United States 

Department of 

Agriculture 

Forest Service 

Pacific Southwest 

Research Station 

General Technical 

Report 

PSW-GTR-198 

December 2005 

Proceedings of the Symposium 

on Ponderosa Pine: Issues, 

Trends, and Management 

October 18 - 21, 2004 Klamath Falls, Oregon 
Abstract 

Ritchie, Martin W.; Maguire, Douglas A.; Youngblood, Andrew, Technical 

Coordinators. 2005. Proceedings of the Symposium on Ponderosa Pine: 

Issues, Trends, and Management. 2004 October 18-21; Klamath Falls, OR. 

Gen. Tech. Rep. PSW-GTR-198. Albany CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture. 281 p. 

Ponderosa pine is one of the most widely distributed tree species in western North 

America. It is highly-valued as a source of lumber, but also is key to the health and 

social value western forests, whether growing in pure stands or in mixture with 

other conifer and hardwood species. In recent years, management objectives for 

forests containing this species have shifted from an emphasis on timber production 

to an emphasis on restoring ecosystem health and reducing the risk of non-characteristic wildfires. The symposium on “Ponderosa Pine: Issues, Trends, and Management” was convened to provide a venue for researchers and managers to explore the 

current state-of-our-knowledge, including management practices that help managers to adapt to constantly changing constraints and objectives. 

Disclaimer 

Papers were provided by the authors and technical coordinators in camera-ready form 

for printing. Authors are responsible for the content and accuracy. Opinions expressed 

may not necessarily reflect the position of the U.S. Department of Agriculture. 

Pesticide Precautionary Statement 

This publcation 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 fish or other wildlife—if they are not applied properly. Use all pesticides 

selectively and carefully. Follow recommended practices for the disposal of surplus 

pesticides and pesticide containers. 
Proceedings of the Symposium 

on Ponderosa Pine: Issues, 

Trends, and Management 

October 18 - 21, 2004 Klamath Falls, Oregon 

Technical Coordinators 

Martin W. Ritchie, Douglas A. Maguire and Andrew Youngblood 

Contents 

v	 Preface

Ponderosa Pine: An Introduction

1 Overview of Ponderosa Pine Ecosystems 

Russell T. Graham and Theresa B. Jain

33 An Overview of Key Silvicultural Information for Ponderosa Pine 

John Fiske and John Tappeiner

Silviculture and Ecosystem Management

49 Silvicultural Systems for Managing Ponderosa Pine 

Andrew Youngblood

59 Multiaged Silviculture of Ponderosa Pine 

Kevin L. O’Hara

71 The West-Wide Ponderosa Pine Levels-of-Growing-Stock Study at Age 40 

William W. Oliver

81 Accelerating Development of Late-Successional Features in Second-Growth Pine 

Stands of the Goosenest Adaptive Management Area 

Martin W. Ritchie and Kathleen A. Harcksen

95 Positive Seedling-Shrub Relationships in Natural Regeneration of Ponderosa Pine 

Christopher R. Keyes and Douglas A. Maguire

i 
GENERAL TECHNICAL REPORT PSW-GTR-198 

Soils and Productivity

109 Managing Ponderosa Pine Forests in Central Oregon: Who Will Speak for the Soil? 

Matt D. Busse and Gregg M. Riegel

123 Management of Ponderosa Pine Nutrition Through Fertilization 

Mariann T. Garrison-Johnston, Terry M. Shaw, Peter G. Mika and Leonard R.		 Johnson

Range and Wildlife Issues and Management

145 Ungulate Ecology of Ponderosa Pine Ecosystems in the Northwest 

Martin Vavra, Kenric Walburger and Timothy DelCurto

159 A Comparison of Bird Species Composition and Abundance Between Late- and Midseral Ponderosa Pine Forests 

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

171 Effects of Site on the Demographics of Standing Dead Trees in Eastside Pine Forests 

William F. Laudenslayer, Jr.

