Papers were provided by the editors in camera-ready form for printing. Authors are responsible for the content and 

accuracy. Opinions expressed may not neccessarily reflect the position of the U.S. Department of Agriculture. 

The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. 

Department of Agriculture of any product or service.

Front cover and cover background photos by Mark Meleason. 

Section divider art and cover design by Kathryn Ronnenberg.

Pacific Northwest Research Station

Forest Service 

U.S. Department of Agriculture

Abstract 

Anderson, Paul D.; Ronnenberg, Kathryn L., eds. 2013. Density Management in the 21st Century: 

West Side Story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Research Station. 249 p.

Since adoption of the Northwest Forest Plan (NWFP) in the early 1990s, there has been a fundamental 

shift in forest management practices on federal lands in western Oregon and Washington. Commoditydriven clearcut regeneration harvests have given way to thinnings intended to enhance development 

of late-successional forest habitats and to conserve important aquatic and riparian ecosystems. Density 

Management in the 21st Century: West Side Story presents abstracts and peer reviewed papers from a 

regional conference highlighting more than twenty years of research related to forest thinning in the 

NWFP area. Presentations from the BLM Density Management and Riparian Buffer Study provide a 

focal point, with presentations from additional studies providing for a more complete overview of the 

west-side thinning science. The contributions are organized as five topical themes: The Regional and 

Landscape Context for Density Management in the Northwest Forest Plan Era; Implementation and 

Influences of Density Management in the Terrestrial Ecosystem; Riparian and Aquatic Ecosystems and 

their Responses to Thinning and Buffers; Socioeconomics and Operations; and Thinning and Adaptation. 

Collectively, the contributions summarize many important forest dynamics and ecosystem responses to 

partial overstory removals. Interactions between aquatic and riparian ecosystem conservation measures 

and upland harvest are emphasized. Targeting resource management practitioners, decision-makers 

and researchers, the collected works provide a reference to the current and future roles and issues of 

density management as a tool for forest ecosystem management.

Keywords: Aquatic Conservation Strategy, biodiversity, density management, forest structure, 

ecosystem processes, late-successional habitat, northern spotted owl, public perception, riparian 

buffers, stream temperature, thinning, wildlife.

Editors

Paul D. Anderson is a supervisory research forester, Pacific Northwest Research Station, Forestry Sciences Laboratory, 

3200 SW Jefferson Way, Corvallis, OR 97331; pdanderson@fs.fed.us.

Kathryn L. Ronnenberg is a research information assistant, Pacific Northwest Research Station, Forestry Sciences 

Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331; kronnenberg@fs.fed.us.
Density Management in the 21st Century: 

West Side Story

Paul D. Anderson 

and 

Kathryn L. Ronnenberg, 

Editors

Proceedings of the Density Management Workshop

4–6 October 2011, Corvallis, Oregon

Density Management in the 21st Century: West Side Story PNW-GTR-880

iii

Table of Contents

Two Decades of Learning about Th inning in the Ecosystem Management Era .............................. 1

Paul D. Anderson

Section 1. The Regional and Landscape Context for Density Management in the 

Northwest Forest Plan Era ................................................................................................................... 9

Th e Intertwining Paths of the Density Management and Riparian Buff er Study and 

the Northwest Forest Plan ........................................................................................................... 10

Kenneth J. Ruzicka, Jr., Deanna H. Olson, and Klaus J. Puettmann

Public Perceptions of West-Side Forests: Improving Visual Impact Assessments and 

Designing Th innings and Harvests for Scenic Integrity ............................................................... 22

Robert G. Ribe

A Satellite’s View of Recent Trends in Forest Harvest Intensity in the Pacifi c Northwest .............. 38

Robert E. Kennedy, Zhiqiang Yang, Justin Braaten, Warren B. Cohen, Peder Nelson, 

and Eric Pfaff

Landscape Context for Density Management: Implications of Land Ownership and 

Ecological Gradients .................................................................................................................... 41

Janet L. Ohmann

Section 2: Implementation and Influences of Density Management in the 

Terrestrial Ecosystem ............................................................................................................................43

Short-Term Responses of Overstory and Understory Vegetation to Th inning Treatments: 

A Tale of Two Studies .................................................................................................................. 44

Klaus J. Puettmann, Erich K. Dodson, Adrian Ares, and Carrie A. Berger

Making the Little Th ings Count: Modeling the Development of Understory Trees in 

Complex Stands .......................................................................................................................... 59

Peter J. Gould and Constance A. Harrington

Th inning Eff ects on Tree Mortality and Snag Recruitment in Western Oregon ............................ 71

Erich K. Dodson, Klaus J. Puettmann, and Adrian Ares

Th inning Eff ects on Spotted Owl Prey and Other Forest-Dwelling Small Mammals ................... 79

Todd M. Wilson and Eric D. Forsman

Above-ground Carbon Storage, Down Wood, and Understory Plant Species Richness after 

Th inning in Western Oregon ....................................................................................................... 91

Julia I. Burton, Adrian Ares, Sara E. Mulford, Deanna H. Olson, and Klaus J. Puettmann

Green-Tree Retention, Ectomycorrhiza Diversity, and Ectomycorrhizal Spore Inoculum ........... 101

Daniel L. Luoma and Joyce L. Eberhart
Density Management in the 21st Century: West Side Story PNW-GTR-880

iv

Managing for Old-growth Forests: A Moving Target ................................................................. 108

Th omas A. Spies and Robert J. Pabst

Stand Density Relationships ...................................................................................................... 110

John C. Tappeiner, II

Adapting Management of Shade-intolerant Douglas-Fir Forests to Provide Maximum 

Diversity of Habitats Continuously and Productively ................................................................ 112

Michael Newton

Westside Th inning and Underplanting Study in 50- to 55-year-old Douglas-fi r and 

Douglas-fi r/Hemlock Stands ..................................................................................................... 114

Elizabeth C. Cole and Michael Newton

Th e Th eoretical and Empirical Basis for Understanding the Impact of Th inning on 

Carbon Stores in Forests ............................................................................................................ 115

Mark E. Harmon

Western Washington and Oregon Elk Foraging: Use and Nutritional Value by 

Vegetative Life-Form ................................................................................................................. 115

John G. Cook and Rachel C. Cook

Songbird Response to Alternative Forest Density Management in Young Douglas-Fir Stands .... 117

Joan C. Hagar

Eff ects of Forest Th inning on Bird-Vegetation Relationships in Young Douglas-Fir Forests ....... 118

Svetlana Yegorova

Lichen Habitat May Be Enhanced by Th inning Treatments ....................................................... 119

Heather T. Root and Bruce McCune

Conservation of Ectomycorrhizal Fungi: Green-tree Retention Preserves Species Diversity ........ 120

Joyce L Eberhart and Daniel L Luoma

Eff ects of Varying Levels of Forest Th inning on Tricholoma magnivelare (American 

Matsutake) ................................................................................................................................ 121

Joyce L Eberhart and Daniel L Luoma

Community Structure of Vascular Plants, Arthropods, Amphibians, and Mollusks in 

Managed Forests of the Pacifi c Northwest (USA) ...................................................................... 122

Stephanie J. Wessell-Kelly and Deanna H. Olson

Leave Islands as Refugia for Low-Mobility Species in Managed Forest Mosaics ......................... 123

Stephanie J. Wessell-Kelly and Deanna H. Olson

Section 3. Riparian and Aquatic Ecosystems and Their Responses to Thinning 

and Buffers ............................................................................................................................................125

Sampling and Modeling Riparian Forest Structure and Riparian Microclimate.......................... 126

Bianca N.I. Eskelson, Paul D. Anderson, and Hailemariam Temesgen
Density Management in the 21st Century: West Side Story PNW-GTR-880

v

A Simulation Framework for Evaluating the Eff ect of Riparian Management Strategies 

on Wood in Streams: An Example Using Oregon’s State Forest Riparian Management 

Regulations ............................................................................................................................... 136

Mark Meleason, Jeremy Groom, and Liz Dent

Riparian Buff ers and Th inning in Headwater Drainages in Western Oregon: 

Aquatic Vertebrates and Habitats ............................................................................................... 148

Deanna H. Olson

Th e Riparian Ecosystem Management Study: Response of Small Mammals to Streamside 

Buff ers in Western Washington ................................................................................................. 163

Martin G. Raphael and Randall J. Wilk

Evaluating Headwater Stream Buff ers: Lessons Learned from Watershed-Scale 

Experiments in Southwest Washington ...................................................................................... 169

Peter A. Bisson, Shannon M. Claeson, Steven M. Wondzell, Alex D. Foster, and Ashley Steel

Applying Four Principles of Headwater System Aquatic Biology to Forest Management ............ 189

Robert J. Danehy and Sherri L. Johnson

Integrated Watershed Analysis: Adapting to Changing Times .................................................... 203

Gordon H. Reeves

Intrinsic Potential: What Is It and What Is It Good For? ........................................................... 204

Kelly M. Burnett

Quantifying Fish Responses to Forestry—Lessons from the Trask Watershed Study .................. 205

Jason Dunham, Douglas Bateman, David Hockman-Wert, Nathan Chelgren, and David Leer

Riparian Microclimate and Stream Temperature: Th inning and Buff er-Width Infl uences .......... 206

Paul D. Anderson

Stream Temperature Responses to Timber Harvest and Best Management Practices—

Findings from the ODF RipStream Project ............................................................................... 207

Jeremy D. Groom

Initial Riparian Down Wood Dynamics in Relation to Th inning and Buff er Width .................. 208

Paul D. Anderson, Deanna H. Olson, and Adrian Ares

Th inning and Riparian Buff er Confi guration Eff ects on Down Wood Abundance in 

Headwater Streams in Coniferous Forests .................................................................................. 210

Adrian Ares, Deanna H. Olson, and Klaus J. Puettmann

Slope Failure as an Upslope Source of Stream Wood .................................................................. 211

Daniel Miller

Plethodontid Salamander Population Ecology in Managed Forest Headwaters in the 

Oregon Coast Range ................................................................................................................. 212

Matthew R. Kluber and Deanna H. Olson
Density Management in the 21st Century: West Side Story PNW-GTR-880

vi

No Eff ects of Th inning With Riparian Buff ers on Terrestrial Salamanders in Headwater 

Forests 5 to 6 Years Post-Harvest in Western Oregon ................................................................. 213

Matthew R. Kluber, Deanna H. Olson, and Klaus J. Puettmann

Log and Soil Temperature Profi les in Managed Headwater Sub-Basins in the Oregon 

Coast Range: Implications for Wildlife Habitat ......................................................................... 214

Matthew R. Kluber, Deanna H. Olson. and Klaus J. Puettmann

Section 4. Socioeconomics and Operations ...............................................................................215

Managers’ Perspectives: Practical Experience and Challenges Associated with Variable-Density 

Operations and Uneven-Aged Management .............................................................................. 216

Kurtis E. Steele

Growth and Yield Considerations and Implications for Alternative Density Management 

Objectives and Approaches ........................................................................................................ 217

David Marshall

Harvest Operations for Density Management: Planning Requirements, Production, 

Costs, Stand Damage, and Recommendations ........................................................................... 218

Loren D. Kellogg and Stephen J. Pilkerton

Section 5. Thinning and Adaptation .............................................................................................219

Geometry of Forest Landscape Connectivity: Pathways for Persistence ...................................... 220

Deanna H. Olson and Kelly M. Burnett

Headwater Stream Flow, Climate Variation, and Riparian Buff ers with Th inning in 

Western Oregon ........................................................................................................................ 239

Julia I. Burton, Deanna H. Olson, and Klaus J. Puettmann

Th inning Impacts on the Resilience of Wildlife Habitat Quality under Climate Change 

in Coniferous Forests of Western Oregon .................................................................................. 240

Andrew R. Neill, Klaus J. Puettmann, and Adrian Ares

English Equivalents ............................................................................................................... 241
Density Management in the 21st Century: West Side Story PNW-GTR-880

vii

Reviewers

John Baily

Pete Bisson

Susan Bolton

Bernard Bormann

Shannon Claeson 

John Colby

Pat Cunningham

Frank Davis

Liz Dent

Jason Dunham

Bianca Eskelson

Paige Fischer

Eric Forsman

Patricia Garvey-Darda

Peter Gould 

Eric Gustafson

Robin Gyorgytalvy 

Joan Hagar

Mark Harmon

Connie Harrington

Sherri Johnson

Stuart Johnston

Craig Kintop

Jeff Kline

John Lehmkuhl

James Lutz

Tom Manning 

Bruce McCune

Randy Molina

Deanna Olson

Rob Pabst 

Nathan Poage 

Karl Polivka

Martin Richie

Mark Schultz

Arne Skaugset

Jane Smith

Hugh Snook

Fred Swanson

Charlie Th ompson

Jim Th railkill

Hart Welsh, Jr.

Ellen Wohl

Th e editors would like to acknowledge all the reviewers who made it possible to evaluate and improve 

the manuscripts for this proceedings. Th ank you for your time and thoughtful comments.

Acknowledgements

Th e Density Management in the 21st Century workshop was the outcome of many people’s eff orts. 

We thank all of the presenters whose contributions are refl ected in the proceedings. We especially 

thank several agency representatives whose presentations are not represented but who were essential to 

placing the relevance of the science into a regional management context. Th ese presenters included: 

Mike Haske, Deputy State Director, Resource Planning, Use & Protection, Oregon/Washington BLM; 

Jeff Walter, Director, Natural Resources, US Forest Service Region 6; George McFadden, Bureau of 

Land Management; Jerry Ingersoll, Forest Supervisor, Siuslaw National Forest; and Craig Kintop, 

Bureau of Land Management.

Th e conference organizing committee consisted of Sally Sovey, Heidi Anderson, Karen Blakney, Klaus 

Puettmann, Deanna Olson, Charles R. Th ompson, Hugh Snook, Craig Kintop, Erich Dodson, and 

Paul Anderson. Excellent support was provided by Kathryn Ronnenberg in developing the conference 

program, by Maya Perez in conference logistics, and by Cheryl Friesen in advertising the conference 

among the resource managers, researchers, and other participants. A special appreciation is due Sally 

Sovey, who stepped up in the fi nal stretch of preparations and made several important contributions 

to the success of the conference.

Th is publication was made possible by funding from the USDA Forest Service, Pacifi c Northwest 

Research Station, Land and Watershed Management Program.
Photo by Brad Catton, USFS.
Density Management in the 21st Century: West Side Story PNW-GTR-880

1

Two Decades of Learning about Thinning in the 

Ecosystem Management Era

Paul D. Anderson

Paul D. Anderson is a supervisory research forester, USDA Forest Service, Pacifi c Northwest Research Station, Forestry 

Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; pdanderson@fs.fed.us

Introduction

Adoption of the Northwest Forest Plan (NWFP, 

USDA and USDI 1993, 1994) in the early 1990s 

signaled a major shift in forest management on 

federal lands in western Oregon and Washington. 

Th e Plan refl ected composite concerns raised by 

various resource managers, conservation groups, 

scientists, and the general public about the 

sustainability of production-oriented forestry as 

practiced from the early 1900s. Specifi cally, the 

plan addressed concerns regarding clearcutting, 

the harvest of old-growth trees and loss of 

related habitat, and threats to more than 1,000 

potentially sensitive species (Th omas et al. 1993; 

USDA and USDI 1993), including regionally 

iconic salmonids and the Northern Spotted Owl 

(Strix occidentalis caurina). As new objectives such 

as ecosystem function and biodiversity became 

higher priorities, federal land managers strove 

to defi ne new silvicultural practices that would 

provide ecologically sustainable alternatives to 

clearcutting and old-growth harvest while still 

providing for wood production and economic 

benefi ts. As a result, partial overstory removals 

—mostly alternative thinning methods—have 

replaced clearcutting as the predominant form of 

harvest on federal lands over the past two decades.

Two concepts that crystallized in the 1990s 

have been important to the development of 

contemporary thinning practices: 1) existing oldgrowth stands with large trees, complex crowns, 

and multiple canopy layers often developed 

at lower densities than those typical of current 

young, unthinned stands (Tappeiner et al. 

1997); and 2) retained down wood, snags, and 

large older trees with complex crowns perform 

important functions in providing habitat for 

late-seral fl ora and fauna in young, managed 

stands (Franklin et al. 1997). When aligned with 

an objective to accelerate development of latesuccessional forests, these two concepts provide 

the rationale for thinning young, dense stands in 

unconventional ways to increase structural and 

compositional variability.

In addition, the 1990s ushered in an era of 

more holistic aquatic-riparian conservation 

and restoration in western forests, with a new 

emphasis on watershed values. Th e Aquatic 

Conservation Strategy (ACS) outlined in the 

Northwest Forest Plan conceptually shifted the 

aquatic management emphasis from individual 

stream-reach conditions to larger-scale watershed 

conditions, in accordance with evolving concepts 

of streams functioning as branched networks 

(Fisher 1997). In this regard, the ecological 

importance of small headwater stream reaches 

emerged as potentially signifi cant. Small streams 

drain typically 70 to 80 percent or more of a 

watershed in the Northwest (Gomi 2002). Hence, 

they encompass signifi cant habitat within a 

watershed context, but also potentially contribute 

signifi cantly to downstream conditions as well as 

providing ecological subsidies to uplands (Baxter 

et al. 2005). Riparian reserve designations of the 

ACS extended protections to small non-fi shbearing streams by codifying interim streamside 

buff er widths. Within riparian reserves, harvest 

activity was not precluded, but must contribute 

to, or not retard, the attainment of ACS 

objectives. However, harvest, predominantly 
Density Management in the 21st Century: West Side Story PNW-GTR-880

2 Two Decades of Learning About Th inning Anderson

commercial thinning, occurred on only about 2 

percent of total riparian reserve area in the fi rst 

decade of ACS (Reeves et al. 2006).

Application, refi nement, and validation 

of northwest forest ecosystem management 

concepts has occurred concurrently in local 

operational trials by practitioners and in formal 

studies conducted as research-management 

collaborations. Given 20 years of learning from 

research and operational experiences, there 

is much to discuss about thinning as a forest 

management tool relevant to local programmatic 

applications and broader regional strategies and 

policies.

Workshop Purpose & Scope

In October 2011, the principal partners of 

the Density Management and Riparian Buff er 

Studies of western Oregon (DMS, Cissel et al. 

2006), the Bureau of Land Management, Forest 

Service, and Oregon State University, convened 

a 3-day conference, entitled Density Management 

in the 21st Century: West Side Story, as a means 

to present and discuss fi ndings of nearly twenty 

20 years of density management research. In 

a narrow sense, the conference provided a 

capstone to a fi rst phase of monitoring, analysis, 

and inference of the varied terrestrial, riparian, 

and aquatic ecosystem responses to the initial 

implementation of the DMS experimental 

treatments in the late 1990s. While various facets 

of the DMS were intentionally featured, the 

conference organizers recognized that the science 

related to thinning within the Northern Spotted 

Owl range of western Oregon and Washington 

has been developed through several important 

studies and in various disciplinary, ownership, 

and interest-group contexts. A broader intent of 

the conference was to highlight this wide array of 

thinning-related science to stimulate a discussion 

of what we know and understand, or have yet to 

resolve, about thinning as a silvicultural practice 

to meet contemporary and future management 

objectives. We purposefully sought representation 

from other west-side studies for comparison and 

synthesis. Stimulation of meaningful dialogue 

was dependent on broad representation of the 

researchers who generated information and the 

practitioners and decision-makers who translate 

the science into outcomes of ecological and social 

importance. To this end, the conference included 

40 oral and 16 poster presentations by more 

than 65 authors, including decision-makers, 

practitioners, and researchers from 11 diff erent 

government, private industry, and academic 

institutions.

Proceedings Overview

We present a number of papers and abstracts 

which highlight the conference themes. Th ese 

themes include: Th e Regional and Landscape 

Context for Density Management in the 

Northwest Forest Plan Era; Implementation 

and Infl uences of Density Management in the 

Terrestrial Ecosystem; Riparian and Aquatic 

Ecosystems and Th eir Responses to Th inning 

and Buff ers; Socioeconomics and Operations; 

and looking forward, Th inning and Adaptation. 

Collectively, the papers and abstracts illustrate 

the degree to which the realm of thinning extends 

beyond a narrow focus on trees to broader forest 

ecosystem considerations. To view the oral 

presentations, visit the interagency ECOSHARE 

website: http://ecoshare.info/products/completedworkshops/thinning-workshop/

To set the context for contemporary thinning, 

Kenneth Ruzicka and coauthors provide an 

overview of the origins of the Density Management 

and Riparian Buff er Study in relation to the 

Northwest Forest Plan. Th e importance of public 

perceptions of forest management activities in 

determining social acceptability is addressed by 

Robert Ribe. At the regional landscape scale, 

trends in harvest intensity and the relationships to 

land ownership patterns and ecological gradients 

are addressed by Robert Kennedy and coauthors 

and by Janet Ohmann. 

Application of thinning and subsequent 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Two Decades of Learning About Th inning Anderson 3

vegetation responses are addressed in several 

papers. Klaus Puettmann and coauthors describe 

understory species abundance and diversity 

responses as observed in the DMS and the Young 

Stand Th inning for Diversity Study (Poage and 

Anderson 2007). Peter Gould and Constance 

Harrington describe the development of new 

models of understory tree development. Kyle 

Dodson and coauthors address tree mortality and 

snag recruitment in the DMS. Mark Harmon 

addresses the fundamentals of thinning eff ects 

on carbon stores, and Julia Burton and coauthors 

discuss trade-off s between development of 

diverse understory vegetation communities 

and the accumulation of carbon stores. Daniel 

Luoma and Joyce Eberhart look below the soil 

surface to characterize mycorrhizal responses 

to the level and pattern of green-tree retention 

harvests as implemented in the Demonstration 

of Ecosystem Management Options (DEMO) 

study (Franklin 1999). Heather Root and Bruce 

McCune describe potential benefi ts to lichen 

diversity associated with retention of large legacy 

trees and decreased stand densities in young 

stands. Th e variable pathways which can lead to 

old-growth structures are described by Tom Spies 

and Robert Pabst. Th e eff ectiveness of alternative 

density management approaches to placing 

young stands on trajectories toward late-seral 

structure is the focus of John Tappeiner and of 

Mike Newton. 

Th e impact of contemporary density 

management practices on enhancing terrestrial 

habitat for a variety of organisms was an 

important conference focus. From the perspective 

of the Northern Spotted Owl, Todd Wilson and 

Eric Forsman discuss the relationships between 

thinning and habitat suitable for fl ying squirrels, 

the principle prey base in portions of the owl’s 

range. John Cook and Rachel Cook discuss the 

importance of understory vegetation nutritional 

value as a determinant of possible Elk (Cervus 

elaphus) forage benefi ts of thinning. Th e fi nding 

that diff erent taxonomic and functional groups 

of birds benefi t diff erentially from thinning is 

discussed by Joan Hagar.

Th e contemporary aquatic and riparian issues 

associated with forest management strategies 

at longer-term, landscape scales are framed in 

the context of integrated watershed analysis 

by Gordon Reeves. Kelly Burnett outlines 

concepts of intrinsic potential—the persistent 

characteristics of streams that defi ne the potential 

to provide quality fi sh habitat. Th e hydrogeomorphic processes responsible for delivering 

wood to streams, and therefore realized fi sh 

habitat are reviewed by Dan Miller. Infl uences 

of thinning and riparian buff er width on aquatic 

and riparian attributes at a fi ner reach scale 

include works addressing microclimate and 

stream temperature responses (Bianca Eskelson 

and coauthors; Paul Anderson and coauthors; 

Jeremy Groom), and stream wood recruitment 

(Mark Meleason and coauthors; Paul Anderson 

and coauthors). Deanna Olson summarizes 

DMS fi ndings on the impacts of thinning and 

alternative riparian buff er widths on amphibian 

habitats and species abundances and assemblages. 

Th e responses of invertebrates, mollusks, fi shes 

and small mammals to alternative streamside 

buff ers in the presence clearcutting in western 

Washington are presented by Peter Bisson and 

coauthors and Martin Raphael and Randall 

Wilk. Jason Dunham and coauthors describe 

fi sh responses to harvest in a paired watershed 

study. Robert Danehy and Sherri Johnson distill 

many of the salient lessons into four principles of 

stream ecology applicable to forest management.

From an operations perspective, Kurt Steele 

draws attention to the practical challenges 

associated with applying variable density 

thinning. David Marshall addresses the 

implications of contemporary thinning practices 

for growth and yield. Loren Kellogg and Steven 

Pilkerton discuss the forest engineering issues of 

harvest planning requirements, production costs, 

and stand damages associated with contemporary 

thinning operations.

Looking to the future, Deanna Olson and 

Kelly Burnett defi ne new concepts for providing 
Density Management in the 21st Century: West Side Story PNW-GTR-880

4 Two Decades of Learning About Th inning Anderson

habitat connectivity in headwater-dominated 

landscapes. Possible implications of climate 

change on stream fl ow, thinning, and riparian 

buff er needs are addressed in a poster by Julia 

Burton and coauthors. Th e impact of thinning 

on the resilience of wildlife habitat to climate 

variation is discussed in a poster by Andrew Neill 

and coauthors. 

Personal Perspectives

Th e conference papers serve well to illustrate 

the science underlying current harvest practices 

as well as some of the larger policy questions 

surrounding forest management. However, 

as pointed out by Mike Haske (Deputy State 

Director for Resources, USDI BLM) and Jerry 

Ingersoll (Forest Supervisor, USDA Forest Service 

Siuslaw National Forest) in their refl ections on 

the presentations, unanswered questions remain, 

some of which are science-oriented and many 

that are social or political. In the following, I take 

the opportunity to address from my perspective 

as a scientist some of the points of discussion that 

occurred outside of the presentations and are not 

necessarily addressed in the proceedings papers. 

Thinning isn’t rocket science, but...

Principles of thinning and density management 

have been established over centuries of 

“conventional” silviculture practice in Europe and 

more recently in North America and elsewhere. 

So what is novel about the contemporary 

application of thinning in western Oregon and 

Washington? For me the answer is driven by both 

why and how we thin. If we change the “why” we 

thin, the “how” we thin changes also. When the 

primary objective of silviculture has been meeting 

wood-production objectives, thinning served 

primarily to harvest slower-growing trees, some 

destined to die, and to reallocate site resources to 

fewer stems of the most economically productive 

species, thereby promoting increased stand 

vigor and growth. Two common consequences 

of conventional thinning practices have been 

increased uniformity of forest structure and 

composition, and removal or delay in the 

development of dead wood as snags or down 

wood to meet decadence and habitat functions. 

Variable densities, skips and gaps, retention of 

minor species and snags, active creation of snags 

and down wood, and underplanting are elements 

that have been explored in contemporary 

density management prescriptions at the 

stand level. Th e fundamental ecological and 

physiological principles underpinning thinning 

eff ects on residual trees remain the same, but 

the interactive infl uences of increased spatial 

variability and structural complexity may alter 

stand development. Our experiences with 

contemporary thinning practices are still too few 

and too recently adopted to state with certainty 

that the broadened array of ecological objectives 

is being met.

Have we chosen the correct references 

from which to gauge observed 

thinning effects?

A concern raised by some conference fi eld trip 

participants was that many of the contemporary 

thinning studies base inferences on the responses 

of thinned young stands relative to responses for 

similarly young but untreated stands: in eff ect, 

a comparison between active management and 

a passive, no-treatment alternative. While this is 

perhaps a statistically sound approach, are young, 

unthinned stands the most relevant standard, 

given the common objective of developing lateseral attributes? Th ere are few if any 30- to 50-yearold stands developing under natural, unmanaged 

conditions that can provide contemporary 

references to the managed stands that are the 

current target of thinning. Further, it has been 

diffi cult to locate late-seral stands to serve as valid 

references to desired conditions. During initial 

planning of the DMS, representative late-seral 

reference stands were sought, but where located, 

the late-seral stands tended to occupy settings 

incomparable to the younger managed stands to 

be thinned—they were often at higher elevations, 

were forest fragments, and did not include 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Two Decades of Learning About Th inning Anderson 5

streams. In the absence of site-specifi c late-seral 

reference stands, there are a limited number 

of published studies that provide defi nitive 

stand structure and composition characteristics 

either qualitatively (e.g., Bauhus et al. 2009) or 

quantitatively (e.g., Poage 2005), that can provide 

late-seral benchmarks. However, published 

characterizations were derived retrospectively, 

and refl ect an unknown range of variability in 

developmental trajectory. 

Th e earliest of the contemporary west-side 

thinning studies was implemented in 1992 and 

1993 on the Siuslaw National Forest (Poage and 

Anderson 2007). Th e study has generated data 

from 17 years of post-treatment monitoring; 

thus, we are only 15 to 20 percent of the way 

to observing the planned late-seral objective. Th e 

developmental path that these recently treated 

stands will ultimately take in approaching lateseral conditions is both empirically unknown and 

relatively poorly modeled. Regardless of these 

uncertainties and the lack of clear standards, 

our research studies may better serve managers 

by focusing on thinning response trends as 

deviations from the desired late-seral conditions 

rather than deviations from untreated, youngstand references.

Morticulture—the management of 

death and decay

Critical to managing for late-successional 

habitats is an improved understanding of how 

alternative silvicultural practices interact with 

processes of tree death and decay and how 

silviculture can be used to augment or enhance 

those processes. Over the past several decades 

our ecological understanding of decadence and 

its importance to habitat and biogeochemical 

processes has increased substantially, but 

translation of the fundamental knowledge 

into coherent goals is lagging. Th ere is likely 

consensus that decadence is needed; however, 

questions of how much, what form, where, and 

when continue to be a subject of debate. We have 

some valuable tools such as DecAID (Mellon et 

al. 2002) that describe the landscape variability 

of terrestrial snag and down wood abundances as 

well as rudimentary wood abundance-species use 

relationships, and NetMAP (Benda et al. 2007), 

which can quantify the probability for delivery 

of wood to stream channels. However, it remains 

a challenge to quantify the incremental gain in 

ecological benefi ts associated with incremental 

increases in snag and down wood abundance. 

Increasingly, simulation modeling is being used 

to explore trade-off s among benefi ts associated 

with alternative silvicultural approaches at stand 

or landscape scales. Our readily accessible forestgrowth simulation models (e.g. Forest Vegetation 

Simulator; ORGANON) were developed 

from relatively strong tree-growth data, but 

unfortunately they prove to be rather poor 

platforms for projecting tree mortality and down 

wood recruitment and persistence. Improvement 

of these simulators will require that we invest 

in the analysis of the empirical snag and downwood data accruing in our long-term silviculture 

experiments to provide more robust functions 

for model improvement. Further, uncertainties 

in stochastic mortality events may require novel 

coupling of stand-level simulators with largerscale process or disturbance models to better 

project snag and down-wood dynamics at 

multiple scales of ecological importance.

Riparian buffers and the ACS

Th inning as conducted in the DMS, other 

studies, and operationally on federal lands is a 

much diff erent disturbance than clearcutting 

when it comes to potential harvest alterations 

of riparian habitats, including microclimate 

and stream temperature. Th e NWFP interim 

guidelines for riparian reserves were relatively 

conservative, and we have learned that in some 

contexts such as small headwater streams, key 

ecological functions such as shading or habitat for 

aquatic and riparian dependent vertebrates can 

often be fulfi lled with narrower buff ers. However, 

as we consider more intensive thinning or 

retention harvests, or other ecosystem functions 
Density Management in the 21st Century: West Side Story PNW-GTR-880

6 Two Decades of Learning About Th inning Anderson

and their interactions, questions remain regarding 

the effi cacy of various buff er confi gurations. At a 

larger scale, the intent of the ACS was to provide 

a watershed focus to assessments of stream 

condition—particularly, recognition that natural 

dynamics will result in periods of poor condition 

at the fi ne scales of stream or stream reaches, and 

therefore trends at the watershed scale may be 

more meaningful for assessing overall landscape 

condition and restoration effi cacy. Th ere is a 

need to reconcile a large-scale ACS approach 

with management actions and condition criteria 

applied at the fi ner stream-reach scale. Until we 

can eff ectively think about important aquatic 

and riparian management issues in the context 

of integrated, multi-scaled ecosystems, confl icts 

between management toward large-scale 

outcomes and fi ner-scale regulatory objectives 

are likely to recur. 

What is the future for thinning?

Whether on BLM or Forest Service lands, 

thinning has become a very important 

silvicultural tool. In the Pacifi c Northwest 

Region, thinning and fuels-reduction treatments 

targeting forest restoration objectives account for 

about 97 percent of the Forest Service vegetation 

management budget (Jeff Walters, Region 6 

Director of Natural Resources, U.S. Forest 

Service). Perhaps the continued predominance of 

thinning is uncertain, both in terms of continued 

availability of suitable stands for thinning 

and in terms of the limited ability of thinning 

to provide some desired landscape elements 

such as early-seral habitat. I am not overly 

concerned about either issue as a determinant 

to whether or not thinning continues to be an 

important silvicultural tool into the future. For 

example, recent discussions proposing increased 

regeneration harvest on federal lands using greentree-retention (Franklin and Johnson 2012) as a 

means to increase the abundance of early-seral 

forest do not preclude restoration thinning. 

Rather, variable-density thinning conceivably 

can be an important intermediate treatment in 

silvicultural systems featuring legacy retention, 

natural regeneration, and longer rotations or 

cutting cycles. However, long production-cycle 

strategies involving the eventual harvest of large 

trees may continue to be constrained by a lack of 

social acceptance. At larger spatial and temporal 

scales, a very large palette of silvicultural 

approaches and management strategies is 

available to meet diverse ecological and societal 

objectives. Given that forests are complex systems 

with varying capacities to respond and adapt to 

disturbance or stressors, uncertainty will be the 

norm that justifi es using a variety of management 

approaches.

In my opinion, the greatest challenge facing 

forest resources management has long been, 

and will continue to be, the development 

and fulfi llment of the implicit social license 

permitting management of public and private 

forest lands to sustainably meet the breadth 

of needed ecological and societal services. As a 

scientist my intent, similar to that of my peers, is 

to objectively deliver information and tools that 

are used to inform forest management options 

and policy. Although scientists may suggest the 

management implications of their work, it is 

intended that considerable room be allowed for 

natural resource managers to exercise innovations 

in application as they integrate among themes and 

prioritize their own goals. To this end, it has been 

personally rewarding to serve as one principal 

investigator for the Density Management and 

Riparian Buff er Studies, and to have participated 

in the planning and conduct of the conference 

which is captured in the individual papers and 

abstracts that follow in this volume.

Acknowledgments:

I thank Dede Olson, Stuart Johnston, and Klaus 

Puettmann for providing a review of an earlier version 

of this manuscript.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Two Decades of Learning About Th inning Anderson 7

Literature Cited

Bauhus, J.; Puettmann, K.; Messier, C. 2009. 

Silviculture for old-growth attributes. Forest 

Ecology and Management. 258: 525–537.

Baxter, C.V.; Fausch, K.D.; Saunders, W.C. 2005. 

Tangled webs: reciprocal flows of invertebrate 

prey link streams and riparian zones. Freshwater 

Biology. 50: 201–220.

Benda, L.E.; Miller, D.J.; Andras, K.; Bigelow, P.; 

Reeves, G.; Michael, D. 2007. NetMap: a new 

tool in support of watershed science and resource 

management. Forest Science. 53: 206–219.

Fisher, S.G. 1997. Creativity, idea generation and 

the functional morphology of streams. Journal 

of the North American Benthological Society. 

16: 305–318.

Franklin, J.F. 1999. The history of DEMO: an 

experiment in regeneration harvest of northwestern 

forest ecosystems. Northwest Science. 73: Special 

Issue: 1–11.

Franklin, J.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., 

eds., Creating a forestry for the 21st century. 

Washington, DC: Island Press: 111–140.

Gomi, T.; Sidle, R.C.; Richardson, J.S. 2002. 

Understanding processes and downstream linkages 

of headwater streams. BioScience. 52: 905–915.

Mellon, K.; Marcot, B.G.; Ohmann, J.L.; Waddell, 

K.L.; Willhite, E.A.; Hostetler, B.B.; Livingston, 

S.A.; Ogden, C. 2002. DecAid: A decaying wood 

advisory model for Oregon and Washington. In: 

Proceedings of the symposium on the ecology 

and management of dead wood in western forests. 

1999 November 2–4, Reno, NV, Laudenslayer, 

W.F., Jr.; Shea, P.; Valentine, B.E.; Weatherspoon, 

C.P.; Lisle, T.E., tech. coords. Gen. Tech. Rep. 

PSW-GTR-181. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest 

Research Station: 527–533.

Poage, N.J. 2005. Variability in older forest structure 

in western Oregon. Open-File Report 2005-1385. 

Reston, VA: U.S. Department of the Interior, 

Geological Survey. 28 p.

Poage, N.J.; Anderson, P.D. 2007. Large-scale 

silviculture experiments of western Oregon and 

Washington. Gen. Tech. Rep. PNW-GTR-713. 

Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Research Station. 

44 p.

Reeves, G.H.; Williams, J.E.; Burnett, K.M.; Gallo, 

K. 2006. The aquatic conservation strategy of 

the Northwest Forest Plan. Conservation Biology. 

20: 319–329.

Tappeiner, J.C.; Huffman, D.; Marshall, D.; Spies, 

T.E.; Baily, J.D. 1997. Density, ages, and growth 

rates in old-growth and young-growth forests 

in coastal Oregon. Canadian Journal of Forest 

Research. 27: 638–648.

U.S. Department of Agriculture and U.S. 

Department of the Interior [USDA and USDI]. 

1993. Forest Ecosystem Management Assessment 

Team (FEMAT): an ecological, economic, and 

social assessment. Portland, OR: U.S. Department 

of Agriculture and U.S. Department of the Interior. 

Available from the Regional Ecosystem Office, 

P.O. Box 3623, Portland, OR 97208-3623.

U.S. Department of Agriculture and U.S. Department 

of the Interior [USDA and USDI], 1994. Record 

of decision on management of habitat for latesuccessional and old-growth forest related species 

within the range of the Northern Spotted Owl 

[Northwest Forest Plan]. Portland, OR: U.S. 

Department of Agriculture and U.S. Department 

of the Interior. Available from the Regional 

Ecosystem Office, P.O. Box 3623, Portland, OR 

97208–3623.

Citation:

Anderson, Paul D. 2013. Two decades of learning about thinning in the ecosystem management era. In: Anderson, Paul D.; 

Ronnenberg, Kathryn L., eds. Density management in the 21st century: west side story. Gen. Tech. Rep. PNW-GTR-880. 

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacifi c Northwest Research Station: 1–7.
Photos, facing page—Top: View from Green Peak 

toward the Willamette Valley. Photos by Paul Anderson. 

Center left: Variable-width buffer at Green Peak. 

Photo by Paul Anderson. Center right: Unthinned 

two tree-height buffer at Keel Mountain, with Andy 

Neill for scale. Photo by Paul Anderson. Bottom left:

Stream wood and Western Skunk Cabbage (Lysichiton 

americanus) at Keel Mountain. Photo by Mark Meleason, 

USFS. Bottom right: Edge of federal and private 

forest industry ownerships, Green Peak. Photo by Paul 

Anderson.
Section 1. The Regional and Landscape Context for 

Density Management in the Northwest Forest Plan Era
Density Management in the 21st Century: West Side Story PNW-GTR-880

10

The Intertwining Paths of the Density Management 

and Riparian Buffer Study and the Northwest Forest 

Plan

Kenneth J. Ruzicka, Jr., Deanna H. Olson, and Klaus J. Puettmann

Kenneth J. Ruzicka, Jr. is a doctoral student, Department of Forest Ecosystems and Society, Oregon State University, 

Corvallis, OR 97331, kenneth.ruzicka@oregonstate.edu; Deanna H. Olson is a research ecologist, USDA Forest Service, 

Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; Klaus J. 

Puettmann is Edmund Hayes Professor in Silviculture Alternatives, Department of Forest Ecosystems and Society, Oregon 

State University, Corvallis, OR 97331.

Abstract

Initiated simultaneously, the Density Management and Riparian Buff er Study of western Oregon 

and the Northwest Forest Plan have had intertwining paths related to federal forest management 

and policy changes in the Pacifi c Northwest over the last 15 to 20 years. We briefl y discuss the 

development of the Northwest Forest Plan and how it changed the way forest policy was developed 

in the region. Th e concurrent conceptualization and implementation of the Density Management 

and Riparian Buff er Study within this new management framework resulted in a proof-of-concept 

for adaptive management approaches outlined in the Plan, especially relative to riparian and 

upland restoration practices. Th e Density Management Study serves as a model for integrated 

knowledge discovery and adaptive management within the context of the federal forest plan. Th e 

future of the study appears to be similarly interconnected with the interagency plan for federal 

lands management. 

Keywords: Forest thinning, western Oregon, Bureau of Land Management, Forest Service.

Introduction

Th e Density Management and Riparian Buff er 

Study (DMS) originated in 1993 as a longterm, operational-scale experiment to investigate 

silvicultural techniques intended to accelerate 

development of late-successional and old-growth 

forest characteristics in western Oregon (Cissel 

et al. 2006). To accomplish this, the study tested 

alternative thinning prescriptions that were 

not yet tested or established in the scientifi c 

literature at the time of study establishment. Th e 

upland thinning design of DMS was conceived 

before fi nalization of the Northwest Forest Plan 

(hereafter, the Plan) (USDA and USDI 1994a), 

but was implemented within the new policy 

framework created by the Plan. Although not an 

initial goal of the study, the implementation of 

the DMS identifi ed ways that federal agency land 

managers in western Oregon, in particular the 

U.S. Bureau of Land Management (BLM), could 

adapt to work within the new policy framework 

and more quickly achieve Plan goals, especially in 

reserved land allocations. 

By examining the DMS study, we explore 

the intertwining threads of policy changes, 

knowledge discovery, and new management 

questions asked during development and 

implementation of the Plan. We briefl y discuss 

the history of the Northwest Forest Plan and how 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al. 11

it changed the way forest policy was developed. 

We show how the DMS arose within the new 

management framework, and fi nally discuss how 

the DMS has aff ected federal forest management 

at district and forest levels relative to regional 

management policy. It appears certain that 

western Oregon forest managers will continue to 

employ adaptive management to adjust to new 

challenges. Th e future of the DMS appears to be 

similarly interconnected with the Plan.

The Northwest Forest Plan: 

Abbreviated Synopsis

Th e listing of the Northern Spotted Owl (Strix 

occidentalis caurina) as a threatened species under 

the U.S. Endangered Species Act in 1990 (55 FR 

26114 26194) was neither the beginning nor the 

end of the struggle between old-growth forest 

preservation and timber management. Regional 

scientists had been concerned about loss of owl 

habitat since the early 1970s (Forsman 1975; Yaff ee 

1994). Although the spotted owl was the poster 

child for the forest-management confl icts coming 

to a head in the early 1990s, numerous scientists 

had been researching forest fragmentation eff ects 

on many diff erent species, characterizing specieshabitat relationships, and conducting species risk 

assessments (e.g., Ruggiero et al. 1991; Th omas 

et al. 1993). In addition to threatened species 

concerns, an emerging paradigm shift toward 

ecosystem management with multiple resource 

and restoration objectives came into confl ict 

with conventional management practices on 

federal forests in the Pacifi c Northwest (Yaff ee 

1994). Historical timber harvest practices were 

geared toward wood commodity production 

and implemented to “get the cut out” (Th omas 

2008; Williams 2009). Clashes between oldgrowth forest preservationists and federal land 

management agencies climaxed with a series 

of lawsuits that prevented timber sale and 

harvesting activities throughout the range of the 

Northern Spotted Owl (Th omas et al. 2006). 

Th ese lawsuits in part defi ned a new era for 

natural resource management in the U.S. where 

the management of public land was decided by 

legal determinations made by judicial courts 

(Th omas 2008).

In the polarized forest management climate 

of the early 1990s, President Clinton assembled 

the Forest Conference in 1993 to discuss the 

diff erent social, economic, and environmental 

issues concerning old-growth forests. He ordered 

federal land management agencies to draft a 

balanced, long-term policy that would direct 

the management of federal forests in the Pacifi c 

Northwest in the range of the spotted owl (USDA 

and USDI 1994b). 

President Clinton mandated that the “policy 

must:

• Never forget the human and the economic 

dimensions

• Protect long-term health of our forests, our 

wildlife, and our waterways

• Be scientifi cally sound, ecologically credible, 

and legally responsible

• Produce predictable and sustainable levels of 

timber sales and nontimber resources

• Make the federal government work together 

and work for you” (FEMAT 1993). 

Th e Forest Ecosystem Management and 

Assessment Team (FEMAT), which included 

representatives from the BLM, U.S. Forest Service, 

Fish and Wildlife Service, National Park Service, 

National Marine Fisheries Service, National 

Oceanic and Atmospheric Administration, and 

Environmental Protection Agency, was created 

to craft this diffi cult policy. Th e fi nal report was 

released in July of 1993 (FEMAT 1993) and was 

adapted into the Northwest Forest Plan in 1994 

(USDA and USDI 1994a; 1994b). Numerous 

detailed discussions of the Plan are available 

(e.g., see USDA and USDI 1994a; Yaff ee 1994; 

Marcot and Th omas 1997; Th omas 2008). 

Th e Northwest Forest Plan started a process 

toward implementing ecosystem-scale, sciencebased forest management (Th omas 2008). One 

hallmark of the Plan was that for the fi rst time, 

scientists led development of land management 
Density Management in the 21st Century: West Side Story PNW-GTR-880

12 Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al.

alternatives and played a key role in crafting federal 

policy (Bormann et al. 2007). FEMAT consisted 

of a team of scientists with expertise in various 

aspects of forest management and its economic, 

ecological and social impacts. Th e team was led 

by the “Gang of Four plus Two”—wildlife and 

fi sheries researchers from the Pacifi c Northwest 

aided by a cadre of hundreds of consultants 

(FEMAT 1993). Th is unique set of expertise 

manifested itself in a new management approach. 

Th e Plan was the fi rst eff ort to manage a forest 

ecosystem at the regional scale across an expansive 

area of ~10 million hectares (24.5 million acres) 

using a science-based, multi-resource approach. 

Th e original FEMAT design conceptually 

ensured that management actions taken on a 

local scale would not impair ecosystem function 

at a regional scale (FEMAT 1993). Fine-scaled 

management elements were later integrated into 

the regional Plan, providing for a multi-scaled 

management framework. “Survey and manage” 

requirements were added by President Clinton’s 

Council on Environmental Quality to manage 

sensitive species with restricted distributions that 

were not otherwise protected by the Plan. Finescale survey and manage requirements combined 

with coarser-scale land-use allocations (LUAs) 

were intended to facilitate Plan implementation 

without triggering additional environmental 

regulations for species protections. With these 

requirements in place, the intent of the Plan 

was to assess projects by their outcomes as part 

of the interconnected regional ecosystem rather 

than assessing management impacts only on 

individual stand-level land parcels (Diaz 2004). 

Th e integrated management of a regional 

ecosystem required that federal agencies, 

which had previously operated as fragmented 

administrative units, become partners. However, 

integrated management led to several operational 

challenges. Previous forest management actions 

had been planned through the local district 

personnel, including foresters and silviculturists, 

and were approved based on District or Area 

plans for inventory and timber harvests. When 

the fi rst comprehensive meetings between 

federal and state land managers and researchers 

were convened to discuss the spotted owl and 

old-growth management, participants lacked 

standardized approaches among agencies 

to assess multi-ownership forest blocks. For 

example, region-wide maps of forest resources 

were not available, and local or agency-specifi c 

mapping conventions made existing smallerscale maps incompatible (Yaff ee 1994). Plan 

implementation was delayed as procedural issues 

were worked out. 

The Density Management and 

Riparian Buffer Study as an 

adaptive learning platform

Much of what the FEMAT discussed was 

founded in research conducted in the 1980s 

to 1990s to address characterization of oldgrowth forest (e.g., Franklin and Spies 1991), 

and to understand its development (Spies and 

Franklin 1988). Other researchers sought to 

understand how to manage young Douglas-fi r 

(Pseudotsuga menziesii) plantations for eventual 

old-growth characteristics. Dr. John Tappeiner, 

a Senior Research Forester of the Bureau of 

Land Management Cooperative Research Unit 

and Oregon State University Professor, wanted 

to investigate new restoration management 

practices on BLM lands. Contemporary studies 

such as forest thinning in the Black Rock Forest 

Research Area (Del Rio and Berg 1979) or the 

Young Stand Th inning and Diversity Study 

(Hunter 1993) were designed to contribute 

to this topic. Th ose studies provided excellent 

information on the growth of forest stands, 

especially the relationships between tree and 

stand characteristics and stand density. However, 

they did not represent the variability that would 

occur in the overstory and understory at the stand 

level (J. Tappeiner, emeritus professor, Oregon 

State University College of Forestry, personal 

communication). Th e need for studies with 

broadened scope, such as the DMS, was apparent 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al. 13

as other large-scale silvicultural experiments 

were also implemented during this time (Poage 

and Anderson 2007). Th e DMS treatments 

were designed to be implemented at the largestand scale (50- to 300-ha treatments), with 

study sites encompassing the range of managed 

stand conditions more representative of western 

Oregon managed forests.

Th e Riparian Buff er Study component was 

added to the initial density management study 

objectives in 1994 (Cissel et al. 2006; Olson 

2013). Th is component addressed the “interim” 

provision in the NWFP regarding riparian 

reserves. Th e riparian reserve land-use allocation 

in the Northwest Forest Plan was defi ned to 

provide specifi c conservation and mitigation 

for aquatic and riparian resources. Th e interim 

riparian reserve widths (ranging from two sitepotential tree heights for fi sh-bearing stream 

reaches to one site-potential tree height for 

intermittent streams) were intended to be adjusted 

after watershed and project-specifi c analyses of 

aquatic-riparian resources. Th e riparian buff er 

aspect of DMS was designed specifi cally to test 

various widths of riparian buff ers in conjunction 

with upland thinning according to Plan Standards 

and Guidelines (USDA and USDI 1994b), as 

well as possible management options within 

riparian reserve boundaries (Hohler et al. 2001; 

Cunningham 2002; Diaz and Haynes 2002). 

Th us, by 1994, the DMS had become the 

fi rst stand-scale test of joint riparian and 

upland management prescriptions in the Pacifi c 

Northwest, and sought to address knowledge 

gaps identifi ed during Plan development. In 

summary, the DMS was implemented to answer 

two general questions: 1) How well do alternative 

thinning pathways accelerate the development 

of late-successional forests? and 2) What are the 

eff ects on aquatic-riparian resources of riparian 

buff ers of varying widths in conjunction upland 

thinning?

Th e DMS presented logistical and 

organizational challenges that echoed other 

hurdles in implementing the Plan. Processes 

developed during early DMS implementation 

were later used to address questions and concerns 

about Plan implementation. For example, DMS 

site selection and study implementation processes 

helped to frame later discourse about procedures 

for forest management planning under the Plan. 

During study-site selection for the DMS, several 

criteria were weighed. Th ese included geographic 

representation, forest type and condition, and 

land-use allocation as described in the Plan on 

lands owned by the BLM. In the early 1990s, 

much of the federal landscape (52 percent of 

BLM holdings) in western Oregon consisted of 

Douglas-fi r plantations younger than 80 years 

old (Cissel et al. 2006), with 35 percent of BLM 

holdings younger than 40 years (Muir et al. 2002). 

Th inning projects in young Douglas-fi r stands 

had already been proposed on some national 

forests and BLM resource areas, and hence areas 

suitable for the study were easily found. Some 

administrators expressed doubt about the effi cacy 

of the heavy thinning prescription proposed in 

the variable-density treatment (Cissel et al. 

2006), and local natural-resource managers raised 

concerns about the use of treatments within the 

range of the spotted owl or the Marbled Murrelet 

(Brachyramphus marmoratus). On the heels of 

the forest management paradigm shift signaled 

by the entire Plan, which included a new set 

of land-use allocations for the federal lands 

of the Pacifi c Northwest, fi eld-level personnel 

also raised concerns about potentially locking 

up lands that were intended to be managed for 

later regeneration harvests (“matrix” land-use 

allocation) into a long-term study (C. Th ompson, 

BLM, personal communication). Others held the 

opinion that the study aims might be irrelevant 

because the BLM had been thinning stands for 

a number of years and knew its eff ects on stand 

development, and also because with a new 

[federal] administration, public land-use policy 

would revert to what it had been (J. Tappeiner, 

emeritus professor, OSU College of Forestry, 

personal communication). Eventually, the scope 

of the study was narrowed, when the Medford 
Density Management in the 21st Century: West Side Story PNW-GTR-880

14 Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al.

BLM district was dropped from the study because 

the forest types and stand conditions in this subregion were deemed to be too diff erent from 

the other BLM ownerships to warrant inclusion 

in the study. DMS sites were selected from 

four western Oregon BLM districts, including 

seven stands in lands allocated as matrix and 

three stands in late-successional reserves (LSR). 

Th ree additional sites on LSR-designated lands 

managed by the Siuslaw National Forest were 

selected specifi cally for implementation of the 

Riparian Buff er Study component, with elements 

of the moderate upslope thinning (Cissel et al. 

2006). DMS study sites were among the fi rst 

forest management projects implemented by 

fi eld units after fi nalization of the Northwest 

Forest Plan, and in many cases, set the stage for 

later Plan management-unit implementation.

Th e study was conducted at an operational 

scale, addressing many logistical issues that arose 

later in other thinning operations. Th e DMS 

treatments were designed to diversify stands 

with gaps and, leave islands, as well as variabledensity thinning. Consequently, sale-preparation 

crews had to be trained in new methods to select 

trees for harvest to achieve a heavier and more 

spatially variable thinning, compared to more 

conventional thinning operations. Marking 

crews were quick to adapt to the challenge, with 

most stands being adequately marked to meet 

prescriptions with a single eff ort (C. Th ompson, 

BLM, personal communication). Additionally, 

methods for marking riparian buff ers also needed 

to be developed. Researchers from the PNW 

along with BLM personnel developed approaches 

at DMS sites that were subsequently used along 

headwater streams in other areas of western forests. 

Th ese have been general guidelines, however, and 

many districts still implement a buff er width of 

one or two site-potential tree heights for riparian 

buff ers as proposed in the Plan (USDA and USDI 

1994a). Study site coordinators from the BLM 

were also able to resolve concerns about sensitive 

species and microhabitats by adjusting how leave 

islands were placed. Although random selection 

of upland treatment units and reaches for buff er 

treatments was preferred, site-specifi c delineation 

adjustments to address implementation barriers 

allowed the DMS to act as a model for resolving 

project confl icts at multiple scales (Olson et al. 

2002). Loggers and other equipment operators 

adjusted to felling and maneuvering trees in and 

around riparian reserves and leave islands. 

Furthermore, socioeconomic considerations of 

implementing the DMS were projected relative 

to both operational and implementation costs. 

To make DMS sales profi table, patch openings 

and off -site parcels were included in some 

DMS sales, as they increased harvest amounts 

and market values (Olson et al. 2002). Wood 

harvest as a result of DMS implementation at 

individual BLM study sites was estimated to 

range from ~1 to 8.5 mmbf (million board feet; 

2359 to 20 058 m3

) from site-specifi c project 

areas ranging from 73 to 162 ha (Olson et al. 

2002). DMS harvest volumes exceeded those of 

conventional thinnings, largely due to inclusion 

of patch cuts. As with any profi table harvest on 

BLM-administered land at the time, the DMS 

harvests provided timber benefi ts to the economy 

of local counties (Olson et al. 2002). Th e DMS 

demonstrated that despite various hurdles, 

complicated management prescriptions can be 

implemented in a way that provides silvicultural 

and operational learning opportunities. 

Subsequent timber-project planning eff orts 

benefi ted from the lessons learned from DMS 

implementation.

In contrast, reviews of the success of adaptive 

management in the Northwest Forest Plan have 

mostly identifi ed short-comings in adaptive 

management areas. Problems with the application 

of adaptive management generally lie in the lack 

of a learning framework for management and 

a failure to close the learning loop even after 

monitoring is completed. Adaptive management 

areas included fl exible provisions to address the 

need for development of innovative management 

approaches and integration of site-specifi c 

contexts into local projects. Surveys of federal land 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al. 15

managers who have operated designated adaptive 

management areas identifi ed factors limiting 

successful implementation, such as regulations, 

especially the Endangered Species Act, a lack of 

support from higher-level administrators, and 

a lack of cooperation between researchers and 

managers (Stankey et al. 2003). Other criticisms 

such as risk aversion, poor record keeping 

and budget misallocation also were identifi ed 

as hurdles to implementation (Bormann et 

al. 2007). Th e primary failures of adaptive 

management were the lack of integrating learning 

opportunities from project inception through to 

fi nal monitoring and the testing of alternative 

strategies. Th ese aspects would heighten the 

effi cacy of adaptive management approaches, and 

go beyond the collection of just monitoring data 

(Bormann et al. 2007). 

However, there were some bright spots in 

implementing adaptive management, such as the 

creation of a formal monitoring program (Haynes 

et al. 2006), increased stakeholder involvement 

(Stankey et al. 2006), and increased respect and 

cooperation between researchers and decision 

makers (Bormann et al. 2007). Suggestions to 

improve the way adaptive management areas 

function included defi ned leadership and support 

roles, continuity, standardized documentation, 

and a commitment to learning (Stankey et al. 

2003, 2006). After receiving the interpretive 

report (Haynes et al. 2006), federal regional 

managers developed and approved a formal 

adaptive management framework, and refocused 

questions for future eff orts. Th is completed the 

cycle of adaptive management for the fi rst 10 

years of the Plan. Th e DMS sets forth a model 

of how a more formal question-focused learning 

eff ort can be carried out and fi t within a learning 

environment across multiple land allocations. 

Application of the DMS 

Th e DMS study is an example of eff ective 

active management and research in support 

of the Plan. In line with the objectives of the 

study, the DMS has: shown that variable-density 

thinning, including gaps and heavy thinning, 

moved canopy heterogeneity closer to oldgrowth conditions (Wilson and Puettmann 

2007); demonstrated that 15-m buff ers largely 

maintained the stream microclimate within the 

upland thinning context (Anderson et al. 2007); 

and identifi ed headwater-dependent aquatic 

species that may warrant consideration during 

forest management, for their habitat maintenance 

and landscape connectivity considerations 

(Olson et al. 2007; Olson and Burnett 2009, 

2013; Olson 2012). Although set up primarily to 

answer basic questions about forest and riparian 

management, the study has included additional 

studies on bryophytes, lichens, songbirds, 

macroinvertebrates, and other natural-resource 

elements (Cissel et al. 2006). Over 100 research 

papers and technology-transfer products have 

resulted from the study (http://ocid.nacse.org/nbii/

density/pubs.php). Additionally, through fi eld 

trips, presentations, and outreach programs such 

as “Teachers in the Woods”, over 5000 people 

were exposed to the DMS or visited the study 

sites from 2003–2006 (USDI, unpublished 

data). Th e study has provided an opportunity for 

prolifi c knowledge discovery, and has become a 

platform for diverse discussions regarding forest 

management.

From the outset, the DMS was designed to 

be relevant to forestry operations. Many of the 

original study designers from the BLM and 

PNW are still involved in the study. Th e result 

of this continuity has been a steady stream of 

management-relevant products and face-to-face 

workshops to disseminate the results of the study. 

In this way, the DMS has been, by design, not 

only relevant to the researchers, but has intimately 

involved managers and resource specialists as 

well. As a result of eff ective technology transfer, 

the DMS study has had a direct eff ect on the 

way forest thinning projects are planned by 

fi eld management units. Research produced 

by the DMS has been cited in several recent 

Environmental Assessments to provide evidence 
Density Management in the 21st Century: West Side Story PNW-GTR-880

16 Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al.

that the planned management is scientifi cally 

sound. BLM districts with DMS experience as 

well as Forest Service projects in western Oregon 

have used the DMS in project planning. Projects 

in the Salem BLM district like the Gordon Creek 

Restoration Project (USDI BLM 2009) cited the 

district’s experience with the DMS as evidence 

for the eff ectiveness of variable-density thinning 

treatments. Th e Highland Fling Project used 

the DMS to predict eff ects on riparian species 

(USDI BLM 2010). Th e Forest Service also uses 

results from the DMS. Th e Siuslaw National 

Forest used results from the DMS to predict the 

response of the understory to project actions in 

the environmental assessment for the Salmon/

Neskowin Project (USDA FS 2011). 

In addition to the technology transfer provided 

by the DMS, direct alliances among DMS 

researchers, fi eld managers, and natural-resource 

specialists have aided in bridging science and 

application to on-the-ground forest thinning 

and riparian management. Th e combined 

eff ort from the DMS and other large-scale 

silvicultural experiments provides a wealth of 

useful information for project planners and 

implementers (Poage and Anderson 2007; 

Anderson and Ronnenberg 2013). Th e sustained 

fl ow of technology transfer, including science 

publications as well as summary articles and 

workshops geared for managers, is an essential 

part of applied research programs. Furthermore, 

DMS has been used as a demonstration project 

for broader learning opportunities. University 

classes, natural-resource specialist training 

workshops, and national to international forestry 

and natural-resource specialists have visited 

the sites in order to understand the relevance 

of the variety of treatments established there. 

Flyers, brochures, and Web-site materials have 

allowed further outreach to the broad forestry 

community. DMS concepts have been presented 

to forestry organizations such as the Society of 

American Foresters and the International Union 

for Forest Research Organizations, raising the 

profi le of DMS research applications. Finally, 

the DMS is an example of the evolving concept 

of adaptive management. Findings from the 

fi rst 10 years of the study have led to “phase 2” 

treatments, with heavier thinning treatments and 

further-modifi ed riparian buff ers. Phase 2 of the 

DMS now tests the application of an additional 

thinning harvest at the sites, conducted within 

the existing treatments, and includes a case study 

of thinning without a riparian buff er. Additional 

response variables could be investigated within 

this new context to expand the learning paradigm 

off ered by the overarching study template. If 

DMS sites can be retained as designated research 

areas beyond the scheduled end point of current 

studies, they could continue to be used to refi ne 

the ideas of adaptive management in the future.

Although the DMS has shown its relevance 

to individual projects conducted by local 

administrative units, it has had less impact on 

recent regional planning eff orts like BLM’s 

Western Oregon Plan Revision (WOPR; USDI 

BLM 2008) or national-level planning such as 

the recently proposed Planning Rule Revision 

from the Forest Service. Th e WOPR included 

provisions to increase timber harvest on BLM 

lands in western Oregon. Increased harvest 

would be accomplished by increasing the amount 

of land where harvest was allowed, reducing the 

width of riparian buff ers and streamlining the 

process to approve higher thinning intensities. 

Although directly relevant to many WOPR issues, 

DMS fi ndings were seldom referenced (USDI 

BLM 2008), with exception of microclimate 

results. Th e DMS fi ndings can contribute more 

to science-based forest management decisions 

in western Oregon; closing this apparent gap is 

a challenge to the DMS researchers and their 

partners who directly navigate this sciencemanagement interface. Th is is an area for further 

development as DMS outreach to managers and 

decision-makers continues into the future.

Whereas the vacated WOPR was unsuccessful 

in changing provisions in the Northwest Forest 

Plan on the regional level, the Forest Service 

is working to alter how forest management 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al. 17

decisions are being made at the local level. In 

the last decade, the Forest Service has tried to 

implement policies to make it easier to conduct 

thinning projects or other forest management 

activities. A sample of these policies includes 

President G.W. Bush’s Healthy Forests Initiative 

in 2003, and the 2008 Planning Rule Revision 

(USDA FS 2008), which was suspended in 

2009. A new fi nal planning rule was recently 

released (http://www.fs.usda.gov/planningrule), 

and includes national-level process guidance for 

programmatic planning at the unit (national 

forests and grasslands) and regional scales, to set 

the context for local project and landscape-scale 

decision-making. It also emphasizes learning while 

planning and direct stakeholder involvement in 

collaborative assessments. Local project National 

Environmental Policy Act (NEPA) compliance 

will need to be constrained within regional and 

individual national forest plans, but will most 

likely be less prescriptive than the Northwest 

Forest Plan (B. Bormann, USFS, PNW Research 

Station, personal communication). Th e proposed 

Planning Rule Revision also emphasizes 

consideration of climate change and carbon 

storage in management decisions, and increasing 

public participation in project planning (USDA 

FS 2011). Approval of the revision will increase 

opportunities for DMS fi ndings to signifi cantly 

inform project planning, especially in westside national forests. Continued development 

of informational products geared toward fi eld 

managers will be important for DMS technology 

transfer to stay current. Bridging science and 

management across organizational scales of 

local areas to regions presents new challenges for 

studies such as the DMS and their proponents. 

Finally, the DMS and density management 

research must stay relevant in the face of trends 

of declining research support from the federal 

government. With the DMS, the BLM has 

shown that it can incorporate research and sound 

management practices using agency personnel 

and agency land. By involving researchers and 

management personnel from multiple agencies, 

fi eld offi ces, and districts, management projects 

have been funded and implemented to benefi t all 

parties. New research paradigms may be needed 

to expand research capacity, because funding 

may be lacking in an economically austere 

environment. However, by partnering researchers 

with specialists at fi eld units who manage lands, 

new projects can be conceived and implemented 

by a suite of collaborators, not by scientists alone: 

DMS has been a model in this regard. Th e DMS 

has shown how multiple agencies can work 

together and solve problems at study, design, 

implementation, and information delivery stages 

(Olson et al. 2002). 

Several ongoing and emerging research 

questions included or brought about by the 

DMS still need attention. Further study is 

needed on the management of young stands for 

late-successional and old-growth characteristics, 

including the age-range within which 

management toward the development of these 

characteristics can be eff ective; on how to manage 

fuel loads; and on how to work within the “80-

year rule” (Tappeiner 2009). Th ere is also a need 

to use matrix lands, especially those controlled 

by the BLM, for biodiversity management 

research, especially on early-seral habitat (Spies 

et al. 2007). Many questions remain about the 

effi cacy of riparian reserve widths with upland 

regeneration harvests. Most managers do not 

vary from widths prescribed in the Plan, although 

studies from western Washington including those 

by Bisson et al. (2013) and Raphael and Wilk 

(2013) are contributing to this arena. In recent 

years, the initial success of the DMS has carried 

the momentum to other inquiries, such as the 

interplay between upslope treatment and water 

availability in riparian areas (Burton et al. 2013; 

K. Ruzicka, unpublished data) and modeling 

how climate change will aff ect the trajectory of 

the stands (K. Ruzicka, unpublished data). Th ese 

projects rely on the long-standing relationships 

among Oregon State University, the Forest 

Service Pacifi c Northwest Research Station, and 

the BLM. Cooperation between researchers and 
Density Management in the 21st Century: West Side Story PNW-GTR-880

18 Intertwining Paths of the DMS and NW Forest Plan Ruzicka et al.

land management agencies is more important 

than ever. 

Many collaborative land-management research 

projects, including the DMS, can improve 

their communication and partnering eff orts 

with regional to national interest groups. 

Local managers of BLM and Forest Service 

lands understand the importance of research 

fi ndings for the development of sciencebased management proposals. Th ey can apply 

research results directly to management plans, 

including citing appropriate publications in 

NEPA documents. Th e absence of integration 

of DMS fi ndings in recent national and regional 

management planning eff orts suggests that 

research communication and advocacy to higherlevel managers and policy-makers needs more 

attention. Project scientists and their science 

managers need to consider development of more 

eff ective mechanisms to actively engage regional 

administrators in dialogues about the outcomes 

and impacts of their work for regional-to nationalscale management and policy development. 

Ensuring the integration of science fi ndings 

at higher administrative scales would result in 

improved science-based policy decisions. Science 

communication across geographic scales of 

natural resource management and administration, 

and across agencies, makes this a complex task. 

Without integrated communication, including 

both the processes and the personnel such liaisons 

would entail, the outcome and impact of valuable 

studies such as DMS are not fully realized. In an 

era of constantly emerging issues, such as global 

climate change, invasive species, disease, and fi re 

and pest management, science communication 

across administrative boundaries has never been 

more important.

Conclusion

Th e Northwest Forest Plan was the fi rst regional 

ecosystem management plan, and tested the 

logistical, operational, and cooperative capacities 

of land managers in the region. Th e Density 

Management Study originated in an atmosphere 

of new forest and riparian management questions, 

with important policy implications proposed to 

be answered through adaptive management. Over 

a decade of research in adaptive management 

has identifi ed that the opportunity for learning 

must be realized at all stages of the project for 

management to be successful. Th e DMS also 

has provided a set of lessons-learned for how to 

successfully plan, implement, and communicate 

stand-scale research to a wide audience. With 

climate change and other emerging natural 

resource issues on our horizon, increased 

uncertainty in research funding, and anticipated 

changes in forest policy, the importance of the 

DMS will only increase. Th e DMS can serve as 

a model for integrative studies conducted jointly 

by collaborative partners from diverse research 

communities and land-management agencies. 

Furthermore, DMS study sites can continue 

to be relevant as documented locations that 

provide opportunities to effi ciently address new, 

emerging forest-management questions. Th e 

DMS remains a golden opportunity for cuttingedge forest research in the future.

Acknowledgments

We thank John Tappeiner and Charley Th ompson 

and Hugh Snook for their conversations about 

these topics, their recollections of past events, and 

their key roles in the DMS implementation. Wesley 

Mouw provided comments on an early draft of the 

manuscript. Paul Anderson, Bernard Bormann and 

an anonymous reviewer commented on the accepted 

version. We also thank the BLM State Offi ce and 

Forest Service Pacifi c Northwest Research Station for 

support.

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Citation:

Ruzicka, Kenneth J., Jr.; Olson, Deanna H.; Puettmann, Klaus J. 2013. Th e intertwining paths of the Density Management 

and Riparian Buff er Study and the Northwest Forest Plan. In: Anderson, Paul D.; Ronnenberg, Kathryn L., eds. Density 

management for the 21st century: west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacifi c Northwest Research Station: 10–21.
Density Management in the 21st Century: West Side Story PNW-GTR-880

22

Public Perceptions of West-side Forests: Improving 

Visual Impact Assessments and Designing Thinnings 

and Harvests for Scenic Integrity

Robert G. Ribe

Robert G. Ribe is a professor, Department of Landscape Architecture and Institute for a Sustainable Environment, 5234 

University of Oregon, Eugene, OR 97403; rribe@uoregon.edu

Abstract

Perceptions of public forests’ acceptability can be infl uenced by aesthetic qualities, at both 

broad and project levels, aff ecting managers’ social license to act. Legal and methodological issues 

related to measuring and managing forest aesthetics in NEPA and NFMA decision-making are 

discussed. It is argued that conventional visual impact assessments—using descriptive pictorial 

qualities against a naturalistic scenery standard—have limitations as legal evidence, in addressing 

other popular aesthetic values, and helping public participation in planning processes. But such 

descriptive assessments do have merit: they are similarly perceived by diverse people, they describe 

landscape attributes that managers can manipulate, and they are strongly related to the public’s 

broad-trust perceptions of forests’ acceptability. Evidence-based guidelines are off ered for the 

production of scenic quality in Pacifi c Northwest west-side forests. Th ese guidelines are derived 

from extensive studies of forests and perceptions in the region, and estimate and interpolate 

average public perceptions of average forest conditions. Th ey inform in-stand perceptions related 

to forest density measurements and regeneration harvest prescriptions, of percent and pattern 

of tree retention, and of retained down wood. Other guidelines related to percent and pattern 

of retention and harvest unit design apply to vista views of harvests. Th ese guidelines can assist 

planners and managers in designing forest treatments, implementing wholesale forest plans to 

maintain broad-trust acceptability perceptions, more reliably meeting scenic integrity standards, 

and making more accurate visual impact assessments at regional and project scales.

Keywords: Forest visual impacts, scenery management, timber harvest design, social acceptability, 

public participation.

