399 p. 

 Sokal, Robert R.; Rohlf, F. James 1981. Biometry, the principles and practice of statistics 

in biological research. 2d ed. San Francisco, CA: W.H. Freeman and Company; 859 p. 

 Zar, Jerrold H. 1996. Biostatistical analysis. 3d ed. Upper Saddle River, NJ: Prentice-Hall 

Inc.; 662 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 257 

The Pileated Woodpecker as a Keystone 

Habitat Modifier in the Pacific Northwest1

Keith B. Aubry2 and Catherine M. Raley2

Abstract 

We propose that the pileated woodpecker (Dryocopus pileatus) is a keystone habitat modifier 

in the Pacific Northwest. It is the largest woodpecker in this region and the only species that 

forages primarily by excavating; only pileateds are capable of creating large cavities in hard 

snags and decadent live trees. A wide array of species, including many that are of 

management concern in the Pacific Northwest, use old pileated nest and roost cavities. In 

addition, pileateds provide foraging opportunities for other species, accelerate decay 

processes and nutrient cycling, and may facilitate inoculation by heart-rot fungi and mediate 

insect outbreaks. Because of the potential keystone role of pileated woodpeckers in Pacific 

Northwest forests, it may be appropriate to give special attention to their habitat needs in 

forest management plans and monitoring activities. 

Introduction 

A keystone species is an organism that has a significant influence on the 

ecosystem it occupies that is disproportionately large compared to its abundance or 

biomass (Power and others 1996, Simberloff 1998). In other words, a keystone is a 

relatively uncommon species that is functionally linked to the persistence of an array 

of other species and plays a critical role in the organization and/or functioning of the 

ecosystem. The term “keystone species” was first introduced by Paine (1966, 1969) 

to describe a starfish that maintained the organization of a rocky intertidal 

community by selectively preying on a mussel that would otherwise have been 

competitively dominant and prevented numerous other species from coexisting. Not 

all species that exert strong influences on an ecosystem are considered keystones; for 

example, the primary tree species in a forested ecosystem would be considered an 

“ecological dominant” rather than a keystone species, because its effects are a 

function of its importance in the ecosystem (Power and others 1996). Keystones may 

or may not influence ecosystem structure and function through trophic interactions, 

as in Paine's original example involving starfish and mussels; five broad categories of 

keystone species were described by Mills and others (1993), including keystone 

predators, prey, mutualists, hosts, and habitat modifiers. 

The usefulness of the keystone species concept in ecology and conservation has 

been questioned recently (Mills and others 1993), but others (deMaynadier and 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Principal Research Wildlife Biologist and Wildlife Biologist, respectively, Pacific Northwest Research 

Station, USDA Forest Service, 3625 93rd Ave. SW, Olympia, WA 98512 (e-mail addresses: 

kaubry@fs.fed.us and craley@fs.fed.us) 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

258 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Hunter 1994, Power and others 1996, Simberloff 1998) have argued strongly for its 

continued usage, largely because of its potential application to management and the 

conservation of biodiversity. Power and others (1996) suggested that if keystone 

species can be identified in threatened ecosystems, critical areas should be set aside 

to maintain keystones, rather than focusing management efforts solely on endangered 

species or “hot spots” of biodiversity. There is also concern that the current focus of 

ecosystem management on ecological processes, rather than on individual species, 

could result in a loss of biodiversity without detectable changes in key processes 

(Simberloff 1998, Tracy and Brussard 1994). 

Simberloff (1998) argued that the conservation approach most likely to unite the 

best features of single-species and ecosystem management is to focus management 

efforts on keystone species because it involves explicit consideration of the 

mechanisms that underlie ecosystem function and structure. Unlike indicator, 

umbrella, or flagship species, keystones are functionally linked to a suite of other 

species; thus, management for the persistence of keystone species benefits other 

species by maintaining key ecosystem functions or structures. Furthermore, by 

studying keystone species and their role in ecological processes, we can significantly 

improve our understanding of ecosystems, identify ways to maintain or replace 

various functions, and increase the efficiency and success of conservation efforts. 

 

The Pileated Woodpecker as a Keystone Habitat 

Modifier 

Keystone habitat modifiers, also called “ecosystem engineers” (Lawton and 

Jones 1995), are species whose activities substantially alter the physical structure of 

the environment, influencing both available habitat for other species and various 

ecosystem processes (Mills and others 1993, Simberloff 1998). Examples include the 

beaver (Castor canadensis), because its dam-building and feeding activities create 

habitat for many other species and alter hydrological processes, channel 

geomorphology, biogeochemical pathways, and community productivity (Naiman 

and others 1986, Pollack and others 1995); the Brazilian termite (Cornitermes 

cumulans), because the large, abundant, and uniquely structured mounds it produces 

support a wide array of both obligate and opportunistic users (Redford 1984); and 

various species of burrowing animals, because their activities have a profound 

influence on available habitat for other species, and on microbial activity, soil 

fertility, the structure of plant communities, and sediment stability (Meadows and 

Meadows 1991). 

We propose that the pileated woodpecker is a keystone habitat modifier in the 

Pacific Northwest, because the effects of its excavations on habitat for many other 

species and on various ecological processes are both large and unique. The 

importance of woodpecker cavities to a broad array of secondary cavity-using species 

(those that use cavities but do not create them) has long been recognized by 

ecologists and forest managers (Balda 1975, Conner 1978, Davis and others 1983, 

Neitro and others 1985, Thomas and others 1979), but the unique contribution of 

pileated woodpeckers to cavity creation and ecosystem function has received little 

attention (Machmer and Steeger 1995). To provide a focus for discussing 

management implications that may result from this designation, we have limited our 

evaluation of management prescriptions to those on USDA Forest Service lands 

administered under the Northwest Forest Plan (i.e., within the range of the northern 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 259 

spotted owl [Strix occidentalis caurina] in western Washington and Oregon and 

northwestern California; Anonymous 1994a, Tuchmann and others 1996). 

The Ecological Role of Pileated Woodpeckers in the 

Pacific Northwest 

Nesting, Roosting, and Foraging Requirements 

The pileated woodpecker resides year-round in a variety of forested habitats. 

About the size of a crow, it is the largest woodpecker in the western United States, 

ranging from 40-49 cm in length and 250-350 g in body mass; males are 10-15 

percent heavier than females (Bull and Jackson 1995). The pileated woodpecker is a 

primary cavity excavator and, because of its large size, selects correspondingly large 

(generally >65 cm d.b.h. in the Pacific Northwest) snags or live trees with heartwood 

decay for nesting and roosting. Pileateds generally occupy mid- to late-successional 

forests where such structures are abundant, but they also occur in younger forests 

with large remnant trees and snags. Their diet consists primarily of wood-dwelling 

ants and beetle larvae, but other insects, fruit, and nuts are eaten when available (Bull 

1987). Pileated woodpeckers excavate new nest cavities each year and exhibit strong 

selection for nest trees on the basis of tree diameter and the structural quality of the 

wood. Trees containing relatively sound wood in the early stages of decay from 

heart-rot fungi are preferred, presumably because soft wood in advanced stages of 

decay cannot support the large nest cavities of pileated woodpeckers (Harris 1983). 

Before selecting a final nest site in the spring, pileated woodpeckers often excavate 

multiple cavity-starts (Bent 1939, Bull and Meslow 1988, Hoyt 1957, McClelland 

1977). Cavity-starts we found in western Washington were in various stages of 

completion; several had dimensions similar to active nest cavities and others, though 

not as large, were deep enough to function as potential nesting or roosting habitat for 

some secondary users.3

 Pileateds roost individually at night or during inclement 

weather in hollow trees to reduce the incidence of predation and conserve heat; roost 

chambers are large and generally have multiple openings to provide escape routes 

from predators (Bull and Jackson 1995). 

Creating Habitat for Secondary Cavity Users 

Pileated woodpeckers provide nesting and roosting habitat for secondary cavity 

users through three processes: excavation of nest cavities and cavity-starts, 

excavation of openings into roost cavities, and foraging excavations. Over 20 species 

of secondary cavity users occurring in the Pacific Northwest have been documented 

nesting or roosting in old cavities or openings excavated by pileated woodpeckers 

(table 1). The common merganser, silver-haired bat, fisher, and American marten 

were included as species of concern in the Final Supplemental Environmental Impact 

Statement for management of late-successional forests within the range of the 

northern spotted owl (Anonymous 1994b); the bufflehead, flammulated owl, and 

Vaux’s swift are on priority or sensitive species lists in Washington and Oregon 

(Anonymous 1995, Marshall 1992); and the northern flying squirrel is a primary prey 

of the northern spotted owl (Forsman and others 1984). 

 

3

 Unpublished data on file, Pacific Northwest Research Station, Olympia, Wash. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

260 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

 Table 1—Bird and mammal species known to use cavities, entrance holes, or foraging holes 

excavated by pileated woodpeckers in coniferous forests of the western U.S. and Canada. All 

species listed occur within the management area of the Northwest Forest Plan (Anonymous 

1994a). 

Species Location

Wood duck (Aix sponsa) Western Montana, western Washington 1, 2

Common goldeneye (Bucephala clangula) Western Montana, Alberta 1, 3

Bufflehead (Bucephala albeola) Western Montana, Alberta 1, 3

Hooded merganser (Lophodytes cucullatus) Western Montana 1

Common merganser (Mergus merganser) Western Montana 1

American kestrel (Falco sparverius) Western Montana 1

Flammulated owl (Otus flammeolus) Northeastern Oregon 4

Western screech-owl (Otus kennicottii) Western Montana 1

Northern pygmy-owl (Glaucidium gnoma) Western Montana 1

Boreal owl (Aegolius funereus) Western Montana, central Idaho 1, 5

Northern saw-whet owl (Aegolius acadicus) Western Montana, western Oregon, western 

Washington 1, 6, 7 

Vaux’s swift (Chaetura vauxi) Northeastern Oregon, western Washington 7, 8

Hairy woodpecker (Picoides villosus) Western Montana 1

Northern flicker (Colaptes auratus) Western Montana, eastern Oregon, western 

Washington 1, 9, 7

Brown creeper (Certhia americana) Western Montana 1

Silver-haired bat (Lasionycteris noctivagans) Northeastern Oregon 10

Big brown bat (Eptesicus fuscus) South-central British Columbia 10

Douglas’ squirrel (Tamiasciurus douglasii) Western Washington 7

Red squirrel (Tamiasciurus hudsonicus) Western Montana, northeastern Oregon 1, 8

Northern flying squirrel (Glaucomys sabrinus) Western Montana, northeastern Oregon, western 

Washington 1, 8, 7

Bushy-tailed woodrat (Neotoma cinerea) Northeastern Oregon 8

Ringtail (Bassariscus astutus) West-central Oregon 11

American marten (Martes americana) Western Montana, northeastern Oregon 1, 9

Fisher (Martes pennanti) Southwestern Oregon 12

1 McClelland 1979, 2 Bottorff 1999, 3 Bonar 1997, 4 Bull and others 1990, 5 Hayward and others 1993, 6 Mellen 1999, 7 Unpublished data, 8 Bull and others 1992, 9 Bull and others 1997, 10 Betts 1999, 11 Farrell 

1999, 12 Aubry and others 1997. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 261 

Several characteristics of pileated woodpeckers and the cavities they excavate 

are unique among woodpeckers in the Pacific Northwest. Both the entrance hole and 

nest cavity of pileated woodpeckers are larger than those of other woodpeckers (table 

2); thus, pileated excavations may provide the majority of suitable tree cavities for 

larger mammals and birds. For example, in southwestern Oregon, female fishers 

typically used old pileated woodpecker cavities for natal den sites (Aubry and others 

1997); based on our field observations and video taken at den sites, fishers would be 

unable to enter tree cavities with smaller openings. In northeastern Oregon, 

flammulated owls preferred pileated woodpecker cavities over flicker cavities for 

nest sites, possibly due to the larger cavity size and higher placement of the cavity in 

the tree bole (Bull and others 1990). In central Idaho, 18 of 23 boreal owl nests found 

were in pileated woodpecker cavities (Hayward and others 1993). Because boreal 

owls need large cavities and appear to prefer relatively high nest sites, Hayward and 

others (1993) recommended that management for boreal owl nesting habitat include 

management provisions for pileated woodpeckers. Eastern gray squirrels (Sciurus 

carolinensis) and raccoons (Procyon lotor) were observed using red-cockaded 

woodpecker (Picoides borealis) nests after the entrance and cavity were enlarged by 

pileated woodpeckers (Dennis 1971), and in British Columbia, buffleheads nested in 

cavities that had greater volume and larger entrance holes than those used by smaller 

secondary cavity-nesting species (Peterson and Gauthier 1985). In addition, some 

species may lay bigger clutches in cavities that have a larger floor area (Rendell and 

Robertson 1989). 

Table 2—Average dimensions of nest cavities for 12 woodpecker species occurring within the 

management area of the Northwest Forest Plan (Anonymous 1994a). Data are compiled from 

Terres (1980) except where noted. 

Entrance 

hole size 

(cm)

Cavity 

depth 

(cm)

Cavity 

width 

(cm)

Species with broad distributions within the management 

area of the Northwest Forest Plan: 

 Pileated woodpecker 1 9.0 x 12.0 57 21 

 Northern flicker 2

 6.3 x 7.0 30 15 

 Hairy woodpecker 3.8 - 5.0 25 - 38 ? 

 Red-breasted sapsucker (Sphyrapicus ruber) 3.1 - 3.8 35 ? 

 Downy woodpecker (Picoides pubescens) 3.1 20 - 30 ? 

Species with limited distributions within the 

management area of the Northwest Forest Plan: 

 Lewis’ woodpecker (Melanerpes lewis) 3

 5.0 - 7.6 23 - 76 13 - 20 

 Black-backed woodpecker (Picoides arcticus) 3.8 - 5.0 25 ? 

 White-headed woodpecker (Picoides albolarvatus) 4

 3.8 - 5.0 20 - 38 9 - 13 

 Acorn woodpecker (Melanerpes formicivorus) 5

 4.0 22 - 70 15 

Species whose distribution is primarily east of the 

Cascade crest: 

 Three-toed woodpecker (Picoides tridactylus) 3.8 - 5.0 25 ? 

 Williamson’s sapsucker (Sphyrapicus thyroideus) 6

 4.2 20 - 27 9 - 13 

 Red-naped sapsucker (Sphyrapicus nuchalis) 3.1 20 10 

1 Bull 1987, 2 Erskine and McLaren 1972, 3 Tobalske 1997, 4 Garrett and others 1996, 5 Koenig and 

others 1995, 6 Dobbs and others 1997. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

262 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

In the Pacific Northwest, pileated woodpeckers typically locate nest cavities 

high in the bole of both snags and live trees (Aubry and Raley 1995, Bull 1987, 

Madsen 1985, McClelland 1979, Mellen 1987). Several studies have suggested that 

nest cavities located high off the ground may reduce the incidence of nest predation. 

Observed predation by raccoons on yellow-bellied sapsucker (Sphyrapicus varius) 

nests was attributed to the cavities being too shallow or too close to the ground 

(Kilham 1971), and higher cavities increased the reproductive success of tree 

swallows (Tachycineta bicolor) by reducing the probability of predation (Rendell and 

Robertson 1989). 

Pileated woodpeckers are strong excavators capable of creating nest cavities in 

sound wood of both snags and live trees (Bull 1987, Christy 1939, Harris 1983). The 

sill width (an indicator of cavity wall thickness) of nest cavities in northeastern 

Oregon averaged 6 cm (Bull 1987), and two cavities we measured in western 

Washington had sill widths of 5.7 and 6.9 cm.3

 The sills of yellow-bellied sapsucker 

and northern flicker cavities in central British Columbia averaged 5.1 and 1.9 cm, 

respectively (Erskine and McLaren 1972), suggesting that pileated woodpecker 

cavities may have thicker walls than those of other woodpeckers. Thicker cavity 

walls decrease the rate of thermal conduction, which increases heat retention within 

the cavity (Betts 1998, Desch and Dinwoodie 1996, McComb and Noble 1981). In 

addition, cavities surrounded by a thick shell of sound sapwood provide better 

protection from predators, such as raccoons and black bears (Ursus americanus) that 

climb trees and break open nest cavities (Conner 1977, Conner and others 1976, 

Daily 1993, Erskine and McLaren 1972, Kilham 1971). These characteristics also 

increase the structural integrity of the cavity and reduce the likelihood that the tree 

will break at the cavity (Bull 1987, Harris 1983). Thus, nest cavities and cavity-starts 

excavated by pileated woodpeckers may provide more protection from potential 

predators, have greater longevity, and provide habitat for secondary users over a 

longer period of time than those excavated by other woodpeckers. 

Hollow chambers in snags and live trees, which are created by the process of 

heartwood decay, are important to a wide array of bird and mammal species for 

nesting, roosting, denning, and resting (Bull and others 1997). Openings excavated 

into hollow trees by pileated woodpeckers for roosting enable secondary cavity users 

to access tree hollows they would otherwise be excluded from (i.e., the tree does not 

have a broken top or other natural openings that provide access to the hollow 

interior). In northeastern Oregon, radio-tagged pileated woodpeckers used an average 

of seven roost trees within a 3-10 month period (Bull and others 1992). In western 

Washington, pileateds also used an average of seven roost trees during an 8-month 

period, and one individual used 29 different roost trees during the 3 years we radiotracked it.3

 However, because birds were not tracked daily in either study, the actual 

number of roost trees used by pileated woodpeckers each year is probably much 

higher. For each individual to have an adequate number of roost sites within its 

territory, it would need to excavate openings into several new roost sites each year. 

Thus, tree cavities that are used as nesting, roosting, and resting sites by other species 

are being created or made available by pileated woodpeckers throughout the year. 

Lastly, the foraging excavations of pileated woodpeckers may also create 

important microhabitats for other species. Pileateds excavate deep into heartwood to 

reach carpenter ants (Camponotus spp.). These excavations may create openings into 

the decaying bole of snags and live trees that provide access to hollow chambers that 

are used by other species for nesting or roosting. For example, in south-central 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 263 

British Columbia, a maternal colony of big brown bats was located in the hollow 

interior of a ponderosa pine (Pinus ponderosa) snag that they accessed through an 

opening created by a foraging pileated woodpecker (Betts 1999). Furthermore, 

foraging excavations that do not access hollow chambers can still be deep enough to 

provide roosting habitat for smaller cavity-users, such as the hairy woodpecker and 

brown creeper (McClelland 1979). 

Providing Foraging Opportunities for Other Species 

The pileated woodpecker is the only species that excavates extensively into 

sapwood and heartwood for invertebrate prey. Other Pacific Northwest woodpeckers 

are relatively weak excavators that typically locate prey by scaling bark, pecking 

substrates without penetrating the subcambial layers, surface gleaning, ground 

foraging, or hawking (Bull and others 1986; Conner 1979, 1981). Thus, pileated 

foraging excavations enable other species to prey on invertebrates that would 

otherwise be unavailable to them. Downy and hairy woodpeckers have been 

documented following foraging pileateds and gleaning or pecking in freshly 

excavated areas as soon as the pileateds leave (Bull and Jackson 1995, Christy 1939, 

Maxson and Maxson 1981).3

 Commensal foraging has also been observed between 

pileated and red-bellied woodpeckers (Melanerpes carolinus), northern flickers, and 

Williamson’s sapsuckers (Bull and Jackson 1995). 

Accelerating Decomposition and Nutrient Cycling 

Pileated woodpeckers directly and indirectly accelerate wood decomposition 

and, ultimately, nutrient cycling by physically breaking apart sound and decayed 

wood as they excavate nest and roost cavities and forage for invertebrate prey and by 

exposing wood in live trees, snags, and logs to insect attack and fungal infection. 

Although pileated woodpeckers will obtain food by other methods, they are primarily 

excavators (Bull and Holthausen 1993, Bull and Jackson 1995, Conner 1979). A 

single foraging excavation can be large, often measuring 10-20 cm wide, >30 cm 

long, and extending deep into the heartwood (Christy 1939). One bird observed for 2 

hours excavated two holes 15-cm deep with openings 15 x 15 cm and 15 x 25 cm in 

size (Christy 1939). In coastal forests of western Washington and Oregon, pileated 

woodpeckers forage mainly on standing dead and live trees, and only occasionally on 

downed logs (Aubry and Raley 1992, Mellen 1999); this differs from observations 

made by Bull (1987) in northeastern Oregon, where logs comprised a major 

proportion (36 percent) of foraging substrates used by pileateds. Thus, pileateds may 

have a greater impact on the decomposition of standing wood in coastal regions of 

the Pacific Northwest than in interior areas. 

Facilitating Inoculation by Heart-rot Fungi 

When woodpeckers excavate in dead wood, they expose new sites to insect 

attacks and fungal infection; additionally, it has been suggested that woodpeckers 

may facilitate the inoculation of live, healthy trees by heart-rot fungi (Otvos 1979, 

Parks 1999). Wood softened by heart-rot is essential for nest-cavity excavation by 

most woodpeckers (Conner and others 1976, Daily 1993, Kilham 1971), and 

heartwood decay in live, standing trees is the process by which hollow chambers in 

both trees and logs are formed (Bull and others 1997). Airborne spores of heart-rot 

fungi invade living trees through wounds that expose the heartwood to infection (Bull 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

264 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

and others 1997). Pileated woodpeckers are capable of creating cavities in live trees 

with no decay (Bent 1939, Harris 1983). Almost half of the cavity-starts we located 

in western Washington were in live trees, and most were deep enough to have 

penetrated the heartwood (Aubry and Raley 1992). Thus, it is possible that pileateds 

create wounds in healthy trees that become infection courts for heart-rot fungi. 

Mediating Insect Outbreaks 

The importance of woodpeckers in the control of insect populations, especially 

beetles, has long been recognized (Otvos 1979). Woodpeckers are adapted to forage 

on a variety of substrates and can access insect prey in the crevices of rough bark that 

are unavailable to other avian predators (Jackson 1979a). In addition, because most 

woodpeckers are non-migratory, they are the primary avian insectivores during the 

winter months (Jackson 1979b); predation on overwintering arthropods is believed to 

reduce the potential of population increases during the following year (Jackson 

1979b, Kroll and Fleet 1979). 

When woodpeckers scale bark or excavate into wood for insects, there are both 

direct and indirect effects on prey populations. Woodpeckers affect insect mortality 

rates through direct consumption. Indirect effects include altering insect 

microhabitats, increasing parasite densities, and exposing remaining prey to 

consumption by both vertebrate and invertebrate predators (Machmer and Steeger 

1995, Otvos 1979). Woodpecker foraging physically alters tree and log surfaces by 

reducing bark thickness or removing bark and sapwood, potentially exposing 

remaining insects (particularly broods) to extreme temperatures and desiccation. 

These changes in microclimatic conditions can be significant mortality factors for 

beetles and other arthropods (McCambridge and Knight 1972, Otvos 1979). 

Woodpecker foraging activity changes bark color, which may also influence its 

thermal properties and suitability as arthropod habitat (Jackson 1979b). Scaling, by 

reducing bark thickness, exposes remaining insect broods to parasites with short 

ovipositors (Machmer and Steeger 1995, Otvos 1979). For example, in the central 

Sierra Nevada in California, parasites were observed swarming over sites that had 

recently been scaled by woodpeckers and ovipositing through the thinned bark layers 

(Otvos 1970). 

Whether pileated woodpeckers have a greater impact on insect populations than 

other woodpeckers has not been investigated, but they are clearly the best-adapted 

species for digging larvae and pupae out of bark, sapwood, and heartwood, regardless 

of the stage of wood decay. Carpenter ants generally comprise >50 percent of 

pileated woodpecker diets (Beckwith and Bull 1985, Jackman 1975), but during 

outbreaks, beetles may comprise a higher percentage of the diet (Bull 1987, Kroll and 

Fleet 1979). In Texas, pileated, hairy, and downy woodpeckers significantly reduced 

numbers of overwintering pupae and brood adults of the southern pine beetle 

(Dendroctonus frontalis) (Kroll and Fleet 1979). We commonly found larval 

Coleoptera in pileated woodpecker scats in western Washington (Aubry and Raley 

1996), and in Montana, pileateds commonly foraged on both carpenter ants and 

wood-boring beetles (McClelland 1979).
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 265 

Implications for Management Under the Northwest 

Forest Plan 

Regulations pursuant to the National Forest Management Act of 1976 require 

that each National Forest identify “management indicator species” (MISs) to focus 

management attention on a species, species group, or habitat element to improve 

resource production, population recovery, maintenance of population viability, or 

ecosystem diversity (Anonymous 1984). Prior to the implementation of the 

Northwest Forest Plan (NWFP) in 1994 (Anonymous 1994a), the pileated 

woodpecker was an MIS for mature and old-growth forest conditions on all National 

Forests currently managed under the NWFP. Each Forest was required to establish a 

series of pileated woodpecker habitat areas that included both tracts of mature and 

old-growth forest and minimum densities of large snags (Anonymous 1986). To 

evaluate the effectiveness of these habitat areas, monitoring of occupancy and 

population trends was also required (Anonymous 1982). 

The Northwest Forest Plan represents an ecosystem management strategy 

designed to provide for long-term ecological integrity throughout the range of the 

northern spotted owl, and includes specific provisions for late-successional reserves 

in both upland and riparian areas, as well as the retention of snags for cavity-nesting 

birds in lands open to timber harvesting (matrix lands). With the implementation of 

the NWFP in 1994, pileated woodpecker habitat areas were no longer maintained on 

most National Forests within the range of the northern spotted owl because it was 

believed that standards and guidelines (S&Gs) in the NWFP were adequate to 

maintain viable populations of pileated woodpeckers on federal lands.3

 Standards and 

guidelines in the NWFP for green-tree, snag, and log retention in timber harvest units 

on matrix lands in Forest Service ownership are summarized in table 3. Monitoring is 

a key component of management strategies in the NWFP and includes three types: 

implementation monitoring to determine if S&Gs are being followed, effectiveness 

monitoring to determine if they are achieving desired results, and validation 

monitoring to determine if underlying assumptions are sound (Anonymous 1994a). 

Because of the potential keystone role of the pileated woodpecker in the Pacific 

Northwest, it may be appropriate to give special attention to their habitat needs in 

forest management plans and monitoring activities. Standards and guidelines for 

green-tree retention in the NWFP were strongly influenced by the Species Analysis 

Team’s recommendation to emphasize clumped green-tree and snag retention in 

harvest units (Anonymous 1994b). Because of safety concerns associated with 

retaining large, hard snags or decadent live trees in harvested areas (Hope and 

McComb 1994, Styskel 1983), the Team believed that retaining green trees in 

relatively large patches would provide the best opportunities for preserving such 

structures in harvest units (K. Aubry, personal observation). However, there are few 

data to indicate that pileated woodpeckers will use large snags in harvest units, 

regardless of their context. Several studies in western Washington and Oregon have 

documented nesting by smaller woodpeckers in both natural and artificially created 

snags in clearcuts (Chambers and others 1997, Mannan and others 1980, Morrison 

and Meslow 1983, Schreiber and deCalesta 1992, Zarnowitz and Manuwal 1985), but 

nesting by pileateds in remnant snags or decaying live trees in clearcuts has not been 

reported. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

266 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 3—Key Forest Service standards and guidelines for retention of green trees, snags, 

and logs during timber harvest on matrix lands in the Northwest Forest Plan (Anonymous 

1994a). 

Emphasize green-tree and snag retention in matrix management 

• Retain at least 15 pct of the harvested area as green trees. 

• Retain 70 pct of those green trees in aggregates 0.2-1.0 ha in size. Retain the 

remainder as dispersed structures, either as individual trees or aggregates <0.2 ha in 

size. 

• To the extent possible, aggregates and dispersed retention should include the largest, 

oldest live trees, decadent or leaning trees, and hard snags occurring in the unit. 

Patches should be retained indefinitely. 

• As a minimum, snags are to be retained within the harvest unit at levels sufficient to 

support species of cavity-nesting birds at 40 pct of potential population levels based 

on published guidelines and models. 

• To the extent possible, snag management within harvest units should occur within 

the areas of green-tree retention. 

Provide specified amounts of coarse woody debris in matrix management 

• In western Washington and Oregon north of and including the Willamette National 

Forest, leave 240 linear feet of logs per acre >20 inches in diameter. Logs <20 feet in 

length cannot be credited toward this total. In western Oregon south of the 

Willamette National Forest, leave 120 linear feet of logs per acre >16 inches in 

diameter and 16 feet long. 

• Decay class 1 and 2 logs can be counted towards these totals. Down logs should 

reflect the species mix of the original stand. 

We do not know if pileateds will nest or roost in suitable snags or decadent live 

trees located within 0.2-1.0-ha retention patches, but available data are not 

encouraging. We could find only one study on the use of remnant patches in 

regeneration harvests by pileateds. Gyug and Bennett (1995) conducted surveys for 

nesting pileated woodpeckers in coniferous forests of southeastern British Columbia 

on three 160-ha study plots including a clearcut, a clearcut with remnant patches 

about 1 ha in size, and an intact forest; experimental treatments were applied 25-30 yr 

prior to the study. Five pileateds were detected in the unharvested control, but none 

was found in either the clearcut or patch-retention treatment. Thus, regardless of the 

number of snags specified in management models, it is uncertain whether harvested 

areas will provide nesting or roosting habitat for pileated woodpeckers prior to the 

reestablishment of late-successional forest conditions. 

Implementation monitoring has involved field visits to 109 randomly selected 

harvest sites since 1996 (Alverts and others 1997, 1998, 1999). Although data 

presented in these reports indicate a high level of compliance with S&Gs overall (>95 

percent), compliance with green-tree and snag retention S&Gs was generally lower. 

Snag and green-tree retention S&Gs were a source of considerable confusion for 

project personnel during all 3 years of monitoring, due to differing interpretations of 

the S&Gs, lack of consensus on definitions, lack of data on snag levels needed to 

support species of cavity-nesting birds at 40 percent of potential population levels, 

and the difficulty of maintaining “legacy” trees when operators are commonly 

confronted with safety concerns and operational constraints. 

Clarifying S&Gs for green-tree and snag retention and providing additional 

guidance on their implementation would ensure that timber harvest administrators 

share a common understanding of their intent relative to ecosystem management and 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 267 

possess reliable strategies for implementing them on the ground. Although 

compliance with most relevant S&Gs is documented thoroughly in implementation 

monitoring reports, many of the details that will influence both the short- and longterm habitat quality of harvest units for pileated woodpeckers are not. For example, 

no data are collected on the number of large snags or decadent live trees that were 

preserved in the unit, how many were in aggregated vs. dispersed green-tree retention 

areas, or how many snags were created from living trees to meet minimum snag 

requirements. The inclusion of such information in implementation monitoring 

activities would greatly improve our ability to evaluate the habitat quality of 

harvested areas for pileated woodpeckers and other species associated with latesuccessional forest conditions (table 1).

Effectiveness monitoring under the NWFP is currently focused on latesuccessional and old-growth forests, aquatic and riparian ecosystems, northern 

spotted owls, and marbled murrelets (Brachyramphus marmoratus); monitoring 

strategies for other late-successional species are still being developed (Mulder and 

others 1999). Because of the large number of potential species in the latter category, 

Noon (1999) recommended that a “focal species” approach be used, and suggested 

that the keystone species concept may be useful for selecting ecological indicators for 

the Northwest Forest Plan. Because of its potential role as a keystone species in the 

Pacific Northwest and its strong association with large snags and decadent live trees, 

the pileated woodpecker may be a particularly appropriate ecological indicator for 

effectiveness monitoring of species associated with late-successional forest 

conditions. Other issues to address in effectiveness monitoring might include the 

prevalence of new pileated woodpecker nest cavities in clearcuts and retention 

patches, the relative abundance of pileated woodpecker cavities and foraging 

excavations in different forest types and moisture regimes, and occupancy levels and 

population trends in managed vs. unmanaged landscapes. 

Several studies have recently been initiated to test or re-evaluate some of the 

assumptions in the NWFP (Aubry and others 1999, Marcot and others 2002), but we 

are not aware of any new or planned field studies of pileated woodpeckers within the 

management area of the NWFP. When validation monitoring strategies for the 

NWFP are formalized, it may be appropriate to include empirical evaluations of 

S&Gs for green-tree and snag retention relative to the habitat needs of pileated 

woodpeckers and of the model used to develop habitat management prescriptions for 

pileated woodpeckers in westside forests (Neitro and others 1985, p. 141-145). 

Lastly, habitat management strategies for woodpeckers in the Pacific Northwest are 

based on the assumption that viable populations can be maintained in managed 

landscapes by providing nesting snags at 40 percent of potential population levels 

(Thomas and others 1979, p. 72), yet this assumption has never been evaluated 

empirically. 

Acknowledgments 

We thank Catherine Parks, Chris Steeger, and Victoria Stevens for helpful 

comments on a previous draft of this manuscript; and Burr Betts, Rick Bonar, Jim 

Bottorff, Terry Farrell, Kim Mellen, and Catherine Parks for making unpublished 

information available to us. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

268 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

References 

Alverts, Bob; Horton, Al; Mehrhoff, Loyal; Stone, Brian. 1998. Results of the FY 1997 

implementation monitoring program. Portland, OR: Regional Implementation 

Monitoring Team, Regional Ecosystem Office; 62 p. 

Alverts, Bob; Horton, Al; Stone, Brian. 1997. Results of the FY 1996 (pilot year) 

implementation monitoring program. Portland, OR: Regional Implementation 

Monitoring Team, Regional Ecosystem Office; 46 p. 

Alverts, Bob; Hsin, Liang; Horton, Al; Shon, Fay; Mehrhoff, Loyal; Stone, Brian. 1999. 

Results of the FY 1998 implementation monitoring program. Portland, OR: Regional 

Implementation Monitoring Team, Regional Ecosystem Office; 25 p. 

Anonymous. 1982. National Forest System land and resource management planning.

Federal Register 47(190): 43026-43052. 

Anonymous. 1984. Wildlife, fish, and sensitive plant habitat management. Title 2600, 

Amendment No. 48. Washington, DC: Forest Service, U.S. Department of Agriculture. 

Anonymous. 1986. A report on minimum management requirements for forest planning 

on the National Forests of the Pacific Northwest Region, USDA Forest Service.

Portland, OR: Pacific Northwest Region, Forest Service, U.S. Department of 

Agriculture; 12 p. 

Anonymous. 1994a. Record of decision for amendments to Forest Service and Bureau of 

Land Management planning documents within the range of the northern spotted 

owl. Portland, OR: Forest Service, U.S. Department of Agriculture, and Bureau of Land 

Management, U.S. Department of Interior. 

Anonymous. 1994b. Appendix J2: results of additional species analysis. Final 

supplemental environmental impact statement on management of habitat for latesuccessional and old-growth related species within the range of the northern 

spotted owl. Portland, OR: Forest Service, U.S. Department of Agriculture, and Bureau 

of Land Management, U.S. Department of Interior. 

Anonymous. 1995. Priority habitats and species list: habitat program. Olympia, WA: 

Washington Department of Fish and Wildlife; 24 p. 

Aubry, Keith B.; Amaranthus, Michael P.; Halpern, Charles B.; White, James D.; Woodard, 

Brenda L.; Peterson, Charles E.; Lagoudakis, Cynthia A.; Horton, Alan J. 1999. 

Experimental design of the DEMO study: evaluating the ecological and social 

effects of different levels and patterns of green-tree retention in harvest units.

Northwest Science 73(Special Issue): 12-26. 

Aubry, Keith B.; Raley, Catherine M. 1992. Landscape-level responses of pileated 

woodpeckers to forest management and fragmentation: a pilot study. Progress 

Report: 1990 and 1991. Olympia, WA: Pacific Northwest Research Station, Forest 

Service, U.S. Department of Agriculture; 73 p. 

Aubry, Keith B.; Raley, Catherine M. 1995. Ecology of pileated woodpeckers in managed 

landscapes on the Olympic Peninsula. Annual Report FY 1995. Olympia, WA: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 61-64. 

Aubry, Keith B.; Raley, Catherine M. 1996. Ecology of pileated woodpeckers in managed 

landscapes on the Olympic Peninsula. Annual Report FY 1996. Olympia, WA: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 70-74. 

Aubry, Keith B.; Raley, Catherine M.; Catton, T. J.; Tomb, Gregory W.; Wahl, Fred E. 1997. 

Ecological characteristics of fishers in southwestern Oregon. Annual Report FY 

1997. Olympia, WA: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 72-77. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 269 

Balda, Russell P. 1975. The relationship of secondary cavity nesters to snag densities in 

western coniferous forests. Technical Bulletin 1. Albuquerque, NM: Southwestern 

Region, Forest Service, U.S. Department of Agriculture; 37 p. 

Beckwith, Roy C.; Bull, Evelyn L. 1985. Scat analysis of the arthropod component of 

pileated woodpecker diet. The Murrelet 66(3): 90-92. 

Bent, Arthur Cleveland. 1939. Life histories of North American woodpeckers. Bulletin No. 

174. New York, NY: Dover Publications, Inc.; 334 p. 

Betts, Burr J. 1998. Roosts used by maternity colonies of silver-haired bats in 

northeastern Oregon. Journal of Mammalogy 79(2): 643-650. 

Betts, Burr J. [Letter to Keith B. Aubry]. 1999 November 5. Located at: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Research Station, Olympia, WA. 

Bonar, Rick [Letter to CAVNET internet discussion group]. 1997. Located at: U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station, 

Olympia, WA. 

Bottorff, James, Biologist, Washington State Department of Natural Resources, Olympia, 

WA. [Conversation with Catherine M. Raley]. 30 March 1999. 

Bull, Evelyn L. 1987. Ecology of the pileated woodpecker in northeastern Oregon. Journal 

of Wildlife Management 51(2): 472-481. 

Bull, Evelyn L.; Holthausen, Richard S. 1993. Habitat use and management of pileated 

woodpeckers in northeastern Oregon. Journal of Wildlife Management 57(2): 335-

345. 

Bull, Evelyn L.; Holthausen, Richard S.; Henjum, Mark G. 1992. Roost trees used by 

pileated woodpeckers in northeastern Oregon. Journal of Wildlife Management 

56(4): 786-793. 

Bull, Evelyn L.; Jackson, Jerome A. 1995. Pileated woodpecker (Dryocopus pileatus). In: 

Poole, Alan; Gill, Frank B., editors. The birds of North America, No. 148. Philadelphia, 

PA: The Academy of Natural Sciences; 24 p. 

Bull, Evelyn L.; Meslow, E. Charles. 1988. Breeding biology of the pileated woodpecker:

management implications. Res. Note PNW-RN-474. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 8 p. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Bull, Evelyn L.; Peterson, Steven R.; Thomas, Jack Ward. 1986. Resource partitioning 

among woodpeckers in northeastern Oregon. Res. Note PNW-444. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 19 

p. 

Bull, Evelyn L.; Wright, Anthony L.; Henjum, Mark G. 1990. Nesting habitat of 

flammulated owls in Oregon. Journal of Raptor Research 24(3): 52-55. 

Chambers, Carol L.; Carrigan, Tara; Sabin, Thomas E.; Tappeiner, John; McComb, William 

C. 1997. Use of artificially created Douglas-fir snags by cavity-nesting birds.

Western Journal of Applied Forestry 12(3): 93-97. 

Christy, Bayard Henderson. 1939. Northern pileated woodpecker. In: Bent, Arthur 

Cleveland. Life histories of North American woodpeckers. New York, NY: Dover 

Publications, Inc.; 171-189. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

270 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Conner, Richard N. 1977. The effect of tree hardness on woodpecker nest entrance 

orientation. Auk 94(2): 369-370. 

Conner, Richard N. 1978. Snag management for cavity nesting birds. In: Workshop 

proceedings: management of southern forests for nongame birds. Gen. Tech. Rep. SE14. Asheville, NC: Southeastern Forest Experiment Station, Forest Service, U.S. 

Department of Agriculture; 120-128. 

Conner, Richard N. 1979. Seasonal changes in woodpecker foraging methods: strategies 

for winter survival. In: Dickson, James G.; Conner, Richard N.; Fleet, Robert R.; Kroll, 

James C.; Jackson, Jerome A., editors. The role of insectivorous birds in forest 

ecosystems: proceedings of the symposium; 1978 July 13-14; Nacogdoches, TX. New 

York: Academic Press; 95-105. 

Conner, Richard N. 1981. Seasonal changes in woodpecker foraging patterns. Auk 98(3): 

562-570. 

Conner, Richard N.; Miller, Orson K., Jr.; Adkisson, Curtis S. 1976. Woodpecker 

dependence on trees infected by fungal heart rots. Wilson Bulletin 88(4): 575-581. 

Daily, Gretchen C. 1993. Heartwood decay and vertical distribution of red-naped 

sapsucker nest cavities. Wilson Bulletin 105(4): 674-679. 

Davis, Jerry W.; Goodwin, Gregory A.; Ockenfels, Richard A., technical editors. 1983. Snag 

habitat management: proceedings of the symposium. Gen. Tech. Rep. RM-99. Ft. 

Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture; 226 p. 

deMaynadier, Phillip; Hunter, Malcolm L. 1994. Keystone support. BioScience 44(1): 2. 

Dennis, John V. 1971. Species using red-cockaded woodpecker holes in northeastern 

South Carolina. Bird-banding 42(2): 79-87. 

Desch, H. E.; Dinwoodie, J. M. 1996. Timber: structure, properties, conversion and use.

7th ed. Binghamton, NY: Haworth Press; 306 p. 

Dobbs, R.C.; Martin, T. E.; Conway, C. J. 1997. Williamson’s sapsucker (Sphyrapicus 

thyroideus). In: Poole, Alan; Gill, Frank B., editors. The birds of North America, No. 

285. Philadelphia, PA: The Academy of Natural Sciences; 20 p. 

Erskine, A. J.; McLaren, W. D. 1972. Sapsucker nest holes and their use by other species. 

Canadian Field-Naturalist 86(4): 357-361. 

Farrell, Terry, Biologist, Oregon Department of Fish and Wildlife, Roseburg, OR. [Telephone 

conversation with Keith B. Aubry]. 19 October 1999. 

Forsman, Eric D.; Meslow, E. Charles; Wight, Howard M. 1984. Distribution and biology of 

the spotted owl in Oregon. Wildlife Monographs 87: 1-64. 

Garrett, Kimball L.; Raphael, Martin G.; Dixon, Rita D. 1996. White-headed woodpecker 

(Picoides albolarvatus). In: Poole, Alan; Gill, Frank B., editors. The birds of North 

America, No. 252. Philadelphia, PA: The Academy of Natural Sciences; 24 p. 

Gyug, Les W.; Bennett, Stephen P. 1995. Bird use of wildlife tree patches 25 years after 

clearcutting. In: Bradford, Peter; Manning, Todd; l’Anson, Bill, editors. Wildlife 

tree/stand-level biodiversity workshop proceedings; 1995 October 17-18; Victoria, BC. 

Victoria, BC: British Columbia Ministry of Forests and BC Environment; 15-33. 

Harris, Roger D. 1983. Decay characteristics of pileated woodpecker nest trees. In: Davis, 

Jerry W.; Goodwin, Gregory A.; Ockenfels, Richard A., technical coordinators. Snag 

habitat management: proceedings of the symposium; 1983 June 7-9; Flagstaff, AZ. Gen. 

Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain Forest and Range Experiment 

Station, Forest Service, U.S. Department of Agriculture; 120-128. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 271 

Hayward, Gregory D.; Hayward, Patricia H.; Garton, Edward O. 1993. Ecology of boreal 

owls in the northern Rocky Mountains, U.S.A. Wildlife Monographs 124: 1-55. 

Hope, Sharon; McComb, William C. 1994. Perceptions of implementing and monitoring 

wildlife tree prescriptions on National Forests in western Washington and Oregon.

Wildlife Society Bulletin 22(3): 383-392. 

Hoyt, Sally F. 1957. The ecology of the pileated woodpecker. Ecology 38(2): 246-256. 

Jackman, Siri Marion. 1975. Woodpeckers of the Pacific Northwest: their characteristics 

and their role in the forests. Corvallis: Oregon State University; 147 p. M.S. thesis. 

Jackson, Jerome A. 1979a. Insectivorous birds and North American forest ecosystems. In: 

Dickson, James G.; Conner, Richard N.; Fleet, Robert R.; Kroll, James C.; Jackson, 

Jerome A., editors. The role of insectivorous birds in forest ecosystems: proceedings of 

the symposium; 1978 July 13-14; Nacogdoches, TX. New York; Academic Press; 1-7. 

Jackson, Jerome A. 1979b. Tree surfaces as foraging substrates for insectivorous birds.

In: Dickson, James G.; Conner, Richard N.; Fleet, Robert R.; Kroll, James C.; Jackson, 

Jerome A., editors. The role of insectivorous birds in forest ecosystems: proceedings of 

the symposium; 1978 July 13-14; Nacogdoches, TX. New York; Academic Press; 69-93. 

Kilham, Lawrence. 1971. Reproductive behavior of yellow-bellied sapsuckers I. 

Preference for nesting in Fomes-infected aspens and nest hole interrelations with 

flying squirrels, raccoons, and other animals. Wilson Bulletin 83(2): 159-171. 

Koenig, Walter D.; Stacey, Peter B.; Stanback, Mark T.; Mumme, Ronald L. 1995. Acorn 

woodpecker (Melanerpes formicivorous). In: Poole, Alan; Gill, Frank B., editors. The 

birds of North America, No. 194. Philadelphia, PA: The Academy of Natural Sciences; 

24 p. 

Kroll, James C.; Fleet, Robert R. 1979. Impact of woodpecker predation on over-wintering 

within-tree populations of the southern pine beetle (Dendroctonus frontalis). In: 

Dickson, James G.; Conner, Richard N.; Fleet, Robert R.; Kroll, James C.; Jackson, 

Jerome A., editors. The role of insectivorous birds in forest ecosystems: proceedings of 

the symposium; 1978 July 13-14; Nacogdoches, TX. New York; Academic Press; 269-

281. 

Lawton, John H.; Jones, Clive G. 1995. Linking species and ecosystems: organisms as 

ecosystem engineers. In: Jones, Clive G.; Lawton, John H., editors. Linking species and 

ecosystems. New York, NY: Chapman & Hall; 141-150. 

Machmer, Marlene M.; Steeger, Christoph. 1995. The ecological roles of wildlife tree users 

in forest ecosystems. Land Management Handbook 35. Victoria, BC: BC Ministry of 

Forests; 54 p. 

Madsen, Sarah J. 1985. Habitat use by cavity-nesting birds in the Okanogan National 

Forest, Washington. Seattle; University of Washington; 113 p. M.S. thesis. 

Mannan, R. William; Meslow, E. Charles; Wight, Howard M. 1980. Use of snags by birds in 

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44(4): 787-797. 

Marcot, Bruce G.; Mellen, Kim; Livingston, Susan A.; Ogden, Cay. 2002. DecAID: wildlife 

component. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; 

Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the 

symposium on the ecology and management of dead wood in western forests. 1999 

November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; [this 

volume]. 

Marshall, David B. 1992. Threatened and sensitive wildlife of Oregon's forests and 

woodlands. Portland, OR: Audubon Society of Portland; 66 p. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

272 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Maxson, Stephen J.; Maxson, George-Ann D. 1981. Commensal foraging between hairy 

and pileated woodpeckers. Journal of Field Ornithology 52(1): 62-63. 

McCambridge, William F.; Knight, Fred B. 1972. Factors affecting spruce beetles during a 

small outbreak. Ecology 53(5): 830-839. 

McClelland, B. Riley. 1977. Relationships between hole-nesting birds, forest snags, and 

decay in western larch-Douglas-fir forests of the northern Rocky Mountains.

Missoula: University of Montana; 495 p. Ph.D. dissertation. 

McClelland, B. Riley. 1979. The pileated woodpecker in forests of the northern Rocky 

Mountains. In: Dickson, James G.; Conner, Richard N.; Fleet, Robert R.; Kroll, James 

C.; Jackson, Jerome A., editors. The role of insectivorous birds in forest ecosystems: 

proceedings of the symposium; 1978 July 13-14; Nacogdoches, TX. New York; 

Academic Press; 283-299. 

McComb, William C.; Noble, Robert E. 1981. Microclimates of nest boxes and natural 

cavities in bottomland hardwoods. Journal of Wildlife Management 45(1): 284-289. 

Meadows, Peter S.; Meadows, Azra, editors. 1991. The environmental impact of 

burrowing animals and animal burrows. Oxford, UK: The Zoological Society of 

London; 349 p. 

Mellen, Teresa Kim. 1987. Home range and habitat use of pileated woodpeckers, western 

Oregon. Corvallis: Oregon State University; 96 p. M.S. thesis. 

Mellen, Teresa Kim, Wildlife and Forest Program Ecologist, U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Region, Mt. Hood National Forest, Sandy, OR. 

[Telephone conversation with Catherine M. Raley]. 20 October 1999. 

Mills, L. Scott; Soulé, Michael E.; Doak, Daniel F. 1993. The keystone-species concept in 

ecology and conservation. BioScience 43(4): 219-224. 

Morrison, Michael L.; Meslow, E. Charles. 1983. Avifauna associated with early growth 

vegetation on clearcuts in the Oregon Coast Ranges. Res. Paper PNW-305. Portland, 

OR: Pacific Northwest Forest and Range Experiment Station, Forest Service, U.S. 

Department of Agriculture; 12 p. 

Mulder, Barry S.; Noon, Barry R.; Spies, Thomas A.; Raphael, Martin G.; Palmer, Craig J.; 

Olsen, Anthony R.; Reeves, Gordon H.; Welsh, Hartwell H., technical coordinators. 

1999. The strategy and design of the effectiveness monitoring program for the 

Northwest Forest Plan. Gen. Tech. Rep. PNW-GTR-437. Portland, OR: Pacific 

Northwest Research Station, Forest Service; U.S. Department of Agriculture; 138 p. 

Naiman, Robert J.; Melillo, Jerry M.; Hobbie, John E. 1986. Ecosystem alteration of boreal 

forest streams by beaver (Castor canadensis). Ecology 67(3): 1254-1269. 

Neitro, William A.; Mannan, R. William; Taylor, Douglas; Binkley, Virgil W.; Marcot, Bruce 

G.; Wagner, Frank F.; Cline, Steven P. 1985. Snags (wildlife trees). In: Brown, E. 

Reade, technical editor. Management of wildlife and fish habitats in forests of western 

Oregon and Washington: part 1. Publ. R6-F&WL-192. Portland, OR: Pacific Northwest 

Region, Forest Service, U.S. Department of Agriculture; 129-169. 

Noon, Barry R. 1999. Scientific framework for effectiveness monitoring of the Northwest 

Forest Plan. In: Mulder, Barry S.; Noon, Barry R.; Spies, Thomas A.; Raphael, Martin 

G.; Palmer, Craig J.; Olsen, Anthony R.; Reeves, Gordon H.; Welsh, Hartwell H., 

technical coordinators. The strategy and design of the effectiveness monitoring program 

for the Northwest Forest Plan. Portland, OR: Pacific Northwest Research Station, Forest 

Service, U.S. Department of Agriculture; 49-68. 

Otvos, I. S. 1970. Avian predation of the western pine beetle. In: Stark, R. W.; Dahlsten, 

Donald L., editors. Studies on the population dynamics of the western pine beetle, 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 273 

Dendroctonus brevicomis LeConte (Coleoptera: Scolytidae). Berkeley, CA: University 

of California, Division of Agricultural Science; 119-127. 

Otvos, Imre S. 1979. The effects of insectivorous bird activities in forest ecosystems: an 

evaluation. In: Dickson, James G.; Conner, Richard N.; Fleet, Robert R.; Kroll, James 

C.; Jackson, Jerome A., editors. The role of insectivorous birds in forest ecosystems: 

proceedings of the symposium; 1978 July 13-14; Nacogdoches, TX. New York; 

Academic Press; 341-374. 

Paine, Robert T. 1966. Food web complexity and species diversity. American Naturalist 

100: 65-75. 

Paine, Robert T. 1969. A note on trophic complexity and community stability. American 

Naturalist 103: 91-93. 

Parks, Catherine G., Research Plant Pathologist, U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station, La Grande, OR. [Telephone conversation 

with Catherine M. Raley]. 20 October 1999. 

Peterson, Barbara; Gauthier, Gilles. 1985. Nest site use by cavity-nesting birds of the 

Cariboo Parkland, British Columbia. Wilson Bulletin 97(3): 319-331. 

Pollock, Michael M.; Naiman, Robert J.; Erickson, Heather E.; Johnston, Carol A.; Pastor, 

John; Pinay, Gilles. 1995. Beaver as engineers: influences on biotic and abiotic 

characteristics of drainage basins. In: Jones, Clive G.; Lawton, John H., editors. 

Linking species and ecosystems. New York, NY: Chapman & Hall; 117-126. 

Power, Mary E.; Tilman, David; Estes, James A.; Menge, Bruce A.; Bond, William J.; Mills, 

L. Scott; Daily, Gretchen; Castilla, Juan Carlos; Lubchenco, Jane; Paine, Robert T. 

1996. Challenges in the quest for keystones. BioScience 46(8): 609-620. 

Redford, Kent H. 1984. The termitaria of Cornitermes cumulans (Isoptera, Termitidae) 

and their role in determining a potential keystone species. Biotropica 16(2): 112-119. 

Rendell, Wallace B.; Robertson, Raleigh J. 1989. Nest-site characteristics, reproductive 

success and cavity availability for tree swallows breeding in natural cavities.

Condor 91(4): 875-885. 

Schreiber, B.; deCalesta, D. S. 1992. The relationship between cavity-nesting birds and 

snags on clearcuts in western Oregon. Forest Ecology and Management 50: 299-316. 

Simberloff, Daniel. 1998. Flagships, umbrellas, and keystones: is single-species 

management passe in the landscape era? Biological Conservation 83(3): 247-257. 

Styskel, Edward W. 1983. Problems in snag management implementation—a case study.

In: Davis, Jerry W.; Goodwin, Gregory A.; Ockenfels, Richard A., technical 

coordinators. Snag habitat management: proceedings of the symposium; 1983 June 7-9; 

Flagstaff, AZ. Gen. Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 24-27. 

Terres, John K. 1980. The Audubon Society encyclopedia of North American birds. New 

York, NY: Alfred A. Knopf; 1109 p. 

Thomas, Jack Ward; Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: 

Thomas, Jack Ward, technical editor. Wildlife habitats in managed forests: the Blue 

Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: Forest 

Service, U.S. Department of Agriculture; 60-77. 

Tobalske, Bret W. 1997. Lewis’ woodpecker (Melanerpes lewis). In: Poole, Alan; Gill, 

Frank B., editors. The birds of North America, No. 284. Philadelphia, PA: The Academy 

of Natural Sciences; 28 p. 

Tracy, C. Richard; Brussard, Peter F. 1994. Preserving biodiversity: species in landscapes.

Ecological Applications 4(2): 205-207. 
The Pileated Woodpecker as a Keystone Species—Aubry and Raley 

274 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Tuchmann, E. Thomas; Connaughton, Kent P.; Freedman, Lisa E.; Moriwaki, Clarence B. 

1996. The Northwest Forest Plan: a report to the President and Congress. Portland, 

OR: USDA Office of Forestry and Economic Assistance; 253 p. 

Zarnowitz, Jill W.; Manuwal, David A. 1985. The effects of forest management on cavitynesting birds in northwestern Washington. Journal of Wildlife Management 49(1): 

255-263. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 275 

Characteristics and Dynamics of Cavity 

Nest Trees in Southern British Columbia1

Christoph Steeger2 and Jakob Dulisse3

Abstract 

We report on the characteristics, persistence, and temporal use patterns of nest trees of cavitynesting wildlife in coniferous forests of southern British Columbia, Canada. Our goal is to 

identify the types of trees required to be retained during forestry operations if viable 

populations of cavity nesters are to be maintained in managed forests. Between 1994 and 

1999, we recorded nesting species and tree characteristics during the year of first detection of 

active nest trees and in subsequent years, to document changes in wildlife use and tree 

condition. We located a total of 602 nests of 16 cavity-nesting species in 420 trees. 

Predominant tree species with active nests were Douglas-fir (Pseudotsuga menziesii), western 

larch (Larix occidentalis), trembling aspen (Populus tremuloides), and paper birch (Betula 

papyrifera). More than half of all nest trees were dead and/or partially broken when first 

detected. Three to 4.5 percent of nest trees were lost due to uprooting or total breakage each 

year. Partial breakage occurred at average annual rates of 1.1 to 6.2 percent each year. During 

the study period, 30 percent of nest trees were reused by breeding cavity nesters. 

Introduction 

Trees suitable for cavity excavation are an essential resource for wildlife species 

that require cavities in trees for breeding, roosting, and shelter from inclement 

weather and predators. The suitability of trees for cavity excavation is primarily 

determined by their size and the degree and pattern of decay present in the main stem 

or major branches of trees (Bull and others 1997). However, patterns of use may 

differ among cavity nester guilds and over time. Cavity nesters are typically grouped 

as strong excavators (i.e., woodpeckers) and weak excavators (i.e., nuthatches and 

chickadees)—both of which groups excavate their own cavities—and secondary 

cavity nesters (e.g., squirrels, bluebirds, swallows, and tree-nesting ducks and owls), 

which use cavities created by woodpeckers, broken branches, or wood decay 

processes (McClelland and others 1979, Newton 1994). Trees with cavities are often 

used repeatedly over time, either by the same breeding pair, by different pairs of the 

same species, or by multiple species either sequentially or simultaneously (Daily and 

others 1993, Loeb 1993, Sedgwick 1997). The dependence of secondary cavity 

nesters on the excavations of primary cavity nesters has been well established 

(Machmer and Steeger 1995). 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Senior Biologist, Pandion Ecological Research, 532 Park Street, Nelson, British Columbia, Canada 

V1L 2G9 (e-mail: csteeger@netidea.com) 

3

 Biologist, Pandion Ecological Research, 532 Park Street, Nelson, British Columbia, Canada V1L 2G9. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

276 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Numerous studies have examined attributes of trees preferred by various cavity 

nesters (Bate 1995, Bull and others 1997, Harestad and Keisker 1989, Raphael and 

White 1984, Sedgwick and Knopf 1990, Steeger and Hitchcock 1998). Because nestsite availability can be dramatically altered by forest-cutting regimes (Zarnowitz and 

Manuwal 1985), active nest trees with potential for reuse are among the most 

important wildlife habitat components that require retention in forestry operations. 

There is, however, general lack of information on the longevity and repeated use of 

nest trees. 

In this paper, we report on cavity nesters and their choice of nest tree 

characteristics (i.e., tree species, condition, and size), rates of complete loss or partial 

breakage of nest trees, and reuse of nest trees by breeding cavity nesters in coniferous 

forests of southern British Columbia, Canada. Our primary objectives are to examine 

condition and use of cavity nest trees over time and provide management 

recommendations for nest-tree retention in operational forestry. 

Study Area 

We conducted surveys for breeding cavity nesters in the 9,000-hectare Deer 

Creek watershed of Arrow Forest District, in the Columbia River basin of southern 

British Columbia (49°30’N, 118°00’W). Elevation of the area surveyed ranges from 

500 to 1,450 meters, and the area is generally southwest-facing. Most of the stands 

surveyed are managed stands of mature forest (85 to 95 years). Dominant conifer 

species are Douglas-fir (Pseudotsuga menziesii), lodgepole pine (Pinus contorta),

and western larch (Larix occidentalis), with a minor component of localized western 

redcedar (Thuja plicata), western hemlock (Tsuga heterophylla), western white pine 

(P. monticola), and ponderosa pine (P. ponderosa). The minor hardwood component 

is dominated by trembling aspen (Populus tremuloides) and paper birch (Betula 

papyrifera). The most significant forest insects and pathogens include endemic 

populations of mountain pine beetle (Dendroctonus ponderosae), root disease 

(Armillaria ostoyae), and larch dwarf mistletoe (Arceuthobium laricis). Based on 

visible fungal fruiting bodies, common heart-rot fungi responsible for the wood 

decay that facilitates cavity excavation by primary cavity nesters include white 

spongy trunk rot (Fomes fomentarius), hardwood trunk rot (Phellinus igniarius) and 

aspen trunk rot (Phellinus tremulae) on broad-leafed tree species, and red ring rot 

(Phellinus pini) and brown crumbly rot (Fomitopsis pinicola) on conifers. Snag 

densities varied throughout the study area. Some managed stands contained hardly 

any snags (less than 1 snag per hectare), whereas other stands contained low to 

moderate densities (10 to 50 snags per hectare). Unmanaged stands with relatively 

high levels of Armillaria root disease contained high densities of snags (greater than 

100 snags of 10 cm diameter at breast height or more per hectare; Steeger and 

Machmer 1995). 

Methods 

Nest Searching 

We conducted nest searches in approximately 50 percent (4,500 hectare) of the 

Deer Creek watershed, primarily in areas where road access facilitated ground 

surveys. We searched for active nests of cavity nesters between May and early July 

1996 to 1999 by inspecting trees for cavities, examining the ground for fresh wood 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 277 

chips, following adult birds, and listening for begging chicks. We considered a nest 

cavity to be active if a bird or mammal was observed incubating eggs or caring for 

young. Most trees were visited at least twice each breeding season to confirm 

occupation. 

Nest Tree Assessments 

For each confirmed active nest tree, we recorded tree species, tree diameter at 

breast height (dbh) measured with a dbh tape, tree height measured with a clinometer, 

tree condition (alive, dead, hard or soft snag), and location using a global positioning 

system device. We also noted presence of broken tops or stems, fungal decay (on the 

basis of visible conks), old excavated cavities, and identified the species of cavity 

nester using the tree. 

We revisited nest trees at least twice during the survey period (no reassessments 

were conducted in 1995) to determine current tree condition (i.e., unchanged, 

uprooted, partially or completely broken). We also examined each tree for evidence 

of new nesting, visually and by tapping on trees. Most breeding cavity nesters were 

easily flushed from their cavities by this method, with the exception of red squirrels. 

Our sample, therefore, may underestimate cavity occupancy by red squirrels. 

For data analysis on the choice of nest trees by cavity nesters, we took into 

account that a subset of nest trees contained more than one nest over the study period. 

To avoid potential pseudoreplication of individual cavity nesters, we removed 

additional nests of the same cavity-nesting species from the nest tree data set, if 

individual nest trees were occupied repeatedly by the same species. We performed 

statistical analyses with JMP statistical software4

 (Sall and Lehman 1996). With 

respect to the descriptions of nest trees, our study reports on use but not on 

availability of nest trees; hence, no inference about preference for certain trees can be 

made. 

Results 

Cavity Nesters and Their Nest Trees 

From 1994 to 1999, we found seven woodpecker, four weak excavators, and 

five secondary cavity-nesting species (table 1) occupying a total of 602 active nests. 

The proportional distribution of woodpeckers, weak excavators, and secondary cavity 

nesters in our sample was 59, 26, and 15 percent, respectively. The sample was 

dominated by 207 red-naped sapsucker and 117 red-breasted nuthatch nests, which 

together comprised about 54 percent of the sample. 

 

4

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

278 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 1—Tree species used by cavity nesters for breeding in the Deer Creek watershed, 

southern British Columbia, 1994-19991

. 

 Tree species2

Wildlife species n3 Tr 

As 

Pa 

Bi 

We 

La 

Do 

Fi 

Lo 

Pi 

Po 

Pi 

WR 

Ce 

WW 

Pi 

Woodpeckers: 263 47 24 14 7 4 4 0.4 0 

 Red-naped sapsucker 

Sphyrapicus nuchalis 

138 51 38 4 7 0 1 0 0 

 Hairy woodpecker 

Picoides villosus 

46 52 20 28 0 0 0 0 0 

 Northern flicker 

Colaptes auratus 

36 50 8 19 11 0 11 0 0 

 Three-toed woodpecker 

Picoides tridactylus 

23 9 0 30 9 43 4 4 0 

 Pileated woodpecker 

Dryocopus pileatus 

11 73 0 0 0 0 27 0 0 

 Black-backed woodpecker 

Picoides arcticus 

6 0 0 66 33 0 0 0 0 

 Downy woodpecker 

Picoides pubescens 

3 66 0 0 33 0 0 0 0 

 

Weak excavators: 148 17 21 15 42 3 2 0.7 0 

 Red-breasted nuthatch 

Sitta canadensis 

110 7 19 15 54 2 3 0 0 

 Blacked-capped chickadee 

Poecile atricapillus 

15 33 53 0 13 0 0 0 0 

 Mountain chickadee 

Poecile gambeli 

12 50 8 33 0 8 0 0 0 

 Chestnut-backed chickadee 

Poecile rufescens 

11 55 9 9 9 9 0 9 0 

 

Secondary cavity nesters: 84 17 25 36 4 12 2 2 2 

 Northern flying squirrel 

Glaucomys sabrinus 

45 29 33 22 4 9 0 2 0 

 Red squirrel 

Tamiasciurus hudsonicus 

19 0 32 47 5 11 0 5 0 

 Brown creeper

Certhia americanus 

18 0 0 56 0 22 11 0 11 

 

All species combined 495 33 23 18 17 5 3 0.8 0.4 

1 Numbers are percent of each sample (n = number of nest trees).

2

 TrAs = trembling aspen, PaBi = paper birch, WeLa = western larch, DoFi = Douglas-fir, LoPi = 

lodgepole pine, PoPi = ponderosa pine, WRCe = western redcedar, WWPi = western white pine. 3

American kestrel (Falco sparverius) and Common goldeneye (Bucephala clangula) had a sample size 

of 1 and were in a trembling aspen and western larch, respectively. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 279 

Nest Tree Species 

A total of 420 nest trees (containing 602 nests) were occupied by cavity nesters 

over the six breeding seasons. Some trees contained more than one nest, concurrently 

or in different years, and of the same or a different cavity-nesting species. 

Discounting 107 potentially pseudoreplicated nests, a total of 495 nests of different 

species were observed in the 420 nest trees. Eight tree species were used for nesting 

(table 1) of which, in order of most frequent use, trembling aspen, paper birch, 

western larch, and Douglas-fir accounted for most (91 percent) nest trees. Use of the 

four most-commonly used tree species by cavity-nesting guilds was significantly 

different from expected frequencies (chi-square = 134; d.f. = 6; p < 0.0001; table 1). 

In addition, pair-wise comparisons between guilds indicated different use patterns of 

tree species (p < 0.001 for all three comparisons). However, some similarities 

existed: woodpeckers and the secondary cavity-nesting guild (especially squirrels that 

use woodpecker cavities) primarily nested in aspen, birch and larch, whereas weak 

excavators most often used Douglas-fir. Aspen was used more often for nesting than 

any other tree species by five of the seven woodpecker species. A total of 75 percent 

of the 16 cavity-nesting species used aspen at least once. 

The three-toed woodpecker used mostly coniferous species, especially larch and 

lodgepole pine (30 and 43 percent, respectively). Douglas-fir was very important to 

one species in particular, the red-breasted nuthatch, accounting for 54 percent of its 

nests. All cavity-nesting species with a nest sample greater than two used more than 

one tree species for nesting. The pileated and black-backed woodpeckers appeared to 

be selective in our study area with respect to tree species, using only two species: 

aspen and ponderosa pine and larch and Douglas-fir, respectively. Four cavitynesting species showed considerable flexibility with respect to the species of tree 

they chose to nest in: three-toed woodpecker, red-breasted nuthatch, chestnut-backed 

chickadee, and northern flying squirrel each used six different tree species. 

Nest Tree Condition 

With the exception of aspen, most nest trees of all species (particularly 

ponderosa pine and Douglas-fir) were dead at the time of first detection (fig. 1). Dead 

nest trees were predominantly classified as hard snags, except for Douglas-fir, most 

of which were classified as soft snags (fig. 1). A high proportion of Douglas-fir, 

ponderosa pine and birch were partially broken and a high proportion of birch had 

visible evidence of wood decay (i.e., conks) (fig. 1). 

More than half (55 percent) of 495 nest trees located in this study were dead 

when first recorded with an active nest (table 2). Selection of dead trees for nesting 

differed among the three guilds (chi-square = 55.5; d.f. = 2; p < 0.0001). 

Woodpeckers used living trees more than dead trees, whereas weak excavators used 

primarily dead trees and did so more than did secondary cavity nesters (Fisher’s exact 

2-tailed test; d.f. = 1; p = 0.06). The trend for woodpeckers to use living trees for 

nesting, however, is largely a result of their extensive use of living aspen. Removing 

aspen from this analysis shows that the majority of woodpecker nests (63 percent of 

139 nests) were also located in dead trees. The proportional use of dead trees by 

individual cavity nesters (with sample size greater than 5) ranged from 33 – 50 

percent in woodpeckers, 18 – 89 percent in weak excavators, and 51 – 94 percent in 

secondary cavity nesters. Almost all brown creeper nests found were in dead trees 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

280 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

and constructed behind loose bark rather than in cavities in the stem or major 

branches of trees. 

100

80

40

60

20

0

100

80

40

60

20

0

100

80

40

60

20

0

Percent trees Percent trees Percent trees

Partially broken

Visible conks

Hard

Soft

Live

Dead

Douglas-fir Western

larch

Lodgepole

pine

Ponderosa

pine

Trembling

aspen

Paper

birch

a.

b.

c.

Douglas-fir Western

larch

Lodgepole

pine

Ponderosa

pine

Trembling

aspen

Paper

birch

Douglas-fir Western

larch

Lodgepole

pine

Ponderosa

pine

Trembling

aspen

Paper

birch

Figure 1—Proportion of nest trees that were (a) either living or dead, (b) dead with 

hard or soft stemwood, and (c) partially broken (> 2 meters standing) and/or showing 

visible sign of fungal decay (conks) in the Deer Creek watershed, southern British 

Columbia. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 281 

Table 2—Proportion of nest trees that were dead when used by cavity nesters in the Deer 

Creek watershed, southern British Columbia, 1994-1999. 

Wildlife species n1 Percent dead nest trees 

Woodpeckers: 263 40 

 Red-naped sapsucker 138 41 

 Hairy woodpecker 46 33 

 Northern flicker 36 36 

 Three-toed woodpecker 23 48 

 Pileated woodpecker 11 36 

 Black-backed woodpecker 6 50 

 Downy woodpecker 3 67 

Weak excavators: 148 76 

 Red-breasted nuthatch 110 89 

 Blacked-capped chickadee 15 60 

 Mountain chickadee 12 33 

 Chestnut-backed chickadee 11 18 

Secondary cavity nesters: 84 4 

 Northern flying squirrel 45 51 

 Red squirrel 19 68 

 Brown creeper 18 94 

All species combined 495 55 1

American kestrel and Common goldeneye had a sample size of 1 and were in a live and dead tree, 

respectively. 

Nest Tree Size 

Comparison of the six tree species that contained more than one percent of 

active (table 1) showed that the interquartile range of diameter values increased with 

increase in median, with ponderosa and lodgepole pine showing the widest and 

narrowest range, respectively (fig. 2). Mean diameters of nest trees differed 

significantly among the conifers (F3,185 = 14.1; p < 0.0001); however, post-hoc 

comparison of means between the two most commonly-used conifer species, 

Douglas-fir and western larch, indicated no significant difference (Tukey Kramer test 

α = 0.05). The two species of broad-leafed nest trees, trembling aspen and paper 

birch, also differed significantly in mean diameter (t1,223 = 4.6; p p < 0.0001), and 

were, on average, smaller in diameter than the coniferous nest trees (t1,412 = 6.2; p < 

0.0001). Douglas-fir nest trees showed the second largest mean diameter, despite 

being used primarily by small-sized, weak excavators (table 1). For all tree species, 

90 percent of all nest trees were larger than 18.5 cm in diameter. 

Comparison of the three cavity nester guilds showed similar patterns of the 

range of diameter values around the median (fig. 2), especially between woodpeckers 

and secondary cavity nesters. Mean diameters of nest trees did not differ significantly 

(F2,418 = 1.08; p = 0.34) among the three guilds of cavity nester. Ninety percent of 

nest trees used by woodpeckers and secondary cavity nesters were larger than 23.1 

cm in diameter, while 90 percent of nest trees used by weak excavators were larger 

than 16.4 cm in diameter. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

282 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

a. 

 

b. 

Figure 2—Central tendencies and associated variations in diameter (cm) values of 

nest trees by tree species (a) and cavity nester guild (b), Deer Creek watershed, 

southern British Columbia. Shown are distribution of all points, quantile box plots with 

medians, interquartile ranges (boxes) and 10 percent and 90 percent quantile lines, 

and means diamonds with means (center lines) and 95 percent confidence intervals 

(top and bottom of the diamonds). Sample sizes and mean values are given at the 

top and bottom of the panels, respectively. 

0

20

40

60

80

100

120

140

DoFi LoPi PaBi PoPi TrAs WeLa

Tree species

Diameter

44.6 23.3 29.7 65.5 36.5 43.4

81 20 93 13 132 75

0

20

40

60

80

100

120

140

Cavity Nester Guild

Woodpeckers Weak Excavators Secondary Cavity 

 Nesters

Diameter

39.2 36.6 37.4

223 134 57
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 283 

Nest Tree Dynamics 

Changes in Nest Tree Conditions 

We considered all trees with active nests located within one season as a “nesttree cohort” (table 3). Over time, trees within a cohort either changed condition (e.g., 

they partially broke) or they were completely lost due to total breakage, uprooting, or 

forestry operations (i.e., tree cutting or road building). Over the study period, the 

average annual rate of nest tree loss due to natural causes (range: 3.0 to 4.5 

percent/year, table 3) was fairly constant for each cohort, although there were 

differences in rates between the causes of tree loss. The annual proportion of nest tree 

loss due to natural causes for individual years (n = 15 for the five cohorts) ranged 

from 1.5 to 6.1 percent (data not shown). Average annual rates of partial tree 

breakage were generally similar to those for complete losses. We also report annual 

rates of nest tree loss due to forestry operations for comparative purposes, although 

these values are based on forest management decisions and vary accordingly. For the 

oldest nest-tree cohort (1994), we observed a total reduction in available nest trees of 

48.5 percent over the 5-year period (fig. 3).

Table 3—Changes in nest-tree cohorts found annually from 1994-98; numbers are average 

(except for the 1998 cohort) annual rates of change (in percentages) of the original samples. 

 Nest-tree cohorts (initial number of trees) 

 1994 

(66) 

1995 

(99) 

1996 

(70) 

1997 

(64) 

1998 

(89) 

Tree loss due to natural causes: 1 3.0 3.0 3.8 3.1 4.5 

Trees partially broken (> 2 meters standing) 5.1 6.5 2.8 3.1 1.1 

Tree loss directly due to forestry operations 6.7 3.3 0.9 1.6 2.3 

1

Causes included total breakage (< 2 m standing) or uprooting. Note that uprooting of some trees may 

have been indirectly caused by forestry operation via windthrow along the margins of cutblocks or 

roads. 

Figure 3—Reduction of the 1994 nest tree cohort (initial n = 66 nests) over 5 years in 

the Deer Creek watershed, southern British Columbia. Partially broken trees (> 2 

meters standing) are included. 

95.5

72.7

59.1 56.7

51.5

0

20

40

60

80

100

1994 1995 1996 1997 1998 1999

Year

Percent trees remaining
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

284 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Reuse of Nest Trees 

All tree species showed multiple excavated (nest or roost) cavities in individual 

trees, but there was a wide range of variation in the average and maximum number of 

cavities among species (table 4). 

Table 4—Number of excavated cavities in individual trees, by tree species, in the Deer Creek 

watershed, southern British Columbia, 1994-1999. 

Species n Mean # of cavities (s.e., range) 

Trembling aspen 132 3.6 (0.3, 1-14) 

Ponderosa pine 13 3.4 (1.0, 1-11) 

Paper birch 93 2.9 (0.3, 1-14) 

Western larch 75 2.5 (0.3, 1-14) 

Douglas-fir 81 2.0 (0.1, 1-7) 

Lodgepole pine 20 1.2 (0.2, 1-4) 

 

Reuse of nest trees involving new cavity excavation is generally higher in broadleafed trees compared to conifers, primarily due to the woodpeckers’ (especially rednaped sapsucker) frequent use of living aspen (table 1, fig. 1). Among conifers, 

ponderosa pine and larch showed relatively high mean, maximum and variation in 

number of cavities. Lodgepole pine had the lowest mean, maximum and variation in 

number of cavities (table 4); we only detected three-toed woodpeckers and the 

occasional weak excavator constructing nest cavities in lodgepole pine (table 1).

Overall, we detected multiple excavated cavities in 55.5 percent of all nest trees (n = 

420), with larger trees containing more cavities than smaller trees (r = 0.13, P < 

0.01). The proportion of trees with different numbers of multiple cavities was: 

Number of cavities Percent of nest trees 

2 18.6 

3 11.2 

4 7.9 

5 4.8 

6 5.7 

7-14 7.4 

During the study period, 30 percent of all available nest trees (n = 385) were 

reused, by the same and/or one or more different species in at least one subsequent 

year. Reuse by the same, one or two different species occurred in 19, 14, and 2 

percent of nest trees, respectively. We observed two simultaneously active cavity 

nests in 4 percent of all nest trees (n = 420), always by two different cavity-nesting 

species. The frequency of reuse of nest trees (maximum = five times) and the 

proportion of trees in each category was: once = 21 percent, twice = 5 percent, three 

times = 2 percent, four times = 0.8 percent and five times = 0.3 percent. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 285 

Discussion 

Cavity nesters detected within our study area used a total of eight tree species 

for breeding sites, with variation in the pattern of use among the different cavitynesting species and guilds. Based on the tree species used and the condition of nest 

trees, woodpeckers primarily used living trees (e.g., aspen) and hard snags (e.g., larch 

and lodgepole pine) for nesting. The pileated and black-backed woodpeckers were 

found in only two tree species which is consistent with the results of an extensive 

woodpecker study by Bull (1980). Our sample sizes for these species are low, 

however, and both species have been reported breeding in tree species different from 

the species reported in this study (Bull 1980, Raphael and White 1984). We found 

weak excavators nesting mostly in dead trees with advanced decay (e.g., Douglas-fir 

killed by Armillaria root disease and infected by Phellinus pini) and in partially 

broken trees. Red-breasted nuthatches, for example, most often nested near the break 

of broken-top trees (Steeger and Hitchock 1998). Eighty-five percent of 110 nuthatch 

nest trees located in the present study were partially broken. While we recorded 

presence of visible conks on nest trees, many living trees did not show any sign of 

fungal wood decay. However, because they were excavated by primary cavity 

nesters, they likely contained some wood decay at the level of the nest cavities 

(Conner and Locke 1982, Parks and others 1996). Most nest trees in our study were 

dead. 

Ponderosa and lodgepole pine nest trees showed the highest (65.5 cm) and 

lowest (23.3 cm) mean diameter, respectively. We do not have information on the 

proportions of different tree species and their diameter distributions in the study area 

and therefore cannot address preference for certain species and diameters by breeding 

cavity nesters. However, preference for large-diameter snags has been well 

documented for a variety of cavity nesters (see references in Bull and others 1997). In 

our study, mean diameter of all nest trees was 38.1 cm. Mean diameter of nest trees 

of woodpeckers, weak excavators, and secondary cavity nesters was 39.2 cm, 36.7 

cm, and 37.1 cm, respectively. These mean diameter (dbh) values are notably lower 

than those reported for cavity nest trees by, for example, Mannan and others (1980; 

greater 60 cm in western Oregon), Raphael and White (1984; 62.3 cm in northern 

California), and Lundquist and Mariani (1991; 75.8 cm in southern Washington) but 

are similar to those reported by Harestad and Keisker (1989; 32.3 cm in southcentral 

British Columbia). This difference in mean nest tree diameter between these United 

States and British Columbia studies may be related to the tree species and their 

diameter distribution available for cavity nesting in the respective study areas. 

However, regardless of the reason for this difference, our study shows that trees less 

than 40 cm in diameter are frequently used for cavity nesting, but we do not know the 

reproductive success of the breeding pairs we observed. A valuable contribution by 

further studies on cavity nest trees would be to examine reproductive success of pairs 

breeding in trees within a range of different characteristics. 

Average annual nest tree losses due to natural breakage or uprooting (i.e., not 

directly caused by tree cutting) ranged from 3.0 to 4.5 percent. These values are 

higher than the average annual 1.7 and 1.1 percent reported for attrition of pileated 

woodpecker nest trees by Bull (1987) and Bonar (2000), respectively. Our sample 

included nest trees of 16 cavity-nesting species, some of which are weak excavators 

that generally breed in dead and more decayed trees with presumably higher fall rates 

than those reported by Bull (1987) and Bonar (2000). The fall rates in our study are 

lower than those reported by McCelland (1977) who observed for seven cavity 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

286 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

nesters a loss of 9 out of 83 nest trees over 2 years (or 5.4 percent annually), but at 

least two of his nine trees were cut. The average annual rates of nest tree losses 

documented in our study are based on annual cohorts of all nest trees sampled. 

Therefore, the rates primarily represent nest tree loss of the most common nest tree 

species (i.e., aspen, birch, Douglas-fir, and larch) together. Rates of individual 

species may differ and will be evaluated when sample sizes are sufficient. 

Most nest trees (55.5 percent) in this study showed evidence of multiple cavity 

excavation. The number of multiple cavities in some trees may be underestimated as 

trees that were partially broken when first detected may have had other cavities in the 

part of the trunk that had broken off. Also, because more than half of all nest trees 

already contained two or more excavated cavities when first detected, our values for 

reuse of nest trees are potentially underestimates and some cavities may have gone 

undetected. Multiple nest cavities in trees have previously been documented by 

Sedgwick and Knopf (1986), who found 38.5 percent of all cavity trees had multiple 

excavations and that, consistent with our results, larger trees had more cavities than 

smaller trees. The observed multiple use of large-sized trees by cavity nesters, either 

sequentially over several years or simultaneously, indicates the high habitat and 

conservation value of such trees. 

Management Implications 

The low-elevation coniferous forests of the southern interior of British Columbia 

are characterized by a high diversity of tree species (Meidinger and Pojar 1991) that 

supports a variety of primary and secondary cavity nesters. Seven sympatric 

woodpecker species occur in our study area, which is near the maximum number 

reported for North America (Short and Horne 1990). Because woodpeckers and other 

cavity nesters play important ecological roles in forest ecosystems (e.g., regulation of 

insect populations, [Machmer and Steeger 1995], keystone cavity excavators in nest 

webs [Martin and Eadie 1999]) and are potentially negatively affected by intensive 

forestry, preservation of their nest trees has become part of forest management in 

British Columbia. 

Although some tree species such as aspen and larch are used by a variety of 

cavity nesters, other tree species are used by only a few individual cavity nesters 

(e.g., use of lodgepole pine by three-toed woodpeckers). Retention of nest trees 

during forestry and other land-use operations, therefore, may be most beneficial to 

the diversity of cavity nesters if sets of tree species are retained that are 

representative of the pre-harvest stand composition. Of particular importance for any 

retention strategy are broad-leafed trees with evidence of nest cavities, especially in 

stands in which these species constitute a minor component of the tree species 

composition. Large-diameter ponderosa pine snags are important nest trees for 

woodpeckers potentially over long periods of time, as indicated by the high number 

of nest cavities they contain in our study area; they should be retained wherever 

possible. In stands with high levels of bark beetle populations, selective harvesting of 

infested or susceptible pine should include some pine retention to provide current and 

future nesting as well as foraging opportunities, especially in three-toed woodpecker 

home ranges. 

For cavity nesters in general, dead and partially broken coniferous and broadleafed trees and trees with fungal wood decay are essential habitat components. 

Under endemic levels of natural disturbance agents (insects and diseases) and in the 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 287 

absence of catastrophic winds and fires, the annual rate of nest tree loss due to natural 

causes is less than 5 percent in our study area and may be in balance with new trees 

becoming suitable for cavity nesting. However, forestry operations such as road 

building and logging along with unregulated firewood cutting can lead to dramatic 

reductions in habitat for cavity nesters over extensive areas of the landscape. Because 

primary cavity nesters are territorial during the breeding season (i.e., they exclude 

conspecifics from a given area), establishment of zones where intensive forestry is 

practiced without retention of dead and diseased trees will lead to declines in cavity 

nester populations, as these zones will not be able to contain more breeding pairs as 

set by the species’ territory size requirements. Cavity nester populations fluctuate 

naturally in any given area according to the often ephemeral availability of essential 

resources such as nest sites and feeding opportunities (Baldwin 1968, Otvos 1979). 

However, elimination of dead and diseased trees that provide habitat for cavity 

nesters is a systematic and, to some extent, inevitable process in industrial forestry 

that most probably effects the natural dynamics of populations. If intensive forestry 

zones are too wide-spread, species of cavity nesters may become endangered or 

locally extirpated as, for example, in the managed taiga forests of Sweden that are 

suffering severe losses of broad-leafed and dead trees (Angelstam 1990, Angelstam 

and Mikusinski 1994). In British Columbia, the Wildlife/Danger Tree Assessor’s 

Course and the recently revised occupational health and safety regulations of the 

Workers’ Compensation Board now allow for retention of dead trees in all forestry 

operations, provided they do not pose a hazard to forest workers (Manning and others 

2002). Successful implementation of these new initiatives will be an important step in 

conserving the habitat of cavity nesters in British Columbia. 

Acknowledgments 

In addition to the authors, the following people participated in the field data 

collection: Marc-André Beaucher, Rachel Holt, Carl Savignac, and Maryann 

McDonaugh. Rachel Holt, Keith Aubry, Evelyn Bull, and Lisa Bate reviewed the 

manuscript. Special thanks go to Bill Laudenslayer for his valuable input. The study 

was funded by Forest Renewal British Columbia and administered by Darryl 

Atkinson of the Science Council of British Columbia. 

References 

Angelstam, Per. 1990. Factors determining the composition and persistence of local 

woodpecker assemblages in taiga forest in Sweden—a case for landscape ecological 

studies. In: Carlson, Allan; Aulén, Gustaf, eds. Conservation and management of 

woodpecker populations. Swedish University of Agricultural Sciences, Department of 

Wildlife Ecology, Report 17. Uppsala Sweden; 147-164. 

Angelstam, Per.; Mikusinski, G. 1994. Woodpecker assemblages in natural and managed 

boreal and hemiboreal forest—a review. Annales Zoologici Fennici 31: 157-172. 

Baldwin, Paul H. 1968. Predator-prey relationships of birds and spruce beetles.

Proceedings of the North Central Branch Entomological Society of America 23: 90-99. 

Bonar, Richard L. 2000. Availability of pileated woodpecker cavities and use by other 

species. Journal of Wildlife Management 64(1): 52-59. 

Bate, Lisa J. 1995. Monitoring woodpecker abundance and habitat in the central Oregon 

Cascades. Moscow, ID: University of Idaho; 116 p. M.S. thesis. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

288 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Bull, Evelyn L. 1980. Resource partitioning among woodpeckers in northeastern Oregon.

Moscow, ID: University of Idaho; 109 p. Ph.D. dissertation. 

Bull, Evelyn L. 1987. Ecology of the pileated woodpecker in northeastern Oregon. Journal 

of Wildlife Management 51(2): 472-481. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Research Station; 55 p. 

Conner, Richard N.; Locke, Brian A. 1982. Fungi and red-cockaded woodpecker cavity 

trees. Wilson Bulletin 94: 64-70. 

Daily, Gretchen C.; Ehrlich, Paul R.; Haddad, N. M. 1993. Double keystone bird in a 

keystone species complex. Proceedings of the National Academy of Sciences 90: 592-

594. 

Harestad, Alton S.; Keisker, Dagmar G. 1989. Nest tree use by primary cavity-nesting 

birds in south central British Columbia. Canadian Journal of Zoology 67: 1067-1073. 

Loeb, S. C. 1993. Use and selection of red-cockaded woodpecker cavities by southern 

flying squirrels. Journal of Wildlife Management 57: 329-335. 

Lundquist, Richard W.; Mariani, Jina M. 1991. Nesting habitat and abundance of snagdependent birds in the southern Washington Cascade range. In: Ruggiero, L. F.; 

Aubry, Keith B.; Carey, Andy B.; Huff, M. H., technical coordinators. Gen. Tech. Rep. 

PNW-GTR-285. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 221-239. 

Machmer, Marlene M.; Steeger, Christoph. 1995. The ecological roles of wildlife tree users 

in forest ecosystems. Victoria, BC: British Columbia Ministry of Forests, Land 

Management Handbook 35; 54 p. 

Mannan, R. William; Meslow, E. Charles; Wight, Howard M. 1980. Use of snags by birds in 

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44(4): 787-797. 

Manning, Todd E.; Bradford, Peter; White, Carry; Rowe, David. 2002. British Columbia’s 

dangerous tree assessment process—a summary. In: Laudenslayer, William F., Jr.; 

Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., 

technical coordinators. Proceedings of a symposium on the ecology and management of 

dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSWGTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; [this volume]. 

Martin, Kathy; Eadie, John M. 1999. Nest webs: a community-wide approach to the 

management and conservation of cavity-nesting forest birds. Forest ecology and 

mangement 115: 243-257. 

McClelland, Riley B. 1977. Relationships between hole-nesting birds, forest snags, and 

decay in western larch-Douglas-fir forests of the northern Rocky Mountains.

Missoula, MT: University of Montana. 483 p. Ph.D. dissertation. 

McClelland, Riley B.; Frissell, Sidney S.; Fischer, William C.; Halvorson, Curtis H. 1979. 

Habitat management for hole-nesting birds in forests of western larch and Douglasfir. Journal of Forestry 77: 480-483. 

Meidinger, Del; Pojar, Jim. 1991. Ecosystems of British Columbia. Victoria, BC: British 

Columbia Ministry of Forests; 330 p. 

Newton, Ian. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a 

review. Biological Conservation 70: 265-276. 
Nest Tree Characteristics and Dynamics of Cavity-nesting Species—Steeger and Dulisse 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 289 

Otvos, Irme S. 1979. The effects of insectivorous bird activities in forest ecosystems: an 

evaluation. In: Dickson, James G.; Connor, Richard N.; Fleet, Robert R.; Kroll, James 

C.; Jackson, Jerome A., editors. The role of insectivorous birds in forest ecosystems. 

New York: Academic Press; 341-374. 

Parks, Catherine G; Bull, Evelyn L.; Filip, Gregory M.; Gilbertson, R.L. 1996. Wood decay 

fungi associated with woodpecker nest cavities in living western larch. Plant Disease 

80: 959. 

Raphael, Martin G.; White, M. 1984. Use of snags by cavity-nesting birds in the Sierra 

Nevada. Wildlife Monograph 86: 1-66. 

Sall, John; Lehman, Ann. 1996. JMP start statistics. SAS Institute, Inc., New York: 

Duxbury Press; 521 p. 

Sedgwick, James A. 1997. Sequential cavity use in a cottonwood bottomland. Condor 99: 

880-887. 

Sedgwick, James A.; Knopf, Fritz L. 1986. Cavity-nesting birds and the cavity-tree 

resource in plains cottonwood bottomlands. Journal of Wildlife Management 50(2): 

247-252. 

Sedgwick, James A.; Knopf, Fritz L. 1990. Habitat relationships and nest site 

characteristics of cavity-nesting birds in cottonwood floodplains. Journal of Wildlife 

Management 54: 112-124. 

Short, Lester L.; Horne, Jennifer F.M. 1990. Woodpeckers—a world perspective and 

conservation concerns. In: Carlson, Allan; Aulén, Gustaf, eds. Conservation and 

management of woodpecker populations. Swedish University of Agricultural Sciences, 

Department of Wildlife Ecology, Report 17. Uppsala Sweden; 5-12. 

Steeger, Christoph; Machmer, Marlene M. 1995. Wildlife trees and their use by cavity 

nesters in selected stands of the Nelson Forest Region. Nelson, BC: British Columbia 

Ministry of Forests, Technical Report TR-010; 28 p. 

Steeger, Christoph; Hitchcock, Christine L. 1998. Influence of forest structure and diseases 

on nest-site selection by red-breasted nuthatches. Journal of Wildlife Management 

62(4): 1349-1358. 

Zarnowitz, Jill E.; Manuwal, David A. 1985. The effects of forest management on cavitynesting birds in Northwestern Washington. Journal of Wildlife Management 49(1): 

255-263. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 291 

How Dead Trees Sustain Live Organisms in 

Western Forests1

Fred L. Bunnell,2 Isabelle Houde,2 Barb Johnston,2 and Elke Wind3 

Abstract 

Dead wood contributes to biological richness as substrate, cavity sites, foraging sites, and 

shelter or cover. In the Pacific Northwest, 69 vertebrate species commonly use cavities, 47 

species respond positively to down wood, and prevalence of both uses is related to natural fire 

regimes. Almost 80 percent of nests of weak excavators are in dead trees; strong excavators 

make greater use of live trees. Most bat roosts are in dead trees, whereas carnivores use 

mostly declining, living trees. Selection of both cavity and foraging sites is governed by decay 

patterns. Some species prefer large pieces of down wood. Management implications are 

discussed. 

Introduction 

Dying trees, snags, and down wood are common in unmanaged forests and 

required by many species, including fungi, cryptogams, invertebrates, and vertebrates 

(Berg and others 1994, Harmon and others 1986). We focus on vertebrates, and note 

contributions to non-vertebrates only briefly. We also focus on the Pacific Northwest, 

which we define as Alaska, Alberta, British Columbia, Washington, Oregon, Idaho, 

Montana, and northern Nevada and California. References to other regions are 

included to indicate trends where forestry has been practiced longer, or where 

particular species are well documented. 

As concern for sustaining all organisms has grown, interest in natural 

disturbance regimes as models for guiding forest practices has also increased 

(Attiwill 1994, Hunter 1993). We first examine relations among natural fire regimes 

and vertebrates that use dead wood. We then review the diverse uses forest-dwelling 

organisms make of dead wood under four broad categories: substrate, cavity sites, 

foraging sites, and shelter or cover (down wood). We finish by noting management 

implications. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Professor and Research Technicians, respectively, Center for Applied Conservation Research, 

Department of Forest Sciences, University of British Columbia, 3004-2424 Main Mall, Vancouver, 

British Columbia, Canada, V6T 1Z4 (e-mail: fbunnell@interchange.ubc.ca and houde@intergate.ca). 3

 Research Technician, E. Wind Consulting, 1-2817 Glenayr Dr., Nanaimo, British Columbia, Canada, 

V9S-3S7 (e-mail: ewind@telus.net). 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

292 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Natural Disturbance Regimes and Use of Dead Wood 

Fire is the major natural agent of disturbance in Pacific Northwest forests, and 

natural fire regimes differ among forest types, influencing the amounts of dead wood 

present (Agee 1993). We examined relationships of the forest-dwelling vertebrate 

fauna with natural fire regimes in the 12 forested biogeoclimatic zones of British 

Columbia, applying the approach of Bunnell (1995) to more recent data. We 

expected predictable differences. The proportion of species positively associated with 

down wood should increase as the fire-return interval increased and down wood 

accumulated. Cavity users should be negatively correlated with fire size, because size 

and intensity often are related, and fewer snags remain standing where fires are more 

intense. 

The proportion of down wood users in the fauna increased with increasing firereturn interval, and proportions of bird and mammal cavity users decreased with 

increasing fire size (table 1). Species using down wood are mainly mammals 

(appendix A), and both numbers of species and proportions of mammalian users of 

down wood increased with increasing fire size. That is expected if larger, more 

intense fires create a more reliable supply of down wood. The number of species 

using cavity sites decreased significantly as fire return interval lengthened, and snags 

were created less frequently (table 1). Fire regimes vary with the precipitation 

regime, but associations between the vertebrate fauna and precipitation regimes were 

not found. The lack of relations with total precipitation suggests that fire regime had 

more influence on composition of the vertebrate fauna than precipitation itself (the 

two wettest types were also higher elevation and obscured any relationship between 

amphibian richness and precipitation). 

Forest-dwelling vertebrate faunas appear to respond to amounts and duration of 

down wood as these are influenced by the natural disturbance regime, suggesting a 

mechanism for the differences in richness of dead wood users across broad forest 

types. 

Table 1—Significant Spearman's rank coefficients among vertebrates using dead wood and 

mean annual precipitation, and characteristics of natural fire regimes in the 12 forested 

biogeoclimatic zones of British Columbia. 1

Cavity users Downed wood users 

All Birds Mammals All Mammals 

 

N2 Pr2 N Pr N Pr N Pr N Pr 

Precipitation 0.59* 

Fire Size - 0.85** - 0.75** - 0.70* 0.66* 0.68* 

Fire Return - 0.58* - 0.79** 0.83** 1

 * = P < 0.05; ** = P < 0.01 

2

 N = Number of species; Pr = Proportion of species in the native vertebrate fauna. 

Dying and Dead Wood as Substrate 

Dead wood makes its greatest contribution to biological richness as substrate for 

fungi, cryptogams, and invertebrates. There are no sharp distinctions between 

declining trees and snags as the most favored habitat. Some pendent lichens are 

common on both, but appear more abundant on snags (e.g., Usnea longissima, Berg 

and others 1994; Letharia vulpina, Bernes 1994). Berg and others (1994) reviewed 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 293 

habitat requirements of 1,487 threatened forest-dwelling organisms in Sweden. Dying 

trees were favored habitat for 89 species of fungi and cryptogams and 252 species of 

invertebrates. Snags provided substrate for 21 percent of all threatened non-vertebrate 

species, including 36 macrofungi and cryptogam species and 266 invertebrates. Logs 

hosted more species. Berg and others (1994) estimated that about 30 percent of 

threatened cryptogams and macrofungi and 28 percent of the invertebrates were 

dependent on down wood. 

The role of dead wood as substrate is less well known in the Pacific Northwest, 

but likely is similar to the role in Sweden. Of 636 lichen species reported from 

British Columbia 46 are largely restricted to old-growth stands (Goward 1999; 

Goward and others 1994). Goward and Arsenault (1997) reported a snag-specific 

community of lichens from Englemann spruce (Picea englemanni; scientific names 

for most species are found in appendix A) and subalpine fir (Abies lasciocarpa)

forests. At least 25 lichen species are found on decaying wood (data in Goward 1999, 

and Goward and others 1994). Of 93 forest-dwelling bryophytes reviewed by Vitt 

and others (1988) for the Pacific Northwest, 30 species (32 percent) preferentially 

grow on down wood that frequently is well rotted. Well-rotted logs also serve as foci 

for dispersal of mycorrhizal fungi critical to tree productivity (Maser and others 

1978). Some “saprophytic” vascular plants (e.g., Allotropa, Hemitomes) rely upon 

mycorrhizal fungi that often are found in down wood for delivery of nutrients (Leake 

1994). In British Columbia, 526 species of macrofungi are dependent on down wood, 

including some harvested commercially (Lofroth 1998). Because some vertebrates 

forage on fungi and insects in down wood, reductions of these food sources may 

appear higher in the food chain. 

Features of logs considered to influence non-vertebrates include tree species, 

decay state, size, and distribution. Conifer logs are more durable than hardwood logs. 

Natural successions of cryptogams, fungi, and invertebrates on and in down wood 

(e.g., McCullough 1948, Söderström 1988) indicate the importance of a range of 

decay states. Larger logs provide better substrate than smaller logs for bryophytes 

and lichens, because larger logs last longer, have more surface area, and have higher, 

steeper sides that discourage ground-dwelling species from invading (Samuelsson 

and others 1994). Forest-floor bryophytes generally have very limited dispersal 

ability (Khanna 1964, Söderström 1987), and dispersal is from log to log for epixylic 

species. For these reasons, Samuelsson and others (1994) argued that logs should be 

close together, but not gathered into piles. Similarly, several small logs may provide 

more habitat than a single large log. 

Dead wood is a critical substrate for hundreds of non-vertebrate species in the 

Pacific Northwest. Large, dispersed pieces of a range of decay states are preferred. 

Sustaining a range of decay requires sustained recruitment of down wood. 

Dead Wood as Cavity Sites

Cavity sites are easily studied and hence well-documented. Foraging on snags is 

a year round activity, is less frequently studied, and less well known. Lack of cavity 

nesting sites has limited abundance of some birds in intensively managed forests 

(Angelstam and Mikusinski 1994, Newton 1994). 

Because of the importance of heart rot for cavity sites, most nests of primary 

cavity nesters were in dead trees (table 2). Of 2,674 nesting records of weak 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

294 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

excavators, 2,154 (78 percent) were in dead trees (table 2). Although conifers are 

less prone to decay than most hardwoods, the proportion of dead trees used as nest 

sites by weak excavators did not change with the proportion of conifers used. Most 

strong excavators located < 50 percent of their nests in dead trees (table 2), but the 

proportion of nests in dead trees increased significantly with the proportion of 

conifers used (Bunnell and others 2002). That relationship explains apparently 

anomalous values in table 2. For example, in the largest sample for pileated 

woodpecker in table 2 (Bull 1987; n = 105 nests) all available nest trees were 

conifers, and 99 percent of the nests were in dead trees. Conversely, another sample 

was gathered4

 where hardwoods were available but scarce (< 10 percent of stems), 

but six of seven nest trees were living trembling aspen (Populus tremuloides). Dead 

trees were the main source of cavity sites for 16 of the 21 primary excavators (table 

2). For most of the remaining species, dead trees were more commonly used as cavity 

sites when nests were in conifers. Weaker excavators largely restricted to conifers 

(e.g., Lewis’s woodpecker, white-headed woodpecker) may be particularly 

threatened in managed, conifer forests, because trees do not become old enough for 

heart rots to develop. Both Lewis’s and white-headed woodpeckers are designated 'at 

risk' in the Pacific Northwest (appendix A). 

Table 2―Percentages of nests located in dead trees by strong and weak excavators of the 

Pacific Northwest. 

 Pct dead n1

 Sources 

Strong 

Excavators 

 

Yellowbellied 

sapsucker 

41.4 63 Scott and others 1980; BC Nest Records. 

Red-naped 

sapsucker 

24.0 557 Campbell and others 1990; Li and Martin 1991; C. 

Steeger2

; W. Klenner and D. Huggard3; K. Martin4

 

Red-breasted 

sapsucker 

55.3 132 Raphael and White 1984; Campbell and others 1990; Li 

and Martin 1991. 

Williamson’s 

sapsucker 

59.3 303 Bull 1980; Scott and others 1980; Raphael and White 

1984; Li and Martin 1991; Conway and Martin 1993; BC 

Nest Records. 

Hairy 

woodpecker 

62.4 190 Kelleher 1963; Bull 1980; Scott and others 1980; Raphael 

and White 1984; Campbell and others 1990; Li and 

Martin 1991; W. Klenner and D. Huggard3

; K. Martin4; 

C. Steeger2

Three-toed 

woodpecker 

42.9 161 Scott and others 1980; Klenner and Huggard 1997; C. 

Steeger2

; K. Martin4; BC Nest Records. 

Blackbacked 

woodpecker 

46.7 56 Bull 1980; Raphael and White 1984; C. Steeger 

(unpublished)2

; BC Nest Records. 

Acorn 

woodpecker 

7.8 238 Scott and others 1980; Li and Martin 1991; Hooge and 

others 1999. 

Pileated 

woodpecker 

73.2 202 Bull 1987; Mellen 1987; Campbell and others 1990; C. 

Steeger 2

; W. Klenner and D. Huggard3; K. Martin4; K. 

Aubry and C. Raley 5

 

 

4

 Unpublished data on file, British Columbia Ministry of Forests, Kamloops, British Columbia. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 295 

(table 2 continued) 

 Pct dead n1 Sources 

Weak 

Excavators 

 

Lewis's 

woodpecker 

62.4 367 Raphael and White 1984; BC Nest Records 

Downy 

woodpecker 

60.4 109 Scott and others 1980; Campbell and others 1990; Li and 

Martin 1991; C. Steeger2

; K. Martin4

Whiteheaded 

woodpecker 

97.4 123 Raphael and White 1984; Milne and Hejl 1989; Dixon 

1995a; Dixon 1995b. 

Northern 

flicker 

55.9 717 Bull 1980; Scott and others 1980; Raphael and White 

1984; Campbell and others 1990; Li and Martin 1991; 

W. Klenner and D. Huggard3

; K. Martin4; C. Steeger2

Nuttall's 

woodpecker 

94.0 48 Miller and Bock 1972 (review within). 

Blackcapped 

chickadee 

59.3 17 C. Steeger2

; K. Martin4

Mountain 

chickadee 

65.8 433 Scott and others 1980; Raphael and White 1984; W. 

Klenner and D. Huggard3

; K. Martin4; BC Nest Records. 

Boreal 

chickadee 

87.3 31 Peck and James 1987; Campbell and others 1997. 

Chestnutbacked 

chickadee 

58.0 132 C. Steeger2

; BC Nest Records. 

Red-breasted 

nuthatch 

71.9 394 Raphael and White 1984; W. Klenner and D. Huggard3

; 

K. Martin4

; C. Steeger2; BC Nest Records. 

Whitebreasted 

nuthatch 

74.2 62 McEllin 1979; Scott and others 1980; Raphael and White 

1984; Li and Martin 1991; Campbell and others 1997. 

Pygmy 

nuthatch 

78.0 331 McEllin 1979; Scott and others 1980; Raphael and White 

1984; Li and Martin 1991; BC Nest Records. 1 Number of nest trees. 

2 Unpublished data on file, Pandion Ecological Research, Ltd., Nelson, BC, Canada. 3

 Unpublished data on file, BC Ministry of Forests, Kamloops Region, BC, Canada. 4 Unpublished data on file, Centre for Applied Conservation Biology, University of British Columbia, 

Vancouver, BC, Canada. 

5 Unpublished data for K. Aubry and C. Raley, sight unseen from Bull and Jackson (1995).

Figure 1 illustrates preferences by woodpeckers for trees in different stages of 

decay. Decay classes in figure 1 are those of Thomas and others (1979), and classes 1 

and 2 represent healthy and declining, but living, trees. We used the electivity index 

of Ivlev (1961) to compare within studies, because it is largely symmetrical, ranging 

from -1.0 at complete avoidance to about +1.0 when all nests are in a particular 

category. Living conifers were not selected by either woodpeckers or cavity-using 

mammals (primarily red and flying squirrels). Living trembling aspen trees were used 

more in proportion to their availability, except by mammals that cannot excavate 

their own cavities. The most strongly preferred decay classes were recently dead trees 

(decay classes 3 and 4). Decay classes 4 and 5 of lodgepole pine (Pinus concorta) 

were strongly avoided because they were long dead, understory trees, too small to 

support cavities. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

296 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 1—Apparent preference among decay classes shown by: a) woodpeckers 

nesting in conifers (data of Bevis 1996); b) woodpeckers nesting in Douglas-fir [ ◆] 

and trembling aspen trees [ O ] (data of Klenner and Huggard 1998); c) mammals in 

lodgepole Pine [ ■ ] and trembling aspen trees [ O ] (data of K. Martin unpublished). 

Preference evaluated by the electivity index of Ivlev (1961). 

a)

b)

c)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Decay Class

Electivity

1 2 3 4 5 6+

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Decay Class

Electivity

1 2 3 4 5 6+

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Decay Class

Electivity

1 2 3 4 5 6+
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 297 

There are more secondary than primary cavity nesters (appendix A), but often 80 

percent or more of their nest sites are created by primary nesters (Dobkin and others 

1995, Li and Martin 1991, Schreiber and deCalesta 1992). Other nest sites are in 

cavities created by rot. For both forms of nest sites, dead trees are the major source of 

nesting opportunities. Several bat species also locate 70 to 100 percent of their roosts 

in dead trees (table 3). Less than 50 percent of denning trees of flying squirrels, 

American marten, and black bears were dead, indicating the importance of sustaining 

older trees with large rot pockets. Most black bear dens recorded from coastal forests 

of the Pacific Northwest were associated with wooden structures, including trees, 

logs, and stumps. Den sites in southern, inland forests also were commonly in trees 

(Bull and others 1996, Lindsay 1999). Mean sizes of den trees for mammals usually 

exceeded 50 centimeter (references of table 3). Amphibians and reptiles make 

occasional use of cavity sites (McComb and Noble 1981). Bunnell and Dupuis (1995) 

reported that snags used by amphibians were recently dead with sloughing bark. 

Table 3―Percentage of denning and roosting sites located in snags and dead trees by 

mammals of the Pacific Northwest. Logs and stumps not included. 

Species Pct dead n1 Sources 

Bats 

Big brown 

bat 

45.8 57 Rasheed and Holroyd 1995; Betts 1996; Vonhof 1996; 

Kalcounis and Brigham 1998; Rabe and others 1998. 

California 

myotis 

100.0 25 Vonhof 1996; Brigham and others 1997; Grindal 1997. 

Fringed 

myotis 

100.0 15 Rabe and others 1998. 

Little brown 

myotis 

63.2 23 Crampton and Barclay 1995; Rasheed and Holroyd 

1995; Kalcounis and Hecker 1996; Grindal 1997. 

Long-legged 

myotis 

90.2 54 Rasheed and Holroyd 1995; Ormsbee and McComb 

1998; Rabe and others 1998. 

Northern 

long-eared 

myotis 

42.9 7 Caceres 1997. 

Pallid bat 100.0 3 Rabe and others 1998. 

Silver-haired 

bat 

72.0 50 Crampton and Barclay 1995; Rasheed and Holroyd 

1995; Betts 1996; Campbell and others 1996; Vonhof 

1996. 

Southwestern 

myotis 

0.0 2 Rabe and others 1998. 

Western 

long-eared 

myotis 

89.5 47 Caceres 1997; Grindal 1997; Vonhof and Barclay 1997; 

Rabe and others 1998. 

Rodents 

Flying 

squirrel 

32.1 627 Mowrey and Zasada 1984; Carey and others 1997. 

Carnivores 

Black bear 32.1 249 Lindzey and Meslow 1976; Noble and others 1990; 

Immell and Boulay 1994; Akenson 1994; Bull and others 

1996; Davis 1996; Lindsay 1999. 

American 

marten 

40.3 470 Spencer 1987; Martin and Barratt 1991; Jones and others 

1997; Raphael and Jones 1997; Ruggiero and others 

1998. 1 Number of denning or roosting sites. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

298 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Dying and Dead Trees as Foraging Sites 

Long-term management of snag-using species requires provision of both 

foraging and cavity sites. Several studies suggest that cavity sites are less often 

limiting to cavity nesters than foraging habitat (Hutto 1995, Walankiewicz 1991, 

Welsh and Capen 1992). Given the relative lack of data for foraging sites, a key 

question is: are the kinds of trees that should be retained for foraging similar to those 

that provide nesting sites? 

Among larger excavators, sapsuckers feed primarily on sap and insects 

associated with their sapwells. Northern flickers feed on ants on the ground (Bull and 

others 1986). Several woodpeckers feed primarily by flaking bark or probing after 

insect larvae in the cambium or sapwood. Pileated woodpeckers specialize on 

carpenter ants excavated from decayed sap- or heartwood (Bull and others 1986). For 

the latter two feeding techniques, decay state may reflect the likelihood of hosting 

preferred insects and the ease of excavating. It is less clear that size of tree should 

influence feeding preference, although duration of decay states and size of tree often 

are correlated. If decay state indicates foraging opportunities, we expect patterns 

specific to individual tree species, because species decay differently. 

Figure 2 shows that conifers were avoided as feeding sites until they attained 

decay class 3 (recently dead). Their attractiveness as foraging sites then increased 

with further decay (see also Gyug and Bennett 1996), although that pattern differs 

among cavity-nesting species (Morrison and others 1987). In Englemann sprucesubalpine fir forests, three-toed woodpeckers strongly preferred recently dead snags 

(Klenner and Huggard 1997). Pileated woodpeckers use more decayed wood, 

provided it hosts carpenter ants (Bull and others 1992). Among conifers, Douglas-fir 

(Pseudotsuga menzieseii) is a possible exception (fig. 2), and appears to become less 

attractive to woodpeckers once all bark is shed (decay class 6+). That may reflect 

Douglas-fir tending to rot from the outside in, so the sapwood becomes less favorable 

to breeding insects. On Bevis’ (1996) study area, Douglas-fir was not sought as a 

foraging site (electivity = -0.04), and selection was shown only for western larch 

(Larix occidentalis) (electivity = 0.25). Douglas-fir snags also were not selected on 

Madsen’s (1985) study site (electivity = -0.21), whereas western larch and ponderosa 

pine (Pinus ponderosa) were selected (electivity = +0.15 and +0.20, respectively). 

Selection of trembling aspen followed a different pattern than for conifers. 

Foraging woodpeckers were indiscriminate in their use of decay classes 1 through 3 

(apparently healthy to recently dead trees), but tended to avoid trees of decay class 4 

or greater (fig. 2). Woodpeckers tend to use more of the smaller diameter trees when 

foraging than when nesting, especially when foraging on hardwoods (fig. 3).

We draw two broad points from comparisons of nesting and foraging sites. First, 

when foraging on conifers, woodpeckers select dead wood. The wood need not be 

standing, and several species forage on down wood when it is not snow covered (Bull 

and others 1997). Second, woodpeckers will use smaller trees when foraging than 

when nesting. Birds select similar decay states when foraging or nesting (compare 

figs. 1, 2), but smaller snags are used when foraging (fig. 3). The tendency for nesting 

trees to be larger than foraging trees makes biological sense: a cavity site must be 

large enough to contain an adult bird and its young; a foraging site need only be large 

enough to contain wood-boring larvae or ants. The trend is consistent across studies 

(e.g., Bevis 1996, Gyug and Bennett 1996). Small snags do not remain standing for 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 299 

as long as large snags (Morrison and Raphael 1993), and may never be used as nest 

trees. Nonetheless, they do serve as foraging sites. 

Figure 2—Apparent preference among decay classes shown by foraging cavity 

nesters. a) Woodpeckers foraging on Douglas-fir [– –◆– –], lodgepole pine [—■—], 

spruce [—∆—], and trembling aspen trees [– – O – –] (from data of Klenner and 

Huggard 1998). b) Cavity nesting birds foraging on conifers (from data of Madsen 

1985). c) Woodpeckers foraging on conifers (from data of Bevis 1996). Values of 

0.95 represent instances where specific decay or size classes were sufficiently 

uncommon that they did not appear in the random sample of availability. Preference 

evaluated by the electivity index of Ivlev (1961). Decay classes of Thomas and 

others (1979). 

a)

b)

c)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Decay Class

Electivity

1 2 3 4 5 6+

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Decay Class

Electivity

1 2 3 4 5 6+

0.95 0.95

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Decay class

Electivity

1

2

2 3 4 5 6+
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

300 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 3—Comparisons of electivity shown by foraging [– – O – –] and nesting [—

◆— ] woodpeckers across diameter classes. Data for a) Douglas-fir from Klenner 

and Huggard (1998), b) Trembling aspen from Klenner and Huggard (1998), c) 

Conifers from Madsen (1985). 

a)

b)

c)

Aspen

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Electivity

<10 10-20 20-30 30-50 >50

Diameter class

Douglas-fir

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Electivity

<10 10-20 20-30 30-50 >50

Diameter class

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Electivity

>15-23 >23-38 >38-53 >53

Conifers

Diameter class
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 301 

Some species foraging habitats are particularly difficult to incorporate into forest 

management. Both the black-backed and three-toed woodpeckers are specialized 

feeders commonly exploiting conditions after fires (Apfelbaum and Haney 1981, 

Hutto 1995). Three-toed woodpeckers feed primarily on larvae of bark beetles 

(Murphy and Lehnhausen 1998) that respond dramatically to forest fires, laying eggs 

in surviving trees and snags almost immediately after the fire. Adults emerge 2 to 3 

years later, and secondary outbreaks appear rare. Although they do eat larvae of 

wood-boring beetles (Cerambycidae) in other snags, food is most abundant for these 

woodpeckers for only a 2- to 3-year, post-fire period. Black-backed woodpeckers 

specialize on larvae of wood-boring beetles that bore into the sapwood of fire- or 

beetle-killed trees. Populations of both woodpecker species are therefore irruptive 

and concentrated in areas of beetle-infested trees, and both are listed “at risk”’ in the 

Pacific Northwest (appendix A).

Kreisel and Stein (1999) found foraging woodpeckers in winter to be ten times 

more abundant in recently burned forest than in unburned forest. Hutto (1995) 

reported that 15 bird species occurred more frequently in burns than any other cover 

type, including four cavity nesters: hairy, three-toed, and black-backed woodpeckers, 

and the mountain bluebird. The black-backed woodpecker is the most vulnerable, 

because of its specialization on wood-boring larvae (rather than bark beetles or freeflying insects). In short, 15 bird species have recent burns as their favored habitat and 

at least one is dependent upon burns. 

The problem for forest management is that beetle-infested stands provide the 

ideal (and possibly only productive) habitat for some woodpecker species. Numbers 

of black-backed woodpecker are much lower in older forests than among recent firekilled trees so that even maintenance of old stands may not be a sufficient 

management tactic. Both fire suppression and salvage logging work to the detriment 

of the species. The life history of the black-backed woodpecker illustrates that 

commitment to maintaining all of biological diversity is also a commitment to 

sustaining some areas of dying and dead forest. 

Dead Wood as Shelter and Cover 

Dead wood on the ground influences vertebrate abundance and richness by 

providing: 

• Necessary substrate, energy, and nutrients for many invertebrates and fungi 

upon which a wide range of amphibian, reptile, bird, and small mammal 

species depend for forage (e.g., Bull and others 1997, Maser and Trappe 

1984; Rhoades 1986). 

• Sheltered areas for reproduction in a range of vertebrates from salamanders 

to black bears, and cover from aerial predators (e.g., Corkran and Thoms 

1996, Harestad 1991). 

• A modified microclimate (cooler, moister, more stable temperature than 

surrounding habitat) that is essential to species that cannot tolerate extremes 

in temperature or humidity (several amphibians; Heatwole 1962). 

• Runways for small mammals and display or lookout posts for birds (e.g., 

Bull and Henjum 1990, Lofroth 1998). 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

302 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

• Increased habitat diversity and aeration in water by forming riffles, small 

waterfalls, and pools, thereby creating habitat for amphibians and fish which 

are in turn fed on by other vertebrates. 

• Structures exploited by near-aquatic vertebrates as cover, foraging sites, or 

basking (e.g., river otter [Lontra Canadensis], mink, painted turtles 

[Chrysemys picta]; Lofroth 1998). 

• Access routes for predators, especially under snow cover (e.g., weasels, 

marten; Corn and Raphael 1992). 

Among terrestrial vertebrates, strict dependence on down wood is most likely 

among species breeding in rotten wood (e.g., some salamanders). Other species, 

including shrews and several birds, forage on insects that are abundant in down wood 

and are often more abundant at sites with more down wood (e.g., Craig 1995, 

Waterhouse and Dawson 1999). Although several bird species opportunistically 

exploit down wood for nesting sites (e.g., blue grouse [Dendracapus obscurus] and 

ruffed grouse [Bonasa umbellus], Townsend’s solitaire [Myadestes townsendi]), only 

one bird species relies largely on down wood for nesting opportunities―the winter 

wren (Waterhouse 1998). Opportunistic use can be high. For example, Campbell and 

others (1990) reported that 31 percent of blue grouse nests were alongside logs. 

Several mammal species, ranging from little brown myotis to black bears, use down 

wood as resting or denning sites, but most show flexibility across substrates. Rodents, 

snowshoe hare (Lepus americanus), gray wolf (Canis lupus), and wolverine (Gulo 

gulo) not only use down wood as maternal or resting dens but also use thickets or 

earth dens. Hagar and others (1995) estimated that 52 species of mammals in Oregon 

responded positively to greater amounts of dead wood. Among the 52, 40 were 

associated with logs as cover for themselves or their prey, but it has proven difficult 

to associate consistent positive responses in population size or fitness with abundance 

of down wood (Bunnell and Huggard 1999, Bunnell and others 1999b). We 

acknowledged that flexibility in appendix A by including only species for which a 

positive response appeared likely from current literature. By using that criterion, 12 

to 18 percent of terrestrial forest-dwelling vertebrate species respond positively to 

increasing amounts of down wood in the 12 major forest types of British Columbia 

(Bunnell and others 1999b). 

The strongest responses to down wood are among terrestrial-breeding 

salamanders (seven of eight salamander species in appendix A). Among habitat 

variables surveyed, down wood is most consistently related to abundance of 

terrestrial-breeding salamanders (reviews of Bunnell and others 1999b, deMaynadier 

and Hunter 1995). Some workers reported these salamanders to be associated with 

large pieces of down wood (Aubry and others 1988, Whitaker and others 1986). Corn 

and Bury (1991) found that densities of clouded and western redback salamanders 

were relatively constant per unit volume of down wood regardless of stand age, 

indicating the benefits of retaining down wood in younger stands. Other authors have 

documented positive responses of small mammals to down wood (e.g., Carey and 

Johnson 1995, Corn and others 1988, Gilbert and Allwine 1991), but results are 

highly variable within species and among locations. Bunnell and others (1999a) 

offered four reasons for the observed variability in response to down wood, of which 

the most troubling is that critical lower thresholds have not been reached. 

Where forestry has been practiced longer than in the Pacific Northwest, many 

organisms are threatened by reductions in down wood (e.g., Anglestam 1997, Berg 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 303 

and others 1994). Current evidence suggests that species dependent upon down wood 

in the Pacific Northwest are surviving on legacies of past practices, not the results of 

current practices (e.g., Bunnell and others 1997, Spies and others 1988). We believe 

that if current accumulations are not replenished, down wood accrued under past 

practices will decline, as will some species. 

Management Implications 

In the Pacific Northwest, 69 vertebrate species consistently seek cavities in 

dying or dead trees, and more use such cavities opportunistically. Another 47 or more 

species respond positively to increasing amounts of down wood (appendix A). The 90 

species of forest-dwelling vertebrates in the Pacific Northwest listed as “sensitive” or 

“at risk,” include 30 species requiring cavities and 21 species strongly associated 

with down wood. (A definition of “forest-dwelling” is problematic, and we excluded 

species such as peregrine falcon (Falco peregrinus), Swainson’s hawk (Buteo 

swaisoni), and barn owl (Tyto alba) whose relationship with forest cover is 

marginal.) Thus, about 57 percent of listed vertebrate species are reliant upon or 

strongly associated with dead wood. Many more cryptogams, fungi, and invertebrates 

are dependent upon dead wood. Where the goal of management is to sustain or 

restore native biodiversity, forest practices must include ways of sustaining dead 

wood. Most managed stands have smaller volumes of dead wood than do unmanaged 

stands (Maser and Trappe 1984, Spies and others 1988). The trend is pronounced 

where forestry has been practiced longer. Angelstam (1997) reported that dead wood 

comprised 30-40 percent of the total wood volume in unmanaged stands and declined 

to about 20 percent after one rotation and to about 1 percent after several rotations of 

intensive fiber extraction. The trend is consistent with projections of Spies and others 

(1988) for the Pacific Northwest. Our review suggests that if managers desire to 

sustain biodiversity they should: 

• Ensure sustained provision of dying and dead wood—Hundreds of species 

depend on dying and dead logs and trees. Where the goal is to sustain all of 

the biological diversity, patchwise retention incorporating all structures is 

helpful. 

• Retain trees and snags of both hardwoods and favored conifer species (larch, 

Douglas-fir, ponderosa pine), particularly where hardwood species are not 

abundant. Avoid creating monocultures of less preferred species, such as 

lodgepole pine―Although they are favored nesting sites and provide the 

only substrate for some bryophytes, we cannot rely solely on more decayprone hardwoods. The varied needs of forest organisms include well-decayed 

snags, large hollow snags, and snags with loose slabs of bark. Hardwood 

species will not accommodate all these needs, nor will any one species of 

conifer. Because conifers are longer-lived and provide a longer-lasting 

source of cavities than do hardwoods (Erskine 1977, Harmon and others 

1986), they are more likely to sustain snags late into rotations. Conifer snags 

are required by species foraging on bark beetles and wood-boring beetles, 

and conifer logs last longer than do hardwood logs. 

• Retain a range of size and age classes of dead wood―Where safety 

considerations eliminate older snags at harvest, managers should ensure that 

snags can develop through the rotation. Although larger diameters usually are 

selected by vertebrates, smaller snags and logs are used. The desirability of a 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

304 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

range of decay classes is well documented for bryophytes, insects, terrestrial 

breeding salamanders, and birds. Well-decayed snags present greater safety 

risks and are more easily retained in patches. Unless reserve patches are very 

large, recruitment of well-decayed snags must occur outside of reserve 

patches. Snags may never become well decayed if operational guidelines 

require snag-falling. Either no-work zones are required during subsequent 

entries, or silvicultural systems that do not require frequent entries should be 

employed in at least some areas. Well-decayed snags will not develop at all 

during a rotation if no trees die until late in the rotation. Retaining declining 

live trees, or recently-dead snags, ensures timely onset of decay. 

• Ensure that some large trees or snags are retained―Although individual 

birds use a wide range of tree or snag sizes, they tend to select larger ones 

when available. Current data suggest that conifer cavity trees > 50 cm would 

accommodate most bird species, and most hardwood trees can be smaller 

(Bunnell and others 2002). Studies of vertebrate-forest relations have 

concentrated where trees are larger and more valuable, so existing data 

overestimate requirements where trees are smaller. A diameter > 30 

centimeter will accommodate most bird species in less productive, inland 

forest types (Bunnell and others 2002). Some mammals select trees or snags 

> 50 centimeters in diameter (e.g., marten, black bear), and use down wood 

50 to 150 centimeter in diameter (Davis 1996, Raphael and Jones 1997, 

USDA Forest Service 1996). Given how larger mammals use space, large 

pieces of down wood for such species can be well distributed across large 

areas. Large trees and snags provide nesting or denning sites longer than do 

small snags (Graham 1981, Morrison and Raphael 1993). However, smaller 

snags provide foraging sites, and many more foraging sites are needed than 

nesting sites.

• Meet dead wood requirements for larger species in areas where the emphasis 

is not on intensive fiber production―Binkley (1997) and Bunnell and others 

(1999a) reviewed economic and ecological advantages of zoning the 

intensity of fiber production. In some forest types, larger mammals prefer 

significant amounts (100 to 200 cubic meters/hectare or more) and sizes (> 

50 centimeter diameter) of down wood (review in Lofroth 1993). Needs of 

those species are best provided in areas where late-successional attributes are 

being maintained. Provision of some large pieces of dead wood in forests 

where the dominant goal is fiber production may facilitate dispersal among 

areas of more favorable habitat. 

• Don’t do the same thing everywhere―Retention of trees in patches reduces 

safety risks of snag retention and windthrow (Coates 1997, Franklin and 

others 1997) and facilitates retention of a range of size and decay classes. It 

also concentrates recruitment of down wood. Debris piles are used by some 

vertebrates (Morris 1984, Raphael and Jones 1997), but scattered pieces of 

down wood favor other organisms. Dispersed retention of individual snags, 

or declining live trees intended to become snags, may be particularly 

advantageous for perching birds, and for territorial secondary users, such as, 

raptors and some small birds, but impact shrub nesters negatively by 

encouraging aerial predators (Vega 1993). Any single approach will 

disadvantage some group of species, so a range of practices is preferable if a 

range of species is to be sustained in an area. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 305 

• Limit salvage logging after forest fires―Fire suppression has reduced the 

area of recent burns favored by several vertebrates. If all vertebrates are to be 

sustained, salvage logging should not be performed over all burns, or the 

entire area of large burns. 

Acknowledgments 

Our research and synthesis was supported by the Canadian Wildlife Service’s 

Fraser River Action Plan, Forest Renewal British Columbia, Lignum, MacMillan 

Bloedel (now Weyerhaeuser BC); and Western Forest Products. R. W. Campbell 

provided unpublished data from the British Columbia Nest Records Scheme; D. 

Huggard, W. Klenner, K. Martin, and C. Steeger also generously provided 

unpublished data or unreduced data for us to reanalyze. The manuscript benefited 

from reviews by D. Huggard and B. Marcot. This is Publication No. R-36 of the 

Centre of Applied Conservation Biology, University of British Columbia. 

References 

Agee, James K. 1993. Fire ecology of Pacific Northwest forests. Washington, DC: Island 

Press; 493 p. 

Akenson, James. 1994. Black bear den summary NE Region―Interim progress report.

Starkey Bear Study, 1994 February. La Grande, OR: Oregon Department of Fish and 

Game; 3 p. 

Angelstam, Per. 1997. Landscape analysis as a tool for the scientific management of 

biodiversity. Ecological Bulletin (Copenhagen) 46: 140-170 

Angelstam, Per; Mikusinski, Grzegorz. 1994. Woodpecker assemblages in natural and 

managed boreal and hemiboreal forest―a review. Annales Zoologica Fennici 31: 

157-172. 

Apfelbaum, Stephen; Haney, Alan. 1981. Bird populations before and after wildfire in a 

Great Lakes pine forest. Condor 83: 347-354. 

Attiwill, Peter M. 1994. The disturbance of forest ecosystems: the ecological basis for

conservative management. Forest Ecology and Management 63: 247-300. 

Aubry, Keith B.; Jones, Lawrence L.C.; Hall, Patricia A. 1988. Use of woody debris by 

plethodontid salamanders in Douglas-fir forests in Washington. In: Szaro, R.; 

Severson, K. E.; Patton, D. R., technical coordinators. Management of amphibians, 

reptiles, and small mammals in North America; 1988 July 12-21; Flagstaff, AZ. Gen. 

Tech. Rep. RM-166. Ft. Collins, CO: Rocky Mountain Forest and Range Experimental 

Station, U.S. Department of Agriculture; 32-37. 

Berg, Åkes; Ehnström, Bengt; Gustafsson, Lena; Hallingbäck, Tomas; Jonsell, Mats; Weslien, 

Jan. 1994. Threatened plant, animal, and fungus species in Swedish forests: 

distributions and habitat associations. Conservation Biology 8: 718-731. 

Bernes, Claes, editor. 1994. Biological diversity in Sweden. A country study. Monitor 14. 

Stockholm, Sweden: Swedish Environmental Protection Agency; 280 p. 

Betts, Burr J. 1996. Roosting behaviour of silver-haired bats (Lasionycteris noctivagans)

and big brown bats (Eptesicus fuscus) in northeast Oregon. In: Barclay, R. M. R.; 

Brigham, R. M., editors. Bats and forests symposium; 1995 October 19-21; Victoria, 

BC. Victoria, BC: British Columbia Ministry of Forests; 56-61. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

306 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Bevis, Kenneth R. 1996. Primary excavators in grand fir forests of Washington's east 

Cascades and forestry on the Yakima Indian Nation, Washington. In: Bradford, P.; 

Manning, T.; I'Anson, B., editors. Wildlife tree/stand-level biodiversity workshop 

proceedings; 1995 Oct. 17-18, Victoria, BC. Victoria, BC: British Columbia Ministry of 

Environment, Lands and Parks, and Ministry of Forests; 77-86. 

Binkley, Clark S. 1997. Preserving nature through intensive plantation management: the 

case for forestland allocation with illustrations from British Columbia. Forestry

Chronicle 73: 553-559. 

Brigham, Mark R.; Vonhof, Maarteen J.; Barclay, Robert M. R.; Gwilliam, John C. 1997.

Roosting behavior and roost-site preferences of forest-dwelling California bats 

(Myotis californicus). Journal of Mammalogy 78: 1231-1239. 

British Columbia Ministry of Environment, Lands, and Parks. 1992. 1992 red and blue lists 

for terrestrial vertebrates. Victoria, BC: British Columbia Ministry of Environment, 

Lands, and Parks; 4 p. 

British Columbia Ministry of Environment, Lands, and Parks. 1996. 1996 red and blue lists 

for terrestrial vertebrates. Victoria, BC: British Columbia Ministry of Environment, 

Lands, and Parks; 4 p. 

Bull, Evelyn L. 1980. Resource partitioning among woodpeckers in northeastern Oregon. 

Moscow, ID: University of Idaho; 109 p. Ph.D. dissertation. 

Bull, Evelyn L. 1987. Ecology of the pileated woodpecker in northeastern Oregon. Journal 

of Wildlife Management 51: 472-481. 

Bull, Evelyn L.; Henjum, Mark G. 1990. Ecology of the great gray owl. Gen. Tech. Rep. 

PNW-265. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 39 p. 

Bull, Evelyn L.; Jackson, Jerome A. 1995. Pileated woodpecker. The Birds of North 

America no. 148: 20 p. 

Bull, Evelyn L.; Peterson, Steven R.; Thomas, Jack W. 1986. Resource partitioning among 

woodpeckers in northeastern Oregon. Research Note PNW-444. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 19 p. 

Bull, Evelyn L.; Beckwith, Roy C.; Holthausen, Richard S. 1992. Arthropod diet of pileated 

woodpeckers in northeastern Oregon. Northwestern Naturalist 73: 42-45. 

Bull, Evelyn L.; Akenson, Jim J.; Betts, Burr J.; Torgensen, Torolf R. 1996. The 

interdependence of wildlife and old-growth forests. In: Bradford, P.; Manning, T.; 

I'Anson, B., editors. Wildlife tree/stand-level biodiversity workshop proceedings; 1995 

Oct. 17-18, Victoria, BC. Victoria, BC: British Columbia Ministry of Environment, 

Lands, and Parks, and Ministry of Forests; 71-75. 

Bull, Evelyn L., Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Bunnell, Fred L. 1995. Forest-dwelling vertebrate faunas and natural fire regimes in 

British Columbia: patterns and implications for conservation. Conservation Biology 

9: 636-644. 

Bunnell, Fred L.; Dupuis, Linda A. 1995. Riparian habitats in British Columbia: their 

nature and role. In: Morgan, K. H.; Lashmar, M. A., editors. Riparian habitat 

management and research. Special Publication of the Fraser River Action Plan. Delta, 

BC: Canadian Wildlife Service; 7-21. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 307 

Bunnell, Fred L.; Huggard, Dave J. 1999. Biodiversity across spatial and temporal scales: 

problems and opportunities. Forest Ecology and Management 115: 113-126. 

Bunnell, Fred L.; Kremsater, Laurie L.; Wells, Ralph W. 1997. Likely consequences of 

forest management on terrestrial, forest-dwelling vertebrates in Oregon. Portland, 

OR: Oregon Forest Resources Institute; 130 p. 

Bunnell, Fred L.; Wells, Ralph W.; Nelson, John D.; Kremsater, Laurie L. 1999a. Effects of 

harvest policy on landscape pattern, timber supply and vertebrates in an East 

Kootenay watershed. In: Rochelle, J. A.; Lehmann, L. A.; Wisniewski, J., editors. 

Forest fragmentation: wildlife and management implications. Leiden, Netherlands: Brill; 

271-93. 

Bunnell, Fred L.; Kremsater, Laurie L.; Wind, Elke 1999b. Managing to sustain vertebrate 

diversity in forests of the Pacific Northwest: relationships within stands.

Environmental Reviews 7: 97-146. 

Bunnell, Fred L.; Wind, Elke; Boyland, Mark; Houde, Isabelle. 2002. Diameters and heights 

of trees with cavities: their implications to management. In: Laudenslayer, William 

F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas 

E., technical coordinators. Proceedings of the symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; [this volume]. 

Bunnell, Fred L.; Wind, Elke; Wells, Ralph W. 2002. Dying and dead hardwoods: their 

implications to management. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Caceres, Carolina. 1997. Northern long-eared bat. Progress report no. 014. Columbia 

Basin Fish and Wildlife Compensation Program. Nelson, BC: BC Hydro and British 

Columbia Ministry of Environment; 21 p. 

Campbell, Lori A.; Hallett, James G.; O’Connell, Margaret A. 1996. Conservation of bats in 

managed forests: use of roosts by Lasionycteris noctivagans. Journal of Mammalogy 

77: 976-984. 

Campbell, Wayne R.; Dawe, Neil K.; McTaggart-Cowan, Ian; Cooper, John M.; Kaiser, Gary 

W.; McNall, M. C. E. 1990. The birds of British Columbia. Vol. 2. Diurnal birds of 

prey through woodpeckers. Vancouver, BC: University of British Columbia Press; 514 

p. 

Campbell, Wayne R.; Dawe, Neil K.; McTaggart-Cowan, Ian; Cooper, John M.; Kaiser, Gary 

W.; McNall, Michael C. E. 1997. The birds of British Columbia. Vol. 3. Passerines: 

flycatchers through vireos. Vancouver, BC: University of British Columbia Press; 693 p. 

Carey, Andrew B.; Johnson, Murray L. 1995. Small mammals in managed, naturally 

young, and old-growth forests. Ecological Applications 5: 336-352. 

Carey, Andrew B.; Wilson, Todd M.; Maguire, Christine C.; Biswell, Brian L. 1997. Dens of 

northern flying squirrels in the Pacific Northwest. Journal of Wildlife Management 

61: 684-699. 

Coates, K. D. 1997. Windthrow damage 2 years after partial cutting at the Date Creek

silvicultural systems study in the interior cedar-hemlock forests of northwestern 

British Columbia. Canadian Journal of Forest Research 27: 1695-1701. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

308 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Conway, Courtney J.; Martin, Thomas E. 1993. Habitat suitability for Williamson’s 

sapsuckers in mixed-conifer forests. Journal of Wildlife Management 57: 322-328. 

Corkran, C. C.; Thoms, C. R. 1996. Amphibians of Oregon, Washington and British

Columbia. Vancouver, BC: Lone Pine Publishing; 175. 

Corn, Stephen P.; Bury, Bruce R. 1991. Terrestrial amphibians in the Oregon Coast 

Range. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. F., technical 

coordinators. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. 

Rep. PNW-GTR-285. Portland, OR: Pacific Northwest Research Station, Forest Service, 

U.S. Department of Agriculture; 305-317. 

Corn, Janelle G.; Raphael, Martin G. 1992. Habitat characteristics at marten subnivean 

access sites. Journal of Wildlife Management 56: 442-448. 

Corn, Stephen P., Bury, Bruce. R.; Spies, Thomas A. 1988. Douglas-fir forests in the 

Cascade Mountains of Oregon and Washington: is the abundance of small 

mammals related to stand age and moisture? In: Szaro, R. C.; Severson, K. E.; 

Patton, D. R., technical coordinators. Management of amphibians, reptiles, and small 

mammals in North America―proceedings of the symposium; 1988 July 19-21; 

Flagstaff, AZ. General Technical Report RM-166. Fort Collins, CO: Rocky Mountain 

Forest and Range Experiment Station, U.S. Department of Agriculture, Forest Service; 

340-352. 

 Craig, Vanessa J. 1995. Relationships between shrews (Sorex spp.) and downed wood in 

the Vancouver watersheds, BC. Vancouver, BC: University of British Columbia; 88 p. 

M.Sc. thesis. 

Crampton, Lisa H.; Barclay, Robert M. R. 1996. Habitat selection by bats in fragmented 

and unfragmented aspen mixedwood stands of different ages. In: Barclay, R. M. R.; 

Brigham, R. M., editors. Bats and forests symposium; 1995 October 19-21; Victoria, 

BC. Victoria, BC: British Columbia Ministry of Forests; 238-259. 

Davis, Helen. 1996. Characteristics and selection of winter dens by black bears in coastal 

British Columbia. Burnaby: Simon Fraser University; 144 p. M.Sc. thesis. 

deMaynadier, Phillip G.; Hunter, Jr., Malcom L. 1995. The relationship between forest 

management and amphibian ecology: a review of the North American literature.

Environmental Reviews 3: 230-261. 

Dixon, Rita D. 1995a. Density, nest-site and roost-site characteristics, home-range, 

habitat-use, and behavior of white-headed woodpeckers: Deschutes and Winema 

National Forests, Oregon. Nongame Report 93-3-01. Portland, OR: Oregon 

Department of Fish and Wildlife; 90 p. 

Dixon, Rita D. 1995b. Ecology of white-headed woodpeckers in the central Oregon 

Cascades. Boise, ID: University of Idaho; 148 p. M.Sc. thesis. 

Dobkin, David S.; Rich, Adam C.; Petare, Jennifer A.; Pyle, William H. 1995. Nest-site 

relationships among cavity-nesting birds of riparian and snowpocket aspen 

woodlands in the northwestern Great Basin. Condor 97: 694-707. 

Erskine, Anthony J. 1977. Birds in boreal Canada: communities, densities and 

adaptations. Ottawa, ON: Canadian Wildlife Service Report Series 41; 73 p. 

Franklin, Jerry F.; Berg, Dean R.; Thornburgh, Dale A.; Tappeiner, John C. 1997. 

Alternative silvicultural approaches to timber harvesting: variable retention 

harvest systems. In: Kohm, K. A.; Franklin, J. F., editors. Creating a forestry for the 

21st Century: the science of ecosystem management. Washington, DC: Island Press; 

111-139. 

Gilbert, Frederick F.; Allwine, Rochelle. 1991. Small mammal communities in the Oregon 

Cascade Range. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. F., technical 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 309 

coordinators. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. 

Rep. PNW-GTR-285. Portland, OR: Pacific Northwest Research Station, Forest Service, 

U.S. Department of Agriculture; 256-267. 

Goward, Trevor. 1999. The lichens of British Columbia―illustrated keys. Part 2 Fruticose 

species. Special Report Series 9. Victoria, BC: British Columbia Ministry of Forests; 

319 p. 

Goward, Trevor; Arsenault, Andre. 1997. Notes on the assessment of lichen diversity in 

old-growth Engelmann spruce-subalpine fir forests. In: Hollstedt, C.; Vyse, A., 

editors. Sicamous Creek silvicultural systems project: workshop proceedings; 1996 

April 24-25; Kamloops, B.C. Victoria, BC: British Columbia Ministry of Forests; 67-78. 

Goward, Trevor; McClure, Bruce; Meidinger, Del. 1994. The lichens of British Columbia— 

illustrated keys. Part 1 Foliose and squamulose species. Special Report Series 8. 

Victoria, BC: British Columbia Ministry of Forests; 181 p. 

Graham, Robin L. L. 1981. Biomass dynamics of dead Douglas-fir and western hemlock 

boles in mid-elevation forests of the Cascade Range. Corvallis, OR: Oregon State 

University; 152 p. Ph.D. dissertation. 

Grindal, Scott D. 1997. Upper Kootney River bat survey. Athalmere, BC: Columbia Basin 

Fish and Wildlife Compensation Program; 60 p. 

Gyug, Les. W.; Bennett, Stephen P. 1996. Bird use of wildlife tree patches 25 years after 

clearcutting. In: Bradford, P.; Manning, T.; I'Anson, B., editors. Wildlife tree/standlevel biodiversity workshop proceedings; 1995 Oct 17-18; Victoria, BC. Victoria, BC: 

British Columbia Ministry of Environment, Lands, and Parks, and Ministry of Forests; 

15-33. 

Hagar, Joan C.; McComb, William C.; Chambers, Carol C. 1995. Effects of forest practices 

on wildlife. In: Beschta, R. L.; Boyle, J. R.; Chambers, C. C.; Gibson, W. P.; Gregory, 

S. V.; Grizzel, J.; Hagar, J. C.; Li, J. L.; McComb, W. C.; Parzybok, T. W.; Reiter, M. 

L.; Taylor, G. H.; Warila, J. E., editors. Cumulative effects of forest practices in Oregon: 

literature and synthesis. Corvallis, OR: Oregon State University; chapter 9. 

Harmon, Mark E.; Franklin, Jerry F.; Swanson, Fred J.; Sollins, Phil; Gregory, S. V.; Lattin, J. 

D.; Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, Jr., K.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advanced Ecological Research 15: 133-302. 

Harestad, Alton S. 1991. Activity of Townsend’s chipmunks and habitat structure. Acta 

Theriologica 36: 247-254. 

Heatwole, Harold. 1962. Environmental factors influencing local distribution and activity 

of the salamander Plethodon cinereus. Ecology 43: 460-472. 

Hooge, Philip N.; Stanback, Mark T.; Koenig, Walter D. 1999. Nest-site selection in the 

acorn woodpecker. The Auk 116: 45-54. 

Hunter, Malcom L. Jr. 1993. Natural disturbance regimes as spatial models for managing 

boreal forests. Biological Conservation 65: 115-120. 

Hutto, Richard L. 1995. Composition of bird communities following stand-replacement 

fires in northern Rocky Mountain (U.S.A.) conifer forests. Conservation Biology 9: 

1041-1058. 

Immell, Dave; Boulay, Margaret C. 1994. Progress report—Black bear ecology research 

project. Oregon: Wildlife Research Project, Oregon Department of Fish and Wildlife; 

17 p. 

Ivlev, Viktor. 1961. Experimental ecology of the feeding of fishes. CT: Yale University 

Press. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

310 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Jones, Lawrence C.; Raphael, Martin G.; Forbes, J. T.; Clark, L. A. 1997. Using remotely 

activated cameras to monitor maternal dens of martens. In: Raphael, Martin G.; 

Jones, Lawrence, C.; Proulx, G.; Bryant, H. N.; Woodard, P. M., editors. Martes: 

taxonomy, ecology, techniques, and management. Edmonton, AB: Provincial Museum 

of Alberta; 329-349. 

Kalcounis, Matina C.; Hecker, Kerry R. 1996. Intraspecific variation in roost-site selection 

by little brown bats (Myotis lucifugus). In: Barclay, R. M. R.; Brigham, R. M., editors. 

Bats and forests symposium; 1995 October 19-21; Victoria, BC. Victoria, BC: British 

Columbia Ministry of Forests; 81-90. 

Kalcounis, Matina C.; Brigham, Mark R. 1998. Secondary use of aspen cavities by treeroosting big brown bats. Journal of Wildlife Management 62: 603-611. 

Kelleher, Kelvin E. 1963. A study of hole-nesting avifauna of southwest British Columbia. 

Vancouver, BC: University of British Columbia; 169 p. M.Sc. thesis. 

Khanna, K. R. 1964. Differential evolutionary activity in bryophytes. Evolution 18: 652-

670. 

Klenner, Walter; Huggard, David J. 1997. Three-toed woodpecker nesting and foraging at 

Sicamous Creek. In: Hollstedt, C.; Vyse, A., editors. Sicamous Creek silvicultural 

systems project: workshop proceedings; 1996 April 24-25; Kamloops, BC. Working 

Paper 24/1997.Victoria, BC: Research Branch, British Columbia Ministry of Forests; 

224-233. 

Klenner, Walter; Huggard, David J. 1998. Nesting and foraging habitat requirements of 

woodpeckers in relation to experimental harvesting treatments at Opax Mountain.

In: Hollstedt, C.; Vyse, A.; Huggard, D., editors. Managing the dry Douglas-fir forests 

of the southern interior: workshop proceedings; 1997 April 29-30; Kamloops, BC. 

Working paper 34/1998. Victoria, BC: Research Branch, British Columbia Ministry of 

Forests; 277-291. 

Kreisel, Karen J.; Stein, Steven J. 1999. Bird use of burned and unburned coniferous 

forests during winter. Wilson Bulletin 111: 243-250. 

Leake Jonathan R. 1994. The biology of myco-heterotrophic (‘saprophytic’) plants. New 

Phytologist 127: 171-216. 

Lindsay, Dave J. 1999. Black bear den catalogue. Crofton, BC: Timberwest Forest Ltd.; 

unnumbered. 

Lindzey, Frederick G.; Meslow, Charles. 1976. Characteristics of black bear dens on Long 

Island, Washington. Northwest Science 50: 236-242. 

Lofroth, Eric C. 1993. Scale dependent analyses of habitat selection by marten in the subboreal spruce biogeoclimatic zone, British Columbia. Burnaby, BC: Simon Fraser 

University; 109 p. M.Sc. thesis. 

Lofroth, Eric C. 1998. The dead wood cycle. In: Voller, J.; Harrison, S., editors. 

Conservation biology principles for forested landscapes. Vancouver, BC: University of 

British Columbia Press; 185-214. 

Madsen, Sarah J. 1985. Habitat use by cavity-nesting birds in the Okanogan National 

Forest, Washington. Seattle, WA: University of Washington; 113 p. M.Sc. thesis. 

Marshall, David B.; Chilcote, Mark W.; Weeks, Hal. 1996. Species at risk. Sensitive, 

threatened, and endangered vertebrates of Oregon. Portland, OR: Oregon 

Department of Fish and Wildlife; unpaged. 

Martin, Sandra K.; Barrett, Reginald H. 1991. Resting site selection by marten at Sagehen 

Creek, California. Northwestern Naturalist 72: 37-42. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 311 

Maser, Chris; Trappe, James M. 1984. The seen and unseen world of the fallen tree. Gen. 

Tech. Rep. PNW-GTR-164. Portland, OR: Pacific Northwest Research Station, Forest 

Service, U.S. Department of Agriculture; 56 p. 

Maser, Chris; Trappe, James M.; Ure, D. C. 1978. Implications of small mammal 

mycophagy to the management of western coniferous forests. Transactions North 

American Wildlife and Natural Resource Conference 43: 78-88. 

McComb, William C.; Noble, Robert E. 1981. Nest-box and natural-cavity use in three 

mid-south forest habitats. Journal of Wildlife Management 45: 93-101. 

McCullough, Herbert A. 1948. Plant succession on fallen logs in a virgin spruce-fir forest. 

Ecology 29: 508-513. 

McEllin, Shaun M. 1979. Nest sites and population demographics of white-breasted and 

pygmy nuthatches in Colorado. Condor 81: 348-352. 

Mellen, Teresa K. 1987. Home range and habitat use of pileated woodpeckers, western 

Oregon. Corvallis, OR: Oregon State University; 96 p. M.Sc. thesis. 

Miller, Alden H.; Bock, Carl E. 1972. Natural history of the Nuttall woodpecker at the 

Hastings Reservation. The Condor 74: 284-294. 

Milne, Kathleen A.; Hejl, Sallie J. 1989. Nest-site characteristics of white-headed 

woodpeckers. Journal of Wildlife Management 53: 50-55. 

Morris, Douglas W. 1984. Patterns and scale of habitat use in two temperate-zone small 

mammal faunas. Canadian Journal of Zoology 62: 1540-1547. 

Morrison, Michael L.; Raphael, Martin G. 1993. Modeling the dynamics of snags. 

Ecological Applications 3: 322-330. 

Morrison, Michael L.; Timossi, Irene C.; With, Kimberly A. 1987. Development and testing 

of linear regression models predicting bird-habitat relationships. Journal of Wildlife 

Management 51: 247-253. 

Mowrey, Robert A.; Zasada, John C. 1984. Den tree use and movements of northern flying 

squirrels in interior Alaska and implications for forest management. In: Meehan, 

W. R.; Merrel, T. R.; Hanley, T. A., editors. Fish and wildlife relationships in oldgrowth forests: proceedings of a symposium; 1982 April 12-15; Juneau, Alaska. 

Moorhead City, NC: American Institute of Fishery Research Biologists; 351-356. 

Murphy, Edward C.; Lehnhausen, W. L. 1998. Density and foraging ecology of 

woodpeckers following a stand-replacement fire. Journal of Wildlife Management 

62: 1359-1372. 

Newton, Ian. 1994. The role of nest sites in limiting the numbers of hole-nesting birds. 

Biological Conservation 70: 265-276. 

Noble, William O.; Meslow, Charles E.; Pope, Michael D. 1990. Denning habits of black 

bears in the central Coast Range of Oregon. Corvallis, OR: Department of Fisheries 

and Wildlife, Oregon State University; 28 p. 

Ormsbee, Patricia C.; McComb, William C. 1998. Selection of day roosts by female longeared myotis in the central Oregon Cascade Range. Journal of Wildlife Management 

62: 596-603. 

Peck, George K.; James, Ross D. 1987. Breeding birds of Ontario: nidiology and 

distribution. Volume 2: passerines. Toronto, ON: Royal Ontario Museum; 290 p. 

Rabe, Michael J.; Morrell, Thomas E.; Green, Heather; deVos, Jr., James C.; Miller, Richard 

C. 1998. Characteristics of ponderosa pine snag roosts used by reproductive bats in 

northern Arizona. Journal of Wildlife Management 62: 612-621. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

312 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Raphael, Martin G.; Jones, Lawrence L. C. 1997. Characteristics of resting and denning 

sites of American martens in central Oregon and western Washington. In: Proulx, 

G.; Bryant, H. N.; Woodward, P. M., editors. Martes: taxonomy, ecology, techniques 

and management. Edmonton, AB: Provincial Museum of Alberta; 146-165. 

Raphael, Martin G.; White, Marshall 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada. Wildlife Monographs 86: 1-66. 

Rasheed, Sadig A.; Holroyd, Susan L. 1995. Roosting habitat assessment and inventory of 

bats in the Mica Wildlife Compensation Area. Columbia Basin Fish and Wildlife 

Compensation Program. Nelson, BC: BC Hydro and British Columbia Ministry of 

Environment, Lands, and Parks; 77 p. 

Rhoades, Fred. 1986. Small mammal mycophagy near woody debris accumulations in the 

Stehekin River Valley, Washington. Northwest Science 60: 150-153. 

Rodrick, Elizabeth; Milneer, Ruth, technical editors. 1991. Management recommendations 

for Washington's priority habitats and species. Olympia, WA: Washington 

Department of Wildlife; unpaged. 

Ruggiero Leonard F.; Pearson, Dean E.; Henry, Stephen E. 1998. Characteristics of 

American marten den sites in Wyoming. Journal of Wildlife Management 62: 663-

673. 

Samuelsson, Johan; Gustaffson, Lena; Ingelog, Torlelf. 1994. Dying and dead trees: a 

review of their importance for biodiversity. Uppsala, Sweden: Swedish Threatened 

Species Unit, 110 p. 

Schreiber, Barry; deCalesta, David S. 1992. The relationship between cavity-nesting birds 

and snags on clearcuts in western Oregon. Forest Ecology and Management 50: 299-

316. 

Scott, Virgil E.; Whelan, Jill A.; Svoboda, Paul L. 1980. Cavity-nesting birds and forest 

management. In: DeGraaf, R.M., technical coordinator. Management of western forests 

and grasslands for nongame birds workshop proceedings; 1980 February 11-14; Salt 

Lake City, UT. Gen. Tech. Rep. INT-86. Fort Collins, CO: Intermountain Research 

Station, Forest Service, U.S. Department of Agriculture; 311-324. 

Söderström, Lars. 1987. Dispersal as a limiting factor for distribution among epixylic 

bryophytes. In: Pócs, T.; Simon, T.; Tuba, Z.; Podani, J., editors. Proceedings of the 

IAB Conference of Bryoecology; 1985 August 5-10; Akadémiai Kiadó, Budapest, 

Hungary. Symposia Biologica Hungarica 35: 475-484. 

Söderström, Lars. 1988. The occurrence of epixylic bryophye and lichen species in an old 

natural and a managed forest stand in northeast Sweden. Biological Conservation 

45: 169-178. 

Spencer, Wayne D. 1987. Seasonal rest-site preferences of pine martens in the northern 

Sierra Nevada. Journal of Wildlife Management 51: 616-621. 

Spies, Thomas A.; Franklin, Jerry F.; Thomas, Ted B. 1988. Coarse woody debris in 

Douglas-fir forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Thomas, Jack W.; Maser, Chris; Rodiek, Elizabeth J. 1979. Edges. In: Thomas, J. W., 

technical editor. Wildlife habitats in managed forests: the Blue Mountains of Oregon and 

Washington. Agric. Handb. 533. Portland, OR: Wildlife Management Institute, Forest 

Service, U.S. Department of Agriculture; 48-59. 

USDA Forest Service. 1996. Ecological characteristics of fishers in southwestern Oregon.

Progress Report, June 1996. Olympia, WA: Pacific Northwest Research Station, U.S. 

Forest Service, Department of Agriculture; 84-90. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 313 

Vega, Robyn M. S. 1993. Bird communities in managed conifer stands in the Oregon 

Cascades: habitat associations and nest predation. Corvallis, OR: Oregon State 

University; 78 p. M.Sc. thesis. 

Vitt, Dale H., Janet E. Marsh, and Robin B. Bovey. 1988. Mosses, lichens, and ferns of 

northwest North America. Vancouver: Lone Pine Publishing; 296 p. 

Vonhof, Maarteen J. 1996. A survey of the abundance, diversity, and roost-site 

preferences of bats in the Pend d’Oreille valley, British Columbia. The Columbia 

Basin Fish and Wildlife Compensation Program. Nelson, BC: BC Hydro and British 

Columbia Ministry of Environment; 69 p. 

Vonhof, Maarteen J.; Barclay, Robert M.R. 1997. Use of tree stumps as roosts by the 

western long-eared bat. Journal of Wildlife Management 61: 674-684. 

Walankiewicz, Wieslaw. 1991. Do secondary cavity-nesting birds suffer more from 

competition for cavities or from predation in a primeval deciduous forest. Natural 

Areas Journal 11: 203-212. 

Waterhouse, Louise F. 1998. Habitat of winter wrens in riparian and upland areas of 

coastal forests. Burnaby, BC: Simon Fraser University; 130 p. M.Sc. thesis. 

Waterhouse, Michaela J.; Dawson, Rick. 1999. Bird communities in Interior Douglas-fir 

forests. In: Hollstedt, C.; Vyse, A.; Huggard, D., editors. Managing the dry Douglas-fir 

forests of the southern interior: workshop proceedings; 1997 April 29-30; Kamloops, 

BC. Working paper 34/1998. Victoria, BC: Research Branch, British Columbia Ministry 

of Forests; 90-112. 

Welsh, Christopher J. E.; Capen, David E. 1992. Availability of nesting sites as a limit to 

woodpecker populations. Forest Ecology and Management 48: 31-41. 

Whitaker, John O., Jr.; Maser, Chris; Storm, Robert M.; Beatty, Joseph J. 1986. Food habits 

of clouded salamanders (Aneides ferreus) in Curry County, Oregon (Amphibia: 

Caudata: Plethodontidae). Great Basin Naturalist 46: 228-240. 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

314 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Appendix A—Native cavity and downed wood using vertebrates breeding in forests in the 

Pacific Northwest and their state or provincial status. 

 State or Province1

Common 

name 

Scientific name Cavity2 DW3 BC AB WA OR CA 

Amphibians 

Pacific giant 

salamander 

Dicamptodon 

tenebrosus 

 X R 

Arboreal 

salamander 

Aneides lugubris X 

Black 

salamander 

Aneides 

flavipunctatus 

 X S 

Clouded 

salamander 

Aneides ferreus X S 

Coeur 

D’Alene 

salamander 

Plethodon 

idahoensis 

 X R 

Ensatina 

salamander 

Ensatina 

eschscholtzii 

 X 

Western 

redback 

salamande 

Plethodon 

vehiculum 

 X 

Reptiles 

Western skink Eumeces 

skiltonianus 

 X 

Western fence 

lizard 

Sceloporus 

occidentalis 

 X 

Ruber boa Charina bottae X B S 

CA mountain 

kingsnake 

Lampropeltis 

zonata 

 X 

Racer Coluber mormon X 

Ringneck 

snake 

Diadophis 

punctatus 

 X 

Sharptail 

snake 

Contia tenuis X R S 

 

Birds 

Order 

Anseriformes 

Barrow’s 

goldeneye 

Bucephala 

islandica 

S S 

Bufflehead Bucephala albeola S S 

Common 

goldeneye 

Bucephala clangula S 

Common 

merganser 

Mergus merganser S 

Hooded 

merganser 

Lophodytes 

cucullatus 

S 

Red-breasted 

merganser 

Mergus serrator S 

Wood duck Aix sponsa S 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 315 

(appendix A continued) 

 State or Province1

Common 

name 

Scientific name Cavity2 DW3 BC AB WA OR CA 

Order 

Falconiformes 

 

American 

kestrel 

Falco sparverius S 

Barred owl Strix varia S S 

Boreal owl Aegolius funereus S S S 

Flammulated 

owl 

Otus flammeolus S B S 

Northern hawk 

owl 

Surnia ulula S 

Northern 

pygmy-owl 

Glaucidium gnoma S B S 

Northern sawwhet owl Aegolius acadicus S B 

Spotted owl Strix occidentalis S R T T T 

Western 

screech-owl 

Otus kennicottii S R/B 

 

Order 

Apodiformes 

 

Vaux’s swift Chaetura vauxi S 

 

Order 

Piciformes 

Acorn 

woodpecker 

Melanerpes 

formicivorus 

P 

Black-backed 

woodpecker 

Picoides arcticus P S S 

Downy 

woodpecker 

Picoides pubescens wP 

Hairy 

woodpecker 

Picoides villosus P B 

Lewis’s 

woodpecker 

Melanerpes lewis wP B S 

Northern 

flicker 

Colaptes auratus wP 

Nuttall’s 

woodpecker 

Picoides nuttallii wP 

Pileated 

woodpecker 

Dryocopus pileatus P S S 

Red-breasted 

sapsucker 

Sphyrapicus rubber P 

Red-naped 

sapsucker 

Sphyrapicus 

nuchalis 

P 

Three-toed 

woodpecker 

Picoides tridactylus P S 

White-headed 

woodpecker 

Picoides 

albolarvatus 

wP R S 

Williamson’s 

sapsucker 

Sphyrapicus 

thyroideu 

P R\B 

Yellow-bellied 

sapsucker 

Sphyrapicus varius P 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

316 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(appendix A continued) 

 State or Province1

Common 

name 

Scientific name Cavity2 DW3 BC AB WA OR CA 

Ash-throated 

flycatcher 

Myiarchus 

tyrannulus 

S 

Purple martin Progne subis S R S 

Tree swallow Tachycineta bicolor S 

Violet-green 

swallow 

Tachycineta 

thalassina 

S 

Boreal 

chickadee 

Poecile hudsonicus wP 

Chestnutbacked 

chickadee 

Poecile rufescens wP 

Mountain 

chickadee 

Poecile gambeli wP 

Plain titmouse Parus inornatus wP 

Siberian tit Parus cinctus wP 

Pygmy 

nuthatch 

Sitta pygmaea wP S 

Red-breasted 

nuthatch 

Sitta canadensis wP 

White-breasted 

nuthatch 

Sitta carolinensis wP 

Brown creeper Certhia americana C S 

Bewick’s wren Thryomanes 

bewickii 

S 

House wren Troglodytes aedon S 

Winter wren Troglodytes 

troglodytes 

S X 

Mountain 

bluebird 

Sialia currucoides S 

Western 

bluebird 

Sialia mexicana S S 

 

Mammals 

Order 

Insectivora 

Common 

shrew 

Sorex cinereus X 

Dusky shrew Sorex monticolus X 

Pacific shrew Sorex pacificus X R 

Pygmy shrew Sorex hoyi X 

Trowbridge’s 

shrew 

Sorex trowbridgii X B 

 

Order 

Chiroptera 

Big brown bat Eptesicus fuscus S 

California 

myotis 

Myotis californicus S 

Fringed myotis Myotis thysanodes S B 

Hoary bat Lasiurus cinereus S 

Keen’s longeared myotis Myotis keenii S R 

Little brown 

myotis 

Myotis lucifugus S 

Long-legged 

myotis 

Myotis volans S S 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 317 

(appendix A continued) 

 State or Province1

Common 

name 

Scientific name Cavity2 DW3 BC AB WA OR CA 

Northern longeared myotis Myotis 

septentrionalis 

C B B S 

Silver-haired 

bat 

Lasionycteris 

noctivagans 

S S 

Southern red 

bat 

Lasiurus blossevilli S 

Yuma myotis Myotis yumanensis S 

Order 

Rodentia 

 

Creeping vole Microtus oregoni X 

Heather vole Phenacomys 

intermedius 

 X 

Northern redbacked vole Clethrionomys 

rutilus 

 X 

Southern redbacked vole Clethrionomys 

gapperi 

 X R/B 

Western redbacked vole Clethrionomys 

occidentalis 

 X 

White-footed 

vole 

Phenacomys 

albipes 

 X S 

Columbian 

mouse 

Peromyscus oreas X 

Deer mouse Peromyscus 

maniculatus 

 X 

Pinon mouse Peromyscus truei X 

Sitka mouse Peromyscus 

sitkensis 

 X 

Douglas’ 

squirrel 

Tamiasciurus 

douglasii 

S 

Least 

chipmunk 

Tamias minimus X R 

Long-eared 

chipmunk 

Tamias 

quadrimaculatus 

 X 

Northern 

flying squirrel 

Glaucomys 

sabrinus 

S 

Red squirrel Tamiasciurus 

hudsonicus 

S 

Sonoma 

chipmunk 

Tamias sonomae X 

Townsend’s 

chipmunk 

Tamias townsendii X 

Western gray 

squirrel 

Sciurus griseus S S 

Yellow-pine 

chipmunk 

Tamias amoenus X 

Order 

Carnivora 

 

Red fox Vulpes vulpes X 

Bobcat Lynx rufus X S 

Lynx Lynx Canadensis X S 

Ermine Mustela erminea X R/B 

Fisher Martes pennanti S X B S S 

Least weasel Mustela nivalis X 
How Dead Trees Sustain Live Organisms—Bunnell, Houde, Johnston, and Wind 

318 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(appendix A continued) 

 State or Province1

Common 

name 

Scientific name Cavity2 DW3 BC AB WA OR CA 

Long-tailed 

weasel 

Mustela frenata R S 

American 

marten 

Martes Americana S X S 

Mink Mustela vison X 

Black bear Ursus americanus S X R 

Raccoon Procyon lotor S X 1 R = red listed; B = blue listed; S = sensitive species; E = endangered species; T = threatened species; 

Sources include: Alaska Department of Fish and Game internet site as of July 1997 

(www.state.ak.us/adfg/); British Columbia Ministry of Environment, Lands and Parks (1992, 1996); 

Alberta Environmental Protection Status of Wildlife internet site as of December 1996 

(www.gov.ab.ca/env/fw/); Rodrick and Milner (1991) for Washington; Marshall and others (1996) for 

Oregon; and the U.S. Fish and Wildlife Service Division of Endangered Species internet site as of April 

1999 for California. Other jurisdictions of the Pacific Northwest listed no species dependent upon cavity 

sites or downed wood. 

2

 P = Primary Cavity Nester, wP = Weak Primary, S = Secondary Cavity Nester (obligate), C = Cave or 

Crevice; (may use cavities, especially during winter). 

3

 Uses downed wood for breeding and/or feeding; X = Strongly Associated. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 319 

Summer and Fall Use of Logging Residue 

Piles by Female Short-tailed Weasels1 

Kimberly A. Lisgo,2 Fred L. Bunnell,2 and Alton S. Harestad3

Abstract 

Female short-tailed weasels (Mustela erminea) used piles of logging residue more than 

expected and used areas without logging residue less than expected when they were in 3-yearold regenerating aspen (Populus tremuloides) cutblocks during summer and fall (P < 0.001). 

Female weasels may prefer piles of logging residue because they offer greater amounts of 

food, larger numbers of rest sites, and greater availability of travel corridors. Our data indicate 

that food abundance, specifically the southern red-backed vole (Clethrionomys gapperi), best 

explains the preferential use of logging residue piles by female weasels. Recommendations 

for the management of logging residue piles are discussed. 

Introduction 

Downed wood provides structure in habitats of mustelids and small rodents, 

including secure travel corridors and, in winter, subnivian access and thermal cover. 

The importance of downed wood for mustelids, particularly marten (Martes 

americana) and fisher (M. pennanti), is well documented (Buskirk and Powell 1994, 

Buskirk and Ruggiero 1994, Corn and Raphael 1992) and is expressed in habitat 

quality as both amount of cover and available prey. For small rodents, downed wood 

can function as travel routes (Carter 1993, Maser and others 1979, Maser and Trappe 

1984), provide fungal fruiting bodies for food (Maser and Trappe 1984, Rhoades 

1986), and supply nest sites (Weaver 1996). Combined, these factors may encourage 

positive association of red-backed voles (Clethrionomys spp.) with downed wood 

(Nordyke and Buskirk 1991, Thompson 1996) through increased survivorship and 

reproduction. The relationship of weasels to downed wood is less clear. There are 

only a few anecdotal accounts that describe use of downed wood by short-tailed 

weasels (Mustela erminea). In areas that have been clearcut, logging provides 

substantial amounts of residual downed wood that can be dispersed or left in piles. 

Gyug (1994) reported that short-tailed weasels used cutblocks with logging residue 

piles more than those with none. Because of the shape and size of weasels, it is likely 

that the benefits of logging residue piles accrued to small rodents may apply to the 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Technician and Professor, respectively, Center for Applied Conservation Research, 

Department of Forest Sciences, University of British Columbia, 3004-2424 Main Mall, Vancouver, 

B.C., Canada, V6T 1Z4 (e-mail: kim_lisgo@hotmail.com) 

3

 Associate Professor, Department of Biological Sciences, Simon Fraser University, 8888 University 

Drive, Burnaby, B.C., Canada, V5A 1S6 (e-mail: harestad@sfu.ca) 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

320 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

short-tailed weasel (e.g., travel routes). As well, higher abundance of small rodents 

could attract weasels to downed wood as foraging sites. 

Our objectives were to determine if female weasels, when they were in 

cutblocks, preferred logging residue piles to areas without logging residue piles; 

examine factors that could account for such behavior; and propose enhancement of 

short-tailed weasel habitat through management of logging residue piles. 

Study Area 

Our study area (54°58'N, 111°55'W), in the southern portion of the mixedwood 

boreal forest, is located at Owl River, approximately 300 kilometers northeast of 

Edmonton, Alberta. The mixedwood boreal forest is circumpolar. In Canada, it 

extends from northeastern British Columbia, through Alberta and Saskatchewan, to 

southeastern Manitoba. The province of Alberta contains approximately 40 percent or 

290,000 square kilometers of Canada’s mixedwood boreal forest (Rowe 1972). 

The mixedwood boreal region is characterized by a complex mosaic of stands 

varying in age, species composition, and structure, interspersed with rivers, lakes, 

bogs, and fens. The dominant coniferous tree species are white spruce (Picea glauca)

and black spruce (P. mariana), with balsam fir (Abies balsamea), jack pine (Pinus 

banksiana) and larch (Larix laricina) also present (Rowe 1972). Dominant deciduous 

species are trembling aspen (Populus tremuloides) and balsam poplar (Populus 

balsamifera), with lesser amounts of white birch (Betula papyrifera) (Rowe 1972). 

Although relatively pure stands of all these tree species exist, the most common later 

seral stages are a mix of species, most often trembling aspen, balsam poplar, and 

white spruce. The dominant natural disturbance regime in the mixedwood boreal 

forest is fire (Johnson 1992, Rowe 1961). Other disturbances include cutting of 

seismic lines for oil and gas exploration, white spruce saw-timber operations, 

harvesting of timber for pulp production, windstorms, and pathogens. These 

disturbances vary in size and contribute to the complex mosaic of stands that 

characterize the landscape. 

Our study area is located within the Forest Management Area of Alberta Pacific 

Forest Industries Inc. (AlPac) and is located within two townships (Township 69 

Range 13 W4M and Township 70 Range 13 W4M), each approximately 10 

kilometers by 10 kilometers. The townships are dominated by jack pine stands (1930 

origin), black spruce-larch mixed stands (1880 origin), and mature mixed and pure 

stands of trembling aspen and balsam poplar (1930-1950 origin). Large wet shrubby 

areas of dwarf birch (Betula pumila var. glandulifera), alder (Alnus spp.), and willow 

(Salix spp.) also are present. Pure stands of white spruce and mixed deciduousconiferous stands are relatively uncommon. There are several small lakes in the area. 

Some agricultural land occurs adjacent to the southern edge of the study area. 

Portions of both townships were harvested by clearcutting and partial cutting for 

aspen and poplar in winter 1993/94. Based on Alberta Vegetation Inventory mapping 

(Alberta Forestry, Lands and Wildlife 1991), cutblocks range in size from 1 to 62 

hectares and account for approximately 6.5 percent of the area. During our study, 

July to December 1996, cutblocks were densely vegetated with naturally regenerating 

aspen and poplar saplings, wild rose (Rosa spp.), herbs, and grasses. 

The mean daily temperature for this region is 3.9 to 10.9 degrees Celsius in 

summer (May-September) and -1.1 to -22.4 degrees Celsius in winter (October-
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 321 

April). The annual mean precipitation is 432.3 millimeters including 131.5 

centimeters of snow. Major snowfall months are November to April with a mean 

monthly snowfall of 11.9 to 25.0 centimeters during this period (Environment 

Canada 1998). 

Methods 

Radio-tagging and Telemetry 

During February-December 1996, we live-trapped weasels in wooden box traps 

modified from King (1973) and insulated with cotton. The traps were baited with 

bacon or carcasses of white laboratory mice and placed systematically in cutblocks, 

but near downed wood or other cover. We used data from four female weasels in this 

analysis (females 1 to 4). All four females were adults (> 1 year of age) and were 

known to inhabit cutblocks prior to collaring. Each female was fitted with a Holohil

MD2C4

 transmitter weighing 2-3 grams, < 4 percent of an adult female’s body 

weight. As recommended by King (1989), we held weasels in-hand when attaching 

collars rather than anaesthetizing them. We monitored the four females between July 

and December 1996 and located them by radio-triangulation (White and Garrott 

1990) from fixed telemetry stations. We recorded at least three bearings from 

separate stations for each location. After we determined a general location, we 

approached the site to confirm activity (i.e., resting versus foraging), specific 

location, and habitat type. We flagged the site and returned later to locate it using a 

hand-held global positioning system (GPS). The GPS data were corrected to ± 1 

meter. Because of equipment problems, telemetry sampling was sometimes erratic. In 

general, females were located every 1 to 2 days. Female weasels often damaged their 

transmitters, and 1-week periods without locations were not uncommon. We 

attempted to obtain the locations over the 24-hour day, but despite our efforts and 

because of safety issues working at night, daytime locations dominate our data. 

We used variations in signal strength to deduce activity of radio-collared 

weasels. Hunting or traveling activity was indicated by changes in the volume of the 

radio signal. When inactive, the signal volume remained constant. We identified an 

inactive location using zone of receiver (i.e., when the signal could be heard on the 

receiver without an external antenna). We moved to the edge of the signal range 

where reception was most sensitive to changes in the weasel’s location. We listened 

to the signal for 15 minutes. If a change in signal strength was not observed, we 

deemed the weasel inactive. 

Logging Residue Piles 

We defined logging residue piles (LRPs) as the tops and branches of felled trees, 

dispersed along the main road, and spurs passing through cutblocks. We determined 

the areas of LRPs in four cutblocks used by females 1 to 4. The cutblocks were all 

harvested for trembling aspen (Populus tremuloides) during winter, 1993-94, using 

dispersed retention with 1-2 percent of the trees left uncut and the logging residue 

distributed along access roads in the cutblocks. Approximately 35-68 meters of main 

road and spurs occurred per hectare of cutblock. 

 

4

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

322 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

In May 1997, we walked the perimeter of each LRP taking Universal Transverse 

Mercator (UTM) coordinates via hand-held GPS every 5 seconds or approximately 

every 2-5 meters. The GPS point data were corrected to ± 1 meter. We converted the 

point data into vector polygons using Arc/Info Version 7.1 (ESRI 1997) and imported 

the vector polygons into ArcView version 3.1 (ESRI 1996). We calculated the area of 

LRPs and cutblock habitat available for use within each female’s home range using a 

raster overlay of home range, LRP polygons, and digitized Alberta Vegetation 

Inventory maps with a 0.1- x 0.1-meter raster resolution. We defined home range as 

“the area traversed by an individual during its normal activities of food gathering and 

resting within the period when sampling occurred” (Lisgo 1999). We calculated 

home ranges using a fixed kernel estimator based on a 95 percent utilization 

distribution (Lisgo 1999). 

Use of Logging Residue Piles by Weasels 

We tested selective use of LRPs in cutblocks using the log-likelihood ratio (Zar 

1984). Availability of cutblocks and LRPs for each weasel was based on their 

respective area within a female’s home range. We used both active (i.e., hunting or 

traveling) and inactive (i.e., resting or consuming prey) observations in the analyses. 

Small Rodent Abundance Estimates 

We live-trapped small rodents in two cutblocks, Sites 1 and 2, that 3 female 

weasels (females 2 to 4) were known to use. We placed four Multi-capture Tin Cat®

live traps 25 meters apart in a diamond configuration with an additional trap placed 

in the centre (five traps in total). We placed six trap arrays in each cutblock: three 

trap arrays in areas of LRPs and three trap arrays in areas of no-LRPs. We trapped 

each cutblock for three nights from October 4 to 6, 1996. We identified each small 

rodent to species and then sexed, weighed, marked it with picric acid, and released it. 

Although the rodents were not uniquely marked, we later recorded the number of 

marked (previously captured) and unmarked animals during trapping sessions. We 

estimated abundance for four areas: 1) Site 1 areas of LRPs; 2) Site 1 areas of noLRPs; 3) Site 2 areas of LRPs; and 4) Site 2 areas of no-LRPs. In each case, data 

from the three tray arrays were pooled. 

We used the Schumacher and Eschmeyer method, a version of the Schnabel 

method, to estimate the abundance of small rodents with 95 percent confidence limits 

(Krebs 1989). This method estimates the abundance for a closed population (i.e., 

population size is constant without recruitment or loss). It is appropriate for this study 

because the trapping occurred over a short period. The Schumacher and Eschmeyer 

method distinguished two types of individuals: 1) marked individuals caught 

previously at least once; and 2) unmarked individuals not caught previously. We 

calculated 95 percent confidence limits for each population estimate using a Poisson 

distribution as recommended for cases in which total number of recaptures is less 

than 50 (Krebs 1989). 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 323 

Results 

Area of Logging Residue Piles and Their Use by Weasels 

On average, 57 percent (112/198) of the females’ locations were in cutblocks 

and 43 percent (86/198) in uncut forest and shrubby habitats. Within cutblocks, the 

area of LRPs in female home ranges varied from 2.03 to 3.93 hectares (table 1).

When in cutblocks, all four females preferred areas of LRPs to areas without LRPs (P 

< 0.001, table 2). Collectively, observations of inactive females in areas with LRPs 

and without LRPs account for only a small proportion of the data, 11 percent and 18 

percent, respectively (table 2). 

Table 1―Cutblock area found within the home range of each female weasel and area within 

the cutblock designated as areas with logging residue piles (LRPs) or without logging residue 

piles (no-LRPs) based on GIS analyses. 

Weasel Home range 

size 

(hectare) 

Cutblock 

area 

(hectare) 

Area of noLRPs (hectare) Area of LRPs 

(hectare) 

Percentage LRPs 

in cutblock area 

Female 1 82.6 24.43 22.40 2.03 8.3 

Female 2 94.8 34.70 32.59 2.11 6.1 

Female 3 65.5 32.09 28.16 3.93 12.2 

Female 4 76.8 23.53 21.21 2.41 10.2 

Table 2―Selective use of logging residue piles within cutblocks by female short-tailed 

weasels in the mixedwood boreal forest of central Alberta, based on the log-likelihood ratio. 

Values in parentheses are the number of inactive observations in areas with logging residual 

piles (LRPs) and without logging residue piles (no-LRPs). 

Weasel Observed 

locations in 

LRPs 

Observed 

locations in 

no-LRPs 

Expected 

locations in 

LRPs 

Expected 

locations in 

no-LRPs 

Loglikelihood 

ratio P 

Female 1 

Female 2 

Female 3 

Female 4 

11 (4) 

14 (0) 

21 (2) 

7 (0) 

7 (0) 

18 (5) 

34 (7) 

6 (0) 

1.5 

2.0 

6.7 

1.3 

16.5 

30.0 

48.3 

11.7 

31.82 

36.09 

24.10 

15.55 

< 0.001 

< 0.001 

< 0.001 

< 0.001 

Abundance of Small Rodents 

We caught three species of small rodents: southern red-backed voles (C. 

gapperi), meadow voles (Microtus pennsylvanicus), and deer mice (Peromyscus 

maniculatus) (table 3). We captured relatively few meadow voles with most 

individuals appearing in traps on the last trap night. Estimates of abundance for redbacked voles showed a trend for greater numbers in areas of LRPs, while estimates of 

abundance for deer mice did not differ between areas of LRPs and no-LRPs (fig. 1). 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

324 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 3―Species and the number of captured and recaptured small rodents in areas with 

logging residue piles (LRPs) and without logging residue piles (no-LRPs) for Sites 1 and 2 

from October 4-6, 1996 in the mixedwood boreal forest of central Alberta. 

Treatment Species 

Site 1 

No. captured No. recaptured 

Site 2 

No. captured No. recaptured 

no-LRPs red-backed vole 33 11 13 3 

 deer mouse 33 16 38 14 

 meadow vole 2 0 0 0 

 

LRPs red-backed vole 42 7 29 8 

 deer mouse 35 14 31 11 

 meadow vole 5 0 2 0 

Figure 1―Abundance estimates of southern red-backed voles and deer mice with 95 

percent confidence limits based on the Schumacher and Eschmeyer method (Krebs 

1989), October 4-6 1996, in areas of no logging residue piles (no-LRP) and logging 

residue piles (LRP), in regenerating aspen cutblocks (harvested winter 1993/94), in 

the mixedwood boreal forest of central Alberta. 

























































0 

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

s p ec ies o f s ma ll ro d en ts

e s tima te o f a b un d an c



n o -LRPs

LRPs

 site 1 site 2 site 1 site 2 

 red-backed vole deer mouse

 species of small rodents 

estimate of abundance 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 325 

Discussion 

There are two features to our study that could potentially bias our results. First, 

the high proportion of daylight locations in our data set may bias our estimates of 

habitat use. However, in summer, North American and European weasels are 

predominantly diurnal in activity (Debrot and others 1985, Erlinge 1979, Samson and 

Raymond 1995). Second, it is also possible that radio-tagging compromised the 

behavior of collared weasels and that these weasels do not accurately represent the 

population. White and Garrott (1990) stress the importance of testing the effect of 

radio-tagging on study animals. Lisgo (1999) found that collared weasels did not 

suffer nutritionally; however, we do not know if the normal hunting behavior of 

weasels was affected by the presence of a radio-collar. For example, the increased 

diameter of a weasel’s neck caused by a radio-collar may have limited the size of 

mouse and vole tunnels that could be explored. 

In the mixedwood boreal forest of Alberta, four female weasels preferentially 

used areas with LRPs in cutblocks during summer and fall. They spent three to seven 

times more time in LRPs than expected. Although our sample size was small, all 

females showed similar behavior. Also, our results are consistent with the behavior of 

weasels in southern British Columbia during winter (Gyug 1994). We think that 

female weasels may selectively use areas with LRPs for three reasons: the amount of 

food; availability of rest sites; and availability of travel corridors with security cover. 

Our findings suggest that abundance of food, specifically red-backed voles, best 

explains the preferential use of LRPs by female weasels. 

We think that food resources promoted use of LRPs because LRPs had a higher 

abundance of prey. Abundance of prey, at least for Site 1 and particularly red-backed 

voles, tended to be higher in LRPs than in areas without LRPs. Deer mice were 

distributed evenly throughout both cutblocks. Lisgo (1999) found red-backed voles 

were an important component of the weasel’s diet, significantly preferred over deer 

mice (P < 0.05). Higher abundance of prey, especially red-backed voles, in LRPs 

would reduce hunting effort for weasels and make these areas attractive as foraging 

sites. 

Other studies also have found positive associations between red-backed voles 

and downed wood (Nordyke and Buskirk 1991, Thompson 1996). In the mixedwood 

boreal forest, Roy and others (1995) found both red-backed voles and deer mice 

positively associated with downed woody material. Roy and others (1995) also 

concluded that deer mouse populations are flexible in their habitat requirements 

while red-backed vole populations are less so and “select areas of dense shrubs with 

abundant downed woody material.” The flexible habitat requirements of deer mice 

explain their even distribution throughout the cutblocks. The red-backed voles 

positive association with downed wood explains their trend for greater abundance in 

LRPs. 

In our study area, Weaver (1996) found that red-backed voles and deer mice 

nested beneath LRPs, rotting downed wood, and the base of stumps and snags in 

cutblocks. Female weasels also rested in LRPs; thus, rest site availability may also 

encourage the use of LRPs by female weasels. Weasels rely on natural cavities or the 

nests of other species for rest sites (King 1989). Hence, we expect more resting 

activity by female weasels in LRPs due to a greater availability of nests, which may 

be associated with the higher abundance of small rodents. It does not appear, 

however, that LRPs are necessary for female weasels to find suitable rest sites in 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

326 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

cutblocks because female weasels also rested at the bases of stumps and snags in 

portions of cutblocks without LRPs (Lisgo 1999). 

The response of weasels to LRPs may be an anti-predator behavior by which 

they choose travel routes with the least risk of predation (Harestad 1991). Although 

LRPs may function as secure travel corridors for female weasels, we think it unlikely 

that this would be the sole attractant for females because dense vegetation throughout 

the cutblocks provided alternative sources of security and thermal cover. However, 

LRPs may facilitate movements of weasels by providing travel routes less hindered 

by dense vegetation while providing security cover. 

Despite our small sample size, this information on habitat use is valuable to 

forest managers. There are few data on the ecology of the short-tailed weasel in 

North America or the effects of silvicultural practices on the behavior of weasels. 

However, caution must be used when applying our findings to weasels outside our 

study area, and in particular, to male weasels. The behavioral response of male 

weasels to the presence of logging residue piles is not known and, based on work in 

our study area, males use the landscape differently than females (Lisgo 1999). 

Caution is also necessary when interpreting the responses of small rodents to 

LRPs. First, the level of replication was small and our findings for small rodents may 

be restricted to the cutblocks that we sampled. Second, the sampling period was short 

and may not be representative of the full 6 months during which female weasels were 

observed. 

Management Recommendations 

Female weasels preferred areas with LRPs that were used for resting, hunting, 

and possibly travel routes. Small rodent abundance, in particular red-backed voles, 

suggests that prey abundance may be a factor promoting the use of LRPs by females. 

At the time of our study (3 years post-harvest), LRPs were not essential for providing 

suitable rest sites because female weasels also rested in portions of cutblocks without 

LRPs. Based on our findings, LRPs tend to support a higher abundance of red-backed 

voles and appear to be a beneficial attribute of 3-year-old regenerating aspen 

cutblocks in our study area. 

Because female short-tailed weasels prefer logging residue piles, timberharvesting practices could be altered to provide residual downed wood. Besides 

amount, distribution of logging residue piles may be important to supplying suitable 

habitat for both small rodents and weasels. Logging residue can be dispersed, piled, 

or removed from a site depending on silvicultural prescriptions and harvesting 

methods. We recommend that LRPs be retained and distributed linearly along main 

roads and spurs to ensure they occur in home ranges of several female weasels. Many 

other wildlife species inhabit cutblocks and the habitat quality for some likely would 

be diminished if this recommendation was applied throughout the landscape. To 

sustain all wildlife species, the same practices should not be used everywhere 

(Bunnell and others 2002). A diverse approach, managing for multiple species, is 

more appropriate for sustaining wildlife in the mixedwood boreal forest. Moreover, 

the data provided are based on a 6-month study, and weasel home ranges fluctuate 

with prey abundance (Erlinge 1977). Declines or increases in abundance of prey may 

result in expansion or contraction of home range size and could change use of 

habitats by weasels. Also, over time, the reduction of LRPs through decay may lower 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 327 

the suitability of cutblocks as habitat for weasels. Lastly, because of the mixedwood 

boreal forest’s diverse landscape, the habitats studied are not representative of the 

entire mixedwood boreal forest. Recommendations suitable for the forest types in our 

study area may be inappropriate for other locations, such as those dominated by older 

mixedwood stands. 

Acknowledgments 

Funding and logistical support for this project were provided by Alberta Pacific 

Forest Industries Inc., Natural Sciences and Engineering Research Council of 

Canada, Challenge Grant in Biodiversity Program (Department of Biological 

Sciences, University of Alberta, and the Alberta Conservation Association), the 

Sustainable Forest Management Network, and the Alberta Sport, Recreation, Parks, 

and Wildlife Foundation. We thank Dr. Rich Moses and Robin Weaver from the 

University of Alberta and Dr. Gitte Grover from Alberta Pacific Forest Industries for 

their support while in the field. A special thanks to all field assistants for their hard 

work: Josephine Osborne, Mandy Kellner, Robin Weaver, Kelly Scott, Lindsay 

Tomyn, Gloria Lisgo, and Zak Calloway. The manuscript benefited from reviews by 

Rich Moses and Doug Steventon. This is publication R-38 of the Centre for Applied 

Conservation Biology, University of British Columbia. 

References 

Alberta Forestry, Lands and Wildlife. 1991. Alberta vegetation inventory standards 

manual. Edmonton, AB: Resource Information Branch, Alberta Forestry, Lands and 

Wildlife; 53 p. 

Bunnell, Fred L.; Houde, Isabelle; Johnston, Barb; Wind, Elke. 2002. How dead trees 

sustain live organisms in western forests. In: Laudenslayer, William F., Jr.; Shea, 

Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Buskirk, Steven W.; Powell, Roger A. 1994. Habitat ecology of fishers and American 

martens. In: Buskirk, Steven W.; Harestad, Alton S.; Raphael, Martin G.; Powell, Roger 

A., compilers and editors. Martens, sables, and fishers: biology and conservation. Ithaca, 

New York: Cornell University Press; 283-296. 

Buskirk, Steven W.; Ruggiero, Leonard F. 1994. American marten. In: Ruggiero, Leonard 

F.; Aubry, Keith B.; Buskirk, Steven W.; Lyon, L. Jack; Zielinski, William J., editors. 

The scientific basis for conserving forest carnivores: American marten, fisher, lynx, and 

wolverine in the western United States. Gen. Tech. Rep. RM-254. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service; 7-37. 

Carter, David W. 1993. The importance of seral stage and coarse woody debris to the 

abundance and distribution of deer mice on Vancouver Island, British Columbia.

Burnaby: Simon Fraser University; 105 p. M. Sc. Thesis. 

Corn, Janelle G.; Raphael, Martin G. 1992. Habitat characteristics at marten subnivian 

access sites. Journal of Wildlife Management 56: 442-448. 

Debrot, S.; Weber, J.-M.; Marchesi, P.; Mermod, C. 1985. The day and night activity 

pattern of the stoat (Mustela erminea L.). Mammalia 49: 13-17. 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

328 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Environment Canada. 1998. Canadian climate normals, 1961-1990 Cold Lake, Alberta.

Ottawa: Environment Canada; http://www.ns.doe.ca/climate/index.html. 

Erlinge, Sam. 1977. Home range utilization and movements of the stoat, Mustela erminea.

XIII International Congress of Game Biologists 13: 31-42. 

Erlinge, Sam. 1979. Movements and daily activity pattern of radio tracked male stoats, 

Mustela erminea. In: Amlaner, Charles J., Jr.; MacDonald, David W., editors. A 

handbook on biotelemetry and radio tracking. Proceedings of an international conference 

on telemetry and radio tracking biology and medicine; 1979 March 20-22; Oxford, 

England. Oxford, England: Pergamon Press; 703-710 p. 

ESRI. 1996. Using Arcview GIS. Redlands, California: Environmental Systems Research 

Institute, Inc.; 359 p. 

ESRI. 1997. Understanding GIS: the Arc/INFO method. Redlands, CA: Environmental 

Systems Research Institute; various pagings. 

Gyug, Les W. 1994. Wildlife use of logging debris piles in clearcuts. Penticton, BC: British 

Columbia Ministry of Environment; 45 p. 

Harestad, Alton S. 1991. Cover and habitat use by wildlife in managed forests. In: 

Maruyama, Naoki; Bobek, Boguslaw; Ono, Yuiti; Regelin, Wayne; Bartos, Ludek; 

Ratcliffe, Philip R., editors. Wildlife conservation: present trends and perspectives for 

the 21st century. Proceedings of the international symposium on wildlife conservation; 

1990 August 21-25; Tsukuba and Yokohama, Japan. Yushima, Bunkyo-ku, Tokyo: 

Japan Wildlife Research Centre; 102-106. 

Johnson, Edward A. 1992. Fire and vegetation dynamics: studies from the North 

American boreal forest. New York: Cambridge University Press; 129 p. 

King, Carolyn M. 1973. A system for trapping and handling live weasels in the field.

Journal of Zoology, London 171:458-464. 

King, Carolyn M. 1989. The natural history of weasels and stoats. New York: Cornell 

University Press; 253 p. 

Krebs, Charles J. 1989. Ecological methodology. New York: Harper and Row; 654 p. 

Lisgo, Kimberly A. 1999. Ecology of the short-tailed weasel (Mustela erminea) in the 

mixedwood boreal forest of Alberta. Vancouver: University of British Columbia; 65 p. 

M. Sc. thesis. 

Maser, Chris; Anderson, Ralph G.; Cromack Jr., Kermit; Williams, Jerry T.; Martin, Robert 

E. 1979. Dead and down material. In: Parker, J. Louise; Thomas, Jack W., editors. 

Wildlife habitats in managed forests: the Blue Mountains of Oregon and Washington. 

Agricultural Handbook No. 553, U.S. Department of Agriculture. Washington, DC: 

Wildlife Management Institute, U.S. Department of Interior, Bureau of Land 

Management; 78-95. 

Maser, Chris; Trappe, James M. 1984. The seen and unseen world of the fallen tree. Gen. 

Tech. Rep. PNW-164. Portland, OR: U.S. Department of Agriculture, Forest Service; 56 

p. 

Nordyke, Kirk A.; Buskirk, Steven W. 1991. Southern red-backed vole, Clethrionomys

gapperi, populations in relation to stand succession and old-growth character in the 

central Rocky Mountains. Canadian Field-Naturalist 105: 330-334. 

Rhoades, Fred. 1986. Small mammal mycophagy near woody debris accumulations in the 

Stehekin River valley, Washington. Northwest Science 60: 150-153. 

Rowe, John S. 1961. Critique of some vegetational concepts as applied to forests of 

northwestern Alberta. Canadian Journal of Botany 39: 1007-1017. 
Use of Logging Residue by Short-tailed Weasels―LIsgo, Bunnell, and Harestad 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 329 

Rowe, John S. 1972. Forest regions of Canada. Ottawa: Canadian Forest Service; 166 p. 

Roy, Lawrence D.; Stelfox, J. Brad; Nolan, Jack W. 1995. Relationships between mammal 

biodiversity and stand age structure in aspen mixedwood forests in Alberta. In: 

Stelfox, J. Brad, editor. Relationships between stand age, stand structure, and 

biodiversity in aspen mixedwood forests in Alberta. Vegreville and Edmonton, AB: 

Alberta Environmental Centre (AECV95-R1) and Canadian Forest Service (Project No. 

0001A); 159-189. 

Samson, Claude; Raymond, Michel. 1995. Daily activity pattern and time budget of stoats 

(Mustela erminea) during summer in southern Quebec. Mammalia 59: 501-510. 

Thompson, Rebecca L. 1996. Home range and habitat use of western red-backed voles in 

mature coniferous forests in the Oregon Cascades. Corvallis: Oregon State 

University; 88 p. M. S. thesis. 

 Weaver, Robin L. 1996. The effects of timber harvesting in the boreal forest on deer mice 

and red-backed voles. Edmonton, AB: University of Alberta; 57 p. M. Sc. Thesis. 

White, Gary C.; Garrott, Robert A. 1990. Analysis of wildlife radio-tracking data. New 

York: Academic Press, Inc.; 383 p. 

Zar, Jerrold H. 1984. Biostatistical analysis. Englewood Cliffs, New Jersey: Prentice-Hall, 

Inc.; 718 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 331 

Dead Wood and the Richness of Small 

Terrestrial Vertebrates in Southwestern 

Oregon1

Chris C. Maguire2

Abstract 

In southwestern Oregon, 24 mature forest stands were used to test the hypothesis that species 

richness of small terrestrial vertebrates is positively correlated with dead wood volume, and to 

compare dead wood loads between capture and non-capture sites for species encountered. 

Dead wood was separated into two components: coarse woody debris (CWD)—defined as 

down wood of any length ∃ 10 cm in diameter—and snags, defined as standing dead wood ∃

0.5 m in height and ∃ 25 cm in diameter. The volume of CWD in stands ranged from 50 to 

860 m3

/ha and snag volumes ranged from 10 to 240 m3/ha. Small terrestrial vertebrates 

numbered between 8 and 20 species per stand based on a pitfall sampling effort of 

approximately 3,600 trap nights per stand over 2 years. Regression analysis revealed that the 

species richness of all terrestrial vertebrates taken as a single group increased with increasing 

volumes of CWD. Viewed as separate taxonomic groups, species richness of small mammals, 

insectivores, and amphibians all correlated positively with CWD volume; rodent richness 

showed no significant relationship with CWD. None of the vertebrate groups disclosed 

significant correlations between species richness and snag volume. Although some individual 

species at the stand scale did not appear to associate with dead wood, the study results do not 

preclude the importance of dead wood as a microhabitat feature. The results of this study 

predict that if all stands are managed to Federal CWD targets in southwestern Oregon, the full 

component of small terrestrial vertebrates typical of Pacific Northwest forests will not be 

realized. 

Introduction

Many species of wildlife use dead wood as breeding habitat, for cover, or as a 

source of prey (Bartels and others 1985). In the Pacific Northwest, regulations exist 

for the management of dead wood on forestlands for the purpose of accommodating 

wildlife (Oregon Department of Forestry 1991, USDA and USDI 1994). Despite 

specific number, dimensions, and decay class requirements, dead wood targets 

frequently vary little for vastly different forest community types partly because of 

limited available data on natural dead wood conditions and threshold levels of snags 

and down wood needed to maintain species diversity. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and 

Management of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Assistant Professor, Department of Forest Science, Richardson Hall, Oregon State University, 

Corvallis, Oregon 97331 (e-mail: chris.maguire@orst.edu) 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

332 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Appropriate amounts of dead wood for managed forests continue to be debated. 

Safety and economic concerns often are at odds with wildlife needs particularly when 

snags and down wood are created from green trees to meet management objectives, 

thereby compromising potential revenue (Hope and McComb 1994, Wick and others 

1985). Compounding the issue is a poor database correlating wildlife diversity and 

abundance with varying levels of dead wood, and hence, a lack of basic information 

on which to base reliable dead wood goals (McComb and Lindenmayer 1999). 

Therefore, research is necessary to identify critical levels of dead wood needed to 

support diverse forest wildlife communities, ascertain the level of dead wood above 

which diversity is no longer served, and evaluate whether current dead wood 

guidelines are adequately meeting the needs of the wildlife for which they were 

created. In short, quantification of the relationship between amount of dead wood and 

small terrestrial vertebrates will allow explicit recognition of the biological costs and 

benefits of establishing a given dead wood target. 

The objectives of this study were to test the hypothesis that species richness of 

small terrestrial vertebrates is positively correlated with dead wood volume, and to 

shed light on richness trends by comparing dead wood loads between capture and 

non-capture sites for species encountered. These relationships were tested with data 

from upland forest stands in southwestern Oregon. 

Methods 

Study Area 

Twenty-four 13-ha Douglas-fir (Pseudotsuga menziesii) dominated mature 

upland stands from the Umpqua National Forest in southwestern Oregon were 

selected for study (table 1) (see Aubry and others [1999], and Abbott and others 

[1999] for site selection criteria). Six stands are located in each of four separate areas 

with stands within areas frequently adjacent. The stands generally have southeast to 

southwest aspects and slopes ranging from flat to approximately 60 percent. Most 

stands have a history of thinning or salvage logging. The stands make up the Oregon 

component of DEMO (Demonstration of Ecosystem Management Options), a USDA 

Forest Service funded study initiated in the 1990s to examine the responses of diverse 

groups of forest organisms and processes to variation in the amount and/or pattern of 

residual live trees after harvest (Halpern and Raphael 1999). Information presented 

represents pre-harvest conditions in the overall DEMO study plan. 

Vertebrate Sampling 

An 8 x 8 or 7 x 9 grid with 40-m spacing between grid points was established as 

the template for animal trapping and dead wood sampling (see Aubry and others 

[1999)] for grid spacing justification). Pitfall traps constructed of 2 number 10 cans 

(final dimensions: 15-cm diameter x 72-cm length) were sunk into the ground at each 

grid point and operated as removal traps for 28 consecutive days in October and 

November 1995 and 1996 (approximately 1,800 trap nights per stand per year) to 

assess small terrestrial mammal and amphibian abundance. Although time 

constrained searches (TCS) often are recommended for sampling amphibians directly 

utilizing down wood, pitfall traps have the benefit of more successfully sampling the 

array of species present (Bury and Corn 1988). In addition, TCS are not always more 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 333 

effective than pitfall traps (Maguire, pers. observ.). Captured animals were 

transported to the laboratory and identified. 

Voucher specimens from this study are housed in museums at Harvard in 

Cambridge, Massachusetts; Shippensburg University in Pennsylvania; Texas A & M 

in College Station; and the University of Alaska in Fairbanks. Museum staff verified 

species. 

Table 1—Pre-harvest characteristics of the 24 DEMO stands in the Umpqua National Forest 

in southwestern Oregon. 

Block/stand 

no. 

Stand 

age (yr) 

Elevation 

(m) 

BA1

(m2/ha) 

Mean 

DBH2(cm) 

Snags 

(m3/ha) 

CWD3 

(m3/ha) 

Watson 

Falls 

 

1 110 1,312 46.90 61 120.9 188.7 

2 110 946 42.99 51 83.1 67.4 

3 110 1,159 42.99 51 25.0 190.9 

4 130 1,312 58.62 61 109.4 185.8 

5 130 946 42.99 51 41.5 142.6 

6 130 946 58.62 51 48.2 96.6 

Little River 

1 400-520 1,281 128.74 122 193.2 547.9 

2 250-300 1,373 91.95 91 175.3 205.4 

3 300 1,281 103.45 97 70.9 219.0 

4 200-250 1,312 80.46 114 240.1 183.2 

5 300 1,251 103.45 97 100.0 261.7 

6 225-325 1,312 74.71 86 25.7 94.1 

Layng 

Creek4

 

1 80 763 35.86 46 34.1 425.8 

2 60 671 27.82 41 100.4 383.9 

3 80 763 35.86 46 38.3 565.2 

4 60 671 30.34 43 54.0 862.1 

5 65 488 27.82 41 11.0 262.6 

6 80 671 28.05 48 38.6 374.5 

Dog Prairie 

1 165 1,647 68.97 61 78.7 58.4 

2 165 1,647 68.97 61 54.8 91.1 

3 165 1,525 68.97 61 125.5 180.0 

4 165 1,647 68.97 61 57.1 62.4 

5 165 1,647 68.97 61 28.4 50.5 

6 165 1,525 68.97 61 142.5 232.9 

1 BA = basal area 

2 DBH = diameter at breast height 

3

 CWD = coarse woody debris 

4 All six stands are second growth. 

Dead Wood Sampling 

Dead wood was sampled on an average of 42 (range: 32 to 64) grid points per 

stand during snow-free months in 1994 through 1996. Selection of points was based 

on planned harvest treatments (Halpern and others 1999). Snags were counted on a 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

334 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

circular 0.08-ha (15.96-m radius) plot centered on each of 1,037 sampling points, and 

diameters, height classes, and decay classes (Cline and others 1980) were recorded. 

Snags were defined as standing dead wood ∃ 25 cm in diameter and ∃ 0.5 m in 

height. Coarse woody debris (CWD) was measured (Brown 1974) at 851 sampling 

stations across the 24 stands using four 6-m transects radiating out at 90o

 angles 4 

meters from each sample point. Diameter of CWD at the point of intersection with 

the line transects, length, and decay class were recorded. CWD was defined as down 

wood of any length ∃ 10 cm in diameter. Snag and CWD volume estimates were 

calculated for each stand. 

Analytical Methods 

The number of species found in a location is tied to the number of captures 

(Rosenzweig 1995), i.e., the likelihood of encountering rare species increases with 

increasing sample size. When comparing species richness across sites where captures 

are unequal, the sample issue can be overcome by standardizing counts as in the 

rarefaction method outlined in Krebs (1989). In this richness estimation method, the 

number of species within each stand is predicted from a set number of randomly 

sampled individuals taken from the population. In this study, the mid-value from the 

range of stand captures for each vertebrate group was used to compute expected 

richness estimates by the rarefaction method. 

Relationships between dead wood volume across the 24 stands and species 

richness estimates for standardized captures were examined by regression analysis. 

Both linear and log model forms were explored. To examine individual species 

associations with CWD volume that contributed to the richness trends observed at the 

stand level, Welch’s approximate-t for unequal variance (Zar 1984) was used to test 

for differences in CWD volumes between capture and non-capture sites of each 

species. Siskiyou and Townsend’s chipmunks (Tamias siskiyou and T. townsendii, 

respectively), northern flying squirrels (Glaucomys sabrinus), and ermines (Mustela 

erminea) were excluded from t-test analysis because pitfall traps are not the best 

method for capturing these species; and other methods employed in the DEMO study 

showed that these species occurred on some sites additional to those on which they 

were captured in pitfalls (Lehmkuhl and others 1999). Significance was tested at ∀ #

0.05. 