183 Woodpecker-snag Interactions: an Overview of Current Knowledge in Ponderosa 

Pine Systems 

Kerry L. Farris and Steve Zack

Forest Disturbance

197 Fire Ecology of Ponderosa Pine and the Rebuilding of Fire-Resilient Ponderosa Pine 

Ecosystems 

Stephen Fitzgerald

227 Diseases as Agents of Disturbance in Ponderosa Pine 

Gregory M. Filip

233 Bugs in the System: Development of Tools to Minimize Ponderosa Pine Losses from 

Western Pine Beetle Infestations 

Chrisopher J. Fettig

Project and Case Studies

245 Reintroducing Fire into the Blacks Mountain Research Natural Area: Effects on Fire 

Hazard 

Carl N. Skinner

259 Three Studies on Ponderosa Pine Management on the Warm Springs Indian 

Reservation: Stocking Control in Uneven-aged Stands, Forest Products from Firedamage Trees, and Fuels Reduction 

John V. Arena

267 Lessons Learned on 50,000 Acres of Ponderosa Pine Plantations in Northern 

California 

Jeff Webster

ii 
Proceedings of the symposium on ponderosa pine: issues trends and management 

Preface 

As early exploitation of standing timber yielded to intensive reforestation and active 

stand management, our silvicultural knowledge base has expanded tremendously. 

Changing public perception of timber harvesting and different societal values of 

forest resources, coupled with rapid expansion of the wildland/urban interface has 

compelled foresters to pursue multiple-resource management with less emphasis on timber production on many public and private lands. Conversely, demand 

for ponderosa pine wood has intensified management on other private lands, and 

large disturbances from fire, insects, and disease have fueled intense debates about 

rehabilitation efforts. The result of these debates and the accompanying information 

need has been a notable increase in our knowledge of ponderosa pine ecosystems 

and better understanding of human values and perceptions. 

The presentations at the symposium were selected to cover a broad spectrum of 

topics and to update forest landowners, professional foresters, and forest scientists 

about the current issues, trends and management of ponderosa pine ecosystems. 

The presentations in this compilation are arranged by broad topical categories. 

Two introductory papers serve to set the foundation for science-based management of ponderosa pine ecosystems. Graham and Jain first present characteristics 

and key functional elements of ponderosa pine systems. Fiske and Tappeiner follow 

with an overview of important silvicultural research findings over during the last 

century, findings that will remain important as we manage ponderosa pine forests 

for the 21st century. Their work focuses on two broad themes: timber stand improvement and stand dynamics. 

Silviculturists today often are challenged to manipulate stand structures to meet 

an increasingly varied set of objectives. In the section dealing with silviculture and 

ecosystem management, Youngblood presents an overview of silvicultural systems 

applicable to ponderosa pine. His presentation covers traditional systems designed 

to produce commodities such as timber, forage, and water, as well as changes in 

silvicultural practices prompted by forest health and fuel reduction issues. O’Hara 

describes an approach for promoting and managing multi-cohort stands of ponderosa pine. Various alternative methods have been proposed for stocking control 

in uneven-age systems, and he compares these to one based on allocating leaf area 

among cohorts. Productivity is predicted to be comparable to that of even-aged 

silvicultural systems. Because, the fundamental tool of siliviculture remains the 

manipulation of stand structure regardless of objectives or issues, and stand density is probably the most commonly manipulated aspect of stand structure. Oliver 

presents results from 40 years of research on alternative stand density regimes in 

iii 
GENERAL TECHNICAL REPORT PSW-GTR-198 

ponderosa pine, referred to as the West-wide levels-of-growing-stock study. The 

initial objective was to evaluate the long-term effects of density management on 

tree growth and mortality, but many insights have also been gained into the range 

of stand structures obtained by varying stand density regime. Ritchie and Harcksen describe a new large-scale interdisciplinary study designed to accelerate the 

development of late-successional features in pine-dominated ecosystems. Keyes 

and Maguire then describe the complex relationships between shrubs and natural 

seedling recruitment in ponderosa pine, and show that shrubs can enhance early 

seedling survival. 