Introduction

Perhaps in an ideal world, public forest planners 

and managers would only need to make decisions 

to optimize the technical achievement of welldefi ned natural-science-based objectives. Recent 

experience suggests that it is also important to 

manage forests’ social acceptability to avoid 

popular and antagonistic perceptions of forest 

plans and projects (Bengston 1994). Th is can 

help forestry professionals regain and maintain 

their “license” to plan and execute projects 

with professional discretion. Th is paper seeks to 

provide practical aesthetic theory and evidencebased guidance to forest planners in estimating 

visual impacts and keeping forestry projects from 

going past “tipping points” of acceptability.

Perceptions of “social acceptability” are often 

not the same as those that forest managers 

encounter in public meetings, hearings, or 

other legal contexts. Th ey are more intuitive, 

emotional, and holistic (Hansis 1995; Wyatt 

et al. 2011). Th ey are not primarily motivated 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Ribe 23

23

Public Perceptions of West-side Forests

to refl ect the needs of a particular individual, 

community, corporation, or interest group. 

Such perceptions can be positive or negative, 

and become powerful when they are widely and 

deeply felt. Th ey are not always formed according 

to criteria defi ned by elites, stakeholders, activists, 

or lawyers. A well-defi ned legal story usually 

lies behind forest management confl icts. But 

behind that story often lie aesthetic perceptions 

reinforced by political narratives, typically 

related to winners and losers, justice and trust in 

government (Tindall 2003). Together these can 

create adverse perceptions of forest management 

(Ford et al. 2009). Such shared perceptions can 

rely on cognitive simplifi cations of the complex 

world of forest policy and planning more than 

on the technical details of forest science, policy, 

litigation, or implementation (Shindler et al. 

2002; Tindall 2003; Olsen et al. 2012).

Public agencies gain acceptance of forest 

management at two social scales. Th e fi rst 

can be called “broad-trust acceptability”, and 

encompasses regional or national populations 

and relates to many people’s trust in an agency 

to serve public interests and take good care of 

forests. Th e second can be called “project-level 

acceptability” and is more focused on the details, 

trade-off s, and confl icts of interest that are 

manifest in “hot spot” projects, area plans, and 

the rules and policies that drive these. Gaining 

and maintaining license to manage land and 

harvest timber requires both kinds of acceptance. 

Th e spotted owl controversy involved a loss of 

broad-trust acceptability and regional/national 

loss of social license. Forest management projects 

or forest plan revisions held up by local opposition 

and legal/administrative challenges involve loss 

of project-level acceptability (Blahna and YontsShepard 1989; Trosper 2003).

Social acceptance of forest management 

is driven by perceptions at both these scales 

(Shindler et al. 2002). Perceptions that drive 

broad-trust acceptability occur among members 

of the “general public” who are extensively 

interested in public forests because they serve 

generally understood values. Th ese concerns are 

not typically intensely focused on particulars 

or places but are infl uenced by ideological or 

intuitive perceptions of public landscapes and by 

stories and social narratives found in news media 

and social networks (Allen et al. 2009; Clement 

and Cheng 2011). Perceptions that drive detailed 

project-level acceptability are mainly those of 

smaller numbers of activists and stakeholders 

focused on specifi c, confl icting agendas and 

values. Perceptions of power relationships and 

justice typically frame these perceptions because 

they are seen to weaken or strengthen these 

competing goals (Cheng and Mattor 2006; 

Daniels and Walker 1995). Technical, functional, 

and spatial details can matter much more in 

negotiating solutions that gain acceptance among 

confl icting parties.

Forest managers who design thinnings and 

harvests are familiar with these facts of political 

life. Th ey are also aware of the general importance 

of aesthetic forest perceptions (Ribe 1989), 

but the role of aesthetics in decision-making 

is challenging (Shindler et al. 2002). Th ey face 

at least three problems: (1) how to predict the 

aesthetic impact of forestry projects in advance 

for the various required environmental impact 

assessments; (2) how to go about managing the 

larger public forest landscape to maintain broadtrust acceptability; and (3) how to understand 

and communicate about forest aesthetics in local 

negotiations and public participation processes 

aimed at gaining project-level perceptions of 

acceptability across diverse constituencies. A 

basic, simplifi ed discussion of practical aesthetics 

to address these problems is sketched below. 

Th en, evidence-based recommendations are 

off ered to aid forestry project design.

Practical Forest Aesthetics

Th e National Environmental Policy Act of 

1969 (NEPA) promulgated a decision process 

that emphasizes scientifi c analysis (Bartlett 1986). 

Th e original NEPA process requires few and 
Density Management in the 21st Century: West Side Story PNW-GTR-880

24 Public Perceptions of West-side Forests Ribe

inadequate opportunities for public participation, 

and these are constrained and located in the 

process so as to be unlikely to infl uence the 

design of alternatives or to yield useful and 

accountable perceptions of projects’ acceptability 

(Hourdequin et al. 2012). Congress did, 

however, require assessments of visual impacts, 

while recognizing that this might fl y against 

the science-based rationalism of the rest of the 

law. NEPA states: “...assure for all Americans...

aesthetically...pleasing surroundings...and...

develop methods and procedures...which will 

insure that presently unquantifi ed environmental 

amenities and values may be given appropriate 

consideration in decision making...” Th e 

National Forest Management Act of 1976 

affi rmed this mandate with respect to forest 

landscapes: “...cuts... shaped and blended to the 

extent practicable with the natural terrain.”

In principle, such visual impact assessment 

methods must pass evidentiary due process tests 

to avoid being deemed an inadmissibly arbitrary 

and capricious basis for public decisions (Tassinary 

et al. 2010). Th is arguably amounts to passing 

the same tests of reliability and validity applied 

to other scientifi c assessments required by NEPA 

(Palmer 2000; Palmer and Hoff man 2001). Th e 

U.S. Forest Service addressed this requirement 

for visual assessment methods (Smardon 1986) 

by adoption of the Visual Management System 

(VMS, USDA FS 1974), now modifi ed as 

the Scenery Management System (USDA FS 

1995). A pragmatic core approach to making 

purportedly reliable and valid visual assessments 

in these methods is to restrict forest aesthetics 

to formalistic descriptions of pictorial aesthetic 

qualities. Th ese must conform to a normative 

standard of naturalistic scenery (Selman and 

Swanwick 2010; Sheppard 2001).

Visual assessments based upon naturalistic 

form, line, color, scale, contrast, etc., were 

assumed to have intuitive “face validity” 

(Litton 1972; Wohlwill 1976). Th is is the 

fi rst-impression, ‘primary aesthetic quality’ of 

forest landscapes (Ingarden 1973). Th ese have 

been assumed to be reasonably reliable if made 

systematically by trained experts (i.e., landscape 

architects) using standard procedures (Litton 

1968; Smardon 1986). Reliance on such experts 

also has the advantage of producing assessments 

related to the form of landscapes managers can 

actually control. It also has the advantage of 

avoiding assessments based on hearsay public 

opinion “driven” by various value agendas, 

which can defi ne their own aesthetic qualities 

(Parsons and Daniel 2002). Th ese might 

range into diverse, “special”, and potentially 

contentious or contradictory ad-hoc conceptions 

and perceptions of aesthetic value diff erent than 

those specifi ed by NEPA. NEPA was crafted to 

avoid creating an intractably irresolute political 

process and to keep pure judgments and decision 

authority in the hands of objective experts and 

offi cials with democratically vested authority 

(Bartlett 1986).

NEPA-compliant methods of assessing the 

aesthetic impacts of forest management, i.e., 

the SMS, have been legally accepted as “best 

available professional practice.” Th is is because 

(1) they have been formally adopted by agencies; 

(2) some sanctioned method is required 

and the institutional cost of changing those 

methods would be prohibitively high even if 

they were found legally invalid; (3) lawyers and 

judges instinctively avoid contesting aesthetic 

measurements as a risky, cost-ineff ective “can of 

worms”; and (4) demonstrably valid and reliable, 

widely-applicable alternatives, not requiring slow 

and expensive methods, have not been proposed. 

Nevertheless, the reliability and validity of SMS 

scenic impact assessment methods have not been 

demonstrated (Palmer 2000), and they have 

remained essentially unchanged for more than 

30 years, while hundreds of scientifi c studies of 

landscape perception have been published.

Studies of visual-aesthetic perceptions of 

landscapes frequently confi rm that public 

perceptions of scenic aesthetics can be predicted 

by descriptive formalistic or cognitive sensemaking attributes of landscape scenery (Ode et 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Ribe 25

25

Public Perceptions of West-side Forests

al. 2008; Ryan 2005). Th e exact degree of these 

relations varies in diff erent landscape settings, 

cultural contexts, and with diff erent research 

methods (Stamps 1999). Other studies confi rm 

that perceived naturalism is a powerful, positive 

aesthetic value among most people everywhere, 

perhaps in “hard-wired” ways (Ulrich 1979), 

with psychological health benefi ts (Th ompson 

2011; Grinde and Patil 2009).

An advantage of expert visual impact assessments 

using naturalistic, pictorial standards is that this 

simple, face-valid concept of aesthetic quality is 

strongly related to public perceptions of broadtrust acceptability (Carvalho-Ribeiro and Lovett 

2011). Ribe (2002) showed that perceptions of 

scenic beauty versus acceptability were strongly 

correlated among large samples of people with 

diverse environmental attitudes in the Pacifi c 

Northwest (fi g. 1). Th is is consistent with other 

fi ndings from the region (BCMF 1996; Kearney 

2001; Kearney et al. 2011). Ribe (2006) also 

found that scenic beauty was the third-strongest 

predictor of informed perceptions of forests’ 

overall acceptability (behind perceived habitat 

quality and economic value) in the same region 

(fi g. 2). Th is is similar to other regional fi ndings 

(Bradley and Kearney 2007; BCMF 2006; 

Brunson and Shelby 1992). Th e formalistic, 

pictorial naturalistic aesthetics specifi ed by NEPA 

can therefore serve as a guidepost, among other 

considerations, in designing forest management 

plans and projects aimed at maintaining broadtrust acceptability.

Predicting Scenic Impacts of 

Forestry Projects

Th e problem remains of how visual assessments 

can be made more valid and reliable. When 

it comes to forests of the west-side Pacifi c 

Northwest, empirical evidence is available to 

serve as one major basis for more accurate visual 

impact assessments. Appropriately designed 

research can off er a strong contribution to legally 

Figure 1—The relationship between uninformed acceptability ratings of 110 photos of west-side 

forests and uninformed scenic beauty ratings of the same photos among people with different 

environmental attitudes. Adapted from Ribe (2002).
Density Management in the 21st Century: West Side Story PNW-GTR-880

26 Public Perceptions of West-side Forests Ribe

valid and reliable visual assessments of forest 

changes, using methods explained in detail by 

Tassinary et al. (2010).

Research cannot set the normative standards 

for visual impact assessment. Th ese are socially 

defi ned and expressed through democratic due 

process of law and administrative procedures, i.e., 

NEPA and the SMS. But research can measure 

perceptions against these legally specifi ed 

aesthetic concepts and standards. Representative 

samples of people’s aesthetic perceptions can be 

elicited for well-sampled forest scenes. Ratings 

of legally appropriate scenic qualities can be 

statistically related to forest attributes depicted in 

the photographs. Such ratings of photographs 

correspond closely to perceptions in the fi eld 

(Trent et al. 1987).

To understand how research can inform visual 

impact assessments of public forests, readers 

who are not landscape architects fi rst need to 

understand the basics of SMS scenic standards. 

Th e SMS divides national forest landscapes into 

sub-areas where diff erent desired “scenic integrity 

level” standards are applied (USDA FS 1995). 

Th ese are based upon the beauty of each area’s 

natural scenery, how visible the area is (hidden or 

seen at greater distances), how many people view 

it, whether what they are likely to be doing there 

is more sensitive to scenic quality, and how much 

aesthetic value local residents and recreators 

place upon each area. Th ese integrity levels are 

conceptually defi ned and range from “very low” 

to “very high.”

A critical problem with making admissibly valid 

and reliable visual assessments lies in predicting 

which scenic integrity level a thinning or harvest 

will conform to after it is fi nished. If a landscape 

architect is actively involved in designing a project, 

they can shape the cut unit as seen in a vista view 

to minimize visual impact and aff ect the scenic 

integrity level it should achieve. But a shortage 

of landscape architects may mean that this task 

is only performed for more sensitive projects. 

When silviculturists, engineers, and biologists 

design projects, they have no qualifi cations to 

make visual impact assessments, and landscape 

architects or outdoor recreation planners may be 

expected to provide post-hoc, conjectural visual 

Figure 2—The relative strength and 

functional form of perceptions of 

information and of photos’ beauty 

as these were associated with average 

overall acceptability perceptions of 

forest treatments in west-side forests. 

Adapted from Ribe (2006).
Density Management in the 21st Century: West Side Story PNW-GTR-880

Ribe 27

27

Public Perceptions of West-side Forests

impact assessments. If these assessments are only 

made for in-stand views, none of these design or 

non-design professionals may have a clear enough 

idea what the forest landscape will look like 

after logging operations. It may be impractical 

to control the visual consequences of logging 

operations to the degree needed to predict fi nal 

scenic integrity levels using SMS procedures with 

high confi dence, either soon after logging or over 

the long term.

When extensive programs of forestry projects 

are planned, in specifi c or as-yet-unspecifi ed 

locations (e.g., as the product of a forest plan or 

long-term timber sale program), there is typically 

little basis for valid and reliable descriptive 

assessments of “ungrounded and un-designed” 

projects using SMS methods. Th is wholesale 

decision-making is where full EIS assessments 

are most often required and where strong 

visual impact assessments are most needed and 

potentially subject to scrutiny.

Research can assist in improving visual impact 

assessments in both these situations. It can’t 

explain the full variability in perceived impacts 

as a consequence of the detailed or accidental 

forest scenery produced by each and every 

forestry project. But it can inform reliable and 

valid predictions of average perceived visual 

impacts by an average member of the public in 

relation to scenic integrity standards. Th is can be 

done in relation to attributes of forest structure 

that managers intentionally manipulate in their 

prescriptions.

Practical Extra-NEPA Planningprocess Aesthetics

Pro-forma NEPA- and NFMA-based decision 

processes have encountered political and legal 

challenges. Successful appeals have created 

precedents, case law, rules, and statutes that 

can be demanding of decision-makers and 

contradictory or confounding. Th ese have 

empowered stakeholder and activist groups 

more than NEPA and similar organic planning 

laws arguably intended. One solution forest 

management agencies are pursuing is to engage 

in more intensive and meaningful public 

participation (Arnstein 1969) that promotes 

collaborative learning and collective decisionmaking (Daniels and Walker 1996). Th ese aim 

to negotiate decision design and the trade-off s 

needed to arrive at a solution acceptable among 

multiple interests. Th is approach seems to be 

headed for eff ective use (e.g., Gordon et al. 2012) 

and codifi cation in the “new forest planning rule” 

for national forests (USDA FS 2011).

Aesthetics’ role in this emerging new forest 

planning process will be potentially important 

and interesting. Some brief speculative comments 

are off ered here. Th ere are many kinds of aesthetic 

experiences and qualities that might become 

salient or powerful in participatory planning. 

Philosophers and aesthetic theorists make very 

weak and subtle distinctions between aesthetic 

perceptions that occur in a passionate cognitive 

mode versus dispassionate claims of intrinsic 

or inherent value (Santayana 1896; Richards 

2001; Kiester 1997). Forest planning activists 

tend to have passionate values based upon strong 

aesthetic experiences and consequent longstanding forest aff ections (Buijs 2009; Brown 

and Raymond 2007). Th ese typically motivate 

their participatory agendas. Examples are 

perceptions of the beauty of a river basin rich in 

healthy salmon habitat; the pleasing social and 

economic vitality of a rural town supported by a 

strong timber industry; the harmonious ecology 

of an old-growth forest; or the sublime historical 

process by which resource development has over 

time inexorably, powerfully, and exploitatively 

lifted untold numbers of people into the middle 

class and provided them with greater freedom. 

Such aesthetic perceptions underlie spoken or 

unspoken claims of transcendent, intrinsic values 

that ought to be preserved in and of themselves 

as wonderful, ingenious, and vulnerable (suigeneris).

Obviously, such strong aesthetic perceptions 

behind claims of intrinsic value can be in 
Density Management in the 21st Century: West Side Story PNW-GTR-880

28 Public Perceptions of West-side Forests Ribe

confl ict. Indeed, they form a powerful basis 

for social confl icts that block forest decisionmaking and enliven attempts at participatory 

planning. Assessing and pursuing these kinds 

of aesthetic qualities in forests is quite diff erent 

from the much safer, broadly shared (commondenominator) goal of producing as much 

naturalistic, formalistic pictorial landscape 

as possible, as Congress has directed. Many 

planning participants are embarrassed to voice 

aesthetic concerns. Th ey seem “too religious”, 

outside the technical aspects of decision-making 

that civil democratic discourse emphasizes, or 

divorced from the most relevant social narratives 

of who has power, gets what, and pays the price 

in political decision-making. Claims of intrinsic 

aesthetic value are vulnerable to the retort: “So 

what exactly do we decide to do to satisfy your 

aesthetic needs and all the other competing 

intrinsic (aesthetic) values?” Conventional visual 

impact management arguably avoids this problem 

by focusing on “superfi cial” appearances that are 

subject to manipulation in the landscape rather 

than in people’s minds.

Naturalistic pictorial aesthetics may not be 

a major player in many public participation 

negotiations, as they can be too narrow and 

irrelevant to the most salient values in a confl ict. 

Obvious exceptions will occur when important 

economic values fl ow from local exceptional visual 

aesthetic resources. But care should be taken not 

to sacrifi ce naturalistic pictorial visual landscape 

qualities when negotiating collectively acceptable 

solutions. Th is can put broad-trust acceptability 

perceptions at risk. Pictorial qualities may not be 

“at the table”, but they still matter.

It may not be a waste of time to seek and 

propose specially crafted conceptions of aesthetic 

quality that cut across or transcend participants’ 

competing, intrinsic aesthetic aff ections. 

Some of the ecological aesthetic ideas behind 

ecosystem management can be of this kind. 

Th ese can seek to appreciate how active resource 

management can aesthetically resonate with the 

function of natural systems in ways most people 

perceive as intrinsically good (Gobster 1999; 

Carvalho-Ribeiro and Lovett 2011). Within a 

public participation process, it may be possible 

to promote shared aesthetic perceptions of 

the quality of the participation process itself. 

Th is might be a means to promote a sense of 

common purpose, and of the “intrinsic” value 

of an agreement that to some extent supersedes 

its privately perceived aesthetic inadequacies. 

But don’t expect such internal process aesthetic 

perceptions to be shared outside the group.

Evidence-Based Aesthetic 

Decision Assistance for Pacific 

Northwest Forestry

Th is section provides evidence-based aesthetic 

decision guidance to forest planners regarding 

the density and structure of managed forests, 

particularly in the Pacifi c Northwest. Th e aims 

are (1) to help keep forest projects from going 

past “tipping points” of broad-trust acceptability 

perceptions that can jeopardize forest managers’ 

social license; and (2) to more accurately predict 

average visual impacts of forestry projects that 

use the “standard” logging procedures used in 

the research studies from which the fi ndings 

came. Th ese impacts can be improved to some 

unverifi ed extent by use of aesthetic forestry 

techniques, such as those advocated by Klessig 

(2002), the University of New Hampshire 

Cooperative Extension (1993), and others.

“Broad-trust tipping point” guidelines are 

off ered based upon where source studies estimated 

that scenic integrity tends to be perceived to cross 

from low to moderate level. Th e aim is not to 

suggest that all public forestry projects should 

follow these guidelines. Biological and economic 

goals will sometimes necessitate otherwise. 

Instead, the suggestion is that if a preponderance 

of projects seen in the landscape meet or exceed 

the guidelines, then broad-trust acceptability 

perceptions should be maintained. Th e focus is 

on the author’s studies of perceptions of westside forests of Oregon and Washington. Only the 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Ribe 29

29

Public Perceptions of West-side Forests

most useful results of these studies are extracted 

and sketched. Refer to the original publications 

for details of methods and all fi ndings.

In-Stand Views

Several studies are reviewed here that 

investigated the production of scenic beauty 

against measures of forest structure and types of 

forest treatments, including unmanaged forests. 

Th ese studies investigated only treatments in 

forests at least 40 years old, and only the scenery 

found within six months after treatments. 

Improvements do occur in scenic beauty in the 

early “green-up” years after regeneration harvests, 

but these are not as appreciable to the general 

public as might be hoped for (Kearney et al. 

2011).

Mean changes in average scenic beauty 

perceptions attributable to diff erent forest 

treatments were measured via public surveys 

where many groups of respondents rated 

numerous matching forest photographs of preand post-treatment conditions (Ribe 2005a). Th e 

resulting aesthetic changes are shown in fi g. 3, 

without regard to diff erences in the initial scenic 

beauty of the pre-treatment forests. Th e resulting 

sequence of magnitudes of scenic change is 

similar to that found by Bradley and Kearney 

(2007). More intense treatments tend to produce 

greater reductions in scenic beauty, particularly 

if one accounts for the extent of open clearcut 

areas produced within harvest units, such as in 

aggregated retention harvest patterns.

Density Management and 

Scenic Beauty

Ribe (2009) found that the density and basal 

area of mature forests’ structure are signifi cantly 

related to average in-stand perceptions of scenic 

beauty. Th ese results, described below, were 

derived from large samples of photographs of 

diverse pre- and post-treatment forests as rated by 

a large sample of residents of western Washington 

and Oregon.

A best-fi t polynomial regression function 

(fi g. 4) relating forests’ density to scenic beauty 

estimated on an interval scale (Ribe 1988) was 

graphed against U.S. Forest Service Scenery 

Figure 3—Comparisons of 

changes in average perceived 

scenic beauty ratings 

attributable to different forest 

treatments. From Ribe (2005b).
Density Management in the 21st Century: West Side Story PNW-GTR-880

30 Public Perceptions of West-side Forests Ribe

Management System integrity levels (USDA FS 

1995). On average, forests with 400 to 1500 

stems >5 cm·ha-1 tend to achieve the highest 

perceptions of scenic beauty, with the peak at 

about 750 stems·ha-1. Very low, potentially 

adverse, aesthetic perceptions will tend to result 

from in-stand views of forests with less than 100 

stems·ha-1. Th e “broad-trust tipping point” 

threshold is about 400 stems >5 cm·ha-1.

A best-fi t polynomial regression function 

relating forests’ basal area (BA) to in-stand 

scenic beauty perceptions (fi g. 5) suggests that, 

on average, forests with 120 to 170 m2

·ha-1 BA 

will tend to achieve very high scenic integrity 

characteristic of the most beautiful old-growth 

forests. Forests with more than 170 m2

·ha-1 BA 

will tend to achieve high scenic integrity, likely 

due to the inclusion of larger trees within dense 

forests with broad diameter distributions; while 

those with 50 to 120 m2·ha-1 BA will also tend 

to achieve high scenic integrity, likely due to 

moderate densities of mainly moderately large 

trees. Very low, potentially adverse, aesthetic 

perceptions will tend to result from in-stand 

Figure 5—The relationship 

between west side forests’ basal 

area and their average in-stand 

scenic beauty ratings interpreted 

by scenic integrity levels. Adapted 

from Ribe (2009).

Figure 4—The relationship between 

west-side forests’ stem density and 

their average in-stand scenic beauty 

ratings interpreted by scenic integrity 

levels. Adapted from Ribe (2009).
Density Management in the 21st Century: West Side Story PNW-GTR-880

Ribe 31

31

Public Perceptions of West-side Forests

views of forests with less than about 30 m2·ha-1 

BA. Th e “broad-trust tipping point” threshold is 

about 50 m2·ha-1 BA.

For regeneration harvests seen from within, 

the relation between post-treatment retention 

levels and scenic integrity levels also accounted 

for levels of down wood (fi g. 6) (Ribe 2009). 

Harvests with 40 percent dispersed retention and 

low down wood can achieve, on average, as much 

scenic integrity as pre-harvest forests. Other 40 

percent retention harvests will tend to produce 

more marginal, moderate to low scenic integrity. 

Harvests with 15 percent aggregated retention 

and high down wood will tend to produce very 

low scenic integrity, comparable to clearcuts. 

Other 15 percent retention harvests can be 

expected, on average, to produce low scenic 

integrity. Ribe (2006) found that informed 

acceptability perceptions (as opposed to 

uninformed scenic beauty) were not signifi cantly 

aff ected by high down wood levels. Th is suggests 

that public education should improve broadtrust perceptions of forests with high down wood 

in spite of their low scenic quality.

Th e same study (Ribe 2009) statistically 

interpolated average scenic integrity levels other 

than those produced at the 15 percent and 40 

percent levels photographed and presented to 

respondents. Th is model has high margins of 

error (fi g. 7). Th e key fi nding there is not so much 

the exact average scenic integrity level predicted 

for any retention level, but the interaction 

of favoring dispersed retention patterns and 

low residual down wood in producing scenic 

beauty, particularly at moderate (15–70 percent) 

retention levels. Th e broad-trust harvest retention 

levels are at about 15 percent for dispersed tree 

patterns with low down wood; about 30 percent 

in aggregated patterns with low down wood; 

about 35 percent in dispersed patterns with high 

down wood; and about 55 percent in aggregated 

patterns with high down wood.

Scenic Beauty of Harvests in 

Vista Views

Perception of scenic beauty in vista views 

(fi g. 8) appears to be related to the design of 

the shape of harvest units rather than down 

wood (Ribe 2005b). Th ese results suggest 

that aggregated-retention harvests will tend to 

produce low to very low scenic integrity, similar 

to clearcuts, irrespective of retention level. 

Dispersed retention patterns are more eff ective 

at mitigating scenic impacts in vista views than 

harvest shapes. At 15 percent retention, dispersed 

as opposed to aggregated retention patterns 

will tend to produce low, rather than very low, 

average scenic integrity. At 40 or 75 percent 

Figure 6—The relationship 

between west side forest 

regeneration harvests’ 

variable tree retention 

levels and patterns, as well 

as down wood levels, and 

their average in-stand scenic 

beauty ratings interpreted 

by scenic integrity levels. 

Adapted from Ribe (2009).
Density Management in the 21st Century: West Side Story PNW-GTR-880

32 Public Perceptions of West-side Forests Ribe

retention, dispersed patterns will tend to produce 

high to very-high scenic integrity, instead of the 

low to very low integrity levels associated with 

aggregated patterns. Th e “broad-trust tipping 

point” is 25 percent retention for dispersed 

retention harvests, irrespective of unit design. 

All aggregated retention harvests, including 

traditional clearcuts, fall below the “broad-trust 

tipping point” of scenic integrity. Th is perception 

is unlikely to be signifi cantly mitigated by public 

education (Bliss 2000; Hansis 1995). However, 

Ribe (2006) found that informed acceptability 

perceptions of 15 percent dispersed retention 

harvests were substantially higher, albeit still 

a bit negative, than for clearcuts. Th is suggests 

that where ecological or economic goals call for 

cutover areas within cutblocks, if a few trees are 

left standing there (and remain so until greenup), 

then informed public observers may see these as 

evidence of visible forest stewardship, even if they 

otherwise see such areas as ugly.

Guidance for Predicting Average 

Visual Impacts of Forestry Project 

Designs

Standard SMS practice prescribes that if a 

forestry project will produce a visual change that 

conforms to the “expected or desired” standard at 

its location, then it is assessed as having a “low” 

visual impact. If it is predicted to fall one integrity 

level short of the local standard, it is assessed as 

a “high” impact. If it is expected to produce a 

visual change more than one level below the local 

standard it is assessed as having a “very high” 

impact. If projects may exceed the standard they 

are typically assessed as a “very low” impact. 

Average, evidence-based, estimated scenic 

integrity and visual impact levels achieved by 

forest and harvest structures described above are 

summarized in table 1. Th e SMS-derived visual 

impact of these designs will depend on the scenic 

integrity level standard set for the corresponding 

area of landscape, as described earlier.

Figure 7—An estimated general statistically interpolated 

model of perceived scenic integrity levels in relation to 

a continuum of regeneration harvests’ tree retention 

levels, sorted by retention pattern and down wood level. 

Adapted from Ribe (2009).

Figure 8—The relationship 

between average, vista-view scenic 

beauty ratings of forests and 

regeneration harvests interpreted by 

scenic integrity levels, as sorted by 

retention level, retention pattern, 

and harvest unit shape-type. 

Adapted from Ribe (2005a).
Density Management in the 21st Century: West Side Story PNW-GTR-880

Ribe 33

33

Public Perceptions of West-side Forests

Table 1—Summary of evidence-based guidelines for estimating scenic integrity levels achieved by different forest 

conditions and regeneration harvest prescriptions; followed by a guide to corresponding visual impacts as related to 

project site scenic integrity standards. These can be used to predict expected average perceived integrity levels for the 

average west-side forest in assessments of multiple harvests in forest plans or for single, not-visually-controlled harvests. 

Levels can be improved when specific projects are designed or contextually assessed by landscape architects.

Designing Forests to Meet Scenic Integrity Standards Predicting Estimated Average Visual 

Impacts

If one or more of these criteria are met, then the integrity level in the left 

column is estimated to be met for an average forest seen by an average 

member of the public.

Estimated visual impact resulting if a 

project area’s scenic integrity standard 

is a column header and the forest meets 

criteria in a row in the left matrix. 

Scenic 

integrity 

level 

achieved

In-stand Views Vista Views Scenic Integrity Standard

Forest 

density 

(stems >5 

cm·ha-1)

Basal area 

(m2·ha-1)

Forest type or 

harvest design

Forest type or 

harvest design

Very 

low Low Moderate High

Very 

high

Very high 700-1000 120-170 Old-growth 

forest

75-100% disp ret

95-100% agg ret

very 

low

very 

low

very low very 

low

low

High 700-1000 50-120 

or >170

Mature forest or:

40-100% disp 

ret, low dn wd;

60-100% disp 

ret, high dn wd;

60-100% agg 

ret, low dn wd;

75-100% agg ret, 

high dn wd

35-75% disp ret;

90-95% agg ret

very 

low

very 

low

very low low high

Moderate 400-700 

or 1000-

1500

30-50 20-40% disp ret, 

low dn wd;

35-60% disp ret, 

high dn wd;

30-60% agg ret, 

low dn wd;

55-75% agg ret, 

high dn wd

25-35% disp ret;

85-90% agg ret

very 

low

very 

low

low high very 

high

Low 100-400 

or >1500

15-30 2-20% disp ret, 

low dn wd;

5-35% disp ret, 

high dn wd;

3-30% agg ret, 

low dn wd;

10-55% agg ret, 

high dn wd

15-25% disp 

ret, rectilinear 

shape;

0-25% disp ret, 

designed shape;

40-85% agg ret, 

any shape

very 

low

low high very 

high

very 

high

Very low <100 0-15 0-2% disp ret, 

low dn wd;

0-5% disp ret, 

high dn wd;

0-3% agg ret, 

low dn wd;

0-10% agg ret, 

high dn wd

0-15% disp ret, 

rectilinear 

shape;

0-40% agg 

ret, any shape 

(designed shape 

might help 

0-15%)

low high very high very 

high

very 

high
Density Management in the 21st Century: West Side Story PNW-GTR-880

34 Public Perceptions of West-side Forests Ribe

Discussion

Designing forest treatments and regeneration 

harvests is always complex and fraught with 

confl icting goals and trade-off s. Th ese goals 

are rooted in social values often instigated 

by aesthetic experiences and fundamentally 

understood by aesthetic sensibilities (Grob1995). 

Th e search for good forestry decisions can be 

understood as a search for “elegant” solutions 

that optimally achieve and express physical, 

biological, perceptual, and social functions. In a 

sense, such decisions can aesthetically transcend 

particular technical goals, biological criteria, or 

narrowly conceived social and aesthetic values. 

Th is is arguably a goal of ecosystem management, 

but this paradigm could be more explicitly 

attentive to broadly conceived aesthetics as they 

aff ect public perceptions (Lessard 1998). Forests 

that express ecological health by emulating 

ecological processes and attributes might gain 

public approval (Olsen et al. 2012), even when 

not of high scenic quality, by virtue of exhibiting 

“visible stewardship” (Sheppard 2001) to gain 

perceptions of their “ecological aesthetic” quality 

(Gobster 1999).

Th e challenge for forest managers is to 

design forest treatments that express visible 

stewardship and also public education programs 

that broaden public appreciation of ecological 

aesthetics among more people. If agency claims 

of ecological aesthetic value, as opposed to scenic 

value, are to gain legal validity, they have to be 

similarly perceived by at least a majority of the 

relevant public. Meanwhile, naturalistic scenic 

aesthetics are already similarly perceived by most 

people (McCool et al. 1986; Magill 1992), and 

are required by law and established visual impact 

assessment standards and methods.

Th e best approach seems to be the simultaneous 

pursuit of a mix of forests with naturalistic 

scenic quality and ecological aesthetic qualities 

(especially both at once), along with education 

programs seeking to increase appreciation of the 

latter. Over time, the socially acceptable “recipe” 

of these two aesthetic types may shift toward 

more ecological aesthetics, but the public’s desire 

for naturalistic scenic quality is powerful, indeed 

likely hard-wired, and will not go away (Parsons 

and Daniel 2002; Th ompson 2011). Managers 

should attend to the creation of ecological features 

like micro-habitats for insects, amphibians, and 

fungi, forests that serve as refugia or riparian 

or interior habitats, key habitat elements for 

wide-ranging sensitive vertebrate species, or the 

stabilization and enrichment of soil. Th ese eff orts 

should also pay attention to locally applicable 

scenic integrity standards and favor project 

designs, whenever possible, that tend to achieve 

these in the ways described above. Where scenic 

integrity standards are less constraining on forest 

attributes, projects should often, and whenever 

possible, seek to avoid crossing the scenic “tipping 

points” described above to maintain broad-trust 

public license to manage forests.

Acknowledgments

Th e studies drawn from were mainly supported 

by the Demonstration of Ecosystem Management 

Options (DEMO) project, a joint eff ort of 

the USDA Forest Service Region 6 and Pacifi c 

Northwest Research Station. Research partners 

include the University of Washington, Oregon State 

University, University of Oregon, Giff ord Pinchot 

and Umpqua National Forests, and the Washington 

State Department of Natural Resources. Th ey were 

also supported by the Young Stands and Diversity 

Study and the Long Term Ecosystem Productivity 

Study of the USDA Forest Service Pacifi c Northwest 

Research Station. Th e numerous people who assisted 

all the studies reviewed here are acknowledged in the 

corresponding original articles.

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Citation:

Ribe, Robert G. 2013. Public perceptions of west-side forests: improving visual impact assessments and designing thinnings 

and harvests for scenic integrity. In: Anderson, Paul D.; Ronnenberg, Kathryn L., eds. Density management for the 21st

century: west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, 

Pacifi c Northwest Research Station: 22–37.
Density Management in the 21st Century: West Side Story PNW-GTR-880

38

A Satellite’s View of Recent Trends in Forest Harvest Intensity 

in the Pacific Northwest

Robert E. Kennedy, Zhiqiang Yang, Justin Braaten, Warren B. Cohen, 

Peder Nelson, and Eric Pfaff

Extended Abstract

As a silvicultural treatment, forest harvest through thinning may serve multiple management 

goals at the site level. To the extent that these goals aff ect processes or species populations that span 

landscapes, their cumulative impacts can only be assessed if landscape-wide patterns of thinning 

are monitored. Th is is particularly relevant when policy or management patterns change abruptly 

for large land ownerships, as was intended with the implementation of the Northwest Forest Plan 

(NWFP) in 1994. 

Satellite images provide consistent views of large landscapes and thus have the potential to 

monitor forest harvest, but these have typically focused only on stand-replacing harvest. In the 

Pacifi c Northwest, imagery from the Landsat family of satellites has long been used to quantify 

such harvest (Cohen et al. 2002), to estimate its impacts on carbon fl ux (Cohen et al. 1996), 

and to evaluate its potential impacts on critical habitat (Healey et al. 2008). Mapping partial 

harvest, however, is more challenging. If the approximate location of such harvest is known, the 

mathematical signal of partial harvest is discernible in the signal of the imagery (Healey et al. 

2006), but the challenge is separating that relatively subtle signal from background noise. 

Recent improvements in data access, computing power, and algorithms, however, have led to 

more robust mapping of partial harvest. Th e US Geological Survey recently opened the Landsat 

data archive to free access (Woodcock et al. 2008), and also simplifi ed its delivery of the imagery, 

making management of large data sets practical. Combined with new algorithms that tap this 

archive (Kennedy et al. 2010), separation of partial harvest from background noise is now both 

mathematically and logistically tractable (fi g. 1). 

In support of the eff ectiveness monitoring for the NWFP (http://www.reo.gov/monitoring/), we 

developed yearly maps of forest disturbance, including partial harvest, for the entire NWFP area 

for the period from 1985 to 2007 (Kennedy et al. 2012). Th ese maps are available in digital form 

at http://landtrendr.forestry.oregonstate.edu/content/download-data. 

For the purposes of evaluating partial harvest patterns, these data provide information on 

the estimated magnitude of vegetation removal occurring in each 30-m cell in the map. Th ese 

magnitude quantities are satellite-based refl ections of reality and thus are not strictly biophysical 

quantities that equate precisely with proportional basal-area removal or other similar quantities 

familiar to silviculturists. In particular, the quantities are expected to have diff erent biophysical 

Robert E. Kennedy is assistant professor, Department of Earth and Environment, Boston University, 675 Commonwealth 

Ave., Boston, MA 02215; kennedyr@bu.edu; Zhiquiang Yang is a research associate and Justin Braaten is a faculty 

research assistant, Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR 97331; Warren B. 

Cohen is a research forester, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 

SW Jeff erson Way, Corvallis, OR 97331; Peder Nelson is a senior faculty research assistant, and Eric Pfaff is a faculty 

research assistant, Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR 97331.
Density Management in the 21st Century: West Side Story PNW-GTR-880

A Satellite’s View of Forest Harvest Intensity Kennedy et al. 39

meaning in diff erent forest types (e.g., Douglas-fi r vs. Lodgepole Pine [Pseudotsuga menziesii, Pinus 

contorta]). Nevertheless, within a given forest type and region, they have utility to distinguish among 

harvests of diff erent severities. 

Grouping these data into relative intensity classes of high, medium, and low, and separating by 

ownership, temporal trends in harvest practice over time can be documented. In the Cascades province 

of the NWFP in Oregon, for example (fi g. 2), overall area harvest fell after court injunctions in the 

early 1990s, and the harvest intensity since then has been focused on lower-intensity harvest types. 

Private lands, on the other hand, saw an eventual rise in harvest rate, with an increasing proportion of 

that harvest being high-intensity harvest. Similar summaries can be replicated over the entire NWFP 

area. 

Keywords: Th inning, satellite mapping, Northwest Forest Plan.

Figure 1—A partial 

harvest (purple outline) 

within a matrix 

of prior clearcuts 

(yellow-shaded areas), 

overlaid on a highresolution air photo for 

reference. LandTrendr 

algorithms applied to 

30-m pixels of Landsat 

imagery were used to 

detect disturbance in 

individual cells, which 

were then aggregated 

into a single patch 

delineated here.
Density Management in the 21st Century: West Side Story PNW-GTR-880

40 A Satellite’s View of Forest Harvest Intensity Kennedy et al.

Figure 2—Harvest rates over time by relative intensity in federal (a) and private (b) ownership 

classes in the Cascades province of Oregon in the NWFP area. As expected, harvest rates fell 

on federal lands in the early 1990s, with a greater proportion of harvest in low and medium 

intensity classes. On private lands, rates increased from the mid 1990s onwards, with an 

increasing proportion of that rate occurring in higher-intensity harvest.

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replacement disturbance in western Oregon forests 

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Braaten, J.; Nelson, P. 2012. Spatial and temporal 

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Citation:

Kennedy, R.E.; Yang, Zhiquiang; Braaten, Justin; Cohen, Warren B.; Nelson, Peder; Pfaff , Eric. 2013. A satellite’s view of 

recent trends in forest harvest intensity in the Pacifi c Northwest [Extended abstract] In: Anderson, Paul D.; Ronnenberg, 

Kathryn L., eds. Density management for the 21st century: west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, 

OR: U.S. Department of Agriculture, Forest Service, Pacifi c Northwest Research Station: 38–40.
Density Management in the 21st Century: West Side Story PNW-GTR-880

41

Landscape Context for Density Management: Implications of Land 

Ownership and Ecological Gradients

Janet L. Ohmann

Presentation Abstract

Density management is implemented at a local (stand) scale, but is based on conservation goals 

that address a broader landscape. Although regional conservation eff orts such as the Northwest 

Forest Plan (NWFP) focus primarily on public lands, all land ownerships and allocations contribute 

unique benefi ts over the regional landscape that need to be considered as context for federal land 

management. In addition, whereas the NWFP emphasizes older forest and associated species, 

an ecosystem and multi-species management approach encompasses the full sequence of forest 

development. Recent results from NWFP Eff ectiveness Monitoring for late-successional and oldgrowth forest provide detailed maps of forest composition and structure over all ownerships, and 

for all stages of forest development, including trends over the NWFP period (1994 to present). 

More than two-thirds of older forest (overstory conifers >20 inches [50.8 cm]) was federally owned, 

whereas most early-seral forest was on nonfederal lands. However, early-seral stands have developed 

primarily following timber harvest and lacked the structural diversity typical of natural stands. 

Over the NWFP period, harvesting removed about 13 percent (491,000 acres [198,700 ha]) of 

older forest on nonfederal lands, whereas the loss of older forest from federal lands (about 200,000 

acres [80,937 ha]) was attributed primarily to wildfi re. Overall, the monitoring data suggest there 

was a slight net loss of older forest on federal lands since the beginning of the NWFP, so losses of 

older forest to wildfi re apparently were roughly balanced by recruitment. However, recruitment 

was most likely through incremental stand growth over the 20-inch [50-cm] threshold, or from 

understory disturbances (including thinning) that eliminated smaller-diameter trees and increased 

average stand diameter, rather than from increases in stands of much larger and older trees. Land 

ownerships and allocations also were unevenly distributed across regional environmental gradients. 

Federal forests generally occupied higher elevations and lower-productivity sites, and a substantial 

portion of most of the mid- to high-elevation forest types were contained within reserves and 

managed for conservation objectives. In contrast, several forest types, such as oak woodlands, 

occurred predominantly at low elevations on nonfederal lands where they are managed for a 

variety of objectives, and are not well-represented in reserves. I will discuss potential implications 

of the monitoring results for stand-level management and for the conservation of older forests and 

associated species across the region.

Keywords: Old growth, late-successional forest, early-successional forest, forest monitoring, 

change detection, Pacifi c Northwest, Northwest Forest Plan, conservation planning.

Janet L. Ohmann is a research forester, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences 

Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; johmann@fs.fed.us
Photos, facing page—Top left: Leave island at Green 

Peak, photo by Paul Anderson. Top right: Regeneration 

at the Yachats STUDS site, Siuslaw National Forest. 

Photo by Paul Anderson. Center left: Chanterelles, 

Cantharellus sp. Photo by Paul Anderson. Bottom left: 

Dan Mikowski, USFS, at North Soup Creek, Feb. 2009. 

Photo by Paul Anderson. Center right: Patch opening 

at Keel Mountain, April 2005. Photo by Paul Anderson. 

Bottom right: Two Oregon Slender Salamanders 

(Batrachoseps wrighti) and a rarely-seen nest of this 

species in a down log. Photo by Loretta Ellenburg, USFS.
Section 2: Implementation and Influences of Density 

Management in the Terrestrial Ecosystem
Density Management in the 21st Century: West Side Story PNW-GTR-880

44

Short-term Responses of Overstory and Understory 

Vegetation to Thinning Treatments: A Tale of Two 

Studies

Klaus J. Puettmann, Erich K. Dodson, Adrian Ares, and Carrie A. Berger

Klaus J. Puettmann is Edmund Hayes Professor in Silvicultural Alternatives, Oregon State University, Department of 

Forest Ecosystems and Society, Corvallis, OR, 97331; klaus.puettmann@oregonstate.edu; Erich K. Dodson is a faculty 

research assistant, Dept. of Forest Ecosystems & Society, Oregon State University, Corvallis, OR, 97331; Adrian Ares is 

project director, SANREM CRSP (Sustainable Agricultural and Natural Resource Management Collaborative Research 

Support Program) Offi ce of International Research, Education and Development (OIRED) Virginia Tech, 526 Prices 

Fork Road Blacksburg, VA 24061; Carrie A. Berger, 7 Rue Dimitri Ignatieff , Lotiss CPS Receiving, Noumea, Nouvelle 

Calédonie 98800.

Abstract

Th e Density Management Study and Young Stand Th inning and Diversity Study were initiated 

to investigate whether alternative thinning treatments can accelerate the development of forests 

toward late-successional structures. An overview of overstory and understory vegetation responses 

indicates that the magnitude and direction of thinning eff ects initially varied among structural 

stand components. Average crown length, diameter growth, and seedling and sapling density 

increased rapidly after thinning. However, diameter growth of the largest trees was less responsive 

to thinning, at least in the short term. Overall shrub cover was initially reduced by thinning, 

which was likely a consequence of harvesting damage. Th inning tended to increase overall species 

diversity by benefi tting early-successional species, and had little infl uence on late-successional 

species diversity. Th is trend appeared to reverse itself quickly, as early-seral vegetation declined 

within a decade. It appears that silvicultural treatments may best target specifi c stand structural 

components, e.g., large trees, crown length, or an understory shrub layer, rather than attempting 

to achieve all late-successional structural elements simultaneously. Increasing variability at smaller 

and larger spatial scales may be an option to achieve multiple management goals. 

Keywords: Th inning, late-successional habitat, Douglas-fi r, overstory, understory vegetation, 

regeneration.

Introduction 

Th e dispute about management of federal 

forest land resulted in the Northwest Forest Plan 

in 1994, which emphasized development of latesuccessional habitats in a context of sustainable 

wood production. Concurrently, new research 

indicated that many old-growth stands in 

western Oregon had originated at densities that 

were substantially lower than densities found 

in current Douglas-fi r (Pseudotsuga menziesii) 

plantations (Tappeiner et al. 1997). Th e eff ect of 

thinning on tree growth and timber production 

had been well researched (e.g., Marshall and 

Curtis 2002). Lacking, however, was information 

on the potential for thinning (or uneven-age 

management) to balance wood production with 

ecological concerns, such as wildlife habitat 

and biodiversity. Of specifi c interest to federal 

foresters were forest structures associated with 

late-successional habitat features (Bauhus et 

al. 2009), such as large trees, a layered canopy, 

advanced regeneration, and well-developed 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Short-term Responses of Overstory & Understory Vegetation Puettmann et al. 45

understory layers (Old Growth Defi nition Task 

Group 1986). As a consequence, several studies 

were initiated in the western portion of the 

Pacifi c Northwest region to investigate whether 

thinning young, even-aged stands dominated 

by Douglas-fi r can accelerate the development 

of late-successional forest structures (Poage and 

Anderson 2007). We present results from the fi rst 

decade of two Large-scale Management Studies 

(Monserud 2002): 1) the Density Management 

Study (DMS); and 2) the Young Stand Th inning 

and Diversity Study (YSTDS), which were 

established in the Coast Range and western 

Cascades of Oregon. 

Th e main objective of this paper is to present a 

brief overview of fi ndings regarding the vegetation 

response to various thinning treatments applied 

in the two studies. Specifi cally, we present 

responses of overstory trees, including tree 

and stand growth patterns, tree mortality, and 

overstory canopy closure. Understory responses 

include seedling and sapling densities, as well as 

cover and composition of understory vegetation, 

separated by life-form (tall shrubs, low shrubs, 

herbs, and bryophytes) and origin (exotic species). 

We present up-to-date fi ndings from the two 

studies, including previously unpublished results. 

Findings already published are highlighted by 

referring to the appropriate publications, where 

detailed fi ndings, methods, and discussions can 

be found. 

Methods 

Study Sites and Treatments

To represent the variety of conditions in the 

Bureau of Land Management (BLM) ownership 

in Oregon, the DMS includes study sites in the 

Coast Range and western Cascades of Oregon. 

Study details are described in Cissel et al. (2006). 

Seven 40- to 60-year-old stands (between 100 and 

150 ha in size) that had never been commercially 

thinned were selected, and each stand received 

one complete set of treatments. Treatment 

units ranged from 15 to 40 ha and included an 

unthinned control treatment (approximately 600 

trees per hectare [tph]), a high-density retention 

(around 300 tph), a moderate-density retention 

(200 tph) and a variable retention which 

included areas with 100, 200, and 300 tph. For 

interpretation of average treatment conditions, 

it is important to note that 4 to 18 percent of 

the unit in all thinning treatments was reserved 

in circular leave islands (0.1-, 0.2-, and 0.4-ha). 

In addition, 4 to 18 percent of the moderateand variable-density treatments were cut as 

circular gap openings (0.1-, 0.2-, and 0.4-ha). 

Units with 100 tph and the gap openings were 

planted with a mix of conifer species. Th inning 

was implemented between 1997 and 2000, and 

data described in this report were taken 6 and 

11 years after the thinning operation. More 

detailed results from these studies can be found 

in Fahey and Puettmann (2007, 2008), Wilson 

and Puettmann (2007), Kuehne and Puettmann 

(2008), Ares et al. (2009, 2010), Wilson et al. 

(2009), Dodson et al. (2012), and Berger et al. 

(2012). 

Th e YSTDS is located on the McKenzie and 

Middle Fork Ranger Districts of the Willamette 

National Forest on the western slopes of the 

Oregon Cascade Range. Four stands between the 

ages of 35 and 50 years that were dominated by 

even-aged Douglas-fi r were selected. Each stand 

received a set of thinning treatments, which 

included an unthinned control (C; approximately 

700 tph), a heavy thin (HT; 125 tph), a light thin 

(LT; 250 tph), and an additional light thin, in 

which 20 percent of the unit was cut in circular 

0.2-ha gaps (LG). Th e heavy thin and the gaps in 

the light thin with gaps were planted with a mix 

of conifer species. Th e thinning was implemented 

between 1994 and 1997 (mostly 1995 and 1996) 

and the data described in this report are from 

measurements 1, 3, 5, and 10 years after thinning. 

More detail about the study establishment can 

be found in Manning and Friesen (in prep.1

). 

Detailed results from this study are provided 

by Berger and Puettmann (2007), Davis et al. 

(2007), Kuehne and Puettmann (2008), and 
Density Management in the 21st Century: West Side Story PNW-GTR-880

46 Short-term Responses of Overstory & Understory Vegetation Puettmann et al.

Davis and Puettmann (2009).

Both studies generally used a thinning from 

below, but hardwoods and other minority species 

were maintained wherever possible. Conditions 

such as slope and aspect varied widely among the 

study sites and treatment units, and also within 

the treatment units. Th is resulted in large withintreatment variation in tree densities and other 

conditions (Cissel et al. 2006). Th e studies were 

implemented using operational timber sales, and 

variation in terrain and logging operators led to 

the use of both cable and ground-based harvest 

systems within several individual treatments. 

Th is increased the variability within individual 

treatment blocks compared to the homogeneity 

that can be achieved in small experimental 

units. However, this also means that the study 

includes many issues associated with operational 

treatments and results do not have to be scaled 

up, as is commonly done with small experimental 

plots. 

Measurements and Analysis

Th e DMS sampling protocol is presented in 

Cissel et al. (2006). Th e sampling design for 

over-and understory vegetation of the YSTDS 

is presented in Davis et al. (2007) and Davis 

and Puettmann (2009). For the presentation 

below, mean values of each treatment unit in the 

YSTDS were calculated by averaging the plot 

means, with the exception of the treatment units 

that included gaps. A weighted average of subtreatment (gap, edge, interior forest) means was 

used to calculate these treatment unit means. 

Weights for each sub-treatment were based on 

the proportion of areas in each sub-treatment to 

total treatment units (Davis et al. 2007). 

Th e statistical analysis of the YSTDS data 

presented below used ANOVAs with a randomized 

complete block model in conjunction with 

the Tukey-Kramer adjustment for all multiple 

comparisons (PROC GLM). Data aggregated 

to the treatment unit level (n = 16 treatment 

units) were approximately normal; therefore, no 

transformations were performed. Signifi cance 

level in the analysis and fi gures below indicate P 

≤ 0.05. Analysis procedures for the DMS varied, 

but are described in detail in the publications. 

Results and Discussion

Overstory Responses

Stand growth patterns showed inconsistent 

responses. Overall, basal area after thinning was 

reduced in both studies. Basal area growth for the 

measurement interval from 5 to 10 years after 

thinning in the YSTDS averaged 86, 73, and 

88 percent of control for the Heavy, Light, and 

Light with Gap treatments, respectively (table 

1). Note, that these values were not signifi cantly 

diff erent from each other, and the low basal area 

growth in the Light treatment is mainly due to a 

single site (Mill Creek). In the DMS study, basal 

area growth 6 to 11 years after thinning was not 

signifi cantly diff erent from the controls (Dodson 

et al. 2012). Such discrepancies may be due to a 

combination of variability in age, site quality, and 

associated ability of trees to respond to canopy 

openings. Douglas-fi r can maintain stand growth 

under a relatively wide density range (Marshall 

and Curtis 2002), and little impact would 

be expected in the lower-intensity thinnings. 

Apparently, such eff ects in conjunction with site 

variability did not allow detection of statistically 

signifi cant diff erences. 

Diameter growth showed a consistent response 

in both studies. Average diameter growth of trees 

increased after thinning (table 2, also Dodson et 

al. 2012). Th is is due to a combination of the 

removal of slower-growing trees by thinning 

from below (i.e., the chainsaw eff ect), as well as 

improved growing conditions for residual trees. A 

more detailed analysis suggested that smaller trees 

especially benefi tted from thinning by increasing 

their growth rate. Th e largest trees were growing 

faster prior to thinning and did not experience as 

large an increase in growth rates as smaller trees 

1

Manning, T.; Friesen, C., eds. [n.d.] The Young Stand 

Thinning and Diversity Study establishment report and 

study plan. Manuscript in preparation.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Short-term Responses of Overstory & Understory Vegetation Puettmann et al. 47

Table 1—Mean basal area (m2·ha-1) for all trees ≥8 cm dbh in post-treatment years 1, 3, 5, and 

10. Data are from the Young Stand Thinning and Diversity Study. 

Block Treatment

Mean basal area for all trees ≥8 cm dbh (m2·ha-1)

1997 1999 2001 2006

Cougar Reservoir 

(CR)

Control 39.8 45.0 47.2 51.4

Heavy thin 13.2 15.7 17.5 22.3

Light thin 24.6 27.6 29.6 35.6

Light thin with gaps 17.6 20.5 22.9 27.3

Mill Creek (MC) Control 46.7 50.3 52.5 56.3

Heavy thin 21.1 23.2 24.9 25.0

Light thin 31.5 33.7 35.6 35.3

Light thin with gaps 27.0 29.7 29.4 30.0

Christy Flats 

(CF)

Control 53.2 55.1 56.4 61.6

Heavy thin 14.4 15.4 16.8 20.7

Light thin 20.8 21.9 23.5 27.8

Light thin with gaps 19.1 20.2 21.9 25.6

Sidewalk Creek 

(SC)

Control 38.7 39.7 41.0 41.5

Heavy thin 11.8 13.3 14.6 17.6

Light thin 20.4 22.0 23.4 25.4

Light thin with gaps 15.4 16.8 18.0 19.4

Table 2—Mean dbh (cm) for all trees ≥8 cm dbh in post-treatment years 1, 3, 5, and 10. Data 

are from the Young Stand Thinning and Diversity Study. 

Block Treatment

Mean dbh for all trees ≥8 cm dbh (cm)

1997 1999 2001 2006

Cougar Reservoir 

(CR)

Control 24.3 25.8 26.8 28.5

Heavy thin 31.1 31.6 32.5 33.1

Light thin 29.0 30.7 31.8 33.7

Light thin with gaps 29.8 31.3 32.2 31.9

Mill Creek (MC) Control 26.8 28.7 29.9 31.4

Heavy thin 26.9 27.8 28.5 30.3

Light thin 27.8 28.9 29.6 30.9

Light thin with gaps 26.9 27.5 27.9 28.4

Christy Flats 

(CF)

Control 25.5 27.2 29.1 30.3

Heavy thin 35.2 36.6 38.7 40.6

Light thin 32.8 34.6 37.0 41.1

Light thin with gaps 32.6 35.2 37.2 39.9

Sidewalk Creek 

(SC)

Control 22.5 23.2 24.0 25.0

Heavy thin 26.6 25.6 24.5 22.8

Light thin 28.4 29.4 30.5 31.8

Light thin with gaps 26.9 26.7 26.9 26.9
Density Management in the 21st Century: West Side Story PNW-GTR-880

48 Short-term Responses of Overstory & Understory Vegetation Puettmann et al.

(Davis et al. 2007; Dodson et al. 2012). Quite 

likely, the largest trees did not experience a major 

improvement in growing conditions as part of 

the standard thinning operation. However, the 

more open growing conditions resulting after 

thinning will likely mean that growth rates of 

larger trees can be maintained longer than under 

unthinned conditions (Latham and Tappeiner 

2002). As an indication of this trend, the largest 

trees responded with increased growth under 

very heavy thinnings (Davis et al. 2007) and 

when adjacent trees were removed as part of gap 

creation (Dodson et al. 2012). 

In general, mortality rates were higher in 

the control treatments than in the thinning 

treatments (tables 3 and 4, Dodson et al. 2012). 

Most tree mortality in the controls was in the 

smaller diameter classes, suggesting competitionrelated mortality as the major factor. On the other 

hand, mortality rates in the thinned units were 

minor and did not show a size-related pattern 

(table 4), indicating that most trees were able 

to withstand the exposed conditions created by 

thinning. Th ese results also imply that most snags 

in unthinned conditions are in smaller size classes, 

limiting their wildlife value. Even recruitment 

of small snags was reduced by thinning; thus 

current snag densities and expected mortality 

may not be suffi cient to reach snag levels similar 

to those found in old-growth stands (Ares et al. 

2012). Active snag creation may be necessary to 

achieve specifi c habitat goals, especially if these 

goals include larger snags (Dodson et al. 2012). 

Overstory cover is an important measure 

of wildlife habitat, but for practical purposes 

overstory closure is often used as an indicator 

of canopy density (Jennings et al. 1999), as 

was done in the YTSDS (no overstory closure 

data were available for the DMS). Typical 

overstory canopy closure under unthinned 

control conditions in the YSTDS was around 80 

percent (table 5, fi g. 1). As expected, thinning 

reduced overstory closure to around 30, 50, and 

42 percent of the controls in the Heavy, Light, 

Table 3—Mean trees per hectare for all trees ≥8 cm dbh in post-treatment years 1, 3, 5, and 10.

Data are from the Young Stand Thinning and Diversity Study. 

Block Treatment

Mean trees per hectare, all trees ≥8 cm dbh (tph)

1997 1999 2001 2006

Cougar Reservoir 

(CR)

Control 753 741 723 697

Heavy thin 151 165 172 199

Light thin 312 312 309 327

Light thin with gaps 221 229 237 266

Mill Creek (MC) Control 655 614 594 589

Heavy thin 283 290 292 304

Light thin 415 408 408 425

Light thin with gaps 346 357 327 378

Christy Flats 

(CF)

Control 869 791 717 724

Heavy thin 133 131 129 139

Light thin 207 198 188 185

Light thin with gaps 1498 184 178 180

Sidewalk Creek 

(SC)

Control 792 771 747 733

Heavy thin 165 191 216 288

Light thin 277 279 276 290

Light thin with gaps 225 241 244 267
Density Management in the 21st Century: West Side Story PNW-GTR-880

Short-term Responses of Overstory & Understory Vegetation Puettmann et al. 49

Table 4—Conifer and hardwood (≥5 

cm dbh) percent mortality by block and 

treatment. Data were collected in 2006, ten 

years post-treatment and are from the Young 

Stand Thinning and Diversity Study. 

Block Treatment

Mortality of trees ≥5 

cm dbh (percent)

Conifers Hardwoods

Cougar Reservoir 

(CR)

Control 4.0 10.6

Heavy thin 0.3 0.0

Light thin 1.1 0.0

Light thin with gaps 1.6 1.1

Mill Creek (MC) Control 2.2 4.0

Heavy thin 1.3 4.8

Light thin 0.5 0.9

Light thin with gaps 1.3 0.4

Christy Flats 

(CF)

Control 4.5 33.3

Heavy thin 0.9 0.0

Light thin 1.5 3.0

Light thin with gaps 0.0 4.8

Sidewalk Creek 

(SC)

Control 1.4 2.5

Heavy thin 0.0 0.0

Light thin 0.9 0.0

Light thin with gaps 0.4 0.5

Block Treatment

Overstory cover (percent)

1997 1999 2001 2006

Cougar Reservoir 

(CR)

Control 82 83 89 85

Heavy thin 25 37 37 51

Light thin 50 62 72 73

Light thin with gaps 40 47 55 60

Mill Creek (MC) Control 82 76 76 85

Heavy thin 46 54 60 62

Light thin 62 68 75 77

Light thin with gaps 50 57 62 71

Christy Flats 

(CF)

Control 79 79 71 80

Heavy thin 17 22 27 30

Light thin 37 44 46 56

Light thin with gaps 36 44 45 54

Sidewalk Creek 

(SC)

Control 70 77 73 76

Heavy thin 31 27 36 46

Light thin 53 58 63 62

Light thin with gaps 42 46 49 54

Table 5—Mean percent overstory cover in post-treatment years 1, 3, 5, and 10. Data are from 

the Young Stand Thinning and Diversity Study. 
Density Management in the 21st Century: West Side Story PNW-GTR-880

50 Short-term Responses of Overstory & Understory Vegetation Puettmann et al.

and Light with Gap treatments, respectively. 

However, the overstory recovery was quite rapid 

in the fi rst decade, with average canopy closure 

increasing from 1 to 2 percent per year (fi g. 2), a 

value similar to other studies in the region (e.g., 

Chan et al. 2006). Similarly, crown lift stopped 

fairly quickly after thinning (Chan et al. 2006; 

Davis et al. 2007). Even though overstory closure 

is still signifi cantly lower 10 years after thinning, 

the trends suggest that long-term maintenance 

of open canopy conditions will require repeated 

thinning operations. 

Tree Regeneration 

Partial harvests, such as thinning, provide 

opportunity for establishment of a new cohort 

of trees through increased vigor, and thus seed 

production by residual trees (Reukema 1961), 

exposure of mineral soil that provides seed beds, 

and resource availability for seedlings (Nyland 

2002). Generally, natural regeneration was 

signifi cantly more abundant after thinning than 

in control treatments in both studies (fi g. 3, 

Kuehne and Puettmann 2008; Ares et al. 2010; 

Dodson et al. 2012). Seedling establishment 

likely increased due to a combination of seedbed 

preparation through harvesting disturbances 

and increased resource availability as a result 

of the removal of overstory trees and damaged 

understory vegetation. However, short-term 

eff ects on tree regeneration did not diff er among 

thinning treatments (Kuehne and Puettmann 

2008), but the variability within treatments 

and among replications of treatments was high. 

Figure 1—Overstory cover (percent) 

by year (includes 95 percent confidence 

intervals). Letters indicate significant 

differences among treatments 

(treatments with the same letter do not 

differ at P ≤ 0.05 level).

Figure 2—Ten-year post-treatment mean 

percent overstory cover by block (includes 

standard error bars).
Density Management in the 21st Century: West Side Story PNW-GTR-880

Short-term Responses of Overstory & Understory Vegetation Puettmann et al. 51

In some plots, the regeneration density was 

suffi ciently high to initiate a discussion about 

future pre-commercial thinning (Cissel et al. 

2006). 

Saplings also showed higher densities in 

thinned units than in controls 11 years following 

thinning (fi g. 3, Dodson et al. 2012). Th ey likely 

were established prior to implementation of 

thinning treatments, and interpretation of these 

numbers needs to consider that at least some 

saplings were damaged during the harvesting 

operation (Dodson et al. in prep.2

). Since 

saplings were not infl uenced by thinning impacts 

on seedbed conditions, the growing environment 

in thinned units appears more conducive than in 

unthinned controls. Th is has also been shown by 

greater growth of some species under less dense 

conditions (Shatford et al. 2009). Th e patterns 

in in-growth also suggest that diff erences in 

overstory density among thinning treatments 

will be refl ected in the diameter distributions 

in the long run, with higher seedling and 

sapling densities in the more intensive thinning 

treatments (Dodson et al. 2012; Dodson et al. in 

prep.2

). 

Th e dominant species on the study sites 

(usually Douglas-fi r, and in some cases Western 

Hemlock, Tsuga heterophylla) were also dominant 

in the seedling and sapling pool. Species richness 

of seedlings was higher in thinned units, and 

the spatial patterns suggest that the presence of 

“minority” species in the overstory is also refl ected 

in the seedling pool (Kuehne and Puettmann 

2008). Diff erential growing patterns, especially 

in response to competition from overstory trees, 

suggest that the density of light-demanding 

species such as Douglas-fi r may decline over time 

(Shatford et al. 2009) unless repeated overstory 

thinning maintains open growing conditions. 

Th inning operations also damage regeneration, 

which can become problematic when the density 

of regenerating seedlings is low, e.g., in understory 

plantings (Newton and Cole 2006). However, 

fi ve years after a second thinning, density values 

of natural tree regeneration were similar to units 

that had not been thinned a second time (Berger 

et al. 2012). In terms of seedling densities, the 

damage due to the harvesting operation during 

this treatment was apparently balanced out by 

new recruitment. 

Understory Vegetation

Responses to thinning varied among 

understory life-forms. Tall shrubs showed a large 

decline right after thinning in the YSTDS to 

less than half of cover values found in control 

Figure 3—Ten-year post-treatment 

mean seedling and sampling density 

(tph) by block (includes standard 

error bars). 

2

Dodson, E.K.; Ares, A.; Burton, J.; Puettmann, K.J. 

[n.d.] Natural regeneration after thinning Douglas-fir 

stands in western Oregon. Manuscript in preparation for 

the Canadian Journal of Forest Research.
Density Management in the 21st Century: West Side Story PNW-GTR-880

52 Short-term Responses of Overstory & Understory Vegetation Puettmann et al.

units (fi gs. 4a and 4b, table 6a and 6b). Since 

we do not have any evidence to suggest a bias 

in pre-thinning conditions, it appears that the 

harvesting operation led to physical damage of 

shrubs (Davis and Puettmann 2009; Dodson and 

Puettmann, unpublished data). Tall shrub cover 

was not signifi cantly diff erent on thinned units 

after a decade, suggesting that some recovery 

occurred. However, values remained lower than 

on control units. 

A meta-analysis of fi ve thinning studies in the 

region suggests that thinning does not consistently 

reduce shrub cover (Wilson et al. 2009). Instead, 

thinning reduced shrub cover only when shrub 

cover is initially high (>30 percent cover), with 

little eff ect in stands not dominated by shrubs, 

suggesting that mechanical damage occurs during 

the harvesting operations. 

In contrast to shrubs, cover of herbaceous 

vegetation did not experience a post-harvest 

decline (Wilson et al. 2009, fi g. 4c, table 6c). 

Instead, herbaceous cover increased quickly 

Figure 4—Mean percent cover for a) tall shrubs/small trees, b) low shrubs, c) herbs, and 

d) bryophytes in post-treatment years 1, 5, and 10. 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Short-term Responses of Overstory & Understory Vegetation Puettmann et al. 53

after thinning, apparently benefi ting from 

reduced competition (Ares et al. 2009). Further 

increases of herbaceous cover may be limited due 

to increased competition, as shrubs and trees 

respond to thinnings. Similar to herbs, bryophyte 

ground cover showed an initial increase, likely 

covering ground that was exposed during the 

harvesting operation (Davis and Puettmann 

2009, fi g. 4d, table 6d). Over time, ground cover 

of bryophytes increased slightly in the YSTDS, 

but diff erences among treatments were not 

statistically signifi cant. Bryophyte cover in the 

DMS study was signifi cantly lower in the heavily 

thinned treatments than controls a decade after 

thinning (Ares et al. 2010).

A decade after thinning, other categories of 

ground cover, such as bare soil, stumps, rocks, 

or logs, typically covered less than 5 percent of 

the area in the DMS. Treatment patterns were 

hard to detect, but duff layers still appear to be 

lower in thinned units than in controls (Ares et 

al. 2009). Th e absolute cover value of litter was 

higher in controls, with cover in thinned units 

being approximately two-thirds of control value 

Figure 4, continued.
Density Management in the 21st Century: West Side Story PNW-GTR-880

54 Short-term Responses of Overstory & Understory Vegetation Puettmann et al.

a. Tall Shrubs/Low Trees Tall shrub/small tree understory cover (percent)

Block Treatment 1997 1999 2001 2006 Trend

Cougar Reservoir 

(CR)

Control 38.4 35.2 28.7 32.9 ↓ ↑

Heavy thin 25.0 36.2 36.1 55.5 ↑

Light thin 12.8 16.2 12.7 19.6 ↑

Light thin with gaps 24.3 31.0 32.0 42.3 ↑

Mill Creek (MC) Control 42.8 44.9 42.2 47.3 ↑

Heavy thin 21.3 32.2 33.0 43.7 ↑

Light thin 13.4 20.8 21.4 30.4 ↑

Light thin with gaps 14.2 22.5 30.1 31.3 ↑

Christy Flats 

(CF)

Control 53.5 54.6 56.2 56.9 ↑

Heavy thin 0.9 2.9 3.3 12.7 ↑

Light thin 6.5 12.4 13.2 19.1 ↑

Light thin with gaps 9.9 11.7 11.6 17.2 ↑

Sidewalk Creek 

(SC)

Control 39.8 46.0 48.4 45.8 ↑

Heavy thin 27.4 36.3 27.4 37.9 ↑

Light thin 20.6 31.3 28.6 39.4 ↑

Light thin with gaps 15.0 16.2 16.0 21.2 ↑

Table 6—Mean percent cover for a) tall shrubs/small trees, b) low shrubs, c) herbs, and d) bryophytes in 

post-treatment years 1, 3, 5, and 10. Data are from the Young Stand Thinning and Diversity Study. 

b. Low Shrubs Low shrub understory cover (percent)

Block Treatment 1997 1999 2001 2006 Trend

Cougar Reservoir 

(CR)

Control 34.1 29.5 19.6 20.1 ↓

Heavy thin 13.9 36.5 50.6 53.8 ↑

Light thin 9.0 22.5 33.4 32.8 ↑

Light thin with gaps 13.0 28.9 47.2 46.8 ↑

Mill Creek (MC) Control 28.4 23.1 22.6 13.5 ↓

Heavy thin 13.8 37.0 43.7 44.6 ↑

Light thin 16.9 30.6 48.5 39.9 ↑

Light thin with gaps 16.8 25.3 38.0 37.6 ↑

Christy Flats 

(CF)

Control 21.7 16.1 18.8 13.4 ↓

Heavy thin 4.1 10.3 20.2 27.1 ↑

Light thin 8.4 18.5 28.9 44.8 ↑

Light thin with gaps 12.7 30.1 27.9 33.2 ↑

Sidewalk Creek 

(SC)

Control 42.7 35.7 47.8 27.6 ↓

Heavy thin 23.6 34.1 34.8 49.0 ↑

Light thin 23.3 33.1 31.2 45.4 ↑

Light thin with gaps 33.6 39.8 44.6 55.7 ↑
Density Management in the 21st Century: West Side Story PNW-GTR-880

Short-term Responses of Overstory & Understory Vegetation Puettmann et al. 55

c. Herbs Herbaceous understory cover (percent)

Block Treatment 1997 1999 2001 2006 Trend

Cougar Reservoir 

(CR)

Control 16.5 16.9 15.8 14.1 ↓

Heavy thin 21.5 30.2 32.8 26.0 ?