Results and Discussion 

Dead Wood 

The volume of CWD in stands ranged from approximately 50 to 860 m3/ha 

(table 1). These amounts represent volumes approximately 5 to 80 times the amount 

mandated by the Northwest Forest Plan (USDA and USDI 1994) for the Umpqua 

National Forest, but they are within the previously recognized range for terrestrial 

forest ecosystems (Harmon and others 1986). 

Despite past salvage and selective harvest in the stands, CWD volumes still 

tracked the chronosequence “U”-shaped trajectory predicted by Spies and Franklin 

(1988) and observed in a variety of vegetation types for naturally regenerated forests 

(e.g., Agee and Huff 1987, McCarthy and Bailey 1994, Spies and others 1988, 

Sturtevant and others 1997, Wells and Trofymow 1997); that is, the largest CWD 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 335 

volumes are associated with both the youngest and the oldest stands (fig. 1). High 

numbers and volumes of down wood occur early in stand development after a 

catastrophic disturbance and in old-growth forests as dead wood accumulates (Spies 

and others 1988). Human disturbance in these forests did not significantly alter this 

pattern. 

 

Figure 1―Mean stand volumes of coarse woody debris (CWD) and snags across 

stand ages for the 24 stands presented in table 1. Age groupings are 60/65, 80, 110, 

130, 165, 275 (200-325), and 460 (400-520) years. 

Snag volumes ranged from 10 to 240 m3

/ha across stands. Spies and Franklin 

(1988) also predicted a “U”-shaped developmental trajectory for snags in addition to 

CWD, but this pattern was not observed in these stands (fig. 1), possibly due to 

significant sacrifice or salvage of snags during past harvesting or the lack of snags 

during stand establishment. Nonetheless, similar non-“U” trends for snag volume 

have been found in other forest types (Sturtevant and others 1997, Tyrrell and Crow 

1994). Snags and CWD volumes were poorly correlated (r2

 = 0.001, p = 0.87). 

Species Richness 

Regression analysis revealed that the species richness of all terrestrial 

vertebrates taken as a single group increased with increasing volumes of CWD and 

all dead wood (snags and CWD), but had no significant relationship with snag 

volume (table 2). Small mammals taken as a group, insectivores, and amphibians all 

reflected the same trends. The significance and linear relationship between richness 

and total dead wood volume was impacted by the substantial CWD component of 

total dead wood. Rodent richness was not correlated with any measure of dead wood 

volume. 

0

100

200

300

400

500

600

0 100 200 300 400 500

stand age (yrs)

volume (m3/ha)

CWD 

SNAGS 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

336 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 2—Best fit regression models for the relationship between a variety of dead wood 

volumes and species richness of small terrestrial vertebrates estimated from the rarefaction 

technique (Krebs 1989). Species richness was estimated for the sample sizes in parentheses; 

sample sizes represent the mid-value of captures across 24 stands in the Umpqua National 

Forest, Oregon. 

Coarse woody debris volume (m3

/ha)

Species group Model form1 r

2

 p 

All vertebrates (n = 326) log (SR) = 0.785 + 0.160 log (CWD) 0.42 0.0007 

All mammals (n = 301) log (SR) = 0.797 + 0.101 log (CWD) 0.32 0.004 

Rodents (n = 117) log (SR) = 0.451 + 0.105 log (CWD) 0.14 0.07 

Insectivores (n = 212) log (SR) = 0.507 + 0.109 log (CWD) 0.28 0.009 

Amphibians (n = 20) log (SR) = -0.152 + 0.289 log (CWD) 0.33 0.003 

Snag volume (m3

/ha)

Species group Model form r

2

 p 

All vertebrates (n = 326) SR = 14.890 - 0.007 SNAG 0.02 0.48 

All mammals (n = 301) SR = 11.203 - 0.006 SNAG 0.05 0.30 

Rodents (n = 117) SR = 5.559 - 0.007 SNAG 0.12 0.09 

Insectivores (n = 212) SR = 5.905 - 0.002 SNAG 0.01 0.59 

Amphibians (n = 20) log (SR) = 0.311 + 0.103 log (SNAG) 0.04 0.33 

Total dead wood volume (m3

/ha) 

Species group Model form r

2

 p 

All vertebrates (n = 326) log (SR) = 0.744 + 0.166 log (DW) 0.30 0.005 

All mammals (n = 301) log (SR) = 0.786 + 0.099 log (DW) 0.20 0.03 

Rodents (n = 117) log (SR) = 0.481 + 0.086 log (DW) 0.06 0.24 

Insectivores (n = 212) log (SR) = 0.480 + 0.113 log (DW) 0.20 0.03 

Amphibians (n = 20) log (SR) = -0.296 + 0.329 log (DW) 0.29 0.007 

1

SR = species richness = number of species estimated for a sample of n individuals; CWD = coarse 

woody debris volume; SNAG = snag volume; DW = total dead wood volume = CWD + SNAG 

volumes. 

The results indicate that CWD volume is a better predictor of species richness at 

the stand level for small terrestrial vertebrates than either snag or total dead wood 

volumes in southwestern Oregon, even though snags provide a future source of down 

wood (Spies and others 1988). Many amphibians and mammals exploit snag cavities, 

flaking bark on snags, or insect and fungal food resources inhabiting snags (Dupuis 

and others 1995); but for many small terrestrial vertebrates, the absence of snags does 

not appear to be a limiting factor (Bunnell and others 1997). 

Mammals represent the largest number of terrestrial vertebrate species 

associated with down wood (Brown 1985). Although species abundance may 

increase as dead wood abundance increases, many mammalian species that use down 

wood are not believed to require it (Bunnell and others 1997). The exception may be 

the insectivores. Down wood and insect levels often are tightly linked (e.g., 

Torgersen and Bull 1995), and insect outbreaks frequently are associated with 

unnaturally high levels of dead wood resulting from active fire suppression 

(Campbell and Liegel 1996). Because of the insect/dead wood linkage, animals that 

primarily consume insects, such as the insectivores, often have close ties to CWD, as 

is evident in this study. Conversely, insects represent only a portion of most rodent 

diets, and rodent richness was not strongly tied to down wood. 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 337 

Amphibians also feed on insects, and they too had richness levels significantly 

correlated with CWD volume. In addition, amphibians, particularly salamanders, 

require moist habitat conditions, and the stable, moist micro-environment provided 

by the space beneath logs or the decomposing interior of logs is well suited to their 

life requisites (Bury and Corn 1988, Corn and Bury 1991a, DeMaynedier and Hunter 

1995). 

Individual Species 

The number and type of animal species encountered varied widely across the 24 

stands (table 3). Twenty-nine species were captured, including 7 salamanders, 2 

frogs, 6 insectivores, 13 rodents, and 1 carnivore. The number of species in any stand 

ranged from 8 to 20, a richness range consistent with other studies (Bury and Corn 

1988, Gomez and Anthony 1998). 

With the exception of the rough-skinned newt (Taricha granulosa) and the 

spotted frog (Rana pretiosa)—species that both spend a major portion of their lives in 

or near water—previous studies suggest that the remaining seven species of 

amphibians associate with down wood when on land (Brown 1985, Bury and Corn 

1988, Bury and others 1991, Corn and Bury 1991a, Stelmock and Harestad 1979). To 

evaluate the consistency of these relationships, CWD volumes between capture and 

non-capture stands for each species were tested for differences. Results did not 

always reflect the trends noted above. Dunn’s salamander (Plethodon dunni) and 

western red-backed salamander (P. vehiculum) were captured on stands with greater 

volumes of CWD than non-capture stands. This positive association with down wood 

also extended to the rough-skinned newt. Conversely, Pacific treefrog (Pseudacris 

regilla) was located on stands with less CWD. Species that did not express 

significant relationships with down wood include clouded salamander (Aneides 

ferreus), northwestern salamander (Ambystoma gracile), and Pacific giant 

salamander (Dicamptodon tenebrosus). The spotted frog and ensatina (Ensatina 

eschscholtzii) were not analyzed because spotted frog was captured on only one stand 

while ensatina was captured on all stands but one (table 3).

Insectivores as a group were encountered more frequently than amphibians 

(table 3). Both the Trowbridge’s and Pacific shrews (Sorex trowbridgii and S. 

pacificus, respectively) were present in all stands, and the vagrant shrew (S. vagrans) 

was located in all but one stand. Trowbridge’s shrew is the most common shrew in 

Pacific Northwest forests west of the Cascade crest (Carey and Johnson 1995, Gomez 

and Anthony 1998); however, Dalquest (1941) stated that it is rarely found when the 

vagrant shrew is present. The results of the current study document the consistent 

overlap of Trowbridge’s and vagrant shrews. Some research suggests that the vagrant 

shrew prefers moist open areas (Gomez and Anthony 1998, Hawes 1977) and is 

uncommon or absent in Douglas-fir forests (Terry 1981). These findings are 

inconsistent with the results of this study as all 23 sites where the vagrant shrew was 

found were upland Douglas-fir stands (table 1). Although some past research 

indicates that the vagrant shrew does indeed inhabit forested areas (e.g., Corn and 

Bury 1991b, Hooven and Black 1976), this earlier work has been met with skepticism 

because of the lack of voucher specimens (Verts and Carraway 1998) and earlier 

confusion concerning the taxonomic status of the species (Carraway 1990). 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

338 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 3—Species of terrestrial vertebrates captured in pitfall traps in 24 stands located in 4 

blocks across the Umpqua National Forest in southwestern Oregon. Number 1 indicates that 

the species was captured; 0 represents no capture. 

Research blocks 

Stand No. 

 Watson Falls 

1 2 3 4 5 6

Little River 

1 2 3 4 5 6

Layng Creek 

1 2 3 4 5 6

Dog Prairie 

1 2 3 4 5 6

Amphibians 

Salamanders 

Ambystoma 

gracile 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 0 0 1

Aneides ferreus 0 0 0 0 0 0 1 0 0 1 1 1 1 1 0 0 1 1 0 0 0 0 0 1 

Dicamptodon 

tenebrosus 0 0 0 0 0 0 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 0 0 0 

Ensatina 

eschscholtzii 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 

Plethodon 

dunni 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 

Plethodon 

vehiculum 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 

Taricha 

granulosa 0 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 

Frogs 

Pseudacris 

regilla 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 

Rana pretiosa 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Mammals 

Insectivores 

Neurotrichus 

gibbsii 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 0 1 1 0 1 1 

Scapanus 

orarius 1 0 1 0 0 0 0 0 1 1 0 0 1 1 1 1 1 1 0 1 0 1 0 1 

Sorex bendirii 0 0 0 0 0 0 0 1 0 1 1 0 1 1 1 1 1 1 0 1 0 0 0 0 

Sorex pacificus 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Sorex 

trowbridgii 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Sorex vagrans 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

 

Rodents 

Arborimus 

albipes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 

Arborimus 

longicaudus 0 0 0 0 0 0 1 0 1 0 1 1 1 1 1 0 0 0 0 1 0 0 0 0 

Clethrionomys 

californicus 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Glaucomys 

sabrinus 0 0 0 0 0 0 1 0 1 1 0 0 0 0 1 0 1 1 0 0 1 0 0 0 

Microtus 

oregoni 1 1 1 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 

Microtus 

richardsoni 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 

Microtus 

townsendii 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 1 1 0 0 0 1 0 0 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 339 

(table 3 continued) 

Research blocks 

Stand No.

 Watson Falls 

1 2 3 4 5 6

Little River 

1 2 3 4 5 6

Layng Creek 

1 2 3 4 5 6

Dog Prairie 

1 2 3 4 5 6

Peromyscus 

maniculatus 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Phenacomys 

intermedius 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Tamias siskiyou 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Tamias 

townsendii 0 0 0 0 0 0 0 1 1 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 

Thomomys 

mazama 1 1 1 1 0 1 0 0 1 0 0 1 0 0 0 0 0 0 0 1 1 1 0 0 

Zapus 

trinotatus 0 1 0 0 1 0 1 0 0 0 1 0 1 1 1 1 1 1 1 0 0 0 0 0 

Carnivores 

Mustela 

erminea 0 0 1 0 1 1 1 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 1 

All six of the insectivorous species observed in this study are believed to derive 

habitat benefits from down wood (Brown 1985, Carey and Johnson 1995, Gilbert and 

Allwine 1991). The almost uniform presence of Pacific, Trowbridge’s, and vagrant 

shrews across the 24 stands would imply that these shrews are not limited by CWD. 

However, studies at the micro-habitat scale suggest otherwise (reviewed in Verts and 

Carraway 1998). Of the three insectivorous species for which t-tests could be 

performed (table 4), coast mole (Scapanus orarius) did not demonstrate differences 

in CWD volume between capture and non-capture stands, but both the shrew-mole 

(Neurotrichus gibbsii) and the Pacific water shrew (Sorex bendirii) were captured on 

stands where CWD volumes were more than twice that found on non-capture stands. 

Interestingly, although the shrew-mole and the Pacific water shrew are both thought 

to favor moist habitats (Gomez and Anthony 1998), they only overlapped on 9 stands 

while one or the other species was present on 22 of the 24 study stands. These results 

suggest that for at least some species, down wood likely works in conjunction with 

other habitat features to influence stand suitability. 

Rodents had a wide range in site occurrence, but only two species showed 

significant differences in CWD volumes between capture and non-capture stands 

(table 4). Western pocket gopher (Thomomys mazama) was observed on stands with 

less down wood, and Pacific jumping mouse (Zapus trinotatus) was observed on 

stands with greater down wood compared with non-capture sites. Neither species is 

believed to have strong dead wood habitat relationships (Brown 1985, Gilbert and 

Allwine 1991, Gomez and Anthony 1998); however, little is known of the habitat 

requirements of the jumping mouse (Verts and Carraway 1998) despite its apparent 

preference for riparian areas (Gomez and Anthony 1998). In addition, Verts and 

Carraway (1998) contend that the western pocket gopher does not occupy dense 

forest areas, but results from this study and others, and confirmed voucher specimens 

conflict with this claim. 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

340 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 4—Results of Welch's approximate t-tests for comparing differences in mean coarse 

woody debris (CWD) volumes (m3

/ha) in stands in the Umpqua National Forest, Oregon, 

where small terrestrial vertebrate species were and were not located. 

 Located Not located 

 Stands 

(n) 

CWD Stands 

(n) 

CWD t df p 

Amphibians 

Salamanders 

Ambystoma gracile 21 236 3 325 0.33 2 0.77 

Aneides ferreus 9 307 15 211 1.32 21 0.2 

Dicamptodon 

tenebrosus 

7 399 17 185 2.14 7 0.07 

Ensatina eschscholtzii 23 254 1 94 -- -- -- 

Plethodon dunni 3 441 21 219 2.97 4 0.04 

Plethodon vehiculum 7 419 17 176 2.46 7 0.04 

Taricha granulosa 16 304 8 133 2.85 20 0.01 

 

Frogs 

Pseudacris regilla 3 100 21 268 3.42 19 0.003 

Rana pretiosa 1 205 23 249 -- -- -- 

 

Mammals 

Insectivores 

Neurotrichus gibbsii 21 268 3 101 2.79 8 0.02 

Scapanus orarius 13 311 11 172 1.88 20 0.07 

Sorex bendirii 10 362 14 166 2.51 13 0.03 

Sorex pacificus 24 247 0 -- -- -- -- 

Sorex trowbridgii 24 247 0 -- -- -- -- 

Sorex vagrans 23 248 1 219 -- -- -- 

 

Rodents 

Arborimus albipes 3 500 21 211 1.54 2 0.26 

Arborimus 

longicaudus 

8 324 16 209 1.40 14 0.18 

Clethrionomys 

californicus 

24 247 0 -- -- -- -- 

Microtus oregoni 22 234 2 392 0.89 1 0.54 

Microtus richardsoni 5 362 19 217 1.40 5 0.22 

Microtus townsendii 7 206 17 264 0.86 21 0.4 

Peromyscus 

maniculatus 

24 247 0 -- -- -- -- 

Phenacomys 

intermedius 

1 186 23 250 -- -- -- 

Thomomys mazama 10 138 14 326 3.01 15 0.009 

Zapus trinotatus 11 359 13 152 2.78 11 0.02 

Of the remaining species, four are believed to require down wood in their habitat 

and four appear little impacted by it (Brown 1985). Three of the four species that use 

CWD were common across the study sites and their routine occurrence in Oregon 

forests is well documented (e.g., Carraway and Verts 1985, Doyle 1987, Gomez and 

Anthony 1998, Rosenberg and others 1994, and reviewed in Verts and Carraway 

1998). These include western red-backed vole (Clethrionomys californicus), creeping 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 341 

vole (Microtus oregoni), and deer mouse (Peromyscus maniculatus). The fourth 

species, white-footed vole (Arborimus albipes), is one of the rarest microtines in 

North America (Voth and others 1983). Although it is captured infrequently in a 

variety of habitats (reviewed in Verts and Carraway 1998), it appears to closely 

associate with abundant deciduous vegetation (Gomez and Anthony 1998, McComb 

and others 1993, Voth and others 1983). 

The four rodent species captured that do not appear to associate with dead wood 

at the stand level include red tree vole (Arborimus longicaudus), water vole 

(Microtus richardsoni), Townsend’s vole (M. townsendii) and heather vole 

(Phenacomys intermedius). Red tree voles are primarily arboreal rodents, water voles 

inhabit streamsides, Townsend’s voles occupy moist environments, and heather vole 

habitat remains under review (Verts and Carraway 1998). Only one heather vole was 

captured in this study. 

There are a number of potential reasons for the inconsistency of some of the 

wildlife/CWD relationships observed in this study versus other published works: 

Type I or Type II errors may occur in the statistical analysis of species associations 

with down wood; the prospective rather than experimental nature of the study may 

have produced some false results; sampling method bias may have affected the 

number of species encountered; stand scale associations may not adequately reflect 

microhabitat associations; and sampling an incomplete range of all possible down 

wood conditions may have masked species sensitivities to low CWD levels. 

The lack of representation of all possible dead wood conditions in any given 

study is probably the biggest disadvantage to using mean CWD values to evaluate 

species relationships with dead wood based on capture/non-capture data. In addition, 

capture and non-capture site comparisons unite stands with varying amounts of down 

wood based solely on the encounter of as few as a single individual with no 

consideration of population size. Because population abundance for dead wood 

associates likely correlates with amount of dead wood, regression analysis is more 

suited to express this relationship and also to identify volumes above which 

populations are no longer served by additional dead wood. The reliability of 

regression results, however, is significantly influenced by the reliability of the 

abundance estimate. Regardless, mean dead wood comparisons between capture and 

non-capture stands or stands of different age, structure, or management history is the 

most published statistic for animal/dead wood relationships, and it is frequently used 

to compare results among studies. Included in the scope of the current study, 

regression analysis was performed with animal abundance data to expand on the 

CWD mean comparisons, but regression results will be reported elsewhere. 

Conclusions 

Although some small terrestrial species at the stand scale do not appear to 

associate with dead wood, current results do not preclude the importance of dead 

wood as a micro-habitat feature. Amphibian and insectivore richness correlates 

highly with CWD volume and most likely is linked to the importance of dead wood 

as a habitat moderator for these species and as a source of insect food items. Because 

of the tie between small vertebrates and CWD coupled with the noted importance of 

down wood at the micro-habitat scale for many species, CWD manipulation at the 

stand scale should have a large impact on the richness of ground dwelling 

vertebrates. 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

342 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The CWD volumes examined in the 24 stands of this study were greater than 

five times the current CWD Federal targets for southwestern Oregon. If the richness 

trends observed with down wood volume determined in this study extend to the lower 

Federal target levels of CWD, then terrestrial vertebrate richness is predicted to be 

lower than richness observed in this study on sites where minimum Federal CWD 

targets are implemented. To maintain the full component of small vertebrates typical 

of Pacific Northwest forests, a logical dead wood management strategy would be to 

provide for heterogeneity in down wood across the landscape representing the full 

range of natural levels. The challenge, however, will be to determine the natural 

range of CWD conditions and to provide an ecological rationale for the proportional 

allocations of different CWD volumes. 

Acknowledgments 

This research is a product of the Demonstration of Ecosystem Management 

Options (DEMO) study, a joint effort of the USDA Forest Service’s Pacific 

Northwest Region and Pacific Northwest Research Station. Research partners include 

the University of Washington, Oregon State University, University of Oregon, 

Gifford Pinchot and Umpqua National Forests, and the Washington State Department 

of Natural Resources. Special thanks are due to C. B. Halpern, S. A. Evans, T. 

Manning, and numerous field assistants for data collection, and to T. Manning for 

assistance with data analysis. The helpful comments of A. B. Carey, J. G. Hallett, W. 

F. Laudenslayer, Jr., D. A. Maguire, and T. Manning significantly improved the 

quality of the manuscript. 

References 

Abbott, R. A.; White, J. D.; Woodard, B. L. 1999. The benefits and challenges of largescale silvicultural experiments: perspectives from forest managers on the 

Demonstration of Ecosystem Management Options (DEMO) study. Northwest 

Science 73 (Special Issue): 118-125. 

Agee, J. K.; Huff, M. H. 1987. Fuel succession in a western hemlock/Douglas-fir forest. 

Canadian Journal of Forest Research 17: 697-704. 

Aubry, K. B.; Amaranthus, M. P.; Halpern, C. B.; White, J. D.; Woodward, B. L.; Peterson, 

C. E.; Lagondakis, C. A.; Horton, A. J. 1999. Evaluating the effects of varying levels 

and patterns of green-tree retention: experimental design of the DEMO study.

Northwest Science 73 (Special Issue): 12-26. 

Bartels, R.; Dell, J. D.; Knight, R. L.; Schaefer, G. 1985. Dead and down woody material.

In: Brown, E .R., technical editor. Management of wildlife and fish habitats in forests of 

western Oregon and Washington. Part I—Chapter narratives. PNW R-6-F&WL-192-

1985. Portland, OR: USDA Forest Service; 171-186. 

Brown, E. R., technical editor. 1985. Management of wildlife and fish habitats in forests of 

western Oregon and Washington. Part II—Appendices. PNW R-6-F&WL-192-1985. 

Portland, OR: USDA Forest Service; 332 p. 

Brown, J. K. 1974. Handbook for inventorying downed woody material. Gen. Tech. Rep. 

INT-16. USDA Forest Service; 24 p. 

Bunnell, F. L.; Kremsater, L. L.; Wells, R. W. 1997. Likely consequences of forest 

management on terrestrial, forest-dwelling vertebrates in Oregon. Report M-7 of 

the Centre for Applied Conservation Biology, University of British Columbia; 130 p. 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 343 

Bury, R. B.; Corn, P. S. 1988. Douglas-fir forests in the Oregon and Washington 

Cascades: relation of the herpetofauna to stand age and moisture. In: Szaro, R. C.; 

Severson, K. E.; Patton, D. R., technical coordinators. Management of amphibians, 

reptiles, and small mammals in North America. Gen. Tech. Rep. RM-166. USDA Forest 

Service; 11-22. 

Bury, R. B.; Corn, P. S.; Aubry, K. B. 1991. Regional patterns of terrestrial amphibian 

communities in Oregon and Washington. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. 

B.; Huff, M. H., technical coordinators. Wildlife and vegetation of unmanaged Douglasfir forests. Gen. Tech. Rep. PNW-GTR-285. USDA Forest Service; 341-350. 

Campbell, S.; Liegel, L., technical coordinators. 1996. Disturbance and forest health in 

Oregon and Washington. Gen. Tech. Rep. PNW-GTR-381. Portland, OR: USDAForest Service; 105 p. 

Carey, A. B.; M. L. Johnson. 1995. Small mammals in managed, naturally young, and oldgrowth forests. Ecological Applications 5: 336-352. 

Carraway, L. N. 1990. A morphologic and morphometric analysis of the “Sorex vagrans

species complex” in the Pacific Coast region. Special Publications, The Museum, 

Texas Tech University 32: 1-76. 

Carraway, L. N.; Verts, B. J. 1985. Microtus oregoni. Mammalian Species 233: 1-6. 

Cline, S. P.; Berg, A. B.; Wight, H. M. 1980. Snag characteristics and dynamics in 

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44: 773-786. 

Corn, P. S.; Bury, R. B. 1991a. Terrestrial amphibian communities in the Oregon Coast 

range. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. H., technical 

coordinators. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. 

Rep. PNW-GTR-285. USDA Forest Service; 305-317. 

Corn, P. S.; Bury, R. B. 1991b. Small mammal communities in the Oregon Coast range. 

In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. H., technical coordinators. 

Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR285. USDA Forest Service; 241-253. 

Dalquest, W. W. 1941. Ecologic relationships of four small mammals in western 

Washington. Journal of Mammalogy 22: 170-173. 

DeMaynadier, P. G.; Hunter, K. L. 1995. The relationship between forest management and 

amphibian ecology: a review of the North American literature. Environmental 

Reviews 3: 230-261. 

Doyle, A. T. 1987. Microhabitat separation among sympatric microtines, Clethrionomys 

californicus, Microtus oregoni, and M. richardsoni. The American Midland Naturalist 

118: 258-265. 

Dupuis, L. A.; Smith, J. N. M.; Bunnell, F. L. 1995. Relation of terrestrial-breeding 

amphibian abundance to tree-stand age. Conservation Biology 9: 645-653. 

Gilbert, F. F.; Allwine, R. 1991. Small mammal communities in the Oregon Cascade 

range. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. H., technical 

coordinators. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. 

Rep. PNW-GTR-285. USDA Forest Service; 257-267. 

Gomez, D. M.; Anthony, R. G. 1998. Small mammal abundance in riparian and upland 

areas of five seral stages in western Oregon. Northwest Science 72: 293-302. 

Halpern, C. B.; Evans, S. A.; Nelson, C. R.; McKenzie, D.; Liguori, D. A.; Hibbs, D. E.; 

Halaj, M. G. 1999. Response of forest vegetation to varying levels and patterns of 

green-tree retention: an overview of a long-term experiment. Northwest Science 73 

(Special Issue): 27-44. 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

344 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Halpern, C. B.; Raphael, M. G. 1999. Special issue on retention harvests in northwestern 

forest ecosystems: the Demonstration of Ecosystem Management Options (DEMO) 

study. Northwest Science 73 (Special Issue); 125 p. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Lienkaemper, G. W.; Cromack, K., Jr.; Cummins, K. W. 1986. 

Ecology of coarse woody debris in temperate ecosystems. Advances in Ecological 

Research 15: 135-302. 

Hawes, M. L. 1977. Home range, territoriality, and ecological separation in sympatric 

shrews, Sorex vagrans and Sorex obscurus. Journal of Mammalogy 58: 354-367. 

Hooven, E. F.; Black, H. C. 1976. Effects of some clearcutting practices on small-mammal 

populations in western Oregon. Northwest Science 50: 189-208. 

Hope, S.; McComb, W. C. 1994. Perceptions of implementing and monitoring wildlife 

tree prescriptions of national forests in western Washington and Oregon. Wildlife 

Society Bulletin 22: 383-392. 

Krebs, C. J. 1989. Ecological methodology. New York: Harper & Row, Publishers; 654 p. 

Lehmkuhl, J. F.; West, S. D.; Chambers, C. L.; McComb, W. C.; Manuwal, D. A.; Aubry, K. 

B.; Erickson, J. L.; Gitzen, R. A.; Leu, M. 1999. An experiment for assessing 

vertebrate response to varying levels and patterns of green-tree retention.

Northwest Science 73 (Special Issue): 45-63. 

McCarthy, B. C.; Bailey, R. R. 1994. Distribution and abundance of coarse woody debris 

in a managed forest landscape of the central Appalachians. Canadian Journal of 

Forest Research 24: 1317-1329. 

McComb, W.; Lindenmayer, D. 1999. Dying, dead, and down trees. In: Hunter, M. L., Jr., 

editor. Maintaining biodiversity in forest ecosystems. Cambridge, England: Cambridge 

University Press; 335-372. 

McComb, W. C.; McGarigal, K. M.; Anthony, R. G. 1993. Small mammals and amphibians 

in streamside and upslope habitats of mature Douglas-fir stands, western Oregon.

Northwest Science 67: 7-15. 

Oregon Department of Forestry. 1991. Oregon Forest Practices Act. Oregon Revised 

Statutes 527.670, Section 9, Chapter 9. 

Rosenberg, D. K.; Swindle, K. A.; Anthony, R. G. 1994. Habitat associations of California 

red-backed voles in young and old-growth forests in western Oregon. Northwest 

Science 68: 266-272. 

Rosenzweig, M. L. 1995. Species diversity in space and time. Cambridge, England: 

Cambridge University Press; 436 p. 

Spies, T. A.; Franklin, J. F. 1988. Old-growth and forest dynamics in the Douglas-fir 

region of western Oregon and Washington. Natural Areas Journal 8: 190-201. 

Spies, T. A.; Franklin, J. F.; Thomas, T. B. 1988. Coarse woody debris in Douglas-fir 

forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Stelmock, J. J.; Harestad, A. .S. 1979. Food habits and life history of the clouded 

salamander (Aneides ferreus) on northern Vancouver Island, British Columbia. 

Syesis 12: 71-75. 

Sturtevant, B. R.; Bissonette, J. A.; Lond, J. N.; Roberts, D. W. 1997. Coarse woody debris 

as a function of age, stand structure, and disturbance in boreal Newfoundland.

Ecological Applications 7: 702-712. 

Terry, C. J. 1981. Habitat differentiation among three species of Sorex and Neurotrichus 

gibbsii in Washington. The American Midland Naturalist 106: 119-125. 
Dead Wood and Southwestern Oregon Vertebrates—Maguire 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 345 

Torgersen, T. R.; Bull, E. L. 1995. Down logs as habitat for forest-dwelling ants--the 

primary prey of pileated woodpeckers in northeastern Oregon. Northwest Science 

69: 294-303. 

Tyrrell, L. E.; Crow, T. R. 1994. Structural characteristics of old-growth hemlockhardwood forests in relation to age. Ecology 75: 370-386. 

USDA and USDI. 1994. Record of decision for amendments to Forest Service and 

Bureau of Land Management planning documents within the range of the northern 

spotted owl; standard and guidelines for management of habitat for latesuccessional and old-growth forest related species within the range of the northern

spotted owl. Washington, DC: U.S. Government Printing Office. 1994—589-III/00003 

Region 10; 74 p. & Attachment A. 

Verts, B. J.; Carraway, L. N. 1998. Land mammals of Oregon. Berkeley, California: 

University of California Press; 668 p. 

Voth, E. H.; Maser, C.; Johnson, M. L. 1983. Food habits of Arborimus albipes, the whitefooted vole, in Oregon. Northwest Science 57: 1-7. 

Wells, R. W.; Trofymow, J. A. 1997. Coarse woody debris in chronosequences of forests 

on southern Vancouver Island. BC-X-375. Victoria, British Columbia: Natural 

Resources Council, Canadian Forestry Service, Pacific Forestry Centre; 35 p. 

Wick, H. L.; Fauss, D.; Zalunardo, R. 1985. Impacts on wood production. In: Brown, E. R., 

technical editor. Management of wildlife and fish habitats in forests of western Oregon 

and Washington. Part I—Chapter narratives. R-6-F&WL-192-1985. Portland, OR: 

USDA Forest Service; 307-313. 

Zar, J. H. 1984. Biostatistical analysis. 2nd ed. Englewood Cliffs, New Jersey: Prentice-Hall, 

Inc.; 718 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 347 

Stag Retention and Use by Arboreal 

Marsupials in Eucalypt Forests of 

Southeast Queensland, Australia: 

Implications for Management1

Damien Moloney,2 Kevin Wormington,3 and Stephen DeStefano4

Abstract 

Dead standing trees (“stags” in Australia) are critical for wildlife in forests throughout the 

world. Dynamics of stag recruitment and retention are an interaction of tree mortality, size, 

deterioration rate, human intervention, and variables related to the structure and physiognomy 

of the forest. Historically in Australia and elsewhere, timber management involved the 

removal of stags and resulted in additional stags being lost to fire and wind at greater rates 

than under “natural” conditions. The current status of stags and the relative importance of live 

versus dead trees to arboreal mammals were investigated on permanent inventory plots 

throughout southeast Queensland, Australia. Hollow development was correlated with rates of 

wood decay and time since death. Density of hollow-bearing trees was 10.2 + 0.2 stems per 

hectare (mean + SE); approximately 50 percent of the hollow-bearing trees were stags. 

Proportion of standing dead versus live trees was about 1:30. However, dead versus live tree 

use by arboreals was difficult to determine. Longevity of all stags was estimated to be 50 to 

100 years. Although live hollow-bearing trees are more important to hollow-using wildlife in 

Australia, stags may provide a significant additional hollow resource in managed stands. 

Adequate densities and distribution of both live hollow-bearing trees and stags are extremely 

important to forest wildlife communities in both Australia and North America. 

Introduction 

Over the last decade, countries around the world have been addressing the issue 

of ecological sustainable development. In 1992, Australia adopted a National 

Strategy for Sustainable Development, which promotes using, conserving, and 

enhancing the community’s resources so that ecological processes are maintained 

(Australian Forestry Council 1992). Since that time legislation has been enacted to 

further this goal, including comprehensive planning and assessment systems. 

The sound use and management of land, water, and native plants and animals is 

critical to the long-term productivity and profitability of forestry, the health of the 

environment, and the viability of rural communities. As such, sustainable natural 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Manager, Environmental Management and Conservation Branch, Maroochy Shire Council, P.O. Box 

76, Nambour, Queensland 4560, Australia (e-mail: moloney@maroochy.qld.gov.au) 3

 Post-graduate Student, Botany Department, The University of Queensland, Queensland, 4072, 

Australia. 

4

 Unit Leader and Associate Professor, U.S. Geological Survey, Massachusetts Cooperative Fish and 

Wildlife Research Unit, Holdsworth Natural Resources Center, University of Massachusetts, Amherst, 

MA 01003, USA. (e-mail: sdestef@forwild.umass.edu) 
Stag Use in Australia—Moloney, Wormington, and DeStefano 

348 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

resource management is one of the greatest challenges in the new century. Forest 

managers are continuously faced with the task of limiting pressures on forest 

resources (e.g., water and timber production, recreation, biodiversity) as human 

demands and community expectations increase, and the conservation of biodiversity 

in forests managed for timber is arguably one of the most complex and controversial 

management issues. In Australia, the National Forest Policy Statement commits 

governments and industry to develop management systems that cater effectively to 

the conservation of all indigenous species throughout their natural ranges. 

The forests of eastern Australia provide habitat for a wide assemblage of 

arboreal vertebrates (Ambrose 1982, Lamb and others 1998, Smith and Hume 1984, 

Smith and Lees 1998, Taylor and Savva 1988). Many of these species make 

extensive use of tree cavities, or hollows as they are called in Australia, for denning, 

roosting or nesting, including 42 percent of mammals, 21 percent of birds, and 28 

percent of reptiles and amphibians (Ambrose 1982, Saunders and others 1982). Loss 

of trees with hollows has been identified as the most significant cause of biodiversity 

reduction in timber production forests of eastern Australia (Lindenmayer and others 

1991a, Loyn 1985). Live trees selected to be retained in harvest areas because they 

contain hollows or future hollows are referred to as hollow-bearing or habitat trees 

(Lindenmayer and others 1991b). Dead standing treescalled snags in North 

America and stags in Australiacan also provide hollows for arboreal wildlife and 

may be selected for retention, but can be expected to decay and fall more rapidly than 

live hollow-bearing trees (Borsboom 1991a,b; Wormington and Lamb 1999). 

This paper is a collation of existing scientific knowledge of hollow use and 

habitat tree resources in southeast Queensland, Australia, production forests, 

compiled from a number of studies conducted over many years. We focus on the 

number and arrangement of habitat trees (including stags) required to support 

populations of hollow-dependent vertebrate species, particularly arboreal marsupials. 

Measurements of hollow trees made in permanent inventory plots within the 

production forests of southeast Queensland have provided baseline information for 

silvicultural prescriptions that address both sustainable timber production and the 

habitat requirements of hollow-dependent fauna. Our objectives are to introduce 

North Americans to the hollow-using terrestrial fauna of eastern Australia, describe 

the formation of hollows in Australian forests, quantify the abundance of both live 

hollow-bearing trees and stags, and discuss the relative importance of stags to 

arboreal marsupials in eucalypt forests of southeast Queensland. 

Study Area 

Surveys for hollow-bearing trees took place on state-owned forest lands in 

southeast Queensland, Australia. The major forest type was inland dry sclerophyll at 

elevations ranging from 50 to 500 meters. Dominant trees were lemon-scented gum 

(Corymbia citriodora), grey gum (Eucalyptus propinqua), brown, red, and pink 

bloodwood (Corymbia trachyphloia, C. gummifera, and C. intermedia), and broadleaved red, narrow-leaved red, and grey ironbark (Eucalyptus fibrosa, E. crebra, and 

E. siderophloia). Sites were often on well-drained soils with level to moderate slopes. 

Annual rainfall varied between 1 to 2 meters and fell mostly during the warmer 

months (October-April). Selective tree logging (i.e., harvest of trees above prescribed 

diameters) and treatment (i.e., killing by ringbarking or poison injection) of decayed 

and diseased trees were the dominant timber management practices in the region 
Stag Use in Australia—Moloney, Wormington, and DeStefano 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 349 

(Florence and others 1970, Queensland Forest Service 1992). Historically, stags were 

removed for safety and fire concerns (Crowe and others 1984). These practices, 

especially the treatment of decayed and diseased trees, are perceived to be the main 

cause of decrease in numbers of hollow-bearing trees. 

Methods 

Over the last 50 years, the Queensland Department of Primary Industries, 

Forestry Division, has established a series of permanent survey plots in native 

hardwood forests to determine individual tree and forest stand growth rates, as well 

as other parameters. These plots are located in commercial forests and are managed 

no differently from the surrounding forest. Periodic measurements (approximately 

every 5 years) have provided data to calculate periodic annual increment (PAI) of 

diameter at breast height (DBH); PAI of species can be used to estimate the age of 

individual trees in the plots. Stand tables and frequency distributions of hollowbearing live trees and stags were compiled from plot measurement data. Plots were 

grouped by rainfall, soils, geographical location, species mix, stand productivity, 

harvesting regime, and silvicultural management history. 

In southeast Queensland, 294 permanent plots within 86 state forests, covering a 

broad range of forest types and totaling 137 ha, were surveyed for habitat trees and 

arboreal mammals (Ross 1998). We defined a habitat tree as any tree, either alive or 

dead (i.e., stag), having at least one visible hollow with an entrance diameter >10 

centimeters. As many animals use hollows with openings <10 centimeters, our 

estimate of habitat tree density is conservative. Plots were surveyed for number of 

live and dead habitat trees. Densities of live and dead habitat trees were calculated 

from counts on permanent plots, and age was estimated by the PAI and DBH of each 

tree species. In addition, stags >3 m in height were measured and number of hollows 

were counted in trees >30 centimeters DBH (Ross 1998). We report means and 

standard errors for tree and stag densities, measurements, and ages. 

At an additional 38 sites in southeast Queensland, surveys for nocturnal arboreal 

mammals were conducted at night on 1-km transect lines running through permanent 

plots wherever possible. Twenty of these transects were close to or passed through 20 

of the 294 permanent plots. At pre-designated stations, located every 25 meters along 

transect lines, surveyors waited quietly for about 3 min., and then used a portable 

spotlight to search the canopy for arboreal marsupials. Living and dead 

hollow-bearing trees within 30 m of the transect were counted to obtain density of 

hollow-bearing trees. Other habitat data (e.g., forest type, basal area) were obtained 

from three 0.25-hectare plots on each transect.5

Results 

Current Status of Hollow Trees 

Of 294 permanent plots surveyed, 242 (82 percent) contained hollow-bearing 

stems (Ross 1998). Hollow-bearing trees occurred at a mean density of 10.2 + 0.2 

stems per hectare across all forest types, with about 50 percent being stags (table 1).

 

5

 Unpublished data on file at The University of Queensland, Brisbane, Queensland, Austrialia. 
Stag Use in Australia—Moloney, Wormington, and DeStefano 

350 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

For trees >30 centimeters DBH, 12 percent of live trees and 93 percent of stags had 

hollows. 

Table 1Densities (mean + standard error) of live and dead (i.e., stags) trees >10 

centimeters diameter at breast height on permanent plots located on commercial forest lands 

in southeastern Australia. Habitat trees are any tree having at least one visible hollow with 

an entrance diameter >10 centimeters in size (adapted from Ross 1998). 

 Live trees Stags Total 

Total stems per ha 2501 8.21 258.21

Hollow-bearing stems per ha 5.7 + 0.3 4.4 + 0.2 10.2 + 0.2 

Habitat trees per ha 2.4 + 0.2 3.0 + 0.2 5.5 + 0.2 

1 Standard error (SE) was not provided by Ross (1998). 

The proportion of hollow-bearing stems in a given size class increased with 

increasing DBH: 4 percent of trees 30-39 centimeters DBH had hollows, whereas 70 

percent of trees 40-90 centimeters DBH contained hollows. These larger trees 

contained many more hollows on average than smaller trees, and many of these 

hollows had larger entrance diameters. In general, live stems bore an average of 2.2 

hollows overall (all hollows), with an average of 1.0 hollow per tree for entrance 

diameters >10 centimeters (Ross 1998). Stags averaged 2.8 hollows per stem, with 

1.4 hollows per stem for entrance diameters >10 centimeters. 

Hollow-bearing trees represented 42 species, the majority being eucalypts or 

closely related genera. Hollow development appeared to be species dependent, with 

some species developing hollows earlier in life (i.e., those species more prone to limb 

breakage) (Wormington and Lamb 1999). No difference was found in the rate of 

hollow development within forest types (Ross 1998). Hollow development was 

correlated with rates of wood decay and time since death. 

The majority of permanent plots were altered by selective logging, where larger 

merchantable trees were removed, in addition to treatments that removed a small 

number of “healthy” (i.e., no deformities) trees and killed most older hollow-bearing 

trees. Thus stocking rates of stags increased with increasing level of disturbance. 

Undisturbed stands had a mean stag density of 4.4 stems per hectare, but stands with 

three to four logging and/or treatment events had 7.4 stags per hectare. In essence, 

stags comprised 27 percent of the total tree hollow compliment in undisturbed stands 

as compared to 68 percent in intensively managed stands. 

Ross (1998) examined 660 standing dead trees in the permanent plots. The 

majority of deaths (about two-thirds) were attributed to natural causes (e.g., 

senescence, wind, fire, drought, or lightning) or silvicultural treatment (about onethird), with the density of treated stags correlated positively with treatment. The 

effect of silvicultural treatment at our 38 survey sites was to lower the total number 

of hollow-bearing trees from 14 to 6 per hectare and change the ratio of stags to live 

hollow-bearing trees from 1:4 to 2:1.5
Stag Use in Australia—Moloney, Wormington, and DeStefano 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 351 

Survey of Arboreal Mammals 

Six species of arboreal marsupials were detected in the dry sclerophyll forests of 

southeast Queensland: common brushtail possum (Trichosurus vulpecula), greater 

glider (Petauroides volans), yellow-bellied glider (Petaurus australis), sugar glider 

(P. breviceps), squirrel glider (P. norfolcensis), and feathertail glider (Acrobates 

pygmaeus). Species diversity and abundance were most dependent upon forest type, 

but a minimum of four hollow-bearing trees per hectare was also required before all 

species of arboreal marsupials were detected along a transect at any site. Most sites 

(22 of 38) contained <2 live hollow-bearing trees per hectare (some contained none), 

with the majority of hollow-bearing trees being stags. The sites that contained low 

numbers of live hollow-bearing trees were often the sites with other attributes (e.g., 

preferred tree species, higher leaf nutrient levels and forest productivity) most suited 

to arboreal marsupials (i.e., good site characteristics except for low numbers of 

habitat trees).5

Discussion 

In Queensland, at least 13 species of arboreal and scansorial mammals, 63 

species of birds, 23 species of bats, and 35 species of herptiles may either utilize or 

be dependent on hollows (Queensland Department of Natural Resources 1998, Smith 

and Lees 1998). Hollow-dependent fauna are defined as species that rely 

predominantly (i.e., >50 percent of the time) on tree hollows for shelter, roosting, or 

nesting at some stage in their life cycle. Three broad guilds of hollow-dependent 

fauna are recognized in Queensland (Lamb and others 1998). Group 1, which are 

evenly spaced, territorial species with small or medium daily home ranges and 

require moderate to high densities (2-12 per hectare) of habitat trees, include 

mammals such as gliders (Petaurus spp. and other genera) and possums 

(Pseudocheirus spp. and Trichosurus spp.) and birds such as treecreepers 

(Climacteris spp., Cormobates leucophaea), kingfishers (Todriamphus spp., Syma 

torotoro), kookaburras (Dacelo spp.), rosellas (Platycercus spp.), many genera of 

parrots, and several other species. Group 2 are non-territorial species that breed or 

roost in clusters and include lorikeets (Trichoglossus spp. and others), several 

additional species of birds, and 28 species of bats. These species require low to high 

densities of habitat trees, but these trees may be clustered or distributed unevenly. 

Group 3 are large territorial species with large home ranges, such as cockatoos 

(Calyptorhynchus spp. and others), several species of owl, and the lace monitor 

(Varanus varius). These large-bodied animals require very large trees with very large 

hollows, but these trees may be at low densities. 

Specific information on the hollow requirements for most Australian species is 

lacking, and only limited empirical data are available on the density and spacing of 

habitat trees required by hollow-dependent fauna. As a group, the arboreal marsupials 

have been the most extensively studied. Estimates for numbers of habitat trees 

required to sustain populations of arboreal hollow-dependent mammals in southeast 

Queensland are wide ranging (<1-48 per hectare). However, based on our analyses, 

we recommend an average of five to eight habitat trees per hectare, which is a 

reasonable general management goal and follows Lamb and others (1998). They 

recommended 8-12 habitat trees per hectare to maintain natural densities of hollow 

users, with at least half that (i.e., 4-6 per hectare) providing an appropriate 
Stag Use in Australia—Moloney, Wormington, and DeStefano 

352 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

compromise for sustaining populations of hollow-dependent fauna in logged forests, 

though probably below natural densities. 

Eyre (1993) and Eyre and Smith (1997) found that yellow-bellied gliders used 

only one dead standing tree as a den site, as compared with 44 live habitat trees. In 

contrast, a site in this study that contained very few live hollow-bearing trees had a 

high abundance of all six species of arboreal marsupials (common brush-tail possum 

and greater, yellow-bellied, squirrel, sugar, and feathertail gliders). All species except 

the feathertail glider were observed to use stags regularly for denning.5

 Silvicultural 

treatments such as ringbarking or poison injection can increase numbers of stags, as 

was evidenced on some of our plots that had higher levels of disturbance, but stag 

longevity is lower than that of live hollow-bearing trees. Thus, the retention of treated 

stags provided a significant hollow resource in altered areas, but with the caveat that 

stags are more susceptible to fire, wind, and other disturbances and their longevity is 

far less than live hollow trees. 

Dynamics of natural stag retention is an interaction of tree mortality, stag size, 

stag deterioration rate, site conditions, and other variables (Cline and others 1980, 

Raphael and Morrison 1987). In North America, the cavity formation process often 

involves the activities of primary excavators (woodpeckers, family Picidae) (Conner 

and others 1976, Mannan and others 1980, Raphael and White 1984). In Australia, 

however, primary excavator species do not exist, and hollow development in 

commercially important gum forests is an interaction involving mechanical process 

(e.g., limb breakage, fire scars), fungal infections, and termite activity (Mackowski 

1984, Saunders and others 1982, Wilkes 1982, Wormington and Lamb 1999). The 

process of hollow formation and the relative importance of live versus standing dead 

trees is thus a dynamic process dependent on several variables, and differs between 

Australia and North America, at least with regard to primary cavity excavators. 

However, Waters and others (1990) reported that nonexcavated hollows (i.e., those 

formed by limb breakage and decay rather than woodpeckers) were more common in 

oaks (Quercus spp.) than digger pines (Pinus sabiniana) in California; hollows in 

pines were exclusively the work of excavators. Thus, hollow formation in North 

American hardwoods is probably similar to hollow formation in Australian 

hardwoods. Nonetheless, adequate densities and distribution of hollow-bearing trees 

and stags is extremely important to forest wildlife communities on both continents. 

One of the challenges in managing stags is determining not only how many 

stags should be on an area, but in what kinds of distributions (i.e., uniform, scattered, 

clumped). Different wildlife species not only require different sized stags and 

hollows, but often different distributions, as noted previously in this discussion. A 

management program for stags on either continent will be a multifaceted problem, 

involving a diversity of sizes of stags and hollows distributed across the landscape in 

a variety of patterns. Clearly, thorough knowledge of the life history requirements for 

the diversity of species involved is a prerequisite. 

The current status of hollow-bearing trees in production forests throughout 

southeast Queensland is determined largely by past silvicultural management. On our 

plots, the development and abundance of tree hollows was related to stem size and 

estimated age. Depending on the species, trees need to reach 145 to >200 years of age 

to provide adequate hollows, with older trees corresponding to larger hollows 

(Wormington and Lamb 1999). Recent analyses indicate an overall depletion of the 

hollow tree resource in native production forests (Ross 1998). 
Stag Use in Australia—Moloney, Wormington, and DeStefano 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 353 

The government of Queensland is required to provide a “Code of Environmental 

Practice for Native Forest Timber Production,” which includes the retention of 

habitat trees (Lamb and others 1998). The Technical Advisory Group that was 

assembled to address management issues pertinent to retention of habitat trees in 

native forests of Queensland acknowledged that stags were more susceptible to fire 

and wind-throw than live trees, but did recognize the importance of stags to wildlife. 

The advisory group recommended that stags be retained unless there were compelling 

safety or fire management reasons to remove them. Not only does this benefit 

wildlife, but assists in restoring the multiple functions that dead wood provides to 

forest ecosystems, including associations with invertebrate and fungi diversity and 

the role dead wood plays in carbon pathways and recycling of nutrients. 

Loss of stags is only part of the concern, however. Loss of forest habitat is 

probably the greatest concern in Queensland. Over 400,000 ha of native forest cover 

is currently being cleared per annum. In most cases this is for agriculture and urban 

expansion, but vast areas have been converted to plantations, particularly exotic 

pines. The problem has been further compounded by fragmentation of forest cover 

and edge effects, i.e., where remnant forest exists between exotic or native 

plantations. These edges are often exposed when the plantation is felled, leading to 

additional loss of stags to wind throw. Also, the remnant areas are burnt quite 

regularly to protect the commercial plantation, leading to increased loss of stags. 

The information we present is incomplete and clearly preliminary concerning 

the requirements of hollow-dependent fauna in Queensland forests. Silvicultural 

practices have the potential to remove or destroy hollow-bearing trees, leaving 

insufficient younger trees to replace the losses and thereby modifying forest 

microhabitats, possibly to the detriment of hollow-dependent fauna. Many other 

parameters, such as alteration of forest structure and composition, successional age, 

and fire regimes can affect the distribution and abundance of habitat trees, 

particularly stags. In addition, management recommendations for the retention of 

habitat trees should be in accordance with the assemblage of hollow-dependent fauna 

expected to occur on a particular site or forest type (as requirements vary among 

species), and not applied uniformly across the landscape. The maintenance of forest 

biodiversity, particularly hollow-dependent fauna, must be undertaken as part of an 

integrated strategy that includes consideration of the full range of wildlife habitat 

requirements such as the structure and composition of the forest matrix resulting 

from timber harvesting and other disturbances. Because the process of hollow 

development takes a considerable period of time (Mackowski 1984, Wormington and 

Lamb 1999) and hollows are more prevalent and larger in large trees, it is important 

that long term considerations be made to ensure a perpetual supply of hollow-bearing 

trees for hollow-dependent fauna (Gibbons and Lindenmayer 1996). 

Acknowledgments 

We appreciate critical reviews of this manuscript by Drs. David Lamb, William 

F. Laudenslayer, Jr., and R. William Mannan, and the efforts of the Queensland 

Departments of Primary Industry (Forestry) and Natural Resources in collecting, 

collating, analyzing, and publishing such important data. 
Stag Use in Australia—Moloney, Wormington, and DeStefano 

354 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

References 

Ambrose, G. J. 1982. An ecological and behavioural study of vertebrates using hollows in 

eucalypt branches. Bundoora, Victoria, Australia: La Trobe University: 435 p. Ph.D. 

dissertation. 

Australian Forestry Council. 1992. National forest policy statement: a new focus for 

Australia's forests. Canberra: Commonwealth of Australia; 52 p. 

Borsboom, A. 1991a. Commonwealth funded, joint management, wildlife research 

program for the Conondale Ranges of southeastern Queensland, section A: 

senescent tree survey. Brisbane, Queensland, Australia: Consultancy Report, 

Department of Primary Industries; 9 p. 

Borsboom, A. 1991b. Commonwealth funded, joint management, wildlife research 

program for the Conondale Ranges of southeastern Queensland, section B: habitat 

tree census of the major forest types in the Conondale Ranges. Brisbane, 

Queensland, Australia: Consultancy Report, Department of Primary Industries; 9 p. 

Cline, S. P.; Berg, A. B.; Wight, H. M. 1980. Snag characteristics and dynamics in 

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44: 773-786. 

Conner, R. N.; Miller, O. K., Jr.; Adkisson, C. S. 1976. Woodpecker dependence on trees 

infected by fungal heart rots. Wilson Bulletin 88: 575-581. 

Crowe, M. P.; Paxton, J.; Tyers, G. 1984. Felling dead trees with explosives. Australian 

Forestry 47: 84-89. 

Eyre, T. 1993. Distribution, habitat and conservation status of the Yellow-bellied Glider 

Petaurus australis in Southern Queensland. Brisbane, Queensland, Australia: 

Queensland Department of Primary Industries; 112 p. 

Eyre, T. J.; Smith, A. P. 1997. Floristic and structural habitat preferences of 

yellow-bellied gliders (Petaurus australis) and selective logging impacts in southeast 

Queensland, Australia. Forest Ecology and Management 98: 281-285. 

Florence, R. G.; Shea, G. M.; Pegg, R. E. 1970. Development of a logging schedule for 

spotted gum (Eucalyptus maculata) forest. Commonwealth Forestry Review 49: 235-

244. 

Gibbons, P.; Lindenmayer, D. B. 1996. Issues associated with the retention of hollowbearing trees within eucalypt forests managed for wood production. Forest Ecology 

and Management 83: 245-279. 

Lamb, D.; Loyn, R.; Smith, A.; Wilkinson, G. 1998. Managing habitat trees in Queensland 

forests. Brisbane, Queensland, Australia: Queensland Department of Natural Resources, 

Forest Resources; 62 p. 

Lindenmayer, D. B.; Cunningham, R. B.; Tanton, M. T.; Nix, H. A.; Smith, A. P. 1991a. The 

conservation of arboreal marsupials in the montane forests of the Central 

Highlands of Victoria, South-East Australia: III. The habitat requirements of 

leadbeater’s possum Gymnobelideus leadbeateri and models of the diversity and 

abundance of arboreal marsupials. Biological Conservation 56: 295-315. 

Lindenmayer, D. B.; Cunningham, R. B.; Tanton, M. T.; Smith, A. P.; Nix, H. A. 1991b. 

Characteristics of hollow-bearing trees occupied by arboreal marsupials in the 

montane ash forests of the central highlands of Victoria, south-eastern Australia.

Forest Ecology and Management 40: 289-308. 

Loyn, R. F. H. 1985. Strategies for conserving wildlife in commercially productive 

eucalypt forest. Australian Forestry 48: 95-101. 
Stag Use in Australia—Moloney, Wormington, and DeStefano 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 355 

Mackowski, C. M. 1984. The ontogeny of hollows in blackbutt (Eucalyptus pilularis) and 

its relevance to the management of forests for possums, gliders and timber. In: 

Smith, A. P.; Hume, I. D., eds. Possums and gliders. Sydney: Surrey Beatty & Sons; 

553-567. 

Mannan, R. W.; Meslow, E. C.; Wight, H. M. 1980. Use of snags by birds in Douglas-fir 

forests, western Oregon. Journal of Wildlife Management 44: 787-797. 

Queensland Department of Natural Resources. 1998. Code of Practice for native forest 

timber production. Brisbane Queensland, Australia: Queensland Department of Natural 

Resources; 96 p. 

Queensland Forest Service. 1992. Harvesting, marketing and resource manual, Vol 3.

Brisbane, Queensland, Australia: Department of Primary Industries; 21 p. 

Raphael, M. G.; Morrison, M. L. 1987. Decay and dynamics of snags in the Sierra Nevada, 

California. Forest Science 33: 774-783. 

Raphael, M. G.; White, M. 1984. Use of snags by cavity-nesting birds in the Sierra 

Nevada. Wildlife Monograph 86; 66 p. 

Ross, Y. 1998. Hollow-bearing trees in permanent plots in south-east Queensland.

Brisbane, Queensland, Australia: Sustainable forest management technical report, 

Resources Science and Knowledge, Department of Natural Resources; 1-18 p. 

Saunders, D. A.; Smith, G. T.; Rowley, I. 1982. The availability and dimensions of tree 

hollows that provide nest sites for cockatoos (Psittaciformes) in western Australia. 

Australian Wildlife Research 9: 541-556. 

Smith, A. P.; Hume, I. D., eds. 1984. Possums and gliders. Sydney: Australian Mammal 

Society. 598 p. 

Smith, G.; Lees, N. 1998. Density and distribution of habitat trees required to support 

viable populations of hollow-dependent species. Brisbane, Queensland, Australia: 

Sustainable forest management technical report, Resources Science and Knowledge, 

Department of Natural Resources; 19-74 p. 

Taylor, R. J.; Savva, N. M. 1988. Use of roost sites by four species of bats in State Forest 

in south-eastern Tasmania. Australian Wildlife Research 15: 637-645. 

Waters, J. R.; Noon, B. R.; Verner, J. 1990. Lack of nest site limitation in a cavity-nesting 

bird community. Journal of Wildlife Management 54: 239-245. 

Wilkes, J. 1982. Stem decay in deciduous hardwoodsan overview. Australian Forestry 

45: 42-50. 

Wormington, K.; Lamb, D. 1999. Tree hollow development in wet and dry sclerophyll 

eucalypt forest in south-east Queensland, Australia. Australian Forestry 62: 336-345. 
Importance to Soils and Other 

Forest Resources

357
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 359 

Fire as a Coarse Filter for Snags and Logs1

James K. Agee2

Abstract 

Fire played an important role in maintaining and creating conditions suitable for native flora 

and fauna in the forests of western North America. Recent coarse filter conservation strategies 

have advocated creating future landscapes that incorporate historic or natural ranges of 

variability, including fire regimes. Historic fire regimes were variable across the West, and 

created quite unique coarse woody debris dynamics in low-, mixed-, and high-severity fire 

regimes. Moving towards more historic landscape structures will require variable standards 

for coarse woody debris retention. 

Introduction 

Fire has been the most pervasive natural disturbance factor across western forest 

landscapes (Barnes and others 1998), but it did not work independently of other 

disturbances. Fire has had both local and broad scale effects on the forests of western 

North America (Agee 1993), but these effects differ considerably by fire regime. For 

many decades, foresters, ecologists, and others neglected the contribution of dead 

wood to biodiversity in the forest. In a typical interior West forest, about two-thirds 

of the birds and up to 90 percent of the small mammals, reptiles, and amphibians 

utilize dead wood for cover, roosting, or foraging for food (Thomas 1979). The dead 

wood can be snags (standing dead trees) or logs (dead trees or portions of them lying 

on the ground). 

The concept of ecosystem ranges of variability (Morgan and others 1994) has 

been suggested as a framework for coarse filter conservation strategies (Hunter 

1990). A coarse filter conservation strategy seeks to preserve biological diversity by 

maintaining a variety of naturally-functioning ecosystems across the landscape. If it 

is possible to produce or mimic the historic ranges in stand size, composition, and 

connectivity by forest type on current and future landscapes, then much of the habitat 

for native flora and fauna might well be present. Mimicking the historic ranges of 

coarse woody debris should also help these conservation strategies. Fine-filter 

strategies, such as individual species plans or snag retention, might still be needed, 

but most species and ecosystem elements should be present if natural ranges in 

habitat are provided (Haufler and others 1996). Although coarse woody debris is an 

important structural component of forest ecosystems, managing for maximization of 

coarse woody debris, or having uniform standards across historically variable 

landscapes, is a fine-filter strategy that can literally backfire. The use of coarse 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Professor, College of Forest Resources, Box 352100, University of Washington, Seattle, Washington 

98195 (e-mail: jagee@u.washington.edu) 
Fire as a Coarse Filter—Agee 

360 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

woody debris levels characteristic of historical disturbance regimes is recommended 

as an alternate system more likely to be sustainable (Edmonds and Marra 1999). 

The Historical Fire Regime 

Natural disturbances range from benign to severe and can be generated from 

within or outside of the ecosystem (White 1987). The disturbance effects in either 

case are due in part to current pattern or structure and to the nature of the disturbance. 

Disturbance is usually characterized by a combination of factors: type, frequency, 

variability, magnitude, extent, seasonality, and synergism with other disturbances 

(White and Pickett 1985). The fire regimes of western forests are usually described in 

terms of historical fires (defined here as pre-European settlement). They are 

interpreted much the same way as potential vegetation (Daubenmire 1968), namely 

what occurred historically and what the trajectories of change may be with or without 

management (Agee 1993). The effect of Native Americans on fire ignitions is 

inextricably confounded with lightning ignitions, and the historical fire regime 

therefore includes native ignitions. 

Fire regimes based on fire severity (Agee 1993) are defined by effects on 

dominant organisms, such as trees, and, although broadly described in three classes, 

can be disaggregated to the forest type or plant association level if desired. The 

historical high-severity fire regimes were those in which the effect of a fire was 

usually a stand replacement event. Fire return intervals were generally 100 or more 

yrs. The mixed-severity fire regimes had a complex mix of severity levels, with fire 

return intervals usually 25 to 75 yrs. The low-severity fire regimes were those in 

which the typical fire was benign to dominant organisms across much of the area it 

burned, and fire return intervals were generally 5 to 25 yrs. The Interior Columbia 

Basin Ecosystem Management Project (ICBEMP) has the synonymous fire regimes 

of lethal, mixed, and nonlethal, respectively (Quigley and others 1996). Because 

landscape ecology varied widely across the forest landscapes of western North 

America (fig. 1), coarse-filter conservation strategies, including attention to coarse 

woody debris, should recognize that variability. 

The Low-Severity (Nonlethal) Fire Regimes 

Low-severity fire regimes typically had large fires (Wright 1996) but small 

patch sizes. Fires burned frequently in these forests (Agee 1993), and by regularly 

consuming fuels, killing small trees, and pruning the boles of residual trees, 

maintained a relatively fire-resistant landscape. Forests with significant components 

of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) had very small patch sizes, 

ranging from 0.02 to 0.35 ha (Agee 1998b, Bonnicksen and Stone 1981, Cooper 

1960, Morrow 1985, West 1969, White 1985), due to group kill of pines by bark 

beetles (Dendroctonus spp.), or perhaps root disease pockets, and subsequent 

consumption of the debris by several fires. Because these dead patches were small 

and limited in extent, patch edge was also limited. Most of the forest was a fairly 

uniform mosaic of mature tree clusters and grassy understories. 

Before getting carried away by the idyllic vision of an equilibrium forest, it is 

important to note that exceptions did occur, even in ponderosa pine forests. 

Defoliation by pine butterfly (Neophasia menapia [Felder and Felder]) created much 

larger patches, at least in some areas of south-central Washington (Weaver 1961), 
Fire as a Coarse Filter—Agee 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 361 

and the Black Hills of South Dakota had pine stands that appear to have had less 

frequent but more severe fires, and much larger patch sizes (Shinneman and Baker 

1997). These latter stands are transitional to boreal forest, containing some white 

spruce (Picea glauca [Moench] Voss). Clearly, though, the wide range of studies in 

low-severity fire regimes support the notion of an equilibrium system, including at 

least some of the Black Hills (Shinneman and Baker 1997). 

Figure 1—A schematic landscape pattern of fire regimes. Black dots in low-severity 

fire regimes are very old patches of large, old trees being killed by insects and 

decomposed by fire, and gray dots are emerging small-sized stands that have lessdefined edge with older forest than the recently killed patches. The mixed-severity fire 

regime is typically a complex mosaic of larger patches of the three fire severity levels, 

while the high-severity fire regime has large, stand replacement patches (Agee 

1998b). 

As individual tree clusters became senescent, they would be attacked by bark 

beetles, creating a patch of coarse woody debris that would be consumed by the next 

several fires passing under the forest. Coarse woody debris under such a regime, both 

snags and logs, would have been limited and clustered. Over the landscape was a 

highly connected system of older forest, dotted with regenerating patches and clusters 

of coarse woody debris. 

For example, a small set of stands in an eastern Cascades mixed-conifer forest 

might be divided into 16 age classes (patches), each separated from the next by 25 

years so that the age range covers 400 years. Each is 0.1 ha in size, and every 25 

years, pine beetles attack the oldest stand and group-kill it. Every 10 years fires 

underburn through the stands. Most thinning occurs when stands are young, so that 

little substantial snag component is produced except in the beetle-killed patches. Tree 

density averaged 50 to 60 trees ha-1 in historic Pinus ponderosa and Pseudotsuga 

menziesii ([Mirb.] Franco) forest series in the eastern Cascades (Agee 1998a, Harrod 

and others 1999). Therefore, six trees per 0.1 ha were used as the average tree density 

of an individual patch. 

Fires will help to decompose a snag patch by consuming the woody debris, and 

in this example it will be assumed that after five fire events (50 years) the snags are 
Fire as a Coarse Filter—Agee 

362 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

completely burned down. At any time in this scenario, there is one fresh snag patch 

(0 to 25 yrs) and one patch in advanced “decay” (25 to 50 yrs). Harrington (1996) 

found about 80 percent of fire-killed small ponderosa pine fell in less than 10 years; 

thus, an assumption that a fresh snag patch will have six large, old trees and a 

decaying patch (25 to 50 yrs) two trees appears reasonable, if perhaps a bit on the 

high (conservative) side. Therefore, on our landscape of 1.6 ha, composed of sixteen 

0.1 ha patches, we have at any one time about eight snags. This is equivalent to 500 

snags 100 ha-1 (about 200 100 ac-1) and would constitute a sustainable snag density 

over time in the natural forest. Harrod and others (1998) estimated higher densities of 

1,457 to 3,483 100 ha-1 (590 to 1,410 100 ac-1) but assumed snags would fall on their 

own rather than fall being accelerated by fire. 

Logs will be a limited resource in this scenario, as they are clustered in the snag 

patches and the concentration aids ignition and consumption of the logs. Just as the 

snags were spatially dynamic, logs were as well, but probably had a shorter residence 

time than the snags because of their proximity to the recurring surface fires. If we 

assume that the average tree size in the mature clumps was about 75 cm dbh, then 

snag biomass would have totaled about 8.1 Mg ha-1, and log biomass somewhat less 

than 5 Mg ha-1 for the frequently burned low-severity fire regime. 

The Mixed-Severity (Moderate) Fire Regimes 

Mixed-severity fire regimes had larger patch sizes and considerable edge (fig. 

1). These fires maintained both a naturally fragmented forest structure and fuel 

structure. Patch size in the mixed-severity fire regimes is typically larger than for the 

low-severity fire regimes. Patch size for mixed-severity forests (including some drier 

westside Cascade forests) ranges from 2.5 to 250 ha (Agee 1998b). Patch edge is 

typically much higher for mixed-severity fire regimes than for high-severity fire 

regimes (although the methods for defining a patch will significantly influence any 

edge metric). The result, both from fire and other disturbances, was considerable 

local-scale patchiness on the landscape (Taylor and Halpern 1991). Patches burned 

with light fires had surface fuels removed and only understory trees killed. Patches 

burned with higher intensity fires had some overstory removed (similar to the first 

entry on a shelterwood) and resulted in a favorable environment for regeneration of a 

new age class of trees (generally shade-tolerant species: white fir [Abies concolor 

{Gord. and Glend.} Hildebr.] or grand fir [Abies grandis {Dougl. ex D. Don} Lindl.], 

Douglas-fir [on dry sites], red fir [Abies magnifica A. Murr.], and/or sugar pine 

[Pinus lambertiana Dougl.]). Patches burned with very high intensity within the 

mixed-severity fire regime had all the overstory killed and created an environment 

for shrubfields or new shade-intolerant tree species (typically western larch (Larix 

occidentalis Nutt.) or lodgepole pine (Pinus contorta Dougl.) (Antos and Habeck 

1981, Cobb 1988). Landscape position in part explains differential severity: lower 

slope positions had the least amount of severe fire, while upper slopes, particularly of 

west or south aspect, and ridgetops experienced more severe fire (Taylor and Skinner 

1998). 

Coarse woody debris dynamics were quite complex in the mixed-severity fire 

regimes (Agee 1993). Periodic fires consumed log biomass, and in underburned 

patches, coarse woody debris would decrease. In the patches where either thinning or 

stand-replacement fire occurred, some log consumption occurred, but snags were also 

created. A net increase, or pulse, of coarse woody debris was likely after a typical fire 

event. Decomposition would decrease woody debris loads over time, but 
Fire as a Coarse Filter—Agee 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 363 

replenishment would occur from the periodic fires at 25- to 100-year intervals. Data 

from Wright (1998) showed for a mixed-severity fire regime in Douglas-fir about 40 

Mg ha-1 in snags and 55 Mg ha-1 in logs, with the totals varying among stands from 

20-250 Mg ha-1. Because this fire regime has low-, moderate-, and high-severity 

patches closely mixed, these levels would probably serve as an integrated average 

level of coarse woody debris across the variety of patch types and sizes in this fire 

regime. 

The High-Severity (Lethal) Fire Regimes 

Disturbance events in high-severity fire regimes often have large patch sizes 

(fig. 1). Although the large majority of fires historically remained quite small, the 

vast majority of area affected by fire is from the few large events that cover 

thousands of hectares (Bessie and Johnson 1995, Romme 1982, Romme and Despain 

1989). Small fires tend to have little edge, while larger events tend to be more patchy 

and leave more residual islands (unburned stringers) (Eberhart and Woodard 1987). 

Generally, the edge created in the high-severity fire regimes is less than in the mixedseverity fire regimes (Agee 1998b). 

The distribution of stand ages in the high-severity fire regimes is not clear. Even 

if an assumption about the nature of disturbance allows a fit of age classes to a 

distribution such as the Weibull or negative exponential, there are still assumptions 

about long-term stability (e.g., stable climate over centuries) that may alter the age 

class structure. Several characteristics of the high-severity fire regimes of western 

forests are unquestionable: the fire return intervals were long (usually >100 yrs); 

some stand ages exceed the average fire return interval, suggesting that either the 

concept of “refugia” (Camp and others 1997) or just random chance are operating; 

and fires often impose a new landscape mosaic by burning stands of various ages 

(Bessie and Johnson 1995). 

Coarse woody debris dynamics in the high-severity fire regimes typically 

followed a “boom and bust” cycle (Agee and Huff 1987, Spies and others 1988). 

After a large fire event, coarse woody debris was at a high, as the live trees were all 

converted to snags and then logs (fig. 2). As the new stand developed, the coarse 

woody debris levels dropped as the fire-created material slowly decomposed, and 

snags created by self-thinning of the new stand were too small to add much volume. 

In mid-succession, perhaps 100 to 200 years, severe thinning by disease and insects 

could create pulses of coarse woody debris, and as succession proceeded these levels 

slowly increased by additions of individual trees. Wright (1998), working in highseverity Douglas-fir forests of the Oregon Cascades, showed an average of 150 Mg 

ha-1 in stands generally 200 years post-fire and older. Agee and Huff (1987) showed 

the variability over a chronosequence in moist western hemlock (Tsuga heterophylla

[Raf] Sarg) Douglas-fir forest (table 1). 
Fire as a Coarse Filter—Agee 

364 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 2—Trends in variation in coarse woody debris loads in high-severity fire 

regimes in moist western hemlock/Douglas-fir forest, Olympic Mountains, 

Washington (Agee and Huff 1987). 

Table 1—Coarse woody debris loads over a 500-year chronosequence in western hemlock 

forest in the Olympic Mountains, Washington (Agee and Huff 1987). This is a high-severity 

fire regime. 

Type of coarse woody debris Post-fire stand age (years) 

 1 3 20 100 180 500 

 ————————mg ha-1———————— 

Snags 775 1,066 279 35 33 84 

Logs 282 230 438 118 112 441 

Total 1,057 1,296 717 153 145 525 

Coarse Filter Implications 

The examples of coarse woody debris dynamics discussed imply quite unique 

amounts and patterns among the low-, mixed-, and high-severity fire regimes (fig. 3).

The low-severity fire regime had quite low biomass with minor fluctuations; the 

mixed-severity fire regime had higher loads on a sustainable basis but more 

fluctuation in levels over time; and the high-severity fire regimes had the highest 

loading, and substantial fluctuation over time. Coarse woody debris standards, if they 

are to mimic the natural forest, must be designed to fit the forest to which they are 

applied. 
Fire as a Coarse Filter—Agee 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 365 

Figure 3—A model of coarse woody debris dynamics in low-severity, mixed-severity, 

and high-severity fire regimes in western forests. Average amounts of coarse woody 

debris and fluctuations vary by fire regime. 

Natural processes such as fire can be restored to create ecologically sustainable 

forests (e.g., Dale and others 1999) only if coarse woody debris standards are tailored 

to the forest type and historic fire regime. For example, in a mixed conifer forest with 

a historic low-severity fire regime, prescribed fire in either spring or fall (fig. 4) will 

substantially reduce coarse woody debris. Residual coarse woody debris loads in this 

example were about 40 Mg ha-1 (Thomas and Agee 1986), still well above the levels 

of historic forests with a similar historic fire regime. Burning prescriptions designed 

to retain most coarse woody debris can produce a “non-window”: duff moisture 

levels so high that such moisture contents are rarely if ever attained on these sites. 

Constraints to preserve all or most coarse woody debris effectively eliminate the use 

of fire for restoration purposes and leave the dry forest types at risk for standreplacing fire. When such high-severity fire occurs, it brings with it the “boom and 

bust” coarse woody debris dynamics of the high severity fire regimes. This is a 

classic case of the fine-filter (log preservation) trumping the coarse-filter (restoring 

the natural process), and in the long run is likely to result in a failed conservation 

strategy (Agee 1999). 

Unfortunately, few coarse-filters can be successful on their own. We can 

reintroduce the friendly flame, but in many western forests the historic structure is 

gone: too few large trees, too many little ones, and substantial time before new large 

coarse woody debris will be produced. Today many species are at the brink of 

extinction so that natural processes like fire, reintroduced at historic levels in a 

damaged ecosystem, may be inappropriate. The role of fire as a coarse-filter 

conservation strategy (Agee 1999) cannot be blindly applied as a “natural” solution; 

it will have to come in many shapes and sizes. However, understanding the historic 

role of fire will provide a template for designing appropriate coarse woody debris 

loads in our western forest landscapes. Levels of coarse woody debris, as well as 

temporal and spatial variability, need to be addressed. 
Fire as a Coarse Filter—Agee 

366 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 4—Consumption of logs in spring and autumn burning in mixed-conifer forest 

of southern Oregon (data used in Thomas and Agee 1986). Plots are 0.25 ha in size 

(50 x 50 m). 

Acknowledgments 

I would like to thank Dr. Robert Edmonds and Dr. Richard Fonda for 

constructive comments on an earlier version of the manuscript. 

References 

Agee, J. K. 1993. Fire ecology of Pacific Northwest forests. Washington, DC: Island Press; 

493 p. 

Agee, J. K. 1998a. Historic vegetation in the central eastern Cascades of Washington. 

Unpublished report to Boise Cascade Corporation. Ellensburg, WA; 45 p. 

Agee, J. K. 1998b. The landscape ecology of western forest fire regimes. Northwest 

Science 72 (special issue): 24-34. 

Agee, J. K. 1999. A coarse-filter strategy. Forum 14(1): 15-19. 
Fire as a Coarse Filter—Agee 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 367 

Agee, J. K.; Huff, M. H. 1987. Fuel succession in a western hemlock/Douglas-fir forest. 

Canadian Journal of Forest Research 17: 697-704. 

Antos, J. A.; Habeck, J. R. 1981. Successional development in Abies grandis (Dougl.) 

Forbes forests in the Swan Valley, western Montana. Northwest Science 55: 26-39. 

Barnes, B. V.; Zak, D. R.; Denton, S. R.; Spurr, S. H. 1998. Forest ecology. 4th ed. New 

York: John Wiley and Sons; 774 p. 

Bessie, W. C.; Johnson, E. A. 1995. The relative importance of fuels and weather on fire 

behavior in subalpine forests. Ecology 76: 747-762. 

Bonnicksen, T. M.; Stone, E. C. 1981. The giant sequoia-mixed conifer forest community 

characterized through pattern analysis as a mosaic of aggregations. Forest Ecology 

and Management 3: 307-328. 

Camp, A.; Oliver, C. D.; Hessburg, P.; Everett, R. 1997. Predicting late-successional fire 

refugia pre-dating European settlement in the Wenatchee Mountains. Forest 

Ecology and Management 95: 63-77. 

Cobb, D. F. 1988. Development of mixed western larch, lodgepole pine, Douglas-fir, and 

grand fir stands in eastern Washington. Seattle: University of Washington; 99 p. M.S. 

thesis. 

Cooper, C. F. 1960. Changes in vegetation, structure, and growth of southwestern pine 

forests since white settlement. Ecological Monographs 30: 129-164. 

Dale, V. H.; Agee, J. K.; Long, J.; Noon, B. 1999. Ecological sustainability is fundamental 

to managing the national forests and grasslands. Bulletin Ecological Society of 

America 80(3): 207-209. 

Daubenmire, R. F. 1968. Plant communities: a textbook of plant synecology. New York: 

Harper and Row; 300 p. 

Eberhart, K. E.; Woodard, P. M. 1987. Distribution of residual vegetation associated with 

large fires in Alberta. Canadian Journal of Forest Research 17: 1207-1212. 

Edmonds, R. L.; Marra, J. L. 1999. Decomposition of woody material: nutrient dynamics, 

invertebrate/fungi relationships, and management in Northwest forests. In: 

Meurisse, R. T.; Ypsilantis, W. G.; Seybold, C., technical coordinators. Proceedings: 

Pacific Northwest forest and rangeland soil organism symposium. Gen. Tech. Rep. 

PNW-GTR-461. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 68-79. 

Harrington, M. G. 1996. Fall rates of prescribed fire-killed ponderosa pine. Res. Paper 

INT-RP-489. Ogden, UT: Intermountain Research Station, Forest Service, U.S. 

Department of Agriculture; 7 p. 

Harrod, R. J.; Gaines, W. L.; Hartl, W. E.; Camp, A. 1998. Estimating historic snag density 

in dry forests east of the Cascade Range. Gen. Tech. Rep. PNW-GTR-428. Portland, 

OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 16 p. 

Harrod, R. J., McRae, B. H.; Hartl, W. E. 1999. Historic stand reconstruction in ponderosa 

pine forests to guide silvicultural prescriptions. Forest Ecology and Management 114: 

433-446. 

Haufler, J. B.; Mehl, C. A.; Roloff, G. J. 1996. Using a coarse-filter approach with species 

assessment for ecosystem management. Wildlife Society Bulletin 24(2): 200-208. 

Hunter, M. L. 1990. Wildlife, forests, and forestry. Englewood Cliffs, NJ: Prentice-Hall; 

370 p. 
Fire as a Coarse Filter—Agee 

368 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Morgan, P.; Aplet, G. H.; Haufler, J. B.; Humphries, H. C.; Moore, M. M.; Wilson, W. D. 

1994. Historical range of variability: a useful tool for evaluating ecosystem change. 

Journal of Sustainable Forestry 2: 87-112. 

Morrow, R. J. 1985. Age structure and spatial pattern of old-growth ponderosa pine in 

Pringle Falls Experimental Forest, central Oregon. Corvallis: Oregon State 

University; 80 p. M.S. thesis. 

Quigley, T.; Haynes, R. W.; Graham, R. T. 1996. Integrated scientific assessment for 

ecosystem management in the interior Columbia Basin. Gen. Tech. Rep. PNW-GTR382. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department 

of Agriculture. 

Romme, W. H. 1982. Fire and landscape diversity in subalpine forests of Yellowstone

National Park. Ecological Monographs 52: 199-221. 

Romme, W. H.; Despain, D. G. 1989. Historical perspective on the Yellowstone fires of 

1988. Bioscience 39: 695-699. 

Shinneman, D. J.; Baker, W. L. 1997. Nonequilibrium dynamics between catastrophic 

disturbance and old-growth forests in ponderosa pine landscapes of the Black Hills. 

Conservation Biology 11: 1276-1289. 

Spies, T. A.; Franklin, J. F.; Thomas, T. B. 1988. Coarse woody debris in Douglas-fir

forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Taylor, A. R.; Skinner, C. N. 1998. Fire history and landscape dynamics in a Douglas-fir 

late-successional reserve, Klamath Mountains, California, USA. Forest Ecology and 

Management 111: 285-301. 

Taylor, A. R.; Halpern, C. B. 1991. The structure and dynamics of Abies magnifica forests 

in the southern Cascade Range, USA. Journal of Vegetation Science 2: 189-200. 

Thomas, J. W. 1979. Wildlife habitats in managed forests of the Blue Mountains of 

Oregon and Washington. Agric. Handb. 553. Washington, DC: U.S. Department of 

Agriculture; 512 p. 

Thomas, T. L.; Agee, J. K. 1986. Prescribed fire effects on mixed conifer forest structure 

at Crater Lake, Oregon. Canadian Journal of Forest Research 16: 1082-1087. 

Weaver, H. 1961. Ecological changes in the ponderosa pine forest of Cedar Valley in 

southern Washington. Ecology 42: 416-420. 

West, N. E. 1969. Tree patterns in central Oregon ponderosa pine forests. American 

Midland Naturalist 81: 584-590. 

White, A. S. 1985. Presettlement regeneration patterns in a southwestern ponderosa pine 

stand. Ecology 66: 589-594. 

White, P. S. 1987. Natural disturbance, patch dynamics, and landscape pattern in 

natural areas. Natural Areas Journal 7: 14-22. 

White, P. S.; Pickett, S. T. A. 1985. Natural disturbance and patch dynamics: An 

introduction. In: Pickett, S. T. A.; White, P. S., editors. The ecology of natural 

disturbance and patch dynamics. New York: Academic Press; 472 p. 

Wright, C. S. 1996. Fire history of the Teanaway River drainage, Washington. Seattle: 

University of Washington; 94 p. M.S. thesis. 

Wright, P. J. 1998. The effect of fire regime on coarse woody debris in the west central 

Cascades, Oregon. Corvallis: Oregon State University; 109 p. M.S. thesis. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 369 

Assemblages of Vascular Plants on Logs 

and Stumps within 28-year-old Aspendominated Boreal Forests1

Philip Lee2,3 and Kelly Sturgess2 

Abstract 

This study examined the impact of logs and stumps on the understory composition of 28-yearold aspen-dominated boreal forests. Suitable logs covered more than five times the area of 

stumps in both harvest and wildfire stands. Logs and stumps were colonized by a significantly 

different assemblage of vascular plants than the forest floor. Initial colonization patterns on 

dead wood in both wildfire and harvest stands were similar. However, as dead wood decayed, 

assemblages of vascular plants diverged and became more similar to their respective forest 

floor assemblages. Regenerating trees and shade tolerant forbs were disproportionately more 

abundant on logs and stumps, while grasses, shrubs, and shade intolerant forbs were 

disproportionately more abundant on the forest floor. 

Introduction 

Treefalls produce a number of different microhabitats (Beatty and Stone 1986). 

These include root throw pits and mounds, downed boles, stumps, canopy gaps, and 

leaf and branch piles created from downed canopies. In turn, these microsites create 

favorable habitats for the establishment of vascular plants by reducing competition 

with non-vascular and other vascular plants (Harmon and Franklin 1989), facilitating 

establishment of mycorrhizal relationships (Harvey and others 1987), changing 

substrate nutrient and moisture conditions (Hale and Pastor 1998), providing suitable 

physical substrate for establishment of roots (DeLong and others 1997), and 

increasing light and temperature regimes as with canopy gaps (Canham and others 

1990). However, it is unlikely that all plants have an equal ability to utilize these 

sites. Hence, the differential abilities of plants to colonize sites potentially adds to the 

spatial and temporal variability within the understory. 

In aspen-dominated (Populus tremuloides Michx.) boreal forests, treefall 

microsites may play a significant role in determining the spatial and temporal pattern 

of understories. Tree falldown rates caused by self-thinning produce elevated 

densities of logs and stumps. The forest floor coverage of downed logs in 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Scientist and Research Technician, respectively, Forest Resources Business Unit, Alberta 

Research Council, Postal Bag 4000, Vegreville, Alberta, Canada, T9C 1T4 (e-mail addresses: 

philipl@ualberta.ca and kellys@arc.ab.ca) 

3

 Current address: Senior Research Associate, Integrated Landscape Management Program, Room 

Z1107, Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9 (e-mail: 

philipl@ualberta.ca) 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

370 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

unharvested stands is relatively high (~10 to 20 percent) compared to other deciduous 

forests (reviewed in Harmon and others 1986). In turn, the abundance of microsites is 

potentially an important causal factor in the relatively high diversity of herbaceous 

and woody-stemmed understory found in boreal forests. Within the boreal forest, the 

role of stumps and logs as safe sites for tree species has been explored (Cornett and 

others 1997, DeLong and others 1997, Hornberg and others 1997). Crites and Dale 

(1998) demonstrated that as logs decay the assemblage of plants shifts from 

bryophytes to vascular plants. 

The overall objective of this study was to examine the contribution to understory 

heterogeneity created by dead wood on the forest floor. In order to do this we needed 

to characterize the physical parameters of logs and stumps colonized by vascular 

plants, measure and project the percent cover of suitable logs and stumps, and 

compare the composition and relative abundance of species among microsites and 

forest floor assemblages. 

Materials and Methods 

Site Description 

This study was located in the Marten Hills Forest District, near the town of 

Slave Lake, Alberta, between 55° and 56° North latitude and 114° and 115° West 

longitude. We selected four wildfire and four harvest stands from this region. Stands 

were mesic and dominated (> 80 percent basal area) by trembling aspen, with balsam 

poplar (Populus balsamifera L.), paper birch (Betula papyrifera Marsh.), white 

spruce (Picea glauca Moench.), and balsam fir (Abies balsamea L.) occurring as 

secondary tree species. 

Selection of the wildfire and harvest stands was based on their close 

geographical proximity to each other, similar pre-disturbance structure, similar 

timing of disturbances, and lack of human interference during post-disturbance 

succession. We used a number of data sources to ensure the wildfire and harvest 

stands were of similar pre-disturbance composition, age, and post-disturbance 

succession. All stands were disturbed in 1968. During that year, parts of the Sawridge 

Hills were subject to a large spring wildfire (> 100,000 ha). Wildfire stands burned as 

part of that conflagration. Harvest stands were cut during the previous winter as part 

of regular harvest operations scheduled for that year. These stands did not burn in the 

subsequent wildfire. Harvest was accomplished by using full tree extraction with 

conventional feller-buncher and grapple skidder. 

Ground measurements, aerial photographs, pre-disturbance timber inventories, 

and interviews with government and industry personnel confirmed that stands were 

110-120 years, aspen-dominated, and had basal areas of ~35 m2

/ha prior to 

disturbance. Wildfire stands were > 75 ha while harvest stands ranged in size from 35 

to 75 ha. To control for disparities in size and shape, all measurements were taken 

inside of a 50-m buffer from the stand edge. Within each of the stands ten 1-ha plots 

were randomly established. Within each of these plots, four 50 x 50-m blocks were 

established. 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 371 

Field Methods 

To sample the suitability of logs for vascular plants, we surveyed 200 to 300 m 

of line intersects within each stand. On each line a minimum of 200 logs (> 5 cm 

diameter at the point of intersection) were sampled. The vascular plants were 

identified to species and recorded on each side (< 50 cm) of the intersecting line. The 

diameter and length of log sampled were also recorded. 

To estimate the projected area of logs, three randomly placed 25-m transects per 

plot were surveyed using a line intersect method. We only recorded the most 

common classes and sizes of logs supporting vascular plants. Only logs from decay 

classes 5 to 7 and ≥ 20 cm diameter were used in estimations of percent microsite 

cover. Decay classes 5 to 7 represent progressively more decayed logs (Lee and 

others 1997). Decay class 5 represents logs with < 50 percent of large wood 

fragments lost, presence of small decayed blocks, and a deformed trunk outline. 

Decay class 7 logs have nearly 100 percent humification and no evidence of hard 

wood. 

The suitability and percent cover of stumps was based on walking searches in all 

plots. The area searched was 100 x 50 m (5,000 m2

). Within each search area, stumps 

with a top diameter of > 4 cm were recorded. Each stump was measured along the 

longest axis and the bisecting perpendicular axis. An elliptical formula was used to 

calculate the approximate area covered by each. From these surveys, we developed a 

“hard” and “soft” classification system for stumps. Hard stumps were visually 

characterized by a distinct outline with some evidence of hard wood, while soft stumps 

exhibited a deformed outline and little evidence of hard wood. Soft stumps had 

characteristics similar to those of decay class 7 logs. 

To quantify the percent cover of vascular plants on logs and stumps, we focused on 

the common decay and diameter classes supporting vascular plants. From a random 

point within each block, the nearest (> 20 cm diameter) logs of decay classes 5, 6, and 7 

were selected. A 20 x 20-cm quadrat was randomly placed on the logs and visual 

percent cover estimates were made for each species of vascular plants. Non-vascular 

plants were also recorded in broad groups: lichens, mosses, and liverworts. In a similar 

fashion, the nearest hard and soft stumps were selected from the same point within each 

block. Stumps had to have a top diameter of > 30 cm. A 20 x 20-cm quadrat was placed 

on the top of the stump, and on the side in each cardinal direction. Percent cover was 

visually estimated for each species. Estimations on stump sides were based on 

placement of the quadrat parallel to the stump surface. Forest floor coverages were 

estimated from quadrats randomly placed at least 2 m from logs or stumps. 

Analysis 

Comparisons of species per sample and percent forest floor cover were made 

using an ANOVA with a Standard-Neuman-Kuels post hoc. In all cases, significance 

differences were set at P<0.05. Detrended correspondence analysis (DCA) was the 

primary ordination technique used to evaluate the relationships between microsites 

and species assemblages (Hill 1979). The statistical package PCord was used to 

perform all DCAs (McCune and Mefford 1995). Detrending was accomplished by 

dividing the first axis into 26 segments. Ninety-five percent confidence ellipses were 

assigned based on algorithms from the JMP statistical package (Anonymous 1995). 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

372 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Results 

Physical Characteristics 

Both the diameter and decay stage of logs and stumps were important factors in 

determining the degree of colonization by vascular plants. We found that logs and 

stumps > 20 cm diameter captured 95 percent of the colonizing species. In general, 

smaller diameter logs and stumps were only colonized by small forbs such as Mitella

nuda L., Linnaea borealis L., and Cornus canadensis L., whereas larger diameter 

logs and stumps were colonized not only by forbs but also by shrubs and saplings 

such as Salix spp. L., P. glauca, and B. papyrifera. Decay class 4 logs and stumps 

were the earliest stage colonized by vascular plants. However, only two species, L.

borealis and Mertensia paniculata were found on these stumps and logs. 

Patterns of Species Richness 

The overall species richness of the wildfire and harvest stands was identical: 70 

species for each. This indicated that the background number of species available for 

colonization on dead wood was similar between the stands. Species richness on logs 

ranged from 21 to 26 species, while stumps varied from 22 to 38 species depending 

on disturbance type and decay class. 

To facilitate comparisons among different microsites, we analyzed the richness 

data on a per sample basis. Forest floor samples from wildfire and harvest stands 

exhibited a similar mean species richness of 12.9 and 11.7 per sample, respectively 

(table 1; P > 0.05). Species per sample on logs or stumps were lower than those 

found on the forest floor (table 1; P < 0.05). In comparisons between wildfires and 

harvest, four of eight microsite types exhibited more species per sample in the 

wildfire stand while other microsites exhibited no differences between wildfire and 

harvest stands. 

In both stand types, the number of species per sample increased on greater decay 

classes of logs and stumps (table 1; P < 0.05). In wildfire stands, decay of logs from 

class 5 to 7 increased 4.2 species while decay over the same stages in harvest stands 

increased only 1.4 species. In wildfire stands, decay from hard to soft stumps 

increased richness by 1.3 species on the sides and increased richness by 3.2 species 

on stump tops. In harvest stands, decay from hard to soft stumps increased richness 

by 3.3 and 3.2 species per sample on stump sides and tops, respectively. 

Percent Microsite Cover 

In both stand types, percent microsite cover was ordered logs > stumps 

(ANOVA; df=1, F range 29.9 to 38.9, P<0.001; fig. 1). In general, the wildfire stand 

had a greater percentage of the forest floor covered by suitable dead wood (fig. 1). 

Decay and Assemblages 

Both logs and stumps exhibited different assemblages of vascular plants than the 

forest floor of either wildfire or harvest stands. In both stands, decay stages of logs 

and stumps were spread along the first DCA axis (fig. 2). In general, species 

assemblages on logs and stumps converged with that of the forest floor as logs and 

stumps decayed. Decay class 5 logs were the least similar to forest floor samples, 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 373 

while decay class 7 logs were the most similar. Hard stump sides were the least 

similar to the forest floor while soft tops, hard tops, and soft sides were the most 

similar. 

Table 1―Mean species per sample quadrat ( +1 S.E.) for each type of microsite within 28-

year-old wildfire- and harvest-origin aspen-dominated boreal forests.1

 

Microsite Wildfire Harvest 

 

Forest floor* 12.9±0.46 11.7±0.48 

 

Log decay class 5 6.2±0.51a 6.1±0.62a 

Log decay class 6 7.7±0.57b 7.0±0.35a,b 

Log decay class 7* 10.4±0.64c 7.5±0.37b 

 

Hard stump side* 6.9±0.34b 4.6±0.30a 

Hard stump top* 7.2±0.41b 6.7±0.30b 

Soft stump side 8.2±0.32c 7.9±0.34b,c 

Soft stump top 10.4±0.42d 9.9±0.57d 

1

 Superscript letters denote significant differences within log or stump decay classes (P < 0.05). All 

microsites were significantly less than forest floor sample. Asterisks denote significant differences 

between wildfire and harvest samples (P <0.05). 

Figure 1―Percentage of the forest floor covered by suitable logs and stumps within 

aspen-dominated boreal forest. 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

374 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350

DCA AXIS 1

DCA AXIS 2

Log Decay Class 5

Log Decay Class 6

Log Decay Class 7

Forest Floor

Decay Class 5

Decay Class 6

Decay Class 7 Forest Floor

a

0

50

100

150

200

250

0 50 100 150 200 250 300 350

DCA AXIS 1

DCA AXIS 2

Forest Floor

Hard stump side

Hard stump top

Soft stump side

Soft stump top

Soft stump side

Hard stump topSoft stump top Forest Floor

Hard stump side

b

Figures 2―DCA ordination of plot of decay class 5, 6, and 7 logs and forest floor 

plots from wildfire (a) and plot of hard and soft stumps and forest floor plots from 

harvest (b) stands. Ordination plots of decayed logs from harvest stands and stumps 

from wildfire stands exhibit similar patterns but are not shown. 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 375 

Wildfire and Harvest Assemblages 

Assemblages of vascular plants on wildfire and harvest forest floors were 

different. Most of the variance between disturbance types was partitioned along the 

second DCA axis (fig. 3). Regardless of whether logs or stumps were associated with 

wildfires or harvests, initial assemblages of plants were similar. As both logs and 

stumps decayed the assemblages diverged and became more similar to their 

respective forest floor types. 

Figures 3―DCA ordination of log and stump plots and forest floor plots from wildfire 

(a) and harvest (b) stands. 

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350

DCA AXIS 1

DCA AXIS 2

Wildfire logs

Harvest logs

Wildfire forest floor

Harvest forest floor

Harvest forest floor

Wildfire forest floor

Harvest logs

Wildfire logs

a

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350

DCA AXIS 1

DCA AXIS 2

Wildfire stumps

Harvest stumps

Wildfire forest floor

Harvest forest floor

Harvest forest floor

Wildfire forest floor

Harvest stumps

Wildfire stumps

b
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

376 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Species Associations 

In general, life history and physiognomy of species determined associations with 

microsites and forest floor sites. To reduce the complexity of plotting and interpreting 

all species, we classified species with > 1 percent mean cover into the following 

categories: non-vasculars, grasses, shade tolerant forbs, shade intolerant forbs, low 

shrubs, tall shrubs, and regenerating trees (fig. 4). Non-vascular plants were classified 

by broad taxonomic categories, in this case, lichens and mosses. 

The ordination plot of species can be crudely divided into four quadrats. Each 

quadrat represented species associations with particular types of microsites (fig. 4).

The right portion of the first DCA axis represents species whose greatest abundance 

was associated with the forest floor, while the left portion represents species whose 

greatest abundance was associated with logs or stumps (fig. 4). In a similar manner, 

the upper portion of the second DCA axis represents species whose greatest 

abundance was associated with the wildfire stands, while the lower portion suggests 

an association with harvest stands. 

By using this classification, the relationship between species groups and 

microsites becomes clearer. Lichens and mosses were found on the extreme left of 

DCA axis 1, indicating dominance in the early stages of log and stump decay. 

Species groups of vascular plants primarily associated with stumps and logs included 

some of the shade tolerant forbs and seedlings of the common trees (fig. 4). Seven of 

the eleven common shade tolerant forbs were associated with logs and stumps. These 

included Arailia nudicaulis L., C. canadensis, Galium triflorum Michx., L. borealis, 

M. nuda, Rubus pubescens Raf., and Trientallis borealis Raf. Common tree species 

included A. balsamifera, B. papyrifera, P. glauca, and P. balsamifera. In contrast, a 

number of groups were primarily associated with forest floor assemblages. These 

included the common grasses, shade intolerant herb species, low shrubs, and tall 

shrubs. One notable exception was Salix spp. whose seedlings, like those of 

regenerating trees, tended to be found on decaying logs and stumps. 

Figures 4―DCA ordination of common (≥ 1 percent cover) species categorized by 

groups: regenerating trees, tall shrubs, low shrubs, shade intolerant forbs, shade 

tolerant forbs, grasses, and non-vascular plants. See appendix A for species within 

each group. 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 377 

Discussion 

This study demonstrated the importance of logs and stumps in aspen-dominated 

boreal forests. Our results indicated that logs in advanced stages of decay and stumps 

were colonized by a significantly different subset of species than the forest floor. 

Though this study did not track the decay and subsequent colonization of individual 

microsites, the sequence of decay stages strongly suggested a patterned succession of 

vascular plants on decaying logs and stumps. As found by McCullough (1948) in 

spruce forest, we also observed that the domination of lichens and mosses on logs 

and stumps began to succeed to vascular plants about midway through the decay 

process. As logs or stumps continued to decay, the assemblage of plants on logs or 

stumps also changed, eventually becoming more similar to forest floor assemblages. 

With our two stand types, microsite communities diverged and became more similar 

to their respective wildfire or harvest forest floor communities. 

Changes in the assemblages of plants with decay stage were presumably related 

to the ability of plants to disperse and establish on logs and stumps through 

vegetative means, and the ability of both seeds and clones to establish roots. Our first 

indication of colonization was on decay class 4 logs. This decay class was 

characterized by the initial breakdown and softening of the log or stump surface. The 

opening of cracks on the surface allowed for the accumulation of organic matter in 

cracks and perhaps access to softer heartwood and sapwood in the interior of the log. 

In contrast, even hard stumps maintained assemblages of vascular plants. The 

cracks on the surface and sides of even hard stumps were sufficient to allow the 

establishment of roots. In part, the relative permanency of stumps, first as part of a 

living tree, allowed for an accumulation of organic matter within cracks prior to tree 

death. Aside from being a suitable medium for the germination of seeds and 

penetration by stolons or rhizomes, both water holding capacity and available 

nutrients increased with decay (reviewed in Harmon and others 1986). Though the 

availability of nutrients is less on logs and stumps than on the forest floor, seedlings 

and clonal plants require less than larger, established plants. In the case of vegetative 

plants, nutrients may be shunted from ramets on the forest floor to those on the log. 

In turn, ramets on logs may provide photosynthates and moisture to forest floor 

ramets. 

Aside from decay stage, our results strongly indicated that larger diameter logs 

accumulated more species than smaller logs. This is not surprising since a wider and 

taller log provides a greater isolating effect from the influence of the forest floor. 

Huenneke and Sharitz (1986) demonstrated that logs (> 30 cm diameter) were more 

readily colonized by trees, shrubs and vines in natural and second growth bald 

cypress-tupelo swamps (Taxodium distichum-Nyssa aquatica) than smaller diameter 

branches (5 cm to 30 cm) or twigs (< 5 cm diameter). In this and other swamp forest 

systems, larger diameter logs provided a measure of protection against the frequent 

flooding (Hornberg and others 1997, Titus 1990). Harmon and Franklin (1989) 

concluded that competition with moss and herbaceous understories on the forest floor 

was the driving mechanism for the dominance of regeneration of P. sitchensis and T.

heterophylla on logs in Oregon and Washington. Although we have no direct 

measures for the underlying release mechanisms on logs or stumps, the prevalence of 

tree seedlings and smaller, shade tolerant forbs suggests that it may be competitive 

release. Grasses such as Calamagrotis canadensis and shrubs were found primarily 

on the forest floor. Both these groups are highly effective competitors of tree 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

378 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

seedlings (Lieffers and Stadt 1994, Place 1965) and possibly of low, shade tolerant 

forbs. 

The percent microsite cover value for the wildfire stand (> 5 percent) in this 

study is more comparable to conifer rather than other deciduous systems. Harmon 

(1989) projected a suitable cover of 5.4 percent in Picea-Tsuga forests of coastal 

Oregon and Washington. Takahashi (1994) found projections of 2.6 to 6.0 percent 

within Abies-Picea forests of northern Japan depending upon soil type. In contrast, 

Thompson (1980) found suitable logs covering only 1.9 percent of an oak-hickory 

(Qurecus-Carya) forest floor in Illinois. The cover for all logs (suitable and 

unsuitable) in deciduous forests were generally lower (1.6 to 4.0 percent) than in 

aspens stands (reviewed in Harmon and others 1986). 

Our analysis suggested that log, stump, and forest floor assemblages between 

wildfire and harvest were different. Species associations within harvest stands were 

comprised of more tall shrubs and shade intolerant forbs. Furthermore, harvest stands 

exhibited lower coverage of logs and stumps than the wildfire stand. This is largely 

caused by the absence of a falldown of fire-killed snags as in wildfire stands. Harvest 

stands exhibited an increased shrub richness and cover, and lower richness and cover 

of low, shade tolerant herb species. Our results suggest that the lack of logs may, in 

part, explain this difference in understory communities. A fuller comparison of the 

role of microsites in producing differences between wildfire and harvest stands would 

require a larger sample size of stands while controlling or accounting for within-stand 

variance. 

This study has shown the importance of logs and stumps to the understory 

heterogeneity of aspen-dominated boreal stands. Although this study did not directly 

measure a temporal sequence, we hypothesize that selective colonization of logs and 

stumps plays a significant role. The succession of upland boreal forests often features 

a conversion from early aspen domination to later mixed wood or conifer domination, 

while understory communities shift from shrub and shade intolerant species to low, 

shade tolerant forbs (Rowe 1956). Our results suggest that logs and stumps facilitate 

these successional shifts in the understory and canopy. Further research is needed to 

fully determine whether the input and decay of logs and stumps, in part, mediates 

vegetation succession in boreal forests. 

Acknowledgments 

The research in this paper was collected as part of the Fire and Harvest Residual 

Project at the Alberta Research Council. Steve Hanus, Dave McKinnon, and Brenda 

Dew provided technical assistance. Elaine Cannan, Pat Soldan, and Debby Franchuk 

provided administrative support. Karen MacNeil and Al Hoven with Alberta Lands 

and Forests Service in Slave Lake provided accommodation and logistical support. 

Support for this research came from the Alberta Research Council, Vegreville 

(formerly the Alberta Environmental Centre), Alberta Environmental Protection, 

Alberta-Pacific Forest Industries Inc., Alberta Conservation Association, and 

Diashowa-Marubeni Industries. Thanks to Steve Bradbury, William De Groot, and 

Cheryl Smyth for reviewing earlier drafts of this manuscript. 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 379 

References 

Anonymous. 1995. JMP statistics and graphics guide, version 3.1. Cary, NC: SAS 

Institute. 

Beatty, S. W.; Stone, E. L. 1986. The variety of soil microsite created by tree-falls. 

Canadian Journal of Forest Research 16: 539-548. 

Canham, C. D.; Denslow, J. S.; Platt, W. J.; Runkle, J. R.; Spies, T. A.; White, P. S. 1990. 

Light regimes beneath closed canopies and tree-fall gaps in temperate and tropical 

forests. Canadian Journal of Forest Research 20: 620-631. 

Cornett, M. W.; Reich, P. B.; Puettmann, K. J. 1997. Canopy feedbacks and 

microtopography regulate conifer seedling distribution in two Minnesota coniferdeciduous forests. Ecoscience 4: 353-364. 

Crites, Susan; Dale, Mark R. T. 1998. Diversity and abundance of bryophytes, lichens and 

fungi in relation to woody substrate and successional stage in aspen mixedwood 

boreal forests. Canadian Journal of Botany 76: 641-651. 

DeLong, H. B.; Lieffers, V. J.; Blenis, P. V. 1997. Microsite effects on first-year 

establishment and overwinter survival of white spruce in aspen-dominated boreal 

mixedwoods. Canadian Journal of Forest Research 27: 1452-1457. 

Hale, C. M.; Pastor, J. 1998. Nitrogen content, decay rates, and decompositional dynamics 

of hollow versus solid hardwood logs in hardwood forests of Minnesota, U.S.A. 

Canadian Journal of Forest Research 28: 1276-1285. 

Harmon, M. E. 1989. Retention of needles and seeds on logs in Picea sitchensis-Tsuga 

heterophylla forests of coastal Oregon and Washington. Canadian Journal of Botany 

67: 1833-1837. 

Harmon, M. E.; Franklin, J. F. 1989. Tree seedlings on logs in Picea-Tsuga forests of 

Oregon and Washington. Ecology 70: 48-59. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K. Jr.; Cummins, K. W. 1986. Ecology of coarse woody material in 

temperate ecosystems. Advances in Ecological Research 15:133-302. 

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J.; Graham, R. T. 1987. Relationships among 

soil microsite, ectomycorrhizae, and natural conifer regeneration of old-growth 

forests in western Montana. Canadian Journal of Forest Research 17: 58-62. 

Hill, M. O. 1979. DECORANA―a FORTRAN program for detrended correspondence 

analysis and reciprocal averaging. Ithaca, NY: Cornell University, Department of 

Ecology and Systematics; 87 p. 

Hornberg, G.; Ohlson, M.; Zackrissen, O. 1997. Influence of bryophytes and microrelief 

conditions on Picea abies seed regeneration patterns in boreal old-growth swamp 

forests. Canadian Journal Forest Research 27: 1015-1023. 

Huenneke, L. F.; Sharitz, R. R. 1986. Microsite abundance and distribution of woody 

seedlings in a South Carolina cypress-tupelo swamp. American Midland National 

115: 328-335. 

Lee, P. C.; Crites, S. C.; Nietfeld, M.; Van Nguyen, H.; Stelfox, J. B. 1997. Characteristics 

and origins of snags and downed woody material in aspen-dominated boreal forests 

of northeastern Alberta. Ecological Applications 7: 691-701. 

Lieffers V. J.; Stadt, K. J. 1994. Growth of understory Picea glauca, Calamagrostis 

canadensis and Epilobium angustifolium in relation to overstory light transmission. 

Canadian Journal of Forest Research 24: 1193-1198. 
Plant Assemblages on Logs and Stumps in Boreal Forests—Lee and Sturgess 

380 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

McCullough, H. A. 1948. Plant succession on decaying logs in a virgin spruce-fir forest. 

Ecology 29: 508-513. 

McCune, B.; Mefford, M. J. 1995. PC-ORD. Multivariate analysis of ecological data, 

version 3.0. Glenedon Beach, OR: MjM Software Design; 126 p. 

Place, I. C. M. 1965. The influence of seed-bed conditions on the regeneration of spruce 

and balsam fir. Bulletin 117. Ottawa, Ontario: Canadian Department of Northern 

Affairs Natural Resources, Forestry Branch; 87 p. 

Rowe, J. S. 1956. Uses of undergrowth plant species in forestry. Ecology 37: 461-473. 

Takahashi, K. 1994. Effect of size structure, forest floor type and disturbance regime on 

tree species composition in a coniferous forest in Japan. Journal of Ecology 82: 769-

773. 

Thompson, J. N. 1980. Treefalls and colonization patterns of temperate forest forbs. 

American Midland National 104: 176-184. 

Titus, J. H. 1990. Microtopography and woody plant regeneration in a hardwood 

floodplain swamp in Florida. Bulletin Torrey Botany Club 117: 429-437. 

Appendix A―Species names of the 25 most common species (≥ 1 percent cover) categorized 

by functional groups. 

Regenerating trees Shade tolerant forbs 

Populus tremuloides Rubus pubescens 

Betula papyrifera Cornus Canadensis 

Populus balsamifera Mitella nuda 

Picea glauca Linnaea borealis 

Galium trifolium 

Tall shrubs Maianthemum canadense 

Salix spp, Galium boreale 

Amelanchier alnifolia Galeopsis tetrahit 

Alnus tenuifolia Aralia nudicalis 

Alnus crispa Mertensia paniculata 

Prunus virginiana Viola Canadensis 

Trientalis borealis 

Low shrubs 

Viburnum edule Grasses 

Rosa acicularis Elymus innovatus 

Lonicera involucrata Calamagrostis canadensis 

Rubus idaea

Lonicera dioica 

Ribes triste 

Shade intolerant forbs Non-vasculars 

Epilobium angustifolia Lichens 

Aster ciliolatus Mosses 

Solidago gigantea 

Smilacina stellata 

Aster conspicuus 

Solidago canadensis 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 381 

The Nutritional Significance of Coarse 

Woody Debris in Three Rocky Mountain 

Coniferous Forests1

Cindy E. Prescott2 and Raija Laiho3

Abstract 

The contribution of coarse woody debris (CWD) to carbon, nitrogen, and phosphorus cycles 

was assessed in forests of lodgepole pine, white spruce-lodgepole pine, and subalpine firEngelmann spruce in southwestern Alberta. Mass loss and changes in C, N, and P 

concentrations in decomposing log segments were measured over a 14-year period. Organic 

matter input was measured during 10 years for CWD, 1 year for ground vegetation, and 5 

years for other aboveground litter types. Carbon, N, and P release from decomposing litter 

were simulated for a period of 40 years to determine the relative contributions of each 

aboveground litter type, including CWD. After 14 years, pine log segments had lost 71 

percent of their dry mass; spruce and fir lost 38 percent and 40 percent, respectively. The 

nitrogen (N) content of the logs increased in pine, changed little in spruce, and decreased by 

almost 30 percent in fir logs. Phosphorus (P) accumulated in decaying log segments of all 

three species, especially fir logs in which the P content was nearly five times the initial 

content after 14 years. Tree species with the lowest initial concentration had the greatest 

relative accumulation. Thus, wood decay organisms may compete with vegetation for limiting 

nutrients in these forests. The proportion of coarse woody debris (CWD) in aboveground litter 

input was 19 percent at the pine site, 3 percent at the spruce site, and 24 percent at the fir site. 

The contribution of CWD to N and P release was 2 percent or less, except at the fir site where 

CWD released 5 percent of the N. Coarse woody debris does not appear to make a significant 

contribution to N and P cycling in these forests. 

Introduction

The role of coarse woody debris (CWD) as a critical habitat element for many 

species of organisms is well recognized (Freedman and others 1996), but less is 

known about the role of CWD in element cycling and productivity of forest 

ecosystems (Harmon and others 1986). Studies in the coastal forests of the Pacific 

Northwest, where CWD is particularly abundant and large (Harmon and others 1986, 

Keenan and others 1993, Sollins and others 1987), have suggested that CWD is an 

integral component of forest ecosystems, acting as a long term stabilizing storage 

pool for nutrients. In other coniferous forests, the role of CWD in nutrient cycling has 

been found to be small (Busse 1994). There is some controversy about the 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Associate Professor, University of British Columbia, Department of Forest Sciences, 3037-2424 Main 

Mall, Vancouver, BC, V6T 1Z4 (e-mail: cpres@interchg.ubc.ca) 3

 Senior Scientist, University of Helsinki, Department of Forest Ecology, P.O. Box 24, FIN-00014 

Helsinki University, Finland.
Nutritional Importance of CWD—Prescott and Laiho 

382 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

importance of CWD to forest productivity (Fahey 1983, Harmon and others 1986, 

Spies and others 1988). 

Assessing the role of CWD in element cycling requires measurements of the 

rates of input and decomposition of CWD relative to other litter types. The long time 

span and considerable temporal variation make it difficult to directly measure CWD 

input and decomposition. Most previous studies have relied on indirect methods for 

estimating rates of decomposition and have usually involved chronosequence 

techniques. Decomposition estimates have usually been based on log inventories by 

using various backdating techniques (e.g., Brown and others 1998, Sollins and others 

1987) that report changes in wood density, as the original mass of the logs was not 

known (Alban and Pastor 1993, Fahey 1983, Graham and Cromack 1982, Means and 

others 1985, Sollins and others 1987). In other studies, the mass of CWD was 

inventoried and rates of decay were estimated with the assumption of constant input 

(Sollins 1982). These rough estimates may be adequate for management guidelines, 

but ecosystem models require more precise information on the pattern of mass loss 

and nutrient release from CWD. 

In this study, the rate of CWD input (treefall) was measured for 10 years in three 

Rocky Mountain forests: a self-thinning lodgepole pine (Pinus contorta Loud.) 

forest, a mature white spruce (Picea glauca [Moench] Voss) forest, and an oldgrowth forest of Engelmann spruce (Picea engelmannii Parry ex Engelm.) and 

subalpine fir (Abies lasiocarpa [Hook.] Nutt.). Mass loss and changes in C, N, and P 

concentrations were measured over a 14-year period in portions of recently fallen 

logs of the dominant species in each forest (pine, spruce, and fir, respectively). The 

role of CWD in nutrient cycling in these forests was assessed by determining 1) the 

proportion of the annual aboveground inputs of C, N, and P that is derived from 

CWD, and 2) the proportion of the C, N, and P released from aboveground litter that 

is derived from CWD during a simulated 40-year period. 

Study Sites 

The study sites were in the Kananaskis Valley in the Front Range of the Rocky 

Mountains of southwestern Alberta (51°2'N, 115°3'W). Average monthly 

temperatures range from -10°C in January to 14°C in July. Average annual 

precipitation is 660 mm, of which 290 mm occurs as snow. Soils are well-drained 

brunisols overlying primarily limestone glacial deposits. The three study sites were 

within 5 km of one another in the Lusk Creek basin, adjacent to the Kananaskis Field 

Station of the University of Calgary. The sites were identified according to the 

dominant species of overstory tree in the stand, as pine, spruce, or fir (Prescott and 

others 1989a). 

Methods 

Wood Decomposition 

Standing dead or recently fallen trees approximately 15 cm in diameter of the 

dominant species at each site were harvested and cut into segments 20 cm long. In 

September 1984, 70 log segments were placed on the litter surface at 3 m intervals 

within one 20 x 30 m plot at each site. Unused portions of the harvested logs were 
Nutritional Importance of CWD—Prescott and Laiho 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 383 

used to determine the average moisture content and C, N, and P concentrations—the 

original dry mass and C, N, and P content of each log segment. 

Ten log segments were collected from each site after 2, 6, 10, and 14 years. 

Logs were cleaned of litter and vegetation, and end pieces were removed. Each piece 

was weighed fresh, dried at 80°C to constant mass, and weighed. The central pieces 

were then ground for C, N, and P analyses. 

Litter Input 

Input of CWD (treefall) was estimated on two 20 x 30 m plots at each site. All 

fallen trees were marked with paint in August 1984. New (unmarked) downed trees 

were checked annually for the first 5 years, and once again after another 5-year 

period. At each time, the species and decay class of each downed tree was recorded 

and their dbh and length (within the plot) measured. Decay classes were adapted 

from Triska and Cromack (1979). After calculating the stem volumes, the total dry 

mass and C, N, and P content of each log was estimated using average density values 

and nutrient concentrations for each species-decay class combination. 

Input of “small woody litter” (i.e., twigs, branches, intact female cones, and 

bark) was harvested annually for 5 years on ten 3 x 3 m plots at each site. 

“Nonwoody litter” (i.e. needles, leaves, male cones, female cone scales, and seeds) 

was collected in fifteen 0.25 m2

 litter traps placed randomly in one 20 x 30 m plot at 

each site. The traps were emptied at least twice a year for 5 years. Litter input from 

ground vegetation was estimated during 1985 as described by Prescott and others 

(1989b). The litter samples were separated into components and dried to constant 

mass at 80°C. 

Carbon, N, and P concentrations were analyzed in five composite samples of 

each litter type, and used to estimate the mass of nutrients in the annual inputs of 

each litter type. Samples were ground in a Wiley mill and C concentrations were 

measured with a Leco carbon analyzer. Nitrogen and P concentrations were analyzed 

with a Technicon II autoanalyzer after a sulphuric acid-hydrogen peroxide digestion 

in 360°C (Lowther 1980). Nutrient concentrations were measured only in the original 

and 14-year logs. 

Statistical Analyses 

Three equation types were tested to describe the pattern of mass loss from logs 

over time: linear, exponential and sigmoidal. Linear and exponential equations have 

been used in earlier studies of wood decomposition, and a sigmoidal curve was 

suggested by locally weighted regression procedures used for preliminary smoothing 

of the data. Statistical outliers in the wood decomposition data were identified and 

excluded from the regression analyses. Nonlinear estimation was done using a GaussNewton method and a least squares loss function (SYSTAT 6.0 for Windows 1996).4

Final equation forms were selected after checking the residuals and assessing the bias 

of the estimates. 

 

4

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Nutritional Importance of CWD—Prescott and Laiho 

384 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Decomposition and Nutrient Release Simulations 

To examine the relative importance of the litter types in the nutrient cycles of 

these forests, organic matter accumulation and annual release of C, N, and P from 

each litter type were simulated for a period of 40 years. A 1-year time step was used; 

each year, the mean annual litter input of each litter type was added to the system. 

Mass loss equations from the log decomposition experiment were used for CWD. 

Decomposition of other litter types was simulated using the negative exponential 

decay model (e.g., Olson 1963): 

Mass remaining at time t / Initial mass = exp(-k • t) (1) 

with the decomposition constants (k-values) presented in Taylor and others (1991). 

For materials for which decomposition data were not available, the k-value for a 

material most similar to it was used (e.g., k-values for Epilobium angustifolium were 

used for all herbaceous materials). Each litter cohort was progressively decomposed 

until the mass of the cohort became negligible or the simulation period ended. 

Organic matter accumulation was then calculated as the sum of the remaining mass 

of each cohort at each time step, and annual decomposition as the mass lost from 

each cohort between the time steps. Release of N and P was simplified by assuming 

nutrients were lost at the same rate as mass. 

Results 

Wood Decomposition 

Mass loss during the 14 years averaged 71 percent in pine logs, 38 percent in 

spruce logs and 40 percent in fir logs. Carbon concentrations in the decaying log 

segments changed little during the 14 years, whereas N and P concentrations 

increased (table 1). There was an average net import of 0.78 mg N per g remaining 

mass in each pine log, and net releases of 0.05 and 0.65 mg N g-1 from spruce and fir 

logs, respectively (fig. 1). Phosphorus accumulated in decaying wood of all three 

species, particularly in fir logs; the amounts of P imported into the logs after 14 years 

were 0.02, 0.03, and 0.07 mg P g-1 in pine, spruce, and fir logs, respectively. For both 

N and P, the increases in nutrient content during decay were greatest in logs with the 

lowest initial concentration (pine logs for N and fir logs for P). 

Table 1―Carbon, nitrogen, and phosphorus concentrations of the log segments initially and 

after 14 years of decomposition. 

____________________________________________ 

Site Percent C mg N g-1 mg P g-1

________________________________________________

Initial 

Pine 47.76 ± 0.44 0.61 ± 0.12 0.04 ± 0.02 

Spruce 49.07 ± 0.82 0.88 ± 0.20 0.03 ± 0.00 

Fir 49.76 ± 0.59 1.55 ± 0.35 0.01 ± 0.01 

14-year 

Pine 49.77 ± 1.65 2.78 ± 1.08 0.16 ± 0.06 

Spruce 50.84 ± 1.08 1.53 ± 0.92 0.08 ± 0.04 

Fir 48.44 ± 0.91 2.03 ± 0.94 0.09 ± 0.05 

________________________________________________ 
Nutritional Importance of CWD—Prescott and Laiho 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 385 

Figure 1―Dry mass, C, N, and P contents of 20-cm log segments of lodgepole pine, 

white spruce, and subalpine fir after decomposing for 14 years at the pine, spruce, 

and fir sites, respectively. Values are relative to the initial content: values more than 

100 percent indicate net import; values less than 100 percent indicate net release. 

Each value is the mean of 10 log segments; error bars are one standard deviation. 

Litter Input 

Total aboveground litter input averaged 362 g m-2 year-1 at the pine site, 237 g 

m-2 year-1 at the spruce site, and 205 g m-2 year-1 at the fir site. Foliar litter (needles 

and leaves) made up the greatest proportion of the litter input at all sites (fig. 2).

CWD input accounted for 19 percent of the litter input at the pine site, 3 percent at 

the spruce site, and 24 percent at the fir site. For C, the values were 18, 3, and 23 

percent, respectively. CWD accounted for 2.6, 0.4, and 5.1 percent of the annual 

aboveground N input and 1.4, 0.5, and 2.2 percent of the annual aboveground P input 

at the pine, spruce, and fir sites, respectively. 

Decomposition and Nutrient Release Simulations 

Nonwoody litter (mostly foliage and cone scales) also dominated release of C, 

N, and P (figs. 3-5). CWD accounted for 18 percent of the total C released from 

decomposing litter at the pine site, 2 percent at the spruce site, and 20 percent at the 

fir site. The contribution of CWD to N and P release was 2 percent or less, except at 

the fir site where CWD released 5 percent of the N. 

Site

Pine Spruce Fir

% rem aining

0

100

200

400

500

600

Dry mass

C

N

P
Nutritional Importance of CWD—Prescott and Laiho 

386 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

 

Figure 2―Average annual inputs of dry mass, C, N, and P in each litter type at the 

pine, spruce and fir sites. CWD = coarse woody debris; FWD = fine woody debris. 

Pine Spruce Fir

Dry mass input, g m-2 year-1

0

20

40

60

80

100

120

140

160

180 CWD

FWD

Reproductive 

Foliage 

Ground veg. 

Pine Spruce Fir

N input, mg m-2 year-1

0

200

400

600

800

1000

1200

1400 CWD

Small woody

Nonwoody

Ground veg.

Site

Pine Spruce Fir

P input, mg m-2 year-1

0

20

40

60

80

100

120

140

CWD

Small woody

Nonwoody

Ground veg.

68

7

48 56

26

5

41

49

38

42

40

9

150

124

103

49

151

1026

637

6

330

830

318

67

296

874

71

3

14

89

105

1

28

121

67

2

24

59

5
Nutritional Importance of CWD—Prescott and Laiho 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 387 

Figure 3―Contributions of the various litter types to annual C release from the 

accumulated organic matter at the pine, spruce, and fir sites during a 40-year 

simulation period. 

0 10 20 30 40

0

2 0

4 0

6 0

8 0

P ine

0 10 20 30 40

C released, g m - 2 year- 1

0

2 0

4 0

6 0

8 0

S pruce

T im e, years

0 10 20 30 40

0

2 0

4 0

6 0

8 0

CW D

FW D

F oliage

R eproductive

G round veg.

F ir

0 10 20 30 40

0

20

40

60

80

Pine

0 10 20 30 40

C released, g m-2 year-1

0

20

40

60

80

Spruce

Time, years

0 10 20 30 40

0

20

40

60

80

CWD

FWD

Foliage

Reproductive

Ground veg.

Fir
Nutritional Importance of CWD—Prescott and Laiho 

388 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 4―Contributions of the various litter types to annual N release from the 

accumulated organic matter at the pine, spruce, and fir sites during a 40-year 

simulation period. 

0 10 20 30 40

0

200

400

600

800

1000

Pine

0 10 20 30 40

N released, mg m-2 year-1

0

200

400

600

800

1000

Spruce

Time, years

0 10 20 30 40

0

200

400

600

800

1000

CWD

Small woody

Nonwoody

Ground veg.

Fir
Nutritional Importance of CWD—Prescott and Laiho 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 389 

Figure 5―Contributions of the various litter types to annual P release from the 

accumulated organic matter at the pine, spruce, and fir sites during a 40-year 

simulation period. 

0 10 20 30 40

0

50

100

150

Pine

0 10 20 30 40

P released, mg m-2 year-1

0

50

100

150

Spruce

Time, years

0 10 20 30 40

0

50

100

150

CWD

Small woody

Nonwoody

Ground veg.

Fir
Nutritional Importance of CWD—Prescott and Laiho 

390 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Discussion 

Our results indicate that CWD contributed a maximum of 5 percent of the N and 

P returned in annual aboveground litter and a maximum of 5 percent of the N and P 

released during decomposition. Other studies have also indicated that the contribution 

of CWD to nutrient cycling in undisturbed forests is relatively minor. Downed wood 

comprised less than 3 percent of the soil nutrient pools in lodgepole pine stands in 

central Oregon (Busse 1994). Fahey and others (1985) found that downed wood 

accounted for less than 3 percent of the soil N pool in two lodgepole pine ecosystems 

in Wyoming. In an old-growth mixed conifer forest in central Oregon, well-decayed 

logs contributed only 4 to 6 percent of annual plant N uptake (Hart 1999). 

CWD was clearly more important for the C flows, accounting for 18, 3, and 23 

percent of the C returned in aboveground litter, and 18, 2 and 20 percent of the C 

released during decomposition at the pine, spruce, and fir sites, respectively. 

Our observation that logs with the lowest initial concentrations of N or P 

immobilized the greatest amount of N or P during decomposition has implications as 

to the role of CWD as a nutrient source in these forests. The initial concentrations of 

N and P in the logs corresponded to the availability of the nutrient at the site, as 

determined in previous studies (Prescott and others 1992). For example at the fir site, 

availability of N was high and P was low, and the logs released N and immobilized P 

during decomposition. In contrast, N availability was lowest at the pine site, and the 

logs at this site were the only ones to immobilize N. Release dynamics of N and P in 

other litter types have been found to depend on the initial concentrations (Prescott 

and others 1993), and a similar pattern has been noted for decaying wood (Alban and 

Pastor 1993). Wells and Boddy (1990) and Wells and others (1990) have shown that 

wood-decaying fungi translocate P from surroundings to the substrate they are 

colonizing. Our findings of greatest N import into logs at the pine site and greatest P 

import at the fir site suggest that wood decay organisms may be competing with 

vegetation for limiting nutrients. 

Our estimates are only valid for these forests at the time of measurements, but 

the sites represent a variety of common forest types and stand development stages: a 

dense self-thinning lodgepole pine stand, a mature post-thinning spruce stand, and an 

old-growth spruce-fir stand. 

In conclusion, our findings indicate that CWD is not a significant source of 

available N and P in these forests; it may actually compete with vegetation for 

limiting nutrients. Guidelines for management of CWD should be based on 

management objectives related to other potential values, rather than its role in N and 

P cycling. 

Acknowledgments 

This study was supported by the Academy of Finland grant 41817 to R.L. The 

installation of the experiments was funded by an NSERC grant to D. Parkinson; 

remeasurements were funded by B.C. Ministry of Forests and Forest Renewal B.C. 

grants to Cindy Prescott. We thank the staff of the Kananaskis Field Station for the 

continued cooperation in maintaining the long-term field experiments. Special thanks 

to the technical reviewers of the manuscript and to T. Penttilä and D. MacCarthy for 

assistance with sample preparation. 
Nutritional Importance of CWD—Prescott and Laiho 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 391 

References 

Alban, D. H.; Pastor, J. 1993. Decomposition of aspen, spruce, and pine boles on two sites 

in Minnesota. Canadian Journal of Forest Research 23: 1744-1749. 

Brown, P. M.; Shepperd, W. D.; Mata, S. A.; McClain, D. L. 1998. Longevity of 

windthrown logs in a subalpine forest of central Colorado. Canadian Journal of 

Forest Research 28: 932-936. 

Busse, M. D. 1994. Downed bole-wood decomposition in lodgepole pine forests of central 

Oregon. Soil Science Society of America Journal 58: 221-227. 

Fahey, T. J. 1983. Nutrient dynamics of aboveground detritus in lodgepole pine 

ecosystems, southeastern Wyoming. Ecological Monographs 53: 51-72. 

Fahey, T. J.; Yavitt, J. B.; Pearson, J. A.; Knight, D. H. 1985. The nitrogen cycle in 

lodgepole pine forests, southeastern Wyoming. Biogeochemistry 1: 257-275. 

Freedman, B.; Zelazny, V.; Beaudette, D.; Fleming, T.; Flemming, S.; Forbes, G.; Gerrow, J. 

S.; Johnson, G.; Woodley, S. 1996. Biodiversity implications of changes in the 

quantity of dead organic matter in managed forests. Environmental Reviews 4: 238-

265. 

Graham, R. L.; Cromack, K., Jr. 1982. Mass, nutrient content, and decay rate of dead 

boles in rain forests of Olympic National Park. Canadian Journal of Forest Research 

12: 511-521. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15: 133-302. 

Hart, S. C. 1999. Nitrogen transformations in fallen tree boles and mineral soil of an oldgrowth forest. Ecology 80: 1385-1394. 

Keenan, R. J.; Prescott, C. E.; Kimmins, J. P. 1993. Mass and nutrient content of woody 

debris and forest floor in western red cedar and western hemlock forests on 

northern Vancouver Island. Canadian Journal of Forest Research: 1052-1059. 

Lowther, J. R. 1980. Use of a single sulphuric acid―hydrogen peroxide digest for the 

analysis of Pinus radiata needles. Communications in Soil Science and Plant Analysis 

11: 175-188. 

Means, J. E.; Cromack, K., Jr.; MacMillan, P. C. 1985. Comparison of decomposition 

models using wood density of Douglas-fir logs. Canadian Journal of Forest Research 

15: 1092-1098. 

Prescott, C. E.; Corbin, J. P.; Parkinson, D. 1989a. Biomass, productivity, and nutrient-use 

efficiency of aboveground vegetation in four Rocky Mountain coniferous forests. 

Canadian Journal of Forest Research 19: 309-317. 

Prescott, C. E.; Corbin, J. P.; Parkinson, D. 1989b. Input, accumulation, and residence 

times of carbon, nitrogen, and phosphorus in four Rocky Mountain coniferous 

forests. Canadian Journal of Forest Research 19: 489-498. 

Prescott, C. E.; Corbin, J. P.; Parkinson, D. 1992. Availability of nitrogen and phosphorus 

in the forest floors of Rocky Mountain coniferous forests. Canadian Journal of Forest 

Research 22: 593-600. 

Prescott, C. E.; Taylor, B. R.; Parsons, W. F. J.; Durall, D. M.; Parkinson, D. 1993. Nutrient 

release from decomposing litter in Rocky Mountain coniferous forests: influence of 

nutrient availability. Canadian Journal of Forest Research 23: 1576-1586. 
Nutritional Importance of CWD—Prescott and Laiho 

392 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Sollins, P. 1982. Input and decay of coarse woody debris in coniferous stands in western 

Oregon and Washington. Canadian Journal of Forest Research 12: 18-28. 

Sollins, P.; Cline, S. P.; Verhoeven, T.; Sachs, D.; Spycher, G. 1987. Patterns of log decay in 

old-growth Douglas-fir forests. Canadian Journal of Forest Research 17: 1585-1595. 

Spies, T. A.; Franklin, J. F.; Thomas, T. B. 1988. Coarse woody debris in Douglas-fir 

forests of western Oregon and Washington. Ecology 69: 1689-1702. 

SYSTAT 6.0 for Windows. 1996. Statistics. SPSS Inc., Chicago, IL. 

Taylor, B. R.; Prescott, C. E.; Parsons, W. F. J.; Parkinson, D. 1991. Substrate control of 

litter decomposition in four Rocky Mountain coniferous forests. Canadian Journal of 

Botany 69: 2242-2250. 

Triska, F. J.; K. Cromack, Jr. 1979. The role of woody debris in forests and streams. In: 

Waring, R. H. editor. Forests: Fresh perspectives from ecosystem analysis. Corvallis, 

OR: Oregon State University Press; 171-190. 

Wells, J. M.; Boddy, L. 1990. Wood decay, and phosphorus and fungal biomass 

allocation, in mycelial cord systems. New Phytologist 116: 285-295. 

Wells, J. M.; Hughes, C.; Boddy, L. 1990. The fate of soil-derived phosphorus in mycelial 

cord systems of Phanerochaete velutina and Phallus impudicus. New Phytologist 

114: 595-606. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 393 

The Effects of Microsite (Logs versus 

Ground Surface) on the Presence of Forest 

Floor Biota in a Second-growth Hardwood 

Forest1

Charlotte Pyle2 and Michelle M. Brown2

Abstract 

A study conducted in forests at the University of Connecticut investigated the value of logs 

for biodiversity in second-growth hardwoods. Forest floor microsite (log versus featureless 

ground surface [soil and leaf litter only]) was significant (P < 0.001) for the frequency of 

occurrence of representatives of all seven broadly defined life form groups examined. Algae, 

non-vascular plants, and fungi were found on logs, but not on the ground. Small mammal and 

bird perching was noted on logs, but not on the ground. Seedlings and non-seedling vascular 

plants occurred on both microsites, but were found in significantly greater frequency on the 

ground surface. 

Introduction 

Forest floor structure is the result of a variety of natural and anthropogenic 

processes that create features that persist for a wide variety of time periods. Features 

resulting from glacial activity (for example, erratic boulders or hard-packed soils 

underlying ephemeral ponds) are more or less permanent features. The pit and mound 

topography created when strong winds uproot trees may persist for centuries 

(Stephens 1956). The bare soil created when a tree is first uprooted is relatively soon 

covered by new vegetation or leaf litter while the trunks, stumps, and large branches 

of broken-off or uprooted trees may persist for decades or even centuries. Variation 

in forest floor structure results in habitat diversity for both plants and animals. 

The habitat value of forest floor logs in particular has been recognized for many 

groups of species, including birds, small mammals, herpetofauna, insects and other 

invertebrates, vascular plants, non-vascular plants, and fungi (Bull and others 1997, 

Elton 1966, Harmon and others 1986, Maser and others 1979, McMinn and Crossley 

1996, Samuelsson and others 1994). Logs contribute to forest biological diversity by 

providing animals and plants with substrate, e.g., for feeding, perching, or residence. 

Organisms that reside on, under, or in logs also may contribute to the diversity of 

ecological functioning that occurs in forest ecosystems. For example, log-related 

organisms are involved in nitrogen fixation (Hendrickson 1991, Larsen and others 

1978), nutrient cycling (Harmon and others 1994), mycorrhizal fungal associations 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Adjunct Assistant Professor and Graduate Student, respectively, University of Connecticut, 

Department of Natural Resources Management and Engineering, Dept. NRME, U-4087, University of 

Connecticut, Storrs, CT 06269-4087 (e-mail: cpyle@canr.uconn.edu) 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

394 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(Graham and others 1994, Molina and others 1993), and food chains (Maser and 

Trappe 1984). 

Not every study from which the habitat value of logs has been inferred has 

involved quantitative, controlled comparisons of the value of log microsites versus 

other forest floor microsites. However, examples of such studies may be found for a 

variety of species and more broadly-defined life forms, for example, Barnum and 

others 1992 (Peromyscus leucopus), Bratton 1976 (herbaceous plants), Christy and 

Mack 1984 (Tsuga heterophylla [Raf.] Sarg.), Coney and others 1982 (land snails), 

Harmon and Franklin 1989 (conifer seedlings), Hofgaard 1993 (tree seedlings), 

Kruys and Jonsson 1999 (moss/liverwort/lichen/fungi), Minore 1972 (conifer 

[mostly] seedlings), Nakashizuka 1989 (woody plant seedlings), Olszewski 1968 

(small mammals), Rambo and Muir 1998 (moss/liverworts), Steel and others 1999 

(small mammals), Summers and Uetz 1979 (woodland centipedes), Szewczyk and 

Szwagrzyk 1996 (tree seedlings), Tallmon and Mills 1994 (Clethrionomys gapperi),

and Thompson 1980 (herbaceous plants). In some cases, the extent to which logs are 

important microsites has been shown to be affected by log decay class. 

The purpose of the present study was to compare statistically the use of logs to 

the use of the ground surface in a second-growth, eastern hardwood forest. Our goal 

was to evaluate the general significance of logs for a broad range of organisms that 

use logs in other forest cover types. The organisms we considered represented seven 

life forms: algae, non-vascular plants, fungi, seedlings, non-seedling vascular plants, 

small mammals, and birds. The specific study objectives were to determine the 

significance of forest floor microsite (log versus ground surface) for the frequency of 

occurrence of representatives of the seven broadly-defined life forms; and for logs 

only, to determine whether the frequency of representatives of each life form is 

affected by log species and decay class. 

Study Area 

The study was conducted in the summer of 1996 in forest on the North 

Eagleville Tract of the University of Connecticut (latitude 41o

 48' 30", longitude 72o

17') located in the vicinity of Storrs, Connecticut. The forest, dominated by naturally 

regenerated, mature, second-growth oak (Quercus L.) stands, lies within the central 

broad-leaved region of the eastern deciduous forest (Duffield 1990). Annual 

precipitation averages 1,170 mm, spread more or less evenly throughout the year. 

The average mean January and July temperatures are -3o

C and 21oC, respectively, 

with an average frost-free season of 156 days (Brumbach 1965). Soils in the North 

Eagleville Tract are primarily fine sandy loams developed from a glacial till derived 

from schist, gneiss, and granite. The soils are typically very stony with slopes ranging 

from 3-15 percent. However, soils with poor or very poor drainage as well as steeper 

(15-35 percent slope) shallow soils are also included within the area sampled (USDA 

Soil Conservation Service 1966). 

Field Procedures 

Following the guidelines of Harmon and Sexton (1996), logs were defined as 

pieces of coarse woody debris (CWD) at least 1.5 m long. Length was measured 

from the large end to the point where the log diameter tapered off to less than 10 cm. 

To locate logs for sampling, a line intersect method was used (Ringvall and Ståhl 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 395 

1999) with randomly located transects laid out within the hardwood forest. Log 

diameter was measured at the base, mid-point, and upper end of each log intersected 

by the transect. Each log was identified as “oak” or “non-oak” (Panshin and de 

Zeeuw 1980) and assigned to one of five hardwood log decay classes (Pyle and 

Brown 1998). The presence of under-log habitats (leaf litter and soil) was tallied. 

Seven broadly defined “life forms” (table 1) were chosen to enable quick 

categorization of organisms into groups that reflected their taxonomy and/or function. 

We did not explore the relationship of the species included in our life form groups to 

typical indices of diversity (Swindel and others 1991). For each life form, the 

presence or absence of any representative species (or, for small mammals and birds, 

the presence or absence of evidence of perching by any representative species) was 

tallied for each log. Presence/absence observations of representatives of each life 

form also were tallied for under-log habitat when it occurred. 

Table 1―Life forms used to categorize the diversity of biota. 

Life form Description 

Algae Only those visible to the unaided eye 

Non-vascular plants Including mosses, liverworts, lichens 

Fungi Fungal fruiting bodies and hyphae visible to the unaided eye without 

disturbance of the microsite; and slime molds 

Seedlings Trees <0.50 m tall; other species with cotyledons 

Vascular plants Excluding seedlings and grass-like plants (Poaceae, Cyperaceae, 

Juncaceae) 

Small mammals Perching use assessed by presence of scat or nuts/seeds with tooth marks 

Birds Perching use assessed by presence of guano, nests, or proliferations of 

seeds 

The ground surface adjacent to each log was sampled at a distance of 3 meters 

from the log. For each log, an equivalent area of featureless ground surface (equal to 

the length times the mid-point diameter of the log) was sampled for the 

presence/absence of the seven life forms by ground surface substrate (decaying leaf 

litter and soil). The ground surface samples were taken on alternating sides of the 

transect and were relocated as needed to avoid forest floor features such as other 

pieces of CWD or rocks and fine woody debris that might have a different habitat 

value than leaves and soil. 

Data Analysis 

For each life form, the significance of microsite type (log versus ground surface) 

was analyzed using a Haber-corrected chi-square test (Zar 1999) for a 2 X 2 

contingency table of microsite type and presence/absence. For each life form, chisquare goodness of fit analysis (Zar 1999) was used to test the significance of log 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

396 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

decay class and log species. For decay classes I-IV, the null hypothesis was that the 

frequency of the jth life form on logs of the ith decay class is proportional to the 

occurrence of logs in the ith decay class within the sample. With reference to vascular 

plants, expected values of less than 5 were deemed acceptable for testing extreme 

departures from a uniform distribution at alpha values of 0.01 because the average 

expected value (of 7.5 in the case of vascular plants) was at least 4.0 (Zar 1999). For 

log species (oak or non-oak), a Yates-corrected chi-square goodness of fit (Zar 1999) 

was applied to the null hypothesis that the frequency of the jth life form on logs of ith

species is proportional to the occurrence of logs of the ith species within the sample. 

The independence of log species and log decay class (for decay classes I-IV) was 

tested with the log-likelihood ratio (G statistic; Zar 1999). For all statistical tests, Pvalues of less than 0.01 were considered significant. The quadratic mean diameter for 

the basal end of the logs was calculated as the square root of the average squared 

diameter. 

Results 

Two hundred seventy-seven logs and an equal number of adjacent forest floor 

areas were sampled. The quadratic mean diameter at the basal end of the logs was 31 

cm; the median basal diameter was 22 cm. The majority (156) of the 277 logs were 

decay class II, while 15, 64, 39, and 3 logs were decay classes I, III, IV, and V, 

respectively (table 2). Two hundred nine logs (75 percent) were identified as oak. 

Nearly half the total sample (46 percent) was class II oak logs (table 2). The null 

hypothesis that log species is independent of decay class was rejected (P < 0.0001). 

Table 2―The occurrence of oak and non-oak logs by decay class in the North Eagleville 

Tract of the forests at the University of Connecticut. 

_________________________________________________________ 

Decay class 

Log group I II III IV V Total 

________________________________________________________ 

Oak 6 128 50 22 3 209 

Non-Oak 9 28 14 17 0 68 

Total 15 156 64 39 3 277 

________________________________________________________ 

Strong microsite preferences were found (table 3). Algae, non-vascular plants, 

fungi, and signs of small mammal and bird perching were found on logs, but not on 

the leaf litter or soil of the adjacent, featureless forest floor. Vascular plants and 

seedlings were found significantly more frequently on the forest floor samples than 

on logs. More than 99 percent of the forest floor observations of seedlings and 

vascular plants involved plants rooted in soil (usually with the roots first going 

through leaf litter). Under-log habitat also provided shelter for seedlings and to a 

lesser extent for vascular plants and small mammals (table 3).
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 397 

Seedlings and vascular plants were the only life forms for which decay class was 

significant (P < 0.01). With increasing decay, a larger proportion of the logs in a 

decay class supported seedlings and vascular plants (table 4). Both seedlings and 

vascular plants occurred in lower (but not significantly lower) proportions than 

expected on oak logs. This did not alter the trend in the effect of decay class (table 4).

Log species was not statistically significant for any of the life forms.

Table 3―The frequency of representatives of seven life forms by forest floor microsite.1

Microsites 

Log Ground surface2 Under log3

Life 

forms 

 Soil Leaf litter Soil Leaf litter 

 

Algae 218 0 0 0 0 

 

Nonvascular 

plants 

246 0 0 1 0 

 

Fungi 261 0 0 0 0 

Seedlings 145 4267 1 71 2 

 

Vascular 

plants 

30 4265 1 10 0 

 

Birds 17 0 0 0 0 

Small 

mammals 

31 0 0 3 0 

1

A total of 277 logs and corresponding areas of ground surface was sampled. 

2

 The ground surface sample areas that included seedlings and vascular plants on leaf litter also included 

these life forms on soil; thus, the tally for ground surface as a whole is equal to the tally for soil. 3 The under log tallies were neither statistically analyzed alone nor included in the log tallies. 4 Almost all the seedlings and vascular plants tallied under “soil” grew out of leaf litter but were found to 

be actually rooted in soil after the leaf litter was moved to inspect the rooting medium. 

Table 4―The proportion of available oak and non-oak logs on which seedlings and vascular 

plants occurred. 

 Seedlings Vascular plants 

 Log species group Log species group 

 Decay 

 Class1

Oak Non-Oak Oak Non-Oak 

 I 0.33 0.33 0 0 

 II 0.41 0.50 0.04 0.14 

 III 0.54 0.64 0.10 0.14 

 IV 0.91 0.88 0.32 0.41 

1

 Decay class was significant (P<0.01) for both seedlings and vascular plants, and log species group was 

not independent of decay class; however, the differences in occurrence of seedlings and vascular plants 

by log species group (oak versus non-oak) were not significant. 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

398 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Discussion 

We found a wide range of differences among the seven life forms with regard to 

the importance of log habitat. We cannot quantify the absolute importance of forest 

floor logs because we did not quantify the proportions of the forest floor area 

occupied by logs and by featureless zones. Further, we did not sample all available 

types of forest floor microsites. Non-vascular plants, for example, were encountered 

only on logs in our study, but during sampling they were observed to be common on 

unsampled forest floor microsites, particularly rock surfaces. Similarly, another 

unsampled microsite, fine woody debris, provides an additional forest floor microsite 

for algae, non-vascular plants, and fungi in our study area (Kruys and Jonsson 1999). 

Forest floor logs and buried wood have been cited as important substrates for 

tree seedlings in a wide variety of locales, for example, in the Cascade Mountains 

(Christy and Mack 1984), the Adirondacks (McFee and Stone 1966), and the Great 

Smoky Mountains (White and others 1985). Our results, which show a lesser 

importance of logs as habitat for vascular plant seedlings, contrast with these reports. 

Some seed characteristics, seedbed conditions, seed sources, and the climatic 

conditions typical of second-growth, eastern hardwood forests may explain why we 

found more seedlings and vascular plants on the forest floor than on logs. Our study 

area is dominated by large- or medium-seeded species, for example oaks and maples. 

This contrasts with the small-seeded western hemlock (Tsuga heterophylla [Raf.] 

Sarg.) of Christy and Mack (1984), the red spruce (Picea rubens Sarg.), Fraser fir 

(Abies fraseri [Pursh] Poir.), and yellow birch (Betula alleghaniensis Britt.) studied 

by White and others (1985), or the studies involving spruce seedlings in Canada cited 

in support of the notion of foresters' frequently-voiced belief in the significance of 

decaying trunks and stumps for conifer seedlings (McFee and Stone 1966). Large 

seeds are less likely to lodge on a log (Szewczyk and Szwagrzyk 1996). The 

likelihood of seeds lodging on a log is promoted by surficial fissures (Goder 1961), 

such as those found on large trees, particularly rough-barked conifers. The eastern 

deciduous forest of North America is typically second-growth where the average 

overstory tree diameter is much less than that of old-growth forests (particularly 

those old-growth forests of the moist Pacific Northwest). Further, the microclimate of 

oak-dominated forests is considerably drier than that of moist coniferous forests. 

Thus, in comparison to moist old-growth conifer forests, the regeneration of vascular 

plants on logs in the eastern deciduous forest may be hampered by a combination of a 

less moist microclimate, larger seeds, and typically smaller logs. 

The seedbed conditions provided by logs in second-growth, eastern deciduous 

forests are less conducive to seedling germination and establishment than the 

conditions found on the forest floor or on logs in other locales. Seedling germination 

and establishment on logs requires moisture that may be provided by duff collected 

on the log surface (Goder 1961) or by decayed wood. The leaves of broad-leaved, 

deciduous forest trees are much less likely to remain on top of logs to decay into duff 

than are leaves of small-needled conifers, such as hemlock, spruce, or fir. Further, in 

our study area (and elsewhere in the eastern deciduous forest), the pool of available 

logs is dominated by a cohort of hard-surfaced, decay class II oaks believed to be the 

result of widespread mortality related to heavy infestations by the introduced gypsy 

moth (Lymantria dispar L.).3

 In addition, on the forest floor of oak-dominated 

forests, there is little competition from moss or herbaceous plants compared to 

 

3

 Unpublished data on file, C. Pyle, Storrs, Connecticut. 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 399 

conditions found in other forest cover types (Harmon and Franklin 1989). Thus, even 

where seedlings on logs are quite numerous (e.g., in canopy gaps), forest floor 

seedlings also are likely to be equally or more numerous. 

Although oak seed source is plentiful, the presence of oak seedlings on logs is 

largely curtailed by factors that affect seedling placement and establishment. 

Squirrels bury acorns in soil rather than in logs. Further, the establishment of oak 

seedlings depends upon the development of a tap root (unlikely to be successful on 

logs in the early stages of log decay). 

Despite these reasons for logs as likely to provide less suitable habitat than that 

found on the forest floor, some logs in our study area did support the growth of 

seedlings and vascular plants. We did not tally seedlings by species, but we did 

observe that in the vicinity of the occasional eastern hemlock (Tsuga canadenis [L.] 

Carr.) trees, certain logs had high concentrations of hemlock seedlings. In areas 

where the forest floor is covered by a thick layer of oak-dominated litter, the roots of 

newly germinated hemlock seedlings are unable to send roots through the forest floor 

litter to the soil. Eastern hemlock regeneration is typically restricted to CWD except 

where the forest floor has been disturbed (by mixing of organic and mineral soil or by 

fire) to expose a “partially decomposed layer” (Godman and Lancaster 1990). We 

speculate that in oak-dominated forests, logs may be found to be more important than 

the featureless forest floor for the regeneration of other small-seeded species in 

addition to hemlock. 

Our results corroborate the importance of logs for small mammals and birds. 

Because we used evidence of log use (table 1), rather than field sightings of small 

mammals and birds, our results for these two life forms address the habitat quality of 

logs only in the context of their preferred use as perches. 

Small mammals, seedlings, and vascular plants were observed under, as well as 

on, logs. Because not every log had habitat under it, our observations of the 

occurrences of organisms in this type of habitat (table 3) were not included in the 

statistical analysis of log use. However, the deterrent to browsing provided by logs 

situated above seedlings (Graham and others 1992) may be noteworthy in 

Connecticut and other locales where ungulate browsing is extensive. 

Log decay class was less frequently significant than expected. The state of log 

decay previously has been found to be important for a great variety of organisms 

(Crites and Dale 1998, Goder 1961, Hofgaard 1993, Kruys and others 1999, 

McCullough 1948, Muhle and LeBlanc 1975, Rambo and Muir 1998, Seastedt and 

others 1989, Szewczyk and Szwagrzyk 1996, Tallmon and Mills 1994). Stronger 

relationships to decay class might have been found had we used less broadly defined 

groups of organisms. Finally, it is worth considering that there are multiple decay 

classes present within most logs of a given decay class classification (Pyle and 

Brown 1999). In our study, the degree of habitat differences among logs of different 

decay classes may have been obscured with the tallying of presence/absence, rather 

than percent cover estimations for life forms, such as algae, fungi, and non-vascular 

plants. 

In contrast to other features of the forest floor (such as rock surfaces and fine 

woody debris), logs are a relatively long-lasting substrate that may be subject to 

control through forest management activities. The number, the decay class 

distribution, and the size of forest floor logs may be strongly influenced by 

management decisions in commodity forests. As knowledge increases concerning the 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

400 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

effects of log-related habitat on biological diversity, managers will be better prepared 

to make decisions concerning the desired characteristics of the woody debris to be 

left on the forest floor in logged areas. 

Summary and Conclusions 

Forest floor logs are an important and manageable habitat component for the 

promotion of biological diversity. In our study of the frequency of occurrence of 

seven broadly-defined forms of life on logs as compared to the featureless forest 

floor, logs were found to be better habitat for non-vascular plants, fungi, and algae, 

and preferred for perching by small mammals and birds. Further study is needed to 

quantify the importance of other forest floor features and the importance of the 

various microsites relative to the proportion of the forest floor they occupy. 

Although the frequency of logs with an observed presence of vascular plants and 

seedlings was significantly less than that for corresponding areas of ground surface, 

some seedlings and vascular plants did occur on logs in the second-growth hardwood 

forest study area. The presence of seedlings and vascular plants on logs was 

independent of log species (oak vs. non-oak), but not of decay class. The more 

decayed a log, the greater the likelihood that seedlings and vascular plants were 

present. 

Acknowledgments 

This paper is Scientific Contribution Number 1922 of the Storrs Agricultural 

Experiment Station and represents work supported by McIntire-Stennis project 

number CONS00691, C. Pyle, Principal Investigator. We thank James K. Agee, 

Jeffrey H. Gove, Jo Ann Reynolds, and Martin A. Spetich for helpful comments on 

the manuscript. 

References 

Barnum, Sarah A.; Manville, Christiana J.; Tester, John R.; Carmen, William J. 1992. Path 

selection by Peromyscus leucopus in the presence and absence of vegetative cover. 

Journal of Mammalogy 73(4): 797-801. 

Bratton, Susan Power. 1976. Resource division in an understory herb community: 

responses to temporal and microtopographic gradients. American Naturalist 110: 

679-693. 

Brumbach, Joseph J. 1965. The climate of Connecticut. Bulletin 99. State Geological and 

Natural History Survey of Connecticut; 215 p. 

Bull, Evelyn L.; Parks, Catherine G.; Torgerson, Torolf R. 1997. Trees and logs important 

to wildlife in the Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Christy, E. Jennifer; Mack, Richard N. 1984. Variation in demography of juvenile Tsuga 

heterophylla across the substratum mosaic. Journal of Ecology 72: 75-91. 

Coney, C. Cliff; Tarpley, Wallace A.; Warden, John C.; Nagel, Jerry W. 1982. Ecological 

studies of land snails in the Hiwassee River Basin of Tennessee, USA. Malacological 

Review 15: 69-106. 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 401 

Crites, Susan; Dale, Mark R. T. 1998. Diversity and abundance of bryophytes, lichens, and 

fungi in relation to woody substrate and successional stage in aspen mixedwood 

boreal forests. Canadian Journal of Botany 76: 641-651. 

Duffield, John W. 1990. Forest regions of North America and the world. In: Young, 

Raymond A.; Giese, Ronald L., ed. Introduction to forest science. New York: Wiley & 

Sons; 35-65. 

Elton, Charles S. 1966. Dead and dying wood. In: Elton, Charles S. The pattern of animal 

communities. New York: John Wiley & Sons; 279-305. 

Goder, Harold A. 1961. Hemlock reproduction and survival on its border in Wisconsin. 

Transactions of the Wisconsin Academy of Sciences, Arts and Letters 50: 175-181. 

Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr. Eastern hemlock. 

In: Burns, Russell M.; Honkala, Barbara H., technical coordinators. Silvics of North 

America: 1, Conifers. Agric. Handb. 654. Washington, DC: U.S. Department of 

Agriculture; 602-612. 

Graham, R. T.; Kingery, J. L.; Volland, L. A. 1992. Livestock and forest management 

interactions. In: Black, H., technical editor. Silvicultural approaches to animal 

damage management in Pacific Northwest forests. Gen. Tech. Rep. PNW-GTR-287. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 351-364. 

Graham, Russell T.; Harvey, Alan E.; Jurgensen, Martin F.; Jain, Theresa B.; Tonn, Jonalea 

R.; Page-Dumroese, Deborah S. 1994. Managing coarse woody debris in forests of 

the Rocky Mountains. Res. Pap. INT-RP-477. Ogden, UT: Intermountain Research 

Station, Forest Service, U.S. Department of Agriculture; 12 p. 

Harmon, Mark E.; Franklin, Jerry F. 1989. Tree seedlings on logs in Picea-Tsuga forests of 

Oregon and Washington. Ecology 70: 48-59. 

Harmon, Mark E.; Sexton, Jay. 1996. Guidelines for measurements of woody detritus in 

forest ecosystems. Publication No. 20. Seattle, WA: U.S. LTER Network Office, 

University of Washington; 73 p. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, Phillip; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15: 133-302. 

Harmon, Mark E.; Sexton, Jay; Caldwell, Bruce A.; Carpenter, Steve E. 1994. Fungal 

sporocarp mediated losses of Ca, Fe, K, Mg, Mn, N, P, and Zn from conifer logs in 

the early stages of decomposition. Canadian Journal of Forest Research 24: 1883-1893. 

Hendrickson, O. Q. 1991. Abundance and activity of N2-fixing bacteria in decaying wood. 

Canadian Journal of Forest Research 21: 1299-1304. 

Hofgaard, Annika 1993. Structure and regeneration patterns in a virgin Picea abies forest 

in northern Sweden. Journal of Vegetation Science 4: 601-608. 

Kruys, Nicholas; Jonsson, Bengt Gunnar. 1999. Fine woody debris is important for species 

richness on logs in managed boreal spruce forests of northern Sweden. Canadian 

Journal of Forest Research 29: 1295-1299. 

Kruys, Nicholas; Fries, Clas; Jonsson, Bengt Gunnar; Lämås, Tomas; Ståhl, Goran. 1999. 

Wood-inhabiting cryptogams on dead Norway spruce (Picea alba) trees in managed 

Swedish boreal forests. Canadian Journal of Forest Research 29: 178-186. 

Larsen, Michael J.; Jurgensen, Martin F.; Harvey, Alan E. 1978. N2 fixation associated with 

wood decayed by some common fungi in western Montana. Canadian Journal of 

Forest Research 8: 341-345. 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

402 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Maser, Chris; Trappe, James M. 1984. The seen and unseen world of the fallen tree. Gen. 

Tech. Rep. PNW-164. Portland, OR: Pacific Northwest Forest and Range Experiment 

Station, Forest Service, U.S. Department of Agriculture; 56 p. 

Maser, Chris; Anderson, Ralph G.; Cromack, Kermit, Jr.; Williams, Jerry T.; Martin, Robert 

E. 1979. Dead and down woody material. In: Thomas, Jack Ward, technical editor. 

Wildlife habitats in managed forests in the Blue Mountains of Oregon and Washington. 

Agric. Handb. 553. Washington, DC: U.S. Department of Agriculture, Forest Service; 

78-95. 

McCullough, Herbert A. 1948. Plant succession on fallen logs in a virgin spruce-fir forest. 

Ecology 29: 508-513. 

McFee, W. W.; Stone, E. L. 1966. The persistence of decaying wood in the humus layers 

of northern forests. Soil Science Society of America Proceedings 30: 513-516. 

McMinn, James W., Crossley, D. A., Jr., technical coordinators. 1996. Biodiversity and 

coarse woody debris in southern forests. Gen. Tech. Rep. SE-94. Asheville, NC: 

Southern Research Station, Forest Service, U.S. Department of Agriculture; 146 p. 

Minore, Don. 1972. Germination and early survival of coastal tree species on organic 

seed beds. Res. Pap. PNW-135. Portland, Oregon: Pacific Northwest Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 18 p. 

Molina, Randy; O'Dell, Thomas; Luoma, Daniel; Amaranthus, Michael; Castellano, Michael; 

Russell, Kenelm. 1993. Biology, ecology, and social aspects of wild edible 

mushrooms in the forests of the Pacific Northwest: a preface to managing 

commercial harvest. Gen. Tech. Rep. PNW-GTR-309. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 42 p. 

Muhle, H.; LeBlanc, F. 1975. Bryophyte and lichen succession on decay logs. I. Analysis 

along an evaporational gradient in eastern Canada. Journal of the Hattori Botanical 

Laboratory 39: 1-33. 

Nakashizuka, Tohru. 1989. Role of uprooting in composition and dynamics of an oldgrowth forest in Japan. Ecology 70: 1273-1278. 

Olszewski, Jerry L. 1968. Role of uprooted trees in the movements of rodents in forests. 

Oikos 19: 99-104. 

Panshin, A.J.; de Zeeuw, Carl. 1980. Textbook of wood technology. 4th ed. New York: 

McGraw-Hill Book Co; 722 p. 

Pyle, Charlotte; Brown, Michelle M. 1998. A rapid system of decay classification for 

hardwood logs of the eastern deciduous forest floor. Journal of the Torrey Botanical 

Society 125: 237-245. 

Pyle, Charlotte; Brown, Michelle M. 1999. Heterogeneity of wood decay classes within 

hardwood logs. Forest Ecology and Management 114: 253-259. 

Rambo, Thomas R.; Muir, Patricia S. 1998. Bryophyte species associations with coarse 

woody debris and stand ages in Oregon. The Bryologist 101(3): 366-376. 

Ringvall, Anna; Ståhl, Göran. 1999. Field aspects of line intersect sampling for assessing 

coarse woody debris. Forest Ecology and Management 119: 163-170. 

Samuelsson, Johan; Gustafson, Lena; Ingelög, Torleif 1994. Dead and dying trees--a review 

of their importance for biodiversity. Swedish Environmental Protection Agency, 

Report 4306, ISBN 91-620-4306-4; 109 p. 

Seastedt, T. R.; Reddy, M. V.; Cline, S. P. 1989. Microarthropods in decaying wood from 

temperate coniferous and deciduous forests. Pedobiologia 33: 69-77. 
The Effects of Microsite on Forest Floor Biota—Pyle and Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 403 

Steel, E. Ashley; Naiman, Robert J.; West, Stephen D. 1999. Use of woody debris piles by 

birds and small mammals in a riparian corridor. Northwest Science 73(1): 19-26. 

Stephens, Earl P. 1956. The uprooting of trees: a forest process. Soil Science Society of 

America Proceedings 20: 113-116. 

Summers, Gerald; Uetz, George W. 1979. Microhabitats of woodland centipedes in a 

streamside forest. American Midland Naturalist 102: 346-352. 

Swindel, Benee, F.; Smith, Joel E.; Abt, Robert C. 1991. Methodology for predicting 

species diversity in managed forests. Forest Ecology and Management 40: 75-85. 

Szewczyk, J.; Szwagrzyk, J. 1996. Tree regeneration on rotten wood and on soil in oldgrowth stand. Vegetatio 122: 37-46. 

Tallmon, David; Mills, L. Scott. 1994. Use of logs within home rages of California redbacked boles on a remnant of forest. Journal of Mammalogy 75: 97-101. 

Thompson, John. N. 1980. Treefalls and colonization patterns of temperate forest herbs. 

American Midland Naturalist 104: 176-184. 

U.S. Department of Agriculture, Soil Conservation Service. 1966. Soil survey, Tolland 

County, CT. Series 1961, No. 35. Washington, DC: U.S. Government Printing Office; 

114 p. 

White, Peter S.; MacKenzie, Mark D.; Busing, Richard T. 1985. Natural disturbance and 

gap phase dynamics in Southern Appalachian spruce-fir forests. Canadian Journal of 

Forest Research 15: 233-240. 

Zar, Jerrold H. 1999. Biostatistical analysis. 4th ed. Upper Saddle Cliffs, NJ: Prentice-Hall; 

663 p. 
Demographics and Dynamics of Dead Wood

405
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 407 

Overview of Agents and Patterns of 

Mortality and Resulting Coarse Woody 

Debris Recruitment in Western Forests1

Brytten E. Steed2 and Michael R. Wagner2

Abstract 

We present an overview of many of the mortality agents in western coniferous forests of the 

United States that are responsible for coarse woody debris recruitment under natural 

conditions. Patterns and scale of occurrence of mortality agents for the six western USDA 

Forest Service Regions are examined at both historic and projected-risk time periods. The 

data indicates that bark beetles have been the most important source of mortality in the 

western U.S., and with the exception of the Northern Region, this trend is expected to 

continue. Defoliators, although important in growth loss, have not had as large a mortality 

impact. Recent-past and projected-risk data indicate that root disease may be an even more 

important factor in tree mortality and recruitment of coarse woody debris than indicated in 

recent literature. Although regional measures of actual mortality are not available, all western 

Regions show high impacts by dwarf mistletoe (Arceuthobium spp.) during the past 20 years. 

Fire affects relatively few hectares compared to insect and disease, but the effects on coarse 

woody debris (recruitment and conditioning) are important. Additional concerns for managers 

wishing to augment coarse woody debris are also presented. 

Introduction 

Coarse woody debris, both standing and fallen, is an important component in 

many physical, chemical, and biological processes of forested ecosystems (Graham 

and others 1994). Important functions include erosion control, nutrient cycling, and 

wildlife and microbial habitat (Harmon and others 1986, Li and Crawford 1994, 

Light and Burbridge 1985, Lofroth 1998, McGregor 1985b). The role of dead wood 

in these functions depends largely on such characteristics as size and form, 

orientation (standing or down), and resident flora and fauna. These characteristics, in 

turn, are formed by a number of environmental factors including habitat type, forest 

structure, site quality, climate, geography, disturbance agents, and decay organisms 

(Harmon and others 1986). Many of these environmental factors are integral to the 

ecosystem in which the dead wood is found. In other words, the forces that define 

what may be called a dead wood regime also comprise many of the processes that 

define ecosystems and communities (biologically delineated zones). 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Graduate Student and Regent’s Professor, respectively, Northern Arizona University, School of 

Forestry, PO Box 15018, Flagstaff, AZ 86011-5018 (e-mail adddresses: Brytten.Steed@nau.edu and 

Mike.Wagner@nau.edu) 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

408 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Dead wood regimes are processes of intermediate time and spatial scales, and 

interrelated to disturbance and environmental processes, suggesting that analysis of 

dead wood in the western United States should be done by regions definable by such 

characteristics as forest type, geography, disturbance regimes, climate, and history; 

for time frames somewhere between seasonal and geologic; and by including aspects 

of the various processes in a dead wood regime, such as tree growth, method of 

death, decomposition and decay. If one process of a dead wood regime is to be used 

for analysis, disturbance or mortality agents are obvious choices. 

The agent responsible for dead wood recruitment often acts on conditions of the 

live tree (Wargo 1995). These characteristics of the live tree, together with the unique 

attributes of the killing agent, determine much of the functional pathway followed by 

the wood in the ecosystem as it deteriorates (Bull and others 1997, Castello and 

others 1995, Geils and others 1995, Hadfield and Magelssen 1999). Impacts on 

characteristics of the living tree, either directly on the disturbance agent or on any 

part of the “death” processes, could change the disturbance process. 

Changes in primary mortality agents over time or space could alter the character 

and distribution of dead wood in the system. Such changes could have important 

effects on many ecosystem processes (Graham and others 1994, Hagle and others 

1995, Harmon and others 1986, Light and Burbridge 1985), and recognition of these 

changes would constitute valuable information for forest health management. For 

example, insect outbreaks, fire history, and rangeland condition in the Southwest can 

be directly related to changes in climate disturbances (Swetnam and Baisan 1994, 

Swetnam and Betancourt 1998, Swetnam and Lynch 1993). 

Our analysis presents an overview of many of the mortality agents in western 

coniferous forests of the U.S. that are responsible for mortality and subsequent 

recruitment of coarse woody debris under natural conditions. Spatial and temporal 

differences in the importance of these agents are examined. Implications of these 

differences on the ecosystem, on management of coarse woody debris, and on forest 

health in general are discussed. Finally, risks associated with management activities 

designed to create coarse woody debris and their mitigation are summarized. 

Material and Methods 

Analysis Area 

Data on the impact of mortality agents was gathered for western coniferous 

forests of the U.S. Most information was obtained from the USDA Forest Service, in 

particular, Forest Health Protection. Thus, discussion of patterns and scale of 

mortality agents will be presented by Forest Service Regions (fig. 1). Because there is 

relatively little hardwood area in the West, data on forest health in western forests is 

largely data for coniferous species (USDA Forest Service 1958). 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 409 

Figure 1―State boundaries and USDA Forest Service Regions. 

Patterns and Scale of Occurrence of Mortality Agents

Studies in landscape ecology note that disturbance agents may operate at 

different spatial and temporal scales and are interrelated (Eng 1998, Harmon and 

others 1986, Holling 1992, Parminter 1998, Swetnam and Lynch 1993, White and 

others 1999). The most commonly recognized spatial scales include gap, stand, 

watershed, and landscape, while common temporal scales include seasonal, annual, 

and long term. These scales are intermediate in nature between the smallest, fastest, 

vegetation-directed scale and the largest, slowest, geologic, or evolutionary scale. 

Because activity at one level both influences the next higher level and contains all the 

levels found below it (Harmon and others 1986, Parminter 1998), our analysis of the 

effects of mortality agents on coarse woody debris could be done at many levels 

(Holling 1992). Ideally, the scale used to evaluate a process should be helpful in the 

explanation of observable patterns (Eng 1998). However, the availability and the 

scale (temporal and spatial) of that data may dictate at least the first steps in 

determining what sizes and time frames are considered. 

In our analysis, we chose to review the entire western U.S. Thus, we were 

limited to a landscape spatial scale of Forest Service Regions and three long-term 

(approximately 15-20 years) temporal periods: up to and including 1952 (past), 1978-

97 (recent past), and 2000-2015 (future based on projected risk). The availability of 

data for these temporal periods did differ, and in some cases the evaluation of the 

effects of some mortality agents was not possible. Also, the use of the geo-political 

Forest Service Region boundaries complicated analysis that ideally should have been 

related to biologically delineated boundaries. 

Measurement of an agent’s impact (severity and extent) also was limited. Total 

area affected was used as the measure for the recent-past and projected-risk data. 

However, volume measures were used in the 1952 data. The relationship of area 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

410 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

affected to the volume of coarse woody debris or number of trees killed has not been 

determined, and no measure of dispersion (density and patchiness) is available. 

However, all three measures of impact (area affected, tree volume, stem number), as 

well as spatial and temporal scales and dispersion, are likely important in assessing 

the relative effects of any one agent on the ecosystem. 

Specific Mortality Agents: Patterns and Scale 

Historical (Recent past)―Recent data was compiled for five specific 

mortality agents for the 20-year period of 1978 to 1997 (recent past). The mortality 

agents chosen, based on overall importance and data availability, included mountain 

pine beetle (MPB) (Dendroctonus ponderosae Hopkins), western spruce budworm 

(WSBW) (Choristoneura occidentalis Freeman), root disease (RD) (most likely 

Armillaria spp., Phellinus weirri Gilbertson, Heterobasidion annosum Bref., 

Phaeolus schweinitzii Pat., and Ceratocystis spp.), dwarf mistletoe (DM) 

(Arceuthobium spp.), and wildfire (FIRE). MPB was chosen as a principal bark beetle 

and WSBW as a principal defoliator. 

Because of the nature of the mortality agent (slow or fast acting over a large or 

small area), the data available on the effects of these agents varied. For the insect 

pests and fire, data generally consisted of annual hectares affected, although the 

number of trees killed and volume killed were sometimes calculated. Information in 

national and many regional annual Forest Insect and Disease Conditions Reports

(issued by the Forest Service’s Forest Health Protection) was used to determine 

annual impacts (hectares) and calculate an annual average impact (total 

hectares/years) for the six Forest Service Regions and the West as a whole, and to 

evaluate discrepancies in reported numbers (Bridgwater 1985, DeNitto 1985, Johnson 

and Hawksworth 1985, McGregor 1985a). In the case of MPB, adequate data was not 

available for 1978 or 1984. For FIRE, national records were not available until 1984 

(USDA Forest Service 1992, USDA Forest Service 1998), although longer fire 

histories have been reconstructed for areas such as the Southwestern Region by using 

tree ring data (Swetnam and Betancourt 1998) 

Records of annual mortality for RD and DM are not readily available. Aerial 

detection of these diseases is more difficult and their impact is more gradual, creating 

problems in making annual mortality calculations. However, average annual impacts 

of these two agents were evaluated in the early 1980s by the Forest Service. Numbers 

from these studies and an updated summary of forest health conditions were used in 

our analysis (DeNitto 1985, Drummond 1982, Johnson and Hawksworth 1985, Smith 

1984). RD mortality was estimated as the average annual volume killed (cubic 

meters) (Smith 1984). Estimates of effects of DM mortality were not available. 

Rather, volume loss (mortality plus growth loss) was given in both cubic meters and 

hectares of infestation (Drummond 1982). 

In order to display RD mortality on a graph in terms of “number of hectares 

affected,” a ratio was calculated using the available cubic meter measurement of RD 

from Smith (1984), and the cubic meter and hectare measurements of DM from 

Drummond (1982). Although these RD ‘hectares’ are not a true measure of the area 

of mortality, they do retain the relationship of the relative importance of RD to DM 

indicated in the volume measurements. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 411 

Projected Risk―Projections of future importance of principal mortality 

agents are found in the Forest Service’s Forest Health Protection national risk 

assessment project. The risk assessment project delineates general areas that are 

expected to experience 25 percent or more tree mortality over the next 15 years based 

on the expert opinion of professional pest management specialists. Although this risk 

assessment process is both coarse as well as iterative (changing as better numbers 

become available), current predictions provide us an opportunity to evaluate possible 

future changes in mortality agent importance. Information on future trends may help 

managers prepare for possible changes in coarse woody debris recruitment. Because 

of regional differences in data availability and mortality agent activity, modeling of 

expected mortality was left to the discretion of the regional Forest Service Forest 

Health Protection specialists. Risk assessment methodologies are discussed by Lewis 

(2002). 

We used preliminary risk data (hectares) to create graphics showing the relative 

importance of the same five mortality agents used in the evaluation of the recent-past 

data.3

 Fire data for the risk assessment project was not obtained, but the insect and 

disease agents were comparable. Actual hectares will not be presented here, but 

eminent modifications in the risk data are not expected to greatly alter the relative 

importance of the various agents. However, in the more distant future, introduction of 

exotic insects and diseases, or dramatic changes in forest type or climate could cause 

significant shifts in realized agent importance. 

Mortality Agent Groups: Patterns and Scale 

Projected Risk―The projected risk data contains a more complete list of 

mortality agents than the five specific agents we used. In order to evaluate the 

importance of bark beetles as a group (including MPB) as well as defoliators 

(including WSBW) and other insects and disease, the risk data was partitioned into 

the following six agent groups: bark beetles (BB), defoliators (DF), other insects 

(IO), root disease (RD), dwarf mistletoe (DM), and other pathogens (PO). 

Organisms within each group include: mountain pine beetle, Douglas-fir beetle 

(Dendroctonus pseudotsuga Hopkins), spruce beetle (D. rufipennis [Kirby]), western 

pine beetle (D. brevicomis LeConte), Jeffery pine beetle (D. jeffreyi Hopkins), roundheaded pine beetle (D. adjunctus Blandford), southern pine beetle (D. frontalis

Zimmerman), pine engraver (Ips pini Say), fir engraver (Scolytus ventralis LeConte), 

and western balsam bark beetle (Dryocetes confusus Swaine) for BB; western spruce 

budworm and Douglas-fir tussock moth (Orgyia pseudotsugata [McDunnough]) for 

DF; balsam woolly adelgid (Adelges piceae [Ratzeburg]) for IO; annosus root 

disease, subalpine fir decline, and other unnamed root diseases for RD; various dwarf 

mistletoes (Arceuthobium spp.) for DM; and comandra blister rust (Cronartium 

comandrae Peck) and white pine blister rust (C. ribicola Fisch) under PO. The 

relative importance of each of theses groups was calculated and presented graphically 

for comparison. 

Historical (1952)―The best data on historical mortality trends for most of the 

same six agent groupings was collected in 1952 (USDA FS 1958). The more recent 

forest health data (recent past) contained too much missing data to calculate adequate 

 

3

 Unpublished date on file (12/24/99), USDA Forest Service, Forest Health Protection (Washington and 

Regional Offices). 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

412 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

numbers for the BB, DF, IO, and PO categories. Because of the differences in the 

1952 data standards, two graphics were created. The first graphic uses information 

from the year 1952 for mortality groups similar to those delineated for the risk data: 

bark beetle (BB), defoliators (DF), other insects (IO), root disease (RD), heart rot, 

and stem disease (includes DM, heart rot, and blister rust) (HR/SD), and other 

pathogens (PO). The second graphic uses trend data as determined in 1952 for the 

broader groupings of insects, disease, fire, and other (USDA Forest Service 1958, 

specifically, Basic Statistical Tables 17, 66, and 76). 

Mortality of sawtimber (board feet) was chosen to be most comparable to our 

other data. Thus, information on growth loss and on growing stock was not used. As 

with all data in this study, hardwoods are minimal and were not separated from 

conifers. 

The 1952 information was not available for the Forest Service Regions (fig. 1). 

Instead, data was either given by state or by different regional areas. For example, in 

place of the Northern, Rocky Mountain, Southwestern and Intermountain Regions, 

the 1952 study combines these four Regions into two larger Regions: the Northern 

Rocky Mountains and the Southern Rocky Mountains. The Northern Rocky 

Mountains contains all of the Northern as well as part of the Rocky Mountain and 

Intermountain Regions (Idaho, Montana, South Dakota and Wyoming). The Southern 

Rocky Mountain contains all of the Southwestern as well as the remainder of the 

Rocky Mountain and Intermountain Regions (Arizona, New Mexico, Colorado, Utah, 

Nevada). Differences in the measure of impact (volume, not area) and in regional 

delineations complicate comparisons, but relative importance of mortality agents is 

expected to remain indicative. 

Results 

Patterns and Scale of Occurrence of Mortality Agents 

The terms “impact” and “area affected” used in the following results and 

discussion should be clearly understood to avoid confusion in interpretation of the 

data. As noted previously, impact of a mortality agent on a tree can be measured as 

volume, number of trees, or area killed. Available data, however, limited us to the 

measurement of “hectares affected.” Thus, the word “impact” refers to this 

measurement of hectares only and should not be directly equated to “biological 

impact.” The term “area affected” should also be clarified. Although we are 

principally interested in dead trees, mortality data was not always available. For 

agents whose principal consequence is growth loss and not death, the relationship 

between the number of hectares affected and hectares that experienced mortality are 

unclear. Thus, for agents such as WSBW and DM many of the hectares affected may 

not have experienced mortality. 

Specific Mortality Agents: Patterns and Scale 

Historical (Recent past)―Examples of the differences in the scales and 

temporal patterns of the five specific mortality agents from 1978 to 1997 are 

presented for the Forest Service’s Northern Region (fig. 2) and the Southwestern 

Region (fig. 3). As expected, area affected by insects (MPB and WSBW) and fire 

vary considerably from year to year, although long-term patterns often occur. MPB 

levels in the Northern Region show a clear example of an activity cycle spanning 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 413 

multiple years (fig. 2). RD and DM are more pervasive (more area affected) than 

insects and fire. The depiction of RD and DM effects using a straight-line average 

(annual values not available) does not display fluctuations known to occur in 

response to variations in environmental factors (e.g., drought stress). However, these 

yearly fluctuations are known to be less dramatic than those experienced by insects 

and fire (Dahms and Geils 1997, Drummond 1982, Smith 1984). 

The average annual area affected (thousands of hectares/year) by MPB, WSBW, 

RD, DM, and for each of the six Forest Service Regions of the West was determined 

using regional data from 1978 through 1997 (fig. 4). Although numbers used for RD 

are not actually the ‘area affected,’ they do maintain the relationship between DMand RD-affected volume. Interestingly, in the Northern, Rocky Mountain, and 

Southwestern Regions these calculations of RD hectares resemble the ‘area of 

management concern’ for RD presented in the 1985 forest health summary (DeNitto 

1985). Also, comparison with other data for the Pacific Southwest shows that our 

relative area for RD preserves relationships among agents in terms of overall impact 

(USDA Forest Service 1979). The difficulty in interpreting these hectare totals lies in 

the disproportional area within each Region. 

Figure 2―Fluctuation patterns of hectares affected by five specific mortality agents 

in the Forest Service’s Northern Region, 1978-1997. Agents included mountain pine 

beetle (MPB) (Dendroctonus poderosae), western spruce budworm (WSBW) 

(Choristoneura occidentalis), root disease (RD) (most likely Armillaria spp., Phellinus 

weirri, Heterobasidion annosum, Phaeolus schweinitzii, and Ceratocystis spp.), dwarf 

mistletoe (DM) (Arceuthobium spp.), and wildfire (FIRE). Areas of WSBW and DM 

are affected hectares rather than hectares of mortality. In order to graphically display 

RD in terms of “number of hectares affected,” a ratio was calculated using the 

available cubic meter measurement of RD mortality (Smith 1984) and the cubic meter 

and hectare measurements of DM volume loss (Drummond 1982). Although the RD 

“hectares” are not a true measure of area, they do retain the relationship of the 

relative importance of RD volumes to DM volumes. RD and DM are known to 

fluctuate somewhat, but these patterns have not been followed closely. FIRE 

numbers for the Northern Region are actually for Idaho and Montana rather than the 

Forest Service regional area. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

414 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 3―Fluctuation patterns of hectares affected by five specific mortality agents 

in the Forest Service’s Southwestern Region, 1978-1997. Agents included mountain 

pine beetle (MPB) (Dendroctonus ponderosae), western spruce budworm (WSBW) 

(Choristoneura occidentalis), root disease (RD) (most likely Armillaria spp., Phellinus 

weirri, Heterobasidion annosum, Phaeolus schweinitzii, and Ceratocystis spp.), dwarf 

mistletoe (DM) (Arceuthobium spp.), and wildfire (FIRE). Areas of WSBW and DM 

are affected hectares rather than hectares of mortality. In order to graphically display 

RD in terms of “number of hectares affected,” a ratio was calculated using the 

available cubic meter measurement of RD mortality (Smith 1984), and the cubic 

meter and hectare measurements of DM volume loss (Drummond 1982). Although 

the RD “hectares” are not a true measure of area, they do retain the relationship of 

the relative importance of RD volumes to DM volumes. RD and DM are known to 

fluctuate somewhat, but these patterns have not been followed closely. 

All hectares affected by the five specific agents were combined, and the relative 

importance (as a percent of the total affected area) was determined for each Region 

(fig. 5). This interpretation lacks the ability to show quantitative levels of agent 

impact (e.g., hectares/Region or hectares affected/hectares available). However, it 

does provide a basis for the evaluation of which agents may be principal in creation 

of coarse woody debris within a Region. 

As expected, MPB is relatively important in the Northern, Rocky Mountain, 

Intermountain, and Pacific Northwest Regions where it attacks mostly lodgepole pine 

(Pinus contorta Dougl. ex. Loud.) and some ponderosa pine (P. ponderosae Dougl. 

ex. Laws.) (fig. 5). However, MPB is relatively less important in the Southwestern 

and Pacific Southwest Regions. WSBW incidence is widespread but is relatively 

more important in the Rocky Mountain Region. RD has been active in the Northern, 

Pacific Northwest, and Pacific Southwest Regions with some impact noted in the 

Southwestern and very little noted in the Rocky Mountain and Intermountain 

Regions. DM is the most active agent over the entire West and is particularly 

important in the Southwestern, Intermountain, and Pacific Southwest Regions. The 

limited number of hectares affected by other agents in these Regions would explain 

why DM shows higher importance in the southern Regions. Fire affects few hectares 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 415 

on average but is active in all Regions. Over the entire West, diseases affect a greater 

area than do insects and fire combined. 

Figure 4―Average annual area (in thousands of hectares) affected by five specific 

mortality agents in each of six of the Forest Service’s western Regions: recent past 

(1978-1997). Agents included mountain pine beetle (MPB) (Dendroctonus

ponderosae), western spruce budworm (WSBW) (Choristoneura occidentalis), root 

disease (RD) (most likely Armillaria spp., Phellinus weirri, Heterobasidion annosum, 

Phaeolus schweinitzii, and Ceratocystis spp.), dwarf mistletoe (DM) (Arceuthobium

spp.), and wildfire (FIRE). Areas of WSBW and DM are affected hectares rather than 

hectares of mortality. In order to graphically display RD in terms of “number of 

hectares affected,” a ratio was calculated using the available cubic meter 

measurement of RD mortality (Smith 1984) and the cubic meter and hectare 

measurements of DM volume loss (Drummond 1982). Although the RD ‘hectares’ are 

not a true measure of area, they do retain the relationship of the relative importance 

of RD volumes to DM volumes. RD and DM are known to fluctuate somewhat, but 

these patterns have not been followed closely. FIRE numbers for the Regions are 

actually by state boundaries resulting in slightly different areas for the Northern, 

Rocky Mountain, and Intermountain Regions. 

Projected Risk―The expected importance of the four insect and disease 

agents (fire excluded) over the next 15 years is based on predicted mortality (not 

growth loss) (fig. 6), which may explain the principal changes in importance between 

predicted and past agent importance. In the recent-past data MPB was not the 

principal active agent in any Region. However, when predicted mortality is 

considered, MPB is expected to be the principal mortality agent in half of the 

Regions (Rocky Mountain, Intermountain, and Pacific Northwest). RD was and is 

predicted to be the principal active agent in the Northern Region and is predicted to 

be the principal agent in the Pacific Southwest. In the Southwestern Region, DM is 

predicted to be the most important mortality agent, with considerable activity in the 

Pacific Southwest. Despite their large area of influence in all Regions during the past 

20 years (recent past), predicted importance of WSBW and DM is much lower due to 

the minimal associated mortality. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

416 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Differences in agent past and predicted importance (figs. 5, 6) may be indicative 

of changes in host availability, advances in detection of agents, increased recognition 

of agent roles, differences between area affected (recent past) and area of mortality 

(projected risk), or differences in methodologies used to determine affected area. 

Small changes are also expected due to the exclusion of fire from the projected 

mortality data. We should note that relative importance of an agent over the entire 

western U.S. differs depending on whether relative importance (by hectares) or 

average percent importance (sum of percentages divided by six Regions) is used. 

These differences between relative importance values are due to the very high 

number of hectares of RD mortality predicted by the Northern Region. 

Figure 5―The historical relative importance of five specific mortality agents in the 

western U.S.: recent past (1978-1997). Agents included mountain pine beetle (MPB) 

(Dendroctonus ponderosae), western spruce budworm (WSBW) (Choristoneura

occidentalis), root disease (RD) (most likely Armillaria spp., Phellinus weirri, 

Heterobasidion annosum, Phaeolus schweinitzii, and Ceratocystis spp.), dwarf 

mistletoe (DM) (Arceuthobium spp.), and wildfire (FIRE). Data from 1978 to 1997 

were used to calculated annual averages. In some cases data was missing. MPB 

data was complete for 18 of the 20 years. FIRE data was available from 1984 to 1997 

for a total of 14 years. Data for RD and DM were from the early 1980s. Importance of 

WSBW and DM are based on affected hectares rather than hectares of mortality. RD 

importance was calculated based on a ratio of the volume impacts of RD to DM. 

FIRE numbers for the Regions are actually by state boundaries resulting in slightly 

different areas for the Northern, Rocky Mountain, and Intermountain Regions. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 417 

Figure 6―The predicted relative importance of four specific insect and disease 

mortality agents in the western U.S.: projected risk (2000-2015). Agents include 

mountain pine beetle (MPB) (Dendroctonus ponderosae), western spruce budworm 

(WSBW) (Choristoneura occidentalis), root disease (RD) (most likely Armillaria spp., 

Phellinus weirri, Heterobasidion annosum, Phaeolus schweinitzii, and Ceratocystis

spp.), and dwarf mistletoe (DM) (Arceuthobium spp.). Data are from a Forest Service 

risk assessment project being conducted by the Washington, D.C. office and is 

preliminary only. Revisions are being completed by the Forest Service. However, 

relative importance relationships are expected to remain similar. Because FIRE is not 

graphed, the importance of each agent is not directly comparable to figure 5. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

418 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Mortality Agent Groups: Patterns and Scale 

Projected Risk―Because of the inclusion of many other bark beetles species 

and of white pine blister rust (under other pathogens [PO]) (fig. 7), the expected 

relative importance of the “agent groups” differs somewhat from the “specific 

agents” (figs. 5, 6). MPB used in figures 5-6 is only one of many important bark 

beetles of the western U.S. Risk data predicts MPB will contribute approximately 

half of the bark beetle mortality over the next 15 years in the Northern, Rocky 

Mountain, and Pacific Northwest Regions. In the Southwestern Region, MPB 

constitutes only about 7.5 percent of the predicted BB mortality, while in the 

Intermountain and Pacific Southwest, MPB constitutes only 13 and 22 percent, 

respectively. Additional mortality in the West is expected from Douglas-fir beetle, 

western pine beetle, round-headed pine beetle, Jeffery pine beetle, spruce beetle, fir 

engraver, western balsam bark beetle, and ips (Ips spp.).3 Most Regions maintain 

similar importance profiles whether “specific agents” or “agent groups” are used. 

Only in the Southwestern and the Pacific Southwest Regions did MPB impact fail to 

represent BB impact. WSBW successfully represented DF in all of the Regions 

except Intermountain, where Douglas-fir tussock moth (Orgyia pseudotsugata

McDunnough) is expected to cause considerable defoliation impact. Information 

indicates that insects other than BB and DF are not expected to contribute significant 

additional mortality to western conifers. However, recent and future exotic insect 

introductions could have considerable unpredicted impacts. 

The “specific agents” and “agent groups” (figs. 6, 7) used the same hectare 

numbers for RD and DM quantities. Thus, changes in relative importance are due to 

changes in hectare values of the other agent groups. Notably, the inclusion of other 

pathogens (PO) was important in representing both historic and predicted impact of 

disease in the western U.S. In all Regions except the Pacific Southwest, the exotic 

white pine blister rust (included in PO) is predicted to cause significant areas of 

mortality.3

 In the Rocky Mountain Region, comandra blister rust is also expected to 

be important.3

 The relatively high RD impact is still evident in the Northern Region 

and influences the overall importance value of RD in the West when total hectares at 

risk are considered. 

Historical (1952)―Data from 1952, using similar mortality agent groupings 

for slightly different regional delineations, shows a number of variations between 

historical and predicted importance values. In 1952 bark beetles were the primary 

source of mortality (by tree volume) over all Regions (fig. 8). Future predictions 

indicate the continued relative importance of bark beetles, except in the Northern 

Region where the dramatic increase in RD importance overshadows effects of all 

other agents. Both historical data and future predictions indicate limited DF mortality 

across the West with highest impact in the Southern Rocky Mountains. It is unclear 

which insect was responsible for the significant “other insect” mortality in California 

in 1952 (fig. 8). However, over the West, other insects (IO) besides bark beetles and 

defoliators have not had a large effect. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 419 

Figure 7―The predicted relative importance of six insect and disease agent groups 

in the western U.S.: projected risk (2000-2015). Agent groups are bark beetles (BB), 

defoliators (DF), other insects (IO), root disease (RD), dwarf mistletoe (DM), and 

other pathogens (PO). Organisms within each group include: Douglas-fir beetle 

(Dendroctonus pseudotsuga), fir engraver (Scolytus ventralis), pine engraver (Ips

pini), Jeffery pine beetle (D. jeffreyi), MPB, roundheaded pine beetle (D. adjunctus),

spruce beetle (D. rufipennis), southern pine beetle [in Arizona] (D. frontalis), western 

pine beetle (D. brevicomis), and western balsam bark beetle (Dryocetes confusus) for 

bark beetles; Douglas-fir tussock moth (Orgyia pseudotsugata), and western spruce 

budworm (Choristoneura occidentalis) for defoliators; balsam woolly adelgid (Adelges 

piceae) for other insects; annosus root disease (Heterobasidion annosum), subalpine 

fir decline, and other unnamed root diseases under root disease; various dwarf 

mistletoes (Arceuthobium spp.); comandra blister rust (Cronartium comandrae) and 

white pine blister rust (C. ribicola) for other diseases. Data are from a Forest Service 

risk assessment project being conducted by the Washington, D.C. office and is 

preliminary, only. Revisions are being completed by the Forest Service. However, 

relative importance relationships are expected to remain similar. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

420 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 8―The historical relative importance of six insect and disease agent groups 

in the western U.S.: historical (1952). Regions in the 1952 data are different from the 

Forest Service Regions. In place of the Northern, Rocky Mountain, Southwestern and 

Intermountain Regions, the 1950s study combines these four Regions into two 

Regions; the Northern Rocky Mountains and the Southern Rocky Mountains. The 

Northern Rocky Mountains contains all of the Northern as well as part of the Rocky 

Mountain and Intermountain Regions (Idaho, Montana, South Dakota, and 

Wyoming). The Southern Rocky Mountain contains all of the Southwestern, as well 

as the remainder of the Rocky Mountain and Intermountain Regions (Arizona, New 

Mexico, Colorado, Utah, and Nevada). The six insect and disease agent groups 

include bark beetles (BB), defoliators (DF), other insects (IO), root disease (RD), 

heart rot and stem disease (HR/SD) and other pathogens (PO). Organisms within 

each group are not defined. However, IO includes borers, tipmoths, turpentine 

beetles, and balsam wooly aphid. RD is primarily Douglas-fir root rot (possibly 

Phellinus weirii = Inonotus sulphurascens). HR/SD is heart rot, blister rusts 

(Cronartium spp.) and dwarf mistletoe (Arceuthobium spp.). OP includes foliage and 

systemic diseases (Elytroderma deformans and pole blight). Differences in the 

measure of impact (volume not hectares) and in regional delineations complicate 

comparisons, but relative importance of mortality agents is expected to remain 

indicative. Data are from the year 1952 and are similar to trend data, except in the 

Northern Rocky Mountains where insect mortality was higher and disease mortality 

was lower than trends had indicated (USDA Forest Service 1958). 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 421 

Historically, only the Pacific Northwest was noted for important RD mortality, 

while future expectations are of significant mortality in all Regions except the 

Intermountain (part of both the historic Southern Rocky Mountain and Northern 

Rocky Mountain Regions). In the 1952 data DM is grouped with heart rots and other 

stem diseases (HR/SD). This inclusion of other agents could explain why the historic 

Pacific Northwest HR/SD value (fig. 8) is higher than predicted DM values (fig. 7).

In the Pacific Southwest, however, the only explanation for the predicted increase in 

the DM value over the historic HR/SD is an actual increase in DM in the Region. 

Other pathogens have also changed. In 1952 elytroderma (Elytroderma deformans

Darker) and pole blight were the principal “others,” while future predictions denote 

white pine blister rust and comandra blister rust as important “other” pathogens. 

Primary causes for these differences likely include the use of volume impact (1952 

data) in place of area, progress in understanding and detection of agents, differences 

in assigning causal agent in areas where many agents are active, and actual changes 

in forest susceptibility due to exotic pests, fire exclusion, and silvicultural practices 

(USDA Forest Service 1988). 

Our analysis focused principally on insect and disease mortality agents, and on 

fire where data was available. It is important to remember, however, that there are 

other agents that can be locally very important in the recruitment of coarse woody 

debris. Mortality due to wind is very important in some regions, as are snow and ice, 

floods, drought, lightning, avalanches, animals, and suppression by other trees 

(USDA FS 1958, Harmon and others 1986, Parminter 1998). In the Rocky Mountain 

and Southwestern Regions, “other” agents may actually have caused greater mortality 

of sawtimber than insects, diseases, or fire (USDA FS 1958) (fig. 9). In all Regions 

except the Pacific Southwest, “other” mortality was caused by weather with some 

animal damage. In the Pacific Southwest mortality was due to suppression by other 

trees. More recent regional information on mortality due to weather is patchy but 

indicates its continued importance (Harmon and others 1986). Also locally important 

may be the effects of pollution (e.g., air, water, or ground) (Carlson and Dewey 

1971). 

Discussion

Temporal and Spatial Scales of Coarse Woody Debris 

Recruitment 

Recent mortality data (1978-1997) presented here show some of the differences 

in the spatial and temporal patterns of the various mortality agents (figs. 2, 3). Such 

differences in disturbance regimes have been previously noted (Geils and others 

1995, Parminter 1998) but not often quantified (see Swetnam and Betancourt [1998] 

for a quantitative example.) It is these differences in mortality patterns, as well as the 

character of the mortality agent, that affects the scales (spatial and temporal) of the 

coarse woody debris recruitment (Clark and others 1998, Li and Crawford 1994, 

Lundquist and others 1998). 

This paper presents spatial scale only in terms of the number of hectares affected 

within a geo-political landscape unit (Regions) and does not give information on the 

distribution or extent of mortality incidences within the Region. For example, it is 

possible for an agent to create many small patches of mortality across the landscape, 

or to disturb a large contiguous area and yield similar values of hectares affected. 

However, literature on past effects of various disturbance agents does provide 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

422 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

qualitative understanding of the possible differences in the spatial distribution of 

created dead wood. For example, epidemic MPB in monotypic stands of lodgepole 

pine are likely to create a larger, more continuous area of mortality than will 

Douglas-fir beetle in mixed forest type under endemic conditions. 

Figure 9―Relative importance of four mortality agent groups in the western U.S.: 

historical (pre-1952 trend). Region delineations differ from the Forest Service 

Regions. Because data were given by state, the Northern, Rocky Mountain, and 

Intermountain Regions had to be approximated using state boundaries (e.g., 

Northern Region as Montana and Idaho; Rocky Mountain as Wyoming, Colorado, 

and South Dakota; Intermountain as Nevada and Utah). The “other” category is 

principally suppression by other trees, timber harvest damage, weather, and animals. 

West and U.S. graphs show values for all sawtimber and softwood sawtimber on 

commercial lands (USDA Forest Service 1958). 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 423 

Parminter (1998) makes two important points for understanding the differential 

spatial effects of agents. First, small-scale disturbances are the primary source of 

heterogeneity in forest structure and composition, including the dead wood 

component. Regular patches created by BB tree- or patch-attacks, RD pockets, or 

some windthrow events operate at the tree or stand level but cause landscape patterns 

and landscape consequences. Second, large-scale disturbances such as wildfire, 

blowdown, floods, and other often weather-related events act on all tree species, 

sizes, and ages, resulting in significant or complete mortality over a large area. Often 

the result is a shift in successional stage and sharp increases or pulses of coarse 

woody debris input. Additional discussion on the role of disturbance scale on the 

resulting ecosystem structure can be found in Holling (1992). 

Data on the effects of agents over the past 20 years (1978-1997) (figs. 2, 3)

exhibit annual differences, as well as possible long-term temporal patterns of 

mortality agents. For example, MPB activity shows a long-term cycle, while fire 

hectares appear to fluctuate greatly on a yearly basis. Likely, this is due to the 

population dynamics of the beetles and continuity of stand structure from year to 

year, as compared to the high variability of precipitation, temperature, wind, and 

humidity that greatly affect fire. Longer-term patterns in fire activity are not evident 

(figs. 2, 3), but have been found in long-term data sets (e.g., Swetnam and Betancourt 

[1998]). Seasonal variations, also, are not visible, but literature indicates that seasonal 

coarse woody debris recruitment often occurs in relation to seasonal weather patterns 

(e.g., heavy rains, wind, fire, floods, etc.). We should also note that, although 

hectares affected do not directly translate into mortality or amount of coarse woody 

debris created, figures 2-3 do illustrate the dynamic variability inherent in the agents. 

Differences in agent activity between Regions, such as the Northern and 

Southwestern, are indicative of the principal regional ecosystem processes at work 

(figs. 2, 3). For example, RD is much more active in the Northern than in the 

Southwestern Region while the opposite is true of DM. These differences are directly 

related to precipitation and principal forest types of the two areas. However, because 

these two Regions are not comprised of equal acreages, it would be incorrect to 

assume that DM has a nearly equal impact over the Northern as the Southwestern 

Region. 

The Pacific Northwest has both the most forested hectares and the most 

commercial forest hectares of the six Regions (USDA FS 1958). Because of this 

larger area, agent impacts (as total hectares) are likely to appear greater in the Pacific 

Northwest than in smaller Regions (fig. 4). Data on the total number of hectares 

surveyed is not readily available, although reports indicate that more than just the 

commercial forested lands are surveyed. If hectares affected were related to average 

yearly hectares surveyed, some additional regional trends might be visible. 

Although an agent may act principally at one spatial or temporal scale, it is 

important to recognize its effects at all scales (Parminter 1998). The determined 

importance of an agent on the ecosystem depends on which of these levels is being 

evaluated. For example, outbreaks of bark beetles such as Douglas-fir beetle can kill 

many trees at the patch or stand scale within 3 or 4 years. Yet, over the landscape, 

these clustered or widely dispersed groups of dead trees can create greater landscape 

heterogeneity over many decades (Parminter 1998). At the patch level the beetle may 

be described as a negative influence, killing trees. Yet, at the landscape level the 

positive effects of heterogeneity might be noted. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

424 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Differential Activity of Mortality Agents 

In addition to differences in spatial and temporal scales of coarse woody debris 

recruitment, mortality agents produce types of dead wood that serve varying roles in 

the ecosystem (Bull and others 1997, Harmon and others 1986). A basic 

understanding of the differences in agent groups will augment further interpretation 

of the significance of the regional variations presented. 

Bark beetles tend to be tree species- and size-specific, generally affecting trees 

already weakened, diseased, or otherwise stressed (Amman and McGregor 1985, 

Barbosa and Wagner 1989, Dahms and Geils 1997). The area affected may fluctuate 

annually with weather and stand conditions, but when considerable amounts of 

favorable host become suitable habitat, outbreaks can occur, killing trees over entire 

watersheds (Amman and others 1989). Defoliator populations are more influenced by 

favorable synchrony between host phenology and defoliator life cycles, and are often 

influenced by environmental factors, such as weather, stand and site conditions, and 

enemy populations (Barbosa and Wagner 1989, USDA Forest Service and others 

1999, Wulf and Cates 1985). Although defoliators don’t generally kill trees, they can 

have significant impacts with repeated and complete defoliation (Barbosa and 

Wagner 1989, Swetnam and Lynch 1989, 1993). The dead wood that remains after 

insect attacks is often in the form of snags (Harmon and others 1986). Longevity of 

these snags, rate of bark slough, amount of stem breakage, and other traits depends 

on factors such as the tree species, tree size, other biotic agents (e.g., heart rot, 

staining fungi, arthropods, other animals) and abiotic forces (e.g., soil type, wind, 

rain, fire, temperature) (Brown and others 1998, Dahm 1949, Harrington 1996, 

Lowell and others 1992, Morrison and Raphael 1993, Schmid and others 1985). 

Diseases are numerous and their effects so variable that a generalization of 

effects is difficult. Disease species may act principally on one host species (e.g., DM) 

or have effects on several host species in an area (e.g., RD) (USDA Forest Service 

and others 1999). Regional variation in effects may be due to disease virulence, tree 

or species resistance, climate, and other site conditions (Hawksworth and Wiens 

1996, USDA Forest Service and others 1999). In many ecosystems disease 

contributes little coarse woody debris directly but predisposes large areas to other 

killing agents such as bark beetles (Otrosina and Ferrell 1995). In other ecosystems, 

disease, especially RD, may directly contribute considerable amounts of coarse 

woody debris (Byler 1978). The types and sizes of debris created by disease are also 

variable (Lundquist and others 1998). RD may kill several tree species of various 

sizes, and often causes trees to fall, creating mostly downed material of many sizes. 

DM may cause only top-kill or dropping of infected branches (Hawksworth and 

Wiens 1996), while, in large western white pine (Pinus monticola Dougl. ex. D. 

Don), white pine blister rust can create large snags (Monnig and Byler 1992). 

All fire size classes and sources of ignition were included in the fire data, yet 

these can be biologically very different. Actual effects of fire depend largely on the 

type of fire (e.g., ground, surface, or crown) and its intensity, as well as the tree 

species and stand structure. Low intensity fire (surface or ground) acts more like DF 

or DM in that it does not cause large-scale mortality. Such fire generally consumes 

the downed debris. Mortality that does occur is selective for less fire tolerant tree 

species and smaller individuals. High intensity crown fire, however, is different from 

most insects and disease in that it can kill all trees of all species, sizes, and ages over 

a large area. Mortality in high intensity fires is condensed in time and space, 

providing considerable dead wood in relation to the area affected. It is calculated that 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 425 

a single intense fire could create between 105 and 575 years’ worth of “normal” 

coarse woody debris input (Harmon and others 1986). 

The dead wood created by other, often weather related agents (wind, snow and 

ice, avalanches, and flood) will likely include many tree species and sizes as 

described for high-intensity fire. However, because the tree is killed “by force,” the 

coarse woody debris is usually downed material with broken snags. Other forces such 

as lightning, animals, and suppression by other trees may be more tree-selective or 

act on smaller patches, resulting in more specific species or size class mortality 

visible as standing snags. 