In the section on soils and productivity, Busse and Riegel describe the response 

of soil quality to thinning and prescribed fire, and emphasize the role that N-fixing 

shrubs play in offsetting losses of soil N during prescribed fire. In addressing soil 

amendments, Johnson and others show that response to fertilization is dependent 

on the soil and parent material, and note that ponderosa pine often does not show a 

strong growth response to N fertilization alone. Multi-nutrient fertilization, however, may provide a better growth response. 

The value of ponderosa pine forests for wildlife habitat and forage production 

for domestic livestock is well documented. Our understanding of the role of specific 

species and the related structural component in these ecosystems is less complete. 

Vavra and others note that both domestic and native ungulates can have an impact 

on understory composition and structure in ponderosa pine systems, and that these 

changes can impact nutrient cycling, energy flow, biodiversity, stand density, and 

fire regimes. George and others compare species composition of birds in late- and 

mid-seral ponderosa pine forests. Their results are consistent with other studies 

suggesting that woodpeckers and bark gleaners are strongly associated with large 

trees and snags; however, they found no difference in overall species diversity. 

Snags are considered an important element for habitat suitability for some avian 

species. Laudenslayer describes a long-term study of snag demography demonstrating that snag longevity varies with tree species, tree size, soil characteristics, and 

topography. He recommends that these factors be considered when developing 

snag management guidelines. The means by which snags are created may also be 

an important factor in determining habitat suitability. Farris and Zack show that 

snags created by fire or bark beetles decay more rapidly than those resulting from 

other mortality agents, but also experience the greatest foraging and nesting use by 

woodpeckers. 

Forest disturbance regimes strongly influence the dynamics of ponderosa pine 

ecosystems. Currently high fuel levels resulting from fire suppression, the attendant 

high risk of severe fire, and very recent extreme fire events have created an urgent 

iv 
Proceedings of the symposium on ponderosa pine: issues, trends and management 

need to re-asses the role fire in ponderosa pine ecosystems. Fitzgerald discusses the 

importance of understanding historic fire regimes if managers are to develop effective restoration treatments. Disturbances created by disease also contribute significantly to the long-term dynamics of ponderosa pine forests. Filip describes the role 

of forest diseases in forest succession and in the maintenance of biological diversity, 

as well as their interaction with insect outbreaks and fire frequency and severity. 

The risk of insect outbreaks has also heightened with the disruption of historic fire 

regimes. Fettig describes chemical, silvicultural and semiochemical techniques for 

minimizing insect-induced mortality in ponderosa pine stands. 

Finally, experience gleaned from operational projects and case studies can 

extremely valuable in developing effective management strategies for ponderosa 

pine. In recent years, the application of prescribed fire in reducing fuel levels and 

maintaining healthy, resilient stands has received greater attention. However, the 

paper by Skinner shows that applying prescribed fire in stands that have had many 

decades of fire exclusion can be difficult, and that benefits related to reducing 

fire danger may be very short lived under such conditions. Arena describes three 

ongoing studies on the Warm Springs Indian Reservation designed to evaluate the 

feasibility and efficacy of removing small (unmerchantable) material from dense 

stands, identify appropriate stocking levels for uneven-aged ponderosa pine stands, 

and assess the utilization potential of material typically removed in fuel reduction 

treatments but otherwise considered unsuitable for most forest products.. Webster 

and Fredrickson finish the proceedings with a set of very practical guidelines for 

establishing and managing young plantations of ponderosa pine. 

v 

Ponderosa Pine Ecosystems1

Russell T. Graham2 and Theresa B. Jain2

Abstract 

Ponderosa pine is a wide-ranging conifer occurring throughout the United States, southern