Light thin 16.5 21.9 26.2 29.2 ↑

Light thin with gaps 16.2 22.0 25.4 23.8 ↑

Mill Creek (MC) Control 21.8 19.2 15.5 24.8 ↓ ↑

Heavy thin 16.0 19.1 17.9 25.0 ↑

Light thin 12.9 20.1 22.7 24.6 ↑

Light thin with gaps 23.0 25.3 30.1 36.0 ↑

Christy Flats 

(CF)

Control 23.1 18.1 20.6 23.0 ↑

Heavy thin 19.7 24.5 27.6 26.5 ↑

Light thin 21.1 20.9 22.5 39.3 ↑

Light thin with gaps 20.0 29.3 22.2 32.0 ?

Sidewalk Creek 

(SC)

Control 16.4 11.7 14.9 31.2 ↓ ↑

Heavy thin 16.2 20.5 15.7 24.0 ↑

Light thin 13.7 15.7 14.8 21.4 ↑

Light thin with gaps 13.7 16.6 13.1 18.7 ?

Table 6, continued—Mean percent cover for a) tall shrubs/small trees, b) low shrubs, c) herbs, and 

d) bryophytes in post-treatment years 1, 3, 5, and 10.

d. Bryophytes Bryophyte understory cover (percent)

Block Treatment 1997 1999 2001 2006 Trend

Cougar Reservoir 

(CR)

Control 25.1 21.5 21.8 25.4 ↓ ↑

Heavy thin 4.5 5.8 23.1 12.1 ↑ ↓

Light thin 11.5 27.3 53.1 47.9 ↑

Light thin with gaps 3.0 5.0 21.1 12.0 ↑ ↓

Mill Creek (MC) Control 19.5 16.7 16.8 23.5 ↓ ↑

Heavy thin 7.8 11.7 23.7 18.1 ↑

Light thin 19.0 20.8 34.4 33.6 ↑

Light thin with gaps 29.5 24.6 51.0 49.3 ↑

Christy Flats 

(CF)

Control 23.0 24.9 28.9 39.9 ↑

Heavy thin 2.5 2.3 5.3 4.7 ↑

Light thin 4.8 5.8 10.8 16.3 ↑

Light thin with gaps 4.4 6.6 4.5 6.1 ?

Sidewalk Creek 

(SC)

Control 30.2 36.3 46.5 44.9 ↑

Heavy thin 1.4 21.9 42.2 37.3 ↑

Light thin 12.0 25.3 37.7 43.9 ↑

Light thin with gaps 7.7 26.6 29.0 27.3 ↑
Density Management in the 21st Century: West Side Story PNW-GTR-880

56 Short-term Responses of Overstory & Understory Vegetation Puettmann et al.

(Ares et al. 2009). 

Vegetation composition showed a consistent 

trend toward higher species richness, which 

was mainly attributable to increases in earlyseral species after thinning (Davis et al. 2007; 

Ares et al. 2009, 2010). Th e combination of 

ground disturbance and increased resource 

availability likely allowed establishment of these 

species, especially in harvested gaps (Fahey 

and Puettmann 2007, 2008). Species richness 

of mid- to late-seral species did not appear to 

be reduced. Notable exceptions include the 

reduction of obligate mycotrophs, plants in 

symbiotic relationships with fungi (Davis et al. 

2007). Th is may be related to lower numbers and 

production of selected mushrooms after thinning 

(Pilz et al. 2006). Exotic species increased 

slightly after thinning operations, but absolute 

cover values typically remained under 2 percent 

(Davis and Puettmann 2009; Ares et al. 2009). 

One exception was a single treatment unit at a 

single site that had a nearby seed source of Scotch 

Broom (Cytisus scoparius), where cover values 

of exotic species increased to over 3 percent. 

However, it appears that within a decade the cover 

values of exotic species are declining, suggesting 

that most of these species are not invasive and 

expanding. In the long run, one would expect 

that the transitory increase in resources would 

be declining, but still be refl ected in species 

composition for an extended time period, even 

after the overstory closure has reached high levels 

(Lindh and Muir 2004). 

Conclusion 

Th e short-term responses to thinning in 

the two studies show that questions regarding 

the effi cacy of thinning for accelerating latesuccessional development do not have a simple 

answer. Instead, diff erent measures of latesuccessional habitat appear to respond in 

diff erent ways and at diff erent time scales. For 

example, rapid increases in crown length and 

tree growth suggest that thinning is accelerating 

some features of late-successional structure. In 

contrast, late-successional attributes such as 

tall shrub cover and cover of late-seral species 

were not accelerated by thinning. Instead, they 

showed the opposite trends toward open and 

early-successional conditions, at least in the short 

term. Few responses varied signifi cantly among 

alternative thinning treatments, suggesting that 

in the short term the thinning activity itself 

is more important than the actual choice of 

residual densities, or that the range of thinning 

treatments in these two experiments was too 

narrow. However, in the long run, one would 

expect that growth of overstory trees, tree 

regeneration, as well as species composition of 

understory vegetation, would refl ect the diff erent 

thinning intensities, including gap creation. 

While long-term data are not available, the 

short-term trends in overstory development 

suggest that in thinned units most responses 

are transitory: they may be still detectable after 

canopy closure, but development trends will 

have slowed down. To maintain the benefi ts of 

an accelerated development of late-successional 

characteristics in thinned stands likely requires 

multiple entries (Del Rio and Berg 1979). 

Alternatively, very heavy thinning and gaps may 

provide suffi cient conditions to accelerate latesuccessional habitat with a single entry. Including 

a variety of treatments in thinning operations, 

especially gaps and leave island treatments, also 

provides opportunities to increase the smallscale spatial variability within stands, a major 

characteristic of old-growth stands (Franklin and 

Van Pelt 2004). 

Th e diff erential responses to thinning of 

various aspects of forest structure in these two 

studies suggest that managers should assess which 

specifi c structural attributes and processes are 

critical. Because all attributes cannot be achieved 

simultaneously, setting priorities is important. 

Alternatively, managing for heterogeneity can be 

used to emphasize diff erent attributes at diff erent 

spatial scales within and among stands. Tying 

silvicultural treatments and stand development 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Short-term Responses of Overstory & Understory Vegetation Puettmann et al. 57

into a multi-scale landscape plan will facilitate 

achievement of multiple management goals 

(Wilson and Puettmann 2007). 

Acknowledgments

Th e authors acknowledge the support of the USFS 

Willamette National Forest and the Bureau of Land 

Management for provision and management of the 

study sites and fi nancial support. We also thank 

researchers initially involved in the study setups and 

the numerous dedicated site coordinators and fi eld 

personal who worked on the studies over the years. 

Th e publication improved through contributions of 

two anonymous reviewers and Craig Kintop. 

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Citation:

Puettmann, Klaus J.; Dodson, Erich K.; Ares, Adrian; Berger, Carrie A. 2013. Short-term responses of overstory and 

understory vegetation to thinning treatments: a tale of two studies. In: Anderson, Paul D.; Ronnenberg, Kathryn L., 

eds. Density management for the 21st century: west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacifi c Northwest Research Station: 44–58.
Density Management in the 21st Century: West Side Story PNW-GTR-880

59

Making the Little Things Count: Modeling the 

Development of Understory Trees in Complex Stands

Peter J. Gould and Constance A. Harrington

Peter J. Gould is inventory lead, Washington State Department of Natural Resources, Olympia, WA; peter.gould@dnr.

wa.gov; Constance A. Harrington is a research forester, USDA Forest Service, Pacifi c Northwest Research Station, Forestry 

Sciences Laboratory, 3625 93rd Ave SW. Olympia, WA 98512; charrington@fs.fed.us

Abstract

Forest growth models are useful for asking “What if?” questions when evaluating silvicultural 

treatments intended to increase the complexity of future stands. What if we thinned to level A or 

B? How would it aff ect the growth rates of understory trees? How many trees would survive? To answer 

these types of questions, a growth model needs to accurately predict the growth and survival 

of understory trees. Some users of the Forest Vegetation Simulator (FVS) growth model have 

commented that model predictions for understory trees do not match their fi eld observations or 

data. To study the relationships which govern growth of understory trees, we assembled a large 

database from silvicultural experiments and operational inventory data. Th is database provided an 

opportunity to look at the major factors that aff ect the growth and survival of understory Douglasfi r (Pseudotsuga menziesii), Western Hemlock (Tsuga heterophylla), and Western Redcedar (Th uja 

plicata). Tree attributes like diameter and crown ratio were the best predictors of tree growth, 

followed by measures of stand density and competition. We found that the potential and average 

growth of all three species decreased as the density of larger trees increased, but the growth of 

Douglas-fi r was reduced the most by increasing overstory density. Similarly, competition with 

larger trees reduced the survival of Douglas-fi r more than the other species. Western Hemlock 

generally had greatest growth at moderate to high levels of overstory density. Survival of Western 

Redcedar was the highest of the three species. Overall, we found the eff ect of overstory density on 

understory tree growth was less, but the eff ects on mortality were greater, than predicted in earlier 

versions of FVS. Incorporating these new relationships into future versions of FVS should provide 

forest managers with better tools to evaluate alternative management scenarios.

Keywords: Growth and yield models, Forest Vegetation Simulator, thinning, competition, underplanting, regeneration.

Introduction

In recent decades, a goal of silvicultural 

treatments on some forest ownerships has been 

to increase the complexity of future stands. Forest 

managers often want to take “simple” even-aged 

stands that are dominated by a single species 

and create complex stands that are spatially 

heterogeneous and contain multiple species, 

canopy layers, and age classes. Silvicultural 

treatments to create complex stands include 

variable-density thinning, thinning with “skips 

and gaps” (Harrington et al. 2005), and planting 

trees in the understory. Since we have little 

experience in creating these types of complex 

stands by design, we often turn to growth models 

to ask “What if?” questions. What if we alter 

overstory density and species? How do we know 

when we have enough understory trees so that 
Density Management in the 21st Century: West Side Story PNW-GTR-880

60 Modeling Development of Understory Trees Gould and Harrington

at least some will survive to become big trees? 

To answer these questions, we need a growth 

model that does a good job of predicting the 

development of understory trees.

Th e Forest Vegetation Simulator (FVS) is 

a widely used growth model in the Pacifi c 

Northwest (Crookston and Dixon 2005). We 

have evaluated the performance of FVS with data 

from research trials and found that it generally 

under-predicts growth and over-predicts survival 

of trees in an understory position. We are in the 

process of developing new models of understory 

growth and survival that will be incorporated into 

FVS. Th ese models will better refl ect the growth 

rates and survival of small trees that have been 

observed throughout the Pacifi c Northwest. In 

addition, the understory environment for small 

trees is more variable, in terms of light and other 

environmental conditions, in complex stands 

than in simpler, even-aged stands. Th us, the new 

models will be more sensitive to variation in 

overstory density and predict greater variability 

in growth rates than previous models. We have 

assembled a large data set describing smalltree growth from many diff erent silvicultural 

experiments, as well as operational inventory data. 

Part of developing models to predict growth and 

survival is evaluating how diff erent factors aff ect 

these processes. Th is provides an opportunity to 

highlight which factors are generally important 

in the Pacifi c Northwest.

Our goal for this paper was to draw together 

diff erent sources of information to make some 

general observations about the growth and 

survival of small trees under diff erent conditions. 

We used the database that we assembled to revise 

FVS to address the following questions:

1. Which set of factors best predicts the growth 

of understory trees?

2. How is the growth of understory trees aff ected 

by stand structure?

3. How is the survival of understory trees aff ected 

by stand structure?

Methods

Th e database was assembled from measurements 

of seven large-scale silvicultural experiments 

in western Washington and Oregon and from 

measurements of the US Forest Service’s current 

vegetation survey (CVS) plots (USDA Forest 

Service 2009) (table 1 and fi g. 1). Th ese data 

cover the ranges of the PN and WC variants of 

FVS. We defi ned small trees as those that were 

<16 cm dbh (diameter at breast height) at the 

beginning of a growth period. We only used data 

from trees which were measured at least twice, 

so that growth increments and survival could be 

calculated. Th e period between measurements 

ranged from 3 to 11 years. We calculated 

diameter and basal-area growth increments (at 

breast height) for all trees that were >1.3 m tall 

at the beginning of the growth period. For small 

trees where only height-growth increments were 

measured, we used a height-diameter equation 

to calculate equivalent diameter and basal-area 

increments from the height increments. Growth 

increments were normalized to a 5-year period 

by assuming constant growth during the period. 

Each of the silviculture experiments (full 

names appear in table 1) includes treatments 

with diff erent levels of overstory removal and, 

in some cases, diff erent spatial patterns (e.g., 

gaps versus uniform thinning). In fi ve of the 

experiments, seedlings were planted following 

overstory treatments. Th e small trees that were 

selected from the ODS, STUDS, and WOTUS 

experiments were almost entirely those that 

were planted after the overstory treatment. Trees 

were not planted in the OHDS experiment, but 

the stands were old enough that our selection 

criterion ensured that only trees that were in 

an understory position at the beginning of 

the experiment or established afterward were 

selected. Stands in the Blue River and Clearwater 

experiments were fairly young; therefore, only 

trees that were planted, established naturally, or 

were too small to measure at the beginning of 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Modeling Development of Understory Trees Gould and Harrington 61

Table 1—Silvicultural experiments that provided data for modeling the growth and survival of understory trees. 

Additional sources of information on these experiments can be found in the cited references.

Experiment

Understory tree 

development

Overstory 

age (years) References

Forest Ecosystem Study Transects (FES) natural 50-65 Carey et al. 1999

Olympic Habitat Development Study (OHDS) natural 40-80 Harrington et al. 2005; 

Comfort et al. 2010

Overstory Density Study (ODS) planted 40-70 Curtis et al. 2004; 

Poage and Anderson 2007

Western Oregon Th inning and Underplanting 

Study (WOTUS)

planted 50-55 Cole and Newton 2009

Clearwater and Blue River most natural, 

some planted

15 Poage and Anderson 2007

Siuslaw Th inning and Underplanting for Diversity 

Study (STUDS)

planted 30-35 Chan et al. 2006; 

Poage and Anderson 2007

Figure 1—Locations of 

silvicultural experiments 

and CVS data in the 

modeling database.
Density Management in the 21st Century: West Side Story PNW-GTR-880

62 Modeling Development of Understory Trees Gould and Harrington

the experiment (ingrowth) were selected for the 

database to avoid selecting overstory trees. 

Small trees were selected from the CVS plots 

if they were <16 cm dbh at the beginning of the 

growth period. CVS plots were excluded from 

the database if there was evidence of thinning 

or another disturbance between measurements, 

leaving a total of 3988 plots. Unlike the largescale experiments, the treatment histories and 

stand structures of the CVS plots were not 

known. We could not be sure which CVS plots 

were in complex stands. On the other hand, data 

from the CVS plots are valuable because they are 

representative of small-tree growth throughout 

much of the Pacifi c Northwest. For some 

analyses, we used only plots that had at least one 

tree >30 cm dbh to indicate the plot was located 

in a relatively complex stand. We compared 

results between the silviculture experiments and 

CVS plots to ensure our results would hold for 

both types of conditions. 

A set of predictor variables was calculated 

from the database to explain small-tree growth 

and survival (table 2). Th ere are three types of 

predictor variables: 

1. Tree attributes such as dbh and crown ratio 

(CR); 

2. Variables describing stand structure and the 

competitive environment, including basal area 

(BA) and crown-competition factor (CCF) 

(Krajicek et al. 1961); and

3. Variables describing site productivity and 

climate, such as site index (SI) and precipitation 

(PPT). Climate variables were derived from 

Rehfeldt’s (2006) climate surfaces (Crookston 

2011). Site index was measured on some of 

the plots and estimated for the remaining 

plots using nearest-neighbor imputation 

(Crookston and Finley 2008).

We chose to focus on Douglas-fi r (Pseudotsuga 

menziesii), Western Hemlock (Tsuga heterophylla), 

and Western Redcedar (Th uja plicata) for 

this paper. Our database contained 32,534 

observations for Douglas-fi r, 22,593 observations 

for Western Hemlock, and 12,143 observations 

for Western Redcedar. We used the following 

methods to address each question:

Which set of factors best explains the 

growth of understory trees?

We looked at how well diff erent combinations of 

predictor variables could predict 5-year basal-area 

growth of individual trees. We used a best-subset 

regression method to pick the best predictors for 

linear regression models that had between 1 and 

10 coeffi cients (Lumley 2009). We repeated the 

subset selection process 100 times using data that 

were randomly selected from 25 percent of the 

plots each time. Th is iterative selection process 

helped to identify robust predictor variables that 

should work well in all of the diff erent conditions 

found in the modeling data set. Th e predictor 

variables were ranked based on the numbers of 

times they appeared in a best regression model.

How is the growth of understory trees 

affected by stand structure?

Th e predictor variables that describe stand 

structure and the competitive environment are 

closely related, so we chose to look at only one 

of them, basal area of trees larger than the subject 

tree (BAL). Th is variable is a measure of the 

competitive position of individual trees, but it is 

also related to stand structure. For example, small 

trees that are growing in an understory position 

in complex stands will have high values of BAL, 

whereas those that are growing in gaps or evenaged stands will typically have low values of BAL. 

We looked at how BAL aff ected both average 

growth and potential growth by fi tting cubic 

splines (Hastie and Tibshirani 1990). Spline 

fi tting is a fl exible modeling technique that is 

not constrained to produce a straight line or a 

particular curve shape; therefore, it allows for a 

detailed evaluation of the relationship between 

variables. Potential growth was evaluated by 

fi tting a quantile spline (He and Ng 1999) to 

the 97th percentile of growth observed for each 

species. 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Modeling Development of Understory Trees Gould and Harrington 63

Some of the silvicultural experiments included 

thinning with gaps, which creates a diff erent 

stand structure than uniform thinning. Where 

we had such information, we evaluated how gap 

creation aff ects growth by comparing growth of 

small trees in unthinned areas (skips), uniform 

(matrix) thinned areas, and gaps. 

How is the survival of understory trees 

affected by stand structure?

Survival was evaluated across the range of BAL 

by examining survival rates graphically and fi tting 

a logistic-regression equation (Schabenberger and 

Pierce 2002) for each species to compare average 

survival among species. 

Results and Discussion

Which set of factors best explains the 

growth of understory trees? 

Tree DBH at the beginning of the growth 

period was the most frequently selected variable 

to predict 5-year basal-area growth for each 

species (table 3). Crown ratio ranked second 

for Douglas-fi r and Western Hemlock, and 

third for Western Redcedar. Measures of stand 

Variable type Variable Description

Tree attributes CR Crown ratio (proportion)

DBH Diameter at breast height (cm)

HT Total tree height (m)

Stand structure / 

competitive environment

BA Basal area (m2·ha-1)

BAI , BAM , BAT BA of shade-intolerant, moderately tolerant, or tolerant species

BAL Basal area of trees larger than the subject tree (m2·ha-1)

BAL/DBH BAL divided by DBH

BALI , BALM , 

BALT

BAL of shade-intolerant, moderately tolerant, or tolerant species

CCF Crown-competition factor: f(crown width, tree density) (%)

CCF100 , CCF200 Height above ground where CCF = 100% or 200% (m)

CCFD CCF x crown depth

CCFR CCF x CR

CVDBH ,CVHT Coeffi cient of variation of DBH or HT

DBHSUM Sum of tree DBH (cm)

HT100 Average height of 100 largest trees per hectare (m)

HTSUM Sum of tree HT (m)

RELHT HT/HT100

Productivity, climate DD100 Date when sum of DD5 = 100 (measure of spring warmth) (days)

DD0, DD5 Degree-days <0°C, >5°C (°C·days)

JUNEDRY June temperature / June precipitation (°C∙mm-1)

PP, PPTGS Total precipitation, growing-season precipitation (mm)

PSUMR Ratio of summer-to-spring precipitation (proportion)

SDAY, FDAY, FFP Date of last spring frost, fi rst fall frost, and frost-free period (days)

SI Site index (m)

TAVE, TMIN, TMAX Average, minimum, and maximum temperature (°C)

TCOLD, TWARM Average temperature in the coldest and warmest month (°C)

Table 2—Abbreviations and descriptions for variables that were evaluated to predict the growth of understory trees.
Density Management in the 21st Century: West Side Story PNW-GTR-880

64 Modeling Development of Understory Trees Gould and Harrington

density or the competitive environment such 

as BAL/DBH and CCFD (CCF x crown depth) 

were the next most frequently selected predictor 

variables. Some of the predictor variables related 

to overstory height ranked highly for Douglasfi r and Western Redcedar. Th e climate variables 

were generally not as highly ranked as those 

that describe tree attributes, stand structure, 

and density; however, at least two climate 

variables were found to be good predictors of 

growth in some cases. Climate variables related 

to temperature (TMIN , minimum temperature, 

and DD100, a measure of spring warmth) were 

among the top 10 predictors for each species. 

Growth was predicted to increase with increasing 

temperature, refl ecting the lower productivity 

of cold, high-elevation sites. Site index ranked 

among the top 10 predictor variables for Western 

Hemlock and Western Redcedar but not for 

Douglas-fi r.

Tree attributes are generally good predictors 

of future growth (Hann et al. 2006). Th e 

size and crown ratio of an understory tree is a 

good indicator of its growth capacity following 

thinning (Shatford et al. 2009). Maintaining 

a high crown ratio may be more important to 

Douglas-fi r than to more shade-tolerant conifers. 

Th e presence of vigorous understory trees can 

indicate that things are going right when trying 

to create a complex stand, but it is not a factor 

that can be readily changed by forest managers. 

Th e competitive environment of understory trees 

as measured by BAL or CCF has an important 

impact on growth and can be changed through 

silvicultural treatments that reduce overstory 

densities. We suspected that BAT (basal area 

of shade-tolerant species) would be a better 

predictor of growth than BA alone, as shadetolerant species typically allow less light to reach 

the understory than intolerant species (Canham 

et al. 1994); however, it was not a frequently 

selected predictor. Measures of the competitive 

environment that account for dominant tree 

height (e.g., RELHT, height divided by the 

average height in meters) and diff erences in 

crown width among species (e.g., CCFD) were 

important predictors in some cases, suggesting 

that understory growth is aff ected to some degree 

by stand composition and vertical structure. 

Changes to the understory light environment 

are an obvious result of reducing overstory 

density, but competition between overstory and 

understory trees for soil moisture and nutrients 

is also important (Devine and Harrington 2008; 

Harrington 2006). Plants growing below the 

main canopy are in a more complex competitive 

environment than those in the main canopy, 

thus, tree responses may be more variable and 

models to predict response may require greater 

complexity (Harrington et al. 2002).

Table 3—Ranking of variables 

for predicting individual-tree 

basal-area growth of small 

Douglas-fir, Western Hemlock, 

and Western Redcedar. Ranks 

are based on how frequently 

the predictors were selected 

using best subset regression on 

100 randomly selected subsets 

of the modeling data. Variables 

definitions are in table 2.

Rank

Frequency of selected predictors by species

Douglas-fi r Western Hemlock Western Redcedar

1 DBH 100 DBH 96 DBH 100

2 CR 91 CR 85 BAL/DBH 79

3 CCFD 71 BAL/DBH 77 CR 69

4 HT100 53 CV 59 HT100 52

5 RELHT 52 FDAY 47 CCF100 34

6 CCF100 49 SI 44 DD100 24

7 PSUMR 45 TCOLD 24 SI 20

8 DSUM 38 DD5 23 JUNEDRY 17

9 TMIN 18 TWARM 20 CCF200 15

10 BAL/DBH 13 HTSUM 18 BA 15
Density Management in the 21st Century: West Side Story PNW-GTR-880

Modeling Development of Understory Trees Gould and Harrington 65

How is the growth of understory trees 

affected by stand structure?

Potential and average growth rates were 

negatively aff ected by increasing competition 

(as measured by BAL) but the species responded 

diff erently to competition (fi g. 2). When BAL 

was low, potential and average growth rates of 

Douglas-fi r and Western Hemlock were about 

equal and both species had higher growth rates 

than Western Redcedar. Th e average growth of 

Western Redcedar was much lower than that of 

the other species at low BAL. Th e potential and 

average growth rates of Douglas-fi r decreased 

more than those of the other species with 

increasing BAL. When BAL was greater than 

about 20 m2

·ha-1, the species’ ranks for potential 

and average growth were Western Hemlock 

> Western Redcedar > Douglas-fi r. When we 

looked at data from the silviculture experiments 

only, we found that the species’ ranks were the 

same, but the potential and average growth rates 

were generally lower.

We predicted the growth of small Douglas-fi r 

using the current (2011) version of FVS (before 

our revisions) and compared it with the average 

growth in our data set (inset in bottom left panel 

of fi g. 2). Observed growth was greater than 

predicted growth (in the 2011 version of FVS) 

throughout the range of our data. Predicted 

growth at moderate to high BAL dropped to 

less than 1.0 cm2

·5 y-1 while observed growth 

remained around 4.5 cm2·5 y-1. Although values 

for both observed and predicted growth were 

low, the diff erence has a big impact on growth 

projections. For example, it could take more than 

3 times longer for an understory tree to move into 

a midstory position in an FVS projection than 

it should based on our data. Predicted growth 

Figure 2—Potential 

basal-area growth 

(top row) and average 

basal-area growth 

(bottom row) of 

small trees across 

a range of basal 

area in larger trees 

(BAL). The potential 

growth curves show 

the 97th percentile 

of growth. Curves 

were fit to the entire 

modeling data set 

(left column) and to 

data from silvicultural 

experiments only 

(right column). The 

inset in the bottom 

left panel shows 

how the current 

version of FVS 

predicts the average 

growth of small 

Douglas-fir (observed 

growth is shown for 

comparison).
Density Management in the 21st Century: West Side Story PNW-GTR-880

66 Modeling Development of Understory Trees Gould and Harrington

will more closely match observed growth in the 

revised version of FVS.

Our results agree with previous studies that 

have ranked Western Hemlock as the fastest 

growing species across a range of overstory 

densities (Chan et al. 2006; Cole and Newton 

2009; Shatford et al. 2009), including complete 

overstory removal (Harrington 2006). Western 

Redcedar also showed greater potential growth 

compared to Douglas-fi r at moderate to high 

overstory densities; however, its average growth 

was generally lower. Some of our data sets recorded 

high browse damage on Western Redcedar that 

hampered its growth (Cole and Newton 2009; 

Harrington 2006). Th e diff erences between 

average growth rates and potential growth rates 

highlight the variability in growth rates that can 

be found among trees in the same competitive 

position. Th e fi nal FVS models will reproduce 

some of this variability by fi rst predicting the 

average growth under a set of conditions and 

then adding a random component so that some 

trees are predicted to grow near their maximum 

rates. 

Trees in gaps generally grew more rapidly 

than those in thinned and unthinned areas. Two 

installations of the OHDS experiment had large 

numbers of understory Western Hemlock within 

skips, matrix thinned areas, and 400-m2

 gaps 

(fi g. 3). At the Rail installation, understory trees 

in gaps grew about 50 percent more than those 

in thinned areas and about 70 percent more than 

those in unthinned skips. Understory trees in 

both thinned areas and gaps at the Snow White 

installation grew about 40 percent more than 

those in skips. 

Planted understory trees in the WOTUS 

experiment grew much more rapidly in gaps (600 

m2

 or 1000 m2 in size) than in uniformly thinned 

areas (fi g. 4). Western Hemlock had the greatest 

growth of the three species in both thinned areas 

and gaps. Th e growth of Western Redcedar was 

damaged by browsing both in gaps and thinned 

areas. 

Treatments to develop complex stands may 

be successful if they allow some trees to grow 

rapidly into midstory canopy positions, even if 

the average growth of understory trees is low. 

From this perspective, we looked at the range 

of growth rates within the OHDS experiment 

(fi g. 5). Many of the trees in thinned areas and 

small gaps continued to grow at similar rates as 

in unthinned skips; however, the range of growth 

rates increased substantially. Th e range of growth 

rates in gaps was about twice that of unthinned 

skips. 

How is the survival of understory trees 

affected by stand structure?

Th e survival of all three species was reduced 

in stands with high overstory densities, but the 

survival of Douglas-fi r decreased much more 

than survival of the other species with increasing 

BAL (fi g. 6). Th e mortality rate of Douglas-fi r 

doubles between about 5 and 40 m2

·ha-1 of BAL. 

Western Redcedar had the greatest survival across 

the range of BAL. Survival was generally higher 

Figure 3—Diameter growth of understory Western 

Hemlock in skips (unthinned areas), matrix thinned 

areas, and gaps at the Rail and Snow White installations 

of the Olympic Habitat Development study.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Modeling Development of Understory Trees Gould and Harrington 67

in the silvicultural experiments (not shown) than 

in the CVS plots, possibly owing to the eff ects of 

other treatments (e.g., vegetation control in some 

cases) and the initially high vigor of the planted 

growing stock. We also compared predicted 

survival in the 2011 version of FVS with observed 

survival of Douglas-fi r (inset in fi g. 6). Observed 

survival was lower across the range of BAL and 

it decreased more sharply with increasing BAL 

than predicted in the 2011 model. FVS will be 

revised so that predicted survival better matches 

the survival rates observed in our data set.

Th e low survival of understory Douglasfi r in particular may require forest managers 

to maintain relatively low overstory densities 

or create large gaps if they want it to survive 

as an understory tree. In contrast, Western 

Hemlock and Western Redcedar may become 

established and survive across a much greater 

range of densities. For example, we have found 

that Western Redcedar can survive under dense 

overstory conditions for decades with very little 

growth (e.g., Harrington and Devine 2011). We 

did not account for mortality that can occur 

after planting in the understory owing to low 

seedling vigor or unfavorable environmental 

conditions (e.g., low soil moisture) (Cole and 

Newton 2009). Survival may be poorer than our 

Figure 4—Basal diameter growth of understory Western 

Redcedar, Douglas-fir, and Western Hemlock in matrix 

thinned areas and gaps in the Western Oregon Thinning 

and Underplanting study.

Figure 5—Range of 

diameter growth rates in 

skips (unthinned areas), 

matrix thinned areas, 

and gaps in the Olympic 

Habitat Development study. 

Thinning and gap creation 

greatly increased the range 

of growth rates among the 

fastest-growing 25 percent 

of trees, which should 

allow some trees to reach 

midcanopy positions rapidly.
Density Management in the 21st Century: West Side Story PNW-GTR-880

68 Modeling Development of Understory Trees Gould and Harrington

data indicates during the fi rst year or two after 

planting in some cases.

Management Implications

To create complex stands, forest managers 

need to create conditions that allow understory 

trees to establish, survive, and grow. Density 

management is an important tool for improving 

growing conditions for understory trees. Without 

thinning or other disturbances, most of the 

relatively young stands in the Pacifi c Northwest 

will maintain densities that will severely reduce 

the growth of understory trees (e.g., >40 m2

·ha-1

of basal area). Uniform thinning can improve 

the growth and survival of understory trees, but 

thinning with gaps will create a wider range in 

understory tree growth rates, allowing some 

understory trees to grow more rapidly into the 

midstory. Treatments that create a range of 

overstory densities (i.e., thinning with skips 

and gaps) may be the best approach for creating 

conditions where some understory trees can thrive 

while meeting other management objectives.

Future Use of West-side FVS 

Variants

Our results will be incorporated initially 

into the PN and WC variants of FVS in 2012. 

Growth of understory trees will be predicted on 

a point basis, which will allow users to simulate 

variable thinning densities and gaps. FVS has 

a set of keywords (POINTREF, SETPTHIN, 

THINPT) that can be used to thin points to 

diff erent densities or to simulate gaps. Because 

the variants of FVS used in the Pacifi c Northwest 

do not have full regeneration models, users will 

still need to add regeneration to the model runs 

to refl ect understory planting or expected natural 

regeneration. 

FVS can predict the average growth of 

understory trees under a given set of conditions, 

but it does not account for all factors that may 

be important in a particular case. Not every 

factor that is known to aff ect growth can be 

incorporated when developing the kind of databased, empirical models that are used in FVS. 

Th is does not mean that these factors are not 

important. For example, competition with shrubs 

Figure 6—Survival of Douglas-fir, 

Western Hemlock, and Western Redcedar 

across a range of basal area in larger trees 

(BAL). Each point represents the survival 

rate of 400 trees; curves show fits of 

logistic regression equations. The inset 

shows how the current version of FVS 

predicts survival of small Douglas-fir.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Modeling Development of Understory Trees Gould and Harrington 69

and herbaceous vegetation may strongly aff ect 

growth of understory trees, but competition 

with vegetation other than trees is not modeled 

by FVS. Forest managers will always need to 

use their judgment and experience to determine 

whether conditions are favorable for the growth 

of understory trees. Stands should also be revisited 

periodically to determine if treatments have been 

successful and whether FVS projections were 

accurate. We invite users to provide feedback to 

us on how well they think the models perform.

Acknowledgments

We thank Paul Anderson, Elizabeth Cole, Mike 

Newton, and Leslie Brodie for generously sharing data 

from their silvicultural experiments, Robert Brown for 

making the CVS database available, David Th ornton 

for his help in assembling the research database and 

Erin Smith-Mateja for her help in integrating our 

results into FVS. We also thank the Oregon State 

Offi ce of the Bureau of Land Management and the 

Olympic National Forest for fi nancial support. 

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Citation:

Gould, Peter J.; Harrington, Constance A. 2013. Making the little things count: modeling the development of understory 

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Density Management in the 21st Century: West Side Story PNW-GTR-880

71

Thinning Effects on Tree Mortality and Snag 

Recruitment in Western Oregon

Erich K. Dodson, Klaus J. Puettmann, and Adrian Ares

Erich K. Dodson is a faculty research assistant and Klaus J. Puettmann is Edmund Hayes Professor in Silvicultural 

Alternatives, Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR, 97331; Erich.Dodson@

oregonstate.edu; Adrian Ares is Project Director, SANREM CRSP (Sustainable Agricultural and Natural Resource 

Management Collaborative Research Support Program) Offi ce of International Research, Education and Development 

(OIRED) Virginia Tech, 526 Prices Fork Road Blacksburg, VA 24061.

Abstract

Tree mortality shapes forest structural development and the resulting dead wood provides habitat 

for many species. However, the eff ects of thinning on mortality and large snag recruitment have 

been variable and remain poorly understood. We examined thinning eff ects on tree mortality at 

eleven Density Management Study (DMS) sites in western Oregon. Th inning reduced mortality 

rates for small trees, especially Douglas-fi r (Pseudotsuga menziesii), but had little infl uence on 

mortality of large trees (≥50 cm dbh). Gaps created by harvest did not result in increased mortality 

during the sampling period (6 to 11 years following gap creation). Few large snags (≥50 cm dbh) 

were produced regardless of treatment. Th inning likely reduced ongoing suppression mortality of 

small trees, but in the short-term did little to provide the large snags that are characteristic of latesuccessional forests. Large snags may be created in subsequent planned thinning entries, but low 

mortality after the fi rst thinning implementation suggests that active creation of large snags may 

be necessary to accelerate their development. 

Keywords: Coarse woody debris, Douglas-fi r, multi-cohort management, variable-density 

thinning, wildlife habitat.

Introduction

Tree mortality is an important ecosystem process 

(Franklin et al. 1987). It shapes community 

composition and forest structure, with direct 

implications for snags and down wood, which 

provide habitat for many species (Hayes and Cross 

1987; Berg et al. 1994). Intensive management 

has resulted in young, homogeneous stands in the 

Pacifi c Northwest, with higher tree densities than 

found in many old-growth stands (Tappeiner et 

al. 1997). Consequently, these young stands lack 

many habitat features of late-successional forests, 

including large snags and large-diameter down 

wood (Spies et al. 1988; Hayes et al. 1997). 

Th inning has been widely proposed as a means 

to accelerate the development of late-successional 

structure (Muir et al. 2002; Bauhus et al. 2009), 

but its eff ects on mortality and snag recruitment 

are still not well understood. For example, 

thinning has been found to reduce (Williamson 

1982; Marquis and Ernst 1991; Davis et al. 

2007) or increase (Walter and McGuire 2004; 

Maguire et al. 2006) mortality rates. Th inning 

from below can remove small, stressed trees that 

are at high risk for mortality and leave a residual 

stand of large, vigorous trees with low mortality 

rates (Powers et al. 2010). Th inning also increases 

the resources available to smaller, residual trees, 

thus reducing suppression mortality (Williamson 

1982; Marquis and Ernst 1991). In contrast, 

thinning can increase physical damage to residual 
Density Management in the 21st Century: West Side Story PNW-GTR-880

72 Th inning, Tree Mortality, and Snag Recruitment Dodson et al.

trees due to wind, snow, and ice (Harrington 

and Reukema 1983; Franklin et al. 1997), with 

especially strong eff ects for trees along harvest 

edges (Chen et al. 1992; Zeng et al. 2004). We 

examined data from 11 Density Management 

Study (DMS) sites in western Oregon with a 

variety of site histories and conditions (Cissel 

et al. 2006) to better understand the eff ects of 

alternative thinning treatments on tree mortality.

Large snags (≥50 cm dbh [diameter at breast 

height]) are common in late-successional forests 

of the Pacifi c Northwest (Spies et al. 1988; North 

et al. 2004; Ares et al. 2012; Lutz et al. 2012), 

provide habitat for numerous species (Schreiber 

and de Calesta 1992; Barbour et al. 1997; Marcot 

et al. 2002), and may be critical for some species 

(Mannan et al 1980). Young stands may have an 

abundance of small snags (Carey and Johnson 

1995; Van Pelt and Nadkarni 2004). However, 

without management intervention, more than 

250 years may be required for large snag formation 

in natural stands (Van Pelt and Nadkarni 2004; 

Gerzon et al. 2011). A better understanding of 

large snag recruitment in thinned and unthinned 

forests is needed to guide management actions 

that seek to accelerate the development of latesuccessional forest characteristics. 

We examined rates of mortality with and 

without thinning, with an emphasis on 

understanding eff ects of thinning on developing 

late-successional stand structure, using two 

components of the DMS study: initial thin (seven 

sites) and rethin (four sites). We use a combination 

of previously reported mortality results (Dodson 

et al. 2012) and new data analyses to address the 

eff ects of thinning on mortality. Specifi c research 

questions included: 

1. Does thinning aff ect mortality rates of residual 

overstory trees?

2. Are large snags being created, and is this 

process aff ected by thinning? 

3. Does gap creation during harvest alter 

mortality rates of nearby trees?

Methods

Study Sites

Th e DMS initial and rethin studies (Cissel 

et al. 2006) were each established on land 

managed by the Bureau of Land Management 

in western Oregon. Sites were selected to be 

relatively homogeneous and were generally 

dominated by Douglas-fi r (Pseudotsuga menziesii

(Mirb.) Franco). Common conifer species 

included Douglas-fi r, Western Hemlock (Tsuga 

heterophylla (Raf.)) and Western Redcedar (Th uja 

plicata Donn ex D. Don). Common hardwoods 

included Big-leaf Maple (Acer macrophyllum 

Pursh), Red Alder (Alnus rubra Bong), California 

Hazel (Corylus cornuta Marsh), Pacifi c Madrone 

(Arbutus menziesii Pursh, Frangula purshiana 

(DC.) Cooper) and Golden Chinkapin 

(Chrysolepis chrysophylla (Douglas ex Hook.) 

Hjelmqvist). Th e initial thin sites were at least 80 

ha in size and ranged from about 40 to 60 years 

old at the time of thinning. Rethin sites were are 

least 16 ha in size, ranged from 50 to 80 years 

old and had been thinned 25 to 30 years prior 

to study initiation to a density of ≥250 trees per 

hectare (tph). Detailed site characteristics are 

provided in Cissel et al. (2006) and details of tree 

species composition are given in tables 1 and 2. 

Treatments

Initial thin treatments were implemented in a 

randomized-block design with one replication 

of four thinning treatments (including controls) 

applied at each of seven sites for a total of 28 

treatment units. Individual treatment units 

ranged from 14–58 ha. Control stands were 

unthinned and had an average density of 565 tph. 

Th e high-density (HD) treatment was thinned to 

a residual stand density of 300 tph with 3 to 13 

percent of the total stand retained in non-thinned 

circular reserves. In the moderate-density (MD) 

treatment, stand density was reduced to 200 tph. 

Additionally, 4 to 18 percent of the stand was 

cut in circular gap openings and 4 to 13 percent 

of the stand was left in unthinned circular leave 

islands. Th e variable-density (VD) treatment 

was designed to create the maximum spatial 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Th inning, Tree Mortality, and Snag Recruitment Dodson et al. 73

variability and complexity within the stand. Th is 

treatment included both the high (300 tph) and 

moderate-density retention (200 tph) treatments 

each applied over 25 to 30 percent of the stand 

and an additional 8 to 16 percent of the stands 

were thinned to a residual density of 100 tph. 

Finally, 4 to 18 percent of the stand was assigned 

to leave islands and gap openings, respectively. 

Gaps and leave islands in all treatments were a 

mixture of 0.1-, 0.2- and 0.4-ha circular areas. 

Th inning was completed between 1997 and 

2000. All thinning was “from below” focusing 

on taking out the smaller trees. Less-abundant 

species (typically all species other than Douglasfi r), especially hardwoods, were preferentially 

reserved. Details of treatment implementation 

at individual sites are presented in Cissel et al. 

(2006). 

Th e rethin study included stands that had 

previously been thinned in a clumpy distribution 

25–30 years before study initiation. It included 

just two treatments, a control (270 to 580 tph) 

that was not thinned again, and a second thinning 

to a residual tree density between 80 and 150 tph 

(Cissel et al. 2006; Berger et al. 2012). No gaps 

or leave islands were included in the rethin study. 

Sampling

In the initial thin study, 77 permanent 0.1-

ha circular plots were established at each of 

the seven sites to measure overstory trees. Plot 

locations were randomly selected across the entire 

treatment unit including gaps and leave islands, 

with 21 plots in each of the thinned treatment 

units and 14 plots in each control treatment unit 

at each site. All trees ≥5 cm dbh were tagged, 

identifi ed to species, measured for dbh, and 

recorded as live or dead. Clumped hardwood 

trees were measured as separate trees provided 

their dbh was ≥5 cm. Data were collected in 

the summer 6 years after thinning (2003–2005) 

and 11 years after thinning (2008–2010), with 

sample years varying among sites.

Plots in the rethinning study were nonrandomly established in areas where residual tree 

density was within 20 percent of target density 

and distributed to maximize coverage of the 

treatment unit. Spacing between plots varied 

among sites to establish a total of 20–25 plots 

per site. All overstory trees (>5 cm dbh) were 

Table 1—Total number of trees and number of trees dying over the period 6 to 11 years following thinning 

for each species or species group and treatment in the initial thinning study.

Treatment

Hardwood Douglas-fi r Western Hemlock

Trees 

sampled

Mortality

(5 years)

Trees 

sampled

Mortality

(5 years)

Trees 

sampled

Mortality

(5 years)

Control 266 36 3716 516 1686 142

High density 528 82 3260 195 1022 100

Moderate density 607 92 2463 189 1027 93

Variable density 475 55 2203 114 840 44

Table 2—Total number of sampled trees and the number of sampled trees that died from 1 to 11 years following 

thinning for each species or species group in each treatment for the rethin study.

Treatment

Cedar1 Hardwood Douglas-fi r Western Hemlock

Trees 

sampled

Mortality

(10 years)

Trees 

sampled

Mortality

(10 years)

Trees 

sampled

Mortality

(10 years)

Trees 

sampled

Mortality

(10 years)

Once-thinned 262 26 104 15 1038 104 161 11

Rethinned 168 13 170 25 615 43 191 10

1

Includes Western Redcedar (Thuja plicata) and Incense Cedar (Calocedrus decurrens).
Density Management in the 21st Century: West Side Story PNW-GTR-880

74 Th inning, Tree Mortality, and Snag Recruitment Dodson et al.

tagged, identifi ed to species, measured for dbh, 

and recorded as live or dead. Data were collected 

for each site 1, 6, and 11 years after thinning. 

Statistical analyses

We selected a signifi cance level α = 0.05 prior to 

statistical analysis. All analyses were performed in 

SAS (SAS Institute, Cary, NC, v. 9.3). We report 

results from a previous study (Dodson et al. 2012) 

that examined the average annual mortality rate 

in the initial thinning study for the fi ve-year 

sampling period as the number of trees that 

died between the fi rst and second measurements 

divided by the total number of trees present at 

the fi rst measurement for each treatment unit 

(n = 28 treatment units). For this study, average 

annual mortality rates were compared among 

treatments using a mixed model with thinning 

treatment as a fi xed eff ect and site as a random 

eff ect. Post-hoc tests were conducted between 

each combination of individual treatments with 

a Tukey correction for multiple comparisons 

(Dodson et al. 2012). Residuals were inspected 

to ensure that assumptions of normality, equal 

variance, and independence were not violated. 

Mortality for the rethin study was evaluated 

over a ten-year period, from 1 to 11 years 

following rethinning, with a mixed-model 

logistic regression. Th e analyses focused on 

Douglas-fi r because this species was wellrepresented at all sites, spanned a range of initial 

sizes, and comprised the majority of trees (table 

2). Individual trees that were alive in the fi rst 

sample, one year after thinning, were assigned a 

“yes” or “no” based on whether they were also 

alive 11 years after thinning. Th e probability of 

mortality was modeled as a function of initial 

tree size, with treatment included as a categorical 

fi xed eff ect. Site, treatment unit within site, and 

plot within treatment unit were included in the 

model as random eff ects to account for the nested 

structure of the sampling design. Model fi t was 

evaluated visually by overlaying mortality rates 

for 10-cm dbh classes with predicted values. Th e 

Kenward-Roger method was used to calculate 

the denominator degrees of freedom due to the 

unbalanced sampling design.

We compared mortality rates among plots of 

diff erent treatment “strata” (gaps, leave islands, 

and thinned areas) to examine whether smallscale treatment eff ects had an impact on mortality 

rates. Only the initial thinning treatment 

included gap creation, and only the MD and VD 

included all three strata; therefore, the analyses 

used only plots from these treatments. A total of 

286 plots were included in this analysis, of which 

71 plots included at least a portion of a gap and 32 

plots included at least a portion of a leave island. 

Plots that included any portion of a gap or leave 

island were included in these strata, respectively. 

Gap plots included some residual trees (plots 

were not entirely in the gap) which were used to 

calculate rates of mortality. Th e remaining plots 

were considered as the “thinned” stratum for the 

analysis. Th e average annual mortality over fi ve 

years (from 6 to 11 years following treatment) was 

calculated for each plot as described above for the 

initial thin study. A mixed model with stratum as 

a fi xed factor and site as a random factor was used 

to analyze the eff ects of strata on mortality rates. 

A random eff ect was also included for treatment 

unit to account for nesting of plots within 

treatments units at a site. Post-hoc tests were 

conducted between the three strata with a Tukey 

correction for multiple comparisons. Residuals 

were inspected to ensure that assumptions of 

normality, equal variance and independence 

were not violated. Th e Kenward-Roger method 

was used to calculate the denominator degrees of 

freedom due to the unbalanced sampling design.

Results and Discussion

Douglas-fi r was the dominant tree species in 

most stands (tables 1 and 2) and the vast majority 

of the large trees were Douglas-fi r (Dodson et al. 

2012). Douglas-fi r also comprised the majority 

of the mortality in both the initial and rethin 

studies (tables 1 and 2). Douglas-fi r is less shadetolerant than the other conifer species on these 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Th inning, Tree Mortality, and Snag Recruitment Dodson et al. 75

sites (Minore 1979; Shatford et al. 2009). Th is 

lower shade-tolerance many have contributed to 

higher rates of mortality for small Douglas-fi r 

relative to other species (Dodson et al. 2012). 

Th inning signifi cantly aff ected mortality in 

both the initial thinning (Dodson et al. 2012) 

and rethin studies (table 3). In the initial thinning 

study, the VD treatment had signifi cantly lower 

mortality than the control (fi g. 1; Dodson et 

al. 2012). Th e HD and MD were intermediate 

and not signifi cantly diff erent from any other 

treatment (fi g. 1; Dodson et al. 2012). In the 

rethin study, thinning eff ects varied signifi cantly 

with initial tree size (table 3). Th inning reduced 

the probability of mortality for small Douglasfi r, but had little eff ect on mortality of larger 

trees (≥50 cm dbh; fi g. 2). A similar eff ect was 

observed in the initial thinning study (Dodson 

et al. 2012). Th e decreased average annual 

mortality rate after thinning from below in these 

two component studies (Dodson et al. 2012; 

fi g. 2) is similar to patterns observed in other 

Douglas-fi r forests (Davis et al. 2007) and other 

forest types (Marguis and Ernst 1991; Powers 

et al. 2010). However, thinning from above can 

result in the opposite pattern (Marguis and Ernst 

1991; Powers et al. 2010), which may contribute 

to some of the variability reported by previous 

studies.

Small trees had higher mortality rates than 

large trees in both the initial and rethin 

studies. Th is pattern is consistent with ongoing 

suppression mortality, which is common in 

young forests (Carey and Johnson 1995; Van Pelt 

and Nadkarni 2004). More than 80 percent of 

the trees that died across all sites and treatments 

in the initial thinning study were relatively small 

(≤35 cm dbh). In contrast, large trees (≥50 cm 

Table 3—Type III tests of fixed 

effects for the mixed model logistic 

regression for individual tree 

mortality in the re-thin study.

Eff ect

Numerator 

DF

Denominator 

DF F-value P

Treatment 1 6 9.9 0.018

dbh 1 1649 94.7 <0.001

dbh · treatment 1 103 15.3 <0.001

Figure 1—Annual mortality rates of all species 

combined in the initial thin study for each treatment 

for the period from 6 to 11 years following thinning. 

Different letters represent statistically significant 

differences in Tukey-HSD pair-wise comparisons. Con = 

Control, HD = High-density, MD = Moderate-density, 

VD = Variable-density.

Figure 2—Probability of mortality as a function of 

initial tree size for a 10-year period after thinning in the 

once-thinned and twice-thinned units of the rethin study 

for Douglas-fir. Lines are predicted values from mixedmodel logistic regression. Scatterplot points are mortality 

rates calculated from the data with trees divided into 10-

cm size classes. Open circles are rethinned values, closed 

circles are once-thinned values.
Density Management in the 21st Century: West Side Story PNW-GTR-880

76 Th inning, Tree Mortality, and Snag Recruitment Dodson et al.

dbh) had much lower mortality rates in both 

the initial thin study (Dodson et al. 2012) and 

rethin studies (fi g. 2). For example, just one 

large snag per 10 ha was formed on average each 

year across all treatments in the initial thinning 

study, despite an average of about 75 large live 

trees per ha. Th ese low rates of large-tree death 

suggest that few large snags form under current 

conditions, regardless of thinning treatments. 

Th is suggests that current management practices 

are not suffi cient for the accelerated development 

of large snags in young forests in the short term; 

and indeed active creation of large snags may be 

implemented as part of the DMS study plan if 

this pattern continues over subsequent thinning 

entries (Cissel et al. 2006). 

Average annual mortality rates varied 

signifi cantly among strata (F = 3.0, P = 0.05). 

However, gap formation appeared to have little 

eff ect on mortality during our study period (6 

to 11 years following gap creation). Average 

annual mortality rates on plots with gaps, which 

included both portions of gaps and neighboring 

forest interior, was 1.4 percent. Th is was 

intermediate between thinned plots (1.2 percent 

annual mortality) and leave island plots (1.9 

percent annual mortality) and not signifi cantly 

diff erent than either (fi g. 3). However, mortality 

rates were signifi cantly lower on thinned 

plots than plots in leave islands (P = 0.046), 

consistent with the overall eff ect of thinning 

reducing mortality. Additionally, trees located 

directly on gap edges (Dodson et al. 2012) had 

an annual mortality rate of just under 2 percent 

from 6–11 years following thinning, or nearly 

equivalent to the rate observed in the control 

and leave islands. However, previous studies 

have reported increased mortality along clearcut edges (Chen et al. 1992; Zeng et al. 2004) 

suggesting that gap size may be an important 

consideration. Furthermore, mortality due to 

physical agents such as wind is often episodic 

(Lutz and Halpern 2006) or may occur soon 

after thinning operations are completed (Chan 

et al. 2006), which may not have been captured 

in this study. Th inning eff ects on mortality likely 

also depend on the timing of thinning relative to 

stochastic events such as wind and ice storms. For 

example, if a severe storm immediately follows 

thinning, thinning may increase mortality, but 

if no such storm happens thinning may decrease 

mortality. Th e lack of an obvious increase in 

mortality with gap formation across the seven 

sites in this study, which have a variety of site 

histories and site conditions and were thinned in 

diff erent years (Cissel et al. 2006) suggests that 

thinning treatments including gap creation can 

often be done without large increases in mortality 

(Roberts et al. 2007).

Acknowledgements

We thank the U.S. Department of the Interior, 

Bureau of Land Management (BLM) for continued 

funding for the Density Management Study, BLM 

research liaisons, site coordinators and district offi ce 

personnel, and Oregon State University. We are 

grateful to numerous people who were involved in 

experimental design, setup, and data collection. Th is 

manuscript benefi ted from reviews by Hugh Snook, 

Paul Anderson, Ariel Muldoon, Kathryn Ronnenberg, 

and an anonymous reviewer.

Figure 3—Annual mortality rates for all species 

combined from 6 to 11 years following thinning in the 

three different plot types in the MD and VD treatments. 

Different letters represent significant differences in 

Tukey HSD pair-wise comparisons. “Gap” plots included 

both portions of gaps and neighboring forest.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Th inning, Tree Mortality, and Snag Recruitment Dodson et al. 77

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Citation:

Dodson, Erich K.; Puettmann, Klaus J.; Ares, Adrian. 2013. Th inning eff ects on tree mortality and snag recruitment in 

western Oregon. In: Anderson, Paul D.; Ronnenberg, Kathryn L., eds. Density management for the 21st century: west side 

story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacifi c Northwest 

Research Station: 71–78.
Density Management in the 21st Century: West Side Story PNW-GTR-880

79

Thinning Effects on Spotted Owl Prey and Other 

Forest-Dwelling Small Mammals

Todd M. Wilson and Eric D. Forsman

Todd M. Wilson is a wildlife biologist and Eric D. Forsman is a research wildlife biologist, USDA Forest Service, 

Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; 

twilson@fs.fed.us

Abstract

Th inning has been promoted as a method for accelerating the development of late-seral habitat 

and improving the overall health and function of young forests in the Pacifi c Northwest. Population 

studies have shown early and positive responses to thinning by some small forest-fl oor mammals 

(primarily mice, terrestrial voles, and shrews). However, thinning reduces the abundance of some 

tree-dwelling rodents, especially Northern Flying Squirrels (Glaucomys sabrinus) and Red Tree 

Voles (Arborimus longicaudus), that are important prey species for Northern Spotted Owls (Strix 

occidentalis caurina). Recent studies suggest that reductions in Northern Flying Squirrel abundance 

following thinning may be driven by increased susceptibility to predation created by removal of 

critical above-ground cover. Predation, lack of canopy connectivity, and reduction in suitable nest 

substrates may all contribute to reduced Red Tree Vole abundance following thinning. Th e longterm benefi ts of some thinning treatments may be positive for both fl ying squirrels and Red Tree 

Voles, but may not be realized for several decades or more, as the development of a midstory layer 

of trees may be critical to the success of thinning in promoting habitat for these species. Additional 

research into the ecology of the two woodrat species (Neotoma fuscipes and N. cinerea) found 

in the Pacifi c Northwest is needed to provide a more complete understanding of the eff ects of 

forest management activities on spotted owls and their prey. It may be possible to design thinning 

prescriptions that lessen the short-term negative eff ects on arboreal rodents. Long-term goals 

should focus on creating more structurally and biologically complex forests across the landscape 

at scales and patterns compatible with the ecologies of spotted owl prey and other organisms. 

Joint research-management eff orts to test new silvicultural prescriptions, expand current predictive 

models of high-quality prey habitat, and develop management strategies that consider the temporal 

eff ects of management on owl prey at the stand, landscape, and regional levels, could advance our 

understanding of owl prey ecology and help ensure that healthy populations of spotted owls and 

their prey persist on the landscape over the long term. 

Keywords: Th inning, variable-density thinning, Northern Spotted Owl, Northern Flying Squirrel, 

Red Tree Vole, Northwest Forest Plan, old-growth forest.
Density Management in the 21st Century: West Side Story PNW-GTR-880

80 Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman

Introduction

Th e Pacifi c Northwest is rich in forest-dwelling 

small mammals, including mice, voles, shrews, 

tree squirrels, chipmunks, and woodrats. 

Collectively, these species serve as important 

prey for a wide variety of avian, mammalian, and 

reptilian predators. Small mammals also consume 

and disperse fungal spores essential for tree 

growth, help regulate invertebrate populations, 

disseminate vegetation through caching of seeds, 

nuts, and other fruiting bodies, and promote 

soil and carbon dynamics through excavation 

of down wood and soil (Carey and Harrington 

2001). Th us, small mammal populations have 

been used as indices for the overall health and 

sustainability of forests in the region, including 

evaluation of the ecological eff ects of forest 

management activities like timber harvesting 

(Carey and Johnson 1995; Carey and Harrington 

2001; Lehmkuhl et al. 1999; Suzuki and Hayes 

2003). Four species, Northern Flying Squirrels 

(Glaucomys sabrinus), Red Tree Voles (Arborimus 

longicaudus), and Dusky-footed and Bushy-tailed 

Woodrats (Neotoma fuscipes and N. cinerea) 

dominate the diets of the federally threatened 

Northern Spotted Owl (Strix occidentalis caurina) 

(Forsman et al. 1984, 2004a,b; USFWS 1990). 

Spotted owl home-range size has been shown to 

decrease with increasing fl ying squirrel densities 

(Carey and Peeler 1995; Carey et al. 1992; Zabel 

et al. 1995), suggesting that understanding 

habitat needs for owl prey may be critical to the 

recovery of spotted owls and their habitat across 

the region (USFWS 2008). 

One way to partition the small mammal 

community is by the relative degree to which 

each species uses the vertical strata of a forest (fi g. 

1). At one end of the continuum are forest-fl oor 

specialists like shrews and terrestrial voles that 

spend virtually all their time on or beneath the 

forest fl oor. At the other end of this continuum 

are arboreal (tree-dwelling) rodents like fl ying 

squirrels and Red Tree Voles that spend most of 

their time in the forest canopy (Maser et al. 1981, 

Wilson 2010). In addition, there are habitat 

generalists including deer mice (Peromyscus spp.), 

Trowbridge’s Shrews (Sorex trowbridgii), and 

chipmunks (Tamias spp.) that spend considerable 

amounts of time on the forest fl oor but also 

regularly use forest canopies.

Figure 1—Illustration of the relative degree of use of the 

vertical component of a forest for several common rodent 

species in Pacific Northwest forests.

Th inning has become the management tool of 

choice for accelerating the development of lateseral wildlife habitat and improving the overall 

health and function of young forests in the 

Pacifi c Northwest. Th e eff ectiveness of thinning 

to either promote or maintain habitat has been 

demonstrated for a number of forest-fl oor 

specialists and generalists (Carey and Wilson 

2001; Gitzen et al. 2007; Hayward et al. 1999; 

Klenner and Sullivan 2003; Suzuki and Hayes 

2003; Wilson and Carey 2000). Th is is true in 

large part because the understory layer of a forest 

is usually the fi rst and quickest to respond to the 

increase in growing space, light, and nutrients 

created by thinning. Th is understory response 

results in increased structure and plant diversity 

on the forest fl oor, providing food, shelter, and 

protective cover for small mammals. Positive 
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Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman 81

responses have generally been strongest in forests 

that lacked substantial understory prior to 

thinning (e.g., young, even-aged, stem-exclusion 

forests with a primarily moss-dominated forest 

fl oor), but increases in abundance have also been 

noted for several small mammals in forests with 

a well-established understory prior to treatment 

(e.g., Carey and Wilson 2001). In this latter case, 

additional growth and maturation of a tall shrub 

and deciduous tree layer may provide additional 

habitat components important for some species. 

In marked contrast, there is growing evidence 

that thinning can have negative eff ects on 

some arboreal rodent populations (Forsman 

2004; Wilson 2010). For example, several 

studies have shown declines in fl ying squirrel 

abundance following thinning, empirically (but 

not necessarily statistically) higher numbers of 

squirrels in untreated stands compared to stands 

treated with thinning, or generally higher squirrel 

abundances in unthinned stands compared to 

thinned stands (Bull et al. 2004; Carey 2000, 

2001; Gomez et al. 2005; Herbers and Klenner 

2007; Holloway and Malcolm 2006, 2007; 

Holloway et al. 2012; Manning et al. 2012; 

Meyer et al. 2007a; Ransome et al. 2004; Waters 

and Zabel 1995; Waters et al. 2000; Wilson 

2010). Th is includes arboreal rodent responses 

to the Forest Ecosystem Study (FES), a study 

specifi cally designed to test whether variabledensity thinning (see Carey et al. 1999c) could 

accelerate the development of habitat for 

spotted owls and their prey in 50- to 60-yearold Douglas-fi r (Pseudotsuga menziesii) forests of 

western Washington (Carey 2001, 2007; Wilson 

2010). 

Th e goals of this paper are to: (1) briefl y 

highlight what is known about the ecology of 

each of the four major spotted owl prey species as 

it relates to thinning forests; (2) provide rationale 

for why thinning has negative consequences for 

some species in the near term; and (3) discuss 

possible management options and research 

directions that could benefi t owls and their prey 

over the long term. 

Flying Squirrels

Northern Flying Squirrels comprise 50 percent 

or more of the prey in spotted owl diets across 

much of Oregon and Washington (Forsman 

1984; Forsman et al. 1991, 2004a), and most 

of the research into the ecology of owl prey in 

the Pacifi c Northwest has focused on this species. 

In general, two forest conditions can support 

relatively high numbers of fl ying squirrels—

closed-canopy forest (old or young) with high 

stem density, and classic multi-layered old forest, 

with the latter generally providing the highest 

abundances (Wilson 2010). 

Several habitat components have been 

associated with high-quality fl ying squirrel 

habitat, including understory cover, patch-level 

(40–80 m) changes in vegetation composition, 

large snags, large trees, ericaceous shrubs, high 

canopy cover, nearness to conifer forest, nearness 

to water, abundant down wood, large down 

wood, increased litter depth, and availability 

of fungi (Carey 1991, 1995; Carey et al. 1992, 

1999a; Ford et al. 2004; Gomez et al. 2005; 

Holloway and Malcolm 2006, 2007; Hough 

and Dieter 2009; Lehmkuhl et al. 2004, 2006; 

Menzel et al. 2006; Meyer et al. 2007a, b; Payne 

et al. 1989; Pyare and Longland 2002; Rosenberg 

and Anthony 1992; Smith et al. 2004, 2005). 

However, these associations have not always held 

true across studies. For example, some forests 

that support high squirrel abundances have few 

large snags or little down wood (Wilson 2010). 

Likewise, some forests (including old forest) with 

relatively large quantities of snags, large live trees, 

or down wood have been found to support few 

squirrels (Carey 1995; Wilson 2010). 

Part of the issue in associating squirrel 

abundance with habitat components is that most 

studies have only examined a limited number 

of forest conditions (e.g., comparing forest type 

A vs. B) or conducted analyzes based on broad 

categories (e.g., old forest vs. young forest). To 

help address this problem, Wilson (2010) used 

multivariate, structural equation models to 
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82 Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman

examine fl ying squirrel populations and habitat 

across 33 managed and unmanaged stands in 

the Puget Trough and Olympic Mountains 

physiographic provinces. Collectively, these 

stands were chosen to represent broad gradients in 

forest structural conditions found across low- and 

mid-elevation mesic forests west of the Cascade 

Range. Wilson (2010) found that important 

habitat components used in stand-level statistical 

models to predict fl ying squirrel abundance 

could all be associated with above-ground 

protective cover, and hypothesized that predation 

was a primary limiting factor regulating squirrels 

in these forests (Wilson 2010; fi g. 2). Wilson 

suggested that structural occlusion (the degree 

to which physical structures inhibit detection of 

squirrels by predators and help squirrels escape 

direct attacks) was an important component of 

protective cover. When there is a high degree 

of occlusion in the midstory (e.g., high stem 

density, deep crowns, live crowns in the midstory 

layer, with few canopy gaps across the stand), 

it provides suffi cient protection for squirrels to 

attain and sustain relatively high population 

levels (fi g. 3). Even with relatively high predation 

rates (e.g., during spotted owl breeding years), 

enough female squirrels can survive each year 

in these forests to quickly restore populations to 

a relatively high level. In contrast, when there 

are too many gaps, too many large gaps, lack 

of a midstory canopy layer, or overall low stem 

density, squirrels succumb to predation pressure 

and few squirrels survive to reproduce. 

Figure 2—Forest 

structure, particularly 

in the midstory, 

provides the interface 

between predators like 

northern spotted owls 

and one of their major 

prey, northern flying 

squirrels. (Spotted owl 

photo by Stan Sovern; 

flying squirrel photo 

by Wes Colgan III.) 

Figure 3—Black line illustrates a hypothetical glide 

path of a Northern Flying Squirrel and the structural 

occlusion created by different forest conditions that 

provide different levels of detection risk by avian and 

mammalian predators.
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Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman 83

Most thinning prescriptions reduce occlusion 

in a way that appears to leave fl ying squirrels more 

vulnerable to predators than before thinning. 

Th is eff ect may be further compounded once 

the understory begins to develop in response 

to thinning, as abundance of forest-fl oor small 

mammals can quickly increase and, in turn, attract 

predators to the area that may opportunistically 

prey on vulnerable fl ying squirrels (e.g., spillover 

predation; Oksanen et al. 1992). 

Red Tree Voles 

Red Tree Voles are the most arboreal of all the 

rodents in the Pacifi c Northwest (Carey 1999). 

Similar to fl ying squirrels, the highest tree vole 

populations are found in old forests and forests 

with high stem density (Dunk and Hawley 

2009). Tree voles also appear to be susceptible 

to increased predation brought on by reduced 

canopy density after thinning, as few are found in 

recently thinned forests (Forsman et al. 2004b). 

However, tree voles also have three additional 

ecological constraints that may make them 

especially susceptible to thinning. First, small 

trees in young forests generally have insuffi cient 

food resources (conifer needles) in a single tree 

to support breeding females, so individuals often 

forage in multiple trees surrounding their nests 

(Swingle and Forsman 2009). In closed-canopy 

forest, they can simply travel across interlocking 

branches to reach adjacent trees. Th inning 

breaks these connections, and voles must travel 

down (usually on bare, exposed boles) and 

across the ground to reach other trees. Th is not 

only increases their energetic demands, it also 

puts them at additional exposure to predation. 

Second, tree voles build nests composed of small 

twigs and conifer needles on platforms created by 

dwarf mistletoe (Arceuthobium spp.), epicormic 

branching, forked boles, and other irregularities 

in tree-branching patterns. Such nests need more 

support than the nests built of larger twigs and 

branches used by tree squirrels. If trees with 

complex limb structure, forked tops, broken 

boles, and dwarf mistletoe infections are removed 

during thinning, it may greatly restrict the ability 

of tree voles to fi nd suitable nest substrates. Th ird, 

young tree voles have limited dispersal ability, 

and the absence of tree voles across much of 

northwest Oregon suggests that they may not be 

able to disperse across broad areas of intensively 

managed forest (Maser et al. 1981). 

Woodrats 

Th e Dusky-footed Woodrat and Bushy-tailed 

Woodrat are two of the most important species in 

the diet of Northern Spotted Owls, particularly 

in northwestern California, southwestern 

Oregon, and along the eastern slopes of the 

Olympic Mountains and eastern Cascades of 

Washington (Forsman 1975, 1991; Forsman 

et al. 2004a; Ward et al. 1998). Th e Duskyfooted Woodrat is a resident of California and 

southwestern Oregon, whereas the Bushy-tailed 

Woodrat occurs throughout much of the Pacifi c 

Northwest. 

Sakai and Noon (1993) found that Duskyfooted Woodrats were most abundant in 

young (15- to 40-year-old) forests with brushy 

understories, with lower densities in seedling/

shrub and old growth forests, and few or no 

woodrats in forests with merchantable timber 

but little understory. Th ey hypothesized that 

young, brushy forest may provide important 

source areas for woodrats in adjacent old forests 

that are more suitable for spotted owls. Carey 

et al. (1999b) surveyed for woodrats in western 

Oregon and western Washington and suggested 

that the distribution of Dusky-footed Woodrats 

could be explained by a preference for dense 

shrub cover and the ability to consume plants 

toxic to other mammals. In contrast, Carey et 

al. (1999b) found that Bushy-tailed Woodrats 

were irregularly distributed, possibly as a result 

of their aggregated social structure (harems) that 

may allow predators to cue in and prey on family 

groups. In eastern Washington, Lehmkuhl et al. 

(2006b) found that large snags, dwarf mistletoe 
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84 Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman

brooms, and partly decayed logs were good 

predictors of Bushy-tailed Woodrat abundance 

in dry forests. Lehmkuhl et al. (2006b) suggested 

that conventional fuels reduction prescriptions 

that reduced the amount of snags, dwarf mistletoe 

brooms, and logs would have a negative eff ect on 

Bushy-tailed Woodrat populations. However, 

there have been no subsequent studies conducted 

on woodrats in Washington or Oregon to further 

investigate these hypotheses. 

Management Considerations

Th inning designed to create late-seral conditions 

in young forests has shown early success in 

promoting habitat for a number of vertebrate 

species. However, development of a midstory 

layer of trees appears important before species 

like fl ying squirrels and Red Tree Voles respond 

positively to thinning, and this will take time to 

develop. In fact, it may take several decades or 

longer for a midstory to develop to a point where 

it provides adequate protective cover and canopy 

connectivity. Th is is especially true when thinning 

young forests with small-crowned trees, sparse 

natural regeneration, and a large gap between the 

existing understory and the bottom of the tree 

canopy. Th e primary question, therefore, is how 

best to move landscape trajectories toward more 

complex forest while, at the same time, ensuring 

that the short-term negative eff ects on prey 

populations do not result in long-term negative 

eff ects for either spotted owls or their prey. 

It is important to recognize that some arboreal 

rodents like fl ying squirrels have been found in 

fairly high numbers in forests that are relatively 

simple (e.g., high-stem-density young forest) or 

that lack habitat components often associated 

with fl ying squirrels (e.g., few snags, understory, 

or down wood; Wilson 2010). However, the 

ultimate goal when promoting owl prey habitat 

through thinning should be toward developing 

structurally and biologically complex forests that 

include multi-layered canopies including trees 

of varying sizes and species, snags, and down 

wood. Not only are these forests generally better 

habitat for spotted owls and their prey, they are 

the scarcest forest type on the landscape, they 

provide habitat for a wide array of other wildlife, 

and they help meet broader biodiversity goals 

including those outlined in the Northwest Forest 

Plan. 

Th ere are several specifi c management strategies 

that may help ameliorate some of the near-term 

negative eff ects of thinning on owl prey: 

1. Accelerate and monitor mid-story 

development. 

One of the primary objectives of variabledensity thinning is to develop late-seral 

characteristics sooner by moving a forest 

through stages of forest development more 

quickly compared to leaving stands to develop 

as a result of natural stochastic events without 

management intervention (Carey et al. 1999c). 

However, without intentional focus on midstory 

tree growth, site-specifi c conditions can prevent 

or even forestall midstory development. For 

example, if a well-developed understory exists 

prior to thinning, it may outcompete new tree 

seedlings. If there is a limited shade-tolerant tree 

seed source, then midstory development may 

be patchy or sparse. In contrast, if the natural 

shade-tolerant seed source is too abundant, then 

regeneration competition may occur, slowing 

growth of the next layer of trees. Additionally, for 

a midstory to fully develop, new trees must grow 

tall enough to fi ll the structural void between the 

ground and the bottom of the existing overstory 

canopy. Th e larger this distance is, the longer it 

will take for a full midstory to develop. 

Th ere are a number of ways to promote a 

midstory. Underplanting can be considered for 

forests that lack a natural seed source of shadetolerant trees. Patchy brush control could be 

used in conjunction with underplanting for 

thinning forests that have a well-established 

understory layer of aggressive shrub species 

like Salal (Gaultheria shallon). If shade-tolerant 

tree species regenerate aggressively on the forest 
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Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman 85

fl oor, then early thinning of tree saplings can be 

considered. Because both thinning treatment 

and site-specifi c conditions aff ect development 

of a midstory, regular monitoring should occur 

to ensure that this critical forest layer continues 

along an accelerated path. 