Wind has been noted as being a particularly important mortality agent in some 

regions. For example, hurricanes and typhoons have damaged large areas of coastal 

North America, Europe, and Asia (Harmon and others 1986). Smaller patches of 

wind damage are also possible and occurrence can range from chronic seasonal 

damage to sporadic high recruitment spikes. Damage may differ by forest type as 

well as by soil type, topographic position, and edaphic conditions (Harmon and 

others 1986). Wind can leave broken snags, but the majority of the coarse woody 

debris is downed material. 

Implications of Findings for Ecosystem Managers 

Kile and others (1991) noted that until the 1970s, the overall impact of RDs such 

as Armillaria had not been appreciated. Smith (1984) calculated that 18 percent of 

the tree mortality in the western U.S. was due to RD. Recent past and projected-risk 

data presented here indicate that RD may be an even more important factor in tree 

mortality and recruitment of coarse woody debris than recent literature has indicated. 

Areas where RD is a principal agent of mortality include the Northern and Pacific 

Northwest Regions (fig. 5). Projections also indicate that in the Pacific Southwest, 

RD is expected to be of increasing importance (fig. 6). A greater proportion of 

susceptible tree species (Douglas-fir [Pseudotsuga menziesii Franco] and true firs 

[Abies spp.]) in these areas could account for the greater impact compared to areas 

dominated by more resistant pines. Overall, it is expected that harvest practices 

(especially selective logging), fire exclusion, and mortality caused by white pine 

blister rust have resulted and will continue to result in less tolerant forests and 

increased incidence of RD (Castello and others 1995, Smith 1984). 

All Regions throughout the West show high hectare impacts by DM during the 

past 20 years—the Southwestern, Intermountain, and Pacific Southwest Regions in 

particular (figs. 4, 5). The principal effect of DM is growth loss. However, increased 

DM would result in weakened trees that may succumb to secondary agents (e.g., BB) 

or environmental stress (e.g., drought) (Byler 1978, Wood 1983). Unfortunately, 

pulses of mortality due to these additional stressors have not been well documented 

but should be expected. The Southwestern and the Pacific Southwest Regions are 

predicted to experience DM as an important mortality agent in the years to come 

(figs. 6, 7). 

Pathogens other than RD and DM have caused mortality in the past (pre-1952) 

and are projected to continue doing so in the future. Historically, pathogens of 

importance included elytroderma and pole blight. In the future, pathogens of 

importance in the Northern, Rocky Mountain, Southwestern, and Intermountain 

Regions are predicted to be white pine blister rust (exotic) and comandra blister rust. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

426 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The introduction of additional exotic pathogens could also cause significant future 

tree mortality. 

BB have historically been the most important source of tree mortality in the 

western U.S. and, in 1952, made up 60 to 90 percent of insect- and disease-caused 

mortality (fig. 8). With the exception of the Northern Region, mortality risk 

projections predict that 50 to 80 percent of insect- and disease-caused mortality in the 

next 15 years also will be due to bark beetles (fig. 7). Except in the Southwestern and 

Pacific Southwest Regions, MPB is expected to be the principal BB. Differences in 

the resulting snags will depend on site conditions, tree species and pre- and postmortality agents. 

The principal DF in the West is WSBW, but Douglas-fir tussock moth is also 

noted (USDA Forest Service 1988). Although these insects can affect large areas, 

defoliation rarely results in death unless nearly complete defoliation occurs over 3 or 

more years, or secondary agents take advantage of the tree’s stressed condition (van 

Sickle 1985). The only area that shows relatively high defoliation in the recent past is 

the Rocky Mountain Region (fig. 5). High WSBW incidence is closely related to 

available host forests (Douglas-fir, true fir and spruce forest types), a history of fire 

exclusion and selective logging, and conducive climate patterns (Fellin 1985). 

Projected defoliation-related mortality (although limited) is expected in the 

Southwest (by WSBW) as well as the Intermountain, Pacific Southwest, and Pacific 

Northwest Regions (by Douglas-fir tussock moth) (fig. 7).

Also of importance to dead wood recruitment is the build-up of dead wood 

during the period of fire exclusion, and the resulting increased incidence of 

catastrophic (high intensity) fire (Carlson and others 1995, Johnson 1995). In areas 

like the Southwestern Region where fire (low intensity) is the primary force cycling 

nutrients (Carlson and others 1995, Harvey 1994), the actual pathway through which 

the dead wood passes is altered by changes in fire regimes. Moreover, this history of 

fire exclusion has helped alter forest types across the West towards dense, multi-story 

stands of shade-tolerant, fire-intolerant tree species (Schmidt 1985). These new 

stands, in turn, have different insect, disease, and fire susceptibilities, and produce 

different types of coarse woody debris. Unique regional and forest-type fire regimes 

are well described in other literature (DeBano and others 1998, Mooney and others 

1981, Swetnam and Betancourt 1990). 

In general, management of insects and disease is management of the forest and 

use of proper silvicultural practices (Barbosa and Wagner 1989, USDA Forest 

Service 1988, USDA Forest Service and others 1999). For example, outbreaks of 

most bark beetles require a large amount of susceptible host of suitable size, age, and 

stem density (Amman and others 1977). Decreasing stem densities, removing the 

preferred hosts, and allowing controlled burning are all considered important 

strategies in control of most bark beetles (USDA Forest Service and others 1999). In 

many cases, these same practices may also be used to control other insects and 

diseases (Miller 1979). The idea is that insect and disease problems can be mitigated 

by increasing the vigor of the tree and decreasing the amount of susceptible host 

(Kegley and others 1997). 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 427 

Implications for Ecosystem Processes 

Changes in the regimes of deadwood recruitment can have effects on various 

ecosystem processes, including soil retention (physical), nutrient cycling (chemical), 

and wildlife habitat (biological) (Harmon and others 1986). For example, because 

orientation and size of coarse woody debris effects soil retention on slopes and in 

streams (Harmon and others 1986), large quantities of small ‘jack straw’ stems 

broken from an ice storm might not have the same soil stabilizing effect that large, 

ground-contacting root diseased trunks would have. Since logs from older trees decay 

faster than young trees (Harmon and others 1986), debris from MPB activity might 

exhibit faster nutrient cycling than that from a windstorm (due to beetles selecting the 

larger, older trees) (Amman and others 1977, Amman and McGregor 1985, Cole and 

Amman 1980). And in terms of wildlife habitat, a large tree with heart rot that 

succumbs to bark beetles differs from a small tree that falls from RD (Bull and others 

1997) or a RD-created brush field (Monnig and Byler 1992). 

Available information about changes in regional disturbance regimes may help 

determine regional changes in the coarse woody debris recruitment. For example, we 

would expect that historic low intensity, high frequency fires of the Southwestern 

Region would have created different coarse woody debris properties than the more 

recent high intensity, low frequency fires (Harvey 1994, DeBano and others 1998, 

Touchan and others 1994). And in the Pacific Northwest, the effects of white pine 

blister rust, selective logging, and fire suppression in changing forest type from pine 

to Douglas-fir and true firs have already begun to produce a higher incidence of RD 

(Kile and others 1991, Monnig and Byler 1992). In both examples, the resulting dead 

wood will influence insect communities, fire patterns, and numerous other biological 

processes. 

Management of Coarse Woody Debris 

Management of coarse woody debris must consider not only active mortality 

agents and needs for specific types of debris but also the interaction of the coarse 

woody debris within the ecosystem. The agents we have mentioned not only create 

woody debris but also may take advantage of dead wood created by other agents 

including humans. For example, bark beetles may build to epidemic proportions in 

blowdown or logging slash, and RD can proliferate via freshly dead root systems 

(stumps, snags, etc.; USDA Forest Service and others 1999). An understanding of the 

management of human created coarse woody debris and its interactions with insects 

and disease is important for forest managers. The influence of coarse woody debris 

on BB populations is just one of many considerations. 

A good example of the importance of coarse woody debris management is the 

case of the pine engraver (Ips pini Say) in the Southwestern Region. Slash left from 

thinning or logging operations is often suitable habitat that allows for a dramatic 

population increase leading to pine engraver outbreaks. However, we know that 

proper treatment of the slash can prevent these population buildups. Preventative 

treatments emphasize cutting and disposing of trees in such a way as to dry out the 

slash, rendering it less suitable for beetle reproduction (Kegley and others 1997, 

Massey and Parker 1981, Wilkinson and Foltz 1982). In addition to outbreak 

prevention techniques, there are suppression techniques that can kill beetle larva, 

adult beetles, or disrupt future mating (Kegley and others 1997, Massey and Parker 

1981, Shea 1994, Wilkinson and Foltz 1982). 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

428 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

If managers are interested in creating coarse woody debris for the ecological 

services it provides, it may be beneficial to look at both past and projected agent 

activity. Although we have presented mortality agents as isolated forces, interaction 

between agents is the rule not the exception (Rogers 1996). Geils and others (1995) 

note that most managers work at the gap or stand level. However, our analysis is at a 

much larger scale. A finer scale evaluation of the mortality agents and the forest 

types in the stands of interest will result in better management decisions. 

Acknowledgments 

We wish to thank the many people who provided assistance with this project. 

The Forest Health Protection offices in Missoula, Montana (Northern Region), 

Flagstaff, Arizona (Southwestern Region), Sandy, Oregon and Wenatchee, 

Washington (Pacific Northwest Region), and Washington, D.C. (Washington Office) 

provided us with “Insect and Disease Conditions” reports and other important 

resources. Special thanks are given to Dr. Ann M. Lynch and Dr. Brian Geils of the 

Rocky Mountain Research Station, and Dr. Jill Wilson of the Southwestern Region 

Forest Health Protection for review of this paper and assistance with literature. Dr. 

Pete Fulé of Northern Arizona University, Jim Steed, and an anonymous reviewer 

provided additional comments. Dr. Bob Mathiasen of Northern Arizona University 

assisted with dwarf mistletoe literature. 

References 

Amman, Gene D.; McGregor, Mark D. 1985. The beetle. In: McGregor, Mark D.; Cole, 

Dennis M., editors. Integrating management strategies for the MPB with multipleresource management of lodgepole pine forests. Gen. Tech. Rep. INT-174. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 2-6 

Amman, Gene D.; McGregor, Mark D.; Cahill, Donn B.; Klein, William H. 1977. Guidelines 

for reducing losses of lodgepole pine to the MPB in unmanaged stands in the Rocky 

Mountains. Gen. Tech. Rep. INT-36. Ogden, UT: Intermountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 19 p. 

Amman, Gene D.; McGregor, Mark D.; Dolph, Robert E., Jr. 1989. MPB. Forest insect and 

disease leaflet 2. Washington, DC: Forest Service, U.S. Department of Agriculture; 10 

p. [Available at Web site: http://willow.ncfes.umn.edu/fidl-mpt/mt_pine.htm (November 

1999)]. 

Barbosa, Pedro; Wagner, Michael R. 1989. Introduction to forest and shade tree insects.

San Diego: Academic Press, Inc.; 639 p. 

Bridgwater, David R. 1985. Western spruce budworm. In: Loomis, Robert C.; Tucker, 

Susan; Hofacker, Thomas H., editors. Insect and disease conditions in the United States 

1979-83. GTR WO-46. Washington, DC: Forest Pest Management, Forest Service, U.S. 

Department of Agriculture; 44-47. 

Brown, Peter M.; Shepperd, Wayne D.; Mata, Stephen A.; McClain, Douglas L. 1998. 

Longevity of windthrown logs in a subalpine forest of central Colorado. Canadian 

Journal of Forest Research 28: 932-936. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 429 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Byler, James W. 1978. The pest damage inventory in California. In: Proceedings of the 

symposium on dwarf mistletoe control through forest management; 1978 April 11-18; 

Berkely, CA. Gen. Tech. Rep. PSW-31. Berkely, CA: Pacific Southwest Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 162-171. 

Carlson, Clinton E.; Arno, Stephen F., Chew, Jimmie; Stewart, Catherine A. 1995. Forest 

development leading to disturbance. In: Eskew, Lane G., compiler. Forest health 

through silviculture. Proceedings of the 1995 national silviculture workshop; 1995 May 

8-11; Mescalero NM. Gen. Tech. Rep. RM-GTR-267. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, U.S. Department of Agriculture, Forest 

Service; 26-36. 

Carlson, Clinton E.; Dewey, Jerald E. 1971. Environmental pollution by fluorides in 

Flathead National Forest and Glacier National Park. Missoula, MT: Division of 

State and Private Forestry, U.S. Department of Agriculture, Forest Service; 57 p. 

Castello, John D.; Leopold, Donald J.; Smallidge, Peter J. 1995. Pathogens, patterns, and 

processes in forested ecosystems. Bioscience 45(1): 16-24 

Clark, D. F.; Kneeshaw, D. D.; Burton, P. J.; Antos, J. A. 1998. Coarse woody debris in subboreal spruce forests of west-central British Columbia. Canadian Journal of Forest 

Research 28: 284-290. 

Cole, Walter E.; Amman, Gene D. 1980. MPB dynamics in lodgepole pine forests. Part I: 

course of an infestation. Gen. Tech. Rep. INT-89. Ogden, UT: Intermountain Forest 

and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 56 p. 

Dahms, Walter G. 1949. How long do ponderosa pine snags stand. Res. Note PNW-57. 

Portland, OR: Pacific Northwest Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture; 3 p. 

Dahms, Cathy W.; Geils, Brian W., technical editors. 1997. An assessment of forest 

ecosystem health in the Southwest. Gen. Tech. Rep. RM-GTR-295. Fort Collins, CO: 

Rocky Mountain Forest and Range Experiment Station, Forest Service, U.S. Department 

of Agriculture; 97 p. 

DeBano, Leonard F.; Neary, Daniel G.; Ffolliott, Peter F. 1998. Fire’s effects on ecosystems.

New York: John Wiley and Sons; 333 p. 

DeNitto, Gregg A. 1985. Root disease. In: Loomis, Robert C.; Tucker, Susan; Hofacker, 

Thomas H., editors. Insect and disease conditions in the United States 1979-83. GTRWO-46. Washington, DC: Forest Pest Management, Forest Service, U.S. Department of 

Agriculture; 76-84. 

Drummond, David B. 1982. Timber loss estimates for the coniferous forests of the United 

States due to dwarf mistletoes. Report No. 83-2. Fort Collins, CO: Forest Pest 

Management, Forest Service, U.S. Department of Agriculture; 24 p. 

Eng, Marvin. 1998. Spatial patterns in forested landscapes: implications for biology and 

forestry. In: Voller, Joan; Harrison, Scott, editors. Conservation biology principals for 

forested landscapes. Vancouver: University of British Columbia Press; 42-75. 

Fellin, David G. 1985. Western budworm and its host. In: Brookes, Martha H.; Colber, J. J.; 

Mitchell, Russel G.; Stark, R. W., technical editors. Managing trees and stands 

susceptible to western spruce budworm. Technical Bulletin No. 1695. Washington, DC: 

Cooperative State Research Service, Forest Service, U.S. Department of Agriculture; 7-

14. 

Geils, Brian W.; Lundquist, John E.; Negron, Jose F.; Beatty, Jerome S. 1995. Disturbance 

regimes and their relationships to forest health. In: Eskew, Lane G., compiler. Forest 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

430 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

health through silviculture. Proceedings of the 1995 national silviculture workshop; 

1995 May 8-11; Mescalero NM. Gen. Tech. Rep. RM-GTR-267. Fort Collins, CO: 

Rocky Mountain Forest and Range Experiment Station, U.S. Department of Agriculture, 

Forest Service; 67-73. 

Graham, Russel T.; Harvey, Alan E.; Jurgensen, Martin F.; Jain, Theresa B.; Tonn, Jonalea 

R.; Page-Dumrose, Deborah S. 1994. Managing coarse woody debris in forests of the 

Rocky Mountains. Res. Paper INT-RP-377. Ogden, UT: Intermountain Research 

Station, Forest Service, U.S. Department of Agriculture; 12 p. 

Hadfield, James S.; Magelson, Roy W. 1999. Wood changes in fire-killed eastern 

Washington tree species-year 4 progress report. Wenatchee, WA: Wenatchee 

National Forest, Forest Service, U.S. Department of Agriculture; 35 p. 

Hagle, Susan K.; Kegley, Sandra; Williams, Stephen B. 1995. Assessing pathogen and 

insect succession functions in forest ecosystems. In: Eskew, Lane G., compiler. Forest 

health through silviculture. Proceedings of the 1995 national silviculture workshop; 

1995 May 8-11; Mescalero NM. Gen. Tech. Rep. RM-GTR-267. Fort Collins, CO: 

Rocky Mountain Forest and Range Experiment Station, U.S. Department of Agriculture, 

Forest Service; 117-127. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, Jr., K.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15: 133-302. 

Harrington, Michael G. 1996. Fall rates of prescribed fire-killed ponderosa pine. INT-RP489. Ogden, UT: Ogden, UT: Intermountain Research Station, Forest Service, U.S. 

Department of Agriculture; 7 p 

Harvey, Alan E. 1994. Integrated roles for insects, diseases and decomposers in fire 

dominated forests of the inland western United States: past, present and future 

forest health. In Sampson, R. Neil; Adams, David L., editors. Assessing forest 

ecosystem health in the inland West. Binghamton, NY: Food Products Press; 211-220. 

Hawksworth, Frank G.; Wiens, Delbert. 1996. Dwarf mistletoes: biology, pathology, and 

systematics. Agric. Handb. 709. Washington, DC: Forest Service, U.S. Department of 

Agriculture; 410 p. 

Holling, C. S. 1992. Cross-scale morphology, geometry, and dynamics of ecosystems.

Ecological monographs 62(4): 447-502. 

Johnson, David W.; Hawksworth, Frank G. 1985. Dwarf mistletoe. In: Loomis, Robert C.; 

Tucker, Susan; Hofacker, Thomas H., editors. Insect and disease conditions in the 

United States 1979-83. GTR WO-46. Washington, DC: Forest Pest Management, Forest 

Service, U.S. Department of Agriculture; 48-55. 

Johnson, Marlin A. 1995. Changes in Southwestern forests: stewardship implications. 

U.S. Department of Agriculture, Forest Service, Southwestern Region; 6 p. 

Kegley, Sandra J.; Livingston, Ladd R.; Gibson, Kenneth E. 1997. Pine engraver, Ips pini

(Say), in the western United States. Forest Insect and Disease Leaflet 122. 

Washington, DC: Forest Service, U.S. Department of Agriculture; 6 p. [Available at 

Web site: www.fs.fed.us/r6/nr/fid/fidls/f122.htm (November 1999)]. 

Kile, Glen A.; McDonald, Geral I.; Byler, James W. 1991. Ecology and disease in natural 

forests. In: Shaw, Charles G. III; Kile, Glen A., editors. Armillaria root disease. 

Agriculture Handbook No. 691. Washington, DC: Forest Service, U.S. Department of 

Agriculture; 102-121. 

Lewis, Joseph W. 2002. Mapping risk from forest insect and disease. Unpublished draft 

supplied by author. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 431 

Li, C. Y.; Crawford, R. H. 1994. The biological significance of coarse woody debris in 

forest ecosystems. In: Horng, Fu-Wen; Yang, Jenq-Chuan, editors. Sustainable 

management of temperate and subtropical plantation ecosystems. Proceedings of SinoAmerican Forestry Technology Cooperation Workshop; 1993 January 11-12; Taipei, 

Taiwan, ROC. Taiwan Forestry Research Institute, Taipei, Taiwan, Republic of China; 

3-12. 

Light, Jerome T.; Burbridge, William B. 1985. Effects of outbreaks and management 

responses on big game and other wildlife. In: McGregor, Mark D.; Cole, Dennis M., 

editors. Integrating management strategies for the MPB with multiple-resource 

management of lodgepole pine forests. Gen. Tech. Rep. INT-174. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 37-43. 

Lofroth, Eric. 1998. The dead wood cycle. In: Voller, Joan; Harrison, Scott, editors 

Conservation biology principles for forested landscapes. Vancouver: University of 

British Columbia Press; 185-214. 

Lowell, Eini C.; Willits, Susan A.; Krahmer, Robert L. 1992. Deterioration of fire-killed 

and fire-damaged timber in the western United States. PNW-GTR-292. Portland, 

OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 27 p. 

Lundquist, John E.; Geils, Brian W.; Ward, James P. Jr. 1998. A method for examining the 

impact of forest disturbance on small mammal distribution. Unpublished draft 

supplied by B.W. Geils. 

Massey, C. L.; Parker, Douglas L. 1981. Arizona five-spined Ips. Forest Insect and Disease 

Leaflet 116. Washington, DC: Forest Service, U.S. Department of Agriculture; 6 p. 

McGregor, Mark D. 1985a. MPB. In: Loomis, Robert C.; Tucker, Susan; Hofacker, Thomas 

H., editors. Insect and disease conditions in the United States 1979-83. GTR WO-46. 

Washington, DC: Forest Pest Management, Forest Service, U.S. Department of 

Agriculture; 16-23. 

McGregor, Mark D. 1985b. Soil and water quality. In: McGregor, Mark D.; Cole, Dennis M., 

editors. Integrating management strategies for the MPB with multiple-resource 

management of lodgepole pine forests. Gen. Tech. Rep. INT-174. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 44 p. 

Miller, William E. 1979. Fire as an insect management tool. Entomological Society of 

America Bulletin 25(2): 137-140. 

Monnig, Edward; Byler, James. 1992. Forest health and ecological integrity in the 

northern Rocky Mountains. FPM Report 92-7. Missoula, MT: Northern Region, 

Forest Pest Management, Forest Service, U.S. Department of Agriculture; 19 p. 

Mooney, H. A.; Bonnickson, T. M.; Christensen, N. L.; Lotan, J. E.; Reiners, W. A. 1981. 

Fires regimes and ecosystem properties. Gen. Tech. Rep. WO-26. Washington, DC: 

U.S. Forest Service, Department of Agriculture 

Morrison, Michael L.; Raphael, Martin G. 1993. Modeling the dynamics of snags.

Ecological applications 3(2); 322-330. 

Otrosina, William J.; Ferrell, George T. 1995. Root diseases: primary agents and 

secondary consequences of disturbance. In: Eskew, Lane G., comp. Forest health 

through silviculture. Proceedings of the 1995 national silviculture workshop; 1995 May 

8-11; Mescalero NM. Gen. Tech. Rep. RM-GTR-267. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, U.S. Department of Agriculture, Forest 

Service; 87-92. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

432 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Parminter, John. 1998. Natural disturbance ecology. In: Voller, Joan; Harrison, Scott, 

editors. Conservation biology principles for forested landscapes. Vancouver: University 

of British Columbia Press; 3-41. 

Rogers, Paul. 1996. Disturbance ecology and forest management: a review of the 

literature. Gen. Tech. Rep. INT-GTR-336. Ogden, UT: Intermountain Research Station, 

Forest Service, U.S. Department of Agriculture; 17 p. 

Schmid, J. M.; Mata, S. A.; McCambridge, W. F. 1985. Natural falling of beetle-killed 

ponderosa pine. Res. Note RM-454. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture; 3 p. 

Schmidt, Wyman C. 1985. Historical considerations. In: Brookes, Martha H.; Colber, J.J.; 

Mitchell, Russel G.; Stark, R. W., technical editors. Managing trees and stands 

susceptible to western spruce budworm. Technical Bulletin No. 1695. Washington, DC: 

Cooperative State Research Service, Forest Service, U.S. Department of Agriculture; 1-

6. 

Shea, Patrick J., technical coordinator. 1994. Proceedings of the symposium on 

management of western bark beetles with pheromones: research and development; 

June 22-25, 1992, Kailua-Kona, Hawaii. Gen. Tech. Rep. PSW-GTR-150. Albany, 

CA: Pacific Southwest Research Station, Forest Service, U.S. Department of 

Agriculture; 53 p. 

Smith, Richard S. Jr. 1984. Root disease-caused losses in the commercial coniferous 

forests of the western United States. Report No. 84-5. Washington, DC: Forest Pest 

Management, Forest Service, U.S. Department of Agriculture; 13 p. 

Swetnam, Thomas W.; Baisan, Christopher H. 1994. Historical fire regime patterns in the 

southwestern United States since AD 1700. In: Allan, Craig D., editor. Fire effects in 

Southwestern forests, proceedings of the Second La Mesa Fire Symposium; 1994 March 

29-31; Los Alamos, NM. Gen. Tech. Rep. RM-GRT-286. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, Forest Service, U. S. Department of 

Agriculture; 11-32. 

Swetnam, Thomas W.; Betancourt, Julio L. 1990. Fire-southern oscillation relations in the 

southwestern United States. Science 249: 961-1076 

――. 1998. Mesoscale disturbance and ecological response to decadal climatic 

variability in the American Southwest. Journal of Climate 11: 3128-3147. 

Swetnam, Thomas W.; Lynch, Ann M. 1989. A tree-ring reconstruction of western spruce 

budworm history in the southern Rocky Mountains. Forest Science 35(4): 962-986. 

――. 1993. Multicentury, regional-scale patterns of western spruce budworm 

outbreaks. Ecological Monographs 63(4): 399-424. 

Touchan, Ramzi; Allan, Craig D., Swetnam, Thomas W. 1994. Fire history and climatic 

patterns in ponderosa pine and mixed-conifer forests of the Jemez Mountains, 

northern New Mexico. In: Allan, Craig D., editor. Fire effects in southwestern forests, 

proceedings of the Second La Mesa Fire symposium; 1994 March 29-31; Los Alamos, 

NM. Gen. Tech. Rep. RM-GRT-286. Fort Collins, CO: Rocky Mountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 33-46. 

USDA Forest Service. 1958. Timber resources for America’s future. Forest resource 

Report No. 14. Washington, DC: U.S. Forest Service, Department of Agriculture; 713 p. 

USDA Forest Service. 1979. Forest insect and disease conditions in the United States, 

1979. Washington DC: Forest Health Protection, Forest Service, U.S. Department of 

Agriculture; 81 p. 
Agents and Patterns of Mortality and Coarse Woody Debris Recruitment—Steed and Wagner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 433 

USDA Forest Service. 1988. Forest health through silviculture and integrated pest 

management: a strategic plan. Washington, DC: Forest Service, U.S. Department of 

Agriculture; 26 p. 

USDA Forest Service. 1992. 1984-1990 Forest fire statistics. Washington, DC: Fire and 

Aviation Management, Forest Service, U.S. Department of Agriculture; 226 p. 

USDA Forest Service. 1998. 1991-1997 Wildland fire statistics. Washington, DC: Fire and 

Aviation Management, Forest Service, U.S. Department of Agriculture; 141 p. 

USDA Forest Service; Idaho Department of Lands; Montana Department of Natural 

Resources and Conservation. 1999. Forest insect and disease identification and 

management. Forest insect and disease management workshop. Coeur d’Alene, ID: 

Forest Service, U.S. Department of Agriculture; [unpublished training manual]. 

van Sickle, G. A. 1985. Effects of infestations on trees and stands. In: Brookes, Martha H.; 

Colber, J. J.; Mitchell, Russel G.; Stark, R. W., technical editors Managing trees an 

stands susceptible to western spruce budworm. Technical Bulletin No. 1695. 

Washington, DC: Cooperative State Research Service, Forest Service, U.S. Department 

of Agriculture; 15-21. 

Wargo, Philip M. 1995. Disturbance in forest ecosystems caused by pathogens and 

insects. In: Eskew, Lane G., comp. Forest health through silviculture. Proceedings of the 

1995 national silviculture workshop; 1995 May 8-11; Mescalero NM. Gen. Tech. Rep. 

RM-GTR-267. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Forest and Range Experiment Station; 20-25. 

White, Peter S.; Betancourt, Julio; Chew, Jimmie D.; Harrod, Jon; Romme, William H.; 

Stephenson, Nathan. 1999. Role of disturbance and temporal dynamics. ST-15. 

[Available at Web site: www.fs.fed.us/eco/s15pre.htm {November 1999)]. 

Wilkinson, R. C.; Foltz, J. L. 1982. Ips engraver beetles: identification, biology, and 

control. Georgia Forest Research Paper 35. Research Division, Georgia Forestry 

Commission; 10 p. 

Wood, R. E. 1983. Mortality caused by root diseases and associated pests on six national 

forest in Arizona and New Mexico. Forest Pest Management Report R-383-13. 

Albuquerque, NM: Forest Health Protection, Forest Service, U.S. Department of 

Agriculture; 31 p. 

Wulf, William N.; Cates, Rex G. 1985. Site and stand characteristics. In: Brookes, Martha 

H.; Colber, J. J.; Mitchell, Russel G.; Stark, R. W., technical editors Managing trees an 

stands susceptible to western spruce budworm. Technical Bulletin No. 1695. 

Washington, DC: Cooperative State Research Service, Forest Service, U.S. Department 

of Agriculture; 15-21. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 435 

Comparing Deterioration and Ecosystem 

Function of Decay-resistant and Decaysusceptible Species of Dead Trees1

Paul E. Hennon,2 Michael H. McClellan,3 and Patricia Palkovic4

Abstract 

The pattern and rate of deterioration of dead trees vary by species, which leads to important 

differences in their ecosystem function. This is illustrated by two species with different modes 

of death and decay: yellow-cedar (Chamaecyparis nootkatensis) and western hemlock (Tsuga 

heterophylla). The heartwood of yellow-cedar contains compounds that inhibit decay. Most 

yellow-cedar trees die standing and persist as snags with intact tops for 80 years or more. 

Western hemlock lacks these specialized heartwood compounds and exhibits a more rapid 

deterioration. Also, modes of tree death, heart rot levels, and type of saprophytic decay may 

differ considerably by stand age for western hemlock. A greater diversity of structures is 

produced by the death and deterioration of western hemlock than yellow-cedar. 

Introduction 

Our research on dead trees in southeast Alaska has two origins. For yellowcedar (Chamaecyparis nootkatensis), we developed a snag class system and 

conducted ground surveys in an attempt to reconstruct the epidemiology (i.e., timing 

of onset and population changes) for the extensive mortality problem that this species 

is experiencing. A more applied continuation of that research led us to describe the 

patterns of deterioration and recovery of the dead yellow-cedar resource. A separate 

line of research has focused on the mortality of trees in the western hemlock (Tsuga 

heterophylla) dominated old-growth forests. Here, it was necessary to reconstruct 

mortality of canopy-level trees so that we could interpret the factors that were driving 

small-scale disturbance in these forests. An applied aspect of this latter research is to 

evaluate the extent to which the factors that contribute to structural diversity and 

small-scale disturbance are maintained after different silvicultural treatments. 

The objective of this paper is to contrast what we have learned about the death, 

decay, and ecosystem function of these two tree species: yellow-cedar and western 

hemlock. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Pathologist, State and Private Forestry and Pacific Northwest Research Station, USDA Forest 

Service, 2770 Sherwood Lane, 2A, Juneau, AK 99801 (e-mail: phennon@fs.fed.us) 

3

 Research Ecologist, Pacific Northwest Research Station, USDA Forest Service, 2770 Sherwood Lane, 

2A, Juneau, AK 99801 (e-mail: mmcclellan@fs.fed.us) 

4

 Forester, Department of Natural Resources, Division of Forestry, 2030 Sealevel Dr. #217, Ketchikan, 

AK 99901. 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

436 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Snag and Log Classification Systems

Existing snag and log classification systems proved to be inadequate for our use 

in both tree species. Such schemes (Cline and others 1980, Maser and others 1979) 

typically have classes in which tops progressively break, gradually reducing the 

heights of snags through time. For yellow-cedar, our early observations indicated that 

dead trees do not appear to have their tops break repeatedly as they deteriorate. For 

western hemlock, a tree species that contains considerable heart rot as a live tree in 

old forests, classifying snags and logs based on the decay levels of wood was not 

appropriate. Otherwise, some live trees or recently-killed trees would by classified as 

dead long ago. One of our objectives is to reconstruct tree mortality patterns through 

time (i.e., establish epidemiology rather than simply report structural condition of 

dead trees). Thus, we needed to use characteristics other than wood decay to 

distinguish groups of dead trees. We chose to develop a new system where we 

focused on the presence of primary limbs, secondary limbs, and twigs; we suspected 

that their presence was a more reliable indicator of how long trees had been dead. For 

western hemlock, our classes were aligned with an established snag and log 

decomposition system (Maser and others 1979, table 1).

Table 1—Description of the snag/log class system and time-since-death estimates for each 

class of dead overstory trees of yellow-cedar (Hennon and others 1990) and western 

hemlock.1

 Yellow-cedar Western hemlock 

Structures retained, soil 

contact 

Snag/log 

class # 

Mean, timesince-death (yrs) Snag/log2

class # 

Range, timesince-death (yrs) 

Foliage 1 4 - - 

Twigs 2 14 1 0-12 

Secondary branches 3 26 2 12-33 

Primary branches 4 54 3 33-63 

No limbs 5 81 4 63-117 

Bole broken at soil level 6 Not dated - - 

Integrated into soil - - 5 Not dated 1 Unpublished data on file at the Department of Natural Resources, Division of Forestry, Ketchikan, AK. 2 For western hemlock, our snag/log classes 1 through 4 align with snag stages 3 through 6, respectively, 

as described by Maser and others 1979; for downed material, our snag/log classes align with their log 

decomposition classes as follows, respectively: 1=1; 2 and 3=2; 4=3; 5=4 and 5.

We used two methods to date the death of yellow-cedar snags (Hennon and 

others 1990b): determining radial growth release of previously suppressed western 

hemlock and mountain hemlock (Tsuga mertensiana) that grew directly beneath 

larger yellow-cedar snags, and counting annual growth rings from a strip of callus 

tissue that connected one or more live roots to a single live branch in yellow-cedar 

trees that had a dead top and most of the bole was dead. For dead western hemlock, 

we determined time-since-death by finding trees cut and left at known times of partial 

timber harvesting (n=16), counting annual rings in wounds of adjacent trees that were 

scarred when live trees were windthrown (n=20), and aging conifer regeneration that 

had established on downed logs (n=15). 

The snag/log classification systems that we develop for yellow-cedar and for 

western hemlock and average time-since-death for each class are given in table 1. 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 437 

Note the comparable time-since-death for dead cedar and hemlock with similar 

branch conditions. The condition of the wood and persistence of snags standing for 

the two species are extremely different, however. 

Patterns of Deterioration 

The difference in heartwood chemistry between yellow-cedar and western 

hemlock is the key to understanding the vastly different pattern and rate of wood 

deterioration. Yellow-cedar has generally received little research attention until 

recently, but its heartwood chemistry is quite well known. Of the compounds 

reported in yellow-cedar heartwood (table 2), only nootkatin and chamic acid have 

been tested for their biological activity against fungi. Nootkatin is active at 

concentrations as low as 0.001 percent (Rennerfelt and Nacht 1955). These various 

compounds give the heartwood its color and aroma, as well as the wood’s 

classification as being “resistant or very resistant” to decay (Forest Products 

Laboratory 1987). Western hemlock heartwood lacks these specialized compounds 

and is known as “slightly or non-resistant” to decay (Forest Products Laboratory 

1987). 

Table 2—The known heartwood constituents of yellow-cedar (Hennon and Harris 1997). 

Compound Identification, conformation, synthesis, or assay

Alaskene Marx and Lewis 1973

Carvacrol Erdtman 1952, Carlsson and others 1952 

Chamic acid1 Carlsson and others 1952, Erdtman 1955, Rennerfelt and Nacht 1955, 

Erdtman and others 1956, Nordin 1964, Gensler and Solomon 1973, 

Nordin and others 1982

Chaminic acid Erdtman 1955, Erdtman and others 1956, Nordin 1964

Chanootin Nordin 1964, Karlsson and others 1973

Isochamic acid Nordin 1964

Nootkatene Erdtman and Topliss 1957

Nootkatin2 Aulin-Erdman 1950, Campbell and others 1952, Erdtman and Harvey 

1952, Carlsson and others 1952, Duff and Erdtman 1954, Duff and 

others 1954, Johnson and Cserjesi 1975

Nootkatone Erdman and others 1962, Ishida and others 1970, Odom and Pinder 

1972, Dastur 1974, Yanami and others 1980 

Valerianol Odom and Pinder 1972

Vetivone Dastur 1974 1 Active against fungi at 0.01 percent (Rennerfelt and Nacht 1955).

2 Active against fungi 0.001 percent (Rennerfelt and Nacht 1955).

For trees that die standing, yellow-cedar and western hemlock show differences 

soon after death. The needles on dead western hemlock trees are shed within a few 

months after trees die, but the scale-like foliage of yellow-cedar trees adheres to 

twigs for several years (table 1). Bark becomes loose and begins to slough away 

within several years for both species. The sapwood of both cedar and hemlock is 

colonized by fungi that initiate stain and wood decay. These sapwood fungi and other 

wood decay fungi continue their decay in the heartwood of western hemlock. Until 

this stage, the deterioration of the wood for the two tree species does not differ 

appreciably, but profound differences appear later. Eighty years after death, the 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

438 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

penetration of decay in yellow-cedar wood is typically limited to less than 4 cm (fig. 

1). Finally, approximately a century after death, soil-borne fungi create sufficient 

decay in the wood at the ground level so that the limbless tree boles of yellow-cedar 

break and fall. Soil-borne fungi are less influenced by yellow-cedar’s heartwood 

compounds than other fungi (DeGroot and others 2000). 

Figure 1—(A) Sapwood width, and (B) radial penetration of stain, decay, and checks 

(cracks) into the wood of yellow-cedar trees by classes of live trees, dying trees, and 

five snags. 

 For western hemlock, the decay process continues relatively unchecked as fungi 

penetrate into the heartwood. One fungus, Fomitopsis pinicola, causes a great amount 

of the decay in both the sapwood and heartwood. It degrades wood chemically in a 

process that selectively removes cellulose (i.e., brown rot) and leaves a residue of 

partially-modified lignin. A white rot fungus, Ganoderma applanatum, is also 

common as a wood decomposer of dead hemlock. As decay develops in the bole of 

dead hemlocks, the tops break, reducing the heights of snags in a pattern similar to 

many other conifers. We observed dead hemlocks 38 years after they were killed 

standing on Cat Island in southeast Alaska (Hennon and Loopstra 1991). Only one of 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 439 

42 hemlocks had a standing portion taller than 10 m and most had broken within a 

few meters of the ground. The wood from all of these dead hemlocks was in a 

condition of advanced decay, most commonly colonized by F. pinicola or G. 

applanatum or both. These logs were all in the class 3 to 4 conditions (table 1). In 

the final stages of decomposition, tree boles of western hemlock become fully 

incorporated into the soil (Graham and Cromack 1982). 

Which Trees Die? How Do They Die?

Most dead yellow-cedar trees within the stands experiencing yellow-cedar 

decline are overstory trees that died standing (Hennon and Shaw 1997). Of the more 

than 250 dying yellow-cedars that we have monitored for nearly 20 years, fewer than 

2 percent have died by uprooting or bole breakage. Declining yellow-cedar forests 

cover more than 200,000 ha in Southeast Alaska. In declining stands, dead yellowcedars in all five standing snag classes made up two-thirds of the yellow-cedar basal 

area (Hennon and others 1990a). 

The type of tree death for western hemlock is more variable and is influenced by 

stand age. Hemlocks dying in young-growth forests are predominantly small, 

suppressed trees that die standing from competitive stresses. Biotic agents are not 

generally important tree mortality factors in these stands. Uprooting of young trees is 

usually caused by the collapse of unstable organic rooting substrates (such as 

decaying logs or stumps) and not by wind. 

Recently, we sampled tree mortality in a maturing even-aged stand near Sitka, 

the oldest known clearcut in Southeast Alaska. Many western hemlock trees had died 

standing, but many also died through bole breakage (table 3). Unlike in younger 

stands, much of the mortality in this stand was of the largest dominant trees. We 

suspect that much of this damage was from wind or snow loading and that these trees 

were predisposed to break because of their excessive height: diameter ratio. Heart rot 

was not involved with tree death in this stand. 

In old-growth forests, western hemlock trees die standing, by bole breakage, and 

by uprooting. Many agents kill standing hemlocks; heart rot and gravity or wind 

often lead to bole breakage; and storms with associated heavy precipitation and wind 

cause much of the uprooting in upland forests. When large trees die by any of these 

mechanisms, gaps appear in the canopy and contribute to small-scale disturbance. We 

sampled 1180 dead hemlock trees in 27 old-growth stands in Southeast Alaska 

(Hennon and McClellan 1999) and found that uprooting is not the principal form of 

tree mortality, unlike in Washington (Graham and Cromack 1982). In reconstructing 

tree mortality, death by uprooting can be interpreted long after tree death because of 

the presence of the upturned root system. Distinguishing death as a standing tree or 

by bole breakage is more challenging because dead standing trees deteriorate and are 

reduced in height until they acquire the same broken-off, stump-like structure as that 

of trees that die by bole breakage. Our reconstruction showed that western hemlock 

trees most frequently die standing, fewer died from bole breakage, and fewer yet died 

from uprooting (table 3).
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

440 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

 

Table 3—Origins and functional characteristics of woody debris produced by three forms of 

tree mortality of western hemlock in different stages of stand development of upland forests in 

southeast Alaska. Type of tree mortality is very common (++), common (+), or uncommon (-) 

for each forest stage. 

Ecosystem Roles of Dead Yellow-cedar and Western 

Hemlock 

For yellow-cedar, three insects (a bark beetle [Phloeosinus cupressi], one or 

more longhorned beetles [e.g., Opsimus quadrilineatus], and a woodwasp [Sirex sp.]) 

are common in dying trees and class 1 snags but have completed their life cycles and 

abandoned the snags just 2 years after tree death (Schultz, pers. comm.) (fig. 2). The 

larvae residing under bark and the emerging adults are both potential food items for 

foraging birds. Little insect activity appears to occur in dead standing trees after they 

reach the class 2 stage. Loose and hanging bark could provide habitat for roosting 

bats on snags dead up to 14 years. We are beginning to evaluate these possible 

wildlife uses of each of the snag classes, but little is currently known about the extent 

to which dead cedars are used. Cavity nesting is apparently rare in dead yellowcedars, likely because of the undecayed condition of heartwood even 81 years after 

death (fig. 1).

Johnson (1997) found a high rate of landslides associated with dead yellow-cedar 

forests on steep slopes where most of the trees were in snag class 4 (dead 

approximately 54 years). This probably occurs because the roots of these snags are 

decayed to the extent that hillsides become unstable (Johnson and Wilcock 1998). 

We know little about the deterioration of dead yellow-cedar trees and their 

interaction with soil processes and vegetation once they reach class 6, roughly 100 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 441 

years after death. Possible roles of these downed yellow-cedar logs as they decay 

could be hiding cover for small mammals, seedling establishment for trees and other 

vegetation (i.e., nurse logs), and a nutrient source and substrate for roots, 

mycorrhizae, and soil invertebrates. Where yellow-cedar grows and dies in riparian 

areas, woody debris produced by this tree would likely persist as long or longer than 

any other wood in southeast Alaska. Thus, ecosystem function for dead yellow-cedar 

appears to be greatest immediately after tree death, is limited for above-ground 

processes as snags remain standing, and may increase about 100 years after tree death 

when snags break and fall to the forest floor. 

Understanding the type of tree death for western hemlock is important because 

of the dominance of this species in the forests of coastal Alaska and the wide range of 

structures and processes that result from the different forms of tree mortality (table 

3). Some structures are uncommon or absent during particular stages of forest stand 

development; also, several structures can only be produced by a specific form of tree 

death. 

For example, uprooting of large conifers is the only form of tree mortality that 

produces large, dead trees with an attached root system. Uprooting mixes the 

inorganic and organic soil layers, counteracts some effects of soil development, and 

may maintain site productivity (Bormann and others 1995). In contrast, there is no 

soil mixing with trees that die standing or by bole breakage. When small trees in 

young-growth forests sometimes uproot on unstable, decayed woody substrates, they 

do not affect inorganic soil layers. The large anchoring root system attached to dead 

conifers that uproot in old-growth riparian forests may limit their mobility as woody 

debris and thereby enhance their function in streams and rivers. 

Hollow logs develop with the combination of white rot fungi and tree response 

(i.e., “compartmentalization”) in live trees. Heart rot of western hemlock is extremely 

common in old-growth forests of southeast Alaska where 30 to 40 percent of the 

volume of live trees is defective and 62 percent of this decay is white rot (Kimmey 

1956). Heart rot levels are directly proportional to tree and stand age in southeast 

Alaska (Farr and others 1976) with little to none occurring in forests younger than 

100 years (Kimmey 1956). 

Dead standing trees and downed logs, whether colonized by heart rot fungi 

before death or decayed after death, can function as important habitat for a wide 

range of wildlife species, both large and small (Maser and others 1979, 1988). At 

least twelve species of birds rely on tree cavities for roosting and nesting in southeast 

Alaska (Hughs 1985). But snags of western hemlock have a limited persistence as a 

dead standing tree. Our observations on 42 western hemlocks made 38 years after 

they were intentionally killed indicate two outcomes: 37 percent broke at the lower 

bole before developing extensive decay and then they decomposed intact on the 

ground, and 63 percent developed decay as a standing dead tree and then shattered 

into many fragments upon impact with the ground (Hennon and Loopstra 1991). 

Most hemlock mortality in young forests involves small trees that die standing 

from suppression. Fungi colonize these small dead stems and their wood is partially 

decomposed before falling to the forest floor or into streams. Thus, woody debris 

produced in these young forests may provide a limited function compared with oldgrowth forests because of small piece size and lack of an attached root system. The 

decomposition process of conifer wood may differ between young and old forests as 

well; Edmonds (1999) reports that wood decay of conifers in young-growth forests 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

442 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

may favor white rot fungi over the more common brown rot found in old-growth 

forests. Repeated short rotations of young-growth forest could reduce the effects of 

brown rot, which produces stable residues that can contribute 30 percent of the 

volume in the upper layers of soil (McFee and Stone 1966). Generally, the variable 

type of tree mortality and the responding number of structures and processes in oldgrowth forests probably contributes to the structural diversity present in old-growth 

forests of southeast Alaska (Alaback 1982). 

Figure 2—Potential ecosystem function of dead trees in each of the snag classes for 

yellow-cedar in southeast Alaska. 

Summary 

The defensive compounds in the heartwood of yellow-cedar alter the rate and 

pattern of deterioration in dead trees. Perhaps one compound, nootkatin, is 

responsible for the differences in decay between dead yellow-cedar and western 

hemlock trees and the corresponding structures that are produced. The tree containing 

this compound in its heartwood stands after death for nearly a century, possibly 

producing little in the way of terrestrial wildlife habitat, and finally breaks at the 

ground level to be decayed by soil organisms. The tree whose heartwood lacks this 

compound deteriorates rapidly, standing for a few decades at most, is used by many 

organisms in the complex number of structures produced, and falls to the forest floor 

where it becomes an integral part of the humus layer of soils. 

Acknowledgments 

Some results presented in this paper are from the USDA Forest Service study, 

“Alternatives to Clearcutting in the Old-Growth Forests of Southeast Alaska,” a joint 

effort of the Pacific Northwest Research Station, the Alaska Region, and the Tongass 

National Forest. We thank Mark Schultz and Adelaide Johnson for helpful 

suggestions on a draft of this manuscript. 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 443 

References

Alaback, P. B. 1982. Dynamics of understory biomass in Sitka spruce-western hemlock 

forests of Southeast Alaska. Ecology 63: 1932-1948. 

Bormann, B. T.; Spaltenstein, H.; McClellan, M. H.; Ugolini, F. C.; Cromack, K.; Nay, S. M. 

1995. Rapid soil development after windthrow disturbance in pristine forests. 

Journal of Ecology 83: 747-757. 

Cline, S.; Berg, A. B.; Wight, H. M. 1980. Snag characteristics and dynamics in Douglasfir forests, western Oregon. Journal of Wildlife Management 44: 773-786. 

DeGroot, R. C.; Woodward, B.; Hennon, P. E. 2000. Natural decay resistance of heartwood 

from dead, standing yellow-cedar trees: laboratory evaluations. Forest Products 

Journal 50: 53-59. 

Edmonds, Robert L. 1999. Brown versus white rot in forest ecosystems: does it matter?

In: Trummer, L., editor. Proceedings of the 46th western international forest disease 

work conference. Sep. 28-Oct. 2, 1998. Reno, NV. Anchorage, AK: State and Private 

Forestry, USDA Forest Service; 119-124. 

Farr, W. A.; LaBau, V. J.; Laurent, T. H. 1976. Estimation of decay in old-growth western 

hemlock and Sitka spruce in southeast Alaska. Res. Paper PNW-204. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 24 

p. 

Forest Products Laboratory. 1987. Wood handbook: wood as an engineering material. 

Agric. Handb. 72. Washington, DC: U.S. Department of Agriculture; 466 p. 

Graham, R. L; Cromack, K., Jr. 1982. Mass, nutrient content, and decay rate of dead boles 

in rain forests of Olympic National Park. Canadian Journal Forest Research 12: 511-

521. 

Hennon, P. E.; Harris, A. S. 1997. Annotated bibliography of Chamaecyparis nootkatensis. 

Gen. Tech. Rep. PNW-GTR-413. Portland, OR: Pacific Northwest Research Station, 

Forest Service, U.S. Department of Agriculture; 112 p. 

Hennon, P. E.; Hansen E. M.; Shaw, C. G. III. 1990a. Dynamics of decline and mortality of 

Chamaecyparis nootkatensis in southeast Alaska. Canadian Journal Botany 68: 651-

662. 

Hennon, P. E.; Shaw, C. G. III; Hansen, E. M. 1990b. Dating decline and mortality of 

Chamaecyparis nootkatensis in southeast Alaska. Forest Science 36: 502-515. 

Hennon, P. E.; Loopstra, E. M. 1991. Persistence of western hemlock and western 

redcedar trees 38 years after girdling at Cat Island in southeast Alaska. Res. Note 

PNW-RN-507. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 5 p. 

Hennon, P. E.; McClellan, M. H. 1999. Heart rot and other causes of small-scale 

disturbance in the temperate rain forests of Southeast Alaska. In: Trummer, L., 

editor. Proceedings of the 46th western international forest disease work conference. Sep. 

28-Oct. 2, 1998. Reno, NV. Anchorage, AK: State and Private Forestry, USDA Forest 

Service; 97-105. 

Hennon, P.; Shaw, Charles G. III. 1997. The enigma of yellow-cedar decline: what is 

killing these defensive, long-lived trees in Alaska? Journal of Forestry 95(12): 4-10. 

Hughs, J. H. 1985. Characteristics of standing dead trees in old-growth forests on 

Admiralty Island, Alaska. Pullman, WA: Department of Forestry and Range 

Management, Washington State University; 103 p. 
Ecosystem Function of Dead Trees—Hennon, McClellan, and Palkovic 

444 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Johnson, A. C. 1997. Hillslope stability in cedar decline forests of southeast Alaska.

Baltimore, MD: Johns Hopkins University; 52 p. Unpublished Master's thesis. 

Johnson, A. C.; Wilcock, P. 1998. Effect of root strength and soil saturation on hillslope 

stability in forests with natural cedar decline in headwater regions in SE Alaska. In: 

Haigh, M. J.; Krecek, J.; Rajwar, G. S.; Kilmartin, M. P., editors. Headwaters—water 

resources and soil conservation, Rotterdam, Netherlands; 381-390. 

Kimmey, J. W. 1956. Cull factors for Sitka spruce, western hemlock and western 

redcedar in southeast Alaska. Station Paper No. 6. Juneau, AK: Alaska Forestry 

Research Center, Forest Service, U.S. Department of Agriculture; 31 p. 

Maser, C.; Anderson, R. G.; Cromack, K., Jr.; Williams, J. T.; Martin, R. E. 1979. Dead and 

down woody material. In: Thomas, J. W., editor. Wildlife habitats in managed forests, 

the Blue Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: 

Forest Service, U.S. Department of Agriculture. 

Maser, C.; Cline, S. P.; Cromack, K., Jr.; Trappe, J. M.; Hansen, E. M. 1988. What we know 

about large trees that fall to the forest floor. In: Maser, C.; Tarrant, F. F.; Trappe, J. 

M.; Franklin, J. F., editors. From the forest to the sea: a story of a fallen tree. Gen. Tech. 

Rep. PNW-GTR-229. Portland, OR: USDA Forest Service; 25-45. 

McFee, W. W.; Stone, E. L. 1966. The persistence of decayed wood in the humus layers of 

northern forests. Proceedings, Soil Sciences of America 30: 513-516. 

Rennerfelt, Erik; Nacht, Gertrud. 1955. The fungicidal activity of some constituents from 

heartwood of conifers. Svensk Botanisk Tidskrift 49: 419-432. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 445 

Influence of Fire on the Dynamics of Dead 

Woody Material in Forests of California and 

Southwestern Oregon1 

Carl N. Skinner2

Abstract 

The frequent occurrence of fire in most forested areas of California and southwestern Oregon 

before this century has been well established. Likewise, the importance of dead woody 

material to various wildlife species as snags and downed logs has been well documented. It is 

unlikely that much large woody material survived fire long enough to decompose fully in fire 

regimes that preceded the fire-suppression era. Observations of fire effects on dead woody 

material, as well as some recent limited data, indicate that fire often consumes most material 

that is in advanced stages of decay. However, though many appear to be consumed as well, 

hard snags and logs may, at least in part, survive low severity fires. Fires also help to create 

snags and, ultimately, downed logs. The frequent low-moderate-severity fires that 

characterized much of the forested landscapes of California and southwest Oregon burned 

with varying severity related to topography and weather conditions. The probable result was a 

landscape with many of the snags and logs clustered both in time and in space and very 

sparsely distributed in the intervening time and space. 

Introduction 

Although dead woody material (DWM; snags and logs) is recognized as having 

great importance for many wildlife species and ecological process (Harmon and 

others 1986, Hunter 1990), little information is available concerning its interaction 

with fire before the implementation of fire suppression. As a result, a great deal of 

uncertainty exists about the long-term role of fire in the dynamics of DWM. Most 

information that exists about DWM has been developed in temperate forests outside 

of areas classified as Mediterranean or in forests that have experienced artificially 

long periods without fire (Harmon and others 1986, Harmon and others 1987, Hunter 

1990). Such studies provide little information concerning the historical interactions of 

fire and dynamics of DWM in forests that developed under the influence of chronic, 

frequent, low-moderate-intensity fires. Indeed, when the effects of fire are discussed, 

it is usually in terms of stand destroying events that create large amounts of DWM 

that then becomes available to the system (Spies 1997). Fire is not usually treated as 

a recurring ecological process that may have often removed more dead wood than it 

added. However, the latter was probably characteristic of the type of fires that were 

common in the forests of southwest Oregon and California (Agee 1993, Skinner and 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Geographer, Pacific Southwest Research Station, USDA Forest Service, 2400 Washington Ave, 

Redding, CA 96001 (e-mail: cskinner@fs.fed.us) 
Influence of Fire on Dead Woody Material—Skinner 

446 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Chang 1996, Taylor and Skinner 1998). Persistent, recurring fires in concert with 

other agents of change (e.g., wind, insects, disease) created the conditions and habitat 

that wildlife in these areas adapted to and lived with before fire suppression and other 

management activities of the 20th century. Fire ecologists recognize that conditions 

in today’s forests are probably, at least in part, an artifact of many decades of fire 

suppression (Agee 1997, Chang 1996, Taylor and Skinner 1998). 

Fire: An Ecological Process 

Fire history studies provide strong evidence that fires of the past occurred quite 

frequently—many times within the life spans of the dominant tree species (Skinner 

and Chang 1996). Unlike today, fires of the past did not occur as unusual isolated 

events. Rather, they occurred regularly and greatly influenced the development of 

forest conditions (habitat) (Agee 1993, Chang 1996, Skinner and Chang 1996, Mohr 

and others 2000). Thus, it is more appropriate that fire be viewed as a persistent 

ecological process rather than as a single event. The forest conditions (habitat) 

historically available to wildlife were those created and maintained by this process. 

Indeed, the late-successional forests of today have a long history of frequently 

recurring fire during their development (Taylor and Skinner 1998). 

However, over the 20th century, fire suppression has been successful in limiting 

the cumulative area burned by fires. The result is that fire has become the exception 

rather than the rule (Husari and McKelvey 1996). Although we may have some sense 

of effects associated with individual fires of abnormal severity, we have only limited 

understanding of the effects of incessant, recurring fires of mostly low-moderate 

intensity with which these forests originally developed (Agee 1997). It is likely that 

the interaction of fire and dead wood dynamics were very different under historical 

fire regimes than those of today. A fire regime in which fires burn only infrequently 

and often severely will probably produce very different long-term habitat trends than 

a fire regime in which fire is a frequent visitor and is characterized by mostly low and 

moderate severity. The former serves mostly to add dead wood to the system in 

pulses and may lead to a boom-and-bust cycle of DWM. The latter is more likely to 

limit the accumulation of dead wood over both space and time (Kauffman 1990) and 

may result in less extreme variations of DWM. 

It is necessary to consider both the ecological role and physical potential of fire 

in these forests in order to increase the long-term likelihood for success of 

management strategies (Millar and others 1998, Skinner and Chang 1996). Natural 

resource managers are attempting to balance what is thought to be best in terms of 

accumulations of DWM with the reality of an environment that tends to burn 

frequently. It is well known that, although fire spread is mostly related to smallersized (fine) fuels, the severity of fire effects and difficulty of fire suppression are 

primarily associated with the total amount of fuel available and consumed (Martin 

and Brackebush 1974). As DWM accumulates under a fire suppression management 

regime, fire hazard increases, often dramatically (Kauffman 1990). In order to assess 

realistically the likelihood of long-term success of various management strategies, it 

is necessary to understand why fire was historically frequent in the forests of 

southwestern Oregon and California and then to consider the ecological role of fire. 
Influence of Fire on Dead Woody Material—Skinner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 447 

Climate 

A fundamental reason that fire is an integral factor in the dynamics of forests of 

California and southwest Oregon is climate. This region has a Mediterranean climate 

characterized by hot, dry summers and cool, wet winters. Although this climate 

provides ample annual precipitation to grow productive forests, there is a pronounced 

annual drought. The Mediterranean climate guarantees that, even in years that are 

much wetter than average, the conditions for fire to spread easily are achieved 

annually in the dry season (Stine 1996). Considering the features of the 

Mediterranean climate and the fact that fire history research shows that fires were 

generally frequent, it is logical to surmise that fires regularly influenced the patterns 

and accumulations of DWM. 

Dynamics of Dead Woody Material in Forests of 

Mediterranean Climates 

Because of spatial and temporal patterns of fire frequency, severity, and 

seasonality, fires are likely to have influenced the spatial and temporal patterns of 

DWM accumulations in historical landscapes. Variation in fire regime parameters 

probably contributed significantly to and helped support habitat and species diversity 

(Martin and Sapsis 1992). The variation within the fire regime at broad, landscape 

scales helped contribute to the dynamics of habitat pattern over time (Agee 1998). 

However, few landscape-scale, fire-history studies have been undertaken, primarily 

because of time and costs involved (Skinner 1997a). Most fire history studies have 

been conducted on small areas or a few plots that were widely scattered over large 

areas. Fire ecologists are just beginning to understand fire regimes at landscape 

scales. The interpretation of the dynamics of fire and vegetational patterns at the 

landscape scale are primarily focused on live vegetation because little DWM survives 

from before the fire suppression era except in rare cases. Even so, recent landscapescale, fire-history studies may eventually help in understanding historical patterns of 

DWM through describing the developmental patterns of stand structure that appear 

related to variation in fire regime parameters. 

Fire Frequency 

In California and southwestern Oregon, fires are known to have been frequent 

historically in most locations studied (Skinner and Chang 1996, Taylor and Skinner 

1998). Median fire return intervals (FRI) for most sites from the southern Cascades, 

Klamath Mountains, and Sierra Nevada in the foothills, mixed-conifer, eastside pine, 

and some upper montane areas are generally less than 20 years (McKelvey and others 

1996, Taylor and Skinner 1998). 

From the perspective of DWM, the variation in fire frequency is probably at 

least as important as average or median FRI. Fire history studies indicate that before 

fire suppression it was rare for forested landscapes larger than a few hundred hectares 

to go for long periods (e.g., > 30 years) without fire (Skinner and Chang 1996, 

Swetnam 1993, Taylor and Skinner 1998). However, individual sites occasionally 

experienced longer (several decades) periods without fires severe enough to cause 

fire scars. FRI variation appears to be related to topography of the landscape (Beaty 

and Taylor 2001, Taylor and Skinner 1998), elevational gradients (Skinner and 

Chang 1996), and riparian corridors (Skinner 1997b). Notably, considerable variation 
Influence of Fire on Dead Woody Material—Skinner 

448 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

in FRI within any given site is often present. These and other factors influencing 

variation in FRI undoubtedly helped to create diverse and changing patterns of DWM 

across landscapes. As a result, DWM would probably be clustered both in time and in 

space and sparsely distributed in the intervening time and space. 

Several important patterns of variation appear to be emerging from intensive, 

landscape-scale, fire-history studies. Two studies in the Klamath Mountains have 

shown that fires were historically frequent (median FRI <20 yrs) throughout the 

studied landscapes regardless of tree species composition patterns (Taylor and 

Skinner 1998).3

 However, variation in fire frequency was found to be associated with 

slope orientation (aspect) (Beaty and Taylor 2001, Taylor and Skinner 1998) and 

broad elevational gradients (Agee 1991, Caprio and Swetnam 1995, Taylor 2000). 

Notably, the variation of FRI within a sample site is often as great or greater than are 

the differences among sample sites within a particular study. Generally, it appears 

that FRI is more closely related to a landscape’s topographical structure than to the 

species composition of vegetation. 

Although the frequency of past fires is important, it is but one of many factors 

that define fire regimes. In order to understand how fires may have influenced the 

dynamics of DWM, there is a need to better understand other characteristics of fire 

regimes, such as patterns of seasonality and severity. 

Severity 

Intensive landscape-scale studies in both the southern Cascades and the Klamath 

Mountains have shown that patterns of fire severity appear to be strongly related to a 

landscape’s topography (Beaty and Taylor 2001, Taylor and Skinner 1998). The 

pattern that emerged in these studies indicates that slope position and aspect 

influenced fire severity (fig. 1). Generally, within the local topography, the upper 

third of slopes displayed the highest proportion of area burned at greater severity, the 

middle third was intermediate, while the lowest third of the slopes displayed the least 

amount of severely burned area. When aspect was considered, a higher percent of 

area burned at higher levels of severity on south and west facing slopes. These are the 

slopes that are more strongly exposed to afternoon sun and the up-slope winds 

associated with more severe burning conditions. In contrast, the east and north facing 

slopes, associated with cooler, more humid conditions, had considerably less area 

with evidence of severe burns. 

Seasonality 

Time of year is important for understanding potential effects of fire on DWM. 

Fires are primarily spread by smaller dead fuels that dry out rapidly following the 

cool, wet season (Rothermel 1983). Notably, the larger the DWM, the longer it will 

take to dry out sufficiently to burn (Agee 1993, Martin and Brackebusch 1974). Thus, 

fires that occur in late summer and early fall are likely to consume more DWM than 

fires that occur in spring and early summer (Kauffman and Martin 1989). 

 

3

 Unpublished data for the Hayfork Adaptive Management Area on file at the Silviculture Laboratory, 

Pacific Southwest Research Station, Redding, Calif. 
Influence of Fire on Dead Woody Material—Skinner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 449 

Figure 1—Topographical pattern of historical fire severity found by Taylor and 

Skinner (1998).

Season of burn may be inferred from the position of the fire scar within a 

particular tree ring (Caprio and Swetnam 1995). Generally, in California and 

southwestern Oregon, earlywood scars are interpreted as late spring/early summer 

fires, latewood scars as midsummer fires, and dormant season fires as late-summer or 

fall (Caprio and Swetnam 1995, Taylor 1998a, Taylor and Skinner 1998). 

Fire history studies from the Klamath Mountains, southern Cascades, and 

northern Sierra Nevada commonly record the predominance of fire scars in the 

dormant period (fig. 2). This suggests that most fires occurred in the late summer and 

fall—the driest part of the fire season and the time of year supporting the most 

consumptive burns (Thornburgh 1995). In the southern Sierra Nevada most fires 

were recorded in latewood, suggesting mid- to late-summer fires (fig. 2). Fires 

burning at this time, while not necessarily at the driest part of the fire season, would 

also have burned under relatively dry conditions and would have been consumptive. 

The likelihood that DWM will be consumed in a fire is related not only to 

season of the burn, but also to the degree of decomposition. Generally, the more 

decomposed the wood, the more likely it is to be consumed by fire during the drier 

portions of the fire season (Kauffman and Martin 1989, Martin and Brackebush 

1974). Thus, in southwestern Oregon and California, it is unlikely that much DWM 

was able to decompose fully before fire suppression was implemented. The annual 

dry season and the frequency of fire suggest that a major role of fire was to accelerate 

the removal of DWM from the forests of this region. 

It appears that landscape patterns of seasonality may be similar to patterns of 

severity. South and west facing slopes, especially the upper thirds and ridgetops, 

often have a portion of fires recorded in earlywood. In contrast, the fire scars found 

on trees occupying the lower thirds of slopes, especially on east and north facing 

aspects, are almost exclusively found in the dormant season (Beaty and Taylor 

2001).3

 It is unlikely that early-season fires are necessarily more severe. Rather, these 
Influence of Fire on Dead Woody Material—Skinner 

450 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

data suggest that those places that undergo early drying and can burn early in the fire 

season are also those that will probably burn more severely later in the season in 

other years. This is probably a result of more complete drying over the course of the 

fire season. 

Figure 2—Intra-annual locations of fires scars in fire history studies from the Klamath 

Mountains, southern Cascades, and Sierra Nevada ranges arranged from north to 

south. Dormant season scars indicate late summer and fall fires; latewood scars 

indicate mid to late summer fires; and earlywood scars indicate spring and early 

summer fires. Where ‘Growing Season’ is used the study did not differentiate 

between late and early wood scars. Sources of data: A—Taylor and Skinner (1998); 

B—Unpublished data for the Hayfork Adaptive Management Area on file at the 

Silviculture Laboratory, Pacific Southwest Research Station, Redding, Calif.; C—

Bekker and Taylor (2001); D—Solem (1995); E—Taylor (1998b); F—Norman and 

Taylor (1996); G—Norman and Taylor (1997); H—Taylor (2000); I—Beaty and Taylor 

(2001); J—Taylor (1998a); K—Swetnam and others (1992); L—Caprio and Swetnam 

(1995). 

In climate regions characterized by less frequent fires and significant moisture in 

the warm season wood is often able to more fully decompose over time. In these 

more moist climates DWM has been found to be an important factor influencing 

patterns of nutrient cycling, micro-site moisture regimes, and development of 

invertebrate and fungal habitats among others (Harmon and others 1986). However, 

since it is unlikely that much DWM was able to decompose fully under historical fire 

regimes in the summer-dry climate of this region, very different ecological processes, 

of which there is only limited understanding today, were operating to influence these 

same ecological factors. 

There are many other factors that may influence the variation of fires as they 

move across landscapes: fuel loading (often influenced by site quality), weather 

conditions, past history of fires, riparian corridors, rock outcrops, lakes, and patterns 

of insect activity and windthrow, among others. The factors that have been discussed 

in this paper are those that have been found to be important ipso facto. 
Influence of Fire on Dead Woody Material—Skinner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 451 

Summary 

Before this century, fires in the forests of southwestern Oregon and California 

were frequent and mostly of low and moderate severity. This was primarily because 

of the Mediterranean climate that virtually guaranteed a fire season every year 

regardless of total annual precipitation (as it does today) coupled with ample ignition 

sources and an absence of fire suppression. As a result, it was rare that any sizable 

areas would have escaped fire for more than a few decades. The frequency of the 

fires suggests that it was rare for DWM to have decayed fully before being 

consumed. Variability in fire regime characteristics has been found to be related to 

topography of landscapes. This variability probably contributed to variation in the 

spatial distribution of DWM over time. How past fire regimes would have affected 

the spatial patterns of accumulations of DWM through time is not yet known and is 

an important question for future research. Fire history research can help one to 

understand the variation in fire regimes and their contribution to vegetation patterns. 

This will help to suggest patterns of stand structures and dynamics that would have 

influenced spatial and temporal patterns of DWM. At the same time, there is a great 

need for empirical studies that evaluate the effect of fire on DWM under a variety of 

burning conditions (Kauffman and Martin 1989) in different landscapes and forests. 

Long-term experimental studies or adaptive management projects that monitor 

repeated prescribed burns over time would be especially useful. 

Without further research, we will continue to be limited to conjecture in regards 

to the historical or reference spatial/temporal dynamics of DWM in regions 

characterized by annual summer drought and frequent fires. To fill the lack of 

knowledge, we will probably continue to impose standards from forests of other 

climate types that will carry with them a great deal of uncertainty in terms of the 

potential to successfully achieve long-term goals in our fire prone environments. 

Acknowledgments 

I greatly appreciate the helpful comments of Diane White, Phil McDonald, and 

Phil Weatherspoon on an earlier version of this manuscript. 

References 

Agee, James K. 1991. Fire history along an elevational gradient in the Siskiyou 

Mountains, Oregon. Northwest Science 65: 188-199. 

Agee, James K. 1993. Fire ecology of Pacific Northwest forests. Washington, DC: Island 

Press; 493 p. 

Agee, James K. 1997. Fire management for the 21st Century. In: Kohm, K.; Franklin, J.F., 

editors. Creating a forestry for the 21st century: the science of ecosystem management.

Washington, DC: Island Press; 191-202. 

Agee, James K. 1998. The landscape ecology of Western forest fire regimes. Northwest 

Science 72: 24-34. 

Beaty, R. Mathew; Taylor, Alan H. 2001. Spatial and temporal variation of fire regimes in 

a mixed conifer forest landscape, southern Cascades, California, USA. Journal of 

Biogeography 28: 955-966. 
Influence of Fire on Dead Woody Material—Skinner 

452 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Bekker, Mathew F.; Taylor, Alan H. 2001. Gradient analysis of fire regimes in montane 

forests of the southern Cascade Range, Thousand Lakes Wilderness, California, 

USA. Plant Ecology 155: 15-28. 

Caprio, Anthony C.; Swetnam, Thomas W. 1995. Historic fire regimes along an elevational 

gradient on the west slope of the Sierra Nevada, California. In: Brown, James K.; 

Mutch, Robert W.; Spoon, Charles W.; Wakimoto, Ronald H., technical coordinators. 

Proceedings: symposium on fire in wilderness and park management; 1993 March 30-

April 1, Missoula, MT. Gen. Tech. Rep. INT-GTR-320. Ogden, UT: Intermountain 

Research Station, Forest Service, U.S. Department of Agriculture; 173-179. 

Chang, C. 1996. Ecosystem responses to fire and variations in fire regimes. In: Sierra 

Nevada ecosystem project: final report to Congress. Vol II, Assessments and scientific 

basis for management options. Water Resources Center Report No. 37. Davis: Centers 

for Water and Wildland Resources, University of California; 1071-1099. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15: 133-302. 

Harmon, Mark E.; Cromack, Kermit, Jr.; Smith, Bradley. 1987. Coarse woody debris in 

mixed-conifer forests, Sequoia National Park, California. Canadian Journal of Forest 

Research 17: 1265-1272. 

Hunter, Malcolm L. 1990. Wildlife, forests, and forestry: principles for managing forests 

for biological diversity. Englewood Cliffs, NJ: Prentice-Hall; 307 p. 

Husari, Susan J.; McKelvey, Kevin S. 1996. Fire management policies and programs. In: 

Sierra Nevada ecosystem project: final report to Congress. Vol II, Assessments and 

scientific basis for management options. Water Resources Center Report No. 37. Davis: 

Centers for Water and Wildland Resources, University of California; 1101-1117. 

Kauffman, J. Boone. 1990. Ecological relationships of vegetation and fire in the Pacific 

Northwest. In: Walsted, John D.; Radosevich, Steven R.; Sandberg, David V., technical 

coordinators. Natural and prescribed fire in Pacific Northwest forests. Corvallis, OR: 

Oregon State University Press; 39-52. 

Kauffman, J. Boone; Martin, R. E. 1989. Fire behavior, fuel consumption, and forest-floor 

changes following prescribed understory fires in Sierra Nevada mixed conifer 

forests. Canadian Journal of Forest Research 19: 455-462. 

Martin, Robert E.; Brackebusch, Arther P. 1974. Fire hazard and conflagration prevention.

In: Cramer, Owen P., technical coordinator. Environmental effects of forest residues 

management in the Pacific Northwest. Gen. Tech. Rep. PNW-24. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; G1-G30. 

Martin, Robert E.; Sapsis, David B. 1992. Fires as agents of biodiversity: pyrodiversity 

promotes biodiversity. In: Harris, Richard R.; Erman, Don E.; Kerner, H. M., technical 

coordinators. Proceedings of the symposium on biodiversity of northwestern California; 

1991 October 28-30, Santa Rosa, CA. Wildland Resources Center Report No. 29. 

Berkeley, CA: University of California; 150-157. 

McKelvey, Kevin S.; Skinner, Carl N.; Chang, Chi-ru; Erman, Don C.; Husari, Susan J.; 

Parsons, David J.; van Wagtendonk, Jan W.; Weatherspoon, C. Phillip. 1996. An 

overview of fire in the Sierra Nevada. In: Sierra Nevada ecosystem project: final 

report to Congress. Vol. II, Assessments and scientific basis for management options. 

Water Resources Center Report No. 37. Davis: Centers for Water and Wildland 

Resources, University of California; 1033-1040. 

Millar, Constance; Lind, Amy; Skinner, Carl; Verner, Jared; Zielinski, William; Ziemer, 

Robert. 1998. Sierra Nevada science review. Report of the Science Review Team 
Influence of Fire on Dead Woody Material—Skinner 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 453 

charged to synthesize new information of rangewide urgency to the national forests of 

the Sierra Nevada. Albany, CA: Pacific Southwest Research Station. 

Mohr, Jerry A.; Whitlock, Cathy; Skinner, Carl N. 2000. Postglacial vegetation and fire 

history, eastern Klamath Mountains, California. The Holocene 10: 587-601. 

Norman, Steven P.; Taylor, Alan H. 1996. Fire history of selected sites in the Deer Creek 

& Mill Creek watersheds, Lassen National Forest, California. Unpublished report on 

file at Supervisor's Office, Lassen National Forest, Susanville. 

Norman, Steve; Taylor, Alan H. 1997. Variation in fire-return intervals across a mixedconifer forest landscape. In: Cooper, Sandra; Sugihara, Neil, technical coordinators. 

Symposium on fire in California ecosystems: integrating ecology, prevention, and 

management; 1997 November 17-20, San Diego, CA. NA: International Association of 

Wildland Fire. Available online at Web site: http://www.ice.ucdavis.edu/cafe/agenda97/ 

FireEcology/History/6FENorman.html 

Rothermel, Richard C. 1983. How to predict the spread and intensity of forest and range 

fires. Gen. Tech. Rep. INT-143. Ogden, UT: Intermountain Research Station, Forest 

Service, U.S. Department of Agriculture; 161 p. 

Skinner, Carl N. 1997a. Toward an understanding of fire history information. In: 

Sommarstrom, Sari, ed. What is watershed stability? Proceedings of the sixth biennial 

watershed management conference. 1996 October 23-25. Lake Tahoe CA/NV. Water 

Resources Center Report No. 92. Davis: Centers for Water and Wildland Resources, 

University of California; 15-22. 

Skinner, Carl N. 1997b. Fire history in riparian reserves of the Klamath Mountains. In: 

Cooper, Sandra; Sugihara, Neil, technical coordinators. Proceedings—fire in California 

ecosystems: integrating ecology, prevention, and management. 1997 November 17-20, 

San Diego, CA. International Association of Wildland Fire. Available online at the Web 

site: http:// www.ice.ucdavis.edu/cafe/agenda97/FireEcology/History/4FESkinner.html 

Skinner, Carl N.; Chang, Chi-ru. 1996. Fire regimes, past and present. In: Sierra Nevada 

ecosystem project: final report to Congress. Vol. II Assessments and scientific basis for 

management options. Water Resources Center Report No. 37. Davis: Centers for Water 

and Wildland Resources, University of California; 1041-1069. 

Solem, Michael N. 1995. Fire history of the Caribou Wilderness, Lassen National Forest, 

California, U.S.A. State College, PA: The Pennsylvania State University; 102 p. M.S. 

thesis. 

Spies, Thomas. 1997. Forest stand structure, composition, and function. In: Kohm, 

Kathryn A.; Franklin, Jerry F., editors. Creating a forestry for the 21st century: the 

science of ecosystem management. Washington, DC: Island Press; 11-30. 

Stine, Scott. 1996. Climate, 1650-1850. In: Sierra Nevada Ecosystem Project: Final report to 

Congress. Vol. II Assessments and scientific basis for management options. Water 

Resources Center Report No. 37. Davis: Centers for Water and Wildland Resources, 

University of California; 25-30. 

Swetnam, Thomas W. 1993. Fire history and climate change in giant sequoia groves.

Science 262: 885-889. 

Swetnam, Thomas W.; Baisan, Christopher H.; Caprio, Anthony C.; Touchan, Ramzi; Brown, 

Peter M. 1992. Tree-ring reconstruction of giant sequoia fire regimes. Unpublished 

final report to Sequoia, Kings Canyon and Yosemite National Parks, Cooperative 

Agreement No. DOI 8018-1-1002. 

Taylor, Alan H. 1998a. Reconstruction of pre-Euroamerican forest structure, 

composition, and fire history in the Carson Range, Lake Tahoe Basin Management 

Unit. Unpublished final report for cooperative agreement 0024-CA-95 between the U.S. 
Influence of Fire on Dead Woody Material—Skinner 

454 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Department of Agriculture, Pacific Southwest Research Station (PSW) and The 

Pennsylvannia State University. On file at the PSW Silviculture Laboratory, Redding, 

CA. 

Taylor, Alan H. 1998b. Fire regimes and forest dynamics along a mixed conifer-red fir 

forest gradient in the southern Cascades. Unpublished final report for cost share 

agreement between the Pennsylvania State University and Lassen National Forest. On 

file at Lassen National Forest Supervisor's Office, Susanville, CA. 

Taylor, Alan H. 2000. Fire regimes and forest changes along a montane forest gradient, 

Lassen Volcanic National Park, southern Cascade Mountains, USA. Journal of 

Biogeography 27: 87-104. 

Taylor, Alan H.; Skinner, Carl N. 1998. Fire history and landscape dynamics in a latesuccessional reserve in the Klamath Mountains, California, USA. Forest Ecology 

and Management 111: 285-301. 

Thornburgh, Dale A. 1995. The natural role of fire in the Marble Mountain Wilderness. 

In: Brown, James K.; Mutch, Robert W.; Spoon, Charles W.; Wakimoto, Ronald H., 

technical coordinatiors. Proceedings: symposium on fire in wilderness and park 

management; 1993 March 30-April 1. Missoula, MT. Gen. Tech. Rep. INT-GTR-320. 

Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department of 

Agriculture; 273-274. 
Demographics and Dynamics 

in Coastal Mesic Forests

455
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 457 

Simulation of Stream Wood Source 

Distance for Small Streams in the Western 

Cascades, Oregon1

Mark A. Meleason,2 Stanley V. Gregory,2 and John Bolte3

Abstract 

The model, STREAMWOOD, is an individual-based stochastic model designed to simulate 

the dynamics of wood in small streams of the Pacific Northwest. We used STREAMWOOD 

to examine source distance as a function of tree fall regime and stand age. Our results suggest 

that source distance increased with stand age for the first 400 years of stand development and 

then declined. Simulated source distance for mature conifer forests (81 to 200 years old) were 

consistent with observed data, but simulated source distances for old-growth forests (201 to 

1,000 years old) were below observed data. Further information on stand ages for the forests 

used in the observational study would refine the compassion with simulated data. 

Introduction 

One consideration of riparian forest management is the long-term recruitment of 

wood to the stream. The chance of a riparian tree entering the channel is related to its 

source distance (Van Sickle and Gregory 1990). We define source distance as the 

slope distance between the stream bank and the base of the tree perpendicular to the 

stream channel. Several studies have addressed the relationship between source 

distance and riparian forest width in the Pacific Northwest. McDade (1987) and 

McDade and others (1990) surveyed 39 streams adjacent to either mature conifer (80 

to 200 years old) or old-growth conifer (> 200 years old) riparian forests in western 

Oregon and Washington. The source distance for 90 percent of the wood inputs was 

found to originate within 26 m for mature conifer and 36 m for the old-growth stands. 

McDade and others (1990) also modeled the source distances for riparian stands 

composed of uniform heights. The simulated source distance for 90 percent of the 

trees 40 m and 50 m tall was 32 m and 40 m, respectively. 

Van Sickle and Gregory (1990) developed a computer model that simulates the 

recruitment of stream wood from riparian forests with trees of mixed heights. They 

applied this model to a mixed-hardwood/conifer stand in the Oregon Cascades and 

found that 90 percent of the pieces originated within 18 m from the bank. The authors 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno Nevada. 2

 Ph.D. Candidate and Professor, respectively, Fisheries and Wildlife Department, Oregon State 

University, 104 Nash Hall, Corvallis OR 97331 (e-mail: streamwoodv1@hotmail.com and 

Stanley.Gregory@orst.edu) 

3

 Professor, Bioresource Engineering Department, Oregon State University, Corvallis OR 97331 (e-mail: 

boltej@engr.orst.edu) 
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

458 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

also proved mathematically that, for a forest of uniform height, approximately three 

times as many trees would enter the channel falling directly towards the stream bank 

as opposed to falling randomly. 

These studies provide valuable insights into the relationship between width of 

the riparian zone and recruitment of wood into a stream. However, these studies give 

limited insight into how source distance varies with stand age. The purpose of this 

study was twofold: to compare the results of the simulations reported here with the 

results from this previous studies and to investigate changes in source distance 

through time as a function of stand age. 

Model Description 

We developed STREAMWOOD, a computer simulation model, to investigate 

the dynamics of wood in streams. (A brief description of STREAMWOOD is 

provided here; further information can be found at our Web site: http://www. 

fsl.orst.edu/lter/research/compplfr.htm). STREAMWOOD is an individual-based 

stochastic model that operates on an annual time step at the reach scale. Stream 

systems that can be simulated range from a single reach to a small basin. Stream 

wood dynamics represented in the model are tree entry, breakage, movement, and 

decomposition. Riparian forest inputs are generated either from a simplified forest 

gap model built within STREAMWOOD or from a user-specified input file. The 

model is run under a Monte Carlo procedure and the results are reported as average 

conditions per reach. The current version of STREAMWOOD was developed for 

fifth-order and smaller streams in the coniferous forests of the Pacific Northwest. 

Species considered include Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco), 

western hemlock (Tsuga heterophylla [Raf.] Sarg.), western red cedar (Thuja plicata

Donn ex D. Don), and red alder (Alnus rubra Bong.). 

The forest model within STREAMWOOD was based largely on three existing 

forest–gap models: ZELIG (Pacific Northwest version by Steven Garman, Forest 

Science Laboratory, Corvallis Oregon), JABOWA (Botkin 1993, Botkin and others 

1972), and CLIMACS (Dale and others 1986, Dale and Hemstrom 1984, Hemstrom 

and Dale 1982). Since the forest model adheres closely to the original design of 

Botkin and others (1972) and Shugart (1984), it inherits many of their limitations 

(Schenk 1996). 

Riparian Zone Definition in STREAMWOOD 

A simulated stream reach consists of a length, bankfull width, and a riparian 

forest adjacent to each bank. The dimensions of each riparian forest is the reach 

length by a width selected between 0 m to 100 m. A tree fall regime is associated 

with each riparian forest. In a random fall regime, trees have an equal chance of 

falling in any direction. In a directional fall regime, tree fall angle is normally 

distributed around a mean (and standard deviation) fall angle. A directional fall 

regime defined with a mean of 180 degrees and a standard deviation of zero forces all 

trees to fall directly towards the channel. 
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 459 

Initial Conditions 

We conducted two simulations with STREAMWOOD using the forest model to 

grow identical riparian forests. Both simulations were run for 1,000 years and 200 

iterations. In the first simulation, trees could fall in any direction (random fall), and in 

the second all trees were forced to fall directly across the channel (directional fall). 

Both simulations represented riparian forests in the Oregon Cascades at an elevation 

of 300 m. Soil moisture content was set such that the growth of red alder was 

negligible, but supported Douglas-fir, western hemlock, and western red cedar. The 

reach dimensions were 100 m long and 15 m wide. The thermal growth index was set 

at 1,500 growing degree-days (5.5oC base) with a standard deviation of 100 growing 

degree-days. 

The simulated riparian forests were 75 m wide and started with no trees. The 

riparian forest was divided into 31 intervals, or source distances, parallel to the 

stream bank. The first 30 intervals were 2 m wide, and the last interval was for 

recruitment of all pieces > 60 m from the bank. For each source distance, the mean 

number of input events that entered the channel during each 10-year period was 

calculated. An input event included any tree that contributed a piece at least 10 cm 

top diameter and 1 m in length to the stream. 

Results and Discussion 

Comparison with Previous Studies 

The first purpose of this study was to compare the results from the simulations 

with the results of previously published studies. Van Sickle and Gregory (1990) 

proved mathematically that, given a stand composed of trees of the same height, 

exactly 1/л less input events would result from trees falling randomly as opposed to 

falling directly across the channel. We extend this proof to stands composed of mixed 

heights. Consider a riparian forest containing trees of two different heights. The ratio 

of input events between random and directional fall would be identical (1/л) for both 

heights. The ratio for the entire stand would also be 1/л since it is the sum of all 

random fall inputs over the sum of directional fall inputs. Extending this argument, 

the ratio of 1/л would hold for any number of height classes. 

The input ratio described by Van Sickle and Gregory (1990) provided a simple 

test for evaluating STREAMWOOD’s performance. The two simulations reported 

had identical initial conditions except for the fall regime used. The ratio of the 

number of input events from the two simulations was determined (fig. 1). The mean 

ratio between the number of input events from random and directional fall was 0.307 

with a standard deviation of 0.018. The mean input ratio from the simulations was 3.6 

percent lower than the predicted value and could be due to small differences between 

the two simulated forests. The coefficient of variation was 5.8 percent and most 

likely could be reduced with an increase in the number of iterations. Thus, the 

performance of the model was consistent with the predictions of Van Sickle and 

Gregory (1990). 
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

460 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

0.2

0.25

0.3

0.35

0.4

0 200 400 600 800 1000

time (years)

random / directional 

Figure 1―Ratio of input events from random and directional fall. The mean ratio of 

input events for each 10-year period was determined using the two simulations. The 

global mean obtained over the 1,000-year simulation was 0.31 (solid line). This value 

is consistent with the expected value of 0.32 (Van Sickle and Gregory 1990). 

The second comparison with previous work was with the source distance 

estimates presented in McDade and others (1990) (fig. 2, table 1). The old-growth 

curve from McDade and others (1990) lies entirely below both source distance curves 

from this study, while the majority of the mature conifer curve lies between the 

source distance curves from this simulation. In addition, both source distance curves 

from McDade and others (1990) were very similar for the first 5 meters and below 

either of the simulated source distance curves. 

Figure 2―Comparison of source distances, western Cascades, Oregon. The two 

source distance curves from this study are compared with those presented in 

McDade and others (1990). The simulated source distance curves include all input 

events over a 1,000-year period. The simulated random fall curve is consistent with 

observed mature conifer curve, but the observed old-growth curve is greater than 

both simulations. 

0

25

50

75

100

0 20 40 60

source distance (m)

cumulative number of input events 

(percent)

Old-Growth (McDade 1990)

Mature Conifer (McDade 1990)

Directly Across Channel

Fall Any Direction
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 461 

Table 1―Comparison of source distances between the two simulations and data in McDade 

and others (1990). Two source distances are reported for each forest age class. These 

distances represent 50 and 90 percent of the input events associated with a forest age class. 

Possible explanations for the discrepancies in source distance between the 

results of McDade and others (1990) and the simulations may be related to the biases 

inherent in each approach. The tree fall regimes in the study sites surveyed may not 

be completely random. Thus, it would be expected that the source distance curve for 

the old-growth would lie between the random and directional source curves. In the 

simulations, the density of trees within the plot was assumed uniform. However, tree 

densities in the field plots surveyed by McDade and others (1990) may not be 

uniform, especially within the first few meters from the stream bank. The region 

adjacent to the stream bank is more susceptible to disturbance from high flows and 

typically has higher light levels reaching the forest floor—conditions favoring the 

establishment of early successional species. 

The cumulative percent of input events for the first 2 meters was substantially 

less in the field study (2 and 5 percent) than in the simulations (15 and 21 percent). 

This difference suggests that the number of input events close to the stream bank was 

overestimated by STREAMWOOD. However, the simulations accounted for all input 

events that occurred over a 1,000-year period. In contrast, since the persistence of 

input events is not equal, larger and more recent events would be favored in the field 

surveys. Most likely, the cumulative percent of inputs 2 m and less from the channel 

are between the field and simulation estimates. 

Source Distance and Stand Age 

The second objective of this study was to investigate how cumulative input of 

wood into a stream varies through time as a riparian forest matures. Maximum source 

distance is equivalent to the maximum effective height (height to 10 cm top diameter) 

for a given species. In STREAMWOOD, the maximum effective height for the three 

species used in the simulation are approximately 80 m for Douglas-fir, 60 m for 

western hemlock, and 55 m for western red cedar. As noted previously, the riparian 

zone was divided into 30 source distance sub-zones 2 m wide, and one additional 

category for all input events occurring > 60 m from the stream bank. In our 

Study Forest age class Source distance (m) 

(years) 50 percent 90 percent 

McDade (1990) 81 – 200 10 26 

> 200 12 36 

All Ages 6 26 

≤ 80 3 14 

81 – 200 8 26 

201 – 400 6 30 

Random fall 

(this study) 

> 400 6 24 

All Ages 10 31 

≤ 80 4 20 

81 – 200 12 32 

201 – 400 10 36 

Directional fall 

(this study) 

> 400 9 30 
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

462 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

simulations, trees obtained sufficient height in approximately 450 years to contribute 

stream wood 60 m from the channel. 

The source distance associated with 90 percent of the input events as a function 

of stand age was determined for both simulations (fig. 3). The maximum value for 

both simulations occurred between stand ages of 200 to 400 years: 40 m for 

directional and 34 m for random fall. The source distances reflect the initial 

dominance of Douglas-fir (200 to 400 years) followed by the eventual dominance of 

western hemlock (fig. 3). 

0

5

10

15

20

25

30

35

40

45

0 200 400 600 800 1000

time (years)

source distance (m)

directional

random

Figure 3―Source distance for 90 percent of the input events from directional and 

random fall through time. The greatest source distance is associated with a riparian 

forest dominated by the tree species with the greatest height, Douglas-fir. As the 

stand matures, Douglas-fir is eventually replaced by western hemlock. 

To investigate how source distance varies by stand age, cumulative input events 

were determined for each of four riparian forest age classes: young conifer (0 to 80 

years old), mature conifer (81 to 200 years old), Douglas-fir dominated old-growth 

(201 to 400 years old), and hemlock dominated conifer (> 400 years old) (figs. 4, 5; 

table 1). Results were similar for both runs (figs. 4, 5), with young conifer stands 

having the shortest source distance, Douglas-fir dominated old-growth stands having 

the longest source distance, and the mature conifer and western hemlock dominated 

old-growth having almost identical source distances. The difference between the two 

runs can be illustrated by comparing the source distance at the 50 percent and 90 

percent cumulative input levels (table 1). At the 50 percent level, the source distances 

for all forest age classes, save for the young conifer, were within 3 meters. For the 90 

percent level, the three older forest age classes were within 6 meters. 

Finally, comparisons were made between the simulation results of the mature 

conifer (fig. 6) and old-growth stands (fig. 7, table 1) with those of McDade and 

others (1990) (fig. 2). For the mature conifer age class, source distances ≥ 14 m were 

almost identical between the field survey and the random fall simulation (fig. 6, table 

1). This suggests that trees tend to fall randomly in the interior of the stand. This 

warrants further testing. 
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 463 

0

25

50

75

100

0 20 40 60

source distance (m)

cumulative number of inputs 

events (percent)

0 to 80

81 to 200

201 to 400

>400

Figure 4—Cumulative number of input events from random fall as a function of the 

riparian forest age class. The four forest age classes represent young conifer, mature 

conifer, old-growth dominated by Douglas-fir, and old-growth dominated by western 

hemlock. 

Figure 5―Source distance for the directional fall simulation as a function of the 

riparian forest age class. The four forest age classes represent young conifer, mature 

conifer, old-growth dominated by Douglas-fir, and old-growth dominated by western 

hemlock. 

0

25

50

75

100

0 20 40 60

source distance (m)

cumulative number of input

events (percent)

0 to 80

81 to 200

201 to 400

>400
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

464 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 6―Comparison of source distance estimates for mature conifer, western 

Cascades, Oregon. Comparison of mature conifer source distance curves from the 

two simulations and McDade and others (1990). Each simulated source distance 

curve includes only those input events from stand ages between 81 to 200 years. 

The random fall source distance is consistent with the observed for source distances 

≥ 14 m. This suggests that in the surveyed plots, trees ≥ 14 m from the stream bank 

tended to fall in any direction. 

Figure 7―Comparison of source distance estimates for old-growth conifer, western 

Cascades, Oregon. Comparison of old-growth source distance curves from the two 

simulations and McDade and others (1990). Each simulated source distance curve 

includes only those input events from stand ages between 201 and 400 years. The 

directional fall source distance is consistent with the observed for source distances ≥

14 m. This suggests that in the surveyed plots, trees ≥ 14 m from the stream bank 

tended to fall directly towards the channel, which is unlikely. The forest age-class of 

201 to 400 years old may not be the appropriate age class for this comparison. 

Further information on stand ages of the surveyed plots is needed to construct an 

appropriate comparison. 

0

25

50

75

100

0 20 40 60

source distance (m)

cumulative number of input 

events (percent)

Mature Conifer (McDade 1990)

Random fall: 81 to 200

Directional fall: 81 to 200

0

25

50

75

100

0 20 40 60

source distance (m)

cumulative number of 

input events (percent)

Old-Growth (McDade 1990)

Random fall: 201 to 400

Directional fall: 201 to 400
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 465 

For the old-growth age class between 201 and 400 years, source distances ≥ 14 

m were almost identical to the field surveys and the directional fall simulation (fig. 7, 

table 1). This would suggest that trees of this age class tend to fall directly towards 

the channel, which is highly unlikely. However, the source distance curves appear to 

be sensitive to the definitions used for the forest age classes. Evidence for this can be 

found by comparing the simulation results (fig. 2), which includes all input events 

over the 1,000-year period, with the simulation results divided by forest age class 

(figs. 6, 7). Note that both the directional and random source curves have shifted 

down with respect to the mature and old-growth curves from McDade and others 

(1990). 

The majority of input events identified in a field survey may be associated with 

the recent history of the forest stand. The close agreement with the mature conifer 

age class may be attributed in part to a well-defined forest age class. In contrast, the 

old-growth age classes used to classify the simulation results may not be equivalent 

to the old-growth stands surveyed by McDade and others (1990). Further information 

on stand age of surveyed sites would be necessary to define appropriate forest age 

class to use in this comparison. 

Conclusion 

Van Sickle and Gregory (1990) provided a mathematical proof that 

approximately one-third as many trees would enter the stream falling in any direction 

than falling directly across the channel. The results of this study were found to be 

consistent with this ratio. McDade and others (1990) found that 90 percent of the 

input events occurred within 26 m and 36 m from the stream bank for mature conifer 

and old-growth respectively. Over the entire 1,000-year simulation, 90 percent of the 

input events occur within 26 m and 31 m for the random and directional fall, 

respectively. A closer agreement between the two studies was found after accounting 

for stand age (table 1).

Large wood in streams is an important component in a stream ecosystem. One 

goal in managing riparian forests is to ensure the long-term supply of wood to the 

stream. The results from this study suggest that source distance varies with stand age. 

Based on a 1,000-year simulation, the largest source distance occurred with stand 

ages between 200 and 400 years old (fig. 3). These results may be useful in 

determining the appropriate riparian buffer width to ensure an adequate supply of 

wood to a stream. However, the recruitment of wood to streams is only one of many 

criteria that should be considered when developing management plans for riparian 

forests and the protection of the stream ecosystems. 

Acknowledgments 

We thank Linda Ashkenas, Randy Wildman, and Toby Minear for reviewing 

this article. We also like thank Steve Garman, Mark Hutchinson and Edin Zudin for 

advice and assistance with the computer programming. Finally, we thank Steve 

Acker for providing data on riparian old-growth conditions in the Oregon Cascades, 

and Aaron Drew, Fred Swanson, Mark Harman, Marganne Allen, Kris Wright, 

Jochen Schenk, and Jason Hamilton for numerous discussions on this work. This 

research was sponsored by a National Science Foundation (NSF) Grant supporting 

the Long Term Ecological Research Program, H. J. Andrews Experimental Forest. 
Simulation of Stream Wood Source Distance for Small Streams in the Western Cascades, Oregon—

Meleason, Gregory, and Bolte 

466 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

References 

Botkin, D. B. 1993. Forest dynamics: an ecological model. Oxford: Oxford University 

Press. 

Botkin, D. B.; Janak, J. F.; Wallis, J. R. 1972. The rationale, limitations and assumptions 

of a northeastern forest growth simulator. IBM J. Res. Dev. 16: 101-116. 

Dale V. H.; Hemstrom, M. 1984. CLIMACS: a computer model of forest stand 

development for western Oregon and Washington. Res. Paper PNW-327. Portland, 

OR: Pacific Northwest Research Station, USDA Forest Service. 

Dale V. H.; Hemstrom, M.; Franklin, J. 1986. Modeling the long-term effects of 

disturbances on forest succession, Olympic Peninsula, Washington. Canadian 

Journal of Forest Research 16: 56-67. 

Hemstrom, M; Dale Adams, V. H. 1982. Modeling long-term forest succession in the 

Pacific Northwest. In: Means, J. E., ed. Forest succession and stand development 

research in the Northwest. Corvallis OR: Forest Research Laboratory, Oregon State 

University. 

McDade, M. H. 1987. Source area of coarse woody debris in small streams in western 

Oregon and Washington. M.S. thesis, Oregon State University, Corvallis OR. 

McDade, M. H.; Swanson, F. J.; McKee, W. A.; Franklin, J. F.; Van Sickle, J. 1990. Source 

distances for coarse woody debris entering small streams in western Oregon and 

Washington. Canadian Journal Forest Research 20: 326-330. 

Shugart, H. H. 1984. A theory of forest dynamics: The ecological implications of forest 

succession models. New York: Springer-Verlag. 

Schenk, H. J. 1996. Modeling the effects of temperature on growth and persistence of tree 

species: A critical review of tree population models. Ecological Modeling 92: 1-32. 

Van Sickle, J.; Gregory, S. V. 1990. Modeling inputs of large woody debris from falling 

trees. Canadian Journal Forest Research 20: 1593-1601. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 467 

Standing Dead Tree Dynamics Extracted 

from Growth and Yield Permanent Sample 

Plots in British Columbia1,2

Jeff Stone,3 John Parminter,4 and Joe Braz5

Abstract 

Permanent sample plots established to study the growth and yield of live trees can provide 

valuable information on standing dead tree dynamics. Even if dead trees were not traditionally 

measured, a subsequent measurement of dead trees enables extraction of information on past 

dynamics. In British Columbia (BC), Canada, the Ministry of Forests administers over 5,500 

growth and yield permanent sample plots that could provide important information on dead 

tree dynamics. In this paper we discuss the standing dead tree information obtainable from 

these plots, the time needed for and costs of measuring, and current findings on standing dead 

tree dynamics in BC. 

Introduction 

In British Columbia (BC), Canada, the ecological value of wildlife trees (i.e., 

standing dead trees and defective live trees) is well recognized within forest 

management and operational practices. The BC Wildlife Tree Committee, established 

in 1985, has worked to improve the conservation of wildlife trees while addressing 

the legislative needs for safety in forest operations. Legislation and associated 

guidelines under the Forest Practices Code of British Columbia Act identify and 

require the conservation of wildlife trees through reserve and management zones. 

Knowledge and tools about the dynamics of standing dead trees (e.g., fall rates) 

can assist forest managers with decisions at the tree level (e.g., safety concerns of 

individual trees) to the landscape level (e.g., characteristics of wildlife tree patches). 

These dead tree decisions can influence and are influenced by decisions made for 

other resources including timber and wildlife. Tools to assist dead tree decisions must 

be integrated with both traditional forest management tools for timber values (e.g., 

growth and yield models) and for non-timber values (e.g., habitat suitability indices). 

However, basic information on the dynamics of standing dead trees that would enable 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 This paper reflects government organization, legislation, or policy as of December 1999. 3

 Timber Supply Analyst, Ministry of Forests, Kamloops Forest Region, 515 Columbia St., Kamloops, 

BC V2G 2T7 Canada (e-mail: jeff.stone@gems7.gov.bc.ca) 4

 Research Ecologist, Research Branch, Ministry of Forests, P.O. Box 9512 Stn. Prov. Govt., Victoria, 

BC V8W 9C2 Canada (e-mail: john.parminter@gems7.gov.bc.ca) 5 Growth Sampling Officer, Terrestrial Information Branch, Ministry of Sustainable Resource 

Management, P.O. Box 9993 Stn. Prov. Govt., Victoria, BC V8W 9R7 Canada (e-mail: 

joe.braz@gems1.gov.bc.ca) 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

468 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

appropriate projections for forest management and silvicultural planning is generally 

lacking. 

Backhouse and Lousier (1991) and Caza (1993) noted the potential of BC’s 

extensive growth and yield (GY) permanent sample plot (PSP) program to provide 

information on dead tree dynamics. A GY PSP is typically a fixed area in which trees 

of a minimum size are permanently marked and regularly remeasured at a fixed 

interval between 2 and 10 years. Minimally, the individual trees are measured for 

species, diameter at breast height (DBH), and a few other characteristics. On a subset 

of trees, more detailed measures such as height and age may be included. On more 

intensive PSPs, the location of individual trees will be recorded and each tree will be 

measured in greater detail. 

In BC and elsewhere, GY PSPs have historically provided information only on 

the live tree dynamics of forest stands. The measurement of a tree typically stopped 

at its death. With increased ecological concerns, the continued monitoring of a tree 

past its death is now a more common practice. Fortunately, the repeated measures 

nature of a PSP enables some of the past dynamics to be extracted immediately upon 

the first measurement of standing dead trees in an existing plot. 

The initial measurement of standing dead trees on an established GY PSP 

creates a cohort data set of standing dead trees identified as dead in each of the past 

remeasurements. These data can be analyzed or modeled by many methodologies—

some more appropriate than others. The data may be fit to a negative exponential 

decay function, and general decay (i.e., fall rates) can be reported (Harmon and 

others 1986). A life-table or transition matrix approach can be used to present rates of 

fall (Huggard 1999, Krebs 1978, Raphael and Morrison 1987). Lee (1998) extracted 

the dynamics of fall for aspen trees in Alberta with failure analysis techniques on a 

large PSP data set. Logistic regression models have also been used to predict dead 

tree fall both at the tree and stand levels (Raphael and Morrison 1987, Stone 1996). 

Standing dead trees provide a link between forest stands and many animal 

habitat/population dynamics. Standing dead tree models have been structured to 

enable input from forest stand growth and yield models and provide output useful for 

habitat/population models (Raphael and Morrison 1987). Marcot (1992) directly 

linked the fall model, Snag Recruitment Simulator, with habitat requirements of 

woodpeckers (Ohmann and others 1994, Schuster and others 1993). Fall models built 

into growth and yield models such as Tree and Stand Simulator (TASS) (Mitchell 

1975, Stone 1996) or as extensions such as the Forest Vegetation Simulator Fire and 

Fuels Extension (Beukema and others 1997) have been linked to habitat suitability 

type models to look at the impacts of direct management regimes (Greenough and 

Kurz 1996, Greenough and others 1999). Standing dead tree models are not limited to 

fall dynamics only. They may provide other characteristics, such as decay stage, 

important to habitat linkages (Huggard 1999, Raphael and Morrison 1987). 

Underlying the usability of any standing dead tree model are the basic data of 

dead tree dynamics. In this paper, we discuss the information about standing dead 

trees currently collected on GY PSPs in BC and further describe an example of 

standing dead tree data from one of BC’s earliest growth and yield sample plots. We 

note that our viewpoint is primarily from the perspective of the Ministry of Forests’ 

Growth and Yield programs and might not reflect other programs (e.g., those of the 

forest industry). 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 469 

PSP Dead Tree Measurement in British Columbia 

The BC Ministry of Forests (MOF) has an extensive GY PSP program (> 5,000 

PSPs), typically establishing and remeasuring between 200 and 700 plots annually. 

The earliest PSPs were established as part of research studies in the 1920s, although 

much of the PSP program was established after the 1960s: 

Period Number of PSPs established1

1920-39 90 

1940-49 487 

1950-59 319 

1960-69 2,163 

1970-79 1,528 

1980-89 994 

1990-97 1,412 

1 The number of PSPs shown represent those maintained by the Ministry of Forests, Resources 

Inventory Branch. 

GY PSPs are established and remeasured by several programs within the MOF. 

The Resources Inventory Branch (RIB) administers the largest program that is 

conducted through regional offices. These PSPs tend to be in unharvested rather than 

treated forests. Researchers from Research Branch and Regional Offices maintain 

PSPs within research installations and silvicultural systems trials that have a wide 

range of research objectives and treatments. Industry and academia also have 

established PSP programs adding over 4,000 PSPs to the provincial PSP program. 

The Forest Productivity Council (FPC) of BC—whose members are from 

government, industry, and academia—has taken a lead role provincially to coordinate 

PSP establishment and remeasurement. The FPC maintains a matrix of forest stand 

conditions in which existing PSPs in BC are located, thus enabling the determination 

of where best to place new PSPs. The FPC also maintains provincial minimum 

standards for GY PSP installation and measurement that are mostly followed by 

government and industry. 

Information collected on dead trees has changed from early PSP establishment 

in the 1920s to the present. Early PSP measurements may have identified simply that 

a tree had died. This was later modified to some indication of the merchantable 

condition of a tree at death through the use of a standardized “tree class” measure 

assigned to a tree on each remeasurement. Three of the six tree classes concern dead 

trees: cut (removed by human activity); dead potential (>50 percent sound wood by 

volume and > 10 cm DBH and 3 m height or length); and dead useless (not cut or 

dead potential). As interest in dead trees increased in the 1990s, further information 

on dead trees has been collected within the MOF RIB GY PSP program. In 1991 a 

tally of standing dead trees by DBH size class was added to the establishment 

procedures. In 1994, a measure indicating whether a tree that had recently died was 

standing or fallen was added, as it was not previously possible to differentiate this. 

These data provided information on dead tree recruitment and inventory at plot 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

470 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

establishment. However, little information on dead tree dynamics could be obtained 

as trees were not revisited after being recorded dead. 

In the mid-1990s, several organizations started using GY PSPs to obtain 

information on dead tree dynamics in BC. In 1993/94, the BC MOF Research Branch 

initiated the collection of information on standing dead trees from a limited number 

of PSPs in research trials to determine basic fall rate information (table 1). Wells 

(1996) analyzed a subset of PSPs of MacMillian Bloedel Ltd. in coastal western 

hemlock forests to investigate developmental trends of stand structure and tree 

mortality. Large silvicultural systems trials were initiated during this period in which 

PSPs were installed and dead tree information was collected (Holstedt and Vyse 

1997). Further during this time period, wildlife/danger tree assessment was initiated 

and standing dead trees were included in new resource inventory standards (Stone 

and others 2002). 

Table 1—British Columbia Ministry of Forests research trial growth and yield permanent 

sample plots on which standing dead trees have been measured. 

Research 

Trial 

Treatment Species1

 Number 

of PSPs 

Date 

established 

No. of 

measurements 

Date of 

first dead 

tree 

measure 

Aleza 

Lake EPs 

Residual 

cutover 

Se, Bl 17 1926-1936 7-9 1998 

EP364 Commercial 

thinning 

Fd 12 1950 8 1996 

EP368 Species trial Fd, Hw, 

Cw, Bg, 

Ba, Ss, Co 

49 1958 7 1998 

EP370 Partial cutting Pw, Hw, 

Lw, Fd 

20 1957 6 1994 

EP384/38

5 

Thinning Pl 12 1953 7 1994 

EP388 Commercial 

thinning 

Hw 20 1953 5 1997 

EP429 Espacement Fd, Cw, 

Bg 

18 1963 6 1999 

EP534 Juvenile 

spacing 

Fd 46 1959-1963 8-11 1995 

EP554 CCT trial Fd 47 1959 9-11 1997 

EP571 Espacement Fd, Cw, 

Ss, Hw 

157 1962 5-8 1998 

EP703 Thinning/ 

fertilization 

Fd, Hw 940 1971-1975 8 1994-2000 

EP1065 Pruning Hw, Cw, 

Fd 

102 1990-94 3 1997-1998 

EP1097 Thinning/ 

fertilization 

Hw 36 1992 2 1996 

EP1177 Biosolids Fd 32 1992 4 1998 1

 Ba: Amabilis fir (Abies amabilis), Bb: Subalpine fir (Abies lasiocarpa), Bg: Grand fir (Abies grandis), 

Co: Port-Orford-cedar (Chamaecyparis lawsoniana), Cw: Western red cedar (Thuja plicata), Fd: 

Douglas-fir (Pseudotsuga menziesii), Hw: Western hemlock (Tsuga heterophylla), Lw: Western larch 

(Larix occidentalis), Pl: Lodgepole pine (Pinus contorta), Se: Engelmann spruce (Picea engelmannii)

Ss: Sitka spruce (Picea sitchensis).
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 471 

Despite the above initiatives, the need for broader information on standing dead 

tree dynamics was identified by BC dead wood experts (Stone 1997). Measuring 

standing dead trees within the provincial GY PSPs was potentially an economical 

method to obtain such information. To determine the feasiblity of this need, the FPC 

through the MOF RIB conducted a pilot study in 1998 to investigate the cost of 

including dead tree measures as a minimum GY PSP standard (Forest Productivity 

Council 1999). We discuss this pilot study later. As a result of the study, the FPC 

added standing dead tree measures to provincial GY PSP standards and the MOF RIB 

GY program commenced measuring standing dead trees in the fall of 1999. A review 

of the standards and the use of the information will be conducted in 2001. 

Example Data 

In August 1927, George H. Barnes established a 0.405 ha (1 acre) permanent 

sample plot (this permanent sample plot was originally identified as EP 

[Experimental Plot] 82 and is currently identified as 6-01L-2R by the Resources 

Inventory Branch, Ministry of Forests, Victoria, BC) in an unmanaged stand in the 

municipal Mount Douglas Park (Saanich, British Columbia). Over the past 70 years, 

the BC MOF has measured this PSP 10 times for tree species, DBH, and selected 

heights and ages of live trees until their death (table 2). Currently the PSP is 

predominantly Douglas-fir (Pseudotsuga menziesii var. menziesii) with a small 

component of big-leaf maple (Acer macrophyllum). 

Table 2—The number of live Douglas-fir stems per plot on Mt. Douglas Park (Saanich, 

British Columbia) growth and yield permanent sample plot. The plot size is 0.405 ha (1 acre). 

The site index is 27 m @ 50 years (Bruce 1981). 

 Trees per plot by DBH (cm) class 

Measurement 

year 

Stand 

age 

Stems (>7.5 

cm) per plot 

<20 20-30 30-40 40-50 50+ 

1927 70 282 40 130 73 29 10 

1933 76 262 28 117 66 40 13 

1937 80 247 25 106 64 45 17 

1943 86 222 14 76 62 48 27 

1947 90 208 5 63 50 52 38 

1953 96 195 4 50 46 44 51 

1957 100 195 4 49 45 42 55 

1967 110 174 1 30 41 31 71 

1977 120 163 1 23 36 18 85 

1987 130 154 0 15 33 18 88 

1997 140 154 1 15 29 18 91 

In the fall of 1998, all standing dead trees (> 1.3 m height) were recorded on the 

PSP. The individual trees were identified either by the presence of a tag or by 

comparison with the information for trees known to have died. The height (ocular 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

472 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

estimate) and several characteristics (e.g., bark presence, wood condition, branch 

condition) were measured for each tree. In the description below we discuss only 

Douglas-fir dynamics. Other conifers are a minor component of this stand. 

Hardwoods were not included in the PSP measurement until 1987. 

Data such as found on this PSP may be analyzed and presented in several 

formats. A raw summary of the 10 cohorts (based on the number of years since the 

tree’s death was recorded) shows some common features of this type of information 

(table 3). We note that the size distribution of the dead trees lags behind the size 

distribution of the live tree dynamics (i.e., trees that die are usually growing slower), 

and no dead trees have been standing longer than a certain age (i.e., 60 years in this 

data set). These data can also be graphed as survival curves (fig. 1). Studies such as 

Harmon and others (1986) report the decay rate derived from simple negative 

exponential models. For Mt. Douglas data we find a decay rate of 0.035 per annum 

(standard error [s.e.] = 0.007) for dead trees in the 21-30 cm dbh range. Similarly, the 

data could be fit to a logistic regression model (Raphael and Morrison 1987). One 

such fitted model for the Mt. Douglas data is Prob[yrs,DBH] = 1/(1+ EXP(-0.459 + 

0.046*yrs – 0.028*DBH)) where Prob[yrs,DBH] is the probability that a dead tree 

with a given diameter (DBH in cm) will be still standing after x years (yrs). 

Table 3—The number of Douglas-fir stems per plot on Mt. Douglas Park (Saanich, British 

Columbia) growth and yield permanent sample plot that had died since the previous 

measurement and the number of dead Douglas-fir that remain standing in 1998. The plot size 

is 0.405 ha (1 acre). Values in parentheses indicate trees that were cut and thus excluded 

from fall calculations. A dead standing tree must be at least 1.3 m tall. 

Measurement 

year 

Number of trees in plot that died 

since previous measurement 

period by DBH (cm) 

Years since 

death 

recorded 

Number of standing dead trees 

still standing in 1998 by period 

of death and DBH (cm) 

 <20 20-30 30-40 40-50 <20 20-30 30-40 40-50 

1927 0 0 0 0 71 0 0 0 0 

1933 11 8 (1) 0 0 65 0 0 0 0 

1937 3 (5) 3 (5) 0 0 61 0 0 0 0 

1943 5 (4) 13 (1) 0 (1) 55 2 4 0 0 

1947 5 9 0 0 51 2 2 0 0 

1953 1 9 3 0 45 1 3 1 0 

1957 0 0 0 0 41 0 0 0 0 

1967 2 15 3 0 31 0 7 0 0 

1977 0 8 2 0 21 0 2 1 0 

1987 1 6 3 0 11 0 3 2 0 

1997 0 8 9 0 1 0 5 7 0 

1998 0 0 1 0 0 0 0 1 0 

However, as is well recognized, the robustness and interpretation of the results 

of any method is dependent upon the underlying data and how they were obtained. 

These Mt. Douglas data provide a small data set, probably insufficient for most 

analyses including the above, and are from a single site that would unlikely be 

representative of a larger population of interest. Appropriate sampling schemes 

should be employed or, alternatively, a good understanding of the potential biases is 

needed if the results are to be applied for management purposes. 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 473 

Figure 1—The proportion of dead Douglas-fir stems still standing in 1998 by age 

group (i.e., years since death) on the Mt. Douglas PSP. The data have been grouped 

into 10 year periods. 

Time Trial 

To estimate the cost of obtaining dead tree information within the Ministry of 

Forests’ GY PSP program, we conducted a pilot study (Forest Productivity Council 

1999). Nine existing plots that covered a range of characteristics in terms of stand 

density, age, and time since establishment were chosen. Four plots were located in 

the Kamloops Forest Region of interior British Columbia and five plots in the 

Vancouver Forest Region of coastal British Columbia. On each plot, all standing 

dead trees were located and measured for a variety of characteristics. These measures 

included base (e.g., standing or fallen, height to breakage, wildlife tree appearance) 

and special informational needs (e.g., bark condition, lichen loading), as identified in 

a needs assessment by 44 individuals interested in dead tree data in British Columbia 

(Stone 1997). 

The time study found that for the base set of measures (species if needed, DBH 

if needed, tag identification if needed, vertical position [standing or fallen], breakage, 

height to break if needed, and wildlife tree visual appearance), the average time 

required per tree was 51 seconds (s.e. = 2.0). For the typical tree (i.e., has a tag and 

does not require DBH or species), the average time required to collect these base 

measures was 19 seconds (s.e. = 0.7). 

The PSPs in the pilot study were selected to sample a range of conditions, not to 

be representative of the entire sampling program. The average number of dead trees 

per plot of the MOF PSP sampling program is expected to differ from the average of 

the pilot study. To determine an estimate of the standing dead trees that might be 

found on an average MOF PSP, we randomly selected 100 PSPs with at least two 

remeasurements (i.e., 20 years since establishment) from the active provincial 

sampling program. From these 100 PSPs (mean size 0.087 ha), we obtained an 

average of the expected number of trees over 10 cm DBH at a remeasurement (8.6 

per plot, s.e. = 0.72) that died since the previous measurement. We then estimated 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 20 40 60 80

Years Since Death

Proportion Standing

< 20 cm

21-30 cm

31-40 cm
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

474 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

that 10.7 (s.e. = 0.79) trees per plot that died before the previous measurements 

would still standing. The latter was estimated by applying, as a best guess, a logistic 

fall model for Douglas-fir to tree mortality information in each PSP (Stone 1996). 

We were interested in the incremental costs of measuring all standing dead trees 

during the regular PSP remeasurement. If we assume that the 1998 average 

contracted bid price for plot measurement in the MOF GY PSP program was $1,000 

for 10 hours per plot, we find that the inclusion of the base measures for dead trees 

greater than 10 cm DBH added $29 to $39 to the cost of measurement. This low cost 

was also reflected in the MOF Research Branch coastal research PSP program. In the 

second year of the collection of dead tree measures in 1997, accepted bid prices were 

similar to those in 1993 for the same plots when no dead tree measures were 

collected (de Montigny 1998). However, in the initial year of the collection of dead 

tree measures, an increase in bid cost did occur probably due to the uncertainty 

among contractors about the costs of dead tree measures. 

Use of PSP Data in BC 

Dead tree information needs in British Columbia have been identified in various 

reviews (Backhouse and Louiser 1991, Caza 1993, Lofroth 1998, Machmer and 

Steeger 1995). These needs can be summarized into four categories: the development 

of policy and management guidelines; understanding the ecological role of dead 

trees; understanding the status and dynamics of dead trees; and operational forest 

management (Stone 1997). Most uses of dead tree information in current forest 

management practice (e.g., wildlife/danger tree assessment, residue and waste 

surveys, wildlife tree patch determination and mapping) involve a static field 

identification of dead wood resources. However, most of the identified needs require 

information on the dynamics of dead trees and the linkages to their ecological roles. 

Information from PSPs can satisfy many of the basic needs on dead tree 

dynamics. Simple summaries of fall rate information by species and forest type will 

provide insight for researchers and forest managers needed for developing 

prescriptions related to wildlife tree reserves. Fall and breakage rates in relation to 

live and dead tree conditions can assist in assessing wildlife/danger tree assumptions. 

Data from the MOF PSP program are publicly available. Researchers might make use 

of the PSPs to collect further non-destructive measures to address specific 

information needs (e.g., decay development, bark sloughing) and potentially correlate 

these to the larger PSP information base. 

The primary identified use of the raw data from the MOF GY PSP program will 

be for the development of empirical models of dead tree fall included within the 

MOF growth and yield models TASS, TIPSY, and PrognosisBC (for description of 

the models, see http://www.for.gov.bc.ca/research/gymodels). TASS is an individual 

tree distance-dependent growth model that is currently suitable for modeling BC’s 

major commercial species in single species even-aged stands (Di Lucca 1999, 

Mitchell 1975, Stone 1996). The model enables silvicultural treatments such as 

thinning, fertilization, and pruning and has a wide array of outputs. However, the 

model is not publicly distributed. TIPSY is a publicly distributed model that 

interpolates yield tables derived from TASS. TIPSY has a limited set of silvicultural 

options but provides a wide range of growth and yield outputs as well as economic 

summaries. PrognosisBC is a BC derivative of the Forest Vegetation Simulator 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 475 

(FVS) that has been parameterized for use in several ecosystems of southeastern BC 

(Robinson 1997). 

The empirical dead tree fall models currently used in TASS and TIPSY are 

logistic models derived from a limited number of PSPs in BC for Douglas-fir, 

western hemlock (Tsuga heterophylla), and lodgepole pine (Pinus contorta) (table 4). 

Other species either use Douglas-fir parameters as a default or have been modified to 

reflect a perceived relative rate of fall as compared to Douglas-fir. The logistic 

models used time since tree death and DBH at death as the independent variables. 

While both TASS and TIPSY use logistic models, they are applied in different 

manners. In TASS the models are applied to individual trees and if the probability of 

fall is greater than a randomly assigned value, the tree is considered to have fallen. In 

TIPSY the models are applied to stand level information (average DBH class and 

time since death) and the probability is treated as the percentage of the number of 

trees in that class that will have fallen during a time period. These fall models will be 

reparameterized as new data become available. Furthermore, the dead tree model 

structure in TASS is also expected to change to reflect greater biological/mechanical 

relationships. 

Table 4—Standing dead tree logistic fall models incorporated as default parameters within 

dead tree fall models of the Ministry of Forests’ growth and yield model TIPSY. The model is 

ProbStanding = 1/(1+ EXP(b0 + b1*YearsSinceDeath + b2*DBHatDeath)). Only nontreated plots dominated by the species of interest were used. 

Source Establishment date Dead tree 

measurement date 

No. of 

PSPs 

DBH 

range 

(cm) 

Species Standing 

dead trees 

Total trees 

died since 

establishment 

b0 b1 b2 

EP7031 1971-75 1994-95 46 4.2 - 

54.6 

Fd 1,518 3,986 -1.369 0.132 -0.063 

EP7031 1971-74 1994-95 16 4.9 - 

48.8 

Hw 1,063 2,137 -2.094 0.169 -0.057 

EP384/852 1953 1994 2 3.3 – 

26.9 

Pl 28 255 0.662 0.146 -0.074 

1

 EP703 consists of 940 PSPs located at 85 installations on Vancouver Island and the coastal mainland 

of British Columbia (Darling and Omule 1989, Stone 1996). Species composition of these PSPs varies 

but is dominated either by Douglas-fir (Fd) and/or western hemlock (Hw). 2 EP384/85 consists of 12 PSPs located near Canal Flats, BC. These installations are composed of 

lodgepole pine (Pl) with scattered western larch. 

PrognosisBC can use the FVS Fire and Fuel Extension model to generate 

standing dead tree information. For a planning study in Nelson Forest Region of BC, 

Greenough and others (1999) adjusted this extension based on fall information from a 

limited set of regional PSPs. The standing and fallen dead tree information was 

linked to a number of indicators to provide an environmental assessment. The Fire 

and Fuel Extension has not been parameterized for use in other areas. 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

476 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Discussion 

The integrated collection of dead and live trees on PSPs enables a tree to be 

followed through its entire development and breakdown. Knowledge of the source of 

death or timing of decay onset provides valuable information for understanding the 

breakdown of a dead tree. Likewise, the management of dead trees is tied to the 

management of live trees as a source of dead tree recruits. The integrated collection 

provides direct data ties for modelling the growth and yield of live and dead trees. 

The measurement of standing dead trees in conjunction with live trees on GY 

PSPs is also more economical, as much of the measurement cost is associated with 

travel to the site. Furthermore, within the BC RIB GY PSP program we made a 

tradeoff between information and cost by measuring only standing dead trees greater 

than 10 cm DBH, while live trees are currently measured down to 2 cm DBH. The 10 

cm limit reduces the variability of the number of dead trees per plot to measure and, 

therefore, the contractor uncertainty about the number of trees that will be measured. 

The use of existing GY PSPs to obtain dead tree information is not without 

potential problems. As with any sampling, the user of the information must determine 

whether the information and any biases are appropriate. Biases may exist in plot 

placement. In BC, areas with forest health problems tended to be avoided when the 

PSP objective was assessment of potential tree growth. PSPs also tend to be located 

in areas with easier access (i.e., roads hopefully are not randomly located). Biases 

might also be caused by the physical act of measurement. In certain PSP programs in 

BC, at least until the mid-1970s, some sampling crews tended to push over standing 

dead trees to simplify plot establishment and measurement as dead trees were not 

considered important at the time. 

The collection of dead tree information on PSPs must serve a use, whether it is a 

current need or a perceived future need. Managers must ensure that data are properly 

collected, stored, and summarized so that they are available to the users. The users 

must demonstrate to the managers that the data are serving a purpose and provide 

feedback to collection or data management needs. Furthermore, to ensure the success 

of a long-term information collection program, managers and users both must 

communicate the value of PSPs in the face of changing information needs to those 

who ultimately fund the program. 

PSPs should be considered as one source for information on dead tree dynamics. 

PSPs may not be able to provide all needed information, some of which may have to 

be obtained by destructive methods. The small size of PSPs and their placement will 

most likely be inappropriate for investigating the role of standing dead trees in 

relation to organisms with larger space needs, and the appropriate linkages must be 

made through other knowledge and sampling tools. Additionally, information 

obtainable on PSPs might be obtained by other methods sooner (e.g., Huggard 1999). 

In BC, we still have a large need for basic dead tree information, and we need to use 

all the tools possible. 

Acknowledgments 

We thank Ralph Wells and Rob Drummond for their timely review of this paper. 

We thank Kim Bartlett, Roman Bilek, Kevin Hardy, Jack Louie, Bob MacDonald, 

Todd Manning, Carlos Martins, and Fraser Russell for their efforts on the dead tree 

pilot study. We thank Louise de Montigny for her early and continued support of 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 477 

dead tree measures within the normal data collection of research growth and yield 

PSPs. Lisa Meyer provided background information on research PSPs in BC. Jeff 

Beale provided initial dead tree data for EP703 from a pathological study. John 

Pollack and Harry Quesnel supported the remeasurement of EP370 and EP384/385. 

Financial support was provided by Forest Renewal BC, a Crown corporation 

committed to renewing the forest sector in British Columbia. 

References 

Backhouse, Frances; Lousier, J. Daniel. 1991. Silviculture systems research: wildlife tree 

problem analysis. Unpublished report prepared for Ministry of Forests, Ministry of 

Environment, and B.C. Wildlife Tree Committee, Victoria, BC. 

Beukema, S. J.; Greenough, J. A.; Robinson, D. C. E.; Kurz, W. A.; Reinhart, E. D.; 

Crookston, N. L.; Brown, J. K.; Hardy, C. C.; Stage, A. R. 1997. An introduction to the 

fire and fuels extension to FVS. In: Teck, R.; Moeur, M.; Adams, J. Proceedings of the 

Forest Vegetation Simulator Conference; 1997 February 3-7; Fort Collins, CO. Gen. 

Tech. Rep. INT-GTR-373. Ogden, UT: Intermountain Research Station, Forest Service, 

U.S. Department of Agriculture; 191-195. 

Bruce, David. 1981. Consistent height-growth and growth-rate estimates for remeasured 

plots. Forest Science 27: 711-725. 

Caza, Caroline L. 1993. Woody debris in the forests of British Columbia. Land 

Management Handbook No. 78. Victoria, BC: Research Branch, Ministry of Forests; 99 

p. 

Darling, L. M.; Omule, S. A. Y. 1989. Extensive studies of fertilizing and thinning coastal 

Douglas-fir and western hemlock: an establishment report. FRDA Report No. 54. 

Victoria, BC: Research Branch, Ministry of Forests; 19 p. 

de Montigny, Louise. Research Silviculturalist, Ministry of Forests, Victoria, BC. 

[Conversation with Jeff Stone]. 15 November 1998. 

Di Lucca, C. M. 1999. TASS/SYLVER/TIPSY: systems for predicting the impact of 

silvicultural practices on yield, lumber value, economic return and other benefits.

In: Proceedings of stand density management conference: using the planning tools; 1998 

November 23-24: Edmonton, AB. Edmonton: Clear Lake Ltd; 7-16. 

Forest Productivity Council. 1999. Pilot study for dead tree information on growth and 

yield permanent sample plots. Victoria, BC: Forest Productivity Council, Ministry of 

Forests; 19 p. Available at Web site: http://www.forestproductivity.gov.bc.ca/ 

publications/ Dead_Tree_Pilot.pdf

Greenough, Julee A.; Kurz, Werner A. 1996. Stand tending impacts on environmental 

indicators. Victoria, BC: Ministry of Forests; 58 p. Available from Forest Practices 

Branch, Ministry of Forests, Victoria, BC. 

Greenough, J. A.; Robinson, D. C. E.; Beukema, S. J.; Kurz, W. A 1999. Prognosis 

Environmental Indicators Model Description. Vancouver, BC: ESSA Technologies Ltd; 

66 p. Available from Forest Practices Branch, Ministry of Forests, Victoria, BC. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. W.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K. Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in temperate 

ecosystems. Advances in Ecological Research. 15: 133-302. 

Hollstedt, Chris; Vyse, Alan, editors. 1997. Sicamous Creek silvicultural systems project: 

workshop proceedings; 1996 April 24-25; Kamloops, BC. Working Paper 

24/1997.Victoria, BC: research Branch, Ministry of Forests; 283 p. 
Standing Dead Tree Dynamics—Stone, Parminter, and Braz 

478 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Huggard, David J. 1999. Static life-table analysis of fall rates of subalpine fir snags.

Ecological Applications 9: 1009-1016. 

Krebs, Charles J. 1978. Ecology: the experimental analysis of distribution and 

abundance. 2d ed. New York: Harper & Row Publishers Inc.; 678 p. 

Lee, Phillip. 1998. Dynamics of snags in aspen-dominated midboreal forests. Forest 

Ecology and Management 105: 263-272. 

Lofroth, Eric. 1998. The deadwood cycle. In: Voller, J.; Harrison, S., ed. Conservation 

biology principles for forested landscapes. Vancouver, BC: UBC Press; 185-214. 

Machmer, Marlene M.; Steeger, Christoph. 1995. The ecological role of wildlife tree users 

in forest ecosystems. Land Management Handbook 35. Victoria, BC: Ministry of 

Forests; 54p. 

Marcot, Bruce, G. 1992. SRS: Snag recruitment simulator. Unpublished draft available 

from author at http://www.spiritone.com/~brucem/whrtext.htm. 

Mitchell, Kenneth J. 1975. Dynamics and simulated yield of Douglas-fir. Forest Science 

Monograph 17; 39 p. 

Ohmann, Janet L.; McComb, William C.; Zumrawi, Abdel Azim. 1994. Snag abundance for 

primary cavity-nesting birds on nonfederal forest lands in Oregon and 

Washington. Wildlife Society Bulletin 22: 607-620. 

Raphael, Martin G.; Morrison, Michael L. 1987. Decay and dynamics of snags in the Sierra 

Nevada, California. Forest Science 33: 774-783. 

Robinson, D. C. E. 1997. Prognosis southern interior (SI 1.0g) geographic variant 

description. Vancouver, BC: ESSA Technologies Ltd prepared for Forest Practices 

Branch, Ministry of Forests, Victoria, BC; 178 p. Available from Forest Practices 

Branch, Ministry of Forests, Victoria, BC. 

Schuster, Ervin G.; Leefers, Larry A.; Thompson, Joyce E. 1993. A guide to computerbased analytical tools for implementing National Forest plans. Gen. Tech. Rep. INT296. Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department of 

Agriculture; 269 p. 

Stone, Jeff. 1994. Extensive studies of fertilizing and thinning coastal Douglas-fir and 

western hemlock: an installation report. FRDA Report No. 227. Victoria, BC: 

Research Branch, Ministry of Forests; 116 p. 

Stone, Jeff. 1996. Modeling the dynamics of dead trees in TASS and WinTIPSY. FRDA 

Research Memo 227. Victoria, BC: Ministry of Forests; 3 p. 

Stone, Jeff. 1997. Recommendations of dead tree data needs to be collected on growth 

and yield permanent sample plots. Unpublished report to Forest Productivity Council 

of British Columbia supplied by author. 

Stone, Jeff; Parminter, John; Arsenault, André; Densmore, Nancy; Manning, Todd; Davis, 

Gerry; MacKinnon, Andy. 2002. Dead tree management in British Columbia. In: 

Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. 

Phillip; Lisle, Thomas E., technical coordinators. Proceedings of a symposium on the 

ecology and management of dead wood in western forests. 1999 November 2-4; Reno, 

NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; [this volume]. 

Wells, R.W. 1996. Developmental trends of stand structure and tree mortality in Coastal 

Western Hemlock forests. Burnaby, BC: Simon Fraser University; 72 p. Master of 

Natural Resource Management Research Report. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 479 

Dead Wood and Fire Relationships in 

Southwestern Oregon Western Hemlock 

Forests1

Diane E. White,2 Thomas Atzet,3 Patricia A. Martinez,4 and Lisa A. 

McCrimmon4

Abstract 

The densities of large snags and down wood in western hemlock forests of southwestern 

Oregon are highly variable. Fire is a major disturbance process that contributes to the 

composition and structure of these complex forests. This study examines levels of dead wood 

by plant association, and relationships of dead wood with fire. Data were collected from 169 

plots on the Rogue River, Siskiyou, and Umpqua National Forests in Oregon. Median snag 

densities ranged from 3 up to 18 snags/ha over the plant associations. Down wood medians 

ranged from 0 to 113 pieces/ha. Variation was high and there were no significant differences 

between plant associations within the Western Hemlock Series. Median fire return intervals 

ranged from 26 years to 85 years. Elevation, slope, and median fire return interval were the 

best predictors of dead wood density. The R-squared values improved when the warmest, 

driest plant associations were removed from the analyses. The high degree of variability in 

dead wood density and fire return intervals suggests that a single standard is not appropriate 

across southwestern Oregon. Landscape level prescriptions should incorporate extremes along 

with median values. 

Introduction 

Snags and down wood are important structure components of forest ecosystems 

(Harmon and others 1986). They play a role in microclimatic variation in the forest 

and provide habitat for a variety of life. Little data have been published on levels of 

dead material in southwestern Oregon. 

The abundance of snags and down wood is determined by several factors. The 

initial density and size of a forest stand will regulate the potential for providing snags 

and down wood. Agents such as fire, wind, insects, and diseases kill trees often in 

episodic disturbances. The extent of this mortality depends on the severity and 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Associate Ecologist, Umpqua National Forest, USDA Forest Service, P.O. Box 1008, Roseburg, OR 

97470 (e-mail: dewhite01@fs.fed.us) 

3

 Area Ecologist, Siskiyou National Forest, USDA Forest Service, P.O. Box 440, Grants Pass, OR 97526 

(e-mail: tatzet@fs.fed.us) 

4

 Associate Ecologist, Rogue River National Forest, U.S. Department of Agriculture, 333 W. 8th Street, 

Box 520, Medford, OR 97501 (e-mail: pmartinez@fs.fed.us) 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

480 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

frequency of the disturbance. Fire and decay cause breakdown and consumption of 

snags and down wood. 

Although all sizes of snags and down wood are important, recent emphasis by 

wildlife biologists has been on large diameter material. This material takes longer to 

grow and would take more time to replace if it were removed from a site. 

Standards for large down wood and snags are found in the Northwest Forest 

Plan (Anonymous 1994). These standards are uniform across the complex climatic, 

edaphic, and vegetation conditions of southwestern Oregon. In this paper we analyze 

relevant data to examine variation and pattern of density of dead wood, and the 

relationship of dead wood with fire. Our objective is to provide a framework and 

understanding of processes for managers to make landscape level prescriptions for 

down wood and snags greater than 50 cm diameter. 

Study Area 

Data were collected from the Rogue River, Siskiyou, and Umpqua National 

Forests in areas that are characterized as Western Hemlock Plant Series (Tsuga 

heterophylla is the climax tree species). The Western Hemlock Series is partitioned 

into 14 plant associations, based on floristics and environment (Atzet and others 

1996) (table 1). The sites on the Siskiyou National Forest are in the mid-coastal 

sediments ecoregion, and sites on the Rogue River and Umpqua National Forests are 

in the southern Cascades and Umpqua Cascades ecoregions (Anonymous 1995). The 

climatic range is broad, from a mean annual temperature of 12 ◦

C to 6 ◦C, and a mean 

annual precipitation of 292 cm to about 127 cm (Atzet and others 1996). 

Table 1—Plant associations, common names, and plant association codes in the Western 

Hemlock plant series in southwestern Oregon. 

Plant association Common name Code 

Tsuga heteropylla-Abies concolor/

Acer circinatum-Berberis nervosa

Western hemlock-white fir/ vine 

maple-Oregon grape 

TSHE-ABCO/ 

ACCI-BENE2 

Tsuga heterophylla-Abies concolor/ 

Berberis nervosa

Western hemlock-white fir/ 

Oregon grape 

TSHE-ABCO/ 

BENE2 

Tsuga heterophylla-Castenopsis 

chrysophylla/Gaultheria shallonRhododendron macrophyllum

Western hemlock-golden 

chinkapin/salal-Pacific 

rhododendron 

TSHE-CACH6/ 

GASHRHMA3 

Tsuga heterophylla-Pseudotsuga 

menziesii/Gaultheria shallon-SWO 

Western hemlock-Douglasfir/Salal-SWO TSHE-PSME/ 

GASH-SWO 

Tsuga heterophylla-Thuja plicata 

Rhododendron macrophyllum /

Western hemlock-Western red 

cedar/Pacific rhododendron 

TSHE-THPL/ 

RHMA3 

Tsuga heterophylla/Acer 

circinatum/Gaultheria shallon-SWO 

Western hemlock/Vine 

maple/Salal-SWO 

TSHE/ACCIGASH-SWO 

Tsuga heterophylla/Acer circinatumRhododendron macrophyllumWestern hemlock/Vine maplePacific rhododendron TSHE/ACCIRHMA3 

Tsuga heterophylla/Gaultheria 

shallon-Berberis nervosa-SWO 

Western hemlock/Salal- Oregon 

grape-SWO 

TSHE/GASHBENE2-SWO 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 481 

Tsuga heterophylla/Gaultheria 

shallon-Rhododendron 

macrophyllum-SWO 

Western hemlock/Salal- Pacific 

rhododendron-SWO 

TSHE/GASHRHMA3-SWO 

Tsuga heterophylla/Gaultheria 

shallon/Polystichum munitum-SWO 

Western hemlock/Salal/ Western 

swordfern-SWO 

TSHE/GASH/ 

POMU-SWO 

Tsuga heterophylla/Polystichum 

munitum-SWO 

Western hemlock/Western 

swordfern-SWO 

TSHE/POMUSWO 

Tsuga heterophylla/ Rhododendron 

macrophyllum- Berberis nervosaSWO 

Western hemlock/Pacific 

rhododendron-OregongrapeSWO 

TSHE/RHMA3

- BENE2-SWO 

Tsuga heterophylla/ Rhododendron 

macrophyllum- Gaultheria shallonSWO 

Western hemlock/Pacific 

rhododendron-Salal-SWO 

TSHE/RHMA3

- GASH-SWO 

Tsuga heterophylla/Vaccinum 

ovatum/Polystichum munitun

Western hemlock/Evergreen 

huckleberry/Western swordfern 

TSHE/VAOV2/ 

POMU 

Soils are of sedimentary and volcanic origin. Soils on the Siskiyou National 

Forest sites are most commonly derived from sandstones, while sites from the 

Cascade Mountains of the Rogue River and Umpqua National Forests are commonly 

derived from andesites and basalts. Other parent materials are present, but at lower 

proportions. 

Field Data Collection 

Data were collected from permanent plots that were located on the Rogue River, 

Siskiyou, and Umpqua National Forests. Plots were located so that the variation in 

vegetation over the landscape was represented. Within plots, a single plant 

association was present. The full range of elevation, aspect, slope, and rock types 

were sampled. Plots were selected to minimize previous human disturbance, and 

tended toward fully stocked, mature stands. 

Five subplots were established around each plot using the USDA Forest 

Service's Pacific Northwest Region 10-point timber inventory diamond cluster 

protocol (Anonymous 1970). Within each variable radius subplot, the diameters of all 

species of trees and snags were recorded. The heights and ages of five site trees of 

each dominant species and three to five site trees of each codominant species were 

recorded. The ages were estimated as number of annual rings at dbh when the core 

reached the pith. Where the cores did not reach the pith, age was estimated by 

extrapolation using the diameter and rings per inch closest to the inner end of the 

core. Height, diameter, species and decay class (Cline and others 1980) were 

recorded for each snag. 

The topographic variables of elevation, aspect, percent slope, and microposition 

were recorded for each plot. Microposition was defined as ridge top, upper one-third 

of slope, middle one-third of slope, lower one-third of slope, bench, toe of slope, 

canyon bottom, edge or in wetland basin, and draw or intermittent stream bottom. 

Down wood data were collected along three, 21-meter transects with randomdirection segments. At the point of intersection with a discernible piece of wood at 

least 12.5 cm in diameter, we recorded the diameter at the intersect, large end and 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

482 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

small end diameters, length, species, and decay class were recorded. Decay was 

recorded as classes 1 to 5 (Fogel and others 1972). 

Analyses 

Analyses were conducted at the landscape scale and show the relationship of 

snags and down wood by plant association. 

Densities of live trees, snags, and down wood exhibit a distribution that is 

skewed to the right. Measures of central tendency were expressed as Weibull 

medians and quartiles, which account for this skewedness, compared with medians 

from normal distributions, which simply describe the middle value of the distribution. 

The Kruskall-Wallace H-test was used to test differences between plant associations. 

Linear and nonlinear regression were used to show relationships between dead wood 

density and environmental variables and disturbance variables. The SPSS software5

(Anonymous 1998) was used for all analyses. 

The disturbances were derived by first listing, by species, the aged trees within 

each plot in descending order of age. Patterns of age and/or species change were 

noted. When a pioneer species (Douglas-fir, ponderosa pine, Shasta red fir) was 

present, the age was noted. If one or more trees of a pioneer species in a discernible 

age class (approximately a 30 year period) were present, that was assumed to be the 

result of a disturbance event. A surety rating for each disturbance event was assigned 

based on the tree age estimate, whether more than one tree was present in the age 

cohort (with multiple trees indicating higher surety), and the species of trees present. 

The rating ranged from 1 (unsure) to 10 (positive) and only events with a rating of 8 

or higher was used in this analysis. A fire severity rating was also assigned: 1 = low 

severity—climax trees established after the disturbance; 2 = moderate severity—

pioneer species established after the disturbance, but with older climax species that 

survived the event; and 3 = high severity—pioneer species established after the 

disturbance with climax species coming in later. These are patterned after Brown's 

(1994) fire regime severity classes. Date of disturbance was calculated using tree 

ages and plot data. Disturbance dates derived from tree age and stand structure data, 

rather than fire scar data, is a more liberal approach. It will likely detect disturbances 

not usually shown by fire scars. This technique has been used by others (Agee 1991, 

Arno and others 1997). It may be possible that disturbances other than fire were 

detected. Our data show that fire was overwhelmingly the dominant disturbance in 

this plant series; hence, the probability of a fire disturbance is quite high. Only 

disturbances before 1930 were used in the analyses because we believe fire regimes 

could have been altered by substantial European influence after that time. 

Density of down wood was calculated using the methods described by De Vries 

(1973). Total dead wood was calculated as the sum of snags and down wood. 

Results and Discussion 

The live tree community forms the pool from which snags are derived. The 

median density of large live trees range from about 67 to over 134 trees per hectare 

and provide an abundance of potential dead wood (table 2). The median number of 

 

5

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 483 

snags ranges from about 3 up to about 18 per hectare, although there are no 

significant differences between plant associations. The quartile range of snags shows 

that snags were absent on several of the plant association plots and that a high degree 

of variability is associated with these data. Abundance of down wood reflects the 

same pattern. Large down wood was absent on plots in half of the plant associations. 

The variation was quite high: for example, in the TSHE-CACH6/GASH-RHMA3 

Plant Association, the quartile range was zero to 132 pieces per hectare (table 2). 

Table 2—Comparison of live tree, snag, and down wood (50 cm+ diameter) density per 

hectare in Western Hemlock Plant Associations in southwestern Oregon. 

Plant association N1

 Median and quartile range of trees or pieces per 

hectare2

 Live trees Snags Down wood 

TSHE-ABCO/ACCI 

BENE2 

13 93.5 (66.3-118.4) 10.0 (0-13.8) 25.9 (8.2-95.1) 

TSHE-ABCO/BENE2 11 100.5 (66.9-147.7) 3.6 (0-19.2) 30.9 (0-52.4) 

TSHE-CACH6/ GASHRHMA3 6 88.1 (68.3-117.2) 12.2 (7.1-20.6) 13.3 (0-132.2) 

TSHE-PSME/GASHSWO 5 72.9 (27.7-105.8) 8.1 (2.2-20.9) 17.8 (0-60.8) 

TSHE-THPL/RHMA3 6 98.4 (81.3-138.0) 16.2 (0-31.8) 18.5 (0-101.3) 

TSHE/ACCI-GASHSWO 10 69.0 (51.5-81.2) 9.6 (0.8-14.8) 91.2 (10.9-147.3) 

TSHE/ACCI-RHMA3 29 134.7 (99.1-156.4) 12.2 (3.8-18.9) 16.1 (0-92.7) 

TSHE/GASH-BENE2-

SWO 

17 77.2 (67.5-123.2) 12.3 (7.8-20.8) 32.1 (10.9-118.9) 

TSHE/GASH-RHMA3- 

SWO 

20 94.9 (79.3-122.2) 11.0 (3.1-19.9) 24.7 (0-84.8) 

TSHE/GASH/POMUSWO 14 77.5 (63.2-88.6) 13.8 (8.3-30.6) 113.4 (22.7-175.7) 

TSHE/POMU-SWO 7 79.7 (72.1-97.9) 13.3 (8.3-30.1) 59.6 (26.9-107.2) 

TSHE/RHMA3-BENE2- 

SWO 

5 114.5 (74.1-139.5) 13.2 (7.3-24.5) 3.7 (0-52.1) 

TSHE/RHMA3-GASHSWO 14 103.9 (93.3-166.4) 18.0 (6.3-27.3) 0 (0-13.8) 

TSHE/VAOV2/POMU 12 67.3 (50.1-155.3) 12.3 (6.8-20.1) 58.1 (6.7-190.5) 

1

 Number of plots. 

2 Median values of live trees per acre are significantly different between plant associations (P<0.001; 

Kruskal-Wallis H-test), median values of snags per acre are not significantly different between plant 

associations (P=0.42, Kruskal-Wallis H-test), and density of down wood is not different between plant 

associations (P=0.52; Kruskal-Wallis H-test). 

Disturbance intervals were recorded from about 900 ybp to about 60 ybp. 

Median fire return intervals for plant associations range from a low of 26 years for 

the TSHE/RHMA3-BENE2 plant association, to a high of 85 years for the 

TSHE/VAOV2/POMU association (table 3), The confidence intervals are wide, 

reflecting a high degree of variability. 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

484 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 3—Weibull medians and confidence intervals for the plant associations in the Western 

Hemlock Series. 

Plant association Weibull median (years) 80 percent CI 

TSHE/RHMA-BENE2 26 12-165 

TSHE-PSME/GASH-SWO 34 15-164 

TSHE-CACH6/GASH-RHMA3 43 19-147 

TSHE/ACCI-GASH-SWO 43 14-151 

TSHE/ACCI-RHMA3 48 15-145 

TSHE-ABCO/BENE2 53 17-156 

TSHE-ABCO/ACCI-BENE2 59 21-192 

TSHE/RHMA3-GASH-SWO 61 14-265 

TSHE/GASH-BENE2-SWO 67 20-188 

TSHE-THPL/RHMA3 67 20-251 

TSHE/POMU-SWO 69 33-297 

TSHE/GASH-RHMA3-SWO 81 26-190 

TSHE/GASH/POMU-SWO 81 26-275 

TSHE/VAOV2/POMU 85 30-243 

Snags or down wood alone showed poor correlations with fire and 

environmental variables when compared with total dead wood density. 

Percent slope explained 68 percent of the variation in total dead wood (table 4). 

The highest densities of dead wood occurred on the gentlest slopes and the lowest on 

slopes over 50 percent. Elevation explained 41 percent of the variation in total dead 

wood density. The highest amounts were at elevations less than 689 m and densities 

decreased as the elevation increased. Sites on gentle slopes and lower elevations 

often correspond to riparian areas in the Western Hemlock Series and are areas where 

fires are often less severe. Aspect explained a little over 28 percent of the variation, 

though the equation was not significant, and microposition explained virtually none 

of the variation in total dead wood density (table 4). Because elevation and slope are 

highly correlated in our data, it is not appropriate to use them together in a multiple 

regression. 

Table 4—Regression analyses of environmental variables and total dead wood densities. 

 

 RSQ df sigf b0 b1 b2 

Total dead wood 

 Elevation 0.410 11 0.055 78.90 -0.026 2.9E-06 

 Slope 0.680 11 0.002 -19.27 1.264 0.0006 

 Microposition 0.063 11 0.699 

 Median aspect 0.283 11 0.160 19.15 0.028 0.0001 

The variables mean fire severity, severity of the last fire, and length of the last 

fire interval were all highly correlated, and as such, were not appropriate for use 

together in multiple regression. When density of snags and density of down wood 

were combined into a total dead wood pool, regression showed that the length of the 

last fire interval explained over 27 percent of the variation (R-squared = 0.274), and 

fire severity explained slightly less (table 5). Median fire return interval (FRI) 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 485 

explained over 42 percent of the variation with a quadratic function. In all cases 

except median FRI, nonlinear regression did not improve the fit of the data. The large 

amount of variation made it difficult to detect a difference between linear and 

nonlinear relationships. Fire severity was negatively related to total dead wood, and 

length of the last fire interval was positively related. 

Table 5—Regression analyses of mean fire severity, last fire severity, last fire interval length, 

and Weibull median fire return interval as predictors of total dead wood densities. Equations 

are shown for all data, and data with two outliers removed. 

 R-SQ df sigf b0 b1 b2 

Total dead 

 Mean fire severity 0.221 12 0.090 111.43 -40.99 

 Last fire severity 0.201 12 0.108 51.68 -19.93 

 Last fire interval 0.274 12 0.055 1.75 0.22 

 Median FRI 0.422 11 0.049 33.96 - 0.76 0.011 

Total dead–no outliers 

 Mean fire severity 0.637 9 0.010 406.27 -323.83 66.31 

 Last fire severity 0.609 9 0.015 97.56 - 86.01 20.92 

 Last fire interval 0.422 9 0.085 12.56 - 0.12 0.002 

Interestingly, when the two outliers with the highest total dead wood values are 

removed from the data set, and nonlinear analyses are used, the R-squared values 

increase dramatically. Mean fire severity has an R-squared value of 0.637 (p=0.01), 

and length of time between the last two fires has an R-squared of 0.422 (p=0.085). 

These two outlier data points represent the warmest, driest plant associations, which 

may follow a different pattern than the warm, moist western hemlock areas. 

Multiple regression with elevation and median FRI was highly significant in 

explaining the densities of dead wood, where density = -27.023 + 0.245 (median FRI) 

+ 1.116 (slope). (R-squared = 0.76). 

Overall, the length of the last fire interval is positively correlated with total dead 

wood. This suggests that for 50 cm+ dead material, fire suppression has likely caused 

an increase in material, and plant associations with longer fire return intervals are 

capable of carrying more dead wood. Average fire severity and severity of the last 

event are negatively correlated with total dead material; that is, the more severe the 

event, the less 50 cm+ material remains. This may seem counter-intuitive, because 

high severity fires generally correspond to stand replacement fire, which may yield 

high levels of dead wood. In southwestern Oregon, in the mature stands we sampled, 

multiple intervening low intensity fires likely consumed a great deal of the dead 

wood generated by stand-replacing events. The median FRI data show an inflection 

point around 50 years, after which the amount of dead wood increases sharply. 

Our data show levels of snags and down wood are highly variable over the 

landscape. This variability should be retained, and stratification by plant association 

will aid prescriptions. Some portion of the landscape will have little or no dead wood, 

while other portions will have a great deal. The distribution should be based on an 

integration of desired conditions. For example, fire and wildlife managers may 

suggest leaving most in riparian areas, a prescription that is supported by the data on 

elevation and percent slope. If the management objective is to remove dead material, 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

486 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

leave some part of the landscape with the extremes and remove wood from areas with 

median amounts. 

Fire return intervals in Western Hemlock Plant Associations in southwestern 

Oregon are shorter than those further north. They are variable, as are the severities. 

This chaotic nature of fire across the landscape is the primary means of creating 

diversity in composition and structure for which the southwestern Oregon forests are 

known. Fire should be returned to the forest with landscape level planning and 

allowed to burn in non-uniform, chaotic patterns. 

Our data indicate, the higher the severity the fire, the less large material will 

remain. Attempting to retain too much coarse wood will have an effect similar to fire 

control. Over the long run, the proportion of high intensity fire will increase. 

Consequently, the potential for soil damage and reduction of late seral conditions will 

increase. This “boom-and-bust” cycle is more characteristic of the temperate forests 

to the north. It may have negative effects on local species that evolved with frequent, 

but low intensity fire. 

Acknowledgments 

We would like to thank Jim Agee and Carl Skinner for reviewing this paper. We 

would also like to thank Jim Agee for conducting the Weibull analyses of the fire 

return intervals. 

References 

Agee, James K. 1991. Fire history along an elevational gradient in the Siskiyou 

Mountains, Oregon. Northwest Science 65: 188-199. 

Anonymous. 1997. SPSS Base 7.5 for Windows User’s Guide. Chicago, IL: SPSS Inc. 

_______. 1970. Field instructions for integrated forest survey and timber management 

inventories, Oregon, Washington and California. Pacific Northwest Forest and Range 

Experiment Station, USDA Forest Service. 

_______. 1994. Record of decision for amendments to Forest Service and Bureau of 

Land Management planning documents within the range of the northern spotted 

owl [Northwest Forest Plan]. Forest Service, U.S. Department of Agriculture, and the 

Bureau of Land Management, U.S. Department of Interior; 74 p. 

_______. 1995. Level III Ecoregions of the Continental United States, Map M-1 

[Topographic]. Corvallis, OR: Corvallis Environmental Research Laboratory, U.S. 

Environmental Protection Agency. 

Arno, Stephen F.; Smith, Helen Y.; Drebs, Michael A. 1997. Old growth ponderosa pine 

and western larch stand structure: influences of pre-1990 fires and fire exclusion.

Res. Paper INT-RP-495. Intermountain Research Station, USDA Forest Service. 

Atzet, Tom; White, Diane E.; McCrimmon, Lisa A.; Martinez, Patricia A.; Fong, Paula R.; 

Randall, Vince D. 1996. Field guide to the forested plant associations of 

southwestern Oregon. Pacific Northwest Region, USDA Forest Service. Technical 

Paper R6-NR-ECOL-TP-17-96; 356 p. 

Brown, James K. 1994. Fire regimes and their relevance to ecosystem management. A 

paper presented at the 1994 Society of American Foresters Canadian Institute of 

Forestry Convention, September 18-22, Anchorage, Alaska. 
Dead Wood and Fire Relationships—White, Atzet, Martinez, and McCrimmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 487 

Cline, Steve P., Berg, Alan, Wight, Howard. 1980. Snag characteristics and dynamics in 

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44: 773-787. 

DeVries, P. G. 1973. A general theory on line intersect sampling with application to 

logging residue inventory. Mededdlingen Landbouw Hogeschool No. 73-11. 

Wageningen, The Netherlands; 23 p. 

Fogel, Robert; Ogawa, M.; Trappe, James. 1972. Terrestrial decomposition: a synopsis.

Coniferous Forest Biome Internal Report 135. Seattle, WA: College of Forest, 

Resources University of Washington; 12 p. 

Harmon, Mark E.; Franklin, Jerry F.; Swanson, Frederick J.; Gregory, Stanley V.; Lattin, John 

D.; Anderson, Norm H.; Cline, S. P.; Aumen, N. G.; Sedell, James R.; Lienkaemper, 

George W.; Cromack, Kermit, Jr.; Cummins, Kenneth W. 1986. Ecology of coarse 

woody debris in temperate ecosystems. Advances in Ecological Research 15: 133-302. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 489

The Number and Composition of Snags in

the Pine-Spruce Stands of the Bialowieza

National Park, Poland1

Wieslaw Walankiewicz2

Abstract

This paper documents data on standing dead trees (snags) in the pine-spruce (Norway spruce

Picea abies, Scots pine Pinus sylvestris) natural stand in Bialowieza National Park (BNP) in

northeast Poland. Trophically, this mostly coniferous stand represents one of the poorest

habitats of the BNP, and this stand has never been cut. There are few tree species of

significance, i.e., Scots pine, Norway spruce, hornbeam Carpinus betulus and two birch

species Betula verrucosa, B. pubescens. Other tree species are scarce. Altogether 6.25 ha were

measured within 25 samples. Among tree species, the proportion of dead standing trees was

0-58 percent of the total basal area and 0.9-59 percent of total density. The tree species

dominance pattern shows a different pattern of change. Pine is declining, while hornbeam is

invading the stand from bordering deciduous stands and now is a well regenerating tree

species. Spruce regeneration slowed within the last 20 years. Until about 10 years ago, birches

were not regenerating and were declining from the plot. Recently, within no more than the last

10 years, birches are regenerating within the plot again. All these changes reflect snag

characteristics and composition.

Introduction

Most of the lowland forests of the European temperate zone underwent severe

anthropogenic transformations before modern research started. However, the forests

of the Bialowieza National Park are an exception. The Bialowieza Forest complex

(total area 1,500 km2

) is situated on the Polish-Belarussian border (fig. 1). Its western

part (c. 600 km2

) belongs to Poland. This forest is a remnant of the vast lowland

forest that once covered central parts of Europe. The majority of stands in the Polish

part of the forest are now under management, but 47.5 km2 of the best preserved

primeval stands has been protected within the Strict Reserve of the Bialowieza

National Park (SR BNP) (Falinski 1986, Tomialojc 1991). This part has never been

cut because it was protected as hunting grounds for the Polish kings and later the

Russian czars since the early 15th century. After World War I it became the first

Polish national park. Human presence is very restricted to some tourist trails only.

 1 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada.

2 Adjunct Professor/Lecturer, Department of Zoology, University of Podlasie, Prusa 12, 08-110 Siedlce,

Poland (e-mail: wwalan@ap.siedlce.pl)
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

490 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

Figure 1_A map of the Polish part of the Bialowieza Forest showing the location of

the strict reserve (SRBNP) and study plot (NW).

The old-growth preserved in SR BNP are mainly the linden-hornbeam TilioCarpinetum type (44.4 percent), swampy deciduous (26.6 percent), and dry

coniferous (28.1 percent) stands. The old-growth stands of SR BNP are multi-storey,

mixed-species, uneven-aged, composed of trees reaching exceptional height, and

contain large amount of dead standing trees (snags) and uprooted trees. In spite of the

fact that many authors stressed the high amount and the importance of the dead wood

in this forest, the quantitive data are scarce and only general (Falinski and Herezniak

1977, Kirby and others 1991, Piotrowski and Wolk 1975). Although most of the SR

BNP is covered by deciduous woodland, the coniferous stands (i.e., pine-spruce

stands [Norway spruce Picea abies, Scots pine Pinus sylvestris]) contribute greatly to

sustaining biological richness of BNP. For instance, several bird species are recorded

mostly or exclusively in this conferous habitat (Tomialojc and others 1984).

Structure and dynamics of the BNP natural stands have been studied for almost

80 years (Falinski 1986, Paczoski 1925). Both deciduous and coniferous stands of SR

BNP are not in a state of climax. In the linden-hornbeam Tilio-Carpinetum type, the

spruce has decreased steadily in number (Falinski 1986). In coniferous forests, i.e.

pine-spruce type, the pine share has decreased as well. Comparing tree distribution

maps from 1903 and 1958, Czerwinski (1968) stated that during the investigated

period, pine decreased substantially and it was replaced by the spruce and oak

Quercus robur. Wloczewski (1972) and Kowalski (1972) also noticed directional

change of the pine stands into the spruce stands. Even more, an increase of the

hornbeam Carpinus betulus in number in coniferous stands has been noticed (Gunia

1972; Kowalski 1972, 1982).
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 491

This study aims to describe the occurrence and characteristics of the snags (i.e.,

dead standing trees) within the pine-spruce stands of the SR BNP under the dynamic

process ongoing in this stand with time. Snag characteristics have never been

described in details in these forests, and only Jakubowska-Gabara and others (1991)

have assessed how many dead standing trees were among all trees in the same type of

stand of BNP.

Study Plot

The NW 25-ha study plot (500 m x 500 m, located in compartment 318A;

Tomialojc and others 1984) was chosen. It is covered by the pine-spruce natural

stand, which has never been cut. The association of this kind usually develops on

sandy soils in upper parts of the BNP. Trophically, it represents one of the poorest

habitats in SR BNP. The main canopy is formed of pines, while the lower one is

composed of spruces with few pines, birches (Betula verrucosa, B. pubescens), and

oak. In the plot, spruce dominates numerically over pine. The young tree-layer is

composed mostly of hornbeams and spruces. The herb layer is sparse, composed of

Oxallis acetosella and Vaccinium myrtillus. Forest openings are dominated by

Calamagrostis arundinacea and Pteridium aquilinum.

The plot has been subdivided into a 50-m grid. That area has been under

ornithological investigation since 1975 (Tomialojc and others 1984). Since that time

an increase of hornbeam in number is very visible. The young generation of Carpinus

betulus invades the area from the north and especially from the south, i.e., from the

transition border zones with the deciduous stands. This transition, where coniferous

stands turn gradually into deciduous stands, is 50-80 m wide. Matuszkiewicz and

Matuszkiewicz (1954) mapped the whole study plot as the pine forest Pinetum

Myrtylli association.

Methods

In June and July 1998 I counted and measured the diameter at breast height

(dbh) of all trees that reached at least 1.5 m tall within the 50 m x 50 m squares

(samples). One such square (0.25 ha each) was chosen randomly within every ha of

the study plot (fig. 2). Altogether 6.25 ha were measured within 25 square samples.

Both live and dead trees were identified to species. The recognition of dead trees

caused no serious problems, since there were only two coniferous and a few

deciduous species. The exception is the two birch species, which I treat jointly since

they were uncommon and I was unable to distinguish snags of those species.

Additionally, to illustrate the hornbeam invasion in the northwest plot, I

compared the diameter distribution within the central part of the plot with that of the

ecotonal (southern) part of the plot. For this, five samples were chosen in both parts

(fig. 2).
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

492 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

1 2 3 4 5 6 7 8 9 10

 A

 B

 C

 D

 E C

 F C C C C

 G

 H

 I E E E

 K E E

500 x 500 m = 25 ha

Figure 2_Distribution of measured squares within the study plot (E = ecotone, C =

center).

Results and Discussion

Snag Density by Diameter Class

Among live trees, spruce and hornbeam together comprise 86 percent of the

stand by number of trees. Pine (9 percent) is the third most abundant species (fig. 3).

Snag species composition is utterly different. Spruce and pine snags comprise 88

percent of all dead trees (fig. 4). When considering only trees with diameter ≥ 10 cm,

the share of spruce snags and pine snags altogether increased to 92 percent (fig. 5).

Together with birch, these three species compose 98 percent of all such defined

snags. The very small share of the hornbeam among snags is easy to explain when I

compare the dbh class distribution of pine, spruce, and birch with dbh distribution of

the hornbeam (figs. 6-9). The hornbeam is represented almost exclusively by trees

with dbh not bigger than 20 cm (fig. 8).
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 493

Hornbeam

50%

Spruce

36%

Linden

1%

Other

1%

Oak

1% Birch

3%

Pine

9%

N=5955

Figure 3_Share of different species in the living tree community.

Spruce

59%

Pine

29%

Hornbeam

6%

Birch

4%

Other

2%

N=884

Figure 4_Share of different dead tree species among the snags within the study plot.

 

Spruce

53%

Pine

39%

Other

2%

Birch

6%

N=641

Figure 5_Share of different dead tree species with the ≥ 10 cm diameter classes.
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

494 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

Pine

-100 -50 0 50 100 150 200 250

?10cm

11-20cm

21-30cm

31-40cm

41-50cm

>50cm

Dbh classes

No. of individuals

Snags Alive

Figure 6_Structure of the pine tree stand according to diameter classes (dbh).

Spruce

-250 0 250 500 750 1000

?10cm

11-20cm

21-30cm

31-40cm

41-50cm

>50cm

Dbh classes

No. of individuals

Snags Alive

Figure 7_Structure of the spruce tree stand according to diameter classes (dbh).

Hornbeam

-500 0 500 1000 1500 2000 2500 3000

?10cm

11-20cm

21-30cm

31-40cm

41-50cm

>50cm

Dbh classes

No. of individuals

Snags Alive

Figure 8_Structure of the hornbeam tree stand according to diameter classes (dbh).

 Spruce

 Hornbeam
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 495

Birch

-25 0 25 50 75 100 125 150

?10cm

11-20cm

21-30cm

31-40cm

41-50cm

>50cm

Dbh classes

No. of individuals

Snags Alive

Figure 9_Structure of the birch tree stand according to diameter classes (dbh).

Total snag density concerning only trees with ≥ 10 cm dbh is 102.6/1ha. The

spruce and the pine snags are the most numerous, reaching density 54.9/ha and

39.5/ha, respectively. Birch snags occur in much lower density (5.8/ha). High density

of the spruce snags is a result of bark beetle (Ips typographus) outbreak in BNP

during 1994-1996 years. Jakubowska-Gabara and others (1991) reported from 1990

(i.e., data collected before bark beetle outbreak appeared) that the same forest type in

SR BNP had about three times lower spruce snag density. They also found that the

pine snags were denser, exceeding 50 snags/1ha.

What Proportion of Standing Trees are Dead?

Pine and spruce compose 91.0 percent of the total basal snag area and 93.1

percent of standing dead trees. Total basal area of dead standing trees is relatively

high compare to other measured stands (Tritton and Siccama 1990). The pine and

spruce proportion of dead standing trees of the total basal area was similar (table 1).

Birches, which are uncommon, have high proportion of dead trees expressed either as

basal area or percent of stand.

Table 1_Basal area and density of living and dead steams ≥ 10 cm dbh, and standing dead

trees as a percent of stand total.

Living Dead Pct dead Living Dead Pct dead

 m2 ha-1 stems ha-1

Species

Scots pine 15.5 4.2 21.3 89 40 31.0

Norway spruce 12.1 3.9 24.4 224 55 19.7

Hornbeam 0.9 0.0 0.0 56 0 0.0

Birch 0.5 0.7 58.3 4 6 60.0

Other 0.9 0.1 10.0 11 1 8.3

Total 29.9 8.9 23.1 384 102 21.0

 Birch
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

496 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

Diameter of Snags (Dbh)

The diameter of the two birch species and pine (birch x = 37.1 cm, S.D. = 12.7,

n = 38, pine x = 34.0 cm, S.D. = 14.5 n = 247) are greater than that of spruce (x =

27.8 cm, S.D. = 11.5, n = 343). This is because the pine and birch snags originated

mostly from older trees (figs. 6, 9). Spruce snags have thinner dbh because they

originated mostly from trees of lower dbh classes, including young trees that died due

to a self-thinning process (fig. 7). The composition and characteristic of snags are

affected by such processes as retreat (pine) and regeneration and competition (spruce,

birch and hornbeam).

Regeneration of Different Tree Species

Within the smallest dbh class, 2,591 hornbeams, 649 spruces, 135 birches, and 8

pines were found. This suggests ongoing intense change in the composition of the

stands that were analyzed.

According to Falinski (1986), the spruce regenerates fairly well in coniferous

forests on dry hills of the BNP. The spruce diameter distribution, especially the high

number of trees in the smaller diameter classes (1-2), indicates good regeneration of

this species (fig. 7). It is also the most numerous among tree species in the middle

diameter classes (750 spruces versus 176 pines in diameter 21-40 cm). This species

will likely remain an important component of the analyzed stand for many years.

The large number of pines in the larger (4-6) diameter classes and few in the

lower classes (1-3) indicates that this species has ceased to regenerate and is

retreating from the stand (fig. 6). In the first diameter class only eight pine trees were

found. The retreat of the pine from BNP has been well documented (Czerwinski

1968, Gunia 1972, Kowalski 1972, Matuszkiewicz 1952, Paczoski 1930, Wloczewski

1972). Some old pines occur in linden-hornbeam stands farther than 1 km from the

conifer part of the forest (Walankiewicz, pers. observ.), suggesting that in the past the

pine had much wider distribution than at present and that the area covered by pine

has decreased. Korczyk (1994) found that this species lives up to 400 years in the

Bialowieza Forest.

Although hornbeam is the most numerous tree species, it occurs almost only in

the first and second dbh classes (fig. 8) (an average dbh of all hornbeams equals 4.0

cm, S.D. ± 4.17, n = 3,984 and 41 percent of all living hornbeams have dbh £ 2cm).

Because it grows in SR BNP up to a diameter of 100 cm (Falinski 1977), this means

that occurrence of this species within the plot is a new phenomenon. I have visited

this plot several times a year from 1975 to 1998 conducting ornithological research

(Tomialojc and others 1984). During that period, in the northwest plot, I observed a

continuous increase of young hornbeams in number. The first hornbeam dbh class is

three times more numerous than the same class of the spruce (figs. 7, 8).

Furthermore, 25 years ago many hornbeams in the study plot were shaped like trees

that suffer poor growth conditions (i.e., poor soil). Currently, hornbeams look

different, and they are shaped like young fast growing trees. Apparently this species

is a very new invader in this stand. It is visibly more numerous in both the southern

and northern parts of the plot, which border linden-oak-hornbeam stands, than it is in

central part. Furthermore, within the study plot, there are few if any hornbeams old

enough to produce seeds. As a matter of fact, well regenerating hornbeam originated

mostly, if not only, from trees that are outside the study plot. Gunia (1972) and

Kowalski (1972, 1982) noticed an increase in the number of hornbeam in coniferous
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 497

stands of the BNP, but they did not expect the fast transformation described in this

work.

The birches are represented mostly in the youngest class. Older/mature birches

were low in the plot (fig. 9). Only 22 birches within classes 2-6 were found within the

6.25 ha studied. In the 2-6 dbh classes there are more dead (62.1 percent) than live

(37.9 percent) birch trees. This shows that until 10 years ago birches were not

regenerating and retreating from the plot. Every year since 1975, I conducted

ornithological observations in the northwest plot and observed within no more than

the last 10 years that the birches started to regenerate within this plot again (fig. 9). It

happened in gaps where spruces were knocked down by wind. Birches are very rare

in neighboring linden-hornbeam stands as well.

Directional Changes in Tree Stand Composition

Each tree species within the study plot are showing a different pattern of change.

Pine density is declining while spruce, hornbeam and birches all seem to be wellregenerating tree species. However, because young birches are 5-20 times less

numerous than hornbeam and spruce, the two latter species are most important for the

future of the stand. But is the proportion of spruce-hornbeam stable within the

studied plot?

To answer this question I compared separately the stand diameter structure of

both species the the central and ecotonal (southern) parts of the plot. Such

comparisons reveal that hornbeam regenerates in ecotonal part very well, but the

spruce regeneration there is poor (fig. 10). Clearly in this part of the study plot, the

smallest spruce dbh classes are less numerous than the middle diameter classes of this

tree species. Within the first dbh class, 1,651 hornbeams were found and only 20

spruces (figs. 10, 11). This suggests that spruce regeneration slowed down there

within the last 20 or so years. It is very likely that hornbeam will soon overtake this

part of the stand reducing substantially the proportion of spruce. In 1975, young

spruces 1-1.5 m tall were common in this northwest plot (Tomialojc and others 1984;

Walankiewicz, pers. observ.). In the central part of the plot, however, the number of

spruce and hornbeam in the first dbh class are similar (96 spruces vs. 94 hornbeams;

figs. 10, 11). This means that in the future this part of the stand will be covered by

mixed spruce-hornbeam forest with a mixture of some old pine.

Summing up, there are five visible processes/changes ongoing in the tree stand

within the study plot:

Decrease of the pine in density; this species does not regenerate.

Spruce, which dominates numerically over pine, regenerates well in the

central part of the plot.

In the ecotone, close to deciduous stands, the spruce regeneration is

hampered by invasive young hornbeams.

Hornbeams invade the plot from bordering deciduous stands and regenerate

very well between older spruces and pines.

Birches, which were close to extirpation, show renewed regeneration within

the study plot.
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

498 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

-100 -50 0 50 100 150

?10cm

11-20cm

21-30cm

31-40cm

41-50cm

>50cm

dbh classes

no. of individuals

Spruce

ecotone center

Figure 10_The structure of the spruce stand (live trees) in diameter classes within

the central and ecotonal parts of the NW study plot.

-2000-1500-1000 -500 0 500

?10cm

11-20cm

21-30cm

31-40cm

41-50cm

>50cm

dbh classes

no. of individuals

ecotone center

Hornbeam

Figure 11_The structure of the hornbeam stand (live trees) in diameter classes within

central and ecotonal parts of the NW study plot.

Durability of Snags and Ratio of Different Tree Species as

Snags

Most of the snags (98 percent) are composed of spruce, pine, and birch. All of

them are represented among live trees less numerously than among dead ones (figs. 3,

5). This is the result of the numerous occurrence of the hornbeam, which is too young

to produce snags.

The ratio of different snag species tells us nothing about mortality of the

different tree species. The relatively high share of pine among dead standing

trees—39 percent among dead and only 9 percent among alive (figs. 3, 5)—does not

mean high mortality of this species. Rather, it reflects high durability of pine snags.

Many pine trees within northwest plot were dead in 1975 when the plot was
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 499

marked—after 25 years they remain standing. One well-known pine snag has been

standing next to the tourist path more than 50 years. Spruce’s high share of snags,

among other dried trees, actually reflects the high mortality of this species that was

caused by the bark beetle outbreak in 1994-1996. In May 2000, many spruce snags

within the plot are fell after the previous winter. Spruce snags apparently stand only

for a few years after the tree is dead.

Assuming that the observed tendencies of the tree stand development will last, I

predict the following changes in the snag composition within the studied stand:

Within 2-3 years, the number of spruce snags will decrease by about twothirds. The spruce snags will fall down due to the rotting processes in lower

part of trunk.

Birch snags, which are much less numerous than other species, will gradually

disappear from the stand.

The number of pine snags will remain rather stable for many years because

of their high durability.

It will take another 20 or more years before the first hornbeam snags of

diameter 20-30 cm appear in the stand.

Some processes within the study plot were recorded in other parts of the SR

BNP, especially a decrease of the spruce and an increase of linden in deciduous

stands. This change was explained as a return of the forest to its natural state after

extensive disturbance from excessive game foraging (Falinski 1986), as a directional

change caused by changing climate (Bernadzki and others 1991, Kowalski 1882), or

as a result of marshland drainage in the Belarussian part of the BNP (Bucholz 1968).

All those factors seem to be additive, not compensatory.

Acknowledgments

I heartily thank D. Czeszczewik, A. Derlukiewicz, J. Fronczek M. Nowaczyk,

A. Pawluczuk, M. Woszczynska, A. Chmielak, C. Choinska, L. Golebiowska, K.

Zieba for their participation in the field work. I express my gratitude to Ludwik

Tomialojc for constructive help on previous drafts of the manuscript. Important

assistance in statistical analyses was provided by Dorota Czeszczewik. This study

was supported by the University of Podlasie and by State Committee for Scientific

Research-KBN project no. 015/PO4/99/16. I also thank the very kind cooperation of

the Bialowieza National Park administration.

References

Bernadzki, E.; Bobolik, L.; Brzeziecki, B.; Zajaczkowski, J.; Zybura, H. 1991. Development

of natural forest stands in the Bialowieza National Park_a case study of two

research plots. In: Paschalis, P.; Zaj_czkowski, J., eds. 1996. Biodiversity protection of

Bialowieza Primeval Forest. Grant GEF 05/21685 POL; 51-61.

Bucholz, E. 1968. Der Urwald Bialowieza in Polen. Forest- und Holzwirt (Hanover) 23: 24.

Czerwinski, A. 1968 Lasy i gospodarka lesna w Puszczy Bialowieskiej. In: Falinski, J. B.,

ed. Park Narodowy w Puszczy Bialowieskiej PWRiL, Warszawa.
Snags in the Pine-Spruce Stands of the Bialowieza National Park—Walankiewicz

500 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002.

Falinski, J. B. 1977. Research on vegetation and plant population dynamics conducted by

Bialowieza Geobotanical Station of the Warsaw University in the Bialowieza Forest

and in the environ (1952-1977). Phytocenosis 6: 1-133.

Falinski, J. B. 1986. Vegetation dynamics in temperate zone lowland primeval forests:

Ecological studies in the Bialowieza Forest. W Junk Publ. Dordrecht; 573 p.

Falinski, J. B.; Herezniak, J. M. 1977. Zielone grady i czarne bory Bialowiezy. Nasza

Ksiegarnia. Warszawa; 67 p.

Gunia, S. 1972. Zmiany struktury grubosciowej drzewostanow w oddziale 319

Bialowieskiego Parku Narodowego. Folia Forest. Pol. A. 20: 67-92.

Jakubowska-Gabara, J.; Przemyski, A.; Bednorz, L. 1991. Relationship between Pine and

Spruce in the fresh oligotrophic forest (Peucedano-Pinetum) in the Bialowieza

National Park (in Polish with English summary). Phytocoenosis 3: 151-159.

Kirby, K. J.; Webster; Antczak, A. 1991. Effects of forest management on stand structure

and the quantity of fallen dead wood: some British and Polish examples. Forest,

Ecology and Management 43: 167-174.

Korczyk, A. 1994 Najstarsze drzewa w Puszczy Bialowieskiej 1. Sosna zwyczajna (Pinus

sylvestris) [The oldest trees from Bialowieza Primeval Forest 1, Scots Pine (Pinus

sylvestris)]. Rocznik Dendrologiczny 42: 131-143.

Kowalski, M. 1982. Development of natural stands on an experimental area in

Bialowieza Natonal Park. Treatises and Monographs of Warsaw Agricultural

University, Poland. (in Polish); 87 p.

Kowalski, M. 1972. Dynamika odnowien naturalnych w oddziale 319 Bialowieskiego

Parku Narodowego. Folia Forest. Pol. 20: 93-109.

Matuszkiewicz, W. 1952. Zespoly lesne Bialowieskiego Parku Narodowego. Annales

UMSC, Suppl. VI Sectio C: 1-218.

Matuszkiewicz, A.; Matuszkiewicz, W. 1954. Die Verbreitung der Waldassoziationen des

Nazionalparkes von Bialowieza. Ekol. Pol. A 2: 33-60.

Paczoski, J. 1925. Swierk w ostepach Bialowiezy. Las pol. 5: 358-371.

Paczoski, J. 1930. Lasy Bialowiezy. PROMP, Monogr. Nauk. 1: 1-575.

Piotrowski, W.; Wolk, K. 1975. O biocenotycznej roli martwych drzew w ekosystemach

lesnych. [On the biocoenotic role of dead trees in forest ecosystems] Sylwan 8: 31-

35.

Tomialojc, L.; Wesolowski, T.; Walankiewicz, W. 1984. Breeding bird community of a

primaeval temperate forest (Bialowieza National Park, Poland). Acta Orn. 20: 241-

310.

Tomialojc, L. 1991. Characteristics of old growth in the Bialowieza Forest, Poland.

Natural Areas Journal 11: 7-18.

Tritton, L. M.; Siccama, T. G. 1990. What proportion of standing trees in forest of the

Northeast are dead? Bulletin of the Torrey Botanical Club 117: 163-166.

Wloczewski, T. 1972. Dynamika rozwoju drzewostanow w oddziale 319 Bialowieskiego

Parku Narodowego. Folia Forest. Pol. 20: 5-37.
Demographics and Dynamics in the 

Cascades Forests

501
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 503 

A Coarse Wood Dynamics Model for the 

Western Cascades1 

Kim Mellen2 and Alan Ager3

Abstract 

The Coarse Wood Dynamics Model (CWDM) analyzes the dynamics (fall, fragmentation, and 

decomposition) of Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga 

heterophylla) snags and down logs in forested ecosystems of the western Cascades of Oregon 

and Washington. The model predicts snag fall, height loss and decay, and log decay at 5-year 

intervals for a period of 300 years. Snags either fall whole or in parts, creating down logs. 

Snags also decay from a hard to soft condition. Logs decay more slowly than snags, from 

sound to decayed conditions, and eventually disappear into the forest floor as duff. Snag fall 

and height loss rates were derived from Forest Inventory and Analysis (FIA) remeasurement 

data on private lands in western Washington. Decay rates were obtained from various studies 

conducted in the western Cascades of Oregon and Washington. The model can track remnant 

snags and logs (i.e., those existing on site at the beginning of the assessment time) and new 

snags and logs created from green trees. 

Introduction 

Managers of forested lands in the Pacific Northwest are required to manage for 

snags and logs, or coarse woody debris (CWD), in timber harvest units. Coarse 

woody debris is a highly dynamic ecosystem component, as snags fall over time and 

both snags and logs decay. Therefore, managing for these habitat components 

through time requires knowledge of the dynamics of CWD. Snag dynamics models 

that predict the general rate of fall and decay of snags have been available for several 

years (Marcot 1992, McComb and Ohmann 1996). These models estimate the 

number of green trees that need to be retained in harvest units to replace existing 

snags that will fall during a rotation, and to estimate when to convert green trees to 

snags. Mortality estimates from growth and yield models can be input into these 

models to track snag recruitment in forest stands. The Snag Recruitment Simulator 

(SRS) (Marcot 1992) has been widely used in Land and Resource Management Plans 

by the USDA Forest Service in the Pacific Northwest. 

The main drawback of these models is that they do not assess the dynamics of 

logs. In order to manage logs through time, it is important to know how they 

decompose over time. Wright (1998) developed a model that predicted the dynamics 

of CWD mass through time, although snag and log biomass were aggregated. The 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Regional Wildlife Ecologist, Pacific Northwest Region, P.O. Box 3623, Portland, OR 94208-3623 (email: kmellen@fs.fed.us) 

3

 Operations Research Analyst, Umatilla National Forest, USDA Forest Service, 2517 SW Hailey Ave., 

Pendleton, OR 97801 (e-mail: aager@fs.fed.us) 
Coarse Wood Dynamics Model—Mellen and Ager 

504 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

objective of our Coarse Wood Dynamics Model (CWDM) is to predict the dynamics 

of snags and logs as separate entities through time. The CWDM provides output on 

amounts of CWD, distinguishing between snags and logs of different size and decay 

classes, every 5 years for a period of up to 300 years. 

Model Overview 

The CWDM analyzes the dynamics of CWD in forested ecosystems of the 

western Cascades in Oregon and Washington. The CWDM models Douglas-fir 

(Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) snags and logs. 

The model predicts snag fall, height loss and decay, and log decay at 5-year intervals 

for a period of 300 years. Snags either fall whole or partially break off, creating down 

logs. Snags also decay from hard to soft. Logs decay from sound to decayed 

conditions, and eventually disappear into the forest floor as duff. The model 

simulates the decomposition of remnant snags and logs (those existing on site at the 

beginning of the assessment time) and new snags and logs created from green trees or 

from mortality. A growth and yield model can be used to determine number and sizes 

of snags created by suppression mortality. These snags can then be input into the 

model at the appropriate time during the rotation. 

The CWDM follows individual CWD pieces or groups of pieces (same species, 

size and decay class) through time. The model varies snag fall and height loss rates 

by species, diameter at breast height (dbh), and decay class. Western hemlock snags 

fall faster than Douglas-fir snags, and smaller more decayed snags fall faster than 

larger, sounder snags. Decay is basically the reduction in density of a piece of CWD. 

Decay rates are different for snags and logs since snags decay faster than logs. The 

model varies decay of snags and logs by species and size. Western hemlock decays 

faster than Douglas-fir (fig. 1). Smaller snags and logs decay faster than larger ones. 

0

0.1

0.2

0.3

0.4

0.5

0

10203040506070

80

90

100110120130140

Time (years)

density (grms/cm3

)

Douglas-fir

snags

Western

hemlock

snags

Figure 1―CWDM decay of Douglas-fir and western hemlock snags ranging from 

38.1 to 63.5 cm dbh. 
Coarse Wood Dynamics Model—Mellen and Ager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 505 

Although the current version of the CWDM uses data from the western 

Cascades of Oregon and Washington, the model could easily be modified to include 

data from other geographic locations. The same approach taken in the model could 

also be used to incorporate other species of snags and logs as data become available. 

The CWDM is compiled to run in DOS. A Windows version will be released 

soon.4

 The program and documentation are available from the lead author. 

Model Input 

CWDM requires input data in the form of two space-delimited ASCII files, one 

each for snags and logs. The following data are required in the snag input file: year 

snag created (0 for existing snags), snag species, decay class, dbh (in), height (ft), 

snags/acre or ha, and site class. The log input includes year log created (0 for existing 

logs) log species, decay class, large end diameter (in), length (ft), and logs/acre or ha. 

A 3-class decay system is used for both snags and logs. Snags are divided into 

green, hard, or soft snags. Logs are divided into green, sound, or decayed logs. Green 

snags and logs are those created at the current time either through natural mortality or 

artificial creation. Hard snags include classes 1-3 and soft snags classes 4 and 5 of the 

5-class system developed by Cline and others (1980). Sound logs include classes 1 

and 2, while decayed logs include classes 3-5 of the 5-class system developed by 

Maser and others (1979) for logs. 

Model Outputs 

The CWDM creates five space-delimited ASCII output files: snagout, logout, 

snlogout, sumsnags.txt and sumlogs.txt. The first three files are intermediate files that 

track individual snags or logs through time. The last two are summary files that most 

users will want to view. The files are sums of snags and logs by time, species, decay 

class, and dbh or diameter class. Dbh classes for snags are <38.1 cm, 38.1-63.5 cm, 

and >63.5 cm. Diameter classes for logs are <30.5 cm, 30.5-50.8 cm, and >50.8 cm. 

If different dbh or diameter breaks are desired, the snagout and logout files can be 

imported into a database and for querying. 

The fields in sumsnags.txt are time, species, decay class, dbh class, and 

snags/acre or ha. The fields in sumlogs.txt are time, species, decay class, diameter 

class, linear feet/acre or ha, and percent cover. 

Example Outputs 

Figures 2-4 are examples of results from the model. The current version of the 

CWDM does not produce graphs. Graphic representations can be developed by 

importing the ASCII files into a spreadsheet or database program with graphing 

capabilities. 

Figure 2 is the result of leaving a mix of species, size, and decay classes of 

snags on site at time 0. The loss of hard snags is a result of some snags falling and 

some snags becoming soft. The first increase in the soft snags is when western 

 

4

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Coarse Wood Dynamics Model—Mellen and Ager 

506 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

hemlock snags change from a hard to soft condition. The second increase is from 

hard Douglas-fir snags becoming soft. The decrease in total numbers of snags is from 

snag fall. 

Figure 3 illustrates the results of recruitment of snags during a time period. In 

this example a mixture of species, sizes, and decay classes of snags is left at time 0. 

A few snags are artificially created at years 25 and 50 to replace snags that have 

fallen. Suppression mortality creates snags > 38.1 cm beginning at year 75. Input 

from suppression mortality continues until year 95 in this example. Realistically, 

suppression mortality would continue beyond 95 years, but this is the limit of some 

growth and yield models. 

0

0.5

1

1.5

2

2.5

3

0 15 30 45 60 75 90 105 120 135 150 165

Time (years)

Number of snags/ha

Soft snags

Hard snags

Total snags

Figure 2―CWDM decrease in the number of snags through time. Loss of total and 

soft snags is a result of snag fall. Loss of hard snags is a result of decay to the soft 

decay class and fall. Input at time 0 includes a mixture of hard and soft Douglas-fir 

and western hemlock snags for a total of 2.5 snags/ha. 

0

2

4

6

8

10

12

14

0

255075

100125

150

175

200

225250275300

Time (years)

Number of snags/ha

Soft snags

Hard

snags

Total

snags

Figure 3―CWDM dynamics of snags through time with recruitment of snags during 

the rotation. Input at time 0 includes a mixture of hard and soft Douglas-fir and 

western hemlock snags. Recruitment of snags includes snags artificially created from 

Douglas-fir trees at years 25 and 50, and from suppression mortality of Douglas-fir 

trees at years 75, 80, 85, 90, and 95. 
Coarse Wood Dynamics Model—Mellen and Ager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 507 

0

0.5

1

1.5

2

2.5

3

3.5

0

255075

100125150175200225250275300

Time (years)

Percent cover of logs

Figure 4―CWDM percent cover of logs through time with recruitment of logs from 

snags. Input of logs at time 0 is < 1 percent cover. Recruitment of logs through time 

is all from snags falling as per figure 3. Initial input of logs at time 0 includes a mixture 

of green and sound Douglas-fir and western hemlock logs. 

Figure 4 illustrates an example of leaving some sound and green logs on site at 

time 0 and then incorporates the snags displayed in figure 3 as they fall partially or 

whole and become logs. Percent cover of logs is also reduced as they decay. 

Assumptions 

Given the available data, a number of assumptions were required to develop the 

model. Foremost is that values for snag and log dynamics reported in the literature 

are “average.” CWD decay is highly variable and highly dependent on site 

conditions, weather, geographic location, etc. Since the model takes each snag or log 

and treats it as an average piece on an average site, the model outputs should be 

considered as general guidelines and should be applied over larger areas or 

landscapes. 

Because data for western hemlock are very limited, we used more substantial 

data for Douglas-fir to develop size-specific values used for western hemlock decay 

and fall rates. It is clear from data that are available that western hemlock CWD falls 

and decays much faster than Douglas-fir CWD. 

The model assumes snags fall at a constant rate over time, varying only by dbh 

and decay class. In reality snags probably are created and fall in “pulses” over time. 

The pulses are difficult to predict and thus are not incorporated in the model. This 

omission should have little effect on the ability of the CWDM to predict the general 

dynamics of CWD levels throughout a rotation or planning cycle. 

It is assumed that there is a lagtime once a green tree becomes a snag before it 

begins to decay and fall. Lagtimes were applied to snags created from green trees. 

Several assumptions were made regarding the process by which snags break and 

fall. It was assumed that snags often break and fall in two to three pieces, although 

some snags also fall whole. At any one time, some snags will lose a portion of their 

original height. Height loss was averaged for snags. Based on Pacific Northwest 

Research Station (PNW) Forest Inventory and Analysis (FIA) program data, it was 

assumed that on average one-third of a snag falls when it loses height. Taper 
Coarse Wood Dynamics Model—Mellen and Ager 

508 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

equations were used to determine two-thirds height diameter of snags to determine 

large end diameter of the log. To calculate the number of log pieces, we assumed that 

27 percent of standing snags lost a portion of their height over a 5-year period (based 

on FIA data). Class 5 snags that fall are not counted as logs. They were assumed to 

disintegrate and contribute to the duff layer. 

For snags it is assumed that volume (m3

/ha) is constant except for the portion of 

snag height that breaks off during the time period. As snags move toward decay class 

5 this assumption is probably violated, as dbh is also reduced by fragmentation of the 

snag. As a result, calculations for very soft snags probably underestimate density. 

 For Douglas-fir logs it was assumed that volume is constant until the log 

reaches the class 4 decay stage (Graham 1982). Volume of class 4 and 5 logs is 

“decayed” using fragmentation rates. Fragmentation rates were obtained from 

Graham (1982). Diameter and length of logs were also reduced for decay class 4 and 

5 logs based on Maser and Trappe (1984). Western hemlock logs do not fragment 

like Douglas-fir because bark remains intact, forming a protective shell around the 

log (Graham 1982). 

It was assumed that, on average, existing snags and logs are halfway through 

either the hard or soft decay class for snags or sound or decayed class for logs. 

Densities were assigned based on midpoint densities of either the hard or soft decay 

class. 

Decay rates were applied to biomass in equations in the CWDM. Decay rates are 

a combination of mineralization and fragmentation of boles. Both types of decay 

reduce biomass: mineralization reduces density, and fragmentation reduces volume. 

In the model the two types of decay were usually combined. In the case of decayed 

logs, fragmentation rates were applied to the log volume. 

The Smalian formula (Wegner 1984) was used to calculate volume. This volume 

is then multiplied by decay class specific density to get biomass. Because the 

Smalian formula tends to overestimate volume by about 10 percent (Wegner 1984), 

biomass is overestimated. This is not a problem with the decay equations in the 

model because decay is relative; thus, differences in biomass do not influence rate of 

decay. However, biomass and volume results should not be used as the absolutes for 

CWD in a stand. 

Data Sources 

Information on decay rates (tables 1, 2) was gleaned from the literature. Decay 

rates for Douglas-fir snags are from Graham (1982). Decay rates for Douglas-fir logs 

are from 3 sources: decay rates for logs >38.1 cm diameter are from Graham (1982); 

decay rates for logs 15.2-38.1 cm diameter are from Means (in Harmon and others 

1986); and decay rates for logs < 15.2 cm diameter are from Erickson and others 

(1985). 

Less data are available for decay of western hemlock. An overall decay rate for 

logs and snags is given by Graham (1982), but size-specific decay rates are not 

available. Decay rates for three size classes are extrapolated based on comparative 

fall rates of snags in the different size classes. It was assumed that fall rates indicated 

relative fragmentation rates. The logic was checked by trying the same extrapolation 

with Douglas-fir snags and comparing to reported decay rates. The result was close; 
Coarse Wood Dynamics Model—Mellen and Ager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 509 

extrapolated decay rates were within 0.003 (or 85 percent). Decay rates for largest 

logs are extrapolated based on Douglas-fir decay rates. Decay rates for logs <15.2 cm 

diameter are from Erickson and others (1985). 

Table 1―Snag decay rates used in the CWDM. 

1 DF = Douglas-fir; WH = western hemlock 

2 Decay lagtime and constant applied to newly created snags only. 

Table 2―Log decay and fragmentation rates used in the CWDM. 

Species1

 Diameter 

class (cm) 

Decay 

rate (k) 

Fragmentation 

rate2 (kf) 

Diameter 

reduction 

rate2 (rd) 

Length 

reduction 

rate2 (rl)

 

DF > 38.1 0.012 0.008 0.0031 0.0026 

DF 15.2 – 38.1 0.015 0.010 0.0037 0.0030 

DF <15.2 0.026 

WH > 38.1 0.019 

WH 15.2 – 38.1 0.023 

WH <15.2 0.030 

1 DF = Douglas-fir; WH = western hemlock

2 Fragmentation, diameter reduction and length reduction rates apply to class 4 and 5 Douglas-fir logs 

only.

Snag fall and height loss rates (table 3) are based on remeasurement data from 

snags on private lands. The data were collected through the PNW FIA program.5

 The 

snags were measured in the late 1970s and again in the late 1980s. Presence or 

absence of snags were noted, and changes in height and decay class were recorded. 

Using FIA data, snags that disappeared during the 10-year remeasurement period are 

assumed to have fallen whole. The 10-year fall and height loss rates were converted 

to 1-year rates. Fall and height loss rates were averaged for size class (<38.1, 

38.1-63.5, >63.5 cm dbh) and decay class (hard vs. soft) (table 3). Size and decay 

classes were lumped if there was no significant difference (alpha=0.20) in rates of 

fall or height loss. A large alpha value was used because the effect of a type 1 error 

was considered less risky to the outcome of the model than a type 2 error. Sample 

sizes are small and data are variable, but the trends in the data supported what is 

known from other data about relative fall rates of snags. 

 

5

 Unpublished data on file, Pacific Northwest Research Station, Janet Ohmann, Portland, Oregon. 

Species1 Dbh class 

(cm) 

Decay 

rate (k) 

Decay 

lagtime2

(years)

Lagtime decay 

constant2

DF > 63.5 0.017 20 0.06 

DF 38.1 – 63.5 0.033 15 0.14 

DF < 38.1 0.053 10 0.25 

WH > 63.5 0.060 15 0.15 

WH 38.1 – 63.5 0.088 10 0.25 

WH < 38.1 0.100 5 0.30 
Coarse Wood Dynamics Model—Mellen and Ager 

510 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 3― Snag fall rates and height loss proportions used in CWDM. 

1 DF = Douglas-fir; WH = western hemlock

2 Decay classes reflect groups of the 5-stage system developed by Cline and others (1980). Hard = 1 and 

2 =; Intermediate 3; Soft = 4 and 5. 

3 Fall lagtimes applied to newly created snags only. 

The sharp change in fall and height loss rates between hard and soft snags 

caused calculation problems for the model because snags gained height as they went 

from hard to soft. As a result, intermediate fall and height loss rates are applied to 

class 3 snags (table 3). Since there are 3 classes in the broad category of “hard,” twothirds of the difference between hard and soft fall and height loss rates is added to the 

“hard” class rates to determine intermediate rates for class 3 snags. Using 

intermediate rates smoothes the decay curves but does not change the long-term 

decay and fall of snags. 

Lagtimes for beginning of snag decay and fall (tables 1, 3) are from Cline and 

others (1980) and Harmon and others (1986). Data on lagtimes for western hemlock 

snags are not dbh specific. Lagtimes for the 3 dbh classes are based on extrapolating 

the relationship of increase in lagtime with increase in dbh for Douglas-fir snags and 

applying the extrapolation to western hemlock snags. 

Taper equations from Walters and Hann (1986) are used to calculate top and 

mid-height diameter of snags. Mid-height diameter is needed to determine large end 

diameter of logs created as snags break. Both diameters are used in volume 

calculations. The taper calculations require knowing the height and crown ratio of the 

tree before it became a snag. Forest Service Continuous Vegetation Survey (CVS) 

data from the Mt. Hood and Gifford Pinchot National Forests were used to determine 

average height and crown ratio of trees of a given dbh on low, moderate, and high 

sites.6

 Only data on live trees without broken or deformed tops were used for the 

 

6

 Unpublished data on file, Pacific Northwest Region, Portland, Oregon. 

Species1 Diameter 

class (cm) 

Decay class2 Fall rate 

(p) 

Height loss 

proportion 

(p) 

Fall 

lagtime3

DF > 63.5 Hard 0.008 0.019 15 

DF > 63.5 Intermediate 0.008 0.019 

DF > 63.5 Soft 0.008 0.019 

DF 38.1 – 63.5 Hard 0.013 0.033 10 

DF 38.1 – 63.5 Intermediate 0.022 0.038 

DF 38.1 – 63.5 Soft 0.027 0.041 

DF < 38.1 Hard 0.021 0.042 0 

DF < 38.1 Intermediate 0.043 0.056 

DF < 38.1 Soft 0.054 0.063 

WH > 63.5 Hard 0.01 0.024 5 

WH > 63.5 Intermediate 0.017 0.029 

WH > 63.5 Soft 0.021 0.031 

WH 38.1 – 63.5 Hard 0.02 0.035 0 

WH 38.1 – 63.5 Intermediate 0.03 0.044 

WH 38.1 – 63.5 Soft 0.035 0.048 

WH < 38.1 Hard 0.03 0.035 0 

WH < 38.1 Intermediate 0.039 0.044 

WH < 38.1 Soft 0.044 0.048 
Coarse Wood Dynamics Model—Mellen and Ager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 511 

estimates of height and crown ratio. Average height was calculated for 12.7 cm-dbh 

classes up to 101.6 cm dbh and by 25.4 cm-dbh classes for dbh greater than 101.6 

cm. Height and crown ratio were determined for dbh classes of <38.1 cm, 38.1-63.5 

cm and >63.5 cm. Only significant differences (alpha =0.05) were used; otherwise, 

height and crown ratio were averaged over two or more dbh classes. Plant 

associations (Brockway and others 1983, Halverson and others 1985, Hemstrom and 

others 1982, Topik and others 1986) were used to determine if data were from high, 

moderate, or low sites. High and moderate sites were in plant association where 

average growth was > 6 m3

/ha/year. Growth on low sites was < 6 m3/ha/year. 

Because there was no significant difference between height crown ratio on high and 

moderate sites, data for those sites were lumped. 

The Walters and Hann (1986) equations used for calculating taper for snags can 

not be used directly on logs, because large end diameter does not necessarily relate to 

dbh of a tree that is needed to calculate taper. Data Jane Kertis and Mark Huff 7

 on 

log length and small end and large end diameters, were used to determine small end 

diameter of logs given large end diameter and length. The data are from the 

Willamette National Forest in the western Oregon Cascades. Small end/large end 

ratios were calculated for each log. Simple linear regression was used to determine 

the relationship between log length and the small end/large end ratio. For Douglas-fir 

logs, sound and decayed logs were assessed separately. For western hemlock logs, 

sound and decayed logs were combined. Class 5 logs were not used in the equations. 

The regressions were highly significant with the following P-values: Douglas-fir = 

9.93 E-33; western hemlock = 5.33 E-10. 

Densities of snags and logs (g/cm3

) (tables 4-7) are needed to convert volume to 

biomass for the decay equations and to determine decay class of snags and down 

logs. Densities for both Douglas-fir and western hemlock class 1-5 snags and logs are 

from Spies and others (1988). Densities for green snags and logs are from Harmon 

(1992). 

Snags and logs are removed from the model when they reach a maximum age 

(tables 4-7). Maximum age of Douglas-fir snags is from Cline and others (1980). 

Maximum ages for all logs and western hemlock snags are from Graham (1982) and 

half-life data are from Harmon and others (1986).

Table 4―Density and ages for decay classes of Douglas-fir snags used in the CWDM. Values 

are for snags as they first enter a decay class. Ages are based on output from the model. 

 

7

 Unpublished data on file, Willamette National Forest, Jane Kertis and Mark Huff, Eugene, Oregon. 

Dbh class (cm) 

Decay 

class 

Density (gm/cm3) > 63.5 38.1 – 63.5 < 38.1 

 Snag ages (yrs) 

1 0.452 0 0 0 

2 0.380 15 15 15 

3 0.284 35 30 25 

4 0.197 60 45 30 

5 0.140 80 60 40 

Maximum age 250 130 75 
Coarse Wood Dynamics Model—Mellen and Ager 

512 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 5―Density and ages for decay classes of western hemlock snags used in the CWDM. 

Values are for snags as they first enter a decay class. Ages are based on output from the 

model. 

Table 6―Density and ages for decay classes of Douglas-fir logs used in the CWDM. Values 

are for logs as they first enter a decay class. Ages are based on output from the model. 

Table 7―Density and ages for decay classes of western hemlock logs used in the CWDM. 

Values are for logs as they first enter a decay class. Ages are based on output from the model. 

Dbh class (cm) 

Decay class Density (gm/cm3) > 63.5 38.1 – 63.5 < 38.1 

 Snag ages (yrs) 

1 0.408 0 0 0 

2 0.348 10 10 5 

3 0.263 20 15 10 

4 0.215 25 20 10 

5 0.138 30 25 15 

Maximum age 85 50 35 

Diameter class (cm) 

Decay class Density (gm/cm3) > 38.1 15.2 – 38.1 < 15.2 

 Log ages (yrs) 

1 0.452 0 0 0 

2 0.380 15 15 10 

3 0.284 40 35 20 

4 0.197 70 60 35 

5 0.140 155 115 45 

Maximum age 315 245 70 

Diameter class (cm) 

Decay class Density (gm/cm3) > 38.1 15.2 – 38.1 < 15.2 

 Log ages (yrs) 

1 0.408 0 0 0 

2 0.348 10 10 10 

3 0.263 25 20 15 

4 0.215 35 30 25 

5 0.138 60 50 40 

Maximum age 95 75 60 
Coarse Wood Dynamics Model—Mellen and Ager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 513 

Calculations 

Equations 

The following are the equations used to calculate parameters in the CWDM: 

Parameter Equation 

Volume 

 snags1

 volume = ((Ab+At)/2)*L

 logs (1-3)1 volume = ((Ab+At)/2)*L 

 logs (4-5)2 current volume = initial volume*(EXP(-kf(t-tIV))) 

Decay 

 green snags3

 current biomass = initial biomass*(1-(1(EXP(-kt))(lt*lc)

 hard/soft snags4 current biomass = initial biomass*(EXP(-kt)) 

 logs4

 current biomass = initial biomass*(EXP(-kt)) 

Snag fall5

 current snag/ha = original snag/ha*(EXP(-pt)) 

Snag height loss6 current height = original height*(1-p)t

Log diameter7 current diameter = initial diameter*(EXP(-rd(t-tIV))) 

Log length8

 current length = initial length*(EXP(-rl(t-tIV))) 

Log taper9 small end diam. = large end diam.*(Yintercept+(slope*L)) 

Log pct. cover10 Pct. cover = (((le diam*L)/2)+((se diam*L)/2))/100 _____________________________________________________________________________________________________________________________ 

1

 Smalian equation from Wegner (1984); Ab=area of base or large end; At=area of top or small end; 

L=snag height or log length. 