Canada, and northern Mexico. Since the 1800s, ponderosa pine forests have fueled the

economies of the West. In western North America, ponderosa pine grows predominantly in

the moist and dry forests. In the Black Hills of South Dakota and the southern portion of its

range, the species primarily occupies ponderosa pine potential vegetation types (PVTs) but, in 

the northern portion of its range, it grows on Douglas-fir, grand fir and/or white fir and

western redcedar PVTs. Within this wide range of biophysical settings it is often associated

with complex vegetation mixes. Non-lethal, mixed, and lethal wildfires historically burned 

through most ponderosa pine forests leaving in their wake a wide variety of species

compositions and vegetative structures arranged in a variety of mosaics. Since the 1800s, fire

exclusion, animal grazing, timber harvest, and climate cycles have contributed to changing

these forests. As a result, succession accelerated, plant compositions shifted, trees and other 

biomass accumulated, soil chemical and physical properties changed, non-native plants were

introduced, and epidemics of insects and diseases are more common. Together these changes

altered fire regimes, displaced native species, and disrupted other ecological processes. 

Although the extent of wildfires that now burn in these altered forests is not noteworthy, their 

severity is. Canopy treatments and surface fuel treatments in combination are most likely to

reduce the risk of severe and intense wildfires in these forests that mean a great deal to 

individuals and society.

Introduction 

Ponderosa pine (Pinus ponderosa P. & C. Lawson), is a wide-ranging conifer

occurring throughout the western United States, southern Canada, and northern

Mexico (fig. 1) (Little 1971). Generally its greatest extent is in the Inland 

Northwestern United States and in northern California. However, it is a prevalent 

species in the Black Hills of South Dakota and Wyoming, along the Front Range of

the Rocky Mountains in Colorado and along the Mogollon Rim in Arizona, the

rugged escarpment that forms the southern limit of the Colorado Plateau. The species 

occupies sites with elevations ranging from sea level to 3,281 m (10,000 ft.) 

depending on latitude (Oliver and Ryker 1990). In terms of area occupied, it is only 

second to Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco var. glauca (Beissn.)

Franco) (Van Hooser and Keegan 1988). Two geographic varieties are recognized, 

the Rocky Mountain (Pinus ponderosa var scopulorum Engelm.) which grows 

primarily in the Rocky Mountains and the Pacific (Pinus ponderosa var ponderosa

which is widely distributed in the mountains of the Pacific Coast from British

Columbia into California and western Nevada (Little 1979). Arizona pine (Pinus 

arizonica Engelm.), once considered to be a variety of ponderosa, grows in southwest 

1

 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine:

Issues, Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Research Forester, Forestry Sciences Laboratory, Rocky Mountain Research Station, Forest 

Service, U.S. Department of Agriculture, 1221 S. Main, Moscow, ID, 83843. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 1 
Ponderosa pine ecosystems—Graham and Jain 

New Mexico, southeast Arizona, and northern Mexico. Within this wide range, 

ponderosa pine grows across highly variable biophysical settings (e.g., soils, slopes, 

aspects, associated vegetation, and fauna). Our objective in this paper is to describe

ponderosa pine ecosystems by drawing heavily from our familiarity with ponderosa 

pine forests within the Rocky Mountains. In addition, we describe briefly the changes 

that have occurred in ponderosa pine forests over the last 100 years as the result of 

disturbances or lack-there-of, vegetative succession, fire exclusion, and wildfires

(Graham and others 2004). We also provide some insight into how treatments might 

be used to restore these forests. We suggest even though our paper may be Rocky 

Mountain centric, the concepts presented most likely have application to any location 

where ponderosa pine occurs within western North America. 

Ponderosa pine is the principle species on over 11 million ha (27 million ac.) 

and for every 2.8 ha (7 ac.) it dominates, it is present on an additional 1.4 ha (3.5 ac.). 