2. Include very young (<25-year-old) 

stands in the mix of stands targeted for 

creating late-seral forest. 

High-quality habitat for spotted owl prey might 

be achieved most quickly by treating very young 

(<25-year-old) stands with pre-commercial 

thinning to stimulate midstory development, 

so that there is a much smaller vertical gap to 

fi ll with mid-story trees as compared to the gap 

that might develop if thinning is delayed until 

stands reach merchantable size. Th is does not 

preclude thinning older (25- to 80-year-old) 

stands, especially given their dominance on the 

landscape, but adding young stands could help 

fi ll a temporal niche in the presence of highquality prey habitat across the landscape through 

time. Th inning at this early age is also not likely 

to aff ect existing fl ying squirrel populations, as 

they generally avoid highly-stocked Douglas-fi r 

forests <25 years old. 

3. Keep some young high-density 

forest on the landscape.

Although optimal spotted owl habitat is multilayered older forest, high-stem-density forests do 

support owl prey and are used by owls as foraging 

habitat. High-stem-density forest can remain in 

a condition favorable for owl prey for several 

decades or more and could serve as a reservoir 

for abundant prey populations while thinned 

stands develop into suitable habitat over the long 

term. It is important to recognize, however, that 

high-stem-density forest can also quickly (<20 

years) leave this stage, as suppression mortality 

and localized stochastic events (e.g., ice storms, 

wind, disease, insect outbreaks) remove existing 

trees (Wilson 2010). 

4. Use defensible buffers to protect 

existing high-quality habitat. 

Fire suppression in dry forests over the last 

century has created habitat that in some cases 

is favorable for owl prey, but such habitat is 

also vulnerable to stand-replacing fi re events. It 

may be important to try to keep some of this 

habitat on the landscape until new suitable 

habitat becomes available. Strategically placed 

buff ers with reduced fuel loads may help provide 

protection from catastrophic fi re for these areas. 

Keeping such buff ers as narrow as possible and 

with as much canopy cover as possible would be 

important to allow squirrels to travel and dispersal 

across the broader landscape and to prevent the 

buff ers from possibly becoming predator traps. 

5. Explore alternative thinning 

prescriptions. 

It may be possible to develop new thinning 

prescriptions that keep moderately high 

populations of arboreal rodents in young forests 

while still achieving long-term management 

objectives for the stand. One such approach would 

be developing prescriptions that focus solely on 

skips (patches of trees left unthinned) and gaps 

(removal of patches of trees). Th is strategy is in 

marked contrast with most current prescriptions 

that typically thin throughout a stand (with or 

without delineated skips or gaps). Under such a 

strategy, it may be important to keep canopy-gap 

sizes small (100-400 m2

 per gap with <30 percent 

of the total stand area in gaps), and horizontal 

occlusion high, as there may be thresholds in 

the amount and extent of gaps distinguishing 

high- and low-quality habitat (Wilson 2010). A 

gap-skip-only approach may be most feasible in 

either young forests with suffi cient bole density 

to provide structural occlusion at a relatively 

small scale (generally less than 20–40 meters), 

or in young mixed-conifer forest with a short, 

but existing multiple-layered canopy. Because 

there have been no demonstrated examples of 

the effi cacy of such a strategy, this approach 

should be experimentally evaluated (testing size, 
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86 Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman

patterning, and spatial distribution of canopy 

gaps) before any widespread application. A gapskip-only approach may be particularly useful 

when the management goal is to reduce fuel loads 

as part of non-commercial restoration eff orts in 

fi re-prone forests, without necessarily wanting 

to accelerate tree regeneration or understory 

plant development. Rather than the common 

practice of removing the vertical component of 

a forest (e.g., ladder fuels) to reduce fuel loads, 

this approach focuses on creating horizontal 

patchiness to reduce fuel loads. Such a strategy 

may also have stronger ecological merit, in that 

it may more closely mimic natural fi re events 

for some regions (Agee 1993; Harrod et al. 

1999; White 1985). Depending on the size of 

canopy gaps, a skips-gaps-only strategy may also 

be suitable for developing late-seral conditions 

in more mesic forest, but only if gaps were 

large enough to accelerate mid- and understory 

development compared to leaving forests to 

develop on their own. 

Future Direction

Th e need for suffi cient structural occlusion to 

protect arboreal rodents from predators provides 

an explanation for why fl ying squirrels and tree 

voles decline in abundance following thinning, 

and provides a rationale for steps that might 

be taken to ameliorate this undesired eff ect. 

However, this hypothesis was developed from 

studying fl ying squirrels in mesic forests of 

western Washington, and may not refl ect other 

limiting factors elsewhere within the range of the 

Northern Spotted Owl. For example, suffi cient 

mid-story structure may be a critical component 

of xeric forests supporting high fl ying squirrel 

abundances in southwest Oregon, but there may 

also be minimum moisture thresholds needed 

for adequate year-round fungal production 

that restrict abundant populations to higher 

elevations, north-facing slopes, or near permanent 

water sources (T. Wilson, unpublished data). 

Likewise, predator load (predator species 

diversity and abundance) may also play a crucial 

role in regulating arboreal rodent populations for 

some forests. Th us there is need to further test 

the applicability of current empirical models 

using similar population and habitat analyses 

elsewhere. Of particular importance would be 

evaluating habitat in areas within and outside the 

range of the Northern Spotted Owl where there 

have been few or no population-level studies or 

where there are habitat conditions substantially 

diff erent than those found in western Washington. 

For fl ying squirrels, these include mixed conifer 

forests in southwestern Oregon, high-elevation 

sites throughout the Oregon and Washington 

Cascades and Olympic Peninsula, dry forests on 

the eastern slopes of the Oregon Cascades and 

southern Washington Cascades, and throughout 

much of the forested area in eastern Oregon and 

Washington (e.g., Blue Mountain and Northern 

Rocky Mountain provinces; fi g. 4). 

For Red Tree Voles, empirical research is needed 

to better understand the eff ects of thinning on 

vole populations, and to determine if thinning 

prescriptions could be modifi ed to allow tree voles 

to persist in thinned stands. Th ere is also a basic 

need for understanding factors that infl uence the 

persistence of tree voles in young stands. Included 

in this is a better understanding of why tree voles 

are apparently slow to disperse through young 

stands, and whether or not specifi c management 

actions could improve dispersal rates. 

Th ere is also a need for further investigation 

into the habitat needs of both species of woodrats, 

given the lack of data on their distribution and 

habitat requirements. Recent controversy over 

the eff ects of broad-scale fi re on distribution of 

spotted owls (e.g., Hansen et al. 2009; Spies et 

al. 2010) suggests that better understanding of 

woodrat ecology could be useful in informing 

such debates. For example, large stand-replacing 

fi res would substantially reduce or eliminate 

fl ying squirrel populations, given the removal 

of above-ground predation cover. Such fi res, 

however, may promote dense shrubs and early 

stages of forest development favorable to Dusky-
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Th inning Eff ects on Spotted Owl Prey & Other Small Mammals Wilson and Forsman 87

footed Woodrats, which could allow owls to 

persist in partially burned areas. 

Finally, the continued decline in spotted owl 

populations throughout their range highlights 

the urgency of further understanding and 

appropriately managing for owl prey across a 

range of spatial scales. An important component 

of this is planning management activities at the 

landscape (e.g., fi fth-fi eld watershed or larger) 

and regional levels in a way that merges the spatial 

and temporal eff ects of thinning on spotted owl 

prey with the ecology and habitat needs of these 

species. Such eff orts could include modeling of 

the: (1) current stand-level distribution of existing 

high-quality habitat for arboreal rodents across 

the region; (2) permeability of the landscape for 

arboreal rodents (e.g., capacity of the landscape 

to allow dispersal and colonization over time); 

and (3) projected changes in the amount and 

distribution of high-quality prey habitat over 

time under diff erent management scenarios and 

stochastic events. 

In summary, thinning has yet to be shown 

eff ective for promoting habitat for arboreal 

rodents like fl ying squirrels and Red Tree Voles. 

However, the importance of midstory cover 

and connectivity suggests that the trajectory of 

some thinned stands will eventually result in 

habitat conditions favorable for these species. 

Extra eff ort will be needed to ensure that the 

short-term negative eff ects of thinning on some 

owl prey species do not have long-term negative 

consequences for owls or their prey. One of the 

fastest and most effi cient ways to move forward 

would be for researchers and forest managers 

to collaborate on projects such as testing novel 

silvicultural prescriptions, assessing habitat and 

prey abundance in diff erent forest types, and 

developing landscape and regional management 

models and strategies for owl prey. A focused 

research-management eff ort over the next 10 

years could greatly advance our understanding 

of owl prey ecology and hopefully result in 

management practices that support healthy 

populations of both owls and their prey in the 

Pacifi c Northwest over the long term. 

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Density Management in the 21st Century: West Side Story PNW-GTR-880

91

Above-ground Carbon Storage, Down Wood, and 

Understory Plant Species Richness after Thinning in 

Western Oregon

Julia I. Burton, Adrian Ares, Sara E. Mulford, Deanna H. Olson, and 

Klaus J. Puettmann

Julia I. Burton is a research associate, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, 

OR 97331; julia.burton@oregonstate.edu; Adrian Ares is the director, Sustainable Agriculture and Natural Resource 

Management Collaborative Research Support Program, Virginia Tech, Blacksburg, VA 24060; Sara E. Mulford was a 

research assistant, Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR 97331; Deanna H. 

Olson is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 

SW Jeff erson Way, Corvallis, OR 97331; Klaus J. Puettmann is Edmund Hayes Professor in Silviculture Alternatives, 

Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331.

Abstract

Concerns about climate change have generated worldwide interest in managing forests for the 

uptake and storage of carbon (C). Simultaneously, preserving and enhancing structural, functional, 

and species diversity in forests remains an important objective. Th erefore, understanding tradeoff s and synergies among C storage and sequestration and diversity in managed forests is key to 

achieving these multiple objectives. Using the experimental framework of the Density Management 

Study in western Oregon, we examined the relationships among a suite of thinning treatments, 

above-ground carbon stocks, and understory vascular plant species richness. Six years following 

treatment implementation, total above-ground C declined with residual density. Total aboveground C in the high-density thinning treatment (300 trees∙ha-1) did not diff er statistically from 

the untreated control treatment (~370–775 trees∙ha-1), and these two treatments stored 33 percent 

and 61 percent more C above ground, respectively, than the moderate density (200 trees∙ha-1) 

and variable density (300, 200, 100 trees∙ha-1) treatments. Diff erences among treatments were 

primarily related to reductions in the live overstory pool. For all treatments, C stored in the live 

overstory > large down wood > snags > stumps > small down wood. Coarse down wood (CDW) 

comprised over 30 percent of the total above-ground C storage. Most of the C in the dead pools 

appears to be legacy (pre-thinning) material; 50–95 percent of snags, stumps, and large down wood 

were in intermediate to late stages of decomposition. Between years 6 and 11 post-treatment, the 

overstory C increment tended to decline with lower residual density, although this trend was not 

statistically signifi cant. In contrast, understory plant species richness was greater in all thinning 

treatments than in untreated controls. Relationships varied slightly among treatments. Moderateand variable-density thinning treatments resulted in a negative relationship between understory 

plant species richness and above-ground C, while no relationship was observed in the high-density 

treatment and unthinned control. Results suggest that thinning increases plant species richness, 

implying that there is a trade-off between management for understory plant species richness and 

above-ground C storage.

Keywords: Biodiversity, carbon sequestration, coarse woody debris, density management, diversity, 

understory vegetation.
Density Management in the 21st Century: West Side Story PNW-GTR-880

92 Carbon Storage, Down Wood, and Understory Plant Richness Burton et al.

Introduction

Concerns about climate change have resulted 

in worldwide interest in managing forests to 

mitigate anthropogenic increases in atmospheric 

carbon dioxide (Gower 2003; Pacala and Socolow 

2004; McKinley et al. 2011). Simultaneously, 

preserving and enhancing structural, functional, 

and biological diversity in forests remain 

important management objectives. However, 

few studies have examined eff ects of thinning 

on carbon (C) storage, as well as the trade-off s 

and synergies among managing for C storage and 

sequestration, and species diversity in managed 

forests. 

Th e majority of above-ground C in temperate 

forests is stored in the live overstory: the ratio of 

understory C to overstory C is typically <0.005 

(Ares et al. 2007). However, the majority of plant 

diversity resides in the understory. Th e ratio of 

understory species richness to overstory species 

richness ranges from 2 to 10, with approximately 

80 percent of the plant species restricted to the 

understory (Gilliam 2007). Forest thinning can 

increase resources available for residual trees in 

the overstory as well as for understory plants 

(Gray et al. 2002), resulting in increases in tree 

diameter growth rates (Dodson et al. 2012) 

and understory plant species diversity (Fahey 

and Puettmann 2007; Ares et al. 2009, 2010). 

However, thinning may decrease C storage within 

forest stands initially and over time (Gower 

2003), with the magnitude depending on the 

percentage of the stand harvested, harvesting 

interval, and spatial pattern of harvesting 

(dispersed vs. aggregated) (Harmon et al. 2009). 

As a result of these positive and negative eff ects 

of thinning on understory plant species richness 

and above-ground C, respectively, a negative 

relationship between above-ground C storage and 

understory diversity is predicted (fi g. 1). Here 

we examine the short-term relationships among 

forest thinning treatments, total above-ground 

C (including live overstory, coarse down wood 

[CDW], snags, and stumps), and understory 

plant species richness. Because rates of soil C 

accumulation are generally low over the period 

of a single rotation, the fate of above-ground C is 

an important focus of mitigation eff orts (Gower 

2003).

Methods

Experimental Design

Using the experimental framework of the 

Density Management Study (Cissel et al. 2006), 

we analyzed the eff ects of a suite of thinning 

treatments on above-ground C stocks and 

understory plant species richness. Th e thinning 

treatments, replicated seven times across the Coast 

Range and northern Cascade Range of western 

Oregon, included three levels of residual density: 

1) a high-density treatment with 300 trees∙ha-1

(HD); 2) a moderate-density treatment with 

200 trees∙ha-1 (MD); and 3) a variable-density 

treatment with 300 trees∙ha-1, 200 trees∙ha-1

and 100 trees∙ha-1 (VD). In addition to an even 

distribution of residual trees (i.e., dispersed 

retention), 3 to 11 percent of the treatment unit 

was left unthinned in circular leave-island reserves 

(patches of undisturbed forest trees) in the HD 

and MD treatments, and 3 to 10 percent of the 

treatment unit was cut in circular gap openings 

Figure 1—Conceptual diagram illustrating the 

contrasting effects of thinning on carbon storage (-) 

and biodiversity (measured as understory plant species 

richness) (+). Here we hypothesize that a trade-off 

emerges as a result of the negative effects of thinning on 

carbon storage in the overstory and positive effects of 

thinning on plant diversity in the understory.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Carbon Storage, Down Wood, and Understory Plant Richness Burton et al. 93

in the MD treatment. In the VD treatment, 

8.2 to 10.3 percent of the area was preserved in 

leave islands, and 8 to 17 percent of the area was 

left in circular gap openings. Gap openings and 

leave islands were 0.1, 0.2, and 0.4 ha in size. 

In addition to comparisons among the three 

thinning treatments, the eff ects of thinning were 

compared with unthinned control areas (CON; 

approximately 600 trees∙ha-1). Each of the seven 

study sites consisted of large forested stands (94 

to 131 ha, with controls on 16 to 24 ha and each 

thinning treatment implemented on 14- and 69-

ha parcels) to allow for operational application of 

treatments and thus avoid the need to scale-up 

the experimental results (fi g. 2).

Field sampling

Seventy-seven permanent 0.1-ha circular plots 

were installed in each site to sample overstory 

trees. Plot centers were located randomly within 

treatment units (n = 21 in HD, MD and VD, n 

= 14 in controls) using a random point generator 

(Cissel et al. 2006). Plot boundaries were 

constrained to be ≥50 m from treatment unit 

boundaries and non-overlapping. Within each 

overstory plot, four 0.002-ha circular understory 

vegetation subplots were installed 9 m from plot 

centers in each cardinal direction. Overstory 

and understory vegetation measurements were 

taken during the summer 6 and 11 years after 

thinning. In each overstory plot, all trees ≥5.1 

cm dbh (diameter at 1.37 m above ground) were 

numbered, identifi ed by species, and measured 

for dbh using a diameter tape. We also measured 

height of 16 trees per plot (10 conifers and 6 

hardwoods) using a laser hypsometer (Laser 

Technology, Centennial, CO, USA). In the 

understory subplots, we visually estimated total 

cover of each vascular plant species present using 

cover classes: 1 percent, 5 percent, and then in 

10 percent increments. Overstory trees and 

shrubs >6 m in height were excluded from cover 

estimates. Species richness was calculated as the 

number of vascular plant species recorded in 

the four understory subplots (a total area of 80 

m2). Detailed vegetation measurement protocols 

and data analyses have been reported previously 

(Cissel et al. 2006; Ares et al. 2009, 2010).

Six years after thinning, all standing dead 

trees (snags) and three types of above-ground 

Figure 2—Example of a treatment layout 

at one site, Bottomline. The high-density 

treatment retained 300 trees∙ha-1, the 

moderate-density treatment retained 200 

trees∙ha-1, and the variable-density retained 

variable densities of trees: 300 trees∙ha-1, 

200∙trees∙ha-1 and 100 trees∙ha-1. The density 

of untreated control plots was approximately 

600 trees∙ha-1. Leave islands were maintained 

in all thinning treatments, canopy gaps were 

also created as part of the moderate- and 

variable-density treatments.
Density Management in the 21st Century: West Side Story PNW-GTR-880

94 Carbon Storage, Down Wood, and Understory Plant Richness Burton et al.

coarse down wood (CDW) were sampled: 

stumps, large CDW (≥25.4 cm in diameter and 

≥0.3 m length), and small CDW (<25.4 cm in 

diameter and <0.3 m length). All stumps (≤1.37 

m in height measured on the uphill side) within 

the northeast quarter-section of the overstory 

plot were measured for diameter and height. 

We measured large CDW along four 12.9-m 

transects connecting the centers of the understory 

subplots. Down wood that crossed transects 

multiple times (e.g., forked logs or long logs that 

spanned two transects) was counted as separate 

pieces (Harmon and Sexton 1996). Elevated 

dead wood at an angle >45° above the ground 

was not considered CDW, but was counted as a 

snag. For each piece of down wood, we measured 

the diameter at the point where it intercepted the 

transect line. Small CDW was measured within 

the understory subplots. Only pieces with their 

large ends inside the subplots were included in 

the measurement. Diameter at both ends and 

total length of each piece (including any part 

extending outside the subplot) were measured. 

Diameter measurements of large and small down 

wood pieces were taken with calipers, length was 

measured using a measuring tape. Decay stage 

was characterized using a fi ve-class scale from 1 

(least decayed) to 5 (most decayed) as per Maser 

et al. (1979). All snags ≥1.37 m tall and ≥5.1 cm 

dbh in the overstory plots were identifi ed as such 

and measured for dbh.

Calculations of Above-ground C 

Storage

We derived above-ground C storage 

from biomass using the specifi c gravity and 

C-concentration values reported by Ares et al. 

(2007). A carbon content of 0.5 kg C∙kg-1 was 

used for tree species not listed in Ares et al. 

(2007). Live tree biomass (bole, bark, live and 

dead branches, and foliage components) was 

estimated using measurements of dbh and height 

in allometric equations using BIOPAK version 

2.50 (Means et al. 1994). Volumes of snags, 

stumps, and large and small down wood were 

calculated and converted to biomass and C stores 

by decay class using the specifi c gravity (mass 

per unit volume) and C-concentration values 

reported by Ares et al. (2007).

Statistical Analysis

A mixed-eff ects model was used to examine 

thinning treatment eff ects on above-ground C, 

diff erences in live C in the overstory between 

year six and year eleven post-treatment, vascular 

plant species richness six years after thinning, and 

diff erences in understory plant species richness 

between year six and year eleven post-treatment. 

Analyses were performed on the averages of all 

plots (subsamples) within a treatment unit. 

Th inning treatment was modeled as a fi xed 

eff ect and site was modeled as a random eff ect 

in order to control for underlying diff erences 

among sites (Littell et al. 1996). Post-hoc 

pairwise comparisons of treatment means used 

orthogonal contrasts with one degree of freedom, 

and Tukey’s HSD was used to correct p-values for 

multiple comparisons. 

Additionally, we examined the relationship 

among understory plant species richness, 

experimental thinning treatments (HD, MD, 

VD, and CON), and above-ground C stocks at 

the plot scale using a mixed eff ects model (Littell 

et al. 1996) of fi xed eff ects (treatments and aboveground C) and random eff ects (site, treatment x 

site). Plots were nested within a treatment unit 

and site. We examined main eff ects of thinning 

treatment, above-ground C, and the interaction 

between richness and above-ground C. In the 

case of a signifi cant interaction, we tested the null 

hypothesis of no relationship between understory 

plant species richness and above-ground C for 

each treatment (CON, HD, MD, and VD) and 

then compared treatment slopes to test the null 

hypothesis of equal slopes between treatments (n 

= 6 comparisons). P-values were not corrected 

for multiple comparisons. We used the mixed 

procedure in SAS 9.2 for all statistical analyses 

reported here (SAS Institute 2004).
Density Management in the 21st Century: West Side Story PNW-GTR-880

Carbon Storage, Down Wood, and Understory Plant Richness Burton et al. 95

Results

Carbon Stocks Year 6 Post-treatment

By the sixth growing season following thinning, 

above-ground carbon (C) decreased with 

decreased residual density (table 1). Moderateand variable-density treatments had lower levels 

of C storage than untreated control and the highdensity retention treatment (diff erence = 78.2 ± 

13.0 Mg∙ha-1, T = -6.01, p < 0.001). Among 

the above-ground stocks, the majority of C was 

stored in the live overstory (~68 percent) relative 

to dead pools: coarse down wood, snags, and 

stumps (~32 percent cumulatively). Within the 

live overstory, the majority of C was stored in the 

bole wood (~72 percent of the live overstory C), 

although nearly 30 percent of the live overstory 

C was found in bark, branches, and foliage. 

Among the dead pools, the largest stock of C was 

in CDW with diameters ≥25.4 cm (large CDW) 

and in later stages of decomposition (classes 3–5).

Overstory C was greater in year eleven than in 

year six in all treatments (p < 0.05). Increments 

ranged from 12.6 to 19.1 Mg∙ha-1, amounting to 

an increase of 10 to 15 percent. Th e diff erence 

in overstory C between year eleven and year 

six post-treatment increased with increases in 

residual density (i.e., CON > HD > MD > VD); 

however, while this trend was apparent, there was 

no evidence for signifi cant diff erences among 

treatments statistically speaking.

Plant Species Richness Six years after 

Thinning 

In contrast to C, understory plant species 

richness was higher (p < 0.001) in all thinning 

treatments than the untreated controls during 

the sixth growing season following treatment 

(table 1). Plant species richness, however, did 

not diff er among high-, moderate- and variabledensity thinning treatments (p > 0.9). Th inned 

treatments (HD, MD, and VD) contained 11.9 

± 1.4 species more than untreated controls on 

average (T = 8.62, p < 0.001). Understory plant 

species richness decreased from year six to year 

eleven in the moderate- and variable density 

thinning treatments, while signifi cant changes 

in richness were not observed in the CON and 

HD treatments (table 1). On average, understory 

plant species declined by 4.4 ± 0.6 more species 

between years 6 and 11 in MD and VD relative 

to CON and HD treatments (T = -7.29, p < 

0.001).

Carbon – Understory Plant Species 

Richness Trade-off

In year six post-treatment, species richness 

was related to above-ground C and thinning 

treatment; evidence for an interaction between 

treatment and above-ground C was weak (p = 

0.07). Th is weak interaction resulted from the 

lack of a relationship between above-ground C 

Table 1—Treatment averages for carbon (C) and diversity: above-ground (C) in year 6 post-treatment, differences and 

live overstory C between years 6 and 11 post-treatment, understory plant species richness in year six post-treatment, and 

differences in understory plant species richness between years 6 and 11 post-treatment. Thinning treatments = HD = 

high-density retention, MD = moderate-density retention, and VD = variable-density; untreated control (CON).

Th inning treatment

CON HD MD VD

Carbon

†

Above-ground C 269.2 a 223.7a 168.0b 168.5b

Diff erence in live overstory C (Yr. 11 – Yr. 6) 19.1 18.2 17.1 12.6

Diversity

†

Understory plant species richness 15.9a 27.3b 28.2b 27.9b

†

Diff erence in richness (Yr. 11 – Yr. 6) 1.6a -0.5a -4.1b -3.7b

†

Different superscripts indicate evidence for significant differences between treatments (p < 0.05).
Density Management in the 21st Century: West Side Story PNW-GTR-880

96 Carbon Storage, Down Wood, and Understory Plant Richness Burton et al.

and understory plant species richness in both 

the untreated control (estimate = -0.01, T = 

-1.1, p = 0.27) and HD treatment (estimate < 

-0.01, T = -0.01, p = 0.99). In contrast, in the 

MD (estimate = -0.02, T = -2.5, p = 0.013) 

and VD (estimate = -0.03, T = -3.3, p = 0.001) 

thinning treatments, the negative relationships 

between understory plant species richness and 

C suggest a trade-off between diversity and C at 

fi ne spatial scales in MD and VD treatments (fi g. 

3). Th ere was evidence for diff erent relationships 

between understory plant species richness and 

above-ground C in between HD and MD (albeit 

weak, estimate = 0.02, T = 0.96, p = 0.051) and 

between VD and HD (estimate = 0.03, T = 2.46, 

p = 0.014). In contrast, there was no evidence 

that the slope of the relationship diff ered between 

HD and CON (estimate = -0.001, T = -0.87, p 

= 0.382).

Discussion

In addition to maintaining or restoring diversity 

and ecosystem function, forest managers are 

now tasked with managing forests to mitigate 

anthropogenic carbon dioxide in the atmosphere. 

Tree boles removed during timber harvesting 

can signifi cantly reduce C storage within forest 

ecosystems (Harmon et al. 2009). Such patterns 

are associated with both C extraction and with 

transient declines in above-ground net primary 

productivity following harvesting (e.g., Dyer et 

al. 2010). 

Although the live overstory comprises the 

largest stock of C above ground, nearly onethird of the total above-ground C at our study 

sites is stored as snags and coarse down wood. 

Th ese proportions are likely associated with 

legacy material that resulted from the previous 

clearcutting operation, as the majority of CDW 

is in the large size classes (≥25.4 cm diameter) and 

later stages of decay. Th e relative importance of 

this portion of the CDW stock of C will decline 

as the legacy wood continues to decompose. 

Further, it appears that natural mortality rates 

Figure 3—Relationship between understory plant 

species richness and above-ground carbon by thinning 

treatment (VD = variable-density, MD = moderatedensity, HD = high-density, and CON = untreated 

control) 6 years post-treatment. Richness is expressed 

for each plot as the aggregate number of species in four 

subplots (80 m2

). Solid lines show model-predicted 

relationship; dashed lines show 95 percent confidence 

intervals. The random effect, site, is not shown.

following thinning are not suffi cient to augment 

the size of the CDW stock (Dodson et al. 2013). 

CDW volumes are typically lower in harvested 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Carbon Storage, Down Wood, and Understory Plant Richness Burton et al. 97

relative to unharvested stands (e.g., Burton et al. 

2009). Th erefore, management activities such 

as creation of down wood may be warranted 

to achieve C storage as well as structural goals 

articulated in the initial study plan (Cissel et al. 

2006). Creation of down wood or snags would 

prevent future C defi cits in CDW in late stages of 

decay as well as below ground in the soil. 

Although not addressed here, the spatial 

distribution of C from large CDW was variable 

and not related to thinning treatments or 

topographic position (Julia Burton, unpublished 

data). Th us, managers may consider establishing 

a spatially heterogeneous, patchy distribution of 

fresh CDW. Alternative designs for down wood 

placement include augmenting wildlife habitat 

and dispersal corridors, for example orienting 

wood toward streams and over headwater 

ridgelines to increase connectivity and the 

dispersal of animals among riparian buff ers 

(Olson and Burnett 2013). 

While thinning resulted in reductions in C 

storage, it increased understory plant species 

richness. Furthermore, the negative relationship 

between species richness and above-ground 

C suggests that thinning results in a trade-off 

between plant diversity and C. As a result of the 

recent logging history, the majority of forests 

in the Coast Range are younger and in earlier, 

even-aged stages of structural development and 

have been managed at high densities to facilitate 

wood production. Because spatial and temporal 

variability in stand structure is associated with 

patterns of biodiversity within forests (Ares et al. 

2009), recent management eff orts have focused 

on using thinning to accelerate the development 

of structural heterogeneity and restore patterns 

of diversity within younger stands (Bauhus et al. 

2009). Trade-off s between plant species richness 

and C therefore suggest that forest management 

for maximum C storage may be at odds with 

management for biodiversity if thinning removes 

C stored in live tree boles. 

A number of mechanisms may contribute to 

the negative relationship between above-ground 

C and plant species richness. First, removal of live 

overstory C during thinning creates gaps in the 

canopy that function to alter the microclimate 

and increase resource availability above and 

below ground (Gray et al. 2002; Burton 2011). 

Such changes in the local abiotic environment 

interact with the traits of the individual plant 

species in the understory to drive changes in 

rates of colonization and competitive exclusion 

to aff ect the composition and structure of the 

plant communities (Roberts and Gilliam 1995; 

Burton 2011). Specifi cally, increases in resource 

availability coupled with physical disturbance of 

the forest fl oor may explain the increased levels 

of plant species richness (Fahey and Puettmann 

2007) and coexistence of early- and late-seral 

species six years after treatments (Ares et al. 

2009, 2010). Declines in richness overtime may 

be associated with increased rates of competitive 

exclusion of late-seral species by competitive 

early-seral species (Ares et al. 2010). Harvesting 

can facilitate the invasion of non-native or weedy 

plant species (Scheller et al. 2002; Aubin et al. 

2007), and our previous studies have reported 

that introduced species richness and cover was 

greater in the thinning treatment units relative 

to the untreated controls. However, nonnative species comprised a small proportion 

of the response of richness and cover (Ares et 

al. 2009). Relationships between understory 

plant species richness and C stored as CDW are 

likely more variable and complex relative to C 

stored in the overstory. Relationships between 

C and understory species richness may vary in 

strength and direction (positive or negative) 

among diff erent pools of CDW (small vs. large 

pieces, early vs. late stages of decay, snags and 

stumps). For instance, the recruitment of fresh 

down wood may decrease plant species richness 

through its direct eff ects on plant survival and 

indirect eff ects on the local environment (e.g., 

increased shading and interference). Over time, 

as wood decays, such relationships may become 

positive as interference decreases and resource 

availability increases (e.g., moisture and nutrients 
Density Management in the 21st Century: West Side Story PNW-GTR-880

98 Carbon Storage, Down Wood, and Understory Plant Richness Burton et al.

released from decaying wood) (Campbell and 

Gower 2000; Spears et al. 2003). Such eff ects 

may be mediated by C storage in the overstory. 

For instance, CDW shading may have a negative 

eff ect on understory plant species richness in a 

shady understory where overstory C is high, but 

a positive eff ect in an opening ( low overstory C) 

where it may mediate environmental extremes 

such as temperature. Apparent trade-off s between 

above-ground C and understory plant species 

richness refl ect the net result of many complex 

relationships among forest structure, resource 

availability and the characteristics of the plants in 

the regional species pool (Burton et al., in press).

Finally, if forests are to be managed to mitigate 

global climate change by reducing atmospheric 

carbon dioxide, simply looking at the eff ects of 

timber harvesting on C storage and sequestration 

within a given stand is not the whole story, and 

may not refl ect the net eff ects of thinning in 

mitigating the global C balance (Gower 2003; 

McKinley et al. 2011). As we demonstrate here, 

thinning can reduce above-ground C storage 

in the short term by removing woody biomass, 

reducing the input of CDW, and leading to 

reductions in the size of the CDW C stock. Such 

activities can also lead to reductions in belowground C stocks in the organic horizon and soil 

(Gower 2003). However, over the life cycle of the 

wood (from establishment to decomposition, be 

it in the forest or in a forest product), thinning 

eff ects on C storage depend on whether forest 

products are long-lived, and on carbon-emissions 

during harvesting operations and processing 

(Gower 2003; McKinley et al. 2011). 

Conclusion

Linkages between carbon (C) storage and 

understory plant diversity may arise from a variety 

of processes and mechanisms operating over 

diff erent temporal and spatial scales. Our work 

suggests that the net eff ect of these interactions 

is a trade-off between understory plant species 

richness and C storage (see also Burton et al., 

in press). Th us, forest management aimed to 

increase above-ground C storage by maintaining 

high-density forests may negatively aff ect aspects 

of restoration and maintenance of biodiversity 

within stands, and vice versa. Integrating C 

storage goals into a larger conservation-oriented 

management scheme may require accepting some 

losses and managing trade-off s by maintaining 

early seral habitat within dense C-rich stands or 

retaining live and detrital C in regenerating earlyseral stands. Alternatively, plans could separate 

these goals across temporal or spatial scales.

Acknowledgments

Funding for the Density Management Study was 

provided by the U.S. Department of Interior Bureau of 

Land Management (BLM) and the U.S. Department 

of Agriculture Forest Service. For helpful comments 

on earlier versions we thank Paul Anderson, Ariel 

Muldoon, Rob Pabst and one anonymous reviewer. 

We also express our appreciation to Aaron Weiskittel, 

Andrew Neill and numerous dedicated personnel, 

in addition to all BLM site coordinators and staff 

who have contributed to the implementation of the 

Density Management Study. 

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101

Green-tree Retention, Ectomycorrhiza Diversity, and 

Ectomycorrhizal Spore Inoculum

Daniel L. Luoma and Joyce L. Eberhart

Daniel L. Luoma is an assistant professor, senior reseatch, and Joyce L. Eberhart is a senior faculty research assistant, 

Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR 97331; daniel.luoma@oregonstate.

edu.

Abstract

Studies from the Pacifi c Northwest indicate that forest management activities can reduce 

the richness and abundance of ectomycorrhizal fungi (EMF). Development of management 

approaches to sustain these essential organisms in forests has been hampered by a lack of knowledge 

of EMF community structure, diversity, and spatial and temporal variability across stands and 

landscapes. Th e ectomycorrhizal fungus community, as seen on root tips, changes signifi cantly in 

disturbed sites compared to nearby undisturbed, nearby forests. Th ese changes might be due as 

much to environmental and biotic factors as to loss of host trees. It has been found that seedlings 

transplanted from mature forests into harvested gaps declined in both EMF species richness and 

abundance. Seedlings closest to an uncut forest edge had the highest values of both response 

variables. In various studies, root colonization percentage and EM diversity have been observed to 

decline with distance from mature trees. Th ese outcomes and others have led several researchers 

to conclude that green-tree retention is important for the recovery of EM fungi in harvested sites. 

Inoculating bare-root conifer seedlings with spores of ectomycorrhizal fungi has been promoted to 

reduce transplant shock, improve growth and nutrient uptake, and improve survival of Douglasfi r (Pseudotsuga menziesii) out-planted on sites subjected to operational forest management. Here, 

from an unpublished study, we summarize the eff ectiveness of EMF spore inoculum to increase 

survival and growth. Th at study also compared locally sourced spore inoculum with inoculum 

obtained from a diff erent ecoregion. On that particular green-tree retention site, EMF spore 

inoculum was largely superfl uous with regard to seedling mortality or growth. It was postulated 

that the site had suffi cient EMF inoculum, either as living mycelium or spores, to rapidly colonize 

the bare-root Douglas-fi r seedlings that were tested. We concur with other researchers that greentree retention can be benefi cial in maintaining EMF diversity and inoculum potential on a site.

Keywords: green-tree retention, ectomycorrhizae; Rhizopogon; soil ecology

Ectomycorrhizal Fungi

Ectomycorrhizal symbioses are formed on 

about 8000 plant species (Dahlberg 2001) and a 

current estimate of the number of ectomycorrhizal 

fungus (EMF) species is 7750 (Rinaldi et al. 

2008). Most of the dominant and economically 

important timber species in the Pacifi c Northwest 

are ectomycorrhiza (EM)-dependent, including 

all members of the pine, oak, and birch plant 

families (Pinaceae, Fagaceae, and Betulaceae) 

(Smith and Read 2008). Douglas-fi r (Pseudotsuga 

menziesii (Mirbel) Franko) has an estimated 2000 

EMF symbionts throughout its range (Trappe 

1977). Douglas-fi r will not grow in soil without 

ectomycorrhizal fungi (Trappe and Strand 1969).

Ectomycorrhizal fungus diversity is an 

important attribute of Pacifi c Northwest forested 

ecosystems, for instance in stabilizing below-
Density Management in the 21st Century: West Side Story PNW-GTR-880

102 Green-tree Retention and Ectomycorrhizae Luoma and Eberhart

ground processes after disturbances (Perry et al. 

1989). Seedlings associated with a high diversity 

of EMF may be better-adapted to disturbance 

as compared to seedlings with lower diversity 

(Simard et al. 1997). In addition, high EMF 

diversity seems to increase trees’ competitive 

abilities. A laboratory study supported this 

hypothesis by documenting that Pinus patula 

Schiede ex Schltdl. & Cham. seedlings inoculated 

with two species of EMF grew taller and put on 

more biomass than seedlings inoculated with 

only one EMF species (Sudhakara and Natarajan 

1997). 

Ectomycorrhizal fungi also form a functional 

guild linking primary producers to soil systems, are 

important in ecosystem response to disturbance 

(Perry et al. 1989), and may be sensitive indicators 

of environmental changes (Temorshuizen and 

Schaff ers 1987; Termorshuizen et al. 1990; 

Arnolds 1991; Arnebrant and Söderström 

1992). Ectomycorrhizal fungi are, with few 

exceptions, asco- and basidiomycetes and mostly 

produce macroscopic sporocarps in the form 

of mushrooms and truffl es (epigeous or aboveground fruiting bodies, and hypogeous or belowground fruiting bodies, respectively). Sporocarps 

produce the spores that disseminate the species 

and provide for genetic recombination within 

and among populations. Many species, especially 

those that produce truffl es, are also important 

dietary items for vertebrates and invertebrates: 

some small mammal species rely on them for 

over 90 percent of their diet (Maser et al. 1978; 

Hayes et al. 1986; Claridge et al. 1996; Carey et 

al. 1999; Jacobs and Luoma 2008). 

Nursery-grown seedlings that have not been 

otherwise inoculated with EMF arrive at a 

planting site with “greenhouse-adapted” fungi 

forming the mycorrhizae on their roots, and 

some roots may be non-mycorrhizal. Species 

diversity is low and the fungi are not usually well 

adapted to the rigors of the out-planting site 

(Alvarez and Cobb 1977; Castellano and Molina 

1989). Over time, the nursery fungi are largely 

replaced by indigenous EMF species (Bledsoe 

et al. 1982). Th e rate of colonization by native 

fungi is dependent on the inoculum potential of 

the out-planting site. Harsh sites tend to have 

low inoculum potential. Hence, applying spore 

inoculum of species that vigorously colonize 

seedling roots on harsh sites should increase 

growth and survival of the out-planted nursery 

stock (Amaranthus and Perry 1987). 

Th e Diamond Lake Ranger District (Umpqua 

National Forest) has been inoculating bare-root 

conifer stock with spores of EMF just before 

out-planting seedlings onto regeneration sites. 

Spores from Rhizopogon species are a dominant 

component of the inoculum. Th e genus 

Rhizopogon is named for its typically conspicuous 

rhizomorphs that effi ciently transport water, 

conferring drought tolerance to seedlings or 

allowing seedlings to quickly recover from 

drought (Parke et al. 1983a).

Th e inoculation treatment is intended to 

reduce transplant shock, improve growth and 

nutrient uptake, and improve survival. Successful 

inoculation of the out-planted seedlings, 

regardless of the growth response, also has the 

potential to aff ect the broader soil ecosystem. 

Because the EMF species that may be established 

by the inoculation treatment are aggressive 

colonists, they have the potential to alter the 

biodiversity of ectomycorrhizal fungi on a wide 

scale. 

Forest Management Implications

Studies from the Pacifi c Northwest indicate 

that forest management activities can infl uence 

patterns of plant succession and reduce 

ectomycorrhizal fungi and forest regeneration 

success (Wright and Tarrant 1958; Harvey et al. 

1980a, 1980b; Amaranthus et al. 1994; Waters 

et al. 1994). Development of management 

approaches to sustain these essential organisms in 

forests has been hampered by a lack of knowledge 

of EMF community structure, diversity, and 

spatial and temporal variability across stands and 

landscapes.

Several studies in northern temperate forests 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Green-tree Retention and Ectomycorrhizae Luoma and Eberhart 103

have examined the eff ects of silvicultural 

practices, particularly clearcutting, on the EMF 

community (see review by Jones et al. 2003). 

Most studies focused on eff ects of disturbance on 

residual fungus inoculum and on the amount and 

diversity of EM types on seedlings planted in situ 

or in greenhouse experiments (Perry et al. 1982; 

Parke et al. 1983b, 1984; Pilz and Perry 1984; 

Dahlberg and Stenström 1991; Harvey et al. 

1997; Jones et al. 1997, 2002). Some studies have 

also examined EM diversity on seedlings planted 

near forest edges or aggregates of retained live 

trees (Kranabetter and Wylie 1998; Kranabetter 

1999; Kranabetter et al. 1999; Kranabetter and 

Friesen 2002). As noted by Jones et al. (2003), 

even though the EMF community structure 

changes in response to clearcut logging, EM 

colonization of root tips remains high in PNW 

forest ecosystems. Th is led them to conclude that 

changes in the EMF community might be due 

as much to environmental and biotic factors as 

to the loss of host trees. Th e long-term eff ects 

of these changes in EMF community structure 

remain to be documented.

Outerbridge and Trofymow (2004) tested the 

hypothesis that retention of mature trees enhances 

colonization and diversity of EM fungi on 

seedlings planted in adjacent areas. It was found 

that root colonization and EM diversity declined 

with distance from mature trees. Th ey concluded 

that green-tree retention was important for the 

recovery of EM fungi in harvested sites.

Kranabetter and Friesen (2002), working with 

Western Hemlock (Tsuga heterophylla (Raf.) 

Sarg.), found that seedlings transplanted from 

mature forests into harvested gaps declined in 

both EMF species richness and abundance. 

Seedlings closest to the uncut forest edge had the 

highest values of both response variables.

On a green-tree retention site, we have found 

that a locally-sourced Rhizopogon sporocarp 

inoculum was associated with higher initial 

seedling mortality (unpublished data). However, 

our inoculum was a biologically-active slurry 

of micro-organisms and was applied during 

a rapid transition from the cool, wet season to 

the hot, dry season. Nitrogen fi xing and other 

bacteria benefi cial to the mycorrhizal symbiosis 

are associated with both EM sporocarps and 

roots (Li and Castellano 1987; Li and Hung 

1987; Garbaye and Bowen 1989; Garbaye 

1991). We hypothesize that simultaneous strong 

physiological demands from the roots, shoots, 

and microbial community (for phosphorus in 

particular) could equate to transplant shock 

and account for the higher initial mortality. In 

contrast, we found that a commercial inoculum 

consisting of a dry spore/clay powder, and lacking 

an active “helper bacteria” community, may have 

imposed less physiological stress on the roots 

during the initial growing season. Garbaye et al. 

(1992) noted diff erential eff ects of treatments on 

soil “helper bacteria” in bare-root nurseries and 

concluded that the outcomes of such complex 

ecological interactions can be diffi cult to predict.

However after three years, neither sporocarp 

inoculum treatment was strongly linked to 

decreased seedling mortality or increased 

seedling growth. Th e level of Rhizopogon EM 

on the planted seedlings did not vary among 

spore inoculation treatments on the green-tree 

retention site (Luoma and Eberhart, unpublished 

report on fi le with the Diamond Lake Ranger 

District, Umpqua National Forest).

Ectomycorrhizae and Green-tree 

Retention

Strong correlations between the EM 

community structure of retained green trees and 

that of subsequently planted seedlings have been 

documented, but the role of direct, EM to EM 

connections via shared mycelium remains unclear 

(Teste et al. 2009). Since only three EM types 

were found on the pre-treatment nursery roots, 

we infer that the EM types found post-treatment 

were largely established from inoculum naturally 

present on the site, or as a result of our inoculation 

treatments. Our observed rapid colonization by 

non-nursery EM types is consistent with the 
Density Management in the 21st Century: West Side Story PNW-GTR-880

104 Green-tree Retention and Ectomycorrhizae Luoma and Eberhart

few similar studies from our region (Bledsoe 

et al. 1982; Castellano and Molina 1989). Th e 

Wilcoxina EM type was found on 50 percent of 

the pre-treatment seedlings and 93 percent of the 

post-treatment seedlings (our unpublished study, 

discussed above), suggesting a strong presence of 

Wilcoxina inoculum on the experimental site.

In our unpublished study, two Rhizopogon

EM types in section Villosuli were broadly 

distributed among the treatments. Th ese taxa 

seem to be important within the native range of 

Pseudotsuga menziesii and where the species has 

been introduced in various parts of the world. 

Sporocarps of Rhizopogon section Villosuli were 

the major component of our local inoculum, 

and were listed as a major component of the 

commercial inoculum. 

Th ere was, however, no overall diff erence in 

Rhizopogon EM abundance among inoculum 

treatments. Such an outcome is consistent with 

green-tree retention concepts of maintaining 

legacy forest structure that, in turn, retains 

elements of biodiversity on sites (Franklin 

et al. 1999) including ectomycorrhizal fungi 

(Luoma et al. 2004; Outerbridge and Trofymow 

2004; Luoma et al. 2006; Jones et al. 2008). 

Additionally, spores of Rhizopogon have been 

found to be relatively long-lasting in the soil, and 

can serve as legacy on-site inoculum (Kjøller and 

Bruns 2003; Bruns et al. 2009). Teste et al. (2004) 

out-planted seedlings that had been inoculated 

with a Rhizopogon spore slurry at a containerized 

nursery. Th ey too, found no benefi t associated 

with the Rhizopogon spore treatment on seedling 

growth or survival, two years after out-planting. 

Th ey inferred that the local EM inoculation 

potential was suffi cient to induce robust EM 

development. 

Conclusions

On the green-tree retention site that we 

studied (unpublished data), use of our particular 

formulations of EMF spore inoculum was largely 

superfl uous with regard to decreasing seedling 

mortality and increasing seedling growth. In 

particular, the level of Rhizopogon EM did not 

vary among fungal treatments. We concluded 

that our study site had suffi cient legacy EMF 

inoculum, either as living mycelium or spores, to 

rapidly colonize the nursery-grown Douglas-fi r 

seedlings that were out-planted. 

A broad fi nding emerges from the various 

studies reviewed here: the EMF community, 

as seen on root tips, changes signifi cantly in 

disturbed sites compared to undisturbed, nearby 

forests. Furthermore, even on clearcut sites, these 

changes might be due as much to environmental 

and biotic factors as to loss of host trees (Jones 

et al. 2003). Th e long-term eff ects of these 

changes in EMF community structure remain 

to be documented. We concur with Outerbridge 

and Trofymow (2004) and Teste et al. (2004) 

that green-tree retention can be benefi cial in 

maintaining EMF diversity and inoculum 

potential on a site. 

Acknowledgments

We would like to thank Rick Abbott and Andy 

Moore for their contributions to the unpublished 

seedling inoculation study. We also thank the 

anonymous reviewers for their helpful comments on 

the manuscript. 

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Citation:

Luoma, Daniel L.; Eberhart, Joyce L. 2013. Green-tree retention, ectomycorrhiza diversity, and ectomycorrhizal spore 

inoculum. In: Anderson, Paul D.; Ronnenberg, Kathryn L., editors. Density management for the 21st century: west side 

story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacifi c Northwest 

Research Station: 101–107.
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Managing for Old-growth Forests: A Moving Target

Thomas A. Spies and Robert J. Pabst

Th omas A. Spies is a research forester, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences 

Laboratory, 3200 SW Jeff erson Way, Corvallis, OR; tspies@fs.fed.us; Robert J. Pabst is a senior faculty research assistant, 

Dept. of Forest Ecosystems & Society, Oregon State University, Corvallis, OR; rob.pabst@oregonstate.edu.

Presentation Abstract

Old-growth Douglas-fi r (Pseudotsuga menziesii) forests are a goal for conservation and restoration 

across millions of acres of federal forest lands in western Oregon and Washington. Where old growth 

currently exists, management is typically focused on protecting stands and watersheds from logging 

and high-severity wildfi re. Where old growth was converted to Douglas-fi r plantations during the 

20th century, the goal is often to actively manage those areas to create ecological diversity and 

accelerate development of old-growth conditions. What does it mean to use old growth as a target 

for management? Most old-growth Douglas-fi r forests are over 200 years old, and many contain 

trees over 500 years old. Yet existing empirical studies and our scientifi c knowledge of forestry 

are less than a century old and have limited value in projecting how silvicultural manipulations 

will infl uence ecosystem function objectives centuries into the future. Old growth as a target can 

mean using the structure and function of current old-growth stands as a goal for manipulating 

plantations. Th is is a challenge because current old-growth stand structure represents centuries 

of succession, disturbance, and climate change—pathways of development that probably will 

not be repeated in nature or through silvicultural manipulations. Or, more realistically, it can 

mean altering conditions in plantations to more closely match what we know about the structure 

and dynamics of old-growth stands when they were young. In this second approach, managers 

would manipulate structure and composition to create conditions in young stands that would be 

more likely to develop the general features of old-growth forests over time than if they were left 

alone. Th is approach is based on several areas of knowledge with diff erent degrees of development: 

(1) a relatively well-developed knowledge of how stand density aff ects stand development; (2) a 

moderately good understanding of current old-growth forest structure; (3) a fair understanding 

of how current old stands developed; and (4) a poor understanding of how any given stand might 

develop over the next several centuries. We review what is known about current old-growth forest 

structure and how old-growth forests develop over time and space. We show how regional and local 

ecological variation can aff ect old-growth structure and development. We use simulation models to 

explore how silvicultural manipulations might aff ect development of old-growth characteristics in 

the short run. We provide some scenarios of how plantations might develop over centuries. Finally, 

we propose some rules of thumb to guide management of dense conifer plantations to restore 

ecological diversity and reset pathways toward desired old-growth structure and composition: 

1. Reduce stem densities in plantations to increase rates of diameter growth to produce largediameter trees and encourage development of large and deep crowns. 
Density Management in the 21st Century: West Side Story PNW-GTR-880

109

2. Use variable-density approaches to create spatial heterogeneity to promote understory 

development and diversity.

3. Favor hardwoods and other conifer species that would have been eliminated under intensive 

management for Douglas-fi r timber production.

4. Plant shade-tolerant tree species where seed sources of desired species are lacking in the stand 

or landscape. 

5. Don’t use the same prescription everywhere—vary densities and frequency of entries.

Keywords: restoration, thinning, plantations, regeneration, structural diversity, species diversity, 

Douglas-fi r, old growth.

Editors’ suggestion: 

Franklin, J.F.; Spies, T.A.; Van Pelt, R.; Carey, A.B.; Thornburgh, D.A.; Berge, D.R.; Lindenmayer, D.B.; 

Harmon, M.E.; Keeton, W.S.; Shaw, D.C.; Bible, K.; Chen, J. 2002. Disturbances and structural development 

of natural forest ecosystems with silvicultural implications, using Douglas-fir forests as an example. Forest 

Ecology and Management. 155: 399–423.
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110

Stand Density Relationships

John C. Tappeiner, II

Presentation Abstract

Th inning stands (managing their densities) aff ects the development of trees and understory 

plants as individuals, as well as stand-level characteristics like structure, microclimate, and stand 

growth, habitat for various species, and fuel and potential fi re severity. Th ese characteristics and 

the rate of changes are aff ected by thinning severity—the reduction in numbers of trees, the stand 

density, and also by the number, sizes, species, and growth rates of the trees retained. In addition, 

site variables like potential for severe wind and ice/snow storms, soil depth/rooting, root diseases, 

and others, have an eff ect. 

Changing stand density simultaneously aff ects a variety of stand characteristics. For example, 

thinning to low stand density favors the growth of trees with large stems, crowns, and branches, 

and may produce considerable volumes of commercial wood in the short term. Th inning stands 

to low density favors growth of large trees; it may reduce long-term commercial wood production 

if densities are quite low, and production of snags and dead wood by competition will probably 

be delayed. Th inning favors development of an understory and a multi-story stand, and generally 

improves wildlife habitat. However, it can lead to a dense understory that may increase risk of 

severe fi re. 

Forest stands are often variable in tree spacing, size, and species composition, even in rather 

uniform plantations, and the application of thinning prescriptions may need to be fl exible to take 

advantage of this. Th inning density may vary to release understory trees, avoid damage to wet 

areas, or leave trees at higher density where wind throw is likely, to protect areas of snags. Presence 

of root disease “pockets” may require variance from the general prescription. Resistant tree species 

may be favored, openings may be left that will fi ll in with shrubs, or immune tree species may 

regenerate. 

Large dominant and codominant trees are usually left in thinning, because they grow faster. 

Where the purpose of thinning is growing late-successional stands, these are the trees that are most 

likely to become the large trees characteristic of old-growth forests. In certain stands, some of these 

trees may be removed to favor minor tree species and help develop a mixed-species stand, or to 

produce valuable products like poles and pilings that will help pay for the costs of thinning. Several 

treatments may be needed to meet stand management objectives. Examples: thinning dense stands 

to low density may require several treatments to avoid damage from wind or ice storms that could 

result from a single, drastic reduction in stand density; or additional treatments may be necessary 

to manage the dense tree understory that can develop after thinning. 

When conducting research on thinning, it is important to specify thinning objectives, and the 

treatments thinning methods, densities, and other characteristics used to achieve them. Often the 

John C. Tappeiner, II is emeritus faculty, College of Forestry, Oregon State University; john.tappeiner@oregonstate.edu.
Density Management in the 21st Century: West Side Story PNW-GTR-880

111

literature on the eff ects of thinning on variables other than wood production does not provide 

enough detail. To interpret the results or repeat the study, stand density immediately before and 

after thinning and for a period (5 to 10 yr) after thinning, and eff ects of variables like root disease, 

wind/ice damage, and others, are needed.

Keywords: density management, thinning severity, stand structure and composition, wood 

production, late-successional stands.

Editors’ suggestions:

Bailey, J.D.; Tappeiner, J.C. 1998. Effects of thinning on structural development in 40- to 100-year-old 

Douglas-fir stands in western Oregon. Forest Ecology and Management. 108: 99–113. 

Poage, N.J.; Tappeiner, J.C. II. 2002. Long-term patterns of diameter and basal area growth of old-growth 

Douglas-fir trees in western Oregon. Canadian Journal of Forest Research. 32: 1232–1243.

Tappeiner, J.C.; Huffman, D.; Marshall, D.; Spies, T.A.; Bailey, J.D. 1997. Density, ages, and growth rates in 

old-growth and young-growth forests in coastal Oregon. Canadian Journal of Forest Research. 27: 638–648.
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112

Michael Newton is emeritus faculty, Department of Forest Engineering, Resources & Management, Oregon State 

University, Corvallis, OR 97331; mike.newton@oregonstate.edu.

Adapting Management of Shade-intolerant Douglas-fir Forests 

to Provide Maximum Diversity of Habitats Continuously and 

Productively

Michael Newton

Presentation Abstract

Managing overstory forest density is the key to energy that shapes the rest of the resource. Th e 

role of the tree layer in westside landscapes over long time-spans is driven by the overwhelming 

infl uence of the dominant cover in the environments of lower canopies. In even-aged stands, 

the manifestations of this infl uence vary markedly after a stand-replacing event by the stage of 

succession as forests recover. In the example of Douglas-fi r (Pseudotsuga menziesii) succession, the 

nature of the event that removes a mature forest cover and initiates succession has an infl uence on 

initial non-coniferous cover. Abundant light near the ground allows diverse species composition 

in the fi rst one or two decades, depending on stocking, that diminishes at an accelerating rate 

with the exponential development of crowns of the dominant conifers. When crown closure is 

nearly complete, a period of very low understory productivity begins that may last 20–50 years, 

depending on frequency of shade-tolerant conifers in the overstory, distribution of gaps in stands, 

or hardwood mixtures. Density management by thinning leads to soil disturbance, increase in light 

in understories, and development of seedlings and sprouts of understory herbs and shrubs. Residual 

density of overstory crowns infl uences the length of periods in which shade-intolerant understory 

species persist and over-all diversity and productivity of understory vegetation. Site quality and 

local overstory density after thinning are major factors in how long each component of understory 

cover persists. Eff orts to create multi-layer canopies by thinning typically encourage understory 

regeneration of both Douglas-fi r and shade-tolerant conifers, as well as tolerant herbs and shrubs. 

Th e persistence of each cohort of recruits is dependent on its energy needs and the duration of 

adequate light before the dominant canopy forecloses shade-intolerant species. In the Douglas-fi r 

Region, expectations for forming uneven-aged stands that retain Douglas-fi r may be realistic only 

on very poor sites, and where overstory stocking is very low or gaps are large. Requirement for 

gap size to recruit long-lived shade-intolerant species is now under investigation. Fast-growing 

hardwoods and shrubs are serious limitations on good and some very poor sites.

 Where hemlock (Tsuga spp.) or other shade-tolerant conifers and hardwoods are present, they 

may regenerate and persist to form mixed stands that eventually become dominated by the tolerant 

species as Douglas-fi r matures and senesces. Th e overwhelming infl uence of the overstory can be 

expected to restrict what can survive and remain viable in the stand, including Douglas-fi r. In 

the absence of even-aged management, one may expect management of late-successional reserves 

to mature as Douglas-fi r-dominant forests, leading eventually to hemlock or true fi r (Abies spp.) 

dominance after several centuries. Maintenance of a diverse landscape dominated by Douglas-fi r 

will likely necessitate patch-wise periodic stand replacement that re-sets early succession lest shadeintolerant species, and wildlife that depends on them, become rare or threatened. Maintenance of 
Density Management in the 21st Century: West Side Story PNW-GTR-880

113

high landscape diversity may require various applications of even-aged management with patch 

sizes large enough to support the full array of wildlife and understory plants, with cycles long 

enough and patches large enough to provide both early-seral and late-seral features to be present 

continuously on a rotating basis. Patches of disturbance may presumably be guided in size and 

location by desired features and continuity of future stands with habitats characteristic of old 

growth.

Keywords: density management, thinning, shade tolerance, disturbance, understory regeneration, 

landscape diversity.
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114

Westside Thinning and Underplanting Study in 50- to 55-year-old 

Douglas-fir and Douglas-fir/Hemlock Stands

Elizabeth C. Cole and Michael Newton

Poster Abstract

Public agencies in the Pacifi c Northwest have engaged in managing for late-successional features or 

structure on lands which also have the possibility for high timber production. Th is study examined 

the potential for developing understory structure while maintaining a productive overstory on two 

sites (Willamette Valley foothills and coastal) in western Oregon. Treatments included thinning 

50- to 55-year-old Douglas-fi r (Pseudotsuga menziesii) or Douglas-fi r/Western Hemlock (Tsuga 

heterophylla) stands to three or four overstory densities 30 to 65 percent below full stocking, either 

in a uniform pattern or by creating gaps. After thinning, plots were underplanted with three or 

four species with varying shade tolerances. Seedling, vegetation, and overstory measurements have 

been made periodically for 10–15 years after thinning. To determine potential timber yields, stand 

conditions after thinning were input into ORGANON and growth projected for 50 years after 

thinning. Tenth-year survival of underplanted seedlings varied by site and species, with the coastal 

site having higher survival than the Valley site. Survival at the Valley site was lowest with the highest 

overstory density, but density did not aff ect survival at the coastal site. In general, the highest-density 

overstories led to the smallest seedlings and the lowest-density overstories the largest. Seedlings 

were usually larger in gaps. Browsing aff ected growth of Douglas-fi r and Western Redcedar (Th uja 

plicata). Natural regeneration of Western Hemlock was abundant at the coastal site and resulted in 

areas of hemlock “thickets”, which limited light for other understory vegetation. Projections from 

ORGANON indicated that overstory trees are dynamic and continuing to grow after thinning. 

Based on these projections for the higher-density thinnings, it is likely that underplanted seedlings 

will have a limited potential for creating a secondary structural layer. Repeated thinnings may be 

necessary to insure adequate growth and survival of underplantings, but removal of overstory trees 

may result in damage to the understory trees. Gaps, especially the larger gaps, may provide an 

opportunity for underplanted seedlings to develop a secondary layer. 

Keywords: Late-seral vegetation; understory structure; thinning.

Elizbeth C. Cole is a senior faculty research assistant, and Michael Newton is emeritus faculty, Department of Forest 

Engineering, Resources & Management, Oregon State University, Corvallis, OR 97331; mike.newton@oregonstate.edu.
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The Theoretical and Empirical Basis for Understanding the Impact 

of Thinning on Carbon Stores in Forests

Mark E. Harmon

Mark E. Harmon is a professor, Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR 

97331; mark.harmon@oregonstate.edu.

Presentation Abstract

Th inning of forests has been proposed as a means to increase the carbon stores of forests. Th e 

justifi cation often off ered is that thinning increases stand productivity, which in turn leads to 

higher carbon stores. While thinning of forests clearly increases the growth of residual trees and 

increases the amount of harvested carbon compared to an unthinned stand, there is little theoretical 

or empirical basis for believing that this activity increases the average carbon stores of forests. By 

removing trees, leaf area is temporarily decreased and carbon input to the forest via photosynthesis 

is also temporarily decreased. In theory, reducing the input of carbon to a forest will reduce its 

average carbon stores. Moreover, by increasing the amount of carbon harvested over a rotation, a 

greater proportion of carbon is removed, which general ecosystem theory also predicts will lower 

average carbon stores. 

Th e few empirical studies that have examined long-term impact of thinning on carbon stores 

have indicated that as thinning intensity increases either in amount or frequency, the average longterm carbon store decreases. Simulation models indicate very similar trends. Both results are in line 

with predictions from general ecosystem theory. Despite the fi nding that thinning reduces average 

carbon stores relative to not thinning, this management practice may lead to increases of carbon 

stores compared to a system of clearcut harvesting. By replacing clearcut harvesting with a series of 

partial harvests, carbon stores in forests could be increased signifi cantly.

Keywords: thinning, uneven-aged management, regeneration, structural diversity, species diversity, 

Douglas-fi r.

Editors’ suggestion:

Harmon, M.E.; Marks, B. 2002. Effects of silvicultural practices on carbon stores in Douglas-fir–western 

hemlock forests in the Pacific Northwest, U.S.A.: results from a simulation model. Canadian Journal of 

Forest Research. 32: 863–877.

Western Washington and Oregon Elk Foraging: Use and 

Nutritional Value by Vegetative Life-form

John G. Cook and Rachel C. Cook

Presentation Abstract

Recent research and modeling of Elk (Cervus elaphus) habitat selection and nutrition is 

establishing the key importance of nutritional value of plant communities (NV, e.g., digestible 

energy and protein of forage in ungulate diets) to habitat use and productivity of Elk herds in 
Density Management in the 21st Century: West Side Story PNW-GTR-880

116

John G. Cook is a wildlife biologist, and Rachel C. Cook is a wildlife biologist, National Council for Air and Stream 

Improvement, La Grande, OR; cookjg.ncasi@gmail.com; cookrc.ncasi@gmail.com.

Editors’ suggestion:

Coe, P.K.; Johnson, B.K.; Wisdom, M.J.; Cook, J.G.; Vavra, M.; Nielson, R.M. 2011. Validation of elk resource 

selection models with spatially independent data. Journal of Wildlife Management. 75(1): 159–170.

western Oregon and Washington. Th ese data show that NV of many sites can be improved via active 

forest management. No exhaustive studies have been conducted in western Oregon and Washington 

to identify relationships between thinning strategies and changes in NV of plant communities. Our 

work, however, suggests general patterns of NV that refl ect interactions between plant community 

composition and forage selection capabilities of Elk and, in turn, between plant succession patterns 

and potential natural vegetation (PNV) zones. Th ese have relevance for understanding and predicting 

eff ects of thinning on large ungulate nutrition and may include four patterns:

I. Th inning signifi cantly changes plant composition in mid- and late-seral stages to include more 

early-seral, shade-intolerant species and (A) these species are considerably more nutritious and 

palatable than pre-thinning shade-tolerant species, or (B) these species are neither more nutritious 

nor palatable than pre-thinning shade-tolerant species.

II. Th inning invokes little change in plant composition but increases abundance of attendant shadetolerant species, and (A) these species are nutritious and palatable, or (B) these species off er low 

nutrition and/or palatability. 

Our foraging/nutrition research evidently off ers examples of these patterns in Oregon and Washington. 

For example, many plant association groups may exhibit the IIB pattern in the Western Hemlock (Tsuga 

heterophylla) PNV, particularly those that support primarily Salal (Gaultheria shallon) and/or Swordfern 

(Polystichum munitum) understories, and in the Douglas-fi r (Pseudotsuga menziesii) zone with Madrone 

(Arbutus menziesii), Manzanita (Arctostaphylos spp.), and Tanoak (Lithocarpus densifl orus) understories 

in extreme southwest Oregon. Th inning may only increase the abundance of these highly unpalatable 

species and thus off er little opportunity to improve the NV of these communities. In contrast, our 

data suggest that thinning increases abundance of a variety of shade-tolerant and -intolerant species 

that are palatable and nutritious in the White/Grand Fir (Abies concolor/A. grandis) and Mountain 

Hemlock (Tsuga mertensiana) plant associations of the Cascades (west slope) (pattern IA). Th inning in 

these communities may off er considerable improvement of their NV. Th inning infl uences on sunlight 

and soil moisture also may alter plant phenology, chemistry, and thus nutrient levels in ungulate 

forage. Integrating data of ungulate nutritional ecology and plant succession patterns eventually will 

be necessary for developing reliable thinning strategies to improve NV and the associated carrying 

capacity of landscapes for large ungulates.

Keywords: Elk, foraging, nutrition, nutritional ecology, plant composition, plant succession, thinning, 

ungulates.
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117

Songbird Response to Alternative Forest Density Management in 

Young Douglas-fir Stands

Joan C. Hagar

Presentation Abstract

Th inning has been increasingly used in the Pacifi c Northwest to restore structural and biological 

diversity to densely-stocked young- to mid-aged forests that have been previously intensively 

managed for timber production. In the short term, thinning promotes development of understory 

vegetation, which in turn can increase habitat diversity for wildlife, particularly for songbirds. 

Th inning also has been identifi ed as a potential approach to accelerate the development of 

characteristics that are typical of older forest stands. Both the immediate and long-term response 

of wildlife and habitat to thinning is likely to be infl uenced by thinning intensity and pattern. Th e 

BLM Density Management Study (DMS) was designed to compare ecological responses among 

various thinning intensities. Th e purpose of our study was to compare songbird abundance among 

these thinning treatments to demonstrate the range of responses that might occur as a result of 

diff erent thinning practices.

We sampled breeding songbird abundance using fi xed-radius point counts at four of the DMS 

sites (Bottomline, Green Peak, O.M. Hubbard, and Ten High). We conducted bird surveys one 

year before treatment and in fi ve non-consecutive years after the fi rst thinning, including surveys at 

two sites in the fi rst season following a re-thinning treatment. Species richness increased following 

thinning, but response to thinning varied among species. Although several species diff ered 

in abundance between control and thinned stands following treatment, few species responded 

diff erentially to thinning intensity. Th e patterns of songbird abundance and species richness that 

we observed represent short-term responses to the disturbance of thinning; documenting bird 

response to variation in structural development among thinning treatments will require long-term 

monitoring.

Keywords: commercial thinning, forest structure, Neotropical migrants, songbirds.

Joan C. Hagar is a research wildlife biologist, US Geological Survey Forest and Rangeland Ecosystem Science Center, 3200 

SW Jeff erson Way, Corvallis, OR 97331; joan_hagar@usgs.gov.

Editors’ suggestion:

Hagar, J.C. 2007. Wildlife species associated with non-coniferous vegetation in Pacific Northwest conifer 

forests: A review. Forest Ecology and Management. 246(1): 108–122.

Hagar, J.; Howlin, S.; Ganio, L. 2004. Short-term response of songbirds to experimental thinning of young 

Douglas-fir forests in the Oregon Cascades. Forest Ecology and Management. 199: 333–347.
Density Management in the 21st Century: West Side Story PNW-GTR-880

118

Effects of Forest Thinning on Bird-vegetation Relationships in 

Young Douglas-fir Forests

Svetlana Yegorova

Poster Abstract

Forest thinning has been widely used in the Pacifi c Northwest as a technique to accelerate latesuccessional vegetation characteristics and promote mature forest habitats for wildlife. Th inning 

treatments aff ect tree and understory vegetation development. Th e eff ects of thinning on bird 

abundance and occurrence vary by bird species and change over time, presumably as a result of 

changes in understory and overstory vegetation after thinning. However, this assumption has rarely 

been tested. Vegetation characteristics, such as canopy cover, understory density and composition 

are frequently used in habitat modeling because they are likely to constitute both proximate cues 

to habitat selection and ultimate resources that contribute to fi tness. However, a disturbance event, 

such as forest thinning, may decouple habitat selection cues from fi tness variables. Th is study 

investigates the potential of such decoupling for eight bird species by examining dynamics in bird 

occurrence or abundance in relation to changes in vegetation characteristics within Douglas-fi r 

(Pseudotsuga menziesii) stands over 10 years since thinning. Our objectives are to: 1) determine if 

specifi c vegetation characteristics account for bird species occurrence or abundance in thinned and 

unthinned forests; and 2) explore whether the relationships between vegetation characteristics and 

bird occurrence changes over time. We conducted bird surveys at 58 point-count stations during 

six breeding seasons in a 10-year period following forest thinning. We obtained detailed local- and 

landscape-level vegetation characteristics for all bird sampling points. We accounted for imperfect 

detection and modeled occurrence or abundance of eight avian species as a function of local and 

landscape-scale vegetation characteristics with generalized linear mixed models. Preliminary results 

suggest that for some species vegetation is a good predictor of occurrence and that relationship to 

vegetation remains consistent over 10 years. However, for other species these relationships vary.

 Bird-vegetation relationships appear to be highly dynamic, even in a system characterized by 

relatively low-impact disturbance. We hypothesize that this variability is best explained by intrinsic 

population processes rather than plasticity in avian habitat selection.

Keywords: thinning, understory vegetation, overstory structure and composition, birds, habitat 

selection.

Svetlana Yegorova was a master’s degree student, Department of Forest Ecosystems & Society, Oregon State University, 

Corvallis, OR 97331.
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119

Lichen Habitat May Be Enhanced by Thinning Treatments

Heather T. Root and Bruce McCune

Heather T. Root is a botanist/analyst, US Forest Service Pacifi c Northwest Region Air Program, Siuslaw National Forest 

Supervisor’s Offi ce, 3200 SW Jeff erson Way, Corvallis, OR 97331, htroot@fs.fed.us; Bruce McCune is a professor, 

Department of Botany & Plant Pathology, Oregon State University, Corvallis, OR 97331.