2

 kf=fragmentation rate (see table 2); t=time elapsed; tIV=time at which logs becomes a class 4. 3

 Green snags are those created at the current time; k=decay rate (see table 1); t=time elapsed; 

lt=lagtime; lc=lagtime constant; see table 1 for lagtime and lagtime constant. 4

 Snags that are hard or soft at the beginning of the planning cycle; k=decay rate (see tables 1 and 2); 

t=time elapsed. 

5 p=proportion of snags falling per year (see table 3); t=time elapsed; applied after lagtime has elapsed. 6

 p=proportion of height lost per year (see table 3); t=time elapsed; applied after lagtime has elapsed. 7

 rd=diameter reduction rate (see table 2); t=time elapsed; tIV=time at which logs becomes a class 4. 8 rl=length reduction rate (see table 2); t=time elapsed; tIV=time at which logs becomes a class 4. 9

 L=length; for Douglas-fir Yintercept=0.884, slope=-0.0044; for western hemlock Yintercept=0.902, 

slope=-0.0055; small and large end diameter and length are used in calculations for volume and percent 

cover. 

10 le diam=large end diameter (in); se diam=small end diameter (in); L=length (ft) 

Discussion of Calculations 

A lagtime decay equation is used for snags created from green trees to account 

for a lag between death of a tree and the beginning of decay. The equation is from 

Harmon and others (1986). Lagtime constants were determined by trial and error. 

Constants that resulted in a decay curve that approximated those in Cline and others 

(1980) were used. 

When modeling decay of snags created from green trees, the results indicate that 

biomass lost during the lagtime was all due to mineralization. In reality, some snags 

probably break or fall, but very few due to lagtime for falling. Lagtime equations 

similar to the one used for decay did not work for fall and height loss calculations. 

The curves became too steep and didn't match fall rates (Cline and others 1980). 

Thus, absolute lagtimes are used. It is assumed that no snags fall during the lagtime. 
Coarse Wood Dynamics Model—Mellen and Ager 

514 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Rates for reduction of log diameter and length are from Maser and Trappe 

(1984). Length of Douglas-fir logs decreases 55 percent between class 1 and class 5, 

and diameter is reduced by 68 percent, mostly due to bark loss. Rates (rd and rl) are 

calculated by taking the number of years to get halfway between the beginning of the 

class 5 condition and the maximum life of the log and then dividing the percent 

reduction by that number of years. 

The density at which a snag changes from hard to soft was determined by 

bracketing the average densities for the decay classes 3 and 4 by the standard 

deviation of the density estimate. The density at which the upper bracket of class 4 

and lower bracket of class 3 meet is used as the density that triggers classifying the 

snag as hard or soft (tables 4, 5). Each snag was tracked through time, and as decay 

class changed the decay-specific fall rates were applied. The density at which logs go 

from sound to decayed was calculated in a manner similar to that for snag 

calculations except that class 2 and 3 densities were used (tables 6, 7). 

Densities for existing snags are assigned based on midpoint densities of either 

the hard or soft decay class. The midpoint density of hard snags was calculated by 

averaging densities for class 3 and green tree densities. The midpoint density for soft 

snags was calculated by averaging densities for class 4 and 5 snags. The midpoint 

density for sound logs was calculated by averaging densities for class 2 and green 

tree densities. The midpoint density for decayed logs was calculated by averaging 

densities for class 3 and class 5 logs. 

Model Validation 

Data from Cline and others (1980) were used to validate the fit of the model for 

Douglas-fir snags against the decay rates used in the model (Graham 1982). Age at 

which a snag went from hard to soft for different dbh classes and the maximum life 

of snags from the CWDM was validated against data in Cline and others (1980). 

Because dbh breaks did not match exactly between the two studies, generalized 

extrapolations were made. Data were not available to validate western hemlock snag 

decay and fall. 

For logs, decay rates and equations in the model were tested against age range 

for each decay class in Graham (1982). This is not a true validation because decay 

rates and ages came from the same data set―it just validates that the equations and 

values used were producing the expected results. Half-lives from two additional 

datasets (reported in table 3 of Harmon and others 1986) were also used to help 

validate decay rates. Data from Sollins and others (1987) were used to check the log 

decay rate against ages of logs in decay classes 1 to 4. 

Acknowledgments 

The inspiration and basic concepts for the CWDM came from a CWD dynamics 

model (FIRECWD) developed by Pamela Wright. Janet Ohmann and Mark Huff 

provided data for use in the model. Thanks to Bruce Marcot, Mark Huff, and Pamela 

Wright for valuable insight and advice during development of the model. We thank 

Pamela Wright and Cay Ogden for review of early drafts of this manuscript. 
Coarse Wood Dynamics Model—Mellen and Ager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 515 

References 

Brockway, Dale G.; Topik, Christopher; Hemstrom, Miles A; Emmingham, William H. 1983. 

Plant association and management guide for the Pacific silver fir zone, Gifford 

Pinchot National Forest. R6-ECOL-130a-1983. Portland, OR: Pacific Northwest 

Region, Forest Service, U.S. Department of Agriculture; 122 p. 

Cline, Steven P.; Berg, Alan B.; Wight, Howard M. 1980. Snag characteristics and 

dynamics in Douglas-fir forests, western Oregon. Journal of Wildlife Management 

44(4): 773-786. 

Erickson, Heather E.; Edmonds, R.L.; Peterson, C.E. 1985. Decomposition of logging 

residues in Douglas-fir, western hemlock, Pacific Silver fir, and ponderosa pine 

ecosystems. Canadian Journal of Forest Research 15(5):914-921. 

Graham, Robin L.L. 1982. Biomass dynamics of dead Douglas-fir and western hemlock 

boles in mid-elevation forests of the Cascade Range. Corvallis: Oregon State 

University; 152 p. Ph.D. dissertation. 

Halverson, Nancy M.; Topik, Christopher; VanVickle, Robert. 1985. Plant association and 

management guide for the western hemlock zone, Mt. Hood National Forest.

R6-ECOL-232a-1986. Portland, OR: Pacific Northwest Region, Forest Service, U.S. 

Department of Agriculture; 111 p. 

Harmon, Mark E. 1992. Long-term experiments on log decomposition at the H.J. 

Andrews Experimental Forest. Gen. Tech. Rep. PNW-GTR-280. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 28 p. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S.V.; Lattin, J. D.; 

Anderson, H. H.; Cline, S. P.; Aumen, N. G.; Seddell, J. R.; Lienkaemper, G. W.; 

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15:133-302. 

Hemstrom, Miles. A.; Emmingham, William H.; Halverson, Nancy M.; Logan, Sheila E.; 

Topik, Christopher L. 1982. Plant association guide for the Pacific silver fir zone, Mt. 

Hood and Willamette National Forests. R6-ECOL-100-1982a. Portland, OR: Pacific 

Northwest Region, Forest Service, U.S. Department of Agriculture; 104 p. 

Marcot, Bruce G. Snag recruitment simulator, Rel. 3.1 [Computer program]. 1992. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture. Available from: Pacific Northwest Research Station. P.O. Box 3890, 

Portland, OR 97208. 

Maser, Chris; Anderson, Ralph G.; Cromack, Kermit, Jr.; Williams, Jerry T.; Martin, Robert 

E. 1979. Dead and down woody material. In: Thomas, Jack W., tech. ed. Wildlife 

habitats in managed forests: the Blue Mountains of Oregon and Washington. Agric. 

Handb. 553. Washington, DC: U.S. Department of Agriculture; 78-95. 

Maser, Chris; Trappe, James M. 1984. The seen and unseen world of the fallen tree. Gen. 

Tech. Rep. PNW-164. Pacific Northwest Forest and Range Experiment Station, 

Portland, OR: Forest Service, U.S. Department of Agriculture; 56 p. 

McComb, William C.; Ohmann, Janet L. Snag Dynamics Projection Model [Computer 

program]. 1996. Corvallis, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture. Available from: Pacific Northwest Research Station. 3200 

SW Jefferson Way, Corvallis, OR 97331. 

Sollins, Phillip; Cline, Steven P.; Verhoeven, Thomas; Sachs, D.; Spycher, G. 1987. Patterns 

of log decay in old-growth Douglas-fir forests. Canadian Journal of Forest Research 

17: 1585-1595. 
Coarse Wood Dynamics Model—Mellen and Ager 

516 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Spies, Thomas A.; Franklin, Jerry F.; Thomas, T. B. 1988. Coarse woody debris in 

Douglas-fir forests of western Oregon and Washington. Ecology 69:1689-1702. 

Topik, Christopher; Halverson, Nancy M.; Brockway, Dale G. 1986. Plant association and 

management guide for the western hemlock zone, Gifford Pinchot National Forest.

R6-ECOL-230A-1986. Portland, OR: Pacific Northwest Region, Forest Service, U.S. 

Department of Agriculture; 132 p. 

Walters, David K.; Hann, David W. 1986. Taper equations for six conifer species in 

southwest Oregon. Res. Bulletin 56. Corvallis, OR: Forest Research Laboratory, 

Oregon State University; 41 p. 

Wegner, Karl F. 1984. Forestry handbook. 2nd ed. New York: John Wiley and Sons; 297 p. 

Wright, Pamela. 1998. The effect of fire regime on coarse woody debris in the west 

central Cascades, Oregon. Corvallis: Oregon State University; 109 p. M.S. thesis. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 517 

Snag Recruitment in Subalpine Forests of 

the North Cascades, Washington State1

Paul T. Flanagan,2

 Penelope Morgan,3 and Richard L. Everett4

Abstract 

We recorded snag species, locations, and causal agents of tree mortality, and estimated fire 

histories and standing dead and downed fuel abundance in polygons in subalpine forests in the 

Entiat watershed in Washington State. The overall snag density was 51 ± 5.2 snags per 

hectare. The density of dominant and codominant snags did not differ by aspect or slope 

categories (p = 0.74), but the density of intermediate and suppressed snags was highest on 

steep south-facing slopes (p < 0.05). Weather-related effects created more snags than any 

other disturbance in the period between stand-replacing fires. More weather-caused mortality 

occurred on northerly aspects than on southerly aspects (p < 0.05) and on mid-slopes than 

either upper or lower slopes (p < 0.05). Standing dead and downed fuel, and tree mortality 

caused by weather (snow, ice, and wind), root diseases, animals, and bark beetles were related 

to stand structural stage. We estimate the mean fire interval was 12 years for the 5,685 ha 

encompassed in the study area. The estimated mean size of stand-replacing fires was 146 ± 95 

ha. 

Introduction 

Vegetation in subalpine forests is not distributed randomly but is closely tied to 

topography, climate, and the cumulative effects of disturbances at various scales. 

Disturbance regimes of subalpine forests differ considerably from those of forests at 

lower elevations where fire was historically a frequent visitor to all stand 

development stages, commonly burning large areas at low severity and selectively 

killing individuals and small groups of trees. In contrast, fires in subalpine forests are 

less common and are typically mixed-severity or stand-replacing (Covington and 

others 1994). 

How a tree dies influences its longevity as a snag and its usefulness to wildlife 

(Bull and others 1997). Snag longevity is site-specific (Everett and others 1999, Keen 

1929) and is enhanced by larger bole diameter, shorter height, and thinner bark 

(Raphael and Morrison 1987). When killed by fire, thin-barked species such as 

Engelmann spruce (Picea engelmannii Parry ex Engelm.), lodgepole pine (Pinus 

contorta var. latifolia Dougl. ex Loud.), and subalpine fir (A. lasiocarpa [Hook] 

Nutt.) dry quickly (Bull 1983), making them resistant to insects and decay fungi 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Entomologist, Wenatchee Service Center, USDA Forest Service, 1133 N. Western Ave., Wenatchee, 

Washington 98801 (e-mail: pflanagan@fs.fed.us) 

3

 Professor, Department of Forest Resources, University of Idaho, Moscow, Idaho 83844 (e-mail: 

pmorgan@uidaho.edu) 

4

 Retired Team Leader, R&C Kona Environmental Research, 77-6491 Marlin Road, Kailua-Kona, 

Hawaii 96740 (e-mail: everettr001@Hawaii.rr.com) 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

518 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(Hadfield and Magelssen 1997, Parry and others 1996) and increasing their longevity 

as snags (Everett and others 1999). 

Over the course of stand development, insects and pathogens kill far more trees 

and recycle more biomass in most forests than do fires (Hagle and others 1995). With 

the exception of large-scale outbreaks of the mountain pine beetle (Dendroctonus 

ponderosae Hopkins) and spruce beetle (D. rufipennis Kirby), most of the conifer 

mortality caused by biotic agents in subalpine forests occurs individually or in small 

groups. The slow accumulation of fuel beds and fuel ladders resulting from insect 

and pathogen activity, as well as by wind, snow, and animals, takes place over a long 

period of time but affects the behavior of subsequent fires. 

Methods 

The study site is located in subalpine forests of the Entiat Ranger District, 

Wenatchee National Forest, on the eastern slope of the Washington Cascade Range 

(fig. 1). The study site was chosen because the range of climatic and vegetation 

conditions are representative of many other sites in the Cascade Mountains of eastern 

Washington State. Elevations in the study area range from 1,280 m to 2,150 m above 

sea level. Mean annual precipitation in the study area ranges from approximately 100 

to 230 cm. Subalpine forests in the upper Entiat watershed are classified into five 

major plant series: whitebark pine (Pinus albicaulis Engelm.), subalpine larch (Larix 

lyallii Parl.), subalpine fir, mountain hemlock (Tsuga mertensiana [Bong] Carr.), and 

Pacific silver fir (Abies amabilis Dougl. ex Forbes) (Lillybridge and others 1995). 

The western-most forests in the study area are in the Glacier Peak Wilderness Area. 

Plummer (1902) commented on burns that occurred in the 1800s: “On the high 

divides between Entiat and Mad Rivers extensive burns occurred years ago, and the 

very life was burned out of the soil, leaving it poor indeed.” 

 

kilometers 

Figure 1—Location of study sites (shaded gray) in the Entiat watershed, Washington 

State. 

Black and white aerial photographs taken in 1992 at a scale of 1:16,000 were 

used to delineate polygons. Eighteen polygons representing several predominant 

aspect and slope categories were randomly selected from a total of 93, allotting 3 

polygons to each slope and aspect category. The total area encompassed by the 18 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 519 

selected polygons was 5,685 ha; the average size was 316 ha ± 181 ha. Stand types 

within polygons were subjectively classified by crown density and whether crowns 

had single or multiple layers. Aerial photographs were also used to assign stand types 

to one of seven structural stages: stand initiation, open stem exclusion, closed stem 

exclusion, understory reinitiation, young multi-strata, old forest multi-strata, and old 

forest single-stratum (O'Hara and others 1996, Oliver 1981). Less than 1 ha in the 

study area was classified as old forest single-stratum. Therefore, data from old forest 

single-stratum and old forest multi-strata were combined. Polygon and stand type 

boundaries were drawn on 1:24,000 scale USDA Forest Service resource orthophotos 

then digitized into a geographic information system. 

Fire histories, occurrences, and extents were estimated from a variety of sources. 

Ages of the oldest appearing conifers in each stand type were measured. Fire atlases, 

which are maps with boundaries of fires hand-drawn at the time of occurrence, 

historical panoramic photographs taken from fire lookouts, and aerial photographs 

supplemented stand age data and improved estimates of fire sizes. The most recent 

fires were mapped for each polygon. FHX2 fire history software (Grissino-Mayer 

1995) was used in this study to calculate the Weibull median fire interval (sensu

Johnson and Gutsell 1994) for the area encompassed by the 18 polygons. 

Downed and dead woody fuel was measured in tones per ha using the planar 

intersect method (Brown 1974) at plot centers. Sampling plane lengths varied from 

0.9 m for continuous heavy slash of 0 to 2.54 cm to 11 m for light slash larger than 

15 cm. 

Both belt transects and fixed area plots were used to collect data on conifer 

mortality. Five variable-length 9.1 m belt transects were systematically established in 

each polygon to cross all stand type, beginning and ending at polygon boundaries. 

The following data were recorded in each transect: extents of stand types 

encountered; conifer species and crown class for each dead tree. Crown classes were 

assigned to individual trees according to Oliver and Larson (1990). All agents 

potentially contributing to mortality were recorded for each dead tree, and a 

determination was made of the primary agent responsible. For example, the primary 

agent recorded for a tree with evidence of moderate to aggressive root disease and 

bark beetle galleries was root disease. Trees that were blown over were recorded as 

killed by weather. Some of these may have been infected by root disease. Trees with 

advanced root disease are more likely to fail than trees with intact root systems 

(Harvey and Hessburg 1992). Fixed circular 0.02 ha plots were established where a 

belt transect crossed closest to the center of each stand type. Diameter at 1.37 m, 

henceforth referred to as dbh (diameter at breast height), and crown position were 

recorded for every live and dead tree in each fixed plot. Statistical tests were 

performed using Statistical Analysis Systems software (SAS 1997). 

Results and Discussion 

Subjective data from fire atlases, historical panoramic photographs from fire 

lookouts, and aerial photographs were analyzed, as were 793 tree age cores. Fortyone fires were recorded, dating from 1505 to 1935. The most recent fire in 14 of the 

18 polygons occurred between 127 and 102 years ago. Between 1880 and 1900, over 

half of the polygons had a fire that burned at least 25 percent of the area, equivalent 

to 2,126 ha. The Weibull mean fire interval was 12 years for the 5,685 ha 

encompassed in the study. Intervals between fires on the same polygon varied from 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

520 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

10 years to 291 years, and it is likely that fires did not overlap much in extent. The 

estimated mean size of stand-replacing fires was 146 ha (standard error [s.e.] = 95 

ha). Lightning directly killed 4 trees, and small lightning-caused fires killed an 

additional 68 trees. 

Downed and dead fuel weight from 116 planar transects were compared to stand 

structural stage (fig. 2). Eight of the 15 possible two-way comparisons differed 

statistically (as indicated by standard error bars). Fuel in tonnes per hectare

0 

 60 

 50 

 40 

 30 

 20 

 10 

si ose cse ur yms of 

Stand structural stage 

Figure 2—Dead and downed fuel by stand structural stage: si = stand initiation, ose 

= open stem exclusion, cse = closed stem exclusion, ur = understory reinitiation, yms 

= young multistory, of = single stratum and multi-stratum old forest. Vertical lines are 

standard errors of the mean. 

A total of 6,629 snags (standing dead trees), were recorded along 142 km of belt 

transects, representing a 130 ha sample size. The overall snag density was 51 ± 5.2 

snags per ha. An additional 329 snags were recorded in the 77 fixed plots in the 18 

polygons. Snags were combined into two groups based on similarities in crown class: 

dominant and codominant snags, and intermediate and suppressed. The majority of 

the snags (83 percent) at one time occupied dominant or codominant crown positions 

relative to the surrounding trees. Mean dbh for dominant and codominant snags was 

32.5 cm (s.e. = 17.6). Mean dbh for intermediate and suppressed snags was 14.1 cm 

(s.e. = 10.8). 

The number of intermediate and suppressed snags per ha was significantly 

higher (p < 0.05) for steep (> 50 percent) south-facing slopes, which had a 

preponderance of relatively pure, dense lodgepole pine stands, than for other slope 

and aspect categories (table 1). The number of dominant and codominant snags per 

ha did not differ significantly by aspect and slope categories (p = 0.74). Mean basal 

area in vegetation plots was 43 m2

 per ha (n = 115; s.e. = 98). 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 521 

Table 1—Snags per hectare by aspect and slope in two crown class categories. 

 Slope (percent) 

Aspect 

10-30 

DC1

 IS 

30-50 

DC IS 

50+ 

DC IS 

North 36 5 36 7 47 7 

South 47 3 48 9 51 372

1

 DC = dominant + codominant, IS = intermediate + suppressed 2

 Significantly different than other aspect/slope combinations for intermediate and suppressed trees. 

 0 

 10 

Snags per hectare 

 20 

 30 

 40 

 50 

 60 

 70 

 80 

 90 

Stand structural stage 

 si ose cse ur yms of 

Figure 3—Snags per hectare by stand structural stage: si = stand initiation, ose = 

open stem exclusion, cse = closed stem exclusion, ur = understory reinitiation, yms = 

young multistory, of = single stratum and multi-stratum old forest. Vertical lines are 

standard errors of the mean. 

Snag density was significantly different (p < 0.01) among the 6 structural stand 

stages for both the dominant and codominant snag category and the intermediate and 

suppressed snag category. A majority of the total snags (88 percent) were found in 

four structural stand stages: closed stem exclusion, understory reinitiation, young 

multi-story, and old forest (fig. 3).

Conifer mortality by crown class was analyzed for Engelmann spruce, subalpine 

fir, whitebark pine, and lodgepole pine. Disturbance groups included in the analyses 

were weather, bark beetles, root diseases, animals, white pine blister rust 

(Cronartium ribicola Fisch.) in whitebark pine and lodgepole dwarf mistletoe 

(Arceuthobium americanum Nutt. ex Engelm.) in lodgepole pine. All four conifer 

species analyzed had the majority of mortality in dominant and codominant crown 

classes, regardless of the disturbance agent species or group (p < 0.05). 

Snow, ice, and wind created significantly more snags than insects, pathogens, 

animals, or fire. A majority of these snags were subalpine fir and lodgepole pine 

broken off at, or near, the base of the live crown. Only weather-caused tree mortality 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

522 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

showed a difference by aspect or slope categories. More weather-caused tree 

mortality occurred on northerly aspects than on southerly aspects (p < 0.05), and on 

mid slopes than on either upper or lower slopes (p < 0.05). The mid-slope on a 

mountain, also called the thermal belt, typically receives the least variation in diurnal 

temperature, has the highest average temperature, and the lowest average relative 

humidity (Anonymous 1981). Therefore, fuels in the study area were most likely to 

accumulate where they would dry quickest and have the lowest fuel moisture. The 

trend in old forest structures is for fewer weather-killed trees than in the intermediate 

structural stages. This might be attributable to the decreased number of trees overall 

in old forest. 

The second and third most common disturbance agents were bark beetles and 

root diseases, respectively. Lodgepole pine was the tree species most commonly 

killed by bark beetles. In the study area, most stands of lodgepole pine were very 

dense, and were attacked not by mountain pine beetles but by secondary bark beetles 

such as Pityogenes spp. and Pityophthorus spp., sometimes in concert with 

Armillaria root disease. Armillaria root disease killed nine different conifer species in 

the study area, accounting for 88 percent of the mortality caused by identified root 

diseases. Fifteen percent of the subalpine fir, 41 percent of the Engelmann spruce, 

and 51 percent of the lodgepole pine infected with root disease were also attacked by 

bark beetles. 

Stand replacement fires create pulses of snags on the landscape. The number of 

standing dead trees per ha was compared to the time since the last stand-replacing 

fire for four disturbance agent groups: weather, bark beetles, root disease, and 

animals. The correlation for each group was not significant, indicating that just using 

time since the last fire is inadequate in predicting conifer mortality from these 

disturbance agent groups. Structures and compositions of the previous stands are 

unknown, as are the intensities and severities of the last fires. These variables, if 

known, might result in better correlations with conifer mortality in the current stands. 

Also, in stands where the last fire date was estimated, the range in number of years 

(62 to 127) since the last fire may be inadequate to demonstrate consistent differences 

in insect- and pathogen-induced mortality. 

The highest standing dead fuels were found in intermediate structural stages (fig. 

3), and the highest downed and dead fuels are found in the earlier structural stages 

and in old forest structure (fig. 2). Perhaps this is carryover from stand replacement 

events. Conifer mortality begins to increase in intermediate structural stages, 

primarily from wind, snow, ice, root diseases, and bark beetles. Wood decay rates are 

relatively slow in the eastern Cascade Mountains due to climatic factors, and as a 

result fuels increase faster than they decompose. 

In subalpine forests in Rocky Mountain National Park, Clagg (1975) found that 

total dead woody fuels increased immediately after a fire, quickly declined to a low 

point at about a stand age of 50 years, rapidly increased to a peak at 100 years, then 

gradually declined until about age 300 years, after which the fuel load remained 

almost constant. In a subalpine watershed in Yellowstone National Park, Romme 

(1982) found that heavy down fuel decreased during early successional stages 

between stand ages 70 and 200 years as large fire-killed stems decomposed, then 

fuels increased in later stages when natural mortality of mature trees began to occur. 

Maximum fuel loading was reached around 350 years. 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 523 

The average fire size was 146 ha ± 95 ha. Current tree harvest units do not 

mimic these sizes or their variability. The legal limitations imposed on sizes of 

harvest units conflict with the size of inherent disturbance regimes, and with the 

intent of ecosystem management. By targeting mid-slopes where lodgepole pine is 

dominant and where subalpine fir is increasing in the understory, multiple-use goals 

can be achieved. On these sites, thinning lodgepole pine and cutting subalpine fir 

would produce larger trees for wildlife and eventual harvest, increase resistance to 

bark beetles and weather (e.g., wind), and decrease potential dead and down fuel. The 

tradeoff is a short-term increase in fuels from logging slash. 

In the last half of this century, subalpine forests have become more uniform and 

dense (Covington and others 1994, Tande 1979), and have greater vulnerability to 

stand-replacing fire (Romme and Despain 1989). In the Northern Cascades 

Ecological Reporting Unit of the Columbia River Basin, there were no significant 

changes in fuel loading among fuel classes from the historical to the current period. 

Similarly, in the Wenatchee subwatershed, there were no significant changes in fuel 

loading from the historical to the current period (Huff 1995). However, in the 

Wenatchee subwatershed, there was a significant decrease in the number of forested 

stands with no dead trees, and a significant increase in the number of forested stands 

with from 1 to 10 percent dead trees (Lehmkuhl and others 1994). In this study, 

standing dead trees were more numerous than required for four species of 

woodpeckers, according to one study (Thomas and others 1979). Although some 

species of wildlife may currently benefit from the bounty, fuels and flammability of 

these forests are increasing, and the inevitable stand-replacing fires may be larger and 

more severe than were historical fires. 

References 

Anonymous. 1981. Atmospheric stability and instability. S-390 Fire Behavior, Unit VII, 

National Wildfire Coordinating Group; 8 p. 

Brown, James K. 1974. Handbook for inventorying downed woody material. Gen. Tech. 

Rep. INT-GTR-16. Fort Collins, CO: Intermountain Research Station, USDA Forest 

Service; 24 p. 

Bull, Evelyn L. 1983. Longevity of snags and their use by woodpeckers. In: Snag habitat 

management. Gen. Tech. Rep. INT-GTR-99. Fort Collins, CO: Intermountain Research 

Station, USDA Forest Service; 64-67. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, USDA Forest Service; 55 p. 

Clagg, Harry B. 1975. Fire ecology in high elevation forests in Colorado. Fort Collins: 

Colorado State University; 137 p. M.S. thesis. 

Covington, W. Wallace; Everett, Richard L.; Steele, Robert; Irwin, Larry L.; Daer, Tom A.; 

Auclair, Allen N. D. 1994. Historical and anticipated changes in forest ecosystems of 

the Inland West of the United States. Journal Sustainable Forestry 2(1/2): 13-63. 

Everett, Richard; Lehmkuhl, John; Schellhaas, Richard; Ohlson, Peter; Keenum, David; 

Riesterer, Heidi; Spurbeck, Donald. 1999. Snag dynamics in a chronosequence of 26 

wildfires on the east slope of the Cascade Range in Washington. International 

Journal of Wildland Fire 9(4): 223-234. 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

524 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Grissino-Mayer, Henri D. 1995. FHX2: Software for the analysis of fire history from tree 

rings. University of Arizona, Tucson: Laboratory of Tree-Ring Research. 

Hadfield, James S.; Magelssen, Roy W. 1997. Wood changes in fire-killed eastern 

Washington tree species—year two progress report. Unpublished draft on file at 

Wenatchee National Forest Supervisors Office, Wenatchee, Washington; 34 p. 

Hagle, Susan K.; Kegley, Sandra; Williams, Stephen B. 1995. Assessing pathogen and 

insect succession functions in forest ecosystems. In: Eskew, L. G., editor. Forest health 

through silviculture. Gen. Tech. Rep. RM-GTR-267. Fort Collins, CO: Rocky Mountain 

Research Station, USDA Forest Service; 117-127 p. 

Harvey, Robert D.; Hessburg, Paul F. 1992. Long-range planning for developed sites in the 

Pacific Northwest: The context of hazard tree management. USDA Forest Service 

FPM-TP039-92; 120 p. 

Huff, Mark H.; Ottmar, Roger D.; Alvarado, Ernesto; Vihnanek, Robert E.; Lehmkuhl, John 

F. Hessburg, Paul F.; Everett, Richard L. 1995. Historical and current forest 

landscapes in eastern Oregon and Washington. Part II: Linking vegetation 

characteristics to potential fire behavior and related smoke production. Gen. Tech. 

Rep. PNW-GTR-355. Portland, OR: Pacific Northwest Research Station, USDA Forest 

Service; 43 p. 

Johnson, Edward A.; Gutsell, Sheri L. 1994. Fire frequency models, methods, and 

interpretations. Advances in Ecological Research 25: 239-286. 

Keen, Frederick P. 1929. How soon do yellow pine snags fall? Journal of Forestry 27: 735-

737. 

Lehmkuhl, John F.; Hessburg, Paul F.; Everett, Richard L.; Huff, Mark H.; Ottmar, Roger D. 

1994. Historical and current landscapes of eastern Oregon and Washington. Gen. 

Tech. Rep. PNW-GTR-328. Portland, OR: Pacific Northwest Research Station, USDA 

Forest Service; 88 p. 

Lillybridge, Terry R.; Kovalchik, Bernard L.; Williams, Clinton K.; Smith, Bradley G. 1995. 

Field guide for forested plant associations of the Wenatchee National Forest. Gen. 

Tech. Rep. PNW-GTR-359. Portland, OR: Pacific Northwest Research Station, USDA 

Forest Service; 337 p. 

O'Hara, Kevin L.; Latham, Penelope A.; Hessburg, Paul F.; Smith, Bradley G. 1996. A 

structural classification for Inland Northwest forest vegetation. Western Journal 

Applied Forestry 11(3): 97-102. 

Oliver, Chadwick D. 1981. Forest development in North America following major 

disturbances. Forest Ecology Management 3: 153-168. 

Oliver, Chadwick D.; Larson, Bruce C. 1990. Forest Stand Dynamics. New York: McGrawHill, Inc; 467 p. 

Parry, David I.; Filip, Gregory M.; Willits, Susan A.; Parks, Catherine G. 1996. Lumber and 

deterioration of beetle-killed Douglas-fir in the Blue Mountains of eastern Oregon. 

Gen. Tech. Rep. PNW-GTR-376. Portland, OR: Pacific Northwest Research Station, 

USDA Forest Service; 24 p. 

Plummer, Fred G. 1902. Forest conditions in the Cascade Range, Washington. 

Professional Paper No. 6, Series H, Forestry 3. United States Geological Survey, 

Department of the Interior, Washington, DC: Government Printing Office; 42 p. 

Raphael, Martin; Morrison, Michael 1987. Decay and dynamics of snags in the Sierra 

Nevada, California. Forest Science 33(3): 774-783. 

Romme, William H. 1982. Fire and landscape diversity in subalpine forests of 

Yellowstone National Park. Ecological Monographs 52: 199-221. 
Snag Recruitment in Subalpine Forests—Flanagan, Morgan, and Everett 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 525 

Romme, William H.; Despain, Donald 1989. Historical perspective on the Yellowstone 

fires of 1988. Bioscience 39: 695-699. 

SAS. 1997. Statistical Analysis Systems. Release 6.12. Cary, North Carolina: SAS Institute 

Inc. 

Tande, Gerald F. 1979. Fire history and vegetation pattern of coniferous forests in Jasper 

National Park, Alberta. Canadian Journal Botany 57: 1912-1931. 

Thomas, Jack W.; Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: 

Thomas, J. W., editor. Wildlife habitats in managed forests. Agric. Handb. No. 553. 

Washington, DC: USDA Forest Service; 60-77. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 527 

DecAID: A Decaying Wood Advisory Model 

for Oregon and Washington1 

Kim Mellen,2 Bruce G. Marcot,3 Janet L. Ohmann,4 Karen L. 

Waddell,3 Elizabeth A. Willhite,5 Bruce B. Hostetler,5 Susan A. 

Livingston,6

 and Cay Ogden7 

Abstract 

DecAID is a knowledge-based advisory model that provides guidance to managers in 

determining the size, amount, and distribution of dead and decaying wood (dead and partially 

dead trees and down wood) necessary to maintain wildlife habitat and ecosystem functions. 

The intent of the model is to update and replace existing snag-wildlife models in Washington 

and Oregon. Whereas the relationship of dead and decaying wood to wildlife habitat is a 

major component of the model, DecAID will also provide expert advice on prescribing and 

interpreting conditions of dead wood for wildland and prescribed fire and fuels, pest and nonpest insects, pathogens and non-pathogenic fungi, and use of inventory data to describe 

current managed and natural levels of dead wood. The model also produces a list of 

ecosystem functions performed by species associated with dead and decaying wood. Advice 

on the distribution of dead wood at the stand and landscape scale is provided in the model. 

Introduction 

Models have been developed in the past to provide managers with tools by 

which they can determine snag sizes (diameter at breast height or dbh) and densities 

(number of snags per unit area) needed to maintain snag-dependent wildlife. These 

models focus on needs of primary cavity excavating species of birds (woodpeckers, 

nuthatches, and chickadees) (Neitro and others 1985, Thomas and others 1979). No 

similar models have been developed for down wood, largely because until recently 

there have been no empirical data relating wildlife species and population densities to 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Regional Wildlife Ecologist, Pacific Northwest Region, USDA Forest Service, P.O. Box 3623, 

Portland, OR 97208 (e-mail: kmellen@fs.fed.us) 

3

 Research Wildlife Ecologist and Research Forester, respectively, Pacific Northwest Research Station, 

USDA Forest Service, 620 S.W. Main Street, Portland, OR 97208 (e-mail: bmarcot@fs.fed.us and 

kwaddell@fs.fed.us) 

4

 Research Forester, Pacific Northwest Research Station, USDA Forest Service, 3200 SW Jefferson 

Way, Corvallis, Oregon 97331 (e-mail: johmann@fs.fed.us) 

5

 Entomologist and Entomologist, respectively, Mt. Hood National Forest, USDA Forest Service, 16400 

Champion Way, Sandy, OR 97055 (e-mail addresses: bwillhite@fs.fed.us and bhostetler@fs.fed.us) 6

 Wildlife Biologist, Oregon State Office, Fish and Wildlife Service, U.S. Department of the Interior, 

2600 SE 98th Ave., Suite 100, Portland, OR 97266-1398 (e-mail: sue_livingston@fws.gov) 7

 Regional Wildlife Ecologist, Intermountain Region, National Park Service, 12795 Alameda Parkway, 

Denver, CO 80225 (e-mail: cogden@nps.gov) 
DecAID Overview—Mellen, Marcot, Ohmann, Waddell, Willhite, Hostetler, Livingston, and Ogden 

528 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

down wood conditions and amounts in Oregon and Washington. Our new model, 

DecAID (Decayed Wood Advisory Model), is intended to replace the currently used 

models for determining snag numbers. DecAID will help resource specialists 

determine how to manage for the amount, type, and distribution of all types of dead 

wood within forest stands and across landscapes. 

DecAID is being developed as part of an update to the existing wildlife habitat 

relationships books for Washington and Oregon (Brown 1985, Maser and others 

1984, Thomas 1979) in a new book entitled Wildlife-Habitat Relationships in Oregon 

and Washington, hereafter referred to as the Species-Habitat Project (SHP). The 

Oregon Department of Fish and Wildlife and Washington Department of Fish and 

Wildlife are leading this effort. The USDA Forest Service is a major partner. DecAID 

is a work in progress; this paper is a report on the current status of the model (Marcot 

and others 2002, Ohmann and Waddell 2002). 

Existing Models 

Existing models of the relationships between wildlife species and snags in the 

Pacific Northwest typically are based on calculating potential densities of bird 

species and expected number of snags used per pair. This approach was first used by 

Thomas and others (1979). Marcot expanded this approach in Neitro and others 

(1985) and in the subsequent Snag Recruitment Simulator (Marcot 1992) by using 

published estimates of bird population densities instead of calculating population 

densities from pair home range sizes. 

Recently there has been criticism of the existing modeling approach, in part 

because the numbers of snags suggested by the models seem far lower than are now 

being observed in field studies (Bull and others 1997, Lundquist and Mariani 1991). 

The existing models have also focused just on snags and have provided only 

deterministic point values of snag sizes or densities and of population response 

(“population potential”) instead of probabilistic estimates more amenable to a risk 

analysis and risk management framework. 

The existing models have focused on terrestrial vertebrate species that are 

primary cavity excavators. The assumption made by Thomas and others (1979) and 

Marcot (1992) is that secondary snag-using species would be fully provided for if 

needs of primary snag-excavating species were met. McComb and others (1992) and 

Schreiber (1987) indicate that secondary cavity nesting birds may be more sensitive 

to snag density than primary cavity excavators. The existing models also do not 

account for species that use different types of snags and partially dead trees, such as 

hollow live and dead trees used by bats (Betts 1998, Campbell and others 1996, 

Ormsbee and McComb 1998) and Vaux’s swift (Bull and Cooper 1990, Bull and 

Hohmann 1993). These new findings are important to improving dead wood models 

for wildlife. 

A New Model: DecAID 

Our goal for developing the DecAID model was to advise managers on the 

numbers, sizes, species, and decay classes of dead wood needed to help maintain 

wildlife habitat and ecosystem functions in forests. We intend for the model to 

provide such advice by wildlife habitat and management objective. In addition to 
DecAID Overview—Mellen, Marcot, Ohmann, Waddell, Willhite, Hostetler, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 529 

snags and down logs, the advisory model will address diseased, partially dead, or 

decaying live trees, including hollow trees, as important wildlife habitat components. 

Whereas providing advice on maintaining wildlife habitat will be a main objective of 

the model, the model will be ecosystem-based and also provide information on 

ecosystem functions performed by wildlife associated with dead wood, maintenance 

of ecological function (e.g., soil productivity), roles of insects and diseases in the 

creation and dynamics of dead wood, and management of fire (fig. 1). The modeling 

process will also help identify gaps in knowledge of dead wood as wildlife habitat 

and its role in ecosystem processes. 

User Inputs 

Three pieces of information will be required as user inputs: wildlife habitat type, 

structure stage, and management objective (fig. 1). The first input, wildlife habitat 

type, is defined by the SHP (Johnson and O’Neil 2001). Examples include major 

vegetation alliances such as eastside mixed-conifer forest, southwest Oregon mixedconifer/hardwood forest, and westside lowlands conifer/hardwood forest (Marcot and 

others 2002). The SHP describes 26 structural stages, which are combined into three 

successional stages for analysis of inventory data (Johnson and O’Neil 2001). The 

successional stages are early, mid-, and late-successional forests (Ohmann and 

Waddell 2002). For species use data we combined the mid- and late-successional 

stages into one class due to the way most data were reported in the literature. The 

management objective is based on the landowner’s expectations for managing for 

ecosystem function and diversity. Management objectives relate to statistical 

tolerance levels for managing for species and functions based on empirical data on 

species-dead wood relations. High, moderate, and low statistical levels have been 

developed (Marcot and others 2002). High confidence level might be applicable 

where maintaining or restoring ecosystem functions is the objective: for example, 

late-successional reserves from the Northwest Forest Plan. Low confidence levels 

might apply where maintaining some wildlife habitat and some level of ecosystem 

function such as site productivity are desired, but timber harvest is the main 

objective. 

Species-Dead Wood Relations 

The wildlife or species component of DecAID focuses on species needs for 

sizes, amounts, and distribution of dead wood, primarily snags and down wood. We 

extensively reviewed the literature, contacted researchers, and summarized 

quantitative data on dead and decaying wood relationships of fungi, amphibians, 

birds, and mammals. We found many data gaps for some habitats and species groups. 

To make the model as complete as possible, we used unpublished data to fill in some 

of the gaps. We arranged the species use data into three cumulative species curves 

representing high, moderate, and low statistical levels for each combination of 

wildlife habitat type and structure stage for which data were available (Marcot and 

others 2002). Expert opinion was used to help interpret the data and species curves. 

The DecAID output produces a list of wildlife species associated with dead 

wood and a list of ecological functions performed by those species (fig. 1). We 

queried data matrices developed by the SHP to develop the lists. One query links to a 

Habitat Features database that lists species associations with different types and 
DecAID Overview—Mellen, Marcot, Ohmann, Waddell, Willhite, Hostetler, Livingston, and Ogden 

530 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

amounts of dead and decaying wood, including snags, remnant trees (that possibly 

have some dead parts), mistletoe and witch’s brooms, dead parts of live trees, hollow 

trees, tree cavities, bark crevices, down wood, litter, and duff. Lists of species 

associated with these elements can be linked to a Key Ecological Functions database 

to produce a list of functions the dead-wood-associated species perform in the 

ecosystem. 

Figure 1—Flowchart of the DecAID model. 

Inventory Data 

We are using inventory data from nearly 17,000 Forest Service Continuous 

Vegetation Survey (CVS) and Forest Inventory and Analysis (FIA) plots, and USDI 

Bureau of Land Management Natural Resource Inventory (NRI) plots to estimate 

current amounts and condition of dead wood across private and public lands in 

Oregon and Washington (Ohmann and Waddell 2002). The data are stratified by 

wildlife habitat type and structure stage. Data from plots in reserved areas, which we 

assume to represent unharvested conditions, are used to estimate range of natural 

conditions (RNC) or historic levels of dead wood. This approach works better for 

wetter areas west of the Cascade crest where fire suppression has had less influence 

on dead wood resources than in drier habitats. In some Wildlife Habitat Types, 

especially east of the Cascade crest, a combination of fire suppression, insect 

outbreaks, salvage, and firewood cutting might limit our ability to determine natural 

levels of dead wood based on existing conditions. In these areas, models such as that 

of Harrod and others (1998) may provide more realistic benchmarks for natural levels 

of dead wood. 
DecAID Overview—Mellen, Marcot, Ohmann, Waddell, Willhite, Hostetler, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 531 

In DecAID, the information based on species’ use of dead wood is compared to 

sizes and amounts of dead wood in unharvested stands. This comparison assists in 

determining if species are using dead wood at different levels than commonly occur 

in natural stands, and the potential of a stand to produce dead wood. The inventory 

data can also give us some ideas about distribution of dead wood in natural systems. 

We should also be able to show how well current conditions are meeting species 

needs and how closely current conditions reflect RNC. 

Natural Processes 

Insects and Diseases 

The influence of insects and diseases (used here to include pathogenic and 

decay-causing fungi and dwarf mistletoes) on recruitment of dead wood through time 

is assessed in the model. We obtained occurrence and severity frequencies of plots or 

trees affected by selected insect and/or disease species from the inventory data for 

each wildlife habitat type and structure stage. This portion of the model provides a 

list of the insects and diseases that are most likely to generate dead or decaying wood 

in each habitat. DecAID will then provide generalized predictions about the future 

amounts and types of dead and decaying wood that may occur naturally in stands. 

Each type of insect or disease produces a different type of dead wood or decay that 

subsequently may provide a different function for dead-wood-associated species. 

This portion of the model also will provide advice on how to mitigate or intensify the 

activity of these agents to decrease or increase dead wood recruitment. 

Fire 

The fire portion of DecAID has not yet been developed. Our plan is to assess the 

fire likelihoods associated with the amount and distribution of dead wood indicated 

by species use data. Information will be provided to help the land manager balance 

the needs of species with the risk of catastrophic fire. 

Ecosystem Function 

Our intent for this portion of the model is to provide qualitative and, where 

available, quantitative information on ecosystem functions affected by decadent 

wood, such as soil productivity, moisture retention, and slope stability. At this point, 

the time and funding necessary to complete a thorough literature review for these 

data are not available. We plan to use the qualitative information to provide a 

narrative review of the importance of dead and decaying wood to ecosystem 

functions (fig. 1). 

Summary 

DecAID is a new decayed wood advisory model currently being developed. 

Displaying the relationship of dead and decaying wood to wildlife habitat and species 

is a major component of the model. DecAID also provides advice on dead and 

decaying wood as an important component of ecosystems and the relationship of 

dead and decaying wood to natural processes. Inventory data are used to compare 

species needs to current amounts of dead wood in managed and unharvested forests. 
DecAID Overview—Mellen, Marcot, Ohmann, Waddell, Willhite, Hostetler, Livingston, and Ogden 

532 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Acknowledgments 

We thank Lisa Bate and Mark Huff for their reviews of earlier drafts of this 

manuscript. 

References 

Betts, Burr J. 1998. Roosts used by maternity colonies of silver-haired bats in 

northeastern Oregon. Journal of Mammology 79(2): 643-650. 

Brown, E. Reade, technical editor. 1985. Management of wildlife and fish habitats in 

forests of western Oregon and Washington. R6-F&WL-192-1985. Portland, OR: 

Pacific Northwest Region, Forest Service, U.S. Department of Agriculture; 332 p. 

Bull, Evelyn L.; Cooper, Howard D. 1990. Vaux’s swift nests in hollow trees. Western Birds 

22: 85-91. 

Bull, Evelyn L.; Hohmann, Janet E. 1993. The association between Vaux’s swifts and old 

growth forests in northeastern Oregon. Western Birds 24: 38-42. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Campbell, Lori A; Hallett, James G.; O’Connell, Margaret A. 1996. Conservation of bats in 

managed forests: use of roosts by Lasionycteris noctivagans. Journal of Mammalogy 

77: 976-984. 

Harrod, Richy J.; Gaines, William L.; Hartl, William E.; Camp, Ann. 1998. Estimating 

historical snag density in dry forests east of the Cascade Range. Gen. Tech. Rep. 

PNW-GTR-428. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 16 p. 

Johnson, David H.; O’Neil, Thomas A., managing directors. 2001. Wildlife-habitat 

relationships in Oregon and Washington. Corvallis, OR: Oregon State University 

Press; 736 p. 

Lundquist, Richard W.; Mariani, Jina M. 1991. Nesting habitat and abundance of snagdependent birds in the southern Washington Cascade Range. In: Ruggerio, Leonard 

F.; Aubry, Keith B.; Carey, Andrew B.; Huff, Mark H., technical coordinators. Wildlife 

and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 221-240. 

Marcot, Bruce G.; Mellen, Kim; Livingston, Susan A.; Ogden, Cay. 2002. The DecAID 

advisory model: wildlife component. In: Laudenslayer, William F., Jr.; Shea, Patrick 

J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Marcot, Bruce G. Snag recruitment simulator, Rel. 3.1 [Computer program]. 1992. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture. Available from: Pacific Northwest Research Station. P.O. Box 3890, 

Portland, OR 97208. 

Maser, Chris; Thomas, Jack W.; Anderson, Ralph A. 1984. Wildlife habitats in managed 

rangelands – the great basins of southeastern Oregon. Gen. Tech. Rep. PNW-GTR-
DecAID Overview—Mellen, Marcot, Ohmann, Waddell, Willhite, Hostetler, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 533 

172. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department 

of Agriculture. 

McComb, Bill; McGarigal, Kevin; Hope, Sharon; Hunter, Matt. 1992. Monitoring cavitynesting bird use in clearcuts and watersheds on western Oregon National Forests.

Unpublished progress report. Corvallis, OR: Department of Forest Sciences, Oregon 

State University; 48 p. 

Neitro, William A.; Bindley, Virgil W.; Cline, Steven P.; Mannan, R. William; Marcot, Bruce 

G.; Taylor, Douglas; Wagner, Frank F. 1985. Snags (wildlife trees). In: Brown, E. 

Reade, technical editor. Management of wildlife and fish habitats in forests of western 

Oregon and Washington. R6-F&WL-192-1985. Portland, OR: Pacific Northwest 

Region, Forest Service, U.S. Department of Agriculture; 129-169. 

Ohmann, Janet L.; Waddell, Karen L. 2002. Regional patterns of dead wood in forested 

habitats of Oregon and Washington. In: Laudenslayer, William F., Jr.; Shea, Patrick 

J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Ormsbee, Patricia C.; McComb, William C. 1998. Selection of day roosts by female longlegged myotis in the central Oregon Cascade Range. Journal of Wildlife Management 

62(2): 596-603. 

Schreiber, Barry. 1987. Diurnal use of snags on clearcuts in central coastal Oregon.

Corvallis: Oregon State University; 63 p. M.S. thesis. 

Thomas, Jack W., technical editor. 1979. Wildlife habitats in managed forests: the Blue 

Mountains of Oregon and Washington. Agric. Handb. 553. Washington, D.C. U.S. 

Department of Agriculture; 512 p. 

Thomas, Jack W.; Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: 

Thomas, Jack W., technical editor. Wildlife habitats in managed forests: the Blue 

Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC; U.S. 

Department of Agriculture; 60-77. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 535 

Regional Patterns of Dead Wood in 

Forested Habitats of Oregon and 

Washington1 

Janet L. Ohmann2 and Karen L. Waddell3

Abstract 

We describe regional patterns of variation in dead wood across 20 million ha of upland forests 

of all ownerships in Oregon and Washington, based on an analysis of data on snags and down 

wood collected on over 16,000 field plots. Current patterns of dead wood are highly variable 

and complex. The strongest differences were among nine habitats that reflect strong regional 

gradients in physical environment and ecosystem processes. Mean snag density was lowest in 

the drier habitats east of the Cascade crest and greatest at higher elevations, ranging from 

0.8/ha to 37.2/ha. The mean volume of down wood ranged from 7.4 m3

/ha in western juniper 

woodland to 183.3 m3/ha in westside conifer-hardwood forest. Differences in dead wood were 

more pronounced among habitats west of the Cascade crest. Dead wood abundance generally 

increased with successional development. Large snags were more than twice as dense within 

wilderness areas than outside wilderness, whereas large down wood was more abundant 

outside wilderness. Dead wood on plots was non-normally distributed and skewed to the right. 

Information on regional patterns of variation in dead wood is being incorporated into the 

DecAID model, which will help guide managers in considering dead wood and processes of 

decomposition in forest management. The regional summaries of dead wood also can be used 

to evaluate forest practice regulations and incentive programs for non-Federal lands, and to 

assess wildlife habitat suitability, ecosystem health, and carbon stores at state, regional, and 

national levels. 

Introduction 

Dead trees are important elements of productive and biologically diverse forests. 

Dead trees form major structural features with many ecological functions, including 

habitat for organisms, energy flow and nutrient cycling, and geomorphic processes 

(Harmon and others 1986). Yet, little is known about how amounts and 

characteristics of dead wood vary across broad regions that encompass a wide range 

of ecological conditions and disturbance histories. 

Although the bulk of published data is from small-scale ecological plots, other 

forms of data exist but have not been analyzed. For example, resource inventories by 

Federal agencies include a wealth of information on snags (standing dead trees) and 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Forester, Pacific Northwest Research Station, USDA Forest Service, 3200 SW Jefferson 

Way, Corvallis, Oregon 97331 (e-mail: johmann@fs.fed.us) 

3

 Research Forester, Pacific Northwest Research Station, USDA Forest Service, P.O. Box 3890, 

Portland, Oregon, 97208 (e-mail: kwaddell@fs.fed.us) 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

536 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

down wood (fallen trees) across the Pacific Northwest. This study describes current 

patterns of dead wood in Oregon and Washington by analyzing data collected on 

regional grids of field plots. In this paper we present a preliminary analysis of dead 

wood abundance in wildlife habitats of upland forests (“habitats”). We focused on 9 

of the 31 major habitats that were developed for the Species Habitat Project 

(Chappell and others 2001). Our goal was to provide basic information about 

ecological patterns, as context for management decisions at stand, landscape, and 

ecoregion scales, and for analyzing forest policies at regional and national levels. 

Study Area 

The study area encompasses a region of temperate forest within the states of 

Washington and Oregon. The Cascade Range is the major topographic and climatic 

divide, and in this paper we refer to areas west of the Cascade crest as “westside” and 

east of the crest as “eastside.” Elevations range from sea level to nearly 3,000 m. 

Vulcanism shaped much of the landscape, but sedimentary and metamorphic rocks 

are plentiful, and deposition of parent materials by alluvial, colluvial, and eolian 

processes is common. Soil types are primarily inceptisols, spodosols, and ultisols. 

The westside has a maritime climate with wet winters and dry summers, and the 

eastside climate is drier and more continental. 

Forests cover 19.6 million ha in the study area, about half of which is publicly 

owned (Powell and others 1993). Forests are dominated by coniferous trees (Franklin 

and Dyrness 1988). Hardwoods tend to occupy harsh sites, riparian areas, or 

disturbed areas, except in southwest Oregon. The mesic temperate coniferous forests 

of northwestern Washington and Oregon contain the greatest biomass accumulation 

and highest productivity rates in the world (Waring and Franklin 1979). See Franklin 

and Dyrness (1988) and Ohmann and Spies (1998) for detailed descriptions of 

Washington and Oregon plant communities and environmental gradients. 

Before European settlement, fire was the predominant natural disturbance (Agee 

1993), but in the last 100 years timber management and wildfire suppression have 

altered forest succession. Even-aged forest management practices are most common 

in northwestern Oregon and Washington, whereas uneven-aged management 

predominates in southwestern Oregon and on the eastside. On the eastside, fire 

suppression has allowed fire-sensitive and late-successional tree species to increase 

in density, and selective harvests have influenced forest composition. 

Source of Data and Sample Design 

Data on dead wood have been collected from extensive grids of field plots as 

part of ongoing, strategic-level inventories conducted by the USDA Forest Service in 

the Pacific Northwest for many years, and more recently by the USDI Bureau of 

Land Management (BLM) (table 1). National, state, and county parks and privately 

owned reserves had not been surveyed at the time of this study. Because plots were 

installed throughout the study area in a systematic fashion, the diversity of forests 

found in both states was sampled. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 537 

Table 1―Sources of data on live trees, snags, and down wood from regional forest 

inventories in Oregon and Washington. 

Inventory 

program 

Ownerships 

sampled 

Sample grid 

spacing1 

Sample 

weight2

Inventory 

dates

Number of 

plots3 

Forest 

Inventory 

and 

Analysis 

(FIA) 

Non-Federal 5.5 km 1.0 1984-1991 43,994 

2.7 km 

outside 

wilderness 

Current 0.25 1991-1995 11,958 

Vegetation 

Survey 

(CVS) 

National 

Forest 

5.5 km 

inside 

wilderness 

1.0 1991-1995 580 

Natural 

Resource 

Inventory 

(NRI) 

Bureau of 

Land 

Management 

in western 

Oregon 

5.5 km 1.0 1997 335 

1

 Plots on the 5.5-km grid represent about 3,000 ha; plots on the 2.7-km grid represent about 750 ha. 2

 Weight applied to plot-level dead wood data in computing descriptive statistics. For NRI and CVS 

plots with multiple condition classes, weights were reduced proportional to the area occupied. 3

 Includes only those plots on which dead wood data were collected. Does not include 319 plots in 

aspen, dunes, riparian, and wetland habitats. 

4

 Down wood data collected only on 886 plots in eastern Washington. Snag data collected on all plots. 

The inventories provided data on stand characteristics, live trees, snags, and 

down wood collected on 16,867 field plots from 1984-1997 on forest land across 

Oregon and Washington (fig. 1). Field plots consisted of a cluster of up to five 

subplots and included a series of fixed- and variable-radius circular plots. The Forest 

Inventory and Analysis (FIA) plot was confined to a single, homogenous forest 

condition by moving subplots according to a predetermined pattern. In contrast, the 

Current Vegetation Survey (CVS) and Natural Resource Inventory (NRI) subplots 

were installed in fixed positions, and the plot could encompass multiple forest 

conditions. Live trees and snags were sampled on circular plots, and down wood was 

sampled along transect lines (DeVries 1973, Waddell 2002) established within plot 

boundaries. The species, diameter at breast height (DBH), and decay class (adapted 

from Cline and others 1980) were recorded for each snag tallied. Down wood 

measurements included the species, diameter at the point of intersection and at large 

end, piece length, decay class, and evidence of use by wildlife. Detailed information 

about inventory sample designs, field procedures, and compilation methods are 

available from the individual agencies that conducted the inventories (see also Max 

and others 1996, USDA Forest Service 1992, CVS Web site “www.fs.fed. 

us/r6/survey”). 

We assigned each plot to an ecoregion (U.S. Environmental Protection Agency 

1995) by overlaying the plot locations on the ecoregion map in a geographic 

information system (GIS). We also obtained data from the agencies on the reserve 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

538 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

status of each plot. Plots were coded as within areas set aside by Congress 

(Wilderness and Wild and Scenic Rivers), by agency administration or as unreserved. 

Figure 1―Locations of Natural Resources Inventory (NRI), Current Vegetation 

Survey (CVS), and Forest Inventory and Analysis (FIA) field plots used in this study, 

Oregon and Washington. Only those plots where dead wood data were collected are 

shown. Black symbols are plots on Federal lands (NRI and CVS); gray symbols are 

plots on non-Federal lands (FIA).
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 539 

Data Compilation and Analysis 

We compiled the source data from the three inventories into one database that 

contains data tables for stand-level attributes, live trees, snags, and down wood. This 

involved converting codes and measurement units, calculating new variables, and 

making other technical modifications to insure that all data were in a common format 

for regional analysis. We calculated new variables from the down wood data 

collected with the line intersect sampling method to produce per-hectare estimates of 

down wood density (number of pieces), volume, and percent cover for each inventory 

plot (DeVries 1973, Waddell 2002). We also calculated per-hectare estimates of snag 

density. We were not able to compute snag volume at the time of this writing because 

many snag heights were missing in the CVS and NRI data. 

We evaluated the CVS and NRI plots for the presence of multiple forest 

conditions. If a plot encompassed more than one land class (forest or nonforest), or 

more than one vegetation series (defined by the tree species that would dominate the 

site in the absence of disturbance) within forest land, we identified separate 

condition-classes on the plot. The live and dead tree data were partitioned among the 

condition-classes accordingly. We treated these condition-class plots as independent 

observations in our analyses, and refer to them simply as “plots” in this paper. 

Stand-level variables and live tree data were used to classify each plot into a 

wildlife habitat type (“habitat”), alliance group, and successional stage. We used the 

habitats and some of the alliances from the classification system defined by the 

Species Habitat Project (Chappell and others 2001). We developed classification 

algorithms that utilized the set of variables we had available in the inventory 

database. Habitat was determined by evaluating the potential vegetation (series) and 

ecoregion assigned to the plot, and alliance was determined by examining a 

combination of potential and current vegetation variables as follows (scientific names 

of tree species are listed in appendix A): 

Habitat and alliance group Definition 

 

Westside conifer-hardwood type: Western redcedar, Sitka spruce, western 

hemlock, grand fir, white fir, and Port-Orford 

cedar series in westside ecoregions. 

 Hardwood alliance Hardwoods >70 pct and conifers <30 pct of 

stocking1

 Conifer-hardwood mixed alliance Hardwoods 31-69 pct and conifers 31-69 pct 

of stocking1

 Conifer alliance Hardwoods <30 pct and conifers >70 pct of 

stocking1

; not a Sitka spruce site (see below). 

 Sitka spruce/western hemlock alliance Hardwoods <30 pct and conifers >70 pct of 

stocking1

; Sitka spruce series or Sitka spruce 

present. 

Westside white oak-Douglas-fir type: Douglas-fir or Oregon white oak series in 

westside ecoregions. 

 Douglas-fir alliance Douglas-fir series outside southwest Oregon; 

Oregon white oak absent. 

 Douglas-fir/white oak alliance Oregon white oak series or Oregon white oak 

present. 

Southwest Oregon mixed conifer-hardwood 

type 

Ponderosa pine, Douglas-fir, jeffrey pine, 

grand fir, white fir, Port-Orford cedar, 

tanoak, or canyon live oak series in 

southwest Oregon. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

540 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Habitat and alliance group Definition 

Montane mixed-conifer type Engelmann spruce, noble fir, Shasta red fir, 

Pacific silver fir, subalpine fir, and mountain 

hemlock series. 

Subalpine parkland type Open parkland series of subalpine fir, 

mountain hemlock, subalpine larch, Alaska 

yellow-cedar, and whitebark pine. 

Eastside mixed-conifer type Douglas-fir, grand fir, white fir, western 

redcedar, western hemlock, and noble fir 

series in eastside ecoregions. 

Lodgepole pine type Lodgepole pine series in eastside ecoregions. 

Eastside ponderosa pine type: Ponderosa pine, Oregon white oak, and black 

oak series in eastside ecoregions. 

 Ponderosa pine/Douglas-fir alliance Oregon white and black oak absent. 

 Ponderosa pine/white oak alliance Oregon white or black oak present. 

 

Western juniper type Western juniper series. 

1

 Relative stocking of all live trees in the stand, sensu Maclean (1979). 

The Species Habitat Project (Chappell and others 2001) identified 26 structural 

stages of forest vegetation that are important as wildlife habitat. Because this 

classification system was too complex for our region-wide analysis, we grouped the 

26 structural stages into three successional stages that we assume to be correlated 

with stand age or time since major disturbance. The stages were defined by current 

vegetation structure as follows: 

 Successional Stage Definition 

 

Early Tree stocking1

 < 10 percent, or tree stocking >10 percent and 

 quadratic mean diameter2

 ranging from 2.5-24.9 cm. 

Middle Tree stocking >10 percent and quadratic mean diameter2

 ranging 

 from 25.0-49.9 cm. 

Late Tree stocking >10 percent and quadratic mean diameter2

 >

50.0 cm. 

___________________________________________________________________ 

 1

 Relative stocking of all live trees in the stand on the plot, sensu Maclean (1979). 2 The diameter of the tree of average cross-sectional area at breast height (1.37 m) on the plot. 

We computed descriptive statistics for snags and down wood within habitats by 

weighting the plots according to the sampling grid intensity (table 1) and the 

proportion of the plot within the condition-class. We summarized the characteristics 

of snags and down wood only for habitats and successional stages sampled by at least 

10 plots. Wetlands, coastal dunes, aspen, and riparian forests were not well 

represented in the inventory sample and were excluded from our analysis. 

We evaluated differences in dead wood among habitats using analysis of 

variance for unbalanced designs, with observations (plots) weighted as described 

above, using generalized linear models in SAS (SAS Institute Inc. 1988). We 

compared successional stages within each habitat and alliance and compared habitats 

with all successional stages combined. Where overall F tests were significant (alpha 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 541 

> 0.05), we conducted multiple comparisons of means using the Tukey-Kramer 

method (SAS Institute Inc. 1988). 

Because we used data collected from different sampling designs, a variety of 

tree tally criteria were applied in the field. Our snag and down wood analyses include 

trees of the following characteristics common to all datasets: snags >25.4 cm DBH 

and >2.0 m tall of decay classes 1-5; down wood >12.5 cm diameter at point of 

intersection and >2.0 m long of decay classes 1-5 (except decay classes 1-4 for FIA 

plots). We summarize dead wood for two groups: “total snags” or “total down 

wood,” which includes snags >25.4 cm DBH or down wood > 12.5 cm diameter at 

large end; and “large snags” or “large down wood,” which includes snags >50 cm 

DBH or down wood > 50 cm diameter at large end. 

Results 

Differences in Dead Wood Among Habitats and Alliances 

We present snag results in terms of density (tables 2-3), and down wood in 

terms of volume (tables 4-5), cover (tables 6-7), and density (tables 8-9). We limit 

our discussion of down wood to volume, but patterns of cover and density were 

similar. All results represent weighted means of plot-level, per-hectare estimates for a 

category of interest. 

The abundance of snags and down wood varied substantially across the region. 

The greatest differences in dead wood were among the habitats, although differences 

among successional stages within habitats also were significant in many cases. Total 

snag densities were greatest at higher elevations: 37.2/ha in montane mixed-conifer 

forest and 36.0/ha in subalpine parks (table 2). Snags were least dense in the drier 

habitats on the eastside: 0.8/ha in western juniper woodland and 5.0/ha in eastside 

ponderosa pine (table 2). Large snags were most abundant in montane mixed-conifer 

forest (9.6/ha) and in westside conifer-hardwood forest (5.5/ha), and least abundant 

in western juniper woodland (0.2/ha) and eastside ponderosa pine woodland (1.0/ha) 

(table 3). The volumes of both total and large down wood were greatest in westside 

conifer-hardwood forest and lowest in western juniper woodland (table 4). Total 

down wood volume among habitats ranged from 7.4 to 183.3 m3

/ha and large wood 

from 4.5 to 131.8 m3

/ha. 

Pairwise differences in total dead wood generally were more pronounced among 

habitats west of the Cascades than among the eastside types. Differences between 

westside habitats (conifer-hardwood, white oak-Douglas-fir, southwest Oregon 

mixed conifer-hardwood) were always significant for both snags and down wood. 

The amounts of total snags and down wood in montane mixed-conifer forests were 

significantly different from almost all other habitats. 

Successional Patterns of Dead Wood 

Snag density generally increased with stand development. Within habitats and 

alliances, total snag density always was lowest in the early successional stage and 

usually was highest in the late stage (table 2). The abundance of large snags 

increased with successional development in all of the habitats and alliances except 

the hardwood alliance of westside conifer-hardwood forest and in western juniper 

woodland, where differences were not significant (table 3). Differences in snag 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

542 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

density were significant between at least two successional stages in all of the habitats 

and alliances except the hardwood alliance of westside conifer-hardwood forest, the 

eastside ponderosa pine alliances, and western juniper woodland (tables 2-3). 

The volume of down wood also generally increased with forest development, 

but successional patterns differed somewhat among the habitats and alliances (tables 

4-5). Late successional stages contained the largest concentrations of both total and 

large down wood in most of the habitats and alliances (tables 4-5). In the westside 

habitats and in montane mixed-conifer forest, down wood volume in the late stage 

usually was significantly different from the early and middle stages, but early and 

middle stages usually were not significantly different from one another (tables 4-5).

Large down wood volumes differed significantly between the early and middle 

successional stages in all of the eastside habitats and alliances except the ponderosa 

pine/white oak alliance and western juniper woodland (table 5). 

Table 2―Weighted mean (standard error) density of “total” snags >25.4 cm DBH, decay 

classes 1-5, and >2 m tall by habitat, alliance, and successional stage, Oregon and 

Washington.1

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 Mean (SE) trees per hectare 

Westside conifer-hardwood: 

 Hardwood 5.6 (1.1) 13.3 (1.2) 9.3 (3.6) 11.0 (0.9) 

 Conifer-hardwood mixed a

5.3 (0.8) b12.3 (0.9) b14.6 (1.9) 10.2 (0.6) 

 Conifer a

5.2 (0.4) b21.4 (0.8) c34.0 (1.1) 16.1 (0.5) 

 Sitka spruce/western 

 hemlock 

a

4.3 (0.7) b16.1 (1.4) b27.8 (3.1) 12.4 (0.9) 

 All alliances a

5.1 (0.3) b17.9 (0.6) c31.4 (1.0) 14.3 (0.3) 

 

Westside white oak-Douglas-fir: 

 Douglas-fir 6.5 (2.3) 12.2 (2.0) 20.7 (4.0) 11.6 (1.5) 

 Douglas-fir/white oak a

6.1 (1.3) a10.6 (1.3) b14.5 (3.0) 9.3 (0.9) 

 All alliances a

6.3 (1.1) a11.3 (1.1) b17.1 (2.5) 10.2 (0.8) 

Southwest Oregon mixed coniferhardwood 

a

9.5 (1.1) b17.1 (0.9) b21.0 (1.0) 15.4 (0.6) 

Montane mixed-conifer a

17.8 (1.4) b49.3 (1.3) c40.3 (1.4) 37.2 (0.9) 

Subalpine parkland 34.8 (7.4) 37.3 (4.3) 2 NA 36.0 (4.3) 

Eastside mixed-conifer a

14.8 (0.9) b21.5 (0.6) 20.7 (1.6) 19.4 (0.5) 

Lodgepole pine a

16.5 (1.5) b27.6 (2.6) 2 NA 19.8 (1.3) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas-fir 4.8 (0.5) 4.8 (0.4) 5.3 (0.8) 4.8 (0.3) 

 Ponderosa pine/white oak 7.1 (1.6) 7.5 (1.9) 2 NA 7.1 (1.2) 

 All alliances 5.0 (0.4) 5.0 (0.4) 5.2 (0.8) 5.0 (0.3) 

Western juniper 0.7 (0.2) 1.6 (0.4) 0.8 (0.5) 0.8 (0.2) 

All habitats a

9.1 (0.3) b21.3 (0.3) c28.4 (0.6) 17.4 (0.2) 1

 Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes.

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 543 

Table 3―Weighted mean (standard error) density of “large” snags >50.0 cm DBH, decay 

classes 1-5, and >2 m tall by habitat, alliance, and successional stage, Oregon and 

Washington.1

 

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 

Mean (SE) trees per hectare 

Westside conifer-hardwood: 

 Hardwood 2.6 (0.6) 3.5 (0.4) 2.0 (1.0) 3.2 (0.3) 

 Conifer-hardwood mixed a

2.1 (0.5) b4.2 (0.3) b7.8 (1.1) 3.7 (0.3) 

 Conifer a

2.1 (0.2) b7.5 (0.4) c15.6 (0.5) 6.4 (0.2) 

 Sitka spruce/western 

 hemlock 

a

2.1 (0.3) b5.3 (0.5) c12.4 (1.4) 4.7 (0.3) 

 All alliances a

2.1 (0.1) b6.0 (0.2) c14.3 (0.5) 5.5 (0.2) 

 

Westside white oakDouglas-fir:  

 Douglas-fir 2.5 (1.1) 3.3 (0.5) 7.6 (1.4) 3.5 (0.5) 

 Douglas-fir/white oak a

0.9 (0.2) b2.0 (0.3) c4.8 (1.0) 1.9 (0.2) 

 All alliances a

1.4 (0.4) a2.6 (0.3) b5.9 (0.9) 2.5 (0.2) 

Southwest Oregon mixed 

conifer-hardwood 

a

2.6 (0.3) b5.0 (0.3) c9.5 (0.5) 5.1 (0.2) 

Montane mixed-conifer a

3.0 (0.3) b10.5 (0.4) c21.7 (0.7) 9.6 (0.3) 

Subalpine parkland a1.7 (0.5) b5.6 (1.0) 2 NA 3.6 (0.6) 

Eastside mixed-conifer a

2.1 (0.2) b4.2 (0.1) c8.0 (0.6) 3.8 (0.1) 

Lodgepole pine a

0.8 (0.1) b2.2 (0.3) 2 NA 1.2 (0.1) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas-fir 0.9 (0.1) 0.9 (0.1) 1.4 (0.3) 0.9 (0.1) 

 Ponderosa pine/white oak 1.0 (0.4) 3.2 (1.0) 2 NA 2.1 (0.6) 

 All alliances 0.9 (0.1) 1.1 (0.1) 1.4 (0.2) 1.0 (0.1) 

 

Western juniper 0.1 (0.0) 0.5 (0.2) 0.1 (0.2) 0.2 (0.1) 

All habitats a

2.0 (0.1) b5.3 (0.1) c13.3 (0.3) 4.9 (0.1) 

1

Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes.

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

544 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 4―Weighted mean (standard error) volume of “total” down wood >12.5 cm large end 

diameter, decay classes 1-4, and >2.0 m long by habitat, alliance, and successional stage, 

Oregon and Washington.1

 

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 

Mean (SE) cubic meters per hectare 

Westside conifer-hardwood: 

 Hardwood 67.0 (20.1) 142.0 (33.1) 2 NA 125.0 (23.7) 

 Conifer-hardwood mixed 192.1 (31.6) 166.6 (24.7) 148.3 (39.1) 172.2 (17.4) 

 Conifer a150.8 (8.2) a168.4 (6.7) b229.2 (9.0) 185.4 (4.7) 

 Sitka spruce/western 

 hemlock 

a

123.6 (27.2) 173.2 (22.2) b232.2 (29.8) 183.4 (15.8) 

 All alliances a

151.8 (7.6) a167.7 (6.2) b226.3 (8.4) 183.3 (4.3) 

 

Westside white oakDouglas-fir:  

 Douglas-fir 82.8 (18.6) 57.7 (13.5) 88.8 (20.6) 70.7 (9.6) 

 Douglas-fir/white oak 26.4 (10.7) 36.3 (4.2) 57.0 (12.0) 37.8 (4.0) 

 All alliances 54.0 (11.7) 44.2 (6.1) 71.2 (12.3) 51.3 (5.1) 

Southwest Oregon mixed 

conifer-hardwood 

a

84.9 (8.6) a68.8 (4.6) b118.6 (8.0) 85.9 (3.8) 

Montane mixed-conifer a

102.1 (6.4) a112.5 (3.3) b198.5 (10.6) 123.8 (3.2) 

Subalpine parkland 35.1 (7.3) 55.2 (10.4) 2 NA 44.0 (6.3) 

Eastside mixed-conifer a

47.0 (2.2) b54.6 (1.3) b58.8 (4.9) 52.7 (1.1) 

Lodgepole pine 50.0 (2.5) 55.4 (4.2) 2 NA 51.4 (2.2) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas-fir a

21.6 (1.4) b27.8 (1.4) 20.2 (3.0) 25.1 (1.0) 

 Ponderosa pine/white oak 16.9 (6.7) 35.5 (9.7) 2 NA 27.4 (6.3) 

 All alliances a

21.3 (1.3) b28.4 (1.4) 19.7 (3.0) 25.3 (1.0) 

 

Western juniper 7.5 (3.1) 7.3 (1.9) 7.5 (4.7) 7.4 (1.9) 

All habitats a

70.0 (1.9) b77.6 (1.3) c161.4 (4.5) 87.8 (1.2) 

1

 Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes. 

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 545 

Table 5―Weighted mean (standard error) volume of “large” down wood >50.0 cm large 

end diameter, decay classes 1-4, and >2.0 m long by habitat, alliance, and successional 

stage, Oregon and Washington.1

 

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 

Mean (SE) cubic meters per hectare 

Westside conifer-hardwood: 

 Hardwood 43.8 (17.8) 109.1 (32.7) 2 NA 95.5 (23.2) 

 Conifer-hardwood mixed 146.9 (29.3) 129.0 (23.0) 112.4 (39.2) 132.3 (16.4) 

 Conifer a95.4 (7.3) a118.6 (6.3) b173.9 (8.5) 132.3 (4.4) 

 Sitka spruce/western 

 hemlock 

a

79.6 (25.7) 129.1 (21.6) b180.8 (27.4) 136.6 (14.9) 

 All alliances a

98.5 (6.8) a119.6 (5.7) b172.1 (8.0) 131.8 (4.0) 

 

Westside white oakDouglas-fir:  

 Douglas-fir 47.5 (17.2) 37.8 (12.1) 48.8 (18.1) 42.6 (8.6) 

 Douglas-fir/white oak 15.0 (8.6) 19.3 (4.0) 37.6 (11.1) 21.6 (3.6) 

 All alliances 30.9 (10.3) 26.1 (5.5) 42.6 (10.8) 30.2 (4.5) 

Southwest Oregon mixed 

conifer-hardwood 

a

53.6 (7.5) a42.6 (4.0) b83.8 (7.4) 56.2 (3.4) 

Montane mixed-conifer a

48.9 (5.6) a46.2 (2.4) b144.9 (9.6) 63.4 (2.8) 

Subalpine parkland 7.3 (3.3) 22.3 (6.4) 2 NA 14.5 (3.8) 

Eastside mixed-conifer a

17.3 (1.8) b23.0 (1.0) c35.9 (4.2) 22.2 (0.9) 

Lodgepole pine a

5.6 (0.9) b14.6 (2.8) 2 NA 8.1 (1.0) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas- 

 fir 

a

10.4 (1.1) b15.1 (1.2) 11.6 (2.4) 13.2 (0.8) 

 Ponderosa pine/white 

 oak 

8.7 (5.3) 20.3 (7.6) 2 NA 15.2 (4.9) 

 All alliances a10.3 (1.1) b15.5 (1.2) 11.2 (2.4) 13.4 (0.8) 

 

Western juniper 5.0 (2.8) 3.5 (1.6) 6.2 (4.6) 4.5 (1.7) 

All habitats a

34.7 (1.6) b40.5 (1.1) c118.6 (4.1) 50.4 (1.0) 

1

Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes. 

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

546 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 6―Weighted mean (standard error) percent cover of “total” down wood >12.5 cm 

large end diameter, decay classes 1-4, and >2.0 m long by habitat, alliance, and successional 

stage, Oregon and Washington.1

 

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 

Mean (SE) percent cover 

Westside conifer-hardwood: 

 Hardwood 2.1 (0.5) 3.4 (0.5) 2 NA 3.1 (0.4) 

 Conifer-hardwood mixed 4.4 (0.6) 4.1 (0.5) 3.5 (0.6) 4.1 (0.3) 

 Conifer a4.5 (0.2) a4.6 (0.1) b5.6 (0.2) 4.9 (0.1) 

 Sitka spruce/western hemlock a

3.5 (0.5) 4.7 (0.4) b5.6 (0.6) 4.8 (0.3) 

 All alliances a4.4 (0.2) a4.5 (0.1) b5.5 (0.2) 4.8 (0.1) 

 

Westside white oak-Douglas-fir: 

 Douglas-fir 2.7 (0.4) 1.7 (0.3) 2.6 (0.5) 2.2 (0.2) 

 Douglas-fir/white oak a

1.0 (0.3) 1.4 (0.1) b1.8 (0.3) 1.4 (0.1) 

 All alliances 1.8 (0.3) 1.5 (0.1) 2.2 (0.3) 1.7 (0.1) 

Southwest Oregon mixed coniferhardwood 

a

2.5 (0.2) a2.2 (0.1) b3.2 (0.2) 2.5 (0.1) 

Montane mixed-conifer a

3.8 (0.2) b4.3 (0.1) c5.1 (0.2) 4.3 (0.1) 

Subalpine parkland 1.6 (0.3) 2.1 (0.4) 2 NA 1.8 (0.2) 

Eastside mixed-conifer 2.0 (0.1) a

2.2 (0.0) b1.9 (0.1) 2.1 (0.0) 

Lodgepole pine 2.9 (0.1) 2.8 (0.2) 2 NA 2.9 (0.1) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas-fir a

0.9 (0.0) b1.0 (0.0) a0.7 (0.1) 0.9 (0.0) 

 Ponderosa pine/white oak 0.7 (0.2) 1.2 (0.3) 2 NA 1.0 (0.2) 

 All alliances a

0.8 (0.0) b1.0 (0.0) a0.7 (0.1) 0.9 (0.0) 

 

Western juniper 0.2 (0.1) 0.3 (0.1) 0.3 (0.2) 0.2 (0.0) 

All habitats a

2.6 (0.1) b2.7 (0.0) c4.1 (0.1) 2.9 (0.0) 

1

Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes.

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 547 

Table 7―Weighted mean (standard error) percent cover of “large” down wood >50.0 cm 

large end diameter, decay classes 1-4, and >2.0 m long by habitat, alliance, and successional 

stage, Oregon and Washington. 

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 

Mean (SE) percent cover 

Westside conifer-hardwood: 

 Hardwood 0.9 (0.3) 1.8 (0.5) 2 NA 1.7 (0.4) 

 Conifer-hardwood mixed 2.5 (0.4) 2.2 (0.4) 1.8 (0.5) 2.2 (0.3) 

 Conifer alliance a1.8 (0.1) a2.2 (0.1) b3.1 (0.1) 2.4 (0.1) 

 Sitka spruce/western hemlock a

1.3 (0.3) 2.6 (0.4) b3.2 (0.4) 2.5 (0.2) 

 All alliances a1.9 (0.1) a2.2 (0.1) b3.1 (0.1) 2.4 (0.1) 

 

Westside white oak-Douglas-fir: 

 Douglas-fir 0.9 (0.3) 0.8 (0.2) 0.9 (0.3) 0.8 (0.1) 

 Douglas-fir/white oak 0.3 (0.2) 0.5 (0.1) 0.8 (0.2) 0.5 (0.1) 

 All alliances 0.6 (0.2) 0.6 (0.1) 0.9 (0.2) 0.6 (0.1) 

Southwest Oregon mixed coniferhardwood 

a

0.9 (0.1) a0.9 (0.1) b1.6 (0.1) 1.1 (0.1) 

Montane mixed-conifer a

1.0 (0.1) a1.0 (0.0) b2.9 (0.2) 1.3 (0.1) 

Subalpine parkland 0.2 (0.1) 0.5 (0.1) 2 NA 0.4 (0.1) 

Eastside mixed-conifer a

0.4 (0.0) b0.5 (0.0) c0.7 (0.1) 0.5 (0.0) 

Lodgepole pine a0.2 (0.0) b0.3 (0.1) 2 NA 0.2 (0.0) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas-fir a

0.2 (0.0) b0.3 (0.0) 0.3 (0.1) 0.3 (0.0) 

 Ponderosa pine/white oak 0.2 (0.1) 0.4 (0.2) 2 NA 0.3 (0.1) 

 All alliances a

0.2 (0.0) b0.3 (0.0) 0.3 (0.1) 0.3 (0.0) 

 

Western juniper 0.1 (0.0) 0.1 (0.0) 0.2 (0.2) 0.1 (0.0) 

All habitats a

0.7 (0.0) b0.8 (0.0) c2.2 (0.1) 1.0 (0.0) 

1

 Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes.

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

548 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 8―Weighted mean (standard error) density of “total” down wood >12.5 cm large end 

diameter, decay classes 1-4, and >2.0 m long by habitat, alliance, and successional stage, 

Oregon and Washington. 

 

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 

Mean (SE) pieces per hectare 

Westside conifer-hardwood: 

 Hardwood 199.4 (43.2) 193.0 (36.3) 2 NA 185.9 (26.5) 

 Conifer-hardwood mixed 277.5 (39.0) 234.6 (22.2) 152.2 (29.5) 233.5 (18.1) 

 Conifer a338.6 (15.7) a255.4 (7.5) b252.9 (7.2) 274.5 (5.5) 

 Sitka spruce/western 

 hemlock 

a

244.8 (40.4) 281.4 (24.3) b276.2 (34.4) 271.3 (18.5) 

 All alliances a

326.5 (13.9) a254.3 (6.8) b250.8 (7.0) 271.0 (5.1) 

 

Westside white oak-Douglas-fir: 

 Douglas-fir 220.8 (34.4) 104.8 (15.9) 140.1 (25.6) 136.7 (13.6) 

 Douglas-fir/white oak a

87.9 (37.9) 97.1 (11.4) b107.0 (19.7) 97.6 (10.4) 

 All alliances 174.1 (27.4) 101.5 (10.2) 128.2 (18.5) 120.8 (9.3) 

Southwest Oregon mixed 

conifer-hardwood 

a

158.9 (14.5) a147.4 (7.8) b172.3 (9.4) 157.0 (5.7) 

Montane mixed-conifer a

254.1 (10.1) b250.3 (6.5) c222.3 (9.3) 246.7 (4.8) 

Subalpine parkland 113.1 (17.2) 129.0 (19.4) 2 NA 118.2 (12.5) 

Eastside mixed-conifer 158.0 (4.9) a142.9 (2.7) b102.2 (6.6) 144.5 (2.3) 

Lodgepole pine 201.6 (8.5) 161.2 (12.3) 2 NA 190.9 (7.0) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas-fir a

71.1 (4.0) b77.5 (3.0) a43.7 (6.9) 73.0 (2.3) 

 Ponderosa pine/white oak 57.4 (23.9) 94.4 (16.9) 2 NA 80.2 (13.5) 

 All alliances a70.1 (3.9) b78.8 (3.0) a44.8 (6.8) 73.5 (2.3) 

 

Western juniper 16.4 (4.3) 23.1 (6.1) 26.9 (16.4) 19.2 (3.4) 

All habitats a

182.9 (3.5) b167.2 (2.1) c191.4 (4.0) 175.5 (1.7) 

1

 Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes.

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 549 

Table 9―Weighted mean (standard error) density of “large” down wood >50.0 cm large end 

diameter, decay classes 1-4, and >2.0 m long by habitat, alliance, and successional stage, 

Oregon and Washington. 

 Successional stage 

Habitat and alliance Early Middle Late All stages 

 

Mean (SE) pieces per hectare 

Westside conifer-hardwood: 

 Hardwood 33.4 (12.6) 52.8 (17.1) 2 NA 45.7 (11.1) 

 Conifer-hardwood mixed 71.8 (11.2) 48.1 (9.9) 32.2 (7.6) 53.4 (6.1) 

 Conifer a60.0 (4.5) a47.4 (2.5) b59.7 (2.8) 54.8 (1.8) 

 Sitka spruce/western 

 hemlock 

a

32.3 (9.4) 67.9 (11.5) b72.7 (11.9) 62.0 (6.8) 

 All alliances a

59.0 (4.0) a48.7 (2.3) b59.6 (2.7) 55.0 (1.7) 

 

Westside white oakDouglas-fir:  

 Douglas-fir 32.9 (8.3) 14.4 (4.2) 19.6 (6.2) 19.4 (3.3) 

 Douglas-fir/white oak 2.3 (3.3) 15.0 (2.8) 9.4 (4.9) 11.9 (2.1) 

 All alliances 22.2 (6.0) 14.6 (2.7) 16.0 (4.5) 16.3 (2.2) 

Southwest Oregon mixed 

conifer-hardwood 

a

19.6 (2.9) a18.3 (2.1) b29.6 (3.0) 21.9 (1.5) 

Montane mixed-conifer a

25.4 (2.3) a21.5 (1.1) b57.8 (3.6) 28.6 (1.1) 

Subalpine parkland 6.5 (3.0) 10.9 (3.4) 2 NA 8.5 (2.2) 

Eastside mixed-conifer a

8.9 (0.6) b10.5 (0.4) c15.7 (1.7) 10.4 (0.3) 

Lodgepole pine a

4.2 (0.7) b7.9 (1.7) 2 NA 5.3 (0.7) 

 

Eastside ponderosa pine: 

 Ponderosa pine/Douglas-fir a

5.8 (0.6) b7.1 (0.6) 6.4 (1.5) 6.6 (0.4) 

 Ponderosa pine/white oak 6.3 (5.5) 8.8 (3.0) 2 NA 7.6 (2.7) 

 All alliances a

5.8 (0.6) b7.2 (0.5) 6.2 (1.4) 6.6 (0.4) 

 

Western juniper 1.0 (0.5) 1.9 (1.0) 11.0 (8.2) 1.8 (0.6) 

All habitats a

17.5 (0.8) b17.1 (0.4) c43.2 (1.4) 21.0 (0.4) 

1

 Significantly different means (alpha < 0.05) within rows (among successional stages) are indicated by 

different letter footnotes.

2 Not applicable—sample size <10 plots. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

550 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Dead Wood in Wilderness Areas 

Our analysis indicated that over all habitats, large snags were more than twice as 

dense in Federal wilderness areas than outside wilderness (fig. 2A). The strongest 

differences were for westside conifer-hardwood forest (5.1/ha outside wilderness vs. 

15.2/ha inside wilderness), eastside mixed-conifer forest (3.2/ha vs. 9.5/ha), and 

lodgepole pine (0.8/ha vs. 3.4/ha). In contrast, large down wood was more abundant 

outside wilderness areas than in wilderness in all of the habitats (fig. 2B), although 

the differences often were not significant. The most pronounced differences in down 

wood volume were for southwest Oregon mixed conifer-hardwood (64.3 m3

/ha 

outside wilderness vs. 22.6 m3

/ha inside wilderness) and montane mixed-conifer 

(74.3 m3

/ha vs. 35.2 m3/ha). 

About 6.5 percent of the total area sampled for dead wood was in federally 

designated wilderness areas. The higher elevation habitats were best represented: 57 

percent of the sampled area in subalpine park and 32 percent of montane mixedconifer forest was in wilderness. Most poorly represented were western juniper 

woodland, eastside ponderosa pine, and westside conifer-hardwood forest (1.0, 0.3, 

and 1.5 percent of the sampled area, respectively). 

Discussion 

Causes of Regional Variability in Dead Wood Abundance 

The regional differences in dead wood abundance among wildlife habitats 

reflect strong underlying gradients in physical environment and biological processes 

that affect community composition and structure, forest dynamics, and rates of dead 

wood input and decomposition. The amount and characteristics of dead wood in an 

ecosystem represent a balance between additions through tree death, breakage, and 

transport, and losses through processes of decomposition and fire consumption 

(Harmon and others 1986). The factors that influence these processes, and thus the 

spatial and temporal patterns of dead wood, are scale-dependent and incredibly 

complex. Our intent in this analysis was to present preliminary regional summaries of 

dead wood within vegetation types that describe distinct wildlife habitats in upland 

forests. (An in-depth analysis of factors that explain these patterns is beyond the 

scope of this paper.) 

Westside conifer-hardwood forests have the highest net primary productivity of 

the habitats (Franklin 1988). Forest stands with greater density of live trees can be 

expected to have greater amounts of dead trees as well, and the high amount of dead 

wood we observed in the westside conifer-hardwood habitat probably can be 

explained by high rates of input within these productive forests. Rates of dead wood 

input also are influenced by rates of live tree mortality, which can increase as tree 

density surpasses that of a fully stocked stand. The large amount of dead wood in 

montane mixed-conifer forest may be explained in part by slow rates of 

decomposition in the cold temperatures at high elevations. The higher density of 

snags in the subalpine parkland and montane mixed-conifer types may be attributed 

to high mortality and low fall rates in these wildlife habitats. Unfortunately, 

published information on regional variation in rates of mortality, dead wood input, 

and decomposition, which would be very useful in interpreting our regional patterns 

of dead wood abundance, is scanty. A summary of existing studies in Washington 

and Oregon (Harmon and others 1986) showed greater input rates of dead wood 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 551 

biomass in mature and old-growth Douglas-fir and Sitka spruce/western hemlock 

forests (0.5-30 mg/ha/yr) than in higher elevation Pacific silver fir (0.3 mg/ha/yr), but 

data were not available for eastside forests. 

Figure 2―Abundance of dead wood by habitat and wilderness status, Oregon and 

Washington: A) is the weighted mean density of snags >50.0 cm DBH, decay classes 

1-5, and >2 m tall; B) is the weighted mean volume of down wood >50.0 cm diameter 

at the large end, decay classes 1-4, and >2 m long. Error bars indicate one standard 

error of the mean. WCNH = westside conifer-hardwood, WODF = white oak-Douglasfir, SWOMCH = southwest Oregon mixed conifer-hardwood, MMC = montane mixedconifer, PARK = subalpine parkland, EMC = eastside mixed-conifer, LP = lodgepole 

pine, EPPWO = eastside ponderosa pine-white oak, JUN = western juniper, ALL = all 

wildlife habitats. There were <10 plots in western juniper in wilderness. 

(a) Snags >=50 cm DBH

0

2

4

6

8

10

12

14

16

18

WCNH

WODF

SWOMCH

MMC

PARK

EMC

LP

EPPWO

JUN

ALL

Mean trees per ha

Outside wilderness

In wilderness

(b) Down wood >=50 cm diameter at the large end

0

20

40

60

80

100

120

140

160

WCNH

WODF

SWOMCH

MMC

PARK

EMC

LP

EPPWO

JUN

ALL

Mean cubic meters per ha

Outside wilderness

In wilderness

A) 

B)
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

552 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Current dead wood on a site also is influenced by disturbance and development 

of the current stand, and by the amounts of wood inherited from the preceding stand. 

Unfortunately, consistent information on the history of natural and human 

disturbance to the plots was not available for our analysis. Nevertheless, the 

successional stages used in our study represent distinct structural conditions that are 

surrogates for a chronosequence of stand development after stand-replacing 

disturbance. Although rate of biomass input and average piece size generally are 

thought to increase with succession (Harmon and others 1986), the amount of dead 

wood can follow a U-shaped pattern if young forests inherit large amounts of dead 

wood and live trees from preceding stands (Spies and others 1988). The snags in our 

study—especially large snags—increased with succession in almost all of the 

habitats. No wildlife habitats exhibited a U-shaped pattern, probably because snags 

tend to be cut within harvest units, which reduces the density found in early 

successional forests. Down wood also most often increased with succession, but this 

pattern was less consistent than for snags, and some habitats did exhibit a U-shaped 

pattern. Because we lacked data on the disturbance history of the plots and on the 

origin of individual pieces (from the current or a preceding stand), we can only 

speculate on why the habitats differed in this regard. 

The lack of a U-shaped successional pattern for snags is not surprising. Snags 

have much shorter lag times in the forest than down wood: natural processes of 

fragmentation and decomposition begin much sooner, and they disappear as 

recognizable structures much faster (Harmon and others 1986). In addition, much of 

the dead wood in westside forests is input directly as down wood rather than snags 

(Harmon and others 1986). Snags also are much more likely than down wood to be 

damaged or intentionally removed by humans through the course of forest 

management and harvest activities. In an analysis of a subset of the same FIA data 

we used in this study (40- to 200-year-old stands on non-Federal lands in 

northwestern Oregon), Hansen and others (1991) found that large snags (>50.8 cm 

DBH) were three to five times as dense in stands that had never been clearcut than in 

stands that had been clearcut at least once. These factors taken together suggest that 

snag levels would more closely track recent disturbance and forest succession, while 

down wood amounts would be more strongly influenced by the long-term history and 

productivity of the site. 

Information on the reserve status of the plots was our only available means for 

identifying forests unlikely to have been disturbed by timber harvesting and 

management. However, our comparisons of dead wood within and outside of 

wilderness areas must be interpreted with caution. Perhaps most importantly, the 

plots in wilderness do not sample complete environmental gradients—they are 

strongly biased towards higher elevations and lower productivities. We suspect these 

inherent productivity differences explain much of the higher amounts of down wood 

outside wilderness. On the other hand, if snags are more strongly influenced (i.e., 

reduced) by timber management activities than down wood as we suspect, then 

wilderness areas would be more likely to contain greater amounts of snags than areas 

outside wilderness—which is indeed what our data showed. In fact, Occupational 

Health and Safety Administration (OSHA) standards require the removal of most 

snags from harvest units for worker safety. Therefore, we would expect to find fewer 

snags in managed stands outside wilderness. If snags are cut and left on site, this 

would contribute to the larger amount of down wood we observed outside wilderness 

areas. In addition, high snag densities in higher elevation wildlife habitats (subalpine 

parkland and montane mixed conifer) could be the result of these areas being less 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 553 

accessible and less likely to be harvested for timber or firewood, regardless of their 

reserve status. Although wilderness areas are off-limits to future timber harvesting, 

they have been affected by other human activities to some degree (e.g., fire 

suppression, roads, recreation, exotic species introduction). Furthermore, many plots 

outside wilderness areas sample old-growth and younger forest on sites that have 

never been harvested. 

Comparisons with Other Studies 

Very few estimates of dead wood abundance at broad geographic scales are 

available for comparison with our numbers. Indeed, the lack of this kind of 

information was the primary motivation for this study. Direct comparisons are 

extremely difficult to make because of differences among studies in geographic 

location; the vegetation types, stand ages, and disturbance histories sampled; 

sampling design; definitions (e.g., dead wood sizes and decay classes); and units of 

measure (numbers of trees, volume, density, cover, or linear meters). Furthermore, 

this information often is not provided in the publications. Other regional studies of 

dead wood in Washington and Oregon have been restricted either to Federal or to 

nonfederal lands, which usually represent very different ecological conditions 

(Ohmann and Spies 1998). The study by Ohmann and others (1994) was limited to 

snags on non-Federal lands (a subset of the FIA data used in this paper), because data 

were unavailable for dead wood on Federal lands and down wood on non-Federal 

lands at that time. The study by Spies and others (1988) was confined to natural 

Douglas-fir forests > 40 years old on Federal lands on the westside. Published 

information for eastside forests is not available (Everett and others 1999), or consists 

of summaries of a few local studies (Bull and others 1997). Scientists for the Interior 

Columbia River Basin Ecosystem Management Project relied on expert opinion and 

local studies to estimate current and historical amounts of dead wood (Korol and 

others 2002). Harmon and others (1986) did not include any studies from eastern 

Washington or eastern Oregon. 

Our large snag densities in westside conifer-hardwood forest (table 3) were 

substantially less than those reported by Spies and others (1988): our estimate of 2.1 

large snags/ha in early stages probably represent stands younger than the 40 yr 

minimum sampled by Spies and others (1988); our estimate for middle-successinal 

stages of 6.0/ha compares to 27/ha in their young stands; and our estimate for late 

stages of 14.3/ha compares to their mature (16/ha) and old-growth (27/ha) classes. 

On first inspection our estimates of down wood volume appear somewhat lower 

than other published numbers, but direct comparisons are not possible for reasons 

cited above. Although our estimates of mean down wood volume in successional 

stages of westside conifer-hardwood forest ranged from 151.8 to 226.3 m3

/ha (table 

4), our maximum value on a plot was 2,142.9 m3

/ha. This compares to a range of 309 

to 1,421 m3

/ha in various studies in westside Douglas-fir-western hemlock 

summarized by Harmon and others (1986) (table 4), and to 148 to 313 m3

/ha reported 

by Spies and others (1988). 

We expect our estimates of down wood to be lower than other published studies 

for several reasons: our minimum diameter of 12.5 cm was slightly larger than the 10 

cm minimum found in many other studies, which would reduce the number of down 

logs in the sample; we included managed as well as natural forests of all ages, not 

just older natural forests originating after fire; we excluded down wood of decay 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

554 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

class 5; and our numbers are means across many stands, including stands where no 

down wood was observed (e.g., zero-tally plots), and maximum values are not 

presented. Our estimates of percent cover of down wood also may be lower than in 

other studies that used plot sampling or total tallies, as percent cover calculated from 

line intersect sampling has been shown to underestimate true values (Bate and others 

1999). 

Our dead wood estimates are not directly comparable to those reported in most 

wildlife studies (Marcot and others 2002). These studies typically are conducted 

within a local area and describe dead wood around nest sites, where it may be 

substantially higher than in surrounding stands because many wildlife species select 

nest sites within clumps of snags (Marcot and others 2002). Limited evidence 

suggests that dead wood is most often distributed randomly within stands, but 

sometimes is clumped (Cline and others 1980, Lutes 1999). Cline and others (1980) 

found that 25 percent of stands sampled in the Oregon Coast Range contained 

patches of 5-10 trees that died simultaneously. 

Spatial Distribution of Dead Wood Abundance 

In this paper we present regional-scale means of dead wood within wildlife 

habitats. The standard errors of these estimates are fairly low because of our very 

large sample sizes for most of the habitats and successional stages. In reality, the 

plot-level amounts of dead wood within the habitats were extremely variable. This 

variability reflects the high spatial and temporal variability in the many interacting 

environmental and disturbance factors that influence dead wood on a site. All of the 

habitats we examined had similar patterns: distributions were non-normally 

distributed and strongly skewed to the right. A large proportion of the plots did not 

contain snags or down wood, and a very small proportion of the plots contained 

extremely large accumulations of dead wood. Mean values for these skewed 

distributions must be interpreted with caution. We present the distributions of snags 

for the conifer alliance of westside conifer-hardwood forest to illustrate this pattern 

(fig. 3). In this habitat, 39 percent of the area sampled had no snags, although the 

percentage of “zero” values is a function of the interaction between plot size and the 

spatial pattern of dead wood. Although plots contained a mean of 16 snags/ha, we 

observed densities as high as 215/ha. 

Strengths and Limitations of the Inventory Data for 

Describing Dead Wood 

The summaries of dead wood abundance we present in this paper represent the 

most extensive information of this kind yet available for Washington and Oregon. 

Valid comparisons among the habitats, alliances, and successional stages were 

possible because the data were derived from systematic grids of field plots, sample 

designs were similar among the datasets, and we applied consistent definitions in our 

analysis. The rigorous sample designs of the regional forest inventories allow 

calculation of unbiased estimates of known confidence for many characteristics of 

dead wood populations. However, because the grid design of the sample size is 

proportional to the vegetation type’s occurrence in the landscape, uncommon habitats 

that may be of particular interest (such as streamside forests) are not represented in 

our study. In addition, some parts of the region were not sampled (down wood on 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 555 

non-Federal lands in Oregon and western Washington, and in national and state 

parks), and wilderness areas within National Forests were sampled at one quarter the 

intensity as areas outside wilderness. 

Figure 3―Density of snags >25.4 cm DBH, decay classes 1-5, and >2 m tall across 

plots in the conifer alliance of westside conifer-hardwood forest, Oregon and 

Washington, displayed as a percent of the sampled area. 

The estimates of dead wood must be interpreted in light of the inherent scale 

imposed by the sample design. Our estimates describe the mean and variability of 

dead wood within vegetation types wherever they occur across Oregon and 

Washington, as sampled on field plots of a fixed, predetermined configuration. An 

individual plot samples an area that is smaller than a typical forest stand, and thus by 

itself does not provide an accurate estimate of stand-level conditions. Neither do we 

represent within-plot variability in this study. Information on stumps also is lacking 

from the forest inventory data. Stumps can serve as wildlife habitat as well as an 

indicator of the belowground system. 

Although the estimates of amounts of dead wood are from plots measured at a 

single point in time, the current conditions express events that have occurred over the 

past decades to centuries. The most important limitation of our analysis was our 

inability—based on inventory data currently available—to investigate the effects of 

past disturbance on current amounts of dead wood. In particular, we were unable to 

compare dead wood in managed and unmanaged forests as defined in this study. The 

classification of the reserve status of the plots provides an imperfect stratification of 

disturbance history, as discussed earlier. Stand age has not been determined for plots 

on federal lands, and information on past harvesting and silvicultural activities is 

available only in narrative form for plots in National Forests. Our successional stages 

are defined by current vegetation structure and should be strongly correlated with 

Snags >=25.4 cm DBH

0

5

10

15

20

25

30

35

40

45

0 1-14 15-34 35-54 55-74 75-94 95-114 115+

Trees per ha

Percent of area

Mean = 16

Median = 10

Max. value = 215
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

556 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

stand age and with length of time since the last stand-replacing disturbance, but we 

could not verify this assumption. Furthermore, the successional stages are less useful 

for describing uneven-aged stands that are common in southwest Oregon and on the 

eastside, and do not reflect the effects of selective timber harvesting or other factors 

that influence tree density and characteristics. Chronosequence studies, in which 

space is substituted for time, also have inherent limitations for assessing disturbance 

effects. The best data for describing dead wood dynamics will come from repeated 

measurements of the permanently established inventory plots. Rates of snag 

decomposition and fall from remeasurement of FIA plots in western Washington 

already have been used in parameterizing a dead wood dynamics model (Mellen and 

Ager 2002). 

Our analysis also could be improved by better information on the occurrence of 

contrasting forest conditions within the CVS plots. While we could identify plots that 

straddled major land classes (forest and nonforest) and potential vegetation types 

(forest series), there currently is no easy way to identify different conditions such as 

successional stages within the series. Although algorithms could be applied to the 

basic tree data, no such computer programs have been developed and their efficacy is 

unknown. Furthermore, there is no way to identify multiple conditions within sample 

points on the CVS plots. As a result of not identifying multiple structural conditions, 

some of our plot-level estimates of dead wood and classifications of habitats and 

structural conditions represent averages across contrasting conditions. This 

introduces an unknown level of error into our regional-level weighted means, but we 

do not think this error is sufficient to compromise our overall findings. 

Management Implications 

Regional summaries of current amounts of dead wood have several potential 

applications to forest management, planning, and policy. One important use is in 

broad-scale assessments of wildlife habitat. In developing management guidelines for 

Federal lands, or in evaluating forest practice regulations or incentive programs for 

state and private lands, managers and planners can compare current amounts of dead 

wood to those needed by wildlife species, and to the basic capabilities of the land to 

produce dead wood over time. Such management guidelines currently are based on 

very limited scientific data. Comparisons of our estimates to those reported in most 

wildlife studies are complicated by the fact that our estimates represent average 

conditions within a habitat at the regional level rather than around specific nest sites 

(see earlier discussion) (Marcot and others 2002). Furthermore, although we present 

data on dead wood abundance, management actions may best be focused on the 

ecological processes that lead to development of these forest structures rather than on 

the structures themselves. In this regard, a major challenge for managers is that 

current disturbance regimes and current patterns of dead wood following decades of 

fire suppression may be vastly different from presettlement conditions. And lastly, 

management decisions will require decisions on how to spatially distribute dead 

wood across stands and landscapes, and guidance on such issues cannot be derived 

from sample-based inventories. 

Information on regional patterns of dead wood currently is being incorporated 

into the DecAID model (Mellen and others 2002), which will help guide managers in 

considering dead wood and processes of decomposition in forest management. The 

regional inventory database contains information on occurrence of pathogens such as 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 557 

stem decays and root diseases that contribute dead wood. In addition, the data contain 

important information about the range of variability in dead wood—both historically 

and in the current landscape. The range of variability in dead wood abundance that is 

present among plots in the region can help guide distribution of dead wood within a 

large landscape or watershed being managed. However, caution must be exercised in 

using the regional plot data, which sample current conditions, to describe the historic 

range of conditions in dead wood. Important data on site history is lacking, as 

discussed earlier. Even if plots in “natural” forest could be identified, current levels 

of dead wood have been altered to an unknown degree by fire suppression and other 

human influences. On the eastside in particular, current levels of dead wood may be 

elevated above historical conditions due to fire suppression and increased mortality, 

and may be depleted below historical levels in local areas burned by intense fire or 

subjected to repeated salvage and firewood cutting. Plot data from natural forests on 

the westside, where fire return intervals are longer (Agee 1993) may provide a 

reasonable approximation of historical conditions. 

At the forest policy level, broad-scale assessments of down wood are needed to 

address Criteria and Indicators for the Conservation and Sustainable Management of 

Temperate and Boreal Forests, developed through the Montreal Process. Although 

dead wood was not considered in the first national-level assessment, dead wood 

abundance will be addressed in the first assessment of forest sustainability to be 

conducted by any state in the U.S. by the Oregon Department of Forestry (Birch 

1999). 

Acknowledgments 

Regional ecological analyses such as this one depend on a group of 

professionals in the regional forest inventory programs, who are too numerous to list. 

We also rely on the ongoing programmatic commitment by the USDA Forest Service 

and USDI Bureau of Land Management for including ecological data in regional 

forest inventory and monitoring programs. We thank David Azuma, Lisa Bate, Andy 

Gray, Mark Harmon, Bruce Hostetler, Jerry Korol, Kim Mellen, Martin Raphael, and 

Tom Spies for their helpful comments on earlier versions of this paper. 

References 

Agee, James K. 1993. Fire ecology of Pacific Northwest forests. Covelo, CA: Island Press. 

Bate, Lisa J.; Garton, Edward O.; Wisdom, Michael J. Estimating snag and large tree 

densities and distributions on a landscape for wildlife management. Gen. Tech. Rep. 

PNW-GTR-425. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 77 p. 

Birch, Kevin. 1999. First approximation report for sustainable forest management in 

Oregon. Salem, OR: Oregon Department of Forestry; 219 p. + appendices. 

Bull, Evelyn L.; Parks, Catherine G.; Torgerson, Torolf R. 1997. Trees and logs important 

to wildlife in the Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Chappell, Christopher B.; Crawford, Rex C.; Barrett, Charley; Kagan, Jimmy; Johnson, David 

H.; O’Mealy, Mikell; Green, Greg A.; Ferguson, Howard L.; Edge, W. Daniel; Greda, 

Eva L.; O’Neil, Thomas A. 2001. Wildlife habitats: descriptions, status, trends, and 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

558 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

system dynamics. In: Johnson, David H.; O’Neil, Thomas A., managing directors. 

Wildlife habitat relationships in Oregon and Washington. Corvallis, OR: Oregon State 

University Press; 736 p. 

Cline, Steven P.; Berg, Alan B.; Wight, Howard M. 1980. Snag characteristics and 

dynamics in Douglas-fir forests, Western Oregon. Journal of Wildlife Management 

44:773-787. 

DeVries, P. G. 1973. A general theory on line intersect sampling with application to 

logging residue inventory. Mededdlingen Landbouw Hogeschool No. 73-11. 

Wageningen, The Netherlands; 23 p. 

Everett, Richard; Lehmkuhl, John; Schellhaas, Richard; Ohlson, Pete; Keenum, David; 

Riesterer, Heidi; Spurbeck, Don. 1999. Snag dynamics in a chronosequence of 26 

wildfires on the east slope of the Cascade Range in Washington. International 

Journal of Wildland Fire 9: 223-234. 

Franklin, Jerry F. 1988. Pacific Northwest forests. In: Barbour, M. G.; Billings, W. D., 

editors. North American terrestrial vegetation. New York: Cambridge University Press; 

104-130. 

Franklin, Jerry F.; Dyrness, C. 1988. Natural vegetation of Oregon and Washington.

Corvallis, OR: Oregon State University Press; 452 p. 

Hansen, A. J.; Spies, T. A.; Swanson, F. J.; Ohmann, J. L. 1991. Conserving biodiversity in 

managed forests. BioScience 41: 382-392. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K., Jr. 1986. Ecology of coarse woody debris in temperate ecosystems. 

Advances in Ecological Research 15; 302 p. 

Korol, Jerome J.; Hemstrom, Miles A.; Hann, Wendel J.; Gravenmier, Rebecca A. 2002. 

Snags and down wood in the Interior Columbia Basin Ecosystem Management 

Project. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; 

Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the 

symposium on the ecology and management of dead wood in western forests. 1999 

November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; [this 

volume]. 

Lutes, Duncan C. 1999. A comparison of methods for the quantification of coarse woody 

debris and identification of its spatial scale; a study from the Tenderfoot Creek 

Experimental Forest, Montana. Missoula, MT: University of Montana; 35 p. M.S. 

thesis. 

Maclean, Colin D. 1979. Relative density: the key to stocking assessment in regional 

analysis -- a Forest Survey viewpoint. Gen. Tech. Rep. PNW-78. Portland, OR: Pacific 

Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 5 p. 

Marcot, Bruce G.; Mellen, Kim; Livingston, Susan A.; Ogden, Cay. 2002. The DecAID 

advisory model: wildlife component. In: Laudenslayer, William F.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Max, Timothy A.; Schreuder, Hans T.; Hazard, JohnW.; Oswald, Daniel D.; Teply, John; 

Alegria, Jim. 1996. The Pacific Northwest Region vegetation and inventory 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 559 

monitoring system. Res. Pap. PNW-RP-493. Portland, OR: Pacific Northwest Research 

Station, Forest Service, U.S. Department of Agriculture; 22 p. 

Mellen, Kim; Marcot, Bruce G.; Ohmann, Janet L.; Waddell, Karen L.; Willhite, Elizabeth 

A.; Hostetler, Bruce B.; Livingston, Susan A.; Ogden, Cay. 2002. DecAID: A decaying 

wood advisory model for Oregon and Washington. In: Laudenslayer, William F., Jr.; 

Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., 

technical coordinators. Proceedings of the symposium on the ecology and management 

of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSWGTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; [this volume]. 

Mellen, Kim; Ager, Alan. 2002. A coarse wood dynamics model for the western Cascades.

In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, 

C. Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the symposium on 

the ecology and management of dead wood in western forests. 1999 November 2-4; 

Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research 

Station, Forest Service, U.S. Department of Agriculture; [this volume]. 

Ohmann, Janet L.; McComb, William C.; Zumrawi, Abdel Azim. 1994. Snag abundance for 

cavity-nesting birds on nonfederal forest lands in Oregon and Washington. Wildlife 

Society Bulletin 22: 607-620. 

Ohmann, Janet L.; Spies, Thomas A. 1998. Regional gradient analysis and spatial pattern 

of woody plant communities of Oregon forests. Ecological Monographs 68: 151-182. 

Powell, Douglas S.; Faulkner, Joanne L.; Darr, David R.; Zhu, Zhiliang; MacCleery, Douglas 

W. 1993. Forest resources of the United States, 1992. Gen. Tech. Rep. RM-234. 

Forest Service, U.S. Department of Agriculture. 

SAS Institute Inc. 1988. SAS/STAT users guide, release 6.03 edition. Cary, NC: SAS 

Institute Inc.; 1,028 p. 

Spies, Thomas A.; Franklin, Jerry F.; Thomas, Ted B. 1988. Coarse woody debris in 

Douglas-fir forests of western Oregon and Washington. Ecology 69: 1689-1702. 

U.S. Department of Agriculture Forest Service. 1992. Forest Service resource inventories: 

an overview. Washington, DC: U.S. Department of Agriculture, Forest Service, Forest 

Inventory, Economics, and Recreation Research; 39 p. 

U.S. Environmental Protection Agency. 1995. Level III Ecoregions of the Continental 

United States, Map M-1 [Topographic]. Corvallis, OR: Corvallis Environmental 

Research Laboratory, U.S. Environmental Protection Agency. 

Waddell, Karen L.2002.Sampling coarse woody debris for multiple attributes in extensive 

resource inventories. Ecological Indicators 1: 139-153. 

Waring, Richard H.; Franklin, Jerry F. 1979. Evergreen coniferous forests of the Pacific 

Northwest. Northwest Science 204: 1380-1386. 
Dead Wood in Oregon and Washington Forests—Ohmann and Waddell 

560 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Appendix A―Scientific and common names of tree species mentioned in this paper.

Scientific name Common name 

Abies amabilis (Dougl.) Forbes Pacific silver fir 

Abies concolor (Gord. & Glend.) Lindl. White fir 

Abies grandis (Dougl.) Forbes Grand fir 

Abies lasiocarpa (Hook.) Nutt. Subalpine fir 

Abies magnifica var. shastensis Lemmon Shasta red fir 

Abies procera Rehder Noble fir 

Chamaecyparis lawsoniana A. Murray Port-Orford cedar 

Chamaecyparis nootkatensis (D. Don) Spach Alaska yellow-cedar 

Juniperus occidentalis Hook. Western juniper 

Larix lyallii Parl. Subalpine larch 

Lithocarpus densiflorus (Hook. & Arn.) Rehder Tanoak 

Picea engelmannii Parry Engelmann spruce 

Picea sitchensis (Bong.) Carr. Sitka spruce 

Pinus albicaulis Engelm. Whitebark pine 

Pinus contorta Dougl. Lodgepole pine 

Pinus ponderosa Dougl. Ponderosa pine 

Pinus jeffreyi Grev. & Balf. Jeffrey pine 

Populus tremuloides Michx. Quaking aspen 

Pseudotsuga menziesii (Mirbel) Franco. Douglas-fir 

Quercus chrysolepis Liebm. Canyon live oak 

Quercus garryana Dougl. Oregon white oak 

Quercus kelloggii Newberry Black oak 

Thuja plicata Donn. Western redcedar 

Tsuga heterophylla (Raf.) Sarg. Western hemlock 

Tsuga mertensiana (Bong.) Carr. Mountain hemlock 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 561 

The DecAID Advisory Model: Wildlife 

Component1

Bruce G. Marcot,2

 Kim Mellen,3 Susan A. Livingston,4 and Cay 

Ogden5

Abstract 

The wildlife component of DecAID is based on a thorough review, analysis, and synthesis of 

the empirical literature on wildlife-dead wood relations. We developed the wildlife 

component by compiling data on snag and log size, snag density, and amounts of down wood 

related to individual species or groups of wildlife species as presented in the literature, for 

various habitats and types of wildlife use (breeding, feeding, roosting). The wildlife use data 

are arranged in three cumulative species richness curves representing means and plus or 

minus one standard error (or equivalent variant). The curves can be consulted to determine 

which species or groups are provided for snag or down wood at three statistical levels, and the 

amounts and sizes of snags and down wood needed to achieve a specified wildlife objective of 

providing for specified species, or some percent of species, at a specified statistical level. 

Other components of the DecAID model can then be consulted to determine hazards or 

mitigation for risks of fire and contribution of insects and disease to the dead wood 

component, and to provide for fungi and non-pest invertebrates associated with snags and 

down wood. 

Introduction 

The DecAID model is a decision-aiding advisory system being developed under 

the aegis of the USDA Forest Service’s Pacific Northwest Region (Portland, 

Oregon), and the multiagency Washington-Oregon Species-Habitat Project (SHP). 

“DecAID” (as in “decayed” or “decay aid”) will provide managers with a synthesis 

of all available empirical data on the relations between wildlife and wood decay 

elements, principally snags and down wood, in the U.S. Pacific Northwest. The 

model is intended to update existing regional databases and advisory models, 

including those of Thomas and others (1979), Marcot (1992), and others. 

The DecAID model will help managers determine which wildlife species might 

be provided for by specific snag and down wood amounts and sizes, the amounts and 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Wildlife Ecologist, Pacific Northwest Research Station, USDA Forest Service, 620 S.W. 

Main Street, Portland, CA 97205 (e-mail: bmarcot@fs.fed.us). 

3

 Regional Wildlife Ecologist, Pacific Northwest Region, USDA Forest Service, P.O. Box 3623, 

Portland, OR 97208 (e-mail: kmellen@fs.fed.us) 

4

 Wildlife Biologist, Oregon State Office, Fish and Wildlife Service, U.S. Department of the Interior, 

2600 SE 98th Ave., Suite 100, Portland, OR 97266-1398 (e-mail: sue_livingston@fws.gov) 5

 Regional Wildlife Ecologist, Intermountain Region, National Park Service, 12795 Alameda Parkway, 

Denver, CO 80225 (e-mail: cogden@nps.gov) 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

562 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

sizes needed to meet specified species management objectives, and the amounts and 

sizes expected under natural and managed conditions based on inventory data. The 

model also will provide information about fungi associated with dead wood and 

insects and diseases as disturbance agents affecting recruitment of dead wood. 

This paper is one of a series of four papers in this proceedings pertaining to the 

DecAID model (see Mellen and Marcot [2002] for an overview of the entire DecAID 

model structure and components). This paper discusses the wildlife component. 

Methods6

DecAID was designed to include empirical and all currently available data; 

address down wood as well as snag relations; and provide a more statistical, riskanalysis basis for assessing and managing snags and down wood for wildlife. 

Step 1: Literature Review 

We first conducted a thorough review of literature on empirical studies of 

wildlife associations with snags, partially dead trees, and down wood. We focused on 

studies conducted within Washington and Oregon, as well as studies in adjacent 

states and Canadian provinces if local studies of species or habitats were not 

available. We included publications in journals, books, conference proceedings, 

theses and dissertations, and agency publications and white papers that had 

undergone at least some peer review. We also obtained unpublished data from 

scientists currently working with dead wood issues. 

Step 2: Data Synthesis 

We compiled all available data on species use of snags and down wood from 

these papers. This involved summarizing nearly 200 papers. The data from these 

papers were synthesized into a master spreadsheet, listing the following information:

• For snags: snag density, decay class, dbh (diameter at breast height), height, 

snag species. 

• For down wood: amount of down wood (volume/ha, no. logs/ha, percent 

cover, etc.), decay class, diameter, length, and tree species. 

• For both snags and down wood: user species (e.g., wildlife or fungi), type of 

use (breeding, feeding, resting, denning), stand age and structure, wildlife 

habitat type, geographic location, explanatory comments, and source citation. 

Next, we abstracted data from each study by SHP wildlife habitat type and 

habitat structure and by individual species or species group depending on how they 

were reported. Habitat types constitute an array of 31 wildlife habitats (24 terrestrial 

and 7 coastal and marine) developed by the SHP (Trevithick and O’Neil 1999). We 

were able to find data for seven of the forested wildlife habitat types. Habitat 

structures pertain to successional and structural stages of the wildlife habitat types 

 

6

 The data and statistics presented in this paper have been updated since this paper was presented. 

Specifically, methods now entail use of tolerance intervals, instead of confidence intervals, and an 

expanded set of research data on species. Thus, tables and figures in this paper should be viewed as 

examples of methods and not final analyses. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 563 

and were also developed by the SHP. We combined habitat structures into two 

categories, post-disturbance (i.e., post-fire or post-harvest) and forested, because 

most studies did not report habitats and structures in any finer resolution.7

Examples presented here pertain to two SHP forest habitat types in Washington 

and Oregon: (1) Eastside Mixed Conifer Forest, which comprises productive closed 

upland forests east of the Cascades, including forests of montane Douglas-fir 

(Pseudotsuga menzeisii), grand fir (Abies grandis), western redcedar (Tuja plicata),

and western hemlock (Tsuga heterophylla) in the east Cascade Mountains, Okanogan 

Highlands, and Blue Mountains; and (2) Westside Lowlands Conifer/Hardwood 

Forest, which comprises lowland to low montane upland forests of western hemlock, 

western redcedar, Douglas-fir, Sitka spruce (Picea sitchensis), red alder (Alnus 

rubra), Port-Orford cedar (Chamaecyparis lawsoniana), and bigleaf maple (Acer 

macrophyllum) in western Washington, the Coast Range of Oregon, the western 

slopes of the Cascade Mountains in Oregon, and around the margins of the 

Willamette Valley in Oregon (Trevithick and O’Neil 1999). The examples presented 

here focus on post-fire structures in Eastside Mixed Conifer Forest, and forested 

structures in Westside Lowlands Conifer/Hardwood Forest, for nesting/breeding 

(appendix A).

For each combination of SHP wildlife habitat type and habitat structure, we 

recorded an array of data pertinent to each individual species or species group 

reported in each study (see below and tables 1-4), although data were not available 

for all wildlife habitat types or habitat structures. In this way, we could track the 

interpretation of each data point back to its source and understand the basis of its 

value. This would later prove essential in interpreting the resulting patterns across 

species. 

The main data recorded from each study was the mean, mean minus 1 standard 

error (SE), and mean plus 1 SE, of snag density, snag dbh, down wood percent cover, 

or down wood diameter, for each individual species or species group, in each 

combination of habitat type and habitat structure. We also recorded the sampling 

basis for these data, the location of each study, and the statistical significance of useavailability analyses or regressions if the data were so derived and reported. We 

noted when studies provided multiple values from different study sites within the 

same habitat types and structures. 

Step 3: Development of Cumulative Species Tables and 

Graphs into Cumulative Species Curves 

We interpreted three statistical levels of data from our synthesis of the literature. 

We referred to mean minus 1 SE, mean, and mean plus 1 SE as low, moderate, and 

high statistical levels, respectively. These three levels refer to the degree to which 

statistical values of snag or down wood amount and size include values reported in 

the literature. Statistically, means minus 1 SE represent 32 percent of the reported 

values, means represent average values, and means plus 1 SE represent 68 percent of 

the reported values. 

All values for each combination of wildlife species, wildlife habitat type and 

habitat structure, and data level (low, moderate, and high, respectively) were 

 

7

 This was later changed to three habitat structures—small/medium trees, open canopy, and large trees— 

as more data became available. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

564 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

averaged (further versions will include weighted averages based on sample sizes). 

We put this summary of data from each study into spreadsheet tables and sorted 

wildlife species in order of increasing values of snag density, snag dbh, down wood 

percent cover, and down wood diameter, for each of the three data levels. In this way, 

for each wildlife habitat type and structure, we graphed curves of cumulative species 

richness as functions of snag density, snag dbh, down wood percent cover, and down 

wood diameter. 

The cumulative species curves summarize the findings among species from 

different studies often conducted in different locations, time periods, and conditions. 

The curves are strictly not functions or regressions. Thus, the curves should not 

necessarily be interpreted as representing an increase in species richness on a given 

site or stand, given increases in size or density of wood decay elements. Rather, the 

curves should be used to suggest overall potential, individual species’ use of wood 

decay elements across broader geographical scales, such as within watersheds or 

larger areas. 

Step 4: Interpretation of the Cumulative Species Curves into 

Potential Management Guidelines 

The final step entailed interpreting the cumulative species curves in terms of 

potential management guidelines to meet objectives for snag and down wood 

management for wildlife. This entailed comparing the cumulative species curves and 

species data with data on inventory conditions of snags and down wood from 

unharvested stands in each wildlife habitat type and structure (Ohmann and Waddell 

2002). From this comparison, we derived a reasonable set of potential management 

guidelines for balancing snag density and dbh and for down wood percent cover and 

diameter. Because local site conditions and management histories vary greatly and 

other people may interpret the cumulative species curves differently, we also 

encourage managers to do their own inspection of the data and curves to validate our 

interpretation or to provide their own. 

Results and Examples 

Some examples will help explain the process and the form of the results. The 

full set of cumulative species curves for all species and habitats will be presented 

elsewhere. 

Snag Density 

Example data on wildlife use, for nesting and breeding, by snag density are 

presented in table 1. Because published studies are not available on wildlife use by 

snag density for nesting or breeding in post-fire structures of Eastside Mixed Conifer 

Forest in Washington and Oregon, we deferred to a similar study in mixed-conifer 

forests of south-central Idaho. Data on 8 bird species were available from one study 

there, depicting snag densities observed at nest sites in post-fire habitat structures 

(Saab and Dudley 1998). For some species, multiple values of snag densities are 

available in different study or treatment areas; these are shown in table 1 and are 

averaged for later use in the cumulative species curves. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 565 

For example, snag density data were presented by Saab and Dudley (1998) on 

hairy woodpecker (see appendix A for scientific names) from three treatment areas. 

Mean values of snag density minus 1 SE (“low” statistical level) in these three areas 

were 48, 77, and 102 snags/ha; mean values (“moderate” statistical level) were 68, 

89, and 118 snags/ha; and mean values plus 1 SE (“high” statistical level) were 84, 

101, and 135 snags/ha. For each statistical level, we averaged the values across the 3 

treatments―that is, 76, 92, and 107 snags/ha corresponding to low, moderate, and 

high statistical values, respectively―to use in the cumulative species curves. 

This first example is one of the simplest cases, as all data came from one study 

and all values represented statistically significant selection by each species for snag 

densities. Further, all values represented snag densities at nest sites instead of standwide averages, which we interpret to mean snag densities within what may have been 

local snag clumps that were selected by the species reported. This last point is an 

important distinction because it has great bearing on interpreting the literature for 

devising management guidelines for snag (and down wood) densities, that is, whether 

reported densities should be applied stand-wide or in locally dense clumps. We 

further address this below. 

Table 1 also presents a more complex case of combining data on wildlife use, 

for nesting and breeding, of snag density for nesting or breeding in Westside 

Lowland Conifer/Hardwood Forest. In this case, the literature did not cleanly 

separate various forest habitat structures (successional or structural stages) but rather 

reported from studies conducted in various structures in mixed forest age classes. 

Eight studies were available, covering seven species and two species groups. Some 

studies, such as McComb (1991), did not report means and SEs of snag density 

values, but rather we interpreted values based on their regression analyses. Studies 

reporting variation reported either SE or standard deviation (SD); we recorded and 

used what was reported. Some studies reported snag density at nest sites, others were 

based on stand averages, and still others reported regressions across study areas (in 

one case based on only hard snags). We used the closest available information to 

populate the data tables. Dealing with data reported in disparate ways is a perennial 

problem in statistics when combining information across studies (e.g., Draper and 

others 1992). Our approach was to record the data that were presented and to footnote 

the specific conditions from each study (e.g., table 2). 

The example data from table 1 on wildlife use of snag density for our two 

example habitat types were then sorted by increasing value for each of the statistical 

levels, and plotted on curves (figs. 1, 2). These example cumulative species curves 

show the number of wildlife species or species groups as a function of, in this case, 

snag density. 

The cumulative species curves should be interpreted with due caution because 

the underlying data were reported in several different ways. For example, in Eastside 

Mixed Conifer Forest, post-fire structures (fig. 1), two sets of cumulative species 

curves represent snag densities for different snag size classes as reported in the 

literature: snags > 23 cm dbh and snags > 53 cm dbh. It is important to separate snag 

size classes, where possible, because, in general, smaller snags tend to be more 

numerous than larger snags, and snag density use and selection by the same wildlife 

species can vary by snag size class. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

566 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 567 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

568 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 2―Example data on wildlife use by snag size (diameter at breast height, dbh) in two 

example habitats. 

 Snag dbh (cm)7

Species1 Low2 Moderate2 High2

Habitat type: Eastside Mixed Conifer/Ponderosa Pine Forest 

Habitat structure: Post-fire 

Type of use: Nesting/breeding

AMKE 46,54 50,59 54,63 

BBWO 20,22,30.35 23,28,32,40 26,35,35,45 

BRCR 72 not avail. 89 

CNB 20,34 35,39 36,58 

EUST 30 31 32 

HAWO 24,32,34,35 28,34,35,53 32,36,37,70 

HOWR 28 30,30 31,32 

LEWO 40,43 45,48 46,56,78 

MOBL 22,29,32 31,32,34,32 36,36,40 

NOFL 30,40,41,34 34,41,43,37 39,42,45,52,40 

NTWO 21,30 22,31 32 

RBNU 32 34 36,56 

TRSW 31 32 33 

WEBL 33 35 36 

WHWO 33 37 42 

Habitat type: Westside Lowland Conifer/Hardwood Forest 

Habitat structure: Various (mixed forest age classes) 

Type of use: Nesting/breeding

AMMA not avail. 81,[80]9 not avail. 

BRCR 41,75 84 92 

CBCH 32,58,103 76,94,103,108 113,120,130 

CNB 49,76 [50]9

,83 117 

HAWO 33,41,49,62 [50] 9,58,72,74,80 82,83,92,107,112 

NFSQ 86,65,60,39,71 [50] 9,64,77,93,42,74 100,89,67,44,77 

NOFL 41,46,[86]8

 53,61,78,96 65,106,109,128 

PCE [83]8

 [50] 9,88 92 

PIWO 44,59 67,69,78,88 75,94,100 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 569 

(table 2 continued) 

Habitat type: Westside Lowland Conifer/Hardwood Forest 

Habitat structure: Various (mixed forest age classes) 

Type of use: Nesting/breeding

PIWO 72 78 84 

PYWO 32,54 56 79 

RBNU 40,75 [50] 9,71,82 89,102,118 

RBSA 52,[103]8

,76 80,101,[113]10 109,123 

SCNB 63,94 98 103 

WIWR not avail. 93 not avail. 

1

 See appendix A for species names and codes. 2

 Low = mean - 1 SE; Moderate = mean; High = mean + 1 SE. Multiple entries denote different study 

sites. 

3

 Min dbh refers to the lower value of snag dbh reported in the study. This is an important factor to track 

because, generally, larger snags are less numerous than smaller snags. 

4

 Type data refers to whether the snag densities were reported only at nest sites (“nest site”), throughout 

the stand (“stand avg”), or for all study sites combined (“regression”). 5

 P value refers to the reported statistical outcome of use-availability analyses. P values > 0.05 pertain to 

studies that failed to demonstrate selection for particular snag densities; however, snag data from these 

studies are still useful for describing stands in which the species was observed to be present, and thus are 

included here. 

6

 Plot size refers to the area of the sample plots in which snag density was calculated. 

7

 Various sources. 

8

 Value is mean - 1 SD, even though it is higher than some mean values. 9

 Preference data; redundant with utilization data, so not included in further analyses. 10 Value is mean from 1 study, even though it is higher than some means + SD. 11 Value is anomalously high and based on snags > 13 cm dbh, and thus not included in the cumulative 

species curve. 

Figure 1―Example cumulative species curves of snag density in Eastside Mixed 

Conifer/Ponderosa Pine Forest, post-fire structural condition, for nesting/breeding 

use by wildlife, in eastern Washington and Oregon. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

570 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 2―Example cumulative species curves of snag density in Westside Lowland 

Conifer/Hardwood Forest, various structural conditions, for nesting/breeding use by 

wildlife, in western Washington and Oregon. 

Because all example data for Eastside Mixed Conifer Forest came from nest 

sites, so these particular cumulative species curves (fig. 1) could all be interpreted as 

representing snag densities within local snag clumps at nest sites, not necessarily as 

stand-wide averages. In contrast, in Westside Lowland Conifer/Hardwood Forest (fig. 

2), the literature presented data not by snag size class, but different studies reported 

snag densities at nest sites (this may be in local snag clumps) or as stand-wide 

averages, and we show these in different sets of curves. The values of snag density 

are generally higher in snag clumps than for stand-wide averages (fig. 2); this makes 

intuitive sense. Another data artifact appears in figure 2, where the curves for 

moderate and high statistical levels for stand averages cross. This occurs because the 

data were not reported in the literature the same way for the same species at each 

statistical level; thus, attention needs to be given to the individual species on the data 

points in each curve. 

The cumulative species curves can be read in two ways for management use: 1) 

by beginning with a known or expected snag density and reading up from the x-axis 

to the curves to determine which species, and what fraction of all reported species, 

would be provided at different levels of confidence by managing within observed 

values; or 2) by beginning with a specific species management target, such as for 

specific species or a specific fraction of all reported species, finding those target 

species on each cumulative species curve or along the y-axis, and reading down to 

the x-axis to determine what snag density would correspond to that reported in the 

literature at a particular statistical level (low, moderate, or high). 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 571 

For example, presume that one is managing some Eastside Mixed Conifer forest 

stand for some purpose such as fuels reduction, and that it is expected that such 

silvicultural treatments will result in providing for snags > 23 cm dbh in local clumps 

averaging 100 snags/ha within each clump. Consulting figure 1, for a density of 100 

snags/ha, at > 23 cm dbh, one would determine that this snag density would provide 

for four of the seven reported nesting or breeding species at the high statistical data 

level, and six of the seven nesting or breeding species at both the moderate and low 

levels. Further, one can determine which conditions for each species would, and 

which would not, match conditions reported in the literature. For example, at the high 

statistical level, the proposed management conditions in this scenario would fit the 

reported use patterns for all species except hairy woodpecker, western bluebird, and 

black-backed woodpecker; studies suggest that these three species use and select for 

higher snag densities in recent burns, although they might select for different 

conditions elsewhere (Bunnell, pers. comm.). 

Alternatively, one could begin with a specific management goal, such as 

providing for all reported snag-using species at a particular statistical level. For 

example, in Eastside Mixed Conifer Forest (fig. 1) this would entail providing local 

clumps of snags > 23 cm dbh with densities within the clumps of at least 110 

snags/ha at low statistical levels of observed species’ nesting or breeding usage, 155 

snags/ha at moderate levels, and 200 snags/ha at high levels. (The question of what 

constitutes a clump, how many clumps to provide, and how to distribute a clump is 

addressed below.) In Westside Lowland Conifer/Hardwood Forest (fig. 2), meeting 

the nesting or breeding use patterns of all reported species or species groups would 

entail providing within-clump average snag densities (the dashed lines in fig. 2) of 

about 26 to over 38 snags/ha. Also, the cumulative species curves for the two forest 

habitats explored here suggest that secondary cavity-using species such as northern 

flying squirrel and western bluebird may select for higher snag densities than many 

of the primary cavity-excavating species. (Values presented here and below are only 

examples of use of DecAID; the final model likely will have different values.) 

Snag Diameter 

Data on wildlife use, for nesting or breeding, by snag diameter (dbh) are far 

more numerous than are data on snag density. Data on 15 individual species or 

species groups are available for Eastside Mixed Conifer Forest and 14 species or 

groups for Westside Lowland Conifer/Hardwood Forest (table 2). However, again, 

the literature inconsistently reports these data. Most studies reported actual dbh of 

snags used by a species for a specific function (e.g., nesting, roosting, foraging). 

Preference studies reported snag dbh in various ways: by disparate snag dbh size 

classes or categories; by snags at nest sites, as averaged throughout the stands, or as 

regressions across study areas; by different sampling designs; and by snags generally 

occurring within the stand or as selected by the species (selection data). 

These differences in reporting make overall interpretation of patterns of snag 

diameter use by nesting or breeding species difficult. However, one can use 

cumulative species curves (figs. 3, 4) for these two example habitats in the same way 

as with the snag density curves―that is, to determine what fits reported patterns. 

Comparing the curves for two habitats shows that in general, species use much larger 

snags in the Westside forest type than in the Eastside forest type for nesting or 

breeding; this makes intuitive sense, as Westside forests typically currently have 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

572 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

larger diameter mature trees and snags, given higher rainfall and more productive 

tree-growing environments there. The example curves suggest that, to meet the use 

patterns of all reported individual species and species groups, snags of at least 72 to 

89 cm dbh are needed in Eastside Mixed Conifer Forest, post-fire structures (fig. 3) 

and 92 to 121 cm dbh in Westside Lowlands Conifer/Hardwood Forest, various forest 

structures (fig. 4), for low to high statistical levels, respectively. 

Also, the cumulative species curves suggest that secondary cavity-using species 

may select larger diameter snags than many of the primary cavity-excavating species. 

This is especially true with Brown Creeper and American Kestrel in the Eastside 

forests (fig. 3), and with Chestnut-backed Chickadee, Red-breasted Nuthatch (which 

can also excavate cavities), and other secondary cavity-nesting birds (species group 

“SCNB”) in Westside forests (fig. 4). (Note that Winter Wren also appears in fig. 4.

This species was shown to correlate with large snags in the associated study, 

although the species generally does not use snag cavities per se. The correlation may 

pertain to use of down wood at the base of the snags or sloughing bark as nesting or 

hiding sites. As well, Brown Creeper often uses sloughing bark higher up on the bole 

of large diameter, tall snags and live trees, and does not typically use cavities per se.) 

Figure 3―Example cumulative species curves of snag diameter in Eastside Mixed 

Conifer/Ponderosa Pine Forest, post-fire structural condition, for nesting/breeding 

use by wildlife, in eastern Washington and Oregon. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 573 

Figure 4―Example cumulative species curves of snag diameter in Westside 

Lowland Conifer/Hardwood Forest, various structural conditions, for nesting/breeding 

use by wildlife, in western Washington and Oregon. 

Down Wood Percent Cover 

Overall, scant data are available on wildlife use of down wood. One of the major 

problems is that down wood is reported in the literature in too many disparate ways: 

as percent ground cover, and as number of pieces, volume, density, and mass per unit 

area. Fuels managers prefer estimates of volume and mass, whereas for wildlife use 

percent ground cover may be the best single estimator (Torgersen, pers. comm.; 

Carey, pers. comm.). In British Columbia, down wood percent cover was a useful 

unit for fungi, most cryptogams, and small mammals, although down wood volume 

seemed more useful for Plethodon salamanders (Bunnell, pers. comm.). We used 

inventory data to develop regression equations to convert among these units, 

although such conversions introduce unknown errors in estimation. 

In Eastside Mixed Conifer Forest, only two studies provided data on wildlife use 

of down wood cover, and one of these pertains to fungi species. The story is far better 

in Westside Lowland/Conifer Hardwood Forest, where 5 studies provide data on 23 

species and 2 species groups (table 3). The example cumulative species curves (figs. 

5, 6) suggest that, to provide for all reported species at high statistical levels, over 4 

percent down wood cover in Eastside forests and 20 percent in Westside forests 

would be necessary to fall within observed values of species use and selection. At 

least for Westside forests, these values are much greater than the 0.5 to 1 percent 

typically specified in the Northwest Forest Plan, but, as with snag densities, they 

might pertain to cover within locally dense clumps of down wood, not necessarily 

stand-wide averages. This is a vital distinction for management. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

574 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 575 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

576 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 577 

________________________________________________________________________________________________ (table 4 continued)_____________________________________________________________________________________________________
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

578 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 5―Example cumulative species curves of down wood percent cover in 

Eastside Mixed Conifer/Ponderosa Pine Forest, various structural conditions, for 

presence and foraging use by wildlife, in eastern Washington and Oregon. 

Ponderosa Pine Forest is included here and in table 3 because the studies did not 

separate the two forest types. 

Figure 6―Example cumulative species curves of down wood percent cover in 

Westside Lowland Conifer/Hardwood Forest, various structural conditions, for 

presence and nesting/breeding use by wildlife, in western Washington and Oregon. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 579 

Down Wood Diameter 

Data on wildlife use of down wood diameter also are very sparse for the 

Eastside Mixed Conifer Forest (3 studies, 4 species) but are somewhat better for 

Westside Lowland/Conifer Hardwood Forest (3 studies, 21 species and 1 species 

group) (table 4). Diameters of Eastside down logs tend to be far larger for denning 

use than for foraging use (fig. 7), ranging up to 50 cm diameter for foraging by 

pileated woodpecker and over 120 cm for denning by American black bear. 

Diameters of Westside down logs range up to 43 cm (fig. 8), although data on 

diameter use by bears is not available there. We presume that all diameter values 

should be interpreted as small-end diameter, although many studies reported transectintercept diameter or large end diameter. 

Overall Interpretations 

Interpreting the cumulative species data and curves for wildlife habitat 

management is going to be a complex process requiring knowledge of local site 

conditions and species’ use patterns or needs. For example, interpreting the 

cumulative species curves independently for amounts and for sizes, of snags and 

down wood, may lead to incorrect estimation or conflicting projections of what is 

needed. Because some species select for different size classes of snags or down 

wood, one size does not fit all. Some combination of sizes may be needed to meet all 

species’ use patterns. 

How should one balance density and size for snag or down wood management 

within a stand? The overall process involves comparing and balancing snag or down 

wood size with snag or down wood density from the cumulative species curves, 

determining if this pertains to stand average values or local snag or down wood 

clumps, and comparing the species use data to inventory data taken in unmanaged 

(unharvested) stand conditions. 

Here is an example with the snag data for Westside Lowland Conifer/Hardwood 

Forest, various forested structures. To manage for all reported nesting or breeding 

wildlife at high statistical levels, focusing on the species’ use data representing stand 

averages, the stand would average about 39 snags/ha (fig. 2) > 25 cm dbh (table 1, 

fig. 2). This total would include at least 20 snags/ha > 50 cm dbh for northern flying 

squirrel (table 1). Also used are a few very large snags up to about 120 cm dbh for 

red-breasted sapsucker, chestnut-backed chickadee, and some cavity-nesting birds in 

general (fig. 4) scattered within and among the clumps, although chestnut-backed 

chickadee might use smaller snags that are well rotted (Bunnell, pers. comm.). 

Retaining any snags > 80 cm dbh would help meet needs of roosting bats and 

American marten as well (based on data for roosting and denning, not shown here). 

Amounts and sizes of snags at low or moderate statistical levels would be 

proportionately lower. 

Values of snag or down wood density and size as interpreted from the 

cumulative species curves should be compared with forest inventory data (namely, 

the Continuous Vegetation Survey [CVS] and Forest Inventory and Analysis [FIA]) 

taken in unmanaged (unharvested) stand conditions (Ohmann and Waddell 2002). 

This provides a cross-check of the potential of the stand for producing snags and 

down wood in unharvested settings. For example, a preliminary analysis of inventory 

data in Westside Lowland Conifer/Hardwood Forest from reserved lands 

(representing unharvested conditions) suggests that natural densities of snags > 25 cm 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

580 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

dbh average 48.4 and 40.0 snags/ha in young and mature stand structural classes, 

respectively, and snags > 50 cm dbh average 16.0 and 17.5 snags/ha in young and 

mature classes, respectively. These average values are close to the values derived 

from the cumulative species curves cited above, verifying that these may be 

appropriate stand-wide goals. In some cases, snags can be managed in clumps if the 

species’ use data were summarized from studies focused on selected use of locally 

dense patches of snags or down wood, and if such values were significantly greater 

than stand averages as denoted in the inventory data. 

The idealized cumulative species curves may not fit what is feasible on a given 

site, given its management history, current conditions, and expected future 

conditions. Disturbance such as stand-replacing fires, timber harvests, intermediate 

silvicultural treatments, and human safety management may result in snag and down 

wood conditions far different than expected or desired in a particular stand. 

How does one balance all these issues and conditions? The answer may be in 

taking a broader view across stands and landscapes. It is imperative, however, to not 

average snag and down wood densities and sizes across too broad an area, such as 

across entire watersheds, potentially leaving large areas within watersheds with snags 

or down wood elements that are too scarce or too small to be of use by wildlife. An 

honest evaluation of watershed conditions, including the current condition and future 

capability of stands within, is a sound basis for devising reasonable management 

goals and expectations for snags and down wood on all lands. 

Choosing Statistical Levels for Management Goals 

How should one interpret the statistical levels represented by the low, medium, 

and high curves? It may be useful to interpret the three statistical levels as confidence 

levels and match them with overall goals for managing snags and down wood as one 

facet of habitat diversity for wildlife. Different landowners may have appropriately 

different expectations for diversity management, and thus for statistical levels to 

manage for, on various land use allocations. 

For example, lands established or allocated mainly for conservation and 

protection of native ecosystems and wildlife communities, such as national parks and 

wilderness areas, could appropriately be operating at high statistical levels for 

amount and size of snags and down wood for wildlife. These lands are managed 

under the strictest set of regulations and laws for nature conservation. Usually, active 

forest management, especially timber harvesting, is not conducted on these particular 

lands, although one important exception is Managed Late-Successional Reserves 

under the Northwest Forest Plan. 

It might be appropriate to allow a lower statistical level on other lands clearly 

designated for timber production and other intensive resource production uses. Such 

lands are subject to State Forestry Practices regulations and the Endangered Species 

Act, but not the Federal regulations for population viability and biodiversity 

management governing national forests. At the least, the information provided by the 

cumulative species curves in the DecAID advisory model will help determine the 

degree to which amounts and sizes of snags and down wood provided on various 

categories of land use, ownership, and allocation, match those reported in the wildlife 

literature and in inventory data from unharvested lands. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 581 

Figure 7―Example cumulative species curves of down wood diameter in Eastside 

Mixed Conifer/Ponderosa Pine Forest, various structural conditions, for foraging and 

denning use by wildlife, in eastern Washington and Oregon. Note that American 

black bear is represented in the denning curves twice, as data came from two 

different studies. 

Figure 8―Example cumulative species curves of down wood diameter in Westside 

Lowland Conifer/Hardwood Forest, various structural conditions, for presence of 

wildlife, in western Washington and Oregon. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

582 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Clumping and Distribution Issues 

We discussed above how we interpreted some reported snag or down wood 

densities as possibly occurring in local clumps instead of stand-wide averages. This 

interpretation seems appropriate for studies reporting densities specifically at wildlife 

use sites, such as nests, dens, and roosts, and especially for studies that also 

demonstrate selection for higher densities over stand averages. 

The management question then becomes one of providing the clumps—how big, 

how many, and how spaced? Essentially no study has provided answers to these 

questions. Thus, we analyzed data on snags and down wood collected systematically 

in one study (Bate, pers. comm.) to determine patterns of clumping within stands. 

Results suggest that snags and down wood do occur in clumps, or at least 

nonuniformly within stands (Marcot and others 2002). In this study, observed 

patterns of snag and down wood distributions (number of snags or down wood pieces 

per line transect segment) best fit an “independent density” model. This model has 

fixed intervals along a line with uniform, randomly varying numbers of snags and 

down wood pieces, rather than a “clump-and-space” model in which uniformly 

randomly varying clump densities are interspersed with empty spaces that also vary 

randomly in size. 

The better fit of empirical data on snag and down wood dispersion to the 

“independent density” model suggests that managers can take opportunistic 

advantage of site-specific occurrences of snags and down wood without having to 

match a particular spatial distribution pattern of clumps. This offers great flexibility 

to managers to provide varying local densities of snags and down wood across the 

ground, within and among stands. Managers would need to add the temporal 

dimension to this, to ensure that sufficient snag and down wood densities and sizes 

are provided over successional time. 

In some cases, snag or down wood clumps occur because of contagious 

distributions of fungal rot such as Armellaria in conifers and Phellinus in aspen, or 

other wood decay agents. The manager may need to consider the tradeoffs and 

likelihoods of retaining fungal wood decay agents on further infection of sound 

wood. 

Caveats and Cautions in Using the Cumulative Species 

Curves 

Interpreting the Cumulative Species Curves 

The cumulative species curves should not be applied to specific sites or 

individual stands. The curves represent only a summary of field studies and, in 

general, what might be expected on average across broad areas such as watersheds or 

larger areas. Most important, wildlife species richness might not increase as orderly 

as the curves suggest, on any given site, with increasing size or densities of snags or 

down wood as the curves suggest, but again this is a scale issue. Species occurrence 

can vary substantially among areas with different spatial patterns of snags and down 

wood, surrounding landscape conditions and site histories, and site conditions 

including presence of tree species and specific wood rot patterns. On a site level, tree 

species-specific rot patterns greatly influence wildlife species occurrence. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 583 

Incomplete Species Lists 

No study provided data on all snag-associated species in any given habitat. 

Thus, the data tables and cumulative species curves in the wildlife component of 

DecAID provide only a partial insight into the full assemblage of wildlife (and fungi, 

cryptogams, and vascular plants, as well as invertebrates) that are associated with 

snags and down wood. In light of this incomplete knowledge, one might use a species 

rarefaction approach (e.g., James and Rathbun 1981, Palmer 1990, Tackaberry and 

others 1997) to estimate the full richness of species associated with snags and down 

wood, although there are potential problems associated with such an extrapolation. 

For now, we preferred to present just the empirical data. 

Smoothing the Curves 

The cumulative species curves jitter and bounce from vagaries in everything 

from sampling design to differences in specific habitat conditions at study sites. One 

could smooth the curves by using a lowess smoothing algorithm with an appropriate 

tension (weighting) value (e.g., 0.40) or some other smoothing function. We tested 

this but chose not to use this, so that the empirical data could be preserved in the 

curves, showing the conditions for each individual species or species group; 

smoothed curves would not provide species-specific information. Also, many curves 

for habitat types and structures not shown here are relatively data poor, and 

smoothing algorithms would not be appropriate in such cases. 

Consider All Uses and Conditions

It is vital that all uses of snags or down wood, such as for breeding, feeding, and 

roosting, for given species be considered simultaneously when assessing impacts on 

species or when devising management guidelines. Considering only one type of 

wildlife use, especially a use that correlates with the smallest or fewest snags or down 

wood pieces, can prove insufficient to meet population needs. 

DecAID and this wildlife component address terrestrial, upland conditions. 

Additional consideration needs to be made for snags and down wood in riparian, 

aquatic, and wetland environments. 

The data and our synthesis do not explicitly represent some features of snags 

found to correlate well with some wildlife use. These data were entered into the 

master spreadsheet but have not been synthesized at this point. Such features include 

snag height and top condition (Raphael and White 1984). For some cavity-using birds 

and bats, snag height relative to live canopy height may be more critical than absolute 

height (Ormsbee, pers. comm.), and live foliage cover near snag cavities may provide 

important cover for birds (Nelson, pers. comm.). 

Also, cautions need to be aimed at interpreting and using data from studies that 

spanned a variety of vegetation structures, treatments, or seral conditions. In a sense, 

each point for each species from such a study is a probability cloud itself representing 

variation among such conditions. Regressions or curves spanning different points 

may represent spurious relations. This is a major concern in meta-analysis methods of 

combining data from different studies. The best thing to do is be aware of the 

conditions in each reported study and interpret results accordingly. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

584 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Consider Other Decadence Elements 

Some species select for decadence conditions not represented here, specifically 

hollow trees and logs, and dead parts of live trees. Such elements should be 

considered in addition to those presented here and will be included in DecAID. In 

many cases they may be rare enough to warrant complete protection where found, in 

coordination with health and safety standards. 

Consider Use vs. Selection 

Data based on patterns of selection (use compared with availability) should be 

interpreted differently than data based on occurrence or just use with no comparison 

to availability. Selection, as for particular sizes or densities of snags or down wood, 

when demonstrated, provides far greater evidence of what is needed to provide for 

wildlife. Still, use data can be applied to develop helpful guidelines for what to 

provide while selection studies get underway to test the guidelines. 

Understanding the range over which snag or down wood sizes or densities were 

studied is also important. In some cases, there may appear to be no correlation or 

selection because more than adequate sizes or densities of snags or down wood were 

already provided, and the wildlife response had already leveled off. 

Even if selection is demonstrated, some species may still be able to persist and 

even thrive if their preferred sizes or densities of snags or down wood were not 

available (e.g., Carey and others 1991). However, it is largely impossible to predict 

this for most species, and it may be prudent nonetheless to provide for sizes or 

densities according to the empirical selection studies. 

Data on stand averages of snag or down wood density may or may not represent 

unmanaged conditions. Often, we could not determine this from the literature, so 

great care needs to be exercised when interpreting such data. 

Population Response 

The ultimate, and really the only authentic, measure of the effectiveness of snag 

and down wood management guidelines is how well they provide for fit, viable 

populations. Fitness is the reproductive vitality of offspring, and viability is the 

persistence of well-distributed populations over the long term. Few if any studies we 

reviewed truly measure fitness and viability. Thus, a major operating assumption is 

that wildlife (i.e., plant and animal) populations associated with snags and down 

wood would be fit and viable if 100 percent of all reported species’ needs were met at 

the high statistical level. This can be empirically tested in large landscapes through 

an experimental approach, if desired, although such a study would be expensive and 

take many years. We encourage the reader to devise more tractable ways to model 

and test this critical assumption. 

Under some conditions, populations of snag- and down wood-associated species 

may be limited by factors other than snag density, size, and condition. For example, 

based on a simulation model, Raphael (1983) suggested that, in Sierra Nevada mixed 

conifer forests, secondary cavity-nesting birds may be limited by territoriality rather 

than cavity abundance when snags are sufficiently numerous to provide nesting 

habitat for primary cavity-excavating species, at least for a time. His model then 

suggests that, in a burned forest with no further recruitment of snags, numbers of 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 585 

both primary cavity excavator species and secondary cavity-nesting species are 

limited by snag abundance as snag numbers decline beyond about year 20. 

Remember Hardwoods 

The data we gathered inadequately represent how hardwood trees provide for 

natural or excavated cavities for many species, such as for downy woodpecker 

(Picoides pubescens) and acorn woodpecker (Melanerpes formicivorous) in Westside 

Lowland Conifer/Hardwood Forests. Hardwoods would have to be added to the 

equation, particularly in forest types in which oaks, maples, and other broadleaf or 

hardwood species naturally occur. 

Conclusions 

We provide a new way to synthesize available scientific data on wildlife use of 

snags and down wood. This approach results in a series of “cumulative species 

curves” depicting low, moderate, and high statistical levels (means +/- SE or 

equivalent variant) of species’ use of snag density, snag size, down wood cover, and 

down wood size. This constitutes the wildlife component of the DecAID snag and 

down wood management advisory model. It provides an empirical and probabilistic 

“risk analysis” basis for determining snag and down wood management to meet 

wildlife management goals. It also provides a means of determining the degree to 

which wildlife species can be provided for a given density and size of snags and 

down wood by comparing to known use patterns from the literature. This approach 

provides a replicable framework by which to summarize existing studies, to integrate 

future studies, and to determine major information needs. The examples we present 

in this paper are but a small portion of all the literature we reviewed and analyzed 

(appendix B). Other publications (Marcot and others 2002) will provide the full set of 

analyses, cumulative species curves, management implications, and research 

guidelines. 

Findings presented here also suggest that secondary cavity-using species 

associated with snags may use or select for greater snag numbers (or more locally 

dense snag clumps) and larger diameter snags than many of the primary cavityexcavating wildlife species. This suggests that the assumption used in previous 

models, that providing for primary species takes care of all species, may be invalid at 

least in some habitat types. This is also one example of how the wildlife component 

of DecAID can be used to generate testable working hypotheses for guiding future 

empirical research. 

Acknowledgments 

The manuscript benefited from reviews by Fred Bunnell, Mike McGrath, and 

Mary Rowland. We appreciate fruitful discussions of our analysis approach with 

Andrew Carey, David Johnson, Martin Raphael, and many others. David Johnson, 

Washington Department of Fish and Wildlife, and Lisa Norris, USDA Forest Service, 

provided logistic and financial support for this project under the auspices of the 

“Oregon-Washington Species-Habitat Project” (Wildlife Habitats and Species 

Associations in Oregon and Washington). We are grateful to Pat Ormsbee for helping 

hold expert panel workshops to review data and interpretations and for helping 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

586 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

summarize literature and data, and to the many experts attending the workshops, 

including Lisa Bate, Evie Bull, Andrew Carey, Tina Dreisbach, Deborah Lindley, 

Chris Maguire, Kim Nelson, Pat Ormsbee, Vicki Saab, Barry Schreiber, Torolf 

Torgersen, and Jennifer Weikel. Many thanks to Keith Aubry, Lisa Bate, Evelyn 

Bull, Chris Maguire, Cathy Raley, Torolf Torgersen, and Dave Vesely for 

contributing data. We gratefully acknowledge that data provided by Chris Maguire 

were a product of the Demonstration of Ecosystem Management Options (DEMO) 

study, a joint effort of the USDA Forest Service’s Pacific Northwest Region (Region 

6) and Pacific Northwest Research Station. Fred Bunnell, Miles Hemstrom, Deborah 

Lindley, Martin Raphael, and Barry Schrieber provided valuable interpretations of 

the cumulative species curves. 

References 

Bull, E. L. 1998. Progress report: diet and habitat use by black bears in northeastern 

Oregon. Unpublished report. La Grande, OR: USDA Forest Service. 

Bull, Evelyn L.; Holthausen, Richard S. 1993. Habitat use and management of pileated 

woodpeckers in Northeastern Oregon. Journal of Wildland Management 57(2): 

335-345. 

Bull, Evelyn L. 2002. The value of coarse woody debris to vertebrates in the Pacific 

Northwest. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; 

Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the 

symposium on the ecology and management of dead wood in western forests. 1999 

November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; [this 

volume]. 

Butts, Sally R. 1997. Associations of forest floor vertebrates with coarse woody debris in 

managed forests, Western Oregon Cascades. M.S. thesis. Corvallis, OR: Oregon State 

University; 60 p. 

Carey, A. B.; Elliott, E.; Lippke, B. R. and others. 1996. A pragmatic, ecological approach 

to small landscape management: final report of the biodiversity pathways working 

group of the WA Forest Landscape Manage. Proj., Rpt 2, WA DNR, Olympia, 150 p. 

Carey, A. B.; Hardt, M. M.; Horton, S. P.; Biswell, B. L. 1991. Spring bird communities in 

the Oregon Coast Ranges. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. 

H., ed. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. 

PNW-GTR-285. Portland OR: USDA Forest Service; 123-144. 

Carey, A. B.; Johnson, M. L. 1995. Small mammals in managed, naturally young, and 

old-growth forests. Ecological Applications 5: 336-352. 

Carey, A. B.; Kershner, J.; Biswell, B. L.; Dominguez de Toledo, L. 1999. Ecological scale 

and forest development: squirrels, dietary fungi, and vascular plants in managed 

and unmanaged forests. Wildlife Monographs 142:1-71. 

Corn, P. S.; Bury, R. B. 1991. Small mammal communities in the Oregon Coast Range.

In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. H., eds. Wildlife and 

vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland 

OR: USDA Forest Service; 533 p. 

Draper, D.; Gaver, D. P. Jr; Goel, P. K.; Greenhouse, J. B.; Hedges, L. V.; Morris, C. N.; 

Tucker, J. R.; Waternaux, C. M. 1992. Combining information. Statistical issues and 

opportunities for research. Contemporary statistics No. 1. Washington DC: National 

Academy Press; 217 p. 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 587 

Graham, R. T.; Harvey, A. E.; Jugensen, M. F. and others. 1994. Managing coarse woody 

debris in forests of the Rocky Mountains. Intermountain Research Station, USDA 

Forest Service. Res. Paper INT-RP-477; 13 p. 

Hallet, J. G.; O'Connell, M. A. 1997. Wildlife use of managed forests: a landscape 

perspective. Volume 3. East-side studies research restults. Timber, Fish and Wildlife 

Workshop. TFW-WL4-98-003. Olympia, WA. 

Hartwig, Carol L. 1999. Effect of forest age, structural elements, and prey density on the 

relative abundance of pileated woodpecker (Dryocopus pileatus abieticola) on 

south-eastern Vancouver Island. M.S. thesis. University of Victoria; 162 p. 

James, F. C.; Rathbun, S. 1981. Rarefaction, relative abundance, and diversity of avian 

communities. Auk 98: 785-800. 

Marcot, B. G. 1992. Snag recruitment simulator, Rel. 3.1 [computer program]. Portland 

OR: Pacific Northwest Region, USDA Forest Service. 

Maser, C.; Anderson, R. G.; Cormack, K. Jr, and others. 1979. Dead and down woody 

material. In: Thomas, J. W., ed. Wildlife habitats in managed forests: the Blue 

Mountains of Oregon and Washington. USDA Agric. Handb. 553. Washington, DC: 

USDA Forest Service; 78-95. 

McComb, W. C. 1991. The role of dead wood in habitat of spotted owl prey and other old 

forest vertebrates. Unpublished report prepared for the Spotted Owl Recovery Team. 

Corvallis OR: Oregon State University; 97 p. 

Mellen, T. K. 1987. Home range and habitat use of pileated woodpeckers, western 

Oregon. M.S. thesis. Corvallis, OR: Oregon State University; 96 p. 

Nelson, S. K. 1988. Habitat use and densities of cavity nesting birds in the Oregon Coast 

Ranges. M.S. thesis. Corvallis, OR: Oregon St. University; 157 p. 

Palmer, M. W. 1990. The estimation of species richness by extrapolation. Ecology 71: 

1195-1198. 

Raphael, M. G. 1983. Cavity-nesting bird response to declining snags on a burned forest: 

a simulation model. In: Davis, J. W.; Goodwin, G. A.; Ockenfels, R. A., ed. Snag 

habitat management: proceedings of the symposium. Gen. Tech. Rep. RM-99. Flagstaff 

AZ: USDA Forest Service; 211-215. 

Raphael, M. G.; White, M. 1984. Use of snags by cavity-nesting birds in the Sierra 

Nevada. Wildlife Monographs 86: 1-66. 

Rosenberg, D. K.; Anthony, R. G. 1993. Differences in Townsend's chipmunk populations 

between second- and old-growth forests in western Oregon. Journal of Wildland 

Management 57: 365-373. 

Saab, V.; Dudley, J. 1998. Responses of cavity-nesting birds to stand-replacement fire 

and salvage logging in ponderosa pine/Douglas-fir forests of southwestern Idaho. 

Res. Paper RMRS-RP-11. Ogden, UT: Rocky Mountain Research Station, USDA Forest 

Service; 17 p. 

Tackaberry, R., Brokaw, N.; Kellman, M.; Mallory, E. 1997. Estimating species richness in 

tropical forest: the missing species extrapolation technique. Journal of Tropical 

Ecology 13: 449-458. 

Thomas, J. W.; Anderson, R. G.; Maser, C.; Bull, E. L. 1979. Snags. In: Thomas, J. W., ed. 

Wildlife habitats in managed forests the Blue Mountains of Oregon and Washington. 

Agric. Handb. No. 553. Portland OR: USDA Forest Service; 60-77. 

Trevithick, M. D.; O'Neil, T. A. 1999. Wildlife habitat and species information Internet 

collection site. Progress report number 4. Johnson, D.; O'Neil, T. A. Wildlife habitats 

and species associations in Oregon and Washington—building a common understanding 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

588 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

for management. Washington Department of Fish and Wildlife and the Northwest 

Habitat Institute, Olympia WA; 52 p. 

Zarnowitz, J. E.; Manuwal, D. A. 1985. The effects of forest management on cavity-nesting 

birds in northwestern Washington. Journal of Wildland Management 49: 255-263. 

Appendix A―Species names and codes used in tables and figures. 

Species codes Species names 

ABBE American black bear (Ursus americanus)

MAKE American kestrel (Falco sparverius)

AMMA American marten (Martes americana)

BBWO Black-backed woodpecker (Picoides arcticus)1

BRCR Brown creeper (Certhia americana)

BTWO Bushy-tailed woodrat (Neotoma cinerea)

CBCH Chestnut-backed chickadee (Parus rufescens)1

CLSA Clouded salamander (Aneides ferreus)

CNB Cavity nesting birds (unspecified species group)1

DEMO mammals Several small mammal species included in the DEMO study 

DOSQ Douglas squirrel (Tamiasciurus douglasii)

DUSA Dunn’s salamander (Plethodon dunni)

ENSA Ensatina (Ensatina eschscholtzii)

EUST European starling (Sturnus vulgaris)

FUNG Fungus spp. (unspecified species group) 

GMGS Golden-mantled ground squirrel (Spermophilus lateralis)

HAWO Hairy woodpecker (Picoides villosus)1

HOWR House wren (Troglodytes aedon)

LEWO Lewis’ woodpecker (Melanerpes lewis)1

MAPG Mazama (western) pocket gopher (Thomomys mazama)

MASH Marsh (Pacific Water) shrew (Sorex bendirii)

MOBL Mountain bluebird (Sialia currucoides)

NFSQ Northern flying squirrel (Glaucomys sabrinus)

NOFL Northern flicker (Colaptes auratus)1

NOSA Northwestern salamander (Ambystoma gracile)

NSOW Northern spotted owl (Strix occidentalis caurina)

NTWO Northern Three-toed Woodpecker (Picoides tridactylus)1

PCE Primary cavity excavators (unspecified species group) 1

PCFR Pacific chorus frog, = Pacific treefrog (Pseudacris regilla, = Hyla regilla)

PGSA Pacific giant salamander (Dicamptodon tenebrosus)

PIWO Pileated woodpecker (Dryocopus pileatus)1

PJMO Pacific jumping mouse (Zapus trinotatus)

PYOW Northern pygmy-owl (Glaucidium gnoma)

RBNU Red-breasted nuthatch (Sitta canadensis)1

RBSA Red-breasted sapsucker (Sphyrapicus ruber)1

RONE Rough-skinned newt (Taricha granulosa)

SCNB Secondary cavity-nesting birds (unspecified species group) 

SHMO Shrew-mole (Neurotrichus gibbsii)

SMMA Small mammals (unspecified species group) 

SPFR Spotted frog (Rana pretiosa)

SPSK Spotted skunk (Spilogale putorius)

SRBV Southern red-backed vole (Clethrionomys gapperi)

STWE Shorttail weasel (Mustela erminea)

TOCH Townsend’s chipmunk (Eutamias townsendi)

TOVO Townsend’s vole (Microtus townsendii)
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 589 

(appendix A continued) 

Species code Species name 

TRSW Tree swallow (Iridoprocne bicolor)

VASH Vagrant shrew (Sorex vagrans)

WEBL Western bluebird (Sialia mexicana)

WHHO White-headed woodpecker (Picoides albolarvatus)1

WIWR Winter wren (Troglodytes troglodytes)

WRSA Western red-backed salamander (Plethodon vehiculum) 1 Primary cavity-excavating species. All others are secondary cavity-using species or down wood-using 

species. 

Appendix B―The full set of habitat types and structures for which snag and down wood data 

have been synthesized for use in the wildlife component of the DecAID advisory model. The 

full data sets, table summaries, and confidence curves for snag and down wood amounts and 

sizes will be presented elsewhere. 

Parameter Habitat type Habitat 

structure 

Type of wildlife use Examples given 

in this paper 

Snag density 

(no. snags 

per ha) 

Eastside mixed 

conifer/ponderosa 

pine forest 

post-fire nesting/breeding table 1, figure 1 

 Eastside mixed 

conifer forest 

forested nesting/breeding and 

roosting/resting 

 Ponderosa pine 

forest 

various nesting/breeding and 

roosting/resting 

 Upland aspen 

forest 

forested nesting/breeding 

 Westside lowland 

conifer/hardwood 

forest 

various nesting/breeding table 1, figure 2 

 Westside lowland 

conifer/hardwood 

forest 

clearcut 

plantations 

nesting/breeding 

 Montane mixed 

conifer/lodgepole 

pine forest 

various roosting/denning 

Snag size 

(diameter) 

Eastside mixed 

conifer/Ponderosa 

pine forest 

post-fire nesting/breeding table 2, figure 3 

 Eastside mixed 

conifer/ponderosa 

pine forest 

various foraging 

 Eastside mixed 

conifer forest 

various roosting/resting 

 Eastside mixed 

conifer forest 

various 

(forested 

mosaic) 

nesting/breeding 

 Ponderosa pine 

forest 

various 

(forested 

mosaic) 

nesting/breeding 

 Ponderosa pine 

forest 

various roosting/resting 

 Upland aspen 

forest 

forested nesting/breeding 
DecAID Wildlife Component—Marcot, Mellen, Livingston, and Ogden 

590 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(appendix B continued) 

Parameter Habitat type Habitat 

structure 

Type of wildlife use Examples given 

in this paper 

Snag size 

(diameter) 

Westside lowland 

conifer/hardwood 

forest 

clearcut 

plantations 

nesting/breeding 

 Westside lowland 

conifer/hardwood 

forest 

various nesting/breeding table 2, figure 4 

 Westside lowland 

conifer/hardwood 

forest 

various 

forested 

roosting/resting 

 Westside lowland 

conifer/hardwood 

forest 

various foraging 

 Lodgepole pine 

forests and 

woodlands 

various nesting/breeding 

 Lodgepole pine 

forests and 

woodlands 

various roosting/resting 

 Lodgepole pine 

forests and 

woodlands 

various foraging 

 Montane mixed 

conifer forest 

various nesting/breeding 

Down wood 

cover 

(percent) 

Eastside mixed 

conifer forest 

various density and foraging table 3, figure 5 

 Southwest 

Oregon mixed 

conifer-deciduous 

forest 

various presence and nesting 

 Westside lowland 

conifer/hardwood 

forest 

various presence, abundance, 

and nesting 

table 3, figure 6 

 Lodgepole 

pine/subalpine fir 

forest 

mature 

forest 

nesting and density 

Down wood 

size 

(diameter) 

Eastside mixed 

conifer/ponderosa 

pine 

various presence and 

foraging 

table 4, figure 7 

(combined) 

 Westside lowland 

conifer/hardwood 

forest 

various presence and 

selection 

table 4, figure 7 

(combined) 

 Lodgepole 

pine/montane 

forest 

various breeding and resting 
Demographics and Dynamics in 

Sierra Nevada Forests

591
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 593 

Dead Branches and Other Wildlife 

Resources on California Black Oak 

(Quercus kelloggii)

1 

Barrett A. Garrison,2 Robin L. Wachs,3 Terry A. Giles,4 and 

Matthew L. Triggs5

Abstract 

In 1995, we began counting dead branches, mistletoe, and acorns on individually tagged 

living California black oak (Quercus kelloggii). On the same plots, data on dead branches and 

mistletoe were recorded from ponderosa pine (Pinus ponderosa) in 1999. Number of dead 

branches per oak varied among the four stands (P = 0.049) and among the 5 years (P < 

0.001). Large diameter oaks had more dead branches, acorns, and oak mistletoe 

(Phoradendron villosum) bunches (P < 0.008) than did small diameter oaks, while large 

diameter pines had more dead branches (P < 0.001) than did small diameter pines. In 1999, 

oaks averaged 1.33 dead branches per tree while pines averaged 0.45 dead branches per tree 

(P < 0.001), and 52 percent and 15 percent of oaks and pines, respectively, had dead branches 

(P < 0.001). Oak mistletoe was more prevalent in oaks (19 percent) than dwarf mistletoe 

(Arceuthobium campylopodium) was in pines (4 percent) (P < 0.001). Basal area of dead 

branches exceeded basal area of snags in the four stands. To some extent, dead branches can 

offset deficiencies in other forms of dead wood resources needed by wildlife. 

Introduction 

Dead wood in live trees is often overlooked by land managers when assessing 

dead wood resources of forest habitats. Because dead branches have value to wildlife 

(Powell and Zielinski 1994, Waters and others 1990), quantifying dead branch 

abundance should be useful when developing and implementing land management 

actions. Models for estimating snag densities required by woodpeckers have no 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Staff Environmental Scientist, California Department of Fish and Game, Sacramento Valley and 

Central Sierra Region, Rancho Cordova, California. Mailing address: 1701 Nimbus Road, Suite A, 

Rancho Cordova, CA 95670 (e-mail: bagarris@dfg.ca.gov) 

3

 Wildlife Biologist, Foresthill Ranger District, Tahoe National Forest, U.S. Department of Agriculture, 

Foresthill, California. Mailing address: 6198 Tule Lane, Foresthill, CA 95631 (e-mail: 

rwachs@hotmail.com) 

4

 Software Specialist, Johnson Controls Worldwide Services, USGS Fort Collins Science Center, Fort 

Collins, Colorado. Mailing address: 2150 Center Avenue, Bldg. C, Fort Collins, CO 80526-8118 (email: terry_giles@usgs.gov) 

5

 District Wildlife Biologist, Foresthill Ranger District, Tahoe National Forest, U.S. Department of 

Agriculture, Foresthill, California. Mailing address: 22380 Foresthill Road, Foresthill, CA 95631 (email: mtriggs@fs.fed.us) 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

594 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

model components for dead branches that might provide cavities for primary and 

secondary cavity-nesting birds (Thomas and others 1979). Furthermore, some 

methods for determining snag densities do not include dead branches (Anonymous 

1995, Bull and others 1990, Bull and others 1997, Morrison and others 1986a). Field 

inventories on National Forest lands include estimates of live crown-ratio and defects 

or decay of live trees but these are not explicit assessments of dead branch abundance 

(Anonymous 1995). In contrast, Chojnacky (1994) developed a method for 

estimating dead wood in live pinyon pines (Pinus edulis) and junipers (Juniperus

spp.) because of decadence in these trees. Dead branches are a “hidden” resource 

that, if ignored, could bias management actions intended to correct deficits in snag 

abundance. Management actions taken to rectify perceived deficiencies in snag 

densities where trees are purposefully killed to create snags (Bull and others 1997, 

Chambers and others 1997, Lewis 1998) may be unnecessary or minimized in some 

cases if dead branches were quantified. 

In mid-elevation mixed-conifer forests in the central Sierra Nevada where 

hardwoods and conifers occur, hardwoods provide important dead wood resources, 

such as dead branches, that may be lacking in conifers. California black oak is the 

dominant hardwood in these forests (McDonald 1988), and dead branches in living 

oaks are used by wildlife (Powell and Zielinski 1994, Waters and others 1990). Oaks 

also produce acorns that are important seasonal food for dozens of species of birds 

and mammals (Barrett 1980, Verner 1980). Leaves and berries of oak mistletoe, 

which occurs in California black oak, are eaten by many species of birds and 

mammals (Martin and others 1951). California black oaks grow differently, become 

decadent sooner, and have different snag characteristics6

 than do conifers (such as 

ponderosa pine), so they may provide substantially different dead wood resources in 

forests. 

Initial field observations of the substantial amount of dead branches in living 

California black oak, lack of dead branches in conifers, and lack of management 

consideration for dead branch resources prompted us to undertake this study. Our 

objectives were to quantify dead branch abundance in California black oak; quantify 

abundance of other attributes in oaks that have wildlife values including acorn 

production and mistletoe infestation; compare dead branches and mistletoe 

infestations between California black oak and ponderosa pine to determine if these 

two species provide similar levels of these resources; and assess the relationship 

between tree diameter and abundance of dead branches, acorns (oaks only), and 

mistletoe. 

Study Area 

We worked on four 21.2-ha study stands in southern Placer County, California. 

The stands were similar in elevation and vegetation characteristics and were selected 

for a study of mule deer (Odocoileus hemionus) and other wildlife in oak-dominated 

habitat in the central Sierra Nevada (Garrison and others 1998a). Each stand 

consisted of two 10.6-ha subplots that were adjacent to each other. The paired 

subplots represented treatment and control units for an experimental timber harvest 

within each of the four stands that was conducted after this investigation. Elevations 

ranged from 1,240-1,450 m, and the stands were on plateaus and upper portions of 

 

6

 Unpublished data on file at California Department of Fish and Game, Sacramento Valley and Central 

Sierra Region, 1701 Nimbus Road, Suite A, Rancho Cordova, CA 95670. 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 595 

steep river canyons. Study stands were located within large homogeneous forest 

stands with a tree layer dominated by large diameter (>40 cm diameter breast height) 

California black oak and ponderosa pine. Other less abundant tree species were 

interior live oak (Q. wislizenii), Douglas-fir (Psuedotsuga menziesii), white fir (Abies 

concolor), sugar pine (P. lambertiana), and incense cedar (Calocedrus decurrens).

Seedling and sapling California black oak and ponderosa pine dominated the 

subcanopy at one stand, while the other stands had little subcanopy. The shrub layer 

was generally sparse, and deerbrush (Ceanothus integerrimus) and manzanita 

(Arctostaphylos spp.) were the most common shrubs. The herbaceous layer was 

dominated by sparse to dense cover of mountain misery (Chamaebatia foliolosa).

Commercial timber harvesting of live conifers has occurred intermittently over the 

past several decades, and cutting of downed California black oak logs for fuelwood 

continuously occurs in all stands. 

Methods 

Each subplot occupied a 325-m x 325-m square area (10.6 ha) inside which we 

established a 250-m x 250-m sampling area (6.3 ha). The sample area was divided 

into a 25-m x 25-m grid with 11 stations per side (121 points in the grid), and a 37.5 

m-wide buffer zone separated the sampling grid from the subplot boundary. All 

sampling occurred within the sampling grid. A total of 30 0.04-ha circular plots (15 

circular plots per subplot) were randomly selected for vegetation measurements in 

each stand. In each subplot, 1 circular plot each was randomly selected in 1994 from 

the 11 points on each of the 11 alphabetized transects on the sampling grid, and 4 

more circular plots were randomly selected from the same transects for each subplot 

in 1995. This resulted in a total of 15 circular plots per subplot and 30 circular plots 

per stand (2 subplots with 15 circular plot each per stand). Data from paired subplots 

were combined because subplots were adjacent to each other in the same stand. 

Vegetation sampling methods are described by Garrison and others (1998a), and data 

on live stems and snags were recorded using stem counts and diameter tapes. 

California black oaks were aged by counting annual growth rings from sections cut 

from trees harvested in 1998 and 1999. 

A total of 32-36 individual California black oaks per stand were individually 

tagged in 1994 with numbered aluminum tags to assess acorn production. One tree 

>25 cm dbh was randomly selected from each 0.04-ha circular plot. An additional 

California black oak 13-25 cm dbh was tagged (2-6 per stand) whenever they 

occurred in the 0.04-ha plots to quantify acorn production by smaller, presumably 

younger, trees. In 1999, 30 individual ponderosa pines >13 cm dbh per stand were 

individually tagged from the 0.04-ha plots for comparisons between the two species. 

The tagged trees were the ones closest to the plot center stake. Diameters of all 

tagged trees were measured in 1994 (oaks) and 1999 (pines), using a diameter tape 

placed at a height of 1.37 m (dbh). 

Beginning in 1995, we counted on each tagged tree the total number of dead 

branches that were >13 cm basal diameter (diameter at attachment to tree) and >0.7-

m long from point of basal diameter to end. The 13-cm diameter threshold is the 

minimum required by some wildlife that use snags and dead branches (Bull and 

others 1997, Raphael and White 1984, Thomas and others 1979). We felt that 13 cm 

represented an appropriate size threshold as most branches had considerably greater 

diameters in oaks and approximately that diameter in pines. 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

596 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Dead branches were identified by lack of bark, shredded bark, broken ends, and 

lack of live foliage. Counts included individual branches that fit the size criteria 

whether they were dead branches off dead branches or off live trunks and branches. 

Basal diameter did not include large, swollen bark wads growing at the base of the 

branch. Dead branches on the ground were measured with dbh tapes to calibrate 

visual measurements. Incidental observations were made of nesting cavities and other 

wildlife use. 

Acorn production by California black oak was determined in late August-early 

September using visual counts of acorns in trees using methods of Garrison and 

others (1998b) and Koenig and others (1994a). The observer visually bisected the 

tree’s live crown area into an upper and lower half, and all acorns observed during 

15-second counts in each half were counted (total of 30 seconds). We also quantified 

infestation of California black oak by oak mistletoe and ponderosa pine by dwarf 

mistletoe by counting the number of mistletoe bunches in the tagged trees using 

binoculars (oaks) or noting mistletoe presence (pines). Mistletoe and acorns in live 

portions of the tree were counted during surveys for dead branches. 

Total number of dead branches, acorns (oaks only), mistletoe bunches (oaks 

only) per tree were averaged among tagged oaks and pines within each stand and 

among years. Frequency of pines with dwarf mistletoe infestation was determined in 

lieu of counting mistletoe bunches because bunches were infrequently encountered 

(see below) and were more difficult to enumerate than oak mistletoe. Statistical 

comparisons for number of dead branches, acorns, and mistletoe bunches for 

California black oaks were made among stands and among years using a repeated 

measures analysis of variance (ANOVAs). Linear regression was used to determine 

linear relationships between California black oak diameter and average number of 

dead branches, acorns, and mistletoe bunches per tree over the 5-yr study. Linear 

regression was also used to determine the relationship between pine diameter and 

number of dead branches. Differences between number of dead branches for oaks and 

pines in 1999 were determined using t-tests. Differences between oaks and pines in 

frequency of trees with and without dead branches and mistletoe was determined 

using Χ2

 tests. Logarithmic (log10) transformations were applied to all variables used 

in the ANOVAs, t-tests, and regressions because the data had non-normal 

distributions (Zar 1996). All analyses were done using SYSTAT (Anonymous 1998), 

and statistical significance was set at P < 0.05. 

Results 

Stand Characteristics 

Trunk diameters at the four stands for all live trees, hardwoods, and conifers >13 

cm dbh averaged (quadratic mean) 39.4-53.9 cm, 37.4-63.5 cm, and 28.2-53.9 cm, 

respectively. Densities for all live trees, hardwoods, and conifers >13 cm averaged 

190-326 trees/ha, 57-153 trees/ha, and 53-270 trees/ha, respectively. Basal area for 

all live trees, hardwoods, and conifers >13 cm averaged 30.5-43.2 m2

/ha, 7.3-21.6 

m2

/ha, and 9.8-21.4 m2/ha, respectively. Overstory canopy cover for all live trees, 

hardwoods, and conifers averaged 70.0-75.8 percent, 36.3-57.6 percent, and 12.9-

33.7 percent, respectively. Height (m) for all live trees, hardwoods, and conifers 

averaged 15.8-22.4 m, 14.8-19.9 m, and 14.9-26.5 m, respectively. Age of California 

black oaks (n=10 for each stand) in the stands averaged 120-166 yrs (age range of 

individual trees 53-347 yrs) (Garrison and others 2002). 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 597 

California Black Oak Attributes 

Number of dead branches per tree in California black oak varied among stands 

(F3,134 = 2.69, P = 0.049) and years (F4,536 = 5.13, P < 0.001) (table 1). There was 

significant interaction between stands and years (F12,536 = 2.52, P < 0.004) as some 

stands had consistently more dead branches per tree during all years. Wildlife 

observed in our stands foraging, nesting, or roosting in dead branches included 

northern pygmy-owls (Glaucidium gnoma), downy woodpeckers (Picoides 

pubescens), mountain chickadees (Poecile gambeli), red-breasted (Sitta canadensis)

and white-breasted (S. carolinensis) nuthatches, and brown creepers (Certhia 

americana).

7

 Mistletoe bunches per tree in California black oak varied among stands 

(F3,134 = 5.43, P < 0.002), and there was no variation among years (F4,536 = 2.08, P = 

0.091) nor any significant stand by year interaction (F12,536 = 1.26, P = 0.240) (table 

1). Acorn production per tree varied among stands (F3,134 = 10.60, P < 0.001) and 

years (F4,536 = 54.96, P < 0.001) (table 1). There was significant interaction between 

stands and years (F12,536 = 12.88, P < 0.001) as some years (1995 and 1999) and 

stands (two and four) produced more acorns than others. Larger diameter oaks had 

more dead branches per tree than smaller diameter oaks (R2

adj. = 0.586, n = 138, t(2) = 

13.87, P < 0.001) (fig. 1). Larger diameter oaks also produced more acorns per tree 

(R2

adj. = 0.051, n = 138, t(2) = 2.69, P = 0.008) and had more mistletoe bunches per 

tree (R2

adj. = 0.125, n = 138, t(2) = 4.41, P < 0.001) than smaller diameter oaks, 

although the relationships were not as strong as with dead branches because many 

trees did not have mistletoe or produce acorns (fig. 1).

Table 1Mean + SD for number of dead branches >13 cm diameter, mistletoe bunches 

(Phoradendron villosum), and number of acorns/30 seconds per tree for California black oaks 

(Quercus kelloggii) from four 21.2-ha stands from 1994-1999, Placer County, California.1 

Attribute Stands n 1995 1996 1997 1998 1999 All years 

Dead 1 32 2.06+2.45 1.69+2.65 1.41+1.79 1.63+2.09 1.91+2.10 1.74+0.25 

 branches 2 36 1.75+2.18 0.75+1.13 0.94+1.51 0.72+1.39 1.53+1.89 1.14+0.40 

 3 36 1.31+1.70 1.64+2.10 1.06+1.79 1.00+1.27 1.08+1.30 1.22+0.26 

 4 34 0.68+1.04 0.65+0.88 0.47+0.83 0.79+1.37 0.62+1.05 0.64+0.12 

 All 138 1.44+1.96 1.17+1.86 0.96+1.55 1.02+1.57 1.28+1.68 1.17+0.20 

Mistletoe 1 32 0.59+1.64 1.28+3.90 0.72+2.26 0.63+1.90 1.09+2.56 0.86+0.31 

 2 36 1.58+3.51 2.25+5.54 2.06+4.76 1.89+3.98 2.25+4.66 2.01+0.28 

 3 36 0.42+1.23 0.89+1.92 0.75+2.06 0.81+1.79 0.50+1.52 0.67+0.20 

 4 34 0.00+0.00 0.03+0.17 0.03+0.17 0.00+0.00 0.00+0.00 0.01+0.02 

 All 138 0.66+2.12 1.12+3.59 0.91+2.93 0.85+2.48 0.97+2.89 0.90+0.17 

Acorns 1 32 2.09+3.77 0.00+0.00 0.03+0.18 0.00+0.00 0.16+0.72 0.46+0.92 

 2 36 4.39+9.16 0.67+2.10 0.00+0.00 1.11+3.46 16.11+20.74 4.46+6.73 

 3 36 5.50+14.53 0.08+0.37 0.00+0.00 0.00+0.00 1.33+3.96 1.38+2.37 

 4 34 10.24+16.07 0.12+0.41 0.18+0.63 0.06+0.24 1.12+3.42 2.34+4.44 

 All 138 5.59+12.22 0.23+1.13 0.05+0.33 0.30+1.82 4.86+12.73 2.21+2.77 

1

 See text for statistical differences among stands and years; data from 2 10.6-ha subplots within each 

stand. 

 

7

 Unpublished data on file at California Department of Fish and Game, Sacramento Valley and Central 

Sierra Region, 1701 Nimbus Road, Suite A, Rancho Cordova, CA 95670. 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

598 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 1Relationships between stem diameter of California black oak (Quercus 

kelloggii) (log10 dbh cm) and (a) average number of dead branches (log10) per tree, 

(b) average number of acorns/30 seconds (log10) per tree, and (c) average number of 

mistletoe bunches (Phoradendron villosum) (log10) per tree. 

a 

b 

c
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 599 

California black oak and ponderosa pine had equivalent stem diameters (t(2) = -

1.72, df = 241.3, P = 0.868), but oaks had almost three times more dead branches 

than pines (t(1) = 5.92, df = 259.0, P < 0.001) (table 2). Dead branches were found in 

52 percent of oaks and 15 percent of pines (X2

 = 39.45, df = 1, P < 0.001). Mistletoe 

was found in 19 percent of oaks and 4 percent of pines (X2 = 13.97, df = 1, P = 

0.0002). Larger diameter pines had more dead branches than smaller diameter trees 

(R2

adj. = 0.261, n = 120, t(2) = 6.46, P < 0.001, dead branches = 0.338*dbh0.420), but 

the relationship was not as strong as with oaks. 

Table 2Mean + SD (min, max) for several characteristics per tree of California black oak 

(Quercus kelloggii) and ponderosa pine (Pinus ponderosa) measured in 1999 at four 21.2-ha 

stands in Placer County, California.1

 

Characteristic California black oak 

(n=144) 

Ponderosa pine 

(n=120) 

P-values

from tests2

DBH (cm) 51.15+27.09 (13.2, 152.0) 60.67+36.89 (15.0, 188.8) 0.087 

Dead branches 

>13 cm diameter 

1.33+ 1.72 (0.0, 8.0) 0.45+ 1.30 (0.0, 8.0) 0.001 

Pct trees with 

dead branches >13 

cm diameter 

52.1 pct 15.0 pct 0.001 

Number of 

mistletoe bunches3

0.98+ 2.86 (0.0, 23.0) — — 

Pct trees with 

mistletoe2

19.4 pct 4.2 pct 0.001 

1

 Data from two 10.6-ha subplots within each of the four stands. 2

 T-tests for dbh and dead branch numbers and Χ2 for frequency of trees with dead branches and 

mistletoe. 

3

 Oak mistletoe (Phoradendron villosum) in California black oak and dwarf mistletoe (Arceuthobium 

campylopodium) in ponderosa pine. 

Discussion 

California black oaks had dead branches with diameters ranging from a few cm 

to large branches >30 cm, while ponderosa pines had dead branches mostly at the 13-

cm diameter threshold. Larger diameter (>40 cm) oaks and pines had more dead 

branches than smaller diameter oaks and pines, but this relationship was stronger 

with oaks. California black oak acorn production and mistletoe infestation were 

variously distributed among stem diameters. There were many oaks without dead 

branches (30 percent) or mistletoe (48 percent) and that did not produce acorns (38 

percent), showing that all trees do not provide these resources. 

Because amounts of dead branches, acorns, and mistletoe in California black 

oak varied by stand and individual tree, there were localized differences in abundance 

of these resources. Stands had some differences in elevation, aspect, slope, age, and 

vegetative characteristics, so some variation could be explained by stand differences. 

Individual trees, however, likely accounted for most differences, as tree dbh 

explained 59 percent of the variance in dead branch number, while stand amounts 

were barely significantly different (P = 0.049). Oak dbh explained only 13 percent 

and 5 percent of the variance in mistletoe bunches and acorns, respectively, because 

many trees of all diameters lacked acorns or mistletoe. Conversely, amounts of 

mistletoe and acorns varied (P < 0.002) among stands, so individual tree 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

600 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

characteristics were less important than stand attributes. Stand-level differences were 

most pronounced with mistletoe and acorns compared to dead branches. 

Numbers of dead branches and acorns from California black oak varied 

annually, although there were no obvious increasing or decreasing trends. Dead 

branch abundance varies as branches fall off and trees are damaged due to storms 

(Matlack and others 1993, Webb 1989). Observer differences (Block and others 

1987) also may have caused some variation. Annual variation occurs in acorn 

production by California black oak due to spring weather conditions (Koenig and 

others 1994b). Annual variation occurs in ponderosa pine cone production 

(McDonald 1992), and nuts from cones also are eaten by wildlife (Martin and others 

1951). Although we did not measure cone production, we feel the two tree species 

provide equivalent food resources to wildlife. Oaks, however, had greater numbers of 

dead branches and more mistletoe than the pines. Dwarf mistletoe in ponderosa pine 

is also food for wildlife (Martin and others 1951). Therefore, live California black 

oaks and ponderosa pines provide multiple resources to wildlife in our study stands. 

Ponderosa pines, however, have less dead branch and mistletoe resources than do 

California black oaks. 

In some areas, management efforts may be necessary to increase snag numbers 

(Chambers and others 1997, Lewis 1998, Morrison and others 1986b, Thomas and 

others 1979), but these efforts may be unnecessary in habitats with large numbers of 

larger diameter California black oak. Managers should quantify dead branch 

resources in live California black oaks and other trees, and snag abundance should be 

combined with dead branch abundance to fully quantify the amount of standing dead 

wood. Basal area of all snags, including hardwoods and conifers, in our study areas 

averaged 2.34 m2

/ha, and that amount was relatively low compared to snag 

abundances reported from spotted owl (Strix occidentalis) habitat in the Sierra 

Nevada (Gutierrez and others 1992) and other locations in the Sierra Nevada 

(Morrison and others 1986a). 

Increasing snag levels in our stands through directed management might be 

justified based on snag basal area alone, but might not be necessary when dead 

branches are considered with other dead wood resources. For example, using grand 

means from the four stands for the number of dead branches per oak (1.17 dead 

branches/tree) and the number of living oaks per ha (113 oaks >13 cm dbh/ha), there 

were 2,803 dead branches >13 cm diameter in each 21.2-ha study stand. In the four 

study stands, there were 11,211 dead branches >13 cm diameter from California 

black oak. Oak dead branch basal area averaged 1.72 m2

/ha with 13-cm diameters, 

and dead branch basal area is certainly greater in the stands because many dead 

branches were >13 cm diameter. 

Using similar calculations for ponderosa pine, which averaged 0.45 dead 

branches/tree in 1999, there were 1,336 dead branches >13 cm diameter in each 21.2-

ha study stand, 5,344 dead branches >13 cm diameter in the four study stands, and an 

average of 0.82 m2

/ha of dead pine branch basal area. Total snag basal area in our 

stands was 2.34 m2

/ha, while total dead branch basal area for California black oak 

and ponderosa pine was 2.54 m2

/ha. While not all dead branches are useful to 

wildlife, particularly smaller diameter branches (Bull and others 1997, Thomas and 

others 1979), we observed many being used by several species of birds for nesting, 

roosting, and feeding. Our limited field observations indicated that wildlife used 

some dead branches of oaks but did not use dead branches of pines. 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 601 

Management of forest and woodland habitats is shifting from traditional 

methods emphasizing single species and individual resources (e.g., snags, acorns, 

etc.) to communities and ecosystems (Chapel and others 1992, Hunter 1990). Forest 

ecosystems are diverse, and ecosystem management efforts require assessments of 

the presence and/or abundance of many habitat attributes. Dead branches are often 

overlooked during these assessments, and our study has shown that these resources 

can be substantial in certain habitats and particular locations. With shorter lengths 

and mostly smaller diameters, dead branches cannot fully duplicate the total dead 

wood volume of many snags, particularly conifers, which provide very tall snags. 

Yet, we observed that dead branches were used by wildlife, and dead branches were 

more numerous and had greater cross-sectional area than snags. 

Variation in dead branches, mistletoe, and acorns among locations and years 

indicates that assessments should be conducted at multiple locations and over many 

years to adequately measure amounts of these resources. In some instances, cavities 

in live and dead trees and branches may not limit populations of cavity-nesting birds 

(Waters and others 1990), so managers should inventory snags and dead branches 

prior to initiating management efforts to increase dead wood abundance. 

Furthermore, where snag abundances are particularly low due to fuel woodcutting 

efforts, dead branches may replace or offset snag losses. Dead branches were more 

prevalent in large diameter oaks, so trees must be allowed to grow old enough to 

provide dead branches of appropriate diameters for wildlife use. Large diameter trees 

also are the oldest oaks in the stand (Garrison and others 2002), so forest 

management should retain these trees as well as replace them as they die. Because 

California black oaks are intolerant to shade and respond favorably to canopy 

openings, individual tree, small group selection, or thinning harvests that open 

canopies, reduce competition from conifers, retain older and larger oaks, and recruit 

young oaks through stump sprouting and acorn germination are appropriate 

management actions (McDonald 1969, Tappeiner and McDonald 1980). 

Acknowledgments 

This project was made possible by funding from the California Deer Herd 

Management Plan Program of the California Department of Fish and Game and the 

Partners in Flight Program of USDA Forest Service. We extend our sincere 

appreciation to Richard Burg, Karen Durand, Catherine Fowler, James Jones, John 

McNerney, David Pratt, and Judy Weisser for their help with field work. Ken Mayer, 

Terry Mansfield, Eric Loft, Sonke Mastrup, Russ Mohr, and Ron Pelzman deserve 

special thanks for their interest and support of this project. The Federal Aid in 

Wildlife Restoration (Pittman-Robertson) Act provided partial support for the staff 

time of Barry Garrison to write this paper. Bill Laudenslayer, Philip McDonald, 

Richard Standiford, and Brad Valentine are thanked for their helpful reviews of the 

manuscript. Gary He provided advice on the statistical analysis. 

References 

Anonymous. 1995. Forest Service handbook 1909.15, forest inventory and analysis user’s 

guide. U.S. Department of Agriculture, Forest Service, San Francisco, CA. 

Anonymous. 1998. SYSTAT® 8.0 Statistics. SPSS Incorporated, Chicago, Illinois. 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

602 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Barrett, Reginald H. 1980. Mammals of California oak habitat―management 

implications. In: Plumb, Timothy R., technical coordinator. Proceedings of the 

symposium on the ecology, management, and utilization of California oaks; 1979 June 

26-28; Claremont, CA. Gen. Tech. Rep. PSW-GTR-44. Berkeley, CA: Pacific 

Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 275-291. 

Block, William M.; With, Kimberly A.; Morrison, Michael L. 1987. On measuring bird 

habitat: influence of observer variability and sample size. Condor 72(2): 241-251. 

Bull, Evelyn L.; Holthausen, Richard S.; Marx, David B. 1990. How to determine snag 

density. Western Journal of Applied Forestry 5(2): 56-58. 

Bull, Evelyn L.; Parks, Catherine G.; Torgerson, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Chambers, Carol L.; Carrigan, Tara; Sabin, Thomas E.; Tappeiner, John; McComb, William 

C. 1997. Use of artificially created Douglas-fir snags by cavity-nesting birds.

Western Journal of Applied Forestry 12(3): 93-97. 

Chapel, Mike; Carlson, Ann; Craig, Diana; Flaherty, Terry; Marshall, Chris; Reynolds, Mark; 

Pratt, Dave; Pyshora, Leo; Tanguay, Steve; Thompson, Wendy. 1992. 

Recommendations for managing late-seral-stage forest and riparian habitats on the 

Tahoe National Forest. Nevada City, CA: Tahoe National Forest, Forest Service, U.S. 

Department of Agriculture; 39 p. 

Chojnacky, David C. 1994. Estimating the amount of dead wood in live pinyon and 

juniper trees. Western Journal of Applied Forestry 9(1): 18-20. 

Garrison, Barrett. A.; Wachs, Robin L.; Giles, Terry A.; Triggs, Matthew L. 1998a. Progress 

report: wildlife populations and habitat attributes of montane hardwood-conifer 

habitat in the central Sierra Nevada. Admin. Report 1998-1. Sacramento, CA: 

Wildlife and Inland Fisheries Division, Department of Fish and Game, State of 

California. 

Garrison, Barrett A.; Wachs, Robin L.; Jones, James S.; Triggs, Matthew L. 1998b. Visual 

counts of acorns of California black oak (Quercus kelloggii) as an indicator of mast 

production. Western Journal of Applied Forestry 13(1): 27-31. 

Garrison, Barrett A.; Otahal, Christopher D.; Triggs, Matthew L. 2002. Age structure and 

growth of California black oak (Quercus kelloggii) in the central Sierra Nevada. In: 

Standiford, Richard B; McCreary, Douglas; Purcell, Kathryn L., technical coordinators. 

Proceedings of the fifth symposium on oak woodlands: oaks in California’s changing 

landscape. Gen. Tech. Report PSW-GTR-184. Albany, CA: Pacific Southwest Research 

Station, Forest Service, U.S. Department of Agriculture; 665-679. 

Gutierrez, Rocky J.; Verner, Jared; McKelvey, Kevin S.; Noon, Barry R.; Steger, George N.; 

Call, Douglas R.; LaHaye, William S.; Bingham, Bruce B.; Senser, John S. 1992. 

Habitat relations of the California spotted owl. In: Verner, Jared; McKelvey, Kevin 

S.; Noon, Barry R.; Gutierrez, Rocky J.; Gould, Gordon I., Jr.; Beck, Thomas W., 

editors. 1992. The California spotted owl: a technical assessment of its current status. 

Gen. Tech. Report PSW-GTR-133. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; 79-98. 

Hunter, Malcolm L. 1990. Wildlife, forests, and forestry: principles of managing forests 

for biological diversity. Englewood Cliffs, New Jersey: Prentice-Hall, Inc.; 370 p. 

Koenig, Walter D.; Knops, Johannes M. H.; Carmen, William J.; Stanback, Mark T.; and 

Mumme, Ronald L. 1994a. Estimating acorn crops using visual surveys. Canadian 

Journal of Forest Research 24: 2195-2112. 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 603 

Koenig, Walter D.; Mumme, Ronald L.; Carmen, William J.; Stanback, Mark T. 1994b. 

Acorn production by oaks in central coastal California: variation within and 

among years. Ecology 75(1): 99-109. 

Lewis, Jeffrey C. 1998. Creating snags and wildlife trees in commercial forest landscapes.

Western Journal of Applied Forestry 13(3): 97-101. 

Martin, Alexander C.; Zim, Herbert S.; Nelson, Arnold L. 1951. American wildlife and 

plants a guide to wildlife food habits. New York: Dover Publications, Inc.; 500 p. 

Matlack, Glenn R.; Gleeson, Scott K.; Good, Ralph E. 1993. Treefall in a mixed oak-pine 

coastal plain forest: immediate and historical causation. Ecology 74(5): 1559-1566. 

McDonald, Philip M. 1969. Silvical characteristics of California black oak (Quercus 

kelloggii Newb.). Res. Paper PSW-53. Berkeley, CA: Pacific Southwest Research 

Station, Forest Service, U.S. Department of Agriculture; 20 p. 

McDonald, Philip M. 1988. Montane hardwood. In: Mayer, Kenneth E.; Laudenslayer, 

William F., Jr., eds. A guide to wildlife habitats of California. State of California, 

Resources Agency, Department of Forestry and Fire Protection. Sacramento, California; 

72-73. 

McDonald, Philip M. 1992. Estimating seed crops of conifer and hardwood species.

Canadian Journal of Forest Research 22: 832-838. 

Morrison, Michael L.; Dedon, Mark F.; Yoder-Williams, Michael P.; Raphael, Martin G. 

1986a. Distribution and abundance of snags in the Sagehen Creek Basin, 

California. Res. Note PSW-389 Berkeley, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; 4 p. 

Morrison, Michael L.; Dedon, Mark F.; Raphael, Martin G; Yoder-Williams, Michael P. 

1986b. Snag requirements of cavity-nesting birds: are USDA Forest Service 

guidelines being met? Western Journal of Applied Forestry 1(2): 38-40. 

Powell, Roger A.; Zielinski, William J. 1994. Fisher. In: Ruggiero, Leonard F.; Aubry, Keith 

B.; Buskirk, Steven W.; Lyon, L. Jack; Zielinski, William J., technical editors. The 

scientific basis for conserving forest carnivores American marten, fisher, lynx, and 

wolverine in the western United States. Gen. Tech. Rep. RM-GTR-254. Fort Collins, 

CO: Rocky Mountain Forest and Range Experiment Station, Forest Service, U.S. 

Department of Agriculture; 38-73. 

Raphael, Martin G.; White, Marshall. 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada. Wildlife Monographs No. 86; 66 p. 

Tappeiner, John; McDonald, Philip. 1980. Preliminary recommendations for managing 

California black oak in the Sierra Nevada. In: Plumb, Timothy R., technical 

coordinator. Proceedings of the symposium on the ecology, management, and utilization 

of California oaks; 1979 June 26-28; Claremont, CA. Gen. Tech. Rep. PSW-GTR-44. 

Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture; 107-111. 

Thomas, Jack, W.; Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: 

Thomas, Jack W., technical editor. Wildlife habitats in managed forests, the Blue 

Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: U.S. 

Department of Agriculture; 60-77. 

Verner, Jared. 1980. Birds of California oak habitats―management implications. In: 

Plumb, Timothy R., technical coordinator. Proceedings of the symposium on the 

ecology, management, and utilization of California oaks; 1979 June 26-28; Claremont, 

CA. Gen. Tech. Rep. PSW-GTR-44. Berkeley, CA: Pacific Southwest Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 246-264. 
Dead Branches in Living California Black Oak—Garrison, Wachs, Giles, and Triggs 

604 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Waters, Jeffrey R.; Noon, Barry R.; Verner, Jared. 1990. Lack of nest site limitation in a 

cavity-nesting bird community. Journal of Wildlife Management 54(2): 239-245. 

Webb, Sara L. 1989. Contrasting windstorm consequences in two forests, Itasca State 

Park, Minnesota. Ecology 70(4): 1167-1180. 

Zar, Jerrold H. 1996. Biostatistical analysis. 3rd edition. Upper Saddle River, New Jersey: 

Prentice Hall. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 605 

Demography of Snags in Eastside Pine 

Forests of California1

F. Michael Landram,2 William F. Laudenslayer, Jr.,3 and Thomas 

Atzet4

Abstract 

Nine years of annual observations of snags on 24, 5-hectare plots in northeast California were 

analyzed. Pinus ponderosa, Pinus jeffreyi, and Abies concolor were the most abundant tree 

species. The rate and timing of snag creation varied between species. Of the snags standing at 

the end of the observation period, 88 percent retained their original height; 6 percent of the 

Pinus jeffreyi and 12 percent of the Abies concolor were rendered generally unsuitable for 

cavity nesting birds by height loss; and 13 percent of the Pinus jeffreyi and 4 percent of the 

Abies concolor lost bark cover during the observation period. On an annual basis, 7 percent of 

the pine snags and four percent of the Abies concolor snags fell over. The “half life” for snags 

was 6 years for the pine species and 8 years for Abies concolor. Increases in snag fall rate 

occurred after prescribed fire. The total amount of snags increased during the observation 

period. 