Within the western United States, California alone contains the greatest

concentrations of ponderosa pine (2.07 million ha (5 million ac.) closely followed by 

Oregon with 1.9 million ha (4.7 million ac.) and, when combined, Arizona and New 

Mexico contain an additional 2.5 million ha (6 million ac.) of ponderosa pine (Van

Hooser and Keegan 1988). Ponderosa pine fueled the economies of the West 

beginning in the 1860s when pines were harvested to supply building material to 

farms, mines, and towns as they developed. With the coming of the railroads in the 

early 1900s, harvesting increased mostly by clearcutting. However, with the advent 

of improved roads allowing access by tractors and trucks, partial cutting became the 

dominant harvesting method. Ponderosa pine’s high value, especially the value of 

mature and old trees, led to efforts in classifying tree vigor and the risk of mortality 

which was used in selection silvicultural systems (e.g., vigor selection) (Dunning 

1928, Keen 1943, Meyer 1934). High risk trees were removed to decrease the 

incidence of bark beetles and capture the value of imminent mortality (Keen 1936, 

Barrett 1979). Ponderosa pine forests presented an opportunity for intensive 

management across large expanses of the West and considerable research and 

managerial effort was directed towards this end (Pearson 1950). 

Ponderosa Pine Characteristics 

Ponderosa pine is three-needled, however, fascicles with both two and three 

needles can be found on the same tree (Harlow and Harrar 1968). Ponderosa pine

trees can exceed 120 cm (48 in.) in diameter on good sites in northern Idaho and 

western Montana and exceed 183 cm (6 ft.) in diameter on sites in California (Van

Hooser and Keegan 1988). The ability of the species to survive low severity wildfires 

is one of its most unique characteristics. At small diameters (e.g., 5 cm, 2 in.), 

ponderosa trees can withstand heat from most surface fires because of the insulating

bark that protects the underlying cambial layers. Large ponderosa pines with yellow 

bark invoke a sense of a majestic forest and spiritual feeling in people who frequent 

these forests. These traits are exemplified by the many historical photos depicting 

people enjoying the presence of large yellow ponderosa pine trees (Grafe and 

Horsted 2002, Gruell and others 1982, Smith and Arno 1999). Moreover, these 

2 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

Figure 1—The range of ponderosa pine (Little 1971).

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 3 
Ponderosa pine ecosystems—Graham and Jain 

conditions provide valuable wildlife habitat (Long and Smith 2000, Reynolds and 

others 1992, Thomas 1979) and protect watersheds for the production of domestic 

water such as those occurring on the Front Range of the Rocky Mountains in 

Colorado (Robichaud and others 2003).

For trees to survive and develop they must be genetically adapted to the site. For 

example, the environmental interval in elevation in which ponderosa pine populations 

show habitat specificity is approximately 453 m (1380 ft.) or 38 frost-free days. In 

contrast, no habitat specificity in elevation has been found for western white pine 

(Pinus monticola Dougl. ex D. Don), and the habitat specificity interval in frost-free 

days is 90. The narrowest habitat specificity for any of the associates of ponderosa 

pine occurs with Douglas-fir which has an environmental interval of 113 m (650 ft.)

in elevation or 18 frost-free days (Rehfeldt 1994). Genetically, ponderosa pine has 

intermediate adaptation to sites compared to Douglas-fir, considered a specialist, and 

western white pine, considered a generalist. The size of ponderosa pine seed crops in

general is smaller than most of its associates and, if it wasn’t for western larch (Larix 

occidentalis Nutt.) flowers being frequently damaged by frost, it would also have the 

most infrequent cone crop of any associated conifer (Minore 1979, Graham and 

others 1995). Ponderosa pine regenerates readily on both mineral and burned over 

seed beds, however, it does not establish well on unburned organic surfaces (Haig 

and others 1941). 