Presentation Abstract

Epiphytic lichen communities have become a focus for ecologists concerned with forest health 

because lichens are particularly responsive to forest management and air quality. Furthermore, they 

can contribute substantially to the diversity and nitrogen fi xation of a stand, and play a valuable 

role in the food web of many forest-dwelling organisms. Can strategic thinning in Pseudotsuga 

-Tsuga forests increase biodiversity or hasten the development of late-successional features in 

young second-growth forests? Approximately 10 years after variable-density commercial thinning, 

N fi xing and forage lichen species richness increased and lichen community composition was 

detectably diff erent from pre-thinning data and from unthinned controls. At two sites in moist 

conifer forests of western Oregon, lichen community monitoring plots were established before 

thinning treatments; the most diverse plots in each treatment were retained as diversity islands, 

whereas the less diverse plots were treated in the thinning prescription. At one site, we found that 

lichen communities in diversity plots were quite similar to those in the surrounding treated forest, 

and that the proportion of Tsuga heterophylla in the stand was negatively associated with alectorioid 

and cyanolichen richness. At both sites, hardwood gaps and open-grown trees were positively 

associated with N fi xing (cyanolichen) species richness. At the other site, surrounding plots were 

more like diversity “leave-islands” after thinning than before. Furthermore, thinned plots had 

more hardwood gaps following the thinning. Th ese thinned plots hosted more Bryoria, Candelaria 

concolor, Leptogium polycarpum, Peltigera collina, Nephroma laevigatum and Physcia tenella than had 

been observed prior to thinning. Most of those species are hardwood associates. Th e forage lichen 

Bryoria, however, is associated with older remnant trees in these stands. Forage lichens may already 

be responding positively to the opened canopy in these stands, as evidenced by their association 

with plots having gaps in the canopy colonized by shrubs, and their increased abundance and 

frequency in 2007 in thinned plots at one of the two study sites. Th e retention of lichen hotspots 

appeared to allow rapid colonization of N fi xers onto shrubs in thinned plots. Promotion of gaps 

in the conifer overstory that are dominated by hardwoods probably stimulated richness of N 

fi xers and forage lichens by providing favorable substrates. We conclude that thinning treatments 

retaining remnants from previous cuttings, open-grown trees, and hardwood gaps have potential 

to favor lichen communities rich in cyanolichen and alectorioid species.

Keywords: community composition, diversity, epiphytes, forage lichens, nitrogen fi xing lichens, 

thinning.

Editors’ suggestions:

Root, H.T.; McCune, B.; Neitlich, P. 2010. Lichen habitat may be enhanced by thinning treatments in young 

Tsuga heterophylla-Pseudotsuga menziesii forests. The Bryologist. 113(2): 292–307.

Root, H.T.; McCune, B. 2010. Forest floor lichen and bryophyte communities in thinned Pseudotsuga menziesii 

-Tsuga heterophylla forests. The Bryologist. 113 (3): 619–630.
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120

Joyce L. Eberhart is a senior faculty research assistant and Daniel L. Luoma is an assistant professor, senior reseatch, in 

the Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR 97331.

Conservation of Ectomycorrhizal Fungi: Green-tree Retention 

Preserves Species Diversity

Joyce L Eberhart and Daniel L Luoma

Poster Abstract

Th e Demonstration of Ecosystem Management Options (DEMO) project is a large, 

interdisciplinary study designed to test the biological and silvicultural eff ects of green-tree 

retention in Douglas-fi r (Pseudotsuga menziesii) forests. Six treatments were replicated on six blocks 

in Washington and Oregon, USA: no harvest, 75 percent aggregated, 40 percent (dispersed and 

aggregated), and 15 percent (dispersed and aggregated) green-tree retention. We studied treatment 

eff ects on ectomycorrhizal fungi in three of the study blocks. Ectomycorrhizae (EM) were sampled 

by use of soil cores. Prior to tree felling, one spring and one fall set of cores were collected from 

each study unit. After the trees were cut, soil cores were again collected in the fall, a full year after 

cutting, and the following spring. A total of 432 cores were assessed. To test for treatment eff ects, 

mean number of EM morphotypes in cores, relative frequency, and species accumulation curves 

were compared among pre-treatment, control, moderate-thin, heavy-thin, clearcut, and leave 

groups. All methods of measure showed a reduction of EM in clearcut and heavy-thin treatments. 

Th e dispersed moderate-thin treatment (40 percent green-tree retention) showed less reduction in 

EM types, except in one block, where compaction during logging may have contributed to root 

mortality. Silvicultural methods that are designed to maintain high levels of biodiversity in a stand 

are relatively new in forestry. Th rough green-tree retention, EM diversity is maintained at higher 

levels than in clearcuts and we expect that retained trees will provide a legacy of ectomycorrhizal 

fungi during the development of the next stand.

Keywords: ectomycorrhizal fungi, green-tree retention, thinning, DEMO.
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121

Effects of Varying Levels of Forest Thinning on Tricholoma 

magnivelare (American Matsutake)

Joyce L Eberhart and Daniel L Luoma

Poster Abstract

Commercial matsutake mushroom (Tricholoma magnivelare) harvest in the Pacifi c Northwest 

is common in Lodgepole Pine (Pinus contorta) forests. Insuffi cient ecological knowledge of 

the mycorrhizae and mycelium has challenged monitoring of this resource. Among many 

management issues are concerns over logging practices, a lack of information on the ecology and 

habitat requirements of American Matsutake, and the potential eff ects of the type and intensity 

of matsutake harvest on future mushroom productivity. Lodgepole Pine and mixed-conifer 

stands provide habitat for growing and harvesting matsutake mushrooms, but these stands have 

developed dense understories that can increase the risk of wildfi re and disease. Th e Deschutes 

National Forest in central Oregon, USA, is implementing a plan to reduce the risk that insects, 

disease, and wildfi re will lead to large-scale loss of forest resources. Our study will monitor the 

eff ects of the vegetation treatments (tree thinning) on shiros of Tricholoma magnivelare by directly 

sampling soil and mycorrhizae obtained from plots established throughout the project area. To 

minimize impact on soil hyphae, all tree-thinning experimental areas were designated for logging 

with snow cover present and by use of a feller-buncher to yard whole trees to landings. Four blocks 

were established. Each block contained three forest cover-types with treated and untreated areas. 

Th irty shiros of matsutake per experimental unit were identifi ed, and four soil samples were taken 

from each shiro. Due to volcanic glass in these soils, it was not possible to amplify DNA using 

extraction techniques that require bead beating or vortexing. In response, we developed a quick, 

inexpensive modifi cation of Xin’s plant extraction methods. Th ese extractions were then PCRed 

using unpublished primers developed by B. Bravi that specifi cally amplify T. magnivelare. To date, 

only pre-treatment samples have been collected. Logging over snow was completed the winter of 

2010/2011, and post-treatment sampling will occur in fall 2011.

Keywords: thinning, Lodgepole Pine, American Matsutake, mycorrhizae.

Joyce L. Eberhart is a senior faculty research assistant and Daniel L. Luoma is an assistant professor, senior reseatch, in 

the Department of Forest Ecosystems & Society, Oregon State University, Corvallis, OR 97331. 
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122

Stephanie J. Wessell-Kelly is the zone silviculturist/research coordinator, USDA Forest Service, Umpqua National

Forest, Diamond Lake Ranger District-North Umpqua Ranger District, 18782 North Umpqua Hwy., Glide, OR 97443; 

swessellkelly@fs.fed.us; Deanna H. Olson is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, 

Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331.

Community Structure of Vascular Plants, Arthropods, Amphibians, 

and Mollusks in Managed Forests of the Pacific Northwest (USA)

Stephanie J. Wessell-Kelly and Deanna H. Olson

Poster Abstract

Increasing global demands on forest resources are driving large-scale shifts toward plantation 

forestry. Simultaneously balancing resource extraction and ecological sustainability objectives in 

plantation forests requires the incorporation of innovative silvicultural strategies such as leave 

islands (green-tree retention clusters). Our primary research goal was to determine how leave islands 

provide refugia for low-mobility, ecologically sensitive species in managed forests of the Pacifi c 

Northwest, USA. We examined patterns in vascular plant, arthropod, amphibian, and mollusk 

assemblages across fi ve types of forest sampling units: unthinned forest (approximately 600 trees 

per hectare [tph]), thinned forests (200 tph), and leave islands of three sizes (0.1-, 0.2-, and 0.4-

ha]) embedded in the thinned forest. Our objectives were to examine gradients in community 

associations to measured environmental variables, to describe diff erences in communities among 

the fi ve types of forest, and to identify species indicative of each type of forest.

We used two multivariate community analysis methods to describe the primary environmental 

variables and gradients driving the species composition of these communities. First, we used nonmetric multi-dimensional scaling (NMS) to ordinate sample units in species space to provide a 

graphical representation of plant, arthropod, amphibian, and mollusk community relationships 

and environmental variables. Correlations between ordination axes and environmental variables 

also were examined to determine the important drivers of community structure and composition 

for each taxonomic group. Joint plots were used to overlay environmental variables on the 

ordination, based on the correlations of the variables with the ordination axes. Ordinations were 

then rigidly rotated to maximize the loading of the strongest gradients in community variation 

on a single axis. Next, we used indicator species analysis (ISA) to characterize plant, arthropod, 

amphibian, and mollusk assemblages associated with the a priori groups of interest. Th ese a priori 

groups included the fi ve types of forest, four study sites, and two mountain ranges, the Oregon 

Coast Range and Cascade Range. Indicator values were calculated for each species within each 

group by combining information about the concentration of species abundance and faithfulness 

of occurrence in a particular group. Indicator values ranged from 0 (no indication) to 100 (perfect 

indication). A perfect indicator for a particular group was present in all sampling units for that 

group and occurred exclusively in that group. Our NMS results indicated strong gradients shaping 

vascular plant, arthropod, amphibian, and mollusk communities across study sites and across 

mountain ranges. In particular, microclimate conditions (relative humidity, ambient temperature, 

and soil temperature) seemed to be especially important in shaping species assemblages in our 

managed forest stands. Finally, ISA identifi ed indicator species for the a priori groups of interest. 
Density Management in the 21st Century: West Side Story PNW-GTR-880

123

Specifi cally, unique indicator species were found for each of the fi ve types of forest, four study 

sites, and two mountain ranges. Th e ecological processes that shape forest biodiversity operate over 

wide spatial and temporal scales. Sustaining forest biodiversity at these multiple scales requires 

that forest managers develop a deeper understanding of the underlying biological patterns and 

environmental gradients aff ecting forest communities. Forest management strategies guided by 

knowledge of these biological patterns and gradients can potentially help sustain biodiversity and 

community composition in intensively managed forests. Our results suggest that leave islands 

represent an eff ective silvicultural strategy for maintaining the environmental conditions needed 

to sustain several low-mobility taxa in intensively managed forests.

Keywords: forest leave islands, thinning eff ects, microclimate, Oregon.

Leave Islands as Refugia for Low-mobility Species in Managed 

Forest Mosaics

Stephanie J. Wessell-Kelly and Deanna H. Olson

Poster Abstract

In recent years, forest management in the Pacifi c Northwest has shifted from one based largely on 

resource extraction to one based on ecosystem management principles. Forest management based 

on these principles involves simultaneously balancing and sustaining multiple forest resource values, 

including silvicultural, social, economic, and ecological objectives. Leave islands, or green-tree 

retention clusters, have been proposed as an alternative silvicultural strategy designed to sustain the 

ecological integrity and biological diversity within intensively managed forests. However, pertinent 

questions regarding the relationship of the physical structure of leave islands to their associated 

microclimates, fl ora, and fauna remain largely unanswered. We evaluated the eff ectiveness of three 

sizes of leave islands (0.1-, 0.2-, and 0.4-ha) within a thinned forest matrix relative to thinned 

and unthinned forest in providing refugia for low-mobility, ecologically sensitive species one to 

fi ve years following forest thinning. Specifi cally, we examined diff erences in microhabitat and 

amphibian, mollusk, arthropod, and vascular plant abundance and diversity with respect to the 

size of leave islands in managed forests. By determining habitat correlates of species and functional 

group occurrence, we envision that this study will provide vital information regarding aggregated 

green-tree retention in managed forest landscapes. Our results indicate that there are treatment 

eff ects of forest thinning and leave islands relative to microclimate and some aspects of amphibian 

and arthropod density, and vascular plant diversity and ground cover. Th ese results suggest that 

leave islands may represent an eff ective sustainable forest management strategy by providing shortterm refugia for some species in managed forests of the Pacifi c Northwest, U.S.A.

Keywords: microclimate, amphibians, mollusks, arthropods, plants.

Stephanie J. Wessell-Kelly is the zone silviculturist/research coordinator, USDA Forest Service, Umpqua National 

Forest, Diamond Lake Ranger District-North Umpqua Ranger District, 18782 North Umpqua Hwy., Glide, OR 97443; 

swessellkelly@fs.fed.us; Deanna H. Olson is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, 

Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331.
Photos on facing page—Top left: headwater stream 

initiation seep area, Keel Mountain, 2008, photo by 

Paul Anderson. Top right: Small headwater stream with 

a camera case for scale, Keel Mountain, 2008. USFS 

photo by Mark Meleason. Center left: Edge of variablewidth buffer with stream, Keel Mountain, 2008, photo 

by Paul Anderson. Center right: Stream temperature 

and channel microclimate measurement station, Keel 

Mountain, 2008, USFS photo by Mark Meleason. 

Bottom left: Streamflow measurement, photo by Brad 

Catton, USFS. Bottom right: Instream wood at Keel 

Mountain. Photo by Paul Anderson.
Section 3. Riparian and Aquatic Ecosystems and Their 

Responses to Thinning and Buffers
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126

Sampling and Modeling Riparian Forest Structure and 

Riparian Microclimate

Bianca N.I. Eskelson, Paul D. Anderson, and Hailemariam Temesgen

Bianca N.I. Eskelson is a research associate, Department of Forest Engineering, Resources and Management, Oregon 

State University, Peavy Hall 280, Corvallis, OR 97331; bianca.eskelson@oregonstate.edu; Paul D. Anderson is a research 

forester, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, 

Corvallis, OR 97331; Hailemariam Temesgen is an associate professor, Department of Forest Engineering, Resources and 

Management, Oregon State University, Peavy Hall 280, Corvallis, OR 97331.

Abstract

Riparian areas are extremely variable and dynamic, and represent some of the most complex 

terrestrial ecosystems in the world. Th e high variability within and among riparian areas poses 

challenges in developing effi cient sampling and modeling approaches that accurately quantify 

riparian forest structure and riparian microclimate. Data from eight stream reaches that are part of 

the Density Management Study were used in a variety of recent studies that explored sampling and 

modeling approaches for riparian forest structure and microclimate, and the results are summarized 

here. When sixteen sampling alternatives were compared based on their performance at accurately 

estimating the number of conifer trees per hectare, conifer basal area per hectare, and height-todiameter ratio in headwater stream reaches, rectangular strip-plots outperformed all other plot 

shapes. Strip-plots oriented perpendicular to the stream generally outperformed strip-plots parallel 

to the stream. Understory vegetation layers form a critical component of forest ecosystems. Hence, 

accurate estimation of their attributes (e.g., percent shrub cover) is gaining increasing importance. 

Percent shrub cover was modeled as a function of distance to stream and canopy leaf area index 

using techniques that easily accounted for spatial dependence within and among riparian areas. 

Th e distinct ecological processes, habitats, and biodiversity of riparian areas are due in part to 

microclimate characteristics such as air temperature (Tair) and relative humidity (RH) that diff er 

from upland forests. Improved sampling designs and predictive models are needed to characterize 

riparian microclimates and their response to forest management. Height above stream and distance 

to stream were found to be important covariates in predicting mean maximum Tair in riparian areas. 

For small sample sizes, optimized sample patterns for Tair outperformed systematic sample patterns. 

Mean maximum Tair and mean minimum RH are strongly correlated, and mean minimum RH 

can be modeled as a function of mean maximum Tair and other covariates such as height above 

stream. Mixed eff ects models can account for within- and among-stream reach variability in RH. 

Application of these results can improve the quantitative estimates and reduce the costs associated 

with riparian forest structure and microclimate monitoring eff orts.

Keywords: relative humidity, air temperature, shrub cover, mixed eff ects models, copula models, 

optimized sampling design.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al. 127

Introduction

Riparian forests represent some of the most 

complex terrestrial ecosystems in the world, play 

an important role in conserving the vitality of the 

landscape and its rivers (Naiman and Décamps 

1997), and provide special habitats for birds and 

other terrestrial wildlife species. Suitable riparian 

forest management strategies and eff ectiveness 

monitoring require detailed information 

about the structure of riparian overstory and 

understory vegetation and riparian microclimate 

in order to ensure provision of suitable wildlife 

habitat, high-quality water, and other ecosystem 

services. Riparian forests are extremely variable 

and dynamic. Th e high variability within 

and among riparian areas poses challenges in 

developing sampling and modeling approaches 

that accurately quantify riparian forest structure 

and riparian microclimate.

Th e distribution and species patterns of riparian 

vegetation are related to local topography (e.g., 

height above stream channel; Naiman et al. 2005, 

p. 97). Typically, early-seral species are found close 

to the stream channel where the environment 

is characterized by low nutrient and high light 

levels. Long-lived, shade-tolerant, woody plants 

are found in greater proportions at higher 

elevations above the wet stream channel (Naiman 

et al. 2005, p. 99), resulting in high variability 

laterally from streams. Sampling methods for 

quantifying riparian vegetation structure need to 

account for variation being greater laterally from 

stream to upslope than along the stream, and for 

the potential of diff erences in vegetation structure 

on opposite sides of the stream (Marquardt et al. 

2011). 

Temperature, light, wind speed, and moisture 

are microclimate attributes that infl uence plant 

distribution through regeneration, growth, and 

mortality, as well as wildlife habitat selection. 

High productivity and species diversity of riparian 

vegetation have been attributed to favorable 

interactions of microclimate and moisture close 

to streams (Naiman et al. 2005, p. 156–158). 

Lateral gradients in microclimate with respect to 

distance from stream have been characterized and 

tend to be nonlinear, with rates of change being 

greater close to the stream channel than upslope 

(Anderson et al. 2007; Olson et al. 2007). 

However, little work has been done to improve 

sampling and monitoring approaches for riparian 

microclimate attributes, and predictive models 

for microclimate attributes are few although they 

are needed to characterize riparian microclimates 

and their response to forest management. 

Overstory and understory vegetation data as 

well as microclimate data collected at eight stream 

reaches that are part of the Density Management 

Study (Cissel et al. 2006) were used to explore 

and advance sampling and modeling approaches 

for riparian vegetation structure and riparian 

microclimate. In this manuscript, we provide an 

overview of the data collected at the eight stream 

reaches and summarize some of the studies that 

used the data to examine: 1) sampling methods 

to quantify overstory structure in riparian areas; 

2) riparian shrub cover models; 3) sampling 

and modeling approaches for air temperature in 

riparian areas; and 4) modeling and monitoring 

relative humidity in riparian areas.

Data

Data were collected at eight stream reaches 

that are part of the Density Management Study 

(DMS; Cissel et al. 2006). Th e eight stream 

reaches are located at four DMS sites: Ten 

High (TH46, TH75), Bottomline (BL13), OM 

Hubbard (OM36), and Keel Mountain (KM17, 

KM18, KM19, KM21) (fi g. 1). At each of the 

eight stream reaches, one square sample plot (72 

m × 72 m = 0.518 ha) was randomly located 

along the stream, running 72 m parallel to the 

stream and 36 m upslope on each side of the plot 

center line that ran approximately parallel to the 

stream (fi g. 2). Detailed overstory and understory 

vegetation data as well as microclimate data were 

collected in the 0.518-ha plot.
Density Management in the 21st Century: West Side Story PNW-GTR-880

128 Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al.

Vegetation Data

A stem map of all woody stems greater than 6.9 

m tall or 7.6 cm diameter at breast height (dbh) 

was created for each of the 0.518-ha plots. For 

each mapped tree, dbh, species, condition (alive/

dead), and canopy classifi cation (dominant, 

codominant, intermediate, suppressed) were 

recorded. For live trees, the crown was classifi ed 

as “live, full crown,” “partially dead crown,” or 

“dead crown,” or for trees with more than one 

crown as “two or more crowns” or “one crown 

broken off .” Standing dead trees (snags) were 

classifi ed by size (>30 m with full bole, >30 m 

without full bole, >15 m and <30 m, >6 m and 

<15 m, <6 m). At each stream reach, 24 trees (12 

on each side of the stream) were subsampled for 

height, crown diameter, height to crown base, 

and age (for details see Marquardt et al. 2011).

Information about the understory vegetation 

by taxonomic class (tree, shrub, fern, and forb) 

was visually assessed using square plots (1 m x 

1 m) every three meters along two transects 

perpendicular to the stream (at 32 m and 68 m 

as measured along the center line) and every ten 

meters along two transects perpendicular to the 

stream at two random locations (<32 m, >32 m 

and <68 m; fi g. 2). Shrubs were defi ned as woody 

vegetation less than 6 m in height. Plants less than 

one meter in height lacking a woody stem were 

classifi ed as forbs. Percent cover of low shrubs 

(<1.4 m), tall shrubs (>1.4 m), forbs, ferns, and 

seedlings was recorded for each 1-m2

 plot, as well 

as the top height of the vegetative layers (to the 

nearest meter). On the transects with the 10-m 

spacing, the 1-m2

 plots were nested within 4-m2

plots (2 m × 2 m), on which the present shrub 

species less than 6 m tall were recorded.

Figure 1—DMS sites where the eight stream reaches 

used in this study are located.

Figure 2—Layout of understory vegetation plots (1 m 

x 1 m and 2 m x 2 m) with microclimate sensors at plot 

center used in the modeling studies. Plots are arrayed 

along transect lines oriented perpendicular to a center 

line (dashed line) that runs approximately parallel to 

stream (solid line).
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Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al. 129

Microclimate Data and Canopy Closure

At the plot center and each corner of the 1-m2 

vegetation plots, estimates of percent canopy 

closure, including understory and overstory 

vegetation above 1-m height, were made 

using hemispherical detection of canopy light 

transmittance (plant canopy analyzer, model LAI2000; LI-COR Biosciences, Lincoln, Nebraska). 

Th e fi ve readings were averaged to provide a plot 

estimate of leaf area index (LAI, m2 foliage∙m-2 

ground) and the diff use non-interceptance 

(DIFN), defi ned as the proportion of visible sky. 

Th ree-channel humidity and dual-temperature 

data loggers (models GPSE 101 203 and GPSE 

301 203, A.R. Harris Ltd., Christchurch, NZ) 

were placed at each plot center of the 1-m2 

vegetation plots to record air temperature, relative 

humidity, and soil temperature for at least 48 

hours (for details see Eskelson et al. 2011a).

Synopsis of riparian structure and 

microclimate studies

Sampling methods to quantify 

overstory structure in riparian areas

A simulation study was used to explore the 

performance of sixteen sampling alternatives to 

quantify the number of conifer trees per hectare, 

conifer basal area per hectare, and conifer heightdiameter ratio (Marquardt 2010, 2011). Some 

of these sampling alternatives were designed 

to capture the variation lateral to the stream 

(perpendicular strips, alternating perpendicular 

strips, perpendicular strips on one stream side 

only), while others were designed to capture the 

variation parallel to the stream (strips parallel 

to the stream). As part of the simulation study, 

circular fi xed-area plots were randomly or 

systematically distributed in the 72-m x 72-m 

study plot that was stem mapped at each stream 

reach, and horizontal line sampling (Lynch 

2006) and sector sampling (Iles and Smith 2006) 

were employed. Each of these sampling methods 

was applied with two plot sizes and two sampling 

intensities (10 and 20 percent). Th e rectangular 

strip-plots outperformed circular fi xed-area plots, 

horizontal line sampling, and sector sampling 

in terms of accuracy. Among the rectangular 

strip-plots, alternating perpendicular strip-plots 

performed best, followed by perpendicular strips, 

and parallel strips. Narrower strip-plots tended to 

be more accurate than wider strip-plots, because 

a greater number of narrower strips may capture 

the spatial variability better than fewer wider 

strips. Alternating perpendicular strip-plots 3.6 

m wide performed best among all tested sampling 

alternatives (fi g. 3).

Although the examined sampling alternatives 

performed quite well for quantifying conifer 

density and basal area per hectare in the coniferdominated stream reaches of the study, the 

methods were not very accurate when used 

to quantify hardwood and snag abundance 

(Marquardt et al. 2012), which were minor 

components of the overall forest structure 

(Marquardt 2010).

Extending this work, Haxton (2010) explored 

the use of n-tree distance sampling to estimate 

density and basal area at the eight stream reaches. 

Th is method, which involves sampling the n trees 

Figure 3—Example of the alternate strip-plot design 

(20 percent sampling intensity). The center line (dashed) 

of the 72-m x 72-m block was oriented approximately 

perpendicular to the stream (solid line).
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130 Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al.

nearest a sample point, performed poorly relative 

to variable-radius and fi xed-radius plot methods 

that provided more accurate estimates of basal 

area and density, respectively. Th e n-tree distance 

method was negatively impacted by the spatially 

clumped distribution of trees.

Riparian shrub cover models

Understory vegetation layers contain most 

of the plant biodiversity in temperate forest 

ecosystems (Halpern and Spies 1995), and are 

of great importance for wildlife species (Hagar 

2007). Ground and shrub cover, as well as canopy 

closure, also conserve bird species richness (Miller 

et al. 2003). Accurate estimation of understory 

vegetation attributes such as percent shrub cover 

is gaining importance, and predictive models of 

understory vegetation characteristics are needed 

(Suchar and Crookston 2010). Eskelson et 

al. (2011b) modeled riparian shrub cover as a 

function of topography and overstory vegetation, 

comparing three diff erent methods: ordinary 

least squares regression, beta regression, and a 

copula model. Distance to stream and LAI were 

the most important explanatory variables in the 

models. Height above stream and interactions 

of height above stream and distance to stream 

with LAI were also signifi cant in the models. 

Th e copula model based on the beta distribution 

accounted for spatial dependence within and 

among riparian areas. Th e ordinary least squares 

regression model resulted in underpredictions of 

shrub cover, while the beta regression and copula 

models did not. All models had low explanatory 

power, which was attributed to shrub cover 

responding to processes and conditions that 

occur at a fi ner scale than the available overstory 

cover variables.

Sampling and modeling approaches 

for air temperature in riparian areas 

Riparian microclimate characteristics such as 

air temperature (Tair) and relative humidity (RH) 

diff er from microclimate in upland forests and 

provide the conditions for the distinct ecological 

processes, habitats, and biodiversity of riparian 

areas. Since intensive sampling of microclimate 

to determine the spatial variation is impractical, 

we may have to rely on predictive models of 

microclimate characteristics. Predictive models 

of Tair can be used to characterize riparian 

microclimates and their response to forest 

management. Eskelson et al. (2011a) used kriging 

with external drift for point prediction of mean 

maximum Tair. Height above stream and distance 

to stream were found to be important covariates 

in predicting mean maximum Tair in riparian 

areas, with distance to stream outperforming 

height above stream as a covariate in stream 

reaches having steeply incised channels. Adding 

covariates that describe the over- and understory 

vegetation cover to the model improved the 

prediction results. Th e importance of understory 

and overstory vegetation cover was dependent 

on the predominant cover type, for example 

understory vegetation cover variables were more 

important in stream reaches with little overstory 

canopy closure.

Microclimate characteristics have typically been 

collected at set intervals along transects across 

stream-riparian gradients (Olson et al. 2007). 

Since the strongest stream eff ects on Tair and RH 

have been observed within 10 to 15 m of the 

stream channel (Rykken et al. 2007; Anderson 

et al. 2007) it has been hypothesized that 

microclimate sensor density should be increased 

close to the stream channel. Eskelson et al. 

(2011a) optimized the sampling patterns for Tair 

within the eight stream reaches using statistical 

methods that eff ectively inferred the spatial 

patterns (a simulated annealing search algorithm 

in combination with kriging). Th e performance 

of sample patterns based on optimization was 

compared to systematic sample patterns for 

which the sample points were evenly spread across 

four transects. Th e optimized sample patterns 

outperformed the systematic samples for small 

sample sizes. Th e optimized samples tended to 

have a higher density of sample points on three of 

the four transects, and points close to the stream 
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Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al. 131

on the remaining transects. Th is suggests that 

it may be advantageous to focus microclimate 

monitoring in riparian areas on a few transects 

with dense sensor deployment instead of many 

transects with sparse sensor deployment, and 

that it is important to deploy sensors close to the 

stream (fi g. 4).

Modeling and monitoring relative 

humidity in riparian areas

Sensors to sample and monitor RH are more 

expensive than sensors that measure Tair. We 

have explored the possibility to benefi t from the 

strong correlation between mean maximum Tair

and mean minimum RH (fi g. 5), and modeled 

RH as a function of Tair, height above stream, and 

DIFN. Mixed eff ects models accounted for the 

within- and among-stream-reach variability in 

RH. Based on a simulation study that examined 

diff erent subsample sizes of RH, we found that 

a minimum of three to fi ve subsamples of RH 

per stream reach seem suffi cient for estimating 

the random eff ects for localizing the mixedeff ects model (Eskelson et al. 2013). We are 

currently working on a model that incorporates 

RH measurements from previous years into the 

model. Application of these models can greatly 

reduce the costs associated with microclimate 

monitoring eff orts.

Discussion and Management 

Considerations

Th e data set collected at the eight stream 

reaches that was used for the above studies is very 

detailed and hence provides unique opportunities 

to explore and advance sampling and modeling 

methods for riparian structure and microclimate. 

Microclimate, understory vegetation cover, and 

overstory vegetation cover are strongly linked 

with each other. Th e ability to adequately 

quantify under- and overstory vegetation cover 

is needed to improve microclimate models. 

However, the presence of understory vegetation 

is also infl uenced by the prevailing microclimate 

conditions that need to be considered, in 

Figure 4—Illustration of optimized 

sampling designs for characterizing 

gradients in air temperature in riparian 

zones based on subsampling from a 

systematic, gridded array of potential 

locations (SYST) or from a statistically 

derived distribution of points that 

accounts for the inherent spatial 

correlation (Kriging and estimated 

variogram, KVAR) at two intensities 

of sampling—either m = 15 or m = 25 

sample points. Regardless of method or 

intensity, the optimized sampling designs 

allocate more sensors to locations close to 

the stream, and fewer sensors upslope of 

the stream. Solid square, sample location 

within 15 m of stream; open square, 

distance to stream of sample location is 

greater than 15 m.
Density Management in the 21st Century: West Side Story PNW-GTR-880

132 Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al.

addition to the interactions between understory 

and overstory vegetation cover. Understanding 

the intricate linkages among overstory vegetation 

structure, understory vegetation structure, and 

microclimate conditions in riparian areas will 

allow improvement of sampling and modeling 

approaches.

Stream to upslope gradients of tree species 

composition and density have been reported 

(Minore and Weatherly 1994). Sampling methods 

in riparian areas need to be able to capture this 

lateral variation. We have demonstrated that 

alternating, rectangular strip-plots oriented 

perpendicular to the stream provide the most 

accurate estimates of conifer density and conifer 

basal area, and outperformed circular fi xedarea plots and strip-plots parallel to the stream 

(Marquardt et al. 2011). However, sampling 

methods that quantify minor components of 

riparian forests such as hardwood and snag 

abundance still need further improvement, since 

the sampling approaches that work well for 

quantifying abundant conifers are not appropriate 

to quantify the abundance of rare features such as 

snags and hardwoods (Marquardt et al. 2012).

Improved models of understory vegetation cover 

in riparian areas will provide important insights 

into availability of wildlife habitat and food 

sources. Similar to the stream-upslope gradients 

observed for overstory tree composition and 

density, stream-upslope gradients for understory 

vegetation have been observed (Pabst and Spies 

1998). Th ese gradients can be incorporated 

into models, by including covariates such as 

Figure 5—Relationships between 

summer daily maximum air 

temperature and daily minimum 

relative humidity for a stream 

reach (GP42): a) observed average 

daily values from July 1 through 

September 15, 2006; and b) linear 

regression and 95-percent confidence 

interval for daily minimum relative 

humidity versus daily maximum air 

temperature.
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Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al. 133

distance to stream and by accounting for spatial 

correlation. Th e poor explanatory power of the 

shrub-cover models developed by Eskelson et al. 

(2011b) was attributed to the fact that overstory 

vegetation variables, which were used as covariates 

in the models, respond to processes at diff erent 

scales than understory vegetation cover. Since 

the variability of soil conditions in riparian zones 

plays a major role in vegetation colonization 

and establishment and in determining plant 

productivity and diversity (Naiman et al. 2005, p. 

92–93), variables describing microsite conditions, 

soil nutrient availability, and soil moisture may 

be necessary predictors in understory vegetation 

cover models. It should be investigated whether 

variables describing microsite conditions can 

improve the explanatory power of understory 

vegetation cover models.

Many of the microclimate variables are 

highly correlated. A good understanding of the 

relationships among individual microclimate 

characteristics may allow focusing monitoring 

eff orts on a single variable such as Tair with 

increased sampling intensity. Th e development 

of RH models based on Tair measurements will 

greatly reduce microclimate monitoring costs 

by reducing necessary RH measurements within 

a stream reach. Developing similar models to 

predict soil temperature (Tsoil) as a function of 

Tair will allow further reduction in monitoring 

costs. However, the correlation between Tair and 

Tsoil is not as strong as the correlation between 

Tair and RH. Hence, model predictions of Tsoil 

are expected to be less accurate than those of 

RH. Nevertheless, the development of RH 

and Tsoil models that incorporate measurement 

information from previous years are expected to 

improve effi ciency of microclimate monitoring 

tremendously.

Monitoring riparian forest structure and 

microclimate for purposes of general habitat or 

watershed assessment or in relation to specifi c 

forest management activities will benefi t from 

sampling protocols that account for the distinct 

physical and biological attributes and processes 

that distinguish riparian areas from adjacent 

terrestrial environments. Emerging from the 

research summarized above, we make the 

following suggestions for consideration by those 

developing riparian monitoring protocols for 

conifer-dominated headwater stream reaches:

1. For vegetation characterization, employ strip 

sampling oriented perpendicular to the stream 

reaches to capture important gradients from 

the stream channel through the riparian zone 

up into the upslope terrestrial zones.

2. For a given intensity of strip sampling 

(proportion of total area sampled), a greater 

number of narrow strips per length of sampled 

reach may provide more accurate estimates 

than fewer wider strips.

3. If sampling both sides of a reach, alternating 

the placement of strips on either side of the 

reach may provide better estimates.

4. Monitor microclimate using transects running 

lateral to the stream reaches, with the density 

of sensors being higher close to the stream to 

capture steep near-stream gradients.

5. If both air temperature and relative humidity 

are of interest, consider a two-phase sampling 

design in which relatively inexpensive air 

temperature measurements are made at a higher 

intensity (more sample points) and relatively 

expensive humidity measurements are made 

at a lower intensity (a subset of points). Th e 

strong empirical correlations between air 

temperature and relative humidity can be used 

to enhance the estimate of relative humidity 

when humidity is measured at a subset of the 

temperature monitoring locations.

6. If important structural elements such as 

snags or hardwoods occur infrequently or in 

patchy distribution, they may be estimated 

using perpendicular strip-plots as previously 

described, but the precision of estimates is 

likely to be lower; more precise estimation 

may require diff erent sampling strategies 

which remain somewhat poorly defi ned. 
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134 Sampling & Modeling Riparian Forest Structure & Microclimate Eskelson et al.

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Citation:

Eskelson, Bianca N.I.; Anderson, Paul D.; Temesgen, Hailemariam. 2013. Sampling and modeling riparian forest structure 

and riparian microclimate. In: Anderson, Paul D.; Ronnenberg, Kathryn L., eds. Density management for the 21st century: 

west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacifi c 

Northwest Research Station: 126–135.
Density Management in the 21st Century: West Side Story PNW-GTR-880

136

A Simulation Framework for Evaluating the Effect of 

Riparian Management Strategies on Wood in Streams: 

An Example Using Oregon’s State Forest Riparian 

Management Regulations

Mark Meleason, Jeremy Groom, and Liz Dent

Abstract

One objective of the Oregon State Forest riparian management strategies is to provide a longterm supply of wood to streams. We explored this objective as a case study by comparing the 

predicted wood loads from a riparian forest managed in accordance with Northwest Oregon State 

Forest Management Plan to an unmanaged riparian forest. We obtained riparian tree inventories of 

plots from an Oregon Department of Forestry’s Riparian Function and Stream Temperature Study 

site. Th e site’s overstory was measured before and after harvest conducted according to the riparian 

management strategies. We used the pre- and post-treatment data as initial conditions for 200-year 

growth simulations in the forest growth model PNW Zelig. Th e forest model results were then 

used to predict wood volume in the stream from two riparian management scenarios using the 

model OSU StreamWood. We found that the stream wood volumes were almost identical in the 

two simulations, suggesting that at least for this particular site, Oregon’s state riparian regulations 

are predicted to provide a long-term supply of wood to streams similar to that in an unmanaged 

riparian forest.

Keywords: large wood, LWD, OSU StreamWood, riparian, management, simulation.

Introduction

Wood is an integral part of streams in the Pacifi c 

Northwest (Bisson et al. 1987). Wood can enter 

the channel from the adjacent riparian forests, 

by fl uvial transport from upstream, and from 

upslope sources. Management plans for upslope 

forests can indirectly infl uence wood recruitment 

to streams by increasing geomorphic processes 

such as landslides and debris fl ows; however, best 

management practices seek to minimize these 

events. In contrast, management of riparian 

forests can directly infl uence the long-term 

supply of wood to streams, and management 

plans typically include this objective. 

Empirical evaluation of riparian management 

prescriptions is diffi cult, due in part to the time 

scales involved to monitor their performance. 

Also, given the variation in local site conditions 

such as slope, aspect, forest structure, and 

temporal pattern in weather and stream fl ow, it is 

diffi cult to generalize the results to a broader scale. 

In addition, inferences drawn from observational 

studies are generally limited to the sites and time 

period of the study. 

Simulation modeling is one useful tool to 

investigate the generalizable eff ects of riparian 

forest prescriptions on wood in streams. By 

Mark A. Meleason is the riparian and aquatic specialist for the State Forests Division, Jeremy Groom is the monitoring 

coordinator for the Private Forests Division, and Liz Dent is deputy chief of the State Forests Division at the Oregon 

Department of Forestry, State Forests Division, 2600 State St, Building D, Salem, OR 97310; mark.meleason@state.or.us; 

jeremy.groom@state.or.us 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Evaluating Riparian Management Strategies on Wood in Streams Meleason et al. 137

defi nition, simulation models are a gross 

simplifi cation of reality. In fact, the often-quoted 

phrase by the famous statistician G.E.P. Box 

“all models are wrong but some are useful” was 

restated in an expanded version that is worth 

repeating: “Models of course, are never true, 

but fortunately it is only necessary that they be 

useful. For it is usually needful only that they not 

be grossly wrong” (Box 1979). 

Th e development of simulation models involves 

many trade-off s, such as the spatial extent (local 

or regional), the temporal scope (seconds to 

centuries), and the selection of processes to 

include or exclude. Th e design of a model must 

be closely aligned with the purpose of the model 

(Mankin et al. 1975). In this light, the OSU 

StreamWood model was designed to explore 

the long-term implications of riparian forest 

management strategies on wood in streams. 

In this paper, we use simulation modeling to 

explore the eff ectiveness of the Oregon State 

Forest riparian management strategies (Oregon 

Department of Forestry 2010) in providing 

long-term recruitment of wood to streams. 

Our approach involves isolating the “treatment 

eff ect” by comparing a reference simulation 

to one or more simulated scenarios that diff er 

from the reference by exactly one factor. Th e 

two simulations, treatment and reference, are 

identical in all respects (e.g., stream and initial 

forest conditions) save for the application of 

the treatment, which in this application is the 

riparian management prescription. Although the 

riparian management prescription is composed 

of numerous components (e.g., number and 

width of subzones, harvest protocols, and other 

rules), it is the overall performance of the riparian 

treatment that we are evaluating. Indeed, 

individual actions within the prescription could 

be evaluated in a similar manner. Our approach 

involved comparing total wood volume (volume 

of all logs that intersect at least one bank at a 

given place and time) from a riparian area 

with and without the management prescribed 

for Oregon State Forests. Th e riparian plots 

used in this study were measured for Oregon 

Department of Forestry’s Riparian Function and 

Stream Temperature study (Dent et al. 2008; 

Groom et al. 2011a, 2011b; referred to hereafter 

as “RipStream”). 

Methods

Model Description 

A brief overview of the model OSU StreamWood 

is provided here; please refer to Meleason (2001) 

for details. It is an individual-based stochastic 

model that operates at an annual time step. Tree 

recruitment as wood to the stream channel from 

the riparian forest can be provided by a forestgap model built within OSU StreamWood, or by 

importing the results from other forest growth 

models. In our case, we modifi ed the model 

to import results from the Pacifi c Northwestspecifi c growth models PNW ZELIG (Garman 

et al. 1992) and ORGANON (Hann 2011). For 

each simulation year and iteration, each riparian 

area was populated with trees that died in that 

simulation interval. Each dead tree had a known 

species, diameter, and height from the forest 

model and was randomly assigned a riparian x-y 

position and tree-fall angle. Th e riparian area was 

subdivided into three riparian subzones on each 

side of the stream. Each subzone was assigned its 

own width, tree-fall regime (random), and tree 

mortality fi le. Trees enter the channel if they 

intersect the channel given the angle of fall and 

distance to channel relative to their height. OSU 

StreamWood subjects trees recruited into stream 

channels to breakage upon entry. Th ose logs at 

least partially within the channel are subjected to 

in-channel processes of breakage, movement, and 

decay (fi g.1). Minimum log dimension, which 

can be defi ned prior to simulation, was set to 1 m 

in length and 10 cm in diameter. Th e model runs 

under a Monte Carlo procedure and results are 

expressed as a mean and standard deviation or as 

a frequency distribution of wood for a given year. 
Density Management in the 21st Century: West Side Story PNW-GTR-880

138 Evaluating Riparian Management Strategies on Wood in Streams Meleason et al.

Figure 1—Fate of a log within OSU StreamWood. Trees 

that fall into the channel, which depends on distance 

to the channel and fall angle, are subjected to treeentry breakage. For each annual time step, all logs that 

intersect at least one bank are subjected to a sequence 

of procedures representing in-channel dynamics. If 

the log is equal to or greater than the minimum size 

criteria (user-specified and set to 1-m length and 10-cm 

diameter for this study), then it is passed to the breakage 

function, otherwise it is “retired” (removed from further 

consideration). Breakage is a two-step function: does the 

log break and if so, then what are the sizes of the new 

logs? Next, new logs that meet minimum size criteria and 

logs that did not break during this cycle are subjected 

to the movement function. Movement is also a two-step 

process—does the log move and if so, how far? Logs 

that move out of the system are retired. Finally, logs 

are “decomposed” and those that meet the minimum 

size criteria are tallied for the results of this reach for 

this year. Both breakage and movement are stochastic 

functions that rely on uniform random numbers to 

determine their outcome.

Riparian Sample Sites 

Th e RipStream study was conducted between 

2002–2010 and included pre- and posttreatment surveys of a suite of riparian and stream 

variables at 33 sites in Oregon’s Coast Range. 

One key objective of this study was to assess the 

performance of state and typical private riparian 

forest practices on stream temperature in western 

Oregon (Dent et al 2008; Groom et al. 2011a, 

2011b). Another key objective was to determine 

whether current management approaches were 

eff ective in maintaining large wood recruitment 

to streams. 

For the analysis reported here, we selected 

three sites on Oregon State Forest lands (fi g. 2). 

Th e proportion of the riparian forest removed 

(pre- versus post-treatment) was assessed for all 

three sites (fi g. 3), but the simulation of wood 

recruitment was considered for site 5301 only, 

which was a second-growth stand from a clearcut 

with a stand age of 48 years and an active channel 

width of 5 m. Each site consisted of an upstream 

reference and a downstream treatment area (fi g. 

4). Each of these areas contained two riparian 

plots, one on each side of the stream. Each 

riparian plot consisted of fi ve sample zones 30 

m in length (paralleled to the stream) and 52 m 

wide, for a total plot area of 0.79 ha (fi g. 5). All 

trees (dbh ≥ 14 cm) were tallied within each zone. 

In addition, all seedlings (dbh < 14 cm) were 

tallied by species within six, 42-m2

 plots within 

each sample zone. Vegetation data were collected 

pre-treatment for all four riparian plots and for 

the treatment riparian plots in the year following 

harvest. For site 5301, very little windthrow was 

noted in the post-treatment survey, so that the 

standing tree survey refl ected the management 

prescription.

Th e treatment reaches on the three selected 

study sites were subjected to harvest according to 

the Northwest Oregon State Forests Management 

Plan (Oregon Department of Forestry 2010; 

table 1), which defi nes unique management 

prescriptions for each of three riparian subzones. Th ese sub-zones are parallel to the stream 

channel. Our perpendicularly defi ned sampling 

zones did not match these parallel sub-zones, so 

we reconfi gured our riparian data to conform to 

State Forest harvest strategies. Since our riparian 

plot data included slope distance of each tree to 

the stream, we were able to assign trees to one 

of the three parallel riparian sub-zones defi ned 

by slope distance (fi g. 5): streambank (0 to 8 

m), inner (9 to 30 m), and outer (31 to 52 m) 

management zones (table 1). 
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Evaluating Riparian Management Strategies on Wood in Streams Meleason et al. 139

Figure 2—Location of three state 

forest sites used in this work.

Figure 3—Cumulative basal areas 

by distance from stream for selected 

state forest harvest sites. The portion 

of the riparian forest removed 

through the riparian management 

strategies is the difference between 

the pre- (solid line) and posttreatment (dash line) curve for each 

site. The dark lines at 8 m and 30 m 

identify the widths of the riparian 

subzones, each of which have their 

own management prescriptions 

(table 1). Of the three sites, 5301 

was selected for the simulations 

reported in the text.
Density Management in the 21st Century: West Side Story PNW-GTR-880

140 Evaluating Riparian Management Strategies on Wood in Streams Meleason et al.

We created a tree list (with corresponding 

expansion factors) for each of the three riparian 

sub-zones per riparian plot including seedlings 

from the regeneration plots. Th ese riparian subplots were then used as the initial conditions 

for the forest simulations using PNW ZELIG 

and ORGANON. Th e dead tree fi les produced 

by the forest models were then used as input to 

OSU StreamWood.

Simulation of Riparian Forest Growth 

OSU StreamWood’s prediction of wood in 

streams depends in part on the input from 

a forest model. In an eff ort to increase our 

confi dence in the forest model results (e.g., basal 

area and tree density through time) as inputs to 

OSU StreamWood, we compared the two forest 

models, ORGANON and PNW Zelig. We used 

the pre-treatment sub-plots for the lower reach as 

Figure 4—Harvest plot layouts and extensions. 

Each RipStream site had two riparian plots 

in the reference (upstream; plots 3 & 4) and 

treatment (downstream; plots 1 & 2) areas. 

These plots are depicted in dark grey. We 

extended these plots (light grey) by doubling 

the data in associated riparian plots to assist 

in modeling down wood recruitment in these 

systems. Upstream reference reaches were 

approximately 330 m in length. Treatment 

reach lengths varied from 300 m to 1500 m 

(1460 m for site 5301).

Figure 5—Conversion of 

the RipStream data to initial 

conditions used in OSU 

StreamWood. Riparian plot layout 

in the RipStream study consisted 

of a 52-m by 150-m riparian zone 

divided into five 30-m strips. All 

trees >10 cm dbh were measured. 

A total of six 0.01-acre (3.7-m 

diameter) shrub sub-plots were 

placed within each 30-m strip at 

8-m intervals. Each shrub-sub 

plot included measurement of tree 

seedlings (<14 cm dbh) and vegetation cover (A) The riparian forest treatment that was applied defined three riparian 

management prescriptions that differed by sub-zones: 0–8 m, 8–30 m, and 30–52 m (B; table 1).

Table 1—Definition of Northwest Oregon State Forest Management Plan (Oregon Department of Forestry 2010) 

management zones.

Management zone Distance to bank Prescription

Streambank zone 0 – 8 m (0 – 25 ft) No cutting

Inner 8 – 30 m (25 – 100 ft) Limited entry, manage for mature forest conditions

Outer 30 – 52 m (100 – 170 ft) Depending on streambank zone conifer density, leave 15–70 

conifers / 1000 ft (305 m)
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Evaluating Riparian Management Strategies on Wood in Streams Meleason et al. 141

initial conditions for both models. Simulations 

were for 100 years (100 iterations for PNW 

Zelig) and the results were compared graphically. 

In an eff ort to assess the consistency between preand post-treatment riparian forest simulations, 

we compared projected basal areas from PNW 

Zelig. For these runs, which were used in the 

simulation experiment described below, the 

simulations were for 100 iterations of 200 years, 

and we compared the results graphically. 

Influence of Oregon’s State Forest 

Riparian Management Strategies on 

Long-term Wood Supply 

Th e purpose of our simulations was to assess 

the eff ect that the Oregon Forest Practices for 

state lands have on the long-term supply of wood 

to streams. Our approach involved comparing 

stream wood volumes attributed to the pre- and 

post-treatment (table 1) riparian forests observed 

at site 5301. We simulated a 4-reach system 

arranged contiguously, with the two upstream 

plots as the reference and lower two reaches as 

the treatment (fi g. 4). Reaches were 152 m long 

(width of the measured plot along the stream, fi g. 

5) with bankfull widths of 5 m, with no wood in 

the channel at the beginning of the simulation. 

Th e tree mortality output from PNW Zelig was 

used as input to OSU StreamWood. For the pretreatment run, we populated the riparian plots 

with the 1-year pre-harvest mortality data, which 

consisted of 12 unique data fi les (3 sub-zones for 

each riparian plot, 2 riparian plots for each reach 

type, 2 reach types—treatment and reference). 

For the treatment simulation, we replaced the 

treatment reaches with six 1-year post-treatment 

mortality data fi les. Both simulations were for 

500 iterations of 200 years. We compared the 

total wood volume in the lower reach between 

simulations of the pre-treatment and posttreatment riparian forests. 

Validation

Our primary goal was to isolate the relative 

impact of a harvest treatment on total wood volume 

by comparing the results of two simulations that 

diff er by management prescription. A question 

that arises is whether our predictions could be 

compared to empirical fi ndings. Validation of 

our simulation results, as compared to empirical 

data, cannot be done directly because of the time 

scales involved. However, our wood volume 

estimates should be at least reasonable in the 

broader context when compared to observed 

wood volume estimates in streams subjected to 

a similar riparian management regime. To this 

end, we obtained wood data from the stream 

habitat surveys collected by Oregon Department 

of Fish and Wildlife as part of their Aquatic 

Inventories Project. Th ese data were collected 

between 1998–2008 using the Aquatic Inventory 

Protocol (Moore et al. 2008). We obtained data 

on total wood volume for 142 streams that were 

within Oregon state forest lands and subjected to 

the management practice used in our treatment 

(table 1). We summarized these data graphically, 

and visually compared them to simulation results. 

Our intent here was to assess whether the model 

predictions are similar enough to the observed 

data to be considered reasonable.

Results

PNW Zelig and ORGANON 

We visually compared predicted basal areas of 

standing trees through time from the two forest 

models for each of the three riparian sub-zones 

(fi g. 6, inner zone not shown). Th e greatest 

divergence between the two models was for the 

streamside zone and least for the outer zone. Th e 

inner zone was dominated by Alnus rubra (Red 

Alder, 95 percent of the basal area) and the outer 

zone was dominated by Pseudotsuga menziesii 

and Tsuga heterophylla (Douglas-fi r and Western 

Hemlock, 93 percent of the basal area).

Riparian Forest Simulations 

Prior to treatment, the four plots from site 5301 

had a mean basal area of 45 m2

∙ha-1, 544 trees per 

ha, and a mean stand age of 48 years. Th e riparian 
Density Management in the 21st Century: West Side Story PNW-GTR-880

142 Evaluating Riparian Management Strategies on Wood in Streams Meleason et al.

treatment reduced basal area by 15 percent in 

plots 1 and 2 (fi g. 3). Pre- and post-treatment 

simulations for the sub-zones predicted similar 

stand development, although the pre-treatment 

had slightly greater basal area and number of 

trees through the 200-year simulation (fi g. 7). 

Pre- and Post-treatment Wood 

Volumes

Mean total wood volume through time was 

virtually identical between the two riparian 

forest management scenarios (fi g. 8). Mean 

wood volumes increased through time, as did 

the variability about the mean. By year 200, the 

mean wood volume was 98 m3∙100 m-1 (standard 

deviation = 33 m3∙100 m-1). Th e coeffi cient of 

variation (standard deviation divided by the 

mean) ranged from 0.38 early in the simulation 

to 0.33 by year 200. To further explore the 

variability within our simulations, we plotted 

box plots for every 10th year of the simulation 

(fi g. 9). Although the maximum wood volumes 

increased with simulation year, the minimum 

was consistently below 20 m3∙100 m-1 for the 

fi rst 100 years and mostly below 30 m3∙100 m-1

for the remaining time periods for both the preand post-treatment simulations. 

Validation

Although not directly comparable, the model 

results do appear to be reasonable when compared 

to the wood volumes from wood surveys in 

Oregon state forest lands (fi g. 11). Th e median 

total wood volume was 25 m3

∙100 m-1 from 

the fi eld data, which was similar to the median 

wood volume of the simulated reach (26 m3∙100 

m-1, fi g. 9) at simulation year 60. Th e greatest 

diff erence is the narrow range in wood volumes 

from the simulations. 

Discussion

Th e results of our simulation experiment 

suggest that the state forest management plan 

strategies could maintain in-stream wood in 

this stream as compared to an untreated stand. 

Additional sites would need to be examined to 

extend this conclusion to other state forests. 

Conceptually however, these regulations (table 

1) appear adequate to maintain long-term supply 

of wood to streams. Th e probability of a tree 

falling into the stream depends on its height 

Figure 6—Comparison of ORGANON and PNW 

ZELIG simulations for the streambank and outer pretreatment riparian sub-zones.

Figure 7—PNW ZELIG forest simulations of mean 

basal area for (a) streambank and (b) outer riparian 

management zones pre- and post-treatment. All 

simulations were identical in environmental and 

site conditions save for the initial tree populations. 

Tree mortality rates vary through time as the forest 

matures. Those trees that died are imported into OSU 

StreamWood where tree entry to the stream is simulated.
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Evaluating Riparian Management Strategies on Wood in Streams Meleason et al. 143

relative to its distance to the stream. For forests 

<200 years old, approximately 90 percent of the 

entry events occurred within the fi rst 30 m from 

streams in both a simulation study (Meleason et 

al. 2002) and an observational study (McDade 

et al. 1990). Maximum source distance equals 

the maximum eff ective height of the tree species, 

although the likelihood of a tree falling and 

entering the stream decreases substantially with 

distance from the stream. Assuming a completely 

random tree-fall regime, approximately a third of 

Figure 8—Mean total stream wood volume 

(± 1 standard deviation) for the pre- and 

post-treatment simulations using OSU 

StreamWood. All simulations were identical 

in stream and riparian conditions save for 

potential dead trees recruited to the channel, 

which were determined in the forest model 

simulations. Total wood volume includes the 

volume of all logs that intersect at least one 

bank.

Figure 9—Post-treatment 

Zelig-simulated total wood 

volume for the downstreammost reach (n = 500 

iterations). The lower and 

upper boundary of the box 

represent the 25th and 75th 

percentile, and the whiskers 

represent the 10th and 90th 

percentiles. The median (solid 

line) and mean (dotted line) 

are represented.

the wood volume would be estimated to originate 

within 6 m of the stream and half the total 

volume would originate within 10 m of the bank 

for a 200-year-old riparian stand (Meleason et al. 

2003). In the state management plan (table 1, 

Oregon Department of Forestry 2010), the 8-m 

streambank subzone is a no-cut area and could 

potentially contribute more than a third of the 

potential wood recruitment assuming a random 

tree fall regime. 
Density Management in the 21st Century: West Side Story PNW-GTR-880

144 Evaluating Riparian Management Strategies on Wood in Streams Meleason et al.

Figure 10—Cumulative frequency of 

post-treatment reach volumes for the 

lower-most reach for simulation years 

50, 100, and 200 (n = 500 iterations). A 

cumulative frequency of 50 is the median 

wood load, where half the iterations were 

greater than and half were less than the 

wood volume, which corresponds to the 

median line in fig. 9. The median wood 

loads went from 20 m3∙100-1 m at year 

50, to 45 m3∙100 m-1 at year 100, to 91 

m3∙100 m-1 at year 200.

Figure 11—Wood survey results for Oregon coastal 

streams within Oregon State Forests collected by the 

Oregon Department of Fish and Wildlife (n = 124). 

The mean total wood volume was 33 m3∙100 m-1 and 

the median was 25 m3∙100 m-1. The lower and upper 

boundary of the box represent the 25th and 75th 

percentile, and the whiskers represent the 10th and 90th 

percentiles. The median (solid line) and mean (dotted 

line) are also represented.

Th e eff ectiveness of these regulations in 

providing a long-term supply of wood to streams 

would depend on the degree to which the 

harvest in the inner subzone reduces long-term 

recruitment. For RipStream site 5301, only 15 

percent of the basal area was removed during the 

treatment and most of this came from the outer 

riparian subzone (>30 m from the stream bank). 

Th is level of harvest appeared to have very little 

eff ect on wood recruitment to the steam.

Th e riparian forests considered here were 

around 50 years old when the treatment was 

applied, so very large riparian trees were initially 

absent. Th e treatment had very little impact 

on the forest structure (fi g. 3), so the reference 

and treatment forests that did develop through 

time were very similar. Th e performance of these 

regulations on older riparian forests is a topic 

worthy of further investigation.

Model Merits and Management 

Implications 

Th e use of ORGANON as input to OSU 

StreamWood to address the question investigated 

here would be a gross misuse of that model. 

ORGANON was not designed to grow alderdominated stands, such as those in our site 5301 

or stands >120 years old as we have modeled here 

(Hann 2011). Th e purpose of our comparison 

of forest models was to assess whether they were 

suitable for our particular application. If the 

long-term projections of basal area were similar, 

we could have compared other forest model 

attributes such as mortality rates, tree size, and 

species composition. Ultimately, however, the 

goal was to compare the results of the simulation 

experiment (e.g., relative performance of the 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Evaluating Riparian Management Strategies on Wood in Streams Meleason et al. 145

two riparian management scenarios on wood 

volume in the stream) to see if the selection of 

forest model infl uenced the fi nal interpretation. 

Although ORGANON is a highly versatile 

model that has proven to be useful for decades, 

it was not suited for our particular application. 

Although we are not aware of an ideal forest model 

for Pacifi c Northwest riparian forests, PNW 

Zelig seemed to provide reasonable trajectories 

of stand development. Since this model has a 

natural seedling recruitment component, longterm simulations were possible. Other questions, 

such as those specifi c to plantation forests, might 

be better addressed with ORGANON. In OSU 

StreamWood, each riparian subzone can be 

associated with a unique forest mortality list, 

which can be produced by various forest models.

Ecological models are gross simplifi cations of 

reality. Th e usefulness of ecological models, given 

our understanding of the processes involved and 

data available, may be seen as “what-if” gaming 

(Haefner 1996). Although they will always 

be inadequate and limited, they do provide a 

means to investigate challenging questions that 

are virtually impossible otherwise. For example, 

these results provide one means of investigating 

the long-term consequences of various riparian 

management strategies on wood loading in 

streams. Th e procedure involved comparing the 

outcome of two simulations that are identical save 

for the one aspect under investigation—namely 

the riparian management prescription. It would 

be diffi cult to assess this question empirically, due 

in part to the time scales involved. In addition, 

observational studies are specifi c to the sites 

considered unless an adequate sample size can be 

randomly drawn from a population of sites. Even 

if this were possible, it would be diffi cult to isolate 

the treatment eff ect from additional confounding 

variables. If the catch phrase for models is “all 

models are wrong but some are useful”, perhaps 

an appropriate catch phrase for observational 

studies is that “observational studies are relevant 

to a time and place; their applicability to another 

time or place may vary”. 

Th is simulation study illustrates that a 

management prescription applied to a given site 

has the potential to produce a range of wood 

volumes in the stream, and this potential range 

can vary through time (fi g. 9). Th ese simulations 

predicted an overall increase of the range of 

volumes over the 200-year period. Although the 

minimum wood volume did increase slightly 

through time, the majority of this increase was 

with the maximum wood volumes through 

time (fi g. 9). Th is suggests that given the same 

forest structure and stream conditions, there is 

always a chance that a given prescription can 

result in a low volume of wood in a given reach. 

Th is has a direct implication for riparian forest 

management targeted at obtaining a desired 

range of wood volume in streams. A reach with 

a low volume of wood does not necessarily 

suggest that the riparian management strategy 

was inadequate nor does an observed high wood 

volume necessarily suggest that the prescription 

is suffi cient. Rather, there is a likelihood of 

obtaining a given volume through time. One way 

of evaluating the likelihood of a given volume is 

to develop cumulative probability distributions 

for a given time period (fi g. 10). For example, the 

simulated results suggest that the management 

prescription, given these forest and stream 

conditions, would have a 50 percent chance of 

obtaining wood loads of 20 m3

∙100 m-1 at year 

50, 45 m3

∙100 m-1 at year 100, and 91 m3∙100 

m-1 at year 200 (fi g.10). Th is approach can be 

used to assess the relative performance of two or 

more simulated management prescriptions. In 

this study, the two scenarios—the treatment and 

reference—produced almost identical results so 

we have chosen not to include both in fi gure 10. 

Validation 

We concluded from our coarse-level assessment 

that the simulation distributions of total wood 

volume compared reasonably with the empirical 

wood volumes. Th e greatest diff erence between 

the simulation and fi eld data was that the range 

of wood volumes was narrower in the simulation 
Density Management in the 21st Century: West Side Story PNW-GTR-880

146 Evaluating Riparian Management Strategies on Wood in Streams Meleason et al.

results than in the fi eld estimates. Th ere are 

several aspects of our approach that did not lend 

themselves to direct comparison with empirical 

data. For example, in the simulation we held all 

stream (e.g., 5-m active channel width) and forest 

(e.g., site index) conditions constant to isolate the 

relative performance of the treatment—the goal 

of this work. Th e real reaches surveyed varied in 

both forest and stream conditions as well as other 

processes that we held constant, such as tree-fall 

regime and contribution of wood from upslope 

sources. Many of these factors can be addressed 

within the modeling framework (e.g., directional 

tree-fall, infl uence of key pieces on log mobility 

in larger channels) provided they are necessary 

for addressing the particular question under 

investigation.

Literature Cited

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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., eds. Streamside management: forestry and 

fishery interactions. Seattle, WA: College of Forest 

Resources, University of Washington: 143–190.

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everyday life. Journal of the American Statistical 

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in headwater streams of the Oregon Coast 

Range. Journal of the American Water Resources 

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P.F. 1992. Alternative silvicultural practices and 

diversity of animal habitat in western Oregon, 

a computer simulation approach. In: Luker, P., 

ed. Proceedings of the 1992 summer computer 

simulation conference. San Diego, CA: The Society 

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Groom, J.D.; Dent, L.; Madsen, L.J. 2011a. 

Stream temperature change detection for 

state and private forests in the Oregon Coast 

Range. Water Resources Research. 47: W01501.

doi:10.1029/2009WR009061.

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2011b. Response of western Oregon (USA) stream 

temperatures to contemporary forest management. 

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principles and applications. New York: Chapman 

and Hall.

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edition 9.1. Corvallis, Oregon: Department of 

Forest Resources, Oregon State University.

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1975. The importance of validation in ecosystem 

analysis. In: Innis, G.S., ed. New directions in the 

analysis of ecological systems, part I. Lajolla, CA: 

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McDade, M.H.; Swanson, F.J.; McKee, W.A.; 

Franklin, J.F.; Van Sickle, J. 1990. Source distance 

for coarse woody debris entering small streams 

in western Oregon and Washington. Canadian 

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wood dynamics in Pacific Northwest streams. 

Ph.D. dissertation. Corvallis, OR: Oregon State 

University.

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small streams in the western Cascades, Oregon. 

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Weatherspoon, C.P.; Lisle, T.E., eds. Proceedings 

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Citation:

Meleason, Mark; Groom, Jeremy; Dent, Liz. 2013. A simulation framework for evaluating the eff ect of riparian management 

strategies on wood in streams: an example using Oregon’s state forest riparian management regulations. In: Anderson, Paul 

D.; Ronnenberg, Kathryn L., eds. Density management for the 21st century: west side story. Gen. Tech. Rep. PNWGTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacifi c Northwest Research Station:136–147.

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2008. Methods for stream habitat surveys: Aquatic 

Inventories Project. Information Report 2007-01, 

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Wildlife. 

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Density Management in the 21st Century: West Side Story PNW-GTR-880

148

Riparian Buffers and Thinning in Headwater Drainages 

in Western Oregon: Aquatic Vertebrates and Habitats

Deanna H. Olson

Deanna H. Olson is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences 

Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; dedeolson@fs.fed.us

Abstract

Th e Density Management and Riparian Buff er Study (DMS) of western Oregon is a template 

for numerous research projects on managed federal forestlands. Herein, I review the origins of 

Riparian Buff er Study component and summarize key fi ndings of a suite of associated aquatic 

vertebrate projects. Aquatic vertebrate study objectives include characterization of headwater fauna 

and habitats, and examination of the eff ects on headwater-dwelling species of combined buff er-andthinning treatments in years 1, 2, 5, and 10 post-treatment. Some treatment eff ects have emerged, 

with negative eff ects on bank amphibian counts occurring in treatments with the narrowest buff ers 

10 years post-thinning. Nevertheless, all taxa appear to be persisting at sites. Instream amphibians, 

in particular, appear to be highly resilient to the types of disturbances resulting from the thinning 

and buff er treatments of the DMS.

Keywords: riparian reserves, density management, small streams, NWFP, Aquatic Conservation 

Strategy Objectives.

Introduction

Th e Density Management and Riparian Buff er 

Study (DMS) of western Oregon is an overarching template for numerous research projects 

on managed federal forestlands, conducted 

collaboratively by scientists and natural resource 

managers with several agency and institution 

affi liations (Cissel et al. 2006). Herein, I provide 

background on the development of the Riparian 

Buff er Study component, and I summarize key 

fi ndings of a suite of DMS projects on aquatic 

vertebrates and their habitats in managed forest 

headwaters. Th is review of the study context 

and compendium of the various aquatic-related 

elements may inform research and management 

decisions regarding riparian management options 

in west-side forests of the Pacifi c Northwest. 

Background

In the early 1990s, ecological knowledge was 

synthesized (fi g. 1) to develop the one and two 

site-potential tree height interim riparian reserves 

of the U.S. federal Northwest Forest Plan (NWFP; 

USDA and USDI 1993, 1994). Although these 

reserves were derived from the science and expert 

opinion of the time, many concepts had not been 

fi eld-tested or were drawn from upland empirical 

studies (e.g., microclimate edge eff ects: Chen et 

al. 1995) because riparian studies had not yet 

been conducted. 

Riparian reserves were conceived to contribute 

to the desired future conditions of aquatic-riparian 

portions of forest landscapes as characterized by 

the list of Aquatic Conservation Objectives (ACS) 

in the NWFP (USDA and USDI 1994; p B-11). 

Th ese included maintenance and restoration of 
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Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson 149

the physical integrity of aquatic systems, species 

composition, and habitats to support welldistributed populations of riparian-dependent 

species, and within- and between-watershed 

connectivity. In addition to riparian reserves, 

ACS objectives were to be attained through 

additional NWFP components including latesuccessional reserves, key watersheds, watershed 

analysis, and watershed restoration (Hohler 

et al. 2001). ACS objectives were written with 

landscape-scale language, and their application 

to project scales and portions of watersheds 

such as headwater drainages was vague. 

However, preliminary analyses of perennial and 

intermittent stream densities in watersheds across 

the region were conducted, which provided some 

baseline information about the scope of the 

intended riparian reserve network: intermittent 

streams comprised the majority of stream lengths 

throughout west-side forests (Appendix V–G: 

USDA and USDI 1993). 

Th e riparian reserve “module” (USDA and 

USDI 1997) of the federal guide for watershed 

analysis (USDA and USDI 1995) provided 

a toolbox of considerations and analyses of 

physical and biological conditions to help forest 

natural resource specialists and land managers 

implement refi nements to the interim riparian 

reserve measures of the NWFP as smaller spatialscale forest planning ensued. Relative to species, 

benefi ts of riparian reserves were recognized 

not only for aquatic- and riparian-dependent 

species, but also for a host of terrestrial 

organisms occurring within west-side forests. 

Riparian reserves conceptually provided habitats 

for reproduction, foraging, overwintering, 

and dispersal of a diverse array of taxa. Before 

alteration of interim riparian reserve boundaries, 

or before decisions about management scenarios 

within boundaries, analysis of additional species 

information was suggested, so that management 

decisions would consider the various uses of the 

newly reserved habitats by an array of target 

species and communities of organisms. Species 

with certain ecological attributes were of specifi c 

interest, including species: 1) with critical habitats 

coinciding with riparian areas; 2) with inherently 

low mobility; 3) occurring over a relatively small 

portion of the NWFP, being “localized”; and 4) 

considered to be rare, found in relatively low 

numbers, including federally listed Survey and 

Manage species (USDA and USDI 1994). Th e 

module aimed to develop a systematic approach 

for the integration of physical and biological 

factors so that the interim riparian reserve widths 

Figure 1—Concepts synthesized from a blend of 

expert opinion, theoretical knowledge, and empirical 

studies conducted in a variety of forest contexts that 

were integral to the development of the interim riparian 

reserve widths of the federal NWFP (redrawn from 

USDA and USDI 1993). (a) Contributing factors to 

stream habitat conditions were expected to be associated 

with distance from a stream channel. (b) Microclimate 

edge effects—predicted changes from a clearcut edge 

into the interior of an old forest stand (from Chen et al. 

1995).
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150 Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson

could be potentially altered and managed. 

However, knowledge of the general ecology of 

headwater portions of forested watersheds was 

largely unavailable, hindering full use of the 

module. 

Th e Bureau of Land Management’s (BLM) 

Density Management Study of western Oregon 

(Cissel et al. 2006) was originally intended to 

explore thinning approaches to accelerate the 

development of upland late-successional forest 

conditions. Th e frequency of streams in the 

study areas complicated BLM site selection and 

potential layout of treatment blocks within sites, 

but also created an opportunity to test the effi cacy 

of riparian buff ers. Th e study was adapted to test 

the eff ects of the NWFP’s riparian reserve widths, 

within upland thinning, on aquatic-riparian 

resources. 

Two new no-entry riparian buff er widths 

(variable-width buff er, streamside-retention 

buff er) were added to the DMS design to 

address thinning within interim riparian reserve 

boundaries. Th ese buff ers were developed with 

a two-fold rationale, to: 1) stretch the concepts 

of the federal riparian reserves, testing narrower 

buff ers with upland forest thinning, which 

was expected to be a relatively more benign 

disturbance compared to historical clearcutting; 

and 2) examine approaches to restore nearstream riparian habitats, accelerating tree growth 

and the development of late-successional oldgrowth (LSOG) conditions near streams, and 

growing future large down wood for instream 

and streamside habitats. Th e variable-width 

buff er (with a 50-ft [~15-m] minimum width 

on each streamside) was designed to follow 

ecological gradients along streams, potentially 

expanding with a signifi cant change in slope 

gradient (becoming a steeper, more incised 

stream channel), seeps and slumps, or unique 

microhabitats or plant species, as detected at 

local scales during pre-project planning. Th e 

variable-width buff er was anticipated to provide 

advantages to natural-resource specialists and 

managers at the layout stage of site-level project 

implementation because stringent fi xed distances 

from streams were not expected; rather, riparian 

edges could be uneven with varying widths. Th e 

streamside retention buff er (~20-ft [6-m] width 

on each streamside) was conceived as a minimum 

width to retain bank stability and direct overhead 

shading of streams. 