Introduction 

The benefits and costs of snags and their derivatives have been well documented 

(Bull and others 1997, Dudley 1982, Maser and Sedell 1994, Valdez 1996, 

Weatherspoon and Skinner 1996). However, information about the rates at which 

snags are created, accumulate, decay, and ultimately fall down is scant. This 

information is useful when making inferences about habitat quality, productivity, fire 

hazard, and human safety, all important components of ecosystem health. It is also 

useful when planning and predicting levels of snags across a landscape through time. 

Two major studies of snag dynamics have been reported from California. Keen 

(1955) summarized 30 years of annual surveys of beetle-killed ponderosa pine (Pinus 

ponderosa) from five 256-ha plots in northeastern California and southern Oregon. 

That study had the advantage of a relatively long observation period and of knowing 

when individual trees died, but was limited to pure ponderosa pine killed by one 

agent. Raphael and Morrison (1987) summarized observations on four species from 

eight 8.5 hectare plots installed over a 4-year period and re-measured 5 years later on 

the eastern slope of the Sierra Nevada near Truckee. That study included several 

agents of tree mortality, several tree species, and some site variation, but was limited 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Regional Silviculturist, USDA Forest Service Pacific Southwest Region, Vallejo, CA. (e-mail address: 

mlandram@fs.fed.us) 

3

 Research Wildlife Ecologist, USDA Forest Service Pacific Southwest Research Station, Fresno, CA. 

4

 Zone Ecologist, USDA Forest Service Pacific Northwest Region, Medford, OR. 
Snag Demography—Landram, Laudenslayer, and Atzet 

606 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

by a relatively short observation period and by not knowing when individual trees 

died. 

This paper uses data from an ongoing study from annual surveys over a 9-year 

period from 24, 5-hectare plots within the Modoc Plateau and Southern Cascade 

ecological sections (McNab and Avers 1994). It includes several agents of mortality, 

several species, and relatively broad site variation, but is limited by not knowing 

when snags in the initial observation died and the relatively short observation period 

to date. Large sample sizes of ponderosa pine (Pinus ponderosa, PP), Jeffrey pine 

(Pinus jeffreyi, JP), and white fir (Abies concolo, WF) are included. Small sample 

sizes of western juniper (Juniperus occidentalis, WJ), lodgepole pine (Pinus 

contorta, LP), incense cedar (Calocedrus decurrens, IC), black oak (Quercus 

californica, BO), and red fir (Abies magnifica, RF) are included. The silvical 

characteristics of these species have been documented (Burns and Honkala 1990). 

Many factors contribute to rates of creation, decay, inventory, and fall, including soil 

characteristics, topographic position, climate, stand density, incidence of root disease, 

windstorms, and firestorms, amount of decay before death, time since death, species, 

diameter, and the proportion of heartwood. The purpose of this paper is to provide 

information on snag demographics and associated variation with tree species, 

diameter, time since death, and fire history, for improving predictions of future 

condition and for planning and implementing landscape and larger scale projects. 

Methods 

Twenty-four sites were selected from a pool of about 2,000 mapped polygons, 

segmented into six density classes. Each site is 5 hectares in size (500m by 100m). 

The sites were established at selected locations in 1988 and 1989. 

Site Characteristics 

The sites are within either the Modoc Plateau or Southern Cascade ecological 

sections on either the Modoc National Forest, the Lassen National Forest, the Blacks 

Mountain Experimental Forest, or the Lassen Volcanic National Park. 

These sites are characterized by long dry summers. Mean annual temperature 

ranges from 7 to 11 oC. Mean annual precipitation ranges from 300 to 760 mm. Table 

1 summarizes site characteristics. These sites exist across a range of temperature and 

moisture. Some sites (Baseball, Four-mile, Pease Cabin, Pease Flat) only support 

ponderosa pine and western juniper. They are relatively warm-dry sites. Other sites 

(Butte Lk 1, Butte Lk 2, Lost Creek 3) support red fir. They are relatively cold-moist 

sites. Still others (Bieber, Pit River) support California black oak. They are relatively 

warm-moist sites. Most sites are relatively cool and moist and support Jeffrey pine, 

ponderosa pine, and white fir in some combination. White fir exists on the edge of its 

range in some of these sites as limited by available water and is relatively more 

abundant now than earlier in the century. 

Over the 9-year period of observation wildfire, prescribed fire, harvest, or some 

combination of the three have occurred on some, but not on most, sites (table 1).
Snag Demography—Landram, Laudenslayer, and Atzet 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 607 

Table 1—Numbers of snags on each of the 24, 5-ha study sites. 

Site Wildfire Rx Fire Harvest JP PP WF WJ LP IC BO RF Total1 

Ashurst 9 37 67 113 

Baseball 66 12 78 

Bieber 17 1 2 2 6 28 

BM34/125 Fall 1997 1996 1 52 53 

BM34/151b 1997 36 55 215 306 

BM34/151 73 93 63 229 

BM34/75 Fall 1997 1996 10 55 65 

BM34/ 

Roseburg 

 Fall 1997 41 106 68 215 

BM34/Snags Fall 1997 1996 8 59 67 

BM34/ 

Squirrel 

 1997 61 47 109 4 221 

BM35/88 1996 118 48 53 5 224 

Butte Lk 1 1990 & 

1995 

 155 32 47 1 235 

Butte Lk 2 128 13 20 4 165 

Butte Lk 4 220 9 35 264 

Four-mile 133 39 172 

Lost Creek 1 Spring 

1999 

 150 3 3 15 2 173 

Lost Creek 3 458 11 469 

N Mud Lake 1996 1 13 14 

Pease Cabin 17 4 21 

Pease Flat 125 8 133 

Pit River 18 18 265 4 32 2 339 

Soup Creek 65 3 9 1 78 

S Mud Lake 6 20 14 40 

Whitehorse 24 3 5 32 

Grand Total 1,599 999 944 84 50 43 8 7 3,734 

1 These snag counts reflect total individual snags that have been observed. The counts disclosed 

elsewhere will not match these totals for various reasons. Twenty snags have no recorded diameters; 90 

snags were consumed or felled by fire; 349 snags were harvested; 13 snags on the Baseball site have 

been topped at 30 or 40 feet to lower the risk of blow-down and promote decay from the top. Individual 

snags come into and out of analysis depending on the question being examined. 

Data Collection 

All snags present in the year of establishment were mapped and individually 

marked. Trees were considered snags when all needles were dead. Jeffrey pine and 

ponderosa pine snags were often hard to distinguish in the field. Species, diameter, 

height, and percent bark cover on the bole were recorded. Year of death for these 

snags is not known. Sites have been resampled with the same protocol each year 

since establishment. New snags were added to the record (year of death is known). 

Status of previously measured snags (standing or down), new height, new percent 

bark cover, and effects of fire or cutting were recorded. 
Snag Demography—Landram, Laudenslayer, and Atzet 

608 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Analysis 

Creation Rates 

Creation rates were established for Jeffrey pine, ponderosa pine, and white fir by 

tallying the number of snags that entered the study in each of the years 1990 through 

1998 (table 2). To compare the patterns of drought and snag creation, annual 

averages of monthly values for the Palmer Drought Severity Index were compiled 

from National Climatic Data Center’s State Division 2 data, which includes the 

Sacramento Valley and Modoc Plateau. 

Table 2—Percent and count by year of snags still standing since death. 

Year of death Years since death 

0 1 2 3 4 5 6 7 8 

Ponderosa pine Percent of snags still standing, by years since death 

1990 100 97 97 90 82 66 53 50 48 

1991 100 98 92 80 61 46 43 39 

1992 100 96 91 80 54 48 46 

1993 100 100 91 72 67 60 

1994 100 100 92 86 83 

1995 100 98 93 86 

1996 100 98 95 

1997 100 94 

Average 98 93 83 69 55 47 45 48 

Keen's Avg 100 97 93 89 85 73 58 50 

 

Ponderosa pine Count of snags still standing, by years since death 

1990 62 60 60 56 51 41 33 31 30 

1991 61 60 56 49 37 28 26 24 

1992 82 79 75 66 44 39 38 

1993 58 58 53 42 39 35 

1994 36 36 33 31 30 

1995 43 42 40 37 

1996 57 56 54 

1997 34 32 

1998 10 

Jeffrey pine Count of snags, by years since death 

1990 49 48 45 36 33 26 18 17 18 

1991 50 49 45 41 38 29 23 23 

1992 33 32 32 28 27 27 22 

1993 91 88 81 73 70 65 

1994 131 128 117 108 104 

1995 216 209 201 197 

1996 138 137 133 

1997 94 94 

1998 17 
Snag Demography—Landram, Laudenslayer, and Atzet 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 609 

(table 2 continued) 

Year of death Years since death 

0 1 2 3 4 5 6 7 8 

White fir Count of snags, by years since death 

1990 20 17 17 11 11 10 7 7 9 

1991 36 36 36 34 30 28 28 32 

1992 39 39 39 39 37 33 35 

1993 89 89 88 88 86 80 

1994 56 55 55 54 54 

1995 256 251 241 227 

1996 76 72 71 

1997 32 31 

1998 43 

Inventory 

Inventory equals initial count plus creation minus fall. The inventory of snags 

through time was calculated for each of four diameter classes (13 + cm, 13-36 cm, 

38-74 cm, and 76 + cm diameter at breast height) for Jeffrey pine, ponderosa pine, 

and white fir. 

Decay Rates 

Decay rates were inferred from reductions in percent bark cover and height. 

Fall Rates 

Fall rates were calculated three ways. First, a value was obtained for each year 

of observation by dividing the number of fallen snags by the total at the beginning of 

the year, then those yearly values were averaged over the years of observation. We 

call this the average annual fall rate. Source data for this calculation is provided in 

table 3. The equation is 

n

X

Number at Beginning

Number Falling

i

i

∑ 













 100

in which: 

i = population based on observation year 

n = number of populations 
Snag Demography—Landram, Laudenslayer, and Atzet 

610 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 3—Average annual snag fall rates by species and diameters. 

Year 1989 1990 1991 1992 1993 1994 1995 1996 1997 

Jeffrey pine–all diameters 

Initial count 657 698 692 699 711 787 929 984 1,023 

Number that fell 8 56 26 79 55 84 83 57 38 

Fall rate for the year 1.2 pct 8.0 pct 3.8 pct 11.3 pct 7.7 pct 10.7 pct 8.9 pct 5.8 pct 3.7 pct 

Avg. annual fall rate 6.8 pct 

Jeffrey pine–13-36 cm 

Initial count 335 363 347 350 338 364 423 455 472 

Number that fell 5 41 13 47 35 54 51 34 21 

Fall rate for the year 1.5 pct 11.3 pct 3.7 pct 13.4 pct 10.4 pct 14.8 pct 12.1 pct 7.5 pct 4.4 pct 

Avg. annual fall rate 8.8 pct 

 Jeffrey pine–38-74 cm 

Initial count 224 234 242 239 254 288 338 365 384 

Number that fell 3 14 9 22 17 16 23 19 17 

Fall rate for the year 1.3 pct 6.0 pct 3.7 pct 9.2 pct 6.7 pct 5.6 pct 6.8 pct 5.2 pct 4.4 pct 

Avg. annual fall rate 5.4 pct 

Jeffrey pine–76+ cm 

Initial count 98 101 103 110 116 132 165 162 164 

Number that fell 0 1 4 10 3 4 8 4 0 

Fall rate for the year 0.0 pct 1.0 pct 3.9 pct 9.1 pct 2.6 pct 3.0 pct 4.8 pct 2.5 pct 0.0 pct 

Avg. annual fall rate 3.0 pct 

Ponderosa pine–all diameters 

Initial count 411 467 510 575 600 579 555 531 528 

Number that fell 6 18 17 33 57 67 81 37 26 

Fall rate for the year 1.5 pct 3.9 pct 3.3 pct 5.7 pct 9.5 pct 11.6 pct 14.6 pct 7.0 pct 4.9 pct 

Avg. annual fall rate 6.9 pct 

Ponderosa pine–13-36 cm 

Initial count 161 183 201 244 250 222 207 198 201 

Number that fell 2 11 11 23 36 47 46 18 17 

Fall rate for the year 1.2 pct 6.0 pct 5.5 pct 9.4 pct 14.4 pct 21.2 pct 22.2 pct 9.1 pct 8.5 pct 

Avg. annual fall rate 10.8 pct 

Ponderosa pine–38-74 cm 

Initial count 131 150 163 171 185 199 191 183 184 

Number that fell 1 5 4 6 8 13 21 8 7 

Fall rate for the year 0.8 pct 3.3 pct 2.5 pct 3.5 pct 4.3 pct 6.5 pct 11.0 pct 4.4 pct 3.8 pct 

Avg. annual fall rate 4.5 pct 

Ponderosa pine–76+ cm 

Initial count 118 133 145 159 165 158 156 149 142 

Number that fell 3 2 2 3 13 7 14 11 2 

Fall rate for the year 2.5 pct 1.5 pct 1.4 pct 1.9 pct 7.9 pct 4.4 pct 9.0 pct 7.4 pct 1.4 pct 

Avg. annual fall rate 4.2 pct 

White fir–all diameters 

Initial count 142 161 193 226 299 345 580 636 645 

Number that fell 1 4 6 16 10 21 21 23 19 

Fall rate for the year 0.7 pct 2.5 pct 3.1 pct 7.1 pct 3.3 pct 6.1 pct 3.6 pct 3.6 pct 2.9 pct 

Avg. annual fall rate 3.7 pct 
Snag Demography—Landram, Laudenslayer, and Atzet 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 611 

(table 3 continued) 

Year 1989 1990 1991 1992 1993 1994 1995 1996 1997 

White fir–13-36 cm 

Initial count 48 63 87 105 151 163 370 411 415 

Number that fell 0 3 3 10 7 11 17 18 12 

Fall rate for the year 0.0 pct 4.8 pct 3.4 pct 9.5 pct 4.6 pct 6.7 pct 4.6 pct 4.4 pct 2.9 pct 

Avg. annual fall rate 4.6 pct 

White fir–38-74 cm 

Initial count 57 62 68 84 110 140 166 181 187 

Number that fell 0 1 2 5 3 6 2 4 6 

Fall rate for the year 0.0 pct 1.6 pct 2.9 pct 6.0 pct 2.7 pct 4.3 pct 1.2 pct 2.2 pct 3.2 pct 

Avg. annual fall rate 2.7 pct 

White fir–76+ cm 

Initial count 37 36 38 37 38 42 44 44 43 

Number that fell 1 0 1 1 0 4 2 1 1 

Fall rate for the year 2.7 pct 0.0 pct 2.6 pct 2.7 pct 0.0 pct 9.5 pct 4.5 pct 2.3 pct 2.3 pct 

Avg. annual fall rate 3.0 pct 

Western juniper–all diameters 

Initial count 66 66 69 68 68 69 69 70 69 

Number that fell 0 1 2 1 1 2 5 2 0 

Fall rate for the year 0.0 pct 1.5 pct 2.9 pct 1.5 pct 1.5 pct 2.9 pct 7.2 pct 2.9 pct 0.0 pct 

Avg. annual fall rate 2.3 pct 

Western juniper–13-36 cm 

Initial count 60 60 61 60 60 61 61 61 60 

Number that fell 0 1 2 1 1 2 5 2 0 

Fall rate for the year 0.0 pct 1.7 pct 3.3 pct 1.7 pct 1.7 pct 3.3 pct 8.2 pct 3.3 pct 0.0 pct 

Avg. annual fall rate 2.6 pct 

Lodgepole pine–all diameters 

Initial count 30 30 34 38 35 36 34 30 36 

Number that fell 0 0 1 4 0 2 4 1 0 

Fall rate for the year 0 0 2.9 pct 10.5 pct 0.0 pct 5.6 pct 11.8 pct 3.3 pct 0.0 pct 

Avg. annual fall rate 0.0379 

Incense cedar–all diameters 

Initial count 27 27 29 30 31 30 36 36 38 

Number that fell 0 0 0 0 1 0 3 3 1 

Fall rate for the year 0.0 pct 0.0 pct 0.0 pct 0.0 pct 3.2 pct 0.0 pct 8.3 pct 8.3 pct 2.6 pct 

Avg. annual fall rate 2.5 pct 
Snag Demography—Landram, Laudenslayer, and Atzet 

612 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Second, the number of years it took for half the snags to fall was calculated. We 

call this the half-life. Snags initially tallied in different years were assigned to 

separate populations. Half-lives were calculated separately for each population. 

Populations where more than a 50 percent decline occurred were included. The 

average value for included populations is reported. Source data for this calculation is 

provided in table 4. The equation is 

( )

n

TimeitTakes for Half the Snags to Fall ∑ i

in which: 

 i = population based on year of death 

 n = number of populations 

Third, the display used in Keen (1955) (table 5, fig. 1) of percent of snags still 

standing by years since death was duplicated for comparison (ponderosa pine only). 

Table 4—Half-life of snags by tree species and diameters. 

Snag counts 

Observation year 

Population 

year 

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 

 Jeffrey pine–all diameters 

1989 679 671 616 596 529 484 431 374 347 330 

1990 55 54 51 42 39 31 21 20 18 

1991 51 50 46 42 38 29 23 23 

1992 35 34 34 30 29 27 22 

Jeffrey pine–13-36 cm 

1989 347 342 302 294 256 227 186 155 142 134 

1990 36 35 33 26 23 19 12 11 12 

1991 26 25 22 20 18 14 11 11 

1992 18 17 17 15 15 13 8 

Jeffrey pine–38-74 cm 

1989 231 228 214 206 186 173 165 148 137 128 

1990 16 16 15 14 14 10 8 8 5 

1991 22 22 21 19 17 12 9 9 

Ponderosa pine–all diameters 

1989 471 465 449 434 413 372 341 305 273 225 

1990 64 62 62 58 53 43 35 33 31 

1991 79 78 74 67 55 36 28 24 

1992 111 108 104 95 58 44 38 

1993 68 67 62 51 43 37 

 Ponderosa pine–13-36 cm 

1989 170 168 159 148 132 105 85 73 63 53 

1990 25 23 23 21 17 12 8 8 7 

1991 45 45 43 40 31 15 9 6 

1992 78 75 73 65 36 23 20 

1993 35 35 30 23 17 14 
Snag Demography—Landram, Laudenslayer, and Atzet 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 613 

(table 4 continued) 

Snag counts 

Observation year 

Population 

year 

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 

Ponderosa pine–38-74 cm 

1989 160 159 154 151 148 143 137 125 114 96 

1990 21 21 21 19 19 16 13 11 11 

1991 18 17 16 13 10 8 7 7 

1992 16 16 16 15 10 9 7 

 White fir–all diameters 

1989 187 186 185 179 169 161 147 130 128 87 

1990 30 27 27 21 21 20 17 17 7 

1991 56 56 56 54 50 47 47 26 

White fir–13-36 cm 

1989 64 64 64 61 57 51 44 38 38 21 

1990 24 21 21 15 15 14 11 11 2 

1991 39 39 39 38 35 34 34 21 

White fir–38-74 cm 

1989 71 71 70 68 63 61 58 54 53 40 

Western juniper–all diameters 

1989 65 65 64 62 60 59 57 52 50 50 

Lodgepole pine–all diameters 

1989 30 30 30 29 25 25 23 20 19 19 

Incense cedar–all diameters 

1989 27 27 27 27 27 26 26 24 24 24 

Table 5—Changes in snag height between 1989 and 1997. 

All snags Jeffrey pine White fir 

Count pct Count pct Count pct 

No height change 2,007 88 892 90 547 86 

New height under 6 meters 165 7 55 6 75 12 

New height over 6 meters 107 5 49 5 14 2 

Total 2,279 996 636 

 

Started over 6 meters and changed 275 

New height is under 6 meters tall 151 55 
Snag Demography—Landram, Laudenslayer, and Atzet 

614 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 1—Numbers of new snags and the Palmer Drought Severity Index.

Results 

Creation Rates 

Ponderosa pine snags were created on a generally declining trend ranging from 

82 to 10 total new snags on all study sites combined per year. White fir increased 

from 20 new snags per year to 256 in the spike year of 1995, then declined to 43 new 

snags in 1998. Jeffrey pine ranged from 33 new snags per year to 216 in the spike 

year of 1995, then declined to 17 new snags in 1998 (table 2). The early part of the 

period was relatively dry; the latter part was relatively wet (fig. 1). 

Inventory 

Total snag levels generally increased during the first 6 years then leveled off. 

Small white fir increased the most. Ponderosa pine exhibited a different pattern than 

Jeffrey pine and white fir (table 3; fig. 2). 

0

50

100

150

200

250

300

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

Number of New Snags

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Palmer Drought Index

Dry Index

Wet Index

JP

PP

WF
Snag Demography—Landram, Laudenslayer, and Atzet 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 615 

Figure 2—Numbers of snags of the three dominant tree species existing on all study 

sites from 1989 through 1998. 

Decay Rates 

Records for snags that were topped, cut, burned, or have no diameter recorded 

were not included in the analysis of decay rates, and only snags that were standing in 

1998 were included. 

For those snags standing in 1998, 88 percent retained their height during the 

period of observation (table 5). Ninety percent of the Jeffrey pine and 86 percent of 

the white fir retained their height. Six percent of the Jeffrey pine and 12 percent of 

the white fir have new heights under 6 meters, which is considered a general 

suitability threshold for cavity nesting birds. This suggests that white fir tend to break 

off more frequently while Jeffrey pine tend to fall over. For those Jeffrey pines that 

did have height reduction, the average height changed from 20 meters to 7 meters. 

For those white firs that did have height reduction, the average height changed from 

17 to 4 meters. About half (55 percent) the snags tall enough to function as cavity 

nesting habitat became unsuitable (under 6 meters tall). 

Over the 9 years, very few snags lost bark cover. Only 4 percent of the white fir 

and 13 percent of the Jeffrey pine lost bark cover (table 6). Among Jeffrey pine 

where bark cover change occurred, average bark cover changed from 89 percent to 

54 percent. The corresponding change for white fir was from 99 percent to 84 

percent. 

Jeffrey pine

0

1000

1989199019911992199319941995199619971998

Number of Snags

76 + cm

38-74 cm

13-36 cm

ponderosa pine

0

1000

1989199019911992199319941995199619971998

Number of Snags

76 + cm

38-74 cm

13-36 cm

white fir

0

1000

1989199019911992199319941995199619971998

number of snags

76 + cm

38-74 cm

13-36 cm
Snag Demography—Landram, Laudenslayer, and Atzet 

616 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 6—Changes in percent bark cover. 

All species Jeffrey pine White fir 

Count pct Count pct Count pct 

No change 1,945 85 870 87 612 96 

Changed 334 15 126 13 24 4 

Total 2,279 996 636 

Fall Rates 

Annual fall rates of snags varied by diameter and species (table 7). Fall rates 

were greater for smaller diameter classes; for the pine species the largest diameter 

classes fall rates were less than half of the smallest diameter class. Both pine species 

had greater fall rates than the non-pines. 

Snag half-life, the time required for 1/2 of the snags to fall, was less for the pine 

species compared to the other tree species. Western juniper snag half-lives were 

about twice as great as the pines (table 8). 

Table 7—Average annual fall rate of snags. 

Diameter class 

Species All 13-36cm 38-74cm 76cm+ 

JP 6.8 pct 8.8 pct 5.4 pct 3.0 pct 

PP 6.9 pct 10.8 pct 4.5 pct 4.2 pct 

WF 3.7 pct 4.6 pct 2.7 pct 3.0 pct 

WJ 2.3 pct 2.6 pct - - 

LP 3.8 pct - - - 

IC 2.5 pct - - - 

BO - - - - 

RF - - - - 

Table 8—Half-life of snags (in years). 

Diameter Class 

Species All 13-36 cm 38-74 cm 76 cm+ 

JP 6 6 7 - 

PP 6 5 8 - 

WF 8 7 101 - 

WJ 171

 -2 - - 

LP 111

 - - - 

IC - - - - 

BO - - - - 

RF - - - - 1 These values are outside the range of observation. They are linear trendline estimates. 2 - Not enough observations to warrant a meaningful calculation. 
Snag Demography—Landram, Laudenslayer, and Atzet 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 617 

Comparison with Keen (1955)

Fall rates for ponderosa pine in this study are a little more rapid than Keen 

reported for pure ponderosa pine observed earlier this century (fig. 3). Half-life in this 

study is about 6 years compared to about 8 years reported by Keen (1955). Some 

difference should be expected due to different average diameter, 46 cm in this study 

compared to 61 cm reported by Keen (1955). 

Figure 3—Losses of snags through time comparing Keen’s (1955) results with those 

reported here. 

The Influence of Fire 

Site BM34/Roseburg, was prescribe-burned after snag observations in the fall of 

1997. Including records for snags consumed or felled by fire, the average annual fall 

rate (all species and diameters combined) for the eight periods prior to the burn was 3 

percent compared to the 20 percent rate that occurred after the burn (table 9). 

Table 9—The influence of Rx fire on snag fall rate. 

Species '89-'90 '90-'91 '91-'92 '92-'93 '93-'94 '94-'95 '95-'96 '96-'97 '97-'98 

JP/PP/WF 0 pct 0 pct 0 pct 3 pct 2 pct 7 pct 9 pct 4 pct 20 pct 

Three sites, BM34/125t, BM34/75Ti, and BM34Snag, were thinned and 

harvested in 1996 and Rx burned in 1997. By eliminating the harvested trees from the 

data, the influence of fire can be inferred. The average annual fall rate (all species 

and diameters combined) for the eight periods prior to the burn was 8 percent 

compared to the 19 percent rate that occurred after the burn (table 10). 

30%

40%

50%

60%

70%

80%

90%

100%

012345678

Number of Years after Death

Percent of Snags Standing

Keen (1955)

This Study
Snag Demography—Landram, Laudenslayer, and Atzet 

618 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 10—The influence of Rx fire on snag fall rate. 

Species '89-'90 '90-'91 '91-'92 '92-'93 '93-'94 '94-'95 '95-'96 '96-'97 '97-'98 

JP/PP 3 pct 3 pct 1 pct 4 pct 13 pct 7 pct 21 pct 15 pct 19 pct 

The Influence of Wildfire and Harvest 

Both wildfire and harvest have affected some of the study sites. Virtually all 

trees on the N Mud Lake site have been killed by wildfire; only 12 snags remain on 

the 5-hectare site. Several of the sites within Blacks Mountain Experimental Forest 

have been harvested as part of a long-term research project. The consequence of 

harvest on fall rate can obviously range from insignificant to highly significant. 

Discussion 

These results should help people predict decay rates and fall rates for snags at 

the landscape and larger scale through time. Variation in these rates may be high, so 

cautious application is warranted and incorporation of variation as an objective is 

suggested. Silvicultural prescriptions designed to provide specified levels of snags by 

species and size over specified timeframes should also be informed by this study. 

Creation Rates 

The variation in rate of snag creation between tree species and between size 

classes within a species is not readily explained. More analysis is needed to gain 

insight in this regard. Among other factors, the density of green trees on these study 

sites is not known. Density can accelerate the formation of snags, especially during 

drought. Host specific insects and diseases may also cause different patterns of 

creation. 

Decay Rates 

The fact that 85 percent to 96 percent of the snags standing in 1998 have had no 

change in height or bark cover over the period of observation is not surprising, 

because many snags are new during the study period and those that existed initially 

are relatively stable. We expect significantly more top breakage and bark loss over 

the next 10 years. 

The relative differences in decay rates between Jeffrey pine and white fir are 

hard to evaluate because the number of years since death is not known for many of 

the snags. What appears to be faster decay in Jeffrey pine may be simply a result of 

older age. Many of the pine initially tagged in 1989 were killed by bark beetles in the 

late 1970s. 

The fact that, of those trees experiencing height loss, about half end up under 6 

meters tall, has significant habitat implications for some cavity dependent species. 

The fall rates disclosed here underestimate the snag habitat loss rates that occurred 

because snags of any height were included. 
Snag Demography—Landram, Laudenslayer, and Atzet 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 619 

Fall Rates 

A presumed negative exponential fall rate is not indicated in this data, probably 

because the observation period is too short to reflect one. Keen (1955) and Everett 

and others (In Press) both report a negative exponential form—one from long term 

observations and one from a chronosequence of wildfires. 

The influence of tree species on fall rate was expected. Average annual fall rates 

of about 7 percent for ponderosa pine/Jeffrey pine, 4 percent for white fir/lodgepole 

pine, 3 percent for incense cedar, and 2 percent for western juniper seem appropriate 

in the absence of fire for mid-term planning at landscape and larger scales. More time 

is needed to verify an exponential rate for longer term planning. 

The influence of tree size on fall rate was generally expected. For ponderosa 

pine/Jeffrey pine, average annual fall rates of about 10 percent for smaller snags, 5 

percent for medium sized snags, and 4 percent for large snags were observed. The 

reader is cautioned that understanding the calculation method is important when 

interpreting these results. As used here, annual fall rate is the number of snags falling 

in a given year expressed as a percentage of snags that were present at the beginning 

of the year. Each year stands on its own. The calculation is made separately each 

year. 

The influence of fire is significant. Prescribed burning significantly increases 

snag fall rates for at least 1-year after the fire occurs. Plans that include periodic 

prescribed burns should combine average annual fall rates with periodic increased 

rates during burn years. 

The effect of site variables such as micro-climate, soil, slope position, disease, 

and disturbance history have not been adequately examined but are expected to 

influence both decay rate and fall rate. 

References 

Bull, E. L.; Parks, C. G.; Torgersen, T. R. 1997. Trees and logs important to wildlife in the 

interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. Portland, OR: 

Pacific Northwest Research Station, Forest Service, United States Department of 

Agriculture; 55 p. 

Burns, R. M.; Honkala, B. H., technical coordinators. 1990. Silvics of North America: 

Volume 1, Conifers, Volume 2, Hardwoods. Agric. Handb. 654. Washington, DC: 

Forest Service, United States Department of Agriculture; 877 p. 

Dudley, T. 1982. A survey of invertebrates associated with wood debris in aquatic 

habitats. Melanderia 39: 1-21. 

Everett, R.; Lehmkuhl, J.; Schellhaas, R.; Ohlson, P.; Keenum, D.; Riesterer, H.; Spurbeck, D. 

In press. Snag dynamics in a chronosequence of 26 wildfire burns on the east slope 

of the Washington Cascades. International Journal of Wildland Fire. 

Keen, F. P. 1955. The rate of natural falling of beetle-killed ponderosa pine snags. Journal 

of Forestry 53(10): 720-723. 

Maser, C.; Sedell, J. R. 1994. From the forest to the sea: The ecology of wood in streams, 

rivers, estuaries, and oceans. Herts, UK: St. Lucie Press; 200 p. 

McNab, W. H.; Avers, P. E., compilers. 1994. Ecological subregions of the United States: 

section descriptions. Washington DC: United States Department of Agriculture, Forest 

Service, Administrative Publication WO-WSA-5; 267 p. 
Snag Demography—Landram, Laudenslayer, and Atzet 

620 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Raphael, M. G.; Morrison, M. L. 1987. Decay and dynamics of snags in the Sierra Nevada, 

California. Forest Science 33(3): 774-783. 

Valdez, M. 1996. Shout, “Watch out—snag!” Fire Management Notes 56(3): 26-27. 

Weatherspoon, C. P.; Skinner, C. N. 1996. Landscape-level strategies for forest fuel 

management. In: Sierra Nevada Ecosystem Project, Final report to Congress, vol. II, 

Assessments and scientific basis for management options. Davis, CA: University of 

California, Centers for Water and Wildland Resources; 1471-1492. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 621 

Assessing the Effect of Fire Regime on 

Coarse Woody Debris1

Pamela Wright,2

 Mark Harmon,3 and Fred Swanson4

Abstract 

This study used field data and modeling to examine how coarse woody debris (CWD) differs 

between two areas that experienced different fire regimes (120- to 300-year mean fire return 

intervals) in the 1500-1850 period. Although fire frequency and severity established the 

overall pattern of CWD succession, the interaction of fire regime with other controlling 

factors caused the differences in CWD mass at the landscape scale. CWD mass was almost 

twice as high in landscapes having an infrequent, stand-replacing fire regime (173 Mg/ha) as 

in landscapes having a moderately frequent, mixed-severity fire regime (95 Mg/ha). Factors 

that appear to have the greatest influence are decomposition rates, fire severity, fire 

frequency, and fuel consumption, suggesting that environment and stand structure—together 

with fire regime—are more important than fire regime alone. CWD levels have greater 

temporal variability in the infrequent, stand-replacing fire regime than in the mixed-severity 

regime, primarily because of the different timing of mortality. 

Introduction 

Although a few studies have examined the relationship between coarse woody 

debris (CWD) and natural disturbance, particularly fire, they have primarily 

examined the most simple, stand-replacing fires in which all trees are killed and no 

subsequent fire occurs for several hundred years. Studies and syntheses by Agee and 

Huff (1987), Harmon and others (1986), and Spies and others (1988) depict the 

succession of CWD conditions after fire. During a stand-replacing fire, large amounts 

of biomass are converted from live to dead matter. While some biomass is consumed 

in a fire, much more is converted from live to dead and is carried into the subsequent 

stand. CWD is therefore highest just after such a fire. This material persists as the 

regenerating stand develops and usually is the dominant source until the live trees 

begin to provide woody debris of a large size. As the pulse from the fire begins to 

decompose, CWD in the stand decreases, reaching its lowest level in the mature 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Ecologist, Oregon Department of Environmental Quality, 1102 Lincoln Street, Suite 210, Eugene, OR 

(e-mail address: wright.pamela@deq.state.or.us) 

3

 Richardson Professor, Oregon State University, 3200 Jefferson Way, Corvallis, OR 97331 (e-mail 

address: harmonm@ccmail.osu.edu) 

4

 Geologist Team Leader, Pacific Northwest Research Station, USDA Forest Service, 3200 Jefferson 

Way, Corvallis, OR 97331 (e-mail address: fswanson/r6pnw_corvallis@fs.fed.us) 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

622 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

stand. CWD rises again in late succession as mortality from the regenerated stand 

increases. It levels off when mortality and decomposition reach a “steady-state.” 

Although this simple pattern occurs in many areas, more complex fire regimes 

with multiple fires during the life of a stand, which kill only some trees, are also 

common. The purpose of this paper is to examine the effect of fire regime on CWD 

amounts. Specifically, we asked: 1) Do the CWD levels differ among two fire 

regimes? 2) How are CWD levels affected by fire severity and frequency? and 3) 

How do the other factors that control CWD vary by fire regime? 

To answer these questions, we contrasted two regimes in the west Central 

Oregon Cascades that were distinguished in fire history studies on the basis of fire 

frequency and severity (Connelly and Kertis 1992, Morrison and Swanson 1990, 

Teensma 1987). One regime had infrequent, high-severity fires. The mean fire return 

interval was more than 300 years, and the oldest trees―more than 450 years 

old―originated from stand-replacing fires that occurred during drought periods in 

the 1500s. This regime occurred in cool, moist environments, such as north-facing 

slopes and headwaters. Fires in this regime created large patch sizes of single-aged 

stands. The second regime exhibited more frequent, mixed-severity fires. Here, the 

fire severity ranged from low to high, creating a mosaic of small patches with 

multiple disturbance cohorts of shade tolerant tree species within single stands. The 

mean fire return interval was 95 to 150 years with a mean of about 120 years. Some 

trees survive these fires, but the oldest trees were usually just 200 years old. This 

regime occurred on south-facing slopes and south-facing drainages. 

Our first step was to develop a conceptual model of how CWD was affected by 

different fire regimes. The second step was to collect data on trees, snags, and 

downed logs, in areas with both fire regimes. Third, we developed a simple model 

that simulated the pattern of CWD mass after fire and did a comparative analysis of 

field data and model results. We then used the model to understand how fire 

frequency and severity, stand growth and development, decomposition and mortality 

rates, and fuel consumption may have affected the CWD levels observed in the field, 

and to investigate how each of these factors may have affected the CWD mass in the 

two regimes. 

Study Area 

The study was conducted on the Willamette National Forest near the town of 

Blue River, in the Central Oregon Cascades. Two areas were sampled that are 35 km 

apart and lie north and south of the McKenzie River in the Willamette Basin. The 

study area has long, wet winters and relatively dry, warm summers, typical of the 

west side of the Oregon Cascades and Coast Range. The average annual temperature 

is 9.5°C at 430 m elevation, and precipitation is 2,400 mm per year with more than 

70 percent falling from November through March. The sampled stands are primarily 

within the Western Hemlock Forest Vegetation Zone (670-1,067 m), although some 

upper elevation plots fell in the ecotone between the Western Hemlock Zone and the 

adjacent Pacific Silver Fir Zone (1,067-1,676 m) (Franklin and Dyrness 1988). Field 

sampling included all parts of the moisture and temperature gradients in the Western 

Hemlock Zone, although it did not include all conditions found in the central Cascade 

Mountains described by Zobel and others (1976) (fig. 1).
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 623 

 Tsuga heterophylla 

 Zone

 Transition Zone

 Abies amabilis

 Zone 

 Moist―――――――――――Moisture――――――――――――Dry 

Figure 1―Vegetation along temperature and moisture gradients for the central 

western Cascade Mountain Range (Dyrness and others 1974, Zobel and others

1976). Shaded boxes are plant associations sampled in the study area. 

Field Sampling 

The study area was stratified by fire regimes defined by other studies and stands 

were sampled in two areas for each of the two fire regimes described above. Field 

sampling included an inventory of a total of 57 stands ranging in size from about 50 

to 150 ha. Stands were delineated on aerial photos to sample the full range of stand 

ages, elevations, and aspects, and to sample the extent of the area identified by the 

fire history studies. Within each stand five randomly selected variable-radius plots 

were sampled. 

At each plot, information was recorded about physical conditions such as 

percent slope, aspect (degrees azimuth), topographic position, plant association 

(Hemstrom and others 1987), and elevation (m). In each stand, variable radius plots 

were used to sample live trees. Diameter at breast height (DBH) of each tree tallied 

>23 cm was recorded to convert basal area to stem count per ha (Dilworth and Bell 

1985). 

To estimate the mass of downed CWD, we sampled logs >23 cm in diameter at 

the point of intersection (Brown 1974, Van Wagner 1968) with two perpendicular 

transects intersecting at plot center 100 m in total length (50 m up and downhill, 50 m 

along contour). Diameters of logs were measured, and species and decay class were 

recorded according to a classification system widely used in the Pacific Northwest 

(Fogel and others 1973, Sollins 1982, Triska and Cromack 1980). 

Tshe/ 

PomuOxor

Tshe/

Pomu

Tshe/ 

Acci/

Pomu Psme/ Acci/ 

Bene

Tshe/ Rhma/ 

Bene Psme/ 

Acci/ 

Gash 

Tshe/ 

Gash

PsmeTshe/ 

Cocoa 

Psme/ 

Hodi 

Tshe/ 

Rhma/ 

Gash 

Cold――――――

―Temperature―――――

―Hot 

Tshe-Abam/ 

Rhma/Bene

Tshe-Abam 

Psme/Acci/ /Rhma/ Lobo

Whmo 

TsheAbam/Libo 

AbamTshe/Xete 

Abam/ Vame/ 

Xete 

Abam/ RhmaVaal/Coca Abam/ Vaal/ 

Coca 

Chno/ 

Opho 

Abam/ 

Tiun

Abpr/ Clun Abpr/ 

Actr 

Abam/ 

Actr
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

624 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Snags were measured in an 800 m2 belt transect. Snags >23 cm diameter and 

greater than 0.5 m tall were measured at breast height and recorded by species, 

diameter, height, and a decay class scheme developed by Cline and others (1980) 

similar to the log decay classification scheme. Heights were estimated visually after 

the heights of a few snags on each transect were measured with a clinometer and 

tape. 

To compare mortality rates for the areas having different fire regimes, we 

calculated the ratio of CWD volume by decay class to live tree volume, and estimated 

the volume of CWD that accumulated each year. We calculated the total CWD 

volume in each decay class and estimated the length of time the trees had been dead, 

using rough estimates of residence time in each decay class. To estimate the average 

mortality rate for each fire regime for the past 2 centuries, we averaged the rates for 

all decay classes in the four sampling areas. The mortality rate was calculated as: 

Mortality Rate year -1 = (CWD Volume/Live Tree Volume)/Residence Time year-1.

in which CWD Volume is the total CWD volume by decay class for each sampling 

area, Live Tree Volume is the mean tree volume for stands in each sampling area, and 

Residence Time is the number of years CWD remains in each decay class. 

This assumes live tree volume is static through time, which is probably only true 

for older stands when tree volume levels off. Residence time for Douglas-fir log 

decay classes are comparable to other studies, and since it dominated species 

composition, it was used to estimate the mortality rate for field data. Residence time 

was estimated by assuming CWD remains in Decay Class 1 for 15 years, in Class 2 

for 15-44 years, in Class 3 for 45-89 years, in Class 4 for 90-145 years, and in Class 5 

for 150-225 years. 

Statistical Analysis 

We performed a randomized block, two-way analysis of variance (ANOVA) and 

paired t-test with the two geographic sites (north of the McKenzie River and south of 

the McKenzie River) as blocks to determine if the CWD mass in the two fire regimes 

varied significantly at a p-value < 0.10. (SAS Institute, Inc. 1992). We also 

performed a Chi-squared test to determine whether the distribution of CWD among 

the decomposition classes differed significantly between the two fire regimes. 

A paired t-test was used to determine whether site productivity of the sampling 

areas with different fire regimes varied significantly. Using the plant associations 

identified in the field, we compared site indices (height of a Douglas-fir in 100 years 

from McArdle and others 1961) and performed a paired t-test at a p-value of 0.10 to 

determine if the differences in mean site indices were statistically significant between 

the two regimes. 

Model Description 

We constructed a simulation model, FIRECWD, based on the conceptual model 

developed by Harmon and others (1986), which considers the store of CWD in an 

ecosystem and how it changes through time. The model accounts for the CWD that is 

input to the system by mortality (e.g., fire events, bark beetles, or root rot), the 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 625 

amount that is lost (e.g., decomposition and consumption by fire), and the levels of 

CWD mass that result. 

The purpose of the model was to simulate CWD dynamics for the two fire 

regimes, compare the mean and standard deviation of CWD between modeled and 

field estimates, and gain insights into the behavior of the system by changing input 

and control variables. The model was built to run in Microsoft Excel or Quatro Pro 

for Windows 5.0,5

 and used to explore the effects of fire frequency, fire severity, site 

productivity, decomposition, mortality, stand growth, and fuel consumption on CWD 

succession. 

A full description of the model can be found in Wright (1998). A general 

description follows. This model expresses the essential elements of vegetation and 

fuel succession using the body of knowledge from previous research. A stochastic 

element allows the model to simulate the variability that might be expected for CWD. 

FIRECWD randomly selects years in which fire occurs within the limits that reflect 

the fire regime, such as once every 200 years or once every 500 years. It is 

programmed to simulate the natural variation expected in maximum biomass, 

decomposition and mortality rates, growth parameters, and pre-fire CWD. 

Live Biomass 

The live biomass function simulates tree growth and biomass that accumulates 

in the stand between fires. In the years when fires occur, a portion of the trees are 

killed and live biomass representing that portion is converted to CWD mass, while a 

small portion is consumed by the fire. The amount of the conversion depends on fire 

severity. The portion of the live biomass remaining continues to grow, and live 

biomass continues to accumulate from the level it was reduced by the fire. In the case 

of the stand-replacing fire regime, the live biomass would be reduced 85 percent +/- 

15 percent, and for a mixed-severity fire regime, it would be reduced 50 percent +/- 

15 percent. For example, in the stand-replacing fire regime, the live biomass begins 

accumulating from an average 15 percent of the live biomass existing in the year of 

the fire. 

The total live biomass of trees was estimated from stand age, a Richards 

function parameterized with the maximum live biomass the site can support, the time 

to reach the maximum biomass, and a parameter that controls the point of inflection 

(Richards 1959). The maximum biomass was estimated from site index based on 

plant associations and a growth and yield model, DFSIM (Curtis and others 1982). 

DFSIM output indicated that a site with average productivity in the study area at a 

stand age of 300 years would have a live biomass of about 700 Mg/ha. 

Fire Disturbance 

This part of the model is used to simulate the direct effects of fire on CWD 

mass. In the year when a fire occurs, the pulse input of CWD mass created by a fire 

depends on the total live biomass currently in the system and the fire severity. Fires 

occur stochastically based on a probability estimated from the fire return interval for 

a site. To simulate randomly occurring fires, a spreadsheet cell indicating fire 

 

5

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

626 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

occurrence is linked to a column in which a random number is produced for each 

annual time step. If this random number is greater than the annual probability of fire, 

a fire occurs. This allows the model to simulate the fire frequency and severity of a 

regime, such that severity is greater when time intervals between fires are longer. 

Fuel Consumption 

This part of the model calculates the mass of CWD lost due to fuel consumption. 

The model also tracks the portion of CWD stores that are not reduced by fuel 

consumption. Fuel consumption, estimated from previous research, is assumed to 

average 20 +/- 5 percent of the total CWD mass already present in the year of the 

fire, and 5 percent of the live biomass converted to CWD mass by the fire (Brown 

and others 1985, Reinhardt and others 1991). 

Non-fire Mortality 

This part of the model is used to simulate the CWD mass that accumulates from 

chronic mortality in the new stand from factors such as stem exclusion, insects, 

pathogens, and wind. We assume that as the new stand grows, 0.005 per year of the 

live tree biomass dies. This amount varies randomly +/- 0.00125 per year for each 

model run. For the first 50 years after a fire, trees are quite small (diameters <10 cm) 

and not considered CWD. The dead trees that accumulate after the fiftieth year are 

considered CWD mass. 

Decomposition 

This part of the model is used to simulate the decomposition of CWD mass. For 

any given year, the total CWD mass has three sources: fire created CWD, old CWD, 

and CWD created by non-fire mortality. The decomposition function is applied to all 

three sources calculating the mass of CWD lost from decomposition. The average 

decomposition rate constant for the ecosystem is assumed to be 0.020+/- 0.005 per 

year. 

Randomization 

The model is stochastic with each simulation run producing a slightly different 

output. Consequently, the model can generate “data” to test effects of different fire 

regimes and control variables using statistics. Each run generally parallels the mean 

value, but individual runs can be quite a bit higher or lower than the mean depending 

on the parameter values selected. To vary the parameters between model runs, we 

created one cell in the spreadsheet for the mean value and one for the standard 

deviation for each parameter, and two associated cells with random numbers. One 

specifies how much to deviate the parameter, and another indicates whether the 

deviation is added to or subtracted from the mean value. We divided this uniform 

distribution into unequal segments so that its frequency distribution took on the form 

of a normal distribution. 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 627 

Results 

Coarse Woody Debris Mass 

The field measurements of CWD indicate that on average stands with the mixedseverity fire regime had about half as much CWD as sites with the stand-replacing 

fire regime (table 1). However, an ANOVA and a paired t-test revealed no 

statistically significant difference (p < 0.29) in total CWD mass between the two 

regimes. 

Table 1―Mean, standard deviation, and range of CWD mass for field data for each regime 

individually and sites combined by regime. 

 CWD mass (Mg/ha) 

Fire 

regime 

Sample 

area 

Number of 

stands 

Mean Standard 

deviation 

Range 

Stand- Lookout 12 190 99 100-420 

replacing Augusta 15 155 105 55-411 

 Combined 27 173 102 55-420 

 

Mixed- Cook-Quentin 14 73 40 30-155 

severity Chucksney 16 115 72 18-258 

 Combined 30 95 56 18-258 

 

The model predicted a more similar CWD mass between the two regimes than 

did the field data (table 2). The model results also indicated less variability in CWD 

mass within the fire regimes than the field data. These model results indicated that 

fire frequency and severity alone are probably not responsible for the different 

amounts of CWD mass found in the field data and that site productivity, 

decomposition and mortality rates, and/or stand growth may also control CWD mass 

differences in the areas with different fire regimes. 

Table 2―Mean, standard deviation, and range of CWD mass (Mg/ha) from model data 

varying all the control factors within the expected range for two fire regimes. Control factors 

include fire-killed biomass, decomposition rate, mortality rate, maximum biomass, and B1 

and B2 in the growth function. Range is the mean minimum and maximum for 30 model runs. 

 -----------CWD mass (Mg/ha)---------- 

Fire regime Mean fire return 

interval 

Mean Standard 

deviation 

Range 

Stand-replacing 300 212 28 133 - 807 

Mixed-severity 125 188 39 102 - 571 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

628 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Site Productivity

Field results of the site indices in the study area overlap considerably. The mode 

of site indices in the study area was 136, and the stands experiencing a standreplacing fire regime had only a slightly higher mean site index than stands with the 

mixed-severity fire regime (135 vs. 132). A paired t-test indicated that site 

productivity was not different statistically (p < 0.80). 

The site indices for the study area span only a small range of the possible values 

for site index, and consequently the effect of site productivity on differences in CWD 

mass between the fire regimes is not significant. Sensitivity analysis indicates that the 

model is highly responsive to this factor. Within the area we sampled, however, site 

productivity probably plays a minor role in controlling the different levels of CWD 

mass found in the two fire regimes because site index is fairly constant. 

Tree Biomass 

Tree biomass measured in the field showed that stands with the stand-replacing 

fire regime had 100 Mg/ha more mass than the average of the stands in the mixedseverity fire regime (752 and 649 Mg/ha respectively). The stands with a standreplacing regime are older (100-450 years) than stands with a mixed-severity regime 

(90-150 years), and older stands would be expected to have greater tree biomass than 

younger stands. The model has low sensitivity to the parameters that influence the 

amount of time necessary for the stand to become established and the time period 

required for mean annual growth to level off. Varying these parameters has little 

effect on differences in CWD mass. Accordingly, these growth, rate-related 

parameters have little effect on CWD over time, and they probably also have little 

influence on the different levels of CWD between the two fire regimes. 

Mortality 

The mortality rates from the field data for the two fire regimes indicate that the 

non-fire mortality rate (i.e., suppression mortality, disease, wind, etc.) is only slightly 

different between the areas having different fire regimes. The model has an 

intermediate level of sensitivity to mortality, but varying the mortality rate within the 

expected range had little effect on the total CWD mass. The combined results from 

the field data and the modeling indicate mortality is a relatively unimportant factor in 

explaining the difference in total CWD accumulation between the areas having two 

fire regimes. 

Decomposition 

Sensitivity analysis indicates that the model is highly responsive to changes in 

the decomposition rate constant. Previous research efforts indicate that a high degree 

of variation exists in decomposition rate estimates (Harmon and others 1986, Sollins 

1982, Spies and others 1988). Varying the decomposition rate within the range found 

in the west central Oregon Cascade Mountains results in considerable differences in 

CWD mass over time. Decomposition rate appears to have the greatest effect on 

CWD of all control factors examined. For example, increasing the decomposition rate 

to 0.050 year-1 would reduce CWD mass to less than one-third the mass that would be 

present if the decomposition rate were 0.010 year-1 (table 3). 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 629 

Table 3―Modeled mean CWD mass (Mg/ha) averaged more than 500 years for the two fire 

regimes for decay rates 0.01 to 0.05 from 30 model runs for each regime. 

Decomposition rate 

constant 

Stand-replacing 

300 yr. MFRI 

Mixed-severity 

125 yr. MFRI 

0.010 387 319 

0.020 212 188 

0.030 153 133 

0.040 127 112 

0.050 111 96 

Fuel Consumption 

Although there are no field data for fuel consumption (the study area has been 

free of fire for decades), we used the model to estimate the effect of fuel consumption 

on CWD mass for the two regimes. The model has a low sensitivity to fuel 

consumption, but model runs of randomly occurring fires indicate that the effect of 

fuel consumption from fires in the mixed-severity regime would be considerably 

higher than for the stand-replacing fire regime because more fires occurred (4 fires 

vs. 1.6 fires per 500-year period). Results indicate that even with this reduction from 

fuel consumption, the mass indicated by the model (206 and 167 Mg/ha) is still 

considerably higher than the CWD field data (173 and 96 Mg/ha). 

Fire Killed Biomass 

Using live tree biomass observed in the field as an estimate of potential CWD 

input from fires and using model data (which indicates low sensitivity), it appears 

that fire-caused mortality has a large effect on CWD mass for the first 100 years after 

a fire, but then the effect rapidly diminishes. This is because decomposition is an 

exponential function and reduces fire-created CWD mass rapidly the first years after 

a fire. The analysis also indicates that a much longer time period is necessary for 

CWD to recover in a stand-replacing regime (more than 200 years) than in a mixedseverity regime (about 100 years). 

Discussion 

CWD Mass in the Two Fire Regimes 

Field data indicated that CWD mass is consistently higher across the stands in 

the stand-replacing regime, with an average CWD mass almost twice as high as the 

stands in the mixed-severity regime. Although the differences were not statistically 

significant, due to high variability, there are readily apparent differences in CWD 

mass (table 1). Furthermore, no recently burned stands were sampled, and therefore, 

stands with high mass created by such fires were not considered. Given that standreplacing fires initially input a higher dead wood mass, one would expect the 

differences between regimes might be even greater. Trends may have been even more 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

630 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

pronounced had the field study included areas where fire regimes are more dissimilar 

than those found in the western Cascades of Oregon. 

Fire suppression probably did not influence the field results greatly; however, in 

areas with the mixed-severity regime it may have some implications for future 

development of CWD. Over the last 50 to 70 years the effects of wildfire on the 

landscape have been minor, and much biomass is now tied up in small live trees. 

Therefore, a wildfire now would probably be more severe than typical for this regime 

because of the high numbers of small, suppressed trees. The fire-created CWD would 

then be more similar to that occurring in a stand-replacing regime, including a larger 

pulse and a much longer recovery time. 

Model Uncertainty 

Model predictions are uncertain for two reasons: 1) the model’s sensitivity to 

parameters, and 2) the observed variation in parameters. If a model is not sensitive to 

a parameter, that parameter probably does not greatly influence uncertainty. In 

contrast, if a model is sensitive to a parameter and its value does not vary, then 

uncertainty is low. If the model is sensitive to a parameter and its value varies widely, 

however, it can introduce major uncertainty to the analysis. For example, modeled 

CWD mass is not especially sensitive to fire frequency and severity, and since the 

regimes are clearly defined in terms of frequency and severity, the model has a 

relatively low degree of uncertainty associated with these factors. In contrast, the 

model has a high degree of sensitivity to maximum biomass (site productivity), but 

given the limited observed range for this study area, it also has little influence on 

uncertainty. The model has a high degree of sensitivity to decomposition rate, and 

given the possible range in this parameter, it has considerable influence on 

uncertainty. Finally, the model has a moderate degree of sensitivity to the mortality 

rate, but modeling indicates the observed variation in mortality rate has little 

influence on CWD accumulation. 

The degree to which each factor influences CWD accumulation also depends on 

whether the factor’s effect is occasional or continuous. The model has low sensitivity 

to both fire frequency and severity, probably because these influence CWD mass 

only for the first 100 years after a fire and not for the subsequent 400 or 500 years. 

The growth rate of the stand is important for the first 80 to 100 years while the stand 

is growing rapidly and less so afterwards. Site productivity continues to have an 

influence on CWD accumulation after the stand has reached its peak in mean annual 

growth. Decomposition, and to some extent mortality rate, have an influence on 

CWD accumulation every year and, therefore, are important regardless of the age of 

the stand. 

Why Are the Fire Regimes Different?

What factors might be controlling the differences in CWD for the two fire 

regimes? Modeling results suggest that, all other things being equal, the two fire 

regimes should have about the same CWD mass. Although the temptation is to 

attribute differences in CWD mass to fire regime per se, differences in fire frequency 

and severity can only account for about 10 percent of the observed difference in the 

amount of CWD predicted by the model. This suggests that, although the mixedseverity regime has about half the CWD of the stand-replacing fire regime, the 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 631 

difference may not be caused by the regime itself. Rather the difference may be due 

to environment and stand structure. In addition to causing more frequent fires, a 

warmer, drier environment speeds decomposition, increases fuel consumption, and 

grows smaller trees (i.e., less biomass). 

Model sensitivity analysis indicates that decomposition and fuel consumption 

may have more effect on CWD mass than fire frequency and severity. Of these two 

factors, decomposition appears to be the more significant. First, the model is most 

sensitive to decomposition. Second, estimates of decomposition rates from previous 

studies vary significantly from 0.018 to 0.029 (Sollins 1982, Spies and others 1988). 

Third, model simulations using a 0.03 year-1 decay rate for the warmer, drier sites 

having a mixed-severity regime, and a 0.02 year-1 for the stand-replacing regime give 

CWD mass that is 52 percent lower for the mixed-severity regime than the standreplacing regime. The field data indicate CWD mass is 45 percent lower for the 

mixed-severity regime. Other research indicates that in this region warm, dry sites 

have increased decomposition rates, and that excess moisture generally limits log 

decomposition (Graham 1981, Harmon 1992, Means 1982). 

Implications for Management of CWD 

CWD mass is much higher in wildfire regenerated stands than in stands 

intensively managed for timber production (Spies and Cline 1988). To retain 

functions and processes associated with green trees, some current forestry projects 

are retaining more live trees in stands in areas that had a mixed-severity regime than 

in areas with high-severity, stand-replacing regimes. A similar approach could be 

used for CWD. 

To mimic the natural succession of CWD, managers need to consider fire 

regime, site potential, decomposition rates, fuel consumption, and management 

objectives. The following questions should be addressed: Does the fire pattern 

generate the large amounts of CWD of the stand-replacing fire regime or the more 

frequent, smaller pulses of the mixed-severity fire regime? The latter may be easiest 

to emulate in stand management, but one should still consider how stand 

management differs from the CWD cycle of the natural fire regime. Managers should 

consider whether recent fire history is typical of the natural fire regime or if it bears 

the influence of post-European settlement burning and suppression. Some 

information about fire influence may be deduced from the ages of the stands and fire 

history studies (see examples in Hyderdahl and others 1993). What are the ages of the 

area’s oldest stands in various forest types? What is known about lightning-caused 

fires and fire suppression? How long since the stand last experienced fire? Managers 

can also consider the forest structure for its relation to fire severity. Are stands evenaged or do various age cohorts suggest multiple fire-caused stand regeneration events 

with shade-tolerant as well as shade-intolerant species present? Do stands contain old 

age cohorts that survived previous fires? If so, what is the proportion of the total 

stand volume represented by remnant trees? 

The rate of decomposition should also be considered, given its substantial effect 

on total CWD mass through time. On cool and/or wet sites in western Oregon, low 

temperature and/or high moisture content can limit the activity of decomposing 

organisms. On the other hand, sites that are excessively dry may also have slow 

decomposition. The results of this analysis suggest that decomposition rates may vary 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

632 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

considerably, even in stands of close proximity, such as those on opposite sides of a 

ridge. 

Finally, managers should consider that the effect of CWD treatments will persist 

for decades, even centuries. Management strategies may strive to emulate the natural 

CWD cycle, but may fall short of this goal because of the volume of potential CWD 

that is removed to the sawmill. For managers to successfully mimic the dead 

structure associated with the types of fire regimes in this study area, it is advisable to 

retain the highest levels of CWD in areas having a stand-replacing regime and lesser 

amounts in areas having a mixed-severity regime. 

We suggest a hybrid approach that combines field data and modeling to address 

difficult management questions. CWD is highly variable through time, and a model 

of the processes that affect CWD allows us to consider CWD succession, including a 

much broader range of conditions than can be observed in the field. It also facilitates 

estimating CWD levels in stages of succession that do not currently exist because of 

the limited number of fires in the past. 

Although the question of “how much” CWD to retain dominates current 

management discussions, understanding the processes that control CWD and its link 

with wildlife and fish may be our greatest challenge. In fact, increased understanding 

of CWD dynamics and functions is our best path not only to answer “how much” but 

also to understand what is necessary to sustain forest functions. The limited 

knowledge about the amount of CWD needed to meet ecological objectives points to 

the need for more discussion between the management and scientific communities on 

this topic. 

Acknowledgments 

We wish to thank Mark Huff and Kim Mellen for valuable discussion and 

helpful suggestions for improving this manuscript. 

References 

Agee, James K.; Huff, Mark H. 1987. Fuel succession in a western hemlock/Douglas-fir 

forest. Canadian Journal of Forest Research 17: 697-704. 

Brown, James K. 1974. Handbook for inventorying downed woody material. Gen. Tech. 

Rep. INT-16. Ogden, Utah: Intermountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 24 p. 

Brown, James K.; Marsden, M. A.; Ryan, K. C.; Reinhardt, E. D. 1985. Predicting duff and 

woody fuel consumed by prescribed fire in the northern Rocky Mountains. Gen. 

Tech. Rep. INT-337. Ogden, Utah: Intermountain Forest and Range Experiment Station, 

Forest Service, U.S. Department of Agriculture; 23 p. 

Cline, Steven P.; Berg, A. B.; Wight, H. M. 1980. Snag characteristics and dynamics in

Douglas-fir forests, western Oregon. Journal of Wildlife Management 44: 773-786. 

Connelly, Kathy P.; Kertis, J.A. 1992. Augusta fire history. Unpublished draft supplied by 

authors. 

Curtis, R. O.; Clendenen, G. W.; Reukema, D. L.; DeMars, D. J. 1982. Yield tables for

managed stands of coast Douglas-fir. Gen. Tech. Rep. PNW-135. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 97 

p. 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 633 

Dilworth, J. R.; Bell, J. F. 1985. Log scaling and timber cruising. Corvallis: Oregon State 

University; 468 p. 

Dyrness, C. T.; Franklin, Jerry F.; Moir, W. 1974. A preliminary classification of forest

communities in the central portion of the western Cascades in Oregon. US/IBP 

Coniferous Forest Biome Bulletin Number 4. Seattle, WA: College of Forest Resources, 

University of Washington; 123 p. 

Fogel, R.; Ogawa, M.; Trappe, James M. 1973. Terrestrial decomposition: a synopsis. 

US/IBP Coniferous Forest Biome Report 135. Seattle. WA: University of Washington; 

300 p. 

Franklin, Jerry F.; Dyrness, C. T. 1988. Natural vegetation of Oregon and Washington. 

Corvallis: Oregon State University Press; 417 p.

Graham, Robin L. 1981. Biomass dynamics of dead Douglas-fir and western hemlock 

boles in mid-elevation forests of the Cascade Range. Corvallis: Oregon State 

University; 188 p. Ph.D. dissertation. 

Harmon, Mark E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Augmen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K.; Cummins, K. W. 1986. Ecology of coarse woody debris in temperate

ecosystems. Advances in ecological research 15: 133-302. 

Harmon, Mark E. 1992. Long-term experiments on log decomposition at the H.J.

Andrews Experimental Forest. Gen. Tech. Rep. PNW-GTR-280. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 28 p. 

Hemstrom, Miles A.; Logan, Sheila E.; Pavlat Warren. 1987. Plant association and

management guide: Willamette National Forest. PNW R6-Ecol 257-B-86. Portland, 

OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 312 p. 

Heyerdahl, Emily K.; Swanson, Frederick J.; Agee, James, K. 1993. Fire history database of 

the western United States: preliminary report covering Oregon and Washington. 

Interagency Agreement Environmental Protection Agency: DW12934530, USDA Forest 

Service, Pacific Northwest Research Station: 93-0300, University of Washington, 

College of Forest Resources: 61-2239; 40 p. 

McArdle, Richard E.; Meyer, Walter H.; Bruce, Donald. 1961. The yield of Douglas-fir in 

the Pacific Northwest. Technical Bulletin 201. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 74 p. 

Means, Joseph E. 1982. Developmental history of dry coniferous forests in the central 

western Cascade Range of Oregon. In: Proceedings of the symposium forest 

succession and stand development research in the Northwest; 1981 March 26; Corvallis, 

OR. Corvallis: Oregon State University; 142-158. 

Morrison, Peter H.; Swanson, Frederick J. 1990. Fire history and pattern in a Cascade 

Mountain Landscape. Gen. Tech. Rep. PNW-GTR-254. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 77 p. 

Reinhardt, Elizabeth; Brown, J. K.; Fischer, W. C.; Graham, R. T. 1981. Gen. Tech. Rep. 

INT-43. Ogden, Utah: Intermountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 22 p. 

Richards, F.J. 1959. A flexible growth function for empirical use. Journal of Experimental 

Botany 10: 290-300. 

SAS Institute, Inc. SAS/STAT [Computer Program]. 1992. Cary, NC: SAS technical report 

P-229: Changes and enhancements, Release 6.07. 
Factors that Control Coarse Woody Debris Mass—Wright, Harmon, and Swanson 

634 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Sollins, Phillip. 1982. Input and decay of coarse woody debris in coniferous stands in 

western Oregon and Washington. Canadian Journal of Forest Research 12: 18-28. 

Spies, Thomas A.; Cline, Steven P. 1988. Coarse woody debris in forests and plantations 

of coastal Oregon. In: Maser, Chris; Tarrant, Robert F.; Trappe, James M.; Franklin, 

Jerry F., eds. From the forest to the sea: a story of fallen trees. Gen. Tech. Rep. PNWGTR-229. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 5-24. 

Spies, Thomas A.; Franklin, Jerry F.; Thomas, Ted B. 1988. Coarse woody debris in

Douglas-fir forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Teensma, Peter D. A. 1987. Fire history and fire regimes of the central western Cascades 

of Oregon. Eugene: University of Oregon; 188 p. Ph.D. dissertation. 

Triska, F. J.; Cromack, Kermit. 1980. The role of wood debris in forests and streams. In: 

Waring, Richard H., ed. Forests: fresh perspectives from ecosystem analysis. Corvallis: 

Oregon State University Press; 171-189. 

Van Wagner, C. E. 1968. The line intersect method in forest fuel sampling. Forest Science 

14: 20-26. 

Wright, Pamela J. 1998. The effect of fire regime on coarse woody debris in the west 

central Cascades, Oregon. Corvallis: Oregon State University; 109 p. M.S. thesis. 

Zobel, Donald B.; McKee, Arthur; Hawk, G. M.; Dyrness, C. T. 1976. Relationship of

environment to composition, structure, and diversity of forest communities of the 

central Western Cascades of Oregon. Ecological Monographs 46: 135-156. 
Demographics and Dynamics in 

Rocky Mountain Forests

635
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 637 

Mortality as a Source of Coarse Woody 

Debris in Managed Stands1

Carl E. Fiedler2 and Todd A. Morgan2

Abstract 

Mortality was recorded annually over a 15-year period after thinning in each of three evenaged stands (one ponderosa pine and two ponderosa pine/Douglas-fir/western larch), and after 

individual tree selection cutting in two uneven-aged ponderosa pine stands. Highest mortality 

occurred in the controls in both the even- and uneven-aged stands, primarily due to 

suppression, while weather was the leading mortality agent in the thinning and selection 

cutting treatments. Beetles were the primary killer of ponderosa pine, and western spruce 

budworm of Douglas-fir. Mortality of trees ≥25 cm diameter was negligible in all silvicultural 

cutting treatments. Absent low-intensity fires that historically promoted open pine stands and 

large-tree development, active management will likely be needed to create desired live tree 

and dead wood stand components in the future. 

Introduction 

A primary objective of prescribing and implementing silvicultural cutting 

treatments in forest management is to achieve a desired future condition in the stand 

while ensuring long-term site productivity. These treatments typically involve 

directing site resources toward fewer treesusually trees of desired species, form, 

and vigorthus increasing the growth rate of residual trees. A secondary but 

traditionally welcome effect of treatment is reduced levels of tree mortality. 

However, recent insights into ecosystem health suggest that stands consisting only of 

live trees may not provide the range of conditions needed to support the full suite of 

life-forms required for sustained ecological function (Cazares and Trappe 1999). 

Dead trees, either standing or down, are important as food sources (Haverty and Shea 

1999, Ross 1999), as refugia for a variety of animal species (Herder and Jackson 

2002, Laudenslayer 2002), as substrate for mycorrhizal infection (Harvey and others 

1981, Harvey and others 1987), and as a primary source of nutrients and large 

organic matter for soil development and maintenance (Prescott and Laiho 2002). 

Therefore, the causes, timing, and distribution of tree mortality, along with 

silvicultural prescriptions that maintain and/or create relatively large trees on-site, 

need to be addressed. 

This paper reports amounts and causes of tree mortality by diameter, species, 

and treatment for the first 15 years after various silvicultural cuttings in even- and 

uneven-aged stands in west-central Montana. Tree mortality has traditionally been 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Associate Professor and Research Specialist in Forestry, respectively, School of Forestry, 

The University of Montana, Missoula, MT 59812. (e-mail addresses: fiedler@forestry.umt.edu and 

todd.morgan@business.umt.edu) 
Mortality in Managed Stands—Fiedler and Morgan 

638 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

sampled on relatively small (0.04- or 0.08-ha) plots—plots designed to sample 

growth of trees, not mortality pattern as part of a larger population. Because tree 

mortality is often clustered (Dale 1999, Lutes 2002) and episodic, sampling small 

fixed plots at 5- or 10-year intervals may not be appropriate for discerning mortality 

relationships and trends. Hence, a combination of small plots (to reflect stand density 

and structure of live trees) and a complete census of dead trees on much larger plots 

(to capture the full range of species, distribution, and diameters) was incorporated 

into this mortality study. 

Methods 

Tree mortality was monitored in five stands on The University of Montana’s 

Lubrecht Experimental Forest in west-central Montana: a pure, even-aged ponderosa 

pine (Pinus ponderosa) stand; two even-aged ponderosa pine/Douglas-fir 

(Pseudotsuga menziesii)/western larch (Larix occidentalis) stands; and two unevenaged ponderosa pine stands. A thinning demonstration was implemented in 1983 in 

each of the three even-aged stands to evaluate growth and mortality among three 

residual densities (6x6, 4x4, and 3x3-m nominal tree spacing) and an unthinned 

control. A second study was installed in the two uneven-aged ponderosa pine stands 

in 1984. In this study, growth and mortality were compared among two management 

treatmentsselection cutting with and without underburningand an untreated 

control. In the even-aged stands, the thinned units and the control were each about 

1.5 ha in size, for a total area of about 6 ha per stand. In the two uneven-aged stands, 

the selection cutting units and the control were each 1 ha in size, for a total area of 3 

ha per stand. This paper reports the amounts and causes of mortality by treatment, 

species, and diameter for the first 15 years after treatment in each stand. 

All five stands are within about 10 km of each other and at nearly the same 

elevation1,200 m. At the time the study was initiated, the even-aged ponderosa 

pine stand was about 80 years old, with 2,620 trees per hectare (tpha), and a basal 

area density of 45.9 m2

/ha in the control. This stand occupies a site classified as a 

Douglas-fir/snowberry (Pseudotsuga menziesii/Symphoricarpus albus) habitat type 

(h.t.) (Pfister and others 1977). The two mixed ponderosa pine/Douglas-fir/western 

larch stands were also about 80 years old at the beginning of the study, with an 

average of 1,300 tpha, and an average basal area density of 36.7 m2

/ha in the 

controls. These stands occur on sites classified as Douglas-fir/snowberry h.t. (Pfister 

and others 1977). Trees in the two uneven-aged ponderosa pine stands ranged in size 

from seedlings to old-growth trees >75 cm dbh, and from 1 to about 400 years old. 

One of the uneven-aged stands occurs on a site classified as a Douglas-fir/snowberry 

h.t., while the other is classified within the Douglas-fir/dwarf huckleberry 

(Pseudotsuga menziesii/Vaccinium caespitosum) h.t. (Pfister and others 1977). At the 

beginning of the study, the uneven-aged controls supported an average of 950 tpha 

with an average basal area density of about 23.0 m2

/ha, while basal area density was 

reduced to 13.8 m2

/ha in the treated stands. 

In each stand, all standing dead trees were marked with spray paint at the 

beginning of the study so that they would not be counted as subsequent mortality. 

Each autumn, a complete survey (census) of all trees in each stand was conducted to 

identify trees that had died during the preceding year. Each dead tree was recorded as 

to species, dbh, and cause of death, and then marked to prevent counting again in 

subsequent years. 
Mortality in Managed Stands—Fiedler and Morgan 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 639 

Mortality patterns were similar between the two mixed ponderosa pine/Douglasfir/western larch stands and between the two uneven-aged ponderosa pine stands; 

hence results were combined in each case for simplicity of presentation and 

interpretation. Mortality data from the even-aged stands were combined into 5.0-cm 

dbh classes for greater resolution in the relatively small range of tree diameters (2.5-

45.7 cm), while uneven-aged mortality data were grouped by 10.0-cm dbh classes 

because of the larger diameter range (2.5-76.2 cm). 

Results 

Even-aged Ponderosa Pine Stand 

Mortality in the pure, even-aged ponderosa pine stand occurred primarily in the 

uncut control (fig. 1). There were 2,620 live tpha in the control at the beginning of the 

study; however, only 1,774 tpha remained alive at the 15-year remeasurement. 

Among the three thinning treatments, mortality was greatest in the treatment with 

3x3-m nominal spacing, where 35 tpha died in the 15-year period. The 4x4 treatment 

lost only 15 tpha, and the 6x6 treatment had no mortality. The smallest diameter 

classes represented in each of the treatments contained the majority of the mortality, 

while little or no mortality occurred among the largest size classes present in each of 

the treatments. In the control, 699 tpha died among trees <15.2 cm. The 3x3 

treatment lost 27 tpha among trees 7.6-17.8 cm dbh, while the 4x4 treatment lost 15 

tpha 12.7-22.9 cm in diameter. 

3 X 3 M eter

S p a c in g

0

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

4 X 4 M eter

S p a cin g

0

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 45

D iam eter (c m )

Trees/ha

6 X 6 M eter

S p a cin g 

0

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 45

D iam e ter (cm )

Trees/ha

C o ntro l

0

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

Figure 1Live trees per hectare by diameter class at the beginning and end of the 

period 1983–1998 in an even-aged ponderosa pine stand with three thinning 

treatments and a control. Total bar height indicates live trees in 1983, the shaded 

portion of each bar indicates trees that died during the 15-year period, and the 

unshaded portion indicates live trees in 1998. 
Mortality in Managed Stands—Fiedler and Morgan 

640 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Causes of mortality in the even-aged ponderosa pine stand varied greatly by tree 

diameter and treatment (fig. 2). In general, suppression was the primary cause of 

death in trees <10.2 cm, while bark beetles were the leading cause of mortality 

among trees >12.7 cm in diameter. Mountain pine beetle (Dendroctonus ponderosa)

was the primary mortality agent in the 3x3 and 4x4 treatments, accounting for 27 

dead tpha in the 10 to 25-cm diameter classes in the 3x3 treatment, and 12 tpha in the 

15 and 20-cm diameter classes in the 4x4 treatment. Beetles also killed a total of 252 

tpha in the control, primarily among trees 5.1-22.9 cm. Pockets of tree mortality due 

to mountain pine beetle are common in second-growth ponderosa pine stands, 

particularly in high-density areas within these stands (Olsen and others 1996). Over 

the 15-year period, the leading cause of mortality in the control was suppression, 

killing a total of 682 tpha <12.7 cm. Weather and other agents were minor 

contributors to mortality across a range of diameters in the control and 3x3 treatment. 

F ig u re 2

F ie d le r a n d M o rg a n

















 

C o ntro l

0

100

200

300

400

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600

5 10 15 20 25 30 35 40 45

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S p a c in g

0

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5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

4 X 4 M eter

S p a c in g

0

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600

5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

6 X 6 M eter

S p a c in g

0

100

200

300

400

500

600

5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

Figure 2Mortality by diameter class and cause for the period 1983–1998 in an 

even-aged ponderosa pine stand with three thinning treatments and a control. Dark 

shading indicates trees killed by bark beetles, stippling indicates trees killed by 

suppression, and the unshaded portion of each bar indicates trees killed by other 

causes (primarily weather). 
Mortality in Managed Stands—Fiedler and Morgan 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 641 

Even-aged Ponderosa Pine/Douglas-Fir/Western Larch 

Stands 

Mortality in the even-aged ponderosa pine/Douglas-fir/western larch stands also 

occurred primarily in the uncut control (fig. 3). There was an average of 1,298 live 

tpha in the controls at the beginning of the study, which dropped to 954 live tpha at 

the end of the 15-year period. Among the three thinning treatments, mortality was 

greatest in the 4x4, with 20 tpha dying in the 15-year period, reducing mean stand 

density from 467 tpha to 447 tpha. The 3x3 treatments lost an average of 12 tpha, and 

the 6x6 treatments lost only 5 tpha. Among the treatments in the even-aged mixed 

conifer stands, the intermediate diameter classes accounted for the majority of the 

mortality. The 3x3 treatment lost 2 tpha in each 5-cm class from 5.0 to 30.5 cm, 

while the 4x4 treatment lost 20 tpha in the 10 to 35-cm classes. In the control, 

mortality was most prevalent among the smaller diameter classes, with an average of 

133 tpha and 121 tpha dying in the 5- and 10-cm dbh classes, respectively. 

F ig ure 3

F ied ler and M o rg an

3 X 3 M eter

S p acing

0

100

200

300

400

5 10 15 20 25 30 35 40 45

D iam eter (cm )

Trees/ha

4 X 4 M eter

S p acing

0

100

200

300

400

5 10 15 20 25 30 35 40 45

D iam eter (cm )

Trees/ha

6 X 6 M eter

S p acing

0

100

200

300

400

5 10 15 20 25 30 35 40 45

D iam eter (cm )

Trees/ha

C ontrol

0

100

200

300

400

5 10 15 20 25 30 35 40 45

D iam eter (cm )

Trees/ha

Figure 3Live trees per hectare by diameter class at the beginning and end of the 

period 1983–1998 averaged for two even-aged mixed-conifer stands with three 

thinning treatments and a control. Total bar height indicates live trees in 1983, the 

shaded portion of each bar indicates trees that died during the 15-year period, and 

the unshaded portion indicates live trees in 1998. 

Causes of mortality in the even-aged ponderosa pine/Douglas-fir/western larch 

stands varied by tree species, diameter, and treatment (fig. 4). Suppression and 

western spruce budworm (Choristoneura occidentalis) were the primary causes of 

death of Douglas-fir in the controls, whereas mountain pine beetle was the primary 

killer of ponderosa pine. Virtually no western larch died in either of the mixed-
Mortality in Managed Stands—Fiedler and Morgan 

642 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

species stands. In general, suppression was the leading cause of mortality in the 

controls, while weather and beetles were primarily responsible for mortality in the 

3x3 and 4x4 nominal spacing treatments. In the controls, suppression killed an 

average of 156 tpha <20.3 cm, while beetles and weather led to the death of 124 tpha 

5.1-35.6 cm in diameter. Western spruce budworm also accounted for the death of 62 

tpha <25.4 cm in the control, where the host species (Douglas-fir) was more 

abundant, the trees were over-stocked and stressed, and a multistoried canopy 

provided better larval habitat (Carlson and Wulf 1989). Neither suppression nor 

budworm was an agent of mortality in the thinning treatments, where beetles and 

weather were responsible for the mortality of 5 tpha in the 3x3 treatment and 12 tpha 

in the 4x4 treatment. 

F ig u re 4

F ie d le r a n d M o rg a n

3 X 3 M eter

S p acin g

0

5 0

100

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5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

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S p a c in g

0

5 0

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5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

6 X 6 M eter

S p a c in g

0

5 0

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5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

















C o ntro l

0

5 0

100

150

200

5 10 15 20 25 30 35 40 45

D ia m e te r (c m )

Trees/ha

Figure 4Mortality by diameter class and cause for the period 1983–1998 averaged 

for two even-aged mixed-conifer stands with three thinning treatments and a control. 

Dark shading indicates trees killed by budworm, stippling indicates trees killed by 

suppression, and the unshaded portion of each bar indicates trees killed by other 

causes (primarily weather and bark beetles). 

Uneven-aged Ponderosa Pine Stands 

Mortality in the uneven-aged ponderosa pine stands was greatest in the uncut 

controls (fig. 5). There was an average of 951 live tpha in the controls at the 

beginning of the study, and 759 live tpha at the end of the 15-year period. In the two 

selection cutting treatments, mortality was greatest in the cut/burn treatment, with an 
Mortality in Managed Stands—Fiedler and Morgan 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 643 

average of 59 tpha dying in the 15-year period, reducing mean stand density from 

326 tpha to 267 tpha. The cut/no-burn treatment lost 30 tpha, reducing stand density 

from 353 tpha to 323 tpha. The smallest diameter classes contained the majority of 

the mortality in the two selection cutting treatments. The cut/burn treatment lost an 

average of 54 tpha <25.4 cm, while the cut/no-burn treatment lost only 25 tpha <25.4 

cm. In the control, mortality was also highest among the smaller diameter classes, 

with an average of 156 tpha <25.4 cm dying in the 15-year period. Fewer than 2 tpha 

≥35.6 cm died in either of the selection treatments, while more than 5 tpha died 

among similarly sized trees in the control. 

Figure 5

Fiedler and M organ

C ut/B urn

Treatm ent

0

200

400

600

800

10 20 30 40 50 60+

D iam eter (cm )

Trees/ha

Control

0

200

400

600

800

10 20 30 40 50 60+

D iam eter (cm )

Trees/ha

C ut/N o B urn

Treatm ent

0

200

400

600

800

10 20 30 40 50 60+

D iam eter (cm )

Trees/ha

Figure 5Live trees per hectare by diameter class at the beginning and end of the 

period 1984–1999 averaged for two uneven-aged ponderosa pine stands with two 

selection cutting treatments (with and without burning) and a control. Total bar height 

indicates live trees in 1984, the shaded portion of each bar indicates trees that died 

during the 15-year period, and the unshaded portion indicates live trees in 1999. 

Causes of mortality in the uneven-aged ponderosa pine stands varied primarily 

by treatment (fig. 6). In general, suppression was the dominant cause of mortality in 

the controls, fire was the leading cause of mortality in the cut/burn treatments, and 

weather was the primary agent in the cut/no-burn treatments. Mortality due to bark 

beetles was present in both treated and untreated portions of the stands, though it was 

much higher in the untreated portions, where higher densities created conditions 

more favorable for beetles. In the controls, suppression killed an average of 99 tpha 

<15.2 cm, while beetles caused the death of 52 tpha <45.7 cm. Weather accounted for 

an average of 44 dead tpha <25.4 cm in the control, 15 dead tpha <25.4 cm in the 
Mortality in Managed Stands—Fiedler and Morgan 

644 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

cut/burn treatment, and 20 dead tpha <35.6 cm in the cut/no-burn treatment. Fire 

killed an average of 32 tpha <15.2 cm and 5 tpha between 15.2 and 25.4 cm in the 

cut/burn treatment. Beetles accounted for the death of 7 tpha <35.6 cm in the cut/burn 

treatment and 5 tpha <25.4 cm in the cut/no-burn treatment. Other agents, including 

root rot, budworm, and animals, killed an average of 3 tpha <15.2 cm among the 

cut/no-burn treatments. 

F ig ure 6

F ied ler and M o rg an



  

C ut/B u rn

T reatm ent

0

2 0

4 0

6 0

8 0

100

120

140

160

180

10 20 30 40 50 60+

D iam eter (cm )

Trees/ha

W eather  F ire

B eetle



 



 

C ontrol

0

2 0

4 0

6 0

8 0

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10 20 30 40 50 60+

D iam eter (cm )

Trees/ha

W eather S uppression

B eetle



C ut/N o B urn

T reatm ent

0

2 0

4 0

6 0

8 0

100

120

140

160

180

10 20 30 40 50 60+

D iam eter (cm )

Trees/ha

W eather

O ther

B eetle

Figure 6Mortality by diameter class and cause for the period 1984–1999 averaged 

for two uneven-aged ponderosa pine stands with two selection cutting treatments 

(with and without burning) and a control. Dark shading indicates trees killed by bark 

beetles; stippling indicates trees killed by suppression, fire, or other causes 

(according to treatment); and the unshaded portion of each bar indicates trees killed 

by weather. 

Discussion 

Mortality for the 15-year period was greatest in the untreated controls for both 

the even- and uneven-aged stands. Mortality in the even-aged stands was lowest in 

the low-density (6x6 nominal spacing) thinning treatment. In the uneven-aged stands, 

mortality was lowest in the cut/no-burn treatment. Suppression was the leading cause 

of mortality among the uncut controls in all stands, primarily affecting trees in the 

smallest diameter classes, while beetles were the leading cause of mortality among 

the larger size classes in the ponderosa pine stands. 

These findings indicate that the thinnings and selection cuttings tended to reduce 

total mortality. However, this reduction in mortality was not distributed evenly across 

the diameter classes. Mortality levels among small-diameter trees in the treatments 
Mortality in Managed Stands—Fiedler and Morgan 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 645 

were consistently much lower than mortality levels of small-diameter trees in the 

controls. However, mortality differences among treatments and controls were not as 

significant for the large-tree stand component. Although overall mortality of large 

trees was reduced by treatment, mortality of large trees was not entirely prevented by 

treatment. The susceptibility of larger pines to bark beetle attack was likely reduced 

by the increased tree vigor resulting from thinning or selection cutting. However, 

scorch from prescribed burning likely stressed some residual trees in the selection 

cut/burn treatment, and may have increased susceptibility to beetle attack. Untreated 

forest with favorable habitat for pests near treated areas may have allowed insects 

access to those larger trees stressed by prescribed burning. 

One important observation over the 15-year monitoring period was the relatively 

low mortality of small trees after prescribed underburning in the individual tree 

selection study. Prescribed burning has been questioned as an appropriate treatment 

in uneven-aged stands because of the potential to incinerate trees in the smaller 

diameter classes. However, over the 15-year period, fewer than 20 percent of the 

trees in the 10-cm class died as a result of burning, and only about 25 percent died 

from any cause. These results indicate that judicious use of prescribed burning can 

achieve a variety of management objectives, such as preparing seedbeds, killing 

small firs, reducing activity fuels, and stimulating growth of important wildlife forage 

species (e.g., willow (Salix spp.) and bitterbrush (Purshia tridentata) [Ayers and 

others 1999]), while limiting mortality of small pines to acceptable levels. 

Conclusions 

The two types of silvicultural cuttings evaluated in this studythinning and 

selection cuttingwere found to reduce mortality in even-aged and uneven-aged 

ponderosa pine stands, respectively. This would be considered a positive outcome 

from a timber production point of view. However, it may be less desirable when 

viewed in the broader context of maintaining conditions favorable to indigenous 

fauna and flora in managed ponderosa pine and drier mixed conifer ecosystems. 

Because mortality was highest in the smallest diameter classes in all stands, relatively 

large snags and downed logs may need to be manufactured in managed stands when 

desired for wildlife or other ecological considerations. 

Standing dead wood may be created by girdling live trees with an axe or 

chainsaw, baiting with pheromones, inoculating with decay fungi, or burning to kill 

either the cambium at the base of the tree, the roots, or the foliage and terminal bud. 

However, as several investigators (Boleyn and others 2002, Parks 1999, Shea and 

others 2002) reported at this symposium, not all dead trees are created equal. For 

example, woodpecker foraging occurred primarily in the younger age classes of 

snags (Farris and others 2002). Huss and others (2002) found that woodpecker nest 

trees were frequently infected by the red-belted conk fungus (Fomitopsis pinicola),

and Laudenslayer (2002) noted that snags with historical and active nests of cavitynesting birds tended to be taller and had greater diameters than those without nests. In 

addition to the size of snag and time since death, how a tree dies may have profound 

effects on how long it remains standing and what function(s) it may serve (Bull 1983, 

Bull and Partridge 1986, Keen 1955). Thus, habitat suitability of dead trees and logs 

for various wildlife species should be considered when selecting which trees are to be 

killed and how to kill them (Bull and others 1980). 
Mortality in Managed Stands—Fiedler and Morgan 

646 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Maintaining desired amounts of large snags and logs both in the near and distant 

future may require silvicultural stand interventions that not only kill and remove trees 

from the stand but also leave some dead trees (Ffolliott 1983). The large live and 

dead trees present in today’s ponderosa pine stands developed under stand densities 

widely documented to be more open than current conditions (Arno and others 1995, 

Covington and Moore 1994). The low-intensity fires that historically accomplished 

thinning are often not possible under current stand conditions, given heavy down-fuel 

loading and the presence of sapling and pole ladder fuels (Fiedler and others 1998). 

Historically, periodic low-intensity fires commonly created open stand structures, 

lowered fuel loadings, and favored survival and development of large-diameter, fireresistant pines. Absent this natural process to reduce density and discriminate against 

Douglas-fir/true firs, development of large pines in the future will likely require welldesigned silvicultural cuttings to release trees, reduce ladder fuels, and 

simultaneously create desired standing and down coarse woody debris structures. 

Such cuttings have been shown to significantly increase diameter growth across the 

full range of tree diameters (including old-growth trees) in uneven-aged ponderosa 

pine stands (Fiedler 2000). It seems unlikely that productive, ecologically functional, 

and sustainable ponderosa pine ecosystems will attain these desired conditions 

without actively managing both live-tree and dead wood stand components. 

References 

Arno, Stephen F.; Scott, Joe H.; Hartwell, Michael G. 1995. Age-class structure of old 

growth ponderosa pine/Douglas-fir stands and its relationship to fire history. Res. 

Paper INT-481. Ogden, UT: Intermountain Research Station, Forest Service, U.S. 

Department of Agriculture; 25 p. 

Ayers, Dayna M.; Bedunah, Donald J.; Harrington, Michael G. 1999. Antelope bitterbrush 

and Scouler’s willow response to a shelterwood harvest and prescribed burn in 

western Montana. Western Journal of Applied Forestry 14: 137-143. 

Boleyn, Pat; Wold, Eric; Byford, Ken. 2002. Created snags and wildlife, is there a common 

connection? In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; 

Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the 

symposium on the ecology and management of dead wood in western forests. 1999 

November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture [this 

volume]. 

Bull, Evelyn L. 1983. Longevity of snags and their use by woodpeckers. In: Snag habitat 

management symposium proceedings; 1983 June 7-9; Flagstaff, AZ. Gen. Tech. Rep. 

RM-99. Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture: 64-67. 

Bull, Evelyn L; Partridge, Arthur D. 1986. Methods of killing trees for use by cavity 

nesters. Wildlife Society Bulletin 14: 142-146. 

Bull, Evelyn L.; Twombly, Asa D.; Quigley, Thomas M. 1980. Perpetuating snags in 

managed mixed conifer forests of the Blue Mountains, Oregon. In: Management of 

western forests and grasslands for non-game birds, workshop proceedings; 1980 

February 11-14; Salt Lake City, UT. Gen. Tech. Rep. INT-86. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 325-336. 
Mortality in Managed Stands—Fiedler and Morgan 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 647 

Carlson, Clinton E.; Wulf, N. William. 1989. Spruce budworms handbook: silvicultural 

strategies to reduce stand and forest susceptibility to the western spruce budworm. 

Agric. Handb. 676. Washington, DC: U.S. Department of Agriculture; 31 p 

Cazares, Efren; Trappe, James M. 1999. Functions of coarse woody debris in forest 

ecosystems. Paper presented at: The symposium on the ecology and management of 

dead wood in western forests; 1999 November 2-4; Reno, NV. Unpublished draft 

supplied by authors. 

Covington, W. Wallace; Moore, Margaret M. 1994. Southwestern ponderosa forest 

structure: changes since Euro-American settlement. Journal of Forestry 92: 39-47. 

Dale, M. R. 1999. Spatial pattern analysis in plant ecology. Cambridge, UK: Cambridge 

University Press; 326 p. 

Farris, Kerry L.; Gartan, Edward O.; Heglund, Patricia J.; Zack, Steve; Shea, Patrick J. 2002. 

Woodpecker foraging and the succesional decay of ponderosa pine. In: 

Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. 

Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the symposium on the 

ecology and management of dead wood in western forests. 1999 November 2-4; Reno, 

NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; [this volume]. 

Ffolliott, Peter F. 1983. Implications of snag policies on management of southwestern 

ponderosa pine forests. In: Snag habitat management symposium proceedings; 1983 

June 7-9; Flagstaff, AZ. Gen. Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture: 

28-32. 

Fiedler, Carl E.; Arno, Stephen F.; Harrington, Michael G. 1998. Reintroducing fire in 

ponderosa pine-fir forests after a century of fire exclusion. Tall Timbers Fire 

Ecology Conference Proceedings, No. 20. Tallahassee, FL: Tall Timbers Research 

Station; 245-249. 

Fiedler, Carl E. 2000. Restoration treatments promote growth and reduce mortality of 

old-growth ponderosa pine (Montana). Ecological Restoration 18: 117-119. 

Harvey, Alan E.; Jurgensen, Marty F.; Larsen, Michael J. 1981. Organic reserves: 

importance to ectomycorrhizae in forest soils of western Montana, USA. Forest 

Science 27: 442-448. 

Harvey, Alan E.; Jurgensen, Marty F.; Larsen, Michael J.; Graham, R. T. 1987. Relationships 

among soil microsites, ectomycorrhizae, and natural conifer regeneration of oldgrowth forests in western Montana, USA. Canadian Journal of Forest Research 17: 

58-62. 

Haverty, Michael I.; Shea, Patrick J. 1999. Dead wood and insects: function of insects in 

the death cycle of conifers. Paper presented at: The symposium on the ecology and 

management of dead wood in western forests; 1999 November 2-4; Reno, NV. 

Unpublished draft supplied by authors. 

Herder, Michael; Jackson, Jennifer G. 2002. Roost preferences of long-legged myotis in 

northern Arizona. Transactions of The Western Section of The Wildlife Society 36: 1-

7. 

Huss, Martin J.; Bednarz, James C.; Varland, Daniel E. 2002. The efficacy of inoculating 

fungi into conifer trees to promote cavity excavation by woodpeckers in managed 

forests in western Washington. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-
Mortality in Managed Stands—Fiedler and Morgan 

648 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Keen, F. P. 1955. The rate of natural falling of beetle-killed ponderosa pine snags. Journal 

of Forestry 53: 720-723. 

Laudenslayer, Jr., William F. 2002. Cavity nesting bird use of snags in eastside pine 

forests of northeastern California. In: Laudenslayer, William F., Jr.; Shea, Patrick J. 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Lutes, Duncan C. 2002. Methods for the quantification of coarse woody debris and the 

identification of its spatial patterning. In: Laudenslayer, William F., Jr.; Shea, Patrick 

J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Olsen, W. K.; Schmid, J. M.; Mata, S. A. 1996. Stand characteristics associated with 

mountain pine beetle infestations in ponderosa pine. Forest Science 42: 310-327. 

Parks, Catherine G. 1999. Decay processes–why simply managing for snag and log quotas 

is not enough. Paper presented at: The symposium on the ecology and management of 

dead wood in western forests; 1999 November 2-4; Reno, NV. Unpublished draft 

supplied by author. 

Pfister, Robert D.; Kovalchik, Bernard L.; Arno, Stephen F; Presby, Richard C. 1977. Forest 

habitat types of Montana. Gen. Tech. Rep. INT-34. Ogden, UT: Intermountain Forest 

and Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Prescott, Cindy; Laiho, Raija. 2002. The nutritional significance of coarse woody debris in 

three Rocky Mountain forests. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Ross, Darrell W. 1999. Importance of dead wood to bark beetles. Paper presented at: The 

symposium on the ecology and management of dead wood in western forests; 1999 

November 2-4; Reno, NV. Unpublished draft supplied by author. 

Shea, Patrick J.; Laudenslayer, William F.; Ferrell, George. 2002. Girdled versus bark 

beetle-created snags: utilization by cavity-dependent species and differences in 

decay rate and insect diversity. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 649 

Snags and Down Wood in the Interior 

Columbia Basin Ecosystem Management 

Project1

 

Jerome J. Korol,2 Miles A. Hemstrom,3 Wendel J. Hann,4 and 

Rebecca A. Gravenmier5

Abstract 

Snags and down wood are major ecosystem and wildlife habitat components of the Interior 

Columbia Basin ecosystem. Their natural abundance and distribution have been altered by 

decades of land conversion, fire suppression, and timber and firewood harvest, but the degree 

and pattern of change have been open to question. Consequently, an analysis of the changes 

that have occurred was a required element of the Interior Columbia Basin Environmental 

Impact Statement. Members of the Science Advisory Group of the Interior Columbia Basin 

Ecosystem Management Project modeled snag and down wood abundance at the landscape 

level for the project analysis area. We constructed 10 density tables for combinations of 3 

Potential Vegetation Groups, 2 temporal regimes, 2 fire regimes, and 2 public land 

management characterization classes. Snags and down wood were divided into two size 

classes, small and large, with a 53 cm DBH break point, and a 13 cm minimum DBH. Forest 

stands were placed into one of four categories: early-seral, mid-seral, late-seral single-strata, 

and late-seral multistrata. We defined five categories of snag and down wood abundance: 

none, rare, uncommon, common, and abundant. Each size class/abundance category 

combination, such as large snag/common, small down wood/rare, etc. had its own unique 

density range. We combined computer simulations using the Columbia River Basin 

Succession Model with geographic information system (GIS) data layers to project historical 

(pre-settlement) and current snag and down wood densities. We also made long-term (100 

year) projections of snag and down wood trends based on the three public land management 

alternatives described in the Interior Columbia Basin Supplemental Draft Environmental 

Impact Statement. Our models for the Basin as a whole showed small and large snag 

abundances currently below the historical levels, and small and large down wood amounts 

currently greater than historical levels. The 100 year simulations projected small snag 

amounts returning to historical levels, large snag amounts increasing above current levels but 

not returning to historical amounts, and the small and large down wood amounts generally 

decreasing from current levels but remaining above historical levels. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Landscape Ecologist, Interior Columbia Basin Ecosystem Management Project, USDA Forest Service, 

ICBEMP, 201 North 3rd St., Walla Walla, WA 99362. 3

 Landscape Ecologist, Regional Office, USDA Forest Service, R6—4th floor, ICBEMP, P.O. Box 3623, 

Portland, OR 97208 (e-mail: mhemstrom/r6pnw~icbmp@fs.fed.us) 

4

 Landscape Ecologist, Pike and San Isabel National Forest, USDA Forest Forest, 2015 North Poplar, 

Leadville, CO 80498 (e-mail: whann@amigo.net) 

5

 Science Coordinator/GIS Team Lead, Regional Office, USDA Forest Service, R6—4th floor, ICBEMP, 

PO Box 3623, Portland, OR 97208 (e-mail: bgravenmier/r6pnw~icbemp@fs.fed.us) 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

650 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Introduction 

The Interior Columbia Basin Ecosystem Management Project, (ICBEMP), was 

established by charter in 1994. The charter, signed by the Chief of the USDA Forest 

Service (FS) and the Director of the Bureau of Land Management (BLM), provided 

instruction to the agencies to develop specific products that would lead to the 

adoption of a scientifically sound, ecosystem-based strategy for managing FS- and 

BLM-administered lands within the Interior Columbia Basin (ICB or "the Basin"). 

The charter also required the preparation of a Basin-wide Environmental Impact 

Statement (EIS). Quigley and Arbelbide (1997) developed an assessment of 

ecosystem components that described the ecological, social and economic conditions 

in the Basin. Two separate but complementary draft environmental impact statements 

(DEIS), known as the Eastside DEIS and the Upper Columbia River Basin DEIS 

(USDA Forest Service and USDI Bureau of Land Management 1997a, USDA Forest 

Service and USDI Bureau of Land Management 1997b), were prepared. Quigley and 

others (1997) developed a scientific evaluation of the management alternatives 

described in the DEIS documents. Subsequently, a supplemental draft environmental 

impact statement (SDEIS, USDA Forest Service and USDI Bureau of Land 

Management 2000) was issued to address public comments concerning the DEIS. 

Our work built from the landscape ecology portion (Hann and others 1997) of the 

assessment of ecosystem components (Quigley and Arbelbide 1997) and was part of 

an evaluation of long-term effects of the three management alternatives described in 

the SDEIS (USDA Forest Service and USDI Bureau of Land Management 2000). 

The SDEIS contains three alternatives for the management of FS- and BLMadministered lands in the Basin. We will not describe them in detail here, but present 

a very brief summary of the key focus of each alternative (more detail is available at 

the Web site: http://www.icbemp.gov). 

Alternative S1 is termed the “no action” alternative. The term “no action” does 

not mean that no management will take place. It means that management of FS- and 

BLM-administered public lands would continue based on the land use plans that are 

currently in place, including existing policies, U.S. Fish and Wildlife Service and 

National Marine Fisheries Service Biological Opinions, and Healthy Rangelands 

standards and guidelines. Analysis of a “no action” alternative is a requirement of the 

National Environmental Policy Act of 1976 (NEPA) and BLM and FS planning 

procedures. 

Alternatives S2 and S3 are termed “action” alternatives that are meant to 

improve the clarity, focus, and ability to implement the proposed management 

direction. In general, the two action alternatives were designed to: 

• Integrate landscape, disturbance regime, aquatic, terrestrial, socio-economic, 

and tribal components into one ecosystem management strategy; 

• Protect important aquatic and terrestrial habitats; 

• Identify priority areas for restoration; and 

• Provide a link to existing management direction through a step-down process 

that will combine some land designations with management flexibility at the 

local level. 

A key emphasis of alternative S2 is to minimize short-term risks, especially to 

threatened, endangered, or proposed species, important species habitats, and riparian 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 651 

areas. The intent of the alternative is to put a greater emphasis on conducting detailed 

analysis prior to conducting management activities. Areas are prioritized for 

restoration in order to make management activities more effective and efficient. 

Alternative S3, on the other hand, has a stronger emphasis on more quickly 

addressing long-term risks from either management activities or natural disturbance 

events; there is less of an emphasis on analysis. There is also a stronger focus on 

locating management activities where they can benefit isolated and/or economically 

specialized communities. 

Snags and down wood are essential ecological components of the ICB 

ecosystem. Standing snags provide foraging, roosting, denning and nesting habitat for 

a number of wildlife species (Bull and others 1997, Marcot and others 1997, Thomas 

1979, Wisdom and others 1999). As snags decay and fall to the ground, and become 

down wood, they provide food and shelter for different species (Bartels and others 

1985, Maser and others 1979). Down wood also stores nutrients and moisture, and 

aids in soil development. Down wood in stream channels influences channel 

morphology; especially in forming pools and in-stream cover, retention of nutrients, 

and storage and buffering of sediment (Lee and others 1997). 

Analysis of changes in snag and down wood densities across the Basin from 

historical times to the present may provide valuable insight into their management for 

the future. In this paper we describe the manner in which the snag and down wood 

abundance values were determined in the ICBEMP, their modeled current conditions 

in the Basin, and projected density trends after 100 years under three public land 

management alternatives. 

Study Area 

The ICBEMP analysis area (fig. 1) covers approximately 58 million hectares 

(145 million acres) in the states of Washington, Oregon, Idaho, Montana, Wyoming, 

Nevada and Utah—an area approximately the same size as the country of France. 

Public lands managed by the Forest Service and Bureau of Land 

Management account for 53 percent of the Basin. This represents approximately 25 

percent of all FS-administered lands and 10 percent of all BLM-administered lands in 

the lower 48 states. Approximately 4 million hectares (10 million acres) in the Basin 

are federally designated wilderness, accounting for nearly one-third of all federally 

designated wilderness lands in the contiguous states. The study area also includes 

about 20 percent of the area in the lower 48 states that is American Indian 

reservation. The amount of timber harvested in the Basin accounts for approximately 

10 percent of the total for the entire United States (Quigley and others 1996). 

Elevations in the Basin range from less than 150 meters to more than 3,000 meters 

above mean sea level. The average annual precipitation values are highly variable, 

and range from less than 20 to more than 250 centimeters per year (USDA Forest 

Service and USDI Bureau of Land Management 1997). More than 17,000 plant and 

animal taxa occur in the study area, including 609 known vertebrate taxa (Arbelbide 

and Quigley 1997). At present, the Basin contains 29 threatened or endangered 

species, including 16 fish species or species stocks. 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

652 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

ICBEMP

OR

WA

ID

MT

WY

NV UT

CA

USA

Scale

0 500

Kilometers

Figure 1—The Interior Columbia Basin Ecosystem Management Project (ICBEMP) 

analysis area. 

Methods 

Snag and Down Wood Tables 

Members of the Science Advisory Group (SAG) formulated the snag and down 

wood density tables through an iterative process of literature review and discussions 

with experts. Our original tables, based on proposals put forward by the 

Environmental Impact Statement team, consisted of four forest stand classes (earlyseral stands, mid-seral stands, late-seral single-strata stands, and late-seral multistrata stands) and six Potential Vegetation Group (PVG)/land management 

combinations (e.g. Cold, Moist or Dry Forest, managed or unmanaged stands). Four 

tables, for current large and small snags and down wood, were constructed. We 

populated the 24 cells of each table with snag and down wood per-hectare values 

derived from the literature. 

It quickly became apparent to us that the amount of usable data available from 

the literature was inadequate to populate most of the cells with values. We found that 

many published reports divided snags and/or down wood into size classes that could 

not be adapted to ours. Furthermore, many studies reported snag and down wood 

densities by vegetation types or age classes that we could not match. Differing units 

of measure were also a problem. For example, down wood amounts reported in 

square meters or tons per hectare could not be accurately converted to pieces per 

hectare. Attempts to fill the holes in the tables with values from the Forest Inventory 

Analysis (FIA) and Current Vegetation Survey (CVS) databases were ruled out due 

to the lack of comprehensive coverage. 

Following discussions with snag and down wood experts and members of the 

EIS team we revised the format of the snag and down wood tables. The new format 

contained the same four forest succession/structure stages as before, but we now 

included a live tree component as a comparison to our snag and down wood amounts. 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 653 

Live trees, snags, and down wood were all divided into small and large sizes. The 

small/large breakpoint was 53 centimeters (21 inches) diameter at breast height 

(DBH). “Small” did not include trees, snags, or down wood less than 13 centimeters 

(5 inches) DBH. These values were taken from the tree DBH size classes defined by 

Oliver (1981), modified by O'Hara and others (1996), and used throughout the 

CRBSUM modeling process (Keane and others l996). The values were also 

commonly used in the literature on cavity nesting animals, particularly birds 

(Raphael and White 1984, Saab and Dudley 1998). 

The new tables also used tree, snag, and down wood density categories instead 

of individual density values. The categories were none, rare, uncommon, common, 

and abundant. Each category represented a range of per-hectare values, and each 

forest component such as large snag, small down wood, etc. had its own definition 

for each category (e.g. “rare” for small live trees did not have the same value range as 

“rare” for large down wood). We also added two fire regimes (high-frequency lowintensity fires and low-frequency high-intensity fires) to the tables. There were 10 

tables in all, covering 3 PVGs (Cold, Moist, and Dry Forest) 2 temporal regimes 

(historical and current), 2 fire regimes, and 2 management categories (unmanaged 

and managed): 

1. Cold forest, historical conditions, low-frequency high-intensity fire regime; 

2. Cold forest, historical conditions, high-frequency low-intensity fire regime; 

3. Moist forest, current conditions, low-frequency high-intensity fire regime, 

unmanaged; 

4. Moist forest, current conditions, low-frequency high-intensity fire regime, 

managed; 

5. Moist forest, historical conditions, low-frequency high-intensity fire regime; 

6. Moist forest, historical conditions, high-frequency low-intensity fire regime; 

7. Dry forest, current conditions, low-frequency high-intensity fire regime, 

unmanaged; 

8. Dry forest, current conditions, low-frequency high-intensity fire regime, 

managed; 

9. Dry forest, historical conditions, low-frequency high-intensity fire regime; 

10. Dry forest, historical conditions, high-frequency low-intensity fire regime. 

We did not include managed conditions for cold forests because, for the most 

part, cold forests have not received extensive management and their fire regimes are 

relatively unaltered from historical conditions. The term “historical” refers to the 

conditions that existed prior to Euro-American settlement of the Basin. Historical and 

current live tree, snag, and down wood values were based on applicable literature 

values, expert opinion, and CRBSUM modeling. We submitted the revised tables to 

experts for review and held meetings to discuss the table attributes, our assumptions 

concerning density categories, snag and down wood dynamics, etc. before a final set 

of 10 tables was considered acceptable. 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

654 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Geographic Information Systems 

Geographic Information System (GIS) modeling of the snag and down wood 

abundances across the Basin required a sequence of computations and data layer 

combinations that can be generalized into four major processes. First, the GIS team 

created a continuous Basin-wide vegetation layer at a one-kilometer scale. This layer 

was a combination of terrestrial community groups with dominant physiognomic 

types and potential vegetation groups for the historical, current, and simulated future 

conditions of the Basin (see Hann and others [1997] and Keane and others [1996] for 

a detailed discussion on the treatment of vegetation in the ICBEMP). This layer 

provided the necessary baseline information on forest vegetation, including 

successional stage and stand structure. A subsequent combination of this layer with a 

layer describing ecological disturbances was then produced to add information on fire 

regimes. 

In the second step, the GIS team combined the vegetation layers with a layer 

detailing the various management prescriptions defined for each of the proposed 

alternatives in the SDEIS. The resulting layer was the basis for different snag and 

down wood management scenarios and allowed comparison of snag and down wood 

levels under the SDEIS alternatives. 

The third step linked the data from the snag and down wood tables constructed 

by the SAG with the vegetation layers described in step one. In this third step, the 

GIS team assigned both snag and down wood density categories and category 

midpoints to the vegetation data, and included the different management 

prescriptions and proposed SDEIS alternatives. The resulting layers provided data 

about snag and down wood amounts across the Basin for the historical, current, and 

long-term (100 year) conditions under three proposed management alternatives. 

In the fourth step the GIS team calculated a weighted average of density per 

subwatershed (6th code Hydrologic Unit or HUC6 level) for small and large snags 

and down wood for the historical, current, and simulated 100-year conditions of the 

Basin. This step allowed the analysis and summation of snag and down wood 

amounts according to various political, management, and land ownership units. 

Results and Discussion 

Our results discussed are preliminary and subject to revision, as is the SDEIS 

document itself. All figures and maps are also draft documents and are subject to 

revision. We used snag and down wood amounts based on the vegetation in the 

historical scenario as the baseline for our comparisons. We present results for only 

the FS/BLM-administered lands and Interior Columbia Basin as a whole. 

Current Conditions 

Our models indicated that small snag amounts increased slightly (7 percent) 

from the historical conditions on FS/BLM-administered lands but declined by 14 

percent across the Basin (fig. 2). Most of the increase on FS/BLM lands occurred in 

the Dry Forest PVG, with some minor increases in the Cold Forest PVG. This 

occurred because the amount of forests in the mid-seral stage increased in the Dry 

Forest PVG, while the amount in the late-seral stage declined. In general, mid-seral 

stage forests contain fewer small snags per hectare than the late-seral forest, 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 655 

especially in managed areas (Ohmann and Waddell, 2001). However, much of the 

increase in mid-seral forests on FS/BLM lands occurred in unroaded and wilderness 

areas. In these areas, fire suppression allowed development of dense stands of 

stressed, shade-tolerant trees having low resistance to insect and disease attack and, 

consequently, abundant small snags. Declines of small snags in the northern Rocky 

Mountains of Montana and Idaho and the foothills of the Cascade, Wallowa and Blue 

Mountains of Oregon (fig. 3) were more than offset by increases in much of central 

Idaho, the northern Cascade Mountains of Washington, portions of the southern 

Cascade, Wallowa, and Blue Mountains in Oregon, and in the Teton Mountains of 

Wyoming. 

Figure 2—Small snag and large snag amounts as a percentage of the historical 

amounts for forest PVGs on FS/BLM ICBEMP lands and for the total Interior 

Columbia Basin. Sl_100, S2_100 and S3_100 represent the values after a 100-year 

simulation of the SDEIS management alternatives. 















































































































































































































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Alternative 

Small snags 

Large snags 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

656 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Large snag amounts declined by approximately 8 percent on FS/BLMadministered lands and 31 percent across the Basin, compared to the historical levels 

(fig. 2). The largest losses occurred in the Dry Forest and Moist Forest PVGs due to 

increases in mid-seral forests and decreases in late-seral forests. Late-seral stage 

forests typically contain higher levels of large snags. Large, fire-created snags may 

also be present in early-seral forests, but usually fall quickly. Few large snags remain 

standing into the mid-seral stage (Everett and others [In press]). There are generally 

fewer surviving large trees in early and mid-seral forests and, hence, reduced sources 

for new large snag recruitment. Furthermore, the new cohort of live trees does not 

become large enough to generate large snags until well into the mid-seral stage and 

often not until the late-seral stage. This may produce a "U-shaped" pattern of 

abundance described by Franklin and Spies (1991) similar to the "boom and bust" 

cycle discussed by Everett and others [In press]). Large snag declines on FS/BLM 

lands are compounded in managed or roaded areas by harvest and firewood cutting. 

The spatial pattern was very similar to that of the small snags; however, greater 

declines occurred in the Wallowa and Blue Mountains and the central and southern 

Cascade Mountains (fig. 3). 

Small

Snags

Large

Snags

Legend: Decreasing Increasing Neutral

ICBEMP

23/06/99

DRAFT

ICBEMP

23/06/99

DRAFT

Figure 3—Current distribution of small snags and large snags trends across the 

Interior Columbia Basin. Neutral represents a value that is with 30 percent, positive or 

negative, of the historical level. Decreasing represents a decline of more than 30 

percent, and increasing represents an increase of more than 30 percent. Unshaded 

areas represent non-forested lands. 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 657 

Small and large down wood amounts have increased from the historical levels 

on both FS/BLM-administered lands and across the Basin (fig. 4). In general, down 

wood has a longer 'life-span' than snags (Bartels and others 1985, Beukema and 

others 1999, Cline and others 1980, Lambert and others 1980, Maser and others 

1979, Parks and Shaw 1996, Spies and others 1988, Stevens 1997,1999). The large 

numbers of trees killed by fires in the early- to mid-1900s generally are no longer 

present as snags, but are often present as down wood. Fire suppression often results 

in over-dense stands prone to insect and disease outbreaks. These conditions favor 

the recruitment of smaller down wood since small trees are more numerous than large 

trees and small snags usually fall sooner than large snags (Beukema and others 1999, 

Figure 4—Small down wood and large down wood amounts as a percentage of the 

historical amounts for forest PVGs on FS/BLM lands and for the entire Interior 

Columbia Basin. S1_100, S2_100, and S3_100 represent the values after a 100-year 

simulation of the SDEIS management alternatives. 











































































































































































































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Large downed wood 

Percent of Historical Amount 

Alternative
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

658 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Bull 1983, Bull and others 1980, Cline and others 1980, Everett and others in press, 

Huggard 1997, Morrison and Raphael 1993, Neitro and others 1985, Raphael and 

Morrison 1987, Raphael and White 1984). Large down wood pieces tend to last 

longer, however, perhaps resulting in similar increases over time. 

Small down wood amounts increased from the historical levels by 25 percent on 

FS/BLM lands and about 10 percent across the Basin (fig. 4). In both cases, the 

increases occurred mostly in the Dry Forest PVG because of large increases in midseral stage forests. Although the mid-seral forests usually do not contain as much 

small down wood as the late-seral forests, the increase in the area of dense, overcrowded mid-seral forests generated by fire suppression produced abundant small 

down wood on FS/BLM lands, especially in unroaded and wilderness areas. Most of 

the increases took place in central Idaho, Washington's north Cascade Mountains, 

and Oregon's south Cascade, Wallowa, and Blue Mountains (fig. 5). Declines 

occurred in small areas, especially in east-central Washington (the southern Selkirk 

Mountains), along the central Oregon/Washington border, and in far northwest 

Montana (the Salish and Purcell Mountains). 

Legend: Decreasing Increasing Neutral

Small

Downed

Wood

Large

Downed

Wood

ICBEMP

ICBEMP

23/06/99

DRAFT

23/06/99

DRAFT

Figure 5—Current distribution of small down wood and large down wood trends 

across the Interior Columbia Basin. Neutral represents a value that is with 30 

percent, positive or negative, of the historical level. Decreasing represents a decline 

of more than 30 percent, and increasing represents an increase of more than 30 

percent. Unshaded areas represent non-forested lands. 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 659 

Amounts of large down wood increased substantially from historical levels on 

FS/BLM lands and, to a lesser extent, Basin-wide (fig. 4). In both cases, the greatest 

increases occurred in the Moist Forest PVG. Large down wood pieces can be very 

long-lived. Large snags created by fire, insect and disease attack often fall within 10 

to 30 years (Bull 1983, Harrington 1996, Keen 1929, Lyon 1977, Mitchell and 

Preisler 1998, Schmid and others 1985), though some may last much longer (Hillis 

1999 personal communication). This means that large down wood amounts are 

generally greater than large snag amounts in the late-seral stage (Ohmann and 

Waddell 2000). Increases in large down wood levels on FS/BLM lands are most 

likely due to a larger proportion of acres in non-roaded and wilderness areas where 

there is less removal of large down wood and large snags. The increases were found 

throughout much of central and northern Idaho, northwest Montana, northeast 

Washington, and the northern and southern Cascade Mountains (fig. 5). Areas that 

exhibited declines in large down wood amounts included northwest Montana, much 

of the Washington and Oregon Cascade foothills, the lower elevation forests of 

northeast Washington, and the mid and lower elevation Blue and Wallowa Mountains 

in Oregon. Only a few areas of south-central Idaho and northeast Wyoming showed 

no change. 

Long-Term Future Conditions 

Both small and large snag levels increased above current levels under all SDEIS 

management alternatives (fig. 2). Small snag levels increased by about 10 percent 

above current conditions on FS/BLM lands after 100 years under all three 

alternatives. The largest increase (for all alternatives) was in the Moist Forest PVG 

where the amount of late-seral stage forest increased greatly in all simulations. This 

increase was driven by the successional transition of large amounts of mid-seral to 

late-seral stage forests over 100 years. Small snags are common in the late-seral 

forests and amounts will continue to increase as succession progresses. Across the 

Basin, small snags increased beyond the current level, and exceeded the historical 

level after 100 years. 

Large snags increased above the current level on both FS/BLM lands and across 

the Basin (fig. 2). Large snag abundance also reached or exceeded the historical level 

on FS/BLM-administered lands under all three alternatives. Across the Basin, large 

snags increased by 6 to 10 percent above the current level for all three alternatives, 

but remained about 75 percent of the historical amount. The major difference 

between alternatives was in the Dry Forest PVG where alternative S1 generated more 

mid-seral than late-seral forest. Alternatives S2 and S3 restored more late-seral 

forests in the Dry Forest PVG, consequently producing higher snag levels. 

Small down wood increased very slightly on FS/BLM-administered lands under 

alternative S1, but decreased by several percent under S2 and S3 after 100 years (fig. 

4). Most of the declines were in the Dry Forest and Moist Forest PVGs where 

decreases in the amounts of mid-seral forest were roughly balanced by increases in 

the late-seral and early-seral stages. Alternatives S2 and S3 include management 

measures designed to decrease fuel loads. The declines in small down wood amounts 

largely reflected those effects. Small down wood amounts remained nearly constant, 

or increased slightly, for all three alternatives at the Basin level, reflecting less 

aggressive fuels reduction efforts on non-FS/BLM lands. 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

660 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Large down wood amounts followed a pattern similar (fig. 4) to that of small 

down wood across the Basin. Amounts increased slightly on FS/BLM-administered 

lands under alternative S1, but decreased under alternatives S2 and S3. Fuel 

reduction efforts in both alternatives S2 and S3 should reduce large down wood 

amounts in actively managed areas. This trend should be offset to some degree by 

large increases in dense late seral forest in unroaded and wilderness areas, generating 

large down wood levels far above historical conditions in those areas. At the Basin 

scale, only alternative S2 resulted in a decline in large down wood, while alternatives 

S1 and S3 produced small increases. This also reflected the emphasis on fuel 

reduction on FS and BLM-administered lands under alternatives S2 and S3. 

Conclusions 

Small snag amounts have declined from the historical level on FS/BLM lands, 

but remained at roughly the historical level for the Basin as a whole. Large snag 

amounts have declined on both FS/BLM lands and across the Basin. Amounts of 

small and large down wood have increased beyond the historical levels on FS/BLM 

lands and across the Basin. Current amounts of snags and down wood have been 

influenced by four major processes: 

• Forest succession; 

• Timber (and firewood) harvest; 

• Fire suppression with its impacts on stand composition and structure; 

• Natural snag and down wood dynamics, including recruitment, fall rates, and 

rates of decay. 

Our 100-year simulations indicated a long-term return to historical amounts for 

small snags on both FS/BLM-administered lands and across the Basin, due mostly to 

the succession of large areas of mid-seral stage forests to the late-seral stage. Large 

snags should return to historical levels on FS/BLM lands, but remain at roughly 75 

percent of the historical amount across the Basin. Both small and large down wood 

amounts should remain above historical levels on FS/BLM lands and across the 

Basin. In this case, the dynamics are most influenced by the succession of large areas 

of mid-seral forest to late-seral forest and the long-lived nature of down wood itself. 

Increased prescribed fire will likely reduce the future accumulation of large down 

wood on FS/BLM lands, especially under alternative S2, but levels across the Basin 

under alternative S2 should approach those of historical conditions. 

Acknowledgments 

We thank Bruce Marcot, Evelyn Bull, Torolf Torgersen, Kim Mellen, Janet 

Ohmann, Karen Waddell, Jeff Jones, Fred Samson, Dave Atkins, and Mike Hillis for 

comments and suggestions. 

References 

Bartels, R.; Dell, J. D.; Knight, R. L.; Schaefer, G. 1985. Dead and down wood material. In: 

Brown, E. Reade, technical editor. 1985. Management of wildlife and fish habitats in 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 661 

forests of western Oregon and Washington. Part 1—chapter narratives. Publication No. 

R6-F&WL-192-1985; 171-186. 

Beukema, S.; Reinhardt, E.; Greenough, J.; Kurtz, W. A.; Crookston, N.; Robinson, D. 1999. 

Fire and fuels extension: model description. Unpublished draft supplied by author; 

58 p. 

Bull, E. L.; Twombly, A. D.; Quigley, T. M. 1980. Perpetuating snags in managed mixed 

forests of the Blue Mountains, Oregon. In: DeGraff, R. M., technical coordinator. 

Management of western forests and grasslands for nongame birds. Ogden, UT: 

Intermountain Research Station, Forest Service, U. S. Department of Agriculture; 325-

336. 

Bull, E. L. 1983. Longevity of snags and their use by woodpeckers. In: Davis, J. W.; 

Goodwin, G. A.; Ockenfels, R. A., technical coordinators. 1983. Proceedings of the 

symposium: Snag habitat management. Gen. Tech. Rep. GTR-RM-99. Fort Collins, CO: 

Rocky Mountain Research Station, Forest Service, U. S. Department of Agriculture; 64-

67. 

Bull, E. L.; Parks, C. G.; Torgersen, R. T. 1997. Trees and logs important to wildlife in the 

Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. Portland, OR: 

Pacific Northwest Region, Forest Service, U. S. Department of Agriculture; 55 p. 

Cline, S.; Berg, A. B.; Wight, H. M. 1980. Snag characteristics and dynamics in Douglasfir forests, western Oregon. Journal of Wildlife Management. 44(4): 773-786. 

Everett, R.; Lehmkuhl, J.; Schellhaas, R.; Ohlson, P.; Keenum, D.; Reisterer, H.; Spurbeck, D. 

[In press]. Snag dynamics in a chronosequence of 26 wildfires on the east slope of 

the Cascade Range in Washington. International Journal of Wildland Fire. 

Franklin, J. F.; Spies, T. A. 1991. Ecological definitions of old-growth Douglas-fir forests. 

In: Aubry, K. B.; Carey, A. B.; Huff, M. H.; Ruggiero, L. F., technical coordinators. 

1991. Wildlife and vegetation in unmanaged Douglas-fir forests. Gen. Tech. Rep. PNWGTR-285. Portland, OR: Pacific Northwest Region, Forest Service, U. S. Department of 

Agriculture; 61-69. 

Hann, W. J.; Jones, J. L.; Karl, M. G.; Hessburg, P. F.; Keane, R. E.; Long, D. G.; Menakis, J. 

P.; McNicoll, C. H.; Leonard, S. G.; Gravenmier, R. A.; Smith, B. G.1997. Landscape 

dynamics of the Basin. In: Quigley, T. M.; Arbelbide, S. J., eds. An assessment of 

ecosystem components in the interior Columbia Basin and portions of the Klamath and 

Great Basins. Gen. Tech. Rep. PNW-GTR-405. Portland, OR: Pacific Northwest 

Region, Forest Service, U. S. Department of Agriculture; 337-1055. 

Harrington, M. G. 1996. Fall rates of prescribed fire-killed ponderosa pine. Ogden, UT: 

Intermountain Research Station, Forest Service, U. S. Department of Agriculture; 7 p. 

Hillis, M. 1999. Forest Wildlife Biologist, Lolo National Forest. Personal communication. 

Huggard, D. 1997. Fall-down rates of subalpine fir snags at Sicamous Creek: 

implications for worker safety and habitat supply. British Columbia Ministry of 

Forests Research Program. Extension Note No. 16; 6 p. 

Keane, R. E.; Long, D. G.; Menakis, J. P.; Hann, W. J. Befins, C. D. 1996. Simulating 

course-scale vegetation dynamics using the Columbia River Basin Succession 

Model-CRBSUM. Gen. Tech. Rep. INT-GTR-340. Portland, OR: Pacific Northwest 

Region, Forest Service, U. S. Department of Agriculture; 51 p. 

Keen, F.P. 1929. How soon do yellow pine snags fall? Journal of Forestry 53: 735-737. 

Lambert. R. L.; Lang, G. E.; Reiners, W. A. 1980. Loss of mass and chemical change in

decaying boles of a subalpine balsam fir forest. Ecology 61(6): 1460-1473. 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

662 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Lee, D. C.; Sedell, J. R.; Rieman, B. E.; Thurlow, R. F.; Williams, J. E.; Burns, D.; Clayton, 

J.; Decker, L.; Gresswell, R.; House, R.; Howell, P.; Lee, K.; MacDonald, K.; McIntyre, 

J.; McKinney, S.; Noel, T.; O'Conner, J.; Overton, C.; Perkinson, D.; Tu, K.;Van 

Eimeren, P. 1997. Broadscale assessment of aquatic species and habitats. In: 

Quigley, T. M.; S. J. Arbelbide, eds. An assessment of ecosystem components in the 

interior Columbia Basin and portions of the Klamath and Great Basins. Volume 111. 

Gen. Tech. Rep. PNW-GTR-405. Portland, OR: Pacific Northwest Region, Forest 

Service, U. S. Department of Agriculture; 1057-1496. 

Lyon. L. J. 1977. Attrition of lodgepole pine snags on the Sleeping Child Burn, Montana. 

Res. Note INT-RN-219. Forest Service, U.S. Department of Agriculture; 4 p. 

Marcot, B. G., Castellano, M. A.; Christy, J. A.; Croft, L. K.; Lehmkuhl, J. F.; Naney, R. H.; 

Nelson. K.; Niwa, C. G.; Rosentreter, R. E.; Sandquist, R. E.; Wales, B. C.; Zieroth, E.; 

1997. Terrestrial ecology assessment. In: Quigley, T. M.; Arbelbide, S. J., eds. An 

assessment of ecosystem components in the interior Columbia Basin and portions of the 

Klamath and Great Basins. Volume 111. Gen. Tech. Rep. PNW-GTR-405. Portland, 

OR: Pacific Northwest Region, Forest Service, Department of Agriculture; 1497-1713. 

Maser, C.; Anderson, R. G.; Cromack, K. Jr.; Williams, J. T.; Martin, R. E.; 1979. Dead and

down woody material. In: Thomas, J. W., ed., Wildlife habitats in managed forests: the 

Blue Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: U. S. 

Department of Agriculture; 78-95. 

Mitchell, R. G.; Preisler, H. K. 1998. Fall rate of lodgepole pine killed by the mountain 

pine beetle in central Oregon. Western Journal of Applied Forestry 13 (1): 23-26. 

Morrison. M. L.; Raphael, M. G.; 1993. Modeling the dynamics of snags. Ecological 

Applications 3(2): 322-330. 

Neitro, W. A.; Binkley, V. W.; Cline, S. P.; Mannan, R. W.; Marcot, B. G.; Wagner, F. F. 

1985. Snags (wildlife trees). In: Brown, E. R., technical editor. Management of wildlife 

and fish habitats in forests of western Oregon and Washington. Part 1—chapter 

narratives. Publication No. R6-F&WL-192-1985. Portland, OR: Pacific Northwest 

Region, Forest Service, U. S. Department of Agriculture; 129-169. 

O'Hara, K. L.; Latham, P. A.; Hessburg, P.; Smith B. 1996. A structural classification of 

inland northwest forest vegetation. Western Journal of Applied Forestry 11(3): 97-

102. 

Ohmann, J. L.; Waddel, K. L. 2001. Regional patterns of dead wood in forested habitats of

Oregon and Washington. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, 

Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. 

Proceedings of a symposium on the ecology and management of dead wood in western 

forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: 

Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 

[this volume]. 

Oliver, C. D. 1981. Forest development in North America following major disturbances. 

Forest Ecology and Management 3: 153-168. 

Parks, C. G.; Shaw, D. C. 1996. Death and decay: a vital part of living canopies. Northwest 

Science (Special Issue) 70: 46-53. 

Quigley, T. M.; Haynes, R. W.; Graham, R. T., technical editors. 1996. Integrated scientific 

assessment for ecosystem management in the interior Columbia Basin and portions 

of the Klamath and Great Basins. Gen. Tech. Rep. PNW-GTR-382. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U. S. Department of Agriculture; 

303 p. 

Quigley, T. M.; Arbelbide, S. J., technical editors. 1997. An assessment of ecosystem 

components in the Interior Columbia Basin and portions of the Klamath and Great 
Snags and Down Wood in the Columbia Basin Project—Korol, Hemstrom, Hann, and Gravenmier 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 663 

Basins. Gen. Tech. Rep. PNW-GTR-405. Portland, OR: Pacific Northwest Research 

Station, Forest Service, U. S. Department of Agriculture; 1057 p. 

Quigley, T. M.; Lee, K. M.; Arbelbide, S. J., technical editors. 1997. Evaluation of EIS

alternatives by the Science Integration Team. Two volumes. Gen. Tech. Rep. PNWGTR-406. Portland, OR: Pacific Northwest Research Station, Forest Service, U. S. 

Department of Agriculture; 1094 p. 

Raphael, M. G.; Morrison, M. L. 1987. Decay and dynamics of snags in the Sierra Nevada.

California. Forest Science 33(3): 774-783. 

Raphael, M. G.; White, M. 1984. Use of snags by cavity-nesting birds in the Sierra 

Nevada. Wildlife Monograph No. 86; 66 p. 

Saab, V. A.; Dudley, J. G. 1998. Responses of cavity-nesting birds to stand-replacement 

fire and salvage logging in ponderosa pine/Douglas fir forests of southwestern 

Idaho. Res. Paper RMRS-RP-11. Fort Collins, CO: Rocky Mountain Research Center, 

Forest Service, U. S. Department of Agriculture; 17 p. 

Schmid, J. M.; Mata, S. A.; McCambridge, W. F. 1985. Natural falling of beetle-killed

ponderosa pine. Res. Note RM-RN-454. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U. S. Department of Agriculture; 3 p. 

Spies, T. A.; Franklin, J. F.; Thomas, T. B. 1988. Coarse woody debris in Douglas-fir 

forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Stevens, V. 1997. The ecological role of coarse woody debris: an overview of the 

ecological importance of coarse woody debris in B.C. forests. Research Branch, 

British Columbia Ministry of Forests, Victoria, British Columbia. Working Paper 30; 

26 p. 

Thomas, J. W., ed. 1979. Wildlife habitats in managed forests: the Blue Mountains of 

Oregon and Washington. Agric. Handb. 533. Washington DC: Forest Service, U. S. 

Department of Agriculture; 512 p. 

U.S. Department of Agriculture, Forest Service, U.S. Department of the Interior, Bureau of 

Land Management. 1997a. Eastside draft environmental impact statement. 2 vols. 

BLM/OR/WA-PL-96-O37+1792. Portland, OR: Bureau of Land Management, U.S. 

Department of the Interior. 

U.S. Department of Agriculture, Forest Service, U.S. Department of the Interior, Bureau of 

Land Management. 1997b. Upper Columbia River Basin draft environmental impact 

statement. 2 vols. BLM/ID-PT-96-021+1610. Boise, ID: Bureau of Land Management, 

U.S. Department of the Interior. 

Wisdom, M. J., Holthausen, R. S.; Wales, B. C.; Lee, D. C.; Hargis, C. D.; Saab, V. A.; Harm, 

W. J.; Rich, T. D.; Rowland, M. M.; Murphy, W. J.; Eames, M. R. 1999. Source 

habitats for terrestrial vertebrates of focus in the Interior Columbia Basin: broadscale trends and management implications. Unpublished draft supplied by author. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 665 

Assessment of the Line Transect Method: 

An Examination of the Spatial Patterns of 

Down and Standing Dead Wood1

Duncan C. Lutes2 

Abstract 

The line transect method, its underlying assumptions, and the spatial patterning of down and 

standing pieces of dead wood were examined at the Tenderfoot Creek Experimental Forest in 

central Montana. The accuracy of the line transect method was not determined due to 

conflicting results of t-tests and ordinary least squares regression. In most instances down 

pieces were randomly distributed along transect segments. Down pieces generally had a 

clumped distribution of their directional orientation. Standing pieces were usually found to be 

randomly distributed within belt transects. Consistent clumping scale of down or standing 

pieces was not found when studied using the paired quadrat variance method. 

Introduction 

Coarse woody debris (CWD), principally logs and snags, plays a key role in a 

wide range of ecological processes in conifer forests. It is important for wildlife, 

plant regeneration, nutrient cycling, water quality, fire fuels and more (Harmon and 

others 1986, Maser and others 1979, Maser and others 1988). 

A number of researchers have used the line transect method (Brown 1974, 

Howard and Ward 1972, Van Wagner 1968, Warren and Olsen 1964) for quantifying 

the down component of CWD. Most studies have assumed the accuracy of the line 

transect method when quantifying down debris. In a literature search for this paper, 

studies were not found that compared volume measured on a fixed area to the volume 

estimated on that same area with the line transect method, in the natural setting. Few 

studies have tested two important assumptions of the line transect method for large 

debris: random piece orientation and spatially random piece distribution. 

Correcting for nonrandom piece orientation requires additional measurement 

effort in the form of additional transect lines or a mathematical correction. 

Identifying a random distribution may reduce the number of line segments and thus 

the effort required to reach some desired level of precision. If pieces are spatially 

clumped at some consistent scale on the forest floor, the identification of that scale 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Consultant, Systems for Environmental Management, P.O. Box 17101, Missoula, MT 59808-7101 

(e-mail: dlutes@fs.fed.us) 
Assessment of the Line Transect Method—Lutes 

666 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

may be used to reduce or eliminate the bias introduced by nonrandom spatial 

distribution. 

The objectives of this study were to 1) compare the volume of down debris 

(logs) measured on fixed-area plots against estimates of down debris made with the 

line transect method on the same area; 2) test two assumptions of the line transect 

method: pieces need to be distributed randomly in their orientation and at random, 

spatially, on the forest floor; 3) identify the spatial distribution of standing pieces 

(snags); and 4) examine for a consistent scale of clumping of down and standing 

pieces. 

Methods 

Study Site 

This study was conducted at the Tenderfoot Creek Experimental Forest (TCEF) 

in central Montana (fig. 1). The forest extends in elevation from approximately 1900 

to 2400 m and covers an area just less than 3,700 ha. Lodgepole pine (Pinus 

contorta) is the predominant cover type with scattered patches of subalpine fir (Abies 

lasiocarpa) and Engelmann spruce (Picea engelmannii) dominating older stands. 

Whitebark pine (Pinus albicaulis) and limber pine (Pinus flexilis) are also found 

throughout the TCEF. 

Figure 1―Study map of the Tenderfoot Creek Experimental Forest in central 

Montana, showing the locations of the13 sampling areas. 

Sampling areas were established in five stands chosen from a fire history map of 

the TCEF (Barrett 1993). Four of the stands had last burned in 1873, 1845, 1765 and 

1726, respectively. The fifth stand had burned in 1845 and again in 1873 (two-burn 

stand). None of the sampled stands showed any significant, identifiable sign of 

disturbance since the time of the last fire event. The 1873, 1845 and the two-burn 
Assessment of the Line Transect Method—Lutes 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 667 

stand were of the lodgepole pine cover type; the 1765 and 1726 stands were of the 

subalpine fir cover type. These stands were chosen because they were large enough 

to allow at least three sampling areas within each, had a wide variety of sizes and 

quantities of CWD, and were on sites with relatively little slope. 

Field Sampling 

Three sampling areas each were established in the 1873, 1845, 1765, and 1845 

fire year stands. The two-burn stand had one sampling area. Each sampling area 

included ten 50-m line segments and ten 50 X 20-m belt transects. Line segments 

were oriented in the four cardinal directions. Belt transects were established by using 

the line segments as a centerline. Additionally, one 50 X 50-m (0.25 ha) fixed-area 

plot was established on five sampling areas (fig. 2). The purpose of the fixed-area 

plots was to provide a “truth” to check the accuracy of line transect estimates of 

down debris. 

Figure 2—Sampling areas consisted of belt transects and 50-m line segments 

oriented perpendicularly. Five of the sampling areas had a 0.25-ha fixed-area plot 

that was positioned at the center of the sampling area. 

Line-transect data in this study were used for three purposes: to provide a 

volume estimate for comparison with volume determined on a fixed area, to identify 

the log distribution pattern, and to examine clumping scale. Perpendicular lines were 

used to reduce or eliminate bias added by non-randomly-oriented pieces (Howard and 

Ward 1972). Estimated volumes were the mean of the 50-m north-south and eastwest line segments. 

Logs (down debris) in this study were defined as pieces leaning at an angle less 

than 45 degrees from the forest floor, ≥ 10 cm diameter—measured at the small end 

for pieces within the fixed-area plots or at the point of intersection for pieces 

measured with the line transect method—and at least 2 m long. Only pieces within 2 

m of the forest floor were sampled. Diameter, directional orientation (large to small 
Assessment of the Line Transect Method—Lutes 

668 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

end), and distance from the start of the line segment were measured for all logs. 

Diameters of logs on the fixed-area plots were taken at three points: large end, midlength, and small end. Diameters of logs recorded with the line transect method were 

measured at the point of intersection. 

Some logs had decayed to the point where they were difficult to find, especially 

in areas of dense down debris, and therefore were extremely hard to quantify. For 

consistency, highly-decayed pieces were included in this study if they were above the 

plane of the ground surface, had no vegetation growing on them, and met the 

minimum log diameter and length criteria. 

Measurements were collected for standing pieces (snags) if at least half of the 

area of the snag base fell within the 20 X 50-m belt. Snags were defined as pieces 

≥ 10 cm diameter breast height (DBH), at least 2 m tall, and at an angle 45 degrees or 

greater from the forest floor. Distance from the start of the belt, measured 

perpendicular to the centerline of the belt, was recorded for each piece. Snags were 

the only component sampled using the belt transects. 

Analysis 

 Logs and snags within the 0.25-ha fixed-area plot were mapped and measured. 

The volume of logs on each plot was calculated using Newton’s formula (Avery and 

Burkhart 1983) and converted to a per-ha basis. Fixed-area volume was compared 

against the volume estimated by two perpendicular 50-m line segments run through 

the center of the fixed-area plot. Comparison of the measured, fixed-area volume and 

estimated, line-transect volume was made with t-tests and ordinary least squares 

(OLS) regression. 

The volume of down woody debris on each 50-m line was estimated with the 

equation proposed by Van Wagner (1968): 

 L

d

v

n

i

i

8

1

2 2

∑= =

π

 (1) 

in which d is diameter in cm, measured perpendicular to the length of the log, n is the 

number of individuals encountered, L is the length of line in meters, and v is the 

volume of down debris (m3

/ha). 

Ordinary least squares analysis of fixed-area volume and line transect volume 

was accomplished by simultaneously testing that the intercept was equal to zero and 

the slope of the relationship was equal to one (Draper and Smith 1981). To test this 

hypothesis the Q-statistic was computed using: 

 Q = ( )( ) β − b ' x' x β − b (2) 

in which β0 and β1 are the hypothesized population parameters (vector), b1 and b2 are 

the regression parameters (vector), and x′x is the matrix term of the independent 

variable (in this case the line-transect estimated volumes). The null hypothesis was 

rejected if the test statistic was greater than the critical value calculated with: 

 ( ) , ,1−α 2

ps F p v (3) 
Assessment of the Line Transect Method—Lutes 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 669 

in which p equals the regression degrees of freedom, s2 is the variance, and the Fvalue is from the appropriate F-statistic table. 

Two popular tests were used to describe the pattern of piece distribution on the 

forest floor and the orientational distribution of logs. The first test used the 

variance:mean ratio (V/M test) as an indicator of spatial pattern. The second test, 

which will be referred to as the distribution test, compared the pooled frequency 

distribution against the frequency that would be expected given the Poisson and 

negative binomial distributions. The distribution test was used to identify 

orientational clumping. 

 Random piece distribution is an assumption of the line-transect method and was 

tested here with the V/M test. Each 250-m east-west and north-south line was divided 

into 10-m, 25-m, and 50-m segments, which resulted in a total of six tests per 

sampling area (two lines, three tests each). Snag distribution was also studied with 

the V/M test at the same three scales, within the belt transects. Tests were conducted 

at three segment lengths because clumps may appear at different scales. The segment 

lengths were chosen to be as long as possible while still allowing a sufficient sample 

size. 

To test the spatial distribution of down pieces and snags with the V/M test 

(Ludwig and Reynolds 1988), the variance was calculated with the formula: 

 

( )

1

0

2

2

−





 



 −

=

∑=

N

x Fx xn

s

k

x (4) 

in which k is the greatest frequency per sampling unit, x is the frequency class, Fx is 

the count in the x frequency class, n is the number of individuals, and N is the 

number of sampling units. 

The chi-square test was used to check if the variance:mean ratio was 

significantly different from 1, where a value < 1 suggests uniform distribution and a 

value > 1 suggests clumped distribution. A random pattern is assumed when the 

variance:mean ratio is equal to 1. The snag data for three of the sampling areas were 

dropped from this analysis due to incomplete data. 

It is important to note that the tests of log distribution using the line transect data 

were actually identifying the pattern of log crossings in one dimension, not in two 

dimensions on the forest floor. It is unclear whether the pattern identified by the V/M 

Test is indicative of the pattern of log distribution on the forest floor. 

The distribution test was used to check for random directional orientation of 

logs. Logs were assigned to 1 of 36 classes by 10-degree increments and pooled by 

frequency. Pooling followed the recommendation of Ludwig and Reynolds (1988): 

when the number of frequency classes is less than five, the expected number in each 

class is not to be less than five; if the number of classes is five or greater, then the 

expected number is not to be less than three. Then the frequency distribution of the 

pooled data was tested against the Poisson and negative binomial distributions of 

expected counts using the chi-square test. On two of the sampling areas, counts 

within each frequency class were pooled to three individuals per class instead of the 

five per class recommended by Ludwig and Reynolds (1988) because of the low 

number of down pieces. The data for one sampling area were not analyzed for 

orientation due to degrees of freedom limitations. 
Assessment of the Line Transect Method—Lutes 

670 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Two hypotheses were tested with the distribution test: the frequency distribution 

followed the Poisson distribution (random distribution); the frequency distribution 

followed the negative binomial distribution (clumped distribution). Rejecting the first 

hypothesis and failing to reject the second implied a clumped pattern. 

The paired quadrat variance (PQV) technique (Ludwig and Reynolds 1988) was 

used to identify any consistent clumping scale. A peak in the graph of variance vs. 

quadrat spacing indicated clumps occurring at about twice the quadrat spacing 

(block) distance. To accomplish the test, a 5-m line segment was chosen to serve as a 

“quadrat” and the variance was calculated using the equation: 

(5) 

( ) ]{[0.5( ) ] [0.5( ) ] ... [0.5( ) ]} 1

var [ 2 2

1 (1 )

2

s 1 1 s s s s N s N x x x x x x

N S

x − + − + + − − = + + + + −

in which S is the spacing (in m) between quadrats, s is the quadrat sequence number, 

N is the number of quadrats, and x is the piece count in the quadrat. The variance was 

calculated to a block spacing of N/2 for each north-south and each east-west line in 

the study. Ludwig and Reynolds (1988) suggest using N/10 as the maximum quadrat 

spacing; however, N/2 was used to extend the analysis to a larger area. This may 

have resulted in some unreliable variance estimates at the larger quadrat spacings. By 

convention, an error level of p = 0.05 was used throughout this study. 

Results and Discussion 

Fixed-Area/Line Transect Volume Comparison 

The accuracy of the line-transect method was tested with t-tests and OLS 

regression on the 0.25-ha fixed-area plots. T-tests indicated that there was no 

significant difference between the mean volume estimated by two 50-m line 

segments and the volume measured on the fixed-area plots using Newton’s formula, 

except on sampling area 221 (table 1). Down pieces were not measured with the linetransect method on sampling area 221; thus, the result may be an indication of the 

estimating power of the line-transect method on lightly loaded areas. Brown (1974) 

and Pickford and Hazard (1978) note that coefficient of variation decreases as sample 

size increases, and they suggest counting at least 25 pieces for dependable results. 

Table 1―T-test results of total fixed-area volume compared against the mean volume 

estimated with two perpendicular 50-m lines found no significant differences, except on 

sampling area 221 where no pieces were measured using the line transect method. 

Plot F/A1

 vol. L/T1 vol. L/T std. dev. t p(t) 

 -------------------------m3/ha------------------- 

001 14.91 33.23 4.26 6.08 0.10 

002 134.52 139.83 77.78 0.09 0.94 

221 7.74 0.0 0.0 - - 

248 277.47 294.18 11.71 2.01 0.29 

280 33.08 24.88 3.19 3.63 0.17 

1 F/A = fixed-area; L/T = line transect 
Assessment of the Line Transect Method—Lutes 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 671 

Ordinary least squares regression of two, 50-m line segments and fixed-area 

volumes resulted in a significant (F = 368.76; p = (368.76) = 0.0003) and highly 

correlated (r2 = 0.99) relationship (fig. 3). However, the Q-statistic was greater than 

the critical value (62895.66 > 1093.12), which indicated that β0 was significantly 

different from 0 and/or β1 was significantly different than 1. Because of the small 

sample size, inconsistent t-test and Q-test results, and inconsistent tests of the 

underlying assumptions of the line transect method, the ability of the line-transect 

method to estimate down volume was not determined. 

Figure 3—Ordinary least squares regression results of volume estimated with two 

perpendicular 50-m line segments vs. the actual volume measured on a 0.25-ha 

fixed-area plot. 

Log Distribution 

The V/M test was used to identify the spatial distribution of logs on the forest 

floor (table 2). Of 78 tests performed on the line-transect data, 18 (23 percent) tested 

as having a clumped log distribution. The remaining 60 (77 percent) tested as having 

a random distribution. No lines were found to have a uniform distribution of logs. 

Table 2―Log distribution indicated by the V/M Test indicated a generally random pattern at 

the three scales tested. 

 Scale 

Pattern 10 m 25 m 50 m 

 ----------------------Number of sampling areas------- 

Uniform 0 0 0 

Random 20 22 18 

Clumped 6 4 8 
Assessment of the Line Transect Method—Lutes 

672 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

In some cases the log distribution pattern changed with the scale of the test data. 

Six of the 13 sampling areas had at least one test indicating a clumped distribution. 

One sampling area had five of the six tests indicate a clumped distribution. Every 

sampling area had at least one test that indicated a random pattern. Six sampling 

areas did not test for a clumped pattern at any scale. An identifiable relationship was 

not found between the number of individuals, whole line or per segment, and 

clumped pattern. A relationship was not found between segment length (scale) and 

clumped pattern. 

On sampling areas in the youngest stand (1873), the low number of logs may 

have led to unreliable estimates of the variance: mean ratio and thus the indicated 

pattern. For the remainder of the sites, however, the V/M method seemed to be 

appropriate. 

 

Log Orientation 

There was an obvious eastward directional bias when down pieces from all 

sampling areas were graphed together (fig. 4). Log orientation data were tested 

separately for each sampling area. Only five sampling areas had pieces that followed 

the Poisson distribution. Log orientation followed the negative binomial distribution 

on 12 of the sampling areas (The low number of down pieces on one sampling area 

did not allow testing against the negative binomial distribution.) This indicated that in 

eight of 12 instances there was evidence of clumped log orientation. 

Figure 4—Log orientation of all sample pieces showed an obvious eastward bias. 
Assessment of the Line Transect Method—Lutes 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 673 

Effects of Scale on CWD Estimates 

The PQV model revealed little evidence of a consistent scale effect on CWD 

estimates. The graphs of variance vs. quadrat spacing for sampling areas 3 and 398 

indicate peaks of variation at some block sizes, but whether these indicate clumps or 

simply the random distribution of logs is unclear (fig. 5). Results of the V/M test only 

confounded any analysis. There was no systematic pattern to the graphs of variance 

for any of the 13 sampling areas in this study. 

Figure 5—A consistent pattern of down or standing piece distribution was not 

identified using the paired quadrat variance method. Four examples of the original 46 

graphs are presented here for the reader’s examination. 

Snag Distribution 

Like logs, snags showed only moderate evidence of clumped distribution (table 

3). Of 60 tests, 37 (62 percent) indicated snags were randomly distributed. Twentytwo (37 percent) indicated a clumped distribution of snags and one test indicated a 

uniform distribution. Six of the 20 belts were found to have a clumped distribution of 

snags at each of the three scales. Half of the belts were found to have clumped snags 

at at least one scale, and nine tests indicated snags were distributed randomly at every 

scale. Only one sampling area tested as having a clumped distribution on both lines at 

every scale. A relationship was not found between the number of individuals and the 

distribution suggested by the V/M test. An identifiable relationship was not found 

between scale and distribution. 
Assessment of the Line Transect Method—Lutes 

674 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 3―Snag distribution indicated by the V/M test indicated a generally random pattern at 

the three scales tested. 

 Scale 

Pattern 10 m 25 m 50 m 

------------Number of sampling areas------- 

Uniform 0 1 0 

Random 12 12 13 

Clumped 8 7 7 

 

Conclusion 

The accuracy of the line transect method could not be determined in this study 

for two reasons: inconsistent test results indicated that two important assumptions of 

the line transect method, random spatial and orientational distribution, could not be 

guaranteed; and the sample size was quite small (n = 5). 

The bias introduced by not meeting the assumptions of the line transect method 

was probably small, however. First, the sampling scheme used in this study 

(perpendicular lines) should have substantially reduced any bias introduced by 

clumped log orientation (Howard and Ward 1972). Secondly, because log 

distribution was found to be generally random at the scales tested in this study (10-m, 

25-m and 50-m) there was likely little bias introduced by clumped pieces. 

Most tests of log and snag distribution indicated a random pattern. Because tree 

regeneration and mortality are generally assumed to occur in aggregated patterns 

(Franklin and others 1987, Harmon and others 1986, Lundquist 1995, Maser and 

others 1988), the results from this study were somewhat surprising. However, 

lodgepole pine tends to regenerate in a relatively uniform manner (Fischer and 

Bradley 1987) with tree mortality and log accumulation possibly following that 

pattern. Lodgepole pine comprised some or all of the tree cover on the sampling areas 

in this study, which may explain finding mostly random patterns. Also, the scale of 

sampling may have had an effect on the results because the line segment and quadrat 

sizes tested for log and snag distributions were quite small. 

The eastward bias of down pieces was likely not due to logs moving to new 

orientations after they fell, since the sampling areas had no or little slope (less than 

15 percent). Also, pieces were probably not greatly affected by wind events 

exacerbated by local geography (ridge-tops, canyons, etc.) but simply fell away from 

the prevailing westerly winds. 

The usefulness of the PQV method was not demonstrated here theoretically due 

to the relatively small quadrat distance tested. The method may prove useful for 

variance and block size relationships over a larger area—1 or 2 ha for example. 

However, the potential effects of disturbance, ridge-tops, differing stand ages, steep 

slopes, and changing aspects on the pattern of piece distribution must be considered. 
Assessment of the Line Transect Method—Lutes 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 675 

Acknowledgments 

This project was funded by the USDA Forest Service, Rocky Mountain 

Research Station, Fire Sciences Laboratory, Missoula, Montana. I would like to thank 

Colin Hardy, Elizabeth Reinhardt, Carl Fiedler, John Chmelik, and Bill Laudenslayer 

for numerous useful review comments. 

References 

Avery, E. A.; Burkhart, H. E. 1983. Forest measurements. New York: McGraw-Hill; 331 p. 

Barrett, S. W. 1993. Fire history of the Tenderfoot Creek Experimental Forest, Lewis and 

Clark National Forest. RJVA INT-92679 on file with RM-RWU-4151, Bozeman, MT; 

19 p. 

Brown, J. K. 1974. Handbook for inventorying downed woody material. Gen. Tech. Rep. 

INT-16. Ogden, UT: Intermountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 24 p. 

Draper, N. R.; Smith, H. 1981. Applied regression analysis, 2d edition. New York: J. Wiley 

and Sons; 709 p. 

Fischer, W. C.; Bradley, A. F. 1987. Fire ecology of western Montana forest habitat types.

Gen. Tech. Rep. INT-223 Ogden, UT: Intermountain Forest and Range Experiment 

Station, Forest Service, U.S. Department of Agriculture; 95 p. 

Franklin, J. F.; Shugart, H. H.; Harmon, M. E. 1987. Tree death as an ecological process.

BioScience 37: 550-556. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G.W.; 

Cromack, K.; Cummins, K. W. 1986. Ecology of coarse woody debris in temperate 

ecosystems. Advances in Ecological Research 15: 133-302. 

Howard, J. O.; Ward, F. R. 1972. Measurement of logging residue―alternative 

applications of the line transect method. Res. Note PNW- 183. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 8 p. 

Ludwig, J.; Reynolds, J. F. 1988. Statistical ecology: primer on methods. New York: J. 

Wiley and Sons; 406 p. 

Lundquist, J. E. 1995. Pest interactions and canopy gaps in ponderosa pine stands in the 

Black Hills, South Dakota, USA. Forest Ecology and Management 74: 37-48. 

Maser, C.; Anderson, R. G.; Cromack, K.; Williams, J. T.; Martin, R. E. 1979 Dead and 

down woody material. In: Wildlife habitats in managed forests: the Blue Mountains of 

Oregon and Washington. Agric. Handb. 553. Washington, DC: U.S. Department of 

Agriculture; 78-95. 

Maser, C.; Tarrant, R. F.; Trappe, J. M.; Franklin, J. F. 1988. From the forest to the sea: a 

story of fallen trees. Gen. Tech. Rep. PNW-GTR-229. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 153 p. 

Pickford, S. G.; Hazard, J. W. 1978. Simulation studies on line intersect sampling of forest 

residue. Forest Science 24: 469-483. 

Van Wagner, C. E. 1968. The line intersect method in forest fuel sampling. Forest Science 

14: 20-26. 

Warren, W. G.: Olsen, P. F. 1964. A line intersect technique for assessing logging waste.

Forest Science 10: 267-276. 
Management of Dead Wood

677
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 679 

Forest Management and the Dead Wood 

Resource in Ponderosa Pine Forests: 

Effects on Small Mammals1

Carol L. Chambers2

Abstract 

Changes in vegetation structure and composition affect habitat for wildlife. Species such as 

small mammals that are restricted to small home ranges and are relatively immobile may be 

most affected since it is more difficult to find and move to new habitat. In the southwestern 

United States, forest management treatments (thinning and prescribed burning) are being 

implemented to alter structure and function of ponderosa pine (Pinus ponderosa) ecosystems 

and recreate pre-settlement (ca. 1870) tree species composition and size class distribution. 

These forest restoration treatments will affect the availability of dead wood to wildlife (e.g., 

prescribed fires may consume dead wood, forest operations may create snags and logs). I livetrapped small mammals in a northern Arizona ponderosa pine forest prior to restoration 

treatment and found that mouse species (Peromyscus species) were associated with some dead 

wood elements (e.g., Gambel oak [Quercus gambelii] snags, ponderosa pine snags, ponderosa 

pine stumps). 

Introduction 

Standing dead trees and logs are important components of wildlife habitat. They 

provide nesting, roosting, feeding, loafing, and storage sites for over 75 species of 

birds, mammals, reptiles, and amphibians in the Southwest (Degenhardt and others 

1996, Rabe 1998, Scott 1979, Scott and Patton 1989). Many of these animals have 

important ecological roles, such as dispersing seeds and mychorrhizal fungi, helping 

to control insect populations, and serving as prey for other species (Bergvinson and 

Borden 1992, Maser and others 1988, Peterson 1980, Ward and Block 1995). 

Vertebrate population densities may change in response to change in vegetation 

structure and composition (see for example, Chambers and others 1999, Scott 1979, 

Szaro and Balda 1986). Although some wildlife species (birds, large ungulates) are 

highly mobile and can move to more favorable habitat (assuming it is unoccupied), 

many species (small mammals, reptiles, amphibians) are often restricted to relatively 

small areas (i.e., 2 to 20 ha per individual or population) (e.g., Hall and Morrison 

1997). Forest management practices may have differential effects on vertebrate 

populations depending on the scale at which the treatments are applied and the size of 

habitat used by an organism. 

Ponderosa pine forests cover about 3.2 million ha in Arizona and New Mexico 

(Klemmedson and Smith 1979). These forests appear to be at increasing risk of 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Associate Professor, School of Forestry, Northern Arizona University, Flagstaff, AZ 86011 (e-mail: 

Carol.Chambers@nau.edu)
Dead Wood Resources and Small Mammals—Chambers 

680 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

catastrophic fire as a result of 130 years of Euro-American influence. A combination 

of fire suppression, logging practices, insect infestations, livestock grazing, and a 

shift towards a warmer and wetter climate has altered the composition of ponderosa 

pine forests (Cochran and Hopkins 1991, Cooper 1960, Covington and Moore 1994, 

Grissino-Mayer and Swetnam 2000, Touchan and others 1996). Livestock grazing 

reduced native grasses and other fine fuels that spread low intensity fires. Grazing 

also exposed bare mineral soil, which allowed establishment of ponderosa pine 

seedlings in years following high cone production (Klemmedson and Smith 1979, 

Touchan and others 1996). Fire suppression has resulted in greater survival of young 

trees, contributing to forest densities of >3,000 trees/ha in the 1990s compared to 60 

trees/ha in 1876 (Mast and others 1999). 

Ecological restoration, using silvicultural tools such as thinning and prescribed 

burning, may help reestablish structure and function of indigenous ecosystems by 

recreating pre-settlement (ca. 1870) tree species composition and size class 

distribution and reestablishing a frequent, low intensity fire regime (Covington and 

others 1997). However, restoration treatments will affect the availability of dead 

wood to wildlife. Thinning and pruning may increase log and slash densities. Slash 

treatments that leave piles or windrows increase habitat for some vertebrates (e.g., 

small mammals, Goodwin and Hungerford 1979). Prescribed fire may increase or 

decrease the dead wood resource. Boucher and others (1999), Gaines and others 

(1958), and Gordon (1996) found that prescribed fire created dead wood; however, 

live trees killed by fire were predominantly small in diameter and therefore not 

effective replacements of large logs and snags. Prescribed fires will also incinerate 

existing snags and logs, removing up to 50 percent of ponderosa pine snags and 60 

percent of logs (Gaines and others 1958, Gordon 1996, Horton and Mannan 1986, 

Randall-Parker and Miller 2002). In addition, Horton and Mannan (1988) found that 

large (>30 cm dbh) and more decayed ponderosa pine snags were more flammable, 

and therefore more likely to be lost. This loss of large dead wood may be particularly 

detrimental to wildlife, because cavity nesters (birds and bats) select larger snags 

(>46 cm diameter), large snags persist longer than small snags (Neitro and others 

1985, Rabe and others 1998, Scott and Oldemeyer 1983), and replacement of large 

snags may take a long time (e.g., >200 years for a ponderosa pine to reach 46 cm dbh 

under normal stocking, site index 70 [Meyer 1961]). Large snags are often the origin 

of large logs, so fires may have both immediate and long-term impacts on both 

standing dead and down wood. 

If not incinerated, snags and logs may be altered by fire and their usefulness as 

wildlife habitat decreased (Gaines and others 1958, Gordon 1996). After a prescribed 

burn, Gordon (1996) suggested that the utility as habitat of >70 percent of logs in her 

study was decreased, because logs were charred and case-hardened, making them 

more difficult for animals to excavate. Most snags fell (50 percent, Gordon 1996), at 

which point they were considered useful as log habitat. Additional fires might further 

reduce available dead wood. 

What do we know specifically about use of dead wood in the Southwest? I 

found 41 articles (table 1) that described either dynamics of dead wood or use of 

dead wood as habitat for wildlife in the Southwest. The literature generally focused 

on ponderosa pine ecosystems (n = 32), although five papers described mixed conifer 

ecosystems and four papers described dead wood in both forest types. Snag dynamics 

or use was the most common topic discussed (n = 33). Of these, 11 papers described 

use of snags by primary or secondary cavity-nesting birds and 10 described other 
Dead Wood Resources and Small Mammals—Chambers 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 681 

types of use by wildlife. The remaining 12 papers described snag recruitment and 

longevity, pre-settlement forest conditions in the Southwest, or effects of prescribed 

fire on dead wood. Fifteen papers discussed dynamics (n = 6) or wildlife use (n = 9) 

of logs. 

Of the 41 papers discussing dead wood in the Southwest, only 4 (Goodwin and 

Hungerford 1979, Kyle 2000, Smith and Mannan 1994, Ward and Block 1995) 

described small mammal use of down wood in ponderosa pine forests. I examined 

small mammal use of ponderosa pine stands in northern Arizona. My objective was 

to determine how the availability of standing and down wood and other habitat 

elements affected abundance of small mammals. The study was conducted in areas 

scheduled for forest restoration treatments (thinning, prescribed burning). From these 

data, I have speculated on how restoration may affect dead wood and impact small 

mammal communities. Following restoration treatments, stands will be resampled 

and pre- and post-treatment comparisons made. 

Table 1Dead wood (snags and logs) in the Southwest reference list. 

Author(s) Year Snags Logs Wildlife 

Mixed conifer 

Vahle and Patton 1983 X X 

Conway and Martin 1993 X X 

Franzreb 1978 X X 

Franzreb and Ohmart 1978 X X 

Li and Martin 1991 X X 

 

Ponderosa pine 

Goodwin and Hungerford 1979 X X 

Smith and Mannan 1994 X X 

Ward and Block 1995 X X 

Smith 1996 X X 

Covington and Sackett 1984 X 

Graham and others 1994 X 

Balda and others 1983 X X 

Crocker-Bedford 1993 X X 

Cunningham and others 1980 X X 

Dwyer 2000 X X 

Hay and Guntert 1983 X X 

Horton and Mannan 1988 X X 

Keller 1992 X X 

Rabe and others 1998 X X 

Reynolds and others 1992 X X 

Scott 1978 X X 

Scott 1979 X X 

Szaro and Balda 1986 X X 

Brawn and Balda 1988 X X 

Ffolliot 1983 X 

Mast and others 1999 X 

Miller and Benedict 1994 X 

Pearson 1937 X 

Scott and Oldemeyer 1983 X 

Wadsworth 1943 X 
Dead Wood Resources and Small Mammals—Chambers 

682 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(table 1 continued)

Author(s) Year Snags Logs Wildlife 

Block and Finch 1997 X X X 

Germaine 1999 X X X 

Kyle 2000 X X X 

Covington and Moore 1994 X X 

Covington and others 1997 X X 

Gaines and others 1958 X X 

Gordon 1996 X X 

 

Mixed conifer and ponderosa pine 

Mollohan and others 1989 X X 

Balda 1975 X X 

Dahms and Geils 1997 X 

Ganey 1999 X 

Methods 

Study Area 

I live-trapped small mammals at Mt. Trumbull, in the Arizona Strip north of the 

Colorado River, in northern Arizona (latitude 36o 22’ 0”, longitude 113o

 11’ 0”). The 

study area ranged from 2,055 to 2,277 m in elevation. Tree density averaged 1,642 

trees per ha, with ponderosa pine dominating (ponderosa pine averaged 90 percent of 

stand basal area). Gambel oak, pinyon pine (Pinus edulis), Utah juniper (Juniperus 

osteosperma), and New Mexican locust (Robinia neomexicana) comprised the 

remaining 10 percent basal area. Log density averaged 6.4/ha, 51.0, 1.6, 107.6, 

respectively, for large (>50 cm diameter) and small (<50 cm) ponderosa pine logs; 

large (>15 cm diameter) and small (<15 cm) Gambel oak logs. Snag density averaged 

1.6/ha, 40.3, 7.8, and 216.6, respectively, for large and small ponderosa pine snags; 

large and small Gambel oak snags. 

Small Mammal and Habitat Sampling 

I established trapping grids within five 32-ha experimental restoration units. 

Each unit consisted of two stands: one treatment and one control, approximately 

equal in size. Treatment stands were to be harvested in 1999; I sampled all stands 

prior to harvest in July 1998. 

I established a 10 x 10 trapping grid (4 ha grid) centered in each 16-ha stand (n 

= 10 grids). Grid points were placed 20 m apart. At each point on the trapping grid, I 

placed one Sherman live trap (8 x 8 x 23 cm). Traps were baited with a peanut heart 

and seed mix. Traps were set for four to five consecutive nights (until recapture rates 

were >80 percent) and checked daily. Traps were closed during the day to prevent 

capture of diurnal animals and reopened approximately 1 hour before dusk. 

Units 1, 2, and 3 were sampled July 11-15, 1998. Units 4 and 5 were sampled 

July 26-29, 1998. All animals were weighed, measured (total body length, lengths of 

tail, ear, and right hind foot), ear-tagged with a unique number, and released at the 

point of capture. 
Dead Wood Resources and Small Mammals—Chambers 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 683 

I obtained vegetation and habitat data for each stand from the Northern Arizona 

University School of Forestry Ecological Restoration Institute. These data were 

collected June through August 1998 for a subset of trap stations (12 to 16 trap 

stations systematically distributed in each grid to equally sample throughout the 

trapping grid). Overstory data (tree density, basal area, canopy cover, snags, logs, 

stumps) were measured on a 0.04 ha plot and shrubs were measured on a 0.01 ha plot 

centered on each trap station location (table 2). Other understory habitat features 

(grasses, forbs, mosses, lichens) were measured by point intercept along a 50-m line 

transect (166 points per transect) and their frequency per trap station calculated (table 

2).

Table 2Habitat variables used in developing habitat relationships models for small 

mammal species (deer mouse, pinyon mouse, brush mouse) at Mt. Trumbull, Arizona, June–

August 1998. 

Variable Definition 

Understory 

Lichen Percentage of lichen and moss cover 

Litter Percentage of litter cover 

Forb Percentage of forb cover 

Grass Percentage of grass cover 

Shrub Percentage of woody plant (shrubs and trees <1.4 m) cover 

Logs Number of logs > 0.15 m long by species (ponderosa pine, Gambel oak, New Mexican 

locust, Utah juniper) and size class (for ponderosa pine: small <50 cm diameter, large 

>50 cm diameter; for Gambel oak, small <15 cm diameter, large >15 cm diameter; size 

classes were not created for New Mexican locust or Utah juniper) 

Stumps Number of stumps by species (ponderosa pine, Gambel oak, New Mexican locust, Utah 

juniper) and size class (for ponderosa pine: small <50 cm diameter, large >50 cm 

diameter; for Gambel oak, small <15 cm diameter, large >15 cm diameter; size classes 

were not created for New Mexican locust or Utah juniper) 

 

Overstory

Basal area Basal area (m2

/ha) for all live trees combined and for each tree species (ponderosa pine, 

Gambel oak, New Mexican locust, Utah juniper, pinyon pine) 

Live trees Number of live trees by species (ponderosa pine, Gambel oak, New Mexican locust, 

Utah juniper) and size class (for ponderosa pine: small <50 cm diameter, large >50 cm 

diameter; for Gambel oak, small <15 cm diameter, large >15 cm diameter; size classes 

were not created for New Mexican locust, or Utah juniper) and decay condition (1 = 

live tree, no sign of decay, 2 = live tree, declining, some evidence of decay (e.g., dead 

branches) 

Snags Number of snags by species (ponderosa pine, Gambel oak, New Mexican locust, Utah 

juniper), size class (for ponderosa pine: small <50 cm diameter, large >50 cm diameter; 

for Gambel oak, small <15 cm diameter, large >15 cm diameter; size classes were not 

created for New Mexican locust, or Utah juniper), and decay condition (3 = recent snag, 

4 = loose bark snag, 5 = snag without bark remaining, 6 = snag broken above 1.4 m) 
Dead Wood Resources and Small Mammals—Chambers 

684 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Live trees and snags or partial snags were classified into decay classes. Decay 

class 1 was a live tree with no evidence of dead branches. Decay class 2 was a live 

tree with dead branches (declining), decay class 3 was a recent snag, decay class 4 

was a snag with loose bark, decay class 5 was a snag with no bark remaining. 

Statistical Analyses 

Stand-Level Analyses 

I calculated capture rates per stand (number of animals per 100 trap nights [TN]) 

(table 3) for each Peromyscus species. I averaged overstory and understory variables 

for each stand. Habitat variables that were not normally distributed or with unequal 

variance were transformed by taking the square root of the variable or by using 

log10(variable + 1) (Sabin and Stafford 1990). 

I reduced the number of habitat variables for multiple linear regression to adjust 

for small sample sizes. For each mouse species, I developed models using subsets of 

<3 habitat variables. I used Spearman correlations to determine univariate 

relationships between each species of Peromyscus and habitat variables that were 

selected in multivariate models (SAS Institute Inc. 1985) (Spearman correlations: R > 

0.6, P < 0.05 for deer mouse, R > 0.5, P < 0.1 for brush mice, and R > 0.7, P < 0.03 

for pinyon mice). 

I used stepwise linear regression analysis to identify habitat variables that, in 

combination, were associated with small mammal capture rates (Sokal and Rohlf 

1981, SAS Institute Inc. 1985). I used Akaike’s Information Criterion (AIC) to select 

models with predictive power that used the fewest variables; low AIC values are 

associated with models that give the best fit of data. To select the best model, I 

compared AICd values (relative AIC value for each model, calculated by taking the 

difference between the model with lowest AIC value). If AICd values were < 4, 

models were assumed equally effective in predicting presence of the animal species 

and the most parsimonious model selected (Burnham and Anderson 1998:43-48). 

Table 3Capture rates (number of animals per 100 trap nights [TN]) for deer mouse 

(Peromyscus maniculatus), brush mouse (P. boylii), and pinyon mouse (P. truei) at Mt. 

Trumbull, Arizona, July 1998. For stand, C represents the control unit (will not be thinned or 

burned) and T represents the treatment unit (untreated at the time of data collection). 

Capture Rate (number/100 TN) 

Stand Deer Mouse Brush Mouse Pinyon Mouse 

1C 3.0 4.8 0.0 

1T 3.6 5.8 0.6 

2C 4.4 0.0 0.4 

2T 12.0 1.0 0.0 

3C 2.6 0.0 0.0 

3T 2.6 0.2 1.2 

4C 1.3 0.0 4.8 

4T 0.8 0.5 5.0 

5C 0.3 0.0 3.8 

5T 0.5 0.8 2.8 
Dead Wood Resources and Small Mammals—Chambers 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 685 

Trap Station Analyses 

I averaged values for each habitat variable by trap station and used these data to 

develop habitat association models. I used logistic regression as a means of selecting 

variables that separated trap stations used by small mammals from unused trap 

stations. I conducted separate analyses for each mouse species (deer mouse, brush 

mouse, pinyon mouse). I used the Hosmer and Lemeshow goodness-of-fit test to 

determine whether the distribution of probabilities produced by my model(s) fit the 

logistic probability distribution (SAS Institute, Inc. 1990). 

Results 

I captured 270 individuals of 3 species during the trapping period: 135 deer mice 

(50 percent of captures), 74 pinyon mice (27 percent of captures), and 61 brush mice 

(23 percent of captures). Deer mice were more abundant in units 1, 2, and 3. Brush 

mice were most abundant in unit 1. Pinyon mice were most abundant in units 4 and 5

(table 3).

Stand-Level Analyses 

Models with two regressors were strongest predictors of deer mouse and pinyon 

mouse habitat use based on AICd values. For brush mouse, there was no difference 

between the 1- and 2-variable models based on AICd values (table 4). 

Large Gambel oak trees and small ponderosa pine snags explained 87 percent of 

the variation in deer mouse abundance (F = 24.3, df = 2, 9, P < 0.0007). Deer mice 

were positively correlated with large Gambel oaks (R = 0.64, P = 0.05) (fig. 1A) and 

negatively correlated with small ponderosa pine snags (R = -0.74, P = 0.01) (fig. 1B). 

Table 4Stepwise linear regression models developed to explain differences in habitat use at 

the stand level by deer mice, brush mice, and pinyon mice, Mt. Trumbull, Arizona, 1998.1

Species Habitat Variable Partial R2

 Model R2 AIC AICd 

Deer >15 cm dbh Gambel oak trees 0.62 0.62 18.0 9.2 

mouse <50 cm dia. ponderosa pine snags 0.26 0.87 8.8 0 

 

Brush >50 cm dia. ponderosa pine stumps 0.37 0.37 13.5 2.6 

mouse Lichen and moss cover 0.23 0.61 10.9 0 

Pinyon Juniper species basal area 0.90 0.90 -6.1 4.9 

mouse Ponderosa pine basal area 0.05 0.95 -10.9 0 

1

Akaike’s Information Criterion (AIC) was used to select models with predictive power using fewest 

variables; lowest AIC values are associated with models that give the best fit of data (best model is 

depicted in bold typeface, if not indicated in bold typeface, either model is equally acceptable). AICd is 

the relative AIC value for each model, calculated by taking the difference between the model with 

lowest AIC value. 
Dead Wood Resources and Small Mammals—Chambers 

686 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Basal area of juniper and ponderosa pine trees explained 95 percent of the 

variation in pinyon mouse abundance (F = 67.2, df = 2, 9, P = 0.0001) (table 4).

Pinyon mice were positively correlated with juniper basal area (R = 0.85, P = 0.002) 

(fig. 1C) and ponderosa pine basal area (R = 0.71, P = 0.02) (fig. 1D).

Large ponderosa pine stumps explained 37 percent of the variation in brush 

mouse abundance (F = 4.8, df = 1, 9, P = 0.06) (table 4). Brush mice abundance was 

negatively correlated with large ponderosa pine stump density (R = -0.61, P = 0.06) 

(fig. 1E). Lichen cover was not significantly correlated with brush mouse abundance 

(R = 0.15, P = 0.7), and it did little to explain more variation in mouse abundance 

(based on AICd values) when included in the multiple regression model (table 4) (F 

= 5.4, df = 2, 9, P = 0.04). 

Trap Station Analyses 

Of 143 trap stations with vegetation data, I captured deer mice at 14 stations, 

pinyon mice at 12 stations, and brush mice at 6 stations. Combining all species, I 

captured mice at 29 of 143 trap stations. 

Trap stations with the highest probability of deer mice capture had higher forb 

cover, higher live tree basal area, and higher densities of small (<15 cm dbh) Gambel 

oak live trees or recent snags (decay class 2 or 3). Pinyon mice were captured at trap 

stations with higher pinyon pine basal area, small (<15 cm dbh) Gambel oak trees, 

and <50 cm diameter ponderosa pine stumps. There was a higher probability of brush 

mouse capture at trap stations with lichen cover, >50 cm dbh ponderosa pines, and 

<15 cm dbh Gambel oak trees or recent snags (decay class 2 or 3). 

Discussion 

Habitat Associations of Small Mammals 

The deer mouse is one of the most widespread rodents. In the Southwest, it is 

common in forest types from high elevation spruce/fir (Picea/Abies) forests to 

ponderosa pine forests. Pinyon and brush mice are more selective of habitat. Brush 

mice occur in areas with dense rock and shrub cover, usually in pinyon-juniper, 

riparian, oak, and pine-oak woodlands (Goodwin and Hungerford 1979, Ward and 

Block 1995). Pinyon mice occur in pinyon-juniper and xeric oak woodlands 

(Cranford 1982, Morrison and Hall 1998). 

Ward and Block (1995) described habitat associations of deer mice in ponderosa 

pine/Gambel oak forests of northern Arizona. They found that deer mice used more 

open sites with less shrub and midstory canopy, and smaller densities of Gambel oak. 

They also found deer mice used sites with more slash piles and greater litter depth. 

Goodwin and Hungerford (1979) found that deer mice were correlated with stump 

and log density. They found that mice hid in larger logs or stumps, fallen logs created 

spaces for nesting, and that mice also nested inside bark that had separated from 

stumps and logs. At the stand level, I found deer mice were more abundant in areas 

with higher densities of large Gambel oak. Deer mice were less abundant in stands 

with high densities of small ponderosa pine snags. Small ponderosa pine snags were 

correlated with high densities of live ponderosa pine (R = 0.71, P = 0.02); deer mice 

were therefore less abundant in dense ponderosa pine stands. At the trap station level, 

deer mice were more abundant in areas with high forb cover and live tree basal area. 
Dead Wood Resources and Small Mammals—Chambers 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 687 

Gambel oak was an important predictor of deer mouse density. Because deer mice 

are generalists positively correlated with Gambel oak and negatively correlated with 

high densities of ponderosa pine, I hypothesize that deer mice will continue to 

increase in density in treated units for several years following treatment; then 

populations will stabilize. 

A. B. 

C. D. 

E. 

Figure 1—Spearman correlations for habitat variables that were used in multiple 

linear regression models for deer mouse (A and B), pinyon mouse (C and D), and 

brush mouse (E). Capture rate is standardized as number of individuals captured per 

100 trap nights (#/100 TN). Large Gambel oak were >15 cm diameter. Small 

ponderosa pine snags were <50 cm dbh; large ponderosa pine stumps were >50 cm 

diameter. 

0

5

10

15

0 100 200 300 400

density of large Gambel oak trees

deer mouse capture 

rate (#/100 TN)

0

5

10

15

0 50 100 150 200

density of small ponderosa pine snags (#/ha)

deer mouse capture 

rate (#/100 TN)

0

1

2

3

4

5

6

01234

basal area of Utah juniper trees (m2/ha)

pinyon mouse capture 

rate (#/100 TN)

0

1

2

3

4

5

6

0 20 40 60

basal area of ponderosa pine trees (m2/ha)

pinyon mouse capture 

rate (#/100 TN)

0

1

2

3

4

5

6

7

0 5 10 15 20 25

density of large ponderosa pine stumps (#/ha)

brush mouse capture 

rate (#/100 TN)
Dead Wood Resources and Small Mammals—Chambers 

688 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Ward and Block (1995) found brush mice more abundant in areas with steeper 

slopes, low vegetation cover, sparse tree canopy cover, greater Gambel oak basal 

area, greater Gambel oak tree and shrub density, greater log volume, and less 

ponderosa pine basal area. Goodwin and Hungerford (1979) found high densities of 

brush mice along rocky slopes. These animals used windrowed slash piles. Goodwin 

and Hungerford (1979) also found that brush mice were much less abundant in areas 

of pure ponderosa pine or in mixed pine-juniper forest. I found few correlations 

between brush mice and habitat variables. The regression model I developed for 

brush mice explained less variation than models developed for pinyon and deer mice. 

Brush mice were negatively correlated with large ponderosa pine stump density. 

Brush mice were captured most frequently at Mt. Trumbull in an area with rocky 

basalt-derived soils adjacent to a recent (~6,000 BP) lava flow. I found large 

ponderosa pine stumps were negatively correlated with large ponderosa pine trees (R 

= -0.55, P = 0.10), which may indicate that brush mice were using more open sites. 

Lichen cover (likely an indicator of rock cover), large ponderosa pine and small 

Gambel oak trees were predictors of brush mouse habitat at the trap-station level, 

indicating their use of more open, brushy, rocky habitats. I hypothesize that brush 

mice populations will remain stable or slightly increase following harvest treatment 

since they are less reliant on overstory cover but use shrub and rock cover for habitat. 

Shrubs will likely increase on treated units; rock cover will not change. 

I found no studies that documented habitat use of pinyon mice in ponderosa pine 

forests. I found that pinyon mice were associated with Utah juniper and ponderosa 

pine basal area. Pinyon mice were captured most frequently in stands with high 

densities of small diameter trees. These sites were lower in elevation, with higher 

densities of Utah juniper and pinyon pine. At the trap-station level, pinyon mice were 

captured in areas with high pinyon pine density, and high abundance of small 

Gambel oak trees and small ponderosa pine stumps. Suppression mortality may have 

resulted in high densities of small logs on the forest floor in these stands, but high 

densities of down wood may not necessarily be the cause of pinyon mouse habitat 

use. Other factors, such as the presence of pinyon pine and Utah juniper, may have 

been more important influences in use of habitat by pinyon mice. I hypothesize that 

pinyon mice populations will decline following harvest since pinyon mice are 

associated with high density of small diameter trees. 

I found associations between habitat elements and relative abundance for each 

Peromyscus species; however, in most cases there was little consistency between the 

trap-station analyses and the stand-level comparisons. Multiple linear regression and 

logistic regression examine habitat relationships at different scales, so these results 

are not necessarily surprising (Block and others 1998). 

Importance of Dead Wood and Effects of Forest Management 

on Dead Wood 

The models that I developed to predict the presence of Peromyscus species 

included elements of dead wood. However, there were no consistent patterns of dead 

wood use at the two spatial scales (trap-station level and stand-level) I examined. 

Either strong patterns of use of dead wood by these species are different at different 

spatial scales, do not exist, or I could not detect them because of small sample sizes. 

Deer mice are considered habitat generalists, so they may use elements of dead 

wood opportunistically. Brush mice and pinyon mice may be more specialized in 
Dead Wood Resources and Small Mammals—Chambers 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 689 

their use of habitat than deer mice, but they also appear able to use a variety of 

habitats. When we released animals, they frequently used stumps or logs as escape 

cover, and I expect they also used these sites as nesting and feeding sites. However, I 

could not provide convincing evidence to link dead wood and Peromyscus species. In 

the Pacific Northwest, Butts and McComb (2000) and Maser and others (1981) 

suggested that other forms of cover (for example, fern cover) might replace logs as 

protective cover. This might also be the case in the Southwest, with animals using 

areas with shrubs or rocky substrates for hiding cover. If mice use logs as movement 

pathways (e.g., we observed pinyon mice running beside or on top of large [>50 cm 

diameter] down wood), logs may not be as readily replaced by other forms of cover. 

Snags have been more studied than down wood. The importance of snags is well 

documented in the Southwest and in other forest ecosystems. Some species (e.g., 

cavity nesters) must use snags or live trees with decay; without them they lack 

breeding sites. Artificial devices (boxes) can be used by some species as substitutes; 

however, these are often costly to set up and maintain. 

How might forest management affect dead wood? Live trees may be retained to 

use as replacement snags and logs in the future. During thinning operations, large 

snags and logs can be protected. Down wood can be added by piling or windrowing 

slash, or by felling trees. However, slash piles break down quickly and their structure 

changes. Slash piles may be useful as cover for only a short period of time, until the 

wood begins to decay and collapses and no longer provides air spaces and movement 

corridors (W. Block, Project Leader, Rocky Mountain Research Station, Flagstaff, 

Arizona, pers. comm.). The effects of prescribed fires on dead wood are less 

predictable. Fire can create dead wood by killing live trees, or it can remove dead 

wood by incinerating snags and logs. Attempts to clear debris around snags and logs 

to protect them during prescribed burning has had mixed success; often a large 

portion of the dead wood is incinerated. Continuation of these studies will help 

clarify the effects of forest management treatments on dead wood and habitat 

relationships of these Peromyscus species. 

Acknowledgments 

I appreciate the excellent work from the field crew in gathering data: Heather 

Shanes, Victor Alm, Nathan Zorich, and Lisa Gelchis. The Northern Arizona 

University Ecological Restoration Program funded this project and provided 

vegetation data for my analyses. I thank Bill Block, Pete Fulé, Heather Shanes, and 

Steve Rosenstock for reviewing early drafts of this manuscript. 

References 

Balda, R. P. 1975. The relationship of secondary cavity nesters to snag densities in 

western coniferous forests. Flagstaff, AZ: Northern Arizona University; Albuquerque, 

NM: USDA Forest Service, Southwest Reg. Wildl. Hab. Tech. Bull. #1; 37 p. 

Balda, R. P.; Gaud, W. S.; Brawn, J. D. 1983. Predictive models for snag nesting birds.

Davis, J. W.; Goodwin, G. A.; Ockenfels, R. A., technical coordinators. Snag habitat 

management: proceedings of the symposium; Flagstaff, AZ. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, USDA Forest Service; 216-222. 
Dead Wood Resources and Small Mammals—Chambers 

690 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Bergvinson, D. J.; Borden J. H. 1992. Enhanced woodpecker predation on the mountain 

pine beetle, Dendroctonus ponderosae Hopk., in glyphosate-treated lodgepole 

pines. Can. Ent. 124: 159-165. 

Block, W. M.; Finch, D. M. 1997. Songbird ecology in southwestern ponderosa pine 

forests. Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, 

USDA Forest Service. 

Block, W. M.; Morrison, M. L.; Scott, P. E. 1998. Development and evaluation of habitat 

models for herpetofauna and small mammals. Forest Science 44: 430-437. 

Boucher, P. F., Block, W. M.; Benavidez, G. V.; Wiebe, L. E. 1999. Implementing the 

expanded prescribed fire program on the Gila National Forest, New Mexico: 

Implications for snag management. Tall Timbers Fire Conference 20: 374-379. 

Brawn, J. D.; Balda, R. P. 1988. Population biology of cavity nesters in northern Arizona: 

do nest sites limit breeding densities? Condor 90: 61-71. 

Burnham, K. P.; Anderson D. R. 1998. Model selection and inference. New York: SpringerVerlag, Inc.; 353 p. 

Butts, S. R.; McComb, W. C. 2000. Associations of forest-floor vertebrates with coarse 

woody debris in managed forests of western Oregon. Journal of Wildlife 

Management 64: 95-104. 

Chambers, C. L.; McComb, W. C.; Tappeiner, II, J. C. 1999. Breeding bird responses to 

three silvicultural treatments in the Oregon Coast Range. Ecological Applications 9: 

171-185. 

Cochran, P. H.; Hopkins, W. E. 1991. Does fire exclusion increase productivity of 

ponderosa pine? In: Harvey, A. E.; Neuenschwander, L. F., compilers. Proceedings 

management and productivity of western-montane forest soils; 1990 April 10-12; 

Boise, ID. Gen. Tech. Rep. INT-280. Ogden, UT: Intermountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 224-228. 

Conway, C. J.; Martin, T. E. 1993. Habitat suitability for Williamson's sapsuckers in 

mixed-conifer forests. Journal of Wildlife Management 57: 322-328. 

Cooper, C. F. 1960. Changes in vegetation, structure, and growth of southwestern pine 

forests since white settlement. Ecological Monographs 30: 129-164. 

Covington, W. W.; Sackett, S. S. 1984. The effect of a prescribed burn in southwestern 

ponderosa pine on organic matter and nutrients in woody debris and forest floor.

Forest Science 30: 183-192. 

Covington, W. W.; Moore, M. M. 1994. Southwestern ponderosa forest structure: changes 

since Euro-American settlement. Journal of Forestry 92: 39-47. 

Covington, W. W.; Fulé, P. Z.; Moore, M. M.; Hart, S. C.; Kolb, T. E.; Mast, J. N.; Sackett, S. 

S.; Wagner, M. R. 1997. Restoring ecosystem health in ponderosa pine forests of the 

southwest. Journal of Forestry 95: 23-29. 

Cranford, J. A. 1982. The effect of woodrat houses on population density of Peromyscus.

Journal of Mammalogy 63(4): 663-666. 

Crocker-Bedford, C. 1993. Large snags are important. Southwest Habitater 6(6): 6 p. 

Cunningham, J. B.; Balda, R. P.; Gaud, W. S. 1980. Selection and use of snags by 

secondary cavity-nesting birds of the ponderosa pine forest. Res. Paper RM-222. 

Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, USDA Forest 

Service; 15 p. 
Dead Wood Resources and Small Mammals—Chambers 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 691 

Dahms, C. W.; Geils, B. W. 1997. An assessment of forest ecosystem health in the 

southwest. Gen. Tech. Rep. RM-295. Fort Collins, CO: Rocky Mountain Forest and 

Range Experiment Station, USDA Forest Service; 97 p. 

Degenhardt, W. G.; Painter, C. W.; Price, A. H. 1996. Amphibians and reptiles of New 

Mexico. Albuquerque, NM: University of New Mexico Press; 431 p. 

Dwyer, J. K. 2000. Response of secondary cavity-nesting birds to wildfire in ponderosa 

pine forests of northern Arizona. Flagstaff, AZ: Northern Arizona University; 58 p. 

M.S. thesis. 

Ffolliott, P. F. 1983. Implications of snag policies on management of southwestern 

ponderosa pine forests. Davis, J. W.; Goodwin, G. A.; Ockenfels, R. A., technical 

coordinators. Snag habitat management: proceedings of the symposium; Flagstaff, AZ. 

Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, USDA Forest 

Service; 28-32. 

Franzreb, K. E. 1978. Tree species used by birds in logged and unlogged mixedconiferous forests. Wilson Bulletin 90: 221-238. 

Franzreb, K. E.; Ohmart, R. D. 1978. The effects of timber harvesting on breeding birds in 

a mixed-coniferous forest. Condor 80: 431-441. 

Gaines, E. M.; Kallander, H. R.; Wagner J. A. 1958. Controlled burning in southwestern 

ponderosa pine: Results from the Blue Mountain Plots, Fort Apache Indian 

Reservation. Journal of Forestry 56: 323-327. 

Ganey, J. L. 1999. Snag density and composition of snag populations on two National 

Forests in northern Arizona. Forest Ecology and Management 117: 169-178. 

Germaine, S. S. 1999. Short-term effects of ponderosa pine forest restoration on wildlife 

at Mt. Trumbull, Arizona: 1997 & 1998 data. Phoenix, AZ: Arizona Game and Fish 

Department; 43 p. 

Goodwin, Jr., J. G.; Hungerford, C. R. 1979. Rodent population densities and food habits 

in Arizona ponderosa pine forests. Res. Pap. RM-214. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, USDA Forest Service; 12 p. 

Gordon, J. V. 1996. Effects of prescribed fire on snags and logs in northern Arizona 

ponderosa pine forests. Flagstaff, AZ: Northern Arizona University; 59 p. M.S. thesis. 

Graham, R. T.; Harvey, A. E.; Jurgensen, M. F.; Jain, T. B.; Tonn, J. R; Page-Dumroese, D. 

S. 1994. Managing coarse woody debris in forests of the Rocky Mountains. Ogden, 

UT: Intermountain Research Station, USDA Forest Service; 12 p. 

Grissino-Mayer, H. D.; Swetnam, T. W. 2000. Century-scale climate forcing of fire 

regimes in the American Southwest. The Holocene 10(2): 213-220. 

Hall, L. S.; Morrison, M. L. 1997. Den and relocation site characteristics and home ranges 

of Peromyscus truei in the White Mountains of California. Great Basin Naturalist 57: 

124-130. 

Hay, D. B.; Guntert, M. 1983. Seasonal selection of tree cavities by pygmy nuthatches 

based on cavity characteristics. Davis, J. W.; Goodwin, G. A.; Ockenfels, R. A., 

technical coordinators. Snag habitat management: proceedings of the symposium; 

Flagstaff, AZ. Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, 

USDA Forest Service; 117-120. 

Horton, S. P.; Mannan, R. W. 1988. Effects of prescribed fire on snags and cavity-nesting 

birds in southeastern Arizona pine forests. Wildlife Society Bulletin 16: 37-44. 

Keller, R. 1992. Effect of ponderosa pine overstory and snags on the songbird 

community, northern Arizona. Stafford, AZ; 19 p. 
Dead Wood Resources and Small Mammals—Chambers 

692 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Klemmedson, J. O.; Smith, E. L. 1979. Vegetation-soil relations of forests, woodlands, and 

grasslands of Arizona and New Mexico. In: Forest soils and land use. Fort Collins, 

CO: Department of Forest and Wood Sciences, Colorado State University; 42-67. 

Kyle, S. C. 2000. Abundance and habitat correlates of small mammals following variedseverity wildfire in ponderosa pine-bunchgrass forests. Flagstaff, AZ: Northern 

Arizona University; 125 p. M.S. thesis. 

Li, P.; Martin, T. E. 1991. Nest-site selection and nesting success of cavity-nesting birds in 

high elevation forest drainages. Auk 108: 405-418. 

Maser, C.; Mate, B. R.; Franklin, J. F.; Dyrness, C. T. 1981. Natural history of Oregon 

coast mammals. Gen. Tech. Rep. PNW-133. Portland, OR: Pacific Northwest Research 

Station: USDA Forest Service. 

Maser, C.; Maser, Z.; Molina, R. 1988. Small mammal mycophagy in rangelands of 

central and southeastern Oregon. Journal of Range Management 41: 309-312. 

Mast, J. N.; Fulé, P. Z.; Moore, M. M.; Covington, W. W.; Waltz, A. E. M. 1999. 

Restoration of presettlement age structure of an Arizona ponderosa pine forest.

Ecological Applications 9(1): 228-239. 

Meyer, W. H. 1961. Yield of even-aged stands of ponderosa pine. Technical Bulletin No. 

630, revised. Washington, DC: USDA; 59 p. 

Miller, R.; Benedict, C. 1994. Arizona Game and Fish Department snag recruitment 

model, snag recruitment and longevity modeling. Feb 4-5, 1994; 16 p. 

Mollohan, C.; Brady, W. W.; LeCount, A. L. 1989. Habitat use of an Arizona ponderosa 

pine-mixed conifer forest by female black bears. Western Journal of Applied Forestry 

41: 6-10. 

Morrison, M. L.; Hall, L. S. 1998. Responses of mice to fluctuating habitat quality I. 

Patterns from a long-term observational study. Southwestern Naturalist 43(2): 123-

136. 

Neitro, W. A.; Binkley, V. W.; Cline, S. P.; Mannan, R. W.; Marcot, B. G.; Taylor, D.; 

Wagner, F. F. 1985. Snags. In: Brown, E. R., technical editor. Management of wildlife 

and fish habitats in forests of western Oregon and Washington. Pub. R6-F&WL-192-

1985. Portland, OR: Pacific Northwest Region, U.S. Department of Agriculture; 129-

169. 

Pearson, G. A. 1937. Mortality in cutover stands of ponderosa pine. Journal of Forestry 35: 

383-387. 

Peterson, S. R. 1980. The role of birds in western communities. In: DeGraff, R. M.; 

Tilghman, N. G., compilers. Management of western forests and grasslands for nongame birds: proceedings of the workshop; 1980 February 11-14; Salt Lake City, UT. 

Gen. Tech. Rep. INT-86. Ogden, UT: Intermountain Forest and Range Experiment 

Station, Forest Service, U.S. Department of Agriculture; 6-12. 

Rabe, M. J.; Morrell, T. E.; Green, H.; deVos, Jr., J. C.; Miller, C. R. 1998. Characteristics 

of ponderosa pine snag roosts used by reproductive bats in northern Arizona.

Journal of Wildlife Management 62: 612-621. 

Randall-Parker, T.; Miller, R. 2002. Effects of prescribed fire in ponderosa pine on key 

wildlife habitat components: preliminary results and a method for monitoring. In: 

Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. 

Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the symposium on the 

ecology and management of dead wood in western forests. 1999 November 2-4; Reno, 

NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; [this volume]. 
Dead Wood Resources and Small Mammals—Chambers 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 693 

Reynolds, R. T.; Graham, R. T.; Reiser, M. H.; Bassett, R. L.; Kennedy, P. L.; Boyce, Jr. D. 

A.; Goodwin, G.; Smith, R.; Fisher, E. L. 1992. Management recommendations for 

the northern goshawk in the southwestern United States. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, USDA Forest Service. 

Sabin, T. E.; Stafford, S. G. 1990. Assessing the need for transformation of response 

variables. Special Publications 20, Forest Research Lab, Oregon State University, 

Oregon; 31 p. 

SAS Institute, Inc. 1985. SAS user’s guide: statistics 5th ed. Cary, North Carolina. 

SAS Institute, Inc. 1990. SAS/STAT user’s guide, version 6, 4th edition, Volume 2. Cary, 

NC: SAS Institute Inc., 1989; 1072-1126. 

Scott, V. E. 1978. Characteristics of ponderosa pine snags used by cavity-nesting birds in 

Arizona. Journal of Forestry 76: 26-28. 

Scott, V. E. 1979. Bird response to snag removal in ponderosa pine. Journal of Forestry 

77: 26-28. 

Scott, V. E.; Oldemeyer J. L. 1983. Cavity-nesting bird requirements and response to snag 

cutting in ponderosa pine. In: Davis, J. W.; Goodwin, G. A.; Ockenfels, R. A., 

technical coordinators. Snag habitat management: proceedings of the symposium. Gen. 

Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain Forest and Range Experiment 

Station, Forest Service, U.S. Department of Agriculture; 19-23. 

Scott, V. E.; Patton, D. R. 1989. Cavity-nesting birds of Arizona and New Mexico forests. 

Gen. Tech. Rep. RM-10. Fort Collins, CO: Rocky Mountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 71 p. 

Smith, G. R. 1996. Habitat use and fidelity in the striped plateau lizard Sceloporus 

virgatus. American Midland Naturalist 135: 68-80. 

Smith, A. A.; Mannan, R. W. 1994. Distinguishing characteristics of Mount Graham red 

squirrel midden sites. Journal of Wildlife Management 58: 437-445. 

Sokal, R. R.; Rohlf, F. J. 1981. Biometry. 2nd ed. New York: W. H. Freeman and Company; 

663-671. 

Szaro, R. C.; Balda, R. P. 1986. Relationships among weather, habitat structure, and 

ponderosa pine forest birds. Journal of Wildlife Management 50(2): 253-260. 

Touchan, R.; Allen, C. D.; Swetnam, T. W. 1996. Fire history and climatic patterns in 

ponderosa pine and mixed-conifer forests of the Jemez Mountains, northern New 

Mexico. In: Allen, C. D., technical editor. Fire effects in southwestern forests: 

Proceedings of the second La Mesa fire symposium; 1994 March 29-31; Los Alamos, 

NM. Gen. Tech. Rep. RM-GTR-286 Fort Collins, CO: Rocky Mountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 33-46. 

Vahle, J. R.; Patton, D. R. 1983. Red squirrel cover requirements in Arizona mixed 

conifer forests. Journal of Forestry 81: 14-15, 22. 

Wadsworth. 1943. Lightning damage in ponderosa pine stands of northern Arizona.

Journal of Forestry 41: 684-685. 

Ward, J. P.; Block, W. M. 1995. Mexican spotted owl prey ecology. In: Mexican spotted owl 

recovery plan. Volume II. Albuquerque, NM: USDI Fish and Wildlife Service; 1-48. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 695 

Dying and Dead Hardwoods: Their 

Implications to Management1

Fred L. Bunnell,2 Elke Wind,3 and Ralph Wells2

Abstract 

Although they usually comprise less than 10 percent of forest cover in western forests, 

hardwoods contribute greatly to sustaining biological richness. Hardwoods are highly 

preferred as cavity sites, are preferred foraging sites for several bird species, encourage 

insectivorous mammals and amphibians, and provide preferred substrate for many cryptogams 

and invertebrates. In the Pacific Northwest, two cavity-nesting species choose hardwoods for 

70 percent or more of their nest sites, while many prefer hardwoods, even in coastal forests 

where hardwoods are scarce. Because many forest-dwelling species in the Pacific Northwest 

show strong preferences for hardwoods, hardwoods should be retained and managed as 

desired trees. 

Introduction 

Hardwoods provide three major resources to forest-dwelling organisms: 

substrate, foraging sites, and suitable places to rear young (including cavity sites). 

They provide these resources differently than do conifers because of differences in 

the chemistry and structure of their leaves, bark, and wood. Though many nonvertebrates species respond positively to those differences, we concentrate on 

vertebrates, and note contributions to non-vertebrates only briefly. We focus on 

species of the Pacific Northwest, including Alaska, Alberta, British Columbia, 

Washington, Oregon, Idaho, Montana, and northern Nevada and California. 

References to other regions are included to indicate trends where forestry has been 

practiced longer, or where particular groups of species are well documented. 

We first note differences between hardwoods and conifers that make hardwoods 

more favorable to some organisms. Because dying and dead hardwoods are recruited 

from living hardwoods, we review contributions of living hardwoods to species 

richness, including the role of riparian areas. We then discuss the three major 

contributions hardwoods make to biological richness as substrate, foraging sites, and 

locations to rear young. Finally, we summarize management implications of our 

review. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, 1999 November 2-4, Reno, Nevada. 2

 Professor and Research Scientist, respectively, Center for Applied Conservation Research, Department 

of Forest Sciences, University of British Columbia, 3004-2424 Main Mall, Vancouver, British 

Columbia, Canada, V6T 1Z4. (e-mail: flbunnell@interchange.ubc.ca) 3

 Research Technician, E. Wind Consulting, 1-2817 Glenayr Dr., Nanaimo, British Columbia, Canada, 

V9S-3S7 (e-mail: ewind@telus.net). 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

696 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Differences Between Conifers and Hardwoods 

From the perspective of forest-dwelling organisms, hardwoods differ from 

conifers in their leaves, bark, and wood. Most conifer trees retain their leaves for 

years. In temperate regions, most broad-leaved trees and shrubs are deciduous, and 

invest less energy than do conifers in the production of secondary compounds to 

deflect herbivory (Longhurst and others 1968, Wahlenberg 1946). As a result, 

hardwood leaves host numerous herbivorous insects that benefit many birds (Schimpf

and MacMahon 1985, Willson and Comet 1996b). As they fall to the ground, these 

leaves form a readily digestible litter that encourages a rich arthropod fauna, thereby 

benefiting ground-foraging insectivores (Hoff 1957, Willson and Comet 1996b). 

Because the bark of many hardwood species is relatively rich in nutrients and has a 

higher pH than most conifer bark (Barkman 1958), hardwoods provide preferred 

substrate for some epiphytic bryophytes and lichens. 

The tendency for hardwood trees of the Pacific Northwest to decay earlier than 

conifers (Cline 1977) may be associated with bark features and is a product of 

differences in wood chemistry. Because hardwood bark is typically much thinner 

than conifer bark, small wounds can provide entry ports for fungi. Once fungi are 

inside, hardwoods of the Pacific Northwest are less resistant to their growth than are 

conifers because hardwoods produce smaller amounts of resins and toxic extractives 

that combat decay fungi (Anonymous 1967). Thus, hardwoods provide potential 

cavity sites at relatively young ages and less durable logs. Differences in wood 

chemistry and structure also favor particular insects. Some woodpeckers feed 

primarily on insects restricted to hardwoods; and where hardwoods have declined 

significantly, these species are threatened. The middle-spotted woodpecker (Picoides 

medius), for example, disappeared from Sweden in 1980 (Bernes 1994). In the 

Pacific Northwest, acorn woodpeckers (Melanerpes formicivorus) and some 

sapsucker species restrict their feeding largely to hardwoods (Beal 1911, Wells and 

Steeger 1999). 

Hardwoods and Species Richness 

Hardwood stands provide an abundant insect fauna and numerous cavity sites 

and have been reported as having greater vertebrate richness than conifer stands 

(Bruce and others 1985). Because birds are the richest vertebrate group of both 

insectivores and cavity users, trends in richness should be most apparent among 

birds. Associations of some birds with hardwoods are especially strong. In the 

Okanagan region of British Columbia, 94 percent of Bullock’s oriole (Icterus 

bullockii) nest sites were in deciduous trees (Cannings and others 1987). In Oregon, 

Hagar and others (1995) reported several bird species almost exclusively associated 

with hardwood stands (e.g., warbling vireo [Vireo gilvus] and yellow warbler 

[Dendroica petechia]), including 19 species associated predominantly with trembling 

aspen Populus tremuloides (e.g., red-breasted sapsucker [Sphyrapicus ruber] and 

lazuli bunting [Passerina amoena]). Bunnell and others (1999) considered birds to 

have strong associations with hardwoods if at least two-thirds of their reported nests 

were in hardwood species. Under that restriction, about 40 bird species in British 

Columbia are strongly associated with hardwoods for nesting, and another 45 to 50 

use hardwoods disproportionately to hardwood abundance. 

Unmanaged stands are rarely completely conifer. Table 1 summarizes bird data 

from the Pacific Northwest by stand type as determined by the most abundant tree 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 697 

species. Riparian was defined by proximity to water, where hardwoods are generally 

more abundant. In seven of the nine studies, bird species richness was highest in 

riparian areas or stands in which the leading species was aspen (Populus 

tremuloides), cottonwood (Populus balsamifera), or spruce (Picea spp). All of these 

stands were mixtures of hardwoods and conifers, occurring on moist, productive 

sites. The riparian area of Theberge (1976) is from gravel outwash plains, where 

understory was less dense than in most forested riparian areas. Because studies 

assessed abundance in different ways (table 1), we standardized measures within 

studies by dividing all abundance measures by the highest in a given study. Like 

richness, highest densities tended to occur in riparian areas or stands in which aspen, 

cottonwood, or spruce were common. The pattern appears to be that mixtures (such 

as spruce-cottonwood) increase both richness and abundance, and that moister sites 

(spruce and riparian) favor richness or abundance as much as the presence of 

hardwood tree species themselves. 

Because deciduous trees and shrubs are concentrated in moister or riparian areas 

in the Pacific Northwest, it is difficult to separate effects of the greater productivity 

of these areas from the presence of hardwoods. The most consistent feature of bird 

communities using riparian areas is that many preferentially nest or forage in 

deciduous trees and shrubs (e.g., Bull and Skovlin 1982, Morgan and Wetmore 1986, 

Sanders and Edge 1998). Of perching birds showing significant preference for 

riparian areas, 70 percent (14/20) nested predominantly in hardwood trees or shrubs 

(Bunnell and others 1999). Deciduous vegetation supports a diverse insect fauna. As 

expected, all (20/20) of the perching birds that were significantly more abundant in 

riparian areas were primarily insectivorous during breeding, which was also true of 

82 percent of the mammals, among which insectivores are less common (Bunnell and 

others 1999). Most forest-nesting waterfowl require cavities that commonly are more 

available in hardwoods than in conifers. Need for cavity sites also may explain why 

fisher (Martes pennanti) maternal dens were located in sites within or next to riparian 

habitat, where large, decay-prone cottonwood trees were available (e.g., Weir 1995). 

Mammals, reptiles, and amphibians showing positive associations to deciduous trees 

and shrubs, also show affinities for riparian areas where deciduous species are more 

abundant (Gomez and Anthony 1996, McComb and others 1993). Thus, much of the 

commonly higher vertebrate richness in riparian areas may be a product of the greater 

abundance of hardwood trees and deciduous shrubs. 

To assess the role of upland hardwoods, we stratified data from 286 50-meter 

radius bird census plots in south central British Columbia into four classes: riparian 

(adjacent to water; > 85 percent conifer), hardwood riparian (> 15 percent trembling 

aspen), upland conifer (primarily Douglas-fir [Pseudotsuga menzieseii] and 

lodgepole pine [Pinus contorta]), and upland hardwood (> 15 percent trembling 

aspen). The richest sites were hardwood riparian sites (fig. 1). Upland hardwoods had 

significantly greater bird richness than upland conifers (least significant difference; P

= 0.04); hardwood riparian hosted greater richness than riparian (least significant 

difference; P = 0.059). We conclude that even on upland areas, small inclusions of 

aspen help to increase vertebrate richness. Huff and Raley (1991) reached a similar 

conclusion for coastal forests. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

698 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
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0

5

10

15

20

C R H H-R

Richness

Figure 1—Mean species richness of birds in 50-m radius plots of four broad habitats: 

C = upland conifer, R = conifer riparian, H = upland hardwoods, HR = hardwood 

riparian. Numbers in parentheses are numbers of plots; error bars are standard 

deviation. 

Hardwoods as Substrate

Hardwoods provide preferred substrate for many non-vertebrates. Aspen is 

particularly favored by bryophytes and lichens (Brodo 1974, Gustafsson and Ahlén 

1996, Kuusinen 1994). In north and central Sweden, 20 percent of the red-listed, 

epiphytic bryophytes occur on aspen, despite the fact that aspen comprises only 1.5 

percent of the total forest volume (Hallinbäck 1996). Berg and others (1994) 

reviewed 1,487 threatened species in Sweden, and found 290 restricted to old, living 

trees. Of those, 85 percent (mostly invertebrates) were restricted to hardwoods. Of 70 

forest-dwelling mosses of the Pacific Northwest reviewed by Vitt and others (1988), 

at least 5 species appear restricted to hardwoods. In British Columbia, 45 lichen 

species are reported as largely restricted to hardwoods (Goward 1999, and Goward 

and others 1994). As with birds, small inclusions of hardwoods apparently encourage 

lichen richness within conifer stands. In montane forests of British Columbia, more 

lichen species occur on conifers adjacent to aspen than on conifers distant from aspen 

(Arsenault and Goward 2000). Among macrofungi, at least 440 species in British 

Columbia have hardwoods as their substrate (Fernando and others 1999). Data on 

invertebrate affinities for hardwoods in the Pacific Northwest are sparse, but 

elsewhere, aspen trunks and litter host rich invertebrate faunas (Niemelä and others 

1992, Siitonen and Martikainen 1994). Small natural or experimental inclusions of 

aspen litter in conifer forests created aggregations of land snails and predatory forestfloor arthropods (Niemelä 1997). 

Data on amounts of hardwoods required are sparse. Hazell and others (1998) 

evaluated responses of four aspen-specific, epiphytic bryophytes in Sweden to a 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

700 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

range of aspen densities and found a positive response only to aspen diameter. We 

believe the response to diameter reflects the fact that larger trees usually have been 

present for a longer time. Because bryophyte dispersal distances are short (Hedenäs 

and others 1989; Miles and Longton 1990, 1992), dispersal must be slow. Larger 

trees have been available to rare colonization events for a longer period of time. 

Moreover, their rougher bark may provide favorable substrate for establishment. 

Because aspen density had little influence on epiphyte abundance but diameter did, 

scattered older trees may be valuable for some epiphytes. Hazell and Gustafsson 

(1999) evaluated survival and vitality of lichen and bryophyte transplants in mature 

forests, aspen patches in clearcuts (aggregated retention), and scattered trees in 

clearcuts (dispersed retention). Both the lichen and the bryophyte species survived on 

the scattered trees. Ås (1993) found that small patches of hardwoods sustained 

woodliving beetles. In short, many more non-vertebrate species than vertebrate 

species require hardwoods, and many respond positively to small hardwood 

inclusions within conifer forests. 

Hardwoods as Foraging Sites 

Insectivorous amphibians, reptiles, and mammals often show preferences for 

hardwood stands and associated deciduous understory, where they forage in a leaf 

litter rich in prey (Bunnell and others 1999). We collated studies that permitted 

estimation of selection by primary excavators while foraging (table 2). Because we 

were interested in direct comparisons between studies, we used Chesson’s alpha 

(Chesson 1983). It ranges from 0.0 at complete avoidance to 1.0 when all foraging 

was on a single species. Of the 11 studies for which we were able to calculate alpha, 

hardwoods ranked first or second in preference in six. Other workers have reported 

foraging concentrated on hardwoods, but their data did not permit calculation of 

preference. For example, foraging of the red-naped sapsucker (Sphyrapicus nuchalis)

in British Columbia was largely limited to trembling aspen and paper birch (Betula 

papyrifera; Wells and Steeger 1999), and acorn woodpeckers are almost completely 

restricted to hardwoods in California (Beal 1911). Although sapsuckers create 

sapwells in hardwoods, most woodpeckers are primarily gleaning rather than drilling 

when foraging on hardwoods, consistent with the rich insect fauna on hardwood 

trunks reported by Sittonen and Martikainen (1994). Hardwoods often provide 

foraging sites at smaller sizes and younger ages than do conifers (Bunnell and others 

2002). 

Hardwoods as Places to Rear Young 

Hardwoods provide favorable sites to rear young in several ways. Many birds 

preferentially nest in hardwoods, and some species nesting upslope bring fledged 

young into hardwood riparian areas to forage on the abundant insects (Bunnell and 

Dupuis 1995). Insectivorous amphibians, reptiles, and mammals exploit the abundant 

prey in deciduous leaf litter. Still more species select hardwoods as cavity, denning, 

or roosting sites. 

Preferential use of tree species as cavity sites usually is related to decay 

characteristics, but can be influenced by foraging specialization. At least 10 primary 

excavators in the Pacific Northwest locate most of their nests in hardwoods, and 

weak excavators are more likely to use hardwoods (fig. 2). Many studies summarized 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 701 

are from locations where hardwoods comprise less than 5 percent of the tree stems, 

yet cavity nesters often chose decay-prone hardwoods for > 80 percent of their nest 

sites. Studies reporting both use and availability permit estimates of selection for 

specific tree species. The most consistently preferred species were trembling aspen, 

western larch (Larix occidentalis), and ponderosa pine (Pinus ponderosa; table 3).

Primary cavity nesters favored trembling aspen, while secondary nesters tended to 

favor western larch and western redcedar (Thuja plicata). Lodgepole pine and true 

firs (Abies sp.) were least favored as cavity nesting sites. Although black-backed and 

three-toed woodpeckers (Picoides tridactylus) often concentrate their foraging in 

beetle-ridden lodgepole pine (Goggans and others 1989; Machmer and Steeger),4

they still seek aspen for nesting (fig. 2). Exceptions exist. Bull and others (1996) 

reported that all cavities used by Vaux’s swift (Chaetura vauxi) were in grand fir 

(Abies grandis). In montane forests of south central British Columbia, all 21 nests of 

three-toed woodpeckers were in subalpine fir (Abies lasiocarpa; Klenner and 

Huggard 1997).5

Comparisons between areas reveal that preference for hardwood nest trees is 

sometimes flexible. In the interior of British Columbia, Harestad and Keisker (1989) 

reported that all 243 nests of primary excavators found occurred in hardwoods, 

despite the fact that hardwood cover comprised only 5 percent of their study area 

(which was dominated by Douglas-fir). In coastal Oregon and British Columbia, the 

identical species nested mainly in Douglas-fir and western hemlock (Tsuga

heterophylla; Bunnell and Allaye-Chan 1984, Mannan and others 1980). 

Flammulated owls (Otus flammeolus) exhibit similar changes over their range. 

Ponderosa pine and Douglas-fir were used where prevalent (Bull and others 1990, 

Reynolds and Linkhart 1987, van Woudenberg 1992), but elsewhere the owl nested 

in oaks (Quercus spp.) and trembling aspen (Marcot and Hill 1980, Webb 1982). 

Flexibility is not universal. Although some sapsuckers select hardwoods for 80 

to 95 percent of their nest sites, other woodpeckers are more emphatically restricted 

to conifers (fig. 2). Throughout its range, only 9 of 167 white-headed woodpecker 

(Picoides albolarvatus) nests have been reported from hardwoods. The restriction is a 

product of a diet high in ponderosa pine seeds (Dixon 1995a, Ligon 1973). Diet also 

may limit black-backed and three-toed woodpeckers to coniferous nest sites unless 

hardwood species are present in small inclusions (appendix A). Weaker excavators 

that nest and forage in conifers are potentially threatened by forest practices because 

the conifers may not become old and decayed enough to be susceptible to excavation. 

In fact, these species (black-backed, Lewis’s, three-toed, and white-headed 

woodpecker) are listed “at risk” in one or more jurisdictions of the Pacific Northwest. 

Patterns of selection of tree species reflect decay patterns. All cavity nesters 

appear to seek pockets of heart rot (Bunnell and Allaye-Chan 1984, Kilham 1971), 

but weaker excavators tend to seek trees exhibiting more advanced decay (Bunnell 

and others 1999). When nesting in hardwoods, bird species tend to use less visibly 

decayed trees than when nesting in conifers (Bunnell and others 1999). This pattern 

reflects both earlier onset of heart rot in hardwoods (Cline 1977, Harmon 1982), and 

poor applicability to hardwoods of decay classes developed for conifers. Current 

decay classes apply poorly to hardwoods, because hardwoods show fewer external 

signs of decay when decay is present. Phellinus ignarius can invade live aspen, 

softening the heartwood, while the sapwood remains unaffected and the tree shows 

no external sign of decay. As a result, cavity nesters are more likely to excavate 

living hardwoods than living conifers. 
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Weak and strong excavators use live trees differently. Weak excavators show no 

change in the proportion of live trees selected as the proportion of hardwood nest 

trees changes. Most nests (78 percent) were in dead trees regardless of the tree 

species used (Bunnell and others 2002). Strong excavators make significantly greater 

use of live trees as the percentage of nest sites in hardwoods increases (P < 0.001 

across the nine species of strong excavators included in fig. 2, after percentages are 

arcsine transformed). 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

704 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

0% 20% 40% 60% 80% 100%

Yellow-bellied sapsucker (107)

Red-naped sapsucker (655)

Red-breasted sapsucker (299)

Williamson's sapsucker (256)

Hairy woodpecker (334)

Three-toed woodpecker (127)

Black-backed woodpecker (81)

Acorn woodpecker (235)

Pileated woodpecker (204)

Lewis's woodpecker (374)

Downy woodpecker (107)

White-headed woodpecker (168)

Northern flicker (1105)

Black-capped chickadee (119)

Mountain chickadee (364)

Boreal chickadee (18)

Chestnut-backed chickadee (9)

Red-breasted nuthatch (342)

White-breasted nuthatch (60)

Pygmy nuthatch (283)

Percent of nests

Weak Primary Excavators

Strong Primary Excavators

Figure 2―Percent (weighted mean) of nest sites in coniferous ( ) and 

hardwood ( ) trees. Number of nests in parentheses. 

We conclude that primary excavators select for sites easy to excavate. 

Generally, that means hardwoods such as aspen, cottonwood and birch (Betula spp.).

More decay-prone hardwood species are selected over more decay-resistant species 

(e.g., Brush and others 1983). Where hardwood species are not common, birds 

excavate conifers, preferring those in which the heartwood is rotting. Smaller, weaker 

excavators, such as chickadees and nuthatches, sometimes seek decay-softened 

sapwood (Lundquist and Mariani 1991, Steeger and Hitchcock 1998). The pattern of 

selection of living and dead nest trees suggests that moribund hardwoods can 

substitute for conifer snags. 

The largest denning mammals rarely find hardwoods big enough to 

accommodate them, but almost half of fisher den sites were in hardwoods, generally 

large cottonwood (table 4). The strong selection of hardwood roost trees, usually 

aspen, by some bats is not simply a product of their distribution. In at least some 

areas, bats actively seek out scattered hardwoods (Crampton and Barclay 1995, 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 705 

Vonhoff 1996). Although fewer mammal than bird species rely on hardwoods for 

cavity sites, hardwoods appear critical to some mammals (table 4). 

Table 4—Grand mean of the percent of mammal dens or roosts located in hardwood trees. 

Species Pct hardwood n1 Source 

Bats 

Big brown bat 

Eptesicus fuscus

14.0 24 Betts 1996; Rasheed and Holroyd 1995; 

Vonhof 1996 

California bat 

Myotis californicus

0.0 25 Brigham and others 1997; Grindal 1997; 

Vonhof 1996 

Little brown myotis 

Myotis lucifugus

100.0 21 Crampton and Barclay 1995; Grindal 1997; 

Rasheed and Holroyd 1995 

Long-legged myotis 

Myotis volans

0.0 41 Ormsbee and McComb 1998; Rasheed and 

Holroyd 1995 

Northern long-eared 

myotis 

Myotis septentrionalis 

0.0 7 Caceres 1997 

Silver-haired bat 

Lasionycteris 

noctivagans

100.0 50 Betts 1996; Campbell and others 1996; 

Crampton and Barclay 1995; Rasheed and 

Holroyd 1995; Vonhof 1996 

Western long-eared 

myotis Myotis evotis

0.0 21 Caceres 1997; Grindal 1997; Vonhof and 

Barclay 1997 

Big brown & silverhaired bat 4.0 24 Bull and others 1996 

Big brown, silverhaired, & California 

myotis 

64.0 31 Steeger and Machmer 1996 

 

Rodents 

Flying squirrel 

Glaucomys spp. 

33.1 650 Carey and others 1997; Mowrey and 

Zasada 1984; C. Steeger2

 

Red squirrel 

Tamiasciurus 

hudsonicus

51.5 22 K. Martin,3

 C. Steeger2

Red tree vole 

Phenacomys 

longicaudus 

0.0 78 Meiselman and Doyle 1996 

Carnivores 

Black bear 

Ursus americanus 

0.0 16 Bull and others 1996 

Fisher 45.0 35 Anonymous 1996; Weir 1995 

 American marten 

Martes Americana

0.0 375 Bull and Heater 1996; Jones and others 

1997; Raphael and Jones 1997 1

 Number of dens and roosts. 

2

 Unpublished data on file, Pandion Ecological Research, Ltd., Nelson, BC, Canada. 3

 Unpublished data on file, Centre for Applied Conservation Biology, University of British Columbia, 

Vancouver, BC, Canada. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

706 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Implications to Management 

A significant portion of the vertebrate fauna in western forests shows affinities 

with hardwoods. Bunnell and others (1999) reported that across forest types of 

British Columbia, 19 to 31 percent of forest-dwelling bird species located two-thirds 

or more of their nests in hardwoods. The degree to which trembling aspen is favored 

by primary cavity nesters (table 3) may be especially significant, because these 

species create cavities for other species. Although most vertebrates associated with 

hardwoods are birds, some amphibians, shrews, and bats are more abundant where 

hardwoods are more common. Because the contribution of hardwoods to vertebrate 

richness is vastly disproportionate to their relative abundance, it is important to 

maintain hardwoods in the forest. 

Where forestry has been practiced longer than in the Pacific Northwest, trends 

are clear. A large portion of the species listed as endangered in Sweden are 

endangered because the original hardwood forest has been converted to conifers 

(Bernes 1994). Britain faces a similar situation. Holmes (1996) noted that about 400 

insect species are associated with “the English oak” (Quercus robur). The decline of 

oaks and other hardwoods in Great Britain has meant that 14 bat species find both 

their roost sites and forage diminished (Holmes 1996). Of the 90 forest-dwelling 

vertebrates in the Pacific Northwest designated by state and provincial agencies as 

“sensitive” or “at risk,” 17 nest primarily in deciduous trees and 5 in deciduous 

shrubs. Other listed species, such as sharp-tailed grouse (Tympanuchus phasianellus), 

also seek hardwoods to forage. 

From our review of vertebrate relations with hardwood species, we conclude 

that managers charged with sustaining biological richness should implement the 

following management practices: 

• Retain hardwoods and manage at least some as desired trees, rather than as 

competition with crop trees—Small amounts of hardwoods intermixed with 

conifers serve to increase the richness of birds, bryophytes, and lichens, but 

there is no apparent need to retain deciduous trees in every stand. Vegetation 

management in young stands should not remove all hardwood stems. Instead, 

brushing should be of variable intensity through a block, or focused on those 

trees directly interfering with coniferous crop trees. A component of 

hardwood stems should be retained intentionally and managed to become 

mature trees. Hardwood snags are less durable than conifer snags and cannot 

substitute completely for conifers.

• Avoid conversion of riparian areas to conifers—Hardwoods often do better 

in riparian areas and little effort is required to promote them there. 

Hardwoods provide a number of values, including cavity sites younger than 

conifers, and tend to be more wind-firm than are conifers. 

• Encourage upland patches of hardwoods in areas where sustaining 

biodiversity is a priority—Several vertebrates are closely associated with 

hardwoods, particularly aspen, willow (Salix spp.), or cottonwood in riparian 

areas. Other vertebrate species appear to benefit, but are more flexible in 

their requirements. Inclusions of > 15 percent aspen stems in upland areas 

significantly increases bird richness (fig. 1), and small patches sustain a 

variety of other organisms (Ås 1993; Hazell and Gustafsson 1999). Where 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 707 

patches are retained, adjacent areas should not be subject to intensive 

vegetation management.

• Control domestic grazing in riparian areas—In many western regions, 

hardwoods are concentrated in riparian areas. In riparian areas subject to 

grazing, declining amounts of hardwoods have affected abundance and 

distribution of vertebrates (Krueper 1992, Skovline 1984). 

Endnotes 

4

 Unpublished data on file, Pandion Ecological Research, Ltd.; Nelson, BC, Canada. 5

 Unpublished data on file, BC Ministry of Forests, Kamloops, BC, Canada. 

Acknowledgments 

Our research and synthesis was supported by the Canadian Wildlife Service’s 

Fraser River Action Plan, Forest Renewal British Columbia, Lignum, MacMillan 

Bloedel (now Weyerhaeuser), and Western Forest Products. R.W. Campbell provided 

unpublished data from the British Columbia Nest Records Scheme; B. Booth, F. 

Bunnell, C. Galindo-Leal, D. Huggard, W. Klenner, K. Martin, and C. Steeger also 

generously provided unpublished data or unreduced data for us to reanalyze. The 

manuscript benefited from reviews by R. W. Campbell and F. K. A. Schmiegelow. 

This is Publication No. R-39 of the Centre of Applied Conservation Biology, 

University of British Columbia. 

References 

Adams, Elizabeth; Morrison, Michael L. 1993. Effects of forest stand structure and 

composition on red-breasted nuthatches and brown creepers. Journal of Wildlife 

Management 57: 616-629. 

Allaye-Chan, Ann C. 1981. Snag use by cavity-nesting birds in the chemainus woodlands 

of southern Vancouver Island, BC. Vancouver, BC: University of British Columbia; 

171 p. Undergraduate thesis. 

Anonymous. 1967. Comparative decay resistance of heartwood of native species. 

Research Note FPL-0153. Madison, WS: Forest Products Laboratory, Forest Service, 

U.S. Department of Agriculture; 2 p. 

Anonymous. 1996. Ecological characteristics of fishers in southwestern Oregon. Progress 

Report, June 1996. Olympia, WA: Pacific Northwest Research Station, Forest Service, 

U.S. Department of Agriculture; 7 p. 

Arsenault, Andre; Goward, Trevor. 2000. The dripzone effect: new insights into the 

distribution of rare lichens. In: Darling, L. M., editor. Proceedings of the symposium 

on biology and management of species and habitats at risk; 1999 February 15-19, 

Kamloops, BC; Victoria, BC: Ministry of Environment, Lands, and Parks; 767-768. 

Ås, Stefan. 1993. Are habitat islands islands? Woodliving beetles (Coleoptera) in 

deciduous forest fragments in boreal forest. Ecography 16: 219-228. 

Barkman, J. J. 1958. Phytosociology and ecology of cryptogamic epiphytes; including a 

taxonomic survey and description of their vegetation units in Europe. [With 

separate booklet containing associated tables.] Assen, Netherlands: Van Gorcum; 628 p. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

708 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Beal, Foster E. L. 1911. Food of the woodpeckers of the United States. U.S. Department of 

Agriculture, Biological Survey Bulletin 37: 1-64. 

Berg, Åke; Ehnström, Bengt; Gustafsson, Lena; Hallingbäck, Tomas; Jensell, Mats; Weslien, 

Jan. 1994. Threatened plant, animal, and fungus species in Swedish forests: 

distributions and habitat associations. Conservation Biology 8: 718-731. 

Bernes, Claes, editor. 1994. Biological diversity in Sweden. A country study. Monitor 14. 

Swedish Environmental Protection Agency and the Swedish Board of Agriculture. 

Stokholm, Sweden: Ingvar Bingman; 280 p. 

Betts, Burr J. 1996. Roosting behaviour of silver-haired bats (Lasionycteris noctivagans) 

and big brown bats (Eptesicus fuscus) in northeast Oregon. In: Barclay, R.M.R.; 

Brigham, R.M., editors. Proceedings of the symposium on bats and forests; 1995 

October 19-21; Victoria, BC: BC Ministry of Forests; 55-61. 

Block, William M. 1991. Foraging ecology of Nuttall’s woodpecker. The Auk 108: 303-

317. 

Bock, Carl E. 1970. The ecology and behavior of the Lewis’ woodpecker (Asyndesmus 

lewis). University of California Publications in Zoology 92: 1-100. 

Brigham, R. Mark; Vonhof, Maarten J.; Barclay, Robert M.R.; Gwilliam, John C. 1997. 

Roosting behavior and roost-site preferences of forest-dwelling California bats 

(Myotis californicus). Journal of Mammalogy 78: 1231-1239. 

Brodo, Irwin M. 1974. Substrate ecology. In: Ahmadjiian, V.; Hale, M.E., editors. The 

lichens. New York: Academic Press; 401-441. 

Bruce, C.; McMillan, A.; Edwards, D.; Owens, T.; Mellen, K.; Sturgis, H. 1985. Wildlife

relationships to plant communities and stand conditions. In: Brown, E. R., editor. 

Management of wildlife and fish habitats in forests of western Oregon and Washington. 

Publ. No. R6-F&WL-192-1085. Portland, OR: Pacific Northwest Research Station, 

Forest Service, U.S. Department of Agriculture; 33-55. 

Brush, Timothy; Anderson, B.W.; Ohmart, R.D. 1983. Habitat selection related to resource 

availability among cavity-nesting birds. In: Davis, J. W.; Goodwin, G. A.; Ockenfels, 

R. A., editors. Proceedings of the symposium on snag habitat management. Fort Collins, 

CO: Forest Service, U.S. Department of Agriculture; 88-98. 

Bull, Evelyn L. 1980. Resource partitioning among woodpeckers in northeastern Oregon. 

Moscow, ID: University of Idaho; 109 p. Ph.D. dissertation. 

Bull, Evelyn L. 1987. Ecology of the pileated woodpecker in northeastern Oregon. Journal 

of Wildlife Management 51: 472–481. 

Bull, Evelyn L.; Heater, T.W. 1996. The effect of management on the American marten in

northeastern Oregon. Progress report—1994-96. La Grande, OR: Forest and Range 

Sciences Lab, Forest Service, U.S. Department of Agriculture; 17 p. 

Bull, Evelyn L.; Jackson, Jerome A. 1995. Pileated woodpecker (Dryocopus pileatus). The 

birds of North America, No. 148; 20 p. 

Bull, Evelyn L.; Skovlin, Jon M. 1982. Relations between avifauna and streamside 

vegetation. Transactions of the North American Wildlife & Natural Resources 

Conference 47: 496-506. 

Bull, Evelyn L.; Akenson, J.J.; Betts, Burr J.; Torgensen, T.R. 1996. The interdependence of 

wildlife and old-growth forests. In: Bradford, P.; Manning, T.; I'Anson, B., editors. 

Proceedings of the workshop on wildlife tree/stand-level biodiversity; October 17-18, 

1995, Victoria, BC; Victoria, BC: British Columbia Ministry of Environment, Lands, 

and Parks, and Ministry of Forests; 71–75.
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 709 

Bull, Evelyn L.; Peterson, Steven R.; Thomas, Jack W. 1986. Resource partitioning among 

woodpeckers in northeastern Oregon. Res. Note PNW-RN-44. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 19 p. 

Bull, Evelyn L.; Wright, A.L.; Henjum, Mark G. 1990. Nesting habitat of flammulated owls 

in Oregon. Journal of Raptor Research 24: 52-55 

Bunnell, Fred L.; Allaye-Chan, Ann C. 1984. Potential of ungulate winter-range reserves 

as habitat for cavity-nesting birds. In: Meehan, W. R.; Merrell, T. R.; Hanley, T. A., 

editors. Proceedings of the symposium on fish and wildlife relationships in old-growth 

forests; 1982 April 12-15; Juneau, Alaska; Morehead City, NC: American Institute of 

Fishery Research Biologists; 357-365. 

Bunnell, Fred L.; Dupuis, Linda A. 1995. Riparian habitats in British Columbia: their 

nature and role. In: Morgan, K. H.; Lashmar, M. A., editors. Proceedings of the 

riparian habitat management and research workshop, 1993 May 4-5; Kamloops, BC. 

Fraser River Action Plan special publication. Delta, BC; Canadian Wildlife Service; 7-

21. 

Bunnell, Fred L.; Houde, Isabelle; Johnston, Barb; Wind, Elke. 2002. How dead trees 

sustain live organisms in western forests. In: Laudenslayer, William F., Jr.; Shea, 

Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Bunnell, Fred L.; Kremsater, Laurie L.; Wind, Elke. 1999. Managing to sustain vertebrate 

richness in forests of the Pacific Northwest: relationships within stands.

Environmental Reviews 7: 97-146. 

Bunnell, Fred L.; Wind, Elke; Boyland, Mark; Houde, Isabelle. 2002. Diameters and heights 

of trees with cavities their implications to management. In: Laudenslayer, William F., 

Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., 

technical coordinators. Proceedings of the symposium on the ecology and management 

of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSWGTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; [this volume]. 

Caceres, Carolina. 1997. Northern long-eared bat progress report. Columbia Basin Fish 

and Wildlife Compensation Program. Progress report number 101-33. Nelson, BC: 

BC Hydro and BC Environment; 21 p. 

Campbell, Lori A.; Hallett, James G.; O’Connell, Margaret A. 1996. Conservation of bats in 

managed forests: use of roosts by Lasionycteris noctivagans. Journal of Mammalogy 

77(4): 976-984. 

Campbell, R. Wayne; Dawe, Neil K.; McTaggart-Cowan, Ian; Cooper, John M.; Kaiser, Gary 

W.; McNall, Michael C. E. 1990. The birds of British Columbia. Vol. 2, Diurnal 

birds of prey through woodpeckers. Vancouver, BC: University of British Columbia 

Press; 635 p. 

Campbell, R. Wayne; Dawe, Neil K.; McTaggart-Cowan, Ian; Cooper, John M.; Kaiser, Gary 

W.; McNall, Michael C. E.; Smith G. E. John. 1997. The birds of British Columbia.

Vol. 3, Flycatchers through vireos. Vancouver, BC: University of British Columbia 

Press; 693 p. 

Cannings, Robert A.; Cannings, Richard J.; Cannings, Sydney G. 1987. Birds of the 

Okanagan Valley, British Columbia. Victoria, BC: Royal British Columbia Museum; 

420 p. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

710 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Carey, Andrew B.; Wilson, Todd M.; Maguire, Christine C.; Biswell, Brian L. 1997. Dens of 

northern flying squirrels in the Pacific Northwest. Journal of Wildlife Management 

61: 684-699. 

Chesson, Jean. 1983. The estimation and analysis of preference and its relationship to 

foraging models. Ecology 64: 1297-1304. 

Cline, Steven P. 1977. The characteristics and dynamics of snags in Douglas-fir forests of 

the Oregon Coast Range. Corvallis, OR: Oregon State University; 106 p. Ph.D. 

dissertation. 

Crampton, L. H.; Barclay, Robert M. R. 1995. Relationships between bats and stand age 

and structure in aspen mixedwood forests in Alberta. In: Stelfox, J. B., editor. 

Relationships between stand age, stand structure, and biodiversity in aspen mixedwood 

forests in Alberta. Jointly published; Vegreville, AB: Alberta Environmental Centre 

(AECV95-R1). Edmonton, AB: Canadian Forest Service (Project No. 0001A); 211-225. 

Crockett, Allen B.; Hadow, Harlo H. 1975. Nest site selection by Williamson’s and Rednaped Sapsuckers. Condor 77: 365-368. 

Deal, John A.; Gilmore, Dan W. 1998. Effects of vertical structure and biogeoclimatic 

subzone on nesting locations for woodpeckers on north central Vancouver Island: 

nest tree attributes. In: Trofymow, J. A.; MacKinnon, A., editors. Proceedings of a 

workshop on structure, process, and diversity in successional forests of coastal British 

Columbia; 1998 February 17-19;Victoria, BC. Northwest Science, Vol. 72 (special issue 

No. 2). Seattle, WA: Washington State University Press; 119-121 

Dixon, Rita D. 1995a. Density, nest-site and roost-site characteristics, home-range, 

habitat-use, and behavior of White-headed woodpeckers: Deschutes and Winema 

National Forests, Oregon. Nongame Report 93-3-01. Portland, OR: Oregon 

Department of Fish and Wildlife; 90 p. 

Dixon, Rita D. 1995b. Ecology of white-headed woodpeckers in the central Oregon 

Cascades. Boise, ID: University of Idaho, 148 p. M.Sc. thesis. 

Erskine, Anthony J.; McLaren, William D. 1972. Sapsucker nest holes and their use by 

other species. The Canadian Field Naturalist 86: 357-361. 

Fernando, Analie; Ring, Fiona; Lowe, Daphyne; Callan, Brenda E. 1999. Index of plant 

pathogens, plant-associated microorganisms, and forest fungi of British Columbia.

Information Report BC-X-385. Victoria, BC: Pacific Forestry Centre; 459 p. 

Franzreb, Kathleen E. 1983. A comparison of avian foraging behavior in unlogged and 

logged mixed-coniferous forest. Wilson Bulletin 95: 60-76. 

Galen, Christie. 1989. A preliminary assessment of the status of Lewis’ woodpecker in 

Wasco County, Oregon. Nongame Project No. 88-3-0. Report to Oregon Dept. Fish & 

Wildlife. 

Garrett, Kimball L.; Raphael, Martin G.; Dixon, Rita D. 1996. White-headed woodpecker. 

The Birds of North America 252: 1-22. 

Goggans, Rebecca; Dixon, Rita D.; Seminara, L. Claire. 1989. Habitat use by three-toed 

and black-backed woodpeckers, Deschutes National Forest. Technical Report 

Number 87-3-02. Portland, OR: Oregon Department of Fish and Wildlife; 50 p. 

Gomez, Douglas M.; Anthony, Robert G. 1996. Amphibian and reptile abundance in 

riparian and upslope areas of five forest types in western Oregon. Northwest 

Science 70: 109-119. 

Goward, Trevor. 1999. The lichens of British Columbia—illustrated keys. Part 2

Fruticose species. Special Report Series 9. Victoria, BC: BC Ministry of Forests; 319 p. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 711 

Goward, Trevor; McClure, Bruce; Meidinger, Del. 1994. The lichens of British Columbia—

illustrated keys. Part 1 Foliose and squamulose species. Special Report Series 8. 

Victoria, BC: BC Ministry of Forests; 181 p. 

Grindal, S. 1997. Upper Kootenay River bat survey. Athalmere, BC: Columbia Basin Fish 

and Wildlife Compensation Program Report File 101-30; 60 p. 

Gustafsson, Lena; Ahlén, I. 1996. The geography of plants and animals. The national atlas 

of Sweden. Stockholm, Sweden: SNA Publishing; 160 p. 

Hagar, Joan C.; McComb, William C.; Chambers, Carol L. 1995. Effects of forest practices 

on wildlife. In: Beschta, R. L.; Boyle, J. R.; Chambers, C. L.; Gibson, W. P.; Gregory, 

S. V.; Grizzel, J.; Hagar, J. C.; Li, J. L.; McComb, W. C.; Parzybok, T. W.; Reiter, M. 

L.; Taylor, G. H.; Warila, J. E., editors. Cumulative effects of forest practices in Oregon: 

literature and synthesis. Corvallis, OR: Oregon State University; chapter 9. 

Hågvar, Sigmund; Hågvar, Geir; Mønnes, Erik. 1990. Nest site selection in Norwegian 

woodpeckers. Holarctic Ecology 13(2): 156-165. 

Hallinbäck, T. 1996. The bryophytes of Sweden and their ecology. Uppsala, Sweden: 

ArtDatabanken; 131 p. (in Swedish with English summary). 

Harestad, Alton S.; Keisker, Dagmar G. 1989. Nest tree use by primary cavity-nesting 

birds in south central British Columbia. Canadian Journal of Zoology. 67: 1067-1073. 

 Harmon, Mark E. 1982. Decomposition of standing dead trees in the southern 

Appalachian mountains. Oecologia 52: 214-215. 

Hazell, Per; Gustafsson, Lena. 1999. Retention of trees at final harvest – evaluation of a 

conservation technique using epiphytic bryophyte and lichen transplants.

Biological Conservation 90: 133-142. 

Hazell, Per; Kellner, Olle; Rydin, Håkan; Gustafsson, Lena. 1998. Presence and abundance 

of four epiphytic bryophytes in relation to density of aspen (Populus tremula) and 

other stand characteristics. Forest Ecology and Management 107: 147-158. 

Hedenäs, Lars; Herben, Tomáš; Ryden, Häkan; Söderström, Lars. 1989. Ecology of the 

invading moss species Orthodontium lineare in Sweden: spatial distribution and 

population structure. Holarctic Ecology 12(2): 163-172. 

Hoff, Clayton C. 1957. A comparison of soil, climate, and biota of conifer and aspen 

communities in the central Rocky Mountains. American Midland Naturalist 58(1): 

115-140. 

Holmes, Mike. 1996. Bats and trees in Britain. In: Barclay, R.M.R.; Brigham, R.M., editors. 

Bats and forests symposium; 1995 October 19-21;Victoria, BC. Victoria, BC: British 

Columbia Ministry of Forests; 49-50. 

Hooge, Philip N.; Stanback, Mark T.; Koenig, Walter D. 1999. Nest-site selection in the 

acorn woodpecker. Auk 116(1): 45-54. 

Huff, Mark H.; Raley, Catherine M. 1991. Regional patterns of diurnal breeding bird 

communities in Oregon and Washington. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. 

B.; Huff, M. F., technical coordinators. Wildlife and vegetation of unmanaged Douglasfir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: Pacific Northwest Research 

Station, Forest Service, U.S. Department of Agriculture; 177-205. 

Jones, Lawrence C.; Raphael, Martin G.; Forbes, J. T.; Clark, L. A. 1997. Using remotely 

activated cameras to monitor material dens of martens. In: Proulx, G.; Bryant, H. N.; 

Woodard, P. M., editors. Martes: taxonomy, ecology, techniques, and management. 

Edmonton, AB: Provincial Museum of Alberta; 329-349. 

Kelleher, K. E. 1963. A study of hole-nesting avifauna of southwest British Columbia. 

Vancouver, BC: University of British Columbia; 169 p. M.Sc. thesis. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

712 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Kilham, Lawrence. 1971. Reproductive behavior of yellow-bellied sapsuckers. I. 

Preference for nesting in Fomes infested aspens and nest hole interrelations with 

flying squirrels, raccoons, and other animals. Wilson Bulletin 83: 159-171. 

Klenner, Walter; Huggard, David. 1997. Three-toed woodpecker nesting and foraging at 

Sicamous Creek. In: Hollstedt, C.; Vyse, A., editors. Proceedings of a workshop on the 

Sicamous Creek silvicultural systems project; 1996 April 24-25; Kamloops, BC. 

Working Paper 24/1997. Victoria, BC: Research Branch, BC Ministry of Forests; 224-

233. 

Krueper, David J. 1992. Effects of land use practices on western riparian ecosystems. In: 

Hagen, J. M. III; Johnston, D. W., editors. Ecology and conservation of neotropical 

migrant landbirds. Washington, DC: Smithsonian Institute Press; 321-330. 

Kuusinen, Mikko. 1994. Epiphytic lichen flora and diversity on Populus tremula in oldgrowth and managed forests of southern and middle boreal Finland. Annales 

Botanici Fennici 31(4): 245-260. 

Li, Pingjun; Martin, Thomas E. 1991. Nest-site selection and nesting success of cavitynesting birds in high elevation forest drainages. Auk 108: 405-418. 

Ligon, J. David. 1973. Foraging behavior of the White-headed woodpecker in Idaho. Auk 

90: 862-869. 

Longhurst, William M.; Oh, K. K.; Jones, Michael B.; Kepner, R. E. 1968. A basis for the 

palatability of deer forage plants. Transactions of the North American Wildlife and 

Natural Resources Conference 33: 181-192. 

Lundquist, Richard W.; Mariani, Jina M. 1991. Nesting habitat and abundance of snagdependent birds in the southern Washington Cascade Range. In: Ruggiero, L. F.; 

Aubry, K. B.; Carey, A. B.; Huff, M. F., technical coordinators. Wildlife and vegetation 

of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 

221-240. 

Mannan, Robert W.; Meslow, E. Charles; Wright, Howard M. 1980. Use of snags by birds in 

Douglas-fir forests, Western Oregon. Journal of Wildlife Management 44: 787-797. 

Manuwal, David A. 1981. Cavity nesting birds of the Olympic National Forest 

Washington. Seattle, WA: Wildlife Science Group, College of Forest Resources, 

University of Washington; 144 p. 

Manuwal, David A.; Zarnowitz, Jill E. 1981. Cavity nesting birds of the Olympic National 

Forest. Seattle, WA: College of Forest Resources, University of Washington; 144 p. 

Marcot, Bruce G.; Hill, Randy. 1980. Flammulated owls in northwestern California. 

Western Birds 11(3): 141-149. 

Marshall, David B.; Chilcote, Mark W.; Weeks, Hal. 1996. Species at risk. Sensitive, 

threatened, and endangered vertebrates of Oregon. Portland, OR: Oregon 

Department of Fish and Wildlife; unnumbered. 

McClelland, B. Riley. 1977. Relationships between hole-nesting birds, forest snags, and 

decay in western larch and Douglas-fir forests of the northern Rockies. Missoula: 

University of Montana; 469 p. Ph.D. dissertation. 

McComb, William C.; Chambers, Carol; Newton, Michael. 1993. Small mammal and 

amphibian associations in red alder stands, central Coast Range. Northwest Science 

67: 181-188.

McEllin, Shaun M. 1979. Nest sites and population demographics of white-breasted and 

pygmy nuthatches in Colorado. Condor 81: 348-352. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 713 

Meiselman, N.; Doyle, A. T. 1996. Habitat and microhabitat use by the red tree vole

(Phenacomys longicaudus). American Midland Naturalist 135: 33-42. 

Mellen, Teresa K. 1987. Home range and habitat use of pileated woodpeckers, western 

Oregon. Corvallis, OR: Oregon State University; 96 p. M.Sc. thesis. 

Miles, C.J.; Longton, R.E. 1990. The role of spores in reproduction in mosses. Botanical 

Journal of the Linnaean Society 104: 149-173. 

Miles, C. J.; Longton, R. E. 1992. Deposition of moss spores in relation to distance from 

parent gametophytes. Journal of Bryology 17(2): 355-368. 

Milne, Kathleen A.; Hejl, Sallie J. 1989. Nest-site characteristics of white-headed 

woodpeckers. Journal of Wildlife Management 53: 50-55. 

Morgan, Kenneth H.; Wetmore, Stephen P. 1986. A study of riparian bird communities 

from the dry interior of British Columbia. Technical Report Series No. 11. Ottawa, 

ON: Pacific and Yukon Region, Canadian Wildlife Service, Ottawa Environment 

Canada; 48 p. 

Morrison, Michael L.; With, Kimberly A. 1987. Interseasonal and intersexual resource 

partitioning in hairy and white-headed woodpeckers. The Auk 104: 225-233. 

Morrison, Michael L.; Timossi, Irene C.; With, Kimberly A.; Manley, P. N. 1985. Use of tree 

species by forest birds during winter and summer. Journal of Wildlife Management 

49: 1098-1102. 

Mowrey, Robert A.; Zasada, John C. 1984. Den tree use and movements of northern flying 

squirrels in interior Alaska and implications for forest management. In: Meehan, 

W. R.; Merrel, T. R.; Hanley, T. A., editors. Proceedings of a symposium on fish and 

wildlife relationships in old-growth forests. 1982 April 12-15; Juneau, Alaska; 

Moorhead City, NC: American Institute of Fishery Research Biologists; 351-356. 

Nelson, S. Kim. 1988. Habitat use and densities of cavity-nesting birds in the Oregon 

coast ranges. Corvallis, OR: Oregon State University; 157 p. M.Sc. thesis. 

Niemalä, Jari. 1997. Invertebrates and boreal forest management. Conservation Biology 

11: 601-619. 

Niemalä, Jari; Haila, Yrjö; Halme, Eero; Pajunen, Timo; Punttila, Pekka. 1992. Small-scale 

heterogeneity in the spatial distribution of carabid beetles in the southern Finnish 

taiga. Journal of Biogeography 19(2): 173-181. 

Ormsbee, Patricia C.; McComb, William C. 1998. Selection of day roosts by female longeared myotis in the central Oregon Cascade Range. Journal of Wildlife Management 

62: 596-603. 

Peck, George K.; James, Ross D. 1987. Breeding birds of Ontario: nidiology and 

distribution. Volume 2: passerines. Toronto, ON: Royal Ontario Museum; 290 p. 

Pojar, Rosamund A. 1995. Breeding bird communities in aspen forests of the sub-boreal 

spruce (dk subzone) in the Prince George forest region. Land Management 

Handbook 33. Victoria, BC: British Columbia Ministry of Forests Research Program; 59 

p. 

Raphael, Martin G.; Jones, Lawrence L. C. 1997. Characteristics of resting and denning 

sites of American martens in central Oregon and western Washington. In: Proulx, 

G.; Bryant, H. N.; Woodward, P. M., editors. Martens: taxonomy, ecology, techniques 

and management. Edmonton, AB: Provincial Museum of Alberta; 146-165. 

Raphael, Martin G.; White, Marshall. 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada. Wildlife Monographs 86: 1-66. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

714 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Rasheed, Sadig A.; Holroyd, Susan L. 1995. Roosting habitat assessment and inventory of 

bats in the Mica Wildlife Compensation Area. Columbian Basin Fish and Wildlife 

Compensation Program Report File 101-26. Nelson, BC: BC Hydro and British 

Columbia Ministry of Environment, Lands, and Parks; 77 p. 

Reynolds, Richard T.; Linkhart, Brian D. 1987. The nesting biology of flammulated owls in 

Colorado. In: Nero, R. W.; Clark, R. J.; Knapton, R. J.; Hamre, R. H., editors. 

Proceedings of a symposium on the biology and conservation of northern forest owls. 

General Technical Report RM-GTR-142. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture; 239-248. 

Sanders, Todd A.; Edge, W. Dan. 1998. Breeding bird community composition in relation 

to riparian vegetation structure in the western United States. Journal of Wildlife 

Management 62: 461-473. 

Schimpf, David J.; MacMahon, James A. 1985. Insect communities and faunas of a Rocky 

Mountain subalpine sere. Great Basin Naturalist 45(1): 37-60. 

Scott, Virgil E.; Whelan, Jill A.; Svoboda, Paul L. 1980. Cavity-nesting birds and forest 

management. In: DeGraff, R. M., technical coordinator. Proceedings of a workshop on 

management of western forests and grasslands for nongame birds. 1980 February 11-14; 

Salt Lake City, UT. Gen. Tech. Rep. INT-86. Fort Collins, CO: Intermountain Research 

Station, Forest Service, U.S. Department of Agriculture; 311-324. 

Siitonen, J. M.; Martikainen, Pertti J. 1994. Occurrence of rare and threatened insects 

living on decaying Populus tremula: a comparison between Finnish and Russian 

Karelia. Scandinavian Journal of Forest Research 9: 185-191. 

Skovlin, Jon M. 1984. Impacts of grazing on wetlands and riparian habitats: a review of 

our knowledge. In: Developing strategies for rangeland management: a report prepared 

by the Committee on Developing Strategies for Rangeland Management. National 

Research Council/National Academy of Science. Boulder, CO: Westview Press; 1001-

1103. 

Steeger, Christoph; Hitchcock, Christine L. 1998. Influence of forest structure and diseases 

on nesting habitat selection by red-breasted nuthatches. Journal of Wildlife 

Management 62: 1349-1358. 

Steeger, Christoph; Machmer, Marlene M. 1996. Use of trees by cavity nesters in managed 

and unmanaged Interior Cedar—Hemlock stands of southern British Columbia. In: 

Bradford, P.; Manning, T.; I’Anson, B., editors. Proceedings of the workshop on wildlife 

tree/stand-level biodiversity. Proceedings of the workshop on wildlife tree/stand-level 

biodiversity; October 17-18, 1995, Victoria, BC; Victoria, BC: British Columbia 

Ministry of Environment, Lands, and Parks, and Ministry of Forests; 45-54. 

Steeger, Christoph; Machmer, Marlene M.; Walters, Eric. 1996. Ecology and management 

of woodpeckers and wildlife trees in British Columbia. Delta, BC: Environment 

Canada, Fraser River Action Plan, Canadian Wildlife Service; 23 p. 

Theberge, John B. 1976. Bird populations in the Kluane Mountains, southwest Yukon, 

with special reference to vegetation and fire. Canadian Journal of Zoology 54: 1346-

1356. 

van Woudenberg, Astrid M. 1992. Integrated management of flammulated owl breeding 

habitat and timber harvest in British Columbia. Vancouver, BC: University of 

British Columbia; 56 p. M.Sc. thesis. 

Vitt, Dale H.; Marsh, Janet E.; Bovey, Robin B. 1988. Mosses, lichens, and ferns of 

northwest North America. Vancouver, BC: Lone Pine Publishing; 296 p. 

Vonhof, Maarten J. 1996. A survey of the abundance, diversity, and roost-site preferences 

of bats in the Pend d’Oreille valley, British Columbia. The Columbia Basin Fish and 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 715 

Wildlife Compensation Program. Nelson, BC: BC Hydro and British Columbia Ministry 

of Environment, Lands, and Parks; 69 p. 

Vonhof, Maarten J.; Barclay, Robert M. R. 1997. Use of tree stumps as roosts by the 

western long-eared bat. Journal of Wildlife Management 61: 674-684. 

Wahlenberg, William G. 1946. Longleaf pine: its use, ecology, regeneration, protection, 

growth, and management. Washington, DC: Charles Lathrop Pack Forestry 

Foundation and U.S. Department of Agriculture, Forest Service; 429 p. 

Waterhouse, Michaela J.; Dawson, Rick. 1999. Bird communities in interior Douglas-fir 

forests (IDFdk3) in the Cariboo Forest Region. In: Hollstedt, C.; Vyse, A.; Huggard, 

D. J., editors. Proceedings of the dry Douglas-fir workshop on new information for the 

management of dry Douglas-fir forests. 1997 April 29-30; Kamloops, BC; Victoria, BC: 

British Columbia Ministry of Forests; 252-266. 

Webb, Bruce E. 1982. Distribution and nesting requirements of montane forest owls in 

Colorado. Part III: flammulated owl (Otus flammeolus). Colorado Field Ornithologist 

6: 76. 

Weir, Richard. 1995. Diet, spatial organization, and habitat relationships of fishers in 

south-central British Columbia. Burnaby, BC: Simon Fraser University; 139 p. M.Sc. 

thesis. 

Wells, Ralph W.; Steeger, Christoph. 1999. Species-habitat relationships and habitat 

supply for cavity-nesting birds in a dry Interior Cedar Hemlock watershed. 

Vancouver, BC: Centre for Applied Conservation Biology Research Report, University 

of British Columbia; 24 p. 

Wesolowski, T.; Tomialojc, Ludwik. 1986. The breeding ecology of woodpeckers in a 

temperate primeval forest—preliminary data. Acta Ornithologica 22: 1-21. 

Willson, Mary F.; Comet, Tallchief A. 1996a. Bird communities of northern forests: 

patterns of diversity and abundance. Condor 98: 337-349. 

Willson, Mary F.; Comet, Tallchief A. 1996b. Bird communities of northern forests: 

ecological correlates of diversity and abundance in the understory. Condor: 98: 350-

62. 

Winternitz, Barbara L. 1976. Temporal change and habitat preference of some montane 

breeding birds. Condor 78: 383-393. 
Dying and Dead Hardwoods: Implications to Management—Bunnell, Wind, and Wells 

716 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Appendix A—Tree species used as nest sites by primary cavity nesters in the Pacific 

Northwest. Unidentified trees, poles, and stumps are not included. 

Number of 

nest trees 

Percent use of 

hardwoods1

Sources2

Strong Excavators 

Yellow-bellied sapsucker 

Sphyrapicus varius

97 79.8 (73-100) 5, 11 

Red-naped sapsucker 715 91.5 (83-100) 3 5, 7, 8, 18, 19, 20, 26, 27 

Red-breasted sapsucker 284 22.2 (1-65) 5, 9, 16, 19, 25 

Williamson's sapsucker 

Sphyrapicus thyroideus

268 35.2 (0-97) 4, 5, 7, 8, 19, 25 

Hairy woodpecker 

Picoides villosus

346 39.4 (0-100) 4, 5, 7, 9, 18, 19, 20, 25, 

27 

Three-toed woodpecker 127 23.5 (0-75) 5, 7, 14, 17, 20, 27, 28 

Black-backed woodpecker 

Picoides arcticus

81 0.8 (0-4) 4, 5, 13, 25, 27 

Acorn woodpecker 235 100.0 (100-100) 15, 19 

Pileated woodpecker 

Dryocopus pileatus 

199 25.0 (0-100) 1, 3, 5, 18, 20, 22, 27 

Weak Excavators 

Lewis’s woodpecker 

Melanerpes lewis

488 36.1 (0-74) 2, 5, 7, 12, 25 

Downy woodpecker 

Picoides pubescens

102 81.7 (50-100) 5, 7, 19, 20, 27 

White-headed woodpecker 173 5.4 (0-7) 5, 7, 10, 23, 25, 29 

Northern flicker 

Colaptes auratus

998 44.7 (0-97) 4, 5, 7, 9, 18, 19, 20, 25, 

27 

Black-capped chickadee 

Poecile atricapillus

27 89.9 (88-100) 5, 7, 20, 27 

Mountain chickadee 

Poecile gambeli

332 46.8 (3-98) 5, 17, 19, 20, 25 

Boreal chickadee 

Poecile hudsonicus

18 56.0 (56-56) 24 

Chestnut-backed chickadee 

Poecile rufescens

8 56.0 (56-56) 27 

Red-breasted nuthatch 

Sphyrapicus ruber

238 31.3 (0-89) 6, 18, 20, 25, 27 

White-breasted nuthatch 

Sitta carolinensis

56 37.1 (0-100) 6, 19, 21, 25 

Pygmy nuthatch 

Sitta pygmaea

300 8.1 (0-89) 6, 7, 19, 21, 25 

1 Weighted mean for all studies. Range among individual studies in parentheses. 2

 1 = K. Aubry and C. Raley (unpublished) in Bull and Jackson 1995, 2 = Bock 1970, 3 = Bull 1987, 4 = 

Bull and others 1986, 5 = Campbell and others 1990, 6 = Campbell and others 1997, 7 = Cannings and 

others 1987, 8 = Crockett and Hadow 1975, 9 = Deal and Gilmore 1998, 10 = Dixon (1995b), 11 = 

Erskine and McLaren 1972, 12 = Galen 1989, 13 = Goggans and others (1989), 14 = Hågvar and others 

1990, 15 = Hooge and others 1999, 16 = Kelleher 1963, 17 = Klenner and Huggard 1997, 18 = Klenner, 

W. and D. Huggard, 19 = Li and Martin 1991, 20 = Martin, K., 21 = McEllin 1979, 22 = Mellen 1987, 

23 = Milne and Hejl 1989, 24 = Peck and James 1987, 25 = Raphael and White 1984, 26 = Steeger and 

others 1996, 27 = Steeger, C., 28 = Wesolowski and Tomialojc 1986, 29 = Western Foundation of 

Vertebrate Zoology (no date) in Garrett and others 1996. 3 Where Cannings and others 1987 and Campbell and others 1990 or 1997 occur together, Cannings and 

others 1987 is not included in the weighted mean. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 717 

Diameters and Heights of Trees with 

Cavities: Their Implications to Management1 

Fred L. Bunnell,2 Elke Wind,3 Mark Boyland,4 and Isabelle Houde4 

Abstract 

Primary cavity nesters select larger trees when nesting in conifers than when nesting in 

hardwoods. Larger birds use larger nest trees, but the trend is more weakly expressed in 

hardwoods, as is expected if rot governs nest tree selection. Birds select larger nest trees in 

more productive coastal forests than in inland forests. Actual nest heights are much shorter 

than nest tree heights, but species-specific averages are rarely below 5 meters. Larger 

mammals require older, larger trees where rot is advanced. Bats also use larger trees, 

particularly when roosting in conifers. Sustaining all cavity users requires sustained provision 

of a range of diameters of decaying and dead trees, including some trees at least 50 cm dbh 

(smaller in less productive forests). 

Introduction 

Dying and dead trees are common in unmanaged forests, and cavity users 

typically represent 25 to 30 percent of the terrestrial vertebrate fauna in forests of the 

Pacific Northwest (Bunnell and others 1999, Thomas and others 1979). Proportions 

are less where trees are smaller, as in the spruce-willow-birch zone of British 

Columbia (Bunnell and others 1999). Forest practices reduce cavity sites by reducing 

amounts of moribund and dead wood and by reducing the size of trees compared to 

that formerly present. As a result, lack of cavity sites is the most frequently reported 

threat to forest-dwelling species, including 28 taxa designated “at risk” in the Pacific 

Northwest (Bunnell and others 1999). 

The only compelling way of selecting goals for what we should retain or 

produce as nest and den trees is to evaluate patterns that the animals exhibit in their 

selection. We first review cavity-using species and broad factors governing snag use. 

We then examine patterns of selection among available trees and as a function of the 

size of bird. From these patterns we derive management implications. We treat both 

birds and mammals, but focus on primary excavators of the Pacific Northwest, 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Professor, Center for Applied Conservation Research, University of British Columbia, 3004-2424 

Main Mall, Vancouver, British Columbia, V6T 1Z4 (e-mail: fbunnell@interchange.ubc.ca) 3

 Research Technician, E. Wind Consulting, 1-2817 Glenayr Dr., Nanaimo, British Columbia, Canada 

V9S-3S7 (e-mail: ewind@telus.net) 

4

 Ph.D. Candidate and Research Technician, respectively, Center for Applied Conservation Research, 

University of British Columbia, 3004-2424 Main Mall, Vancouver, British Columbia, V6T 1Z4 (e-mail: 

markbo@interchange.ubc.ca and houde@intergate.ca) 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

718 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

including Alaska, Alberta, British Columbia, Washington, Oregon, Idaho, Montana, 

and northern Nevada and California. 

Species Using Cavities 

In the Pacific Northwest, 69 vertebrate species consistently use cavities and 

more species make opportunistic use (Bunnell and others 2002). Birds (48 species) 

and bats (13 species) represent 88 percent of the species consistently using cavities. 

More bird than mammal species use cavities, but the proportion of mammalian users 

is higher, ranging in size from long-legged myotis (Myotis volans) to black bears 

(Ursus americanus) (Bunnell and Chan-McLeod 1997, Cannings and Harcombe 

1990, Peterson and others 1993, Whitaker 1993). Other than some bats and squirrels, 

mammal use of cavities is more opportunistic than it is for birds. Amphibians and 

reptiles also use snags and stumps opportunistically (Bunnell and Dupuis 1995, 

Stelmock and Harestad 1979). 

Cavity users can be divided into three groups: species that excavate their own 

cavities (primary cavity nesters such as woodpeckers); species that use holes 

excavated by primary cavity nesters (secondary cavity users such as buffleheads 

[Bucephala albeola]5

 and flying squirrels [Glaucomys sp.]); and species that use 

other types of cavities (e.g., Vaux’s swifts [Chaetura vauxi] and black bears) 

(Bunnell and others 2002). Most woodpeckers are strong primary cavity nesters, 

especially adapted for excavating (Spring 1965), and forage primarily by drilling in 

trees or snags. Weak primary cavity nesters, such as chickadees and nuthatches, are 

less well adapted for excavation and sometimes modify existing cavities rather than 

make their own (McClelland and others 1979). Strong excavators are generally large 

birds, while weak excavators are mainly smaller species. Exceptions to these 

generalizations include some larger species that are relatively weak excavators (e.g., 

Lewis’s woodpecker [Melanerpes lewis], white-headed woodpecker [Picoides

albolarvatus], and northern flicker [Colaptes auratus]). 

If habitat requirements of the primary excavators are not met, secondary cavity 

users also may be lost (Daily and others 1993, Dobkin and others 1995). Larger 

woodpeckers and the northern flicker thus play a key role in forest ecosystems, 

providing nest holes for other cavity-nesting birds and roosts or dens for other birds 

and mammals (Bull and others 1986). Similarly, the sapwells of sapsucker create 

feeding opportunities for at least 23 bird species, 6 mammal species, and 9 Orders 

and 22 Families of arthropods (Foster and Tate 1996, Miller and Nero 1983, 

Sutherland and others 1982). Moreover, woodpeckers can constrain abundance of 

forest “pest” insects (Holmes 1990, and Thomas and others 1979). Because of these 

contributions, strong excavators have been termed “keystone species” (e.g., Dailey 

and others 1993), whose loss would substantially alter forest ecosystems. In the 

Pacific Northwest, only 10 of the 69 cavity-using species present are strong enough 

excavators to create habitat for other vertebrates. We emphasize primary cavity 

nesters because of the role they play in supporting other species. 

 

5

 Unpublished data on file, Center for Applied Conservation Research, University of British Columbia, 

Vancouver, BC, Canada. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 719 

A General Model of Cavity Use 

Cavity-nesting birds benefit from the protection from predators that cavities 

provide their young, as well as shelter and insulation of the nest or roost (Miller and 

Miller 1980, O’Connor 1978). Size of cavity may affect productivity. Eriksson 

(1979) reported greater productivity of common goldeneyes (Bucephala clangula) in 

larger nest boxes. The cost for primary cavity-nesters is the time and energy required 

to excavate the cavity: about 20 days for hairy woodpeckers (Picoides villosus) 

(Ehrlich and others 1988). Ideally, a cavity nest is located where the outer wood is 

hard, to prevent predators from tearing open the nest, but the inner wood is soft, to 

allow easy excavation. Soft inner wood is preferred due to the mechanics of chiseling 

wood in an enclosed space. Heart rots, whether extensive or local, are of prime 

importance. Generally, all primary excavators seek decayed heartwood, although the 

strongest excavators do not require it (Bunnell and Allaye-Chan 1984, Kilham 1971, 

Shigo and Kilham 1968). For weak primary cavity-nesters, harder outer wood 

remains desirable to reduce predation, but these species cannot excavate hard wood. 

They must either compromise with softened sapwood, or find existing holes in hard 

outer wood, such as those created at dead branch stubs. 

The ideal cavity nest also should be high in a tree to avoid terrestrial nest 

predators. The bole where the nest is located must be wide enough to allow a cavity 

large enough to contain nestlings. These factors promote preference for largediameter trees, in which the stem is a suitable width well above the ground. The 

importance of softened heartwood also promotes preference for larger stems, because 

large stems are usually older stems that have developed heart rot. These needs for 

soft or hardwood, appropriate stem diameter at the nest, and height above the ground 

explain many of the preferences researchers have observed among cavity nesters. 

Most recommendations for snag management derive from these same considerations. 

Unlike primary cavity-nesters, secondary cavity-users “take what they can get,” 

with certain limitations. The most obvious limitation is that nest holes must be big 

enough. Mountain bluebirds [Sialia currucoides], for example, rely primarily on 

nests made by flickers rather than those of smaller woodpeckers or sapsuckers 

(Dobkin and others 1995). The nest also needs to be near appropriate habitat, which 

is not the forest for many secondary users (e.g., cavity-nesting ducks, swallows, 

bluebirds, and American kestrels [Falco sparverius]). Because secondary users are 

relatively abundant compared to primary excavators, competition for cavities is often 

intense (Bock and others 1992, von Haartman 1957). Some secondary users, 

however, show strong preferences among cavity sites. For example, because of their 

high energy demands and temperature sensitivity, bats often select cavities with 

favorable microclimates (Kalcounis and Brigham 1998, Lewis 1995). 

In the Pacific Northwest there are 23 primary cavity nesters and 40 secondary 

cavity users. Another six species use dying and dead trees differently. Some cavity 

users (raccoons [Procyon lotor], American martens [Martes Americana], fishers 

[Martes pennanti], black bears) are too large to use cavities excavated by 

woodpeckers. They must rely on large cavities formed by decay or fire. These 

cavities are uncommon, because old, large trees are uncommon. Vaux’s swifts nest 

and roost in hollow snags large enough that they can fly up and down the hollow 

chamber (Baldwin and Zaczkowski 1963). Brown creepers [Certhia Americana] nest 

under slabs of loose bark on snags and old trees (Davis 1978). Some bats do as well, 

but also use cavities. Requirements of these six species can be considered 

individually during management. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

720 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Diameters 

Larger diameter trees or snags are clearly preferred by cavity-nesting birds 

(tables 1, 2). Nest tree diameters must be large enough to accommodate a cavity with 

room for an adult bird and nestlings, but sizes usually exceed that requirement. The 

selection of trees larger than the size of cavity required likely reflects age and the size 

at which heart rot develops. Flammulated owls [Otus flammeolus], for example, are 

only slightly larger than a sparrow, but nested in ponderosa pine [Pinus ponderosa], 

averaging 57.7 centimeters in diameter at breast height (dbh) on southern aspects and 

71.7 centimeters on northern aspects (data of van Woudenberg 1992). The difference 

reflects greater rates of growth on north aspects, and thus size at the age when rot 

appears. 

Table 1—Selection of nest tree diameter within different tree species by cavity-nesting birds 

of the Pacific Northwest (assessed by relative diameter).1

 Highest value in bold. 

Tree 

species2

P3

 S All P S P S 

TA 1.15 1.38 2.15 2.11 

PB 1.57 2.29 

BCo 

DF 3.32 3.93 

SPR 1.03 1.29 1.32 1.32 2.81 

WRC 2.36 1.97 1.40 

PP 1.08 2.59 2.18 

LP 1.81 1.38 1.34 1.59 

WL 1.36 1.49 2.22 1.61 

WP 1.94 

SF 1.57 1.08 

WH 0.81 

GF 

Source and 

Comments 

K. Martin4

 (trees & 

snags > 

12 cm 

dbh) 

Scott and 

others 1980 

(snags > 11 

cm dbh; PP 

> 14 cm) 

McClellan

d 1977 

(trees > 

22 cm 

dbh) 

C. Steeger5 (trees > 

7 cm 

dbh) 

1 Relative diameter = mean diameter used/mean diameter available. 

2 Tree Species Codes: TA = Trembling aspen; PB = Paper birch (Betula papyrifera); BCo = Black 

cottonwood (Populus balsamifera ssp. Trichocarpa); DF = Douglas-fir; SPR = Spruce (Picea) spp.; 

WRC = Western redcedar (Thuja plicata); PP = Ponderosa pine; LP = Lodgepole pine (Pinus contorta); 

WL = Western larch (Larix occidentalis); WP = White pine (Pinus monitcola); SF = Subalpine fir; WH 

= Western hemlock (Tsuga heterophylla); GF =Grand fir. (Sources of tree names are Crittenden 1992, 

Pojar and MacKinnon 1994, and Parish and others 1996.) 3

 All = all cavity nesters, P = Primary cavity nesters, S = Secondary cavity nesters. 4

 Unpublished data of K. Martin, Center for Applied Conservation Research, Faculty of Forestry, 

University of British Columbia, Vancouver, BC. 

5

 Unpublished data of C. Steeger; Nelson, British Columbia. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 721 

Table 2—Selection of nest tree diameter by diameter class in old-growth and second-growth 

stands. Selection is measured by Chesson’s alpha (Chesson 1983). 

Diameter class (cm) 

Second-growth Old-growth Source and 

Notes 

 10-19 20-49 >50 10-19 20-49 >50 Lundquist and 

Mariani 1991 

 

P 0.00 0.10 0.90 0.00 0.23 0.77 (snags & trees) 

 

10-19 20-49 50-99 >99 

All 0.01 0.09 0.25 0.66 Nelson 1988 

(snags) 

15-23 23-38 28-53 >53 Madsen 1985 

 

All 0.03 0.09 0.15 0.73 (snags) 

 

15-19 20-24 25-29 30-34 35-39 >40 Harestad and 

Keisker 1989 

 

P 0.02 0.07 0.18 0.23 0.22 0.27 (trees) 

 

15-27 28-52 53-77 78-102 103-127 >128 Schreiber and 

deCalesta 1992 

 

All 0.05 0.20 0.17 0.22 0.19 0.16 (snags) 

 

 

We collated data from Pacific Northwest forests relating nest tree diameter to 

size of bird when nesting in either hardwoods or coniferous trees, and found 162 

estimates for 19 bird species (fig. 1). The same bird species selected smaller trees 

when nesting in hardwoods than when nesting in conifers (fig. 1).

For example, mean dbh of nest trees of pileated woodpeckers (Dryocopus 

pileatus) nesting in ponderosa pine was 84 centimeters, but only 40.0 and 46.6 

centimeters when nesting in trembling aspen (Populus tremuloides). When nesting in 

hardwoods or inland conifers, there is a significant trend for larger birds to use larger 

trees but not in coastal conifers. The latter observation suggests that coastal conifers 

attain large sizes before even small pockets of rot develop. The same bird species 

selected larger conifers in coastal forests than in inland forests (fig. 1b). Hardwood 

data were combined because we had only seven coastal samples. The trend to select 

larger trees with increasing bird length is more weakly expressed in hardwoods. Each 

finding is expected if rot governs selection of nest trees. In the Pacific Northwest, 

hardwoods generally rot at younger ages and smaller sizes than do conifers (Bunnell 

and others 1999, Cline 1977). Because there is little relationship between degree of 

decay and size of hardwood trees, larger primary excavators need not consistently 

seek larger hardwoods. More time is required for heart rot to develop in conifers, and 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

722 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

trees are larger before sizeable decay pockets accrue. Thus, larger bird species 

seeking larger pockets of heart rot seek older and larger conifers. 

Milling efficiency constrains the sizes of trees grown in managed forests. 

Optimal milling efficiency varies with mill configuration, but for many sawmills in 

the Pacific Northwest the preferred maximum log diameter is < 46 to 50 centimeters 

(Bunnell and others 1997). Primary cavity nesters for which mean diameters of 

conifer trees consistently exceeded 50 centimeters dbh in inland forests include redbreasted, yellow-bellied and Williamson’s sapsuckers [Sphyrapicus thyroideus], 

white-headed and pileated woodpeckers, and the northern flicker (fig. 1). Three of 

these 6 species are designated “at risk” in the Pacific Northwest. In coastal forests, 

some small birds (chestnut backed chickadee [Poecile rufescens], red-breasted 

nuthatch [Sitta canadensis]) consistently selected nest trees with a mean dbh > 50 

centimeters, indicating the dominant role of decay in nest site selection. For inland 

forests, McClelland (1977) suggested that trees must be at least 23 centimeters dbh 

before providing a nesting site. Smaller mean values have been reported for blackcapped and mountain chickadees [Poecile gambeli], red-breasted nuthatches, and 

downy woodpeckers [Picoides pubescens], especially when nesting in hardwoods 

(fig. 1).

Shape of the diameter distribution is more important than the mean. Cumulative 

frequency distributions of diameters and heights of both “active” snags (used by birds 

for nesting) and “inactive” or unused snags tend to have a long tail of larger snags, 

although active snags are more normally distributed (fig. 2). Using non-parametric 

tests, Bunnell and Allaye-Chan (1984) found that active snags were larger (height 

and diameter) than inactive snags in old-growth areas (P < 0.05); and that secondgrowth snags were smaller than either active or inactive old-growth snags (P < 0.01). 

Only 10 to 17 percent of nest sites were located in snags < 46 centimeters dbh (fig. 

2a). Figure 2b illustrates the cumulative frequency distribution of diameters of all 

aspen nest trees on 21 sites (a range of about 15 to 75 centimeters dbh).4

 Somewhat 

more than 50 percent of the nests were in trees < 30 centimeters dbh, and the central 

tendency was located around 30 centimeters dbh. Of 17 cavity nesting species nesting 

in aspen, four had mean nest tree diameters > 30 centimeters dbh (northern flicker, 

pileated woodpecker, American kestrel, and European starling [Sturnus vulgaris]).4

The long tail of the distribution to the right elevates calculated mean diameters for 

most species (fig. 2). That pattern also is evident in data of Steeger and Machmer6

(fig. 2c). Most data on snag use are collected from unmanaged forests. Figure 2d

compares nest trees selected by red-breasted nuthatches in managed and unmanaged 

forests of different tree species. The similarity of snag sizes selected suggests some 

governing relationship within the two disparate forest types. 

 

6

 Unpublished data on file, Pandion Ecological Research Ltd., Nelson, British Columbia, Canada.
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 723 

Figure 1—Mean dbh of primary excavator nest trees or snags as a function of bird 

length (bill to tail length) in inland ( ) and coastal (F) forests of the Pacific 

Northwest: a) nesting in hardwoods; b) nesting in conifer trees. All lengths from 

DeGraaf and others 1991. Other sources: B. Booth (unpublished); Bull 1987; Bull and 

others 1986; Bull and others 1992; Conway and Martin 1993; Cunningham and 

others 1980; Galen 1989; Harris 1982; Keisker 1987; Linder 1994; McClelland and 

others 1979; Peterson and Gauthier 1985; Putnam 1983; Schreiber and deCalesta 

1992; Tashiro-Veirling 1994; Zarnowitz and Manuwal 1985; plus the following that are 

common with figure 3: K. Aubry and R. Raley (unpublished) from Bull 1980; Bull and 

Jackson 1995; Crockett and Hadow 1975; Dixon 1995a; Dixon 1995b; Dobkin and 

others 1995; Goggans and others 1989; Kelleher 1963; W. Klenner and D. Huggard 

(unpublished); Li and Martin 1991; Lundquist and Mariani 1991; M. Machmer and C. 

Steeger (unpublished); Madsen 1985; Mannan 1982; Mannan and others 1980; K. 

Martin (unpublished); McClelland 1977; McEllin 1979; Mellen 1987; Milne and Hejl 

1989; Nelson 1988; Raphael and White 1984; Scott and others 1980; Sedgwick and 

Knopf 1990; Steeger and Hitchcock 1998; Steeger and others 1996. 

y = 1.02x + 36.67

r

2

 = 0.21

0

20

40

60

80

100

120

140

0 10 20 30 40 50

Bird le ngth (cm )

Nest tree dbh (cm) 

conifers

b)

y = 0.55x + 24.10

r

2

 = 0.16

0

20

40

60

80

100

120

140

0 10 20 30 40 50

Bird le ngth (cm )

Nest tree dbh (cm)

hardwoods

a)
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

724 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 2—Cumulative frequency distributions (percent) of snag and nest tree 

measurements: a) dbh of old growth snags without cavities (inactive), old growth 

snags with cavities (active), and snags in younger stands, 70 () and 100 ( ) years 

of age (all inactive; data of Cline 1977:33 and Bunnell and Allaye-Chan 1984:361-

362 for the Coastal Western Hemlock zone); b) dbh of aspen nest trees in the 

Cariboo (data of K. Martin); c) dbh of nest trees used by three species in unmanaged 

Interior Cedar-Hemlock (data of C. Steeger and M. Machmer for the Interior CedarHemlock zone); d) dbh of nest trees used by red-breasted nuthatches. 

We derive three points from (fig. 2). First, birds show a central tendency in nest 

tree selection, even across different forest types (see also Connor 1976, Connor and 

others 1975). Second, because of the long tails to distributions, this tendency is better 

reflected by medians (which typically are smaller than means). Unfortunately, means 

are more often reported. Third, minimum nest tree diameter is a poor management 

target, because it ignores the central tendency.4

 A more appropriate management 

target would be to provide trees larger than the median diameter at which heart rot 

commonly accrues in that forest type. 

Roost trees, as well as nest trees, tend to be large. Unlike nests, which often are 

excavated anew each year, roosts usually are sought in natural cavities. Bull and 

others (1992) reported that the average diameter of 123 pileated woodpecker roost 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Ne s t tre e dbh (cm )

Cum ulative frequency distribution

 

Inactive

A ctive

a)

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Ne s t tre e dbh (cm )

Cum ulative frequency distribution

b)

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Ne s t tre e dbh (cm )

Cum ulative frequency distribution

Unmanaged inland CedarHemlock (C. Steeger & M.

Machmer unpublished data)

Managed inland Douglas-fir

(Booth 1994)

d)

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Ne s t tre e dbh (cm )

Cum ulative frequency distribution

Red-breasted

nuthatch

Northern

flicker

Red-naped

sapsucker

c)
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 725 

trees was 71 centimeters. Most of these were grand fir (Abies grandis) extensively 

decayed by Indian paint fungus (Echinodotium tinctorium). Pygmy nuthatches (Sitta 

pygmaea) use communal roosts housing up to 100 birds during winter (Sydeman and 

Guntert 1983). In Arizona, these roost sites averaged 73.2 centimeters dbh (Hay and 

Guntert 1983). Similarly, the hollow trees or snags used by Vaux’s swift must be 

large enough to allow the swift to fly up and down. Bull and Collins (1993) reported 

the mean dbh of 50 nest trees of Vaux’s swift to be 68 centimeters. 

Mammals also select large trees for cavity sites (table 3). In some instances, the 

trees are uncommonly large. Along the coast, from Vancouver Island south through 

Oregon, most black bear’s dens are in large dead or dying trees and downed wood 

(Bunnell and others 1997, Davis 1996). In drier, inland forests where soil moisture 

favors earth dens, Bull and others (1996) reported that 41 percent (24/59) of black 

bear dens were in wooden structures.5

 Mean dbh of hollow, black bear den trees is > 

100 centimeters in both coastal (Davis 1996) and inland forests (Bull and others 

1996). Bats also use larger trees (table 3) because they often use either natural 

hollows or cavities excavated by woodpeckers. The difference between hardwoods 

and conifers persists. Diameters of bat roost trees in southeastern British Columbia, 

averaged 52.5 centimeters dbh in Douglas-fir (Pseudotsuga menzieseii), but only 42.1 

centimeters in trembling aspen (Steeger and Machmer 1996). Four species in table 3

that use trees or snags > 50 centimeters dbh contain taxa listed as “sensitive” or “at 

risk” in the Pacific Northwest (northern long-eared myotis [Myotis septentrionalis], 

black bear, fisher, and American marten). 

Most cavity-using birds and mammals of the Pacific Northwest seek large trees 

as cavity sites. Eight species “at risk” use trees or snags averaging > 50 centimeters 

dbh, which is greater than optimal milling diameter of most sawmills. Intensive fiber 

production is incompatible with sustaining habitat for these species. 

Heights 

The fact that dbh of trees used for nesting may be much larger than the size of 

cavity sought by birds reflects the benefits of nesting high in trees to afford greater 

protection from mammalian predators (Nilsson 1984). Mean nest heights of all 

species but black-capped chickadee (Poecile atricapillus) are well above 5 meters 

(fig. 3b). In tables 4-5 we collate data on nest heights by tree species and compare 

them to availability. The average height of nest trees is not consistently higher than 

the average height of trees in the stand (table 4), because many nests were in snags 

with broken tops. For example, in interior Douglas-fir of British Columbia, 14 of 20 

nests of red-breasted nuthatches were within 2 meters of the top of decay class 4 

Douglas-fir snags with broken tops (Thomas and others 1979); 21 of 22 nests in 

Englemann spruce-subalpine fir forest were in similar class 4 subalpine fir (Abies 

lasiocarpa) snags, broken off by wind and heart rot.7

 Small, weak excavators seek 

soft substrate, commonly found in short, broken-topped snags or stumps. That 

tendency is more apparent among chickadees than nuthatches, and accounts for some 

of the short nest tree heights in figure 3a. Some mid-sized, weak excavators, also 

seek out well-rotted substrates in older, broken-topped snags or stumps (e.g., downy, 

black-backed, three-toed, and Lewis’s woodpeckers; fig. 3b). 

 

7

 Unpublished data on file, British Columbia Ministry of Forests, Kamloops, British Columbia, Canada. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

726 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 727 

Although larger birds use taller trees and snags (P < 0.001), there is great 

variability due to broken tops (fig. 3a). The same species tended to use taller trees in 

coastal forests than in the less productive inland forests, and the slope of the 

relationship is greater (P < 0.01). Actual nest height shows no relation with size of 

the bird (fig. 3b; r

2

 < 0.05). The lack of relationship between bird size and nest height 

is expected, because the stem taper means that their larger cavities cannot be as near 

the top of the tree as those of smaller birds. Taller trees often are selected by cavitynesting birds, but primarily because birds are seeking a large diameter tree with a nest 

site well above the ground. Management targets can be based on diameters alone. 

Figure 3—Mean height of primary excavator nest trees or snags (a) and nests (b) as 

a function of bird length (bill to tail) in inland ( ) and coastal (F) forests of the Pacific 

Northwest. All lengths from DeGraaf and others 1991. Other sources: Franzreb 1975, 

Hooge and others 1999, Mannan 1977, Manuwal 1981, Medin 1985, Miller and Bock 

1972, Troetschler 1976, Western Foundation of Vertebrate Zoology in Garrett and 

others 1996, plus those common with figure 1. 

y = 0.44x + 8.16

r2 = 0.18

y = 0.50x + 14.28

r2 = 0.21

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Bird length (cm )

Nest tree height (m )

(a)

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Bird length (cm )

Nest height (m )

(b)
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

728 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 4—Selection of nest tree heights within different tree species by cavity nesting birds of 

the Pacific Northwest (assessed by relative height).1

Group2 

Tree species3 P S P S 

TA RH RH RH RH 

PB n/a4 1.90 1.79 

BCo n/a 0.89 1.09 1.25 

DF n/a 0.99 0.56 

SPR 0.48 0.78 1.41 

WL 0.72 1.35 1.42 

WRC 0.77 1.54 1.41 

PP 1.36 0.90 n/a 

SF n/a 1.10 

WH 0.31 1.29 

LP 0.68 

GF 

Source and 

Notes 

McClelland 1977 (Avail. = trees 

> 22 cm dbh) 

C. Steeger5

 (Avail. = trees 

> 20 cm dbh) 

1

 RH = relative height; mean height used/mean height available. 2

 Mean tree height of nests or nest trees/snags for all cavity nesters (P), and secondary cavity nesters (S). 3

 Tree Species Codes: TA = Trembling aspen; PB = Paper birch; BCo = Black cottonwood; DF = 

Douglas-fir; SPR = Spruce; WL = Western larch; WRC = Western red cedar; PP = Ponderosa pine; SF = 

Subalpine fir; WH = Western hemlock; LP = Lodgepole pine; GF = Grand fir; WP = White pine. 4

 Tree species used for nesting, but mean height available data were not provided. 5

 Unpublished data on file, Pandion Ecological Research, Nelson, British Columbia, Canada. 

Table 5—Selection of nest tree heights by height class. Selection is measured by Chesson’s 

alpha (Chesson 1983). 

Height class (m) Source 

and Notes 

2-10 11-20 21-30 31-40 > 40 Nelson 

1988 

0.00 0.02 0.07 0.14 0.76 (snags) 

< 6 6-12 12-18 18-24 > 24 Madsen 

1985 

0.05 0.25 0.18 0.14 0.37 (snags) 

1.8-3.3 3.4-6.3 64-9.3 9.4-12.3 12.4-15.2 > 15.3 Schreiber 

& 

deCalesta 

1992 

0.01 0.06 0.08 0.18 0.36 0.32 (snags) 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 729 

Implications to Management 

There are several ways to create either cavities or snags, but it is more practical 

to sustain them than to create them (Bunnell and others 1999). Creating high stumps 

produces snags that are used (Bennett 1994), but these are well below the heights 

sought by most birds and may encourage high rates of depredation. Although 

diameter appears a more reliable basis of management targets than height, there is no 

simple diameter limit. We offer two broad recommendations: 

• Sustain a range of diameters of decaying and dead trees.

This recommendation follows from the range of diameters selected by cavity 

using species (fig. 1). Smaller snags provide some nesting opportunities, but, more 

importantly, they provide foraging sites (Bull and others 1986, Bunnell and others 

2002). Many more foraging sites are needed than nesting sites. 

• Maintain some conifer snags of at least 50 centimeters diameter (30 

centimeters in less productive forests). 

Because trees grown to provide cavities must rot and are not harvested, there is 

economic incentive to retain small trees. Earlier workers suggested minimum values 

derived from active snags as guidelines for snag retention (e.g., Connor and others 

1975, Thomas and others 1979). Minimum values imply that most individuals are 

equally successful at nesting and reproducing at the lower ends of size distributions 

as those nesting at middle and high portions of the distribution. Available data 

suggest otherwise: while individual species nest in a wide range of tree or snag sizes, 

they tend to select larger ones when available (tables 2, 3). Cavity-nesters appear to 

select median sizes at which heart rot develops. The appropriate diameter is likely to 

be a function of tree species composition, species-specific rot patterns, and site. 

Target diameters for nest trees should not be less than documented median 

diameters for the largest bird species present (fig. 1). Conifer trees must exceed 50 

centimeters dbh to support all bird species (fig. 1a). Hardwood trees can be about 10 

cm smaller (fig. 1b). Because studies have concentrated on forest types where trees 

are larger and more valuable, existing data overestimate requirements for areas where 

trees are smaller. A diameter > 30 centimeters likely will accommodate most bird 

species occurring in less productive forest types, but not the pileated woodpecker. A 

few mammals require still larger trees or snags (e.g., American marten, black bear), 

but need fewer of them than are required to sustain bird populations. Large trees and 

snags also have the advantage of standing longer than small snags (Graham 1981, 

Morrison and Raphael 1993). 

Acknowledgments 

Our research and synthesis was supported by Forest Renewal British Columbia, 

Lignum, MacMillan Bloedel, and Western Forest Products. The manuscript benefited 

from reviews by E. Bull and A. Harestad. We thank B. Booth, D. Huggard, W. 

Klenner, M. Machmer, K. Martin, and C. Steeger for unpublished data. This is 

Publication No. R-37 of the Centre of Applied Conservation Biology, University of 

British Columbia. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

730 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

References 

Akenson, James J. 1994. Black bear den summary NE Region—interim progress report.

Starkey Bear Study, 1994 February. La Grande, OR: Oregon Department of Fish and 

Game; 3 p. 

Anonymous. 1996. Ecological characteristics of fishers in southwestern Oregon. Progress 

Report, June 1996. Olympia, WA: Pacific Northwest Research Station, Forest Service, 

U.S. Department of Agriculture; 7 p. 

Baldwin, Paul H.; Zaczkowski, Nick K. 1963. Breeding biology of the Vaux Swift. Condor 

65(5): 400-406. 

Bennett, Stephen N. 1994. Initiatives in wildlife tree management: an evaluation of the 

high-cut stumping technique. School of Resource and Environmental Management 

Report No. 152. Burnaby, BC: Simon Fraser University; 75 p. 

Betts, Burr J. 1996. Roosting behaviour of silver-haired bats (Lasionycteris noctivagans)

and big brown bats (Eptesicus fuscus) in northeast Oregon. In: Barclay, R. M. R.; 

Brigham, R. M., editors. Proceedings of the symposium on bats and forests; 1995 

October 19-21; Victoria, BC: BC Ministry of Forests; 55-61. 

Bock, Carl E.; Cruz, Alexander Jr.; Grant, Michael C.; Aid, Charles S.; Strong, Thomas R. 

1992. Field experimental evidence for diffuse competition among southwestern 

riparian birds. American Naturalist 140: 815-828. 

Booth, Barry. Personal communication. Unpublished data on file, Centre for Applied 

Conservation Biology, University of British Columbia, Vancouver, BC, Canada. 

Brigham, R. Mark; Vonhof, Maarten J.; Barclay, Robert M.R.; Gwilliam, John C. 1997. 

Roosting behavior and roost-site preferences of forest-dwelling California bats 

(Myotis californicus). Journal of Mammalogy 78: 1231-1239. 

Bull, Evelyn L. 1980. Resource partitioning among woodpeckers in northeastern Oregon. 

Moscow, ID: University of Idaho; 109 p. Ph.D. dissertation. 

Bull, Evelyn L. 1987. Ecology of the pileated woodpecker in northeastern Oregon. Journal 

of Wildlife Management 51: 472–481. 

Bull, Evelyn L.; Collins, Charles T. 1993. Vaux's swift (Chaetura vauxi). In: Poole, A.; Gill, 

F., editors. The Birds of North America No. 77. Washington, DC: The Academy of 

Natural Sciences. 12 p. 

Bull, Evelyn L.; Jackson, Jerome A. 1995. Pileated woodpecker (Dryocopus pileatus). The 

Birds of North America, No. 148; 20 p. 

Bull, Evelyn L.; Meslow, E. Charles. 1977. Habitat requirements of the pileated 

woodpecker in northeastern Oregon. Journal of Forestry 75: 335-337. 

 Bull, Evelyn L.; Holthausen, Richard S.; Henjum, Mark G. 1992. Roost trees used by 

pileated woodpeckers in northeastern Oregon. Journal of Wildlife Management 56: 

786–793. 

Bull, Evelyn L.; Akenson, J. J.; Betts, Burr J.; Torgensen, T. R. 1996. The interdependence 

of wildlife and old-growth forests. In: Bradford, P.; Manning, T.; I’Anson, B., editors. 

Proceedings of the workshop on wildlife tree/stand-level biodiversity; October 17-18, 

1995, Victoria, B.C.; Victoria, BC: British Columbia Ministry of Environment, Lands, 

and Parks, and Ministry of Forests; 71–75. 

Bull, Evelyn L.; Peterson, Steven R.; Thomas, Jack W. 1986. Resource partitioning among 

woodpeckers in northeastern Oregon. Res. Note PNW-RN-44. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 19 p. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 731 

Bunnell, Fred L.; Allaye-Chan, Ann C. 1984. Potential of ungulate winter-range reserves 

as habitat for cavity-nesting birds. In: Meehan, W. R.; Merrell, T. R.; Hanley, T. A., 

editors. Proceedings of the symposium on fish and wildlife relationships in old-growth 

forests; 1982 April 12-15; Juneau, Alaska; Morehead City, NC: American Institute of 

Fishery Research Biologists; 357-365. 

Bunnell, Fred L.; Chan-McLeod, Ann C. 1997. Terrestrial vertebrates. In: Schoonmaker, P. 

K.; von Hagen, B.; Wolf , E.C., editors. The rain forests of home. Profile of a North 

American bioregion. Washington, D.C.: Island Press; 103–130. 

Bunnell, Fred L.; Dupuis, Linda A. 1995. Riparian habitats in British Columbia: their 

nature and role. In: Morgan, K. H.; Lashmar, M. A., editors. Proceedings of the 

riparian habitat management and research workshop, 1993 May 4-5; Kamloops, BC. 

Fraser River Action Plan special publication. Delta, BC: Canadian Wildlife Service; 7-

21. 

Bunnell, Fred L.; Houde, Isabelle; Johnston, Barb; Wind, Elke 2002. How dead trees sustain 

live organisms in western forests. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Bunnell, Fred L.; Kremsater, Laurie L.; Wells, Ralph W. 1997. Likely consequences of 

forest management on terrestrial, forest-dwelling vertebrates in Oregon. Portland, 

OR: Oregon Forest Resources Institute; 130 p. 

Bunnell, Fred L.; Kremsater, Laurie L.; Wind, Elke. 1999. Managing to sustain vertebrate 

richness in forests of the Pacific Northwest: relationships within stands.

Environmental Reviews 7: 97-146. 

Caceres, Carolina. 1997. Columbia Basin Fish and Wildlife Compensation Program. 

Progress report number 014. Nelson, BC: BC Hydro and BC Environment; 21 p. 

Campbell, Lori A.; Hallett, James G.; O’Connell, Margaret A. 1996. Conservation of bats in 

managed forests: use of roosts by Lasionycteris noctivagans. Journal of Mammalogy 

77: 976-984. 

Cannings, Richard A.; Harcombe, Andrew. P. 1990. The vertebrates of British Columbia. 

Scientific and English names. Heritage Record No.20, Victoria, BC: Royal British 

Columbia Museum; 110 p. 

Carey, Andrew B.; Wilson, Todd M.; Maguire, Christine C.; Biswell, Brian L. 1997. Dens of 

northern flying squirrels in the Pacific Northwest. Journal of Wildlife Management 

61: 684-699. 

Chesson, Jean. 1983. The estimation and analysis of preference and its relationship to 

foraging models. Ecology 64(5): 1297-1304. 

Cline, Steven P. 1977. The characteristics and dynamics of snags in Douglas-fir forests of 

the Oregon Coast Range. Corvallis, OR: Oregon State University; 106 p. Ph.D. 

dissertation. 

Conner, Richard N. 1976. Nesting habitat for red-headed woodpeckers in southwestern

Virginia. Bird-Banding 47: 40–43. 

Conner, Richard N.; Hooper, Robert G.; Crawford, Hewlette S.; Mosby, Henry S. 1975. 

Woodpecker nesting habitat in cut and uncut woodlands in Virginia. Journal of 

Wildlife Management 39: 144-150. 

Conway, Courtney J.; Martin, Thomas E. 1993. Habitat suitability for Williamson’s 

Sapsuckers in mixed-conifer forests. Journal of Wildlife Management 57: 322-328. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

732 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Crampton, Lisa H.; Barclay, Robert M.R. 1995. Relationships between bats and stand age 

and structure in aspen mixedwood forests in Alberta. In: Stelfox, J. B., editor. 

Relationships between stand age, stand structure, and biodiversity in aspen mixedwood 

forests in Alberta. Jointly published; Vegreville, AB: Alberta Environmental Centre 

(AECV95-R1). Edmonton, AB: Canadian Forest Service (Project No. 0001A); 211-225. 

Crittenden, Mabel. 1992. Trees of the west. Hancock House Publishers. Surrey, BC; 220 p. 

Crockett, Allen B.; Hadow, Harlo H. 1975. Nest site selection by Williamson’s and Rednaped Sapsuckers. Condor 77: 365-368. 

Cunningham, James B.; Balda, Russell P.; Gaud, William S. 1980. Selection and use of 

snags by secondary and cavity-nesting birds of the ponderosa pine forest. Res. Pap. 

RM-RP-222. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. 

Department of Agriculture; 15 p. 

Dailey, Gretchen C.; Ehrlich, Paul R.; Haddad, Nick M. 1993. Double keystone bird in a 

keystone species complex. Proceedings of the National Academy of Science USA 90: 

592-594. 

Davis, Cheyleen M. 1978. A nesting study of the Brown Creeper. Living Bird 17: 237-263. 

Davis, Helen. 1996. Characteristics and selection of winter dens by black bears in coastal 

British Columbia. Burnaby, BC: Simon Fraser university; 147 p. M.Sc. thesis. 

DeGraaf, Richard M.; Scott, Virgil E.; Hamre, R. H.; Ernst, Liz; Anderson, Stanley H. 1991. 

Forest and rangeland birds of the United States. Natural history and habitat use.

Agric. Handb. 688. Washington DC: Forest Service, U.S. Department of Agriculture; 

625 p. 

Dixon, Rita D. 1995a. Density, nest-site and roost-site characteristics, home-range, 

habitat-use, and behavior of White-headed woodpeckers: Deschutes and Winema 

National Forests, Oregon. Nongame Report 93-3-01. Portland, OR: Oregon 

Department of Fish and Wildlife; 90 p. 

Dixon, Rita D. 1995b. Ecology of white-headed woodpeckers in the central Oregon 

Cascades. Boise, ID: University of Idaho, 142 p M.Sc. thesis. 

Dobkin, David S.; Rich, Adam C.; Pretare, Jennifer A.; Pyle, William H. 1995. Nest-site 

relationships among cavity-nesting birds of riparian and snowpocket aspen 

woodlands in the northwestern Great Basin. Condor 97: 694-707. 

Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl. 1988. The birders handbook: a field 

guide to the natural history of North American birds. New York: Simon and 

Schuster Inc.; 785 p. 

Eriksson, Mats O.G. 1979. Clutch size and incubation efficiency in relation to nest-box 

size among goldeneyes Bucephala clangula. Ibis 121(1): 107-109. 

Foster, William L.; Tate, James, Jr. 1966. The activities and coactions of animals at 

sapsucker trees. Living Bird 5: 87-113. 

Franzreb, Kathleen. 1975. The effects of timber harvesting on an avian community in a 

mixed-coniferous forest. White Mountains, Arizona. Tempe, AZ: Arizona State 

University; 205 p. Ph.D. dissertation. 

Galen, Christie. 1989. A preliminary assessment of the status of Lewis’ woodpecker in 

Wasco County, Oregon. Nongame Project No. 88-3-0. Report to Oregon Dept. Fish & 

Wildlife; (original not seen; cited from Marshall and others 1996). 

Garrett, Kimball L.; Raphael, Martin G.; Dixon, Rita D. 1996. White-Headed woodpecker 

(Picoides albolarvatus). The birds of North America, No. 252: 1-22. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 733 

Goggans, Rebecca; Dixon, Rita D.; Seminara, L.C. 1989. Habitat use by three-toed and 

black-backed woodpeckers, Deschutes National Forest. Technical Report no. 87-3-

02. Portland, OR: Oregon Department of Fish and Wildlife; 50 p. 

Graham, Robin Lee L. 1981. Biomass dynamics of dead Douglas-fir and western hemlock 

boles in mid-elevation forests of the Cascade Range. Corvallis, OR: Oregon State 

University; 152 p. Ph.D. dissertation. 

Grindal, Scott. 1997. Upper Kootenay River bat survey. Athalmere, BC: Columbia Basin 

Fish and Wildlife Compensation Program. 60 p. 

Harestad, Alton S.; Keisker, Dagmar G. 1989. Nest tree use by primary cavity-nesting 

birds in south central British Columbia. Canadian Journal of Zoology. 67: 1067-1073. 

Harris, Mary A. 1982. Habitat use among woodpeckers in forest burns. Missoula, MT: 

University of Montana; 63 p. M.Sc. thesis. 

Hay, Douglas B.; Güntert, Marcel. 1983. Seasonal selection of tree cavities by pygmy 

nuthatches based on cavity characteristics. In: Davis, J.W.; Goodwin, G.A.; 

Ockenfels, R.A., editors. Proceedings of the symposium snag habitat management; 1983 

June 7-9; Flagstaff, AZ. Gen. Tech. Rep. RM-GTR-99. Fort Collins, CO: Rocky 

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 117-120. 

Holmes, Richard T. 1990. Ecological and evolutionary impacts of bird predation on forest 

insects: an overview. Studies in Avian Biology 13: 6-13. 

Hooge, Philip N.; Stanback, Mark T.; Koenig, Walter D. 1999. Nest-site selection in the 

acorn woodpecker. Auk 116: 45-54. 

Kalcounis, Matina C.; Brigham, R. Mark. 1998. Secondary use of aspen cavities by treeroosting big brown bats. Journal of Wildlife Management 62: 603-611. 

Keisker, Dagmar G. 1987. Nest tree selection by primary cavity-nesting birds in southcentral British Columbia. Wildlife Report Number R-13. Victoria, BC: British 

Columbia Ministry of Environment, Lands, and Parks; 67 p. 

Kelleher, Kevin E. 1963. A study of hole-nesting avifauna of southwest British Columbia. 

Vancouver, BC: University of British Columbia; 169 p. M.Sc. thesis. 

Kilham, Lawrence. 1971. Reproductive behavior of yellow-bellied sapsuckers. I. 

Preference for nesting in Fomes infested aspens and nest hole interrelations with 

flying squirrels, raccoons, and other animals. Wilson Bulletin 83: 159-171. 

Klenner, Walter, and David Huggard. BC Ministry of Forests, Kamloops, BC, Canada. 

[Personal communication]. 

Lewis, Susan E. 1995. Roost fidelity of bats: a review. Journal of Mammalogy 76: 481-496. 

Li, Pingjun.; Martin, Thomas E. 1991. Nest-site selection and nesting success of cavitynesting birds in high elevation forest drainages. Auk 108: 405-418. 

Linder, Kathleen A. 1994. Habitat utilization and behavior of nesting Lewis’ woodpeckers 

(Melanerpes lewis) in the Laramie range, southeast Wyoming. Laramie, WY: 

University of Wyoming; 98 p. M.Sc. thesis. 

Lindzey, Frederick G.; Meslow, Charles. 1976. Characteristics of black bear dens on Long 

Island, Washington. Northwest Science 50: 236-242. 

Lundquist, Richard W.; Mariani, Jina M. 1991. Nesting habitat and abundance of snagdependent birds in the southern Washington Cascade Range. In: Ruggiero, L. F.; 

Aubry, K. B.; Carey, A. B.; Huff, M. F., editors. Wildlife and vegetation of unmanaged 

Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 221-240. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

734 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Machmer, Machmer; Steeger, Chris. Pandion Ecological Research Ltd., Nelson, BC, Canada. 

[Personal communication]. 

Madsen, Sarah J. 1985. Habitat use by cavity-nesting birds in the Okanogan National

Forest, Washington. Seattle, WA: University of Washington; 112 p. M.Sc. thesis. 

Mannan, Robert W. 1977. Use of snags by birds, Douglas-fir Region, western Oregon. 

Corvallis, OR: Oregon State University. M.Sc. thesis. 

Mannan, Robert W. 1982. Bird populations and vegetation characteristics in managed 

and old-growth forests, northeastern Oregon. Corvallis, OR: Oregon State 

University; 114 p. Ph.D. dissertation. 

Mannan, Robert W.; Meslow, E. Charles; Wright, Howard M. 1980. Use of snags by birds in 

Douglas-fir forests, Western Oregon. Journal of Wildlife Management 44: 787-797. 

Manuwal, David A. 1981. Cavity nesting birds of the Olympic National Forest 

Washington. Seattle, WA: Wildlife Science Group, College of Forest Resources, 

University of Washington; 144 p. 

Marshall, David B.; Chilcote, Mark W.; Weeks, Hal. 1996. Species at risk. Sensitive, 

threatened, and endangered vertebrates of Oregon. Portland, OR: Oregon 

Department of Fish and Wildlife; unnumbered. 

Martin, Kathy. Centre for Applied Conservation Biology, University of British Columbia, 

Vancouver, BC, Canada. [Personal communcation]. 

Martin, S.K.; Barrett, R.H. 1991. Resting site selection by marten at Sagehen Creek, 

California. Northwest Naturalist 72: 37-42. 

McClelland, B. Riley 1977. Relationships between hole-nesting birds, forest snags, and 

decay in western larch and Douglas-fir forests of the northern Rockies. Missoula, 

MT: University of Montana; 469 p. Ph.D. dissertation. 

McClelland, B. Riley; Frissle, Sidney S.; Fischer, William C.; Halvorson, Curtis H. 1979. 

Habitat management for hole-nesting birds in forests of western larch and Douglasfir. Journal of Forestry 77: 480-483. 

McEllin, Shaun M. 1979. Nest sites and population demographics of white-breasted and 

pygmy nuthatches in Colorado. Condor 81: 348-352. 

Medin, Dean E. 1985. Densities and nesting heights of breeding birds in an Idaho 

Douglas-fir forest. Northwest Science 59: 45-52. 

Meiselman, N.; Doyle, Arlene T. 1996. Habitat and microhabitat use by the red tree vole 

(Phenacomys longicaudus). American Midland Naturalist 135: 33-42. 

Mellen, Teresa K. 1987. Home range and habitat use of pileated woodpeckers, western 

Oregon. Corvallis, OR: Oregon State University; 96 p. M.Sc. thesis. 

Miller, Alden H.; Bock, Carl E. 1972. Natural History of the Nuttall woodpecker at the 

Hastings Reservation. The Condor 74: 284-294. 

Miller, Eileen; Miller, Donald R. 1980. Snag use by birds. In: DeGraaf, R. M., editor. 

Management of western forests and grasslands for nongame birds. Gen. Tech. Rep. INTGTR-86. Logan, UT: Interior Research Station, Forest Service, U.S. Department of 

Agriculture; 337–356. 

Miller, Richard S.; Nero, Robert W. 1983. Hummingbird-sapsucker associations in 

northern climates. Canadian Journal of Zoology 61: 1540-1546. 

Milne, Kathleen A.; Hejl, Sallie J. 1989. Nest-site characteristics of white-headed 

woodpeckers. Journal of Wildlife Management 53: 50-55. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 735 

Morrison, Michael L.; Raphael, Martin G. 1993. Modeling the dynamics of snags. 

Ecological Applications 3: 322-330. 

Mowrey, Robert A.; Zasada, John C. 1984. Den tree use and movements of northern flying 

squirrels in interior Alaska and implications for forest management. In: Meehan, 

W. R.; Merrel, T. R.; Hanley, T. A., editors. Proceedings of a symposium on fish and 

wildlife relationships in old-growth forests. 1982 April 12-15; Juneau, Alaska. 

Moorhead City, NC: American Institute of Fishery Research Biologists; 351-356. 

Nelson, S. Kim. 1988. Habitat use and densities of cavity-nesting birds in the Oregon 

coast ranges. Corvallis, OR: Oregon State University; 156 p. M.Sc. thesis. 

Nilsson, Sven G. 1984. The evolution of nest-site selection among hole-nesting birds: the

importance of nest predation and competition. Ornis Scandinavica 15(3): 167-175. 

Noble, William O.; Meslow, E. Charles; Pope, Michael D. 1990. Denning habits of black 

bears in the central Coast Range of Oregon. Corvallis, OR: Department of Fisheries 

and Wildlife, Oregon State University; 28 p. 

O’Conner, Roslyn J. 1978. Nest-box insulation and the timing of laying in the Wytham 

Woods population of great tits Parus major. Ibis 120: 534-537. 

Ormsbee, Patricia C.; McComb, William C. 1998. Selection of day roosts by female longeared myotis in the central Oregon Cascade Range. Journal of Wildlife Management 

62: 596-603. 

Parish, Roberta; Coupé, Ray; Lloyd, Dennis, editors. 1996. Plants of Southern Interior 

British Columbia. Vancouver, BC: Lone Pine Publishers; 462 p. 

Parsons, Gary L.; Cassis, Gerasimos; Moldenke, Andrew R.; Lattin, John D.; Norman, 

Neville H.; Miller, Jeffrey C.; Hammond, Paul C.; Schowalter, Timothy D. 1991. 

Invertebrates of the H. J. Andrews Experimental Forest, Western Cascades Range, 

Oregon. V: An annotated list of insects and other arthropods. Gen. Tech. Rep. 

PNW-GTR-290. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 168 p. 

Peterson, Barbara; Gauthier, Gilles. 1985. Nest site use by cavity-nesting birds of the 

caribou parkland, British Columbia. Wilson Bulletin 97: 319-331. 

Peterson, Roger T.; Mountford, Guy; Hollom, P.A.D. 1993. The Audubon Society field 

guide to birds of Britain and Europe. Boston, MA: Houghton Lifflin; 261 p. 

Pojar, Jim; MacKinnon, Andy, editors/compilers. 1994. Plants of coastal British Columbia.

Vancouver, BC: Lone Pine Publishers; 526 p. 

Putnam, Betsy J. 1983. Songbird responses of precommercially thinned and unthinned 

stands in east-central Washington. Corvallis, OR: Oregon State University; 58 p. 

M.Sc. thesis. 

Raphael, Martin G.; Jones, Lawrence L.C. 1997. Characteristics of resting and denning 

sites of American martens in central Oregon and western Washington. In: Proulx, 

G.; Bryant, H. N.; Woodward, P. M., editors. Martens: taxonomy, ecology, techniques 

and management. Edmonton, AB: Provincial Museum of Alberta; 146-165. 

Raphael, Martin G.; White, Marshall. 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada. Wildlife Monographs 86: 1-66. 

Rasheed, Sadig A.; Holroyd, Susan L. 1995. Roosting habitat assessment and inventory of 

bats in the Mica Wildlife Compensation Area. Columbian Basin Fish and Wildlife 

Compensation Program. Nelson, BC: BC Hydro and BC Environment; 77 p. 

Schreiber, Barry; deCalesta, David S. 1992. The relationship between cavity-nesting birds 

and snags on clearcuts in western Oregon. Forest Ecology and Management 50: 299-

316. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

736 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Scott, Virgil E.; Whelan, Jill A.; Svoboda, Paul L. 1980. Cavity-nesting birds and forest 

management. In: DeGraff, R.M., technical coordinator. Proceedings of a workshop on 

management of western forests and grasslands for nongame birds. 1980 February 11-14; 

Salt Lake City, UT. Gen. Tech. Rep. INT-86. Fort Collins, CO: Intermountain Research 

Station, Forest Service, U.S. Department of Agriculture; 311-324. 

Sedgwick, James A.; Knopf, Fritz L. 1990. Habitat relationships and nest site 

characteristics of cavity-nesting birds in cottonwood floodplains. Journal of Wildlife 

Management 54: 112-124. 

Shigo, Alex L.; Kilham, Lawrence. 1968. Sapsuckers and Fomes ignarius var. populinus.

Res. Note NE-RN-84. Saint Paul: Northeast Research Station, Forest Service, U.S. 

Department of Agriculture; 2 p. 

Spencer, Wayne D. 1987. Seasonal rest-site preferences of pine martens in the northern 

Sierra Nevada. Journal of Wildlife Management 51: 616-621. 

Spring, Lowell W. 1965. Climbing and pecking adaptations in some North American 

woodpeckers. Condor 67: 457-488. 

Steeger, Cristoph; Hitchcock, Christine L. 1998. Influence of forest structure and diseases 

on nesting habitat selection by red-breasted nuthatches. Journal of Wildlife 

Management 62: 1349-1358. 

Steeger, Cristoph; Machmer, Marlene M. 1996. Use of trees by cavity nesters in managed 

and unmanaged Interior Cedar—Hemlock stands of southern British Columbia. In: 

Bradford, P.; Manning, T.; I’Anson, B., editors. Proceedings of the Workshop on 

Wildlife Tree/Stand-level Biodiversity. Proceedings of the workshop on wildlife 

tree/stand-level biodiversity; October 17-18, 1995, Victoria, BC; Victoria, BC: British 

Columbia Ministry of Environment, Lands, and Parks, and Ministry of Forests; 45–54. 

Steeger, Cristoph ; Machmer, Marlene M.; Walters, Eric. 1996. Ecology and management of 

woodpeckers and wildlife trees in British Columbia. Delta, BC: Environment Canada, 

Fraser River Action Plan, Canadian Wildlife Service; 23 p. 

Stelmock, James J.; Harestad, Alton S. 1979. Food habits and life history of the clouded 

salamander (Aneides ferreus) on northern Vancouver Island. Syesis 12: 71-75. 

Sutherland, Glenn D.; Gass, Clifton Lee; Thompson, Peter A.; Lertzman, Kenneth. P. 1982. 

Feeding territoriality in migrant rufous hummingbirds: defense of yellow-bellied 

sapsucker feeding sites. Canadian Journal of Zoology 60: 2046-2050. 

Sydeman, William J.; Guntert, Marcel. 1983. Winter communal roosting in the pygmy 

nuthatch. In: Davis, J. W.; Goodwin, G. A.; Ockenfels, R. A., technical coordinators. 

Snag habitat management. Gen. Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain 

Research Station, Forest Service, U.S. Department of Agriculture; 121-124. 

Tashiro-Vierling, K.Y. 1994. Population trends and ecology of the Lewis’ woodpecker

(Melanerpes lewis) in southeastern Colorado. Boulder, CO: University of Colorado; 

73 p. M.A. thesis. 

Thomas, Jack W.; Anderson, R. G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: Thomas, 

J. W., editor. Wildlife habitats in managed forests. the Blue Mountains of Oregon and 

Washington. Agric. Handb. 553. Washington, D.C.: Forest Service, U.S. Department of 

Agriculture; 60-77. 

Troetschler, Ruth G. 1976. Acorn woodpecker breeding strategy as affected by starling 

nest-hole competition. Condor 78: 151-165. 

van Woudenberg, Astrid M. 1992. Integrated management of flammulated owl breeding 

habitat and timber harvest in British Columbia. Vancouver, BC: University of 

British Columbia. M.Sc. thesis; 56 p. 
Diameters and Heights of Cavity Trees—Bunnell, Wind, Boyland, and Houde 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 737 

von Haartman, Lars. 1957. Adaptation in hole-nesting birds. Evolution 11: 339-347. 

Vonhof, Maarten J. 1996. A survey of the abundance, diversity, and roost-site preferences 

of bats in the Pend d’Oreille valley, British Columbia. The Columbia Basin Fish and 

Wildlife Compensation Program. Nelson, BC: BC Hydro and BC Environment; 69 p. 

Weir, Richard 1995. Diet, spatial organization, and habitat relationships of fishers in 

south-central British Columbia. Burnaby, BC: Simon Fraser University; 139 p. M.Sc. 

thesis. 

Whitaker, John O. 1993. The Audubon Society field guide to North American mammals. 

Toronto, ON: Random House; 745 p. 

Zarnowitz, Jill E.; Manuwal, David A. 1985. The effects of forest management on cavitynesting birds in northwestern Washington. Journal of Wildlife Management 49: 255-

262.

 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 739 

How Should We Spatially Distribute Dying 

and Dead Wood?1

Fred L. Bunnell,2 Mark Boyland,2 and Elke Wind2 

Abstract 

We consider density and degree of aggregation of dead wood. Cavity nesters as a group 

respond asymptotically to snag density and attain half their maximum density at about 2.4 

large snags/hectare. However, individual species show different responses, and there is no 

apparent effect of territoriality among smaller species. Dispersed retention of trees and snags 

strongly favors secondary cavity nesters and increases their abundance above that found in 

mature or old-growth forests; large patches favor primary nesters. Despite good operational 

and biological reasons for patchwise retention of dead wood, there are negative effects on 

some species. 

Introduction 

Many organisms rely upon dead wood (Bunnell and others 2002), and recent 

forest practices are exploring ways to sustain dead wood in managed stands (e.g., 

Anonymous 1995, Steventon and others 1998). There is a large literature on the sizes 

of dead trees and logs used by forest-dwelling organisms, but less is known about 

how that dead wood should be distributed within managed forests. We review 

relationships between forest-dwelling organisms and the amounts and distribution of 

dying or dead trees and dead wood on the ground. We focus on vertebrates, but 

briefly discuss other organisms that use dead wood. Our review is largely restricted 

to species of the Pacific Northwest defined as including Alaska, Alberta, British 

Columbia, Washington, Oregon, Idaho, Montana, and northern Nevada and 

California. References to other regions are included to indicate trends where forestry 

has been practiced longer, or where particular groups of species are well documented. 

 

Density of Dying and Dead Trees 

Richness and density of cavity-nesting birds are inconsistently related to snag 

densities. Studies surveying stands with many snags have obtained weak relations 

(e.g., Lundquist and Mariani 1991, Morrison and others 1987), while those including 

managed stands, in which some or all snags had been removed, have found stronger 

relations (e.g., Raphael and White 1984, Schreiber and deCalesta 1992). Bevis (1996) 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Professor, Ph.D. Candidate, and Research Technician, respectively, Center for Applied Conservation 

Research, Department of Forest Sciences, University of British Columbia, 3004-2424 Main Mall, 

Vancouver, British Columbia, Canada, V6T 1Z4. (e-mail addresses: fbunnell@interchange.ubc.ca, 

markbo@interchange.ubc.ca, and ewind@interchange.ubc.ca) 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

740 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

surveyed a range of stands from unmanaged to seed tree, and found the strongest 

predictor of red-breasted nuthatch (Sitta canadensis) and chickadee densities to be 

density of snags 25-50 centimeter dbh; r2

 = 0.94 and 0.83, respectively. These 

relationships may indicate nest site limitation, or they may reflect more productive 

foraging opportunities in stands with more snags (e.g., older stands with insect 

outbreaks versus thrifty managed stands). 

Because rot within living trees is more common among hardwoods than among 

conifers, snag density is less important in hardwood stands. Figure 1a illustrates 

relationships for conifer stands with few hardwoods. Because much variation in 

cavity nester response to snag density is due to different size distributions of snags 

within stands, we limited estimates of snag density to larger snags that the birds use 

preferentially. Our diameter limits reflect the different sizes of preferred trees in 

coastal forests (about 50 centimeter dbh) and inland forests (30.5 to 38 centimeter 

dbh; Bunnell and others 2002). Bunnell and others (1999) fit a Michaelis-Menten 

relationship to the data (fig. 1a) under the assumption that the rate of response (cavity 

nesters density) was a function of the concentration of substrate (snags/hectare). The 

relationship implies an upper asymptote and a half-saturation constant. Response of 

the seven studies combined is asymptotic, with little additional increase in density of 

cavity nesters above about three large snags per hectare (fig. 1a). Estimated 

parameters were an asymptote of 2.42 cavity nesting pairs/hectare and a halfsaturation constant of 2.37 snags/hectare with an r2

 of 0.53. That shape is expected 

among territorial species limited by other resources. As the snag density increases, 

other required resources become more important factors in limiting bird density until 

finally the scarcity of other resources are completely limiting the bird density. Birds 

present at 0.0 snags per hectare indicate that some species can nest in snags < 30 

centimeter dbh (some of them hardwoods, unreported in data on conifers). The 

response is consistently expressed, and each individual study of figure 1a shows an 

initial increase in cavity-nester density with increasing snag density. 

Relationships for some bird species appear more linear (fig. 1b,c). They suggest 

that competition for cavity sites is more strongly expressed within the entire cavitynesting fauna than within the smaller species studied. Data of figure 1c also suggest 

that other habitat variables influence the response (compare data of Raphael and 

White 1984 with those of Cunningham and others 1980). We emphasize that smaller 

snags were present in all studies included in figure 1. Smaller snags are used as 

foraging sites, and foraging sites may be more often limiting than cavity sites 

(Walankiewicz 1991, Welsh and Capen 1992). More dead or dying wood than is 

required for nesting is needed to sustain all cavity-nesting species. Moreover, through 

provision of perching, foraging, and hawking sites, snags of all sizes tend to increase 

richness and abundance of birds other than cavity nesters (Dickson and others 1983, 

Scott 1979). 

Species names mentioned in this text are taken from the following references: 

Plants—(Crittenden 1992); Birds—(Cannings and Harcombe 1990, Peterson and 

others 1993); Amphibians—(Cannings and Harcombe 1990); Mammals—(Cannings 

and Harcombe 1990, Whitaker 1993). 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 741 

Figure 1—Density of cavity-nesting bird pairs versus snag density in primarily 

coniferous forests of the Pacific Northwest. Hollow symbols represent coastal forests; 

solid symbols are inland forest types. a) All cavity-nesting species. [O] = Carey and 

others 1991 (snags > 50 cm dbh); [▲] = Cunningham and others 1980 (snags > 30.5 

cm dbh); [] = Mannan 1977 (snags > 48 cm dbh); [■] = Mannan and Meslow 1984 

(snags > 31 cm dbh); [◊] = Manuwal and Zarnowitz 1981 (snags > 51 cm dbh); [∆]= 

Nelson 1988 (snags > 50 cm dbh); [●] = Raphael and White 1984 (> 38 cm dbh); [◆] 

= Steeger and Quesnel 1998 (snags > 50 cm dbh). Solid line is the fitted MichaelisMenten relationship of the form cavity nesters per ha = 2.42 [asymptote] X 

(snags/hectare/ (snags/hectare + 2.37[half saturation constant])) (adapted from 

Bunnell and others 1999). b) Chestnut-backed chickadee pairs [▲] = Cunningham 

and others 1980 (snags > 30.5 cm dbh); [●] = Mannan 1977 (snags > 48 cm dbh). 

[O] = Manuwal and Zarnowitz 1981 (snags > 51 cm dbh); [] = Nelson 1988 (snags > 

50 cm dbh). c) Mountain chickadee (Poecile gambeli) pairs: [▲] = Cunningham and 

others 1980; [■] = Mannan and Meslow 1984; [O] = Raphael and White 1984. 

a)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 2 4 6 8 10 12 14 16

Snags / ha

Cavity-nesting pai

b)

y = 0.11x - 0.05

R2

 = 0.79

0.0

0.5

1.0

1.5

2.0

2.5

0 2 4 6 8 10 12 14 16

Snags/ha

Chestnut-backed chi

pairs/ha

c)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 2 3 4 5 6 7 8 9 10

Snags/ha

Mountain chickadee p

y = 0.05x -0.12

R2

 = 0.48
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

742 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Density of Downed Wood 

The literature is least revealing of the appropriate amounts and distribution of 

downed wood. Of all habitat variables assessed, downed wood is the least 

consistently measured, and it is impossible to equate number of pieces, volume, and 

percent cover to extract broad patterns (e.g., Bunnell and Huggard 1999). In part, the 

variety of measurements reflects the fact that different ones are appropriate for 

different organisms: percent cover for some fungi, volume for terrestrial-breeding 

salamanders, and size for denning mammals. Although biologically appropriate, the 

variety prohibits synthesis. Moreover, when similar measurements exist, responses to 

downed wood within species are inconsistent, suggesting substitution with other 

habitat features, such as shrub cover (Bunnell and others 1999). Three broad points 

are evident from current data. First, hundreds of species in western forests are 

dependent upon decaying wood on the ground (Bunnell and others 2002). Second, 

volume of downed wood is important. That is most evident in data of Corn and Bury 

(1991) who reported that densities of clouded (Aneides ferreus) and western redback 

(Plethodon vehiculum) salamanders were relatively constant per cubic meter of 

downed wood, regardless of stand age. Third, some species seek out large pieces of 

downed wood, particularly marten (Martes americana), fisher (Martes pennanti), and 

black bears (Ursus americanus) (Bunnell and others 2002). Because these species 

also range more widely than most species using downed wood, required densities are 

probably low, provided scattered large pieces are accessible. In short, some downed 

wood is important for many species, and large pieces are critical to some. 

Because different forest types grow and recruit different amounts of downed 

wood, it is misleading to transplant results. Initial studies have tended to focus on 

productive forests, which have little relevance to less productive forest types. What is 

clear is that size, decay class, and total amounts of downed wood have declined with 

the practice of forestry (e.g., Angelstam 1997, Spies and others 1988) to the 

detriment of many species (Berg and others 1994). In other words, we do not know 

what appropriate amounts are, but we do know we have not been recruiting enough 

downed wood (Bunnell and others 1997). 

Distribution of Dying and Dead Trees 

Effects of spatial arrangement of snags on cavity-nesters have received far less 

attention than the attributes of the individual nest trees (Swallow and others 1986). 

Dispersed retention of snags increased abundance and richness of secondary cavity 

nesters beyond that found in mature and old-growth forests, but abundance of 

primary nesters was much reduced (fig. 2). For primary cavity nesters, there are good 

reasons for retaining trees in patches. First, there is increased operational efficiency. 

Aggregated retention is safer during timber falling, especially when snags are 

retained, and windthrow is much reduced relative to dispersed retention or large 

clearcut edges (Coates 1997, Franklin and others 1997). Operational efficiency can 

also be gained in patches with a more desirable range of diameter and decay classes, 

that might prove difficult to select among the individual trees of dispersed retention. 

Aggregated retention also emulates natural patterns. Nests of primary excavators 

often are concentrated in dense patches of snags (Bull 1980, Lundquist and Mariani 

1991, Raphael and White 1984). It is unclear whether this implies selection of dense 

patches for some associated value (e.g., social facilitation) or merely reflects the 

patchy way in which trees are killed by insects or disease. Cavity sites often are 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 743 

concentrated where rots are concentrated in both hardwoods (e.g., Phellinus in aspen 

[Populus tremuloides] and birch [Betula papyrifera]; Merkens and others 1996), 

conifers (e.g., Armillaria in Douglas-fir [Pseudotsuga menzieseii]), and lodgepole 

pine (Pinus contorta; Steeger and Hitchcock 1998). 

Figure 2—Relative abundance of primary [■] and secondary [F] cavity nesters in 

different forms of partial harvest. Data sources are a) Scott and Oldemeyer (1983) in 

Ponderosa pine (Pinus ponderosa). b) Steeger and Quesnel (1998) in interior 

Douglas-fir. c) Gyug and Bennett (1996) in interior western redcedar-hemlock; see 

text for patch sizes. d) Bryant (1997) in coastal western hemlock; dispersed retention 

retained about 25 trees per ha. e) Waterhouse and Dawson (1999) in interior 

Douglas-fir. f) Morgan and others (1989) in interior Douglas-fir; amount removed 

unspecified. g) Steventon and others (1998) in interior western redcedar-hemlock, h) 

Tobalske and others (1991) in western larch-Douglas fir. 

a) e)

b) f)

c) g)

d) h)

0

0.2

0.4

0.6

0.8

1

54% Removal 40% Removal Mature

Relative abunda

0

0.2

0.4

0.6

0.8

1

70% Removal 30% Removal Mature

Relative abunda

0

0.2

0.4

0.6

0.8

1

Clearcut Clearcut with

patches

Mature

Relative abunda

0

0.2

0.4

0.6

0.8

1

60%

Removal

40%

Removal

11%

Removal

Mature

Relative abunda

0

0.2

0.4

0.6

0.8

1

Light Removal Heavy

Removal

Mature (IDF)

Relative abunda

0

0.2

0.4

0.6

0.8

1

60% Removal 30% Removal Mature

Relative abunda

0

0.2

0.4

0.6

0.8

1

66% Removal Mature Old Growth

Relative abunda

0

0.2

0.4

0.6

0.8

1

Dispersed 70% Removal Old-growth

Relative abunda
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

744 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The most compelling reason for aggregated retention of wildlife trees is that it 

has been shown to be effective when larger patches are retained. The utility of small 

patches appears undocumented, but Gyug and Bennett (1996) studied large seed-tree 

reserves in clearcuts 25 to 29 years after harvesting. Patches retained in the 160 

hectare clearcut averaged 0.9 hectare (range 0.3 to 1.5 hectare); in the 1,000 hectare 

clearcut they averaged 3.6 hectares (range 1.6 to 18.9 hectares). Combined, the 

patches represented 7 to 10 percent of the gross area. In both clearcuts, more primary 

cavity nesters were detected in the patches than in the nearby forest, including 

pileated (Dryocopus pileatus) and hairy (Picoides villosus) woodpeckers. Current 

data also suggest that various silviculture systems that maintain some cover 

somewhere at all times (continuous-cover) are effective at sustaining cavity nesters 

(fig. 2). 

Two broad patterns are evident. First, in all studies of figure 2, secondary cavity 

nesters were higher in areas experiencing some timber removal than in mature or oldgrowth forests. That increase likely reflects the fact that many secondary nesters 

forage more effectively in openings. Second, in most instances the abundance of 

primary cavity nesters was little affected by partial harvesting, and in some instances 

increased in abundance. That may reflect the fact that several primary excavators also 

favor small openings and edges (e.g., hairy woodpeckers; Klenner and Huggard 

1998; northern flicker [Colaptes auratus], Campbell and others 1990; three-toed 

woodpecker [Picoides tridactylus], Klenner and Huggard 1997; and perhaps downy 

woodpecker [Picoides pubescens], Petit and others 1985). For three-toed 

woodpeckers, Klenner and Huggard (1997) noted that preferred nest sites were 

within 20 meters of an edge. If regulations encourage snag removal near edges, 

patches must be larger and continuous-cover systems will be less effective. 

Distribution of Downed Wood 

Downed wood can be provided by leaving slash or logs after harvest or by 

retaining trees to fall to the ground and become downed wood. Slash, including logs, 

can be either dispersed over the cutblock or aggregated into piles or windrows. More 

information is available on aggregated retention of downed wood than on dispersed 

retention. 

Several species of small mammals use piles of both fine and coarse logging 

debris, including red-backed voles (Clethrionomys spp.), martens, and short-tailed 

weasels (Mustela erminea) (Lisgo 1999, Morris 1984, Raphael and Jones 1997). 

Jones and Raphael (1995) described 32 maternal den sites of marten in Oregon: 10 

were in slash piles, 10 in logs, 6 in snags, 5 in live trees, and 1 in a stump. Using 

winter tracking, Gyug (1993, 1994) found that marten use of clearcuts without debris 

was very low compared to use of adjacent forests. Use of clearcuts with debris piles 

was significantly higher, but still lower than in adjacent forest. Isolated debris piles 

were not used by marten unless they were on a path of 135 meters or less between 

adjacent forest cover. Lisgo and others (2002) documented similar responses of 

weasels to debris piles in the boreal mixedwood of Alberta. Although marten and 

weasels hunted around debris piles, small mammal responses to debris were 

inconsistent. Gyug (1994) found that the presence and number of debris piles did not 

significantly increase the number of most small mammals. Red-backed voles were 

almost absent from clearcuts except in piles within 40 meters of forest edges, and 

only common shrews (Sorex spp.) were significantly more abundant when debris 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 745 

piles were present. Lisgo and others (2002) found greater abundance of small 

mammals around slash piles than in clearcuts, particularly for red-backed voles. 

Benefits of piling logging residues remain unclear, because current data simply report 

higher densities of small mammals in piles than in clearcut areas without piles. 

Responses to dispersed downed wood have not been compared with aggregated 

downed wood. 

For some organisms, dispersed retention of logging residues is advantageous. 

Because conditions of stable high humidity are favorable for bryophytes (Sharp 

1939), particularly liverworts (Söderström 1988), the humidity and moisture content 

of logs are especially important to bryophytes (Andersson and Hytteborn 1991). 

Forest floor bryophytes generally have limited dispersal ability (Khanna 1964, 

Söderström 1987), and dispersal is from log to log. For these reasons, Samuelsson 

and others (1994) argued that logs should be close together, but not gathered into 

piles. It is probable that other organisms whose favored, or only, habitat is downed 

wood also are poor dispersers. Amaranthus and others (1994) and Carey and Johnson 

(1995) found that the abundance of truffles and truffle-like fungi, was related to the 

amount of forest floor covered by logs. More forest floor is covered if the logs are not 

piled. Encouraging truffles and truffle-eating mammals is a sensible thing to do if 

sustaining forest productivity is a goal (Harley 1969, Marks and Kozlowski 1973, 

Maser and others 1978). A dispersed distribution of downed wood would help to 

disperse both small mammals and mycorrhizae across the site. 

There are tradeoffs between aggregating logging residuals or leaving it 

dispersed. Aggregations are used by several small mammals, both predator and prey. 

More evenly dispersed retention favors some fungi as well as bryophytes restricted to 

downed wood. Because there is not an unequivocal best way to distribute logging 

residuals, the wisest approach is not to do the same thing everywhere. 

The other approach to providing downed wood is through dispersed or 

aggregated retention of living trees. Retained trees die a natural death and likely will 

have incurred fungal invasion. Natural cavities from heart rot are more likely, and 

invertebrates associated with some fungi are more likely to survive. Higher 

windthrow rates in dispersed retention hasten the provision of downed wood, but 

reduce the period when these trees can provide cavity sites. As well as reduced 

susceptibility to windthrow, aggregated retention of older trees (patches) has the 

advantage of immediate provision of downed wood. Additional advantages to 

aggregated retention are those noted with respect to cavity users, notably the 

provision of a range of decay and size classes. The disadvantage is that such 

provision is clearly not dispersed across the landscape. Species restricted to downed 

wood and that disperse poorly will be disadvantaged. 

Implications to Management 

From this review, we offer the following recommendations for the distribution 

of dead wood in managed forest: 

• Maintain a target density of 2-3 large snags (> 50 or 30 centimeter diameter) 

per hectare, among 10-20 smaller snags per hectare through the rotation. 

However, ensure variation in densities, not an even distribution everywhere. 

Cavity sites can become limiting, and there is a density below which species 

disappear (Campbell and others 1990, 1997; Newton 1994). Data of figure 1 suggest 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

746 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

that in conifer types little is gained by sustained provision of more than about three 

large snags per hectare (> 50 centimeter dbh in coastal forests; > 30 centimeters in 

less productive forests). More smaller snags must be present, both as foraging sites 

and because some species find cavity sites in small snags. There are no applicable 

data, but we estimate 10 to 20 smaller snags per hectare as appropriate. In hardwood 

types, there is little need for a target density of snags, because most cavity nests are 

found in living trees. Providing for future recruitment of snags in coniferous stands is 

necessary to ensure that target densities are maintained through the rotation and after 

harvest. Suggested densities do not apply to each hectare of forest. Because of the 

diversity of organisms using snags, variability in density of snags must be maintained 

within and among stands. 

• Amounts of downed wood? 

Logs as small as 6 centimeters are favorable to shrews (Craig 1995), but in some 

forest types larger mammals prefer significant amounts (100 to 200 cubic 

meters/hectare or more) and sizes (> 50 centimeter diameter) of downed wood 

(review of Lofroth 1993). Current data suggest little more than small amounts are 

useful but that mammals such as marten, fisher, and black bear require scattered, 

large pieces, 50 to 100 centimeter diameter. 

• Patches of 1-3 hectares will sustain some smaller species, even in extensive 

clearcuts. 

Such patches sustain most, if not all, cavity nesters (fig. 2). Home ranges of 

some terrestrial-breeding salamanders and shrews are small enough (Craig 1995, 

Nussbaum and others 1983) that groups of individuals can be sustained within 1 

hectare; 3 hectares will sustain groups of rodents (e.g., Mahon 1998, Thompson 

1996). Retention of some logs on site would permit them to recolonize larger areas. 

• Retaining snags in moderate-sized patches has several advantages. It should 

not, however, be the only distribution of snags used. 

Retention of trees in patches helps reduce safety risks of snag retention, 

provided patches are large enough. Aggregates of 1-3 hectares are used by cavitynesters in large openings, and are practical where snag-falling regulations permit 

snag retention within them. Aggregated retention also reduces risks of windthrow and 

provides diverse nesting opportunities over a range of size and decay classes. 

Although aggregating retention in moderate-sized patches has advantages, it should 

not be the only approach used. Dispersed retention of snags, or declining live trees 

intended to become snags, may be particularly advantageous for perching birds, and 

for territorial secondary users, such as raptors, and some small birds. Dispersed 

retention, however, may impact shrub nesters (Vega 1993) and should not be used 

everywhere. 

Continuous-cover systems, such as individual tree selection, group selection and 

small (0.1-3 hectare) patch cut arrays have a number of benefits (fig. 2), and are of 

increasing operational interest (Vyse 1999). Openings of up to 3 hectares appear to 

have little effect on primary cavity nesters when 50 percent of the older forest is 

retained (Bryant 1997). However, repeated entries and need to fall snags in the 

surrounding forest can eliminate snags from large areas (Huggard 1997). Aggregated 

reserves should be considered for snag management in these systems. 

• Meet dead wood requirements for larger species in areas where the emphasis 

is not on intensive fiber production. 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 747 

The economic and ecological advantages of zoning intensity of forest practices 

(Binkley 1997, Bunnell and others 1999) suggests that needs of species requiring 

large amounts of dead wood are best provided in areas where late-successional 

attributes are being maintained. Most (perhaps all) of these species use clearcuts to 

forage and often find preferred food there, but must have denning sites nearby. 

Provision of large amounts of downed wood within clearcuts is incompatible with 

profit incentives of intensive fiber production. 

Acknowledgments 

Our research and synthesis was supported by Forest Renewal British Columbia, 

the Fraser River Action Plan of the Canadian Wildlife Service, Lignum, MacMillan 

Bloedel, and Western Forest Products. The manuscript benefited from reviews by 

Peter Arcese and Glen Dunsworth. This is publication R-40 of the Centre for Applied 

Conservation Biology, University of British Columbia. 

References 

Amaranthus, Michael; Trappe, James M.; Bednar, Larry; Arthur, David 1994. Hypogeous 

fungal production in mature Douglas-fir forest fragments and surrounding 

plantations and it s relation to coarse woody debris and animal mycophagy.

Canadian Journal of Forest Research 24: 2157-2165. 

Andersson, Lars I.; Hytteborn, Hakan 1991. Bryophytes and decaying wood—a 

comparison between managed and natural forest. Holarctic Ecology 14: 121-130. 

Angelstam, Per 1997. Landscape analysis as a tool for the scientific management of 

biodiversity. Ecological Bulletin (Copenhagen) 46: 140-170 

Anonymous. 1995. Sustainable ecosystem management in Clayoquot Sound: planning 

and practices. Victoria, BC: Cortex Consultants; Scientific Panel for Sustainable Forest 

Practices in Clayoquot Sound; 296 p. 

Berg, Åke.; Ehnström, Bengt; Gustafsson, Lena; Hallingbäck, Tomas; Jonsell, Mats; Weslien, 

Jan 1994. Threatened plant, animal, and fungus species in Swedish forests: 

distributions and habitat associations. Conservation Biology 8: 718-731. 

Bevis, Kenneth R. 1996. Primary excavators in grand fir forests of Washington's east 

Cascades and forestry on the Yakima Indian Nation, Washington. In: Bradford, P.; 

Manning, T.; I'Anson, B., editors. Wildlife tree/stand-level biodiversity workshop 

proceedings; 1995 Oct 17-18, Victoria, BC. Victoria, BC: British Columbia Ministries 

of Environment and Forests; 77-86. 

Binkley, Clark S. 1997. Preserving nature through intensive plantation management: the 

case for forestland allocation with illustrations from British Columbia. Forestry

Chronicle 73: 553-559. 

Bryant, Andrew A. 1997. Effect of alternative silvicultural practices on breeding bird 

communities in montane forests. Nanaimo, BC: MacMillan Bloedel Ltd.; 16 p. 

Bull, Evelyn L. 1980. Resource partitioning among woodpeckers in northeastern Oregon.

Moscow, ID: University of Idaho; 109 p. Ph.D. dissertation. 

Bunnell, Fred L.; Houde, Isabelle; Johnston, Barb; Wind, Elke. 2002. How dead trees 

sustain live organisms in western forests. In: Laudenslayer, William F., Jr.; Shea, 

Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

748 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Bunnell, Fredrick ; Huggard, David J. 1999. Biodiversity across spatial and temporal 

scales: problems and opportunities. Forest Ecology and Management 115(2/3): 113-

126. 

Bunnell, Fredrick L.; Kremsater, Laurie L.; Wells, Ralph W. 1997. Likely consequences of 

forest management on terrestrial, forest-dwelling vertebrates in Oregon. Portland, 

OR: Oregon Forest Resources Institute; 130 p. 

Bunnell, Fredrick L.; Kremsater, Laurie L.; Wind, Elke 1999. Managing to sustain 

vertebrate diversity in forests of the Pacific Northwest: relationships within stands.

Environmental Reviews 7: 97-146. 

Campbell, R. Wayne ; Dawe, Neil K.; McTaggart-Cowan, Ian; Cooper, John M.; Kaiser, Gary 

W.; McNall, Michael C.E. 1990. The birds of British Columbia. Vol. 2. Diurnal birds 

of prey through woodpeckers. Vancouver, BC: University of British Columbia Press; 

514 p. 

Campbell, R. Wayne ; Dawe, Neil K.; McTaggart-Cowan, Ian; Cooper, John M.; Kaiser, Gary 

W.; McNall, Michael C.E. 1997. The birds of British Columbia. Vol. 3. Passerines: 

flycatchers through vireos. Vancouver, BC: University of British Columbia Press; 693 

p. 

Cannings, R.A.; Harcombe, A.P. 1990. The vertebrates of British Columbia. Scientific and 

English names. Victoria, BC: Heritage Record No. 20, Royal British Columbia 

Museum; 110 p. 

Carey, Andrew B.; Johnson, Murray L. 1995. Small mammals in managed, naturally 

young, and old-growth forests. Ecological Applications 5: 336-352. 

Carey, Andrew B.; Hardt, M.M.; Horton, Scott P.; Biswell, Brian P. 1991. Spring bird 

communities in the Oregon Coast Range. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. 

B.; Huff, M. F., editors. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. 

Tech. Rep. PNW-GTR-285. Portland, OR: Pacific Northwest Research Station, Forest 

Service, U.S. Department of Agriculture; 123-144. 

Coates, K. David 1997. Windthrow damage 2 years after partial cutting at the Date 

Creek silvicultural systems study in the interior cedar-hemlock forests of 

northwestern British Columbia. Canadian Journal of Forest Research 27: 1695-1701. 

Corn, P. Stephen ; Bury, R. Bruce 1991. Terrestrial amphibians in the Oregon Coast 

Range. In: Ruggiero, L. F.; Aubry, K. B.; Carey, A. B.; Huff, M. F., editors. Wildlife 

and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 305-317. 

Craig, Vanessa J. 1995. Relationships between shrews (Sorex spp.) and downed wood in 

the Vancouver watersheds, BC. Vancouver, BC: University of British Columbia; 88 p. 

M.Sc. thesis. 

Crittenden, M. 1992. Trees of the west. Hancock House Publishers. Surrey, BC; 220 p. 

Cunningham, James B.; Balda, Russell P.; Gaud, William S. 1980. Selection and use of 

snags by secondary and cavity-nesting birds of the ponderosa pine forest. Res. 

Paper RM-RP-222. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, 

U.S. Department of Agriculture; 15 p. 

Dickson, James G.; Conner, Richard N.; and Williamson, J. Howard. 1983. Snag retention 

increases bird use of a clear cut. Journal of Wildlife Management 47: 799-804. 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 749 

Franklin, Jerry F.; Berg, D.R.; Thornburgh, D.A.; Tappeiner, J.C. 1997. Alternative 

silvicultural approaches to timber harvesting: variable retention harvest systems.

In: Kohm, K.A.; Franklin, J.F., editors. Creating a forestry for the 21st Century: the 

science of ecosystem management. Washington, DC: Island Press; 111-139. 

Gyug, Les W. 1993. Furbearer and prey use of logging debris piles in clearcuts: progress 

report 1992/93. Unpublished report. Victoria, BC: British Columbia Ministry of 

Environment, Lands and Parks; 25 p. 

Gyug, Les W. 1994. Wildlife use of logging debris piles in clearcuts. Unpublished report. 

Victoria, BC: British Columbia Ministry of Environment, Lands and Parks; 25 p. 

Gyug, Les W.; Bennett, Stephen P. 1996. Bird use of wildlife tree patches 25 years after 

clearcutting. In: Bradford, P.; Manning, T.; I'Anson, B., editors. Wildlife tree/standlevel biodiversity workshop proceedings; 1995 Oct. 17-18; Victoria, BC. Victoria, BC: 

British Columbia Ministries of Environment and Forests; 15-33. 

Harley, John L. 1969. The biology of mycorrhizae. Second Edition. London, UK: Leonard 

Hill; 334 p. 

Huggard, David. 1997. Fall-down rates of subalpine fir snags at Sicamous Creek: 

implications for worker safety and habitat supply. Extension Note 16. Victoria, BC: 

British Columbia Ministry of Forests Research Program; 6 p. 

Jones, Laurence C.; Raphael, Martin G. 1995. Natural history and habitat use by American 

martens in a central Oregon lodgepole pine system. 1995 annual report: ecology, 

management, and conservation of sensitive wildlife species. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 65-70 p. 

Khanna, Kuldip R. 1964. Differential evolutionary activity in bryophytes. Evolution 18: 

652-670. 

Klenner, Walter ; Huggard, David J. 1997. Three-toed woodpecker nesting and foraging at 

Sicamous Creek. In: Hollstedt, C.; Vyse, A., editors. Sicamous Creek silvicultural 

systems project: workshop proceedings; 1996 April 24-25; Kamloops, BC. Working 

Paper 24/1997.Victoria, BC: Research Branch, British Columbia Ministry of Forests; 

224-233. 

Klenner, Walter ; Huggard, David J. 1998. Nesting and foraging habitat requirements of 

woodpeckers in relation to experimental harvesting treatments at Opax Mountain.

In: Hollstedt, C.; Vyse, A.; Huggard, D., editors. Managing the dry Douglas-fir forests 

of the southern interior: workshop proceedings; 1997 April 29-30; Kamloops, BC. 

Working paper 34/1998. Victoria, BC: Research Branch, British Columbia Ministry of 

Forests; 277-291. 

Lisgo, Kimberly A. 1999. Ecology of the short-tailed weasel (Mustela erminea) in the 

mixedwood boreal forest of Alberta. Vancouver, BC: University of British Columbia; 

65 p. M.Sc. thesis. 

Lisgo, Kimberly A. 2002. Summer and fall use of logging residue piles by female shorttailed weasels. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; 

Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. Proceedings of the 

symposium on the ecology and management of dead wood in western forests. 1999 

November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; [this 

volume]. 

Lofroth, Eric. C. 1993. Scale dependent analyses of habitat selection by marten in the

sub-boreal spruce biogeoclimatic zone, British Columbia. Burnaby, BC: Simon 

Fraser University; 109 p. M.Sc. thesis. 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

750 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Lundquist, Richard W.; Mariani, Jina M. 1991. Nesting habitat and abundance of snagdependent birds in the southern Washington Cascade Range. In: Ruggiero, L.F.; 

Aubry, K. B.; Carey, A. B.; Huff, M. F. Wildlife and vegetation of unmanaged Douglasfir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: Pacific Northwest Research 

Station, Forest Service, U.S. Department of Agriculture; 221-240. 

Mahon, Todd E. 1998. Response of small mammal populations to partial cuts and 

clearcuts in west-central British Columbia. Burnaby, BC: Simon Fraser University, 

87 p. M.Sc. thesis. 

Mannan, R. W. 1977. Use of snags by birds, Douglas-fir region, western Oregon. 

Corvallis, OR: Oregon State University; 123 p. M.Sc. thesis. 

Mannan, R. W.; Meslow, E. Charles. 1984. Bird populations and vegetation characteristics 

in managed and old-growth forests, northeastern Oregon. Journal of Wildlife 

Management 48: 1219-1238. 

Manuwal, David A.; Zarnowitz, Jill. 1981. Cavity nesting birds of the Olympic National 

Forest, Washington. Seattle, WA: Wildlife Science Group, College of Forest 

Resources, University of Washington; 144 p. 

Marks, Geoffrey C.; Kozlowski, Theodore T., editors. 1973. Ectomycorrhizae – their 

ecology and physiology. New York: Academic Press; 444 p. 

Maser, Chris ; Trappe, J. M.; Ure, D. C. 1978. Implications of small mammal mycophagy 

to the management of western coniferous forests. Transactions North American 

Wildlife and Natural Resource Conference 43: 78-88. 

Merkens, Markus; Darling, Laura; Booth, Barry. 1996. Use and availability of wildlife trees 

in aspen stands of northeastern BC. In: Bradford, P.; Manning, T.; I'Anson, B., 

editors. Wildlife tree/stand-level biodiversity workshop proceedings; 1995 Oct 17-18, 

Victoria, BC. Victoria, BC: British Columbia Ministry of Environment, Lands, and 

Parks, and Ministry of Forests; 35-44. 

Morgan, Kenneth H.; Wetmore, Stephen P.; Smith, G. E. J.; Keller, R. A. 1989.

Relationships between logging methods, habitat structure and bird communities of 

dry interior Douglas-fir, ponderosa pine forests of British Columbia. Technical 

Report Series No. 71. Delta, BC: Pacific and Yukon Region, Canadian Wildlife Service; 

48 p. 

Morris, Douglas W. 1984. Patterns and scale of habitat use in two temperate-zone small 

mammal faunas. Canadian Journal of Zoology 62: 1540-1547. 

Morrison, Michael L.; Timossi, Irene C.; With, Kimberly A. 1987. Development and testing 

of linear regression models predicting bird-habitat relationships. Journal of Wildlife 

Management 51: 247-253. 

Nussbaum, R. A.; Brodie, E. D. Jr.; Storm, R. M. 1983. Amphibians and reptiles of the 

Pacific Northwest. Moscow, ID: University Press of Idaho; 332 p. 

Nelson, S. Kim 1988. Habitat use and densities of cavity-nesting birds in the Oregon 

coast ranges. Corvallis, OR: Oregon State University; 157 p. M.Sc. thesis. 

Newton, Ian. 1994. The role of nest sites in limiting the numbers of hole-nesting birds.

Biological Conservation 70: 265-276. 

Petit, Daniel R. Petit; Kenneth E.; Grubb, Thomas C., Jr.; Reichhardt, Lisa J. 1985. Habitat 

and snag selection by woodpeckers in a clear-cut: an analysis using artificial snags.

Wilson Bulletin 97: 525-533. 

Peterson, R. T.; Mountford, G.; Hollom, P. A. D. 1993. The Audubon Society field guide to 

birds of Britain and Europe. Boston, MA; 261 p. 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 751 

Raphael, Martin G.; Jones, L. L. C. 1997. Characteristics of resting and denning sites of 

American martens in central Oregon and western Washington. In: Proulx, G.; 

Bryant, H.N.; Woodward, P.M., editors. Martes: taxonomy, ecology, techniques and 

management. Edmonton, AB: Provincial Museum of Alberta; 146-165. 

Raphael, Martin G.; White, Marshall 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada. Wildlife Monographs 86: 1-66. 

Samuelsson, J.; Gustafson, L.; Ingelog, T. 1994. Dying and dead trees: a review of their

importance for biodiversity. Uppsala, Sweden: Swedish Threatened Species Unit; 110 

p. 

Schreiber, B.; deCalesta, D. S. 1992. The relationship between cavity-nesting birds and 

snags on clearcuts in western Oregon. Forest Ecology and Management 50: 299-316. 

Scott, Virgil E. 1979. Bird responses to snag removal in ponderosa pine. Journal of 

Forestry 77: 26-28. 

Scott, Virgil E.; Oldemeyer, John L. 1983. Cavity-nesting bird requirements and response 

to snag cutting in ponderosa pine. In: Davis, J. W.; Goodwin, G. A.; Ockentels, R. A., 

editors. Snag habitat management: proceedings of the symposium; 1983 June 7-9; 

Flagstaff, AZ. Gen. Tech. Rep. RM-99. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture; 19-23. 

Sharp, Aaron J. 1939. Taxonomic and ecological studies of eastern Tennessee bryophytes. 

American Midland Naturalist 21: 267-234. 

Söderström, Lars 1987. Dispersal as a limiting factor for distribution among epixylic 

bryophytes. In: Pócs, T.; Simon, T.; Tuba, Z.; Podani, J., editors. Proceedings of the 

IAB Conference of Bryoecology; 1985 August 5-10; Akadémiai Kiadó, Budapest, 

Hungary. Symposia Biologica Hungarica 35: 475-484. 

Söderström, Lars 1988. The occurrence of epixylic bryophyte and lichen species in an old 

natural and a managed forest stand in northeast Sweden. Biological Conservation 

45: 169-178. 

Spies, Thomas A.; Franklin, Jerry F.; Thomas, Ted B. 1988. Coarse woody debris in 

Douglas-fir forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Steeger, Christof ; Hitchcock, Christine L. 1998. Influence of forest structure and diseases 

on nesting habitat selection by red-breasted nuthatches. Journal of Wildlife 

Management 62: 1349-1358. 

Steeger, Christof ; Quesnel, Harold 1998. Impacts of partial cutting on old-growth forests 

in the Rocky Mountain trench: interim report. Enhanced Forest Management Pilot 

Project, Report No. 9. Invermere, BC: Invermere Forest District; 9 p. 

Steventon, J. Doug ; MacKenzie, K. L.; Mahon, Todd E. 1998. Response of small mammals 

and birds to partial cutting and clearcutting in northwest British Columbia. 

Forestry Chronicle 74: 703-713. 

Swallow, Stephen K.; Gutiérrez, R. J.; Howard, Ronald A., Jr. 1986. Primary cavity-site 

selection by birds. Journal of Wildlife Management 50: 576-583. 

Thompson, R. L. 1996. Home range and habitat use of western red-backed voles in 

mature coniferous forests in the Oregon Cascades. Corvallis, OR: Oregon State 

University; 88 p. M.Sc. thesis. 

Tobalske, Bret W.; Shearer, Raymond C.; Hutto, Richard L. 1991. Bird populations in 

logged and unlogged western larch/Douglas-fir forest in northwestern Montana.

Res. Pap. INT-RP-442. Logan, UT: Interior Research Station, Forest Service, U.S. 

Department of Agriculture; 12 p. 
How Should We Distribute Dead Wood?—Bunnell, Boyland, and Wind 

752 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Vega, Robyn M. S. 1993. Bird communities in managed conifer stands in the Oregon 

Cascades: habitat associations and nest predation. Corvallis, OR: Oregon State 

University; 78 p. M.Sc. thesis. 

Vyse, Alan 1999. Is everything all right up there? A long term interdisciplinary 

silvicultural systems project in a high elevation fir-spruce forest at Sicamous Creek 

B.C. Forestry Chronicle 75: 467-472. 

Walankiewicz, Wieslaw 1991. Do secondary cavity-nesting birds suffer more from 

competition for cavities or from predation in a primeval deciduous forest. Natural 

Areas Journal 11: 203-212. 

Waterhouse, Michaela J.; Dawson, Richard 1999. Bird communities in Interior Douglas-fir 

forests. In: Hollstedt, C.; Vyse, A.; Huggard, D., editors. Managing the dry Douglas-fir 

forests of the southern interior: workshop proceedings; 1997 April 29-30; Kamloops, 

BC. Working paper 34/1998. Victoria, BC: Research Branch, British Columbia Ministry 

of Forests; 90-112. 

Welsh, Christopher J. E.; Capen, David E. 1992. Availability of nesting sites as a limit to 

woodpecker populations. Forest Ecology and Management 48: 31-41. 

Whitaker, J. O. 1993. The Audubon Society field guide to North American mammals.

Toronto, ON: Random House; 745 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 753 

Evaluating the Effects of Partial Cutting on 

Wildlife Trees and Coarse Woody Debris1

Susan K. Stevenson2 and Dagmar G. Keisker3

Abstract 

In the wet forests of interior British Columbia, Canada, partial cutting can be used to produce 

stands that resemble natural uneven-aged forests. We have begun a long-term study of the 

effects of several partial cutting prescriptions on structural attributes and ecosystem processes 

in these forests. We employ a new classification of functional types of wildlife trees and 

coarse woody debris. A “Type” is a configuration of habitat features required by one or more 

wildlife species for specific functions. We present preliminary data on the occurrence of 

Wildlife Tree and Coarse Woody Debris Types before and after partial cutting in a fir-spruce 

stand. 

Introduction 

The existence of a major conference devoted to the ecology and management of 

dead wood indicates a recognition of the ecological importance of dead wood, and a 

desire to maintain in managed stands the functional processes that it supports. This is 

part of a larger recognition that the structures and processes that occur naturally are 

important to maintaining the biodiversity and productivity of forests, and furthermore 

that those structures and processes will not necessarily survive in managed stands 

unless special efforts are made to maintain them. 

Using selection silvicultural systems in forests that are naturally uneven-aged is 

one approach to maintaining natural structures and processes in managed stands. The 

interior wetbelt of British Columbia, Canada, is an area of high precipitation and low 

fire frequency located on the windward side of the Rocky Mountains. It is dominated 

by western red cedar (Thuja plicata Donn) and western hemlock (Tsuga heterophylla

[Raf.] Sarg.) at low elevations and Engelmann spruce (Picea engelmannii Parry) and 

subalpine fir (Abies lasiocarpa [Hook.] Nutt.) at higher elevations. Many stands are 

naturally uneven-aged. In the interior wetbelt there is increasing interest in selection 

silvicultural systems both for ecological reasons and to meet specific management 

objectives, such as conserving habitat for mountain caribou (Rangifer tarandus 

caribou Gmelin) or protecting scenic quality. 

A research group at the University of Northern British Columbia has begun a 

long-term replicated study of the effects of several partial cutting systems on a 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Silvifauna Research, 101 Burden St., Prince George, BC, V2M 2G8, Canada (sksteven@pgweb.com) 3

 691 Front St., Quesnel, BC, V2J 2K9, Canada. 
Effects of Partial Cutting—Stevenson and Keisker 

754 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

variety of structural attributes and ecosystem processes, including the loss and 

creation of wildlife trees and coarse woody debris (Jull and others 2001). That 

component of our study focuses on comparing the occurrence of damage agents and 

of structural attributes that are important to wildlife in undisturbed and post-harvest 

stands. We employ a new classification of functional types of wildlife trees and 

coarse woody debris. Our objectives in this paper are to describe the new 

classification system of wildlife habitat features associated with standing and fallen 

trees, and to present preliminary results of a pilot project that evaluates the short-term 

effects of partial cutting on those habitat features. 

Background 

In recent years, increased scientific understanding of the ecology of natural 

disturbances has led to a paradigm shift in forest management (Rogers 1996). Forest 

managers have often viewed disturbances negatively and tried to suppress them. 

Many of those attempts, such as fire suppression and insecticide application, have 

had unanticipated negative consequences of their own (Rogers 1996). The 

disturbances themselves have been shown to have a key role in supporting the 

ecosystem processes essential to forest productivity and biodiversity. Increasingly, 

managers have come to view disturbances as natural processes that must be 

maintained if we wish to maintain ecological integrity. 

Furthermore, many scientists and managers today see natural disturbance 

regimes not only as natural processes of value, but as models for forest management 

regimes. British Columbia’s Biodiversity Guidebook states as its first principle, “The 

more that managed forests resemble the forests that were established from natural 

disturbances, the greater the probability that all native species and ecological 

processes will be maintained” (Ministry of Forests and British Columbia 

Environment 1995). 

In the interior wetbelt of central British Columbia, stand-initiating fires occur 

infrequently. The common means of natural forest regeneration are small 

disturbances in which one or a few trees are killed by insects, disease, or windthrow. 

The resulting canopy gaps, standing dead trees, and coarse woody debris have a 

pervasive influence on the ecology of wet forests, including tree recruitment, 

understory vegetation dynamics, wildlife habitat, stream structure and dynamics, 

biomass dynamics, and carbon budgets (Lertzman and others 1996). Whereas 

clearcut silvicultural systems can mimic the effects of stand-destroying fires, partialcut silvicultural systems are better suited to maintain the uneven age- and size-class 

distributions and the structural attributes that result from a natural disturbance regime 

dominated by small-scale mortality events. 

However, selection harvested stands differ from natural stands in several 

important ways, some of which may affect the stands’ ability to provide important 

structures and processes. Felled trees are removed from the block rather than 

remaining on the forest floor. For economic reasons, it is often necessary to remove 

more trees in a single entry than would die naturally at any one time. Trees that could 

be dangerous to forest workers must be felled, even if they are unmerchantable. Over 

time, there is likely to be an increase in the amount of young wood and a decrease in 

the amount of old or dead wood. 
Effects of Partial Cutting—Stevenson and Keisker 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 755 

The landscape pattern that results from logging may be conceptualized as a 

secondary mosaic of disturbance overlaying nature’s disturbance patterns (Ripple and 

others 1991). Regardless of whether or not the human-caused disturbance pattern 

resembles the natural disturbance pattern, the natural agents of disturbance continue 

to operate. However, the frequency, severity, and character of those natural 

disturbances may be affected by forest harvesting. 

Although disturbance ecology is currently an active area of research, we are 

aware of little work on the effects of harvesting on natural disturbance agents in the 

residual stands after partial cutting. Relationships have been documented between 

silvicultural systems and the occurrence of specific disturbance agents, such as 

western spruce budworm (Carlson and Schmidt 1989), windthrow (Coates 1997), and 

decay organisms and insects (Nevill and Whitehead 1996). But there seems to be 

little information on how the overall assemblage of disturbance agents is affected by 

partial cutting. 

In the interior wetbelt of central British Columbia, trees that have been damaged 

by disturbance agents provide a rich variety of habitats for the 61 vertebrate species 

that are obligate or frequent users of wildlife trees, and the 51 vertebrate species that 

are obligate or frequent users of coarse woody debris (Keisker 2000). The habitat 

values of these trees and logs are linked to the damage agents that have affected 

them. If different silvicultural systems result in different levels of occurrence of 

various damage agents, they may also result, over time, in different levels of 

occurrence of the wildlife habitat attributes associated with damaged or dead trees. 

One of the objectives of the research of Jull and others (2001) is to find out how 

various partial-cutting prescriptions affect the assemblage of disturbance agents and 

the occurrence of standing trees and coarse woody debris with wildlife habitat 

attributes. 

Study Area 

The study area for the pilot project is located at Pinkerton Mountain, about 90 

km east-southeast of Prince George, British Columbia, Canada, in the Engelmann 

Spruce-Subalpine Fir zone (Meidinger and Pojar 1991). The mesic to subhygric site 

is on a southwest-facing slope at 1,350-1,470 m a.s.l. Pre-harvest basal area was 

approximately 35 m2

/ha, composed of 78 percent subalpine fir and 22 percent 

Engelmann spruce. 

Harvesting Methods 

The study area comprises a 40-ha single tree selection unit, a 59-ha group 

selection unit, and a 25-ha unharvested control area. The target level of volume 

removal in both units was 30 percent. In the group selection unit, the trees were 

removed in openings that ranged from 0.1 to 0.4 ha. In the single tree selection unit, 

trees to be cut were marked to leave a target diameter distribution with relatively high 

retention of large trees. The block was logged in early 1998 on a late winter 

snowpack by mechanized harvesting machines. The harvesting was described in 

more detail by Stevenson and others (1999). 
Effects of Partial Cutting—Stevenson and Keisker 

756 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Study Methods 

Sampling was based in and around 14 systematically located permanent sample 

plots, 7 in each of the 2 treatment areas. At each location, a 0.05-ha plot was nested 

inside a 0.10-ha plot. In the inner plot, all standing trees > 10 cm dbh were assessed, 

and in the outer plot all trees > 25 cm were assessed. In addition to standard 

mensurational data, we recorded damage agents, evidence of wildlife use, and 

Wildlife Tree Types and two Coarse Woody Debris Types for each sample tree. 

Coarse woody debris was tallied along at least two 24-m transects associated 

with each permanent sample plot. For each piece, we recorded various standard data 

(Ministry of Forests 1997) and Coarse Woody Debris Types. 

Trees and coarse woody debris were assessed in summer 1997 and again in 

summer 1998, after logging was completed. Some trees that were standing after the 

harvest were potentially dangerous to workers and should have been removed 

according to the safety regulations of the Workers’ Compensation Board (WCB) of 

British Columbia (Stone and others 2001). To ensure that the data represented 

realistic conditions, such trees were omitted from the analysis. 

Because of unequal sample sizes between treatment units and before and after 

logging, results are shown as percentages of the number of sample trees or logs in 

each treatment unit exhibiting a given attribute. The log-likelihood ratio G (Sokal and 

Rohlf 1995) was used as a test statistic to compare the frequency distributions of the 

number of Types associated with each sample tree or log in the two treatment units. 

Assessments carried out in the control area are not reported here. 

Wildlife Tree and Coarse Woody Debris Types 

Our classification system of habitat features associated with wildlife trees and 

coarse woody debris is based on the concept of the “Type”—a configuration of 

habitat features that appears to be required by one or more wildlife species for 

specific functions (Keisker 2000). The classification developed from a project in 

which available information on wildlife habitat requirements involving wildlife trees 

and coarse woody debris in the north-central interior of British Columbia was 

reviewed and presented in a summary format that would be useful to managers 

(Keisker 2000). For that purpose, information was condensed by including only those 

habitat features that have functional significance to wildlife and by delineating sets of 

these features, termed “Types,” that serve specific functions for groups of wildlife. 

Ten Wildlife Tree (WT) Types and six Coarse Woody Debris (CWD) Types 

were described by Keisker (2000) and are summarized in tables 1 and 2. The term 

“wildlife tree” refers to a standing dead or live tree with special characteristics that 

are valuable for wildlife and that distinguish it from most other trees in the forest. 

The sets of features that define the Types are often not mutually exclusive. A single 

tree or CWD piece may have 0, 1, or more Types. Although the Types were 

developed for wildlife species and ecosystems occurring in the north-central interior 

of British Columbia, we believe that both the approach and the results have a broader 

geographic applicability. 

CWD Types 1, 2, and 3 may apply to standing trees as well as logs. We included 

CWD-1 and CWD-3 in our assessments of standing trees, but not CWD-2, because it 

applied to almost every tree. 
Effects of Partial Cutting—Stevenson and Keisker 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 757 

Table 1—Types of Wildlife Trees required by wildlife of north-central British Columbia 

(Keisker 2000). 

Main function Type Main users 

Reproduction/resting: 

Substrates for cavity 

excavation 

WT-1 Hard outer wood 

surrounding decaysoftened inner wood 

Woodpeckers (stronger 

excavators) 

 WT-2 Outer and inner wood 

softened by decay 

Woodpeckers (weaker 

excavators), chickadees, 

nuthatches 

Existing cavities WT-3 Small, excavated or 

natural cavities 

Chickadees, nuthatches, 

swallows, bats 

 WT-4 Large, excavated or 

natural cavities 

Ducks, owls, bluebirds, 

swallows, bats, squirrels, 

mustelids 

 WT-5 Very large natural 

cavities or hollow 

trees 

Swifts, owls, bats, mustelids 

 WT-6 Cracks, loose bark, or 

deeply furrowed bark 

Creepers, bats 

Large open-nest supports 

and other non-cavity 

sites 

WT-7 Witches’ brooms Diurnal raptors, owls, 

squirrels, mustelids 

WT-8 Large branches, 

multiple leaders, or 

large-diameter broken 

tops 

Herons, diurnal raptors, owls 

Foraging: 

Feeding substrates WT-9 Arthropods in wood 

or under bark 

Woodpeckers 

Hunting perches WT-10 Open-structured trees 

in or adjacent to open 

areas 

Diurnal raptors, owls 

Table 2—Types of coarse woody debris (CWD) required by wildlife of north-central British 

Columbia (Keisker 2000). 

Main function Type Main users 

Reproduction/resting

/escape: 

 

Concealed spaces CWD-1 Large concealed spaces Grouse, hare, woodrat, 

porcupine, fox, cats, some 

mustelids, bears 

 CWD-2 Small concealed spaces 

(or soft substrate 

allowing excavation of 

such spaces) at or 

below ground-level 

beneath hard material 

Salamander, toad, treefrog, 

snakes, wrens, shrews, voles, 

deer mouse, golden-mantled 

ground squirrel, chipmunk, 

jumping mice, weasels 
Effects of Partial Cutting—Stevenson and Keisker 

758 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

 CWD-3 Small concealed spaces 

above ground-level 

Treefrog, Yellow-bellied 

Flycatcher, wrens, 

Townsend’s Solitaire, some 

wood warblers, some 

sparrows 

Travel: 

Concealed runways CWD-4 Long concealed spaces 

(or soft substrate 

allowing construction 

of runways) 

Salamander, some snakes, 

wrens, shrews, voles, deer 

mouse, weasels 

Exposed, raised travel 

lanes 

CWD-5 Large or elevated, long 

material clear of dense 

vegetation 

Tree squirrels, chipmunk 

Foraging: 

Feeding substrates CWD-6 Invertebrates in wood, 

under bark or mosscover, or in 

litter/humus 

accumulated around 

CWD 

Salamander, treefrog, 

woodpeckers, wrens, some 

sparrows, shrews, deer 

mouse, skunk, bears 

Results and Discussion 

Two of our main interests in this pilot project were to learn about the frequency 

of occurrence of the various WT and CWD Types in a high-elevation fir-spruce 

stand, and to obtain a preliminary indication of the different effects of group and 

single tree selection. We expected that the two different partial cutting prescriptions 

would have different effects on the occurrence of WT Types, but not necessarily 

CWD Types. According to worker safety regulations, if work in a forestry operation 

will expose a worker to a dangerous tree, that tree must be removed (Stone and others 

2002). Harvesting is dispersed throughout a single tree selection unit, and many of 

the danger trees are potentially subject to removal. In a group selection unit, work 

activity is more concentrated, and more of the danger trees are likely to be located 

away from work areas. Because wildlife tree attributes are often associated with 

damage or decay that could make a tree dangerous, we expected that fewer trees with 

WT Types would be retained in the single tree selection unit than the group selection 

unit. 

Most WT Types were uncommon in the study area before harvesting, occurring 

with a frequency of less than 5 percent (fig. 1). Fifteen to 20 percent of the sample 

trees had large concealed spaces at or below ground-level (CWD-1), possibly 

because they had originated on nurse logs which had subsequently rotted away. 

Loose bark or wide cracks (WT-6) were also common (15-20 percent). Hunting 

perches (WT-10) were moderately common (5-10 percent) in this high-elevation 

stand, which had many natural gaps. WT-10 was recorded more often in the unit 

assigned to group selection than the unit assigned to single tree selection (G = 

11.114; df = 1; p = 0.001), although refinements to the identification criteria for that 

Type that were made during sampling may have contributed to the difference. No 

other differences were found between the pre-harvest occurrence of the other Types 

in the two treatment units. 

Because the planned level of volume removal was 30 percent throughout the 

harvest block, we expected that the proportion of sample trees remaining after 

harvesting would be similar in the two treatment units. In fact, however, harvested 
Effects of Partial Cutting—Stevenson and Keisker 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 759 

areas were overrepresented in the group selection sample plots. Of those seven plots, 

one was completely logged, one was completely unlogged, and five were partly 

logged, but only 42 percent of the original sample trees were still present. In the 

single tree selection unit, some trees had been felled in all the plots except one, which 

was located on a short, steep slope; and 67 percent of the sample trees remained after 

logging. Because of the difficulty of obtaining adequate representation of harvested 

and unharvested areas in non-uniform treatment units, we will use a stratified 

sampling scheme in future studies. 

Figure 1—Occurrence of 10 WT and 2 CWD Types associated with standing trees 

before and after group selection and single tree selection logging at Pinkerton 

Mountain, British Columbia. 

Our primary interest was not in the number of trees that remained after logging, 

but in the habitat attributes of those trees. The proportion of sample trees with Types 

did not change as much after harvesting as we had expected, nor was there a 

pronounced difference between the two treatment units. The most conspicuous 

reduction was in the occurrence of WT-6. In our study area, loose bark or wide 

cracks were usually associated with hard subalpine fir snags that had been dead for 

some time (Stage 4 of Thomas 1979). These trees were commonly dangerous and 

often had their full height, which made them more likely than shorter trees to affect 
Effects of Partial Cutting—Stevenson and Keisker 

760 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

work areas. Aside from WT-6, occurrence of Types was similar or only slightly 

reduced after harvesting. 

The results shown in figure 1 are inconvenient for statistical analysis because the 

number of observations in some categories is very small, the categories are not 

ordered, and it is not reasonable in most cases to increase the number of observations 

by grouping categories. We used the number of Types associated with each sample 

tree as a single variable to characterize the habitat value of that tree, and the 

frequency distribution of the number of Types to characterize the stand. Before the 

harvest, 35.8 percent of the 776 sample trees in the 14 plots exhibited one or more 

Types, and the frequency distributions of number of Types in the two treatment units 

did not differ (G = 3.995; df = 4; p = 0.407). After harvesting, 30.6 percent of the 409 

remaining sample trees had one or more Types, and the frequency distributions were 

still not significantly different (fig. 2; G = 5.900; df = 4; p = 0.207). 

Figure 2—Frequency distribution of the number of WT and CWD Types associated 

with standing trees after group selection (GS) and single tree selection (STS) at 

Pinkerton Mountain, British Columbia. 

The relatively high retention of trees with Types after partial cutting and the 

small differences between the group selection and single tree selection units were 

unexpected. We found that some Types occurred in trees that were not dangerous to 

workers, either because the attribute was not associated with any structural defects 

that made the tree hazardous, because the tree was short enough that it would not 

affect any work areas, or because a tree that was otherwise hazardous was buffered 

from work areas by healthy green trees that would break its fall. Also, we found that 

even in the single tree selection unit, there were areas where no logging took place, 

either because they could not easily be accessed or because initial basal area was low 

and no trees had been marked for cutting. 

Unlike WT Types, CWD Types are very common. Ninety percent of the 397 

pieces that were tallied in pre-harvest plots had one or more CWD Types. CWD 

Types 1, 2, and 4 were the most common, occurring consistently in more than 20 
Effects of Partial Cutting—Stevenson and Keisker 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 761 

percent of the sample pieces. Occurrence of the various Types was similar before and 

after harvest in both treatment units, except for an apparent increase in CWD-1—

large concealed spaces—after harvesting in both units. There may have been more 

spaces around and under logs where logging residue had been piled. 

Because CWD Types are common, the frequency distribution of number of 

CWD Types (fig. 3) has a different shape from that of the WT Types (fig. 2). 

Frequency distributions of CWD Types did not differ between treatment units either 

before harvesting (G = 7.358; df = 5; p = 0.195) or after harvesting (G = 3.079; df = 

5; p = 0.688). 

Figure 3—Frequency distribution of the number of CWD Types associated with down 

logs after group selection (GS) and single tree selection (STS) at Pinkerton Mountain, 

British Columbia. 

The results of this pilot project have limitations that restrict their generality: only 

one site was studied, sample sizes were small, and the treatments were not randomly 

assigned. The results described here should not be extrapolated to other sites. 

However, the approach has broad applicability when used in a larger, replicated 

experimental design. 

Conclusion 

The preliminary results of this pilot project suggest that, at least in some cases, 

selection harvesting may have little impact on the percentage occurrence of the 

attributes of standing trees and coarse woody debris that are most important to 

wildlife. However, it would be premature to base any conclusions on an unreplicated 

study in which sample sizes were small and methodological problems were still being 

resolved. 

The classification system of WT and CWD Types described here appears to be a 

useful tool with which to evaluate the effects of various silvicultural systems in both 

the short-term and the long-term. We would expect that with larger sample sizes we 
Effects of Partial Cutting—Stevenson and Keisker 

762 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

might find that some Types, such as WT-6, are more likely than others to be 

substantially reduced by partial cutting. Different methods of partial cutting, such as 

helicopter logging, cable logging, and hand-felling, may affect the occurrence of WT 

and CWD Types differently. We would also expect that the patterns of occurrence of 

the various Types will vary with the age and species composition of forest stands. 

Eventually, the results of these studies should help managers to plan how to maintain 

the full array of structural attributes that are critical to wildlife. 

Acknowledgments 

The silvicultural systems research project described here is funded by the Forest 

Renewal Plan of British Columbia. The Canada-British Columbia Partnership 

Agreement on Forest Resource Development, British Columbia Ministry of 

Environment, Lands and Parks and British Columbia Ministry of Forests supported 

the development of the Type classification system. We thank Mike Jull, Ken Parker, 

David Stevenson, and an anonymous reviewer for their comments on the manuscript. 

References 

Carlson, C. E.; Schmidt, W. C. 1989. Influence of overstory removal and western spruce 

budworm defoliation on growth of advance conifer regeneration in Montana. Res. 

Paper. INT-RP-409. Ogden, UT: Intermountain Research Station, Forest Service, U.S. 

Department of Agriculture; 14 p. 

Coates, K. D. 1997. Windthrow damage 2 years after partial cutting at the Date Creek 

silvicultural systems study in the Interior Cedar-Hemlock forests of northwestern 

British Columbia. Canadian Journal of Forest Research 27: 1695-1701. 

Jull, M.; Stevenson, S.; Rogers, B.; Sanborn, P.; Eastham, A. 2001. Northern wetbelt 

silvicultural systems project: a study of alternative silvicultural systems in 

Northern Wetbelt ICH and ESSF forests. Establishment report. Prince George, B.C.: 

University of Northern British Columbia. 

Keisker, D. G. 2000. Types of wildlife trees and coarse woody debris required by wildlife 

of north-central British Columbia. Working Paper 50. Victoria, BC: British Columbia 

Ministry of Forests; 92 p. 

Lertzman, K. P.; Sutherland, G. D.; Inselberg; A.; Saunders, S. C. 1996. Canopy gaps and 

the landscape mosaic in a coastal temperate rain forest. Ecology 77(4): 1254-1270. 

Meidinger, D.; Pojar, J. 1991. Ecosystems of British Columbia. Spec. Rep. Ser. No. 6. 

Victoria, BC: British Columbia Ministry of Forests.; 330 p. 

Ministry of Forests. 1997. Ground sampling procedures. Victoria, BC: British Columbia 

Ministry of Forests Resources Inventory Branch, Ministry of Forests and Resources 

Inventory Committee. 

Ministry of Forests and British Columbia Environment 1995. Biodiversity guidebook—

Forest Practices Code of British Columbia. Victoria, BC: British Columbia Ministry 

of Forests and British Columbia Environment; 68 p. 

Nevill, R. J.; Whitehead, R. J. 1996. Potential loss due to decay and insect attack following 

selective harvest in coastal montane forests. FRDA Rep. 265. Victoria, BC: CanadaBritish Columbia Partnership Agreement on Forest Resource Development II; 11 p. 

Ripple, W. J.; Bradshaw, G. A.; Spies, T. A. 1991. Measuring forest landscape patterns in 

the Cascade Range of Oregon, USA. Biological Conservation 57: 73-88. 
Effects of Partial Cutting—Stevenson and Keisker 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 763 

Rogers, P. 1996. Disturbance ecology and forest management: a review of the literature.

Gen. Tech. Rep. INT-GTR-336. Ogden, UT: Intermountain Research Station, Forest 

Service, U.S. Department of Agriculture; 16 p. 

Sokal, R. R.; Rohlf, J. F. 1995. Biometry. 3rd ed. New York: Freeman and Co.; 887 p. 

Stevenson, S. K.; Jull,, M.; Coxson, D. S. 1999. Selection silvicultural systems in mountain 

caribou habitat: logging and learning at Pinkerton Mountain. Forest Research Note 

#PG-19. Prince George, BC: Prince George Forest Region Forest Resources and 

Practices Team; 8 p. 

Stone, J.; Parminter, J.; Arsenault, A., Densmore, N.; Manning, T.; Davis, G.; MacKinnon A. 

2002. Dead tree management in British Columbia. In: Laudenslayer, William F., Jr.; 

Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., 

technical coordinators. Proceedings of a symposium on the ecology and management of 

dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSWGTR-181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; [this volume]. 

Thomas, J. W. 1979. Wildlife habitats in managed forests: the Blue Mountains of Oregon 

and Washington. Agric. Handb. 553. Washington, DC: Forest Service, U.S. 

Department of Agriculture; 512 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 765 

Created Snag Monitoring on the Willamette 

National Forest1

Pat Boleyn,2 Eric Wold,3 and Ken Byford2

Abstract 

Management agencies currently create snags from live trees and leave them in stands after 

cutting. Little information exists on the use of these snags by wildlife. This study had two 

objectives: to document whether created snags were used by wildlife, and if used, to elucidate 

stand and snag features associated with the use of these created snags by wildlife. We 

documented sign of woodpecker foraging and/or nesting or roosting use, along with snag and 

stand features in 55 systematically selected stands across the Willamette National Forest in 

Oregon. We found that woodpecker use was associated with created snag characteristics. 

Mainly, the status (live or dead) of the created snag was associated with the presence or 

absence of woodpecker foraging excavations. Management considerations are discussed, 

including the need to monitor wildlife use before and after created snags are killed and in 

subsequent years. 

Introduction 

Standing dead trees (snags) are important resources for vertebrate and 

invertebrate species worldwide and to forested ecosystems. They return essential 

nutrients to the soil and increase soil fertility. Throughout North America, over 85 

species of birds use snags for nesting, foraging, or drumming (Raphael and White 

1984, Scott and others 1977). In the Douglas-fir (Pseudotsuga menziesii) and western 

hemlock (Tsuga heterophylla) forests of the Pacific Northwest, over 100 vertebrate 

species utilize snags for some part of their life cycle (Neitro and others 1985, Thomas 

and others 1979). Approximately 20 percent (34 species) of all bird species in the 

Pacific Northwest depend on snags for nesting and feeding (Carey and others 1991, 

Lundquist and Mariani 1991). Furthermore, the abundance of snag-dependent birds 

has been shown to be correlated with the density of suitable snags (Carey 1995, Scott 

1979, Stribling and others 1990, Zarnowitz and Manuwal 1985). Also populations of 

northern flying squirrel (Glaucomys sabrinus), the primary prey item of the 

threatened northern spotted owl (Strix occidentalis caurina) reach their highest 

densities in forests with large snags (Carey 1995). 

Despite current widespread understanding of their importance for wildlife, and 

their prevalence in natural forested systems (Carey and others 1991, Ohmann and 

others 1994, Spies and Franklin 1991, Spies and Thomas 1988, Tyrrell and Crow 

1994a, 1994b), snags have been systematically eliminated from managed landscapes 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Wildlife Biologist and Forest Wildlife Biologist, respectively, Willamette National Forest, 211 E. 7th

Ave., Eugene, OR 97440 (e-mail: pboleyn@fs.fed.us) 

3

 Natural Resources Planner, Planning Department, City of Eugene, 99 West 10th Avenue, Suite 240, 

Eugene, OR 97401. 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

766 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

for several decades (Carey 1995, Zarnowitz and Manuwal 1985), due to concerns 

about the role that snags may have in creating conditions suitable for fires, insect 

outbreaks, and as hazard trees. Within the past 15 years, however, most State and 

Federal and some private land management agencies have devised strategies to 

maintain, and in some cases enhance, snag abundance on their lands (USDA and DOI 

1994). 

Ways to enhance habitat for snag dependent wildlife are being tested by blasting 

or sawing the tops off of living trees; girdling live trees; inoculating live trees with 

fungus; and inducing bark beetle attacks. During the past 15 years, management 

plans on the Willamette National Forest (WNF) in western Oregon have required that 

varying levels of natural and artificially created snags be retained in units that are 

harvested for timber (USDA and DOI 1994). While snags have been artificially 

created by all three methods on the WNF, the vast majority have been artificially 

created by blasting and sawing off tree tops. At this time, however, very little 

information exists on the use of these artificially created snags by wildlife (Chambers 

and others 1997), or on the decay and fall-down rates of artificially created snags. 

To address this lack of information, we began a long-term monitoring project in 

the summer of 1997. The objectives of this project were to establish a stratified 

sample of snags across the Willamette National Forest to be repeatedly sampled over 

time and to elucidate factors that are associated with the use of snags by wildlife 

(primarily bird) species. 

In this report, we provide summary statistics of 1,267 snags (96 percent were 

artificially created, 4 percent natural) that we monitored during 1997 and 1998. In 

addition, we report the results from statistical analyses that addressed the question: 

Was total woodpecker use of created snags associated with structural characteristics 

of the snag and the stand? 

Methods 

Study Area 

The study occurred on the Willamette National Forest (WNF) in Marion, Linn, 

and Lane counties, Oregon in west central Oregon in the Cascade Mountains.

Criteria for Selecting Stands with Created Snags 

We surveyed a sample of stands that was stratified by elevation, year of snag 

creation, and WNF Ranger District. The initial pool of stands subsampled was 

developed using the WNF’s stand treatment database (STD). This database contains 

details on all management activities for each stand on the WNF. We first queried 

STD for all stands containing created snags. Because we intended to collect data on 

every created snag within a stand, we chose stands that contained only as many snags 

as we thought we could survey during one working day (40 or less). We therefore 

shortened the initial list by selecting only those stands that contained from 10-40 

created snags. 

From this shortened list, we stratified the sample by median elevation (915 m), 

median year of snag creation (1993), and seven WNF ranger districts to obtain a 

diversity of tree species, wildlife using the trees, and tree decay levels (obtained from 

sampling trees killed in different years). In one of the WNF’s Ranger Districts 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 767 

(Lowell), there were no stands above 915 m that met our criteria. We used the 

median values as breaking-points and randomly sorted all the stands from the 

shortened list into the appropriate categories, and then randomly selected stands 

within each cell using Microsoft Excel’s random number generator (table 1).4 For 

each of the randomly selected stands, we intended to locate and monitor all of the 

created (but not natural) snags in the stand, but this did not always occur. 

Table 1—The initial sampling regime for the study. For each of the cells shown in this table, 

four stands were randomly selected from the entire list of stands in the WNF’s STD that 

contained from 10-40 created snags. In the Lowell Ranger District, there were no stands 

above 915 m that met these criteria, so two of the cells (denoted by “NA” in the table) in the 

sampling regime were empty. There were a total of 55 stands sampled. These were evenly 

distributed between each of the Ranger Districts, elevations, and age classes. 

 Elevation < 3,000 feet Elevation > 3,000 feet 

Ranger District Snag created 

≤ 1993 

Snag created 

> 1993 

Snag created 

≤ 1993 

Snag created 

> 1993 

Detroit 

Sweet Home 

McKenzie 

Blue River 

Rigdon 

Oakridge 

Lowell N/A N/A 

Logistical Problems Altered the Sampling Design The trees that we selected for snag creation did not represent an unbiased, 

random sample of trees with or without prior wildlife use because of three major 

problems: 

• Problem 1—Inaccessibility: Several of the stands that were selected at 

random were not accessible due to road closures (e.g., from mudslides or 

extensive tree fall-down over roads). When these road closures occurred > 1 

mile from our randomly selected stand, we omitted the stand from the study. 

When this occurred, we substituted the nearest accessible stand in the same 

cell in our sampling design as the omitted stand. 

• Problem 2—Stands without created snags: All of the stands that were 

selected at random were reported, in the stand treatment database (STD) to 

contain between 10-40 created snags. However, when we arrived at several 

of the stands, we were unable to locate any created snags. When this 

occurred, we substituted the nearest accessible stand in the same cell in our 

sampling design (table 1) as the omitted stand. 

• Problem 3—Stands with more than 40 created snags: A third problem we 

encountered was that the actual number of created snags in a stand far 

exceeded the number reported in the STD. When we encountered stands with 

 

4

 Trade names or products are mentioned for information only and do not imply endorsement by the 

U.S. Department of Agriculture. 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

768 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

> 40 created snags, we arbitrarily chose a starting point within the stand 

(usually near the landing) and sampled the first 40 trees that we encountered. 

Finally, in addition to the stands that we selected and surveyed for the first time, 

we also re-surveyed 311 natural and artificially created snags that had been 

monitored in 1995 following a nonrandom selection process (Shope 1995). 

Features of Created Snags That Were Recorded 

We marked each created snag with a unique number on two aluminum tags (to 

facilitate relocating the snag in the future) and recorded its position (latitude, 

longitude, and elevation) with 1-m accuracy using a global positioning system 

(Trimble Pathfinder Pro XL) with differential correction (Trimble Pathfinder Office, 

version 1.1). We also recorded all the features at each created snag (table 2) and a 

stand level variable called “lscape” that we created. 

Table 2—Description of features recorded at each created snag. 

Snag Feature Units Methods 

Species Species code Visual assessment of snag species 

Year killed Year Year snag created. Obtained from Stand Treatment 

Database at the Willamette National Forest 

Supervisors Office, Eugene, Oregon 

DBH Inches Used a diameter tape to measure diameter at breast 

height of snag. 

Height Feet Used a clinometer and rangefinder to measure current 

height of snag. 

Decay class 1, 2, 3 Visual estimation of decay class (Parks and others 

1997). 

Elevation Meters Obtained from GIS coverage listing the mean 

elevation of all harvested stands on the WNF 

Pct bark 0-100 pct Visual assessment 

Status Live or dead Live snag was one with at least one branch with green 

needles 

Dead snag was one with no branches with green 

needles 

# limbs Count Visual assessment of # dead and live limbs > 0.91 m 

long that extend from bole 

# green branches Count Visual assessment of # green limbs. Green limbs are 

limbs that have at least one green leaf. 

Treatment Natural, 

sawed, blasted, 

inoculated, 

girdled, 

unknown, 

other 

Visual assessment 

Damage type Lightning, 

conch, logging, 

insect, list 

others 

Visual assessment for lightning scars, fungal conchs, 

logging damage, insect damage, wind damage, etc. 

Pct damage 0-100 pct Visual assessment of percentage of tree with specific 

damage types. 

Fire scar Yes, No Visual assessment of fire scars. 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 769 

Snag Feature Units Methods 

Pct fire scar 0-100 pct Visual assessment. 

Sapsucker use Yes, No Visual observation of linear rows of small holes in 

trunk or limbs (Bent 1964). 

New pileated 

foraging 

excavations 

Count Count of rectangular-shaped, approximately 5 cm 

deep and lighter in color than the surrounding wood, 

or with fresh wood shavings at the base (Bent 1964). 

Old pileated 

foraging 

excavations 

Count Count of rectangular-shaped, approximately 5 cm 

deep and the same color as the surrounding wood 

(Bent 1964). 

New woodpecker 

foraging 

excavations 

Count Count of foraging excavations that are not rectangular 

in shape, approximately 5 cm deep, lighter in color 

than the surrounding wood, or with fresh wood 

shavings at base, but are not rows of small holes. 

Old woodpecker 

foraging 

excavations 

Count Count of foraging excavations that are not rectangular 

in shape, approximately 5 cm deep, same color as the 

surrounding wood, but are not rows of small holes. 

New nest cavities Count Count of foraging excavations that appear very round 

or elliptical in shape and appear to be hollow in the 

interior. Also, the foraging excavation appears to a 

lighter color than the surrounding wood and/or fresh 

wood shavings at the base. 

Old nest cavities Count Count of foraging excavations that appear very round 

or elliptical in shape and appear to be hollow in the 

interior. Also, the foraging excavation appears to the 

same color as the surrounding wood. 

Other use Yes, No Visual assessment of other wildlife use. For example, 

bear scratches or current use by a chipmunk, squirrel, 

or bird. Record in notes. 

We classified foraging excavations (holes in the bark, not scalings) and 

nest/roost cavities in the created snags as new or old. New foraging excavations and 

cavities were those that were a lighter color than the surrounding wood and/or had 

fresh wood shavings at the base. Old foraging excavations and cavities were the same 

color as the surrounding wood and did not have fresh wood shavings at the base. The 

new foraging excavations were potentially the more reliable observations for 

addressing use of created snags because they were obviously done after the snag was 

created. Although old use may have occurred after snag creation, it may also have 

been present before the snag was created. Hereafter, foraging excavations and nest 

cavities in the created snags will be referred to as new or old. 

Pileated woodpecker (Dryocopus pileatus) foraging excavations were 

distinguished from all other types of foraging excavations by their rectangular shape 

and depth between 3 cm and 1 m deep (Bent 1964). Sapsucker foraging excavations 

were not classified as new or old but were distinguished from all other foraging 

excavations by their unique pattern of deeply cut holes, less than 0.5 cm in diameter 

and usually arranged in horizontal lines around the trunk (Bent 1964). Nest or roost 

cavities were distinguished from foraging excavations by their round or elliptical 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

770 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

shape typical of certain woodpecker species such as pileated woodpecker and 

Northern flicker (Colaptes auratus), which were common in the study area. 

Creation of Landscape Variable 

We used geographic information systems (GIS) to create a stand level variable 

for the regression analyses called “lscape”: the amount of late-successional forest in 

the adjacent landscape (i.e., within 500 m of the stand). Below we briefly outline the 

series of steps taken in GIS to create this variable. 

The “lscape” variable was created by first identifying the predominant size-class 

of the trees within 500 m of each stand of created snags using ARC INFO, GIS 

software. We then calculated the percent of area in each stand’s 500 m buffer that 

consisted of size classes typical of late successional forest on WNF. The size classes 

in the Veg6 GIS data layer that most closely fit this criterion are codes 6.0 through 

7.1, which correspond to large (83-121 cm dbh) and giant (> 121 cm dbh) trees. In 

addition, the Veg6 data layer contains one size-class category (class 5.5) that includes 

both medium (53-82 cm dbh) and large trees. For the purposes of this analysis, we 

class 5.5 to be large trees. 

Analyses 

Descriptive Statistics 

We calculated descriptive statistics using Microsoft Excel. 

Regression Analyses 

We used logistic regression to analyze the relationship of woodpecker use of 

created snags associated with snag and stand characteristics using S-Plus software 

version 4.5 from MathSoft, Inc. The presence or absence of new woodpecker 

foraging excavations on a created snag was the response variable in the models, and 

the variables listed in table 2, along with Universal Transverse Mercators, “lscape,” 

and elevation, were the explanatory variables representing snag and stand 

characteristics. 

The regression models were constructed using two data sets, one with 1,267 

snags (96 percent created snags) excluding the explanatory variable, “snag age” 

(years since tree killed), and another with 1,223 records that included the explanatory 

variable “snag age.” Two data sets were used because snag age was an additional 

characteristic that might have to be associated with bird use. The different sample 

size in each data set was due to some missing data on the year of snag creation for 

certain stands. 

Results, Discussion, and Recommendations 

Descriptive Statistics 

Types of Snags Monitored 

 We monitored 1,267 snags in 55 harvested stands on seven districts of the 

Willamette National Forest over 1997 and 1998. The elevation of the created snags 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 771 

ranged from approximately 333 m to 1,848 m. Approximately 85 percent of the snags 

were artificially created by blasting or saw topping, 11 percent by girdling or 

inoculating, while 4 percent were natural. The blasted and sawtopped snags were all 

over 27 m in height. The blasted snags ranged in dbh from 38 to 191 cm; the saw-top 

snags ranged from 40 to 183 cm dbh; the one girdled tree was 62 cm dbh; and the 

natural snags ranged from 53-172 cm. Eighty-seven percent were Douglas-fir 

(Pseudotsuga menziesii), 38 percent were still partially alive with green branches, 

and 95 percent were in the first two stages of decay (decay classes follow Parks and 

others [1997] in which class 1 represents those trees that died recently and retain 

most of their bark and branches with their top intact; class 2 represents those snags 

that have been dead at least several years and have lost some branches and some 

bark; and class 3 represents those snags dead a long time and lack branches and 

bark). 

We report only new bird use below because we cannot be certain that old bird 

use was not done before the snag was created. 

• Foraging use by sapsuckers and pileated woodpeckers: Only 1.5 percent of 

the snags had new foraging excavations by pileated woodpeckers. Sapsucker 

use was present on 1.5 percent of the snags. 

• Foraging use by other birds: Nearly half of the created snags monitored (49 

percent) had new foraging excavations from other woodpeckers and other 

unidentified excavators. 

• Nest/Roost cavities in created snags: New cavities were present on 1.2 

percent of the snags. Of the 17 snags with new cavities, 2 were naturally 

created; 1 was girdled; 1 was unknown; and the rest were blasted or sawtopped. Also, of these 17, 2 had class 1 decay, 2 were class 3 decayed, and 

the rest were class 2 decay. The majority of these 17 snags had 80 percent of 

their bark remaining with 7 having 60 percent of their bark remaining. 

• Use by species other than birds: Evidence of use by species other than birds 

on the created snags was present on 1.8 percent of the snags. Detecting use 

by other species was difficult since they did not always leave obvious signs. 

However, we did observe an unidentified species of bat leaving one created 

snag and a chipmunk climbing up another. 

There were few created snags in this project with foraging use by pileated 

woodpeckers and sapsuckers. The majority of created snags that we monitored were 

recently killed (within the last 10 years), had little decay, and therefore, may not 

house carpenter ant colonies, one of the major prey items of the pileated woodpecker 

(Bent 1964). The low level of use by these species could also reflect their limited 

abundance in the forests surrounding the harvested stands we surveyed. We did not 

conduct bird abundance studies in the harvested stands that we monitored. 

Nearly half of the created snags had new foraging excavations by woodpeckers 

and other unidentified excavators, indicating that one or more species that occur in 

the elevation range of our project (e.g., hairy woodpecker [Picoides villosus], downy 

woodpecker [Picoides pubescens], or red-breasted nuthatch [Sitta canadensis]) were 

using these snags for foraging. 

There were few created snags in this project with nesting or roosting cavities. 

The majority of created snags that we monitored had little decay and therefore may 

not have been soft enough for cavity foraging excavation by some birds. The low 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

772 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

level of cavities could also reflect the limited abundance of cavity excavators in the 

forests surrounding the harvested stands we surveyed. 

Bird Use Associated with Created Snag and Stand 

Characteristics 

New Woodpecker Foraging Excavations 

 We conducted regression analyses to investigate whether new woodpecker 

foraging excavations were associated with snag and stand characteristics. This 

analysis was based on the null hypothesis that new woodpecker foraging excavations 

were random events. 

The data set used in the analysis contained 1,267 created snags with the response 

variable presence/absence of “new woodpecker foraging excavations” and the 

explanatory variables listed in table 2 (excluding snag age). Data was analyzed using 

the following steps: 

• First, presence/absence of new woodpecker foraging excavations was 

statistically tested against all explanatory variables using logistic regression 

for binary responses. Stand differences were found to be statistically 

different. Stand-level variables, such as “lscape” and elevation, were not 

found to be significantly associated with stand differences in the response 

variable. 

• Next, the same logistic regression model was rerun with the 1,267 snags and 

this time corrected for stand differences. This means that, within the 

regression model, the stand average count (total count in that stand divided 

by the number of created snags in that stand) was subtracted from each 

individual snag count. This put all of the snags on an even basis, as if they all 

were from the same stand. Obviously, this eliminated all stand-level 

differences. We did this only after checking all stand-level variables for 

significance (and finding none), and only when “stand,” as a categorical 

variable, was significant. 

This second model provided convincing evidence that the status (live or dead) of 

the created snag was associated with the presence/absence of new woodpecker 

foraging excavations (p-value <0.00004). Specifically, the odds of the presence of 

new woodpecker foraging excavations on dead created snags was estimated to be 2.3 

times the odds of the presence of new woodpecker foraging excavations on created 

snags that were still living (95 percent Confidence interval: 1.5 times to 3.4 times) 

(table 3). Many of the foraging excavations were deep (greater than 5 cm) into the 

cambium, where the woodpeckers may have been foraging for insects. Insect 

colonies may be more abundant in dead trees than in live. This inference may be 

useful in selecting a preferred method of snag creation and/or post-creation 

treatments. 

We did not randomly select which trees within each of the harvested stands were 

to be converted to snags, therefore this project was observational. Stronger inferences 

about the association of bird use with created snag characteristics may be gained by 

instituting experimental controls in future snag creation efforts. 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 773 

Table 3—Coefficients and equation for the logistic regression model providing convincing 

evidence that the status (live or dead) of the created snag and the presence of old woodpecker 

foraging excavations were associated with the presence/absence of new woodpecker foraging 

excavations (p-value <0.00004). 

Equation: β ( ) β β ε

π

π  = + ∑ + + 

 





− = 1

1

55

0 tan

1 log i i

i

s d where π is the proportion of 

new woodpecker foraging excavations, “standi” is an indicator variable for each stand 

(correcting for between stand differences), β1 is a binary, categorical variable with a value of 

0 if the created snag is dead and a value of 1 if the created snag is still alive, and ε is error. 

The sample size is 1,267 created snags, null deviance is 1,736.93 on 1,266 degrees of 

freedom, and residual deviance is 1,141.67 on 1,211 degrees of freedom. 

Coefficient Interpretation of coefficient Standard error p-value 

β 0 

0.458401 Intercept 0.874047 0.60000 

β1 

-0.82203 Categorical variable 0.197628 0.00003 

 0=dead created snag 

 1=live created snag 

Future Monitoring 

The created snags in this project should be monitored over several years to 

observe current bird foraging and nesting during the spring breeding season when the 

actual birds, rather than just their foraging sign, can be documented. This could 

provide evidence on which species were not using these snags in the harvested 

stands, as well as information on what density and placement of created snags was 

associated with more frequent bird use. This may provide evidence that species such 

as the red-breasted nuthatch, identified as the primary cavity excavator and upon 

which several Willamette National Forest post-harvest snag retention rules are based 

(USDA Forest Service 1994), were utilizing the snags for nesting or roosting. Also, 

more studies should be initiated to monitor wildlife use of created snags before and 

after the snag is killed and in subsequent years. Wildlife use could also be compared 

between blasted, sawed and fungus and insect inoculated snags to learn more about 

the effect of each of these kill methods on wildlife use. Features monitored at each 

created snags should include insect use, because insects attract birds and other 

wildlife. In addition, fall down rates should be monitored as the snags age. This 

information will assist Willamette National Forest land managers with compliance 

with the Pacific Northwest Regional Forest Planning regulations (USDA Forest 

Service 1990, 1994) regarding selection and monitoring of snags left in harvested 

stands. 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

774 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Acknowledgments 

We greatly appreciate the assistance of Michael Dubrasich from Pacific 

Analytics L.L.C., a biometrics consulting firm in Albany, Oregon, who conducted all 

of the statistical analyses for this project. We also appreciate the careful manuscript 

review of John Guetterman (Wildlife Biologist, Coos Bay District, Bureau of Land 

Management), and Catherine Parks (Ecologist, Pacific Northwest Research Station, 

USDA Forest Service). We appreciate the dedicated field assistance of Jessica 

Metcalf and Alexis Harrison (Apprenticeship in Science and Engineering interns for 

the Willamette National Forest). 

References

Bent, Arthur C. 1964. Life histories of North American woodpeckers. New York, New 

York: Dover Publications, Inc. Reprint; 109 p. 

Carey, A. B. 1995. Sciurids in Pacific Northwest managed and old-growth forests.

Ecological Applications 5: 648-661. 

Carey, A. B.; Hardt, M. M.; Horton, Scott P.; Biswell, Brian. 1991. Spring bird 

communities in the Oregon Coast Ranges. In: Rugiero, L. F.; Aubry, K. F.; Carey A. 

B.; Huff, M. F., technical coordinators. Wildlife and vegetation of unmanaged Douglasfir forests. Portland, OR: Pacific Northwest Research Station, USDA Forest Service. 

Gen. Tech. Rep. PNW-GTR-285; 123-144. 

Chambers, C. L.; Carrigan, R.; Sabin, T. E.; Tappeiner, J.; McComb, W. C. 1997. Use of 

artificially created Douglas-fir snags by cavity-nesting birds. Western Journal of 

Applied Forestry 12: 93-97. 

Lundquist, R. W.; Mariani, J. M. 1991. Nesting habitat and abundance of snag-dependent 

birds in the sourthern Washington Cascade Range. In: Ruggiero, L. F.; Aubry, K. B.; 

Carey, A. B.; Huff, M. H., technical coordinators. Wildlife and vegetation of unmanaged 

Douglas-fir forests. Portland, OR: Pacific Northwest Research Station, USDA Forest 

Service. Gen. Tech. Rep. PNW-GTR-285; 221-240. 

Neitro, W. A.; Binkley, V. W.; Cline, S. P.; Mannan, R. W.; Marcot, B. G.; Taylor, D.; 

Wagner, F. F. 1985. Snags. In: Brown, E. R., technical editors. Management of wildlife 

and fish habitats in forests of western Oregon and Washington. Portland, OR: USDA 

Agric. For. Serv. Publ. R6-F & WL-192-1985; 129-169. 

Ohmann, J. L.; McComb, W. C.; Zumrawi, A. Z. 1994. Snag abundance for primary 

cavity-nesting birds on nonfederal forest lands in Oregon and Washington. Wildlife 

Society Bulletin 22: 607-620. 

Parks, C. G.; Bull, E. L.; Torgersen, T. R. 1997. Field guide for the identification of snags 

and logs in the interior Columbia River Basin. Portland, OR: Pacific Northwest 

Research Station, USDA Forest Service. Gen. Tech. Rep. PNW-GTR-390. 

Raphael, R. G.; White, M. 1984. Use of snags by cavity-nesting birds in the Sierra Nevada.

Wildlife Monograph 86. Bethesda, MD: The Wildlife Society. 

SAS Institute, Inc. 1995. JMP user’s guide: version 3.1 of JMP. Cary, NC. 

Scott, V. E. 1979. Bird response to snag removal in ponderosa pine. Journal of Forestry 

77: 26-28. 

Scott, V. E.; Evans, K. E.; Patton, D. R.; Stone, C. P. 1977. Cavity-nesting birds of North 

American forests. Agric. Handb. No. 511. Washington, DC: U.S. Department of 

Agriculture. 
Created Snag Monitoring on the Willamette National Forest―Boleyn, Wold, and Byford 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 775 

Shope, S. 1995. Created snag monitoring draft report. Unpublished report on file at the

Willamette National Forest, Eugene, Oregon; 2 p. 

Spies, T. A.; Franklin, J. F. 1991. The structure of natural young, mature, and old-growth 

Douglas-fir forests in Oregon and Washington. In: Ruggiero, L. F.; Aubry, K. B.; 

Carey, A. B.; Huff, M. H., technical coordinators. Wildlife and vegetation of unmanaged 

Douglas-fir forests. Portland, OR: Pacific Northwest Research Station, USDA Forest 

Service. Gen. Tech. Rep. PNW-GTR-285; 90-109. 

Spies, T. A.; Thomas, T. B. 1988. Course woody debris in Douglas-fir forests of western 

Oregon and Washington. Ecology 69: 1689-1702. 

Stribling, H. L.; Smith, H. R.; Yahner, R. H. 1990. Bird community response to timber 

stand improvement and snag retention. Northern Journal of Applied Forestry 7: 35-

38. 

Thomas, J. W.; Anderson, R. G.; Maser, C.; Bull, E. L. 1979. Snags. In: Thomas, J. W., 

technical editor. Wildlife habitats in managed forests—the Blue Mountains of Oregon 

and Washington. Agric. Handb. No. 553. Washington, DC: U.S. Department of 

Agriculture; 60-77. 

Tyrrell, L. E; Crow, T. R. 1994a. Structural characteristics of old-growth hemlockhardwood forests in relation to age. Ecology 75: 370-386. 

Tyrrell, L. E; Crow, T. R. 1994b. Dynamics of dead wood in old-growth hemlockhardwood forests of northern Wisconsin and northern Michigan. Canadian Journal 

of Forest Research 24: 1672-1683. 

USDA Forest Service and USDI Bureau of Land Management. 1994. Record of decision for 

amendments to Forest Service and Bureau of Land Management planning 

documents within the range of the northern spotted owl and standards and 

guidelines for management of habitat for late-successional and old-growth forest 

related species with the range of the northern spotted owl. Portland, Oregon. 