Overall, these four buff er widths (fi g. 2) were 

conceptually derived, with their implementation 

on-site reliant on the stream geometry and 

other site conditions and constraints (Olson et 

al. 2002). Th e study design included metrics of 

lateral and longitudinal distances of treatment 

units: laterally, perpendicular to streams, ~200 

ft (~60 m) of thinning treatment was desired 

between the buff er edge and the ridgeline; 

longitudinally along streams, a stream buff er 

Figure 2—Riparian buffer 

widths examined in the Density 

Management and Riparian Buffer 

Study of western Oregon.
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Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson 151

treatment length of about 2.5 site-potential tree 

heights was desired (e.g., Green Peak study site: 

550 ft, ~170 m) (Cissel et al. 2006). Not all stream 

replicates met these exact criteria, and some 

stream geometries resulted in treatment units or 

sites being entirely unsuitable for Riparian Buff er 

Study implementation. Consequently, an attempt 

was made to prioritize replication of riparian 

buff er treatments within the moderate upslope 

thinning treatment unit, which initially reduced 

the overstory tree density to ~200 trees per 

hectare, tph (80 trees per acre, tpa) at most sites. 

Th is DMS upland thinning treatment was more 

intensive than standard commercial thinning 

densities of the early 1990s, and was established 

as the treatment that would be optimal to test 

relative to combined upland and buff er objectives 

for site restoration. In addition, the study design 

included reference streams in unthinned control 

units. Hence, stream geometry was considered 

during assignment of the moderate and control 

treatments within a study site. Even so, when 

few streams occurred at potential study sites, 

some sites could not be implemented, and not all 

buff er treatments could be planned within other 

sites. When stream density was high at a site, the 

one and two site-potential tree height buff ers 

often extended over sub-drainage ridgelines 

into the adjacent stream channel drainage. Th is 

compromised the study layout criterion calling 

for a minimum thinned distance between the 

buff er and ridgeline, and hence, fewer wider 

buff ers could be implemented. For example the 

two site-potential tree height buff er treatment 

could not be implemented at the Green Peak 

study site (fi g. 3). Th e fi nal riparian buff er study 

design was implemented without full replication 

across 12 study sites, on lands managed by BLM 

and the Forest Service (fi g. 4).

Upon examination of sites and stream 

networks proposed for use by DMS, it reinforced 

the fact that DMS was being implemented in 

headwater sub-drainages with relatively abundant 

intermittent streams. Because comparatively 

little was known about the ecology of forested 

headwaters at the time, research needs emerged 

to “down-scale” and add specifi city to the ACS 

objectives. Characterizing site-level conditions 

within headwaters became a second major goal 

of the Riparian Buff er Study component.

At the time of the development of the DMS 

study, aquatic-riparian vertebrates and their 

habitats had become a focus of management 

attention in the Pacifi c Northwest due to three 

factors. First, the US Forest Service’s Forest 

Planning Rule (Sec. 219.19 Fish and wildlife 

resource: http://www.fs.fed.us/emc/nfma/includes/

nfmareg.html#Fish and wildlife resource) specifi ed 

that “Fish and wildlife habitat shall be managed 

to maintain viable populations of existing native 

and desired non-native vertebrate species in the 

planning area.” Second, there was an historical 

taxonomic emphasis on vertebrates for listing 

under the Endangered Species Act. Th ird, many 

aquatic-dependent vertebrates had a status of 

Figure 3—Example implementation of three riparian 

buffer widths in the moderate upslope thinning 

treatment at the Green Peak study site of the Density 

Management and Riparian Buffer Study of western 

Oregon. Reference streams in the unthinned control unit 

are shown. Transects perpendicular to streams were used 

for upland terrestrial salamander assessments (Olson et 

al. 2006; Rundio and Olson 2007) and pre-treatment 

down wood assessment (Olson et al. 2006). From Olson 

and Rugger 2007.
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152 Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson

general concern in the region (see Cissel et al. 

2006), and many of these were amphibians. 

Hence, DMS aquatic ecology research has 

focused on amphibians and habitat attributes 

relevant to these animals (Hohler et al. 2001; 

Cissel et al. 2006). 

In summary, the aquatic vertebrate component 

of the Riparian Buff er Study aimed to characterize 

the ecological values of headwaters relative to 

amphibians and their habitats, and assess the 

eff ects of the thinning and buff er treatments 

on these aquatic-dependent biota and their 

habitats. Key fi ndings of analyses of headwater 

pre-treatment conditions and post-treatment 

conditions in years 1, 2, 5, and ~10 after thinning 

are summarized below (table 1). 

Research Findings

Ecological Characterization of 

Headwater Streams 

Animals

At DMS sites, 13 species of amphibians and 5 

diff erent fi sh taxa have been detected (table 1). 

At a single site, up to 11 amphibian species have 

been detected, and three sites had this species 

richness (OM Hubbard, Keel Mountain, North 

Soup Creek). Up to four fi sh taxa have been 

detected at a single site, with two sites having this 

diversity (Callahan Creek, North Ward). 

Amphibian species found in and along streams 

of the DMS study reaches are organized into 

assemblages based on habitat associations (fi g. 

5; Sheridan and Olson 2003; Olson and Weaver 

2007). Occurring at all DMS sites are the streambreeding Coastal Giant Salamander (Dicamptodon 

tenebrosus) and torrent salamanders (Rhyacotriton 

species; fi g. 6), the semi-aquatic stream-bank 

associated Dunn’s Salamander (Plethodon dunni), 

the pond-breeding Rough-skinned Newt (Taricha 

granulosa), and the terrestrial-breeding Ensatina 

(Ensatina eschscholtzii). 

Of this diverse aquatic-dependent forest fauna, 

torrent salamanders were highly associated with 

the uppermost headwater reaches of streams with 

discontinuous fl ow (Sheridan and Olson 2003; 

Olson and Weaver 2007). Furthermore, streams 

with spatially discontinuous fl ow, or “intermittent” 

streams, were the most frequent hydrological 

fl ow type in our study (fi g. 7). Because torrent 

salamanders are northwest-endemic species and 

are species of concern, they and their stream 

habitats with discontinuous fl ow are ecological 

values warranting consideration relative to forest 

management in headwaters. Th ese salamanders 

Figure 4—Riparian buffer treatments were 

implemented at 12 study sites in western Oregon on 

lands administered by the Bureau of Land Management 

(sites 1-6, 10-12)) and the Forest Service (sites 7-9). 1: 

Delph Cr.; 2: Green Peak; 3: Keel Mountain; 4: North 

Soup Cr.; 5: O.M. Hubbard; 6: Ten High; 7: Cougar; 

8: Grant; 9: Schooner Cr.; 10; Callahan Cr.; 11: North 

Ward; 12: Perkins. From Olson and Weaver 2007.
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Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson 153

Table 1—Amphibian and fish species occurrences at Density Management and Riparian Buffer Study 

sites in western Oregon.

Species

Study site

1 2 3 4 5 6 7 8 9 10 11 12

Amphibians

Ambystoma gracile x x xxxx x

Aneides ferreus xxxx xx

Ascaphus truei x x xxxx x xx

Batrachoseps wrighti x x

Dicamptodon tenebrosus x x x x xxxx x xxx

Ensatina eschscholtzii x x x x xxxx x xxx

Plethodon dunni x x x x xxxx x xxx

Plethodon vehiculum x x x xxxx x xxx

Pseudacris regilla xxxxxx xxx

Rana aurora x x x x xxx x xxx

Rhyacotriton cascadae x xx

Rhyacotriton variegatus x x x xx x xxx

Tarich granulosa x x x x xxxx x xxx

Fishes

Oncorhynchus clarkii x x xxxx x

Oncorhynchus mykiss x

Salmonid sp. age 0+ x x x x x x x

Cottus sp. x x x x

Lamprey sp. (ammocete) x x

Study sites: 1= Callahan Creek; 2 = Cougar Creek; 3 = Delph Creek; 4 = Grant Creek; 5: Green Peak; 6: OM Hubbard; 

7: Keel Mountain; 8: Perkins Creek; 9: Schooner Creek; 10 = North Soup Creek; 11: Ten High; 12 = North Ward Creek.

Figure 5—Amphibian assemblages occurring in headwater drainages of western Oregon. Amphibians can be 

categorized by (a) habitat associations, such as two stream-breeding assemblages (in perennial and ephemeral streams), 

two pond-breeding assemblages (in perennial and ephemeral ponds), two terrestrial-breeding assemblages (wood 

and rock associates), and bank-dwelling species which may include members of other assemblages; or (b) species 

composition by pie-charts within different portions of drainages, showing four dominant assemblages in headwaters 

(Sheridan and Olson 2003; Olson and Weaver 2007). Arrow A depicts direction of cool, moist microclimates from the 

“stream effect”. Arrow B depicts direction of opposing warmer, dryer microclimates from upslope.

a b
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154 Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson

do not appear to be associated with larger 

streams (Olson and Weaver 2007). It is likely 

that dispersal over ridgelines rather than through 

the downstream aquatic network is needed to 

maintain connectivity among sub-populations. 

A torrent salamander has been documented in a 

pitfall trap 200 m (656 ft) from a stream (Gomez 

and Anthony 1996), supporting their ability to 

venture upslope. Although additional research 

is needed on this topic of overland dispersal, 

ongoing genetic studies of headwater amphibians 

in the Oregon Coast Range are confi rming 

over-ridge connectivity among watersheds (L. 

Knowles and M.R. Marchán-Rivadeneira, Univ. 

Michigan, unpubl. data), and genetic studies in 

other landscapes have similarly documented both 

riparian movements (Spear and Storfer 2010) 

and upland dispersal tendencies of amphibians 

(Spear and Storfer 2008). 

Forested uplands at our headwater study sites 

are habitat for a variety of amphibians requiring 

moist microhabitats, but not necessarily 

requiring standing or fl owing water for any part 

of their life history. Th e upslope amphibian 

assemblage is distinct from instream and bank 

assemblages, and is largely composed of downwood-associated species and species associated 

with rocky microhabitats (fi g. 5a; Sheridan and 

Olson 2003; Wessell 2005; Rundio and Olson 

2007; Kluber et al. 2008). Th ese animals may 

be found within near-stream riparian areas, and 

the Western Red-backed Salamander (Plethodon 

vehiculum) was highly associated with nearstream areas (Kluber et al. 2008). Using markrecapture methods to study movement patterns 

of terrestrial-breeding amphibians at the Green 

Peak DMS study site are under investigation. 

Short-distance movements of animals have been 

detected, with more movements occurring in 

near-stream areas. Th is supports the “funnel” 

concept, in which near-stream areas funnel 

animal movements along streams (Olson and 

Burnett 2013), possibly because either the stream 

acts as a barrier to dispersal or due to the cool, 

moist conditions near streams (Anderson et al. 

2007; Olson et al. 2007; Rykken et al. 2007) 

Figure 6—The Southern Torrent Salamander 

(Rhyacotriton variegatus) is reliant on the uppermost 

headwater stream reaches. (Photo by William P. 

Leonard.)

Figure 7—Spatially discontinuous streams that 

flowed intermittently in spring and summer 

were the most common stream-channel type at 

the Density Management and Riparian Buffer 

Study sites in western Oregon. Int = spatially 

intermittent flow. Wet = continuous flow. Dry 

= no water flow, but evidence of scour.
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Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson 155

which are ideal microhabitats for many northwest 

amphibians.

Th e life history of many of these amphibian 

species remains largely unknown, however 

knowledge gained from DMS studies is 

incrementally adding to our understanding of 

the basic biology of these species. For example, 

the nests of two amphibian species that have been 

observed at the DMS sites: Dunn’s Salamanders 

(Nauman et al. 1999) and Ensatina (Olson et 

al. 2006). Although most amphibian species are 

from instream, bank-dwelling, or upland forest 

assemblages, four pond-breeding amphibians 

(Ambystoma gracile, Northwestern Salamander; 

Rana aurora, Northern Red-legged Frog; 

Pseudacris regilla, Pacifi c Chorus Frog; Roughskinned Newt) were found routinely in and along 

streams at our sites. Th ese four species may move 

relatively long distances in forests, and streams 

and near-stream habitats likely “funnel” animals 

from lower in aquatic networks into headwaters 

(Olson and Burnett 2009, 2013). Incidental 

sightings of single egg masses of Northwestern 

Salamanders have been found in shallow pools or 

roadside ditches at DMS sites, confi rming pondbreeder reproduction at some sites.

Various aspects of the population and 

community ecology of headwater forest 

amphibians have been addressed by companion 

studies at locations outside of our study sites, in 

order not to disturb our experimental treatments. 

Sagar et al. (2005) reported on the survival and 

growth of juvenile Coastal Giant Salamanders in 

small streams of the Oregon Coast Range near 

our North Soup Creek study site. Predator-prey 

interactions have been investigated among three 

species. Antipredator behaviors were described 

for Coastal Giant Salamanders in response to 

Cutthroat Trout (Oncorhynchus clarkii) presence 

(Rundio and Olson 2003). Southern Torrent 

Salamanders (Rhyacotriton variegatus) were 

unpalatable to Coastal Giant Salamanders: the 

giant salamanders consistently rejected torrent 

salamanders during predation attempts (Rundio 

and Olson 2001). Th e conceptual model of 

“trophic cascades” may apply to headwater 

stream systems. In this model, a few dominant 

predators (Coastal Giant Salamanders, Cutthroat 

Trout) control the occurrences of other trophic 

levels (Terborgh and Estes 2010). Further 

research is needed to more fully document the 

hypothesis that repeated predation attempts by 

the larger Coastal Giant Salamanders on torrent 

salamanders restrict the downstream distribution 

of torrent salamanders. Also, an abundance of 

sculpins (Cottus species) at some sites indicates 

that they are a potentially dominant predator in 

those systems, and warrants further investigation. 

Biodiversity characterization at DMS sites 

has been conducted in companion studies. 

At four DMS sites, Wessell (2005) examined 

four taxonomic groups in upslope areas: 

vascular plants, mollusks, soil arthropods, and 

amphibians. In her comprehensive study, she 

found 120 vascular plant species, 3,608 mollusks 

of 12 taxa, 30,447 arthropods of 289 taxa, and 

7 amphibian species. Her multivariate statistical 

analyses showed interesting associations between 

species assemblages and habitat attributes, 

microclimate metrics, sites, and mountain ranges 

(Coast, Cascade). Because there were no matched 

old-growth forest sites available in the study 

landscape to compare to the DMS sites, a study 

characterizing amphibian and plant biodiversity 

of unmanaged forested headwaters was conducted 

near one DMS site, Soup Creek, near Coos Bay 

(Sheridan and Olson 2003; Sheridan and Spies 

2005).

Lastly, a case study of detection probabilities and 

occupancies of instream and bank amphibians 

has been conducted at Green Peak. Both giant 

and torrent salamanders had consistently high 

occupancy and detection rates, indicating that 

their distributions were not patchy within our 

treatment reaches and that our light-touch 

hand-sampling (“rubble rousing”) methods were 

eff ective at detecting them. Greater variability in 

occupancy and lower detection probabilities were 

found for bank Plethodon species.
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156 Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson

Habitat

Characterization of DMS headwater habitat 

conditions has focused on instream habitat 

typing. Along each study reach, the dimensions 

(width, length, depth) of fast and slow water units 

(e.g., pools and riffl es/cascades) are recorded, in 

addition to the substrate type and down wood 

per unit. From these data, reach hydrotypes (fi g. 

7) were developed (Hohler et al. 2001; Olson and 

Weaver 2007). Published analyses have focused 

on assessing species-habitat associations (Olson 

and Weaver 2007). 

Using the long-term data set (1994 to present) 

of multiple stream fl ow metrics, the hypothesis of 

“shrinking heads” relative to retrospective annual 

weather patterns is being addressed: do headwater 

streams shrink in size during dry years? (Burton 

et al. 2013a). Th is analysis is relevant to exploring 

eff ects of climate change scenarios on stream 

fl ow conditions, with treatment interactions also 

considered. Additionally, an ongoing companion 

study is examining how water availability in 

headwaters among years may contribute to forest 

vegetation development, again with climate 

change and treatment as interacting factors.

Analyses of DMS down wood metrics are 

ongoing (e.g., Anderson and Meleason 2009; 

Burton et al. 2013b). Instream down wood data 

have been collected during pre-treatment surveys 

and in years 1, 2, 5, and 10 post-treatment. 

Analyses include down wood patterns over time, 

relative to treatments, and distance-from-stream 

of the source tree for each instream down wood 

piece. From preliminary analyses, the number 

of wood pieces for which sources could be 

determined ranged from 425 to 841 per site. Th e 

average slope distance-from-stream of a source of 

down wood ranged from 2.6 to 9 m (8.5–29.5 

ft) for 25 stream reaches, the maximum distance 

at four sites examined ranged from 29.4 to 40.9 

m (96.5–134 ft), and the most frequent decay 

classes (Maser et al. 1979) of instream wood 

were classes 3 and 4. As these data are more fully 

compiled, new information will become available 

about down wood recruitment patterns to small 

streams from sites with riparian buff ers and 

thinning.

Upslope habitat conditions relative to 

amphibian microhabitat requirements have 

been assessed during various DMS studies. At 

two DMS sites (Green Peak, Keel Mountain), 

Olson et al. (2006) reported pre-treatment 

percent cover of down wood which occurred in 

plots along transects spanning stream to upslope 

areas, perpendicular to streams (fi g. 3). At four 

DMS sites (Green Peak, Keel Mountain, Delph 

Creek, Bottom Line) 1–5 years post-treatment, 

Wessell (2005) reported on upslope substrate, 

down wood, and forest structural components 

in leave islands, the moderate-density thinning 

treatment, and the unthinned control. At three 

DMS sites (Green Peak, Ten High, Schooner 

Creek), 5–6 years post-thinning, Kluber et al. 

(2008) analyzed associations of percent cover of 

upslope canopy, down wood, litter, forbs, and 

moss with distance-from-stream and treatment 

eff ects. Habitat within the near-stream survey 

bands diff ered from upslope survey bands relative 

to several attributes, including more down wood 

near streams. Th ermal profi les of large- and smalldiameter logs and soils in near-stream and upslope 

positions, in treatments and unthinned reference 

stands, were examined by Kluber et al. (2009). 

Lastly, riparian-to-upland microclimate gradients 

at the DMS sites were characterized by Anderson 

et al. (2007) and a similar study of streamside 

microclimates along small west-side Oregon 

streams was conducted by Rykken et al. (2007). 

Both studies documented a “stream eff ect” where 

distinctly cooler temperatures occurred within 

~10–15 m (33–49 ft) of headwater streams 

(review: Olson et al. 2007). 

Treatment effects of buffers and 

thinning on amphibians, other taxa, 

and habitat attributes 

Instream and bank species

 Among amphibian species occurring instream, 

along banks, and in upland forests, there have 

been a variety of eff ects of the DMS thinning 
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Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson 157

and buff er treatments. Several caveats are needed, 

however. Statistical analyses have been a challenge 

because most species do not occur at all sites, or 

all reaches within sites, and many species (table 1) 

occur in low numbers within reaches. Th e most 

robust analyses have been possible with the more 

commonly occurring species, including Coastal 

Giant Salamanders, torrent salamanders, Dunn’s 

Salamanders, Western Red-backed Salamanders, 

and Ensatina.

Instream and bank amphibians

In years 1–2 post-thinning, we found no 

reduction in species abundances in and along 

streams (Olson and Rugger 2007). Th is suggests 

that the mechanical disturbance of the thinning 

and the immediate eff ects on animals or their 

habitats was not substantial. Because amphibians 

live several years, we felt that a lag time in 

treatment eff ects on survival and reproduction 

warranted monitoring.

Year-5 and year-10 post-treatment results of 

instream and streambank animal abundances 

have not yet been published, hence I provide 

only general preliminary fi ndings here. In year5 post-treatment, analyses of instream and 

bank species were conducted with data from 

68 stream reaches at 11 sites and the entire 

time series of data to date. Intriguing fi ndings 

include reduced abundances of two streambankoccurring amphibians in year 5 compared to pretreatment. In year-10 post-treatment, diff erent 

analyses have been conducted using the entire 

time series of data among years (Olson et al. in 

press). Results included some eff ects on both 

instream and stream-bank animals, with riparian 

buff ers and interacting factors jointly accounting 

for the diff erences in animal abundances over 

time. In particular, bank-dwelling salamander 

counts decreased over the 10-year post-thinning 

timeframe in treatments with the narrowest 

buff ers. Pre-treatment abundances were 

consistently a factor explaining post-treatment 

species abundances, suggesting that animal 

abundances after thinning and buff er treatments 

are contingent on the site-specifi c contexts of 

pre-treatment abundances. Th e strongest takehome message emerging from our long-term 

instream faunal dataset is the overall resiliency of 

these assemblages to the treatments. 

Analyses of fi sh species have been problematic 

due to their uneven distribution among sites 

(table 1), in addition to their uneven occupancy 

among both stream reaches and riparian buff er 

treatments within sites. Fish species have been 

included in exploratory analyses of year-5 and 

year-10 data, and no signifi cant insights relative 

to treatment eff ects on fi shes resulted.

Upland amphibians

Case studies on upland salamanders at the DMS 

sites tell the same story of variable responses yet 

apparently resilient assemblages. Although some 

eff ects on abundances have been observed, the 

assemblages have remained intact. 

At two DMS sites, 1–2 years post-treatment, 

Rundio and Olson (2007) examined terrestrial 

salamanders occurring in transects arrayed 

perpendicular to streams in the moderate upslope 

thinning treatment (fi g. 3). Th ey reported that 

captures of two salamander species declined 

by 40 percent post-thinning at one site (Green 

Peak), and no treatment eff ect was detected at 

the other site (Keel Mountain). Site diff erences in 

down wood cover were hypothesized to be related 

to these results, with down wood potentially 

ameliorating eff ects of thinning on salamanders.

At four DMS sites (Green Peak, Bottom 

Line, Delph Creek, Keel Mountain), 1–5 years 

post-treatment, Wessell (2005) found various 

treatment eff ects of the moderate thinning 

treatment and leave island sizes on species and 

diversity metrics. For example, for amphibians, 

she found that species richness of amphibians was 

greater in unthinned than thinned forest. Eff ects 

of leave island sizes on amphibian species richness 

and Oregon Slender Salamander (Batrachoseps 

wrighti) abundances also were detected, with 

more animals in the 0.1- and 0.2-ha leave islands 

than in the 0.4-ha leave island (0.25, 0.5, and 1 
Density Management in the 21st Century: West Side Story PNW-GTR-880

158 Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson

ac, respectively).

At three DMS sites (Green Peak, Ten High, 

Schooner Creek), 4–5 years post-treatment, 

Kluber et al. (2008) found no treatment eff ects 

of the moderate thinning treatment on upslope 

salamanders. However, they found that distancefrom-stream was associated with amphibian 

abundance, hence riparian buff ers could play a 

role in upland salamander persistence at sites if 

adverse eff ects of upland disturbance did occur. 

Th eir results also suggested that rocky substrates 

may aid amphibian persistence in thinned forests. 

Case studies ongoing at two DMS sites 

investigate the effi cacy of artifi cial cover boards 

for long-term monitoring of the terrestrial 

amphibian assemblage. Using mark-recapture 

methods, we are documenting movements of 

individual salamanders between boards. At the 

Green Peak study site, cover boards are arrayed 

at diff erent distances from the stream, and we 

have been examining movement patterns related 

to stream proximity since year 2000. At the 

Keel Mountain study site, cover board arrays 

are assessing overland movement patterns of the 

Oregon Slender Salamander, a species of concern 

in western Oregon (Clayton and Olson 2007). 

In summary, although the value of the diff erent 

buff er widths with thinning for amphibians is 

still under investigation, there is evidence that 

thinning near streams may be conducted at a 

relatively minor cost to these animals. Variable 

eff ects on species abundances are being detected, 

and although some species abundances have 

decreased, populations appear to be persisting. 

Given that the treatments are intended to restore 

riparian forests, a short-term cost for a longerterm gain of accelerated development of LSOGforest conditions may be acceptable to land and 

natural-resource managers, and interested public 

groups. If upland areas are to be managed over 

the long term, continued monitoring of both 

instream and upslope aquatic fauna is warranted 

to assess population stability.

Habitat

Analyses of combined riparian buff er and 

upland thinning treatment eff ects relative to 

stream fl ow metrics and instream down wood 

are ongoing. Integrated multivariate analyses of 

additional instream habitat attributes and analyses 

of species-habitat relationships comparing pretreatment to post-treatment years 1, 2, 5, and 10 

data are planned.

Treatment eff ects on water-quality metrics 

have been of interest for monitoring at the 

DMS sites, yet despite multiple proposals 

over the years, we have been unable to gain 

suffi cient funding to deploy sensors to assess 

sedimentation or temperature in stream reaches 

among sites. Nevertheless, at two case-study 

sites, Keel Mountain and Callahan Creek, with 

DMS collaborator Paul D. Anderson, instream 

temperature dataloggers were deployed for yearround temperature monitoring. Unfortunately, 

in the fi rst winter of deployment, high fl ows 

resulted in the loss of many sensors at Callahan 

Creek. Since then, we have maintained a network 

of instream temperature dataloggers only at 

Keel Mountain. Th ey are positioned at stream 

junctions and at the boundaries of treatment 

units along stream reaches. We plan to begin 

analyses following DMS Phase 2 data collection.

Phase 2 – Second-entry DMS 

Thinning Treatments

A second thinning treatment (Cissel et al. 

2006) has now occurred at eight DMS study 

sites that include Riparian Buff er treatments: 

Callahan Creek, Delph Creek, Green Peak, 

OM Hubbard, Keel Mountain, Perkins Creek, 

North Soup Creek, and Ten High. Th is second 

entry was designed to reduce the overstory to 

near-LSOG-forest densities in order to maintain 

accelerated overstory tree-growth rates and 

further enhance understory development. Th e 

retained overstory will become the largest trees 

in the future forest stand. In the initial thinning 

thinning phase, the moderate-density treatment 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson 159

unit had been thinned to 200 tph; in phase 2, this 

unit was reduced to ~90 tph (37 tpa; with two 

trees destined to be future down wood and fi ve 

destined for snag recruitment). Post-treatment 

surveys for instream vertebrates and habitats and 

streambank amphibians in year-1 post-phase-2 

thinning will be completed in 2012 at these eight 

sites. At this time, there is no funding to pursue 

phase 2 treatment eff ects on upslope amphibians, 

with the exception that the upslope cover boards 

deployed at Green Peak and Keel Mountain will 

be monitored as time permits.

Th ree of the four original riparian buff er 

widths are continued as treatments relative to this 

second-entry thinning: one site-potential tree 

height, variable width, and streamside retention 

(fi g. 8). Th e two BLM study sites at which the 

two site-potential tree height buff er had been 

implemented (Callahan Creek, Keel Mountain) 

are now case studies of a “thin-through” two-tree 

buff er, where the buff er has been thinned to ~150 

tph (60 tpa), and the upland thinned to ~90 tph. 

Th ere is no stream buff er in this thin-through 

treatment, meaning that thinning occurred up 

to streambanks. Th ese case studies will assess the 

eff ects on instream resources of thinning without 

buff ers. At one study site, Keel Mountain, 

the number of stream reaches with a variablewidth buff er in the high-density thinning unit, 

initially thinned to ~300 tph (120 tpa), allowed 

a similar examination of thin-through buff ers 

with unthinned reaches for comparison. Th ese 

variable-width buff er reaches were thinnedthrough (no stream buff er) with 150 tph in 

both the buff er and the upland treatment unit. 

Although the inference drawn from case studies is 

limited to the sites at which the studies occur, the 

thin-through treatment eff ects will be monitored 

to provide insights about the utility of thinthrough buff ers for riparian forest restoration 

elsewhere.

Conclusions

Th e aggregate studies outlined above add to 

our knowledge of aquatic vertebrates and their 

habitats in forested headwater basins in western 

Oregon. Relative to ACS objectives from the 

NWFP, additional specifi city of species and 

habitat conditions in headwaters has been 

achieved. Although analyses are still ongoing, 

early fi ndings have reported relatively mixed 

eff ects of these treatments on amphibians or their 

habitats. Th e use of these riparian buff er widths 

in operational thinning projects in west-side 

forests with similar characteristics will likely have 

some short-term eff ects on specifi c resources, but 

are also likely to have long-term gains for site 

restoration. Continued monitoring of species-atrisk in these headwater stream locations, such as 

Figure 8—Riparian buffer design for Phase 2 of the Density Management and Riparian Buffer Study of western 

Oregon. Thin-through buffers were implemented at selected case-study reaches.
Density Management in the 21st Century: West Side Story PNW-GTR-880

160 Eff ects of Riparian Buff ers on Aquatic Vertebrates Olson

torrent salamanders, would be needed to address 

uncertainty about potential long-term or sitespecifi c detrimental eff ects. Similarly, where 

neighboring private-land parcels continue to be 

managed using regeneration-harvest approaches, 

the utility of adjoining federal land parcels such 

as those included in this study is likely to become 

increasingly important for aquatic resource 

protection. Monitoring of selected resources into 

the future will help to gain knowledge about 

cumulative eff ects over time and this potential 

emerging role of federal lands for aquaticresource conservation emphasis when such lands 

are nested within a patchwork (e.g., checkerboard 

pattern) of mixed land ownerships.

Ongoing research eff orts are using these 

study sites and the overall experimental design 

as a template to explore emerging topics. For 

example: 1) knowledge gained by these studies 

has contributed to development of landscapelevel designs for managing joint aquatic-terrestrial 

habitat connectivity (Olson and Burnett 2009, 

2013); and 2) climate change scenarios are under 

study relative to headwater stream-fl ow and 

the interaction of water availability, thinning 

treatments, and vegetation growth. Th ese study 

sites are valuable for the continued monitoring of 

phase 2 treatment eff ects, and for potential future 

research opportunities.

Acknowledgments

Funding was provided by the USDA Forest Service, 

Pacifi c Northwest Research Station and the Oregon 

State Offi ce of the Bureau of Land Management. 

Special thanks to John Tappeiner and Jim Sedell who 

were DMS visionaries during project conception, and 

to Sam Chan, Charley Th ompson, John Cissel, Larry 

Larsen, and Kim Titus who helped in many ways 

during DMS implementation. For their contributions 

to DMS, I also thank my students (Dave Rundio, 

Chris Sheridan, Stephanie Wessell, Jina Sagar, Matt 

Kluber, Lindsey Biga, Jeff Leirness), post-docs (Nobi 

Suzuki, Adrian Ares, Julia Burton), coauthors (see 

references), and ongoing principal investigators of the 

main study components (Paul Anderson and Klaus 

Puettmann). Site coordinators have been crucial to 

DMS implementation, and for their outstanding 

eff orts I thank Charley Th ompson, Craig Kintop, 

Hugh Snook, Peter O’Toole, Rick Schultz, Floyd 

Freeman, Frank Price, Sharmila Premdas, Trixy 

Moser, and Craig Snider (formerly of the Siuslaw 

National Forest). I especially thank Loretta Ellenburg 

for managing my riparian buff er fi eld studies and data 

sets, the countless temporary employees who have 

worked on this project and its data management, and 

Kathryn Ronnenberg for assisting with fi gures and 

editing. I thank Liz Dent, Charley Th ompson and 

Paul Anderson for their comments that improved this 

paper.

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Density Management in the 21st Century: West Side Story PNW-GTR-880

163

The Riparian Ecosystem Management Study: Response 

of Small Mammals to Streamside Buffers in Western 

Washington

Martin G. Raphael and Randall J. Wilk

Martin G. Raphael is a research wildlife biologist, and Randall J. Wilk is a wildlife biologist, USDA Forest Service, Pacifi c 

Northwest Research Station, Forestry Sciences Laboratory, 3625 93rd Ave. SW, Olympia, WA 98512; mraphael@fs.fed.us

Abstract

One of the fundamental concepts behind the conservation strategy in the U.S. federal Northwest 

Forest Plan is the importance of habitat buff ers in providing functional stream and streamside 

ecosystems. To better understand the importance of riparian buff ers in providing habitat for associated 

organisms, we investigated responses of small mammals to various streamside management options 

in western Washington forests. First, we conducted a retrospective study at 49 fi rst- to thirdorder streams on state, federal, and private lands on the Olympic Peninsula, Washington. Streams 

represented six forest and stream-buff er conditions ranging from unlogged control to young second 

growth with no buff ers. Because of high variability among sites within each condition, we found 

few diff erences in responses of mammals to site conditions; however there were species-specifi c 

associations with stream size, gradient, and site elevation. In hopes of reducing site variability, 

we subsequently undertook an experimental study on state lands in western Washington along 

23 fi rst- and second-order headwater streams to evaluate small mammal populations both before 

and after riparian and upland forest treatment. Th e four treatments, grouped within blocks of 

adjacent catchments, included an unlogged control, and continuously buff ered streams, patchbuff ered streams, and unbuff ered streams within upland clearcuts. We sampled small mammals 

in 2003 before logging and then for two years following logging. We found signifi cant changes in 

abundance of most common species following logging, including a decline in abundance of Keen’s 

Mouse (Peromyscus keeni) in all treatments relative to controls, and increases in abundance of the 

Creeping Vole (Microtus oregoni), Southern Red-backed Vole (Myodes gapperi), and Townsend’s 

Chipmunk (Tamias townsendii). We found capture rates of some of the more specialized species 

were too low to allow conclusions about treatment eff ects. For these rarer species, more focused 

autoecological studies will be needed to better evaluate their habitat relationships along headwater 

streams and their potential responses to streamside buff er treatments.

Keywords: Riparian buff ers, small mammals, streamside management.

Introduction

Management of streamside vegetation is a 

major component of the Northwest Forest 

Plan for federally managed lands in western 

California, Oregon, and Washington (FEMAT 

1993). One of the fundamental concepts behind 

the conservation strategy in the Northwest Forest 

Plan is the importance of riparian habitat buff ers 

in providing functional stream and streamside 

ecosystems. Th ese buff ers, as proposed by the 

Scientifi c Analysis Team (Th omas et al. 1993) 

and FEMAT (1993) are meant to conserve 

habitat conditions not only for at-risk stocks of 
Density Management in the 21st Century: West Side Story PNW-GTR-880

164 Response of Small Mammals to Streamside Buff ers Raphael and Wilk

fi sh but also a diverse range of riparian-associated 

organisms including lichens, liverworts, fungi, 

vascular plants, invertebrates, and vertebrates 

(USDA and USDI 1994). Th e size of these 

buff ers, and their placement on all stream orders 

including headwater and intermittent streams, 

has resulted in the reservation of a large portion 

of the landscape, ranging from 30 percent to 

70 percent of the federal land base (USDA 

and USDI 1994). Although the size of these 

buff ers was determined from a thorough review 

of existing literature, very few fi eld data were 

available comparing the effi cacy of alternative 

buff er designs at the time of their conceptual 

development. Understanding relationships 

between biodiversity and watershed function and 

watershed condition may lead to opportunities 

to better balance commodity production and 

protection of streamside habitat. 

Much attention has focused on the role of buff ers 

in conserving spawning habitat for salmonids 

and in providing habitat for streamside and 

aquatic amphibians. Less attention has focused 

on the effi cacy of these buff ers for conservation 

of small mammals. In a recent review, Anthony 

et al. (2003) noted that 95 of the 147 mammal 

species of Oregon and Washington use riparian 

zones to varying degrees. Th ey classifi ed the 

degree of association for each of these 95 species 

and found that 9 are riparian obligates (they 

require free water or riparian vegetation for some 

aspect of their natural history); 33 are riparian 

associates (they are found at statistically greater 

abundance in riparian habitats compared with 

uplands); 5 are early-seral species that use recently 

cut-over forest along streams, and 52 are nonriparian species that use riparian ecosystems but 

whose abundance in riparian habitats does not 

diff er from abundance in upland habitats. Given 

that a large number of mammalian species use 

riparian forest, we undertook retrospective and 

experimental studies to investigate how small 

mammals respond to riparian buff ers retained 

during upland forest harvest practices in western 

Washington.

Retrospective Study

As a preliminary eff ort toward better understanding the importance of riparian buff ers 

in providing habitat of associated organisms, 

we initiated a retrospective study of responses 

of aquatic and terrestrial organisms to various 

streamside management options (Raphael 

et al. 2002). Experimental manipulation of 

riparian systems, evaluated both before and 

after treatment, is a preferable approach, but 

such treatments were not possible on federally 

managed lands during development of our study 

in the mid-1990s in western Washington. We 

gained insights using our retrospective approach 

of past management practices to more eff ectively 

develop a later manipulative study, detailed 

below.

Using a retrospective approach, sixty-two 

study sites were located on the west and south 

sides of the Olympic Peninsula, Washington, 

on state, federal, and private lands outside the 

Olympic National Park. A study site included 

a 300-m stream reach plus the adjacent forest 

area. We chose 300 m as our standard because 

we suspected that a shorter reach would likely 

refl ect the eff ects of upstream infl uences rather 

than the channel and adjacent stands. Streams 

were usually fi rst- to third-order, and <3 m across 

the wetted portion. We selected sites representing 

six forest conditions:

1. Old forest: unmanaged with intact forest on 

both sides of the stream; 

2. Buff ered old forest: old forest with adjacent 

clearcuts leaving buff ers of 10 to 30 m;

3. Young forest: 35- to 100-year-old forest with 

no adjacent harvest;

4. Th inned young forest: 35- to 100-year-old 

forest with commercial thinning extending to 

the stream;

5. Buff ered young forest: 35- to 100-year-old 

forest with adjacent clearcuts leaving 10- to 

30-m-wide buff ers of young forest adjacent to 

the stream; and 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Response of Small Mammals to Streamside Buff ers Raphael and Wilk 165

6. Early regeneration forest: 0- to 35-year-old 

forest on recent clearcuts with no intact buff er.

Stand types were not equally distributed across 

the study area because of diff ering ownerships 

and management practice histories. 

Our approach was a retrospective analysis that 

examined existing forest condition resulting 

from past management practices with diff erent 

intervals since logging, with and without 

streamside buff ers. Raphael et al. (2002) sampled 

mammals along transects that ran parallel to the 

stream. We established two transects along each 

stream reach, one close to the stream (generally 

within 20 m) and one upslope, spaced 100 m 

apart. Raphael et al. (2002) reported results from 

only the near-stream transect, and those are the 

fi ndings reported here because they pertain more 

directly to the riparian buff er portion of the study. 

Small mammals were trapped with Sherman livetraps. Pairs of traps were placed at 10-m intervals 

along transects for a total of 62 traps per transect. 

Total small mammal captures averaged 5.9 

individuals per 100 trap-nights; mean numbers 

of captures did not vary signifi cantly among stand 

conditions (fi g. 1). Raphael et al. (2002) found 

signifi cant diff erences in relative abundance of 

the Pacifi c Jumping Mouse (Zapus trinotatus) 

among stand conditions, with greater abundance 

in younger stands than older stands regardless of 

buff er type. Abundance of the four other more 

common species did not diff er signifi cantly among 

sites. Capture rates of four of the fi ve species were 

correlated with physical stream features. Keen’s 

Mouse (Peromyscus keeni) was more abundant 

in smaller streams at lower elevations. Th e Deer 

Mouse (P. maniculatus) was also more abundant 

in smaller streams, but its abundance was not 

correlated with elevation or stream gradient. 

Th e Dusky Shrew (Sorex monticolus) was more 

abundant at higher elevations in steeper streams. 

Abundance of the Pacifi c Jumping Mouse 

increased with lower elevations. Abundance of 

Trowbridge’s Shrew (S. trowbridgii) did not vary 

signifi cantly with any of the physical attributes 

of streams. O’Connell et al. (2000), in their 

study of riparian sites in managed forests of the 

Cascade Range of Washington, found that total 

abundance and species richness of birds and small 

mammals using areas close to streams before any 

timber harvest were comparable to the number 

and kinds after harvest. At the species level, 

O’Connell et al. (2000) found that abundance of 

Pacifi c Jumping Mouse increased in buff ers along 

streams following harvest; our data, while not 

conclusive, are consistent with their observation. 

Experimental Study

In hopes of reducing the confounding eff ects 

of site variability, we subsequently undertook 

an experimental study on state lands in western 

Washington along 23 fi rst- and second-order 

headwater streams to evaluate conditions both 

before and after treatment (Wilk et al. 2010). 

Th e four treatments, grouped within blocks 

of adjacent catchments to reduce variation in 

stream size, gradient, and elevation, included 

unlogged control streams, continuously buff ered 

streams (strips), patch-buff ered streams, and 

unbuff ered streams within upland cut-over 

Figure 1—Mean number of captures of small mammals 

per 100 trap-nights in a retrospective study of existing 

site conditions on the Olympic Peninsula, Washington 

(from Raphael et al. 2002).
Density Management in the 21st Century: West Side Story PNW-GTR-880

166 Response of Small Mammals to Streamside Buff ers Raphael and Wilk

stands. We sampled small mammals in 2003 

before logging and then for 2 years following 

logging. We sampled by using 36 live traps (half 

on each side of stream) spaced at 5-m intervals 

within 2 m of the stream. We checked traps daily 

over 3 successive nights in 5 bouts that were 2 

to 3 weeks apart. Among all taxa with suffi cient 

numbers of captures for analysis, we found 

signifi cant changes in abundance of each species 

following logging, including a larger decline in 

abundance of Keen’s Mouse in all treatments 

relative to controls (fi g. 2), and increases in 

abundance of the Creeping Vole (Microtus 

oregoni), the Southern Red-backed Vole (Myodes 

gapperi), and Townsend’s Chipmunk (fi g. 3). We 

also observed increases in abundance for the Deer 

Mouse in continuous buff ers and no buff ers, and 

the Pacifi c Jumping Mouse in patch buff ers. Th e 

Shrew-mole (Neurotrichus gibbsii) decreased in 

the streams with no buff ers. Relative to controls, 

diversity of small mammals (including total 

captures, species richness, and species evenness) 

did not change signifi cantly following logging in 

any of the treatments (fi g. 4). Variation among 

sites was large, making diff erences among species 

in each treatment diffi cult to detect (example: 

Figure 2—Mean number of Keen’s Mice (Peromyscus 

keeni) captured per stream reach before and after 

treatment in four different stream buffer treatment types 

(from Wilk et al. 2010). Error bars represent 90 percent 

confidence interval. Figure 3—Mean number of Townsend’s Chipmunks 

(Tamias townsendii) captured per stream reach before and 

after treatment in four different stream buffer treatment 

types (from Wilk et al. 2010). Error bars represent 90 

percent confidence interval. Asterisks indicate differences 

in abundance between pre- and post-treatments; letters 

indicate a difference between treatment and control 

within years.

Figure 4—Mean total number of captures of small 

mammals per 100 trap-nights in an experimental study 

of stream buffer treatments on state lands in western 

Washington (from Wilk et al. 2010). Error bars represent 

90 percent confidence interval.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Response of Small Mammals to Streamside Buff ers Raphael and Wilk 167

Trowbridge’s Shrew and Dusky Shrew that had 

high abundance but large SE). Diff erences we 

observed could be due to change in forest cover, 

not riparian infl uences per se. Overall, we observed 

that total abundance of small mammals did not 

diff er much among treatments, but that species 

composition did change (fi g. 5). We also found 

that capture rates of some of the more specialized 

species such as Water Shrews (Sorex palustris) 

and Marsh Shrews (S. bendirii)] were too low to 

allow conclusions about treatment eff ects. For 

these rarer species, more focused autoecological 

studies will be needed to better evaluate their 

habitat relationships along headwater streams 

and their potential responses to streamside buff er 

treatments.

Although we observed signifi cant eff ects of 

alternative buff er designs on abundance of most 

of the more common small mammal species 

in our study, the experimental approach was 

challenging to implement consistently among 

sites. Th ese challenges need to be acknowledged, 

because they may have aff ected results and 

constrain the scope of inference of our fi ndings. 

Treatments were not assigned randomly and 

the design was not balanced (not all treatments 

occurred in all blocks) owing to logistical 

constraints associated with roads and anticipated 

costs of treatments. Furthermore, treatments 

did not occur when originally planned, due to 

realities of timber markets driving the timing of 

timber sales. Implementation of timber harvest 

among years introduces potential time eff ects 

on small mammal populations that were not 

controlled among sites. Such a time eff ect may 

be refl ected in our single pre-treatment year of 

data collection as well. Implementation of buff er 

design, especially strip buff ers, varied noticeably, 

from dense shading to narrow and open. Finally, 

windstorms caused blowdown of trees within 

buff ers on many of the treated sites, causing 

changes in habitat structure that obscured 

some diff erences among treatments. Despite 

these challenges, stand-scale forest experimental 

studies are valuable for the insights they can 

provide us regarding responses to anthropogenic 

disturbances under conditions that are largely 

controlled. Our mammal responses to combined 

riparian buff ers and upland cut-over area provide 

such insights that can be tested elsewhere.

Overall, our results demonstrate that 

populations of the more common species of 

small mammals in our study changed following 

logging along streams. Changes in abundance we 

observed were species-specifi c, with some species 

abundances increasing and some decreasing 

following harvest. Th e changes we observed 

seemed to refl ect change in amount of preferred 

forest habitat, either early-seral or late-seral, 

depending on species. We could not show that 

these changes were due to retention of streamside 

buff ers per se. Furthermore, none of the common 

species we were able to sample adequately included 

riparian obligates as identifi ed in Anthony et al. 

(2003). Our results do not mean that riparian 

buff ers are not important for small mammals. 

Retention of suitable habitat along streams will 

contribute to the total amount and connectivity 

of habitat at broader scales, and thus should 

Figure 5—Changes in species composition of small 

mammals (percent similarity with control sites) before 

and after logging to create alternative buffer designs 

on state lands in western Washington (after Wilk et al. 

2010). Error bars represent ± SE.
Density Management in the 21st Century: West Side Story PNW-GTR-880

168 Response of Small Mammals to Streamside Buff ers Raphael and Wilk

contribute to conservation of these species in 

managed landscapes. Th e potential role of riparian 

buff ers could include enhanced opportunities for 

dispersal of populations of small mammals (e.g., 

Doyle 1990), but our sampling was not designed 

to evaluate dispersal rates. Future studies should 

include an explicit investigation of the role of 

riparian buff ers as dispersal corridors, as well as 

more detailed investigation of population fi tness 

of selected species in relation to buff er design.

Acknowledgments

We thank the USDA Forest Service, Pacifi c 

Northwest Research Station for funding these studies, 

along with partial support from the Washington State 

Department of Natural Resources and the University 

of Washington, Olympic Natural Resources Center. 

We also thank Larry Jones, who led the fi eld work 

during the early phases of these studies, along with 

the many fi eld assistants who collected the bulk of the 

observations we report. Jim Baldwin and Tim Max 

provided statistical advice. Th e manuscript benefi tted 

from reviews by Eric Forsman, Dede Olson, and an 

anonymous reviewer.

Literature Cited

Anthony, R.G.; O’Connell, M.A.; Pollock, M.M.; 

Hallett, J.G. 2003. Associations of mammals 

with riparian ecosystems in Pacific Northwest 

forests. In: Zabel, C.J.; Anthony, R.G. eds. 

Mammal community dynamics. Cambridge, UK: 

Cambridge University Press: 510–563.

Doyle, A.T. 1990. Use of riparian and upland habitats 

by small mammals. Journal of Mammalogy. 71: 

14–23.

Forest Ecosystem Management Assessment Team 

[FEMAT]. 1993. Forest ecosystem management: 

an ecological, economic, and social assessment. 

Portland, OR: U.S. Department of Agriculture; 

U.S. Department of the Interior [and others]. 

[Irregular pagination].

O’Connell, M.A., Hallett, J.G.; West, S.D.; Kelsey, 

K.A.; Manuwal, D.A.; Pearson, S.F. 2000. 

Effectiveness of riparian management zones in 

providing habitat for wildlife. Final Report, Timber 

Fish and Wildlife. TFW-LWAG1-00-001. Seattle: 

University of Washington.

Raphael, M.G.; Bisson, P.A.; Jones, L.L.C.; Foster, 

A.D. 2002. Effects of streamside forest management 

on the composition and abundance of stream 

and riparian fauna of the Olympic Peninsula. In: 

Johnson, A.C.; Haynes, R.W.; Monserud, R.A., 

eds. Congruent management of multiple resources: 

proceedings from the wood compatibility initiative 

workshop. Gen. Tech. Rep. PNW-GTR-563. 

Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Research Station: 

29–40.

Thomas, J.W.; Raphael, M.G.; Anthony, R.G.; 

Forsman, E.D.; Gunderson, A.G.; Holthausen, 

R.S.; Marcot, B.G.; Reeves, G.H.; Sedell, J.R.; 

Solis, D.M. 1993. Viability assessments and 

management considerations for species associated 

with late-successional and old-growth forests of the 

Pacific Northwest. Portland, OR: U.S. Department 

of Agriculture, Forest Service. 523 p.

U.S. Department of Agriculture, Forest Service; 

U.S. Department of the Interior, Bureau of Land 

Management [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. [Place 

of publication unknown]. 74 p. [plus Attachment 

A: standards and guidelines].

Wilk, R.J.; Raphael, M.G.; Nations, C.S.; Ricklefs, 

J.D. 2010. Initial response of small grounddwelling mammals to forest alternative buffers 

along headwater streams in the Washington Coast 

Range, USA. Forest Ecology and Management. 

260: 1567–1578.

Citation:

Raphael, Martin G., and Randall J. Wilk. 2013. Th e Riparian Ecosystem Management Study: response of small mammals 

to streamside buff ers in western Washington. In: Anderson, Paul D.; Ronnenberg, Kathryn L., eds. Density management 

for the 21st century: west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacifi c Northwest Research Station: 163–168.
Density Management in the 21st Century: West Side Story PNW-GTR-880

169

Peter A. Bisson is a research fi sh biologist (emeritus), Shannon M. Claeson is a professional ecologist, and Alex D. Foster

is a professional ecologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3625 

93rd Avenue SW, Olympia, WA 98512-9193; pabisson@fs.fed.us; Steven M. Wondzell is a research aquatic ecologist, 

USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, 

OR 97331; Ashley Steel is a statistician/research quantitative ecologist, USDA Forest Service, Pacifi c Northwest Research 

Station, Forestry Sciences Laboratory, 400 North 34th Street, Suite 201, Seattle, WA 98103

Evaluating Headwater Stream Buffers: Lessons 

Learned from Watershed-scale Experiments in 

Southwest Washington

Peter A. Bisson, Shannon M. Claeson, Steven M. Wondzell, Alex D. 

Foster, and Ashley Steel

Abstract

We present preliminary results from an experiment in which alternative forest buff er treatments 

were applied to clusters of watersheds in southwest Washington using a Before-After-ControlImpact (BACI) design. Th e treatments occurred on small (~2- to 9-ha) headwater catchments, and 

compared continuous fi xed-width buff ered, discontinuous patch-buff ered, and unbuff ered streams 

to an adjacent unlogged reference catchment. Eight treatment clusters were monitored from 2001 

to 2006; four were located in the Black Hills (Capitol State Forest) and four in the Willapa Hills of 

the Coast Range. Logging took place in 2004 or 2005, depending on the cluster. Th e study streams 

were too small to support fi shes, but catchments did harbor amphibians, aquatic invertebrates, 

and riparian mollusks. In addition to biota, we examined water quality, discharge, and organic 

matter inputs. Th e intent was to monitor the sites two years pre-treatment and three years posttreatment, although unforeseen circumstances caused some exceptions. Overall, results suggested 

that relatively small but measurable changes in ecological condition occurred in most catchments 

where logging occurred. Changes were most apparent in streams having no buff ers. In catchments 

with no buff ers, summer water temperature increases were largest, organic matter inputs declined, 

and drifting invertebrates increased or decreased depending on their trophic guild. Changes in 

catchments with discontinuous patch buff ers were often complex and generally less detectable, and 

streams with continuous fi xed-width buff ers tended to exhibit the fewest changes in invertebrate 

communities and organic matter inputs relative to reference sites. 

Analyses of ecological response, both physical and biological, were fraught with diffi culty. 

Diffi culties in executing the study and analyzing results include operational planning and 

scheduling, spatial and temporal variability, and unplanned environmental disturbances. Based 

on our experience, we off er suggestions for future research on riparian management in small 

watersheds. First, think of watershed-scale studies as interventions that are carried out so as to 

maximize what we can learn from them, rather than as true experiments. Second, if the study 

covers several locations, thoroughly characterize diff erences in physical and biological features 

among the sites before treatments are applied to avoid misinterpreting results. Th ird, be prepared 

to accommodate uncontrolled environmental disturbances (e.g., droughts, fl oods, wildfi res, etc.) 

that are inevitable in multi-year investigations. Fourth, once the basic experimental layout is 
Density Management in the 21st Century: West Side Story PNW-GTR-880

170 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

established, resist the temptation to switch treatments midway through the study, which will only 

confound analyses. Finally, when surprises occur, be fl exible enough to monitor their eff ects to take 

advantage of learning opportunities.

Keywords: riparian management, buff ers, headwater streams, small watershed studies, experimental 

design, BACI.

Pesticide Precautionary Statement

Th is publication reports research involving pesticides. It does not contain recommendations for their use, nor does it 

imply that the uses discussed here have been registered. All uses of pesticides must be registered by appropriate state or 

federal agencies, or both, before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fi sh or other wildlife—if 

they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for 

the disposal of surplus pesticides and pesticide containers.

Introduction

When the Northwest Forest Plan (NWFP) was 

implemented in the late 1990s, one of the most 

signifi cant information gaps was whether the 

new buff er guidelines in the NWFP conserved 

suffi cient amounts of riparian forest to protect 

fi sh habitat in headwater streams. Th e default 

guideline in the NWFP called for riparian buff ers 

as wide as or wider than a site-potential tree 

height on each side of stream channels. While 

there were theoretical reasons to believe that wide 

buff ers protected headwater stream functions 

and processes (Sedell et al. 1994), fi eld studies 

verifying the effi cacy of wide buff ers were lacking. 

Furthermore, the NWFP’s riparian conservation 

areas were focused on habitat protection for 

salmonid fi shes, but questions remained about 

whether the guidelines adequately protected the 

habitats of other aquatic and riparian-associated 

species or the processes that provide organic 

matter and sediment to downstream salmonbearing rivers.

To address the scarcity of information about 

the eff ectiveness of buff ers of diff erent width and 

forest age, we initiated a study in 1996 (Riparian 

Ecosystem Management Study—REMS) that 

employed a synoptic survey approach in which 

a large number of streams in watersheds with 

diff erent logging histories and diff erent buff er 

patterns were compared. Th e research was 

located on Washington’s Olympic Peninsula, and 

included both aquatic and riparian-associated 

vertebrates (Bisson et al. 2002; Raphael et 

al. 2002). As a part of REMS, faunas were 

compared for small, perennially-fl owing streams 

that included sites where no buff ers were left 

during timber harvest, sites where narrow (<20 

m) buff ers were left, sites where wide buff ers that 

had been thinned were left, and sites where intact 

unmanaged buff ers >100 m were left. Using 

correlation analysis, we found that fewer fi sh 

were associated with late-seral riparian buff ers; 

however, fi sh densities were strongly infl uenced 

by local stream habitat conditions such as the 

abundance of pools. Further, fi sh abundance was 

positively correlated with riparian characteristics 

associated with increased primary production 

—light gaps, nutrients and deciduous organic 

matter inputs. Stream-dwelling amphibians 

were positively correlated with late-seral forest in 

riparian zones and the amount of late-seral forest 

in their watersheds. Th eir abundance was also 

negatively associated with roads.

While these observations were interesting and 

our results were consistent with the fi ndings 

of other stream investigations in the Pacifi c 

Northwest, we felt that a broad-scale survey 

approach relying on correlation analysis did not 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 171

yield many new insights into how environmental 

factors related to riparian buff ers directly or 

indirectly infl uenced the vertebrates of interest. 

To learn more about the eff ects of diff erent-sized 

buff ers on headwater streams, we undertook a 

second phase of REMS that applied alternative 

riparian buff er treatments to entire small 

watersheds using a Before-After-Control-Impact 

(BACI) experimental design. We anticipated 

monitoring the study catchments for two years 

prior to treatment and three years after treatment. 

We also decided to focus our research on the very 

smallest non-fi sh bearing headwater streams. 

Th e infl uence of riparian buff ers on very small 

headwater streams had been little studied, and 

the current Forest Practices Act in Washington 

state does not require that buff ers be left along 

non-fi sh bearing channels on state- or privatelymanaged lands.

Th is paper describes the planning, design, 

implementation, and results of the second phase 

of the REMS study. We examine the problems 

and unforeseen surprises encountered over the 

course of the study, and the lessons learned that 

might be applicable to future watershed-scale 

studies of a similar nature. Th e BACI approach 

is widespread in ecological science (Downes 

et al. 2002), but we experienced a number of 

design, implementation, and analytical hurdles 

in applying it to our situation. Th e concluding 

section of the paper suggests general guidelines 

for investigators contemplating similar studies. 

Th ese lessons are largely independent of the 

specifi c results of REMS, but hopefully will be of 

some use in future research.

 Site Selection

We experienced many of the diffi culties in 

conducting landscape-scale experiments in 

AMAs (Adaptive Management Areas—see 

http://www.reo.gov/ama/index.htm) that were 

discussed by Stankey et al. (2003). Our original 

intention was to compare the NWFP default 

buff ers for headwater streams with other buff er 

confi gurations on the Olympic Peninsula where 

the fi rst REMS phase was completed. We hoped 

the study could take place in an AMA that was 

designated as a place where departures from the 

standards and guidelines in the NWFP could 

be tested experimentally. We found, however, 

that the Olympic National Forest was unable 

to implement a watershed-scale experiment that 

involved diff erent stream buff ers in any AMAs 

on the Olympic Peninsula. Two other national 

forests in western Washington also declined 

to participate in the study. Several reasons 

were given, including the scale at which we 

wanted to apply the treatments, concerns over 

potential environmental litigation, and confl icts 

between our proposed experiment and other 

forest management plans. Taken together, these 

restrictions made it impossible for the research to 

take place in an AMA. 

We then approached the Washington 

Department of Natural Resources (DNR) 

to explore opportunities for implementing 

watershed-scale buff er trials in western 

Washington on state-managed lands. Under 

DNR’s guidance several study areas were located 

in the Coast Range of southwestern Washington 

(fi g. 1) where alternative buff er treatments could 

be applied to small non-fi sh bearing streams in 

headwater catchments of approximately 5 ha. 

Objective and Treatments

Th e objective of REMS Phase 2 was to compare 

the ecological eff ects of 15- to 20-m continuous 

(“fi xed-width”) buff ers on each side of the 

channel, discontinuous (“patch”) buff ers, and no 

buff ers (“clearcuts”), with adjacent reference sites 

of mature second-growth forest. One to two sitepotential tree height buff ers in the NWFP were 

not included among the treatments, as these were 

not an option under DNR’s Habitat Conservation 

Plan (Washington State Department of Natural 

Resources 2005).

Current Washington state law does not require 

buff ers on small non-fi sh bearing headwater 

streams, i.e., those extending from the channel 
Density Management in the 21st Century: West Side Story PNW-GTR-880

172 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

initiation point to the confl uence with a larger 

stream. Th ese streams, however, are protected 

from heavy equipment intrusion and in-channel 

yarding during logging operations. Th e fi xedwidth and patch-buff er treatments in our study 

represented alternative protection measures that 

would provide additional protection, beyond 

heavy equipment exclusion, for very small 

headwater streams, but these buff ers would not 

include the relatively wide site-potential tree 

height buff ers that were the default standard on 

federal lands. Th us, our study was most directly 

applicable to headwater streams in state and 

private industrial forests.

We selected clusters of small watersheds in 

two locations—Capitol State Forest southwest 

of Olympia, Washington, and the Willapa Hills, 

an area of mixed forest ownership which drains 

into Willapa Bay north of the Columbia River 

(fi g. 1). Each location contained four clusters of 

headwater streams, and each cluster contained 

a reference catchment and a combination of 

treatment types (table 1). It was our goal at 

the outset to establish a balanced experimental 

design with each treatment represented in each 

cluster; however, this turned out to be impossible 

for operational reasons. Cluster size ranged from 

three to fi ve catchments because timber sale plans 

and forest stand characteristics did not always 

accommodate harvesting small watersheds in 

the exact confi guration we desired. Occasionally 

a cluster would possess two similar treatments 

and omit one treatment type. Furthermore, 

engineering considerations mandated that 

reference catchments be located at an end of a 

cluster in order to avoid roads and other harvestFigure 1—Location of eight clusters of non-fish-bearing headwater streams sampled in REMS Phase 2 (Riparian 

Ecosystem Management Study) within two regions of southwestern Washington, USA. Capitol Forest sites are located 

in the Black Hills area near Olympia, WA, and the Willapa Hills sites are located near Raymond, WA.

Willapa Hills

Black

Hills
Density Management in the 21st Century: West Side Story PNW-GTR-880

Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 173

Table 1—Physical characteristics of eight clusters of 30 headwater catchments in the Pacific Coast Range, 

Washington, USA. Table modified from Janisch et al. (2012).

Cluster

Logging 

initiation

1st postlogging 

year

Catchment 

logging 

treatment

Areaa

(ha)

Channel 

lengthb

(m)

Bankfull

widthc

(m)

Channel 

gradientd

(%) Aspect

Elevatione

(m)

Seasonally 

dry

Black Hills (Capitol Forest)

Moonshine July 2005 2006 Reference 8.5 173 1.2 36 W 393 yes

Patch 8.5 270 0.6 32 W 287 no

Fixed-width 2.7 176 0.4 35 W 318 yes

Patch 4.8 176 1.8 37 W 390 no

Rott April 2004 2004 Reference 6.0 391 0.9 29 S 246 no

Fixed-width 7.3 403 0.8 37 S 288 no

Clearcut 4.5 123 0.9 39 S 303 yes

Patch 5.1 165 0.4 42 S 314 no

See Saw September 

2003

2004 Reference 6.5 173 2.3 27 N 336 no

Clearcut 2.1 229 0.4 13 N 212 no

Fixed-width 4.2 273 0.7 18 NW 212 no

Tags January 

2004

2004 Reference 5.5 206 — 46 NE 193 no

Fixed-width 3.9 241 — 41 NE 203 no

Patch 4.4 270 — 45 NE 218 no

Patch 5.4 280 — 40 NE 230 no

Clearcut 4.9 297 — 38 NE 234 no

Willapa Hills

Ellsworth February 

2005

2005 Reference 1.9 111 — 17 NW 64 no

Clearcut 3.5 255 0.7 18 SW 28 no

Fixed-width 8.1 375 0.7 11 SW 12 no

Lonely 

Ridge

March 

2004

2004 Reference 2.8 209 0.5 24 E 168 yes

Clearcut 1.9 184 0.4 30 E 168 no

Fixed-width 3.3 263 0.6 21 E 168 no

Patch 3.1 282 1.4 25 E 169 no

McCorkle November 

2003

2004 Reference 2.7 311 1.8 24 NW 121 no

Fixed-width 2.6 146 0.4 17 SE 110 no

Fixed-width 3.5 155 0.5 18 S 110 no

Split Rue May 2004 2005 Reference 6.2 229 — 26 N 225 no

Clearcut 4.9 168 — 22 NE 205 no

Fixed-width 8.1 480 — 21 N-NE 292 no

Clearcut 3.4 203 — 27 SE 186 no

a

Headwater catchment area derived from stereo pairs and ERDAS Stereo Analyst®.

b

Channel length defined as the confluence to headwall or uppermost point of channel definition.

c

Channel bankfull width calculated as the weighted mean of sub-segments in 2003.

d

Channel gradient calculated as the weighted mean of sub-segments.

e

Elevation of the channel confluence as determined from state 30-m DEM.
Density Management in the 21st Century: West Side Story PNW-GTR-880

174 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

related factors. For example, the reference 

catchments for the See Saw and Split Rue clusters 

were located 1.2 and 3.3 km, respectively, from 

the treatment catchments. Apart from these 

constraints, treatments were assigned randomly 

to individual catchments. A photograph of one of 

the clusters is shown in fi gure 2. Th e lower reaches 

of the study streams were always forested because 

they passed through the riparian management 

zone (RMZ) of the fi sh bearing stream into which 

they discharged. All measurements of treatment 

eff ects were made at, or above, the boundary of the 

RMZ into which the headwater stream fl owed. 

Typical views of riparian areas after treatments 

were applied are shown in fi gure 3. Th e streams 

maintained surface fl ow continuously during the 

wet season, but the channels occasionally became 

intermittent during the dry season, and surface 

connections with the parent stream were often 

disrupted, although subsurface fl ow pathways 

likely remained active.

Implementation and Monitoring 

Surprises

We experienced several surprises during the 

pre-treatment, treatment, and post-treatment 

periods of the research. Some surprises were 

management-related; others resulted from 

natural events. In addition to being unable to 

establish a complete and balanced study design 

and to fully randomize treatment assignments, 

the desired one-year treatment interval was 

spread over two years when shifts in stumpage 

prices delayed several timber sales. Furthermore, 

the delay in harvesting some catchments took 

place when the regional weather pattern was 

changing from a multi-year warm, dry period to 

a cool, wet period caused by a transition from an 

El Niño to a La Niña weather cycle (Bumbaco 

and Mote 2010). Th e change in temperature and 

precipitation during the treatment period altered 

the hydrologic patterns of the study streams 

and, coupled with the harvesting delay in some 

clusters, added to the diffi culty of sorting out 

treatment eff ects from weather-mediated changes 

in the parameters that were monitored.

In 2006, after the timber had been harvested 

from all study locations, some of the harvest 

units were treated with aerially applied herbicide 

as part of routine site preparation prior to 

reforestation. Although the helicopter operators 

exercised caution when applying the herbicide, 

it is likely that occasional overspray or wind drift 

occurred and some chemical entered the streams; 

however, precise wind strength and direction data 

Figure 2—One of the experimental 

buffer treatment clusters in Capitol 

Forest showing fixed-width, clearcut, 

patch, and reference catchments, 

respectively, from left to right. Stream 

channels are shown in white. (Photo 

by Randall Wilk, USFS.)
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Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 175

at the sites were not available. Because this was 

an unanticipated management action, we were 

not fully prepared to sample its eff ects on stream 

biota, and the fact that some harvest units, but 

not others, were sprayed made it impossible to 

determine if herbicide application signifi cantly 

aff ected the results of the study.

Additional surprises occurred when severe 

windstorms in the winters of 2005, 2006, and 

2007 caused extensive damage to some of the 

buff er treatments, especially at several of the 

Willapa Hills catchments (fi g. 4). As a result of the 

windthrow, some fi xed-width buff er treatments 

were altered to such an extent that they resembled 

patch treatments. Stream channels at sites with 

extensive disturbance often contained large 

amounts of fi ne sediment that entered streams 

when root systems were upturned. Th e windthrow 

also damaged a number of monitoring stations 

for forest litter and riparian-associated mollusks. 

Although windstorms were not factored into the 

original experimental design, we note that coastal 

watersheds in western Washington frequently 

experience high wind events in fall and winter, 

so occurrence of such storms during the REMS 

study was not out of the ordinary.

Finally, in November 2007 an intense storm 

passed through southwestern Washington and 

some watersheds received >30 cm of rain within 

48 hours. Mass wasting was extensive throughout 

the Coast Range, and a large landslide and 

accompanying debris fl ow occurred in one of the 

patch-buff ered study streams (Moonshine cluster) 

in Capitol Forest. Th e debris fl ow caused massive 

channel scouring and entrainment of riparian 

vegetation and destroyed existing monitoring 

equipment. Despite all these challenges, we feel 

the work yielded some valuable information 

with relevance to headwater stream management 

and it taught us several important lessons about 

Figure 3—Post-logging appearance of typical reference and experimental treatments. (Photos by Peter Bisson.)
Density Management in the 21st Century: West Side Story PNW-GTR-880

176 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

pitfalls in designing and executing watershedscale manipulations.

Results

Results are presented for stream temperature, 

aquatic and riparian invertebrates and terrestrial 

litter inputs (fi ne particulate organic matter 

and coarse particulate organic matter). Due to 

time and budget constraints some samples were 

obtained only from a subset of study locations 

(table 2). Other aspects of the study were headed 

by other investigators and those aspects are not 

reported here. We briefl y describe methods and 

statistical tests, but additional details of sampling 

methods and analytical techniques will appear in 

subsequent technical reports and publications. 

Below we present fi ndings of the research thus 

far.

Stream Temperature

All streams were instrumented with recording 

temperature loggers and comparisons among 

treatments focused on the daily maximum 

temperatures during the July-August period of 

peak yearly temperatures (Janisch et al. 2012). 

Relationships between daily maximum stream 

temperatures in the treatment catchments and 

their associated reference sites during the pretreatment phase of the study were used to predict 

daily maximum temperatures during the warmest 

part of the summer. After treatments were 

applied, departures from expected values were 

computed to determine if the treatment streams 

diff ered signifi cantly from what was expected 

(Ho = no diff erence). Results for the fi rst posttreatment year, which would be assumed to show 

the greatest treatment eff ects, are displayed in 

fi gure 5.

Stream temperatures in the unlogged reference 

catchments generally matched predictions, i.e., 

no signifi cant changes occurred during the fi rst 

post-treatment year. Average increases in daily 

maximum stream temperature were greatest in 

the clearcut sites, but the other two treatment 

types also exhibited signifi cant thermal increases. 

Somewhat surprisingly, stream temperatures in 

the fi xed-width buff er treatments exhibited a 

greater increase in the fi rst post-treatment year 

than those in patch buff er treatments, although 

air temperature increases in the fi xed-width 

buff er sites increased less than air temperatures in 

the patch buff ers (Janisch et al. 2012). Maximum 

daily summer stream temperatures rose in each 

treatment category; however, overall temperature 

increases were small, the trends did not entirely 

match expected treatment eff ects (changes 

tended to be greater at sites with continuous 

fi xed-width buff ers than sites with patch buff ers), 

and the responses were highly variable within 

treatment categories. Further analyses by Janisch 

et al. (2012) indicated that water temperature 

Figure 4—Top: extensive windthrow in a fixed-width 

buffer site after a windstorm in 2005. Bottom: view of 

the stream channel showing sediment input caused by 

upturned rootwads. (Photos by Peter Bisson.)
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Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 177

was strongly infl uenced by streambed texture, 

the presence of small wetlands in the catchment, 

and the length of channel exposed to sunlight. 

Th is suggests that, in addition to the presence or 

absence of forest canopy, the length of exposed 

stream channel and the amount of hyporheic 

water exchange are important factors regulating 

headwater stream temperatures.

Aquatic Invertebrates

Th e role of non-fi sh bearing streams in 

exporting aquatic invertebrates (potential 

food items) to fi sh-bearing streams is poorly 

understood; however, there is evidence that 

invertebrates exported from non-fi sh bearing 

streams provide important food resources for 

salmonids downstream (Wipfl i and Gregovich 

2002). Th e extremely heterogeneous substrates 

of the headwater channels, which consisted of a 

wide range of sizes of unsorted inorganic particles 

as well as tree roots and a variety of coarse and fi ne 

wood fragments, precluded benthic invertebrate 

sampling. Instead, invertebrates present in the 

surface water drift were sampled at gauging 

stations located at the downstream boundary of 

the headwater streams where the channel entered 

the riparian management zone of the larger 

stream into which it fl owed.

Drifting invertebrates were collected from six 

of the eight clusters, three clusters in Capitol 

Forest and three in Willapa Hills (table 2). Weirs 

with pass-through PVC pipes were placed in 

each study stream so that drift nets attached to 

the pipes were able to capture the entire surface 

fl ow during spring, summer, and fall sampling. 

Drifting invertebrates were collected in 250-

μm mesh tubular nets, fi shed for one full day 

Figure 5—Changes in the maximum daily stream temperature (°C) in the first post-treatment year (or post-calibration 

year for reference catchments) during July and August at each site. The box and whisker plots denote the mean, 

quartiles, and 10- and 90-percentiles of water temperature deviations (observed minus predicted daily maximum 

temperature) in each catchment. Points represent more extreme daily departures from predictions in the first posttreatment year. The 95 percent prediction intervals for the daily random disturbance (in temperature variation; greyshaded zone) was calculated as 0.00 ± 1.96 · SD of the single largest SD of all pairwise comparisons among reference 

catchments in the calibration year. The average change in maximum daily stream temperature for each treatment is 

indicated by a bold line in each box (after Janisch et al. 2012).
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178 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

Table 2—Type of samples collected from eight clusters of headwater catchments in the Coast Range 

of Washington, USA. “yes” indicates that metric was sampled, “no” indicates that metric was not 

sampled at that particular catchment.