Zarnowitz, J. E.; Manuwal, D. A. 1985. The effects of forest management on cavity-nesting 

birds in northwestern Washington. Journal of Wildlife Management 49: 255-263. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 777 

The Efficacy of Inoculating Fungi into 

Conifer Trees to Promote Cavity Excavation 

by Woodpeckers in Managed Forests in 

Western Washington1

Martin J. Huss,2 James C. Bednarz,2 David M. Juliano,2,3 and 

Daniel E. Varland4 

Abstract 

To develop management prescriptions to promote the use of forests by cavity-using wildlife, 

we have investigated the relationship that wood-decay fungi play in facilitating nest 

excavation by woodpeckers. We located 78 woodpecker nests in western Washington and 

documented the presence of basidiocarps and collected wood samples to identify the decay 

organisms in trees. Basidiocarps of Fomitopsis pinicola (red-belted conk) were found on 47.4 

percent of all woodpecker nest trees. This fungus was also recovered from wood samples of 

7.7 percent of all woodpecker nest trees that did not possess conks. We also identified 32 

other fungal types from 20 genera in woodpecker nest trees. We selected F. pinicola as the 

organism to inoculate into trees experimentally to promote colonization by woodpeckers, 

because this was the most common fungus associated with woodpecker trees and because it 

met several other criteria. In 1997 and 1998, we inoculated 65 clusters of 10 trees in 34 

separate managed forest stands in western Washington. The experimental design of 

inoculations will allow us to examine the effect of blank (control) vs. fungal inoculations, the 

influence of tree species (i.e., Tsuga heterophylla, Pseudotsuga menziesii), the effect of 

available snags, and the effect of size/age classes of trees on future colonization by 

woodpeckers. Visual examinations for presence of mycelia and/or conks, and retrieval of 

wood samples and isolation of fungal cultures from randomly selected trees (N=58) 

inoculated in 1997 and 1998, indicated the successful colonization of F. pinicola in 50 percent 

to 70 percent of the trees inspected in 1998 and 1999. 

Introduction 

Most, if not all, cavity-using wildlife are dependent on woodpeckers (e.g., 

Picoides spp.) that excavate cavities (Jackman 1975, McClelland 1977). In western 

Washington, for example, at least 54 species of birds and mammals require or use 

tree cavities excavated by woodpeckers (Brown 1985). However, woodpeckers 

mostly excavate cavities in trees that have decay caused by certain types of 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Associate Professor of Botany, Professor of Wildlife Ecology, and Master’s Degree Candidate in 

Biology, respectively, Department of Biological Sciences, Arkansas State University, State University, 

AR 72467-0599. (e-mail: mhuss@astate.edu and jbednarz@astate.edu) 3

 Current Address: Wildlife Ecologist, Pacific Northwestern Biological Resources Consultants, Inc., 

P.O. Box 150, Trinidad, CA, 95570 (e-mail: hawo1@yahoo.com) 

4

 Wildlife Biologist, Rayonier, 3033 Ingram Street, Hoquiam, WA 98550. (e-mail address: 

Daniel.Varland@rayonier.com) 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

778 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

filamentous fungi, primarily basidiomycetes, that soften the wood of living, injured, 

and dead trees (Bull and others 1997). Therefore, the interaction between fungi and 

woodpeckers represents a keystone process that may be necessary to support a robust 

diversity of wildlife and to complete the complement of vital processes necessary for 

healthy forest ecosystems. 

Traditionally, cavity-using wildlife have been associated with old-growth forests 

and researchers have suggested or implied that old forests were needed to support 

these species (e.g., Conner and others 1994). However, because cavities are 

correlated with old-growth forest, it is not known whether some species of wildlife 

require mature forests per se, or just require a suitable incidence of cavities or snags. 

The overall objective of this study is to facilitate creation of cavities for wildlife in 

trees of managed forests in western Washington (see Huss and others 1999). 

Specific objectives of this article are to describe the species of fungi associated 

with woodpecker nest cavities, report on our selection of a fungal species for 

inoculation into trees to promote use by woodpeckers, describe the protocol for 

inoculation of a potentially-beneficial fungus into managed forests, and determine the 

efficacy of treatment for the establishment of fungi. 

Materials and Methods 

Woodpecker Nest Surveys 

During woodpecker nest searches in 1996-1997 we established four general 

study areas: (1) North Forks, (2) West Forks, (3) Hoh Valley, and (4) Blue Mountain 

(fig. 1, Bednarz and others 1997). In 1998, we searched for woodpecker nests mostly 

in selected areas in the North Forks and West Forks study areas. The North Forks 

area was located 6 km north and 11 km west of Forks, Washington, in Clallam 

County. The West Forks area was relatively small in size (approximately 31 km2

) and 

was located about 11 km west of Forks, Washington (Clallam County). The Hoh 

Valley area was approximately 78 km2

 in size and was about 32 km east and 16 km 

south of the town of Forks, Washington (Jefferson County). The Blue Mountain area 

covered roughly 93 km2 and was located approximately 13 km west and 8 km south 

of Oakville, Washington (Pacific County). The three Forks study sites were primarily 

dominated by western hemlock (Tsuga heterophylla) with secondary dominant tree 

species consisting of Douglas-fir (Pseudotsuga menziesii) and Sitka spruce (Picea 

sitchensis). Douglas-fir and western hemlock were codominant in the Blue Mountain 

study area. We incidentally collected data at some woodpecker nests located outside 

of the described study areas, but these were in ecologically similar environments. All 

study areas were comprised of state or private lands managed primarily for timber 

production. Forest habitats consisted of a mosaic of different even-aged forest stands 

ranging from recently clearcut areas to stands more than 100 yr old. Stands surveyed 

were generally small, ranging from 10-160 ha in size, and were often bordered by 

stands which had been clearcut within the last 5 yr. 

We conducted nest searches by walking through stands and searching either for 

woodpeckers or for large snags or partially dead trees with fresh cavities. Fresh 

cavities were recognized by the presence of recent wood shavings near the base of 

trees or by recently-exposed wood around the perimeter of the cavity entrance. When 

a fresh cavity entrance was found, we stayed in the vicinity and watched for 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 779 

woodpecker activity for 30-60 min. In addition, if woodpeckers were detected during 

a search, we attempted to follow them to their cavities. 

Figure 1Location of study areas in western Washington. Square and rectangular 

symbols indicate specific study sites.

Collection of Fungi Associated with Nest Trees 

The presence or absence of fungal reproductive bodies or basidiocarps (e.g., 

conks, bracket fungi) were noted for each nest tree or nest snag. When present, 

several samples nearest to the cavity entrance were collected. In most cases, we 

climbed the tree to collect samples. However, when it was unsafe to climb the snag, 

samples of wood were taken as close as possible to the opening of the nest cavity and 

conks were retrieved by knocking them off the tree with a pole. 

Basidiocarps were air-dried at room temperature to help preserve their 

appearance and to inhibit degradation. Specimens were stored with Revenge Bug 

Strips® (Roxide International, Inc., New Rochelle, NY)5

 to prevent pest infestations. 

Fungal species were identified based on micro- and macroscopic features using 

standard identification keys (e.g., Arora 1986, Miller 1972, Overholts 1953, Smith 

and others 1981). Basidiocarps were also examined by Robert L. Gilbertson 

 

5

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 

N or th Fo rk s

W est F o rks FOR KS

PO RT A NG EL ES

H oh V alley

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Blue Mo untain

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Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

780 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(University of Arizona) and N. Jay Justice (Arkansas Department of Environmental 

Quality) to confirm species identification. 

Aging of Basidiocarps 

Air-dried basidiocarps were weighed to determine their mass and then aged. 

Many members of the Order Aphyllophorales develop perennial basidiocarps that 

add a new layer of pores (i.e., spore-producing regions) each year (Alexopoulos and 

others 1996, Moore-Landecker 1996). The age of the basidiocarp can be determined 

by counting the number of pore layers established before the actively-growing 

leading front (1 ridge = 1 yr). In specimens where these outer ridges were less 

distinct, the basidiocarp was cut longitudinally using a saw. The inner surface was 

then planed using a scalpel blade so that the number of pore layers could be counted 

more readily. The age of these perennial basidiocarps indicates when the conk began 

to form on the surface of the tree, and provides a minimum estimate for how long the 

fungus was growing on the tree. 

Isolation of Fungal Cultures from Basidiocarps 

Tissue from the edge of each basidiocarp was removed using a pair of needlenosed pliers and stored temporarily in a sterile petri dish. After sterilizing with 

pressurized steam in an autoclave, 20-25 ml of isolation medium (one of two types; 

Isolation medium #1 and #2; see Bednarz and others 1997) was poured into sterile 

100 x 15 mm petri dishes. After the medium had solidified (due to the presence of 

agar in the culture medium) and cooled, a single fragment of the tissue sample was 

transferred to the center of the plate using a sterile forceps. These isolation media 

were nutritionally weak and contained substances to inhibit the growth of fastgrowing and potentially contaminating microorganisms while selectively encouraging the growth of a fungal culture from basidiocarp tissue (Tsao 1970). All plates 

were incubated at room temperature (~24 °C) and checked periodically for the 

presence of filamentous growth. 

Fungi Associated with Wood Samples from Nest Trees 

Collection of Wood Samples

Wood samples obtained during the 1996 field season were collected from above, 

below, and to the right and left sides of the woodpecker cavities and/or at the base of 

nest trees. Collection of wood samples during the 1997 and 1998 field season was 

restricted to one or two wood samples obtained directly below the nest cavity and/or 

at the base of the nest tree. In cases where the wood was less decayed and sound, the 

sample was removed with an increment borer (5.15 mm diameter). In cases where the 

wood was too soft to remove with the increment borer, we employed a portable 

rechargeable electric drill with an 8.00 mm diameter auger drill bit. A hole was 

drilled 10-15 cm into the tree and particles of wood were collected into sterile plastic 

collecting bags as the drill bit was withdrawn. Samples were kept refrigerated until 

we could isolate resident fungi from the wood. 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 781 

Isolation of Fungi from Wood Samples 

Fungi isolated from wood samples collected in 1996 followed the protocol given 

in Bednarz and others (1997). Culture isolation medium #3 (Bednarz and others 

1997) was employed for isolation of fungi from wood samples collected in 1997 and 

1998. This medium consisted of a mixture of 20 g of dehydrated malt extract broth, 

20 g of agar, 0.2 g of pentachloronitrobenzene (PCNB), and 1 liter of distilled or 

deionized water. The medium was sterilized by autoclaving at 15 psi at 121°C for 15 

min. After cooling to 50-60°C, 2 ml of a filter-sterilized antibiotic stock solution 

(20,000 units/ml of penicillin and 80,000 units/ml of streptomycin in distilled water) 

and 1 ml of a benomyl solution (0.1 percent benomyl in 100 percent ethanol) were 

incorporated into the medium. 

Identification of Fungal Cultures 

For filamentous fungi and some yeasts, identifications were based on the 

morphology of cultures growing on malt extract agar and on microscopic 

characteristics (e.g., reproductive structures, spore morphology, or formation of 

hyphae). Slide cultures for viewing under the microscope (Larone 1995) were 

produced by allowing inoculum of the fungal culture to grow on a block of malt 

extract agar sandwiched between a microscope slide and glass coverslip. Cultures 

were placed in a moist chamber to prevent the medium from drying out and were 

incubated at room temperature (24 °C) for several days. After the fungus had grown 

to the edges of the culture medium onto the surface of the slide and/or glass 

coverslip, the block was removed and the coverslip transferred to a fresh microscope 

slide to which a drop of lactophenol with cotton blue dye (Larone 1995) had been 

added. When enough growth was present, a second slide was prepared by adding a 

drop of the same mounting medium to the surface of the slide and placing a fresh 

coverslip over it. The edges of the coverslips were sealed with clear fingernail polish 

to produce semi-permanent slides. 

A variety of literature sources and identification keys were consulted to identify 

all fungal specimens and cultures to provide some taxonomic category (Arora 1986, 

Barnett and Hunter 1998, Larone 1995, Miller 1972, Nobles 1948, Overholts 1953, 

Rayner and Boddy 1988, Rippon 1988, Smith and others 1981, Taylor 1974). Many 

of the cultures isolated from wood samples were unicellular yeasts. Yeast species are 

not readily identified based on microscopic characteristics; however, yeasts can be 

sorted, sometimes to species, based on the outcome of certain physiological tests 

(e.g., assimilation of various types of sugars). Yeast cultures were tested based on the 

analytical profile index (API) system for diagnosis of yeasts (diagnostic kits, 

bioMérieux Viteck, Inc., Hazelwood, MO). We consulted the API data base and 

identified as many of the yeast species as close to the species level as possible. 

Field Inoculations 

Selection of Inoculation Sites

We developed an experimental design (table 1) to test the effects of tree species, 

available snags, and size/age classes of trees on the resulting use of inoculated trees 

by woodpeckers (table 1). This experiment was set up in a hierarchical fashion so we 

should be able to examine these effects independently and the interaction of these 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

782 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

factors. This evaluation will be done during the next stage of the study to be 

implemented in 3-10 yr. 

Table 1Original experimental design for inoculation experiments of Douglas-fir 

(Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) trees. 

Treatments Presence 

of snags1

Age/size class 

of trees2

Number 

of clusters 

Number of trees 

per cluster 

 Snags 

absent 

Old 4 10 

Control Young 4 10 

Group Snags 

present 

Old 4 10 

 Young 4 10 

----------------------------------------------------------------------------------------------------- 

 Snags 

absent 

Old 4 10 

Treatment Young 4 10 

Group Snags 

present 

Old 4 10 

 Young 4 10 

 

Total: 2 tree species X 64 clusters X 10 trees/cluster = 640 trees 

1

Snags absent = < 7 snags (>50 cm dbh)/ha; Snags present = > 7 snags/ha. 

.2Age class designation; young = approximately 50 years old, 30-45 cm dbh; old = approximately 70 

years old, 40-60 cm dbh. 

Selection of field sites was done with the cooperation of land owners. During 

this process, we worked closely with representatives from Rayonier, the Washington 

Department of Natural Resources (DNR), Weyerhaeuser, Port Blakely Tree Farms L. 

P., I. P. Pacific Timberland Inc., and Hancock Timber Resource Group. Candidate 

stands for inoculation were required to satisfy the following criteria: supported 

western hemlock or Douglas-fir as a dominant or co-dominant species and included 

trees that could be classified as either: (1) relatively small-diameter (<40 cm 

dbh)/relatively young (approximately 30-50-yr-old trees), or (2) relatively largediameter (> 40 cm)/relatively old (> 60 yr) stand. We further classified stands into 

one of two snag-status categories: (1) snags conspicuously present (about 7 per ha), 

or (2) large snags mostly absent. 

In most cases, inoculated and control clusters (each including 10 trees) were 

located in the same forest stand. In some cases, stands were either not large enough to 

accommodate two clusters of experimental trees or the structure varied within the 

stand. In these cases, we located the control cluster in a nearby stand. When 

experimental and control clusters were placed in separate stands, we made an effort 

to use stands of similar characteristics (e.g., same dominant tree species, age, and 

snag density). 

Fungi Used in Field Inoculations

Because of the high incidence of Fomitopsis pinicola observed associated with 

woodpecker nest trees during the 1996 field season and its benign nature as a cause 

of brown rot in wood (e.g., brown-rotter: capable of utilizing primarily cellulose and 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 783 

hemicellulose in wood but not lignin [Rayner and Boddy 1998]), we chose this 

organism in our field tests. Three basidiocarps of F. pinicola, from three different 

study locations in western Washington were used to derive mycelial cultures 

(Bednarz and others 1997). Cultures of these individuals were morphologically 

indistinguishable from one another, but vegetative compatibility analysis (Huss 1993, 

Mounce 1929, Worrall 1997) of the these isolates indicated that these represented 

three genetically-distinct individuals of F. pinicola (i.e., basidiocarps no. 36 and 64 

from hairy woodpecker [Picoides villosus] nests 17 and 36, respectively, and 

basidiocarp no. 43 from northern flicker [Colaptes auratus] nest 22). 

Preparation of Wooden Dowel Spawn 

Dowel plugs (12.8 cm long) were cut from 2.24 cm diameter hardwood. A 0.96 

cm diameter hole was drilled down the center of each dowel using an auger drill bit 

to create an axial channel (C. G. Parks, pers. comm.). Plugs were soaked in distilled 

water (1:4 mass to volume - 1 kg of wood per 4 l of water) for 12 hr. Plugs and water 

were autoclaved (i.e., 121°C at 20 psi) for 30 min. The contents were allowed to cool 

and were soaked overnight. Excess liquid was decanted off the dowel plugs followed 

by a rinsing with distilled water. Dowels to be used for the control inoculations were 

prepared in the same manner but autoclaved a second time for 1.5 hr to insure that 

any resident microorganisms were killed. 

A sterilized grain medium was used in conjunction with dowel plugs to support 

good mycelial growth and reduce the time necessary for the fungus to invade the 

wooden substrate. Dry millet and perlite (4:1 by weight) were mixed together, then 

added to distilled water in a ratio of 1 part by weight of dry ingredients to 1.5 parts by 

volume of distilled water (i.e., 1 kg of grain/perlite for every 1.5 liters of distilled 

water). This mixture was autoclaved (i.e., 121°C at 20 psi) for 30 min, then allowed 

to cool to room temperature and any excess liquid was drained off. Gypsum (2 

percent by weight of CaSO4•2H2O) and powdered chalk or whiting (0.5 percent by 

weight of CaCO3) were mixed into the cooked grain medium to help buffer the pH 

and to help prevent the grain from sticking together (Elliot 1985, Fritsche 1978). 

Plugs were loaded with grain medium by stuffing material into their axial 

channels. Twenty-five wooden dowels were placed into a square aluminum cake pan 

(20.3 x 20.3 x 3.7 cm) and 250 ml of malt extract broth was poured over the surface 

of these dowels. The surfaces of the dowels were lightly covered with grain/perlite 

medium. The pan was placed into an autoclavable spawn bag with filter patch 

(Dimensions: 53.3 x 20.3 x 12.1 cm, Fungi Perfecti, Olympia WA) and the end of the 

bag was sealed with wooden clothes pins. The bag and its contents were autoclaved 

for 1.5 hr, then allowed to cool. After sterilization the dowels were inoculated with 

mycelium of Fomitopsis pinicola (isolates 36A or 64A) that had been grown 

previously on 2 percent malt extract agar. Material was incubated at room 

temperature for 2-3 mo. and growth was monitored. 

Inoculation of Control and Test Stands of Trees

Inoculations of trees were made by climbing approximately 8 m (within one 

standard deviation of the mean height of woodpecker nests) up a Douglas-fir or 

western hemlock tree and a 2.24 cm to 2.56 cm diameter hole was drilled, 5-8 cm 

deep using an battery-operated drill. A manually-operated brace was then used to 

drill out the remaining hole to a depth of 13-15 cm. A blank or inoculated dowel was 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

784 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

inserted into the hole and a piece of PVC tubing (7.70 cm long by 2.56 cm in 

diameter) was inserted in the hole adjacent to the dowel. About 5 cm of the tubing 

remained outside the entrance of the hole to prevent the tree from healing over this 

wound (C. G. Parks, pers. comm.). Holes were made on the north sides of trees, 

which was where woodpeckers most often excavated their nests (Bednarz and others 

1998). Fungal inoculations were made using dowels impregnated with cultures 36A 

and 64A of F. pinicola. 

A subset of the trees were inoculated with culture 64A in a similar manner as 

described above but using dowels of a smaller diameter (1.0 cm and 1.4 cm) with no 

axial channels drilled through the center. Holes drilled for these dowels were 1.28 cm 

to 1.60 cm in diameter. After the blank or inoculated dowel (7.7 cm long piece 1.28 

cm diameter) was inserted into the hole, PVC tubing was driven 2.56 cm into the hole 

with a rubber mallet. 

Inspection and Sampling of Trees Inoculated in 1997 and 1998 

All experimental tree stands that we established in 1997 were visually inspected 

in 1998 and 1999 to determine if there were any signs of fungal establishment or 

other changes. In 1998, we randomly selected 10 clusters treated with viable 

inoculum and collected wood samples from two trees (a total of 20 trees) in each 

cluster to determine if F. pinicola isolates 36A or 64A were established. In 1999, we 

randomly selected 19 clusters and collected wood samples from two trees per cluster 

(20 trees inoculated in 1997 and 18 trees inoculated in 1998). Wood cores were 

extracted from trees using an increment borer (5.15 mm diameter), about 1 cm below 

the inoculation hole and extending 5-10 cm into the tree. Prior to use on each tree, the 

increment borer was rinsed in 70 percent isopropyl alcohol to sterilize the surface. 

Wood cores were placed in sterile plastic bags and kept refrigerated until isolation of 

fungi could be accomplished. Tree wounds were covered with a pruning sealant to 

minimize exposure to other fungi. 

Isolation of Fomitopsis pinicola from Wood Samples 

Four isolation plates per wood sample were established using isolation medium 

#3. Bits or particles of wood were transferred, using a sterile forceps, to the center of 

a 100 x 15 mm petri dish containing 20-25 ml of the isolation medium. All isolation 

plates were incubated at room temperature (24 °C) and checked periodically for the 

presence of fungal growth. After colonies appeared on the plate, a piece was 

transferred and grown on culture plates containing a 2 percent malt extract agar and 

incubated at room temperature for a 1-2 weeks. Culture and microscopic 

characteristics were checked to determine whether the fungus was F. pinicola or 

some other fungal species. Isolation procedures were repeated for wood samples that 

did not yield this fungus to determine its presence or absence in the collected wood 

samples. 

Vegetative Compatibility Analysis 

Isolates of F. pinicola were paired with stock cultures of F. pinicola (36A, 43A, 

and 64A) on malt extract agar plates and incubated at room temperature for several 

weeks. The plates were examined for lines of demarcation that are indicative of 

vegetative incompatibility and suggest when isolates are genetically different. If no 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 785 

lines of demarcation were observed between the two paired colonies then this would 

suggest that isolates represented the same genetic individual. This test was employed 

to determine if the cultures inoculated into trees represented the same fungus 

extracted from the tree (Bednarz and others 1997, Huss 1993). 

Results and Discussion 

Woodpecker Nests 

Between 1996 and 1998, we located and collected data from 78 cavities 

occupied by nesting woodpeckers on or near the study areas (fig. 1). These included 

51 hairy woodpecker cavities, 26 northern flicker cavities, and 1 red-breasted 

sapsucker cavity. We saw and/or heard pileated woodpeckers occasionally but these 

birds were extremely wide ranging and we did not document nesting. In 1997, we 

observed a single downy woodpecker in the Blue Mountain study area, but could not 

locate its nest. While we did occasionally detect red-breasted sapsuckers in the Forks 

area, nesting activity was only recorded in the Blue Mountain study area (fig. 1).

Fungal Diversity Based on Basidiocarp Data (1996-1998) 

Fungal basidiocarps were present on 50.0 percent of the woodpecker nest trees 

(N = 78). Of the 82 conks collected over the course of 3 yr, 93.9 percent represented 

Fomitopsis pinicola (mean age = 7.9 yr; mean mass = 221.6 g), 2.4 percent 

represented Ganoderma applanatum (mean age = 8.5 yr old; mean mass = 105.8 g), 

and 3.7 percent represented Trichaptum fuscoviolaceum (mean age = 1.3 yr; mean 

mass = 2.4 g). Among hairy woodpecker nest cavities for 1996-1998, evidence of 

fungal basidiocarps was present on 54.9 percent of all trees regardless of tree species 

(N = 51). Basidiocarps were found on 42.3 percent of the northern flicker nest trees 

(N = 26). The mass and age of the conks from Fomitopsis and Ganoderma indicate 

that these fungi were growing in the wood for a substantial period of time before 

excavation of the tree by woodpeckers. These organisms are completely 

heterotrophic and obtain all their nourishment from the wood they decay. 

Consequently, inoculation of trees intended for the purpose of attracting woodpecker 

and other cavity utilizing species will likely take a minimum of 5-10 yr before 

colonization occurs. 

Wood Samples and Culture Isolations 

Of the 211 wood samples collected from nest trees during the summer field 

seasons of 1996-1998, at least 33 different fungal types representing 21 genera were 

isolated and identified (N = 471 cultures) (table 2, Huss and others 1999). Bacteria 

represented 2.8 percent of the subcultured microorganisms. 

We extracted a wide diversity of fungi from the wood samples, including yeast 

and filamentous forms. Observations of the mode of sexual reproduction or the 

presence of microscopic structures unique to a phylum (e.g., clamp connections in 

members of the phylum Basidiomycota) are often necessary to designate the fungal 

phylum of a culture (e.g., Oomycota, Ascomycota, Basidiomycota), but this was not 

observed in most of our cultures. Because we could not distinguish phyla, we 

classified most isolates of filamentous fungi as belonging to the Form-Phylum 

Deuteromycota (the asexually reproducing or imperfect fungi) or the Phylum 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

786 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Zygomycota (based on presence of asexual reproductive structuressporangia) and 

discuss these separately from the yeasts. 

Table 2Fungi and other microorganisms recovered from wood samples obtained from 

woodpecker nest trees in western Washington, 1996-1998. 

Category or species Number of samples 

(N = 471) 

Percent 

occurrence 

Aspergillus sp. 7 1.49 pct 

Bacteria 13 2.76 pct 

Basidiomycete #1 9 1.91 pct 

Basidiomycete #2 5 1.06 pct 

Basidiomycete #3 13 2.76 pct 

Basidiomycete #4 1 0.21 pct 

Fomitopsis pinicola 21 4.46 pct 

Basipetospora sp. 3 0.64 pct 

Cladosporium sp. 15 3.18 pct 

Fusarium sp. 28 5.94 pct 

Gliocladium sp. 6 1.27 pct 

Graphium sp. 1 0.21 pct 

Mycelia sterilia 11 2.34 pct 

Oedocephalum sp. 1 0.21 pct 

Oidiodendron sp. 13 2.76 pct 

Oomycete (Saprolegniales) 21 4.46 pct 

Paeciliomyces sp. 7 1.49 pct 

Penicillium sp. 32 6.79 pct 

Rhizoctonia sp. 4 0.85 pct 

Trichoderma sp. (large-spored) 42 8.92 pct 

Trichoderma sp. (small-spored) 27 5.73 pct 

Verticillium sp. 2 0.42 pct 

Yeast (unknown) 88 18.68 pct 

Candida sp. 36 7.64 pct 

Cryptococcus sp. 6 1.27 pct 

Kloeckera sp. 6 1.27 pct 

Rhodotorula sp. 1 0.21 pct 

Torulopsis sp. 4 0.85 pct 

Unidentified Filamentous Fungus 12 2.55 pct 

Zygomycete #1–Mucor sp. 20 4.25 pct 

Zygomycete #2–Mucor sp. 10 2.12 pct 

Zygomycete #3 4 0.85 pct 

Zygomycete #4–Absidia sp. 1 0.21 pct 

Zygomycete #5 1 0.21 pct 

Yeasts were the most common single type of fungus isolated (29.1 percent, N = 

211). Based on the API system, a number of these sorted together into subgroups. 

Most yeasts belonged to the genera Candida, Cryptococcus, or Rhodotorula (table 2)

which are among the most common indigenous microorganisms found in soil (Atlas 

and Bartha 1998). Some species of Cryptococcus are associated with the dried fecal 

material and nesting materials of birds (Rippon 1988). Other genera of yeasts 

observed included Torulopsis and Kloeckera. 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 787 

The remaining fungal isolates (67.3 percent) were filamentous, representing at 

least 27 distinct fungal types, genera, or species. A large number of the samples 

represented the group deuteromycetes (Form-Phylum Deuteromycota). Filamentous 

deuteromycetes isolated and identified included the following genera: Aspergillus, 

Basipetospora, Cladosporium, Fusarium, Gliocladium, Graphium, Oedocephalum, 

Oidiodendron (some cultures may represent the genus Geotrichum instead; the 

culture characteristics of both genera are similar), Paeciliomyces, Penicillium, 

Trichoderma (two types, differentiated by the production of large and small asexual 

spores [conidia]), Verticillium, and several specimens tentatively assigned to Mycelia 

Sterilia (i.e., vegetative hyphae with no spores evident) (table 2). Some isolates were 

lacking distinct characteristics and could not be identified to a specific category and 

thus were listed as unknown. Remaining groups included several species belonging 

to the Phyla Zygomycota, Oomycota, and Basidiomycota. Each group of 

zygomycetes and basidiomycetes that were differentiated into subgroups (#1, #2, 

etc.) were distinctly different from one another, but in most situations, were not 

identified beyond this level. 

Of the basidiomycetes observed during this study, the most commonly 

encountered was Fomitopsis pinicola. We recovered cultures from wood samples 

and/or observed basidiocarps of F. pinicola from 55.1 percent of the nest trees 

examined (N = 78 trees). Basidiocarps of this fungus were found in 47.4 percent, and 

cultures retrieved from wood samples from 15.4 percent of all trees sampled (N = 

78). Cultures of this fungus retrieved both from wood samples and basidiocarps were 

found simultaneously on 7.7 percent of the trees sampled. These data suggest that 

some nest trees without visible conks are also likely to be harboring colonies of F. 

pinicola. Thus, F. pinicola was probably present in woodpecker cavity trees more 

frequently than we were able to document (55.1 percent) due to sampling error 

during the retrieval and culture isolation process. 

Classification of these fungi into major groups indicates that the predominate 

fungi found in nest trees or snags are filamentous deuteromycetes and yeasts, but 

these do not necessarily represent the initial invaders and primary agents of decay in 

the wood. As an agent of decay, F. pinicola, which is a basidiomycete typically 

causing brown rot, produces digestive enzymes capable of removing cellulose and 

hemicellulose. The wood shrinks upon drying and cross-checking occurs making the 

wood brittle (Rayner and Boddy 1988); this probably enables woodpeckers to 

excavate chunks of material more efficiently compared to wood without decay. 

One potential tree pathogen was isolated from one wood sample. At a nest site 

found outside the primary study sites (not shown in fig. 1) we isolated a culture (No. 

13-1) which was identified as belonging to the genus Oedocephalum. One species in 

this genus represents the conidial (asexual) state of the basidiomycete Heterobasidion 

annosum, a common cause of butt and root rot in conifers (Agrios 1997, Barnett and 

Hunter 1998). 

We recorded from 1-10 distinct types of fungi with an average of 3.4 fungal 

types per woodpecker nest tree (N = 78). The presence of an ensemble of fungi in 

decaying wood surrounding a woodpecker nest cavity represents a complex 

community of organisms with the potential for multiple interactions. Some of these 

species interactions may be intricately related, such that a succession of fungi move 

from initial invaders through a series of organisms capable of utilizing various 

components of wood as these become available over the course of time. Some fungi 

may enhance the ability of other fungi to grow more effectively through the 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

788 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

substratum creating mutualistic associations. Conversely, some fungi may become 

antagonistic due to the presence of other microorganisms by competing for the same 

food source. Other organisms may impede the growth of neighboring fungi through 

the production of waste products or secondary metabolites (e.g., antibiotics, toxins). 

For example, Atlas and Bartha (1998) and Rayner and Boddy (1988) indicate that 

species of the soft-rot fungus Trichoderma are antagonistic to the growth of other 

fungi. Additionally, some fungi may exist as parasites or predators on other 

organisms present in the wood (e.g., nematodes, other fungal species). For example, 

cultures No. H97-14-1A and H97-14-2A (two unidentified fungi) were observed to 

be parasitizing either another fungal colony, a co-inhabitant in a mixed culture, or 

themselves (self-parasitism). Self-parasitism has been documented in other wooddecaying fungi (e.g., Stereum hirustutm), but the biological significance of this 

phenomenon is unknown (Rayner and Boddy 1988). 

Many of the fungi identified represent soft-rot fungi (Rayner and Boddy 1988) 

that primarily live off carbohydrates (e.g., hemicellulose, cellulose) found in moist 

wood or by-products of decay that leach into the wood through the activities of other 

microorganisms. These fungi may represent a succession of fungi that grow into the 

wood after gaining entrance in the heartwood and sapwood through the activities of 

primary wood-decay fungi (e.g., white rot and brown rot fungi), fungal pathogens, 

animal vectors (e.g., foraging woodpeckers), and/or wood-inhabiting and woodboring insects in injured living or dead trees. The relative abundance of secondary 

invaders into the wood and the establishment of a decay community in our samples 

suggests that the presence of this community also softens wood and facilitates the 

establishment of nest cavities by woodpeckers. We suggest that initial decay of trees 

is caused by a basidiomycete, such as Fomitopsis pinicola, which sets the stage for 

secondary invasion by a variety of soft-rot fungi and yeast species. The collective 

decay caused by this suite of organisms may then facilitate excavation of cavities by 

woodpeckers. It is possible that the introduction of a variety of fungal organisms, and 

not just one species, could expedite the use of trees by woodpeckers.

Experimental Tree Inoculations 

In 1997 and 1998, we completed inoculation of 650 trees, fulfilling the original 

experimental design (table 1). Fifteen of the inoculated stands were on Rayonier 

lands, nine on lands managed by the Department of Natural Resources, four on I. P. 

Pacific Timberlands Inc. lands, four on Weyerhauser lands, and two on John 

Hancock Timber Resource Group lands (fig. 2). During the summers of 1997 and 

1998, we inoculated 65 clusters of 10 trees each within 34 separate managed forest 

stands (table 3). A total of 650 trees were inoculated, 330 with viable fungus and 320 

trees served as controls and were inoculated with blank dowels. At one stand, we 

determined that the treatment cluster (T97-04; see Huss and others 1999) was most 

appropriately classified as a small-diameter tree stand with snags, but that the nearby 

control cluster (C97-04) contained too few snags. Therefore, two additional smalldiameter stands were located at another site with compatible characteristics to 

complete the pairing for those two mismatched clusters. 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 789 

Figure 2Location of fungal inoculation sites (identified by stars) in western 

Washington. Sites are on land owned by Rayonier (N=15), the State of Washington 

(managed by the Department of Natural Resources; N=9), I. P. Pacific Timberlands 

Inc. (N=4), Weyerhaeuser (N=4), and John Hancock Timber Resources Group (N=2). 

Table 3Summary of experimental inoculation treatments and controls completed during 

1997 and 1998 in western Washington. Each cluster involves the inoculation of 10 trees. 

Stand classification for experiment Treatment 

cluster 

Control 

cluster 

Western Hemlock 

 Large-diameter trees with snags 4 4 

 Large-diameter trees with few snags 4 4 

 Small-diameter trees with snags 4 4 

 Small-diameter trees without snags 5 4 

Douglas-fir 

 Large-diameter trees with snags 4 4 

 Large-diameter trees with few snags 4 4 

 Small-diameter trees with snags 4 4 

 Small-diameter trees without snags 4 4 

FOR KS

PO RT ANG ELES

O LY M PIC PE N INSU LA

0 20

km

O AK V IL LE

CENTRALIA

ABERDEEN

H OQ U IA M
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

790 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

In the process of searching for stands with suitable characteristics, we 

discovered that the age of a stand is not always directly correlated with mean tree 

diameter. For example, one stand (T97-05 and C97-05) had relatively small diameter 

trees, but was 147 yr old. We have classified that stand as a small-diameter tree stand 

with snags. Despite these exceptions, large diameter/older stands were on average 71 

yr old, whereas small diameter/younger stands typically averaged less than 51 yr in 

age (table 4). To facilitate efficient climbing, workers generally inoculated trees with 

the largest diameter (usually > 35 cm dbh) in small-diameter classified stands and the 

relatively small-diameter trees (< 50 cm) in large-diameter classified stands. Despite 

these opposing biases, inoculated trees in small diameter stands (0 dbh = 39 cm) were 

clearly smaller than the trees inoculated in large-diameter stands (0 dbh = 45 cm; 

table 4). These differences in tree diameters between older stands and younger 

inoculated stands were statistically significant (P < 0.001, t = 4.8 for comparison of 

treated plots, N = 33; P < 0.01, t = 3.1 for comparison of control plots, N = 32).

Table 4Mean characteristics of forest stands inoculated with Fomitopsis pinicola in 

western Washington, 1997 and 1998. 

 Treatment stands Control stands 

 Mean1 (N) Range Mean1 (N) Range 

Large diameter/older stands 

DBH (cm) 46.9 (16) 37.7-60.2 44.8 (16) 38.3-61.0 

Age (years) 71.4 (16) 49-197 71.4 (16) 49-197 

 

Small diameter/younger stands 

DBH (cm) 38.9 (16) 31.1-49.9 38.9 (16) 30.6-44.8 

Age (years) 50.8 (16) 30.0-147.0 51.8 (15) 30.0-147.0 1

Values were derived from trees treated and may not be representative of average tree characteristics in 

stand. 

Two classes of stands were particularly difficult to locate: larger tree diameter 

stands without snags and smaller tree-diameter stands with snags. These stand criteria 

are somewhat contrary to natural succession patterns. Later successional-stage forests 

generally exhibit some mortality and thus are very likely to contain a conspicuous 

number of snags. Conversely, early successional-stage forests normally have 

relatively little tree mortality coupled with the fact that small-diameter snags are 

often not persistent and fall over after a few years. For this reason, we accepted some 

stands in these two categories that only marginally fit our original study plan. The 

most difficult stand criteria to meet were older/large diameter tree stands with no 

snags. We will examine samples of inoculated trees at 3-yr intervals and determine if 

cavity-nesting species have colonized these sites. 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 791 

Establishment of Fomitopsis pinicola in Inoculated Trees 

One to three years after inoculation of trees with F. pinicola, fungal mycelia 

have been observed in some trees around the entrance of the original inoculation hole 

created when we introduced the fungus into the wood. The formation of basidiocarps 

or conks consistent with the morphology of this species was also observed in 2000 

(fig. 3), emerging from the bark just below the point of initial inoculation. Of 20 

randomly selected trees inoculated in 1997 and sampled in 1998, F. pinicola (redbelted conk), was retrieved from 14 (70 percent). Of the trees sampled in 1999, 20 

inoculated in 1997, and 18 inoculated in 1998, the success rate of retrieving the 

introduced fungus was 50 percent in both cases. We only took one wood sample from 

each tree; consequently, even trees from which F. pinicola was not recovered, it is 

likely that this fungus was successfully introduced into at least a few of these and 

missed by us during the retrieval and culture isolation process. Once it was 

determined that a tree possessed F. pinicola, we tested whether or not the strain 

recovered matched the strain introduced (i.e., 64A or 36A). Based on vegetative 

compatibility analysis, 100 percent (N = 33) of the samples collected matched the 

fungal isolate introduced previously into that tree (fig. 4). These results demonstrate 

that the fungal inoculations are largely successful (greater than or equal to 50 percent 

to 70 percent success) in introducing the desired fungus into both western hemlock 

and Douglas-fir. 

Figure 3Basidiocarp of the red belted conk (Fomitopsis pinicola) seen emerging 

from surface of a living western hemlock tree (T97-01-02) inoculated in 1997 (3-years 

post treatment). 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

792 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 4Pairing between isolates recovered from wood in 1998 (central colony) 

with trees inoculated with Fomitopsis pincola (64A) in 1997 with three test strains 

(peripheral colonies—36A, 43A, and 64A). Isolate 07-08 retrieved from wood is 

compatible with culture 64A but not with the other two peripheral cultures. 

Acknowledgments 

Funding for this study was provided by the Washington Forest Protection 

Association (directly and indirectly through the Cooperative Monitoring, Evaluation, 

and Research Program), by Rayonier, and by Arkansas State University. We are 

especially appreciative to all those who assisted us in accomplishing the goals of this 

project, especially Kathleen (Dickson) Juliano, who performed a good share of the 

laboratory and field work. Others who contributed substantially to the field and lab 

work include Andrew Beall, Courtney (Gipson) Stites, Kelly Helton, Linh Hoang, 

Kevin Knight, Tom Leeker, Tammy Roush, Cory Davis, Bob Davies, Mark Izatt, and 

Huisheng Chen. We extend our appreciation to Catherine G. Parks and her 

colleagues, whose work in this research area were informative and helpful in 

executing this project. We are also grateful for the helpful comments of Robert W. 

Lichtwardt and Steve Zack on earlier versions of this manuscript. 

36A

64A 

43A 

07-08 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 793 

References 

Agrios, G. N. 1997. Plant pathology. San Diego, CA: Academic Press. 

Alexopoulos, C. J.; Mims, C. W.; Blackwell, M. 1996. Introductory mycology. New York, 

NY: John Wiley & Sons, Inc. 

Arora, D. 1986. Mushrooms demystified: a comprehensive guide to the fleshy fungi. 

Berkeley, CA: Ten Speed Press. 

Atlas, R. M.; Bartha, R. 1998. Microbial ecology. 4th ed. Menlo Park, CA: 

Benjamin/Cummings Science Publishing. 

Barnett, H. L.; Hunter, B. B. 1998. Illustrated genera of imperfect fungi. 4th ed. 

Minneapolis, MN: Burgess Publishing Company. 

Bednarz, J. C.; Huss, M. J.; Varland, D. E. 1995. Interactions between fungi and cavity 

nesters: applications to managing wildlife and forests. State University, AR: Unpubl. 

proposal. Arkansas State University; 30 p. 

Bednarz, J. C.; Huss, M. J.; Varland, D. E. 1997. Interactions between fungi and cavity 

nesters: applications to managing wildlife and forests in western Washington. State 

University, AR: 1996 Annual Report. Unpubl. Report. Arkansas State University; 59 p. 

Bednarz, J. C.; Juliano, D. M.; Huss, M. J.; Beall, A. A.; Varland, D. E. 1998. Interactions 

between fungi and cavity nesters: applications to managing wildlife and forests in 

western Washington. State University, AR: 1997 Annual Report. Unpubl. Report. 

Arkansas State University; 69 p. 

Brown, E. R., technical editor. 1985. Management of wildlife and fish habitats in forests of 

western Oregon and Washington. Part 2-Appendices. Portland, OR: Publication 

Number R6-F&WL-192-1985, Department of Agriculture, Forest Service, Pacific 

Northwest Region. 

Bull, E. L.; Parks, C. G.; Torgersen, T. R. 1997. Trees and logs important to wildlife in the 

interior Columbia river basin. Gen. Tech. Rep. PNW-GTR-391. LaGrande, OR: 

Pacific Northwest Research Station, U.S. Department of Agriculture, Forest Service. 

Conner, R. N.; Rudolph, D. C.; Saenz, D.; Schaefer, R. R.. 1994. Heartwood, sapwood, and 

fungal decay associated with red-cockaded woodpecker cavity trees. Journal of 

Wildlife Management 58: 728-734. 

Elliot, T. J. 1985. Spawn-making and spawns. In: The biology and technology of the 

cultivated mushrooms. Flegg, P. B.; Spencer, D. M., Wood, D. A., editors. Chichester, 

UK: John Wiley & Sons; 131-177. 

Fritsche, G. 1978. Breeding work. In: The biology and cultivation of edible mushrooms. 

Chang, S. T.; Hayes, W. A. editors. New York, NY: Academic Press; 239-250. 

Huss, M. J. 1993. Spatial distribution among mycelial individuals of Lycoperdon 

pyriforme occurring on decaying logs. Mycological Research 97:1119-1125. 

Huss, M. J.; Juliano, D. M.; Bednarz, J. C.; Varland, D. E. 1999. Interactions between fungi 

and cavity nesters: applications to managing wildlife and forests in western 

Washington: summary report 1996-1998. State University, AR: Unpubl. report. 

Arkansas State University; 81 p. 

Jackman, S. M. 1975. Woodpeckers of the Pacific Northwest: their characteristics and 

their role in the forests. Corvallis, OR: Oregon State University, M.S. thesis. 

Larone, D. H. 1995. Medically important fungi: a guide to identification. 3rd. ed. 

Washington, DC: American Society of Microbiology Press. 
Fungal Inoculations to Create Woodpecker Habitat—Huss, Bednarz, Juliano, and Varland 

794 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

McClelland, B. R. 1977. Relationships between hole-nesting birds, forest snags, and 

decay in western larch-Douglas-fir forests of the Northern Rocky Mountains. 

Missoula, MT: University of Montana, Dissertation. 

Miller Jr., O. K. 1972. Mushrooms of North America. New York, NY: E. P. Dutton. 

Moore-Landecker, E. 1996. Fundamentals of the Fungi. 4th ed. Upper Saddle River, NJ: 

Prentice Hall. 

Mounce, I. 1929. Studies in forest pathology. II. The biology of Fomes pinicola (Sw.) 

Cooke. Canadian Department of Agriculture Bulletin No. 111, New Series: 1-65. 

Nobles, M. K. 1948. Studies in forest pathology. VI. Identification of cultures of woodrotting fungi. Canadian Journal of Research, Sect. C, 26, 281-431. 

Overholts, L. O. 1953. The Polyporaceae of the United States, Alaska and Canada. Ann 

Arbor, MI: University of Michigan Press. 

Rayner, A. D. M.; Boddy, L. 1988. Fungal decomposition of wood. Chichester, UK: John 

Wiley and Sons. 

Rippon, J. W. 1988. Medical mycology. 3rd ed. Philadelphia, PA: W.B. Saunders Co. 

Smith, A. H; Smith, F. V.; Weber, N. S. 1981. How to know the non-gilled mushrooms. 

2nd. ed. Dubuque, IA: Wm. C. Brown Company Publishers. 

Taylor, J. B. 1974. Biochemical tests for identification of mycelial cultures of 

basidiomycetes. Annals of Applied Biology 78: 113-123. 

Tsao, P. H. 1970. Selective media for isolation of pathogenic fungi. In: Horesfall, J. G.; 

Baker, K. F., editors. Palo Alto, CA: Annual Review of Phytopathology 8: 157-179. 

Worrall, J. J. 1997. Somatic incompatibility in basidiomycetes. Mycologia 89: 24-36. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 795 

Characteristics of Log Resources in 

Northeastern Oregon: Case Studies of Four 

Management Treatments1

Torolf R. Torgersen2

Abstract 

Logs have complex physical, biological, and functional attributes. The body of literature with 

detailed empirical data on log resources in diverse habitats in the Interior Columbia River 

Basin is sparse. Sampling schemes developed by the USDA Forest Service for assessing logs 

as woody fuel usually have translated amounts of logs into weight or volume per unit area 

(tons or ft3

 per acre). To depict amounts of logs in a more descriptive way—to assess wildlife 

habitat, for example—log resources may be more adequately described in terms of density, 

percentage cover, mean length, and combined length of logs per unit area, in addition to 

weight and volume. Sampling data are presented on log resources in the Blue Mountains of 

northeastern Oregon, which are compared to the standards set forth in the Pacific Northwest 

Regional Forester’s Eastside Forest Plan Amendment No. 2, Alternative 2, for establishing 

riparian, ecosystem, and wildlife standards for timber sales. Data from four case studies are 

presented that characterize log resources in harvested and unharvested mid- and late-structure 

mixed conifer and ponderosa pine stands. Two case studies describe log resources in three 

stands before and after salvage harvest to reduce fuels, but maintain large-diameter logs. Postsalvage numbers of logs (> 15 cm large-end diameter) per ha were 58 to 80 percent higher 

than pre-salvage densities. The proportion of large logs (> 30 cm large-end diameter) among 

all logs remaining after salvage declined by 3 and 10 percent in two stands and increased 6 

percent in one stand. Tonnage of logs increased by 4, 7, and 54 percent in the salvaged stands. 

Breakage of logs from felling and heavy equipment resulted in reductions in log lengths from 

about 8 m pre-salvage to 5 m post-salvage. Post-salvage amounts of log resources observed in 

all the harvested stands were generally higher than prescribed by the Eastside Forest Plan 

Amendment No. 2. 

Introduction 

Coarse woody debris (CWD) in all its forms has important physical, chemical, 

and ecological values in healthy forests. These values are well documented elsewhere 

in these proceedings (Laudenslayer and others 2002). However, what is largely 

unknown about CWD in general, or logs in particular, is how much is needed to 

support the complex of ecological functions dependent upon this stratum. A 

fundamental aspect of understanding ecological functions in a particular stratum such 

as logs is having the tools to quantify or otherwise describe that resource. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Retired Research Entomologist, Pacific Northwest Research Station, Forestry and Range Sciences 

Laboratory, USDA Forest Service, 1401 Gekeler Lane, La Grande, OR 97850 (e-mail: 

ttorgersen@fs.fed.us) 
Log Resources in Northeastern Oregon—Torgersen 

796 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Appropriate log sampling techniques must be able to cope with an array of variables 

over a wide range of densities and distributions, and that will describe the log 

resource in ways that have relevance to managers with a broad spectrum of biophysical and socio-economic views of what a forest ecosystem should be or do. 

Because fire behavior and management are affected significantly by the abundance, 

distribution, and size characteristics of CWD, considerable energy has been devoted 

to portraying amounts of CWD as fire fuels (Brown 1974; Fischer 1981a, b; Koski 

and Fischer 1979; Maxwell and Ward 1976, 1980; Walstad and others 1990). Fuels 

specialists in the USDA Forest Service have typically described CWD in terms of 

tonnage (short tons) or volume (ft3

) per acre. But for the wildlife biologist who wants 

to assess log resources in ways that are relevant to wildlife, these two parameters are 

not very descriptive or useful. For example, tonnage is not a particularly relevant 

parameter for defining requirements for rodents whose numbers are related to 

percentage of the forest floor covered by CWD (Carey 2000, Carey and Johnson 

1995, Wilson and Carey 2000). Similarly, quality of foraging habitat for pileated 

woodpeckers has been found to be related to density and size-class distribution, not 

tonnage, of logs in home ranges (Bull and others 1997, Torgersen and Bull 1995). 

Other forest professionals—mycologists, silviculturists, soil scientists, fire ecologists, 

economists, or logging engineers—will have their own views of useful descriptive 

parameters, and ways of looking at CWD as resource or risk. 

With the broadening appreciation for the values of CWD, management is being 

called on to both quantify these resources, and to provide guidelines for its 

management in planning documents. In the Forest Service’s Pacific Northwest 

Region, one such planning document is the Regional Forester’s Eastside Forest Plan 

Amendment Number 2, Alternative 2. This directive was issued as a “Decision 

Notice for the Revised Continuation of Interim Management Direction Establishing 

Riparian, Ecosystem, and Wildlife Standards for Timber Sales” (Lowe 1995). The 

Decision Notice identified interim vegetative structural stages for ecosystem 

standards, and clarified wildlife standards (hereafter referred to as the “Standards”) 

for nine National Forests on the east side of the Cascade Mountains in the Pacific 

Northwest. These Standards are being applied pending completion of an Eastside 

Ecosystem Management Strategy for the Pacific Northwest Region. A portion of the 

Decision Notice identifies the need for snags and down logs for wildlife nesting, 

roosting, and feeding. The Standards stipulate appropriate amounts and sizes of logs 

in specific stand types. Table 1 shows the prescribed Decision Notice Standards, and 

their approximate metric equivalents, for ponderosa pine (Pinus ponderosa Dougl. ex 

Laws.), mixed conifers, and lodgepole pine (P. contorta Dougl. ex Loud.) stand 

types. 

Embedded in these Standards are four terms for expressing amounts of log 

resources; three of which bear explanation. One of the implicit terms might be called 

“minimum log size.” The Standards stipulate that logs under consideration in mixedconifer and ponderosa pine stands shall be >6 feet long (1.8 m) and >12 inches (30.5 

cm) in diameter at the small end. For convenience, such logs will be referred to here 

as “qualifying logs.” The three explicit terms used to describe qualifying logs in the 

Standards are “diameter at small end,” “total lineal length,” and “pieces per acre.” 
Log Resources in Northeastern Oregon—Torgersen 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 797 

Table 1—Log standards as presented in the Regional Forester’s Eastside Forest Plan, (Lowe 

1995). 

Stand type Pieces per acre Diameter at 

small end 

Piece 

length 

Total lineal length 

Ponderosa pine 3-6 

(7-15 per ha) 

12 in. 

(30 cm) 

>6 ft. 

(2 m) 

20-40 ft. 

(6-12 m) 

Mixed conifer 15-20 

(37-49 per ha) 

12 in. 

(30 cm) 

>6 ft. 

(2 m) 

100-140 ft. 

(30-43 m) 

Lodgepole pine 15-20 

(37-49 per ha) 

8 in. 

(20 cm) 

>8 ft. 

(2.5 m) 

120-160 ft. 

(37-49 m) 

 “Diameter at small end” may be misleading because it does not refer to the 

actual small end of the log. For example, given a ponderosa pine log that is 11 m 

long, 50 cm in diameter at its larger end, and 20 cm at its smaller end, the stipulated 

30.5 cm (12 inches) “small end diameter” is not an “end” at all, but the place along 

the log’s length at which the log is 30.5 cm. This is a relevant point in explaining the 

term—“total lineal length.” First, only qualifying logs in terms of minimum piecelength and diameter can contribute to total lineal length. In the above example of the 

11-m-long ponderosa pine log, only about 7.15 m would count toward its qualifying 

“lineal length” because only that much of the log is equal to or greater than the 

stipulated 30.5 cm “small end diameter.” The sum of the qualifying lineal lengths3

 of 

individual logs in a stand or sampling unit contributes to “total lineal length” per 

acre. “Pieces per acre” is simply an expression of the number per acre of log pieces 

of the stipulated qualifying size. 

Empirical data that present log resources in terms of the explicit log descriptors 

used in the above Standards are scarce. In fact, there are also no well-established 

sampling protocols for estimating either number of logs or their total lineal length per 

unit area. Computer outputs for Forest Service fuels inventories that are conducted 

with the line-intersect sampling protocols of Brown (1974) routinely express log 

resources as tonnage and weight, not in terms of density or total lineal length. To 

determine the parameters stipulated in the Standards, the line intersect sampling 

protocols would have to be expanded to include at least log lengths and large-end 

diameter (LED) of intersected logs. Log-taper factors for particular species of logs 

could then be used to calculate total qualifying lineal length of logs. If samplers 

added small-end diameter (SED) to the measurements collected during line-intercept 

sampling, then total lineal length could be calculated using one or more appropriate 

formulae.3

 But the point is that these additional measurements are not now routinely 

being collected. 

 

3

 The amount of qualifying length (m) in a log may be calculated by using the following equation: QL = 

TL (BPD – LED / SED – LED); where QL is qualifying length of a log; TL is total log length; BPD is 

the qualifying break- point-diameter, e.g. 0.305 m (12 inches); LED is large end diameter; and SED is 

small end diameter of the log. All dimensions in meters. Example: If TL = 11m; BPN = 0.305m; LED = 

0.50m; and SED = 0.20m; then QL = 7.15m. 
Log Resources in Northeastern Oregon—Torgersen 

798 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The objectives of this paper are to describe log resources in selected mixed 

conifer and ponderosa pine stands, before and after treatment, under four 

management scenarios, and to compare this new information with the Standards for 

log retention as set forth in the Region 6 Decision Notice. For these comparisons I 

will use log resource descriptors from four case studies of selected stand types and 

treatments in northeastern Oregon: 1) in late-structure stands 40 years after selective 

harvest; 2) before and after salvage/fuel-reduction harvest; 3) before and after a fuelreduction harvest to conserve late-structure large trees; and 4) after selection harvest 

and prescribed underburn. 

Study Areas and Methods 

The forest stands we examined are all in the Blue Mountain Province in 

northeastern Oregon. For the log inventories reported here, logs had to be > 15 cm (6 

inches) at their large end and > 2 m (6.6 feet) long. For each log, whether in fixedarea plots or on transects, we recorded large-end diameter (LED) and small-end 

diameter (SED) to the nearest cm, and length to the nearest m. Decay class was 

tallied to determine weight of logs (Brown and See 1981). Smalian’s formula 

(Wenger 1984) was used to compute volume. When line-intercept sampling was used 

(as in case study 4), the equations of DeVries (1973) were used to calculate log 

variables on a per ha basis. 

Log resources are presented in terms of the traditional variables of volume and 

tonnage per unit area as used in fire fuels inventories. Density, mean length of logs, 

and total lineal length of logs per ha are presented because these are the variables 

stipulated in the Standards. Total lineal length of logs was obtained by first 

calculating the amount of qualifying length in each log,3

 and adding the qualifying 

lengths to obtain total lineal length per unit area. Although inventories of log 

resources do not routinely use density as an expression of measurement, this variable 

is used in the Standards and in some studies of wildlife use of logs (Bull and others 

1995, 1997; Torgersen and Bull 1995). Percent cover of logs was added as a variable 

to describe log resources because of the wide use of this variable to describe habitat 

for small mammals (Buchanan and others 1999, Carey and Johnson 1995, Carey and 

others 1999, Wilson and Carey 2000). This variable is also referred to as projected 

area or projected cover (Caza 1993, Harmon and Cromak 1987, Marshall and others 

2000). 

Differences between log resources before and after salvage harvesting were 

tested using the t-test (SPSS software).4

Case 1—Late-structure Stands 

Study stands were selected in the Five-Lock Forest Demonstration Area on the 

Umatilla National Forest about 20 km west of Ukiah, Oregon. Twelve stands were 

chosen to represent three stand types: 1) designated old-growth mixed conifers; 2) 

mid- to late-structure mixed-conifers; and 3) late-structure ponderosa pine. These 

stands were relatively natural, i.e., without recent harvest entries. The term “natural” 

for characterizing these stands is used advisedly because virtually all of the stands 

 

4

 Mention of trade names or products is for information only and does not imply endorsement by the 

U.S. Department of Agriculture. 
Log Resources in Northeastern Oregon—Torgersen 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 799 

had some selective harvesting for the largest ponderosa pine and Douglas-fir about 

40 years ago. Also, fire control would certainly have altered fire-return intervals 

compared with patterns existing prior to the time of European settlement in the 19th

century. Each of the three stand types was represented by four study stands 5-12 km 

apart. Within each of the four 10-15 ha stands there were ten randomly located 20 x 

20-m plots on which log inventories were conducted. 

Case 2—Salvage/Fuel-reduction Harvests 

One mixed-conifer stand each was located in the MacKay and Lane Creek 

drainages of the Wallowa-Whitman and Umatilla National Forests 30 and 50 km 

west of La Grande, Oregon. These 12 and 15 ha stands had mid- to late-structure 

Douglas-fir (Pseudotsuga menziesii [Mirib.] Franco) and grand fir (Abies grandis

[Dougl. ex D.Don] Lindl.), with minor amounts of ponderosa pine and western larch 

(Larix occidentalis Nutt.). Both stands had suffered heavy defoliation in the course of 

a western spruce budworm (Choristoneura occidentalis Free.) outbreak from 1980-

1992 (Scott and Schmitt 1996). The heavy mortality sustained in these two areas 

prompted District managers to prescribe salvage sales in 1996 to both reduce fuels 

and to maintain late and old structural components of large-diameter live and dead 

trees and logs. The prescription stipulated that only dead or dying trees with less than 

50 percent live crown and < 38 cm (15 in.) dbh could be harvested. Large logs with 

the same minimum large end diameter were also to be left. In 1994, we did a 

comprehensive pre-salvage log inventory in each of the stands. We sampled 20 and 

30 randomly distributed 10 x 10-m plots at the Lane and MacKay stands, 

respectively. In 1996, we conducted a post-salvage inventory on the same plots to 

characterize changes in log resources. In each plot, we measured all logs with a largeend diameter (LED) >15 cm, a minimum length of 2 m, and whose mid-length-point 

lay within the plot boundaries. 

Case 3—Fuel-reduction Harvest to Retain Old-growth 

Characteristics 

This site was at Frog Heaven on the Umatilla National Forest about 42 km 

southwest of La Grande. This stand was the subject of a study reported by Bull and 

others (1995), in which the management objective was to protect old, large-diameter 

living and dead stems by lowering fire risk, and to encourage regeneration. The study 

was laid out within harvest units designed to examine the effects of a fuel-reduction 

treatment to protect late-structure stands that had a heavy component of large trees. 

There were several large trees in these stands that were nesting or roosting trees for 

pileated woodpeckers (Dryocopus pileatus) and had been used for several years by 

nesting Vaux’s swifts (Chaetura vauxi). The stand had sustained repeated heavy 

defoliation by the western spruce budworm during a local outbreak from 1980-1992 

(Scott 2000). Mortality of many trees of all ages in the site had created a high risk 

that any fire would completely destroy the old-growth character of the site in an area 

that had few stands with large-trees and/or large-log structural components. This 

study site was represented by three stands: two contiguous stands of about 8 ha each 

that would be harvested in 1994 to reduce fuel-loading, and one untreated control 

stand of 22 ha. Sampling was done within 10-m-wide belt transects that were divided 

into contiguous 10-m-long plots. The belt transects were laid out along random 

azimuths such that they were completely within the study stands. There were 750 m 
Log Resources in Northeastern Oregon—Torgersen 

800 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(75 plots) of belt transect in the treated stands and 400 m (40 plots) of belt transect in 

the control stand. The same log parameters as for the other studies were collected and 

summarized on the basis of treatment. Pre-treatment sampling was done in the fall of 

1993; salvage logging was done during the ensuing winter of 1993-94 when the 

forest floor was snow-covered; and post-treatment sampling was done in the summer 

of 1994. We prescribed harvest activities be conducted only when the ground and 

logs were snow-covered to minimize log breakage. Previous experience had shown 

us that the activity of harvesting equipment on bare logs resulted in undue breakage. 

For this paper, summaries of log resources were combined for the two treated stands, 

and the control stand was summarized alone. Because this study was completed and 

published before the Standards were established in 1995, the original data were 

reanalyzed to produce specific information that would permit meaningful 

comparisons with the Standards. 

Case 4—Selection Harvest/Underburn in Ponderosa Pine 

Twelve study stands, approximately 15-75 ha each, were within the La Grande 

Ranger District, Wallowa-Whitman National Forest, in northeastern Oregon. The 

stands were equally divided between two areas in the drainages of the upper Grande 

Ronde River and Spring Creek. Stands were 25-30 km east and south of La Grande. 

These drainages are dominated by extensive stands of ponderosa pine and mixed 

conifers. All of the stands had been underburned between 1993 and 1996, and were 

classified by District silviculturists as being in the understory reinitiation structural 

stage of Oliver and Larson (1990). The underburn treatment was designed to favor 

ponderosa pine and western larch by reducing encroachment of Douglas-fir and true 

firs in the understory. Log sampling was done in 1998. Twenty sampling points 

spaced at 30-m intervals along randomized transect lines were used to characterize 

log resources in each of the 12 stands. Each sampling point became the center for 

three 20-m-long radiating transects along which logs were tallied. Each of the 

radiating transects was begun 2 m from the plot center. This arrangement yielded 60 

m of log-sampling-transect per plot; 1200 m per stand. We tallied each log that was 

intercepted by a transect. 

 

Results and Discussion 

Case 1—Late-structure Stands 

Log inventories in the Five-Lock late- and old-structure mixed-conifer and 

ponderosa pine stands (table 2) showed high densities of both large (> 30 cm LED) 

and small (>15 cm LED) logs, and moderately high densities of large logs as 

compared with the other cases reported here (cf. tables 3-5). These Five-Lock stands 

have remained largely undisturbed by harvesting for about 40 years. However, in the 

old-growth sites and the mid- to late-successional mixed conifer sites, quantities of 

Douglas-fir and grand fir logs were presumably generated as a result of the budworm 

outbreak of 1980-92. The densities of 59-79 large logs per ha we recorded there are 

substantially higher than the 37-49 per ha post-harvest densities prescribed in the 

Standards for mixed conifer stands (table 1). This suggests that well-timed salvage or 

fuel-reduction harvests might have been prescribed on the grounds of reducing 

amounts of CWD, and thereby diminish fire risk and hazard. Research by Bull and 

Holthausen (1993) determined that there were about 240 logs per ha in the pileated 

woodpecker home ranges that included the very same stands that we inventoried for 
Log Resources in Northeastern Oregon—Torgersen 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 801 

this case. Using an approximate value of 35 percent large logs (Torgersen and Bull 

1995) would yield about 84 large logs per ha within those home ranges. This is close 

to the range we determined for these stands. The relationship of the densities of 59 

and 79 large logs per ha to the 84 logs per ha observed by Torgersen and Bull (1995) 

is unclear. They may be either functionally lower or may be approaching an 

acceptable number for use by pileated woodpecker. 

Table 2—Log resources on the Five-Lock Demonstration Area, North Fork John Day Ranger 

District, Umatilla National Forest, Forest Service, U.S. Department of Agriculture, 1993. 

Logs > 15 cm in large-end diameter Logs > 30 

cm LED1

Logs >30 

cm SED2

Stand 

Type 

Logs per 

ha 

Percentage 

cover 

m3 per 

ha 

Metric 

tons 

per ha 

Total lineal 

length (m) 

per ha 

Mean log 

length 

(m) 

Logs per 

ha 

Total 

lineal 

length 

(m) per 

ha 

Oldgrowth 

3

220 (28.2) 6.2 149 48 2,223 10.1 59 206 

Mixed 

conifers 

225 (37.1) 5.4 124 40 1,886 8.4 79 183 

Ponderosa 

pine 

115 (10.8) 1.5 38 12 658 5.7 25 47 

1

 large-end diameter 

2

 small-end diameter 

3

 standard error in parentheses 

With mean log lengths of 8.4-10.1 m, our sites had about 183-206 m of total 

lineal length of qualifying logs. Home ranges of pileated woodpeckers studied by 

Torgersen and Bull (1995) and Bull and others (1997) had total lineal lengths of 

qualifying logs between 294-362 m per ha. These amounts contrast with the 30-43 m 

of total lineal length prescribed in the Standards. However, it should be mentioned 

that the Standards were not designed to specifically provide amounts of CWD that 

would support pileated woodpeckers. Given the contrasts between the Standards and 

use of the Five-Lock stands by pileated woodpeckers, as well as those reported in the 

literature for foraging habitat by pileated woodpeckers, managers need to be 

informed about the presence and needs of certain wildlife species in stands for which 

harvest prescriptions are planned. Unfortunately, quantitative information about the 

log-resource requirements for most species of wildlife is not available. 

In the Five-Lock ponderosa pine stands, the density of 25 qualifying large logs 

per ha was much higher than the 7-15 logs per ha prescribed in the Standards. There 

had been no major insect or fire disturbances in the ponderosa pine stands that 

corresponded to the budworm outbreak in mixed conifers that would have accounted 

for these amounts of CWD. Thus, despite harvesting operations with emphasis on 

removing large pines 40 years ago, there were, nonetheless, relatively large amounts 

of qualifying CWD as a consequence of normal recruitment from standing trees and 

snags. Control of fire undoubtedly played a role in maintaining larger amounts of 

CWD that might otherwise have burned under pre-settlement fire-return intervals. 
Log Resources in Northeastern Oregon—Torgersen 

802 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Case 2—Salvage/Fuel-reduction Harvests 

In the aftermath of the western spruce budworm outbreaks and the subsequent 

activity of the Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) and fir 

engraver beetle (Scolytus ventralis LeConte) in northeastern Oregon from 1980-1992 

(Scott and Schmitt 1996), there were vast acreages of standing dead trees that are 

continually falling and adding to fuel-loading and risk of fire. Because of an active 

market for chips, many harvest sales were designed to salvage the standing dead 

volume to diminish the potential for adding further to fuel-loading, especially in 

mixed conifer stands. This case study followed two such stands in which Forest 

Service District managers chose the management option of salvaging standing dead 

trees and removing smaller down logs that were contributing to fuel loading. 

Prescriptions for these harvests were written with the intent of maximizing the 

retention of large snags and large logs for their wildlife values, but to remove smaller 

snags and logs that represented a present or future risk as fuel for wildfire. Table 3

and Figure 1 show how amounts of CWD changed between pre-harvest and postharvest in the Lane and MacKay harvest units. Post-harvest measures of CWD 

changed in relevant ways. The numbers of all logs remaining post-harvest was 

significantly higher in Lane (n = 20, t = -3.22, p = 0.004) and MacKay (n = 20, t = -

2.65, p = 0.016). The number of large logs increased, but not significantly so. 

Conversely, the proportional representation of large logs among those remaining on 

the ground declined slightly. Percentage cover, volume, and tonnage increased only 

modestly; varying from 1-14 percent (table 3, fig. 1). 

Table 3—Log resources before and after a salvage harvest to reduce fuel-loading in two 

stands with heavy tree mortality resulting from a 12-year outbreak of western spruce 

budworm (Choristonerua occidentalis Free.), in northeastern Oregon, Wallowa-Whitman and 

Umatilla National Forests, Forest Service, U.S. Department of Agriculture, 1994, 1996. 

Logs > 15 cm in large-end diameter Logs > 30 

cm LED1

Logs >30 

cm SED2

Stand 

(year) 

Logs per ha Percentage 

cover 

m3 per 

ha 

Metric 

tons per 

ha 

Total 

lineal 

length 

(m) per 

ha 

Mean log 

length 

(m) 

Logs per 

ha 

Total lineal 

length (m) 

per ha 

Lane Creek 

(1994) 

3

205 (82.3) 2.9 73 23 1,385 6.8 59 132 

Lane Creek 

(1996) 

350 (140.5) 3.3 75 24 1,451 4.1 67 140 

MacKay 

Creek 

(1994) 

385 (156.4) 5.6 95 30 3,565 9.2 37 132 

MacKay 

Creek 

(1996) 

610 (246.3) 6.0 101 32 3,355 5.4 42 197 

1

 large-end diameter 

2

 small-end diameter 

3

 standard error in parentheses 
Log Resources in Northeastern Oregon—Torgersen 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 803 

For these two stands, log density alone would have been a poor descriptor of 

harvest effects on CWD because harvest activity created more but shorter pieces of 

wood than were present pre-harvest. In the MacKay units, post-harvest log lengths 

were significantly (n = 20, t = 3.83, p = 0.001) only about half as long as those at preharvest (5.4 vs. 9.2 m). In the Lane Creek unit, post-harvest log lengths were about 

two-thirds as long as pre-harvest log lengths (4.1 vs. 6.8 m), which was only a 

marginally significant difference (n = 20, t = 2.21, p = 0.041). Taken together, postharvest log lengths in these units were about 40 percent as long as pre-harvest lengths 

(fig. 1). 

The measures of success of these harvests in terms of their having retained the 

prescribed desired large log component are mixed. Specifically, the absolute numbers 

of large logs (> 30 cm in LED) per unit area were increased by 14 percent postharvest, but not statistically significantly so. The percentage composition of large 

logs among the residual logs was about a third less than at pre-harvest. Percentage 

composition of large logs among all residual logs fell from 10 percent to 7 percent at 

MacKay, and from 29 percent to 19 percent at Lane. In something of the same 

manner as for density of logs, the absolute number of linear meters of these large logs 

increased by 6 and 49 percent at Lane and MacKay. The proportions of total lineal 

meters of large logs among all logs remained about constant, at about 5 and 10 

percent for MacKay and Lane, for pre- and post-harvest samples, but the changes 

were not significant in either case. Tonnage of logs was only marginally and nonFigure 1—Percentage change between pre- and post-harvest descriptors of log abundance in

selected stands treated with fuel-reduction harvests, Umatilla and Wallowa-Whitman National

Forests, 1993-1994. “All logs” refers to logs > 15 cm in large-end diameter; “large logs” are those

> 30 cm in large-end diameter. 













 



















 











































 



































-50

-25

0

25

50

75

100

125

150

Lane



 MacKay

 Frog

Logs per 

ha; all 

logs 

Mean 

length; all 

logs 

Logs per 

ha; large 

logs 

Metric 

tons; 

all logs 

Proportion 

of large 

logs 

among all 

logs 

Total lineal 

length; 

large logs

Percentage change from 

pre-harvest amounts

Percent change from pre-harvest amounts 
Log Resources in Northeastern Oregon—Torgersen 

804 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

significantly higher post-harvest but was represented mostly in the smaller diameter 

classes as opposed to the desired larger classes of logs >30 cm (table 3, fig. 1). In the 

overall sense of what sizes and amounts of logs were left at post-harvest, the intent of 

these salvage harvests did not meet expected goals. However, given that most of the 

small-diameter standing dead material was salvaged and that the large standing dead 

trees were retained, then it could be argued that recruitment will come from this 

desired large-diameter standing dead component. 

Case 3―Fuel-reduction Harvest to Retain Old-growth 

Characteristics 

The Frog Heaven site was a designed experiment used to study the potential to 

reduce fuels in a late-structure stand with many large legacy trees while still 

maintaining old growth structural components. The unharvested control site showed a 

large increase in log resources, from 215 to 335 logs per ha, over the course of one 

season: 1993-1994. This was due to some high wind events that brought down many 

of the dead trees in the stand. Percent cover in the control sites increased by only 1 

percent, but volume and tonnage increased dramatically. Windthrow and breakage 

were not confined to smaller trees; density of large logs increased twofold, and total 

lineal length of large logs increased about 40 percent, from 237 to 332 m per ha 

(table 4).

Table 4—Log resources after harvest of dead components to reduce fuel-loading and 

accelerate regeneration in old-growth stands occupied by nesting pileated woodpeckers and 

Vaux’s swifts in northeastern Oregon. Frog Heaven site, La Grande Ranger District, 

Wallowa-Whitman National Forest, U.S. Department of Agriculture, 1993, 1994. 

Logs > 15 cm in large-end diameter Logs > 30 

cm LED1

Logs >30 

cm SED2

Treatment 

(year) 

Logs 

per ha 

Percentage 

cover 

m3 per 

ha 

Metric 

tons per 

ha 

Total lineal 

length (m) 

per ha 

Mean log 

length 

(m) 

Logs per 

ha 

Total 

lineal 

length 

(m) per 

ha 

Pre-salvage 

(1993) 

314 5.6 109 35 3,080 9.5 57 220 

Post-salvage 

(1994) 

566 7.4 168 54 3,754 6.3 136 493 

Control 

(1993) 

215 4.3 101 32 1,830 8.5 57 237 

Control 

(1994) 

335 5.3 165 52 2,160 6.4 106 332 

1 large-end diameter 

2

 small-end diameter 

 In the salvaged stand, the increase in overall log density from 314 to 566 logs 

between pre- and post-salvage was statistically significant (n = 75, t = -7.33, 

p = <0.001) and is no doubt attributable, in part, to the same wind events of the 

intervening winter of 1993-94. Percent cover, volume, and tonnage all increased in 

much the same way as the control stand. Despite the effort to minimize log-breakage 

by confining harvesting activity to the period when there was snow cover, mean log 
Log Resources in Northeastern Oregon—Torgersen 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 805 

length was nonetheless reduced significantly (n = 75, t = 4.36, p = <0.001) in the 

harvested stands, and as compared with the control stand (33 vs. 25 percent shorter 

logs), presumably because of the activity of harvesting equipment. The density of 

large logs in the harvested stands increased statistically, from 57 to 136 logs per ha (n 

= 75, t = -2.95, p = 0.004), compared to large-log density in the control stand where it 

increased from 57 to 106 logs per ha (table 4, fig. 1). Some of this increase in the 

harvested stand might be attributed to the wind events of the winter, and not solely to 

the logging activity. We observed that many of the larger trees, which were intended 

to be left standing, were brought down in the process of felling the smaller trees as 

prescribed. It is interesting how closely the densities of large logs in the late- and oldstructure mixed conifer stands of Case 1 (table 2) approximate those in the pretreatment year (1993) at the old-growth stands of Case 3 (table 4). 

Because this management case at Frog Heaven was carried out in a research 

context, there was greater oversight for adherence to the harvest prescription and 

intent of the harvest. When compared with the Lane Creek and MacKay Creek 

harvests (fig. 1), the Frog Heaven harvest was similar in that it produced more and 

shorter logs; however, the number, proportional representation, linear length, and 

tonnage of large logs retained was vastly different. For all these latter variables, the 

Frog Heaven harvest was significantly higher in the percentage change from the preharvest condition (all p-values <0.001 to 0.002). In part, this may have been a 

function of the greater proportion of large-diameter snags in the stand. It also 

suggests that if rigid standards of performance are demanded from a logging 

contractor that preservation of large, legacy logs is possible. One could argue that the 

greater tonnage of residual logs post-harvest at Frog Heaven constitutes a fuel hazard. 

However, their overall greater proportional representation and physical size makes 

them less likely to ignite and burn except in the hottest of fires; thus, for the time 

being, the intent of reducing fire hazard was met. 

 

Case 4—Selection Harvest/Underburn in Ponderosa Pine 

The number of all logs remaining after harvest and underburning in the Spring 

Creek and Grande Ronde ponderosa pine sites (192 and 72 logs per ha) (table 5) 

bracketed the 115 logs per ha observed in the largely unharvested ponderosa pine 

stands in the Five-Lock Demonstration area (table 2). Thus, in terms of the overall 

CWD component, (i.e., excluding the overstory that would provide recruitment for 

logs in the future), the Spring Creek and Grande Ronde harvest/underburn treatments 

approximated the relatively undisturbed, (i.e., not recently harvested), ponderosa pine 

stands in Case 1. The post-harvest/underburned Spring Creek and Grande Ronde 

stands easily exceeded the Standards for density of large, qualifying logs (20 and 25 

logs vs. the Standard of 7-15 logs per ha) and for total lineal length (85 and 130 m vs. 

the Standard of 6-12 m per ha) (tables 1, 5). As a consequence of the greater mean 

length of logs in these harvested/underburned sites, total lineal length of logs was 

substantially greater (85 and 130 m per ha) than in the Five-Lock ponderosa stands 

(47 m per ha) (tables 2 and 5, respectively). This suggests that even after the 

imposition of selective harvest and underburning in the Spring Creek and Grande 

Ronde stands, post-treatment density of logs still exceeded those observed in the 

relatively unexploited Five-Lock Case, as stipulated in the Standards. 
Log Resources in Northeastern Oregon—Torgersen 

806 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 5—Log resources after selection harvest and underburning to favor ponderosa pine 

and western larch, and reduce encroachment by Douglas-fir and grand fir in northeastern 

Oregon. La Grande Ranger District, Wallowa-Whitman National Forest, Forest Service, U.S. 

Department of Agriculture, 1998. 

Logs > 15 cm in large-end diameter Logs > 30 

cm LED1

Logs >30 

cm SED2

Stand 

(year) 

Logs 

per ha 

Percentage 

cover 

m3 per 

ha 

Metric 

tons 

per ha 

Total lineal 

length (m) 

per ha 

Mean log 

length 

(m) 

Logs per 

ha 

Total lineal 

length (m) 

per ha 

Spring 

Creek 

(1998) 

192 2.7 126 16 184 10.4 20 85 

Grande 

Ronde 

(1998) 

72 0.8 52 6 57 8.5 25 130 

1 large-end diameter

2

 small-end diameter 

This Case contrasts with Cases 2 and 3 that resulted in shorter log lengths as a 

consequence of harvesting activity in mixed conifer stands. Specifically, pretreatment vs. post-treatment lengths of logs in these ponderosa pine stands seemed to 

be less affected by harvesting than in those mixed conifer stands (table 5 vs. tables 3

and 4). Presumably, the lower density of logs on the ground allowed harvesting 

equipment more options of going around rather than over logs, preventing breakage 

of residual logs. 

 

Conclusions 

Overall, it is difficult to assess the success of the salvage/fuel-reduction 

harvests. Post-harvest tonnage of CWD increased modestly, but presumably the 

remaining large standing dead trees, which were maintained for their value to wildlife 

structure, would ultimately contribute less to fuel-loading and hazard on the site than 

if the small standing-dead component (<38 cm dbh) had been left to fall. The 

outcome of these salvage/fuel reduction harvests suggests that fuels were not reduced 

as much as one might intuitively think. However, the reduction in standing dead 

volume would represent a lesser fuel risk, and the crushing and breaking down of 

much of the CWD on the site would lead to fuels being in closer contact with the 

ground. The crushed fuels would be expected to remain moist longer into the fire 

season, and to decay more rapidly, minimizing fire risk and hazard for the near 

future. 

A question that remains, however, is whether the residual stands in these four 

cases will continue to provide the targeted levels of log resources through recruitment 

of some of the residual trees that die and/or fall. The Decision Notice states that, “it is 

not the intention of this direction to leave standing trees for future logs in addition to 

the required snag numbers” (p. 11, Lowe 1995). Thus, it is possible for the Decision 

Notice Standards for logs to be met after harvest, but not have an adequate cohort of 

residual trees left to provide for future log resources. The concept of having a 
Log Resources in Northeastern Oregon—Torgersen 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 807 

sustainable flow of resources, including CWD, is crucial to management, and should 

be addressed in future standards. 

Determining if standards are being met after management prescriptions have 

been applied, or to otherwise quantify CWD, requires statistically valid and efficient 

sampling methods for this stratum. Bate and others (2002) present an alternative to 

the time-honored line-intercept inventory method of Brown (1974) for log sampling. 

Specifically, their alternative uses a time-saving strip-plot method for measuring 

density, percentage cover, total lineal length, weight, and volume of logs in stands 

and landscapes in interior northwest mixed-conifer stands. The method is also 

adapted to sampling in the lower log densities common in ponderosa pine stands. 

 Few inventories of log resources routinely use density as an expression of 

measurement (Bull and others 1995, 1997; Torgersen and Bull 1995), despite the fact 

that desired densities are stipulated in the Decision Notice Standards. Studies in 

wildlife ecology commonly use percentage cover to express log resources (Buchanan 

and others 1999, Carey and Johnson 1995, Carey and others 1999, Wilson and Carey 

2000). This variable is also referred to as projected area or projected cover (Caza 

1993, Harmon and Cromak 1987, Marshall and others 2000). Thus, for future 

standards that describe CWD, use of percentage cover (i.e. projected cover) would be 

a valuable descriptive parameter to include. Overall, for future inventories of CWD, 

sampling designs should supply information on density, percentage cover, and 

volume as minimum descriptive parameters for CWD > 15 cm in large-end diameter. 

Furthermore, measuring large-end diameters as continuous variables—so that they 

can be categorized according to any desired diameter classes—is a valuable data set 

for managers. 

The new information from these case studies suggests that the Decision Notice 

Standards, at least for mixed conifers and ponderosa pine, are attainable. But 

fundamental questions that still beg answers are “How much CWD is enough?” and 

“Are the Standards sufficiently high or too low?” Some newer published data partly 

address these questions. Based on the work of Bull and Holthausen (1993) and 

Torgersen and Bull (1995), for pileated woodpeckers at least, the Standards now 

appear too low! These data suggest that in pileated woodpecker home ranges the 

Standards are little more than half of what they could be in terms of pieces per unit 

area (59 to 77 per ha vs. 37 to 49 in the Standard). The piece-length Standard (> 2 m, 

with small-end diameter of 30 cm), regardless of management intent is only a third of 

what now seems appropriate. The concept in the Standards which stated that “longer 

logs may count for multiple ‘pieces’ without cutting them” (p. 11, Lowe 1995) 

recognized the value of long logs, but fell short of prescribing appropriately longer 

logs in sufficient numbers, largely because of the absence of appropriate data at the 

time. A mean piece-length standard of 6-9 m, for logs with a large-end diameter of >

38 cm, is closer to observed log lengths in mixed conifer stands in northeastern 

Oregon, for example (Bate and others 2002, Bull and others 1997). Also, the largeend diameter is a more efficient parameter to estimate than the Standards’ small end 

diameter of 30 cm somewhere along a log’s length. New piece-length standards of 6-

9 m would yield a new total lineal length standard approximating 300 to 600 m vs. 

the 30-43 m of the existing Standard. 

 The task of prescribing standards for how many, how big, and what kinds of 

logs to retain after management prescriptions is complex. It cannot be done without 

consideration for what there is in the residual standing living and dead components 

from which future CWD will be recruited over time. Having empirical data on CWD 
Log Resources in Northeastern Oregon—Torgersen 

808 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

to incorporate into predictive models—and then using those models to formulate 

realistic, attainable standards—is crucial to sustainable forestry. As science and 

society become more knowledgeable about the complexities of ecosystems and their 

management, the collection and analysis of empirical data on CWD will be as 

important as it has been for living trees. Such inventories also need to be coordinated 

with the habitat needs for selected wildlife species of concern. This will mean 

support, both within the National Forest System and in research, for aggressive 

inventory programs that will provide data on CWD that measure up to the same 

statistical standards as for commodity resources. 

References 

Bate, Lisa J.; Torgersen, Torolf; Garton, Edward O.; Wisdom, Michael J. 2002. Accuracy 

and efficiency of methods to sample logs for wildlife research and management. In: 

Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. 

Phillip; Lisle, Thomas E., technical coordinators. Proceedings of a symposium on the 

ecology and management of dead wood in western forests. 1999 November 2-4; Reno, 

NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; [this volume]. 

Brown, James K. 1974. Handbook for inventorying downed woody material. Gen. Tech. 

Rep. INT-16. Ogden, UT: Intermountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 24 p. 

Brown, James K.; See, Thomas E. 1981. Downed dead wood fuel and biomass in the 

Northern Rocky Mountains. Gen. Tech. Rep. INT-117. Ogden, UT: Intermountain 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 

48 p. 

Buchanan, Joseph B.; Lewis, Jeffrey C.; Pierce, John; Forsman, Eric D.; Biswell, Brian L. 

1999. Characteristics of young forests used by spotted owls on the western Olympic 

Peninsula, Washington. Northwest Science 73: 255-263. 

Bull, Evelyn L.; Holthausen, Richard S. 1993. Habitat use and management of pileated 

woodpeckers in northeastern Oregon. Journal of Wildlife Management 57:335-345. 

Bull, Evelyn L.; Torgersen, Torolf R.; Blumton, Arlene K.; McKenzie, Carol M.; Wyland, 

Dave S. 1995. Treatment of an old-structure stand and the effect on birds, ants, and 

large woody debris: a case study. Gen. Tech. Rep. PNW-GTR-353. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 12 

p. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 55 p. 

Carey, Andrew B. 2000. Effects of new forest management strategies on squirrel 

populations. Ecological Applications 10: 248-257. 

Carey, Andrew B., Johnson, Murray L. 1995. Small mammals in managed, unharvested 

young, and old-growth forests. Ecological Applications 5: 336-352. 

Carey, Andrew B.; Kershner, Janet; Biswell, Brian; de Toledo, Laura Dominguez. 1999. 

Ecological scale and forest development: squirrels, dietary fungi, and vascular 

plants in managed and unmanaged forests. Wildlife Monographs 142: 1-71. 

Caza, C. L. 1993. Woody debris in the forests of British Columbia: a review of the 

literature and current research. Land Management Handbook Number 78. Victoria, 
Log Resources in Northeastern Oregon—Torgersen 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 809 

B.C. Canada, Research Branch, British Columbia Ministry of Forests, Canada Forestry 

Service; 99 p. 

De Vries, P. G. 1973. A general theory on line intersect sampling with application to 

logging residue inventory. Wageningen, The Netherlands: Mededelingen 

Landbouwhogeschool 73-11; 23 p. 

Fischer, William C. 1981a. Photo guide for appraising downed woody fuels in Montana 

forests:grand fir-larch-Douglas-fir, western hemlock, western hemlock-western 

redcedar, and western redcedar cover types. Gen. Tech. Rep. INT-96. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 53 p. 

Fischer, William C. 1981b. Photo guide for appraising downed woody fuels in Montana 

forests: interior ponderosa pine, ponderosa pine-larch-Douglas-fir, larch-Douglasfir, and interior Douglas-fir cover types. Gen. Tech. Rep. INT-97. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 133 p. 

Franklin, J. F.; Cromack, K. Jr.; Denison, W.; McKee, A.; Maser, C.; Sedell, J.; Swanson, F.; 

Juday, G. 1981. Ecological characteristics of old-growth Douglas-fir forests. Gen. 

Tech. Rep. INT-118. Ogden, UT: Intermountain Forest and Range Experiment Station, 

Forest Service, U.S. Department of Agriculture; 48 p. 

Harmon, Mark E.; Cromak, Kermit, Jr. 1987. Coarse woody debris in mixed-conifer 

forests, Sequoia National Park, California. Canadian Journal of Forest Research 17: 

1265-1272. 

Koski, Wayne H.; Fischer, William C. 1979. Photo series for appraising thinning slash in 

north Idaho. Ogden, UT: Intermountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 50 p. 

Laudenslayer, William F., Jr.; Valentine, Brad; Weatherspoon, C. Philip; Lisle, Thomas E., 

technical coordinators. 2002. Proceedings of a symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture. 

Lofroth, E. 1998. The dead wood cycle. In: Voller, Joan, and Harrison, Scott, eds. 

Conservation Biology Principles for Forested Landscapes. Vancouver, British Columbia, 

Canada: University of British Columbia Press; 185-214. 

Lowe, John E. 1995. Decision notice for the revised continuation of interim management 

direction establishing riparian, ecosystem, and wildlife standards for timber sales. 

Regional Forester’s eastside forest plan Amendment No. 2, Alternative 2, 

Appendix B. Correspondence on file at the Pacific Northwest Region, USDA Forest 

Service, Portland, OR; 13 p. 

Marshall, P. L.; Davis, G.; LeMay, V. M. 2000. Using line intersect sampling for coarse 

woody debris. Forest Research Technical Report TR-003 Ecology. Nanaimo, B.C.: 

Vancouver Forest Region, Forest Service British Columbia, Canada Ministry of Forests; 

34 p. 

Maser, Chris; Anderson, Ralph G.; Cromack, Kermit, Jr.; Williams, Jerry T.; Martin, Robert 

E. 1979. Dead and down woody material. In: Thomas, Jack Ward, tech. ed. Wildlife 

habitats in managed forests--the Blue Mountains of Oregon and Washington. Agric. 

Handb. 553. Washington, D.C.: Forest Service, U.S. Department of Agriculture; 78-95. 

Maser, C. T.; Trappe, James M., tech. eds. 1984. The seen and unseen world of the fallen 

tree. Gen. Tech. Rep. PNW-GTR-164. Portland, OR: Pacific Northwest Research 

Station, Forest Service, U.S. Department of Agriculture; 56 p. 
Log Resources in Northeastern Oregon—Torgersen 

810 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Maxwell, Wayne G.; Ward, Franklin R. 1976. Photo series for quantifying natural forest 

residues in the: ponderosa pine and lodgepole pine types. Gen. Tech. Rep. PNWGTR-52. Portland OR: Pacific Northwest Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 73 p. 

Maxwell, Wayne G.; Ward, Franklin R. 1980. Photo series for quantifying natural forest 

residues in common vegetation type of the Pacific Northwest. Gen. Tech. Rep. PNWGTR-105. Portland OR: Pacific Northwest Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 229 p. 

Oliver, C. D.; Larson, B. C. 1990. Forest stand dynamics. New York: McGraw-Hill; 467 p. 

Parks, Catherine G.; Raley, C. M.; Aubry, K. B.; Gilbertson, R. L. 1997. Wood decay 

associated with pileated woodpecker roosts in western redcedar. Plant Disease 81: 

551. 

Scott, Donald W. 2000. Population analysis of Douglas-fir tussock moth in northeastern 

Oregon and southeastern Washington, 1999. Report BMPMSC-00-09. La Grande, 

OR: Blue Mountains Pest Management Zone, Wallowa-Whitman National Forest, Forest 

Service, U.S. Department of Agriculture; 100 p. 

Scott, Donald W.; Schmitt, Craig L. 1996. Forest health on National Forest lands in the 

Blue Mountains 1990-1996: Insects and diseases. Report BMZ-96-12. La Grande, OR: 

Blue Mountains Pest Management Zone, Wallowa-Whitman National Forest, Forest 

Service, U.S. Department of Agriculture; 42 p. 

Tallmon, D.; Mills, S. 1994. Use of logs within home ranges of California red-backed 

voles on a remnant of forest. Journal of Mammalogy 75: 97-101. 

Torgersen, Torolf R.; Bull, Evelyn L. 1995. Down logs as habitat for forest-dwelling ants--

the primary prey of pileated woodpeckers in northeastern Oregon. Northwest 

Science 69: 294-303. 

Walstad, John D.; Radosevich, Steven R.; Sandberg, David V. 1990. Natural and prescribed 

fire in Pacific Northwest forests. Corvallis, OR: Oregon State University Press; 317 p. 

Wenger, Karl F. 1984. Forestry handbook. 2d ed. New York: John Wiley & Sons; 1335 p. 

Wilson, Suzanne M.; Carey, Andrew B. 2000. Legacy retention versus thinning: influences 

on small mammals. Northwest Science 74: 141-145. 

 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 811 

Sampling Methods for Snags and Large 

Trees Important to Wildlife1

Lisa J. Bate,2 Edward O. Garton,3 and Michael J. Wisdom4 

Abstract 

We developed efficient and accurate methods for sampling snags and large trees important to 

wildlife. These methods are described in detail in a recent Forest Service publication, which 

also includes spreadsheets, macros, and instructions to conduct surveys and analyses to 

estimate densities and distributions of snags and large trees on a landscape. These methods 

focus on optimizing sampling effort by choosing a plot size appropriate for specific forest 

conditions encountered. Two methods for assessing density are available. Method I requires 

sampling until a desired precision is obtained for a density estimate. Method II is designed to 

test for differences in observed snag density versus a desired target density. After collecting a 

minimum of 60 samples under method II, one may test for a significant difference between 

the observed and targeted densities. In addition, data can be used to calculate a distribution 

index. The value obtained from the distribution index helps managers assess whether the 

current distribution of snags and large trees across a subwatershed is adequate to meet the 

habitat needs of territorial cavity-nesters and other wildlife species. Wildlife use of snags and 

large trees may also be evaluated. 

Introduction 

Snags and large trees are important to a wide variety of wildlife species for 

survival and reproduction. (Bull and others 1997, Thomas and others 1979). 

Woodpeckers are an especially important group of species that rely on a continuous 

supply of snags and large trees. As primary cavity-excavators, woodpeckers create 

the cavities within snags or trees that they and a myriad of other species use as nest 

and roost sites. In turn, these same cavities also provide thermal and hiding cover for 

many resident wildlife species during the non-breeding season. 

National Forests are required by law to maintain viable populations of all native 

wildlife species (Forest and Rangeland Renewable Resources Planning Act 1974). 

Specifically, National Forests are required to monitor native species or their habitat to 

ensure the presence of viable populations through maintenance of well-distributed 

habitats throughout the planning area (U.S. Laws, National Forest Management Act 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Cooperative Wildlife Biologist, University of Idaho/Pacific Northwest Research Station, USDA Forest 

Service, La Grande, Oregon; 389 LaBrant Road, Kalispell, MT 59901 (e-mail: lisabate@cyberport.net) 3

 Wildlife Professor, University of Idaho, Department of Fish and Wildlife, University of Idaho, 

Moscow, ID 83844. 

4

 Research Wildlife Biologist, Pacific Northwest Research Station, USDA Forest Service, 1401 Gekeler 

Lane, LaGrande, OR 97850. 
Snag Sampling Methods—Bate, Garton, and Wisdom 

812 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

1976). Because woodpeckers play an integral role in forested ecosystems, they have 

been a primary focal species for monitoring efforts on National Forests (Bull and 

others 1991). 

Monitoring requires considerable time and money. Consequently, if resource 

specialists are to monitor habitat for woodpeckers and other cavity-nesters accurately, 

these specialists need efficient and statistically valid sampling methods. In response 

to this need, we produced a Forest Service General Technical Report (GTR) as a 

guide for resource specialists in the sampling and monitoring of snags and large trees. 

Included in the report (Bate and others 1999) are the spreadsheets, macros, and 

instructions needed to conduct all surveys and analyses pertaining to the estimation 

of snag and large tree densities, and their distributions on a landscape. 

This paper highlights the essential considerations for sampling snags and large 

trees on a landscape as a companion to the earlier GTR of Bate and others (1999). 

Specifically, this paper was written to facilitate a better understanding of the methods 

required for accurate estimation of snag and large tree density and distribution, in 

support of monitoring efforts for cavity-nesting birds on National Forests. 

Improvement in the understanding of these methods and their accuracy is particularly 

important in light of findings that indicate failure of National Forest management to 

provide adequate densities of snags and large trees for cavity-nesters (Bate 1995, 

Morrison and others 1986). 

Key Considerations for Sampling Snags and Large 

Trees 

Before beginning a sampling program for snags or large trees, resource 

specialists must first make two key decisions about plots: plot shape and size. In 

general, long, narrow or rectangular plots work better than circular or square plots 

(Krebs 1989). This is because the habitat components of a forest are never uniformly 

distributed; rather, habitat components such as snags tend to occur in clumps or 

patches. Consequently, rectangular plots are better for sampling because they cross 

through more clumps of snags or trees, rather than encircling, or missing clumps 

completely. The outcome is a lowered variance, which translates into smaller sample 

sizes. Rectangular plots, therefore, are recognized as the optimal plot shape for 

sampling in patchy habitats (Krebs 1989) and are the shape that we recommend. 

The second decision, relating to what size of plot to use, is not readily 

discernible. This is because no single plot size is optimal for all forested conditions. 

We define the optimal plot size as that which minimizes sampling effort while 

maintaining accuracy and precision. Each forest situation must be analyzed 

independently, because the optimal plot size depends on a number of factors such as 

density and distribution of snags or large trees, topography, seral stage, and amounts 

of downed wood or shrub cover. 

Analysis for Optimal Plot and Sample Size 

Sometimes a plot size can be selected based on knowledge of the area, but in 

many forested areas the optimal plot size for sampling snags or large trees is 

unknown until a pilot sample is conducted. A pilot sample provides an initial 

estimate of the density of snags or trees likely to exist in a given area. A pilot sample 
Snag Sampling Methods—Bate, Garton, and Wisdom 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 813 

also provides information about the distribution of snags or trees. Information from 

the pilot survey can be used in two specific ways with the spreadsheets found in Bate 

and others (1999): to identify optimal plot size and to calculate the number of 

samples needed to obtain a desired level of precision. 

Eight plot sizes are available for use within the spreadsheets provided by Bate 

and others (1999). As part of the pilot sample, field observers record the 

perpendicular distance to a snag or large tree from the centerline of the transect. 

Based on these distances, a macro within the spreadsheets truncates the number of 

snags or trees in 5-meter intervals. This allows the user to estimate the density and 

variance of snags for each of the eight plot sizes. Subsequently, this information is 

used in the spreadsheets in a variety of ways. First, the spreadsheet calculates the 

total number of plots and hectares required for sampling with each plot size. 

Secondly, this information is combined with a cost factor to help determine which 

plot size is optimal based on the given forest conditions. 

Cost seems to be a function of three factors: visibility, terrain, and density. 

Limited visibility owing to the seral stage or dense shrub cover within a stand can 

increase search time for snags, and therefore cost, if too wide of a plot is used for 

sampling. Too wide of a plot can also lead to biased estimates of density. Similarly, if 

field conditions are difficult for an observer to travel through, or a consistently high 

number of snags or large trees (>15 per plot) are encountered within each plot, a 

narrower plot width is likely a better choice. The optimal plot size is that which 

minimizes sampling effort while maintaining accuracy and precision. 

 

Stratification 

When sampling on a landscape scale of a subwatershed or watershed, it will be 

rare that forest conditions will be similar throughout such large areas. Consequently, 

stratification is critical in reducing variance, and in turn, reducing sampling intensity 

needed to meet sampling goals. As a result, Bate and others (1999) provide a high 

level of detail about effective methods of stratification or the creation of 

homogeneous forest categories to reduce sample size requirements. To guide the 

stratification process, Bate and others (1999) include a spreadsheet called “Sample 

Size.” This spreadsheet calculates the sample size required and how the samples 

should be allocated by stratum (homogeneous categories). Two allocation methods 

are provided: a proportional method and optimal method. The proportional method 

allocates samples among strata based on the proportion of the area within each 

stratum. In contrast, the optimal allocation method incorporates both the proportion 

of the total area and the variance of each stratum. There are advantages and 

disadvantages to both approaches (Bate and others 1999). 

Density Analyses 

Two options for obtaining a density estimate are available. Under the first 

option, a sufficient number of samples are collected to obtain a desired level of 

precision (e.g., within 20 percent of the true mean 90 percent of the time). In areas 

where snag densities are high and not severely clumped, obtaining a density estimate 

within a desired precision usually can be done with a reasonable amount of effort. In 

areas that have been intensively harvested and few snags have been retained, 

however, the number of samples required (in hectares) to obtain a desired precision 
Snag Sampling Methods—Bate, Garton, and Wisdom 

814 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

can exceed the land area available. Consequently, Bate and others (1999) provide a 

second density analysis option, which is a straightforward statistical test to compare 

estimated densities with targeted densities. For example, is the density estimate of 

snags different from the Forest Plan standards, which requires five snags per hectare?

One great advantage of this method is that the test can be conducted after a minimum 

of 60 samples has been collected. 

Further Analyses 

Another feature of the Bate and others (1999) GTR and its spreadsheets is the 

method presented for calculating a distribution index. The distribution index helps 

managers assess whether the current distribution of target snags and large trees across 

a subwatershed is adequate to meet the habitat needs of territorial cavity-nesters and 

other wildlife species. The distribution index is a useful complement to the estimation 

of snag density because small areas of subwatersheds sometimes contain a major 

proportion of all snags in the subwatershed, rendering most snags as unavailable to 

territorial species. Thus, application of the distribution index gives managers 

appropriate insight about how well their snag density goals can be met from the 

standpoint of distribution. 

For resource specialists interested in more than density or distribution, the 

spreadsheets also offer an algorithm to calculate nesting use. This algorithm is given 

as a percent use value and can also be applied to calculate foraging use. 

Acknowledgments 

We thank Kim Mellen and Torolf Torgersen for kindly reviewing our 

manuscript. 

References 

Bate, Lisa J. 1995. Monitoring woodpecker abundance and habitat in the central Oregon 

Cascades. Moscow, ID: University of Idaho; 116 p. M.S. thesis. 

Bate, Lisa J.; Garton, Edward O.; Wisdom, Michael J. 1999. Estimating snag and large tree 

densities and distributions on a landscape for wildlife management. Gen. Tech. Rep. 

PNW-GTR-425. Portland, OR: Pacific Northwest Research Station; U.S. Department of 

Agriculture, Forest Service; 76 p. 

Bull, Evelyn L.; Holthausen, Richard S.; Marx, David B. 1990. How to determine snag 

density. Western Journal of Applied Forestry 5(2): 56-58. 

Bull, Evelyn L.; Carter, Bernie; Henjum, Mark; Holthausen, Richard; Johnson, J.; Mellen, 

Kim; Raphael, Martin. 1991. Protocol for monitoring woodpeckers and snags in the 

Pacific Northwest region of U.S. Forest Service. Unpublished report on file with U.S. 

Department of Agriculture, Forest Service, Pacific Northwest and Range Experiment 

Station, Forestry and Range Sciences Laboratory, LaGrande, OR; 8 p. 

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the interior Columbia River basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland, OR: Pacific Northwest Research Station, U.S. Department of Agriculture, 

Forest Service; 55 p. 

Cochran, William G. 1977. Sampling techniques, 3d ed. New York: John Wiley and Sons; 

428 p. 
Snag Sampling Methods—Bate, Garton, and Wisdom 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 815 

Krebs, Charles J. 1989. Ecological methodology. New York: Harper Collins Publishers, Inc.; 

654 p. 

Morrison, M. L.; Dedon, M. F.; Raphael, M. G.; Yoder-Williams, M. P. 1986. Snag 

requirements of cavity-nesting birds: are USDA Forest Service guidelines being 

met? Western Journal of Applied Forestry 1: 38-40. 

Thomas, Jack W.; Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. Snags. 1979. In: 

Wildlife habitats in managed forests—the Blue Mountains of Oregon and 

Washington. Agric. Handb. 553. Washington, DC: U.S. Department of Agriculture; 60-

77. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 817 

Accuracy and Efficiency of Methods to 

Sample Logs for Wildlife Research and 

Management1

Lisa J. Bate,2 Torolf R. Torgersen,3 Edward O. Garton,4 and 

Michael J. Wisdom5

Abstract 

We evaluated performance (accuracy and efficiency) of the line-intersect and strip-plot 

methods for estimating the density, length, percent cover, and weight of logs important to 

wildlife. To conduct the evaluation, we sampled 17 coniferous stands in northeastern Oregon 

and northwestern Montana. These stands contained a gradient of log conditions based on seral 

stage, physiography, disturbance regime, and history of timber management. A complete 

count (census) of logs in these stands was used to evaluate the precision, bias, and efficiency 

of each sampling method. Preliminary results indicated that both methods were relatively 

unbiased and precise. The strip-plot method, however, was more efficient in estimating 

density, but neither the strip-plot method nor line-intersect method was clearly more efficient 

in estimating length, percent cover, or weight. Consequently, which method is better depends 

on a variety of factors, particularly the stand conditions to be sampled and the log 

characteristics of most interest. Our results also demonstrated the strong difference in methods 

needed to sample logs for wildlife research and management versus conventional methods 

that have been used for fire management. 

Introduction 

Fallen trees, often referred to as logs or coarse woody debris, are a critical 

resource for a myriad of wildlife (Maser and others 1979). Logs act as a foraging 

substrate and a food base for a variety of birds and mammals (Carey and Johnson 

1995, Tallmon and Mills 1994, Torgersen and Bull 1995). Logs also function as 

thermal and hiding cover for many reptiles, amphibians, and mammals (Maser and 

others 1979, Parks and others 1997). Moreover, large hollow logs serve as den, 

hibernation, and shelter sites for black bear (Ursus americana), American marten 

(Martes americana), and a variety of small mammals (Parks and others 1997). 

Despite the importance of logs to survival of wildlife, little work has been done 

to develop and test methods to sample logs from the perspective of meeting wildlife 

 

1 An abbreviated version of this paper was presented at the Symposium on the Ecology and 

Management of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Cooperative Wildlife Biologist, University of Idaho/Pacific Northwest Research Station, USDA Forest 

Service, La Grande, Oregon; 389 LaBrant Road, Kalispell, MT 59901 (e-mail: lisabate@cyberport.net) 3

 Research Entomologist, Pacific Northwest Research Station, USDA Forest Service, 1401 Gekeler 

Lane, LaGrande, OR 97850. 

4

 Wildlife Professor, Department of Fish and Wildlife, University of Idaho, Moscow, ID 83844. 5

 Wildlife Biologist, Pacific Northwest Research Station, USDA Forest Service, 1401 Gekeler Lane, 

LaGrande, OR 97850. 
Wildlife Log Sampling—Bate, Torgersen, Garton, and Wisdom 

818 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

needs. Brown (1974) adapted the line-intersect method (LIM) to estimate the volume 

and weight of logs for managing fuels and predicting fire behavior. Brown’s 

sampling method was based on the line-intersect technique developed by Van 

Wagner (1968), who evaluated the technique using matchsticks of equal length and 

diameter. Hazard and Pickford (1986) further evaluated Van Wagner’s line-intersect 

method using computer-simulated log populations; simulations were drawn from a 

population of logs that were tapered and variable in length, based on data collected 

from stands that were clearcut. Hazard and Pickford (1986) found that the sampling 

effort needed to achieve the same precision as that in Van Wagner’s (1968) study 

increased sixfold when logs of variable length and shape were used. Hazard and 

Pickford (1986), however, verified that the LIM produced unbiased estimates of 

coarse woody debris when sampled using random location and orientation of line 

transects. 

Because the LIM was developed to estimate log characteristics important for 

fuel management, namely volume and weight, not all structural characteristics 

important to log-dependent wildlife are measured with conventional application of 

this method. For example, percent cover of logs, which is not measured for purposes 

of fuel management, was correlated positively with the abundance of small 

vertebrates and their forage base in recent studies (Carey and Johnson 1995, Tallmon 

and Mills 1994). Log density, large-end diameter, and length, none of which are 

outputs of Brown’s line-intersect method, were documented as important variables in 

defining foraging habitat for the pileated woodpecker (Dryocopus pileatus) (Bull and 

Holthausen 1993, Torgersen and Bull 1995). 

In this paper, we describe procedures and preliminary results for testing the 

performance of two sampling methods to estimate the density, length, percent cover, 

and weight of logs considered valuable to wildlife. Specifically, we compare two 

approaches: the line-intersect (Brown 1974, DeVries 1973) and strip-plot methods. 

We compare each method in terms of precision, bias, and efficiency under a variety 

of field conditions. 

Study Area 

Seventeen coniferous stands in the Blue Mountains of Oregon and the Salish and 

Mission Mountains of Montana were selected for sampling. Our main objective in 

selecting stands was to sample a gradient of log densities, lengths, percent cover, and 

weights representing a range of conditions found within the Columbia River basin 

east of the Cascade Mountains. These variable conditions were a function of seral 

stage, shrub abundance, slope, disturbance regime, and history of timber 

management. 

Nine of the 17 stands were unharvested, which we defined as stands composed 

primarily (>90 percent) of logs whose lengths had not been altered by timber harvest 

or gathering of fuelwood. Unharvested stands typically had closed canopies and were 

in mid- or late-seral stages of development. The other eight stands, referred to as 

harvested, had a history of more intensive timber management; clearcutting and seedtree cutting occurred in these stands within the last 10 years. 

Stand size averaged 3.3 ha and ranged from 1.2 to 7.4 ha. Slopes ranged from 0 

to 85 percent. Grand fir (Abies grandis), western larch (Larix occindentalis),

lodgepole pine (Pinus contorta), Douglas-Fir (Pseudotsuga menziesii), and 
Wildlife Log Sampling—Bate, Torgersen, Garton, and Wisdom 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 819 

ponderosa pine (Pinus ponderosa) dominated one or more stands in Oregon. Stands 

in Montana were dominated by two or more of the following: western larch, 

Douglas-Fir, grand fir, lodgepole pine, Engelmann Spruce (Picea engelmannii),

subalpine fir (Abies lasiocarpa), and white pine (Pinus monticola). 

Methods 

Field Procedures 

To evaluate our sampling methods against known parameters, within each stand 

we first conducted a complete count (census) of all logs that had a large-end diameter 

of 15 cm or greater and a length of at least 1 meter. Trees that had fallen and broken 

were tallied as two pieces if the pieces were not touching; otherwise, each fallen tree 

was considered one piece. Only logs whose central axis lay above the ground were 

tallied (Brown 1974). If a log was suspended, only that portion of a log that was 

within 1.8 meters of the ground was tallied. A log was considered downed if it lay 

within 45 degrees of the ground. In the remainder of this paper, we refer to logs of 

these dimensions and characteristics as “qualifying” logs. 

Each log was painted at both its large and small ends where the diameter 

measurements were taken using 1 m-long calipers. Diameters were measured to the 

nearest millimeter. Lengths of logs were measured to the nearest decimeter between 

the painted diameter marks. For large logs with their root systems still attached, the 

large-end diameter was measured just above the butt swell, whereas the length was 

measured along the entire bole from the root wad out to the 2-cm small-end diameter. 

After finishing the complete count of logs, we then sampled along randomly 

established transects. We established six transects in most stands. Because of size 

constraints, however, a few stands only contained five transects. All transects were 

randomly located and oriented to minimize overlap. The typical transect was 100 m 

long and was delineated into 12.5 m subsegments; some stands, however, contained 

shorter transects owing to limitations on stand size. At the midpoint of each transect 

we established a cluster unit. This was a three-legged sampling unit, with each leg 25 

m long and oriented at 120 degrees from other legs. Design of the three-legged 

sampling unit followed the example given by Hazard and Pickford (1986). 

We then sampled along each 12.5 m subsegment using both the line-intersect 

method (LIM) and the strip-plot method (SPM). For the SPM, we conducted a 

complete count of all logs, or portions of qualifying logs, that fell within 2 m of 

either side of the transect line. We used the 1-m long calipers, which by design 

functioned as a square, to determine the outer boundaries of the strip plots. By 

contrast, only logs that were intersected by the transect line were tallied using the 

LIM. For the SPM, we recorded the length, the small- and large-end diameters, and 

the condition (sound or rotten) of each section of a qualifying log that fell within the 

boundaries of the strip plot. In addition, we recorded whether or not the mid-point of 

a log fell within the boundaries of the plot. For the LIM, we recorded the same 

information as with the SPM. In addition, we recorded the diameter of the log at the 

point of intersection. 
Wildlife Log Sampling—Bate, Torgersen, Garton, and Wisdom 

820 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Statistical Analysis 

We used ordinary least squares regression to examine the relation between the 

true values of log density, total length, percent cover, and weight in each stand 

compared to our estimates of these parameters obtained from the SPM and the LIM. 

Specifically, we regressed the true value of log density, total length, percent cover, 

and weight on the estimated values generated by LIM and SPM. This resulted in four 

regression equations for each method, with one equation corresponding to each of the 

four log characteristics of interest. For the preliminary analysis conducted here, we 

used data from all stands to compute each equation, with each stand designated as a 

statistical unit of observation (n=17). 

To evaluate bias of each method, we forced each regression line through zero by 

removing the y-intersect constant. This allowed us to determine whether a method 

over- or underestimated each parameter. Specifically, a regression slope (b) = 1.0 

indicated no bias. By contrast, b > 1.0 indicated that the sampling method 

underestimated the true parameter, whereas b < 1.0 indicated that the sampling 

method overestimated the parameter. 

To evaluate precision of each method, we used the coefficient of determination 

(r2

 values) obtained from the regression analysis. Coefficients of determination at or 

near 1.00 (100 percent) indicated high precision, whereas coefficients at or near 0.00 

(0 percent) indicated extremely low precision. 

 To evaluate efficiency, we used two approaches. Under the first approach, we 

calculated the length of transect line required for each method to obtain an estimate 

of each log characteristic that was within 20 percent of the true mean, 90 percent of 

the time. Sample sizes given were based on the average length of transect required 

per stand. We standardized these calculations by using only straight-line transects 

that were 100 m long (n=75). We then incorporated the true value for each parameter 

obtained from our complete counts, rather than the sample value, into the sample size 

equation. This controlled for any strong influences created by using the sample mean 

statistic. 

Under the second approach, we ranked the amount of field time (sampling 

effort) that was required by each method to measure each of the four log 

characteristics. Ranks were assigned on a relative scale that ranged from 1 to 3, as 

follows: rank 1, least effort; rank 2, moderate effort; and rank 3, most effort. 

Results 

Accuracy 

Both the LIM and SPM produced relatively unbiased estimates of density, 

length, percent cover, and weight of logs. Values of b ranged from 0.99 to 1.04 for 

the LIM and from 0.97 to 1.02 for the SPM. Precisions of these estimates, however, 

were more divergent between the two methods. Coefficients of determination ranged 

from 0.58 to 0.93 for the LIM and from 0.75 to 0.94 for the SPM. In particular, the 

LIM was relatively imprecise in estimating density of logs, accounting for only 58 

percent (0.58) of the variation in the true density. By contrast, the SPM accounted for 

75 percent of the variation in the true density of logs. Finally, precision of both 

methods in estimating length, percent cover, and weight was relatively high, with 

coefficients of determination ≥ 0.82. 
Wildlife Log Sampling—Bate, Torgersen, Garton, and Wisdom 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 821 

Efficiency 

The LIM required more transect length per stand than the SPM to achieve the 

same level of precision for estimating density, length, percent cover, and weight of 

logs under all stand conditions. Transect length required of the LIM ranged from 1.0 

to 3.8 km, while transect length required of the SPM ranged from 0.7 to 1.8 km. 

Differences were most pronounced for estimates of weight in harvested stands, where 

the LIM required an average of 138 percent more transect line per stand (3.8 km) 

compared to the SPM (1.6 km) to obtain the same level of precision. 

Field effort required of LIM also was greater (ranking of 3) than SPM (ranking 

of 1) for estimating density of logs. The LIM required less field effort, however, than 

the SPM to estimate length and weight (LIM rankings of 1 versus SPM rankings of 

2). Finally, either less field effort or the same amount of effort was required using 

LIM versus SPM to estimate percent cover, depending on how log diameters were 

measured with LIM. When large- and small-end diameters of logs were measured as 

part of the estimation of percent cover under LIM, field effort was ranked as 

moderate, the same as that estimated for SPM. Alternatively, when log diameters 

were measured at the point of line intersection under LIM, field effort for estimating 

percent cover with LIM was ranked as low. 

Discussion 

Our results indicate that both the LIM and SPM are relatively unbiased and 

precise estimators of most log characteristics under the conditions tested. The SPM 

appeared to be more precise, however than LIM in estimating density of logs. SPM 

also was more efficient than LIM in estimating density. By contrast, neither SPM nor 

LIM was clearly more efficient in estimating length, percent cover, or weight of logs. 

Consequently, which method is better depends on a variety of factors, particularly the 

stand conditions to be sampled and the log characteristics of most interest. For 

example, if the primary interest is to obtain accurate, efficient estimates of log 

density, then SPM appears to be the better choice. If other log characteristics are of 

primary interest, the choice of method is less clear. Finally, if all four log 

characteristics are of equal interest, SPM is the likely choice owing to its superior 

performance in estimating log density. We are currently exploring questions about 

each method’s performance in relation to a variety of field conditions, using 

additional data collected during our study. Further analysis of our data should help 

clarify the merits of each method under a variety of conditions. 

Our results also demonstrated the strong need for different methods to sample 

logs for wildlife research and management versus conventional methods that have 

been used for fire management. Conventional applications of LIM for fire 

management estimate log volume and weight, but ignore density, percent cover, and 

length. Because wildlife respond to a rich set of log characteristics, it behooves 

wildlife managers and researchers to apply methods like those described here to 

obtain accurate estimates of log characteristics most important to wildlife. 
Wildlife Log Sampling—Bate, Torgersen, Garton, and Wisdom 

822 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Acknowledgments 

Peter Barry, Jennifer Carpenedo, Kent Coe, Darren Hopkins, Daniel Jones, 

Alexa Michel, Damon Page, Gene Paul, Cynthia Sandoval, and Eric Sandoz assisted 

in data collection. Andrew Youngblood and Kerry Mettlen assisted in obtaining land 

area measurements. The Pacific Northwest Research Station, Forestry and Range 

Sciences Lab, LaGrande, Oregon provided major funding. The Flathead National 

Forest in Montana provided equipment, logistical support, and technical advice. We 

thank James Brown for his assistance with sampling methods pertaining to the lineintersect method. Finally, we thank Deb Hennessy, Amy Jacobs and Penelope 

Morgan for technical reviews of our paper, and Jay Shepard for review of statistical 

methods. 

References 

Brown, James K. 1974. Handbook for inventorying downed woody material. Gen. Tech. 

Rep. INT-16. Ogden, UT: Intermountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 24 p. 

Bull, Evelyn L.; Holthausen, Richard S. 1993. Habitat use and management of pileated 

woodpeckers in northeastern Oregon. Journal of Wildlife Management. 57(2): 335-

345. 

Carey, Andrew B.; Johnson, Murray L. 1995. Small mammals in managed, unharvested 

young, and old-growth forests. Ecological Applications 5(2): 336-352. 

De Vries, P. G. 1973. A general theory on line intersect sampling with application to 

logging residue inventory. Wageningen, The Netherlands: Mededelingen 

Landbouwhogeschool 73-11; 23 p. 

Hazard, John W.; Pickford, Stewart G. 1986. Simulation studies on line intersect sampling 

of forest residue, Part II. Forest Science 32(2): 447-470. 

Maser, Chris; Anderson, Ralph G.; Cromack, Kermit, Jr.; Williams, Jerry; Martin, Robert. 

1979. Dead and down woody material. In: Wildlife habitats in managed forests—the 

Blue Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: U.S. 

Department of Agriculture; 78-95. 

Parks, Catherine G.; Bull, Evelyn L.; Torgersen, Torolf R. 1997. Field guide for the 

identification of snags and logs in the interior Columbia River basin. Gen. Tech. 

Rep. PNW-GTR-390. Portland, OR: Pacific Northwest Research Station, Forest Service, 

U.S. Department Agriculture; 40 p. 

Tallmon, David; Mills, Scott. 1994. Use of logs within home ranges of California redbacked voles on a remnant of forest. Journal of Mammalogy 75(1): 97-101. 

Torgersen, Torolf R.; Bull, Evelyn L. 1995. Down logs as habitat for forest-dwelling ants—

the primary prey of pileated woodpeckers in northeastern Oregon. Northwest 

Science 69: 294-303. 

Van Wagner, C. E. 1968. The line intersect method in forest fuel sampling. Forest Science. 

14(1): 20-26. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 823 

Effects of Prescribed Fire in Ponderosa 

Pine on Key Wildlife Habitat Components: 

Preliminary Results and a Method for 

Monitoring1

Tammy Randall-Parker2 and Richard Miller3

Abstract 

We monitored the effects of prescribed fire in ponderosa pine forest on snags, down logs, 

oaks, and old ponderosa pine trees. Five prescribed burns were monitored over a total of 47.7 

ha (118 acres). The prescribed fires consumed more than 50 percent of the 342 down logs and 

approximately 20 percent of the 138 snags monitored. The fires created few snags or down 

logs. Our methodology evolved from a variable plot method to a grid method through a series 

of sites. The final method—using a grid, aluminum tags, and sketch mapping—resulted in 

almost a 50 percent time saving at the end of the first post-burn reading. 

Introduction 

The reintroduction of fire into the current forests has the potential to greatly 

change the frequency and distribution of key wildlife habitat components, such as 

snags, down logs, old trees, and large oaks (Quercus gambeli). Snags are an 

important habitat component and need to be present at appropriate densities in 

forested ecosystems for cavity nesting birds (Cunningham and others 1980, Horton 

and Mannan 1988, Newton 1994). Down logs are important to small mammals and 

need to be well distributed across the landscape to provide for wildlife habitat 

(Goodwin and Hungerford 1979). Oaks provide key habitat for wildlife in the 

Southwest, including birds, bats, ungulates and small mammals. Oaks are one of the 

most important factors affecting bird distribution (Rosenstock 1998) in northern 

Arizona ponderosa pine (Pinus ponderosa) forests. Old-growth ponderosa pine trees 

are used by 80 species of wildlife on the Coconino National Forest for nesting, 

feeding, foraging, and roosting sites. 

Forest managers in the Southwest use prescribed fire to restore the health of 

ponderosa pine ecosystems and reduce the threat of catastrophic wildfire. Prescribed 

fire has become more important recently because of increased emphasis on forest 

restoration, urban interface fire prevention, and fire as a vegetation management tool. 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Wildlife Biologist, Peaks Ranger District, 5075 North Highway 89, Flagstaff, AZ 86004 (e-mail: 

tkrandall@fs.fed.us) 

3

 Habitat Program Manager, Arizona Game and Fish Department, 3500 S. Lake Mary Rd, Flagstaff AZ, 

86001 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

824 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Little published information is available, however, on the effects of prescribed fire on 

snags, logs, oaks, and old-growth ponderosa pine trees. 

Since 1995, we have been monitoring prescribed fire on two national forests and 

a national monument to determine effects on selected wildlife habitat components. 

These data are intended to give resource managers better information about gains and 

losses of key wildlife habitat components following prescribed fire in northern 

Arizona. This paper presents data from five burns. Our study is ongoing and 

eventually will include 10 sites. The data we have collected to date provides needed 

information on the effect of prescribed fire on key wildlife habitat components in 

ponderosa pine forests. 

The prescribed burns we have studied are the first use of prescribed fire on each 

site. The results represent effects of the first entry with prescribed fire, which may 

cause the most change to wildlife habitat depending on the frequency of reentry 

burns. 

Study Area and Methods 

We monitored pre and post-burn habitat components on five sites totaling 47.7 

ha (118 acres). The sites are located near Flagstaff in north central Arizona. The five 

sites include three ranger districts on the Coconino National Forest, one ranger 

district on the Kaibab National Forest, and Walnut Canyon National Monument. The 

sites are named Walnut, Unknown, Stoneman, Twin Springs and Howard. 

All the sites are in the ponderosa pine vegetation type (table 1). Some of the 

sites also include varying proportions of Gambel oak and alligator juniper (Juniperus 

deppeana). 

Table 1―Pre-burn habitat component data by site. 

 Number of components/ha (components/acre) 

Site Snags Logs Oaks Old-growth 

trees 

Ha 

monitored 

Habitat type 

Walnut 6.1 (2.5) 6.1 (2.5) >1 19.8 (8.0) 8.9 (22) Ponderosa pine 

Unknown 1.5 (.6) 3.7 (1.5) >1 26.7 (10.8) 14.2 (35) Ponderosa pine 

Stoneman 1.9 (.77) 7.9 (3.2) 8.4 (3.4) 5.4 (2.18) 8.9 (22) Ponderosa 

pine/Gambel 

oak 

Twin 

Springs 

3.2 (1.3) 9.4 (3.8) 6.8 (2.8) 11.3 (4.6) 9.7 (24) Ponderosa 

pine/Gambel 

oak 

Howard 6.6 (2.7) 13 (5.3) 22 (8.9) 3 (1.2) 6.0 (15) Ponderosa 

pine/Gambel 

oak 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 825 

All the monitoring sites on the national forests have similar histories, with 

logging beginning in the late 1800s and continuing until the present decade. Recent 

logging includes both pre-commercial thinning of trees less than 5 inches (12.7 cm) 

dbh, and varying levels of overstory removal. Wildfire suppression began in the early 

1900s. 

The Walnut Canyon National Monument site is strikingly different because it 

has never been logged, although wildfire suppression history is similar. The Walnut 

site has a substantial old-growth ponderosa pine component and is structurally 

diverse. 

The sites are approximately 6 to 14 ha (15 to 35 acres) in size depending on the 

density of habitat components. On each site, we attempted to monitor an area large 

enough to include at least 50 individuals of each component studied. This number 

was selected to try to balance biological significance and data collection 

practicability. In practice, some sites did not achieve the desired number of all habitat 

components. Snags proved to be the most rare component, and none of the sites 

burned so far contained 50 snags. In each instance, we truncated the sites to keep 

their size manageable or to remain within the prescribed fire area. One site (Howard) 

also failed to meet the desired number of old ponderosa pine. 

Prescribed Fire 

Sites are located within prescribed burns planned in the normal course of forest 

management. The burn prescriptions followed normal agency practice. Sites selected 

are in areas where agency personnel had planned prescribed burning. We made an 

effort to find burns carried out by a variety of crews in order to assess variability 

caused by crews as well as sites. 

All five burns monitored occurred in the fall. Prescribed fire burning plans were 

similar for all burns conducted (table 2). Fuel moisture in the 1,000-hour fuels ranged 

from 13 to 16 percent. Firing techniques and devices were the same for all burns. 

Planned weather conditions and general topography of all sites were similar. 

Table 2―Prescribed fire data and monitoring dates. 

Site 1,000- 

hour fuel 

moisture 

percent 

Firing 

techniques 

Humidity 

percent 

Temperature 

(degrees F) 

Month/ 

year 

burned 

Postburn 

data 

Postburn 

year 3 

Postburn 

year 6 

Postburn 

year 10 

Walnut 15 Head and 

Backing 

 10/96 6/97 6/00 6/03 6/06 

Unknown 12 Head and 

Backing 

15 –60 75 12/95 6/96 6/99 6/02 6/05 

Stoneman 16-50 Head and 

Backing 

15-100 40-80 9/97 10/97 6/01 6/04 6/07 

Twin 

Springs 

15-32 Head and 

Backing 

20-60 40-75 10/97 10/97 6/01 6/04 6/07 

Howard 15-50 Head and 

Backing 

15-100 40-80 9/97 10/97 6/01 6/04 6/07 

 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

826 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

We surveyed sites prior to the prescribed burn and within 1 to 11 months after 

the burn (table 2). Sites will be surveyed again at 3, 6 and 10 years after the burn. 

These follow-up surveys are intended to capture changes such as tree mortality, 

which may be delayed for several years after the burn that caused it. 

Component Data Collection 

We surveyed all the individual habitat components on each site. DBH and height 

were recorded for mature ponderosa pine, oaks, and snags. Down logs were 

characterized by species, minimum diameter, maximum diameter, and length. 

Compass bearing from largest end of the log and whether the tree was cut or fallen 

was recorded. The compass bearing assisted us in identifying the log after the burn. 

Additional data collected on each component included presence/absence of leaves, 

twigs, bark, cracks, cavities, litter depths, and animal usage for later analysis. 

Changes in Data Collection 

As we began study design, we considered a variety of sampling methods. 

Difficulties in estimating the extent of change with rare components led us to believe 

the best method would be a total count of habitat components within known area 

sites. Although we have consistently conducted a total survey of habitat components 

on the sites, the methodology for conducting the total survey has changed as we have 

learned from the post-burn sites. 

Variable Plot Method―Few Tags 

When we began the project, we based surveys on groups of ponderosa pine. The 

location of a central point in each ponderosa pine group was recorded by using a 

global positioning system (GPS), and one or more trees were marked with an 

aluminum tag bearing a group number. One point consisted of either a single 

component or multiple components, i.e., GPS point R080813A recorded presence of 

two down logs and both were tagged with the identifier number. A map of all points 

was produced, showing the relationships of the points to each other on the ground. 

Points were easily relocated; however, because the size of points varied, one could 

not quickly summarize which habitat components were within the point without 

checking tags. 

Variable Plot―All Items Tagged 

The first change we made was to begin tagging all the habitat components with 

aluminum tags, which identified the components associated with the group central 

point. Although some tags melted in the burns, the tagging reduced the total time 

needed for post-burn data collection (table 3). Tagging all the components increased 

the time needed to set up a site by 2 person-days; however, tagging reduced the time 

needed for post-burn monitoring from 14 person-days to 8 person-days. 

We continued to have some confusion on the edges of groups, since often a tree 

or a log could logically be recorded in either of two groups. 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 827 

Table 3―Person-days required for monitoring a plot through the first post-burn reading by 

method. 

Method Setup Post-burn Total 

Variable plot—few tags 8 14 22 

Variable plot—all items tagged 10 8 18 

Grid—all items tagged 10 2 12 

Grid―All Items Tagged 

Post-burn monitoring at Walnut revealed that a better method was needed. We 

could reconstruct some, but not all the groups from our data. It sometimes was very 

time consuming to reconstruct groups, particularly if a group was greatly changed by 

the burn. Since this was our most complex site, the problems with our methods were 

amplified. Because we could not reconstruct all of the groups at Walnut, the postburn data for that site were truncated to include only data from the groups that could 

be reconstructed with certainty. 

The difficult and time-consuming nature of the post-burn monitoring at Walnut 

led us to change our methods. We avoided using a grid at first because we thought it 

would take more time. After experience with the other two methods, we realized that 

laying out a grid could greatly reduce the time needed to read sites after a burn. We 

began laying out grid cells 30.48 m (100 feet) on each side, and continued tagging all 

the habitat components. Grid cell corners were marked with tagged rebar stakes. 

Each 929 sq. m. (10,000 sq. ft.) cell was issued a number. Grid cells were numbered 

so that each cell could be identified by unique alphanumeric code. All habitat 

components were tagged, sketched, and characteristics summarized by cell. 

The final improvement made was a sketch map of each grid cell showing where 

the habitat components were in relation to each other within the cell boundary. The 

net effect of these changes was a dramatic decrease in the time needed to monitor a 

site post burn (table 3). 

Results 

Pre-burn―Site Habitat Description 

 Table 1 shows the pre-burn density of each habitat component for each site we 

monitored. Structural complexity (dog hair thickets, varying diameter of ponderosa 

pine) was low on the Howard and Unknown sites and moderate on the Stoneman and 

Twin Springs sites. The Walnut site is a very complex site with not only an 

abundance of old-growth, but also dog hair thickets and multiple age classes present. 

Snags 

We sampled 138 snags > 15 inches (38 cm) dbh, almost all of which were either 

ponderosa pine (87 percent) or Gambel oak (10 percent). 

At all sites except Walnut Canyon, some snags were lined, i.e., duff and debris 

moved away from the base of snag. Snag lining was a common practice on all USDA 

Forest Service burns. 

Twenty-nine snags (21 percent of all snags) were consumed by fire or converted 

to logs. The individual sites did not differ significantly in numbers of snags lost (fig. 

1). The range of snag loss was 12-38 percent. Nine snags were created. Snags created 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

828 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

by the prescribed fires were created predominately (six of the nine snags) at Walnut 

Canyon National Monument where old-growth trees were converted to snags. Two 

oaks, one each from the Howard and Twin Springs site, became snags. Average 

diameter for the snags gained are larger than the average pre-burn snag diameter. 

Fourteen Gambel oak snags were included in the data. In the post-burn 

condition, 8 of the 14 oak snags remained. Initial results suggest that oak snags might 

be at higher risk of loss from prescribed burns than ponderosa pine snags. The 

additional sites that have not yet been burned will increase our sample size. Oak 

snags, however, are also extremely rare on these landscapes. 





























































































































































 











































































































































































































 

























































 



































































 





































































































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10

15

20

25

30

35

40

Pre-burn Post-burn Gained Pct Gain Pct Lost





Walnut

Unknown

 Stoneman

 Twin Spring

Howard

Figure 1―Snag data by site.

Logs 

We sampled 342 logs > 15 inches (38 cm) dbh. Logs varied in diameter, length, 

decay condition, and use. Ponderosa pine, Gambel oak, and juniper represented 

90.24, 7.38, and 2.38 percent, respectively, of the sample logs. 

Fifty-three percent of all logs were lost. Log loss did not differ greatly by 

species. The range of log loss was 36-61 percent (fig. 2). The prescribed burns 

created 15 logs. New logs created are located predominantly at Walnut Canyon 

National Monument (13 of the 15 logs) where conversions from old-growth tree to 

log and from snag to log were nearly equal. Average diameter and lengths for logs 

lost and created were very similar. Logs remaining in the post-fire condition were 

slightly smaller in diameter and 5 feet (1.5 m) longer based on the average of all logs 

monitored. 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 829 

Figure 2―Log data by site. 

Oaks 

We sampled 282 oaks >10 inches (25.4 cm) dbh. All of our sites had oaks on 

them, but most oaks were on the three sites considered ponderosa pine/Gambel oak 

cover types (Howard, Twin Springs, and Stoneman). Both the Walnut and Unknown 

site recorded a few oaks. 

Six percent of the total oaks were lost. The range of oak loss on the ponderosa 

pine/Gambel oak cover types was 0-9 percent (fig. 3). The one oak at Unknown went 

unscathed; however, two of three oaks on the Walnut burn were killed. The third oak 

was charred badly. The three oaks on Walnut Canyon National Monument site were 

not in a clump; however, all three were adjacent to dog hair thickets where the fire 

got rather hot. 

Figure 3―Oak data by site. 















 



 





















 



 



 





















 



 





 

























 



 



 





 













 





 







 



 









 

















 











 



 



   











 



 



  



 







 





















 



 



 

 















 



 





 

 















 



 





 



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Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

830 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Mean diameter of oaks lost, 40.1 cm (15.8 in.), was slightly higher than the 

average pre-burn diameter (36.1 cm./14.2 inches). The possibility of delayed oak 

mortality and conversion of live oak to snag is one of the reasons for planning a 10-

year monitoring effort. 

Old-growth Ponderosa Pines 

We sampled 680 old-growth trees on the five sites. The Walnut site contained a 

lower number of old-growth trees because of a site selection decision. The crew who 

set up Walnut avoided large clumps of old trees that did not contain other 

components in order to increase the sample size of the more rare habitat components. 

Immediate post-burn monitoring found that few old-growth trees had died 

during or immediately after the prescribed fires (fig. 4). Most of the trees that did die 

were on the Walnut Canyon National Monument site. The affected trees are now 

either snags or logs, and resulted in gains in the log and snag components. Old 

growth tree loss across the sites ranged from 0 to 6 percent. 

Figure 4―Old-growth pine data by site. 

Survey Methods 

Because the time saved by using the grid method will occur each time a site is 

monitored post-burn, the difference in the total time required for each sampling 

method will increase with the second and third post-burn reading. By the end of the 

project, after four post-burn readings of each site, we would have 64 person-days 

invested in a site using our original method, compared with 18 person-days with the 

grid method (table 3). 

Because most monitoring efforts will not require the detailed data we are 

collecting on each habitat item, our recommendation for future monitoring is to use a 

grid, tag each item, and use sketch maps of each cell. The pre-burn setup time 

without the detailed data on each item should be about half of what we have 

















































































































































































































































    







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Pre-burn Post-burn Gained Pct Gain Pct Lost



 Walnut

 Unknown

 Stoneman

 Twin Spring

 Howard
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 831 

estimated. Post-burn site monitoring time is cut by about 25 percent without the 

detailed data collection. We would estimate reducing the total time for setting up a 

site and monitoring it twice to be approximately 8 person-days, or if the site is 

monitored four times after the burn, 11 person-days. Two post-burn measurements 

may well be enough, after the delay between the burn and tree mortality rates are 

well understood. 

Discussion 

 Our monitoring has attempted to determine the effect of prescribed fire on 

wildlife habitat components. Our preliminary monitoring findings represent what we 

would expect to happen when conducting a fall prescribed fire where average 1,000-

hour fuel moistures are approximately 15 percent. Our preliminary results describe 

the effects of prescribed burning in the fall in managed ponderosa pine stands with a 

sparse or scattered overstory of old trees. Under these prescribed burning conditions, 

our results show about 50 percent of the logs and about 20 percent of snags being 

consumed with little or no immediate gains (fig. 5). Live oaks have been reduced by 

6 percent and little immediate mortality of large old-growth ponderosa pines has 

occurred. 

 Recent forest management direction in the southwestern U.S. for snags and logs 

has come primarily through plans for the Mexican spotted owl and northern goshawk. 

These management plans recommend the use of prescribed fire to protect habitat 

from catastrophic wildfire and to improve understory vegetation (grasses, shrubs, 

forbs, wildflowers) beneficial to prey species for these raptors. 

Figure 5―Habitat component data from five sites combined. 













 



























 



 













 







 





 







 









 





 















 

























 







 













 









   

















 



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 Snags

 Logs

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Old growth
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

832 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Horton and Mannan (1988) found that nearly half of all snags burned down, logs 

decreased by 42 percent and 56 percent, and prescribed fires in southeastern Arizona 

killed few large trees. Snags greater that 50 cm dbh were most impacted. 

In a recent study of snag abundance, Ganey (1999) found that Forest Service 

snag standards were seldom met, even in unlogged forests. Our preliminary findings 

as well as these studies, suggest that densities of snags are often below those required 

by Forest Service guidelines and will be reduced further by the use of prescribed fire. 

Our initial results would suggest that oak snags might be at higher risk from 

prescribed burns than ponderosa pine snags. Our results to date are inconclusive; 

however, we have shown that fire kills some oak trees. On one site, the burns killed 

all of the few oaks on the site, potentially greatly altering the habitat for wildlife 

using oak, despite the small statistical effect. 

Data for logs in the pre-fire monitoring found that nearly 66 percent of all logs 

monitored were cut. These logs may have been the snags that were felled in the 

1960s (general practice) to lessen wildfire threat from snags catching fire. They also 

may have been cull trees, which were felled during past logging. These logs were 

generally hard and full of pitch, which may have led to their loss. Many of these 

artificially-created logs might still be standing as snags or old-growth, if not for past 

fire prevention and cull policy. 

Historical logging practices, especially the removal of large old-growth trees on 

many forested areas combined with fire prevention techniques, undoubtedly played a 

role in what we found. It is our opinion, based on the preliminary findings, that gains 

in logs and snags will only occur where there is abundant old-growth to allow for the 

conversions. It will take a long time to grow the trees to be old enough and large 

enough to get us out of this dilemma. Accumulated debris around the base of snags, 

oaks, and mature pines can greatly affect how hot the fires burn and how these 

habitat components are impacted (Harrington 1985, Horton and Mannan 1988). Dog 

hair thickets, stumps in the root zone, or thick duff areas may also be needed before 

enough heat is generated to cause the old-growth kill. Areas such as designated 

wilderness or stands with abundant old-growth trees will allow for gains in logs and 

snags. 

Harrington and Sackett (1992) reported almost 40 percent old-growth ponderosa 

pine mortality at the Chimney Spring Prescribed Fire Research Area at Fort Valley. 

Their study took place within the same general area where we have been doing our 

monitoring. The duff layers and tree densities have been less in our study plots than 

in Harrington and Sackett’s, study and one or both of these factors may account for 

any differences. 

 In Harrington and Sackett’s (1992) study, mortality did not appear until several 

years after the burns; thus, a comparison with their results will be more appropriate 

after long term monitoring. To date, we have not found comparable heavy mortality 

in old ponderosa pine trees. 

An unanswered question is how subsequent re-entries with prescribed fire will 

affect wildlife habitats. The most common thought is that fire events occurred in 

southwestern ponderosa pine every 7-15 years, and some managers would like to 

approximate that interval where possible. Our results raise a question about the gains 

and losses for logs, snags, oaks, and old-growth components with re-entry burns. 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 833 

Management Implications 

Through the evolution of our monitoring method, we have arrived at a relatively 

efficient means of monitoring the effects of prescribed fire on wildlife habitat. The 

use of a grid design, along with tagging each habitat component and sketch mapping 

each cell, proved much more efficient than the variable plot method for us. The grid 

with tagging and cell mapping may often be the best way for managers to obtain 

desired or required monitoring data on the effects of prescribed fire. The pre-burn 

setup time without the detailed data on each item should be about half what we 

currently need, and post-burn plot monitoring time should be cut by about 25 percent. 

We would estimate reducing the total time for setting up a plot and monitoring it 

twice to be approximately 8 person-days, or if the plot is read four times after the 

burn, 11 person-days. After the delay between the burn and expected tree mortality is 

worked out, two post-burn measurements may well be enough. 

Forest managers should expect a decrease in logs and snags immediately after 

prescribed burning activities. Our data show that logs and snags will be reduced by 

approximately 50 and 20 percent, respectively. Managers should expect only a few 

logs or snags to be created immediately by the burn unless the site contains a high 

density of old trees and snags. Some additional snags and down logs may be gained 

later after the burn. Whether or not these changes in key wildlife habitat components 

are acceptable depends on how many are present before the fire. 

The Stoneman burn, which experienced the lowest snag losses, had nearly every 

snag lined. Other Forest Service burns lined only some snags. It appears that lining 

may be an effective mitigation tool for reducing snag losses during prescribed burns. 

Acknowledgments 

Over the years, many field assistants from the Arizona Game and Fish Intern 

Program and Forest Service personnel have conducted field data collection. We 

appreciate all your excellent work. We especially thank Debbie Crisp who has helped 

to complete fieldwork every year and provided training to field crews. A special 

thanks to Chuck Benedict for assistance on the database housekeeping and the forest 

biologists on the Coconino for their continued support of this project. Numerous 

Forest Service personnel from the Kaibab and Coconino National Forests assisted 

with site selection and got these areas burned; thanks to George Sheppard, Larry 

McCoy, Jerry Bradly, Bob Smith and Andy Parker for helping us along. Also, thanks 

to Tom Ferrel at Walnut Canyon National Monument. Thanks to Steve Rosenstock, 

Joe Ganey, and Sandy Nagiller for reviewing this paper. 

References 

Cunningham, J. B.; Balda, R. P.; Gaud, W. S. 1980. Selection and use of snags by 

secondary cavity-nesting birds of the ponderosa pine forest. Res. Paper RM-222. 

Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 15 p. 

Ganey, J. L. 1999. Snag density and composition of snag populations on two National 

Forests in northern Airzona. Forest Ecology and Management 117: 169-178. 

Goodwin, John G., Jr.; Hungerford, C. Roger. 1979. Rodent population densities and food 

habits in Arizona ponderosa pine forest. Res. Paper RM-214. Fort Collins, CO: Rocky 
Effects of Prescribed Fire in Ponderosa Pine on Key Wildlife Habitat Components—Randall-Parker 

and Miller 

834 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 12 p. 

Harrington, M. G; Sackett, S. S. 1992. Past and present fire influences on southwestern 

ponderosa pine old growth. In: Proceedings of old-growth forest in the Southwest and 

Rocky Mountain Regions; Portal, AZ. Gen. Tech. Rep. RM-GTR-213. Fort Collins, CO: 

Rocky Mountain Forest and Range Experiment Station, Forest Service, U.S. Department 

of Agriculture; 44-50. 

Harrington, M. G. 1985. The effects of spring, summer and fall burning on Gambel oak in 

a southwestern ponderosa pine stand. Forest Science 31: 156-163. 

Horton, S. P.; Mannan. R. W. 1988. Effects of prescribed fire on snags and cavity-nesting 

birds in southeastern Arizona pine forest. Wildlife Society Bulletin 16: 37-44. 

Newton, I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: A 

review. Biological Conservation 70: 265-276. 

Rosenstock, S. S. 1998. Influence of Gambel oak on breeding birds in ponderosa pine 

forests of northern Arizona. Condor 100: 485-492. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 835 

Selection of Fire-created Snags at Two 

Spatial Scales by Cavity-nesting Birds1

Victoria Saab,2 Ree Brannon,3 Jonathan Dudley,2 Larry Donohoo,4

Dave Vanderzanden,5 Vicky Johnson,5 and Henry Lachowski5

Abstract 

We examined the use of snag stands by seven species of cavity-nesting birds from 1994-1998. 

Selection of snags was studied in logged and unlogged burned forests at two spatial scales: 

microhabitat (local vegetation characteristics) and landscape (composition and patterning of 

surrounding vegetation types). We modeled nest occurrence at the landscape scale by using 

Landsat Thematic Mapper imagery. At both spatial scales, we observed a continuum in 

habitat use with the extremes represented by black-backed and Lewis’s woodpeckers. A range 

of habitat conditions characteristic of black-backed and Lewis’s woodpeckers would likely 

incorporate habitat features necessary for nest occurrence of other members in the cavitynesting bird community. 

Introduction 

Forests affected by wildfire, and subsequent salvage logging, became 

increasingly prevalent in the early 1990s across much of the inland West. Many 

cavity-nesting birds are associated with burned forests, but little is known about their 

habitat selection in post-fire conditions (Hutto 1995, Kotliar and others [In press], 

Saab and Dudley 1998). Virtually nothing is known about the influence of landscape 

patterns on nest-site selection in burned forests (Kotliar and others [In press]). 

Species of cavity-nesting birds respond variably to post-fire salvage logging 

(Caton 1996, Hitchcox 1998, Kreisel and Stein 1999, Saab and Dudley 1998). Cavity 

nesters, however, often nest (Saab and Dudley 1998) and forage (Kreisel and Stein 

1999) in patches of higher snag densities than that expected based on availability of 

snags. In salvaged forests of western Idaho, snags generally were retained in uniform 

distributions (equal numbers of snags per hectare), while within those burned forests, 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Wildlife Biologist and Wildlife Biologist, respectively, Rocky Mountain Research Station, 

USDA Forest Service, 316 E. Myrtle Street, Boise, ID 83702 (e-mail: vsaab/rmrs_boise@fs.fed.us and 

jdudley/rmrs_boise@fs.fed.us) 

3

 Senior GIS Analyst, Gap Analysis Program, U.S. Geological Survey, 530 S. Asbury Street, Suite #1, 

Moscow, ID 83843 (e-mail: abrannon@uidaho.edu) 

4

 Resource Assistant, Boise National Forest, USDA Forest Service, 2180 American Boulevard, 

Mountain Home, ID 83647 (e-mail address: ldonohoo/r4_boise@fs.fed.gov) 5

 Project Co-Leader, Project Co-Leader, and Program Leader, respectively, Remote Sensing 

Applications Center, USDA Forest Service, 2222 West 2300 South, Salt Lake City, UT 84119 (e-mail: 

dvanderzanden/wo_rsac@fs.fed.us, Vjohnson/wo_rsac@fs.fed.us, and hlachowski/wo_rsac@fs.fed.us) 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

836 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

we previously reported that cavity-nesting birds used clumps (stands) of snags for 

their nest sites (Saab and Dudley 1998). We suggested that salvage prescriptions 

could be improved to favor cavity-nesting birds by changing the distribution of snags 

retained (from uniform to clumped), even when the same number of snags are 

harvested. 

In this paper, we examine the use of snags by cavity-nesting birds at both the 

microhabitat and landscape scales within burned forests. A landscape-level analysis 

is necessary to estimate the area (size) and distribution of snag stands selected by 

cavity nesters. A large-scale analysis, however, is difficult in burned forests because 

snag stands are not easily detected with remote sensing. We have three related 

questions that address the area and distribution of snag stands. First, is pre-fire 

vegetation classification a reasonable index to post-fire stands of snags at the 

microhabitat scale? Second, using pre-fire vegetation classification, what are the 

characteristics of snag stands surrounding nest sites at the landscape scale? Lastly, 

are patterns of nest-site selection at the landscape scale consistent with patterns at the 

microhabitat scale? Information developed from this study is intended to provide 

guidelines for post-fire, snag management that accommodates cavity-nesting birds at 

two habitat scales: microhabitat (nest site) and landscape (composition and patterning 

of surrounding vegetation cover types).

Study Area 

The study areas are in the Foothills and Star Gulch fires on the Boise National 

Forest in southwestern Idaho (Elmore, Ada, and Boise Counties). Elevation ranges 

from 1,100 meters to 2,400 meters. The Foothills fire was a moderate to highintensity crown fire during August/September 1992 that burned 104,328 hectares. 

Prior to the fire, about a third of the burn was forested and the remainder was shrub 

steppe. The Star Gulch Fire occurred in August 1994 and burned 12,350 hectares at 

various intensities, creating a patchy mosaic of green and burned forest. Because of 

the nature of these fires, most standing trees were snags.

Pre-fire overstory vegetation was dominated by ponderosa pine (Pinus 

ponderosa) community types at lower elevations and on southerly aspects, whereas 

Douglas-fir (Pseudotsuga menziesii) community types dominated at higher elevations 

and on northerly aspects. 

We selected at least two replicates each in unlogged and logged treatments. 

Seven study sites averaged 680 hectares in size, based on the area treated, and were 

used to monitor cavity-nesting birds and vegetation in post-fire conditions. One 

unlogged and four logged study sites were used in the Foothills study area, while two 

unlogged study sites were located in the Star Gulch study area. 

Salvage logging prescriptions on the Foothills Fire varied by aspect and 

management for big game security cover (Saab and Dudley 1998). Based on the 

average densities of standing snags in unlogged units, about 50 percent of smaller 

snags (> 23 centimeters to < 53 centimeters diameter breast height [dbh]) and 70 

percent of larger snags (> 53 centimeters dbh) were harvested in the salvage-logged 

units (Saab and Dudley 1998). Densities of small snags averaged 43 per hectare and 

large snags averaged 5 per hectare in logged units, whereas densities in unlogged 

units averaged 81 per hectare for small snags and 17 per hectare for large snags. 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 837 

Methods 

Nest Monitoring and Microhabitat Measurements 

Nest surveys for nine cavity-nesting birds (table 1) were conducted by walking 

200 meter-wide belt transects during May through June 1994-1998. Transect length 

averaged 1.6 kilometers and number of transects per study site varied from 26 to 43. 

Nests were monitored every 3 to 4 days to determine status and fate. Methods for 

vegetation measurements and nest monitoring followed those described for BBIRD 

(Martin and Guepel 1993, Ralph and others 1993) with some modifications. The 

number and dbh of all snags > 23 centimeters were recorded within 11.3 meter-radius 

plots (0.04 hectare) centered at each nest tree. The same data were recorded at 89 

non-nest random locations (40 in unlogged and 49 in logged treatments). Each nest 

tree and the center of each random location were geographically referenced by using 

a global positioning system (GPS), and data were exported into the geographic 

information system, ARC-INFO (Anonymous 1998).

Table 1―Number of nests and non-nest random points monitored in burned ponderosa 

pine/Douglas-fir forests of western Idaho, 1994-1998. 

 

Species Logged Unlogged Total 

American Kestrel (Falco sparverius) 80 20 100 

Lewis’s Woodpecker (Melanerpes lewis) 305 50 355 

Hairy Woodpecker (Picoides villosus) 46 135 181 

White-headed WP (Picoides albolarvatus) 4 10 14 

Black-backed WP (Picoides arcticus) 6 29 35 

Northern Flicker (Colaptes auratus) 87 101 188 

Western Bluebird (Sialia mexicana) 130 60 190 

Mountain Bluebird (Sialia currucoides) 60 132 192 

European Starling (Sturnus vulgaris) 31 0 31 

 

 Nest Total 749 537 1,286 

Non-nest Random Points 49 40 89 

Vegetation Classification and Landscape Measurements 

Vegetation classification was derived from two Landsat Thematic Mapper (TM) 

images. Each TM pixel covers a 30-meter by 30-meter area. A pre-fire classification 

was mapped from a September 1991 image, and post-fire conditions were mapped 

from a September 1995 image. Aerial photography (1:16000) from July 1988 and 

August 1996 were used to assist in the classification process. 

The vegetation classification had two components: (1) cover type, and (2) crown 

closure for each cover type. Decision rules for assigning cover types were derived 

from the Southwest and Central Idaho Ecogroups, who mapped 8 million hectares in 

southwestern Idaho (Redmond and others 1998). Cover types for our study included 

ponderosa pine, Douglas-fir, and a mix of ponderosa pine and Douglas-fir. The 

crown closure classes we used were: low (> 10 to < 40 percent), moderate (> 40 to <

70 percent), and high (> 70 percent). Ninety-eight training sites were visited in the 

field to calibrate the classified images. 

Landscape measurements were determined from ARC-INFO files by using the 

landscape metrics software FRAGSTATS (McGarigal and Marks 1995). Landscape 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

838 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

analyses were conducted only for black-backed and Lewis’s woodpeckers because at 

the microhabitat scale, these species represented different ends of a continuum in 

habitat use (see Saab and Dudley 1998). Landscape variables were measured within a 

1,000-meter radius of nest trees and random points, an area (314 hectares) that 

encompasses the home range sizes of most songbirds (Hansen and Urban 1992) and 

some woodpecker species in the Pacific Northwest of U.S. (Dixon and Saab 2000), 

Goggans and others 1989, Garrett and others 1996). 

 The resolution of TM imagery was too coarse for identifying stands of snags in 

the post-fire image. To describe stand area and distribution of snags and other 

landscape patterns, we developed a vegetation map by combining pre- and post-fire 

classifications. We used pre-fire cover type/crown closure as an index to post-fire 

composition and stand area of snags, based on nine cover type/crown closure classes: 

ponderosa pine/low, moderate, and high crown closure; Douglas-fir/low, moderate, 

and high crown closure; and ponderosa pine-Douglas-fir/low, moderate, and high 

crown closure. Based on earlier microhabitat findings (Saab and Dudley 1998), we 

wanted to know if high and moderate snag densities in burned forests at black-backed 

and Lewis’s woodpecker nest sites, respectively, would correspond to high and 

moderate crown closure in pre-fire conditions. 

For a measure of distribution of snag stands surrounding each nest and random 

point, we calculated the mean nearest neighbor and mean proximity index 

(McGarigal and Marks 1995) of like stands (same cover type/crown closure) for each 

of three cover types in moderate and high crown closures. Nearest neighbor was the 

mean distance (meters) to the nearest like stand, regardless of stand area, within the 

1,000 meter-radius landscape circle. The mean proximity index considered the 

distance (meters) to and area (hectares) of like stands. This index measured both the 

degree of cover type isolation and the degree of fragmentation of the corresponding 

cover type within the 1,000 meter-radius landscape (McGarigal and Marks 1995). 

Analyses 

At the microhabitat scale, type III sums of squares, analysis of variance 

(ANOVA; Anonymous 1996) was used to test for non-random selection of snag 

densities by comparing densities at nest sites with random sites. Differences in 

habitat measurements for microhabitat and landscape variables were considered 

significant at p < 0.05. Means are followed by + one standard error (SE). 

For landscape analyses, we adopted the approach recommended by Burnham 

and Anderson (1998), i.e., we developed a “global” logistic regression model 

containing various landscape predictor variables that may have had important 

influences on nest occurrence of black-backed and Lewis’s woodpeckers. Three 

global models were developed: nest occurrence of black-backed woodpecker vs. 

random points in unlogged units, nest occurrence of Lewis’s woodpecker vs. random 

points in unlogged units, and nest occurrence of Lewis’s woodpecker vs. random 

points in logged units. We were unable to model the response of black-backed 

woodpeckers to landscape features in logged units because of a small sample of nests 

(n = 6). Global models were tested for goodness of fit using the Hosmer and 

Lemeshow (1989) test. From the global model for each set of comparisons, we 

generated a subset of candidate models that contained various combinations of 

variables we deemed biologically relevant. 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 839 

We used the Akaike’s Information Criterion (AIC; Akaike 1973) to rank 

candidate models and assess their relative plausibility given the data. AIC operates on 

the principle of parsimony (Box and Jenkins 1970), where the highest ranked models 

are those that best fit the data with the fewest parameters. The principle of parsimony 

states that there is an ideal point in the balance between increasing the number of 

parameters to decrease bias and decreasing the number of parameters to increase 

precision. We used PROC LOGISTIC in SAS (Anonymous 1996) to produce AIC 

values for all sets of candidate models. Once we selected the best candidate model 

based on the highest AIC value, standardized estimates derived from logistic 

regression were used to evaluate the relative importance of each landscape predictor 

variable to nest occurrence (cf. Manly and others 1993). 

Results 

Microhabitat 

To date, microhabitat data have been analyzed for 1994-1996 (625 nests, 89 

random sites). Based on these data, seven species selected nest sites with 

significantly higher snag densities than that measured at random sites in both logged 

(d.f. = 7, F = 7.2, p < 0.001) and unlogged (d.f. = 7, F = 4.6, p <0.001) treatments 

(fig. 1). Snag densities were highest at black-backed woodpecker nest sites and 

lowest at random sites. Among cavity nesters, snag densities were lowest at Lewis’s 

woodpecker nest sites, yet densities were still higher than those in the random 

unlogged controls. This suggests that cavity nesters as a group selected clumps 

(stands) of snags rather than uniformly-spaced snags (Saab and Dudley 1998). 

Based on 1994-1995 data, we reported that cavity-nesting birds used larger 

diameter snags more than in proportion to availability (Saab and Dudley 1998). 

Among the woodpecker species, Lewis’s woodpecker selected the largest diameter 

snags, whereas black-backed woodpecker used the smallest diameter snags. This 

pattern has continued through 1998: snag diameters were smallest for black-backed 

woodpecker and largest for Lewis’s woodpecker (fig. 2). 

Landscape 

All global models adequately fitted the data (Hosmer and Lemeshow goodness 

of fit test, p > 0.5). The selected model for black-backed woodpecker in unlogged 

units included 15 predictor variables (table 2). Statistically significant predictors 

were proximity of stands characterized by burned, ponderosa pine/high crown 

closure; proximity; and area of burned, Douglas-fir/high crown closure stands; and 

area of burned, Douglas-fir/low crown closure stands. Standardized estimates derived 

from logistic regression indicate the strength and nature of the relationship between 

the predictor variables and the response variable. The strongest positive standardized 

estimates indicated that area and proximity of burned, Douglas-fir/high crown closure 

stands were the best predictors of black-backed nest sites in unlogged landscapes, 

whereas one would be unlikely to find a nest in close proximity of burned ponderosa 

pine/high crown closure or in stands of Douglas-fir/low crown closure (table 2). 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

840 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 1―Mean number of snags (> 23 cm dbh) per hectare (+ 1 SE) surrounding 

nest trees and random trees based on microhabitat measurements during 1994-

1996. Sample size for each species is stated in parentheses. 

Figure 2―Mean diameter (+ 1 SE) at breast height of nest trees during 1994-1998. 

Sample size for each species is stated in parentheses. 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 841 

Table 2―Selected models and coefficients derived from logistic regression for predictors of 

nest occurrence for black-backed woodpecker (unlogged) and Lewis’s woodpecker (unlogged 

and logged). 

Variable 

Parameter 

estimate 

SE Chisquare P Standardized 

estimate 

Unlogged 

Black-backed Woodpecker (n=29 nests) 

vs. Random (n=40 points)

 

Intercept 3.44 4.46 0.60 0.440 

Proximity Index-Ponderosa Pine High CC2 -2.14 0.79 7.27 0.007 -2.55

Proximity Index-Ponderosa Pine Moderate CC 0.02 0.10 0.05 0.820 0.13 

Proximity Index-Doug-Fir High CC 0.34 0.13 6.60 0.010 2.27

Proximity Index-Doug-Fir Mod CC 0.27 0.69 0.16 0.690 0.22 

Proximity Index-Ponderosa/Doug-Fir High CC -3.33 1.83 3.31 0.070 -1.46 

Proximity Index-Ponderosa/Doug-Fir Moderate CC -1.83 1.08 2.82 0.090 -1.09 

Stand Area-Ponderosa Pine High CC -0.49 0.29 2.97 0.080 -2.21 

Stand Area-Ponderosa Pine Moderate CC -0.16 0.17 0.80 0.370 -1.26 

Stand Area-Ponderosa Pine Low CC 0.21 0.12 2.84 0.090 1.64 

Stand Area-Doug-Fir High CC 0.47 0.21 4.90 0.030 4.64

Stand Area-Doug-Fir Moderate CC 0.61 0.34 3.04 0.080 1.36 

Stand Area-Doug-Fir Low CC -1.09 0.49 5.03 0.030 -11.7

Stand Area-Ponderosa Pine/Doug-Fir High CC 0.56 0.59 0.87 0.350 0.84 

Stand Area-Ponderosa Pine/Doug-fir Low CC -0.03 0.17 0.03 0.860 -0.18 

Distance to High or Moderate CC -0.02 0.02 0.54 0.460 -0.24 

Variable Parameter 

estimate 

SE Chisquare P Standardized 

estimate 

Unlogged 

Lewis's Woodpecker (n=50 nests) 

 vs. Random (n=40 points)

Intercept 6.63 7.00 0.90 0.340 

Nearest Neighbor-Ponderosa Pine Moderate CC -0.13 0.08 2.38 0.120 -0.83 

Nearest Neighbor-Doug-Fir Moderate CC -0.01 0.07 0.03 0.860 -0.05 

Nearest Neighbor-Ponderosa/Doug-Fir Moderate CC 0.001 0.05 0.00 0.990 0.009 

Proximity Index-Ponderosa Pine Moderate CC 0.12 0.06 4.03 0.040 0.77

Proximity Index-Doug-Fir Moderate CC 0.4 0.49 0.66 0.420 0.31 

Proximity Index-Ponderosa/Doug-Fir Moderate CC -0.1 0.57 0.03 0.870 -0.05 

Stand Area-Ponderosa Pine Moderate CC -0.22 0.11 3.83 0.050 -1.74

Stand Area-Ponderosa Pine Low CC 0.13 0.09 2.05 0.150 0.87 

Stand Area-Doug-Fir Moderate CC -0.06 0.18 0.09 0.760 -0.11 

Stand Area-Doug-Fir Low CC -0.11 0.09 1.43 0.230 -1.08 

Stand Area-Ponderosa Pine/Doug-fir Mod CC 0.14 0.22 0.45 0.500 0.49 

Stand Area-Ponderosa Pine/Doug-fir Low CC -0.03 0.08 0.11 0.740 -0.17 

Distance to High or Moderate CC -0.03 0.02 3.38 0.070 -0.43 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

842 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(table 2 continued) 

Variable 

Parameter 

estimate 

SE Chisquare P Standardized 

estimate 

Logged 

Lewis's Woodpecker (n=305 nests) 

 vs. Random (n=49 points) 

Intercept 3.26 1.40 5.36 0.020 

Nearest Neighbor-Ponderosa Pine High CC -0.03 0.01 7.50 0.006 -0.27

Nearest Neighbor-Ponderosa Pine/Doug-Fir High CC -0.003 0.00 1.60 0.200 -0.16 

Stand Area-Ponderosa Pine High CC 0.12 0.06 3.71 0.050 0.51

Stand Area-Ponderosa Pine Moderate CC 0.04 0.05 0.48 0.490 0.22 

Stand Area-Ponderosa Pine Low CC -0.02 0.02 1.19 0.280 -0.24 

Stand Area-Doug-Fir High CC -0.02 0.02 0.78 0.390 -0.19 

Stand Area-Doug-Fir Moderate CC -0.04 0.07 0.27 0.600 -0.11 

Stand Area-Doug-Fir Low CC 0.02 0.03 0.26 0.600 0.07 

Stand Area-Ponderosa Pine/Doug-Fir High CC -0.37 0.09 16.04 0.001 -0.66

Stand Area-Ponderosa Pine/Doug-fir Mod CC 0.39 0.15 6.90 0.009 1.2

Stand Area-Ponderosa Pine/Doug-fir Low CC -0.09 0.06 2.27 0.130 -0.45 

1

 The highest standardized estimates are in bold, indicating the most important predictors of nest 

occurrence.

2 CC = Crown closure. Cover types were in burned conditions. Variables represent mean values. 

One goal of the multivariate analysis is to statistically adjust the estimated 

effects of each predictor variable in the model for differences in the distributions of 

and associations among the other predictor variables (Hosmer and Lemeshow 1989). 

When adjusting for other variables in the model, stand area of burned, Douglasfir/high crown closure was the most important variable in predicting the presence of 

black-backed woodpecker nests (table 2). Probability of nest occurrence was most 

consistently high for black-backed woodpecker when stand area of Douglas-fir/high 

crown closure was between 30 and 50 hectares (fig. 3). In landscapes where stand 

area was outside of this range, other landscape features necessary for nesting blackbacked woodpeckers were likely reduced in availability or absent. Nests were not 

present where stand area was less than 12 hectares, and probability was highly 

variable when stand area was between 12 and 25 hectares or when area was greater 

than 55 hectares (fig. 3). The average stand area within landscapes surrounding 

black-backed nests was 37.16 hectares + 3.41, whereas average stand area at random 

points was 24.87 hectares + 3.7 (fig. 4). The stand area for all species of cavity 

nesters was between the areas measured for black-backed and Lewis’s woodpeckers 

(fig. 4), a pattern similar to that reported at the microhabitat scale (figs. 1, 2).
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 843 

Figure 3―Scatter plot of the probability of black-backed woodpecker nest 

occurrence with stand area of burned, Douglas-fir/high crown closure areas. The 

scatter plot was adjusted for other landscape variables in the predictive model. 

Figure 4―Based on measurements taken within landscape circles (1,000 meterradius circle) surrounding nest and random points. (A) Mean area of stands (+ 1 SE) 

characterized as burned, Douglas-fir/high crown closure, and (B) Mean proximity 

index (+ 1 SE) of burned, ponderosa pine/moderate crown closure. Sample size for 

each species is stated in parentheses. 

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 10 20 30 40 50 60 70 80

Stand Area of Doug-fir High CC (ha)

Probability of Bbwo Nest Occurrence
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

844 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The selected model for Lewis’s woodpecker in unlogged units included 13 

landscape predictor variables (table 2). The only statistically significant predictor of 

their nest occurrence was the proximity of burned stands characterized by ponderosa 

pine moderate crown closure, while area of these stands was nearly significant at p = 

0.05. Standardized estimates revealed that the strongest relationship between Lewis’s 

woodpecker and the predictor variables was a negative one with area of burned, 

ponderosa pine/moderate crown closure stands (table 2). The mean area of these 

stands was 33.56 hectares + 1.53 within nest landscapes, and 25.41 hectares + 2.67 

within random landscapes. The positive relationship with proximity of this cover type 

suggests that burned, ponderosa pine/moderate crown closure stands were in close 

proximity of one another within landscapes surrounding Lewis’s woodpecker nests 

(fig. 4). This variable was not important to black-backed woodpeckers or all species 

combined. Once again, measurements revealed a similar pattern as that reported at 

the microhabitat scale: Lewis’s woodpecker was at one end of the continuum of 

habitat use and black-backed woodpecker at the other end (fig. 4). 

Eleven landscape predictor variables were included in the selected model for 

Lewis’s woodpecker within logged units (table 2). Statistically significant predictors 

and the nature of the relationship with Lewis’s woodpecker were: 

• Nearest neighbor of burned, ponderosa pine high crown closure stands, 

negative relationship. 

• Area of burned, ponderosa pine high crown closure stands, positive 

relationship. 

• Area of burned, ponderosa pine/Douglas-fir high crown closure, negative 

relationship. 

• Area of burned, ponderosa pine/Douglas-fir moderate crown closure, positive 

relationship. 

Based on standardized estimates, area of ponderosa/Douglas-fir moderate crown 

closure stands (mean = 6.63 hectares + 0.16) was the most important variable in 

predicting nest occurrence of Lewis’s woodpecker in logged units. Thus, regardless 

of cover type or treatment, moderate crown closure in a burned condition was the 

most important characteristic of a landscape feature in predicting the presence of a 

Lewis’s woodpecker nest. The negative relationship with nearest neighbor of burned, 

ponderosa pine/high crown closure and the positive relationship with stand area of 

the same cover type/crown closure indicates that the close distribution (mean nearest 

neighbor = 61.9 meters + 0.75) and large area (mean = 15.82 hectares + 0.47) of 

these stands was also important for their nest site selection. 

Discussion 

At the microhabitat scale, habitat use by black-backed and Lewis’s woodpeckers 

was represented by different ends of a continuum. Compared to other cavity-nesting 

birds and random sites, black-backed woodpeckers selected nest sites with the 

highest densities of snags of relatively small diameters, whereas Lewis’s selected 

nest sites with moderate densities of snags of large diameters. The microhabitat 

selection by black-backed woodpeckers that we observed in western Idaho is similar 

to that reported elsewhere in the Northern Rocky Mountains. Black-backed 

woodpeckers have consistently selected unlogged conditions of high snag densities 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 845 

for both nesting and foraging habitat (Caton 1996, Hitchcox 1996, Hoffman 1997, 

Hutto 1995, Kreisel and Stein 1999). Perhaps high snag densities provide greater 

foraging opportunities for this species (Saab and Dudley 1998) that feeds primarily 

on bark (Scolytidae) and wood-boring (Cerambycidae) beetles (Dixon and Saab 

2000). In contrast, Lewis’s woodpecker favors open woodlands, especially burned 

pine forests (Tobalske 1997, Saab and Vierling 2001). Unlike most woodpecker 

species, Lewis’s woodpeckers are primarily aerial flycatchers during the breeding 

season. This species is thought to do well in burned forests because of the relatively 

open canopy that allows for shrub development and associated arthropod prey (Bock 

1970), good visibility, and perch sites for foraging (Linder and Anderson 1998), and 

space for foraging maneuvers (Saab and Dudley 1998). 

Pre-fire crown closure of live trees may serve as an index to post-fire stand 

densities of snags. One might expect that unburned stands of Douglas-fir with a high 

crown closure could result in burned high densities of snags with relatively small 

diameters. This was consistent with black-backed woodpecker nest-site selection at 

both the microhabitat and landscape scales in burned forests of western Idaho. 

Likewise, one might expect that unburned moderate crown closure stands of 

ponderosa pine and Douglas-fir could result in burned moderately dense stands of 

snags with relatively large diameters. This characterized nest-site selection by 

Lewis’s woodpecker at the microhabitat and landscape scales. Patterns in nest-site 

selection at the landscape scale were consistent with patterns in nest-site selection at 

the microhabitat scale. Following the microhabitat data, landscapes used by nesting 

black-backed woodpeckers represented one end of a habitat continuum, while 

landscapes used by Lewis’s woodpeckers represented the other extreme. 

Because pre-fire vegetation classification was a reasonable approximation of 

post-fire stands of snags, we used Landsat TM images of pre- and post-fire 

conditions to characterize the area and spatial distribution of snags surrounding nest 

sites. In unlogged burned conditions, black-backed woodpeckers selected landscapes 

where large stands of Douglas-fir/high crown closure occurred in closer proximity 

than in landscapes surrounding random points. Lewis’s woodpeckers chose burned 

landscapes where relatively small stands of ponderosa pine/moderate crown closure 

were in close proximity compared to average, unlogged conditions. 

In logged areas, moderate crown closure was again an important feature of 

landscapes surrounding Lewis’s woodpecker nests. Stand area, however, was smaller 

on average in logged compared to unlogged units. The close distribution and large 

stand area of ponderosa pine/high crown closure was another important characteristic 

of landscapes surrounding nests of Lewis’s woodpecker in logged conditions. Stands 

of burned, ponderosa pine/Douglas-fir with moderate crown closure were the best 

predictor of Lewis’s woodpecker nests. 

Management Implications 

The continuum of habitat use by black-backed and Lewis’s woodpeckers 

reported for the microhabitat scale was consistent at the landscape scale. This 

suggests that management for cavity nesters should be considered not only at the 

local, stand level but also at larger spatial scales. At both scales, we found that a 

range of habitat conditions characteristic of black-backed and Lewis’s woodpeckers 

would likely incorporate habitat features necessary for nest occurrence of other 

members in the cavity-nesting bird community. 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

846 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Our data suggest that pre-fire vegetation classification can be used to develop 

design criteria for cavity-nesting birds in post-fire salvage logging projects. We can 

manage for a diversity of species across burned landscapes by maintaining a 

continuum of habitat features. Unlogged landscapes with large, dense stands of 

Douglas-fir snags in close proximity to one another were typical of black-backed 

woodpeckers. Partially logged landscapes were favored by Lewis’s woodpeckers, 

although they selected unlogged conditions for nesting habitat as well. Burned 

landscapes used by nesting Lewis’s woodpeckers were primarily composed of 

closely distributed, small to medium-sized stands of ponderosa pine/moderate crown 

closure. 

Our future work will be focused on examining the relationships between pre-fire 

crown closure (from remote sensing) and post-fire snag densities and diameters (from 

our microhabitat measurements). Determining these relationships will assist not only 

in developing design criteria for post-fire salvage logging but also in generating stand 

exam information based on remote sensing data. Future work also will include 

developing probabilities of nest occurrence for each species using landscape 

variables and examining the influence of landscape variables on nest success. 

Acknowledgments 

The Rocky Mountain Research Station’s (RMRS) Boise Laboratory and the 

Remote Sensing Applications Center (RSAC), both of the USDA Forest Service, 

contributed most of the funding for this study. Additional support was provided by 

the Boise National Forest (BNF), Intermountain and Pacific Northwest (R6) Regions 

of the Forest Service, the University of Idaho, and the University of Colorado. The 

Mountain Home Ranger District of the BNF assisted with logistics. We acknowledge 

the following Forest Service employees who helped with the development, data 

analysis, and critical reviews of the study: Bill Thompson (RMRS), Christina Hargis 

(Washington Office), Carey Crist (BNF), Kathy Geier-Hayes (BNF), Kim Mellen 

(R6), and Paul Maus (RSAC). Field assistance was provided by Dan Shaw, Holiday 

Sloan, Jennifer Chambers, Gary Vos, Danielle Bruno, Christa Braun, Lottie Hufford, 

David Wageman, Steve Breth, and Suzanne DiGiacomo, Colette Buchholtz, Janine 

Schroeder, Jim Johnson, Joshua Bevan, Melissa Pearcy, Audra Serrian, Jennifer 

Mark, Joshua Schmidt, Douglas Kahill, and Mark Uranga. 

References 

Akaike, H. 1973. Information theory and an extension of the maximum likelihood 

principle. In: Petrov, B. N.; Csake, F., eds. Second international symposium on 

information theory Budapest, Hungary: Akademiai Kiado; 451 p. 

Anonymous. 1996. SAS/STAT software: changes and enhancements, through version 

6.11. Cary, North Carolina: SAS Institute, Inc. 

Anonymous. 1998. ARC version 7.2.1 patch 1. Redlands, CA: Environmental Systems 

Research Institute, Inc. 

Bock, Carl E. 1970. The ecology and behavior of the Lewis Woodpecker. University of 

California Publications in Zoology, vol. 92. Berkeley: University California Press; 100 

p. 

Box, G. E. P.; Jenkins, G. M. 1970. Time series forecasting: forecasting and control.

London, United Kingdom: Holden-Day; 553 p. 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 847 

Burnham, Ken P.; Anderson, David R. 1998. Model selection and inference: a practical 

information theoretic approach. New York: Springer-Verlag; 353 p. 

Caton, Elaine L. 1996. Effects of fire and salvage logging on the cavity-nesting bird 

community in northwestern Montana. Missoula: University of Montana; Ph.D. 

dissertation. 

Dixon, Rita D.; Saab, Victoria A. 2000. Black-backed Woodpecker (Picoides arcticus). In: 

Poole, A.; Gill, F., eds. The birds of North America, No. 509. Philadelphia, PA: The 

Academy of Natural Sciences; and Washington DC: The American Ornithologists’ 

Union. 

Garrett, Kimball L; Raphael, Martin G.; Dixon, Rita D. 1996. White-headed Woodpecker 

(Picoides albalarvatus). In: Poole, A.; Gill, F., eds. The birds of North America, No. 

252. Philadelphia, PA: The Academy of Natural Sciences; and Washington DC: The 

American Ornithologists’ Union. 

Goggans, Rebecca; Dixon, Rita D.; Seminara, L.C. 1989. Habitat use by three-toed and 

black-backed woodpeckers, Deschutes National Forest, Oregon. Oregon Department 

of Fish and Wildlife, Nongame Wildlife Program, Tech. Report 87-3-02; 43 p. 

Hansen, Andrew J.; Urban, D. L. 1992. Avian response to landscape pattern: the role of 

species' life histories. Landscape Ecology 7: 163-180. 

Hitchcox, Susan M. 1998. A comparison of abundance, nesting success, and nest-site 

characteristics of cavity-nesting birds in salvage-logged and uncut patches with a 

burned forest in northwestern Montana. In: Pruden, T. L.; Brennan, L. A., eds. Fire in 

ecosystem management: shifting the paradigm from suppression to prescription. Tall 

timbers fire ecology conference proceedings No. 20. Tallahassee, FL: Tall Timbers 

Research Station; 365. 

Hoffman, Nancy. 1997. Distribution of Picoides woodpeckers in relation to habitat 

disturbance within the Yellowstone area. Bozeman: Montana State University; 

Master’s thesis. 

Hosmer, D. W.; Lemeshow, S. 1989. Applied logistic regression. New York: John Wiley 

and Sons; 307 p. 

Hutto, Richard L. 1995. Composition of bird communities following stand-replacement 

fires in northern Rocky Mountain (U.S.A.) conifer forests. Conservation Biology 9: 

1041-1058. 

Kotliar, Natasha B.; Hejl, Sallie; Hutto, Richard; Saab, Victoria; Melcher, Cynthia McFadzen, 

Mary. [In press]. Effects of wildfire and post-fire salvage logging on avian 

communities of western forests in the United States. Cooper Ornithological Society, 

Studies in Avian Biology. 

Kreisel, I. J.; Stein, S. J. 1999. Bird use of burned and unburned coniferous forests during 

winter. Wilson Bulletin 111: 243-250. 

Linder, K. A.; Anderson, S. H. 1998. Nesting habitat of Lewis’ woodpeckers in 

southeastern Wyoming. Journal of Field Ornithology 69: 109-116. 

Manly, B.; McDonald, L.; Thomas, D. 1993. Resource selection by animals. London, 

England: Chapman and Hall. 

Martin, Thomas E.; Geupel, Geoff R. 1993. Nest monitoring plots: methods for locating 

and monitoring success. Journal of Field Ornithology 64: 507-519. 

McGarigal, Kevin; Marks, Barbara J. 1995. FRAGSTATS: spatial pattern analysis 

program for quantifying landscape structure. Gen. Tech. Rep. PNW-351. Portland, 

OR: Forest Service, U.S. Department of Agriculture. 
Snag Stands and Cavity-nesting Birds—Saab, Brannon, Dudley, Donohoo, Vanderzanden, 

Johnson, and Lachowski 

848 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Ralph, C. J.; Geupel, G. R.; Pyle, P.; Martin, T. E.; DeSante, D. F. 1993. Field methods for 

monitoring landbirds. Gen. Tech. Rep. PSW-GTR-144. Fresno, CA: U.S. Department 

of Agriculture Forest Service. 

Redmond, R. L.; Tady, T. P.; Fisher, F. B.; Thornton, M.; Winne, J.C. 1998. Landsat 

vegetation mapping of the southwest and central Idaho ecogroups. Final Report, 

Contract #: 53-0261-6-25. Boise, ID: Forest Service, U.S. Department of Agriculture. 

Saab, Victoria A.; Dudley, Jonathan G. 1998. Responses of cavity-nesting birds to standreplacement fire and salvage logging in ponderosa pine/Douglas-fir forests of 

southwestern Idaho. Res. Paper RMRS-RP-11. Ogden, UT: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture; 17 p. 

Saab, Victoria A.; Vierling, Kerri T. 2001. Reproductive success of Lewis’s woodpecker in 

burned pine and cottonwood riparian forests. Condor 103: 491-501. 

Tobalske, Bret W. 1997. Lewis’ woodpecker (Melanerpes lewis). In: Poole, A.; Gill, F., 

editors. The birds of North America. No. 284. Philadelphia, PA: The Academy of 

Natural Sciences; and Washington DC: The American Ornithologists’ Union. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 849 

Dead Tree Management in British Columbia1

Jeff Stone,2 John Parminter,3 André Arsenault,4 Todd Manning,5

Nancy Densmore,6 Gerry Davis,7 and Andy MacKinnon8

Abstract 

We highlight the historical development, current legislation, and operational practices 

regarding dead tree management in British Columbia (BC), Canada. BC’s Forest Practices 

Code, which regulates forest management, enables resource managers to leave wildlife tree 

patches in harvested areas, and to consider the retention of coarse woody debris (CWD). At 

the same time, occupational health and safety regulations govern the retention of potentially 

dangerous trees in forestry operations, and current CWD policy enables the management of 

CWD only within harvesting utilization standards. Managing for the ecological values of dead 

trees without impacting timber supply is a challenge facing BC’s forest managers. 

Introduction 

British Columbia (BC) is Canada’s most ecologically and biologically diverse 

province, with areas of extensive alpine, rangeland, and forest. Ownership of the 

province’s 95.2 million ha is predominantly public (94.7 percent). These lands are 

administered for many purposes including fish, wildlife, wilderness, recreation, 

heritage, water, minerals, range, and timber. The Ministry of Forests (MOF) 

manages, in cooperation with other provincial and Federal agencies, the timber, 

range, and recreation resources of the unreserved public forest land (about 59 million 

ha). From these lands about 65-70 million cubic meters of wood are harvested 

annually (Ministry of Forests 1998). The predominant (about 90 percent by area) 

silvicultural system is clearcutting or clearcutting with reserves of individual or 

clumps of trees. 

The ecological values of dead trees are well recognized by the managers of BC’s 

forests. Wildlife trees (standing dead trees and live defective trees) are a vital 

component of biodiversity, providing critical habitat for 80 species of birds, 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. This paper reflects government 

organization, legislation, or policy as of December 1999. 

2

 Timber Supply Analyst, Ministry of Forests, Kamloops Forest Region, 515 Columbia St., Kamloops, 

BC V2G 2T7 Canada (e-mail: jeff.stone@gems7.gov.bc.ca) 3

 Research Ecologist, Ministry of Forests, Research Branch, P.O. Box 9519 Stn. Prov. Govt., Victoria, 

BC V8W 9C2 Canada (e-mail: john.parminter@gems7.gov.bc.ca) 4

 Plant Ecologist, Ministry of Forests, Kamloops Forest Region, 515 Columbia St., Kamloops, BC V2G 

2T7 Canada (e-mail: andre.arsenault@gems8.gov.bc.ca) 5

 Habitat Forester, Manning, Cooper & Associates, 5148 William Head Rd., Victoria, BC V9C 4H5 

Canada (e-mail: tmanning@islandnet.com) 

6

 Silviculture Planning Forester, Ministry of Forests, Forest Practices Branch, P.O. Box 9513 Stn. Prov. 

Govt., Victoria, BC V8W 9C2 Canada (e-mail: nancy.densmore@gems2.gov.bc.ca) 7

 1655 Janes Rd., Nanaimo, BC V9X 1P3 Canada (e-mail: davismoffat@shaw.ca) 8

 Manager Ecosystems Conservation, Ministry of Sustainable Resource Management, P.O. Box 9373 

Stn. Prov. Govt., Victoria, BC V8W 9M3 Canada (e-mail: andy.mackinnon@gems1.gov.bc.ca) 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

850 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

mammals and amphibians in BC, as well as habitat for a myriad of invertebrate and 

fungal organisms (Lofroth 1998, Machmer and Steeger 1995). Coarse woody debris 

(CWD; fallen dead trees) has similar critical roles for many species of plants 

(especially bryophytes and lichens), fungi, invertebrates, and small mammals 

(Harmon and others 1986, Stevens 1997). The value of dead wood, particularly for 

wildlife trees, is acknowledged in forest management in BC through regulations 

issued under legislative acts. 

In this paper, we outline the history and status as of December 1999 of the 

legislation and management of dead wood on crown lands in BC. 

History of Forest Management and the Dead Wood 

Resource 

Forests provided important resources to the First Nations of BC in terms of 

housing, transportation, clothing, household goods, fuel, and food. Dead wood was 

valued for a variety of purposes. Turner (1998) identified specific uses of dead wood 

that include cottonwood (Populus balsamifera ssp. trichocarpa) for the hearth and 

drill for creating friction fires, rotten trembling aspen (P. tremuloides) as an 

absorbent material, decayed wood for smudge for tanning hides, and knots left in 

rotten western hemlock (Tsuga heterophylla) and spruce (Picea spp.) logs for curved 

fish hooks. Little has been summarized specifically on the management of dead wood 

by First Nations, whose population was likely between 200,000 and 300,000 in the 

mid-1700s (Muckle 1998). Undoubtedly forest management did occur, given the 

recognition of resource ownership by many First Nations. Prescribed burning was 

carried out for a number of purposes—primarily to create and/or maintain certain 

vegetative types and to clear the land around habitations. Single burns would add to 

the dead wood resource, while repeated burning would reduce levels of both standing 

and downed material. 

Commercial forest harvesting in BC began in earnest in the late 1800s. It was 

concentrated in the valuable and easily-accessible timber of the west coast and at 

lower elevations of major valleys in the interior of BC. Impacts on the forest were 

generally low because only the more valuable and easily-transported trees were cut. 

Undesirable species may have been felled to provide a cushion and reduce breakage 

of valuable trees felled subsequently. A legacy of high stumps was left due to the use 

of springboards to cut above butt flares. Additionally, the lower portions of felled 

trees were sometimes too massive to move and so were left in place. This increased 

the proportion of large diameter, fresh CWD in forests. 

The use of high-lead yarding and extensive railway logging networks began just 

before World War I, ushering in clearcutting as a harvesting system. At the same 

time, slashburning was promoted by the BC Forest Service to reduce the fire hazard 

on logged coastal sites. The application of fire was deemed appropriate to remove 

fuels and create a seedbed amenable to natural regeneration. Some CWD would be 

removed by these controlled burns, but given that partial cutting (essentially highgrading) was still common, a supply of fire-killed standing dead trees was created at 

the same time. 

Fire prevention has been encouraged since 1905, when fire wardens were first 

appointed. Early controlled burning reduced logging slash loadings but escaped burns 

increased dead wood resources. Human-caused wildfires have done likewise. 

Effective fire suppression began in the late 1950s due to improved fire detection, 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 851 

technological advancements, such as air tankers and lightweight fire pumps. While 

the number of wildfires has increased since the late 1950s (from an average of 1,583 

per year in the 1940s and 1950s to 2,493 in the 1980s and 1990s), the area burned has 

dramatically declined. Total area burned for the respective periods was 3,000,462 ha 

and 1,265,573 ha, as average fire size decreased from 94 to 25 ha. 

Artificial reforestation was initiated in coastal BC in 1939 and in the Interior in 

1950. To reduce the fire hazard and improve safety for planting crews, snags were 

felled on parts of Vancouver Island as early as 1942. In 1946 the Forest Act was 

amended to make snag falling compulsory concurrent with logging operations in the 

Vancouver Forest District (Statutes of British Columbia 1946). All standing dead 

trees taller than 10 feet were felled, that being the height to which a man could apply 

dirt with a shovel to extinguish a burning snag. 

By 1947, changing logging methods, closer utilization and salvage operations 

had reduced the amount of logging residue. A 1943 pulpwood salvage study found 

that salvable wood accounted for 19 percent of the total utilizable stand volume, the 

rest having been taken in the first pass for sawlog production (MacBean 1946). Slash 

burning became less common on the Coast and was replaced either by spot burning 

or no burning at all. This increased the amount of remaining medium-sized CWD. 

Snag falling continued, largely as a fire prevention and safety measure, resulting in 

most dead wood being on the ground and little left standing. 

Environmental concerns became more prominent in the mid-1960s and early 

1970s. Resource management guidelines dealt primarily with wildlife habitat, soil 

conservation, stream protection, riparian zone management, silvicultural systems, 

cutblock size and arrangement and road location. The general guidelines did not 

address site-specific issues such as CWD or wildlife trees, which had not yet been 

identified as items requiring consideration and management. Indeed, in 1978 the 

responsibility to “fall snags progressively with the felling of adjacent live timber” in 

all forest operations was entrenched in the Workers’ Compensation Board (WCB) 

Industrial Health and Safety Regulations (Workers’ Compensation Board of British 

Columbia 1998). 

The Ministry of Forests Act of January 1, 1979 instructed the Ministry of 

Forests to integrate and coordinate the management of timber, range, fisheries, 

wildlife, water, outdoor recreation and other natural resource values (Revised 

Statutes of British Columbia 1979). Integrated use involved altering harvesting 

prescriptions to provide benefits to established resource users, mitigating the effects 

of harvesting, and facilitating change in forest conditions to support new uses. The 

main variables were dispersal of activities, size of cutblocks, time interval between 

the sequential removal of adjacent blocks and location of roads and other 

infrastructure (Ministry of Forests 1984). All of these are landscape level issues and 

no provisions specifically addressed the conservation of dead trees. 

General recognition of the ecological importance of dead trees started to emerge 

in BC in 1979, following the lead of research and management in the U.S. Pacific 

Northwest. In February 1979, Kamloops Forest Ranger Jack Weinard initiated a 

process he called the “rule of thumb” for snag management in the Kamloops Ranger 

District (Stevenson 1999). In the 1980s, the Ministry of Forests and Ministry of 

Environment jointly developed a wildlife tree signing program. This involved 

placement of “Wildlife Tree: Do Not Disturb” signs on selected wildlife trees 

(Backhouse and Lousier 1991). In 1985 the BC Wildlife Tree Committee, a multi-
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

852 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

agency group, was formed to consider the conservation and management of wildlife 

trees—particularly as related to their safe maintenance within forest operations 

(Manning 1995). This committee was instrumental in raising awareness of the need 

for legislation, regulations, guidelines and the importance of management of the dead 

tree resource. 

In the 1990s the importance of dead trees was recognized through significant 

policy, management, and legislative change. A problem analysis by Backhouse and 

Lousier (1991) highlighted the importance of wildlife trees and the need for changes 

in wildlife tree management. The initiatives of the multi-agency BC Wildlife Tree 

Committee began to take root. Through interpretation of the term “hazardous,” the 

WCB began to recognize that not all standing dead trees were dangerous and that 

standing dead trees had ecological value. Wildlife/danger tree assessment procedures 

and training programs were initiated (Manning 2002). Management for wildlife trees 

began to appear in regional and provincial guidelines. 

Initiatives for CWD have lagged behind those of wildlife trees in BC. In fact, the 

Ministry of Forests initiated and still has in place a strict residue and waste policy as 

part of its utilization standards (Caza 1993). This policy requires licensees to remove 

all wood above certain size and soundness limits while harvesting and penalizes them 

if they do not. 

Current Legislation and Regulations 

In 1995, BC introduced major changes to the legislation affecting forest resource 

management with the implementation of the Forest Practices Code of British 

Columbia Act. The Forest Practices Code establishes mandatory requirements for 

planning and forest practices, sets enforcement and penalty provisions, and specifies 

administrative arrangements. The regulations under the act lay out the forest practices 

that apply province-wide, including the planning framework. This act applies to all 

crown lands outside of protected areas, or about 80 percent of the land base in BC 

(Fenger 1995). 

Guidance for planning is provided in a number of ways, including forest 

practices guidebooks and various levels of policy. This guidance is not normally 

binding until it is written into a higher level plan or operational plan (see 

http://www.for.gov.bc.ca/tasb/legsregs/fpc/hilevel/hlp-toc.htm for a detailed outline 

of the hierarchy under the Forest Practices Code). Landscape Unit Planning is the 

higher level process that sets the legal requirements for wildlife tree retention and 

old-growth management. Landscape Units usually cover a watershed or a series of 

watersheds and average about 70,000 ha. Other higher level plans (e.g., Local 

Resource Management Plans that address a region with many landscape units) may 

also provide direction on dead tree management. Further guidance for wildlife trees 

and CWD is found in Forest Practices Code documents, such as the Biodiversity 

Guidebook, Riparian Management Area Guidebook, and the Identified Wildlife 

Management Strategy (Ministry of Forests and BC Environment 1995a, 1995b, 

1999). 

The importance of wildlife trees is well recognized within Forest Practices Code 

regulations and guidelines. The Forest Practices Code of British Columbia Act and 

associated regulations provide the framework for wildlife tree management by 

ensuring that wildlife tree objectives are stated, that wildlife tree and other reserves 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 853 

are clearly mapped within operational plans and marked in the field, and that 

penalties for non-compliance are in place (table 1). Further, changes made in April 

1998 to the WCB Occupational Health and Safety Regulations now enable greater 

retention of standing dead trees that do not pose a safety hazard (table 2). 

Table 1—Forest Practices Code of British Columbia Act and associated regulations that 

relate to dead trees (the act and regulations are available at http://www.for. 

gov.bc.ca/tasb/legsregs/comptoc.htm). 

Act or Regulation What 

Forest Practices Code of British 

Columbia Act 

12. A silviculture prescription must comply with the following: (a) it must 

include, for the area under the prescription, (i) long term management 

objectives set out (A) in a Forest Development Plan... (ii) a description of 

the silvicultural system and post harvesting stand structure and site 

condition 

41(1)(b) “the district manager is satisfied that the plan or amendment will 

adequately manage and conserve the forest resources of the area to which 

it applies.” 

41(2) before approving a plan or amendment the district manager may 

require the holder to submit information that the district manager 

reasonably requires in order to determine if the plan or amendment meets 

the requirements of subsection (1) 

Operational Planning Regulation Section 1 - Definitions: “wildlife tree” means a tree or group of trees that 

are identified in an operational plan to provide present or future wildlife 

habitat 

18(1) A person must ensure that a forest development plan includes the 

following information for the area under the plan: ... (u) the general 

objectives respecting the target levels of retention for coarse woody debris 

and wildlife trees 

32. A person must ensure that a logging plan contains a map of the area 

under the plan illustrating the topography and ... (b) the approximate 

location of (i) mappable reserves including wildlife trees and wildlife tree 

patches 

39(2) A person must ensure, for the area under the silviculture 

prescription, that the silviculture prescription describes the location of the 

following: ... (d) mappable reserves, including wildlife tree patches and 

riparian reserve zones 

39(3) A person must ensure, for the area under the silvicultural system, 

that the prescription does the following ... (c) describes the silvicultural 

system to be used, including the species and function of any trees left 

standing. ... (m) describes (i) the volume and range of piece sizes of 

coarse woody debris, if any, necessary or required to accommodate any 

objectives for coarse woody debris established in a forest development 

plan and that are applicable to the area under the prescription 

50(2) A stand management prescription must ... (b) contain a map 

illustrating ... (ii) for the area under and adjacent to the prescription, the 

following items: ... (D) the approximate location of mappable reserve 

areas, including wildlife tree patches 

Timber Harvesting Practices 

Regulation 

3(1) A person carrying out harvesting must mark in the field, before 

commencement of harvesting, the location of all wildlife trees or wildlife 

tree patches that are (a) 0.25 hectares or more, unless exempted by the 

district manager, and (b) less that 0.25 hectares, if required by the district 

manager 

(2) A person required to mark a wildlife tree or wildlife tree patch, under 

subsection (1) must ensure that the marking is visible during harvesting 

and is marked in a manner that will remain visible for at least 6 months 

after the completion of harvesting 

28. A person must not carry out a minor salvage operation in any of the 

following areas unless harvesting the area has been approved in a 

silviculture prescription or the person has received in writing from the 

district manager the terms and conditions that apply to the carrying out of 

the minor salvage operation: ... (c) wildlife tree patches; 

Timber Harvesting Practices 

Regulation (Administrative 

Remedies Regulations Schedule)

Harvesting or damaging trees that are required by the silviculture 

prescription to be left standing or undamaged—$5000. Failure to mark in 

the field the location of wildlife trees or wildlife tree patches, before 

commencement of harvesting operations—$5000 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

854 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Table 2—Workers’ Compensation Board Occupational Health and Safety Regulation as 

related to dead trees (these regulations can be viewed at http://www.worksafebc.com/policy/ 

regs/contents.asp). 

Act or Regulation What 

Workers’ Compensation Board Occupational 

Health and Safety Regulation 

26.11(1) If work in a forestry operation will expose a worker to 

a dangerous tree, the tree must be removed. 

(2) Trees that will interfere with rig-up, the movement of lines 

and equipment, or that could be pushed or pulled into the work 

area must be removed. 

(3) Saplings over 6 m (20 ft) tall, in an area where cable 

logging is being done, must be removed before yarding 

commences. 

(4) If it is not practicable to comply with subsection (3), such as 

during partial cutting operations, alternative work methods or 

procedures which minimize the risk to workers may be used, 

and the work must be directed by a supervisor who has, as far 

as practicable, controlled the danger to any worker. 

(5) Any dangerous tree, regardless of height, located within an 

active hand falling or cable logging operation must not interfere 

with safe falling or yarding practices, and if it does interfere, it 

must be removed. 

(6) A dangerous tree in a forestry operation may be left 

standing during operations other than construction or harvesting 

if 

(a) no significant ground vibrations are likely to be produced, 

(b) no work will be done within reach of the tree when wind 

speed exceeds 20 km/h (12mph), and 

(c) tree assessor who has completed a training program 

acceptable to the board determines that the tree will not be 

dangerous to workers during the planned activity 

(7) If tree planting is to be done in an area that has more than 

500 dangerous trees per hectare, the board may approve a 

request to work without removing all the dangerous trees if, 

before work commences, 

(a) a representative sample of the dangerous trees is assessed by 

a tree assessor who has completed a training program 

acceptable to the board, 

(b) any findings of the assessment as to the removal of 

dangerous trees or other trees are implemented, and 

(c) no silviculture is done within reach of dangerous trees when 

wind speed exceeds 20km/h (12 mph). 

The importance of CWD is also clearly recognized within the Forest Practices 

Code regulations but, unlike wildlife trees, detailed provincial CWD management 

guidelines are lacking. References to CWD management within the Biodiversity 

Guidebook and the Managing Identified Wildlife Guidebook are less specific than 

references to wildlife trees. Several interim CWD guidelines have been drafted, but 

consensus has not been reached (see http://www.for.gov.bc.ca/research/deadwood/ 

Dtgui.htm#BC for the current short-term strategy). Concerns not only also exist 

where specific CWD volume retention targets may conflict with present timber 

utilization standards as expressed in Ministry of Forests policy, but volume retention 

targets also conflict with wood below the standards that the forest licensees consider 

economical to harvest (Ministry of Forests Policy 8.1—Timber utilization—coastal 

and interior available at http://for.gov.bc.ca/tasb/manuals/policy/resmngmt/rm8-

1.htm). 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 855 

Current Management 

Wildlife tree management includes both the retention of suitable trees at the time 

of harvest and during silviculture activities, and provision for recruitment of suitable 

replacement wildlife trees over the harvest rotation period. Operationally, there are 

three types of wildlife tree management strategies. These are wildlife tree patches 

(WTPs), individual live tree retention, and artificially created wildlife trees. 

Potentially, all three approaches can be applied in a single harvest area, although 

WTPs are generally the most operationally feasible (i.e., easier to accommodate 

various block layouts, topographic considerations, and harvesting methods) and the 

safest method for forest workers to retain wildlife trees. If selected carefully, WTPs 

can incorporate all or some of the habitat attributes commonly associated with the 

conservation of biodiversity at the stand level. These attributes include horizontal and 

vertical stand structure, wildlife trees, CWD, intact forest floor, and various special 

habitats, such as riparian areas, wetlands, gullies and rock outcrops. However, given 

our understanding of the ecological values of wildlife trees, it is prudent to also retain 

dispersed single trees within the landscape. 

In 1995 the Biodiversity Guidebook brought forward a tabular approach to 

determining wildlife tree retention requirements for a particular area. Two variables 

must be known to allow determination of wildlife tree retention: 

• Percent of the area available for harvest (i.e., percent of the total area deemed 

to be operable). 

• Percent of the operable area already harvested without wildlife tree retention. 

Knowing these numbers, an area retention objective ranging from 1 percent 

(where most of the area is inoperable and very little harvesting without wildlife tree 

retention has occurred) to 15 percent (where the area is highly operable and a large 

portion has been harvested without wildlife tree retention) is determined. These 

retention objectives can be applied as area-based WTPs or as a basal area 

equivalency for individual tree retention. 

To date, Ministry of Forests district managers have generally provided policy as 

per the retention objectives and communicated them to licensees for incorporation 

into their silviculture prescriptions (an operational plan required prior to harvesting). 

With the recent issuance of the Landscape Unit Planning Guide, these will now be 

incorporated as landscape unit objectives (Ministry of Forests and Ministry of 

Environment, Lands and Parks 1999). 

A silviculture prescription map must show the location of the WTPs that make 

up the retention objective and state the basal area equivalence for single tree 

management. A significant proportion of this retention will come from inoperable 

areas, such as riparian reserves. In addition, placement of wildlife tree patches should 

consider: 

• Worker safety; only wildlife trees which are assessed as safe may be left 

outside of a patch within the work area. 

• Location of good wildlife tree attributes, e.g., center a patch around a wellused wildlife tree or group of wildlife trees. 

• Areas of tree species that are potentially valuable as wildlife trees and 

relatively uncommon. 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

856 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

• Stability of chosen patch, e.g., it may be advisable to locate patches adjacent 

to standing timber of a riparian reserve if there is concern regarding 

windthrow. 

The decision to retain individual trees as wildlife trees in a harvest block will 

depend on the characteristics and condition of those trees (e.g., species, size, 

evidence of wildlife use, branching structure, decay, wind firmness, and safety 

considerations), and other management objectives (e.g., type of silvicultural system, 

harvesting method, and rotation length). In most cases, individual trees must be 

retained through the rotation in order to receive credit as wildlife trees in the 

management prescription. However, except for initial layout and considerations for 

wind firmness, no long-term management prescriptions for wildlife tree patches have 

usually been expressed. 

In BC, hazard/danger tree assessment procedures developed by the Wildlife 

Tree Committee of BC are in place, along with appropriate training, concerning the 

management and retention of wildlife trees (Manning 2002). These guidelines are 

intended to provide information and technical procedures for assessing and safely 

retaining trees (some of which are potentially dangerous) in all types of forestry 

operations. 

In some circumstances, trees are artificially modified to create or enhance 

wildlife tree habitat values. Methods used in BC include tree-topping, fungal 

inoculation, girdling, “planting snags” with an excavator, or cutting stems at 3 to 6 

metres in height (“stubbing”) with a mechanical harvester (Deal 1995, Harris 1995). 

The practice of modifying trees is usually only undertaken to remove specific safety 

hazards, or to augment other methods of habitat retention. 

CWD management is less advanced than wildlife tree management, particularly 

due to the lack of CWD management guidelines. However, CWD objectives must be 

defined in forest development plans that guide individual silviculture prescriptions. 

CWD objectives must be balanced with other potentially competing stand 

management objectives such as fuel management. 

CWD objectives defined in forest development plans range from general 

statements to more specific CWD volume retention targets. CWD volume targets are 

usually based on a volume that can be easily achieved within standard operational 

practice or a minimum of the range found in unmanaged primary forests (Stevens 

1997). At present, forest companies are encouraged to leave behind as much CWD as 

possible provided it does not exceed the minimum utilization standards or interfere 

with other stand management objectives (i.e., forest health). This may be perceived 

as the status quo and often leads to the development of vague CWD management 

objectives, although it does not necessarily translate into low CWD retention. 

In the case of general CWD management objectives—such as “within the 

requirements of normal utilization standards the licensee will try to maintain current 

levels of CWD on each cutblock providing post-treatment objectives, forest health, 

and fire hazard are not compromised”—the result on the ground depends greatly on 

the type of stand harvested, the pulpwood market, the harvesting and site preparation 

techniques, and the knowledge of the operators. For example, the whole-tree harvest 

of a 60-year old lodgepole pine (Pinus contorta var. latifolia) stand that has a history 

of underburn fires and, similarly, the harvest of coastal second-growth stands which 

were subjected to shake salvage will often result in very low post-harvest levels of 

CWD. On the other hand, clear-cut harvesting of a high elevation subalpine fir (Abies 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 857 

lasiocarpa) stand with many standing dead trees will generally yield high levels of 

CWD. 

Communication between on-the-ground operators, foresters, and ecologists is 

important to minimize the adverse impact on the CWD resource and to maximize 

timber use. However, such communication varies within BC. Through 

communication, the experience of the operators plays an important role in the 

retention of CWD. An experienced on-the-ground operator may be able to leave 

uneconomic wood at the stump rather than hauling it to the landing by identifying 

only economic grade logs that should be yarded to the roadside, bucking out 

unmerchantable sections on the site, and retaining full-length intact uneconomic logs 

(Arsenault 2002). 

Regulations and guidelines not only direct on-the-ground decisions but are 

considered in higher level forest management decisions, such as the determination of 

the allowable annual cut (AAC). In British Columbia, the AAC is determined by the 

Chief Forester of BC every 5 years for each of the 70 forest management units 

administered by the Ministry of Forests. To assist the decision of the Chief Forester 

that is based on social, economic, and ecological considerations, a timber supply 

review is conducted. The timber supply review uses simulation models in which the 

timber flow (merchantable volume that excludes most endemic dead wood) of the 

unit is projected. The models use current forest cover inventory and constraint 

information that reflect existing management practices, such as cutblock adjacency 

and ungulate winter range requirements, to model current and future timber flows 

(although the AAC decision is only for the first 5-year period). 

In the timber supply review, wildlife tree patch requirements are commonly 

modeled by reserving a percentage of forest within a biogeoclimatic subzone in a 

landscape unit. CWD has not been considered directly as operational practices do not 

directly influence the merchantable volumes attributable to the AAC. Current 

practice has only used uneconomic CWD below utilization levels, though recent 

relaxation of utilization accounting could enable the retention of small volumes of 

some lower grades of wood. Non-recoverable losses, such as those caused by pest or 

fire, are excluded from the timber flow projections. 

Management Support 

Forest management planning in BC is supported by a variety of inventories, 

surveys, and projection tools. In the 1990s, under the auspices of the multi-agency 

Resources Inventory Committee, BC initiated substantial standardization and 

updating of resource inventories. The new provincial Vegetation Resources 

Inventory, that is to replace an existing provincial forest cover inventory, includes 

provision for both wildlife tree and CWD sampling (Ministry of Forests 1999). 

However, the majority of ground-based samples are expected to have a timber 

emphasis and not include items such as CWD. Procedures for describing terrestrial 

ecosystems include wildlife tree and CWD sampling (Ministry of Forests and 

Ministry of Environment, Lands and Parks 1998). Pre-harvest timber cruises provide 

counts of standing dead trees but typically only those with >50 percent sound wood. 

Similarly, post-harvest residue and waste surveys only sample merchantable wood 

volumes. Standards for growth and yield permanent sample plots were modified in 

1999 to include standing dead tree measures. This information will be used to 

enhance existing standing and down dead tree models incorporated in growth and 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

858 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

yield models used in forest management planning (Stone and others 2002). Although 

there is an expectation of improved dead tree information, these new sampling 

procedures need to be evaluated to ensure their usefulness. 

Research on dead trees and their ecological values is conducted by the many 

research organizations in BC: provincial and Federal governments, academia, 

industry, and consultants. Little research on CWD was conducted in BC prior to the 

1990s (Candy and Swan 1995, Caza 1993), although as early as 1929 MOF 

researchers showed some interest in CWD dynamics (Stone and others 1998). The 

past decade has seen increased research on the roles and dynamics of dead trees in 

BC and limited investigation of the effects of current harvesting practices on dead 

wood volumes and attributes. Forest Renewal BC, a Crown corporation established in 

1994 that derives monies from stumpage revenues, has funded a variety of recent 

research on dead wood, including experimental manipulation of CWD, snag 

dynamics, CWD dynamics, the ecology of dead wood dependent organisms, and 

forest productivity relationships (Feller 1977, Huggard 1999). However, we still lack 

knowledge of the specifics of many of the ecological roles and dynamics of dead 

trees in conjunction with forest stand development and management (Lofroth 1998). 

Education about dead trees has occurred at many levels in BC. Legislation and 

guidelines have provided many incentives to learn about the value of dead trees. A 

variety of informational brochures and publications have been made available 

(Kremsater and Nicholson 1995; Machmer and Steeger 1995; Ministry of 

Environment, Lands and Parks, and Ministry of Forests 1999; Stevens 1997). 

Hundreds of forest workers and professionals have received formal training for 

wildlife/danger tree assessment and riparian management (Forestry Continuing 

Studies Network of British Columbia: http://www.fcsn.bc.ca). Wildlife trees have 

been included in public school education programs such as Project WILD (Post and 

others 1994). Students themselves have created informational software with a 

wildlife tree and CWD component (Neal and Taylor 1996). 

Discussion 

The abundance and distribution of dead wood is highly variable and depends 

largely on disturbance history, stand age, tree species composition, ecosystem type, 

and decomposition rates. Standing dead trees and CWD will vary in size and stages 

of decay, even within the same forest. Maintaining the natural variability of dead 

wood at both the stand and landscape levels needs to be an objective for sustainable 

forest management. However, there are many real and perceived constraints that 

make this challenging. Some of the constraints limiting the retention of dead wood in 

BC’s forests are: worker safety (particularly with standing dead trees); logging costs; 

utilization policy; resistance to change; harvesting techniques; pulpwood markets; 

salvage initiatives; silvicultural objectives; fuel management; and forest health. 

Another challenge is defining the natural variability of dead wood, considering the 

dynamic nature of ecosystems over time and space. 

BC’s forest management is still mainly concerned with the harvesting of older 

primary (previously unlogged) forests. These primary forests provide opportunities 

for management of the dead tree resource that may not be present in second-growth 

forests established with little consideration for the ecological values of dead trees. Of 

special concern is the recruitment of large standing dead trees and fresh CWD in 

second-growth stands. In some instances, most CWD remaining on such sites 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 859 

originated from the first harvest of the primary forest and is therefore large, but 

usually well-decayed. Where biodiversity is a management objective in secondgrowth stands, specific strategies, such as direct felling and retention of live stems, 

will need to be developed to provide for CWD and wildlife trees of all species, size, 

and decay classes. 

Policy has separated the management of wildlife trees and CWD in BC. To a 

large extent this reflects a lack of specific CWD targets in terms of volume and 

dimensions. As CWD targets or clearer ecological objectives are developed, it will be 

important to evaluate how wildlife tree reserves will address long-term CWD input— 

a current assumption of forest managers. Three main challenges face us. The first is 

implementation and evaluation of no-cost opportunities for retaining CWD (e.g., 

minimizing piles). The second is collection of dead wood attributes on both natural 

and managed stands to provide the necessary background to establish defensible 

CWD targets that are fully integrated with wildlife tree reserve goals. The third is 

integration by resource managers of CWD ecological values and management with 

the traditional view of CWD as salvage, slash, fuel, and waste (Arsenault 2002). 

The management and recognition of the dead tree resource in BC has improved 

since the time when dead trees were left standing only if we could cover their tops 

with dirt. However, the balancing of dead tree ecological values and timber supply is 

a challenge still facing BC's forest managers.

Acknowledgments 

We thank Mike Fenger and David Stevenson for reviewing an earlier draft of 

this manuscript and Doug Steventon for insights. Financial support for attendance by 

Todd Manning was provided by the Wildlife Tree Committee of British Columbia. 

Financial support for attendance by Jeff Stone and André Arsenault at the conference 

and many of the projects indicated within this paper was provided by Forest Renewal 

BC, a crown corporation committed to renewing the forest sector in BC. 

References 

Arsenault, André. 2002. Managing dead wood in British Columbia’s forests: a cultural 

shift for professional foresters? In: Laudenslayer, William F., Jr.; Shea, Patrick J.; 

Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of a symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume].

Backhouse, Frances; Lousier, J. Daniel. 1991. Silviculture systems research: wildlife tree 

problem analysis. Unpublished report prepared for Ministry of Forests, Ministry of 

Environment, and B.C. Wildlife Tree Committee, Victoria, BC; 205 p. 

Candy, Alison; Swan, Bill. 1995 A bibliography of selected literature on wildlife trees 

with annotations and abstracts. Wildlife Working Report No. 66. Victoria, BC: 

Habitat Protection Branch and Wildlife Branch, Ministry of Environment, Lands and 

Parks; 84 p. 

Caza, Caroline L. 1993. Woody debris in the forests of British Columbia. Land 

Management Handbook No. 78. Victoria, BC: Research Branch, Ministry of Forests; 99 

p. 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

860 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Deal, John A. 1995 A “planting” program gone to the birds. In: Bradford, Peter; Manning 

Todd; I’Anson, Bill. Proceedings of wildlife tree/stand-level biodiversity workshop, 

October 1995; Victoria, BC. Ministry of Forests, Ministry of Environment; 61-65. 

Feller, Michael. 1997. Coarse woody debris in forests: an overview of the coarse woody 

debris study and the Sicamous Creek Study Area. In: Hollstedt, Chris; Vyse, Alan, 

editors. Sicamous Creek silvicultural systems project: workshop proceedings; 1996 

April 24-25; Kamloops, BC. Working Paper 24/1997. Victoria, BC: Research Branch, 

Ministry of Forests; 134-143. 

Fenger, Mike. 1995. Implementing biodiversity conservation through the British 

Columbia forest practices code. In: Bradford, Peter; Manning Todd; I’Anson, Bill. 

Proceedings of wildlife tree/stand-level biodiversity workshop, October 1995; Victoria, 

BC. Ministry of Forests, Ministry of Environment; 1. 

Harris, Brian. 1995. The use by wild birds of three-metre stubs as artificial wildlife 

habitat. In: Bradford, Peter; Manning Todd; I’Anson, Bill. Proceedings of wildlife 

tree/stand-level biodiversity workshop, October 1995; Victoria, BC. Ministry of Forests, 

Ministry of Environment; 55-60. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. W.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K. Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in temperate 

ecosystems. Advances in Ecological Research. 15: 133-302. 

Huggard, David J. 1999. Static life-table analysis of fall rates of subalpine fir snags.

Ecological Applications 9: 1009-1016. 

Kremsater, L.; Nicholson, A. 1995. Rotten luck: the role of downed wood in ecosystems. 

Brochure produced by Ministry of Forests; Environment Canada, The Centre for 

Applied Conservation Biology, University of British Columbia; Vancouver, BC; 6 p. 

Lofroth, Eric. 1998. The deadwood cycle. In: Voller, J.; Harrison, S., eds. Conservation 

biology principles for forested landscapes. Vancouver, BC: UBC Press; 185-214. 

MacBean, A. P. 1946. The Ladysmith experiment in salvaging pulpwood from logging 

waste, 1943-1944. The Empire Forestry Review 25(1): 15-24. 

Machmer, Marlene M.; Steeger, Christoph. 1995. The ecological role of wildlife tree users 

in forest ecosystems. Land Management Handbook 35. Victoria, BC: Ministry of 

Forests; 54 p. 

Manning, E. Todd. 1995. Wildlife tree management in British Columbia: current wildlife 

tree committee initiatives. In: Bradford, Peter; Manning Todd; I’Anson, Bill. 

Proceedings of wildlife tree/stand-level biodiversity workshop, October 1995; Victoria, 

BC. Ministry of Forests, Ministry of Environment; 3. 

Manning, E. Todd. 2002. British Columbia’s dangerous tree assessment process—a 

summary paper. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Bradley 

E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical coordinators. Proceedings of a 

symposium on the ecology and management of dead wood in western forests. 1999 

November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; [this 

volume]. 

Ministry of Environment; Lands and Parks; Ministry of Forests. 1999. Wildlife trees and 

dangerous trees: identification and management. Brochure produced by the Resource 

Stewardship Branch, Ministry of Environment, Lands and Parks and Forest Practices 

Branch, Ministry of Forests, Victoria, BC; 8 p. 

Ministry of Forests. 1984. Forest and range resource analysis, 1984. Victoria, BC: Strategic 

Studies Branch, Ministry of Forests. 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 861 

Ministry of Forests. 1998. Ministry of Forests annual report 1996/97. Victoria, BC: 

Ministry of Forests; 94 p. 

Ministry of Forests. 1999. Ground sampling procedures, version 4.0. Victoria BC: 

Resources Inventory Branch, Ministry of Forests and Resources Inventory Committee; 

Unpaged. 

Ministry of Forests; BC Environment. 1995a. Biodiversity guidebook—forest practices 

code of British Columbia. Victoria, BC: Ministry of Forests and BC Environment; 99 

p. 

Ministry of Forests; BC Environment. 1995b. Riparian management area guidebook—

forest practices code of British Columbia. Victoria, BC: Ministry of Forests and BC 

Environment; 68 p. 

Ministry of Forests; BC Environment. 1999. Managing identified wildlife: procedures and 

measures, volume 1. Victoria, BC: Ministry of Forests and BC Environment; 180 p. 

Ministry of Forests; Ministry of Environment, Lands and Parks. 1998. Field manual for 

describing terrestrial ecosystems. Victoria, BC: Resources Inventory Branch, Ministry 

of Environment, Lands and Parks and Research Branch, Ministry of Forests; Unpaged. 

Ministry of Forests; Ministry of Environment, Lands and Parks. 1999. Landscape unit 

planning guide. Victoria, BC: Ministry of Forests and Ministry of Environment, Lands 

and Parks; 101 p. 

Muckle, Robert J. 1998. The first nations of British Columbia. Vancouver, BC: UBC Press; 

146 p. 

Neal, Mary-Anne; Taylor, Steve. 1996. Tree tales interactive forest science computer 

program: teacher's guide & CD. Victoria, BC: Ministry of Forests; 31 p. 

Post, Kerrie; MacDonald, Andrew; MacDonald, Carolyn. 1994. Wildlife trees in British 

Columbia: discovering animal inns. Victoria, BC: Project WILD, Ministry of 

Environment; 56 p. 

Revised Statutes of British Columbia. 1979. Ministry of Forests Act. RS Chap. 272, 28 Eliz. 

2. Victoria, BC: Queen’s Printer; 4 p. 

Statutes of British Columbia. 1946. Forest Act Amendment Act, 1946. Chap. 23, Sec. 

113A(2). Victoria, BC: Queen’s Printer. 

Stevens, Victoria. 1997. Ecological role of coarse woody debris: an overview of the 

ecological importance of CWD in B.C. forests. Working Paper No. 30. Victoria, BC: 

Research Branch, Ministry of Forests; 26 p. 

Stevenson, David. 1999. Forest Ecosystem Specialist, Ministry of Environment, Lands, and 

Parks, Prince George, BC. [E-mail to Jeff Stone]. November 19, 1999. 

Stone, Jeff; Parminter, John; Braz, Joe. 2002. Standing dead tree dynamics extracted from 

growth and yield permanent sample plots in British Columbia. Laudenslayer, 

William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, 

Thomas E., technical coordinators. Proceedings of a symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; [this volume]. 

Stone, Jeff N.; MacKinnon, Andy; Parminter, John; Lertzman, Ken. 1998. Coarse woody 

debris decomposition documented over 65 years on southern Vancouver Island. 

Canadian Journal of Forest Research. 28: 788-793. 

Turner, Nancy J. 1998. Plant technology of first peoples in British Columbia. Vancouver, 

BC: UBC Press; 256 p. 
Dead Tree Management in British Columbia—Stone, Parminter, Arsenault, Manning, Densmore, 

Davis, and MacKinnon 

862 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Workers’ Compensation Board of British Columbia. 1998. Occupational health and safety 

regulations. BC Regulation 296/97, Book 3. Vancouver, BC.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 863 

British Columbia’s Dangerous Tree 

Assessment Process1

Todd Manning,2 Peter Bradford,3 Cary White,4 David Rowe,5 Nancy 

Densmore,6 and Stewart Guy7

Abstract 

New dangerous tree assessment guidelines have recently been developed by the Wildlife Tree 

Committee of British Columbia. They are intended to provide information and technical 

procedures for assessing and safely retaining trees in various situations, ranging from parks 

and urban/municipal settings to industrial forestry activities and wildland fire fighting. The 

decision to retain a wildlife tree must include worker and/or public safety, the type of activity 

occurring around the tree, site factors and tree condition, and wildlife habitat values. These 

guidelines will be of interest to persons involved in any activity where the management of 

trees for wildlife habitat or other purposes is desirable. 

Introduction 

In British Columbia, the historical definition of a standing dead tree or “snag” 

has been: “Any standing dead or dying tree over 3 meters in height.” New Workers’ 

Compensation Board Occupational Health and Safety Regulations (WCB 1998) were 

adopted into law effective April 15, 1998. With these new regulations, the term snag 

was replaced with “dangerous tree.” According to section 26.1 of these regulations, 

a dangerous tree is now defined as:“Any tree that is hazardous to workers because of 

location or lean, physical damage, overhead hazards, deterioration of the limbs, stem 

or root system, or a combination of these.”

Recently, new dangerous tree assessment guidelines and technical criteria were 

developed by the Wildlife Tree Committee of British Columbia in conjunction with 

the changes to the Workers’ Compensation Board regulations. The guidelines were 

first pilot tested throughout British Columbia with a range of individuals experienced 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Coordinator of the Wildlife Tree Committee of British Columbia, and Habitat Forester for Manning, 

Cooper & Associates, 5148 William Head Road, Victoria, B.C., Canada, V9C 4H5 (e-mail: 

tmanning@islandnet.com) 

3

 Forest Practices Forester, British Columbia Forest Service, Forest Practices Branch, 1450 Government 

St., Victoria, B.C., Canada, V8W 3E7 (e-mail: peter.Bradford@gems1.gov.bc.ca) 4

 Occupational Safety Officer, Workers’ Compensation Board of British Columbia, Prevention Division, 

4980 Wills Rd., Nanaimo, B.C., Canada, V9T 6C6 (e-mail: cwhite@wcb.bc.ca) 5

 Program Manager (Forestry), Workers’ Compensation Board of British Columbia, Prevention 

Division, 1066 Vancouver St., Prince George, B.C., Canada, V2L 5M4 (e-mail: drowe@wcb.bc.ca) 6

 Emerging Issues Forester, British Columbia Forest Service, Forest Practices Branch, 1450 Government 

St., Victoria, B.C., Canada, V8W 3E7 (e-mail: nancy.densmore@ gems2.gov.bc.ca) 7

 Identified Wildlife Biologist, British Columbia Ministry of Water, Land and Air Protection, 

Biodiversity Branch, P.O. Box 9338, Stn. Prov. Govt., Victoria, B.C., Canada, V8W 9M1 (e-mail: 

stewart.guy@gems9.gov.bc.ca) 
Dangerous Tree Assessment Process—Manning, Bradford, White, Rowe, Densmore, and Guy 

864 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

in occupational health and safety, logging, forest pathology, and forest and wildlife 

ecology. This information was subsequently incorporated into the provincially 

sponsored “Wildlife/Danger Tree Assessor’s Course” (see WTC 2001), which 

provides technical information and practical field skills to persons who wish to assess 

trees for hazards and wildlife habitat value. 

Determining Tree Danger 

The determination of a tree’s failure potential (i.e., the likelihood that all or a 

portion of a tree will break), and ultimately whether or not it is dangerous, involves a 

four step process: 

 Step 1―Determine the level of ground or tree disturbance around the tree 

 Step 2―Conduct a site assessment overview 

 Step 3―Conduct a visual tree inspection 

 Step 4―Make the appropriate safety decision. 

Step 1―Level of Disturbance 

Various activities are associated with differing levels of ground or tree 

disturbance. Activities rated as low disturbance, such as surveys, tree pruning, or use 

of back country hiking trails, involve negligible ground or tree disturbance, and as a 

result expose people to very little danger. However, as the level of disturbance or 

exposure increases, such as with timber harvesting, heavy machinery use, or in highuse park facilities, the potential danger and risk of injury also increases. 

Consequently, potentially dangerous trees considered for retention in these situations 

must be carefully assessed for any hazards in order to determine tree failure potential 

and reach an appropriate safety decision. 

Step 2―Site Assessment Overview 

The determination of a tree’s failure potential begins with a site assessment 

overview, which involves assessing forest health factors (e.g., root rots, insect 

damage), stand condition (e.g., age, tree species, presence of heart rots), soil profile 

and condition, and other site variables (e.g., windthrow hazard, slope, fire damage). 

The site overview provides a context for subsequent assessment of individual trees 

(i.e., it identifies overall site problems, such as damaged stands or root rot, which can 

influence tree failure). 

Step 3―Visual Tree Inspection 

The third step in the dangerous tree assessment process is a visual tree 

inspection, which results in a failure potential rating (low, medium, or high) for a 

given tree defect. Failure potential is rated according to tree species groupings, and 

considers the following factors: hazardous tops, large dead limbs, witches’ broom, 

split trunk, stem damage (scarring, butt rot), thick sloughing bark, fungal fruiting 

bodies (conks, mushrooms), butt and stem cankers, tree lean, and root condition. 
Dangerous Tree Assessment Process—Manning, Bradford, White, Rowe, Densmore, and Guy 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 865 

Four native tree species groupings have been identified: Douglas-fir-larch-pinesspruces; western redcedar and yellow cedar; hemlocks and true firs; and deciduous 

trees (“soft” hardwoods such as aspen, cottonwood, paper birch, maple, alder). 

Failure potential ratings for a particular defect, such as stem damage, can be 

different based on the tree species grouping (e.g., cedars have a larger permissible 

stem scarring threshold than the other tree species groupings). 

With adequate experience and training, the visual tree inspection can be an 

efficient process that usually requires only a few minutes per tree. If the visual 

inspection is inconclusive as to the condition of the tree (e.g., root rot is suspected 

based on the site assessment), a detailed tree assessment can be conducted in order to 

gather more information on the condition of the bole (stemwood shell thickness) and 

roots. This involves exploratory tests in the lower bole (e.g., increment boring, 

drilling, or sounding) and excavating and probing around the root collar. 

Step 4―Making a Safety Decision 

Once a failure potential rating has been determined from the visual tree 

inspection, a tree can be rated as either safe (S) or dangerous (D), depending on the 

level of disturbance or type of activity around the tree. This procedure is illustrated in 

table 1. A classification for coniferous trees is shown in figure 1.

Table 1—Overall Tree Danger Rating. 

Level of 

disturbance 

Detection failure potential 

Low Medium High 

1 (Low) S1 S1 S1 

2 (Medium) S S D 

3 (High) S S (for veteran and 

 dominant conifers) 2

D (for all other trees) 

D 

4 (Very High) S (for class 1 trees) 

S (for class 2 cedars with 

 low failure potential) 

S (class 2 and 3 trees with 

 no defects) 3

D (all other trees) 

D D 

1 For Low level (1) disturbance activities, any trees that have one or more of the following significant 

tree hazards will become D (dangerous): 

• Insecurely lodged trees, or hung-up limbs or tops 

• Highly decadent or unstable trees (e.g., >50 percent cross-section area stem damage, or >50 

percent lateral roots damaged/unsound) 

• Trees with recent high lean (>15 percent toward work area or target) and damaged root 

system/anchoring soil layer. 2 Employ safe falling and yarding practices around trees assessed as SAFE with Medium failure 

potential; do not hit or disturb the trees, and fall and yard or skid away. 

3 Trees with no defects will not have any defect indicators other than small dead limbs or minor stem 

scrapes that are not associated with decay or loss of structural strength. Class 2 trees with no defects will 

usually be wind- or snow-snapped green trees. Class 3 trees with no defects will usually be insect kill, 

climate kill, or a recent light intensity fire where no structural tree damage occurred. 
Dangerous Tree Assessment Process—Manning, Bradford, White, Rowe, Densmore, and Guy 

866 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 1—British Columbia’s Tree Classification System (adapted from Maser and 

others 1979). 

If a tree is determined to be dangerous for a particular type of work activity, then 

appropriate safety procedures must be implemented. These include removing the tree 

or any hazardous parts (e.g., top, limbs) or establishing an appropriately sized safe 

buffer area (called a no-work or hazard zone) around the tree to eliminate exposure to 

the hazard. However, if a tree is assessed as safe for a given type of activity, work 

can proceed up to the tree regardless of whether it is dead or live. 

Inherent to the implementation of any safety decision is an understanding of the 

concept of “risk.” RISK = HAZARD x EXPOSURE. For example, if there is exposure 

of workers to a dangerous tree or a “target” exists (e.g., buildings or equipment 

within striking distance of a dangerous tree), then an inherent risk of injury or 

property damage also exists. On the other hand, if there is no hazard (i.e., the tree is 

not dangerous) or there is no target exposure, then there is no or very minimal risk. 

Applications 

Wildlife tree patches and other stand-level reserves (e.g., riparian management 

areas) are generally the safest and most operationally efficient means of retaining 

wildlife trees and other biodiversity attributes at the stand level in forestry operations. 

However, the new dangerous tree assessment process now facilitates retention of 

SAFE standing dead and SAFE live defective trees in forest harvesting operations 

outside of patches and reserves. This is particularly relevant to partial-cutting 

silvicultural systems, where the retention of individual standing dead and live 

defective trees is desirable in order to provide additional stand structure, wildlife 

habitat, and biodiversity values over time. 
Dangerous Tree Assessment Process—Manning, Bradford, White, Rowe, Densmore, and Guy 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 867 

The dangerous tree assessment process can be applied to a variety of situations, 

including: 

• Forest harvesting 

• Silviculture operations such as tree planting and stand tending 

• All silvicultural systems, but especially useful for partial-cutting systems 

such as variable retention, group selection, shelterwood, and single tree 

selection 

• Wildland fire fighting 

• Road sides 

• Utility corridors 

• Parks and recreation sites (e.g., trails, campgrounds and other developed 

facilities) 

• Recreational wooded areas such as golf courses and ski hills. 

With these “dangerous tree assessment tools” now available to forest managers, 

there can be more flexibility in the type, condition, density and location of retained 

trees in harvest blocks and other applications where the retention of trees is a 

management objective. 

Dangerous Tree Assessment Research and Training 

The description and quantification of tree conditions and defects, and the 

correlation to the likelihood of tree failure, has received relatively little research. 

There have been a few pioneering studies in this area, however, such as Wagener’s 

assessment of tree hazards in California recreation sites (Wagener 1963). The 

findings of Wagener’s research continue to be broadly applied in North American 

hazard tree and arboriculture management. Some researchers in the southeastern 

United States (Smiley and Fraedrich 1992) and in southern California (Matheny and 

Clark 1991) are relatively active in this field, as are Mattheck and Breloer (1997) in 

Germany. 

In Canada, there is a general lack of research in the field of hazard tree 

pathology and applied management. However, in British Columbia, a research 

project has recently been completed (Manning 2001). This project collected 

quantitative data on visible external tree defects and corresponding internal tree 

conditions. Correlations were tested between the occurrence of external tree defects 

and the incidence of internal decay and the resultant loss of stem shell thickness. 

Highly significant differences (p<0.001) were found between the actual/expected 

stem shell thickness ratios for the three tree defect failure potential ratings (low, 

medium, high). This suggests a strong positive relationship between the actual shell 

thickness measured at the corresponding defect positions and the assigned failure 

potential rating for that defect. For example, where a high failure potential rating was 

recorded for a defect, such as a stem scar, the corresponding shell thickness at that 

position was less than the theoretical required shell thickness at the same position. 

Based on these correlations and related interpretations, the tree failure potential 
Dangerous Tree Assessment Process—Manning, Bradford, White, Rowe, Densmore, and Guy 

868 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

ratings and associated safety procedures used in the “Wildlife/Danger Tree 

Assessor’s Course” (WDTAC) appear to be justifiable and reliable. 

The results of this research will ultimately be used to improve dangerous tree 

assessment procedures and related safety training methods in the WDTAC. Three 

course modules currently exist for the WDTAC: forest harvesting and silviculture; 

wildland fire fighting; and parks and recreation sites. 

The WDTAC is jointly sponsored by the British Columbia Ministry of Forests, 

the Workers’ Compensation Board of B.C., and the B.C. Ministry of Water, Land and 

Air Protection. Specific details (e.g., level of disturbance/work activity ratings) and 

technical procedures associated with the four-step dangerous tree assessment process, 

as well as additional information about WDTAC modules, can be found on the 

Wildlife Tree Committee of British Columbia web site: www.for.gov.bc.ca/hfp/wlt/. 

Acknowledgments 

The authors would like to thank the members of the Wildlife Tree Committee of 

British Columbia and the WDTAC course instructors for their support in the 

development of the new dangerous tree assessment process. We would also like to 

thank Dr. Eric Allen (Canadian Forest Service), Dr. Duncan Morrison (Canadian 

Forest Service), and Alan Lundgren (TimberWest Forest Ltd.) for their help with tree 

pathology and development of defect indicators. 

References 

Manning, E. T. 2001. British Columbia’s dangerous tree assessment process―

Implications for worker safety (destructive sampling field project). Final report 

prep. for IWA Canada-Forest Industry SAFER Council, Weyerhaeuser B.C. Coastal 

Group, and BC Ministry of Forests. June 2001; 15 p. 

Maser, C.; Anderson, R. G.; Cromack, K.; Williams, J. T.; Martin, R. E. 1979. Dead and 

down woody material. In: Thomas, J. W., tech. ed. Wildlife habitats in managed 

forests–the Blue Mountains of Oregon and Washington. Agric. Handb. 553. 

Washington, DC: Forest Service, U.S. Department of Agriculture; 78-95. 

Matheny, N.; Clark, J. 1991. Evaluation of hazard trees in urban areas. Urbana, IL: 

International Society Arboriculture; 72 p. 

Mattheck, C.; Breloer, H. 1997. The body language of trees—a handbook for failure 

analysis.London, UK: The Stationery Office; 239 p. 

Smiley, E. T.; Fraedrich, B. R. 1992. Determining strength loss from decay. Journal of 

Arboriculture 18(4): 201-204. 

Wagener, W. 1963. Judging hazard from native trees in California recreational areas: a 

guide for professional foresters. Res. Paper PSW-P1. Berkeley, CA: Forest Service, 

U.S. Department of Agriculture; 29 p. 

Wildlife Tree Committee of British Columbia (WTC). 2001. Wildlife/danger tree assessor’s 

course workbook―forest harvesting and silviculture module. Victoria BC: British 

Columbia Ministry of Forests, Workers’ Compensation Board, Minerals Water, Land 

and Air Protection, June 2001; 139 p. 

Workers’ Compensation Board of British Columbia (WCB). 1998. Occupational Health & 

Safety regulation, industry/activity specific requirements, parts 20-33. Richmond, 

BC: Workers’ Compensation Board of British Columbia, April 1998; 151 p. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 869 

Managing Coarse Woody Debris in British 

Columbia’s Forests: A Cultural Shift for 

Professional Foresters?1 

André Arsenault2

Abstract 

Coarse woody debris (CWD) is recognized as an important component of British Columbia’s 

forest ecosystems linked to biodiversity and ecosystem processes. CWD represents high 

centers of biological interaction and energy exchange, symbolizing in many ways the 

complexity of forest ecosystems. Our research on lichens and bryophytes demonstrates that 

many species are either partially or entirely dependent on CWD. Long-term management of 

this resource is vital to maintain ecosystem integrity. Previous attempts to recommend 

province-wide CWD management practices were not successful because of potential 

increased logging costs and conflicts between utilization standards and recommended CWD 

volume targets. I demonstrate that small changes to existing forest practices will go a long 

way in minimizing impacts on the CWD resource without affecting logging costs or access to 

timber. I propose that a cultural shift in how foresters perceive CWD is a necessary ingredient 

to improve present practices. This paper promotes such a cultural shift by explaining key 

CWD management principles and by providing some operational examples. 

 

Introduction 

The value of retaining decaying wood in forest ecosystems may be counterintuitive to many foresters trained in traditional silviculture, which has focused on 

converting old “decadent” forests into “productive” plantations. The view that 

decadence (decaying wood) in forests is either undesirable or not necessary has had a 

profound influence on how foresters and loggers perceive and manage dead wood. A 

better understanding of the ecological services provided by coarse woody debris 

(CWD) is essential to initiate sustainable management of this resource. 

Many of the ecological services provided by CWD may even help foresters 

attain some wood production objectives more efficiently and at lower cost. For 

example, CWD may assist foresters directly with natural tree regeneration by 

providing safe sites for seedlings (e.g., nurse logs), by protecting seedlings from 

snowcreep in high-elevation forests, and by reducing trampling damage by livestock 

in range management areas. Coarse woody debris is also believed to contribute to 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno Nevada. 2 Plant Ecologist, Kamloops Forest Region, B.C. Forest Service, 515 Columbia Street, Kamloops, B.C. 

V2C 2T7 (e-mail: Andre.Arsenault@gems8.gov.bc.ca) 
Coarse Woody Debris in British Columbia Forests—Arsenault 

870 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

long-term forest productivity (Stevens 1996) by improving soil-moisture retention, 

contributing to soil structure, maintaining soil stability, and providing nutrient pools. 

Long-term forest productivity is obviously linked with timber supply. The 

contributions of CWD to forest productivity are likely both direct and indirect, 

resulting from complex interactions among organisms of the detritus food web, the 

net effect of which is to transfer and transform organic matter, nutrients, and energy 

from CWD to the forest soils (Harmon and others 1986). In addition to the direct and 

indirect benefits to wood production, CWD is also an important habitat component 

for a wide variety of organisms representing the five biological kingdoms. Although 

the importance of retaining coarse woody debris in managed forests is obvious for a 

range of values, the development of operational recommendations has not been easy. 

The abundance and distribution of coarse woody debris is highly variable in 

forest ecosystems and depends largely on stand history, stand age, tree species 

composition, ecosystem type, and decomposition rates. Coarse woody debris will 

also vary in size and stages of decay even within the same forest. Maintaining the 

natural variability of deadwood at both the stand and landscape levels is probably a 

worthy objective for sustainable forest management. However, there are many real 

and perceived constraints that make the retention of coarse woody debris in forestry 

operations challenging. Some of the issues that need to be considered when 

addressing the retention of CWD in British Columbia's forests include: workers’ 

safety, logging costs, maximum utilization policy, resistance to change, harvesting 

techniques, pulp markets and salvage initiatives, silvicultural objectives, fuel 

management, range management, and forest health. In addition, the natural variability 

of coarse woody debris precludes the development of simple or static retention 

targets, especially considering the dynamic nature of ecosystems over time and space. 

In British Columbia, the ecological value of CWD has been recognized within 

forestry legislation since 1995 (Stone and others 2002). However, the negative 

perception associated with CWD in traditional forestry and the difficulty of 

integrating multiple values has made the development and application of CWD 

management objectives rather challenging. This paper illustrates the ecological 

importance of CWD with recent research on non-vascular plants, describes briefly 

the history of CWD management, and provides an overview of a short-term strategy 

recently adopted in the Kamloops Forest Region to improve the management of 

CWD. 

Non-Vascular Plants and CWD 

Non-vascular plants (i.e., lichens and bryophytes) are important organisms in 

forest ecosystems. These taxa contribute to biological diversity or the many 

associated ecological processes and constitute critical indicators of environmental 

change. The importance of coarse woody debris as habitat for certain bryophyte 

species (particularly hepatics) has been well documented in the literature (Jovet and 

Jovet 1944, Muhle and Leblanc 1975, Shuster 1949, Soderstrom 1988). The reasons 

behind the close association between some non-vascular plants and CWD are not 

fully understood. They probably involve a competitive advantage conferred to these 

organisms over vascular plants when occupying elevated organic substrates as well as 

a combination of unique environmental conditions (i.e., substrate moisture, texture, 

and chemistry), which may be specifically required for some species. 
Coarse Woody Debris in British Columbia Forests—Arsenault 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 871 

In southern British Columbia several hundred species of lichens, mosses, and 

hepatics are associated with coarse woody debris. However, only a portion of these 

species are truly dependent on CWD for their survival. A recent review of the 

literature and consultations with expert botanists revealed that 16 species of lichens 

and 23 species of liverworts are strongly dependent on coarse woody debris (table 1). 

Table 1—Preliminary list of hepatics and lichens specializing on coarse woody debris 

(Godfrey 1977; Goward and others 1994; Goward 1999; Goward, pers. comm.; Schofield, 

pers. comm.). All of these are considered very strongly dependent on coarse woody debris for 

survival in the forest. Some are also found on other substrata, but as forest species they are 

valuable indicators of specific conditions. 

Hepatics 

 Anastrophyllum hellerianum (Nees) Schust 

 Bazzania denudata (Torr.) Trev. 

 Blepharostoma trichophyllum (L.) Dum. 

 Calypogeia muelleriana (Schiffn.) K. Müll. 

 Calypogeia azurea Stotler and Crotz 

 Cephalozia bicuspidata (L.) Dum. 

 Cephalozia lunulifolia (Dum.) Dum. 

 Geocalyx graveolens (Schrad.) Nees 

 Jamesoniella autumnalis (DC.) Steph. 

 Jungermannia leiantha Grolle 

 Kurzia makinoana (Steph.) Grolle 

 Lophocolea bidentata (L.) Dum. 

 Lophocolea heterophylla (Shrad.) Dum. 

 Lophozia guttulata (Lindb. Et H. Arn.) Evans 

 Lophozia incisa (Shrad.) Dum. 

 Lophozia ventricosa (Dicks) Dum. 

 Mylia taylorii (Hook.) S. Gray 

 Odontoschisma denudatum (Nees in Mart.) Dum. 

 Ptilidium pulcherrimum (G. Web.) Vainio 

 Riccardia palmata (Hedw.) Carruth. 

 Riccardia latifrons (Lindb.) Lindb. 

 Scapania umbrosa (Schrad.) Dum. 

 Tritomaria excectiformis (Breidl.) Loeske 

Lichens 

 Cladonia borealis S. Stenroos 

 Cladonia carneola (Fr.) Fr. 

 Cladonia chlorophea (Sommerf.) Sprengel 

 Cladonia cornuta (L.) Hoffm. 

 Cladonia crispata (Ach.) Flotow 

 Cladonia ecmocyna Leighton 

 Cladonia furcata (Hudson) Schrader 

 Cladonia gracilis (L.) Wild. 

 Cladonia pleurota (Flörke) Schaerer 

 Cladonia pyxidata (L.) Hoffm. 

 Cladonia singularis S. Hammer 

 Microcalicium arenarium (A. Massal.) Tibell 

 Lobaria retigera (Bory) Trevisan 

 Nephroma articum (L.) Torss. 

 Peltigera aphtosa (L.) Wild. 

 Peltigera britannica (Gyelnik) Holtan-Hartwig & Tønsb. 
Coarse Woody Debris in British Columbia Forests—Arsenault 

872 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

 In Sweden, many species of bryophytes, lichens, fungi, and invertebrates that 

specialize on decaying wood are in decline (Esseen and others 1992) and some of 

these species are considered threatened (Berg and others 1994). The decline of logdwelling hepatic species appears to be the result of both a reduction in large logs and 

a drier microclimate in managed forests (Soderstrom 1988). At present none of the 

species of lichens or hepatics specializing on coarse woody debris are considered 

threatened or in decline in British Columbia, illustrating the critical role B.C. can 

play in maintaining species at risk globally. This is an obvious incentive for the 

retention of CWD in managed forests of British Columbia. 

Another important consideration from a conservation biology perspective is that 

on certain sites the number of species dependent on CWD will be higher. For 

example, in a study of lichen distribution in interior-cedar-hemlock forests of south 

central British Columbia, Arsenault and Goward (2001) found that over 90 percent of 

terricolous (ground-dwelling) lichens were associated with elevated woody substrates 

of which CWD was the most important component. For lichens at least, it appears 

that the number of species that depend on CWD will increase with increasing soil 

moisture and snow-depth. The variable level of dependence between non-vascular 

plants and CWD on different sites probably also applies to other organisms and 

suggests that CWD retention objectives in managed forests should be site-specific 

insofar as possible. 

Historical Perspective on CWD Management 

There have been three main historical periods for CWD management in British 

Columbia. In the early days of logging low mechanization often meant that only the 

best wood would be taken out, resulting in considerable amounts of CWD when low 

quality timber was left on site. This was followed by a period during which clean cutblocks were considered preferable for silviculture and “fuel management.” More 

recently, with a shift towards an ecosystem management approach, illustrated by the 

Forest Practices Code of British Columbia, CWD has been recognized as an 

important value and its retention is required. 

Although the present policy calls for the retention of CWD in cutblocks, the 

perceptions of prescribing foresters and other forestry professionals have not entirely 

changed from past views. The operational reality of CWD management is further 

complicated by the diversity of “specialists” involved. Numerous disciplines and 

issues are involved with CWD management, often measuring it in different ways, 

referring to it by different names, and even working with different objectives in mind. 

For example, fire protection officers are concerned with fuel loading, forest 

ecosystem specialists are concerned with biodiversity, silviculture foresters are 

concerned with planting spots, harvesting foresters are concerned with logging costs, 

and scaling foresters are concerned with utilization standards. 

CWD management has been the subject of heated debate ever since the 

implementation of the Forest Practices Code. The approach of using specific CWD 

targets within the biodiversity guidebook (Ministry of Forests and BC Environment 

1995a) was delayed in 1995 as a result of a potential conflict between the timber 

utilization policy (e.g., zero waste policy) and CWD retention targets. Since then, 

several attempts to reach a consensus on CWD management have been unsuccessful. 

In the interim the timber utilization standards take priority over CWD retention. The 

result is that CWD management is presently focused on the retention of uneconomic 
Coarse Woody Debris in British Columbia Forests—Arsenault 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 873 

wood. In addition, companies can leave a small amount of green sawlogs behind 

without being billed for waste but are charged volume against the annual allowable 

cut. 

Towards a CWD Management Strategy 

Despite the lack of specific CWD management guidelines, foresters are still 

required to set CWD management objectives in forest development plans and 

silvicultural prescriptions. In addition, foresters also have to balance CWD 

management with other potentially competing stand management objectives such as 

stocking standards, range, and fuel management. In order to provide better guidance 

for CWD management, the Kamloops Forest Region recently developed a short-term 

strategy for CWD management. The general approach of the strategy is to clarify the 

policy and legislation pertaining to CWD management, providing prescribing 

foresters key information to assist in managing CWD. The focus of the strategy is 

educational, i.e., to provide CWD management guiding principles, planning and 

prescription considerations, and CWD management tips. The strategy will be 

implemented for a period of three years, during which monitoring programs will be 

used to assess its efficacy. 

Guiding Principles for CWD Management 

In order to assist prescribing foresters in the development of CWD management 

objectives in forest developments and silviculture prescriptions, the following key 

guiding principles have been developed. In general these principles will help 

foresters avoid wasteful practices, encourage an integrated management approach 

and promote the maintenance of variability across the landscape. 

• CWD accumulations, especially on landings and roadsides, should be 

minimized, bearing in mind that some accumulations will be inevitable for 

reasons of safety and operations. Some small CWD piles dispersed in 

cutblocks may be necessary to provide valuable habitat for some mammals. 

• Larger pieces of CWD are more valuable than smaller pieces—they last 

longer, hold more moisture, are useable structures for a greater number of 

organisms and cannot be easily replaced. 

• Ecologically, it is advantageous to maintain the full range of decay and 

diameter classes of CWD on every site—different functions and ecosystem 

processes require CWD in different stages of decay. 

• Coniferous material decays much more slowly than deciduous material and 

therefore remains part of the useable structure of a stand for a much longer 

period of time. However, the faster decay rate of deciduous CWD also 

provides significant short-term ecological benefits. Retention of a diversity 

of species is advantageous. 

• CWD can be managed in conjunction with wildlife trees and other 

constrained or reserve areas. Standing live and dead trees and/or stubs 

retained on cutblocks represent important sources of CWD recruitment. 

• CWD has additional value in riparian areas, which are a valuable habitat 

resource for many species of wildlife. CWD entering or falling across a 
Coarse Woody Debris in British Columbia Forests—Arsenault 

874 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

stream produces habitat for fish, invertebrates, and vegetation. Most 

importantly, it contributes to stream geomorphology. However, excessive 

amounts of woody debris can have negative effects on stream biology. 

• The composition and arrangement of CWD should be managed within 

acceptable levels of risk of wildfire, insect pest, and forest disease outbreaks. 

• The retention of CWD should be harmonized with all other silvicultural 

objectives. 

• Variability in the levels of CWD should be maintained at the landscape level. 

The natural distribution and amounts of CWD will vary according to 

biogeoclimatic gradients, stand types, and stand development history. 

Although the natural distribution of CWD cannot be mimicked exactly, it is 

important that CWD management capture landscape variation and sitespecific variations through different management practices. 

Sources of CWD 

In many cases, logs already lying on the forest floor will be left after harvesting. 

This constitutes an obvious source of CWD. In addition, all other uneconomic wood 

resulting from harvesting (such as breakage, short pieces, tops, and low-grade timber) 

also provides existing sources of CWD. When the intent is to leave these behind as 

CWD, efforts should be made not to damage them during harvesting operations. 

Ensuring that large pieces of CWD will be maintained through several rotations 

will be a challenge. It would be wise to plan ahead and identify “low cost sources” of 

CWD recruitment. Long-term CWD recruitment may be addressed by leaving 

reserves and wildlife trees, possibly including cull trees. “Stubbing” (leaving high 

stumps, often several meters in height) may be used to complement these reserves, 

particularly when there are few wildlife retained trees or when wildlife trees are 

restricted to portions of the cutblock. 

CWD and Risk Management 

The risk of bark beetle activity should be evaluated where wildlife trees blow 

down or if many large live trees are felled and left in place. If fallen trees are near an 

existing infestation, preventative actions may need to be taken, particularly with 

Douglas-fir and spruce. The actions will depend on the risk of spread of bark beetles, 

the value of the timber, the value of the CWD, and the impact of different actions to 

the standing trees. The level of risk to timber is determined by the probability of bark 

beetle damage (based on the susceptibility of the stand and the proximity of existing 

beetle infestations). The bark beetle management guidebook provides further 

information on hazard and risk rating criteria (Ministry of Forests and B.C. 

Environment 1995b). 

Fuel management plans are no longer required under the Forest Practices Code. 

However, the Forest Fire Prevention and Suppression Regulation states that a person 

who, on Crown or private land that is in a Tree Farm Licence or a Woodlot Licence, 

harvests timber or carries out a prescribed activity must assess the fire hazard existing 

on that land. Fine fuels, i.e. pieces less than 7.5cm in diameter, pose the primary fire 

hazard associated with woody debris. Prescribed burning, under the appropriate 

conditions, can remove these fine fuels and have minimal impact on CWD. 
Coarse Woody Debris in British Columbia Forests—Arsenault 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 875 

CWD Management and Salvage Operations 

When stands affected by catastrophic disturbances (e.g., wildfires, windthrow, 

bark beetle infestations) are salvaged, efforts should be made to ensure a good 

distribution of CWD over the area. Care is necessary when contemplating salvage 

operations within wildlife tree reserves or riparian buffers. In cases where salvage is 

required for risk management, consideration should be given to designating an 

equivalent replacement area. It may be possible to retain incidental windthrow in 

sensitive ecosystems such as riparian areas and wildlife tree patches (WTPs) for long 

term CWD. The Small-scale Salvage Program removes standing dead and downed 

trees from harvested areas. The recovery of this material poses a potential risk to the 

biodiversity values provided by wildlife trees and CWD. However, the integration of 

CWD management within forest district procedures for small-scale salvage will help 

minimize this risk. These procedures may include: identification of areas of access 

and operation; designation of high value habitat; instructions concerning salvage 

from sensitive ecosystems such as WTPs and riparian management zones (RMZs); 

information on CWD and wildlife tree values; and safety concerns. 

CWD and Silviculture Activities 

Management of harvest and post-harvest activities should minimize adverse 

impacts on CWD. The main objectives are to avoid piling CWD, avoid damaging 

CWD with heavy machinery or broadcast burning, and plan stand-tending activities 

to ensure some CWD recruitment. 

In some special circumstances it may be appropriate to modify stocking 

standards to meet CWD objectives due to debris accumulation and reduction of 

plantable spots. Options include: modifying target-stocking levels; modifying the 

minimum allowable distance between trees; and utilizing clumped planting patterns. 

CWD Management Field Tips 

The following field tips have been employed to manage CWD in different parts 

of the province. They are not necessarily applicable to all situations but provide 

several options and perhaps a template, which foresters can use to innovate and 

develop other solutions that would be suitable to specific situations. 

• Bucking on site: An approach to avoid CWD accumulations on landings is to 

buck on the site rather than at the landing. This approach can be applied over 

the whole cutblock or over a portion of it. 

• Delimbing and topping: Where whole tree harvesting is carried out, CWD 

levels can be increased by delimbing and topping on site rather than at 

landings and roadsides. 

• Leaving cull trees standing: Trees (live or dead) that have obvious defects are 

often referred to as cull trees and will usually produce low-grade lumber. In 

many cases the costs of harvesting and manufacturing outweigh any 

economic gain, making cull trees ideal candidates for long-term CWD 

recruitment. Identifying cull trees during operations as potential sources of 

CWD is a good example of improving CWD management and reducing 

logging costs. The major types of defects are forks, multiple tops, spiral 

grain, extensive rot, insect damage, and scars of various kinds. 
Coarse Woody Debris in British Columbia Forests—Arsenault 

876 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

• Avoiding yarding of uneconomic wood to landings and roadsides: Yarding 

uneconomic wood to landings and roadsides reduces its ecological and 

habitat values and can add costs. In addition, it may be expensive and timeconsuming to redistribute this material back onto the site. 

• Reducing the number of empty trips: Redistributing CWD has been 

successful in blocks with very little initial CWD volume. When the burning 

of cull and debris piles is eliminated or lessened, costs may be reduced. 

Licensees will want to determine if the redistribution of uneconomic wood 

should be done over the entire cutblock or only on a portion of it. To help 

facilitate the redistribution of uneconomic wood back onto the cutblock, the 

bucker might be able to place pieces of uneconomic wood in a pile easily 

accessible to the skidder. As the skidder comes to the landing, the operator 

will be able to release a load of incoming logs, grab a turn of uneconomic 

wood and return it to the cutblock. The general approach of returning 

uneconomic wood during operations can also be used in conjunction with 

some grapple yarding operations where safety considerations and terrain 

permit. Communication with the yarding crew to identify uneconomic wood 

is an efficient means of improving CWD retention on the site. 

Red Flags 

Although a detailed assessment of CWD management in the field has yet to be 

conducted, it is clear that certain sites deserve close attention. For example, we 

already know of at least three specific situations that may become problematic: 

• Observations in second harvest stands of coastal temperate rainforests 

suggest very few large pieces of CWD be left behind. 

• Some young thrifty stands being harvested in the southern interior of British 

Columbia have very little decay and leave few opportunities for CWD 

retention within the present policy framework. 

• In dry forests, prescribed burning often eliminates large pieces of CWD in 

the advanced decay stages. Although it is not a widespread practice at this 

time, renewed interest in the application of prescribed burning in these 

forests may pose a serious threat to species dependent on well-decayed logs 

and stumps. 

Assessing CWD management in the field over the next 3 years will help to 

identify other problem areas and make improvements to the CWD management 

strategy. 

Conclusion 

The short-term CWD management strategy proposed by the Kamloops Forest 

Region should assist in minimizing the impact of harvesting on the CWD resource 

and will provide baseline information helpful in the development of more specific 

guidance. Although there is interest in developing CWD volume retention targets, it 

is not clear that this will necessarily translate into “better” CWD management. One 

of the key ingredients to achieving this end is to help professional foresters to 
Coarse Woody Debris in British Columbia Forests—Arsenault 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 877 

develop an understanding of the ecological value of CWD and its role in the 

ecosystem. For some, this may involve a profound cultural shift because the CWD 

resource, often known as slash, waste, fuel has been perceived as a problem for a 

very long time. Addressing the many conflicting forest management objectives that 

deal directly or indirectly with CWD is a perfect example of integrated forest 

management in action, and will no doubt continue to generate a great deal of interest 

and debate. 

Acknowledgments 

I warmly thank Trevor Goward and Walt Klenner for their critical review of an 

earlier version of this manuscript. Trevor Goward and Wilf Schofield generously 

assisted me in improving the preliminary list of species of lichens and hepatics 

dependent on coarse woody debris in southern British Columbia. The research on 

non-vascular plants and coarse woody debris is possible thanks to the financial 

support from Forest Renewal British Columbia and from the B.C. Forest Service. The 

work on the short-term CWD management strategy has benefited tremendously from 

generous feedback provided by colleagues from the forest industry, the British 

Columbia Ministry of Environment, Lands and Parks, and the British Columbia 

Forest Service. In particular I would like to thank Craig Sutherland and Alan Vyse 

for continuous support and guidance, Walt Klenner for insight into translating 

ecology into operations, and Gary Sorensen who generously shared some of the 

CWD management field tips, which were tested in the Kamloops Forest District. 

References 

Arsenault, A., Goward, T. 2001. Patterns of macrolichen diversity in old and young 

unmanaged forests along a moisture gradient in humid inland British Columbia. 

Unpublished manuscript.

Berg, Å.; Ehnström, B.; Gustaffson, L.; Hallingbäck, T.; Jonsell, M.; Weslien; J. 1994. 

Threatened plant, animal, and fungus species in Swedish forests: Distribution 

and habitat associations. Conservation Biology 8(3): 718-731. 

Esseen, P. A.; Ehnström, B.; Ericsson, L.; Sjöberg, K. 1992. Boreal forests: The focal 

habitats of Fennoscandia. In: Hansson, L., ed. Ecological principles of nature 

conservation. London: Elsevier Applied Science; 252-325. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Gregory, S. V.; Lattin, J. D.; 

Anderson, N. H.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.; 

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Advances in Ecological Research 15: 699-702. 

Godfrey, J. L. D. 1977. The Hepaticae and Anthocerotae of southwestern British 

Columbia. The University of British Columbia; 433 p. Ph.D. dissertation. 

Goward, T. 1999. The lichens of British Columbia. Part 2—Fruticose species. B.C. 

Ministry of Forests, Victoria, B.C. Special Report Series 8; 319 p. 

Goward, T.; McCune, B.; Meidinger, S. 1994. The lichens of British Columbia. Illustrated 

keys. Part 1—Foliose and squamulose species. B.C. Ministry of Forests, Victoria, 

B.C. Special Report Series 8; 181 p. 

Jovet, S.; Jovet, P. 1944. Peuplement bryologique des bois pourissants et rochers 

ombragés des environs de Samoëns (Haute-Savoie). Revue Byologie Lichénologie 

14: 120-148. 
Coarse Woody Debris in British Columbia Forests—Arsenault 

878 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Ministry of Forests and B.C. Environment 1995a. Forest practices code of British 

Columbia: Biodiversity guidebook. Victoria, B.C. Ministry of Forests and B.C. 

Environment; 99 p. 

Ministry of Forests and B.C. Environment 1995b. Forest practices code of British 

Columbia: Bark beetle management guidebook. Victoria, B.C. Ministry of Forests 

and B.C. Environment; 57 p. 

Muhle, H.; Leblanc, F. 1975. Bryophyte and lichen succession on decaying logs. The 

Journal of the Hattori Botanical Laboratory 39: 1-33. 

Shuster, R. 1949. The ecology and distribution of Hepaticae in Central and western New 

York. American Midland Naturalist 42: 513-712. 

Söderström, L. 1988. The occurrence of epixylic bryophyte and lichen species in an old 

natural and a managed forest stand in Northeast Sweden. Biological 

Conservation 45:169-178. 

Stevens, V. 1996. The ecological role of coarse woody debris: An overview of the 

ecological importance of CWD in B.C. forests. Research Branch, B.C. Ministry of 

Forests, Victoria, B.C. Working paper 30/1997. 

Stone, J.; Parminter, J.; Arsenault, A.; Manning, T.; Densmore, N.; Davis, G.; Mackinnon, A. 

2002. Dead tree management in British Columbia. In: Laudenslayer, William F., 

Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas 

E., technical coordinators. Proceedings of the symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; [this volume]. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 879 

Water, Wildlife, Recreation, Timber... 

Coarse Woody Debris?1

John R. Mount2

Abstract 

A natural forest ecosystem has two essential components that seem to be in conflict with one 

another: fire and coarse woody debris. If fire originally occurred at regular intervals with each 

acre burning every 10 years, then how could coarse woody debris have existed? As a part of 

my management program, I advocate returning the forest to a natural fire regime. I also 

understand that woody debris in all of its forms is required for a healthy forest ecosystem. 

Given this, I needed additional information on how these two diametrically opposed 

components existed together in the central Sierra Nevada. After 20 years of harvesting timber 

and using prescribed burns, I have determined through an inventory system that coarse woody 

debris and fire can and do co-exist. 

Introduction 

Before 1980, Southern California Edison Company lands were in a condition 

that was less than any desired level as a functioning natural ecosystem. A patchwork 

of brush fields, under-stocked areas, and overstocked stands was the vegetative 

pattern of the lands at that time. This forest composition was a direct result of the 

harvesting methods used at the turn of the century. The large brush fields replaced 

harvested old-growth stands, and the overstocked stands consisted of young, 

untouched stands that had no value to the land managers in those early years. 

Fire exclusion has also significantly skewed the vegetative structure in all of the 

various stand types. There was too much woody debris in all size classes of dead 

material, with the exception of very large snags. Although there was an abundance of 

large downed material, (logs over 40 inches) most of it was over 50 years old and in 

an advanced state of decay. All of these factors contributed to the disrupted, 

unhealthy forest that I would be managing. 

In 1980, I wrote a Land Management Plan for my new employer, Southern 

California Edison Company. As I was outlining my vision of a well-managed forest, 

a conflict between natural fire and coarse woody debris surfaced. I knew both were 

significant to the forest ecosystem, but they seemed mutually exclusive. Because my 

long-range goal was to return the property to a pre-1850 stand structure, the 

challenge was to both maintain a healthy forest ecosystem and affect the needed 

changes within the boundaries of the biome of this area. The very first priorities were 

that I needed to harvest the over crowded stands that occupied 50 percent of the 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Forest Resources Manager, Southern California Edison Company, PO Box 600, Shaver Lake, CA 

93664 (e-mail: mountjr@sce.com) 
Water, Wildlife, Recreation, Timber... Coarse Woody Debris?—Mount 

880 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

property, and at the same time, return fire to the ecosystem. I also needed to consider 

tree species distribution and how to restore it to pre-1850 conditions. 

Early objectives included reduce fuel loading and stocking, restock brush fields, 

and maintain an adequate amount of dead material. In other words, the primary 

management objective for coarse woody debris was to preserve an adequate 

inventory of material that best suited wildlife needs, while also reducing forest fuels. 

My approach had to be fairly rapid and economical. It became apparent that more 

detailed information was needed about the stand structure. The information was 

necessary not only for timber production but also for other components of a balanced 

forest ecosystem. There were several obvious deficiencies, such as large snags and 

snag recruitment, larger size trees, and overstocked areas of young trees (less than 20 

feet in height). However, hard data was lacking. 

Methods 

The first step to understanding the co-existing relationship between coarse 

woody debris and fire was gathering information. In 1993 I was finally able to 

establish a forest inventory system. The availability of geographic information 

systems (GIS) and global positioning systems (GPS) made it possible to include a 

large variety of information and growth modeling of the existing forest composition. 

The inventory system that was designed included data on brush species, oaks, snags, 

and coarse woody debris as well as timber volume and species distribution. 

The field portion of the inventory system used 1/10-acre circular plots. The 

small plot size was used so that more points were sampled with relative uniformity 

within each plot. With larger plot sizes, a large variation exists within each plot in 

terms of canopy cover, brush percentage, or stand type. Using the smaller area size 

encourages variety while maintaining consistency among measurements. Also, the 

measurements of coarse woody debris include a breakdown of dead and downed 

material, as well as snag classification. I divided the measurements into size and 

decomposition levels as expressed by age classifications. 

Another category was added to the inventory system termed “green snag.” A 

green snag was defined as a live tree that would not be harvested due to disease or 

deformity, but would be preserved for wildlife purposes. At this time, there was an 

obvious deficiency in the existing stand structure of unhealthy trees. Because the 

forest was relatively young, I needed to increase the number of trees that for one 

reason or another were dying or damaged. I would mark these “wildlife” trees with a 

“W,” but needed an estimate of size and volume. A “W” is also used for other 

reasons such as nesting trees, perch trees, potential habitat trees, as well as green 

snags. 

Before the collection of any hard data in 1993 the program needed to proceed in 

1980. Timber harvesting is one method of increasing coarse woody debris. High 

stumps (10-15 feet), tops, cull and sound logs, snag, and green snag retention all 

contribute to the inventory of debris. The opposite is true for salvage logging. In my 

management program, I have made every effort to reduce or eliminate salvage 

logging in order to help maintain woody debris. In fact the only salvage logging I 

have done on these lands was conducted in 1991, during the drought. Even during 

those operations, only very recently killed trees or trees actually infested with the 

bark beetles (dendroctonus brevicomus and monticoli) were removed. Edison has 
Water, Wildlife, Recreation, Timber... Coarse Woody Debris?—Mount 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 881 

experienced far less infestation than surrounding forest lands due to harvesting in the 

first 10 years (1980-90). The most difficult choices in both of these salvage 

operations and current harvesting is leaving recent snags that have merchantable 

value. 

Although I have an active coarse woody debris management objective, I have an 

even more active fire management program. After studying all available information 

on natural fires that burned in the Sierra prior to 1850, I learned that they did not burn 

only with low intensity, as many people seem to believe. Even many catastrophic 

fires of today burn in a patchwork manner, leaving many completely unburned 

islands within denuded areas. Natural fire, as a result of a reduction of fuels, burned 

for many days and even months and burned hot as well as with low intensity. 

The burning that I practice duplicates these fires. Initial entry is done under 

conditions that only burn lighter fuels, usually less than 4 inches. Subsequent burning 

allows us to burn very hot in areas that are adjacent to unburned patches. This burn 

pattern allows for areas of high coarse woody debris inventory with open areas 

intertwined. 

Results 

The results of the burn program overlaid with the coarse woody debris retention 

goals have been better than expected. Using available research data as a base, the 

inventory indicates above-adequate volumes of coarse woody debris scattered over 

the entire property. The breaking up of the forest structure and occurrence of coarse 

woody debris also allows better fuels management against large fire incidences. The 

key is how the burning is done. 

More directly, inventory results show an adequate stocking of coarse woody 

debris over the areas treated by fire. Most importantly, these areas are neither 

continuous nor contiguous with each other and are surrounded by openings with no 

woody debris at all. Snag inventory and recruitment numbers are above most 

recommended thresholds and increasing. The firm policy of not salvaging any dying 

tree except for those hazardous to the public has increased numbers of snags. The 

initial burning in a new area has been limited to the reduction of light fuels (less than 

4 inches in diameter). Subsequent burning has been done in such a manner as to 

create the pattern of patchy occurrences of course woody debris. Bird surveys support 

the conclusions that fire has not reduced the incidences of any species after the initial 

burning. Subsequent hotter burns indicate short-term differences followed by 

increases in both richness and diversity. 

Discussion 

By introducing fire under a variety of conditions, the results of each burn are 

different and important. Because of this fact, there are no unsuccessful burns. More 

importantly, by understanding fire behavior, certain desired results can be achieved. I 

have been successful in many respects, including the increase of deer browse, 

creating conditions conducive for natural reproduction, thinning of these new stands, 

rejuvenating vegetation types such as willow, creating small openings, increasing 

coarse woody debris, increasing wildlife diversity, and reducing fire hazard. In fact, 
Water, Wildlife, Recreation, Timber... Coarse Woody Debris?—Mount 

882 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

due to the many legal obstructions that are reducing prescribed burning opportunities, 

the only problem may be that there is too much coarse woody debris. 

The initial process of stem reduction was completed in about 15 years. The 

conversion to the proper species and size composition is ongoing and will take about 

30 more years. There is still a long way to go before I know which variables and 

components to watch in order to determine ecosystem health. 

Where do I go from here? Research is paramount in knowing how to manage the 

forests in the future. However, the overwhelming data and sometimes contradictory 

research findings must be carefully evaluated. There is some good in each research 

project, though one can also find much misleading information. These apparent 

conflicts are due to varied locations of the research projects as well as their differing 

objectives. There is also much personal bias, not only in the data but also in turf wars 

between researchers. 

Monitoring the work is obviously a requirement to determine the program’s 

progress. This alone is a major focus of our program, with continuous debate on cost 

effectiveness. What needs monitoring and how it should be done is one of the most 

time consuming (and fun) discussions that my staff has each year. Relevancy, costs, 

and amount of detail required are some of the issues that are argued. Currently, some 

of our monitoring projects include bird surveys, deer counts, brush growth, tree 

spacing, stand release, competition, hardwood physiology, and effects of fire on the 

ecosystem. 

Reconciliation of the differences between research and monitoring efforts is also 

required before work plans can be initiated in a particular ecosystem. This is mainly 

due to the lack of research done on this subject and also lack of knowledge on 

unaltered forest ecosystems. In the future, research will determine numbers of snags 

per acre and how many tons of coarse woody debris is necessary for a healthy forest. 

Unfortunately, there will be many changes in those results and numerous arguments 

will ensue before any final knowledge is ascertained. Grandiose programs initiated in 

Washington D.C. or Sacramento that may protect a single species is not the answer. 

Natural systems are resilient and most do not require expensive and time consuming 

plans to help them along. As land managers, we must understand the naturally 

occurring cycles and manage within them. We should then use those tools that 

natural systems have provided, such as fire. As a resource component, fire should be 

used as a determinant for the proper amount of coarse woody debris. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 883 

Creating and Maintaining Wildlife, Insect, 

and Fish Habitat Structures in Dead Wood1

Timothy K. Brown2

Abstract 

Dead wood is an important component of the forest for many species. In many locations, 

however, the presence of dead wood has declined, and there is a need to make what is left 

more suitable for the myriad of creatures dependent on this material. In this paper, I will 

summarize the value of dead wood for these species and describe methods for improving the 

dead wood component of the forest to meet the needs of a variety of vertebrates and 

invertebrates. 

Creating Wildlife Habitat Structures in Snags, Logs, and 

Stumps 

In forested ecosystems, habitat diversity is directly related to tree form diversity. 

Snags are trees, dead or living (living snags are live trees with dead sections) that 

have been killed or altered by disease, lightning strikes, and wind. Each snag is 

unique since various factors, such as age, species, location, and cause of mortality or 

alteration, characterize each snag differently. 

Snags (standing or downed trees) and other forms of dead or unmerchantable 

woody structures are recognized by many land managers to benefit wildlife and other 

biota on forested lands. At least 96 vertebrate species are associated with snags found 

in forests of Washington and Oregon (Rose and others 2001). A large proportion of 

forest-associated bird and mammal species require cavities to live in, many provided 

by snags or other forms of woody debris in various stages of decay. Thomas and 

others (1979) documented 62 wildlife cavity users in montane forests of northeast 

Oregon and southeast Washington. To other landowners, snags may represent 

unclaimed firewood, lightning rods, fire hazard, or loss of potential timber 

commodity. Many political jurisdictions have forest practice rules or policies 

requiring prescriptions to retain snags or designate green trees for future snag 

recruitment in managed landscapes. Wildlife habitat prescriptions, whether they are 

scientifically based or not, that are implemented and monitored may provide more 

habitat management options in the future and a more positive effect to increase 

species diversity and/or abundance as the forest matures. 

Both dead and living snags are important and offer somewhat different habitats. 

For example, living snags that retain some lower branches below a sturdy, bare trunk 

or spike provide ideal protection and support for large predatory birds such as hawks 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Principal, T.K. Brown & Associates, P0 Box 6252, Bellevue, WA (e-mail: tkbrown@uswest.net) 
Creating Habitat Structures in Dead Wood—Brown 

884 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

and eagles. When a snag is formed abruptly, for example, by wind or lightning, the 

damaged tissue is quickly colonized by insects and fungi, which in turn provide 

meals for primary excavators such as woodpeckers and predatory insects. Secondary 

cavity users such as owls, chickadees, swifts, bats, and bees extend the usefulness of 

the snag modified by primary excavators. Flaps of loose bark, hollows, and crevices 

often found in snags are favored bat roosting sites (Tim Brown, pers. obs.). 

As the snag decomposes and falls to the ground, it will provide shelter, dens and 

runways for a variety of small mammals and amphibians. Hollow tree trunks, either 

in the partially standing snag or the downed trunk, creates protective habitat for 

denning martens (Martes americana), fisher (M. pennanti), coyote (Canis latrans), and 

raccoon (Procyon lotor). Shrew-moles (Neurotrichus gibbsii), shrews (Sorex sp.), deer 

mice (Peromyscus maniculatus), salamanders, and frogs may use smaller cavities in 

the decaying wood for thermal and protective cover, in addition to foraging on the 

various insect larvae harbored there. Small mammals can act as dispersing carriers 

for fungi, and if they are using a down log as a runway, their feces deposit fungi, 

which in turn, recycle nutrients to the soil. The “dead wood” on the ground is a 

storehouse of energy and nutrients. The decay of this debris steadily contributes to 

the organic layer of the soil. This organic soil is critical to establishing a fertile 

medium for supporting a diverse ecosystem of plants, small mammals, amphibians, 

and invertebrates. 

The purpose of this paper is to review techniques that I have experimented with 

in the last 30 years. As a former professional timber industry tree faller, forest 

firefighter, and owner and operator of a tree-service company, I have witnessed a 

plethora of wildlife using wood habitat, such as cavities, broken tree-tops, and deep 

fissures of lightning-struck trees. From these observations, my goal was to create 

similar habitats using chainsaw and drills. On trees and standing snags, many of the 

enhancements were performed aboveground anywhere from 2 m to as high as 30 m 

or more. Although most of the methods described in this paper were employed in the 

Pacific Northwest, these enhancements should work in other temperate conifer and 

hardwood forests of the U.S. and overseas. Land managers and their biologists can 

likely employ most of these techniques presented in this paper by considering the 

specific type, size, and location of the alteration for the particular target species of 

their area. 

Wood Habitat Planning and Retention

With skill and planning, forest management activities and wildfires resulting in 

wildlife habitat loss may be managed to reduce further impact to wood habitat. In all 

likelihood it will be necessary to prioritize the efforts devoted for snag or other 

habitat preservation. The following are criteria useful for selection of elements of the 

landscape to be retained or managed: 

• Trees or snags with trunks of 30 or more centimeters DBH 

• Snags providing sites for platform nests 

• Snags with obvious wildlife holes 

• Snags with hollows 

• Snags with conks (indicating soft decay is underway) 
Creating Habitat Structures in Dead Wood—Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 885 

• Downed trees with hollows. 

To retain snags in proposed logging operation sites, no harvest or no-work zones 

can be established around designated snag-retention areas. In a forest fire situation, 

crews, at their discretion, can reduce the potential hazard posed by these trees by 

routing fire trails around them and establishing no-work zones around each snag. 

These zones should cover an area with a radius of 1.5 times the height of the snag. 

The hazard zone can be reduced to acceptable limits by topping threatening 

snags. Criteria and procedures for any topping should be introduced by the 

biologist/ecologist of the land management entity and incorporated into the sale 

administration process. Safety regulatory agencies should participate with the land 

managers to review topping prescriptions. Topping prescriptions, as well as other 

restoration techniques, may vary within a planning area depending on, for example, 

existing stand conditions, snag species, and proposed tree harvest methods. Holistic 

forest management planning is especially important to foster long-term stand and 

landscape conditions for wildlife species and other biota associated with snag and 

down wood habitat. 

It is apparent that the same features that make the snag an asset for wildlife 

habitat may be a liability for the forest worker or visitor. Signs of a hazardous tree 

may include: 

• A significant lean 

• A broken top and/or branches that are hanging up in the tree 

• Snags with hollows 

• Root or other disease (noted by needle discolor, poor cone production, etc.) 

• Advanced decay into the bole of the tree 

• Visible cracks or hollows in the bole of the tree 

• Visible wildlife excavations 

• Loose bark 

• Length of time that the snag has been dead or tree stressed 

• Lightning scars. 

In forest fire situations the possibility of the snag serving as a “fire ladder” that 

may spread the fire into the canopy can be reduced by removal of low hanging and 

dead branches from the lower portions of the tree. Snags can be protected by 

removing fine litter and woody undergrowth at its base, thereby eliminating material 

that could fuel the fire near the snag. 

Ultimately, the safety of the crew takes precedence over maintaining wildlife 

habitat. If, for example, establishing a “no-work zone” around a potentially 

hazardous snag is not an option, or if a combination of dangerous features, such as 

degree of lean and amount of decay, are significant, then worker safety requires 

removal of the snag. If a snag must be felled, it may still provide valuable habitat. 

Large, downed hollow or partially hollow logs are among the slowest habitat 

elements to be replaced after harvest or fires. Hollow logs may be homes for 

returning marten, fisher, lynx (Lynx canadensis), bobcat (L. rufus), bear (Ursus spp.), 

raccoon, and numerous other creatures. 
Creating Habitat Structures in Dead Wood—Brown 

886 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Specific Habitat Creation Techniques 

Hollow Trees 

Hollow trees provide the basic ingredient for a blue-ribbon wildlife tree. In the 

Pacific Northwest, for example, tree species such as western red cedar (Thuja 

plicata) or Douglas-fir (Psuedotsuga menziesii) at least 60 cm in diameter should be 

checked for hollowness with a sounding ax. A hollow tree will emit a lower sound 

when struck than a solid tree. An increment borer can be used to determine whether 

the tree is indeed hollow and the extensiveness of the cavity. Once a hollow tree has 

been located, the worker should check to ensure that existing fissures or cracks 

provide entry to the hollow. If there is no suitable entrance, a quick drill with a 

chainsaw may permit access. Bats will enter a hollow tree from all levels, including 

open root areas that lead up into the tree trunk. However, a 9-meter (30 feet) or 

higher entrance hole is desired because it provides enough drop space for the young 

as they launch their first flights. 

Locations for entrance holes should be selected carefully. Enlarging an existing 

partial opening or placing the hole in an already existing dead area, such as a dead 

branch stub are good places. The opening should be free of obstructions for safe 

egress and ingress. The opening should also be placed at a 20-degree angle upward 

from the horizontal. This angle helps keep the interior warm and provides a measure 

of safety from predators. 

Bat Roosting Slits 

On standing trees and snags these installations combine the close quarters and 

large surface areas that bats use. They serve as bat apartment houses and provide a 

dry, warm pocket for roosting or possibly nurse colonies. For a multiple slit dwelling, 

an entry port about 20 cm by 30 cm (8 inches high by 12 inches) long is excavated in

the side of the tree. After the entry port is excavated, the slits are cut up into the 

interior of the tree as vertically as possible. Two to three separate slits may lead off 

from a single entry port. Alternatively, separate entry ports for each slit may be 

excavated. If the selected tree is green, it will be necessary to cut away the bark 

around the entry ports to prevent their closure by heal-over from cambium growth. It 

is also important to cut the cambium away to prevent oozing sap from sticking to the 

bats’ fur and causing flight problems, or perhaps, avoidance of the site because of the 

presence of oozing sap. 

Bat Bark Flange 

A magnificent old Douglas-fir tree typically has bark at least 15 cm (6 inches) 

thick, with many vertically running fissures or crevices up to 15 cm deep and several 

meters long. The crevices in large-diameter (i.e., > 76 cm) Douglas-fir, or other 

species with deep fissures, provide abundant niches for forest bats. Solitary male bats

use these crevices extensively. Smaller-diameter Douglas-firs (< 51 cm) have not

developed the thick-fissured bark, and management of early seral forests for habitat 

restoration requires an innovative approach for creating surrogates for bark crevices. 

To install bark flanges, tangential cuts should be made upwards about 25 cm (10 

inches) on the side of a tree trunk. The depth of the cut should be just through the 
Creating Habitat Structures in Dead Wood—Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 887 

bark with only enough wood to provide a stable flange. Wedge a 19 mm (3⁄4-inch) 

diameter piece of wood up into the top of the flange to keep it open. 

Bat Girdle Flange 

A tree that has been selected for killing by girdling can be utilized as bat habitat 

while the tree is dying. The girdle is designed with multiple collars or flanges 20 to 

25 cm long around the circumference of the tree and hanging down over the shavedoff portion of the girdle. Bats will be attracted to the underside of these flanges. For 

convenience, the bat girdle flange may be placed at breast height (1.4 m above the 

ground). Tree girdled at this height can be expected to remain erect for 20 or more 

years, and the girdle needs to be installed 6 m (20 feet) off the ground. This increased 

longevity is worth the trouble of tree-climbing in most cases. 

Bat Stumps 

Usually a second growth forest has stumps left over from the preceding forest. 

These old, large-diameter (> 76 cm) stumps are particularly valuable habitat and even 

smaller stumps can be used to enrich the habitat. The tallest stumps are most suitable 

for bat stumps. A chainsaw can be used like a drill to bore out a tunnel through the 

stump. The tunnel should be no wider than 19 mm (about twice the kerf width of the 

bar) and at least 20 cm (8 inches) from the top of the stump to keep the interior dry. 

Bats will use these artificial hollows for roosting. 

Sapwells 

Sapsuckers create sap wells in the bark of coniferous and deciduous trees and 

shrubs. Sap is an important seasonal component in the diet of these birds. Sapwells 

are often used by other birds such as chickadees, hummingbirds, warblers, and 

nuthatches. Squirrels and chipmunks also exploit sapwells. Sapwells can be installed 

with a chainsaw by lightly touching the trunk of a tree with a small chainsaw or drill. 

The bark is barely opened up to the cambium, not into the wood. The best time for 

sapwell construction is in the early spring, when the cambium is rapidly producing 

new phloem. Sapwells can be placed at all levels in live trees, but levels 5 m (15 feet) 

or greater seem to be preferred. 

Lightning Strikes 

In late-successional forests in the western Cascade Mountains in Washington, 

many of the tallest surviving trees have been struck by lightning at some time but 

have not burned significantly. If the strike was fairly recent, an irregular charred line 

that runs down the vertical length of the tree should be obvious, but often evidence of 

a lightning strike is not visible. Visible damage to the tree trunks may include 

superficial bark flaking to strip like furrowing along the trunk. Often the tree tops 

have been shattered and lost, and a spiral scar with a crack along its axis winds 

around the trunk. Most have shallow continuous scars 15 to 127 mm (0.6 to 5.0 

inches) wide along their trunks. The average scar extends along 80 percent of the tree 

height, often to the ground level (Taylor 1969). 
Creating Habitat Structures in Dead Wood—Brown 

888 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Lightning strikes expose the cambium of the trees to insect activity that provides 

a bountiful and convenient food source for insectivores. Fungi may enter at splits and 

deep openings made by lightning and begin the process of sapwood and heartwood 

rots. Birds also can readily use the lightning-induced crevices as points to initiate 

excavation. Conner (1975) noted that some lightning-created snags were used by 

cavity-nesting birds. Bats find temporary roosting sites along the strike crevices. 

Since lightning struck trees are usually poor quality for timber, they should be 

retained on the landscape as wildlife trees. The structure of a lightning strike can be 

mimicked by installing a long vertical slit down the trunk of the tree. Strikes often 

travel straight down for some distance but then curve off center nearer the base of the 

tree. Artificial lightning strikes should be installed in this asymmetric way and can be 

installed in either dead or living trees. 

Raptor Perches 

“Healthy” second-growth forests that open along rivers and lakes may be lushlooking, but provide marginal perch habitat for eagles and other large-bodied raptors. 

Bald eagles (Haliaeetus leucocephalus), for example, need lookouts and towers from 

which to locate prey and to begin their hunt. Typically, early-seral hardwood forests, 

such as small-diameter (< 30 cm) red alder (Alnus rubra) and black cottonwood 

(Populus trichocarpa), are densely branched and not useful as raptor perches. 

However, branches in dense crowns can be thinned to create raptor perches. Trees 

along a river in a fairly open location may be improved for use by eagles by thinning 

and girdling branches to provide visibility and convenient perch sites. When pruning, 

branches in the lower third of the trees are removed and those in the upper two-thirds 

of the trees are thinned. 

Mammal Dens 

Most of our forest mammals use some sort of cavity for denning. Insectivorous 

small mammals, such as shrews (Sorex spp.), shrew-moles, and deer mice, are known 

to exploit log or stump cavities for den sites and runways. Larger carnivorous 

mammals, such as members of the weasel family, use hollow logs or hollow trees as 

den sites. Maintenance or creation of some of these den structures can facilitate use 

by these creatures. 

Habitat Logs 

Dens can be constructed in logs of all sizes. Windthrown logs suspended above 

the ground are ideal, because they remain drier longer than logs flush with the surface 

of the soil. With a chainsaw, selected log should be cut laterally to create two halves, 

then sliced at the end of the cut to release the upper half. A den of the target species 

can be cut, contingent upon log size. An entrance hole just large enough for the target 

species should be placed along the side of the cut. The lid on top of the log should be 

secured with nails or cable. 
Creating Habitat Structures in Dead Wood—Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 889 

Jagged Top Snags 

A jagged top snag will collect a greater number of fungal spores to begin the 

decay process. Irregularities in the bole will collect precipitation and fungal spores 

and appear more natural. To “naturalize” a snag, a portion of the top of the newly 

topped tree should be sliced at an angle. Then the top of the snag should be cut to 

create crevices in the top. Finally, the saw should be “bounced” on the top to create a 

number of incisions. 

Improvement of Aquatic Habitats for Wildlife 

Urban development and past management of forests along streams, wetlands, 

and lakes, have reduced the presence of large dead trees that historically fell into 

these wet areas. Introducing wood habitat to lotic ecosystems, for example, may 

require extensive and expensive restoration efforts and may conflict with social, 

political, and scientific efforts to protect Federal-listed salmonids, especially in 

regions within the Pacific Northwest. 

If restoration is practical, especially in urban areas with lentic habitats, reintroducing wood habitat will likely benefit invertebrate and vertebrate species and 

associated biota where future recruitment of wood is unlikely to occur. Adding 

woody debris directly in water and adjacent uplands can increase amphibian 

productivity, for example. Observations show that placement of thin-stemmed woody 

vegetation in the water provides egg oviposition sites for the northwestern 

salamander (Richter and Roughgarden 1998). And water temperatures are crucial for 

the proper development of amphibian egg masses. Areas shaded from direct sunlight 

may not provide appropriate temperatures for quick development of amphibian egg 

masses compared with portions of lakes exposed to sunlight for longer periods. So 

when providing structures designed to provide support for amphibian egg masses, 

one should prioritize areas with warmer water due to longer duration of sunlight. 

Other species of native amphibians, such as the red-legged frog, may also loosely 

secure their egg masses to woody stems. Such woody material would float up and 

down with the water level fluctuations, preventing desiccation during water level 

changes. Aquatic amphibians spend a good deal of time in upland habitats. Addition 

of large woody debris to upland areas enhances amphibian overwintering 

opportunities. 

Waterfowl, amphibians, turtles, and riparian-associated wildlife are attracted to 

open bodies of water, and the presence of logs associated with open water areas 

increases the quality of the habitat for such species. In open bodies of water, a 

mixture of loafing logs for waterfowl, otter, and turtles should be placed to maximize 

use by individual wildlife species. Addition of logs to the area of ponds and lakes 

receiving the greatest amount of daylight provide basking sites for turtles so that they 

can more quickly increase their body temperature in a secure location. Waterfowl 

roost safely on secured logs in the water, and several mammals use floating logs, 

including mink (Mustela vison), river otter (Lutra canadensis), and beaver (Castor 

canadensis). 
Creating Habitat Structures in Dead Wood—Brown 

890 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Maintenance and Improvement of Snags and Logs for 

Pollinating and Predator Insects 

Predaceous and pollinating insects, such as ants, wasps, bees, and ladybugs, 

contribute to forest health and productivity. Taxa including ants and ladybugs prey on 

a number of forest insect pests. Solitary and colonial bees pollinate a variety of 

flowers and berry-producing shrubs. 

Many of these insects use snags and downed woody debris for many of their life 

activities. Some are primary cavity excavators, such as beetles and ants, that create 

cavities in dead wood for rearing their young. Many insects are opportunistic and use 

cavities of all kinds, including those created by wood rotting fungi, for their own 

reproduction or for overwintering habitat. Special structures and installations for 

pollinating and predaceous insects in standing and downed wood materials may be 

created by various mechanical means. Galleries of a variety of dimensions are 

excavated in snags and logs by larvae of wood boring beetles and the vacated 

galleries are often used by a variety of other insects. A native bee, the orchard mason 

bee (Osmia spp.), uses holes approximately 8 mm by several centimeters deep for 

egg laying. Artificial cavities for this beneficial bee can be created with a standard 

drill bit. A portion of the tree facing south should be selected to optimize temperature 

regimes needed by this bee. Holes should be about 8 cm (3 inches) deep with an 8 

mm (5/16-inch) drill bit. The hole should be cleaned out so that rough edges do not 

impede the bees. 

Honey bees (Apis spp.) were originally imported from Europe, but have become 

well established in the U.S. and have become essential pollinators for orchards, 

cranberries, and native plants. They commonly use hollow logs, decayed or hollow 

trees, and various other cavities for their nests. Bee nests are a delicacy for forest 

omnivores such as bears. Creation of cavities in trees, logs, and stumps can enhance 

the habitat for these bees. Suitable cavities can be excavated in erect trees and then 

covered with face-plates, that include small entrance holes, over the cavity. A tree 

should be selected in an open stand that receives plenty of sunlight. With a chainsaw, 

a cavity should be excavated approximately 1 cubic foot. A faceplate should be 

secured onto the cavity with a 1 centimeter entrance hole at the base or one long slit 1 

centimeter in width. Hollow logs or trees with no entrance can be opened up to the 

exterior with a small drill to provide access. In addition to honey bees, wasps also 

commonly use these structures and contribute to both pollination and pest control. 

Lady bugs (Hippodamia spp.) are predaceous insects that overwinter in tiny 

crevices in wood, logs, or stumps in areas with adequate insolation. Suitable size 

crevices can be constructed with a chainsaw in trees and stumps in sunny sites. The 

tip of the chainsaw should run approximately 15 cm beyond the bark layer in several 

locations of a snag and/or stump.

Discussion and Conclusion 

Management activities will, incidentally, contribute to varying levels of habitat 

loss. Losses will vary, but in nearly all cases, rehabilitation can lead to enhancement 

of wildlife components faster than if habitats are unmanaged. 

The first step to rehabilitation is to assess the damage of the activity with respect 

to wildlife habitat. It is important to evaluate the condition of vertical and horizontal 

elements of the habitat. If necessary, for example, cut green trees or partially decayed 
Creating Habitat Structures in Dead Wood—Brown 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 891 

logs can be delivered from off-site to act as nutrition logs and habitat for wildlife. 

Logs should be selected so that they will reach mid-succession in the decay sequence 

when the regenerated forest stand can begin recruiting its own snags and downed 

logs. As a precaution, any downed logs brought into the rehabilitation area should be 

recruited as close as possible from the managed site and inspected to minimize the 

introduction of unwanted fungal diseases and insects.

Taking remedial action over the entire area of interest may not be feasible, 

however, and it is essential that remediation result in creation of a mosaic of habitats 

at a variety of scales that will provide habitat for prey, as well as perching, nesting, 

and denning sites for predators. If small mammals and birds are provided suitable 

cover and rest sites, they may cache seeds harvested in the surrounding green areas. 

Their feces will also inoculate the soil with fungal spores, some of which are 

essential to functioning forest, including mycorrhizal fungi. 

Intensely burned areas may leave significant amounts of downed woody debris 

and standing snags. However, the habitat and nutrient benefits of these snags and 

debris may be severely limited if fire has caused the exterior of the wood to be case 

hardened. Case hardening results from moisture loss coupled with chemical changes 

that occur on the fire-exposed surface of wood. Case hardening increases the 

compressional strength and brittleness of the snag or log, and more importantly, seals 

off the nutritional resources within the tree. This sealing, along with the direct loss of 

bark and cambial nutrients, limits the usefulness of the post-fire dead wood for many 

species. Birds, mammals, and bark beetles cannot penetrate and shape case-hardened 

wood in their usual manner. Furthermore, reduction in vertical cover and loss of 

organic duff on the ground reduces the habitat suitability for numerous forest 

organisms. 

The degree of success of artificial structures is generally proportional to on-site 

supervision by an experienced professional during enhancement activities. Without 

proper training and preparation, application of these methods could place workers in 

hazardous situations. Because the chainsaw is the tool of choice for many of the 

projects, it is strongly advised that workers be properly trained and certified to handle 

such equipment on the ground, and especially, when working above the ground in 

trees. 

In the last three decades in which many of these techniques have been applied, it 

is apparent that there is an information gap in reporting either the success or failure of 

the techniques. Forest land managers and natural resource biologists should ensure 

that existing and future projects are monitored vigorously with the intention of 

documenting enhancement results or lack thereof. Wildlife habitat enhancement 

methods and techniques can be blended to retain and enhance not only threatened, 

endangered, and sensitive species, but also to include the total biotic composition that 

is associated with wood habitat. Some general observations have shed light on the 

suitability of the various restoration techniques presented in this paper and allow 

optimism for the success of many projects. Preservation and management of wildlife 

structures and associated biota that use them, and the workers performing their tasks 

in wood habitat retention areas, can be simultaneously achieved with foresight and 

innovative planning.
Creating Habitat Structures in Dead Wood—Brown 

892 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Acknowledgments 

I thank A. Sonny Paz and Bill Laudenslayer for their helpful reviews of this 

paper. 

References 

Conner, Richard N.; Hooper, Robert G.; Crawford, Hewlette S.; Mosby, Henry S. 1975. 

Woodpecker nesting habitat in cut and uncut woodlands in Virginia. Journal of 

Wildlife Management 39(1): 144-150. 

Richter, Klaus, O.; Roughgarden, Henry A. 1998. Wetland characteristics and oviposition 

site selection by the Northwestern Salamander (Ambystoma gracile). In prep.: 58. 

Rose, Cathy L.; Marcot, Bruce G.; Mellen, T. Kim; Ohmann, Janet L.; Waddell, Karen L.; 

Lindley, Deborah L.; Schreiber, Barry. 2001. Decaying wood in Pacific Northwest 

Forests: Concepts and tools for habitat management. In: Johnson, D. H.; O’Neil, T. 

A., editors. Wildlife-habitat relationships in Oregon and Washington. Corvallis, OR: 

Oregon State University Press; 580-623. 

Spies, Thomas A.; Cline, Steven P. 1988. Coarse woody debris in forests and plantations 

of Coastal Oregon. In: Maser, C.; Tarrant, R. F.; Trappe, J. M.; Franklin, J. F., editors. 

From the forest to the sea: a story of fallen trees. Gen. Tech. Rep. PNW-GTR-229. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 5-24. 

Taylor, Allen R. 1969. Tree-bole ignition in superimposed lightning scars. Res. Note INT90. Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department of 

Agriculture; 4 p. 

Thomas, Jack W., Anderson, Ralph G.; Maser, Chris; Bull, Evelyn L. 1979. Snags. In: 

Thomas, J. W., technical editor. Wildlife habitats in managed forests—the Blue 

Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: Forest 

Service, U.S. Department of Agriculture; 60-77. 
Perspectives and Approaches 

to Management

893
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 895 

An Ecological Functional Basis for 

Managing Wood Decay Elements for 

Wildlife1

Bruce G. Marcot2

Abstract 

The traditional approach to managing decaying wood for wildlife has been to list species 

associated with snags, down wood, and other wood decay elements, and then to provide the 

kinds, sizes, and amounts of wood decay elements presumed necessary to meet their needs. 

An expanded approach more consistent with the spirit of ecosystem management would also 

describe those species’ key ecological functions (KEFs). KEFs influence the ecosystem 

through trophic relations, species interactions, soil aeration, primary cavity and burrow 

excavation, and dispersal of fungi, lichens, seeds, fruits, plants, and invertebrates. These 

“functional webs” can be described for wildlife species associated with various wood decay 

elements (snags, down wood, litter, duff, mistletoe brooms, dead parts of live trees, hollow 

living trees, natural tree cavities, bark crevices, and live remnant or legacy trees) in 

Washington and Oregon. Information on species’ KEFs also is part of the DecAID wood 

decay management advisory model. The challenge is posed for management to think 

functionally beyond simple species-habitat relations, as to the broader role of wood decay in 

supporting functional webs. 

Introduction 

Current approaches to managing wood decay elements for wildlife generally 

focus on identifying the wildlife species associated with such elements and the 

amount and distribution of such elements (mainly snags and down wood) deemed 

necessary to support those species. Appropriate silvicultural or vegetation 

management guidelines are then crafted to provide the snag and down wood levels. 

However, this is but one side of the ecological equation. It may be useful to also 

recognize and manage for the key ecological functions (KEFs) of wildlife because 

they, in turn, influence environmental elements and ecosystem processes affecting 

other species. The term “key ecological functions” refers to the major ecological 

roles of organisms in their ecosystems, as differentiated from abiotic ecosystem 

processes such as fire and disturbance events. A classification of KEFs has been 

proposed elsewhere (Marcot and others 1997, Morrison and others 1998). In a 

database, each wildlife species can be coded as to its KEFs as well as the 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Research Wildlife Ecologist, Pacific Northwest Research Station, USDA Forest Service, 620 S.W. 

Main Street, Portland OR 97205 (e-mail: brucem@fs.fed.us) 
Functional Basis for Managing Wood Decay—Marcot 

896 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

macrohabitats and habitat elements it uses. By using this approach, the manager can 

identify the macrohabitats and habitat elements present in an area, the species 

associated with those habitats, and the array of KEFs associated with those species. 

In this way, the manager can begin to explicitly consider the ecological functions of 

wildlife in a repeatable and rigorous fashion. 

This paper demonstrates how the KEFs of terrestrial vertebrate wildlife species 

associated with decay wood elements in Oregon and Washington can be considered 

in forest management. I draw from species-habitat and species-KEF databases 

developed for the Oregon-Washington Species Habitat Project (SHP) (Johnson and 

O’Neil 2001; Marcot and Vander Heyden 2001) and for the Interior Columbia Basin 

Ecosystem Management Project (ICBEMP) (Marcot and others 1997). I use the term 

“manager” to refer to both natural resource decision-makers and at least some of the 

specialists who support them. 

Methods 

Developing the Species-environment Relations Databases 

The species-habitat and KEF databases I used from SHP and ICBEMP were 

developed from literature surveys and expert peer reviews. The SHP project 

developed databases for terrestrial and marine non-fish vertebrates of Washington 

and Oregon, whereas ICBEMP developed databases for species groups and rare 

species of lichens, bryophytes, vascular plants, soil microorganisms, and terrestrial 

invertebrates, and for all species of non-fish vertebrates, in the interior Columbia 

River Basin and portions of the northern Klamath and Great Basins in the U.S. 

In SHP and ICBEMP, species’ environmental correlates included snags, down 

wood, and other wood decay substrates. The SHP database used the classification 

system listed by Neitro and others (1985) to denote five decay classes of snags: 1 = 

hard and mostly intact, 2 = hard with some loss of small branches, 3 = moderately 

decayed with more extensive loss of small branches and some sloughing bark, 4 = 

decayed with extensive branch and bark loss, and 5 = advanced decay typically with 

loss of most branches and bark. 

KEFs included a wide range of categories of ecological roles of organisms. I 

arranged environmental correlates and KEFs into hierarchical classifications to 

determine which and how many species pertain to general and specific habitat 

elements and ecological roles. The major categories of environmental correlates in 

the classification include sundry biotic and abiotic substrates as well as influences 

from other organisms. The major categories of KEFs include trophic, nutrient, 

organismal, disease, soil, wood, water, and vegetation relations. In the databases, 

environmental correlates and KEFs are mostly represented categorically and should 

be viewed as working hypotheses of species’ environmental and ecological relations. 

The specific categories of environmental correlates and KEFs pertinent to wood 

decay elements are listed in table 1. I queried the databases to determine which 

individual wildlife species and species groups have snags, down wood, and other 

wood decay elements as part of their environmental correlates and ecological 

functional roles. I summarized database queries across species taxonomic classes and 

arrayed the KEFs as functional webs (Marcot and Vander Heyden 2001). Functional 

webs display the array of ecological roles and environmental correlates pertaining to 

species associated with wood decay elements. 
Functional Basis for Managing Wood Decay—Marcot 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 897 

Table 1―Categories of key environmental correlates (habitat elements) and key ecological 

functions of wildlife species related to wood decay elements, from the Oregon-Washington 

Species Habitat Project (Johnson and O’Neil 2001). Category numbers refer to the 

classification systems developed for the species databases. (Similar categories were first 

developed for the Species-Environment Relations database for the Interior Columbia Basin 

Ecosystem Management Project; Marcot and others 1997.) 

Key Environmental Correlates (Habitat Elements): 

 

Forest/woodland elements: 

 

Down wood: 

1.1.1 down wood (includes downed logs, branches, 

and root wads, in any context) 

1.1.1.1 decay class 

1.1.1.1.1 hard [class 1, 2] 

1.1.1.1.2 moderate [class 3] 

1.1.1.1.3 soft [class 4, 5] 

1.1.1.2 down wood in riparian areas 

1.1.1.3 down wood in upland areas 

1.1.2 litter 

1.1.3 duff 

 

Snags: 

1.1.14.1 snags 

1.1.14.1.1 decay class 

1.1.14.1.1.1 hard [class 1,2] 

1.1.14.1.1.2 moderate [class 3] 

1.1.14.1.1.3 soft [class 4,5] 

1.1.14.2 snag size (dbh) 

1.1.14.2.1 seedling <1" dbh 

1.1.14.2.2 sapling/pole 1-9" dbh 

1.1.14.2.3 small tree 10-14" dbh 

1.1.14.2.4 medium tree 15-19" dbh 

1.1.14.2.5 large tree 20-29" dbh 

1.1.14.2.6 giant tree >30" dbh 

 

Other wood decay elements: 

1.1.14.4 mistletoe brooms/witches brooms 

1.1.14.5 dead parts of live tree 

1.1.14.6 hollow living trees (chimney trees) 

1.1.14.7 tree cavities 

1.1.14.8 bark (includes crevices/fissures, loose or 

exfoliating bark) 

1.1.14.9 live remnant/legacy trees 

 

Shrubland/grassland 

elements: 

 

Snags: 

1.2.12.1 snags 

1.2.12.1.1 decay class 

1.2.12.1.1.1 hard 

1.2.12.1.1.2 moderate 

1.2.12.1.1.3 soft 
Functional Basis for Managing Wood Decay—Marcot 

898 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

(table 1 continued) 

Snags (continued): 

1.2.12.2 snag size (dbh) 

1.2.12.2.1 shrub/seedling <1" dbh 

1.2.12.2.2 sapling/pole 1-9" dbh 

1.2.12.2.3 small tree 10-14" dbh 

1.2.12.2.4 medium tree 15-19" dbh 

1.2.12.2.5 large tree 20-29" dbh 

1.2.12.2.6 giant tree >30" dbh 

 

Key Ecological Functions: 

 

Down wood: 

6.1 physically fragments down wood 

 

Snags: 

3.9 primary cavity excavator in snags or live trees 

3.10 secondary cavity user 

6.2 physically fragments standing wood 

8.1 creates standing dead trees (snags) 

Clustering Wood Decay Elements by Species Usage 

I developed a table listing each vertebrate wildlife species’ use of eight wood 

decay elements: snags, remnant, or legacy trees (which may have dead parts), 

mistletoe and witch’s brooms, dead parts of live trees, hollow living trees, tree 

cavities, bark crevices, and down wood (coarse woody debris). I depicted use as a 

binary function: 1 if a species was associated, 0 if not. I then calculated binary 

similarity coefficients among the wood decay elements based on species’ use, and a 

hierarchical cluster classification using single linkage (nearest neighbor) and 

Euclidean distances among clusters. Results describe the similarity of wood decay 

elements according to usage by wildlife species. 

Depicting the Functional Web 

I queried the SHP database to determine the KEFs associated with species tied 

to wood decay elements. I also queried the ICBEMP database to determine the KEFs 

of invertebrates associated with wood decay elements. Results depict the kinds, 

breadth, and redundancy of ecological functions of both vertebrate wildlife species 

and invertebrate species associated with wood decay. This information is also part of 

the DecAID wood decay management advisory model (Mellen and others 2002). 
Functional Basis for Managing Wood Decay—Marcot 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 899 

Results and Discussion―Environmental Relations And 

Functional Roles Of Species Associated With Wood 

Decay Elements 

Relations of Wildlife and Wood Decay Elements 

In this section I describe patterns of terrestrial vertebrate wildlife species in 

Washington and Oregon that are related to wood decay elements. This assessment 

helps determine which sets of species may be uniquely provided by the various wood 

decay elements. 

Standing Tree Elements 

In Washington and Oregon, a total of 96 wildlife species are associated with 

snags in forest (93 species) or grassland/shrubland (47 species) environments. In 

forest environments, these include 4 amphibian, 63 bird, and 26 mammal species (fig. 

1). In addition, 51 wildlife species are associated with tree cavities, 45 with dead 

parts of live trees, 33 with remnant or legacy trees (which may have dead parts), 28 

with hollow living trees, 21 with bark crevices, and 18 with trees having mistletoe or 

witch’s brooms. 

Figure 1―Number of wildlife species associated with standing wood decay elements 

in forest habitats of Washington and Oregon. (Data are from the Oregon-Washington 

Species Habitat Project [Johnson and O’Neil 2001]). 
Functional Basis for Managing Wood Decay—Marcot 

900 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Of the 93 wildlife species associated with snags in forest environments, 21 are 

associated with hard snags (snag decay classes 1 and 2), 20 with moderately decayed 

snags (snag decay class 3), and 6 with soft snags (snag decay classes 4 and 5) (fig. 2).

Five of the 21 species are associated only with hard snags: great blue heron (Ardea 

herodias), hooded merganser (Lophodytes cucullatus), pileated woodpecker 

(Dryocopus pileatus), pygmy nuthatch (Sitta pygmaea), and wood duck (Aix sponsa).

Three of the 20 species are associated only with moderately decayed snags: northern 

flying squirrel (Glaucomys sabrinus), ruffed grouse (Bonasa umbellus), and whiteheaded woodpecker (Picoides albolarvatus) (although white-headed woodpecker 

might not associate only with moderately decayed snags in eastside pine forests 

[Laudenslayer, pers. comm.]). Only chestnut-backed chickadee (Parus rufescens) 

was associated solely with soft snags. The remainder of the 93 species use two or 

more snag decay groups. According to the SHP database, most snag-using wildlife 

species are associated with snags > 36 cm diameter at breast height (dbh), and about 

a third of these species use snags > 74 cm dbh (fig. 3; Marcot and others 2002). 

Figure 2―Number of wildlife species associated with three decay stages of snags in 

forest habitats of Washington and Oregon. (Data are from the Oregon-Washington 

Species Habitat Project [Johnson and O’Neil 2001]). 

Down Wood Elements 

In forest environments, 74 wildlife species are associated with down wood 

(coarse woody debris), 28 with litter (undecomposed fine woody debris), and 11 with 

duff (decomposed woody debris and other vegetation matter underlying the litter 

layer) (fig. 4). Of these species, 58 are associated exclusively with down wood, 10 

exclusively with litter, and none exclusively with duff. 
Functional Basis for Managing Wood Decay—Marcot 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 901 

Figure 3―Number of wildlife species associated with size classes (dbh or diameter 

at breast height) of snags in forest habitats of Washington and Oregon. (Data from 

the Oregon-Washington Species Habitat Project [Johnson and O’Neil 2001]). 

Figure 4―Number of wildlife species associated with terrestrial wood decay 

elements in forest habitats of Washington and Oregon. (Data from the OregonWashington Species Habitat Project [Johnson and O’Neil 2001]). 
Functional Basis for Managing Wood Decay—Marcot 

902 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Similarity in Wood Decay Use 

As may be expected, different species tend be associated with snags and down 

wood. Of 184 wildlife species associated with either snags or down wood, only 30 

use both, 86 use down wood and not snags, and 128 use snags and not down wood. 

Similar trends appear when considering the fuller array of species associated 

with other wood decay elements. Results of clustering wood decay elements by 

species usage (fig. 5) suggest that the most unique sets of wildlife species (at least 50 

percent dissimilar in species associations) are those that use mistletoe or bark 

crevices. Intermediate in similarity are the sets of wildlife species using live hollow 

trees, live remnant or legacy trees, and down wood. The most similar are the sets of 

wildlife species that use tree cavities, snags, and dead parts of live trees, although 

there are still substantial differences in the species associated with each of these three 

elements. This analysis suggests that no one wood decay element provides for all 

wildlife species associated with wood decay. 

Figure 5―Hierarchical cluster classification of wood decay elements by wildlife 

species association in forest habitats of Washington and Oregon. Wood decay 

elements with greater similarity of species usage have shorter between-cluster 

distances than do elements with greater dissimilarity. Data on the 162 species used 

in this analysis were binary (associated or not with each element), and clustering was 

done using single linkage (nearest neighbor) with Euclidean distances based on a 

binary correlation matrix. (Data are from the Oregon-Washington Species Habitat 

Project [Johnson and O’Neil 2001]). 

Functional Roles of Vertebrate Wildlife Species Associated 

with Wood Decay Elements 

Results presented so far pertain to the traditional approach to depicting wildlifehabitat relations. Taking a more functional view adds a new dimension to this 

approach by depicting the varieties of KEFs, beyond those pertaining just to wood 

decay, performed by wildlife species that are associated with wood decay elements 

(Machmer and Steeger 1995). Such ecological roles comprise a surprisingly broad 

array of functional categories, spanning many trophic and dietary relations, dispersal 

roles, and organismal, soil, wood, water, and vegetation relations. 
Functional Basis for Managing Wood Decay—Marcot 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 903 

As an example, I will focus on the functional web of wildlife species in 

Washington and Oregon associated with down wood in forest environments (fig. 6),

as depicted in the SHP databases. This set includes 86 species of heterotrophs and 59 

species that serve as prey for other species. Of the heterotrophs, 57 percent are 

primary consumers, 77 percent are secondary consumers, and others (each < 10 

percent) comprise tertiary consumers, carrion feeders, cannibals, and coprophages 

(percentages may sum > 100 because some species play multiple roles). Of the 49 

primary consumer species associated with down wood, 53 percent are spermivores 

(seed-eaters), 43 percent are fungivores (fungi-eaters), 29 percent are grazers, 27 

percent are frugivores (fruit-eaters), and the rest (each < 20 percent) comprise 10 

other primary consumption categories. Of the 66 secondary consumer species 

associated with down wood, 88 percent are insectivores (consume insects and other 

invertebrates), 33 percent are vertebrate predators, 20 percent are ovivores (eggeaters), and 6 percent are piscivores (fish-eaters). It may come as a surprise to some 

managers that down wood provides habitat, at least in part, for so wide an array of 

species with such a broad set of trophic and dietary functions. 

Organismal relations of wildlife associated with down wood include a number 

of symbiotic and other interspecific interactions beyond those related to dietary and 

trophic habits. Of the 86 wildlife species associated with down wood, 38 percent 

serve as dispersal agents, transporting plants or animals. Of this set, 29 species 

disperse seeds and fruits, 10 disperse fungi, 7 disperse lichens, 1 disperses plants, and 

1 disperses invertebrates. 

Other organismal relations supported by down wood include potential control of 

insect or vertebrate populations, pollination, creation of feeding or nesting 

opportunities for other species, and serving as hosts for nest parasites. 

Some organismal relations are symbiotic functions. For example, seven wildlife 

species associated with down wood create feeding or nesting structures that are in 

turn used by other species. Four wildlife species associated with down wood are also 

primary cavity excavators and 13 are secondary cavity users. Twenty-six wildlife 

species associated with down wood are primary burrow excavators, and another 29 

species are secondary burrow-users. Fourteen wildlife species associated with down 

wood are primary creators of terrestrial runways and paths, and another 29 species 

are secondary users of runways and paths created by other species. 

Twenty-three wildlife species associated with down wood can potentially 

improve soil structure and aeration by burrowing and digging. This, in turn, could 

help maintain or improve soil conditions for plants and other animals. 

Through digging, gnawing, and probing, mostly for foraging, two wildlife 

species associated with down wood serve to fragment standing wood, seven fragment 

down wood, and 2 kill trees and create snags. This could have positive feedback 

ramifications for providing for species associated with wood decay elements and for 

initiating the incorporation of organic matter into soils. 

Two ungulate species associated with down wood can create small ponds and 

wetlands by wallowing. There are seven mammal species associated with down wood 

that browse on trees or shrubs, and four mammal species that graze on grasses or 

forbs, that can alter vegetation composition, structure, cover, and seral conditions for 

other species. 
Functional Basis for Managing Wood Decay—Marcot 

904 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Figure 6―The ecological “functional web” of down wood, showing the number of 

associated wildlife species and their key ecological functions (ecological roles they 

play) in forest habitats of Washington and Oregon. (Data are from the OregonWashington Species Habitat Project [Johnson and O’Neil 2001]). 

In summary, down wood can be viewed as the center of a “functional web” of 

ecological roles. As such, down wood, or any of the wood decay elements, provides 

at least some of the habitats used by many wildlife species that in turn can influence 

their environment and other species in diverse and unexpected ways. Further, 

functional webs can be described for each of the wood decay elements (figs. 1-4), and 

the webs differ slightly or greatly among the elements. For example, there tends to be 

a lesser percentage of primary consumer wildlife species associated with snags (40 

percent of all heterotrophs associated with snags) than with down wood (57 percent 

of all heterotrophs associated with down wood), and a greater percentage of 

secondary consumers associated with snags (95 percent) than with down wood (77 

percent). Grazers and foliovores comprise a greater percentage of primary consumers 

associated with down wood (29 percent and 18 percent of all down wood-associated 

primary consumers, respectively) than with snags (8 percent and 11 percent, 

respectively). These differences suggest that no single wood decay element provides 

for all functional groups of wildlife and that different wood decay elements play 

complementary roles in providing for all functions collectively. 
Functional Basis for Managing Wood Decay—Marcot 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 905 

Functional Roles of Invertebrate Species Associated with 

Wood Decay Elements 

The ICBEMP database includes selected individual species and functional 

groups of invertebrates. In general, invertebrates play key ecological roles, in forest 

ecosystems of the western U.S., pertaining to wood decay functions (Schowalter and 

others 1997). Their ecological roles are poorly studied and no complete functional 

web can be described for them. However, a few examples can be provided. 

Invertebrates associated with down wood in the interior Columbia Basin span a 

range of KEF categories and ecological roles. Here are some examples. As an 

associate of down wood, the checkered beetle Enoclerus sphegeus (Coleoptera: 

Cleridae) is an important predator of bark beetles (Coleoptera: Scolytidae) and other 

subcortical beetles and provides a trophic link in the exo- and sub-cortical 

microhabitats in snags and coarse woody debris. A number of wood-boring 

and―chewing insects associated with down wood, including the carpenter ant 

Camponotus modoc, greatly aid wood fragmentation and decomposition. 

Several invertebrates associated with down wood collaborate in pollination and 

production of native fruits and seeds used as food by mammals, birds, ants, and other 

frugivorous or spermivorous insects. Examples include a number of bee species 

(Hymenoptera), such as small carpenter bees (Ceratina acantha, Anthophoridae), 

plasterer bees (Hylaeus lunicraterius, Colletidae), and several species of leafcutting 

bees (Ashmeadiella sculleni, Hoplitis fulgida, Hoplitis productua subgracilis, Osmia 

bruneri, Osmia cascadica, Proteriades orthognathus, and others; Megachilidae). 

Even more bee species (especially of family Megachilidae) performing this function 

are associated with snags. 

The gossamer-winged butterfly (Mitowra johnsoni; Lycaenidae: Lepidoptera) is 

an example of an invertebrate associated with mistletoe brooms. In its larval form, 

this species is a defoliating herbivore, but it also serves as food for birds, small 

mammals, and predaceous invertebrates. 

Even bark beetle species such as Scolytus ventralis (Scolytidae: Coleoptera) 

have useful ecological functions. By killing trees, this species and its kin may 

increase likelihoods of stand-replacing fires by increasing standing and down woody 

debris. In some management plans, this is not a desirable outcome. However, this 

ecological function has secondary beneficial effects of promoting nutrient cycling, 

and altering tree density, canopy structure, age distribution, and species composition 

of stands. This provides habitat for a wide variety of plants and animals. Bark beetles 

of many species also serve as prey for woodpeckers and other vertebrate species 

(Otvos 1965). 

In summary, invertebrates associated with wood decay elements play multiple 

ecological roles in forest ecosystems, many of them beneficial to other plant and 

animal species. 
Functional Basis for Managing Wood Decay—Marcot 

906 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Management Implications for Structures and Functions 

Considering Ecological Functions in Ecosystem 

Management 

It is well known that many land and resource management activities change the 

type, amount, and distribution of wood decay elements. Less well known are the 

ramifications of those changes on the functioning of ecosystems. 

The SHP databases include a table listing wildlife habitat elements that can be 

directly affected by management activities. The database includes 152 categories of 

management activities listed under 13 general headings of types of land use such as 

fire management, riparian and aquatic resource management, road management, 

agriculture, mining, forest management, and others (Vander Heyden and Marcot 

2001). The database indicates that the wood decay elements (figs. 1, 4) are potentially 

influenced by 44 types of management activities across 9 general headings of land 

use. Clearly, the potential influence of management on wood decay elements for 

wildlife is not trivial. 

If resource management is to provide for “fully functional” ecosystems―one of 

the possible goals of ecosystem management (e.g., Goldstein 1999)―then the 

approach offered in this paper provides one way of determining the degree to which 

an ecosystem is fully functional. The manager can specify land management 

activities under consideration and then determine which habitat elements and 

associated species could be influenced by the activities (positively or negatively). 

Then, the manager can determine the set of KEF categories associated with the 

affected species and compare this with other alternative management activities or 

expected changes in wildlife habitats, structures, and elements over time. 

What patterns should the manager look for? A listing of species- and 

community-patterns of ecological functions was offered by Marcot and Vander 

Heyden (2001). One functional pattern that can be easily determined by querying the 

databases discussed includes that of functional redundancy or the number of different 

wildlife species with the same KEF. As functional redundancy declines, the degree to 

which the community can resist or be resilient to perturbations may also decline 

(MacNally 1995, Naeem 1998). Other functional patterns of potential interest to 

ecosystem managers may include calculating functional richness and total functional 

diversity, describing functional webs and functional profiles, mapping functional hot 

and cold spots, identifying functional keystone and critical link species, and 

identifying other patterns and examples (Marcot and Vander Heyden 2001). 

I interpret the results as testable working hypotheses of ecological roles and 

relations, and I challenge resource managers to think broadly about the functional 

roles of organisms associated with wood decay elements as a facet of ecosystem 

management. Overall, it is my assumption that degrading the functional matrix of a 

community serves to decrease its resilience, stability, natural diversity, and even 

sustainable productivity for desired conditions and products. The manager can 

determine the risk of such degradation by evaluating how a specific set of proposed 

activities can affect functional patterns associated with wood decay elements. 

The manager might also assess KEFs of wildlife in the context of the capability 

of the land to produce wood decay elements. Forest and woodland stands differ in 

their capacity to produce dead wood elements. Such capacity typically changes over 

time as well, and is related to site condition and history, stand structure, occurrence 
Functional Basis for Managing Wood Decay—Marcot 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 907 

of abiotic disturbances such as fire and wind, and other site and landscape factors, as 

well as to some of the ecological roles of organisms, as discussed above, that can 

serve to create or alter wood decay elements. Managing to maintain functional roles 

and groups of organisms, by managing for habitats and environmental conditions 

providing for organisms with desired ecological roles (KEF categories), should 

account for site and landscape conditions that also affect the distribution and 

abundance of wood decay and other habitat elements. 

The analysis showed that no one wood decay element provides for all wildlife 

species associated with wood decay. In fact, it seems that all wood decay elements 

included in this analysis may be necessary to provide for all associated wildlife 

species. Thus, the manager might attend to the fate of all such elements, at least to 

help determine which associated species and functions would be provided. Because 

many of the elements of wood decay are not necessarily represented by snags per se, 

the manager may wish to explicitly include them along with snags in stand 

inventories and in management plans. At the least, managers could determine the 

influence of forest management actions on such elements and on the wildlife and 

their ecological functions associated with them. 

Validation 

Plainly, much empirical research remains to be done to verify and quantify the 

ecological functions of wildlife species, including those associated with wood decay 

elements and especially invertebrates. I have not discussed such functional roles of 

fungi, lichens, bryophytes, vascular plants, and microorganisms, but those associated 

with wood decay elements play many key roles in ecosystems and most need sound 

study. 

Also needing further explication and study is that of quantity: how much 

functionality is enough? How much would match historic, or reference, landscapes 

and desired stand conditions? There is scant research available on the rates of 

ecological roles, such as nutrient redistribution by snag-using bats, or control of 

populations of micorhizzal fungivorous springtails by predatory spiders associated 

with down wood as can affect commercial tree production. 

A related information need is how to distribute wood decay elements in space 

and time to provide for ecological functions of desired associated organisms. Work in 

progress (Marcot and others, in preparation) and recent inventory analyses (Ohmann 

and Waddell 2002) suggest that management standards for numbers of snags and 

down wood in forests of the Pacific Northwest have been far too low as compared 

with unharvested reference conditions, and that densities and local distributions (such 

as clumping) of snags and down wood vary considerably within and among stands 

and according to a variety of local disturbance factors. 

I expect that many of the ecological functional relations described in this 

chapter, even for relatively well-known vertebrate wildlife species, will change in 

kind or degree with empirical study. My intent here is to provide a framework from 

which such functions can be repeatably described as working management 

hypotheses, and then tested through experimental studies in the field. Ultimately, the 

aim is to validate the degree to which land and resource management activities serve 

to support, restore, or compromise the functional vitality of natural communities and 

the sustainable production of resources. 
Functional Basis for Managing Wood Decay—Marcot 

908 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Conclusions 

I challenge land and resource managers to think functionally when prescribing 

activities that influence snags, down wood, hollow trees, and other wood decay 

elements. It is time to move beyond simply identifying which wildlife species (plants 

and animals) are associated with wood decay elements. The approach offered here 

can provide a practical method of establishing standards and guidelines for managing 

attributes that have ecological value but in the past have been ignored or deliberately 

selected against. 

Describing the direct ecological roles of wood decay, including soil 

stabilization, organic matter input to soils, nutrient cycling, provision of 

microhabitats for plants and animals, and other direct ecological benefits (e.g., Means 

and others 1992, O’Connor and Harr 1990), is an important step toward a more 

functional approach to wood decay management. However, a next major step is to 

describe the fuller functional web of the ecological roles of wildlife species that are 

in turn associated with wood decay elements. From this approach, the manager can 

determine the degree to which their management actions will provide for fully 

functional ecosystems, and how management activities influencing wood decay 

components can affect that functionality. 

Acknowledgments 

Many thanks to Madeleine Vander Heyden for reviewing the manuscript. My 

appreciation to all the expert panelists of ICBEMP who originally contributed ideas 

on the ecological functions of plants and animal species, from which I developed an 

ecological functions classification system. Chris Niwa and Roger Sandquist were 

instrumental in providing the information on invertebrates for the ICBEMP database. 

My thanks to Barbara Wales of ICBEMP for overseeing the development of that 

project’s species database. Madeleine Vander Heyden helped refine the ecological 

functions classification and database for non-fish vertebrates in Washington and 

Oregon, and David Johnson and Tom O’Neil ensured the development of the 

databases, under the Oregon-Washington Species-Habitat Project. 

References 

Goldstein, P. Z. 1999. Functional ecosystems and biodiversity buzzwords. Conservation 

Biology 13(2): 247-255. 

Johnson, David H.; O’Neil, Thomas A., eds. 2001. Wildlife habitats and species 

associations in Oregon and Washington: building a common understanding for 

management. Corvallis, OR: Oregon State University Press. 

Machmer, M. M.; Steeger, C. 1995. The ecological roles of wildlife tree users in forest 

ecosystems. Victoria, British Columbia, Canada: Crown Publications, Inc.; 54 p. 

MacNally, R. C. 1995. Ecological versatility and community ecology. New York, NY: 

Cambridge University Press; 453 p. 

Marcot, Bruce G.; Castellano, Michael A.; Christy, John A.; Croft, Lisa K.; Lehmkuhl, John 

F.; Naney, Robert H.; Nelson, Kim; Niwa, Christine G.; Rosentreter, Roger E.; 

Sandquist, Roger E.; Wales, Barbara C.; Zieroth, Elaine. 1997. Terrestrial ecology 

assessment. In: Quigley, Thomas M.; Arbelbide, Sylvia J., editors. An assessment of 

ecosystem components in the interior Columbia Basin and portions of the Klamath and
Functional Basis for Managing Wood Decay—Marcot 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 909 

Great Basins. Volume III. Gen. Tech. Rep. PNW-GTR-405. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 1497-

1713. 

Marcot, Bruce; Mellen, Kim; Livingston, Susan A.; Ogden, Cay. 2002. The DecAID 

advisory model: wildlife component. In: Laudenslayer, William F., Jr.; Shea, Patrick 

J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume].

Marcot, Bruce G.; Vander Heyden, Madeleine. 2001. Key ecological functions of wildlife 

species. In: Johnson, David; O'Neil, Thomas, editors. Wildlife habitats and species 

associations within Oregon and Washington landscapes―building a common 

understanding for management. Corvallis, OR: Oregon State University Press; 168-186. 

Means, Joseph E.; MacMillan, P. C.; Cromack, Jr., K. 1992. Biomass and nutrient content 

of Douglas-fir logs and other detrical pools in an old-growth forest, Oregon, U.S.A.

Canadian Journal of Forrest Research 22: 1536-1546. 

Mellen, Kim; Marcot, Bruce G.; Ohmann, Janet L.; Waddell, Karen L.; Willhite, Elizabeth 

A.; Hostetler, Bruce B.; Livingston, Susan A.; Ogden, Catherine. 2002. DecAID: a 

decaying wood advisory model for Oregon and Washington. In: Laudenslayer, 

William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, 

Thomas E., technical coordinators. Proceedings of the symposium on the ecology and 

management of dead wood in western forests. 1999 November 2-4; Reno, NV. Gen. 

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; [this volume]. 

Morrison, Michael L.; Marcot, Bruce G.; Mannan, R.William. 1998. Wildlife-habitat 

relationships: concepts and applications. 2d edition. Madison: University of 

Wisconsin Press; 435 p. 

Naeem, S. 1998. Species redundancy and ecosystem reliability. Conservation Biology 

12(1): 39-45. 

Neitro, William A.; Binkley, V. W.; Cline, Steven P.; Mannan, R. William; Marcot, Bruce G.; 

Taylor, D.; Wagner, F. F. 1985. Snags (wildlife trees). In: Brown, E. Reed, ed. 

Management of wildlife and fish habitats in forests of western Oregon and Washington. 

Part 1—chapter narratives. Portland OR: USDA Forest Service; 129-169. 

O’Connor, M.; Harr, R. D. 1990. The role of coarse woody debris in sediment routing in 

forested watersheds. The Northwest Environmental Journal 6: 429-430. 

Ohmann, Janet L.; Waddell, Karen L. 2002. Regional patterns of dead wood in forested 

habitats of Oregon and Washington. In: Laudenslayer, William F., Jr.; Shea, Patrick 

J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, Thomas E., technical 

coordinators. Proceedings of the symposium on the ecology and management of dead 

wood in western forests. 1999 November 2-4; Reno, NV. Gen. Tech. Rep. PSW-GTR181. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department 

of Agriculture; [this volume]. 

Otvos, I. S. 1965. Studies on avian predators of Dendroctonus brevicomis LeConte 

(Coleoptera, Scolytidae) with special reference to Picidae. Canadian Entomology 

97:1184-1199. 

Schowalter, Timothy; Hansen, Eric; Molina, Randy; Zhang, Y. 1997. Integrating the 

ecological roles of phytophagous insects, plant pathogens, and mycorrhizae in 

managed forests. In: Kohm, Katherine A.; Franklin, Jerry F., editors. Creating a 
Functional Basis for Managing Wood Decay—Marcot 

910 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

forestry for the 21st century: the science of ecosystem management. Washington, DC: 

Island Press; 171-189. 

Vander Heyden, Madeleine; Marcot, Bruce G. 2001. Terrestrial and marine management 

activities: links to habitat elements and ecological processes. In: Johnson, David; 

O’Neil, Thomas, eds. Wildlife-habitat relationships in Oregon and Washington. 

Corvallis OR: Oregon State University Press; 501-511. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 911 

A Case Study of Habitat Conservation Plans 

and the Protection of Snags and Coarse 

Woody Debris on Industrial Forest Lands1

Lorin L. Hicks2 and Henning C. Stabins2

Abstract 

Forest practices on private industrial timberlands have steadily progressed to incorporate 

many of the issues and approaches currently in use on public forests. One of the most 

significant advances for protecting wildlife habitat on private lands has been the development 

of Habitat Conservation Plans (HCP). Originally developed as a planning process for 

landowners to mitigate for the incidental status of threatened and endangered species, HCPs 

have expanded to become long-term, multi-species landscape plans designed to address many 

aspects of wildlife and fish management. Plum Creek completed a 50-year HCP for 64,751 

hectares of company land in Washington’s central Cascades Mountains in June 1996. The 

HCP addresses the biological needs of all vertebrate species, including anadromous fish and 

cavity-dependent wildlife. 

Introduction 

The recognition of snags and coarse woody debris as important wildlife habitat 

elements and their retention on the landscape has been one of the most dramatic 

changes to commercial forest practices in recent years. Similarly, Habitat 

Conservation Planning as authorized under the Endangered Species Act has recently 

provided the opportunity for industrial landowners to develop innovative land 

management plans with the federal government. These plans provide not only 

substantive habitat protections for fish and wildlife resources but also regulatory 

predictability for private landowners. This paper discusses the development and 

implementation of Plum Creek’s Cascades Interstate-90 (I-90) Habitat Conservation 

Plan (HCP; Anonymous 1996a), with particular emphasis on how the plan addresses 

habitat needs for wildlife associated with snags and coarse woody debris. 

Landowner Considerations 

The content and configuration of landowners’ properties is an important 

determinant to landscape planning. A major portion of Plum Creek’s ownership in 

the Cascades Mountains of Washington is in the I-90 corridor near Snoqualmie Pass, 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Director, Fish and Wildlife Resources and Wildlife Biologist, Rockies Region, respectively, Plum 

Creek Timber Company, Seattle, Washington. Mailing address: 999 Third Avenue, Suite 2300, Seattle, 

WA 98104 (e-mail addresses: lorin.hicks@plumcreek.com and henning.stabins@plumcreek.com) 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

912 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

96 kilometers east of Seattle. The region supports many important resources and 

potentially conflicting land uses, such as roadless and motorized recreation, 

agriculture, water storage, highways, powerline and railroad routes, ski areas, 

communities, and recreational development. The intense and growing public use of 

this area places commercial forestry in a highly visible operating arena. 

Another feature of Plum Creek’s property in the region is the “checkerboard” 

pattern of intermingled ownership with the USDA Forest Service. This ownership 

pattern stems from the railroad land grants of the late 1800s and presents a challenge 

for both public and private land managers. Despite the completion of land exchanges 

to resolve this dilemma, the pattern continues to exist in many areas and requires 

landowners to coordinate and communicate closely on protection of public resources. 

Lessons Learned from Past Management 

Over the past 20 years, a major paradigm shift has occurred in commercial forest 

management. Driving this paradigm shift is the realization that forest practices 

intended to protect wildlife and fish habitat were actually having the opposite effect. 

For instance, dispersing clearcuts was thought to be good for habitat diversity but 

now increases the risk of forest fragmentation. Mandatory stream cleanout to remove 

logging debris was considered prudent to avoid debris dams; however, we now know 

that this practice removed the large wood essential for bank stability and fish habitat. 

Finally, increased use of dead and defective trees and removal of “danger trees” was 

considered efficient years ago but has been shown to contribute to reduction in 

habitat for cavity-dependent wildlife. 

The listing of the northern spotted owl (Strix occidentalis) in 1990 created yet 

another force for changing paradigms on private lands. Experiments with “New 

Forestry” concepts of retaining structural components from older forests laid the 

groundwork for this paradigm on Plum Creek lands (Hicks 1991, Kohm and Franklin 

1997). Silvicultural experiments to extract high-value timber while retaining 

functional spotted owl habitat confirmed that spotted owls could use post-harvest 

stands that normally would have been clearcut and regenerated under conventional 

practices.3

 Moreover, silvicultural alternatives that focused on retention of down logs, 

standing snags, and residual large green trees provided habitat for a wide variety of 

wildlife species (Stofel 1993). 

The need for a new paradigm was both biological and economic. Federal and 

state regulations (Anonymous 1991, 1992, 2000) to address spotted owl habitat 

required the designation of 2.9 kilometer radius circles around spotted owl nest sites 

and the retention of 40 percent (approximately 1,052 hectares) of the area within the 

circle as owl habitat. In 1994, Plum Creek had 107 owl protection circles affecting its 

ownership in the I-90 corridor. 

Incentives for Habitat Conservation Planning 

The voluntary Habitat Conservation Planning process, added to the Endangered 

Species Act (ESA) in 1982, was little understood and seldom used by private 

landowners until recently (Anonymous 1995). Increased interest in HCPs stems in 

 

3

 Unpublished data on file, Plum Creek Timber Company, Seattle, Washington. 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 913 

part from the desire to lessen the economic impact resulting from the ESA’s 

prohibition and from the U.S. Department of Interior’s policies offering regulatory 

incentives. These incentives, including pre-listing agreements, multi-species permits, 

the No Surprises policy, and Safe Harbor agreements, provide valuable regulatory 

certainty to the private landowner willing to commit the resources to complete an 

HCP (Anonymous 1996b). 

For a private landowner like Plum Creek in the Pacific Northwest, the incentives 

to do an HCP include the following: 

• Social―People’s changing expectations for forestry. 

• Scientific―Ecosystem management; assure sustained production of all forest 

resources. 

• Political―Approval and implementation of the Northwest Forest Plan 

(Anonymous 1994) on Federal lands and checkerboard ownership patterns. 

• Legislative―Endangered Species Act mandates the HCP process. 

• Economic―Owl circles and associated costs. 

Description of Plum Creek’s Cascades HCP 

Plum Creek’s Cascades HCP currently covers seven listed species under the 

incidental take permit: spotted owl, marbled murrelet, grizzly bear, gray wolf, 

Canada lynx, steelhead salmon, and bull trout. The plan also identifies over 280 other 

unlisted vertebrate species in the Implementation Agreement. The planning period of 

50 years can be extended to 100 years if certain conditions are met at the end of the 

first 50-year period. The plan was based on both a habitat and species-specific 

approach. 

The HCP was developed as an ecosystem management plan designed to 

complement the Northwest Forest Plan for Federal lands. Approaches and strategies 

in the HCP are tiered to those in the Northwest Forest Plan, such as the protection of 

spotted owl sites near Late Successional Reserves and the extension of a riparian 

reserve network onto the company’s lands. 

The HCP is based on a forest stand classification system that describes forest 

conditions from stand initiation to old-growth. Conditions were mapped across all 

ownerships in the 169,162 hectare planning area. Two hundred and eighty-five 

species of animals known in the HCP area were grouped into guilds based on their 

life history requirements. These guilds, termed “Lifeforms,” were then associated 

with one or more forest stand types of the classification system to identify their 

suitable breeding habitat. These forest stand structures and habitats are “grown” into 

the future using forest growth models that integrate differing harvest levels among 

State, Federal, and private landowners. At any point in the future, the amounts and 

locations of these forest stand types and habitats can be estimated. 

Since riparian areas are important to many fish and wildlife species, a riparian 

management strategy was developed. These areas not only provide the necessary 

protection of elements important for in-stream habitat conditions, such as large 

woody debris, temperature moderation, nutrient input, and erosion control, but these 

areas also provide habitat and dispersal routes for upland species. A network of 

riparian habitat areas forms the core of the HCP’s wildlife habitat protection strategy. 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

914 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

In addition, 38 mitigation measures were developed to provide species-specific 

protection or add to general wildlife and fisheries conservation. Examples of these 

mitigation measures include: 

• Completing comprehensive watershed analyses for the majority of the 

planning area. 

• Maintaining a minimum of 6 percent of the company’s ownership as spotted 

owl nesting, roosting, and foraging habitat.

• Deferring from harvest 751 hectares of owl habitat for 20 years at key owl 

sites.

• Surveying 104 hectares of suitable marbled murrelet habitat.

• Employing a variety of management practices to provide secure grizzly bear 

habitat in the North Cascades Recovery Zone. 

• Delaying operations near active spotted owl and northern goshawk nest sites 

until after the breeding season.

• Adjusting operations to reduce potential disturbance to gray wolves and their 

den sites.

• Maintaining forested wetlands and buffer zones surrounding cave entrances 

and talus slopes. 

How Snag and Course Woody Debris Issues Were 

Addressed in the HCP 

Mitigation measures in the HCP established desired density levels for defective 

trees, recruitment trees, and course woody debris (CWD) for post-harvest conditions 

(e.g., three wildlife reserve trees, three green recruitment trees, and two down logs 

for each acre harvested). Wildlife reserve trees are defined as defective or deformed 

live trees or dead snags that are observably sound, not hazardous to workers, and can 

be retained during the harvest (Anonymous 2000). Green recruitment trees are live 

trees that could serve as wildlife reserve trees in the future. The abundance and 

density of these structural elements are also measured in the forest stands 

representing structural classes to validate the wildlife-habitat associations made 

during modeling. Snag and CWD issues were also addressed indirectly during 

analysis of fuel loading and insect damage potential across the landscape through 

time. Forest health issues that were considered in the HCP development are also 

discussed. 

Modification of Snag-dependent Wildlife Guilds and 

Modeling 

The snag-dependent wildlife guilds, Lifeforms 13 and 14, were modified during 

the HCP peer review process. Lifeform 13 contains the primary cavity excavators, 

and Lifeform 14 contains the secondary cavity users. Species within these Lifeforms 

vary with regard to the size of snags required for life history needs. To better 

associate these species with the appropriate forest stand structures that could supply 

the necessary snag sizes, these Lifeforms were each separated into subgroups based 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 915 

on species’ snag requirements. Lifeform 13 contains species such as hairy and downy 

woodpeckers and included some of the younger forest types (e.g., pole timber and 

dispersal forests) as part of their habitat associations. Lifeform 13a contains species 

such as pileated, white-headed, and Lewis’s woodpecker (which have more stringent 

requirements for large diameter snags or defective trees) and are associated with 

mature and older forest structure stages for modeling and impact analyses. Lifeform 

14 contains species such as chestnut-backed chickadees and red-breasted nuthatches. 

Lifeform 14a contains species such as the fisher and flammulated owl. 

In addition to subdividing these guilds, we recognized that due to a change in 

forestry regulations, older harvest units might not contain as many snags and 

therefore should be weighted accordingly in the Lifeform modeling and impact 

analyses. Some of the previous harvested units did not have snag and leave tree 

requirements that are in effect today. Therefore, during modeling, the previously 

harvested units were not considered to provide suitable habitat until they reached a 

stand age of 10 to 20 years old. 

Forest Health Modeling 

In order to assess the impacts of HCP implementation on forest health, models 

were constructed based on fuel loading and insect damage potential relative to stand 

age, average diameter, and tree species composition. Output from these models were 

intended to broadly estimate how the landscape would respond to the assumptions 

made for varying harvest levels among the different landowners and vegetative 

conditions across the HCP area. Results were mapped to depict the variability in 

these risk factors on the landscape and to show the change of these risks over the 50-

year HCP. The implications for species dependent on snags and CWD are that habitat 

potential is closely linked to conditions that increase the likelihood for fire and insect 

outbreaks. The modifying effect of wildfire on the density and distribution of habitat 

structural elements over the landscape is of course hard to predict, but could be a 

factor in the amount of suitable habitat available to these species in the future. 

Updating of the forest stand structure inventory and growth modeling on a periodic 

basis will assess any significant changes in the landscape as they occur. Plum Creek 

used this information to display and minimize the tradeoffs between provision for 

late successional habitat and economic risks due to forest health. The analysis also 

provided an opportunity to evaluate the cumulative benefits of conservation through a 

combination of Plum Creek’s HCP and the Federal Northwest Forest Plan. 

Increase of Snag Retention Targets on the Eastside of the 

Cascades Mountains 

One mitigation measure in the HCP was to increase the snag retention targets 

within timber harvest units on the eastside Cascades. State forestry regulations 

recognize that eastside managed forests typically have a greater variety of selective 

harvests, compared to westside even-aged management. Selective harvests, combined 

with the greater natural snag recruitment potential of eastside forests due to fire, 

insects and disease, reduced the need for greater regulatory requirements for snag 

retention. Under the HCP, Plum Creek will increase the retention target above the 

state’s requirement for these Eastside forests because much of Plum Creek’s 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

916 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

ownership provides transitional forest habitat between east and westside Cascades 

wildlife species. 

Another feature of the HCP that increases snag retention on the landscape is the 

requirement that post-harvest snag levels be calculated excluding leave trees left 

within the designated riparian habitat areas along fish-bearing and perennial streams. 

This requirement ensures that snags are left in the upland portions of the landscape 

and are not allocated only to riparian areas. 

Development of Sampling Techniques for Snags and CWD in 

the HCP Area 

A mitigation measure was developed in the HCP to increase our knowledge of 

wildlife habitat elements within the various forest stand structures on the HCP 

landscape. An inventory field procedure was developed to collect data on snags, 

CWD, and understory vegetation during timber inventory updating on the company’s 

lands. This information provides data on the abundance and density of snags and 

CWD in various size classes and decay stages. Understory vegetation data is taken in 

the form of percent cover for the three plant groups of shrubs, forbs, and grasses, in 

addition to specific berry and seed producing species. This information on specific 

habitat elements will be used to validate the assumptions (associations between the 

Lifeforms and the structural elements of forest stands) used in developing the HCP 

habitat approach. 

Snag and CWD Opportunities in the HCP 

In addition to the specific mitigation measures for snags and CWD, the HCP 

also contains mitigation measures for other species that benefit snag and CWDdependent or associated species. These additional measures are generally in the form 

of timber harvest prescriptions and leave areas that contain snags and CWD. 

The riparian strategy in the HCP was developed to not only protect and maintain 

the aquatic resources but also to provide habitat for those species that might use these 

areas as part of their life history and dispersal functions. The vegetative condition of 

these riparian areas in terms of canopy cover, tree size, and density are maintained as 

suitable northern spotted owl habitat. If these conditions are met or exceeded, some 

level of harvest in the outer zones of the riparian areas is permitted, but entry is 

generally limited and leads to retention of many of the snags and defective trees. 

Mitigation measures also address the maintenance of forested wetlands and 

protection of springs and seeps by retaining trees along their banks for erosion 

control and temperature moderation. 

Timbered buffers are also provided in the HCP for talus slopes that maintain the 

biological integrity of the site for temperature moderation and a source of future 

CWD (fig. 1). Screening buffers are also maintained along open roads within the 

North Cascades Grizzly Bear Recovery Zone to decrease bear disturbance and 

mortality associated with human use of open roads. These screening buffers are 

maintained at a tree density adequate to obscure a grizzly bear within 100 feet of an 

open road. Figure 2 shows a recently harvested unit that implemented a forested 

wetland prescription in combination with a grizzly bear screening buffer along a road 

that must be kept open to public use. 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 917 

Figure 1―Post-harvest aerial photo of a talus slope buffer prescription from the Plum 

Creek’s Cascades Habitat Conservation Plan. This mitigation measure provides 

upland snag and course woody debris retention widely distributed across the 

landscape. 

Figure 2―Post-harvest aerial photo of a forested wetland buffer and grizzly bear 

visual screening cover along open public roads in the Plum Creek’s Cascades 

Habitat Conservation Plan area. Retention of habitat structure in these settings 

provides additional benefits to cavity-dependent wildlife. 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

918 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Larger protected areas are provided in the plan at specific spotted owl and 

northern goshawk nesting areas to support foraging areas near the nest or allow for 

dispersal and connecting corridors to adjacent USDA Forest Service lands designated 

as late-successional forest reserves. Some of these HCP protection areas will not be 

entered for timber harvest for 20 years as the surrounding areas on Forest Service 

ownership grow into more suitable owl habitat. Other areas can be selectively 

harvested, but vegetative conditions again must meet the canopy cover, tree size, and 

density criteria for suitable spotted owl dispersal habitat. Commitments to the U.S. 

Fish and Wildlife Service are to increase the percentage of spotted owl habitat on 

Plum Creek lands in the HCP area from 29 percent in 2006 to 55 percent in 2045. 

All of these buffers and habitat areas provide the potential for additional snags 

and CWD in the landscape distributed among riparian areas and uplands. 

Monitoring 

Snag and CWD values are being evaluated in three areas. First, habitat 

conditions presently found in the landscape is evaluated. Second, post-harvest 

achievement of desired future conditions relative to snag and down log density is 

monitored. Lastly, the wildlife guilding assumptions used to relate wildlife species to 

HCP forest stand classes is being assessed. 

Existing habitat conditions are being sampled across all forest stand focusing on 

snags, CWD, and understory vegetation. These data are being used to evaluate the 

presence of structural elements in the eight forest stand types described in the HCP 

area. Preliminary analyses indicate that this information will be useful in describing 

how these elements are distributed in the landscape by forest stand type (tables 1, 2). 

Table 1―Preliminary data from an ongoing timber stand inventory update project 

describing snag characteristics of stands in Plum Creek’s Cascades Habitat Conservation 

Plan area, central Cascades, Washington. 

1

 Stand structures follow a successional sequence and are defined in Plum Creek’s Cascade Habitat 

Conservation Plan (Anonymous 1996a). 

 2 Hard snags are defined as decay classes 1 through 3, and soft snags are decay classes 4 and 5 

(following the classification scheme developed by Cline and others 1980). 

Stand 

structure1

No. of 

stands 

Mean 

number of 

snags per 

hectare 

Mean 

snag 

height 

(m) 

Mean snag 

diameter 

at breast 

height 

(cm) 

Pct 

hard 

snags2

Pct soft 

snags2

Stand initiation 17 1.6 6.4 56 39 61 

Shrub sapling 68 0.8 4.6 53 5 95 

Young forest 144 2.4 6.4 46 37 63 

Pole timber 96 4.0 7.0 43 56 44 

Dispersal forest 89 7.7 9.5 41 43 57 

Mature forest 91 8.1 11.3 41 47 53 

Managed old 

growth 7 4.8 11.3 38 37 63 

Old growth 3 4.8 10.1 53 43 57 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 919 

Table 2―Preliminary data from an ongoing timber stand inventory update project 

describing down wood characteristics of stands in Plum Creek’s Cascades Habitat 

Conservation Plan area, central Cascades, Washington. 

1

 Stand structures follow a successional sequence and are defined in Plum Creek’s Cascade Habitat 

Conservation Plan (Anonymous 1996a). 

2

Hard logs are defined as decay classes 1 through 3, and soft logs are decay classes 4 and 5 (following 

the classification scheme in Maser and others 1979). 

Post-harvest stands are sampled to determine if expectations with regard to the 

numbers of retained snags and down logs are being met. A random selection of 

harvest units is sampled by consulting foresters to quantify the leave trees retained in 

harvest units, following HCP guidelines. Results to date indicate that HCP 

implementation is meeting or exceeding targets. Compliance checks are also 

performed by the U.S. Fish and Wildlife Service and National Marine Fisheries 

Service, along with State agencies as part of state forestry monitoring. 

The assumptions used in guiding wildlife species to the various forest stand 

types in the HCP landscape is being evaluated. A Plum Creek/University of 

Washington project is investigating bird use of HCP forest stand types by using point 

counts, territory spot-mapping techniques, and nesting/productivity indication 

indices. This research will help verify the habitat associations for permanent resident 

birds and neotropical migrants that use forest stands in the HCP area. 

Summary 

The Plum Creek’s Cascades HCP is one of the most complex and 

comprehensive HCPs approved. The HCP is a landscape level ecosystem plan that 

was designed to work in concert with the Northwest Forest Plan for Federal lands to 

address multiple wildlife habitat issues across a large area of intermingled ownership. 

After 5 years of implementation, valuable data on species occurrence and habitat 

relationships are being collected. All this information is provided to Federal and State 

Stand 

structure1

No. of 

stands 

Tons of down 

wood per 

hectare 

Mean piece 

diameter at 

transect 

intersection 

(cm) 

Pct hard 

logs2

Pct soft 

logs2

Stand initiation 17 15.8 25 17 83 

Shrub sapling 68 18.6 25 13 87 

Young forest 144 17.0 28 9 91 

Pole timber 96 13.8 28 7 93 

Dispersal 

forest 89 10.5 28 11 89 

Mature forest 91 11.3 28 17 83 

Managed old 

growth 7 8.5 31 26 74 

Old growth 3 13.8 38 19 81 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

920 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

agencies and can be used by public managers and private landowners interested in 

developing HCPs or other landscape planning efforts. 

Current knowledge and research in snag dynamics and cavity-dependent wildlife 

was used during development of the HCP. In addition to specific mitigation measures 

targeting snag and CWD issues, there are many ancillary benefits to species 

associated with these structural elements from other mitigation measures designed to 

address the needs of other species or habitats. Implementation, monitoring, and 

model testing are providing opportunities to work with Federal and State biologists to 

improve the HCP where needed. 

HCPs provide substantive and meaningful incentives to private landowners to 

address a wide range of wildlife issues (including snags and course woody debris) 

while providing the long-term regulatory predictability needed for forest 

management. These plans also provide opportunities to improve knowledge and 

further our understanding of landscape processes. 

Acknowledgments 

We would like to thank Mike Collins, Jeffrey Light, and an anonymous reviewer 

for their helpful comments that improved this manuscript. 

References 

Anonymous. 1991. Protocol for surveying proposed management activities that may 

impact Northern Spotted Owls. Portland, OR: U.S. Fish and Wildlife Service. 

Anonymous. 1992. Protocol for surveying proposed management activities that may 

impact Northern Spotted Owls (revised). Portland, OR: U.S. Fish and Wildlife 

Service. 

Anonymous. 1994. Record of decision for amendments to Forest Service and Bureau of 

Land Management planning documents within the range of the northern spotted 

owl. Forest Service, U.S. Department of Agriculture, and Bureau of Land Management, 

U.S. Department of the Interior; 74 p. 

Anonymous. 1995. Science and the Endangered Species Act. National Research Council. 

Washington, DC: National Academy Press; 271 p. 

Anonymous. 1996a. Cascades habitat conservation plan. Seattle, WA: Plum Creek Timber 

Company; 281 p. with appendices. 

Anonymous. 1996b. Habitat conservation planning handbook. Washington, DC: U.S. Fish 

and Wildlife Service and National Marine Fisheries Service. 

Anonymous. 2000. Washington forest practices. Washington Administrative Code 222. 

Olympia, WA: Washington Department of Natural Resources, Washington Forest 

Practices Board. 

Cline, Steven P.; Berg, Alan B.; Wight, Howard M. 1980. Snag characteristics and 

dynamics in Douglas-fir forests, western Oregon. Journal of Wildlife Management 

44: 773-786. 

Hicks, Lorin L. 1991. Plum Creek Timber Company’s new forestry experiments: lessons 

learned and future directions. Forest Perspectives 1(3): 9-10. 

Kohm, Kathryn A.; Franklin, Jerry F., eds. 1997. Creating a forestry for the 21st century: 

the science of ecosystem management. Washington, DC: Island Press; 475 p. 
Habitat Conservation Plans and Industrial Forest Lands Case Study—Hicks and Stabins 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 921 

Maser, Chris Charles; Anderson, Ralph G.; Cormack, Kermit, Jr.; Williams, Jerry T.; Martin, 

Robert E. 1979. Dead and down woody material. In: Thomas, Jack W., technical 

editor. Wildlife Habitats in Managed Forests: The Blue Mountains of Oregon and 

Washington. Agric. Handb. 553. Washington, CD: U.S. Department of Agriculture; 78-

95. 

Stofel, Julie L. 1993. Evaluating wildlife responses to alternative silvicultural practices.

Seattle, WA: University of Washington, College of Forest Resources; 126 p. M.S. thesis. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 923 

Management of Dead Wood: Perspectives 

of a State Forestry Agency1

Christopher P. Rowney2

A resolution adopted by the California Board of Forestry on July 20, 1887 

(Raymond 1968) reads: 

Whereas, the Government and laws are totally inapplicable to 

forest lands, giving neither protection to the public domain nor to 

legitimate lumber industry, these laws are notoriously evaded and 

entries under them have been fraught with fraud and perjury. To 

carry on the lumber industry at all, fraud is really a necessity. 

Besides these defects, the land system in relation to forests makes no 

provision for a continuous supply of timber, nor does it give any 

attention to the necessity of preserving a due proportion of forest for 

the maintenance of springs and streams and climatic conditions 

favorable to agriculture.... 

This document was not the result of an epiphany in the past few years. But are 

laws better suited to their stated purpose today? 

The 1887 resolution has elements of a continuing theme of the Board: providing 

for sustainable use of natural resources, protection of valuable public resources such 

as water quality, concern about appropriate implementation of regulations, and using 

a system of regulation that assures the continued viability of the timber industry in 

California. 

Those are simple words, but exceedingly difficult tasks. Everyone wants 

something from California’s timberlands. Fish and wildlife depend on it for 

productive and protective habitat, loggers depend on it for a living wage and job 

satisfaction, urban areas need a dependable supply of clean water, some 

environmentalists seek a religious experience, many desire recreational opportunities, 

and all of us depend on these lands for a steady supply of wood for an ever increasing 

population. 

Since the Board of Forestry was formed in 1885, there has been a constant 

evolution of regulatory structure to address the widely varying demands placed on 

our timberlands. Initially, most of the emphasis was placed on wildfire suppression 

and reforestation. That focus shifted substantially in the late 1960s and early 1970s. 

Up to that time, the Board of Forestry was primarily a creature of the timber industry 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Executive Officer, California Board of Forestry and Fire Protection, 1416 Ninth Street, Sacramento, 

CA (P.O. Box 944246, Sacramento, CA 94244-2468). 
Perspectives of a State Forestry Agency—Rowney 

924 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

and reflected those priorities of assuring future crops of trees. As a result of a court 

decision, the Legislature changed the Board composition such that the majority 

represented the public and its interest in the management of timberlands. The Z’bergNejedley Forest Practice Act of 1973 (Public Resources Code §4511, et seq.) 

followed and clearly established that many resource values, such as water quality, 

aesthetics, and wildlife protection were important as well. The Act primarily 

provided that the productivity of California’s forest lands be maintained and 

enhanced “while giving consideration” those associated natural resource values, and 

that language remains today (Public Resources Code §§4512, 4513). The focus, 

however, continues to evolve with a shift that elevates non-timber values. 

As California continues to grow and more people are moving into the less 

populated areas of the state, demands on our forestlands grow as well―more for the 

associated values than for the timber those lands can supply. 

The 1973 Forest Practice Act began a dynamic process of rule development, 

application, review, and adaptation that continues today. Today’s California Forest 

Practice Program is comprehensive, prescriptive, and expensive. It is also accused of 

being unnecessarily burdensome and not founded in good science. 

With the increased involvement of the National Marine Fisheries Service 

(NMFS) and the Environmental Protection Agency (EPA) in their enforcement of 

Federal laws, the California timber harvesting regulatory process, touted by many as 

the most stringent in the nation, has become more regulated. In the case of coho 

salmon (Onchorynchus kisutch), the NMFS has simply stated that the rules do not 

adequately protect the habitat of anadromous salmonids. In the case of compliance 

with the Clean Water Act, the EPA has concluded that the rules do not adequately 

address the problem of sedimentation. Environmental groups compared California’s 

practices to those envisioned on Federal lands in the Pacific Northwest (i.e., Forest 

Ecosystem Management Assessment Team [FEMAT]; Anonymous 1993) and found 

them inadequate. 

A founding principle of the Board was, and continues to be, to care for the 

landscape and its associated natural resources. The priorities of California 

policymakers in developing regulatory mechanisms in the management of both 

public and private land has changed significantly as the roles of ecological attributes 

are better understood. In California, up until the mid-1970s, the key for protection of 

those resources was in the area of fire prevention and suppression. 

This was particularly evident in regulations adopted for control of harvests on 

non-Federal lands in 1948. One regulation required that any snag within a harvest 

area that was 16 inches DBH and 20 feet tall or more, had to be cut down. The 

purpose of that regulation was to reduce the risk of fires spreading to snags and 

throwing sparks for long distances. 

That regulation remained in place until the mid-1970s. With the advent of more 

knowledge and concern about the effects of timber harvesting on avian species, 

particularly those listed under the State or Federal Endangered Species Act, rules 

adopted by the Board not only established minimum retention standards for specific 

species of birds, but provided that snags should be retained for wildlife habitat―

despite the heightened market potential of that resource. Salvage of snags and other 

dead wood was essentially unknown in the 1940s and 1950s, and real market value 

was not present until the late 1970s. Today’s regulations require snag retention. They 

may be removed only if required by the Director of the Department of Forestry and 
Perspectives of a State Forestry Agency—Rowney 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 925 

Fire Protection and they are within 100 feet of main ridges suitable for fire 

suppression and identified on a Timber Harvesting Plan map, or if they are within 

100 feet of roads and railroads. Other exceptions include safety hazards, disease or 

insect control, or when felling would not result in adverse impacts to wildlife habitat. 

Emerging challenges are statute and regulations providing for exemptions for 

removal of dead and dying timber (Public Resources Code §4584; Title 14 California 

Code of Regulations §1038(b)). These exemptions are exempt from the necessity of 

preparing a Timber Harvesting Plan and interdisciplinary review. There is concern 

that such activities may be resulting in significant adverse environmental impacts, 

despite the underlying presumption, by both the Legislature and the Board, of 

insignificant environmental effects. 

Over the past several years more attention has been centered on retention and 

recruitment of large woody debris (LWD) in and near watercourses. This is a radical 

change from earlier regulatory approaches to fisheries habitat. 

I can recall going to a presentation by the Department of Fish and Game in 1973 

with a number of forest industry people in Humboldt County. Included in the pictures 

presented was one of a stream with a large amount of wood in the channel, 

apparently preventing the migration of anadromous salmonids. The presenter then 

showed a picture after state crews had rehabilitated the channel. My supervisor, a 

forester, described it as an ecological desert. There was no wood in the channel and a 

tractor had been used to develop a relatively straight and diked watercourse. There is 

no question that harvesting in the earlier part of the century through the 1960s 

delivered massive quantities of wood debris to watercourses, probably in excess of 

that required in a healthy riparian system. The reaction, unfortunately, has resulted in 

problems we live with today in terms of biological and hydrologic problems and the 

mindset that dead stuff in the streams reduces fish habitat and enhances flood events. 

In contrast to that presentation is one presented by the Department of Forestry 

and Fire Protection in an appeal hearing of a Timber Harvesting Plan at a recent 

Board of Forestry and Fire Protection meeting. A picture was presented that showed 

a large amount of LWD in a watercourse and trees that leaned into the watercourse. It 

looked as “bad” as the pictures used by the Department of Fish and Game almost 30 

years ago, but those conditions were now characterized as demonstrating a healthy 

environment for fish and providing effective sediment metering for that watershed. 

Although changes in agency perceptions of appropriate management of LWD in 

watercourses played an important role in interagency review of Timber Harvesting 

Plans, no regulations actually addressed that resource. The Board of Forestry made 

some initial rulemaking in the early 1990s to address the need for recruitment of 

LWD by requiring that at least two living conifers /acre greater than 16 inches DBH 

and 50 feet tall be retained within 50 feet of Class I and II streams. 

The Scientific Review Panel, a result of an agreement between former Governor 

Wilson and NMFS, recently provided the California Resources Agency a report of its 

comprehensive review of the present Forest Practice Rules as they relate to the 

protection and enhancement of anadromous salmonid habitat (Rynearson and others 

1999). That report recommended permanent retention of 10 trees of the upper 20 

percent of the diameter distribution per 330 feet of stream channel within 50 feet of 

the transition line. That recommendation is included in a regulatory proposal 

considered by the Board during the winter of 1999-2000 for adoption. 
Perspectives of a State Forestry Agency—Rowney 

926 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

The Board is also entertaining proposals that would enhance dead wood 

throughout the hillslope. Many people feel the Forest Service model described in the 

Forest Ecosystem Management Assessment Team report should serve as a basis for 

retention and recruitment standards. It is important to remember that most of those 

lands that the Board regulates are in private ownership. Thus, in order for the Board 

to craft regulatory standards, it must consider the issue of violating the constitutional 

protections against the seizure of private property without compensation. 

From a regulatory standpoint, direct prescriptions for retention and recruitment 

are the subject of a great deal of commentary―too much or too little, depending on 

the interest of the person. Most importantly, regulations that are general by their 

nature are not well suited to address site-specific needs. The Board recognizes that 

comprehensive watershed assessment is the ideal direction to take. Near term 

solutions in the form of statewide regulations must give way to meaningful specific 

watershed analyses. 

The laws developed to protect resources are inadequate if they are not 

implemented. That appeared to be the frustration of the Board back in 1887. 

Requiring something to be done simply because it is the best available technology or 

best management practice is insufficient if no one actually does it. It is even worse if, 

later on, it is found to be the antithesis of what is really needed. 

Nearly three decades ago, the Society of American Foresters (SAF) defined 

forestry as “managing and using for human benefit the forestlands and natural 

resources that occur on and in association with forestlands, including trees, other 

plants animals, soil, water, and related air and climate” (Ford-Robertson 1971). Less 

than 2 decades later, SAF significantly changed the focus to “the science and art of 

attaining desired forest conditions and benefits” (Anonymous 1989). An element of 

the definition is to “sustain and enhance forest resources for diverse benefits in 

perpetuity.” 

In the earliest stages of its rule-making efforts under the Forest Practice Act, the 

Board emphasized a species-specific approach to habitat management and protection. 

This is particularly evident in the Board’s regulations for owls, eagles, and ospreys, 

to name a few. Regulatory policy is shifting from that species-specific approach to a 

landscape-based approach to wildlife and watershed management. To be effective, 

such policy requires stakeholder understanding and support. This is best achieved 

through education and incentive-based approaches, although some level of 

prescriptive regulation is unavoidable. 

As is evidenced by the broad array of dead wood values that were framed in 

topical presentations at this symposium, it is clear that dead wood is more than a 

simple residence for birds or habitat component for fish. The difficulty is applying 

this kind of information on lands. In a landscape consisting of competing resources, 

competing land uses, and even competing regulatory frameworks, there will be 

change in our regulatory process, but in all likelihood it will be compromise of some 

sort. 

There are going to be changes in the Board’s view of appropriate forest 

management, but it is a continuation of thoughts that began with the Board in 1885. 

There is no question that some of those changes will reflect an increasing 

appreciation of the role of dead wood in a healthy ecosystem.
Perspectives of a State Forestry Agency—Rowney 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 927 

References 

Anonymous. 1994. Record of decision for amendments to Forest Service and Bureau of 

Land Management planning documents within the range of the northern spotted 

owl [Northwest Forest Plan]. Washington, DC: U.S. Department of Agriculture, Forest 

Service and the U.S. Department of Interior, Bureau of Land Management; 74 p. 

Anonymous. 1989. Forestry terminology. Washington, DC: Society of American Foresters. 

Ford-Robertson, F. C., ed. 1971. Terminology of forest science: technology practice and 

products. Washington, DC: Society of American Foresters; 109. 

Raymond, F. H. 1968. Transcript of minute records California State Board of Forestry 

April 1, 1885Dec. 10, 1892. Sacramento, CA: State Board of Forestry and Fire 

Protection; 46 p. 

Rynearson, G., coordinator. 1999. Report of the scientific review panel on California 

forest practice rules and salmonid habitat. Sacramento, CA: Prepared for the 

California Resources Agency and the National Marine Fisheries Service; 92 p. plus 

appendices. 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 929 

Moving towards a New Paradigm for Woody 

Detritus Management1

Mark E. Harmon2

Abstract 

Woody detritus has become an important focus of many scientific and management questions 

in forests. Perspectives of the role of this part of the ecosystem have greatly changed over 

time. Today forest managers are moving away from a “blanket” removal of all the woody 

detritus possible to retaining and even enhancing the amounts in forests. To understand how 

much woody detritus is required to sustain ecosystem functions, we need to develop a 

dynamic and specific objective-oriented approach. This can be based on existing data on tree 

mortality and decomposition, but these will have to be coupled with process and species 

responses to coarse wood quantities as well as a landscape perspective. 

Introduction 

In the last decade, woody detritus, particularly the coarse fraction, has become 

an important focus of many scientific and management questions. Although the role 

of this material in providing habitat and carbon cycling is generally understood, 

perspectives on its role in nutrient cycling are still evolving. Based on what is known 

to date, forest managers are moving away from a complete removal of all the woody 

detritus to retaining and even enhancing the amounts in forests. This leaves open the 

question of how much woody detritus is required to sustain ecosystem functions. 

Initially, this has been solved by the application of static minimum standards based 

on a set of general objectives, but in the future a more dynamic and specific 

objective-oriented approach should be developed. The increasing number of studies 

on tree mortality and decomposition are giving a global view of how these processes 

vary with forest type and climate. These data also provide the basis for a dynamic 

rather than a static approach to the management of woody detritus. However, to be 

successful, this perspective must be coupled with a detailed understanding of how 

certain species and ecosystem processes vary with the amount of woody detritus. 

Woody detritus is an important component of forest ecosystems, reducing 

erosion and affecting soil development; storing nutrients and water; providing a 

major source of energy and nutrients; serving as a seedbed for plants and as a major 

habitat for decomposers and heterotrophs (Ausmus 1977, Franklin and others 1987, 

Harmon and others 1986, Kirby and Drake 1993, McCombe and Lindenmayer 1999, 

McMinn and Crossley 1996, Samuelsson and others 1994). As knowledge of these 

important roles in forest ecosystems has increased, the need to manage this material 

 

1

 An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Richardson Professor of Forest Science, Department of Forest Science, 210 Richardson Hall, Oregon 

State University, Corvallis, OR 97331-5752 (e-mail: mark.harmon@orst.edu) 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

930 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

to maintain these functions has also increased. Although we are moving away from a 

period when woody detritus was given only economic, engineering, or safety 

considerations, we have not fully replaced this paradigm with a new one. In this 

paper, I outline what this new paradigm might be and point out the types of scientific 

knowledge that will be required to make it a reality. 

Historical Perspective on Management: The U.S. Pacific 

Northwest Case 

The old adage, “Those who ignore the past are doomed to repeat it,” is sound 

advice. Thus, before describing what the future of woody detritus management might 

look like, it might be best to describe what has happened in the past. As forest resources 

have been harvested throughout the world, the attitudes toward that harvest and the 

value of those resources have changed with time. Although each region of the globe has 

had a unique development, there are certain trends they share. These general patterns 

can be illustrated by the historical trends in the U.S. Pacific Northwest, a major region of 

timber resource development, and one of the regions where woody detritus management 

has been rapidly changing. 

The Unlimited Resource 

The timber resources of the Pacific Northwest were initially regarded as limitless. 

Moreover, the timber resource was often viewed as a roadblock to “progress.” This 

attitude had two consequences: low utilization standards with the highest quality wood 

harvested and the rest left to decompose, and a removal of forests by harvest or other 

means such as fire. Early this century some stumps were up to 6 m tall (Gibbons 

1918), and stumps 3-4 m tall were not unusual (Conway 1982). Trees were cut this 

way to avoid butt rots and flair at the base of the trees. Reports at this time indicate > 

10 percent of the stand volume was left in stumps (Gibbons 1918) with considerably 

more in the form of unharvested “undersized” trees. Between 1920 and 1930, stump 

height was reduced to 1-1.75 m, amounting to 6-7 percent of the total bole volume. In 

the 1910s the average diameter of logs left after harvest was 43 cm (Hanzlik and 

others 1917). During the 1920s it was common to leave logs < 35-56 cm diameter 

depending upon the length (Hodgson 1930). In 1910, the typical harvest of an oldgrowth stand would have retained 65 percent of the live woody organic matter 

aboveground as slash. This is close to the amount that would be retained on site after 

a catastrophic fire or windthrow with no subsequent timber salvage (Agee and Huff 

1987, Spies and others 1988). Although woody detritus in forest ecosystems was not 

deliberately managed at this stage, it was certainly changing. In upland forest the 

amount of wood detritus increased at this time because the catastrophic disturbance rate 

was increasing as timber harvest increased (i.e., the mean fire return interval was 200 

years, whereas timber was harvested at a rate in which the mean return interval was > 

100 years). This change increased the input of woody detritus and therefore increased 

the average landscape level of woody detritus above those of the historical average (fig. 

1). In contrast to the upland system, in the riverine system woody detritus was being 

removed and burned to improve safety and transportation, effectively increasing the 

decomposition rate-constant. This lead to a decrease in woody detritus stores in riverine 

systems at the time that upland stores were increasing. 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 931 

Figure 1―Hypothetical amounts of woody detritus found in upland landscapes 

during various stages in development, using the Pacific Northwest as an example. 

The values were derived using a simulation model (similar to the one described in fig. 

2) and parameterizing it by using data from Harmon and others 1996. The heavy line 

represents the mean, whereas the light lines indicate the range over succession. 

Woody Detritus as Waste 

The next stage of development was largely a response to the previous one. As the 

timber resource was removed deliberately or by accident, it became scarcer and 

therefore more valuable. What was originally an unlimited resource was then seen as a 

limited resource that required more efficient management. Forests were therefore seen to 

be in the need of protection from natural (wind, fire, insects, fungal) and man-caused 

disturbances (fire, agricultural clearing). Moreover, utilization standards that removed 

only the “best” volume became viewed as wasteful. Improvements in utilization 

standards by the 1940s lead to a five- to tenfold drop in stumps height to 0.6 m (Poole 

1950). More significantly a trend of removing smaller diameter trees and tops started 

with a minimum of 30 cm in the 1930s and steadily decreased to 13-15 cm today. 

The forestry literature at that time in the Pacific Northwest was full of examples of 

economic waste. For example, Hodgson (1930) calculated that the mass of sound 

wood retained after harvest in western Oregon and Washington forests during the 

1920s exceeded the entire amount cut for pulp over the entire U.S.! As another 

example, re-logging of former harvest units was economically viable for several decades 

(Hodgson 1930). 

Although changing to a more efficient form of harvest made economic sense as 

resources became scare, it also had some very important consequences that did not make 

ecological sense. The earlier harvest practices were viewed as wasteful, and therefore 

woody detritus became the symbol of that waste regardless of its origin. Forest 

utilization standards were not only improved to reduce this wastefulness but also the 

symbol of that waste had to be removed. It was the latter step that led to potential 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

932 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

ecological problems, but these were not anticipated. Rather, many justifications 

concerning sanitation, productivity, fire protection, and logger safety that went far 

beyond changing wasteful practices were developed. These justifications took on a life 

of their own even though they often had no basis in fact. For example, pathogens were 

thought to spread from dead trees, but with very rare exceptions this was not true as the 

pathogens lived primarily on living trees (Cramer 1974). Fire-killed trees and 

windthrows had to be removed because pathogens and insects would threaten the 

surrounding living trees. Bark beetles became a general rationale for dead tree removal, 

despite that many species of trees (e.g., Tsuga heterophylla and Thuja plicata) are 

generally not attacked by these pest insects. Even those trees that do support these 

insects (Pseudotsuga menziesii) often do not form good habitat for beetles that cause 

extensive and long-term infestations (Powers and others 1999). Snag felling was 

extensively practiced to promote safety, and yet many of the areas in which this practice 

was carried out had vanishingly low probabilities of snags damaging buildings, vehicles, 

or humans (at least there was no detectable increase in incidents when the practice was 

stopped). Logs were removed to ease tree planting, although the major problem in 

slowing planting was small and not large slash material. 

The ultimate expression of this phase of development occurred when not only the 

wasteful practices were stopped and recently killed trees that could be economically 

utilized were removed, but when woody detritus that could not be utilized for anything 

except firewood was removed and eliminated by burning. This era of piling 

unmerchantable material (PUM) and yarding unmerchantable material (YUM) 

represented a phase in which the existence of woody detritus was not to be tolerated 

even if it cost a great deal of money to remove it. As such it represented waste removal 

carried to its illogical extreme. It also led to a landscape in which woody detritus was far 

below any historical level (fig. 1). 

Ecological Functions

Not only did PUM and YUM practices have an economic downside associated 

with the cost of yarding and burning, they started to have impacts on the ecological 

system. Research started in response to these practices that revealed many of the 

functions we take for granted today (Harmon and others 1986, Maser and Trappe 1984). 

The search also began for a more balanced way to deliberately manage woody detritus 

in the ecosystem. The first idea was to develop minimum standards for the amount of 

woody detritus to be retained in harvested units. Minimum standards were set a number 

of ways, but most frequently in the Pacific Northwest they were based on the minimum 

numbers of pieces or volume found in old-growth forests (Spies and Franklin 1991). To 

serve certain functions it was also recognized that minimum diameters and lengths 

needed to be provided. While the emphasis on upland systems was on the time of 

harvest, a point when woody detritus could either be enhanced or retained, the focus on 

riparian systems was on restoration with wood actually either being added artificially 

from outside the system or produced naturally in designated riparian buffer zones. 

Although minimum standards are an improvement in terms of retaining ecological 

functions, they also have certain problems as currently practiced. First, while they have 

the potential to increase woody detritus above the level of the previous era, they also 

have the effect of homogenizing the amount of woody detritus over space and time. As 

woody detritus in a natural system is highly variable it is not clear what this 

homogenization implies for many ecosystem functions. Minimum standards are easy to 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 933 

set and enforce but often are difficult to apply—how should stages of succession or 

forest types be managed in which the amount of woody detritus is naturally lower than 

the minimum? Should wood be added to make it comply with the standards? These 

questions often confront the manager trying to apply one-size-fits-all standards. Second, 

the minimum standard approach is mute on how the minimum should be determined. 

Ideally, this should be determined by the tradeoff between ecological and economic 

gains and desired outcomes (Wilström and Ericksson 2000). However, in practice this 

has been settled by balancing the amount of woody detritus against the economic cost. 

This system inevitably leads to the factor that can be quantified (i.e., economics) 

becoming more important than the qualitative factor (i.e., we need some more woody 

detritus). Third, because the management intervention for the upland system occurs 

during harvest, minimum standards lead to static management of a dynamic entity. 

Thus, once the minimum standard has been met, the tendency is to assume that 

ecosystem functions will be provided despite that the system is very likely to change 

over the decades between harvests. 

“Morticulture” and the Elements of a New Management 

System 

Clearly a paradigm that moves beyond minimum standards needs to be 

developed. But how will it be developed and what will it look like? We might start 

with the name of this new system and see where that leads us. Suppose in the future 

there will be a “morticulture” as well as a silviculture. Although I often offer this 

name in jest, it does have some serious points in its favor. It emphasizes the culturing 

of something, in this case woody detritus. As with silviculture it would meet future 

needs, but instead of the type of logs to be harvested, it would deal with the methods 

to produce woody detritus structures for ecosystem function. It would have a similar 

attitude about manipulating stand structure and, as in modern silviculture, 

acknowledge the dynamic nature of the system being managed. And morticultural 

practices would not be implemented unless the ecosystem response was exactly 

understood (just as in silviculture, methods should not be applied without trying to 

reach some goal in terms of species mixtures, forest product markets, etc.). In 

addition to these obvious parallels, morticulture should take advantage of past 

silvicultural experience. In fact its implementation should be considered in close 

conjunction with silviculture and not in isolation. The next section outlines in more 

detail some of the features of this new system. 

Linking Live and Dead Trees 

Although developing a viable morticulture will require new knowledge, in many 

cases it will require that we apply what we already know. For example, we already 

know that live trees eventually form dead trees, but it is amazing that this dynamic is 

often missing from current forest management thinking. Thus, the current tendency is 

to use wood produced from the old-growth stand at the time of forest conversion and 

harvest to meet the future needs of the system. Unfortunately, the new plantation 

forest system does not have the capacity to maintain this amount of woody detritus 

unless it is modified considerably in terms of rotation length and fraction of live trees 

retained (Franklin and others 1997, Spies and others 1988). 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

934 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

A similar disjunction occurs between standing dead trees (i.e., snags) and 

downed dead trees (i.e., logs). Clearly snags eventually fall to the ground to become 

logs, although some live trees fall to become logs without first becoming snags. An 

examination of management plans, inventories, and even the scientific literature 

indicates that there is both a significant failure to link snags and logs and to link live 

and dead trees. Yet, they are clearly all part of the same overall system. One way to 

functionally link these forms of wood is to use a common currency to examine their 

state and dynamics. The actual units used may differ depending on the objectives, but 

the current tendency to compare, for example, volume of logs to numbers of snags is 

unnecessarily reinforcing their separation. 

The Dynamic Wood Pool 

Managers of woody detritus currently tend to think about woody detritus 

management in static terms. Rather than ask at which rate woody detritus is created 

or lost, they tend to think about the amount that should be there. This is another case 

where we already know the processes that control woody detritus dynamics, but we 

are not applying this knowledge. Clearly, we need to learn more about the processes 

of mortality, disturbance, decomposition, fire consumption, and movement, but I 

maintain the most significant problem is switching from a static to a dynamic 

perspective. 

Mortality is the process that creates woody detritus. It can occur by natural 

causes or by human-related causes. It can occur as single parts (e.g., branch pruning), 

as single individuals, or as entire stands (i.e., as landscape units). Forest management 

in the past century has focused on how to lower mortality rates via thinning, fire 

protection, etc. Ironically, the next century of forest management may be occupied 

with how to increase mortality when and where we want it. Despite the foresters 

preoccupation with reducing mortality, it is surprising how little is known about the 

actual rates of mortality in forests (Franklin and others 1987). This lack of knowledge 

may have been caused by the fact one needs to observe a population over time to 

determine rates and causes, although some stand reconstruction methods can give 

rough approximations of long-term rates (McCune and others 1988). Mortality rates 

are commonly thought to be highest in older forests (shades of our old friend waste 

reduction?), but they actually tend to be highest during the self-thinning stage of 

succession. For the forests that have been studied, old-growth rates appear to be onethird to half those of the self-thinning stage (Franklin and others 1987). There is also 

a tendency to only consider self-thinning in models of mortality, but this too is a 

mistake. Trees are often killed by causes unrelated to density such as wind, ice 

damage, insects, pathogens, and sometimes accidents (e.g., the second highest cause 

of death in Pacific Northwest forests is crushing by another tree or snag [Franklin and 

others 1987]). At the continental scale the tendency is for mortality to increase with 

productivity, although the cause of this relationship is not clear. Tropical forests have 

the highest mortality rates (0.0167 yr-1) followed by deciduous (0.012 yr-1) and then 

evergreen forests (0.01 yr-1) (Harmon and others 2001). 

Although disturbances such as fire and timber harvest obviously cause mortality 

directly, they also increase the chances that the surviving trees will die (Franklin and 

others 1997) because survivors are exposed to increased insect attack and/or to wind 

damage. While often viewed as a waste, this might also be an opportunity if 

increasing woody detritus is the management objective. 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 935 

Decomposition is the fundamental process that regulates the loss of woody 

detritus. Although many insect species are associated with this process, 

basidiomycete fungi are probably the most important wood decomposers. Many 

factors control the rate of wood decomposition, ranging from the chemical and 

physical nature of the wood, to decomposers involved, to the environment at the 

micro- and macro-levels. This leads to a very complicated pattern of decomposition 

that is variable over the scale of meters. In northwestern Russia, for example, one can 

find logs under moss mats that are waterlogged, next to stumps that have optimum 

moisture, next to snags that are too dry to decompose except in their lowest meter of 

height (Krankina and Harmon 1995). There have been some attempts to measure the 

rate of the decomposition process over time (Harmon and others 1999, 2000), but 

these are relatively rare today. The majority of studies of woody detritus 

decomposition use a chronosequence approach that substitutes space for time. There 

is a great deal of data on decomposition rates of wood relative to mortality. On the 

macro-scale decomposition rates decrease from tropical (0.176 yr-1) to deciduous 

(0.080 yr-1) to evergreen forests (0.032 yr-1) (Harmon and others 2001). Deciduous 

shrublands of the tropical zone appears to have the highest decomposition rateconstant, possibly due to the presence of termites. Although tropical forests have the 

highest decomposition rate-constants of any major biome, the distribution of values 

appears bimodal with a peak at < 0.04 yr-1 and another at > 0.12 yr-1 (Harmon and 

others 2001). This may be a reflection of two groups of species: one containing 

compounds toxic to fungi and insects in their heartwood and a second group that has 

little decay-resistance. In contrast, evergreen and deciduous ecosystems appear to 

have unimodal distributions of decomposition rates. 

Fire consumption is another process that removes woody detritus. This process 

is highly variable and likely to change from ecosystem to ecosystem and even from 

fire to fire. Past research indicates consumption of woody detritus increases as 

moisture and piece diameter decrease, and as the degree of decay increases (Brown 

and others 1985, Rienhardt and others 1991). It is also clear that in most situations 

the consumption of large woody detritus is linked to consumption of the forest floor. 

The reason appears to be related to the extremely loose packing of woody detritus. To 

burn there must be a positive feedback of energy between pieces; and given the 

distance between large pieces of wood, this feedback is very low. Therefore, for 

coarse wood this positive feedback is with the underlying forest. This is important 

because it means that without deep forest floor layers, large pieces of woody detritus 

will not be completely consumed even when the moisture content is extremely low 

(similar to attempting to burn a single dry log in a fire place without another log or 

finer fuels). 

The nature of the fire can also determine future decomposition rates. The classic 

idea is that charring slows decomposition, but this is probably only true for wood that 

is in the intermediate stages of decomposition. Fire charred trees are typically quite 

attractive to decomposers such as insects, many of which specialize on this form of 

mortality. Wood that has been fully colonized by decomposers is also likely to be 

little affected by charring, although increasing light absorbance is likely to heat the 

wood and lead to faster biological activity. Charring seems to only slow 

decomposition in logs that have the decayed portions fully removed, thus eliminating 

the normal sequence of colonization. Finally, it is often stated that fires removed 

much of the woody detritus prior to fire protection efforts; therefore, after decades of 

fire suppression current levels of woody detritus are artificially high. Perhaps, but 

these same fires would have killed trees that replaced the dead ones they consumed. 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

936 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

Given the ratio of dead to live trees observed in most forests (0.05 to 0.30 on a mass 

basis), very little mortality would be required to offset these losses (Harmon 1992). 

This may be the reason why two fire regimes in Oregon that differed fourfold in the 

frequency of fires had very similar amounts of woody detritus (Wright 1998). Those 

differences that did exist were more likely caused by environmental differences that 

lead to an increased rate of decomposition in the more frequent fire regime. 

All these process rates vary with time, a dynamic that causes woody detritus to 

undergo changes over succession. Although there are undoubtedly many patterns of 

change after a disturbance, a few common patterns can be created by varying: the 

interval between disturbances, the amount of wood removed by the disturbance, the 

mortality rate, and the decomposition rate. The simplest case is for old-field 

succession where both live and dead mass start at 0 (fig. 2). In this case live and dead 

mass accumulation parallel each other. A more complicated situation occurs after a 

catastrophic natural disturbance. Assuming the disturbance removes a minimum of 

wood (e.g., wind throw), woody detritus at the time of disturbance is equal to former 

live biomass and the dead wood mass just before the disturbance. This peak is 

followed by a monotonic decline to a steady-state mass that is determined by the 

mortality and decomposition rates. When the disturbance removes a fraction of the 

woody mass (e.g., timber harvest) the quantity right after the disturbance can range 

anywhere between zero to that found after windthrow. In the example given in figure

2, the woody detritus mass declines below the steady-state value and then increases 

to this level. This is because the replacement of woody detritus lags behind 

decomposition in the middle stages of succession (Harmon and others 1986, Spies 

and others 1988). Perhaps the most complicated case is when forests are converted to 

intensive, short-rotation forestry. Here the live mass does not recover to the steadystate level and a large fraction of the mortality is removed as intermediate timber 

harvest in thinning and salvage. This leads to a decrease in the store of woody 

detritus to a value much lower than the steady-state value. 

Response Functions 

Knowing the dynamics of the woody detritus is not sufficient for deciding how 

much woody detritus is adequate. This requires knowledge of how various organisms 

or ecosystem functions vary with the amount and arrangement of this material. 

Unfortunately, this is probably the weakest portion of the science behind morticulture 

(and the hardest type of question to answer). The first problem is that we have tended 

to examine ecosystem and habitat functions either with or without woody detritus. 

But what we really need at this stage is a continuous response. Although there are 

few examples of continuous response functions, some do exist. Butts and McCombe 

(2000) examined the response of salamanders in western Oregon to the presence of 

woody detritus (fig. 3). They found that the abundance of some genera (Aneides and 

Ensatina) was highly correlated to the volume of woody detritus present, while others 

were completely indifferent (Taricha). 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 937 

Figure 2―Hypothetical woody detritus stores relative to live woody stores for various 

management regimes. Stores are from a simple simulation model that uses a 

Chapman-Richards function to simulate live biomass and determines woody detritus 

mass from mortality from disturbances and regular death from competition, etc. as 

well as losses from fire and decomposition (Harmon and others 2001). For 

comparative purposes, woody detritus stores have been set relative to live woody 

stores and the maximum live woody stores were set to 1. A) old-field succession with 

no woody detritus at the start, B) succession after a natural disturbance that leaves 

all the woody detritus, C) a single clear-cut without subsequent harvest, and D) 

multiple harvests every 50 years with salvage of half the mortality. 

From a theoretical standpoint, the expectation is that different ecosystem and 

habitat functions would have different responses to the amount of woody detritus (fig. 

4). A relatively small volume of wood might fulfill some functions, such as insect 

habitat, as long as the right species, size, and decay stage are provided. One might 

expect this type of response from any species with a small size, high reproductive 

rate, and high vagility. Vertebrates on the other hand might require larger volumes of 

woody detritus, in part because of their larger individual size, but also because they 

may require more connectivity of the wood itself to serve the function required (e.g., 

travel corridors). Some response functions might increase to a saturation point, 

whereas others might reach an optimum above which the function decreases. A 

possible example of the latter might be the response of fish to increases in woody 

detritus abundance. At first habitat quality might be increased; however, with too 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

938 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

much woody detritus in the stream movements, food production and other factors 

might become limiting. The same might be true for nutrient cycling. Adding wood 

initially might increase the addition of nitrogen via asymbiotic fixation and might 

provide habitat for some mycorrhizae. But at some point woody detritus would tie up 

too many nutrients and cover too much of the forest floor so that plants might have 

limited places to establish. Although all of these are theoretical responses, they 

indicate range of types one is likely to see in nature. 

Figure 3―The response of ensatina salamander (Ensatina eschscholtzi) abundance 

to coarse woody debris volume (Butts and McCombe 2000). 

Figure 4―Hypothetical examples of species and ecosystem response functions to 

changes in the abundance of woody detritus. Note that both scales are relative, with 

the response function having a maximum of 1.0 and a minimum of –1, and the woody 

detritus scale ranging from 0 (no woody detritus) to 100 units of mass or volume. 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 939 

Compensatory Factors 

It would be a simple world indeed if we could treat responses to woody detritus 

in isolation. In reality the woody detritus resource interacts with others to determine 

the overall function of the ecosystem. To some degree these interactions might 

compensate for a decrease in woody detritus. For example, bacteria in woody detritus 

undoubtedly fix nitrogen that eventually becomes available to plants. It stands to 

reason that removal of this woody detritus would therefore decrease nitrogen inputs, 

but this might be compensated for by symbiotic nitrogen fixation in plants or lichens. 

Unfortunately, the same zealous attention to decreasing waste and increasing 

productivity of merchantable volume that has lead to the removal of woody detritus 

has also lead to the removal of both these symbiotic forms of nitrogen inputs. 

Perhaps the more complicated question to answer is why other types of 

structures may or may not compensate for woody detritus. For some organisms, such 

as insects and fungi, this compensation is easily determined given that they often 

require woody detritus to fulfill certain life stages (Jonsell and others 1998, Renvall 

1995, Rydin and others 1997). For others such as small mammals there may not be 

such a clear obligate relationship. If woody detritus serves as cover for small 

mammals, then another form of cover might be able to compensate for a lack of 

woody detritus. This suggests that in addition to developing response curves, we 

must understand what exactly the woody detritus is providing the organism or 

ecosystem. If there are no other ways to provide this function, then the amount of 

woody detritus is crucial. If on the other hand other structures or processes can 

provide them, then we may be more flexible in the amount of material retained. 

Spatial Considerations 

The final element to forming a new management paradigm for woody detritus 

management involves spatial arrangement. This can be at the level of pieces, stands, 

and landscapes. At the landscape level the first consideration might be whether the 

process or habitat provided by woody detritus is ubiquitous or restricted to certain 

locations. If it is ubiquitous then keeping a minimum level throughout the landscape 

may be adequate. An example of a ubiquitous process might be nutrient cycling, as it 

is continual regardless of the amount of woody detritus. If the habitat is restricted, the 

connectivity to other similar habitats or locations must be considered. If the species 

using woody detritus habitats have a high reproductive capacity and are vagile, 

spatial distribution may be of minor concern as long as the habitat appears 

somewhere each year (Jonsell and Norlander 1995, Jonsell and others 1999). On the 

other hand, for species with low reproductive capacity and restricted movements, one 

may need to carefully design where and when the woody detritus habitat occurs in 

the landscape. In addition, metapopulation dynamics may need to be considered 

(Hanski 1991). This problem might be addressed by providing stable areas in which 

populations dependent on woody detritus are kept high and can serve as sources to 

the surrounding, lower quality, and shifting habitats that are population sinks. While 

the latter are temporary, they would function to keep the overall abundance of the 

organism high at the landscape level. Metapopulation structure considerations may be 

influenced by the direction from which the landscape is being developed. In regions 

that have a great amount of high quality habitat, one might be able to design a selfsufficient landscape of source and sink populations. This will not be the case if 

restoring woody detritus functions to a “degraded” landscape is the goal. In this case, 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

940 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

one might have to locate source populations outside the landscape of interest or 

create the woody detritus habitat and then wait for the chance dispersal of the desired 

organisms. 

Although the bulk of recent ecological thinking about the spatial dimension has 

been on the landscape level, spatial considerations may also influence the function of 

woody detritus at finer levels of spatial resolution. If the primary function of downed 

woody detritus for small mammals is as protective cover from predators, the 

connectivity of individual logs might be important. One would hypothesize that the 

greater the connectivity of pieces, the lower the exposure to predation. Unfortunately, 

there are no studies that I know of that have looked at this problem from a theoretical 

or empirical perspective. Another question involving the spatial distribution of logs 

involves the effect of logs on soil forming processes. Tinker and Knight (2001) asked 

how long it takes logs to influence the entire soil surface. In lodgepole pine forests 

they found that it depends on the woody detritus management regime, with natural 

disturbances having a much shorter “log-rotation” time than current intensive forest 

practices. Interestingly, they found that minor modifications of current practices 

would shorten the log-rotation time to that observed for natural disturbances. Further 

work along these lines might add a great deal of insight into the long-term function of 

woody detritus in ecosystems. 

Integration 

Given these elements, how might this new paradigm of morticulture work? It 

would probably start by answering the question of which species or processes are to 

be maintained, restored, or otherwise managed (fig. 5). Then the target levels for 

these functions should be determined. Before assessing the amount of woody detritus 

to be maintained or added to meet this functional target, the landscape context for the 

management action should be assessed. Are there limitations of populations or 

processes that would limit the desired response? If not, a plan to add wood would be 

designed to maintain the desired level. But if there are landscape limitations, then 

these should be addressed before planning at the stand-level proceeds. The ability to 

circumvent these limitations will probably be highly dependent on the given 

landscape; in some cases the particular patch treated might be part of an overall plan 

to reduce these landscape-level limitations. The plan to produce a given amount of 

woody detritus would have to be dynamic, linking the live trees and the different 

forms of dead trees so that there is compensation for losses caused by decomposition 

and fire. The plan would then be implemented and might consist of several 

interventions. Finally, the results of the action should be monitored for effectiveness 

(not just implementation), and a true adaptive management system should be put in 

place. The latter system will have real costs in money, time, and training, but will be 

necessary to really assess if things are working as anticipated. 

This paradigm is admittedly a “fine filter” approach that emphasizes small scale 

processes and patterns. There is no reason, however, why it could not be coupled 

with a “coarser filter” landscape level view of the system. In fact the assessment of 

the landscape context would probably be the most logical point to reconcile these two 

perspectives. 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 941 

Figure 5―Integrating the elements of a new paradigm for woody detritus 

management. 

Science Needs 

Despite the need to improve our understanding of woody detritus dynamics in 

terms of mortality, decomposition, and consumption by fires, we already have 

enough knowledge of these processes to make reasonable projections of temporal 

dynamics at the level of stands. The same cannot be said about the response functions 

that are required to match the amount of woody detritus to the expected level of 

functionality at the ecosystem or landscape level. Clearly science needs to make 

major progress in this arena within the next decade if we are to see a new 

management paradigm take root in the near future. 

Unfortunately, this is difficult research. In some cases it will be long term. For 

example, we have made many assumptions about the irrelevance (and relevance) of 

woody detritus in the nutrient cycles of forests. But very few of these assumptions 

have actually been tested. Perhaps it is time they are tested. Equally problematical, 

but perhaps easier to solve in the short term, is the specific link between woody 

detritus and specific organisms (e.g., is it a nesting site, transport corridor, food 

source, etc.?). We need to be able to establish these relationships if we are to have 

any faith in the response functions that are generated. The design of experiments that 

actually test the response of various organisms to the abundance of woody detritus 

will be harder but by no means impossible. This might be conducted using existing 

gradients in wood amounts, or it could be done in manipulative experiments where 

wood is either added or removed. One complicating factor is the ability of organisms 

to disperse between these treatments. Adding woody detritus to systems that are 

depleted might not result in a response if the organisms cannot find or disperse to 

these locations. Conversely, removing woody detritus in a landscape with an 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

942 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

abundance of this material might not result in a decline if the treatment area is too 

small. Finally, we need to understand the historic and present dynamics of woody 

detritus at the landscape scale. We are beginning to understand these dynamics at the 

level of forest stands and other landscape elements such as streams. We must build 

up this understanding to the landscape level so that we can predict how managed 

landscapes differ from historical ones. 

Conclusions 

We have made progress in the last several decades in the management and 

understanding of woody detritus. Although the creation of minimum standards has 

been a useful first step in acknowledging the ecological function of woody detritus, it 

is not the ultimate solution to the problem. Rather, we need to develop a long-term, 

broad-scale view that is dynamic and that includes everything from proto-dead trees 

(live trees) to snags to logs to highly decomposed material that functions as soil 

organic matter. We also need to move away from arbitrarily setting amounts to a 

system based on the response of specific ecosystem function and species. This will be 

challenging to scientists and managers alike, but will be necessary if we intend to 

preserve, conserve, and restore the role of woody detritus in our forested landscapes. 

Acknowledgments 

I wish to thank two anonymous reviewers for reading and improving this 

manuscript. Funding for this work was sponsored by the National Science 

Foundation Long-term Studies Program (DEB-9632929), USDA-CSRS-NRICGP 

(Contract #95-37109-2181), TECO (DEB-9652618), and the Pacific Northwest 

Research Station, USDA Forest Service. 

References 

Agee, J. K.; Huff, M. H. 1987. Fuel succession in a western hemlock/Douglas-fir forest. 

Canadian Journal of Forest Research 17: 697-704. 

Ausmus, B. S. 1977. Regulation of wood decomposition rates by arthropod and annelid 

populations. Ecological Bulletin (Stockholm) 25: 180-192. 

Brown, J. K. 1985. Predicting duff and woody fuel consumed by prescribed fire on the 

northern Rocky Mountains. Res. Paper INT-337. Ogden UT: USDA Forest Service. 

Butts, S. R.; McCombe, W. C. 2000. Associations of forest floor vertebrates with coarse 

woody debris in managed forests of western Oregon. Journal of Wildlife 

Management 64: 95-104. 

Conway, S. 1982. Logging practices. Revised edition. Miller Freeman. 

Corn, P. S.; Bury, R. B. 1991. Terrestrial amphibian communities in the Oregon Coast 

Range. Gen. Tech. Rep. PNW-GTR-285. USDA Forest Service; 533 p. 

Cramer, O. P., ed. 1974. Environmental effects on forest residues management in the 

Pacific Northwest. Gen. Tech. Rep. PNW-24. USDA Forest Service; 416 p. 

Franklin, J. F. 1997. Alternative silvicultural approaches to timber harvesting: Variable 

retention harvest systems. In: Kohm, K. A.; Franklin, J. F., eds. Creating a forestry for 

the 21st century. Washington DC: Island Press; 111- 139. 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 943 

Franklin, J .F.; Shugart, H. H.; Harmon, M. E. 1987. Tree death as an ecological process.

Bioscience 37: 550-556. 

Gibbons, W. H. 1918. Logging in the Douglas-fir region. United States Department of 

Agriculture Forest Service Contribution Bulletin 711. 

Gore, J. A.; William, A. P. 1986. Mass of downed wood in north hardwood forests in New 

Hampshire: potential effects in forest management. Canadian Journal of Forest 

Research 16: 335-339. 

Hanski, I. 1991. Single species metapopulation dynamics: concepts, models and 

observations. Biol. J. Linn. Soc. 42: 17-38. 

Hanzlik, E. J.; Fuller, F. S.; Erickson, C. 1917. A study of breakage, defect, and waste in 

Douglas-fir. Forest Club Annual, University of Washington; V: 32-39. 

Harmon, M. E. 1992. Fire influences on coarse woody debris. In: Kauffman, J. B. Fire in 

Pacific Northwest Ecosystems: exploring emerging issues. 1992 January 21-23. Portland 

OR: Oregon State University; 13-14. 

Harmon, M. E.; Krankina, O. N.; Yatskov, M.; Matthews, E. 2001. Predicting broad-scale 

carbon stores of woody detritus from plot-level data. In: Lai, R.; Kimble, J.; Stewart, 

B. A. Assessment methods for soil carbon. New York: CRC Press; 533-552. 

Harmon, M. E.; Krankina, O. N.; Sexton, J. 2000. Decomposition vectors: A new approach 

to estimating woody detritus decomposition dynamics. Canadian Journal of Forest 

Research. 30: 74-84. 

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.; Lattin, J. D.; Anderson, N. H.; 

Gregory, S. V.; Cline, S. P.; Aumen, N. G.; Sedell, J. R.; Kienkaemper, G. W.; 

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of coarse woody debris in 

temperate ecosystems. Recent Advances in Ecological Research 15: 133-302. 

Harmon, M. E.; Garman, S. L.; Ferrell, W. K. 1996. Modeling historical patterns of tree 

utilization in the Pacific Northwest: carbon sequestration implications. Ecological 

Applications 6: 641-652. 

Harmon, M. E.; Nadelhoffer, K. J.; Blair, J. M. 1999. Measuring decomposition, nutrient 

turnover, and stores in plant litter. In: Robertson, G. P.; Bledsoe, C. S.; Coleman, D. 

C.; Sollins, P., editors, Standard soil methods for long term ecological research. New 

York: Oxford University Press; 202-240. 

Hodgeson, A. H. 1930. Logging waste in the Douglas-fir region. West Coast Lumberman 

56: 6-13. 

Jonsell, M.; Nordlander, G.; Jonsson, M. 1999. Colonization patterns of insects breeding in 

wood-decaying fungi. Journal of Insect Conservation 3: 145-161. 

Jonsell, M.; Nordlander, G. 1995. Field attraction of Coleoptera to odours of the wooddecaying polypores Fomitopsis pinicola and Fomes fomentarius. Annl. Zool. Fennici 

32: 391-402. 

Jonsell, M.; Weslien, J.; Ehnström, B. 1998. Substrate requirements of red-listed 

saproxylic invertebrates in Sweden. Biodiversity and Conservation 7: 749-764. 

Kirby, K. J.; Drake, C. M. 1993. Dead wood matter: the ecology and conservation of 

saproxylic invertebrates in Britain. English Nature Science No. 7. Peterbourough, UK. 

Krankina, O. N.; Harmon, M. E. 1995. Dynamics of the dead wood carbon pool in 

northwestern Russian boreal forests. Water, Air and Soil Pollution 82: 227-238. 

Maser, C.; Trappe, J. M. 1984. The seen and unseen world of the fallen tree. Gen. Tech. 

Rep. PNW-164. Portland, OR: Pacific Northwest Research Station: USDA Forest 

Service. 
Moving towards a New Paradigm for Woody Detritus Management—Harmon 

944 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

McCombe, W.; Lindenmayer, D. 1999. Dead, dying, and down trees. In: Hunter, M. L., ed. 

Maintaining biodiversity in forest ecosystems. Cambridge University Press; 335-372. 

McCune, B.; Cloonan, C. L.; Armentano, T. V. 1988. Tree mortality and vegetation 

dynamics in Hemmer Woods, Indiana. American Midland Naturalist 120: 416-431. 

McMinn, J. W.; Crossley, D. A. 1996. Biodiversity and coarse woody debris in southern 

forests. Gen. Tech. Rep. SE-94. Southeastern Research Station, USDA Forest Service. 

Pool, C. G. 1950. An analysis of falling and bucking. Timberman 51(7): 78-82. 

Powers, J. S.; Sollins, P.; Harmon, M. E.; Jones, J. A. 1999. Plant-pest interactions in time 

and space: a Douglas-fir bark beetle outbreak as a case study. Landscape Ecology 

14: 105-120. 

Renvall, P. 1995. Community structure and dynamics of wood-rotting Basidiomycetes on 

decomposing conifer trunks in northern Finland. Karstenia 35: 1-51. 

Rienhardt, E. D. 1991. Woody fuel and duff consumption by prescribed fire in northern 

Idaho mixed conifer logging slash. Res. Paper INT-43. Intermountain Research 

Station, USDA Forest Service. 

Rydin, H.; Diekmann, M.; Hallingbäck, T. 1997. Biological characteristics, habitat 

associations, and distribution of macrofungi in Sweden. Conservation Biology 11: 

628-640. 

Samuelsson, J.; Gustafsson, L.; Ingelög, T. 1994. Dying and dead trees: A review of their 

importance for biodiversity. Swedish Environmental Protection Agency Report 4306. 

Uppsala; 109 p. 

Spies, T. A.; Franklin, J. F. 1991. The structure of natural young, mature, and old-growth 

forests in Washington and Oregon. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: 

Pacific Northwest Research Station, USDA Forest Service. 

Spies, T. A.; Franklin, J. F.; Thomas, T. B. 1988. Coarse woody debris in Douglas-fir 

forests of western Oregon and Washington. Ecology 69: 1689-1702. 

Tinker, D.; Knight, D. 2001. Temporal and spatial dynamics of coarse woody debris in 

harvested and unharvested lodgepole pine forests. Ecological Modeling 141: 125-

149. 

Wikström, P.; Eriksson, L. O. 2000. Solving the stand management problem under 

biodiversity-related considerations. Forest Ecology and Management 126: 361-376. 

Wright. P. 1998. Coarse woody debris in two fire regimes of the central Oregon 

Cascades. Corvallis, OR: Oregon State University; M.S. thesis. 
Symposium Synthesis

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Dead Wood Management Issues and 

Opportunities: Future Directions1

Ann M. Bartuska2

Introduction 

October 1999 marked the 50th anniversary of the Sand County Almanac, and 

with the associated celebrations has come a heightened awareness of the Leopold 

Land Ethic. 

The array and depth of the presentations at this symposium underscores the 

increased understanding about dead wood in many forms. I am impressed by the 

collaborative presence of both managers and scientists. In his opening remarks, Jack 

Ward Thomas challenged the group when he said: “All that you folks have presented 

is only useful if synthesized and communicated.” In my remarks I have tried to 

provide some broad themes within which the presentations at this conference are 

linked. I also have tried to capture issues and opportunities, which can provide some 

directions for the future. 

Where Is the Dead Wood: Current and Future? 

We are concerned about all the forests of the West, not just the National Forests 

or Federal lands. At regional and landscape scales, solutions to land management 

problems can only be accomplished by considering all lands. A risk-mapping project 

is one that identifies areas where mortality from insect and disease outbreaks link 

with fire-risk areas at the national and regional scales. The presence of dead wood 

(from mortality) and fuels (from dead wood) is the critical element for assessing risk. 

Using this information for management decisions will involve both ecological and 

social considerations. 

Landscape or site: what intensity of sampling is needed? We heard from several 

presenters about possible approaches. I suggest we need to take a step back and about 

the level of information we need and with what degree of certainty. 

Forest Health Monitoring/Forest Inventory and Analysis programs may provide 

a template that may be good enough at landscape and watershed-scales—although 

tree-centric, they are open to expansion of methodology. More importantly, their 

infrastructure and basic system are funded and incorporate all forested lands. Wildlife 

 

1

An abbreviated version of this paper was presented at the Symposium on the Ecology and Management 

of Dead Wood in Western Forests, November 2-4, 1999, Reno, Nevada. 2

 Director, Forest and Rangelands, USDA Forest Service, P.O. Box 96090, Washington, D.C. 20090-

6090. Current address: The Nature Conservancy, 4245 North Fairfax Drive, Suite 100, Arlington, VA 

2203-1606.
Future Directions—Bartuska 

948 USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 

biologists are finding this system useful in habitat assessments, and measurements to 

assess floristic ground-cover are being evaluated. 

The model development presented in several sessions is really exciting. I was 

struck that these science-based systems are being designed with managers in mind. 

We must be smart to ask “at what scale is the model designed to provide 

information?” 

What Role Does Dead Wood Play in Ecosystems? 

The ecosystem arena is where most of the work seems to have been done and 

where the understanding is the most comprehensive―spanning physical, chemical, 

and biological processes. The science presented provides a sound foundation for 

management. 

Jack Ward Thomas made a strong plea that it is time to integrate and synthesize. 

This integration must be across disciplines and ecosystems. One speaker was 

justifiably proud of getting wildlife biologists and fire managers together. I suggest 

that entomologists, pathologists, and silviculturists also need to be at the table in 

order for planning to be most effective. Silviculturists, in particular, should become a 

wildlife biologist’s best friend. 

Synthesis across ecosystems is overdue. In this way, we can identify the 

underlying patterns and delineate clear ecosystem-specific patterns. 

How Do We Manage with Dead Wood? 

I would suggest what we really need to do is manage with disturbance! As Mark 

Harmon suggested, we should “manage dynamic systems.” 

We must learn to manage with uncertainty. Our plans and analyses must 

recognize that we cannot and will never be 100 percent certain, and in fact, perhaps 

50 percent is good enough. As scientists and as managers trained in the academic 

tradition, we are caught in a “p = 0.01” paradigm. The fact that uncertainty exists in 

science and in functioning ecosystems should be communicated to policymakers. 

Can we focus on the structure and assume the other components (fauna, 

invertebrates, insects, etc.) will fall into place, or do we manage for each of the 

components separately? This is an issue that both scientists and managers need to 

address and resolve or we will continue to chase the parts. 

Missing Pieces

The work presented at this conference has addressed the structure, function, and 

composition of dead wood in the ecosystem. However, ecosystem management 

identifies three interlocking components: ecological, social, and economic. Both 

Aldo Leopold and Gifford Pinchot recognized the importance of integrating 

ecological and social values.

The social and economic components of ecosystem management were generally 

missing. Where are the social scientists? The social values were touched on in some 

papers. For example, Bob Naimann made the link that woody debris provide a source 

of insects, which in turn is the basis for recreation fisheries. A landscape with a lot of 
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USDA Forest Service Gen. Tech. Rep. PSW-GTR-181. 2002. 949 

dead trees visible may not be what the visiting public wants. However, through 

communications with the public, they may understand and accept widespread 

mortality caused by natural events. 

The role of dead wood in the carbon budget, especially carbon sequestration and 

slow release processes, was incompletely addressed. Hennen’s question about the 

ecological role of the longevity of standing dead yellow cedar may have its answer in 

the systems equivalent to long-term carbon storage. 

There was a surprising absence of references to non-native, invasive species. 

The current heightened concern about their spread and introduction is touching all 

aspects of land and water management. One obvious concern is the effect on 

predicted patterns of mortality from insects and disease. We have good knowledge on 

the population dynamics of the major forest insects and diseases, and the geographic 

patterns using the greater than 50 years of annual pest surveys done by the Forest 

Service and the States. We do not have knowledge of the biology and impacts of 

recent introductions. 

Considerations for Future Work 

Standardization of methods is essential and will be more effective if the 

scientific and management community does this; otherwise it will come from the top. 

Scale-specific monitoring systems must be established. Is there such a thing as too 

much dead wood? 

Rapid response to disturbance events at all scales should be developed. There 

are well-established policies and procedures when there are fires, but not with other 

large-scale disturbances. 

Synthesis within and across scales is a major gap in our analyses and must be 

pursued. Are there universal truths or a lot of landscape-specific patterns? 

Information must be communicated in useful forms to managers and to the public. 

My closing thoughts echo those of Jack Ward Thomas: we all must assume 

some responsibility when science is brought to the management table. As scientists, 

we should continue to strive to better understand the structure, function, and 

composition of ecosystems. However, when conveying this information to managers, 

we should ask ourselves questions of practicality and uncertainty. As managers, we 

must continue to use the best available science, but we can’t be ruled by science. 

Ultimately, we have to make policy decisions that incorporate other values. Both 

scientists and managers have a measure of responsibility, and with that, comes 

accountability.