Region Cluster Treatment

Water 

temperature

Aquatic

invertebrates

Riparian 

mollusks

Riparian 

literfall

Black Hills

(Capitol 

Forest)

Moonshine Reference yes* no no no

Patch no no no no

Fixed-width no no no no

Patch yes no no no

Black Hills 

(Capitol 

Forest)

Rott Reference no yes no yes

Fixed-width no yes no yes

Clearcut no no no yes

Fixed-width no yes no yes

Black Hills 

(Capitol 

Forest)

See Saw Reference yes* yes no yes

Clearcut yes yes no yes

Fixed-width yes yes no yes

Black Hills 

(Capitol 

Forest)

Tags Reference yes yes yes yes

Fixed-width yes yes yes yes

Patch yes yes yes yes

Patch yes yes yes yes

Clearcut yes yes yes yes

Willapa Hills Ellsworth Reference yes yes yes yes

Clearcut yes yes yes yes

Fixed-width yes yes yes yes

Willapa Hills Lonely Ridge Reference yes* yes no yes

Clearcut no yes no yes

Fixed-width yes yes no yes

Patch yes yes no yes

Willapa Hills McCorkle Reference yes no no no

Fixed-width yes no no no

Fixed-width yes no no no

Willapa Hills Split Rue Reference yes yes yes yes

Clearcut yes yes yes yes

Fixed-width yes yes yes yes

Clearcut yes yes yes yes

*Stream was dry during the pre-treatment (calibration) year, so an alternative reference catchment 

was used for analysis.
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Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 179

at monthly (2003) or bi-monthly (2004–2006) 

intervals. Water temperature and stream discharge 

were measured at the beginning and end of each 

24-hour period. Drift density (individuals∙m-3 

water) was calculated by dividing invertebrate 

export by the mean discharge of the 24-h 

sampling period. Invertebrates were categorized 

as insect or non-insect, aquatic or terrestrial, and 

by their functional feeding group as defi ned by 

Merritt and Cummins (1996). Drift samples 

were obtained in spring, summer, and fall, but 

snow prevented access to some of the sites in 

winter and no winter data are reported here. We 

tracked all natural log-transformed, post-year 

minus pre-year diff erences of seasonally averaged 

drift densities. Simple linear regression models 

were used to detect signifi cant eff ects (p < 0.05) 

among buff er treatments, post-harvest year, and 

clusters. Because only three of the six clusters 

received a patch treatment, the sample size was 

too small for statistical modeling; therefore, no 

data from the patch treatments are presented 

here. 

Th e most common terrestrial invertebrates 

in the drift were mites (Acari) and springtails 

(Collembola). Drift density proportions of 

terrestrial invertebrates increased signifi cantly in 

clearcuts during summer compared to changes 

at the fi xed-width buff er and reference locations 

(fi g. 6). Th e proportion of terrestrial invertebrates 

also increased at clearcut sites relative to reference 

sites in fall. In spring, no signifi cant diff erences 

were observed among the treatment and reference 

streams.

Mayfl ies (Ephemeroptera) were abundant 

aquatic invertebrates in all headwater streams, 

where they were represented by taxa adapted to 

scraping periphyton from the substrate (scrapers) 

or taxa that consumed organic detritus (collectorgatherers). No signifi cant diff erences in mayfl y 

drift densities were observed among treatment or 

reference streams in the spring or summer, but 

mayfl y densities in both clearcut and fi xed-with 

buff er treatments declined relative to reference 

catchments in fall (fi g. 7). Th is was surprising 

because small mayfl ies have been reported to 

prosper in streams where canopy openings 

have favored increased periphyton production 

(Hawkins et al. 1983). It is possible that logging 

and windthrow-related fi ne sediment inputs 

Figure 6—Change in the mean 

drift proportions of terrestrial 

invertebrates, by season, after 

treatment application compared 

to before treatment (± 1 standard 

error). Sampling intervals include 

one year pre-treatment and two 

or three years post-treatment. 

Photo insets represent typical 

body forms encountered in 

samples. All photos reproduced 

with permission.
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180 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

contributed to mayfl y reductions at the study 

locations, as taxa that occurred there are known 

to prefer coarse substrates.

Midge larvae (Chironomidae) are frequently 

the most ubiquitous invertebrates in small 

streams in the Pacifi c Northwest, and two midge 

groups (Orthocladiinae and Tanytarsini) were 

well represented in drift samples. Small-bodied 

midge larvae commonly enter the drift and 

often constitute a substantial portion of the diet 

of rearing salmonids (Chapman and Bjornn 

1969). Midges decreased in clearcut catchments 

relative to the fi xed-width buff er and reference 

catchments in the fall (fi g. 8). In the spring 

and summer, no signifi cant diff erences among 

treatment and reference streams were observed. 

Extremely high variability in spring prevented 

an apparent increase in midge drift densities in 

the treatment catchments from being statistically 

signifi cant.

We classifi ed aquatic invertebrates in drift 

samples into feeding guilds to determine if buff er 

characteristics aff ected functional feeding groups. 

Feeding guilds included scrapers (organisms 

that feed on periphyton), shredders (organisms 

that “shred” leaves and other riparian inputs), 

and collector-gatherers (organisms that feed on 

fi ne particulate organic material). No changes 

in shredder density proportions were observed 

in spring, summer, or fall (fi g. 9). Signifi cant 

declines in scrapers occurred in fall at clearcut 

catchments relative to fi xed-width buff er and 

reference locations. Likewise, collector-gatherers 

decreased at clearcuts in fall, but not during 

other seasons. Seasonal density proportions of 

other feeding guilds, such as collector-fi lters or 

predators, did not diff er among treatment or 

reference catchments.

Riparian Mollusks

We sampled the ground-dwelling riparian 

mollusk community at three of the clusters (table 

2) to determine if buff er treatments aff ected 

the spring and fall densities of snails and slugs. 

Figure 7—Changes in the mean drift densities of mayflies, by season, after treatment application compared to before 

treatment (± 1 standard error). Sampling intervals include one year pre-treatment and two or three years post-treatment. 

Photo insets represent typical body forms encountered in samples. All photos reproduced with permission.
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Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 181

Figure 8—Changes in the mean drift densities of midge larvae, by season, after treatment 

application compared to before treatment (± 1 standard error). Sampling intervals include one year 

pre-treatment and two or three years post-treatment. Photo insets represent typical body forms 

encountered in samples. All photos reproduced with permission.

Figure 9—Changes in the mean drift proportions of scrapers, shredders, and collector-gatherers, by season, after 

treatment application compared to before treatment (± 1 standard error). Sampling intervals include at least one year 

pre-treatment and two years post-treatment. All photos reproduced with permission.
Density Management in the 21st Century: West Side Story PNW-GTR-880

182 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

We focused on spring and fall seasons because 

mollusks burrow deep into the riparian forest litter 

in summer and some of the sites were inaccessible 

in winter. We used arrays of 30 x 30-cm artifi cial 

substrates made of laminated paperboard set out 

in evenly spaced patterns adjacent to the streams. 

After allowing several weeks for weathering and 

colonization, the laminations were peeled back 

and inspected under magnifi cation for mollusks 

and other organisms. Total mollusk densities (all 

species) in three of the watershed clusters are 

presented in fi gure 10. Once again, because a 

limited number of catchments with patch buff ers 

were sampled, only data for clearcut, fi xed-width, 

and reference catchments are presented.

In general, mollusk densities between treatment 

and reference catchments did not change after 

logging (fi g. 10). Th e reason mollusks were 

less abundant in catchments designated for 

no riparian buff ers (i.e., clearcut) even before 

treatments were applied is not known, although 

we suspect that watershed features unrelated 

to logging (e.g., presence of seeps) played an 

important role in infl uencing them, and the 

Figure 10—Mean total mollusk 

density (+ 1 standard error), by 

season, before and after treatment 

application (vertical dashed line) in 

three watershed clusters.
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Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 183

catchments selected for no buff er treatments 

happened to be less suitable for riparian mollusks 

by chance. As with aquatic invertebrates, the 

greatest divergence in mollusk abundance among 

treatment and reference locations occurred in 

fall.

Riparian Litter Inputs

Litterfall was sampled at six of the eight clusters, 

three in Capitol Forest and three in Willapa Hills, 

with an array of 40 x 40 x 10-cm traps spaced 

along the headwater channels. We placed litter 

traps 0 m, 10 m, and 20 m from the stream’s 

edge on both sides of the channel. Monthly or 

bimonthly samples were collected from spring 

through fall (generally April through November). 

In the laboratory, samples were dried, sorted into 

various categories (coniferous litter, deciduous 

litter including seeds, wood, lichens, and other 

material), and weighed. All dry weights were 

divided by the sampling interval and converted 

to g∙m-2∙day-1. Deciduous litter inputs were 

greatest in fall (October–December), whereas 

coniferous litter inputs dominated in summer 

(July–September). Th e wood component of 

litterfall was variable throughout the year, and 

lichen and other components were generally a 

small fraction of total inputs.

Riparian litterfall in clearcut catchments 

signifi cantly decreased to very low levels after 

treatment application (fi g. 11), although inputs 

were beginning to recover in the second posttreatment year. Litterfall also declined signifi cantly 

along patch-buff ered catchments, but only in the 

fall (fi g. 11). Fixed-width and patch-buff er litter 

inputs were highly variable post-logging, in part 

due to diff erences in windthrow among sites. No 

diff erences in litter amounts were observed at 

increasing lateral distances from the stream (0 m, 

10 m, or 20 m).

Preliminary Ecological Conclusions

Preliminary fi ndings suggest that biophysical 

changes in the headwater streams and 

riparian zones were detectable, but not large, 

after logging. Biological diff erences were most 

apparent in clearcut sites, especially in fall. An 

overall response to treatments was detectable, 

Figure 11—Changes in mean 

riparian litterfall, by season, 

after treatment application 

compared to input rates 

before treatment (± 1 standard 

error). (Photos by Shannon 

Claeson and Alex Foster.)
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184 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

although the signal was not strong. At no 

streams were dramatic changes observed in the 

biophysical response metrics we monitored after 

treatment. Temperature changes were relatively 

minor and, by themselves, did not likely have 

a major impact on the biota of the headwater 

stream communities. Changes in the composition 

of aquatic invertebrate communities were 

observed, but we did not see major reductions 

in macroinvertebrate diversity or feeding guild 

structure after logging. It was also apparent that 

changes were most discernible at catchments 

where no buff ers were left along headwater 

streams.

 Diff erences between continuous fi xed-width 

buff ers, patch buff ers, and reference catchments 

were much more diffi cult to detect. Because of 

the variability in the data and the small number 

of replicates, it was unclear whether these buff ers 

provided some form of protection or whether 

we simply did not have the statistical power to 

detect diff erences between buff ered and reference 

streams. For aquatic invertebrates, riparian 

mollusks, and terrestrial litter, diff erences among 

treatments were most apparent in fall. Concern 

often focuses on conditions in mid-summer, 

when streams are warmest, but our research 

suggests that monitoring in fall may be a more 

sensitive time to look for management impacts.

Watershed-Scale Experiments: 

Lessons Learned

In addition to the scientifi c results, we learned 

much about conducting experiments involving 

operational forest harvest at the scale of whole 

catchments as well as designing and implementing 

large-scale management research. Th ese lessons 

may be useful to others considering similar types 

of studies. 

Watershed-scale manipulations are interventions, designed to maximize what we 

can learn from them. Th ey are not classical 

experiments. Due to numerous implementation 

problems, we found it impossible to achieve a 

complete and balanced experimental design with 

all treatments applied to all watershed clusters. 

We believe that an ideal, balanced BACI statistical 

design with precisely replicated treatments and 

controls may be impractical to achieve in a 

broad landscape setting. Th is is not to imply that 

careful attention should not be given to setting 

up a study where management actions can be 

evaluated, but rather to accept that implementing 

such studies with normal operating constraints in 

disturbance-prone environments may well prove 

impossible. 

One of the major diff erences between a classical 

experiment and watershed-scale ecological 

experiment is the interpretation of control sites. 

Th e classical defi nition of a control would be a 

replicate that is identical to the treated replicated 

except that it does not receive the treatment. In 

lab studies or greenhouse experiments, the ability 

to impose control is an essential part of statistical 

analysis. However, at watershed scales, neither 

identical replicates nor rigid environmental 

control are feasible. Researchers must adapt the 

strengths of designed experiments to the realities 

of reference reaches or reference streams. 

Logistical constraints can prevent true 

random allocation of experimental treatments, 

and therefore “control” sites are diff erent from 

treated sites before treatments are administered. 

Even though reference and treated units in the 

REMS study were in close proximity, there 

were diff erences between catchments that 

presented analytical challenges. Where control 

or reference streams do not follow a similar 

trend pre-treatment, the use of control sites in 

a BACI design may actually reduce statistical 

power (Roni et al. 2005). In the REMS study, 

natural diff erences between reference and treated 

sites made it diffi cult to detect results that could 

be directly attributed to management actions. 

Based on our experience, it seems prudent to 

select reference locations as close as possible 

and as similar as possible to experimental 

treatment areas, and even then to be prepared for 

unanticipated variation among locations.
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Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 185

Natural variability can make it diffi cult to 

detect responses to experimental treatments, 

especially with the small sample sizes that are 

common in large-scale interventions. We were 

surprised that background levels of variability 

were so high, even in the absence of management 

actions. Temporal variability makes detection of 

ecological change diffi cult across a wide range 

of ecological phenomena. Temporal variability 

decreases statistical power, making it diffi cult to 

detect signifi cant treatment eff ects, and thereby 

necessitating either a larger sample size or a longer 

measurement window, or both. Roni et al. (2003), 

for example, re-analyzed data from four streams 

in coastal Oregon and concluded that it might 

take more than 70 years to detect a doubling 

of Coho Salmon (Oncorhynchus kisutch) smolt 

production in response to habitat restoration, 

even using a BACI design. Korman and Higgins 

(1997) found a similar result. Natural variability 

makes detecting eff ects of management very 

diffi cult. Th is poses a particular problem for 

watershed-scale studies that are limited with 

respect to sample size. Having a large sample size 

and randomizing treatments across study units 

can improve statistical power and reduce the 

potential for bias. 

Had we performed statistical power analyses 

to determine the time or sample size needed to 

evaluate the null hypothesis that no diff erences 

were attributable to buff er treatments, we 

would likely have had to either greatly expand 

the number of study sites or extend both the 

pre- and post-treatment monitoring intervals to 

a decade or more, and the post-logging forest 

would be regenerating anyway. Th e importance 

of long-term monitoring to the evaluation of 

environmental change has been a cornerstone of 

the U.S. Long Term Ecological Research network 

(http://www.lternet.edu/). Th is program has 

undoubtedly contributed to our understanding 

of watershed management. However, in an 

environment where decision-makers do not 

have the luxury of multi-decade time horizons 

for evaluating policy choices, we were essentially 

constrained to carry out the study in less time 

than was necessary to properly implement a 

BACI study that could accommodate natural 

variation in headwater areas. For similar reasons, 

increasing the study’s sample size was logistically 

and fi nancially impossible. Natural variability 

is a general problem in designing ecological 

experiments. A common tendency among 

scientists is to more intensively monitor a small 

set of study sites for a longer and longer period 

of time in order to truly understand patterns at 

a particular site; this is exemplifi ed by the Alsea 

Watershed Study in Oregon and the Carnation 

Creek Study in British Columbia. However, 

signifi cant statistical gains can be made by simply 

increasing the sample size, allowing the larger 

number of observations to absorb the natural 

variability so that trends across space and time 

can be quantifi ed (Liermann and Roni 2008). 

We had diffi culty determining whether 

observed changes in response variables were 

related to buff er treatments or to long-term 

changes that had nothing to do with the 

experimental design. Th e use of a BACI design 

with reference watersheds is intended to help 

control for temporal variation but, when all 

treatments are not administered in the same year, 

it is impossible to completely separate the year 

and treatment eff ect. Further, if the pre-treatment 

period does not include conditions experienced 

during the post-treatment phase, the assumption 

of stationarity is violated and the strength of the 

BACI design is weakened. Th is was the situation 

in the REMS study. Staircase designs (Walters et 

al. 1988), in which treatments are implemented 

over a series of years in stepwise fashion, are 

intended to separate the eff ects of environmental 

variation over time from treatment eff ects, and 

to control for time-treatment interactions. Th ese 

designs are also more complicated and expensive 

to carry out at large spatial scales. Th e specifi c 

questions being asked (e.g., How do buff ers 

infl uence the export of invertebrates to larger 

streams?) will determine the most appropriate 

study design, given natural variability. 
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186 Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al.

Experiments over large spatial scales are 

often confounded by unanticipated events.

During the study we encountered both natural 

and anthropogenic events that contributed to 

the diffi culty of detecting treatment eff ects. 

Th e large wind storms that struck the Willapa 

Hills catchments in the fi rst two post-treatment 

years caused so much windthrow in some of the 

fi xed-width and patch-buff er sites (fi g. 4) that 

these treatments departed signifi cantly from the 

original experimental design. In addition, heavy 

sediment inputs that accompanied the storms 

infl uenced many response variables, adding to 

already high levels of background variation. Th e 

landslide and debris fl ow that occurred in one of 

the Capitol Forest catchments in 2007 essentially 

terminated the study at that site. Finally, we 

did not anticipate that some of the catchments 

would be treated with herbicide as part of the 

routine site-preparation process. None of these 

events were factored into the original study 

design; however, in retrospect we believe that 

such surprises are not uncommon in multiyear, watershed-scale studies and may need to be 

accepted as an inevitable part of the research.

Scientists and managers need to work together 

to design, conduct, and interpret, results of largescale studies. Scientists and managers should 

work together to establish realistic expectations 

for what can be done to maximize learning 

opportunities where rigid control of factors 

other than the variables of interest cannot be 

achieved. For managers, this may mean forgoing 

some operational fl exibility to maintain as much 

treatment consistency as possible across study 

locations. For scientists, this may mean having to 

make some concessions in the types of treatments 

and the location and timing at which they are 

applied. Both managers and scientists should also 

collaborate to establish realistic expectations of 

results relative to the questions being asked. For 

example, we were naïve to think that we could 

fully assess the issue of headwater buff er effi cacy 

in a 5-year study. Post-treatment changes were 

still occurring when the study ended, and thus 

our work should be seen as an examination of the 

short-term responses of experimental catchments 

in southwestern Washington to diff erent buff er 

confi gurations. 

Implement the design and stick with it 

until you resolve the important question(s) or 

until the data show that actual uncontrolled 

variation is so diff erent from what was assumed 

during the planning phase that the design is not 

adequate to resolve the question. It is essential 

not to alter treatments in the middle of a study, 

even if the temptation to do so arises. In our 

study there was interest in salvaging trees that 

were blown down in the post-treatment storms. 

We were able to convince the managers that the 

additional disturbances created by salvage logging 

operations would only make it more diffi cult to 

evaluate post-treatment monitoring results at the 

aff ected locations. It is also important to recognize 

that when experimental results are simply so 

variable that there is no hope of answering the 

original questions, there may be no compelling 

reason to continue the study. It may take several 

years (or one exceptionally large disturbance) 

to reach this conclusion, but there is little to be 

gained by continuing research that cannot lead 

to new insights, even if treatment consistency is 

maintained.

Do not be afraid to investigate novel response 

metrics. When surprises occur, be fl exible 

enough to monitor their eff ects to maximize 

learning opportunities. It may become apparent 

after a study has been initiated that adding a 

new metric to the suite of response variables 

in the monitoring plan can yield important 

information. Even if the metric or method 

is relatively untested in the context of the 

study questions, the benefi ts of incorporating 

something novel with the potential to shed new 

light on ecological processes that control system 

response may outweigh the risks of ignoring it. 

Th e metric may not provide useful information, 

and after a reasonable trial period it can be 

dropped. Th e new metric might not help answer 
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Evaluating Headwater Stream Buff ers: Lessons Learned Bisson et al. 187

the original questions, but instead may contribute 

information of diff erent value. For example, we 

collected riparian millipedes along with mollusks 

because we found many millipedes in the artifi cial 

substrate samples. In the process, we captured 

several taxa that were previously unknown to 

science (Foster and Claeson 2011). Finally, 

surprise occurrences such as extreme weather 

events or unexpected management activities can 

add to the diffi culty of evaluating experimental 

hypotheses, but they can also provide unique 

opportunities for learning in a setting where 

a monitoring program is already in place. For 

example, this study could have provided a useful 

design for addressing the question, “Are diff erent 

buff er confi gurations prone to windthrow at 

diff erent rates?” Taking advantage of these rare 

opportunities by investigating the eff ects of 

the event may add to the overall utility of the 

research.

Acknowledgments

Support for REMS was provided by the USDA 

Forest Service, Pacifi c Northwest Research 

Station. We express our sincere appreciation to the 

Washington Department of Natural Resources, 

especially to Richard Bigley and Jeff rey Ricklefs, for 

assistance in all aspects of the REMS study, and to 

William Ehinger, Jack Janisch and the Washington 

Department of Ecology for their contribution to the 

study of stream and air temperatures. We are also 

grateful to the University of Washington, Olympic 

National Forest, and the Washington Department 

of Fish and Wildlife for help with various aspects of 

the investigations. Th is paper benefi ted from helpful 

reviews provided by Sherri Johnson, John Colby, and 

an anonymous referee.

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Density Management in the 21st Century: West Side Story PNW-GTR-880

189

Applying Four Principles of Headwater System Aquatic 

Biology to Forest Management

Robert J. Danehy and Sherri L. Johnson

Robert J. Danehy is forest watershed program manager at National Council for Air and Stream Improvement, 720 

SE 4th St. Corvallis, OR 97333; bdanehy@ncasi.org; Sherri L. Johnson is a research ecologist for the USDA Forest 

Service. Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; 

sherrijohnson@fs.fed.us

Abstract

Headwater systems, including the channel and the adjacent riparian forest, are a dominant 

landscape feature in forested watersheds, draining most of the watershed area, and comprising the 

majority of channel length in drainage networks. Being at the upper extent of watersheds, these 

systems are smaller and steeper than large streams, and create microhabitats that support diverse 

instream communities distinct from those in larger streams. Forest management can disturb 

headwater streams through changes in physical structure, sediment, light, and riparian detrital 

inputs. Locally, the extent of the buff er surrounding the system mediates disturbance intensity 

and responses. At broader scales, the eff ect of the shifting mosaic of stand ages across a landscape 

is less well-described. In addition, as watersheds are periodically harvested, long-term impacts of 

repeated canopy removal are unclear. We synthesize recent research from western Oregon and 

Washington focused on forest eff ects on headwater stream ecology. We draw on over twenty 

published manuscripts from Pacifi c Northwest (PNW) research, as well as seminal work from 

beyond the PNW. Findings of these studies are examined in light of four principles for managing 

forest near streams: system (the stream and riparian area as a system); fl ow (sources and duration); 

disturbance (types and frequency); and topography (elevation, gradient, and aspect). Th e interaction 

between local infl uences and landscape drivers varies among headwater systems. Nevertheless, the 

underlying infl uences on headwater system ecology are repeatedly demonstrated in recent work. 

Consideration of these principles in planning ongoing forest management activities can promote 

the stewardship of headwater systems. 

Keywords: Headwater, headwater systems, fl ow regime, disturbance, landscape, biodiversity.

Introduction

Research focused on the aquatic biology of 

headwater streams has increased as ecologists 

recognize the importance of these ecosystems 

(Lowe and Likens 2005). Th e research stems 

from an interest in better understanding linkages 

between forest and streams, as well as headwaters 

and downstream processes and functions. Recent 

policy questions and concerns about the role 

of headwater systems within stream networks 

(Adams 2007; Leibowitz et al. 2008) have 

also increased interest in understanding these 

ecosystems.

Th ere is also a growing recognition that 

headwater streams are critical components of 

ecosystems and landscapes (Gomi et al. 2002; 

Wipfl i et al. 2007). Th ey comprise the majority 

of stream length and drain the majority of 

watershed area (Leopold 1964). Given their 

small areal extent taken individually, the stream 
Density Management in the 21st Century: West Side Story PNW-GTR-880

190 Headwater Stream Biology and Forest Management Danehy and Johnson

and associated riparian areas which comprise 

the headwater system can blend into the 

dominant vegetation of a landscape, making 

them less obvious. Nonetheless, the cumulative 

extent of their infl uence, together with a clearer 

appreciation of the role of these systems across 

larger spatial scales, is increasingly acknowledged 

(Meyer and Wallace 2001; Richardson and 

Danehy 2007).

Given that small streams drain watersheds and 

therefore link landscapes, how they are managed 

has important consequences. Best management 

practices (BMPs) for forest management vary 

according to ownership. In Oregon, these range 

from wide buff ers on federal lands, to smaller 

buff ers on state lands, to all merchantable 

timber allowed to be harvested near small, nonfi shbearing streams on private lands (Adams 

2007). Th ese diff erences in riparian management 

are linked to the objectives of the landowner 

and the goals of the BMPs. Additionally, in the 

PNW, headwater system BMPs were developed 

with consideration for their potential impact on 

water quality and fi sh populations downstream 

(Adams 2007). For federal buff ers, the default 

is two site-potential trees (90 m) on each side 

of fi shbearing streams, and narrower buff ers on 

non-fi shbearing streams (30–45 m): these can be 

modifi ed with adequate justifi cation. On private 

forests, BMPs are less conservative, taking into 

consideration the socioeconomic objective that 

suffi cient harvestable land is available to support 

the economic needs of logging businesses, and 

thereby local communities (Adams 2007). 

A major diff erence in riparian protection 

for headwater streams between federal and 

private lands stems from Endangered Species 

Act (ESA) requirements. Th e federal forests in 

the region are required to be managed in ways 

that directly promote recovery of ESA-listed 

species, including conservative assumptions 

about riparian conditions to protect fi sh and 

wildlife habitats (Reeves et al. 2006). Although 

take of anadromous fi sh or wildlife listed under 

ESA is to be avoided on private lands, riparian 

protection requirements on those lands are 

primarily intended to meet water quality criteria 

under the Clean Water Act (Adams 2007). 

Defi nitions of headwater systems vary, 

although the upstream end of fi sh distribution 

as the lower bound is a convenient construct 

(Fransen et al. 2006; Moore and Bull 2004). As 

streams shrink to a size, a fl ow, or both that limits 

fi sh habitation, there are often associated changes 

in biotic communities (Olson and Weaver 

2007). Community composition and ecological 

processes in these upper reaches are therefore 

driven by diverse interactions, both biotic (i.e., 

lack of fi sh) and abiotic (small and steep, with 

less stream fl ow) (Richardson and Danehy 2007). 

Vertebrates other than fi sh use headwater 

systems, but few are fully aquatic. Th ere can be 

robust amphibian populations with communities 

of one to as many as twelve species in western 

Oregon streams (Olson and Weaver 2007). Th e 

stream is a source of water and foraging habitats 

for most terrestrial wildlife, creating areas that are 

biologically rich and active (Anthony et al. 1987, 

1996; Meyer et al. 2007; Moldenke and ver 

Linden 2007; Richardson et al. 2005a; Rykken et 

al. 2007a; Wilk et al. 2010). Within the aquatic 

portion of the headwater system, there are rich 

aquatic communities of macroinvertebrates 

and periphyton (Danehy et al. 2007; Dieterich 

and Anderson 2000; Herlihy et al. 2005). Th e 

composition of those communities and the 

abundance of taxa within those communities 

are determined by a suite of factors that we 

summarize as four principles. 

We review research on headwater streams 

primarily from forested landscapes west of the 

Cascade divide in the Pacifi c Northwest, but 

include selected relevant studies from small 

fi shbearing streams, even though these are not 

generally considered headwaters. We group 

these studies by four principles of headwater 

system aquatic biology to assist land managers 

in their understanding of the implications of 

management and types of impacts one might 

expect.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Headwater Stream Biology and Forest Management Danehy and Johnson 191

Four Principles

1. System—Riparian conditions matter. 

Forest-stream interactions are dominated 

by riparian conditions. Tight aquaticterrestrial interactions occur for small 

streams. Generally, riparian detrital inputs 

(allochthonous) greatly exceed production 

from instream plants and primary producers 

(autochthonous production) (fi g. 1).

Th e river continuum concept (Vannote et al. 

1980) describes the types of interactions between 

instream aquatic biology and riparian infl uences 

as changes occur with stream size. Important 

drivers of aquatic biology are direct insolation 

and allochthonous inputs that respectively 

increase and decrease with stream size. Much 

prior research and policy focused on wadeable 

streams with fi sh, but more recent eff orts have 

highlighted the ecology of headwater systems. 

Richardson and Danehy (2007), in a synthesis of 

the underlying factors of the ecology of headwater 

systems, describe how small size creates a tight 

coupling with the surrounding environment, 

how the lack of fi sh can change the structure of 

faunal communities, and how periodic low fl ows 

are common in small streams.

Th e links between the fl owing stream and the 

surrounding riparian forest are infl uenced by 

the condition of the riparian forests. Concerns 

over timber harvest up to the edge of the streams 

have led to buff er requirements across the PNW, 

although the size and effi cacy of those buff ers 

have been an ongoing debate (Adams 2007; 

Dent et al. 2008; Groom et al. 2011). Whereas 

fi shbearing streams are all buff ered to a range of 

requirements, and the smallest streams in some 

jurisdictions have small buff ers, on private lands 

in Oregon, forest practices allow the removal of 

all merchantable timber along fi shless streams. 

Th is typically results in a riparian area dominated 

by shrubs and hardwood trees such as alder (Alnus

spp.). Consequently, headwater systems have the 

potential to be altered more dramatically than 

downstream systems. Th ese impacts have been 

investigated by multiple researchers and are 

discussed in a recent body of literature. 

More than thirty years ago, Murphy and Hall 

(1981) and Hawkins et al. (1982) examined 

eff ects of clearcut logging on stream communities 

in the Cascades, and found a suite of changes 

including increases in algae, aquatic insects, 

and salamander and fi sh biomass where the 

surrounding area has been clearcut. Th ose studies 

have more recently been corroborated by a set of 

studies in both the Coast Range and Cascades 

ecoregions of Oregon. A series of research eff orts 

published over the last decade addresses timber 

harvest impacts on headwater systems (Banks et 

al. 2007; Cole et al. 2003; Danehy et al. 2007; 

Frady et al. 2007; Herlihy et al. 2005; Moldenke 

and ver Linden 2007; Romero et al. 2005; Rykken 

Figure 1—Examples of headwater systems in the Oregon 

Coast Range. Riparian vegetation is tightly woven to the 

stream, with the stream channel fully covered in upper 

image. (Photos by R. Danehy.)
Density Management in the 21st Century: West Side Story PNW-GTR-880

192 Headwater Stream Biology and Forest Management Danehy and Johnson

et al. 2007a). Th e research provides us with 

substantial information concerning the infl uence 

of changes in riparian forests on headwater biota, 

particularly invertebrates. While targeting forest 

management, those eff orts also contribute to our 

broader understanding of headwater systems.

Th e results of the recent research provide 

substantial information on responses of headwater 

stream biota and their habitats following forest 

management and changes in riparian condition. 

After logging near headwaters, many researchers 

have noted major changes in instream physical 

features (Johnson and Jones 2000; Moore and 

Wondzell 2005). Total macroinvertebrate density 

and shifts in composition have been strongly 

correlated with the instream changes (Cole et al. 

2003; Banks et al. 2007; Danehy et al. 2007). 

Banks et al. (2007) found that abundance and 

richness of emerging aquatic insects are slightly 

higher in clearcut reaches. Moldenke and ver 

Linden (2007) found more biomass and density 

of the insect orders Ephemeroptera, Plecoptera, 

and Trichoptera (EPTs) and all feeding groups 

except scrapers at clearcut sites. Danehy et al. 

(2007) examined macroinvertebrates in clearcut, thinned, and forested stands. Th ey found 

no detectable diff erences between thinned 

and forested. However, clearcut sites had 

higher macroinvertebrate abundance, more 

Chironomidae taxa, and higher biomass. Over 

time and with riparian regeneration, these 

diff erences were less apparent. Frady et al. (2007) 

compared streams through second-growth 

forests and old-growth sites and found no clear 

diff erences in macroinvertebrate assemblages 

between treatments. However, where alder had 

re-established in the riparian areas, they collected 

higher densities of shredders than in coniferdominated reaches. 

Herlihy et al. (2005) found that substrate 

condition and topographic features are the 

most important indicators of aquatic insect 

community composition across three western 

Oregon ecoregions. However, when viewed 

at larger spatial scales and across ecoregions, 

they concluded that logging was not a major 

driver in shaping western Oregon headwater 

macroinvertebrate communities; rather, the 

greatest variation in forested stream communities 

was due to substrate size, stream gradient, and 

altitude. Moldenke and ver Linden (2007) also 

found that elevation was a stronger determinant 

than riparian condition for insect communities. 

In addition to research conducted on the role 

buff ers have on forested headwater biota, there 

has been work that evaluates the links between 

the stream and riparian areas. Th is research 

reinforces the importance of viewing them as 

ecosystems with frequent exchange of energy. 

One area of research that was particularly 

insightful is the work that documents reciprocal 

subsidies (Nakano et al. 1999; Baxter et al. 2005) 

from the stream to the riparian areas. It had 

long been recognized that allochthonous inputs 

from areas outside the stream are important to 

instream biology. Moving upstream the ratio of 

allochthonous to autochthonous contribution 

of energy changes, which is a central tenet of 

the river continuum concept (Vannote et al. 

1980). Starting in the 1990s, the role of marinederived nutrients from salmon was documented 

by Cederholm et al. (1999) and Bilby et al. 

(2001); these insights reinforced the importance 

of salmon to forested ecosystems, particularly in 

the Pacifi c Northwest. At about the same time, 

in Japan, Nakano et al. (1999) and Nakano and 

Murakami (2001) developed a comprehensive 

understanding of reciprocal subsidies from 

the stream to the riparian forest. Th at research 

documented the importance of insects emerging 

from the stream for the diets of a suite of riparian 

predators, particularly birds and bats, and has 

been continued by Baxter et al. (2005). In a thirdorder stream, Farrand (2004) also observed that 

insect emergence was a major subsidy of energy 

to the riparian area, with only a small portion 

of adult aquatic insects returning to the stream. 

Gomi et al. (2002) and Moldenke and ver Linden 

(2007) documented that in fi shless streams, 

invertebrates were a vector of energy leaving the 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Headwater Stream Biology and Forest Management Danehy and Johnson 193

stream and subsidizing the riparian zone. Th is 

science of reciprocal subsidies documents a cycle 

of energy fl ow from outside the stream into the 

stream and from within the stream to adjacent 

terrestrial ecosystems. 

In terms of regulatory guidelines, headwater 

systems have been valued for their importance 

in supporting fi sh habitat downstream rather 

than as important biological communities unto 

themselves. Th e connection between upstream 

and downstream systems includes the export of 

heat, food in the form of drifting invertebrates, 

organic material, substrates, and large wood 

(Alexander et al. 2007; Binkley et al. 2010; 

Danehy et al. 2011a; Gomi et al. 2002; Hassan 

et al. 2005; Moore et al. 2005a; Piccolo and 

Wipfl i 2002; Richardson 1992; Richardson et 

al. 2005b; Wipfl i and Gregovich 2002). Th ose 

subsidies were in the form of cold, clean water 

to create appropriate thermal habitat for fi sh 

(Danehy et al. 2005; Dent et al. 2008; Johnson 

2004), organic matter that is processed and 

used by fi sh prey (invertebrates) (Kiff ney and 

Richardson 2010; Richardson et al. 2005a; 

Wipfl i and Gregovich 2002), and nutrients to 

fuel autochthonous production (Compton et al. 

2003; Ashkenas et al. 2004). 

2. Flow—Presence and duration of fl ow are a 

primary driver of aquatic biota composition 

and abundance. In addition, non-fl owing 

wet channels or those with hyporheic fl ows 

provide important habitats for amphibians 

and some insects. Springs can support aquatic 

communities close to ridgelines (fi g. 2). 

Th e duration of fl ow is a critical feature in 

headwater systems, as these streams may be 

perennial, spatially intermittent, seasonally 

intermittent, or ephemeral. Headwater biota 

often have adaptations to annual, pervasive low 

fl ow events. Th e adaptations to low fl ow vary 

with organisms, as recently elucidated by Walters 

(2011). Th ese traits of taxa (i.e., desiccation 

resistance, crawling rate, armoring, size at 

maturity, rheophily, and habit) (Poff et al. 2006)

can help us understand why some taxa survive 

better than others. 

Th e source and type of fl ow for a headwater 

stream varies widely. In a central Coast Range 

study, all the streams had a spring source which 

resulted in fl ows continuing into late summer 

(Danehy et al. 2007). Th e sources of these streams 

were on average 250 m from the ridgeline. Other 

researchers (for example, Banks et al. 2007) found 

that the upper portions of headwater sites were 

intermittent. Yet insects continued to emerge 

from the streambed even as the stream dried. 

Th e duration and magnitude of fl ow have 

strong infl uences on the fl ora and fauna of the 

systems. Yamamuro (2009) observed diff erent 

communities and indicator taxa in runoff -

Figure 2—Headwater streams start in the upper reaches 

of watersheds and increase in flow volume as channels 

join. Throughout the year, flow can be continuous, 

spatially intermittent, or seasonal. B. A headwater stream 

arises from a small spring. (Photos by R. Danehy.)

A

B
Density Management in the 21st Century: West Side Story PNW-GTR-880

194 Headwater Stream Biology and Forest Management Danehy and Johnson

dominated streams versus spring-fed streams in 

the upper McKenzie River basin. Yoraperla spp., 

a Plecopteran which was found in all streams, 

showed shifts in timing of life-history events, with 

more cohorts present in the spring-fed streams. In 

other perennial spring-fed headwater channels, 

Danehy and Bilby (2009) found clear seasonal 

diff erences in both macroinvertebrate and 

periphyton assemblages. Th e macroinvertebrate 

assemblage in springtime was richer, more 

abundant, and had higher biomass. Th ey also 

found that the periphyton community was 

dominated by diatoms, particularly Achnanthes 

lanceolata, with greater richness of diatoms at sites 

with higher base fl ow. Th ese diff erences in fl ow 

conditions are manifested across landscapes and 

undoubtedly contribute to biological diversity of 

headwater systems and forests.

Flow intermittency may be particularly 

important in supporting biological diversity in 

headwater systems. Banks et al. (2007) found 

that community patterns vary by season and 

fl ow duration more than fl ow type, which may 

be due to subsurface fl ow being present in 

the intermittent channels. Others, including 

Dieterich and Anderson (2000), Delucchi 

(1989) and Delucchi and Peckarsky (1989) 

observed substantial diff erences in aquatic 

insect communities in perennial streams versus 

those that go dry in the summer. Dieterich and 

Anderson (2000) captured more species from 

temporary streams (>125) than from permanent 

streams (100). Progar and Moldenke (2002) 

also noted diff erences in composition between 

temporary or intermittent streams compared to 

perennial streams, and found higher densities 

and biomass of insects from temporary streams 

during periods of fl ow. During wet seasons, these 

intermittent streams can be important habitats 

and attract species more typical of larger streams. 

Th ese results suggest that insect life cycles are 

synchronized with annual changes in fl ow, but 

are still susceptible to changes in the timing 

and duration of base fl ow. Given what we have 

learned about these communities at base fl ow, 

research suggests that headwater systems could 

be among the fi rst ecosystems aff ected should 

climate change create drier conditions (Mote and 

Salathe 2010).

3. Disturbance—Various disturbance 

processes aff ect headwater systems, including 

forest harvest, debris fl ows, and fi re. Th ese 

infrequent events shape the channel structure 

and biotic assemblages of headwater systems 

(fi g. 3).

Disturbance is a natural part of the functioning 

of headwater systems. A variety of disturbances 

infl uence streams, and many headwater species 

are well-adapted or quickly recover following 

these episodic events. Debris fl ows are a wellFigure 3—Various types of disturbance periodically 

reshape headwater systems. A. A stream flowing through 

a burned eastside forest. B. This stream channel was 

scoured down to bedrock by a debris flow. (Photos by S. 

Johnson.)
Density Management in the 21st Century: West Side Story PNW-GTR-880

Headwater Stream Biology and Forest Management Danehy and Johnson 195

recognized disturbance to Pacifi c Northwest 

streams, particularly after extreme rainfall (Turner 

et al. 2010; Robison et al. 1999). In the Coast 

Range, May and Gresswell (2003) estimated 

that the mean recurrence interval of debris 

fl ows was between 97 and 357 years. Snyder 

(2000) suggested that in portions of the Cascade 

Range, return intervals of debris fl ows could be 

more frequent. Debris fl ow occurrences can be 

associated with forest management, including 

roads and harvest (Snyder 2000; May 2002; 

Swanson and Dyrness 1975; Turner et al. 2010). 

Fire is a less-frequent disturbance type for western 

Oregon (Agee 1993; Cissel et al. 1999), but when 

severe fi res do occur, they can fundamentally 

change the composition and trophic organization 

of headwater streams. Th e intensity of fi re, 

ranging from small, localized ground fi res to large, 

canopy-replacing fi res, has diff ering consequences 

for forest-stream interactions. Similar to debris 

fl ows, anthropogenic infl uences involving fi re 

suppression can alter fi re regimes and severity 

(Franklin et al. 2002; Moser and Wade 2005). 

Despite the potential for local and larger-scale 

impacts and infl uence by anthropogenic actions, 

disturbances in Pacifi c Northwest ecosystems are 

natural processes that create habitat diversity. 

We also know that after disturbances, stream 

community recovery begins rapidly; the 

magnitude and intensity of disturbance infl uences 

the period of recovery (Anderson 1992; Minshall 

2003). In controlled-fi re experiments in eastern 

Washington, Mellon et al. (2008), using a suite 

of sampling methods (benthic, emergent, and 

drift sampling), found higher macroinvertebrate 

densities but lower diversity at burned sites. 

Instream communities at burned sites were 

dominated by chironomids. In the Yellowstone 

fi res of 1988, Minshall et al. (2003) found similar 

results. After ten years, diff erences between 

reference and burned sites were still evident in 

headwater streams, suggesting that fi re impacts 

decrease with increasing stream size (Minshall et 

al. 2003). 

Th ere have been fewer studies comparing 

stream communities before and after debris fl ows. 

After a debris fl ow in the Cascades, Lamberti 

et al. (1991) found that fi sh recolonize within 

a year of the event and at densities similar to 

pre-disturbance levels. For macroinvertebrates, 

Anderson (1992) and Kobayashi et al. (2010) 

observed rapid recovery, but major shifts in 

functional feeding groups after disturbance. In a 

longer-term study, Danehy et al. (2011b) found 

community diff erences in both periphyton and 

macroinvertebrates eight years after the debris 

fl ows, and predicted that those diff erences would 

remain until a full riparian canopy develops (20 

or more years). Many have suggested that debris 

fl ow disturbances are essential components 

of creation and maintenance of fi sh habitat 

downstream (Benda et al. 2005; Bigelow et al. 

2007; Burnett and Miller 2007; Reeves et al. 

1995, 2003). Wood recruitment to downstream 

fi shbearing reaches by the transport of trees from 

headwaters to mainstem reaches during fl oods 

and debris fl ows creates habitats for fi sh and 

other biota (Reeves 2003).

Floods and drought also disturb headwater 

systems. Floods can rearrange instream habitat 

and aff ect biota as well as disturb adjacent riparian 

areas (Johnson et al. 2000). Although perceived 

to be a major risk, actual washout of organisms 

by high fl ows is often minimal. After a highintensity fl ood in a fi shbearing stream, Swanson 

et al. (1998) observed few changes to resident fi sh 

and amphibians. Droughts can also be extreme 

events that infl uence instream biota. Classifying 

droughts as a disturbance depends on the timing, 

duration, or magnitude (Richardson and Danehy 

2007). Droughts need to be distinguished from 

annual low fl ows, because low fl ows and fl owduration lengths are integral components of 

headwater system ecology.

4. Topography—Topographic diff erences, 

(e.g., gradient, aspect, elevation) contribute 

to biotic diversity. Diff erent taxa occur 

across elevational gradients. As streams 
Density Management in the 21st Century: West Side Story PNW-GTR-880

196 Headwater Stream Biology and Forest Management Danehy and Johnson

steepen, substrate coarsens and channels 

narrow, altering available habitats for 

macroinvertebrates and vertebrates, and 

opportunities for algal colonization (fi g. 4).

Topography of headwater streams and their 

location in the watershed infl uences habitat 

availability, species composition, and life 

histories (Vannote et al. 1980; Montgomery 

1999). Topography and geomorphology also 

strongly shape riparian vegetative composition 

as well as water availability, disturbance regimes 

(see previous section), and stream temperature 

characteristics (Johnson 2004). Development 

rate of instream organisms is linked with 

temperature (Li et al. 2011; Ward and Stanford 

1982), which correlates with elevation and aspect. 

Headwater systems, with all other variables being 

similar, can show diff ering insect community 

compositions across elevations. Frady et al. 

(2007) found 70 percent overlap and 30 percent 

diff erence in macroinvertebrate assemblages in 

old-growth streams of similar size but at diff erent 

elevations. Moldenke and ver Linden (2007) 

suggested that diff erences in macroinvertebrate 

community composition due to elevation were 

more important than silvicultural treatments. 

In a study of 169 randomly selected sites across 

western Oregon, Herlihy et al. (2005) found that 

topographic features of catchment slope, channel 

slope, and elevation are correlates of multiple 

environmental variables and useful in predicting 

macroinvertebrate diversity. 

Headwater stream geomorphology in 

the mountains of the Pacifi c Northwest is 

often dominated by step-riffl e or step-pool 

morphology (Jackson et al. 2002; Benda et al. 

2005; Danehy et al. 2007). Th e distance between 

steps increases as gradient decreases (Bryant et al. 

2007). In highly complex systems, the steps are 

created by small wood or exposed boulders that 

infl uence fl ow paths and modify the rate of fl ow, 

particularly at low fl ows (Kasahara and Wondzell 

2003). Danehy et al. (2007) found that time of 

travel ranges from 0.4 to 3.4 m∙min-1 in Coast 

Range headwater streams. At higher fl ows, the 

retentive features also serve to reduce the export 

of sediment and large wood. Benda et al. (2004) 

hypothesized that headwater streams serve as 

reservoirs or storage areas and transport little 

via episodic transport. However, Gomi et al. 

(2005), in their review of research on suspended 

sediment, concluded that small streams could 

transport tons of sediment annually, particularly 

immediately after a disturbance such as road 

construction.

Th e zone of infl uence of a headwater stream can 

be identifi ed by the changes in microclimate with 

distance from the stream. In Coast Range streams, 

two studies found that the zone of infl uence was 

narrow, with topography having a large infl uence 

on the climatic gradients (Anderson et al. 2007; 

Rykken et al. 2007b). In studies of buff er 

Figure 4—Across landscapes, topography provides a 

range of elevations, aspects, and gradients, creating a 

range of conditions for aquatic and riparian flora and 

fauna. (Photos by R. Danehy.)
Density Management in the 21st Century: West Side Story PNW-GTR-880

Headwater Stream Biology and Forest Management Danehy and Johnson 197

treatments, the strongest gradients have been 

observed to occur within the fi rst 10 m away from 

the stream (Anderson et al. 2007). Headwater 

valleys are often narrow, allowing topographic 

shade to augment riparian-derived shading. 

Topographic shading and sun exposure diff ers 

in east-to-west versus north-south aspect streams 

(Anderson et al. 2007; Moore et al. 2005b). 

While seemingly obvious, these diff erences do 

aff ect air and stream temperatures and insolation 

and therefore headwater system biota. 

Management Implications 

Given the tight linkages between headwater 

streams and their surrounding forests, forest 

management has the potential to infl uence 

instream communities. A reduction in riparian 

buff ers will lead to increased insolation, which 

can lead to more primary production, and 

possibly more food for consumers and predators. 

However, there are also potential trade-off s when 

managing or making a change to one portion of 

a complex ecosystem. Increased insolation raises 

water temperatures (Johnson 2004; Moore et al. 

2005a), which can increase growth rates for some 

taxa but can also negatively infl uence other taxa 

and processes. Changes in species composition 

following forest management have been observed, 

as well as increased biomass and richness in algae, 

insects, and salamanders (Banks et al. 2007; 

Clapcott and Barmuta 2010; Danehy et al. 2007; 

Moldenke and ver Linden 2007). Evaluating 

trade-off s and selecting management strategies 

that benefi t one group or taxon but negatively 

infl uence others is a challenging process for 

managers, researchers, and policy makers.

Headwater streams and adjacent riparian 

areas are generally viewed by ecologists as 

important habitats with unique species and 

valuable ecosystem functions. Others may 

look to headwater systems for the services they 

provide to downstream fi sh and humans, or 

view them from a broad landscape perspective 

with limited individual value. When managing 

headwaters, it is important to consider the tradeoff s among diff ering management activities. We 

know that following disturbance that removes 

riparian forests, headwater ecosystem processes 

and aquatic biota will be aff ected for a few years 

until some shading returns. Changes in resource 

availability (energy, nutrients, detritus inputs) 

also occur with disturbances. Th e extent and 

severity of a management activity or disturbance 

across a landscape will infl uence diversity and 

recolonization rates. 

Th e scientifi c consensus is mixed on how 

far downstream management eff ects are 

propagated. Th e recruitment of large wood to 

create and maintain fi sh habitat is an example 

of an important connection between headwaters 

and downstream (Reeves et al. 1995, 2003). 

Th e processes controlling other links between 

headwaters and downstream continue to be 

examined. Th ere are a range of fi ndings on 

upstream-downstream links, including how far 

potential food items drift (Danehy et al. 2011a; 

Wipfl i et al. 2007), or sediment is transported 

(Gomi et al. 2005; Benda et al. 2005) or thermal 

impacts extend (Danehy et al. 2005; Johnson 

2004; Moore et al. 2005b). Th ere is a clear need 

for more comprehensive study of downstream 

responses to upstream disturbances. Rigorous 

monitoring as well as new watershed studies 

throughout Oregon and Washington will help 

develop our understanding of the mechanisms 

and trade-off s involved in forest management 

along headwater streams.

Summary

Headwater streams and riparian systems are 

ubiquitous and diverse landscape features. Th e 

natural diversity of communities in headwaters 

has been further altered by a legacy of prior forest 

management approaches coupled with natural 

disturbances. Each of the four principles—system, 

fl ow, disturbance, and topography—infl uences 

that diversity. Some research suggest that aquatic 

production in headwater streams increases after 
Density Management in the 21st Century: West Side Story PNW-GTR-880

198 Headwater Stream Biology and Forest Management Danehy and Johnson

harvest for selected taxa, these results need to be 

viewed cautiously, as long-term and landscapescale eff ects are not well understood. To date, there 

have been no long-term assessments or thorough 

systematic evaluations of eff ects of disturbances 

or forest management on full biological diversity 

or on responses across multiple trophic levels in 

PNW headwater systems. 

However, we have learned much from previous 

research: 1. Riparian buff er designs aff ect the 

biology of headwater systems; 2. Th e nature 

of the fl ow regime is a major infl uence on the 

magnitude, distribution, and diversity of aquatic 

biology of a headwater system; 3. Disturbance 

history needs to be included in evaluations of 

possible future conditions; and 4. Location 

in a landscape matters and provides essential 

context—steep, perennial, high-elevation streams 

will have very diff erent biological potential than 

systems that diff er in those characteristics. Th ese 

four principles provide a framework and context 

for responses to management activities around 

headwater streams. 

Acknowledgments

Th is review relies on many who have worked on 

headwater streams in western US. We thank Paul 

Adams, Karl Polivka and two anonymous reviewers 

for their helpful comments and suggestions on 

this paper. Paul Anderson and Dede Olson were 

instrumental in the development of the symposium 

and we appreciate the opportunity to participate. Liz 

Dent and George Ice were catalysts in the initiative 

to increase our understanding of headwater systems 

in the Pacifi c Northwest with the establishment of 

Headwaters Research Cooperative. Special thanks 

to John Richardson for his insights and research 

that were a foundation for the development of these 

principles.

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Citation:

Danehy, Robert J.; Johnson, Sherri L. 2013. Applying four principles of headwater system aquatic biology to forest 

management. In: Anderson, Paul D.; Ronnenberg, Kathryn L., eds. Density management for the 21st century: west side 

story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacifi c Northwest 

Research Station: 189–202.
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Integrated Watershed Analysis: Adapting to Changing Times

Gordon H. Reeves

Presentation Abstract

Resource managers are increasingly required to conduct integrated analyses of aquatic and 

terrestrial ecosystems before undertaking any activities. Th ere are a number of research studies on 

the impacts of management actions on these ecosystems, as well as a growing body of knowledge 

about ecological processes that aff ect them, particularly aquatic ecosystems, which are used to guide 

the analyses. Additionally, new tools are available to assist in the analyses. Th ese developments 

have advanced the potential to conduct these analyses. However, there are some critical issues that 

need to be included in an integrated analysis that are not readily recognized or acknowledged at 

this time. Two of the more important factors are space and dynamics. Watershed and landscape 

analyses require consideration of a diff erent set of rules for considering context and potential 

eff ects of proposed actions than do analyses that are conducted at smaller scales. Th e failure to 

recognize these issues can result in a misinterpretation of the analyses and a failure to understand 

potential impacts. Watershed analysis also focuses on identifying the location of, and accessing 

the magnitude of, various ecological processes in the watershed. Consideration of the dynamic 

nature of processes that aff ect aquatic ecosystems is relatively new, but the implications of these 

dynamics are not fully recognized by many managers and regulators. In consequence of both these 

factors, there is a mismatch between the expectations for management of aquatic and terrestrial 

systems and the way in which these systems actually function that limits our ability to develop and 

implement new approaches to integrated management.

Keywords: integrated ecosystem analysis, temporal and spatial scale, dynamic systems, management 

expectations

Gordon H. Reeves is a research fi sh biologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences 

Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331, greeves@fs.fed.us.

Editors’ suggestion:

Reeves, G.H.; Williams, J.E.; Burnett, K.M.; Gallo, K. 2006. The Aquatic Conservation Strategy of the 

Northwest Forest Plan. Conservation Biology. 20(2): 319–329.
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Intrinsic Potential: What Is It and What Is It Good For?

Kelly M. Burnett

Presentation Abstract

Landscape characteristics are commonly invoked to explain or predict salmonid abundances 

and stream habitat conditions. Such characteristics may be relatively static (e.g., hill slope, rock 

type, and drainage density) or change over time (e.g., forest cover, land use, and road density). 

Ultimately, how landscape characteristics aff ect a particular fi sh species may vary with the 

underlying capacity of a stream to provide high-quality habitat for that species, or in other words, 

the intrinsic potential of a stream. Intrinsic potential is derived from reach-scale stream attributes 

(gradient, stream size, and valley constraint) that infl uence availability of the fi ne-scale habitat 

features (e.g., pools, spawning gravel, and large wood) preferred by salmonids. Collecting data 

on these fi ne-scale habitat features in all streams throughout a region is impossible with current 

technology and budgets. However, intrinsic potential can be mapped over large areas using digital 

elevation and climate data to generate a high-resolution stream network and the necessary reachscale stream attributes. Th e approach and models, though targeted for salmonids, can be adapted 

to any stream-dwelling species for which links to reach-scale stream attributes are known.

Intrinsic potential models have been evaluated using sensitivity analysis and against fi eld data, 

and so model performance and reliability are relatively well understood. Sensitivity of intrinsic 

potential model outputs to model inputs can vary by geographic location, by the form of the model, 

and by species. For example, outputs of intrinsic potential models are most sensitive to gradient for 

Steelhead (anadromous Oncorhynchus mykiss) and Coho Salmon (O. kisutch), but to stream size for 

Chinook Salmon (O. tshawytscha). Because reach-level data on historical fi sh abundances are rare, 

model outputs at the reach level have been evaluated against: 1) current population abundance; 2) 

fi eld and expert-opinion based maps on the current distribution of spawning adults; and 3) results 

from the Ecosystem Diagnosis and Treatment (EDT) model. However, model outputs at the basin 

scale have been evaluated against historical cannery records. 

Models of intrinsic potential exist for several salmonid species and regions. Th ese include Steelhead 

and Coho Salmon in western Oregon, Steelhead, Coho Salmon, and Chinook Salmon in northern 

and central California, and Chinook Salmon in the lower Columbia River. Intrinsic potential 

models can benefi t, and have been used in, a variety of regional land-management and regulatory 

eff orts, such as highlighting areas that may contribute disproportionately to aquatic conservation; 

prioritizing locations to improve fi sh passage or to restore streams from the legacy of splash dams; 

evaluating the distribution of potential fi sh habitat relative to land ownership, use, and cover; 

establishing how much high-quality habitat may be suffi cient to support a “recovered” fi sh species; 

and estimating salmonid population abundances prior to European settlement. Intrinsic potential 

models diff er from other fi sh-habitat suitability models in attempting to estimate the potential 

to provide high-quality habitat and not the actual condition of habitat. Th us, intrinsic potential 

models can open windows into the past and unlock possibilities for the future.

Keywords: fi sh habitat, salmon, streams, restoration, models.
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Presentation Abstract

We describe demographic processes and species interactions that infl uence Coastal Cutthroat 

Trout (Oncorhynchus clarkii clarkii) in small streams that are part of an eff ort designed to evaluate 

forest harvest impacts in the Trask Watershed, an industrial forest located in northwest Oregon, USA. 

Spatial variation in recruitment, individual growth, survival, and movement were quantifi ed during 

summer low fl ows for four years (2007–2010). Th e phenology of recruitment varied substantially 

among sites and years. Movement during summer was limited, and varied inconsistently among 

sites. Individual growth and survival showed consistent size-related patterns, with variability in 

growth showing more consistent diff erences among sites in diff erent years. Processes driving these 

patterns are challenging to identify, but companion studies of instream cover selection and seasonal 

diets of trout and other fi shes suggest strong roles for predators, species interactions, and seasonal 

food limitations. Based on these results, we fi nd that a process-based understanding of forestry 

impacts may prove more useful than traditional trend-based monitoring and impact assessments.

Keywords: forest harvest, cutthroat trout, recruitment, cover selection, food availability.

Jason Dunham is an aquatic biologist, US Geological Survey, US Geological Survey, Forest and Rangeland Ecosystem 

Science Center, Corvallis, Oregon, jdunham@usgs.gov; Douglas Bateman is a senior faculty research assistant, Oregon 

State University, Corvallis, Oregon, Doug.Bateman@oregonstate.edu; David Hockman-Wert is a biologist, dhockmanwert@usgs.gov; and Nathan Chelgren is an ecologist, US Geological Survey, Forest and Rangeland Ecosystem Science 

Center, Corvallis, Oregon, nchelgren@usgs.gov; and David Leer is a Faculty Research Assistant, Oregon State University, 

Corvallis, Oregon, David.Leer@oregonstate,edu.

Kelly M. Burnett is a research fi sh biologist (emeritus), USDA Forest Service, Pacifi c Northwest Research Station, Forestry 

Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; kmburnett@fs.fed.us.

Editors’ suggestion:

Burnett, K.M.; Reeves, G.H.; Miller, D.J.; Clarke, S.; Vance-Borland, K.; Christiansen, K. 2007. Distribution 

of salmon-habitat potential relative to landscape characteristics and implications for conservation. Ecological 

Applications. 17(1): 66-80.

Quantifying Fish Responses to Forestry—Lessons from the Trask 

Watershed Study

Jason Dunham, Douglas Bateman, David Hockman-Wert, Nathan 

Chelgren, and David Leer
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Paul D. Anderson is a supervisory research forester, USDA Forest Service, Pacifi c Northwest Research Station, Forestry 

Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331, pdanderson@fs.fed.us

Presentation Abstract

Th inning of 30- to 70-year-old Douglas-fi r (Pseudotsuga menziesii) stands is a common 

silvicultural activity on federal forest lands in Washington and Oregon west of the Cascade Range 

crest. Decreases in forest cover lead to alterations of site energy balances resulting in changes to 

understory and stream channel microclimates. Uncut vegetative buff ers are commonly used to 

mitigate upland harvest eff ects on aquatic and riparian habitats and functions. To create eff ective 

buff ers, we need to better understand the relationships among thinning treatments, diff erent 

riparian buff er widths, channel topography, and riparian and aquatic microclimates.

As a component of the Density Management and Riparian Buff er Study (DMS) we investigated 

buff er width and thinning eff ects on riparian microclimates of headwater streams in western 

Oregon. Spatial variations in stand density, canopy cover, and microclimate were measured 2–4 

years following harvest along transects extending from stream center upslope into thinned stands, 

patch openings, or unthinned stands, with riparian buff ers ranging from ~5–150 m width. For 

treated stands, the summer mean daily maximum air and soil temperatures increased and mean 

daily minimum humidity decreased with distance from stream. Small headwater streams exerted 

a distinct cool, moist infl uence on riparian microclimate that extended about 10 m upslope 

from stream center. Th inning resulted in subtle changes in microclimate as mean air temperature 

maxima were ~1–4°C higher than in unthinned stands. With variable-width buff ers 17 m or 

wider, daily maximum air temperature above stream center was less than 1°C greater, and daily 

minimum relative humidity was less than 5 percent lower than for unthinned stands. In contrast, 

air temperature was signifi cantly warmer within patch openings (+6–9°C), and within buff ers 

adjacent to patch openings (+3°C) than within unthinned stands. Variable-width buff ers defi ned 

by the transition from riparian to upland vegetation or topographic slope breaks appear suffi cient 

to mitigate the impacts of upslope thinning on the microclimate above headwater streams. 

Intensive studies such as DMS, combined with broader-scale operational monitoring can 

provide much-needed empirical data and analyses to inform management and regulatory strategies 

to conserve important aquatic and riparian functions of headwater streams in managed forests west 

of the Cascades.

Keywords: riparian buff ers, thinning, air temperature, streambed temperature, relative humidity, 

canopy cover, headwater streams, forest structure.

Editors’ suggestion: 

Anderson, P.D.; Larson, D.J.; Chan, S.S. 2007. Riparian buffer and density management influences on 

microclimate of young headwater forests of western Oregon. Forest Science. 53(2): 254–269.

Riparian Microclimate and Stream Temperature: 

Thinning and Buffer-Width Influences

Paul D. Anderson
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Presentation Abstract

Studies over the past 40 years have established that riparian buff er retention along streams 

protects against stream temperature increase. Th is protection is neither universal nor complete; 

some buff ered streams still warm, while other streams’ temperatures remain stable. Oregon 

Department of Forestry developed riparian rules in the Forest Practices Act (FPA) to protect fi shbearing streams from temperature increases, but it did so with acknowledgement that its rules 

might be insuffi cient. It developed the Riparian and Stream Function project, otherwise known as 

RipStream, to validate the eff ectiveness of these rules. Th e FPA stipulates that for Small and Medium 

fi sh-bearing streams, no cutting is to occur within 6 m adjacent to the stream and limited entry 

may occur within 15 and 21 m, respectively. Th e Oregon State Forest Management Plan (FMP) 

builds upon the FPA but includes additional protections in order to meet multiple management 

objectives. State forest riparian protections include an 8-m no-cut zone, an 8- to 30-m zone to 

be managed for producing mature forest conditions, and limited harvest between 30 m and 52 

m. Harvest on state forest can diff er from private lands, as state forest stands may be subject to 

thinning instead of clearcutting. Th e RipStream project represents a joint eff ort between State and 

Private Forest divisions at Oregon Department of Forestry to quantify the eff ects of timber harvest 

on stream temperatures. Th e study includes 15 state forest and 18 private sites. Data on stream 

temperature, riparian vegetation, channel characteristics, and channel shading were collected at 

every site for two years pre-harvest and fi ve years post-harvest. Each site included an upstream 

unharvested control reach and a treatment reach that was harvested after year two. All private sites 

were clearcut; seven out of eight state sites were thinned. By the second year post-harvest we found 

no change in maximum temperatures for state forests while private sites increased pre-harvest 

to post-harvest on average by 0.7°C, with an observed range of response from -0.9 to 2.5°C. 

State sites additionally demonstrated no diff erence in temperatures between clearcut and thinned 

treatments. Th e observed changes in stream temperature were most strongly correlated with shade 

levels measured before and after harvest. Treatment reach length, stream gradient, and changes 

in the upstream reach stream temperature were additionally useful in explaining treatment reach 

temperature change. Shade was best predicted by riparian basal area and tree height. Th ese fi ndings 

suggest that riparian protection measures that maintain higher shade, such as those followed in 

state forests, were more likely to maintain stream temperatures similar to control conditions.

Keywords: riparian buff er, stream temperature, mixed-eff ects, shade, thinning.

Jeremy D. Groom is the monitoring coordinator, Oregon Department of Forestry, State Forests Division, 2600 State St, 

Building D, Salem, OR 97310; jeremy.groom@state.or.us

Editors’ suggestion: 

Groom, J.D., Dent, L., Madsen, L.J. 2011. Stream temperature change detection for state and private forests in 

the Oregon Coast Range. Water Resources Research. 47, W01501, doi:10.1029/2009WR009061 

Stream Temperature Responses to Timber Harvest and Best 

Management Practices—Findings from the ODF RipStream Project

Jeremy D. Groom
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Presentation Abstract

Down wood plays many functional roles in aquatic and riparian ecosystems. Simplifi cation of 

forest structure and low abundance of down wood in stream channels and riparian areas is a 

common legacy of historical management in headwater forests west of the Cascade Range in the 

US northwest. Contemporary management practices emphasize the implementation of vegetation 

buff ers adjacent to streams, and on federal lands thinning has become a predominant form of 

timber harvest. Th e combined eff ects of thinning and riparian buff er width on the down wood 

dynamics in stream channels and riparian areas are being assessed in young, managed headwater 

forests of the Density Management Study of western Oregon.

Th e riparian buff er component of our study includes unthinned controls and four buff er 

confi gurations embedded within upslope thinning treatments, applied to 35- to 80-year-old stands 

at multiple locations in western Oregon. Buff er confi gurations include one- and two-site-potentialtree-height buff ers and two less conservative confi gurations, streamside retention (minimum 20 

foot [6 m] width) and variable width (minimum 50 foot [15.2 m] width), allowing for tree harvest 

within riparian areas. Our assessments include pre- and post-treatment analyses of down wood 

volumes and decay classes within stream channels, origin of instream down wood (distance from 

stream), and down wood cover along transects extending from streams into upslope forests.

Along transects extending from streams through buff ers into upslope forest stands, pre-treatment 

mean percent cover of large down wood (>30 cm diameter) ranged from ~4–17 percent in buff ers 

and from 5–10 percent in the upslope. Pre-treatment cover of small down wood (5–30 cm 

diameter) ranged somewhat less, ~4–13 percent, and also varied less than large wood both within 

and among treatment units. Post-treatment, 2–5 years following thinning, mean down wood cover 

in the buff ers diff ered less among treatments and tended to be less variable within treatments. Th e 

decreased variation among buff er treatments was due primarily to a decrease in the maximum 

mean cover of small down wood in streamside retention buff ers, and in variable-width buff ers 

adjacent to patch openings.

In streams, thinning and buff er confi guration only aff ected down wood (>10 cm diameter) 

volumes in decay classes 1 and 2 (fresh or slightly decomposed detritus). Down wood volume was 

greater in the streamside buff er treatment than in the control one year after thinning, and greater 

than in the control and variable-width buff er treatments 2 years after thinning. 

We determined the source distance-from-stream of 2,323 down wood pieces in headwater stream 

channels ~10 years post-thinning along a total of 25 stream reaches at 4 study sites. Mean distance 

Paul D. Anderson is a supervisory research forester and Deanna H. Olson is a research ecologist, USDA Forest Service, Pacifi c 

Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; pdanderson@

fs.fed.us; Adrian Ares is the director, Sustainable Agriculture and Natural Resource Management Collaborative Research 

Support Program, Virginia Tech, Blacksburg, VA 24060

Initial Riparian Down Wood Dynamics in Relation to Thinning and 

Buffer Width

Paul D. Anderson, Deanna H. Olson, and Adrian Ares
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209

from stream ranged 2.6 to 9.0 m, and maximum distance was 41 m. Most of this wood was in 

decay classes 3+4, indicative of older legacy deposition. Only 9 percent of 9,550 instream pieces 

observed were in decay classes 1+2, indicative of more recent recruitment.

Recent second thinning entries conducted 10–12 years following the initial harvest provide a 

new opportunity to spatially assess stream and riparian large wood dynamics in relation to direct 

inputs associated with harvest as well as the longer-term stability of the original buff ers.

Keywords: riparian buff ers, thinning, down wood, headwater streams, forest structure.

Editors’ suggestion: 

Anderson, P.D.; Meleason, M.A. 2009. Discerning responses of down wood and understory vegetation 

abundance to riparian buffer width and thinning treatments: an equivalence/inequivalence approach. 

Canadian Journal of Forest Research. 39: 2470–2485.
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Thinning and Riparian Buffer Configuration Effects on Down 

Wood Abundance in Headwater Streams in Coniferous Forests

Adrian Ares, Deanna H. Olson, and Klaus J. Puettmann

Poster Abstract

Down wood is associated with the function, structure, and diversity of riparian systems. 

Considerable knowledge has been generated regarding down wood stocks and dynamics in 

temperate forests, but there are few studies on eff ects of silvicultural practices and riparian buff er 

design on down wood, particularly in headwater streams. We analyzed interactive eff ects of upland 

thinning and riparian buff er confi guration on down wood volumes and decay classes at fi ve 

managed forest sites in western Oregon. We tested the eff ects of two thinning treatments—an 

unthinned control and a moderate-density thinning with 200 trees ha-1—and three riparian buff er 

widths: combined one and two site-potential tree heights (to 480 ft [146 m]); variable-width (50 

ft [15.2 m] minimum); and streamside retention (~20 ft [6 m]), in coniferous stands dominated 

by Pseudotsuga menziesii and Tsuga heterophylla. Pre-harvest down wood volumes (59 to 128 

m3

∙100 m-1 reach length) in 29 stream reaches (193 to 792 m long) did not diff er among thinning 

treatments and stream buff er confi gurations. One year after thinning, down wood volumes were 

5–42 percent greater than pre-harvest levels, although thinning and stream buff er eff ects remained 

non-signifi cant. Large increases in down wood volumes with time in our headwater streams may 

be the consequence of severe storms or other events not directly related to silvicultural practices. 

Keywords: down wood, stream habitat, timber harvest, decay class, riparian reserves.

Adrian Ares is the director, Sustainable Agriculture and Natural Resource Management Collaborative Research Support 

Program, Virginia Tech, Blacksburg, VA 24060; aresa@vt.edu; Deanna H. Olson is a research ecologist, USDA Forest 

Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; 

Klaus J. Puettmann is Edmund Hayes Professor in Silviculture Alternatives, Department of Forest Ecosystems and Society, 

Oregon State University, Corvallis, OR 97331.
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Slope Failure as an Upslope Source of Stream Wood

Daniel Miller

Presentation Abstract

Large woody debris is recognized as an important component of stream geomorphology and 

stream ecosystem function, and forest-land management is recognized as an important control on 

the quantity (and size and species distributions) of wood available for recruitment to streams. Much 

of the wood present in streams comes from adjacent forests, and riparian management practices 

now refl ect our understanding of the role these forests play in modulating and maintaining stream 

environments. In steep terrain, slope failures also carry wood (and sediment) to streams from 

upslope source areas. In these environments, periodic inputs of wood and sediment from landslides 

and debris fl ows also play an important role in stream geomorphology and ecosystem dynamics. 

Channel environments are naturally dynamic systems. Depending on where you are in the 

channel network, discharge can vary from none in the summer to bed-scouring, channel-avulsing 

fl oods in the winter. Slope failures also drive variability in this system. Deposition of wood and 

sediment occur at discrete points in time and space, thereby creating temporal and spatial variability 

in channel environments. Redistribution and decay of deposited materials over time further add 

to this variability, and act to hide the original source of these materials, thereby masking the role 

of landsliding in setting stream environments. Landslide eff ects thus depend on when and where 

you look, and can be diffi cult to discern if the landslide occurred some time ago. Th is makes eff orts 

to anticipate the eff ects of landsliding very challenging. Are we interested in the short term? Th e 

long term? Are we interested in a single reach? Or eff ects over a basin? Observations also suggest 

that landslide eff ects depend on a host of factors, including valley geometry, channel geometry, the 

quantity and size of sediment and wood in the deposit, the amount of wood and sediment already 

in the channel, and the amount of wood and sediment that enter the channel over the lifespan of 

the landslide deposit. 

Th is sets the stage for considering slope failure as an upslope source of stream wood, particularly 

if we are to consider in-stream wood in the context of a stream ecosystem. I will briefl y review 

the evidence on which to base conceptual and empirical models for identifying and characterizing 

upslope landslide source areas, and for placing them into a channel-network context. Th en I’ll 

illustrate the data-analysis and modeling approaches that we and our collaborators have been 

experimenting with to identify upslope source areas for stream wood and for anticipating the 

in-stream consequences of management decisions in those areas. Th ese methods span a range of 

complexity. At the most basic, we use digital elevation data coupled with empirical models to 

identify the source areas and runout tracks for landslides that could potentially carry material to 

specifi ed portions of the channel network (e.g., fi sh-bearing streams). To gain insights to eff ects 

of management, we couple stand-growth, wood recruitment, and landscape dynamics models to 

estimate wood abundances over time and space.

Keywords: large woody debris, slope failure, stream wood, wood recruitment modeling.

Daniel Miller is a senior scientist, Earth Systems Institute, 6512 23rd Avenue NW, Suite 201, Seattle, WA 98117-5728; 

dan@earthsystems.net.
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Matthew R. Kluber was a master’s student, Department of Forest Ecosystems and Society, Oregon State University, 

Corvallis, OR 97331, currently 1652 Pineland Avenue, Florence, SC 29501, matt.kluber@gmail.com; Deanna H. Olson

is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW 

Jeff erson Way, Corvallis, OR 97331.

Poster Abstract

We examined temporal and spatial patterns of terrestrial amphibian species abundances and 

individual movements in western Oregon managed headwater forest stands using artifi cial cover 

object (ACO) arrays. Using mark-recapture methods, we estimated the eff ects of species and 

seasonality on apparent survival rates and recapture probabilities. We captured, marked, and 

released over 300 individual salamanders during 18 site visits between 2006 and 2009. Th ese 

captures were dominated by three plethodontid species: Ensatina (Ensatina eschscholtzii), Western 

Red-backed Salamander (Plethodon vehiculum), and Dunn’s Salamander (P. dunni). We observed 

64 animals move between ACOs at least once with most salamanders moving between adjacent 

ACOs (<5 m), and the maximum distance traveled being 31 m (Ensatina). Although total captures 

were evenly distributed between near-stream (<15 m from stream edge) and upslope arrays (>15 

m), species distributions diff ered with distance from stream, and most movement occurred in the 

near-stream arrays (<15 m from stream edge). Using the program MARK, the annual apparent 

survival rate for our dominant species was 0.63; however, recapture probabilities varied among 

species and between site visits. Our results have implications for the effi cacy of forest management 

approaches to address ground-dwelling species with limited dispersal capabilities in headwaters: 

riparian corridors are frequently used by both semi-aquatic and upland species. Stream-to-ridgeline 

dispersal occurs, yet is less frequent, although our ACO design likely was restricted in its utility for 

monitoring plethodontid salamander movements.

Keywords: dispersal, movements, riparian, survival, recapture probabilities.

Plethodontid Salamander Population Ecology in Managed Forest 

Headwaters in the Oregon Coast Range

Matthew R. Kluber and Deanna H. Olson
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Matthew R. Kluber was a master’s student, Department of Forest Ecosystems and Society, Oregon State University, 

Corvallis, OR 97331, currently 1652 Pineland Avenue, Florence, SC 29501, matt.kluber@gmail.com; Deanna H. Olson

is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 

SW Jeff erson Way, Corvallis, OR 97331; Klaus J. Puettmann is Edmund Hayes Professor in Silviculture Alternatives, 

Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331.

No Effects of Thinning With Riparian Buffers on Terrestrial 

Salamanders in Headwater Forests 5 to 6 Years Post-harvest in 

Western Oregon

Matthew R. Kluber, Deanna H. Olson, and Klaus J. Puettmann

Poster Abstract

Th ere are emerging concerns for wildlife species associated with forested headwater systems. 

Given that headwater streams comprise a large portion of the length of fl owing waterways in western 

Oregon forests, there is a need to better understand how forest management aff ects headwater 

forest taxa and their habitats. Forest management strategies that consist of only partial canopy 

removal and retention of riparian buff ers may help ameliorate management eff ects on headwaters, 

especially relative to historical clearcutting practices. Our study investigated eff ects of upland 

forest thinning coupled with riparian buff er treatments on riparian and upland headwater forest 

amphibians, their ground-cover habitat attributes, and species-habitat associations. Amphibian 

captures and habitat variables were examined 5 to 6 years post-thinning, within riparian and 

upland forests thinned to 80 trees per acre with streamside-retention buff er widths (~20 ft [6m] 

wide, each side of streams) and variable-width buff ers (50 ft [15.2 m] minimum width, each 

side of streams), as well as unthinned reference stands. Distance-from-stream was found to be 

associated with amphibian abundance. However, no treatment eff ects of thinning or buff er widths 

were found. We observed that ground surface conditions (e.g., amount of rocky or fi ne substrate, 

microclimates) likely played a role in determining the response of riparian and upland amphibians 

to forest thinning along headwater streams. Moderate thinning and preservation of conditions 

in riparian and nearby upland areas by way of variable-width and streamside-retention buff ers 

may be suffi cient to maintain suitable habitat and microclimatic conditions vital to amphibian 

assemblages in managed headwater forests.

Keywords: plethodontid salamanders, timber harvest, density management, riparian reserves.
Density Management in the 21st Century: West Side Story PNW-GTR-880

214

Log and Soil Temperature Profiles in Managed Headwater Subbasins in the Oregon Coast Range: Implications for Wildlife 

Habitat

Matthew R. Kluber, Deanna H. Olson. and Klaus J. Puettmann

Poster Abstract

Down wood provides important faunal microhabitat in forests for many invertebrate taxa, 

small mammals, and amphibians. Habitat suitability of down wood as refugia is an increasing 

concern in managed forests of the US Pacifi c Northwest, where overstory reduction may result 

in both reduced down wood recruitment and increased temperatures within logs, which may 

make them unsuitable habitat refugia. We examined temperature regimes inside logs and soils to 

assess buff ering capabilities against summer temperature extremes and potential habitat suitability 

for plethodontid salamanders. Temperature profi les of small- (0.3–0.45 m) and large- (0.7–1.0 

m) diameter logs, as well as ambient soil and air temperatures, were measured in a 60-year-old 

forest stand under diff erent slope positions (0–5 m and 35–40 m from stream edge) in three case 

studies: 1) along a headwater stream with a narrow riparian buff er (~6 m) and moderate upland 

thinning; 2) along a headwater stream with a wider riparian buff er (~15 m) and moderate upland 

thinning; and 3) along a headwater stream with an unthinned upland. Streamside and upslope 

maximum air temperatures experienced on all three streams during our study were near to or 

exceeded critical temperatures for western plethodontid salamanders (i.e., ~30°C). Streamside and 

upslope temperatures inside small logs, large logs, and soils stayed below critical temperatures. Our 

results suggest that logs of a wide size range as well as soils may provide suffi cient protection against 

thermal extremes in uncut forests and thinned stands with limited overstory. 

Keywords: Down wood, riparian, thinning, microclimate, salamander habitat.

Matthew R. Kluber was a master’s student, Department of Forest Ecosystems and Society, Oregon State University, 

Corvallis, OR 97331, currently 1652 Pineland Avenue, Florence, SC 29501, matt.kluber@gmail.com; Deanna H. Olson

is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 

SW Jeff erson Way, Corvallis, OR 97331; Klaus J. Puettmann is Edmund Hayes Professor in Silviculture Alternatives, 

Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331.

Editors’ suggestion:

Kluber, M.R.; Olson, D.H.; Puettmann, K.J. 2009. Thermal profiles of downed wood under different forest 

management regimes in the Oregon Coast Range and their potential impact on plethodontid salamander 

habitat. Northwest Science. 83: 25-34.

Photos, facing page—Top: How do we keep understory regeneration standing through the 2nd thinning entry? 

Yachats STUDS site, Siuslaw National Forest, July 2009. Center left: Blowdown along a ridge, North Soup Creek 

DMS site March 2009. Bottom left: Ferns, understory, and underplanting, STUDS site, June 2007. Lower right: 

Future yarding corridors may need to be planned at the time of the first thinning to retain anchor trees. North Soup 

Creek, March 2009. All photos by Paul Anderson.
 Section 4. Socioeconomics and Operations
Density Management in the 21st Century: West Side Story PNW-GTR-880

216

Kurtis E. Steele is a forest silviculturist, formerly with the US Forest Service, Willamette National Forest, McKenzie 

Bridge, OR, now with the Chattahoochee-Oconee National Forest, 1199 Madison Road, Eatonton, GA 31024, ksteele@

fs.fed.us.

Presentation Abstract

Variable-density thinning has received a lot of public attention in recent years and has subsequently 

become standard language in most of the Willamette National Forest’s timber management 

projects. Many techniques have been tried, with varying on-the-ground successes. To accomplish 

variable-density thinning, the McKenzie River Ranger District currently uses combinations of 

techniques such as skips, gaps, dominant tree releases, variable thinning prescriptions, designation 

by description (DxD), and individually marked trees within the same harvest unit. Th e major 

challenge associated with implementing variable-density thinning occurs during pre-sale. 

Depending on the level of variability within the harvest unit, it is estimated that it takes up to 

twice as long to complete a timber sale package from layout through the fi nal contract. Issues for 

pre-sale resulting from variable-density thinning include: 1) more complex physical layout on the 

ground; 2) increased GPSing; 3) increase in cruising time; 4) increased complexity in the maps; 

and 5) increase in requirements of the contract. 

In a recent project the McKenzie River Ranger District has also incorporated an uneven-aged 

management approach for Douglas-fi r (Pseudotsuga menziesii) in many of the proposed harvest 

units. Th is has added yet another complicated element into the planning and implementation 

of the project. During the planning process, consideration of current and possible future logging 

systems as well as layout design must be analyzed early. For example, if a unit requires intermediate 

supports to cable log, more thought must be given to when and where the gaps are placed within 

the unit’s rotation. If a group select (gap) is placed around the intermediate support trees and 

those support trees are damaged or removed by harvesting or wind throw, future cable logging 

opportunities may be compromised for 30–45 years. Locations of the group selects (gaps) may 

be critical to design prior to fi rst implementation. Th e increased complexity of an uneven-aged 

management rotation and variable-density thinning across the landscape will also increase future 

data management costs. Units will need to be stratifi ed further in stand exams and cruises to 

maintain quality data. Although the increased cost may not be an issue on a relatively small scale, 

when applied to a landscape, such as a whole project area, it may be more problematic, especially 

with the Forest Service’s budget continuing to decline. Increased stratifi cation will likely require 

more plots per acre, which in turn, requires an increase in person-hours. It is also recommended that 

locations of skips and gaps (group selects) should be tracked to allow for enhanced management 

in the future.

Keywords: thinning, skips, gaps, group select, variable-density thinning, implementation, 

dominant tree release, stratifi cation, uneven-aged, designation by description, DxD.

Managers’ Perspectives: Practical Experience and Challenges 

Associated with Variable-density Operations and Uneven-aged 

Management

Kurtis E. Steele
Density Management in the 21st Century: West Side Story PNW-GTR-880

217

Presentation Abstract

Density management through thinning is the most important tool foresters have to aff ect stand 

development and stand structure of existing stands. Reducing stand density by thinning increases 

the growing space and resource availability (e.g., light, water, and nutrients) for the remaining 

trees. Th is can result in increased average tree growth. More available site resources can also 

encourage the development of understory vegetation and trees. Alternatively, the highest amounts 

of stand volume (or tree biomass) growth will generally occur when the site is fully occupied. Th e 

competition levels of this high level of site occupancy will lead to self-thinning mortality of the 

less vigorous trees and reduced net stand growth. Reducing stand density reduces site occupancy, 

growing-stock, and total leaf area and generally results in reduced stand volume growth. 

Th e impact of thinning on stand growth rates will depend on the amount of residual growing 

stock retained and the vigor of the trees that remain. Th inning younger stands with adequate 

crown and rapid height growth can be expected to build crown, leaf area, and growing stock 

rapidly. Vigorous trees in older stands may also respond to thinning. Higher average tree growth 

rates and lower mortality in thinned stands maintain rapid growth rates and fl atten out the annual 

increment curve and push culmination of mean annual increment to older ages.

Growth-growing stock relationships have been studied in the Pacifi c Northwest since the 1960s 

and demonstrate the trade-off between individual tree growth and stand growth. Th inning to 

variable densities (growing space) and gaps will also follow these basic growth-growing stock 

principles. Understanding these relationships is important for foresters to achieve desired stand 

production, economic, and structural development goals.

Keywords: thinning, site resources, self-thinning mortality, individual tree growth, stand growth.

David Marshall is a biometrician for Weyerhaeuser NR Company, WTC 1A5, PO Box 9777, Federal Way, WA 

98063-9777; david.marshall2@weyerhaeuser.com.

Growth and Yield Considerations and Implications for Alternative 

Density Management Objectives and Approaches

David Marshall
Density Management in the 21st Century: West Side Story PNW-GTR-880

218

Harvest Operations for Density Management: Planning 

Requirements, Production, Costs, Stand Damage, and 

Recommendations

Loren D. Kellogg and Stephen J. Pilkerton

Presentation Abstract

Since the early 1990s, several studies have been undertaken to determine the planning 

requirements, productivity, costs, and residual stand damage of harvest operations in thinning 

treatments designed to promote development of complex forest structure in order to enhance 

ecological functioning and biological diversity. Th ese studies include the Oregon State Universityled cooperative Coastal Oregon Productivity Enhancement (COPE) project, the Willamette 

(National Forest) Young Stand Project (WYS), and the Siuslaw (National Forest) Th inning and 

Underplanting for Diversity (STUDS) project. Treatments focused on 35- to 50-year-old stands 

with density management targets included light thinning (100–120 residual trees per acre, tpa 

[~250-300 trees per hectare, tph]), heavy thinning (50–60 residual tpa [~125-150 tph]), very 

heavy thinning (30 residual tpa [~75 tph]), and light thinning with gaps. A second treatment was 

applied to the STUDS stands that had light and heavy treatments on the fi rst entry.

Logging planning and layout costs were studied for the WYS project. Production and costs 

results for harvest operations include skyline yarding, ground-based skidding, and mechanized cutto-length systems. Damage to the residual stand was studied for the STUDS stands. 

Planning and layout eff orts are benefi cial to effi cient and successful harvest operations. Harvest 

production infl uences related to the density management treatment were relatively small. More 

importantly, these studies have demonstrated important aspects of successful harvest operations for 

density management in planning, conducting, and assessing residual stand damage. Results of the 

stand damage assessments show high incidence of tree damage close to the yarding corridor / skid 

trail. A stand damage assessment methodology, DAMQUICK, was developed. 

Th is presentation will (1) summarize what we have learned from the harvesting studies for 

successful planning and implementation of density management stand treatments, and (2) report 

the cable harvesting production and stand damage results from the STUDS second thinning entry.

Keywords: harvest planning, thinning costs, logging productivity, skyline yarding, tractor skidding, 

mechanized harvesting, cut-to-length, young stands, commercial thinning, partial cutting, timber 

harvesting, Douglas-fi r, logging damage, riparian buff er.

Loren G. Kellogg is a professor, and Steven J. Pilkerton is a research forest engineer, Department of Forest Engineering, 

Resources, & Management, Oregon State University, Corvallis, OR 97331; loren.kellogg@oregonstate.edu; steven.

pilkerton@oregonstate.edu. 

Editors’ suggestion:

Han, H.; Kellogg, L. 2000. Damage characteristics in young Douglas-fir stands from commercial thinning 

with four timber harvesting systems. Western Journal of Applied Forestry. 15: 27–33.

Photos, facing page—Top left: Anemone in the rain. Photo by Brad Catton, USFS. Top right: Coastal Giant 

Salamander, Dicamptodon tenebrosus. Photo by Loretta Ellenburg, USFS. Center left: Ensatina (Ensatina eschscholtzii). 

Photo by Brad Catton, USFS. Center right: Groundcone, Boschniakia sp. Photo by Brad Catton, USFS. Bottom: Road 

at Keel Mountain. USFS photo by Mark Meleason.
Section 5. Thinning and Adaptation
Density Management in the 21st Century: West Side Story PNW-GTR-880

220

Geometry of Forest Landscape Connectivity: 

Pathways for Persistence

Deanna H. Olson and Kelly M. Burnett

Deanna H. Olson is a research ecologist and Kelly M. Burnett is a research fi sh biologist (emeritus), USDA Forest 

Service, Pacifi c Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; 

dedeolson@fs.fed.us.

Abstract

Streamside areas may be dispersal funnels or runways for a variety of species. For over-ridge 

dispersal, headwaters off er the shortest distance links among riparian zones in adjacent drainages. 

We summarize landscape designs for connectivity of habitats using headwater riparian linkage areas 

as the foundation for a web of landscape-scale links. We developed management considerations for 

placement of headwater linkage areas including: 1) providing connections between larger basins; 

2) maintaining habitat connectivity in the face of climate change; 3) incorporating place-based 

disturbance regimes such as headwater debris-fl ow-prone areas; 4) targeting connectivity areas to 

address sensitive species conservation strongholds; and 5) accounting for geometry at the foreststand scale of a single project or proposed timber sale, including managing habitats to connect 

lands on adjacent federal ownerships, by means of connecting corners of checkerboard landscape 

blocks along diagonals. Although our proposed linkage areas are designed to target headwater 

species, the resulting web of connections across the landscape is expected to benefi t many forestdependent species. 

Keywords: watersheds, forest, headwaters, biodiversity, linkage areas, dispersal.

Introduction

Biodiversity retention and restoration is 

an emerging priority for global ecosystems. 

Astounding losses within major taxonomic groups 

have been reported nationally and internationally 

(41 percent of amphibians, 25 percent of 

mammals, 15 percent of bony fi shes, 13 percent 

of birds: Hoff mann et al. 2010; 50–60 percent of 

turtles: Kiester and Olson 2011). In particular, 

protection and restoration of forests and forest 

biodiversity has become a paramount concern 

worldwide (e.g., Convention on Biological 

Diversity: www.cbd.int/forest/). A toolbox of 

management approaches has been developed 

to conserve forest biodiversity, largely through 

a mixture of fi ne- and coarse-grained habitat 

protections (e.g., United States Northwest Forest 

Plan: USDA and USDI 1993, 1994; Cissel et al. 

1998; Lindenmayer and Franklin 2002; Raphael 

and Molina 2007; Lindenmayer et al. 2007) 

and site-specifi c designs to maintain or restore 

forest structural heterogeneity (McComb 2001; 

Lindenmayer and Franklin 2002; Brockerhoff et 

al. 2008). 

Development of landscape designs to manage 

habitat connectivity for multiple species is 

an especially active research topic in forest 

biodiversity conservation, due to continuing 

trends of forest fragmentation and to an upswing 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Geometry of Forest Landscape Connectivity Olson and Burnett 221

in world reforestation eff orts. Managing forested 

landscapes for connectivity functions benefi ting 

biodiversity requires incorporating several 

fundamental conservation concepts. Th ese basic 

conservation tenets include identifying the critical 

habitats used throughout species’ life histories 

(breeding, foraging, overwintering, and dispersal 

habitats), and commensurate habitat protections 

to ensure that these biotic functions are retained. 

If an organism uses diff erent habitats through its 

life cycle, then maintaining connectivity among 

these habitats is essential to ensure its persistence. 

Of particular relevance is the characterization and 

retention or restoration of dispersal habitat. Th is 

includes the home ranges of individuals and the 

broader dispersal of off spring or individuals that 

tie sub-populations and populations together 

over larger areas. Th is broader-scale dispersal 

function maintains genetic variation within 

natural populations, which may foster resiliency 

needed to adapt to changing environmental 

conditions. Th e future of species may rely on our 

careful attention to managing for connectivity 

now.

Defi ning the adequacy of dispersal habitat 

in forests is a complex topic (Noss et al. 1997) 

and may address a variety of elements, including 

habitat condition, corridor sizes (length, width), 

and corridor redundancy (Pinto and Keitt 2008). 

Redundancy is especially relevant because multiple 

connectivity pathways can assist dispersal across 

landscapes by organisms in diff erent locations 

and increase the probability of movement in 

the face of many interacting site-specifi c factors 

(microsite features, disturbances). Redundancy of 

habitat connectivity hedges against catastrophe, 

uncertainty, and stochastic processes that can 

aff ect individuals and sub-populations that vary 

in their movement propensities, possibly related 

to patch size, habitat quality, and population 

demography. 

Low-mobility species may merit special 

attention devoted to the placement and 

redundancy of connectivity corridors, because 

barriers to dispersal may arise as a result of their 

basic biology and ecology (Raphael and Molina 

2007). Th ese species may move slowly and 

require refugia along corridors because it may 

take them years to move between optimum 

habitat patches. Due to a potentially longer 

residency time within connectivity corridors, 

low-mobility species may be particularly 

vulnerable to sub-optimal corridor conditions 

and stochastic processes. Hence, redundancy 

of connections may be critically important 

to increase their likelihood of successful 

movement across landscapes for such lowmobility species. Patches of higher-quality 

habitat within dispersal corridors may be used 

as stepping stones for such species and may be 

an essential aspect of their long-term persistence 

(e.g., Grant et al. 2010). Such stepping stones 

may function as habitat refugia or “stopover 

reserves” (Dobson et al. 1999), which promote 

survival of individual organisms as they move 

through the environment. Stepping stones 

may have more suitable physical habitat 

conditions than the surrounding area, or may 

allow individuals to forage to replenish energy 

reserves or survive harsh seasons (summer, 

winter) in localized refugia, from which they 

may disperse again later. 

Herein, we synthesize our ongoing studies 

of the utility of headwater riparian areas as 

proposed connectivity corridors, or linkage 

areas, for dispersal of riparian-associated and 

low-mobility species in Pacifi c Northwest 

forests. Once designed, such headwater linkage 

areas may benefi t many taxa. Our studies also 

conceptually integrate aquatic network and 

upland-forest habitats, functions, and processes. 

Th e combination of protections for aquatic 

and upland systems is providing new insights 

into forest ecosystem management approaches. 

We summarize the key considerations for 

the geometric orientation of connectivity 

pathways to assist migration of species across 

watersheds and across webs of connections, to 

maintain linked aquatic-terrestrial populations 

at landscape scales. Our goal here is to provide 
Density Management in the 21st Century: West Side Story PNW-GTR-880

222 Geometry of Forest Landscape Connectivity Olson and Burnett

a summary of these conceptual designs, while 

research continues to address these issues and 

advance design eff ectiveness.

Utility of Watersheds as 

Redundant Landscape-scale 

Linkage Units 

Watersheds are widely accepted units for 

monitoring and evaluating the eff ects of land use 

on aquatic resources (Omernik and Bailey 1997). 

Where their boundaries can be clearly mapped, 

watersheds are increasingly common units for 

forest management planning and conservation 

designs. For example, in the U.S., the Aquatic 

Conservation Objectives of the federal Northwest 

Forest Plan (USDA and USDI 1994: p. B-11), 

address connectivity among watersheds: 

“Maintain and restore spatial and temporal 

connectivity within and between watersheds. 

Lateral, longitudinal, and drainage network 

connections include fl oodplains, wetlands, 

upslope areas, headwater tributaries, and 

intact refugia. Th ese network connections must 

provide chemically and physically unobstructed 

routes to areas critical for fulfi lling life history 

requirements of aquatic and riparian-dependent 

species.”

Hydrologic units (HUs), delineated by the 

U.S. Geological Survey (Seaber et al. 1987), 

are also a convenient and widely used basis for 

forest assessment and planning (e.g., Maxwell 

et al. 1995; Suring et al. 2011). Th e HU coding 

describes a hierarchical system of units nested 

by drainage area; larger code numbers designate 

smaller drainage areas. Watersheds or segments 

of watersheds comprise HUs. Even though the 

majority of HUs at each level of the hierarchy 

are not true topographic watersheds, such a 

perspective can aid biodiversity conservation 

designs, especially as smaller headwater basins 

are delineated and used for replicating protected 

areas (e.g., 6th

-code HUs: Suzuki et al. 2008) 

and creation of redundant connections across 

landscapes (via 6th- and 7th-code HUs: Olson 

and Burnett 2009). 

Th e value of using headwater basins as the 

premise for establishing connectivity corridors 

across forested landscapes is due to their habitat 

conditions, potential use by a variety of organisms, 

frequency of occurrence on the landscape, and 

minimization of dispersal distances (fi g. 1). 

Olson et al. (2007) summarized some of the 

merits of headwater riparian habitats for species 

in the northwest, including providing cool, moist 

microclimates for interior-forest dependent 

organisms and aquatic-riparian associated species 

such as amphibians. Some taxa may use these 

areas due to their habitat suitability; others may 

respond to streams as movement barriers, and 

then move along banks parallel to such barriers. 

Streamside areas may be dispersal funnels or 

runways for a variety of species. For example, 

we have seen terrestrial salamanders (species 

that do not use stream or pond habitats for 

breeding or other life-history functions) moving 

predominantly through near-stream areas (D. 

Olson and M. Kluber, unpubl. data). Additional 

taxa that use riparian corridors in northwestern 

forests include a variety of lichens, bryophytes, 

fungi, vascular plants, mollusks, mammals (e.g., 

ground-dwelling mammals: Wilk et al. 2010), 

birds, and general forest-obligates that may occur 

in legacy forest attributes such as wolf trees along 

riparian buff er zones. As a minimum estimate 

across taxonomic groups, over 100 species were 

identifi ed as likely to benefi t by habitat protections 

of combined intermittent and perennial streams 

provided by riparian reserves in federal forest 

lands in the range of the Northern Spotted Owl 

(Strix occidentalis caurina) (table 1) (USDA and 

USDI 1997). Species with restricted dispersal 

abilities were identifi ed for special consideration 

relative to utility of riparian reserves during 

watershed analyses under the Northwest Forest 

Plan (USDA and USDI 1997).

Furthermore, the high density of small streams 

in upland northwest forests has been widely 

recognized over the last 20 years, as our basic 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Geometry of Forest Landscape Connectivity Olson and Burnett 223

Table 1—Species benefitting from interim riparian reserves developed for the federal Northwest Forest Plan (from 

table B1 in USDA and USDI 1997). Riparian reserve protection includes a one site-potential tree-height or 30.5 m (100 

ft) buffer, whichever is greater, as an interim measure along all intermittent streams, and a two site-potential tree-height 

buffer as an interim measure along perennial streams (see USDA and USDI 1993, page III-9).

Taxonomic group Species

Bryophytes Antitrichia curtipendula, Douinia ovata, Kurzia makinoana, Scouleria marginata, 

Tritomaria exectiformis

Fungi

Rare chanterelles Polyozellous multiplex

Rare gilled mushrooms Clitocybesubditopoda, C. senilis, Neolentinus adherens, Rhodocybe nitida, Rhodocybe 

speciosa, Tricholomposis fulvenscens

Rare cup fungi Helvella compressa, H. crassitunicata, H. elastica, H. maculata

Jelly mushroom Phlogiotis helvelloides

Moss-dwelling mushrooms Cyphellostereum leave, Galerina atkinsoniana, G. cerina, G. hetrocysis, G. 

sphagnicola, G. vittaeformis, Rickenella setipes

Lichens

Riparian lichens Certelia cetrarioides, Collema nigrescens, Leptogium burnetiae var. hirsutum, L. 

cyanescens, L. saturninum, L. teretiusculum, Platismatia lacunose, Ramalina thrausta, 

Usnea longissima

Aquatic lichens Dermatocarpon luridum, Hydrothyria venosa, Leptogium rivale

Vascular plants Bensoniella oregano, Botrychium minganense, B. montanum, Coptis trifolia

Mollusks Ancotrema voyanum, Crypotmastix devia, C. henersoni, Monadenia fi delis 

salmonensis, Verspericola depressa, V. sierranus, Fluminicola spp. nov. 1-20, F. 

seminalis, Helisoma newberryi newberryi, Juga (C.) acutifi losa, J. (C.) occata, J (O.)

spp. nov. 2-3, J. (Oreobasis) orickensis, Lanx alta, Lyogyrus sp. nov. 1, 3, Pyrgulopsis 

intermedia, Vorticifex klamathensis sintsini, V. sp. nov. 1

Amphibians

Riparian Aneides fl avipunctatus, Rhyacotriton cascadae, R. kezeri, R. variegatus, Dicamptodon 

copei, Plethodon vandykei, Ascaphus truei

Fish Coho Salmon (Oncorhynchus kisutch), fall and spring Chinook Salmon (O. 

tshawytscha), resident and sea-run Cutthroat Trout (O. clarkii clarkii), resident 

Rainbow Trout (O. mykiss), summer and winter Steelhead (anadromous O. mykiss)

Birds Common Merganser (Mergus merganser)

[Marbled Murrelet, Brachyramphus marmoratus; Northern Spotted Owl, Strix 

occidentalis caurina]

Bats Fringed, Long-eared, and Long-legged Myotis (Myotis thysanodes, M. evotis, M. 

volans), Hoary Bat (Lasiurus cinereus), Pallid Bat (Antrozous pallidus), Silver-haired 

Bat (Lasionycteris noctivagans)

Other mammals Fisher (Martes pennanti), Marten (Martes americana), Red Tree Vole (Arborimus 

longicaudus)
Density Management in the 21st Century: West Side Story PNW-GTR-880

224 Geometry of Forest Landscape Connectivity Olson and Burnett

Figure 1—Example interim riparian reserve network 

from the US federal Northwest Forest Plan implemented 

in the Pacific Northwest, showing frequency of 

headwater streams on the landscape and the resulting 

one and two site-potential tree-height buffers along 

streams (upper left quadrant). Arrow indicates example 

over-ridge area where the distance between headwater 

riparian reserves in different watersheds is small and 

over-ridge connectivity may be more easily achieved. 

These headwater riparian areas can be used to facilitate 

landscape linkage area designs for organism dispersal and 

aquatic-terrestrial habitat connectivity functions.

knowledge of stream and forest ecology has 

expanded. In some areas, headwaters comprise 

80 percent of a stream network (Gomi et al. 

2002). Th is realization intersected with forest 

management practices when mapping of 

Northwest Forest Plan scenarios revealed that 

large percentages of watersheds were being 

incorporated into interim riparian reserves due 

to the high density of headwater stream networks 

(fi g. 1). An additional value of using headwater 

drainages to plan landscape connectivity designs 

is that the distance from headwater streams to 

ridgelines is the shortest within a watershed, hence 

reducing travel distances for overland dispersal to 

neighboring stream-riparian areas or forest reserve 

blocks. Distance analysis tools, such as for “leastcost path” in landscape modeling (e.g., ArcGIS, 

Environmental Systems Research Institute, Inc., 

Redlands, CA), have been developed to assess 

distances between habitat patches. Th ese tools 

would be useful for designing least-distance 

headwater linkage areas. Least “cost” path is a 

relevant term applied to the economics of animal 

movements, to minimize the distance moved—

especially for mobility-restricted organisms. 

Th is term may also apply to the economics of 

forest management if identifi cation of a dispersal 

corridor results in a fi nancial cost for on-theground implementation or aff ects revenue from 

resource extraction in a managed forest context.

Northwest Forest Plan riparian reserves were 

intended as major contributors to the maintenance 

and restoration of aquatic conservation objectives, 

including aquatic network connectivity (USDA 

and USDI 1994). Th e importance of linking 

headwater stream functions and processes to 

those of downstream stream networks has been 

a focus of much work in the last two decades. 

Welsh (2011) captured many elements of the 

developing history of stream network theory and 

the role of aquatic connectivity in summarizing the 

conceptual frameworks of geomorphic channel 

processes (transfer and depositional zones), 

nutrient cycling (upstream marine infl uence 

via salmonid migration, downstream nutrient 

spiraling via down wood movements), aquaticriparian linkages via reciprocal subsidies, and 

the intersection of herpetofaunal distributions 

with the classic stream continuum concept 

of taxonomic patterns that vary with stream 

order. As we look up the aquatic network into 

headwater streams and beyond, we summarize 

how extending riparian buff ers up drainages 

and connecting them over ridgelines can both 

maintain terrestrial connectivity and functionally 

link aquatic-terrestrial systems.

Several conceptual designs of riparian buff er 

widths and patch reserves have been proposed 

to assist over-ridge migration of organisms 

within forests (fi g. 2; Olson et al. 2007). Overridge connectivity considerations were further 

developed by Olson and Burnett (2009), and 

modeled for the Oregon Coastal Province. Th is 

model of connectivity linked every 6th- and 7thcode HU to each neighboring HU. Focusing on 

the Siuslaw River basin, a 4th-code HU within 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Geometry of Forest Landscape Connectivity Olson and Burnett 225

that area, the linkage design illustrated where 

one over-ridge link could connect each adjacent 

HU (fi g. 3). At the 7th-code HU scale, one 

link between each adjacent 7th-code watershed 

resulted in roughly 15 percent of headwater 

streams being extended and connected For the 

Oregon Coastal Province, this resulted in over 

5,000 links, with about one link per 4.6 km2. 

Th is is an example of redundant connectivity, 

essentially creating a web of connections across 

the landscape. Using the 6th-code HU scale, the 

amount of connectivity created is approximately 

halved, with one link per 9.3 km2 for the Oregon 

Coastal Province. 

Th ere are no defi ned guidelines for how 

many links or how much habitat connectivity is 

necessary to maintain populations. Th e amount 

of dispersal habitat that might be needed to 

sustain even highly researched species, such as Figure 2—Headwater management 

considerations to retain aquaticriparian biodiversity by stream buffers 

of different widths (A, B) and provide 

linkage areas between adjacent 

basins (C-G) using alternative forest 

management practices including uncut 

blocks (C, D, F), thinning (E), and 

leave islands (E, G) (from Olson et al. 

2007).

Figure 3—Linkage areas between 

watersheds can provide connectivity of 

headwater habitats across landscapes. 

In the Oregon Coast Range Province, 

the Siuslaw River basin, a 4th-code 

Hydrologic Unit (HU), is used to 

illustrate: A) a single connection 

between adjacent 6th-code HUs; and B) 

a single connection between adjacent 

7th-code HUs, which results in 376 

connections across the basin and if 

expanded to the entire province, about 

5000 links within 23 000 km2 (from 

Olson and Burnett 2009).
Density Management in the 21st Century: West Side Story PNW-GTR-880

226 Geometry of Forest Landscape Connectivity Olson and Burnett

the northern spotted owl, is unknown; a “more 

is better” attitude prevails in the face of this 

uncertainty. Nevertheless, research is accruing 

about how much dispersal may be needed to 

maintain genetic diversity within and among 

populations. Th e “one migrant per generation” 

rule has been off ered as a minimum level to reduce 

genetic isolation, inbreeding, and bottlenecks 

(e.g., Mills and Allendorf 1996). However, such 

a rule has many underlying assumptions that 

may not be supported when the complexities of 

natural systems are considered (e.g., Wang 2004). 

Furthermore, relating eff ective migration rates 

to habitat protections in managed systems is not 

a straightforward exercise: if we build corridors, 

will they be used? Ongoing mark-recapture, 

radio tracking, and genetic studies are helping 

us to answer this question. For example, genetic 

connectivity analyses of stream-associated Rocky 

Mountain Tailed Frogs (Ascaphus montanus) 

in Idaho supported this species’ affi liation with 

intact forested habitats: their path of connectivity 

followed riparian corridors in managed forests 

(Spear and Storfer 2010). Th is pattern supports 

the “riparian corridors as funnels” concept, 

but it contrasted with Coastal Tailed Frog (A. 

truei) genetic connectivity pathways in the 

Olympic Peninsula, Washington, which were 

primarily overland in areas that had timber 

harvest activities (Spear and Storfer 2008). 

Precipitation and population diff erences between 

these areas were hypothesized as accounting for 

these diff erences, as the more mesic conditions 

that prevail in northwestern Washington may 

facilitate the upland dispersal of moisture-reliant 

tailed frogs. Other studies (Wahbe et al. 2004; 

Johnston and Frid 2002; Dupuis and Steventon 

1999; Nauman and Olson 2004) also found 

diff erences in riparian-corridor associations of 

various amphibian species in response to climate 

and forest conditions, generally supporting 

their ability to respond to microsite gradients 

with an apparent affi liation to cool, moist local 

conditions (e.g., riparian “funnels”) (Olson et al. 

2007). Furthermore, Spear et al. (2012) reported 

that Coastal Tailed Frogs track remnant tree 

patches in their migration pathways after the 

volcanic blast at Mount St. Helens, Washington. 

So, if we build it, will they come? Th e early 

answer is “yes, but...” —meaning that a variety 

of organisms appear to be occurring in or moving 

along pathways of retained habitats, but with 

geographic, taxonomic, and population-specifi c 

contexts being important considerations. A 

similar conclusion has recently been supported 

for hedgerows as corridors between woodland 

fragments (Davies and Pullin 2007). More 

research on the design of eff ective linkage areas 

will be needed. In the interim, conceptual 

priorities for landscape connectivity designs can 

be identifi ed, and these relate directly to emerging 

research priorities.

Priority Areas for Habitat 

Connectivity

Prioritizing linkage area placement may be 

important to address connectivity objectives 

under economic constraints, and to advance 

research into the eff ective design of linkage 

areas. Because linking all adjoining watersheds 

at small HU scales may be diffi cult for land 

managers to plan and implement in the face of 

myriad confl icting resource objectives, priorities 

may guide the fi rst steps in connecting habitats. 

Olson and Burnett (2009) itemized linkage area 

considerations at two spatial scales, landscape and 

drainage area (table 2). Here, we further develop 

fi ve of these priority considerations: 

1. “Triads,” where three large basins, with 

limited or no aquatic connectivity, converge 

at their headwaters; 

2. Climate change considerations including 

north-south, east-west, and altitudinal 

linkages; 

3. Landslide-prone areas; 

4. Species conservation strongholds; and 

5. Diagonal considerations. 
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Geometry of Forest Landscape Connectivity Olson and Burnett 227

Table 2—Design considerations for placement of headwater linkage areas to assist migration of forest-dependent 

species in the Pacific Northwest (Olson and Burnett 2009). Bold-face type indicates new concepts discussed further 

in text.

Linkage Area Design 

Considerations Priorities

Landscape scale

1. Connections across large 

basins

“Triads” – headwater locations that link three adjoining basins having no aquatic 

connectivity.

2. Climate change migration 

corridors

North-south (latitudinal) dispersal routes.

Altitudinal dispersal routes.

Migration across ecoregion boundaries.

East-west dispersal routes.

3. Linking landscape 

fragments

Connecting remnant late-successional and old-growth (LSOG) forest patches to other 

patches or restored habitats may aid dispersal of LSOG-associated species, especially 

those with dispersal limitations such as lichens, bryophytes, and mollusks; creation of 

connected archipelagos of patches.

4. Disturbance frequency Correlating frequency of connections with rates of landscape-scale disturbances, 

natural or anthropogenic; i.e., more linkage areas in more-disturbed places.

5. Redundancy Planning for multiple paths across landscapes will improve dispersal probabilities.

Drainage-basin scale

6. Known sites for target 

species

Low-mobility species.

LSOG-associated species.

Species with status of concern.

Biodiversity hotspots – communities.

Species “strongholds” – priority species management areas such as key watersheds

7. Existing protections Co-location of linkages on current set-asides (e.g., federal late-successional reserves, 

owl “cores”, Survey and Manage species sites, botanical set asides, landslide-prone 

areas included in riparian reserves)

8. Short connections For economy of space, with economic and ecological benefi ts, shorter connectivity 

corridors are preferred; ecologically, shorter distances for dispersal may reduce 

energetic costs for individual movements and time needed for propagules to disperse.

9. Paths of least resistance Easier dispersal routes may be lower-gradient or lower-elevation “saddles” across 

ridgelines.

Wind-dispersers may have least resistance in paths that follow wind directions during 

seasons of dispersal.

10. Risk of disturbance Use hazard models for disturbances such as landslides, debris fl ows, ice/wind damage, 

and fi re in placement of linkage areas, or in decisions about the need for redundant 

linkages. For example, debris-fl ow-prone areas may be headwater set-asides during 

riparian reserve delineation, and such areas may be co-located with dispersal corridors; 

redundant links may be considered in fi re-prone areas. Mapped overlays of roads, 

recreation areas, human development, and mining might be avoided during linkage 

area delineation, when alternative locations exist.

11. Land ownership patterns Co-location of links on federal and state lands, where possible.

Diagonal linkage areas across checkerboard ownerships.
Density Management in the 21st Century: West Side Story PNW-GTR-880

228 Geometry of Forest Landscape Connectivity Olson and Burnett

Each of these fi ve considerations results in a 

geometric view of how connectivity webs may be 

arranged across landscapes. 

Th ese fi ve considerations are not mutually 

exclusive; how they may interact during 

prioritization exercises also is developed briefl y 

here. Although they were derived for northwest 

forest landscapes, these concepts may have 

broader utility worldwide.

1. “Triads”

In the Oregon Coastal Province, Olson 

and Burnett (2009) highlighted the potential 

importance of linking larger river basins, which 

have no freshwater connectivity, through existing 

riparian buff er networks. Over-ridge forest 

habitat linkages may be absent unless reserves 

are placed in the area. Streams in such basins 

may fl ow directly to the Pacifi c Ocean or into 

a much larger river without a forested riparian 

area, and so have headwaters that are functionally 

disconnected. Here, we examined 4th-code HUs 

for the Oregon Coastal province, the scale of the 

Siuslaw River basin highlighted above. We then 

looked for locations where three of these 4thcode HUs joined at their headwaters: we call 

this a “triad” location. For example, headwaters 

of the Siuslaw River, Yaquina River, and Marys 

River converge at Marys Peak (between Corvallis, 

Newport, and Waldport, OR), which would be 

one such triad. Only 18 of these headwater triads 

exist for the Oregon Coastal Province (fi g. 4). We 

suggest that such triads be considered priorities 

for habitat linkage areas because these would 

be spatially economical for land managers to 

implement and potentially ecologically effi cient 

as connections across three watershed boundaries 

simultaneously.

A current research priority is to empirically assess 

the proposed linkage-area function of landscape 

locations such as headwater triads. Using a 

genetic approach, we have sampled northwestern 

amphibians from headwater streams of adjacent 

drainages that are potentially connected across 

ridgelines in the Oregon Coast Range, including 

three adjoining headwaters in triads (such as 

Marys Peak). Preliminary genetic analyses of 

the Coastal Giant Salamander, Dicamptodon 

tenebrosus, generally support our contention 

of over-ridge connectivity among drainages (L. 

Knowles and M.R. Marchán-Rivadeneira, Univ. 

Michigan, unpubl. data). Previous studies have 

supported overland connectivity of streambreeding amphibians (e.g., Spear and Storfer 

2008, 2010), and such animals have been found 

up to 400 m from streams (Olson et al. 2007), 

but no previous published study has designed 

Figure 4—“Triads” are indicated (squares) where 

three 4th-code Hydrologic Units in the Oregon Coast 

Range Province meet at their headwaters. Triads are 

priority locations for linkage area or ‘species stronghold’ 

placement to effectively manage for species dispersal 

simultaneously across three distinct watershed boundaries.
Density Management in the 21st Century: West Side Story PNW-GTR-880

Geometry of Forest Landscape Connectivity Olson and Burnett 229

sampling to specifi cally address headwater overridge connectivity among discrete drainages. 

Th is remains an information gap that could be 

addressed for all forest taxonomic groups, and 

would aid the adaptive management of the triad 

connectivity concept.

2. Climate Change

A second priority consideration for northwest 

forest connectivity is assisting migration in the 

face of climate change (Olson and Burnett 2009). 

Predicted climate change eff ects on northwest 

forest habitats include drought, insect, and fi re 

eff ects on forest stands, with large conifers and 

high-elevation trees being vulnerable to losses 

(Spies et al. 2010). Aquatic habitat changes 

in forested landscapes are anticipated in coldwater mountain streams (Spies et al. 2010) 

and in headwaters (Olson and Burnett 2009). 

Increasing stream temperatures, with negative 

implications for cold-water fauna, are already 

apparent across the northwest (Isaak et al. 2011). 

Given uncertainty in the geographic specifi city 

of climate change trajectories due to complex 

El Niño and Pacifi c Decadal Oscillation cycles, 

“dynamic and adaptive thinking” (Spies et al. 

2010) is needed. A prudent course for linkage 

area placement may be to consider connected 

routes in north-south, east-west, and altitudinal 

directions within and among watersheds (fi g. 5). 

Such consideration may allow multiple potential 

pathways of movement for species facing changing 

conditions. Pockets of suitable microhabitats 

for species persistence may be related to local 

conditions, and may occur as “stepping stones” 

along these linear trajectories, like beads along 

a string. Providing connectivity paths adjoining 

both riparian areas and north-facing slopes is 

one such example, with both near-stream areas 

and hill shading resulting from topographic relief 

providing cool, moist conditions for target species 

such as some late-successional and old-growth 

(LSOG)-associated salamanders (e.g., Suzuki et 

al. 2008). Landscape-scale monitoring of forest 

conditions and species distributions may inform 

adaptive management of likely climate change 

refugia for diff erent taxa.

3. Managing Disturbances: 

Landslide-Prone Areas

A third priority consideration for the design 

of linkage areas is to integrate their placement 

with local disturbance regimes. Landslides 

and debris fl ows can be dominant disturbance 

processes aff ecting headwater streams in forested, 

mountainous regions (e.g., Benda 1990; Iverson 

et al. 1997). Th e Northwest Forest Plan directs 

that riparian reserves incorporate landslide-prone 

areas to reduce the probability that activities 

associated with timber harvest will alter wood 

and sediment inputs to streams by changing 

the rate, magnitude, composition, or timing 

of debris fl ows. Co-locating linkage areas with 

existing riparian reserves, where these include 

steep areas prone to landsliding, can provide 

Figure 5—Designs for assisted migration of species in 

the face of climate change might include prioritizing 

headwater linkage area placement across north-south and 

east-west watershed boundaries. The Siuslaw River basin, 

a 4th-code Hydrologic Unit in the Oregon Coast Range 

Province, is shown highlighting perimeter sub-drainages 

(dark grey) where linkage areas could be made to discrete 

drainages to the north, south, and east.
Density Management in the 21st Century: West Side Story PNW-GTR-880

230 Geometry of Forest Landscape Connectivity Olson and Burnett

Figure 6—Placement of between-drainage 

links might consider other landscape-scale 

provisions such as management scenarios 

to retain the natural disturbance regime, 

including landslide-prone areas managed to 

deliver wood and sediment to streams. Top 

figures show models of 25 percent and 75 

percent of the landslide-prone hillslopes in an 

example forest landscape, and bottom figures 

show their likely traversal paths to streams 

(Burnett and Miller 2007). Headwater riparian 

buffers of these areas provide long-term wood 

and sediment inputs for stream biota. From 

Olson and Burnett 2009.

economic effi ciency and conservation synergy 

for land and resource managers. Burnett and 

Miller (2007) modeled diff erences among hill 

slopes and headwater channels in probabilities 

of initiating and transporting debris fl ows that 

deliver to fi sh-bearing channels for the Oregon 

Coastal Province (fi g. 6). Th ose headwaters with 

the highest likelihood of aff ecting downstream 

areas important for fi sh might be high priorities 

for extending riparian reserves over ridgelines. 

Because debris fl ows can be important sources 

of large wood (May and Gresswell 2003; Hassan 

et al. 2005), a fundamental component of 

stream habitat complexity (Bilby and Bisson 

1998; Gregory et al. 2003), managing these 

expanded riparian reserve areas to accelerate tree 

growth could be an additional consideration. 

Redundancy of connections would be important 

when planning ground-disturbing activities 

for linkage areas with a high probability of 

landsliding. To aid identifi cation and adaptive 

management of landslide-prone areas, these areas 

have been mapped for many northwest forests by 

the NetMap interactive web-tool developed by 

Earth Systems Institute (http://netmaptools.org/).

4. Species Strongholds

“Species strongholds” are areas where 

biodiversity conservation is a priority, and where 

thriving populations can occur to anchor species 

persistence in the region. Retaining connectivity 

among species strongholds enhances the 

likelihood of persistence under the uncertainty 

of stochastic events (catastrophic fi re, disease 

outbreaks) or emerging patterns of disturbance 

(climate change) that may aff ect any particular 

stronghold. Managing stronghold-to-stronghold 

connectivity is a fourth priority to consider in 

developing linkage area designs across forest 

landscapes. Species strongholds may be created 

for communities of diverse taxa at larger 

spatial scales by land-use allocations such as 
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Geometry of Forest Landscape Connectivity Olson and Burnett 231

Congressionally reserved lands (wilderness areas, 

national parks), or the Northwest Forest Plan latesuccessional reserves or key watersheds (USDA 

and USDI 1993, 1994). At smaller spatial scales, 

strongholds for a targeted species of concern may 

be critical habitat areas, such as caves, ponds, 

meadows, botanical set-asides, or areas managed 

for Survey and Manage species under the federal 

Northwest Forest Plan (USDA and USDI 1993, 

1994). Riparian buff ers themselves might be 

considered as strongholds, but here, we expand 

that perspective to other areas. 

Developing new species strongholds is 

particularly important when considering 

connectivity issues. Th ree examples follow. 

First, areas with high “intrinsic potential,” the 

capacity to support high-quality habitats for 

salmon (Burnett et al. 2007), may serve as nuclei 

for designing linkage areas. Intrinsic potential 

models have been developed and broadly applied 

for salmonids in the Pacifi c Northwest and 

elsewhere (e.g., Mollot and Bilby 2008; Sheer et 

al. 2009; Busch et al. 2011; Barnett and Spence 

2011). Streams with high intrinsic potential can 

be identifi ed and then targeted, as appropriate, 

for salmon conservation across a landscape. Such 

areas of high intrinsic potential are essentially 

“species strongholds” from which aquaticterrestrial linkage areas can originate. Areas of 

high intrinsic potential for some salmonid species 

may occur in larger streams, but tools exist to 

easily identify headwater streams that feed into 

these both laterally and from upstream (Clarke 

et al. 2008).

Second, criteria for Priority Amphibian and 

Reptile Conservation Areas (PARCAs) are under 

development for nationwide application (Riley 

et al. 2011). PARCAs are being discussed for 

integration into the landscape planning processes 

of other entities, such as the U.S. Department of 

Interior Landscape Conservation Cooperatives 

(http://www.doi.gov/lcc/index.cfm), which is a 

partnership network to sustain America’s land, 

water, wildlife, and cultural resources. Once 

established, PARCAs would function as species 

strongholds. Similarly, the International Union 

for the Conservation of Nature (IUCN) is 

developing criteria to identify sites of global 

signifi cance for biodiversity conservation, called 

Key Biodiversity Areas. Such areas are synonymous 

with the concept of species strongholds. Th e 

additional element that we suggest is to provide 

connectivity among such areas.

Th ird, triads, as we previously described, 

could be ideal locations for species strongholds, 

as these occur at the ridgeline junction of three 

large basins. However, we note that triads are 

not established biodiversity hotspots, and are 

proposed here as a conceptual design. 

Development of landscape-scale linkage webs 

from either new or existing species strongholds 

is needed to reduce isolation of those areas, and 

as possible to allow them to function as potential 

“source” habitats with optimal conditions that 

can anchor species over time and also connect 

to adjoining areas, in a metapopulation context. 

Linking dispersal pathways from strongholds up 

and over ridgelines to adjacent watersheds and 

neighboring strongholds is a direct approach 

that may off er a least-cost path. Relevant to 

our proposed headwater linkage areas concept, 

connecting such species strongholds to headwaters 

which then extend and connect over ridgelines is 

another consideration. Additionally, strongholds 

may be linked to protected riparian areas along 

larger streams that are subsequently extended 

upstream into headwaters and connected over 

ridgelines. Multiple connectivity pathways may be 

conceived. As a web of connections is considered 

relative to species stronghold connectivity, the 

previous priorities discussed above and outlined 

in table 2 can be overlain, including large basins 

and triads, linear trajectories to address for 

climate change gradients, and occurrence of 

landslide-prone areas.

Adaptive management of strongholds may 

need to be addressed over the long term as future 

conditions unfold. As applied here, the concept of 

a stronghold evokes less of an immovable fortress 

than an anchor. A species stronghold intended 
Density Management in the 21st Century: West Side Story PNW-GTR-880

232 Geometry of Forest Landscape Connectivity Olson and Burnett

to anchor habitat may need to function as do 

real anchors on occasion, and be repositioned or 

“drag” across landscapes in response to changing 

conditions or management priorities (Olson et 

al. 2007). Th e temporal scale of strongholds can 

be addressed at the time of their development, 

and interact with the spatial scale of stronghold 

designs and the frequency of strongholds. For 

example, habitat anchors designed to drag across 

landscapes may be implemented more easily 

if they are smaller and more numerous. Olson 

et al. (2007) suggested considering 6th-code 

watersheds (HUs) as a spatial scale for amphibian 

habitat anchors. Th e anchor concept warrants 

testing, with a suffi cient timeframe to weigh 

success at the landscape scale, in addition to 

replication. It may have greater success if it were 

to be implemented in areas with more resilient 

ecosystems. 

5. Thinking Diagonally: Funnels and 

Chains

Th e geometry and land-management context 

of land-use and land-ownership parcels on the 

landscape is a fi nal set of priority considerations 

for linkage-area placements that we will develop 

briefl y here. Th e northwest forest landscape is 

a patchwork of land ownerships and land-use 

allocations, each with diff ering management 

priorities, which creates a complex challenge 

for biodiversity conservation (Suzuki and Olson 

2007). During planning for large blocks of 

forest land, and during planning of individual 

projects at smaller spatial scales, managing for 

connectivity within and among ownership 

areas can be diffi cult due to diff ering priorities 

across boundaries. To diminish the dilemma of 

achieving eff ective biodiversity conservation in 

such a multi-ownership landscape, it may help to 

think of streams as dispersal “funnels” that serve 

to channel organisms along protected riparian 

areas, and connectivity corridors or linkage areas 

as “chains” functionally moving animals up and 

over ridgelines (Olson and Kluber, unpubl. data). 

Overlaying many of the previously discussed 

priorities can provide an integrated perspective 

for addressing the challenges of land-ownership/

allocation geometries.

Diagonal linkage areas are of specifi c relevance 

in a landscape with a checkerboard ownership 

pattern (fi g. 7), and in other landscape geometries 

that abut at corners or other edge types (Olson 

and Kluber, unpubl. data). Species dispersal 

along such diagonals might be promoted by forest 

management actions that retain habitat elements 

toward the corners of such lands. For example, 

weighted green-tree retention, leave islands, and 

directional felling of down wood (recruitment 

of large logs, in particular) from corners may 

assist migration of species along the diagonal by 

providing chains or stepping stones of suitable 

microhabitats for species refugia. Linking chains 

of habitat elements from corners to stream- and 

riparian-protected areas, especially headwaters 

(fi g. 7B), may functionally extend and connect 

riparian buff ers. Organisms that are funneled 

along riparian areas may venture through corners 

via these habitat chains. A chain of habitat need 

not extend from headwaters, but could extend 

from any part of a riparian buff er, or from a 

species stronghold, as discussed above.

It may be neither feasible nor desirable to address 

habitat connectivity at all corners of adjacent 

lands within an ownership. Similarly, when land 

parcels are in close proximity but do not adjoin, 

it may not be possible to consider linkage areas 

along their entire boundaries. Several additional 

design concepts arise and interface with ideas 

presented above. 

First, linkage areas among land parcels might 

be “stream-lined” if streams align through 

corners (fi g. 8), or connect nearby land 

blocks. When streams follow diagonals in a 

checkerboard landscape, riparian protection may 

more eff ectively promote multi-species diagonal 

dispersal: funnels without the added chains 

linking across diagonals. Streams that loosely 

follow diagonals, not intersecting exactly at 

corners, could be quite functional to assist species 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Geometry of Forest Landscape Connectivity Olson and Burnett 233

migration, in this regard. Streams that link 

disconnected parcels may similarly function to 

funnel organisms’ movements. Th e context of the 

adjoining lands may need to be assessed, however. 

Managing such a stream-line to promote its 

potential connectivity function is a consideration, 

but such stream-lined connectivity does not 

address overland dispersal. Chains from streams 

to ridgelines are needed to fully integrate aquatic 

and terrestrial landscape connectivity functions. 

Collaborative management of such stream-lines 

and overland chains among ownerships and 

Figure 7—In a checkerboard ownership pattern, such as that created by the Oregon and California Lands Act (1937) 

where US Bureau of Land Management (BLM) and private industrial forestlands are intermixed, management for 

connectivity along diagonals may improve likelihood of species dispersal within ownerships. A: Corners are shaded 

to show linkage area considerations. However, routes along selected diagonals to species strongholds, reserves, or 

triads might be used to prioritize which corners are chosen for connectivity emphasis. B: Forest management options 

to facilitate species dispersal from stream corridors (which may serve to funnel species movements) to corners might 

include chains of habitat structures provided by green tree retention, directional log placement from corners to streams, 

or both. Concepts could be applied to other ownership geometries with corners or edges in proximity. 

Figure 8—Connectivity designs to aid 

species dispersal among ownership blocks may 

overlay on streamside riparian management 

zones. This US Bureau of Land Management 

study site for the Density Management and 

Riparian Buffer Study of western Oregon 

(Cissel et al. 2006) shows riparian buffers 

extending along the full diagonal (A) as 

well as laterally toward an opposing corner 

(B), with leave islands and dispersed tree 

retention aiding habitat connectivity, and to a 

neighboring private land block (C). “Streamlined” connectivity (A) may aid withinwatershed dispersal, but overland connectivity 

designs (B and C) may warrant consideration 

to link or “chain” habitats overland between 

watersheds. Photo provided by Oregon 

Bureau of Land Management.
Density Management in the 21st Century: West Side Story PNW-GTR-880

234 Geometry of Forest Landscape Connectivity Olson and Burnett

across land-use allocations within ownerships, 

remains a challenge.

Second, in multi-ownership landscapes, road 

densities may be higher than in single owner 

landscapes. An assessment of the eff ects of 

roads on species connectivity designs may be 

particularly important in these landscapes. In 

particular, paved roads or high-use unpaved 

roads may be barriers to low-mobility species. As 

roads intersect streams, aquatic organism passage 

may be aff ected, with consequences for overland 

connectivity. Site-specifi c designs can include 

these considerations.

Th ird, as hazard models of disturbances are 

developed for a landscape, it may be helpful 

to ask how hazards align with land-ownership 

boundaries, land-use allocations, and existing 

connectivity webs. For example, how are 

landslide-prone areas arranged relative to the 

geometry of lands by ownership and land-use 

allocation? As discussed above, can priority 

linkage areas be designed to overlay on landslideprone areas that are already set-asides for riparian 

reserve management, and now also serve “to 

chain” habitats to adjoin land-ownership blocks? 

Fourth, in a larger landscape context, it may 

be useful to know how larger basins, climate 

change projections, and species strongholds are 

arranged and whether these be used to prioritize 

connectivity area pathways. Can dispersal routes 

be conceived from streams and then through 

land-ownership diagonals or between ownership 

blocks to foster connections relative to these 

issues? 

Multiple overlapping considerations are 

emerging, and a stepwise process may be needed 

to integrate them. Limitations may emerge due 

to topography, geometry of land confi gurations 

at local scales, or pre-existing conditions. For 

example, a dispersal barrier such as a road may 

need to be considered fi rst. Th e existence of 

under-road culverts may create spatially explicit 

bottlenecks for connectivity planning. Routing 

linkage area pathways to those stream corridors 

and culverts may be needed to increase the odds 

of dispersal across the road. Culverts that act as 

dispersal nodes in this way could be prioritized for 

enhancement to provide passage for non-aquatic 

species. Similarly, triads and species strongholds, 

as discussed above, are essentially dispersal 

nodes. Routing dispersal routes via headwater 

linkage area pathways to triads and strongholds 

could increase the overall eff ectiveness of these 

conservation measures. 

Conclusions

Forest biodiversity conservation is an 

ecosystem service that will continue to be 

addressed at local-to-landscape scales in the 

coming century. Retaining organisms across 

managed forest landscapes requires a toolbox 

of approaches including fi ne- and coarse-scale 

habitat protections and restoration practices, 

retaining or creating structural elements that are 

critical habitats for species, and development 

and management of connectivity pathways to 

allow gene fl ow. Renewed eff orts to address 

communities of organisms as well as species 

of concern are called for as emerging stressors 

need evaluation, new knowledge is accrued, and 

adaptive management of existing forest plans are 

needed.

We review the numerous benefi ts of forest 

connectivity designs that rely on headwater 

linkage areas, and emphasize priorities for their 

placement at landscape scales. Th e benefi ts of 

headwater linkage areas include their likely 

functional role in integrating aquatic and 

terrestrial systems, their potential use by multiple 

taxonomic groups, their utility for creating webs 

of connections across forested lands to increase 

their eff ectiveness for biodiversity conservation, 

and their effi ciency in minimizing both the 

distances that animals must move overland and 

the fi nancial burdens of forest manager. 

Placement of headwater linkage areas may 

include consideration of a variety of factors 

(table 2). Prioritizing linkage areas can provide a 

starting point for managing connectivity among 
Density Management in the 21st Century: West Side Story PNW-GTR-880

Geometry of Forest Landscape Connectivity Olson and Burnett 235

critical habitat areas, suggest directional routes 

for dispersal among areas, or identify dispersal 

nodes as anchors for connectivity webs. Th e fi ve 

priority considerations that we developed include 

triads that eff ectively link three larger basins, 

north-south and east-west directional routes 

to address climate change scenarios, linkages 

overlaid on management of disturbances such 

as landslide-prone areas, links among species 

strongholds, and diagonal links that route 

dispersal across management boundaries. Th ese 

fi ve concepts can be integrated into an overall 

geometry of landscape connectivity designs. 

Our conceptualization of headwater linkage 

area utility and these priority considerations are 

posed as hypotheses warranting further study 

and development. We off er these ideas with 

the caveat that they will not benefi t all taxa in 

forested landscapes. Extremely rare or patchily 

distributed organisms with low mobility may 

need a fi ner-grained, site-by-site conservation 

approach (Raphael and Molina 2007).

Acknowledgments

Concepts developed here are outcomes of our 

large-scale projects with the Density Management 

and Riparian Buff er Study of western Oregon 

(DHO) and the Coastal Landscape Analysis and 

Management Study (KMB). We thank the US 

Forest Service and Bureau of Land Management for 

supporting those projects. We thank K. Christiansen 

and K. Ronnenberg for assistance with graphics, and 

P. Garvey-Darda and two anonymous reviewers for 

helpful comments.

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Anderson, Paul D.; Ronnenberg, Kathryn L., eds. Density management for the 21st century: west side story. Gen. Tech. 

Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacifi c Northwest Research Station: 

220–238.
Density Management in the 21st Century: West Side Story PNW-GTR-880

239

Headwater Stream Flow, Climate Variation, and Riparian Buffers 

with Thinning in Western Oregon

Julia I. Burton, Deanna H. Olson, and Klaus J. Puettmann

Poster Abstract

Headwater streams and adjacent riparian areas provide reproductive, foraging, and dispersal 

habitat for many forest-dependent species, especially amphibians. Although previous studies have 

shown that the composition of aquatic and riparian animal communities is associated with spatial 

and temporal patterns of stream fl ow, the relationships among stream fl ow, climate, and thinning 

are not well known. We characterized stream fl ow conditions associated with 78 headwater reaches 

in 13 managed forest sites in the Coast Range and western Cascade Range, Oregon, USA, tracked 

periodically over a 16-year period. Th en, we retrospectively examined relationships among riparian 

buff ers, stream fl ow characteristics, and climate variables over time. We tested the hypotheses 

that: 1) warmer and drier years would be associated with a shrinking of headwater streams (i.e., 

increased proportion of stream length in dry channels); and 2) such eff ects are associated with 

thinning upslope of riparian buff ers, due to the eff ect of thinning to reduce interception and water 

uptake from the soil.

Stream fl ows were only weakly related to interannual climate variability. However, the relationship 

between climate and stream fl ow that was observed, although weak, supported the shrinking 

heads hypothesis (Hypothesis 1). Relationships between climate and stream fl ow classes were not 

related to riparian buff er treatments with upland thinning, thus no evidence was found to support 

Hypothesis 2. Our preliminary results suggest the eff ects of climate change scenarios on headwater 

streams, and dependent fauna, may not be mediated by harvesting within riparian zones.

Keywords: stream fl ow, climate change, thinning, shrinking heads, headwater streams.

Julia I. Burton is a research associate, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, 

OR 97331; Deanna H. Olson is a research ecologist, USDA Forest Service, Pacifi c Northwest Research Station, Forestry 

Sciences Laboratory, 3200 SW Jeff erson Way, Corvallis, OR 97331; Klaus J. Puettmann is Edmund Hayes Professor in 

Silviculture Alternatives, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331.
Density Management in the 21st Century: West Side Story PNW-GTR-880

240

Thinning Impacts on the Resilience of Wildlife Habitat Quality 

under Climate Change in Coniferous Forests of Western Oregon

Andrew R. Neill, Klaus J. Puettmann, and Adrian Ares

Poster Abstract 

To understand the impacts of overstory density reductions on resilience of forest ecosystems 

(i.e., the capacity of an ecosystem to maintain desired ecosystem functions in a fl uctuating 

environment), we examined overstory basal area and understory vegetation cover and richness 

collected 6 years after thinning in seven 40- to 60-year-old forests dominated by Douglas-fi r 

(Pseudotsuga menziesii (Mirb.) Franco) in the Oregon Coast Range and Cascade Range of western 

Oregon. Each site contained an unthinned control (240–1,540 trees∙ha-1 [tph]) and three thinning 

treatment units (high-density = 300 tph; moderate-density = 200 tph; and variable-density with 

a combination of 300 tph, 200 tph, and 100 tph). 

We used a mechanistic, trait based approach to quantify impacts of overstory density on 

understory vegetation components that contribute to wildlife habitat. Vascular plant species that 

produce fl eshy fruits, a major food source for wildlife, were grouped as a functional group. We 

quantifi ed the resilience of this function as the likelihood of being maintained under increased 

environmental stress related to climate change; e.g., drought duration and severity. To accomplish 

this, fl eshy-fruit-producing species were categorized in terms of their response types based on 

traits that assume their ability to tolerate drought conditions.

High variability of overstory densities within and among treatments created an overstory density 

gradient at each site that ranged from 0–87 m2∙ha-1 in basal area. Average cumulative cover and 

species richness of species that produce fl eshy fruits increased with decreasing overstory density, 

suggesting that thinning will increase the potential food sources for wildlife. Similarly, cumulative 

cover and species richness of drought-tolerant species that produce fl eshy fruits also increased at 

lower overstory densities, suggesting that thinning will increase the likelihood that the food source 

for wildlife will be maintained under more droughty conditions. Changes in Pielou’s evenness of 

species cover on a plot along the overstory density gradient were not signifi cant for either species 

group, suggesting that changes are due to general increases in species abundance and richness, 

rather than by increases of dominant or rare species.

Keywords: stand density, plant species richness, functional diversity, vegetation response types, 

habitat quality.

Andrew R. Neill is a graduate student, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, 

OR 97331; Klaus J. Puettmann is Edmund Hayes Professor in Silviculture Alternatives, Department of Forest Ecosystems 

and Society, Oregon State University, Corvallis, OR 97331; Adrian Ares is the director, Sustainable Agriculture and 

Natural Resource Management Collaborative Research Support Program, Virginia Tech, Blacksburg, VA 24060.
Density Management in the 21st Century: West Side Story PNW-GTR-880

241

English Equivalents

When you know: Multiply by: To find:

Millimeters (mm) 0.0394 Inches

Centimeters (cm) 0.394 Inches

Meters (m) 3.28 Feet

Meters 1.094 Yards

Kilometers (km) 0.621 Miles 

Hectares (ha) 2.47 Acres

Square centimeters (cm2

) 0.0155 Square inches

Square meters (m2

) 10.76 Square feet

Square kilometers (km2

) 0.386 Square miles

Cubic meters (m3

) 35.3 Cubic feet

Cubic meters 60,975 Cubic inches

Kilograms (kg) 2.205 Pounds

Kilograms 0.0011 Tons

Kilograms per hectare (kg∙ha-1) 0.893 Pounds per acre

Tonnes per hectare (t∙ha-1) 893 Pounds per acre

Tonnes or megagrams per 0.446 Tons per acre

 hectare (t∙ha-1) (Mg∙ha-1)

 

Square meters per hectare (m2

∙ha-1) 4.37 Square feet per acre

Cubic meters per hectare (m3

∙ha-1) 14.29 Cubic feet per acre

Trees per hectare (tph) 0.405 Trees per acre

Degrees Celsius (°C) 1.8 °C + 32 Degrees Fahrenheit

Diameter at breast height is abbreviated as dbh throughout the proceedings.
Papers were provided by the editors in camera-ready form for printing. Authors are responsible for the content and 

accuracy. Opinions expressed may not neccessarily reflect the position of the U.S. Department of Agriculture. 

The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. 

Department of Agriculture of any product or service.

Front cover and cover background photos by Mark Meleason. 

Section divider art and cover design by Kathryn Ronnenberg.

Pacific Northwest Research Station

Forest Service 

U.S. Department of Agriculture

Abstract 

Anderson, Paul D.; Ronnenberg, Kathryn L., eds. 2013. Density Management in the 21st Century: 

West Side Story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Research Station. 249 p.

Since adoption of the Northwest Forest Plan (NWFP) in the early 1990s, there has been a fundamental 

shift in forest management practices on federal lands in western Oregon and Washington. Commoditydriven clearcut regeneration harvests have given way to thinnings intended to enhance development 

of late-successional forest habitats and to conserve important aquatic and riparian ecosystems. Density 

Management in the 21st Century: West Side Story presents abstracts and peer reviewed papers from a 

regional conference highlighting more than twenty years of research related to forest thinning in the 

NWFP area. Presentations from the BLM Density Management and Riparian Buffer Study provide a 

focal point, with presentations from additional studies providing for a more complete overview of the 

west-side thinning science. The contributions are organized as five topical themes: The Regional and 

Landscape Context for Density Management in the Northwest Forest Plan Era; Implementation and 

Influences of Density Management in the Terrestrial Ecosystem; Riparian and Aquatic Ecosystems and 

their Responses to Thinning and Buffers; Socioeconomics and Operations; and Thinning and Adaptation. 

Collectively, the contributions summarize many important forest dynamics and ecosystem responses to 

partial overstory removals. Interactions between aquatic and riparian ecosystem conservation measures 

and upland harvest are emphasized. Targeting resource management practitioners, decision-makers 

and researchers, the collected works provide a reference to the current and future roles and issues of 

density management as a tool for forest ecosystem management.

Keywords: Aquatic Conservation Strategy, biodiversity, density management, forest structure, 

ecosystem processes, late-successional habitat, northern spotted owl, public perception, riparian 

buffers, stream temperature, thinning, wildlife.

Editors

Paul D. Anderson is a supervisory research forester, Pacific Northwest Research Station, Forestry Sciences Laboratory, 

3200 SW Jefferson Way, Corvallis, OR 97331; pdanderson@fs.fed.us.

Kathryn L. Ronnenberg is a research information assistant, Pacific Northwest Research Station, Forestry Sciences 

Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331; kronnenberg@fs.fed.us.