Ponderosa Pine Forests 

In western North America, ponderosa pine grows within both moist and dry 

forests but seldom occurs in the cold forests (i.e. subalpine forests). Climate, as well

as the associated tree species, distinguishes the two general forest classifications

where ponderosa pine can grow (Hann and others 1997). In dry forests, associated 

species, beginning with the most intolerant to shade and competition, include quaking

aspen (Populus tremuloides Michx.), western larch, lodgepole pine (Pinus contorta

Dougl. ex Loud), Douglas-fir, and grand fir (Abies grandis (Dougl. ex D. Don) 

Lindl.) or white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.). In moist 

forests, the species most often grows on south facing aspects, but can occur in small

amounts throughout the entire forest type. Early-seral associates include western 

larch and lodgepole pine while Douglas-fir, western white pine, and grand fir/white 

fir are more tolerant than ponderosa pine (Minore 1979). The most tolerant tree 

species associated with ponderosa pine in the moist forests is western redcedar 

(Thuja plicata Donn ex D. Don) (Cooper and others 1991, Daubenmire and 

Daubenmire 1968). The combination of species and their variable tolerances to

competition and shade gives rise to a variety of forest compositions and structures in

both forests types. 

Succession In Ponderosa Pine Forests 

Succession is a term applied to the gradual supplanting of one community of 

plants by another on a given site through time (Smith and Arno 1999). Vegetative 

complexes evolve after a disturbance such as a lethal fire (i.e. fires that kill the 

majority of the dominant and codominant canopy layers) (Hann and others 1997).

Early-seral stages often begin with a grass/forb/shrub stage, succeeded by tree

seedlings and saplings which grow to young trees, and subsequently develop into the

late-seral mature and old vegetative complexes. In some systems, such as those

4 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

dominated by ponderosa pine, these or similar stages may develop in less than 250 

years but in other systems, such as Pacific coastal Douglas-fir (Psuedotsuga 

menziesii (Mirbel) Franco var. menziesii), it may take in excess of 1,000 years for the

full compliment of structural stages inherent to the system to develop (Franklin and 

others 2002, Reynolds and others 1992).

A very useful characteristic of vegetative succession is that for a given 

biophysical environment and species mix, the vegetative development over time from 

early-seral (pioneer) through late-seral (climax) is predictable. Because of this 

predictability it can be used to classify sites by the potential vegetation that will

occur. These classifications are usually identified by indicator species occurring at 

the late-seral stage (Daubenmire and Daubenmire 1968, Hann and others 1997, Smith

and Arno 1999). 

Besides the conceptual endpoint vegetation, and depending on the intensity and

severity of disturbances that may occur on a site, there can be many successional and

developmental pathways along with many vegetative and structural mixes possible 

for a given site and species mix (Smith and Fisher 1997). For example, figure 2 

shows the successional pathways for a Douglas-fir potential vegetation type (PVT)

based on a fire’s severity. Sites exhibiting this succession would be classified as a 

Douglas-fir potential vegetation type; however, it could be perpetually dominated by

ponderosa pine (e.g., D2 – fig. 2). Of the PVTs on which ponderosa pine occurs this 

is one of the simpler in terms of potential species and disturbance interactions, yet a

large number of vegetative compositions and structures are possible. This

heterogeneity in composition and structure can be arranged in a variety of

interspersed mosaics ranging in size from less than 0.1 ha (0.25 ac.) to 100s of

hectares (Long and Smith 2000).

Albeit potential vegetation can be a superb classification with excellent 

interpretative relations, care must be exercised when using such systems. Two sites

may have the same potential vegetation classification but their physical locations

often reflect a different environment. Ponderosa pine growing on a Douglas-fir/nine 

bark (Physocarpus malvaceus (Greene) Kuntze) PVT in Montana, for example, 

usually occur on northerly aspects while sites similarly classified in Idaho regularly

occur on south facing slopes (Cooper and others 1991, Pfister and others 1977).

These differences are reflected in the classification systems used and the different 

environments expressed by similar species. Nevertheless, even with these 

differences, potential vegetation is very useful for classifying sites which provide

interpretative value for ecological concepts such as successional pathways, fire 

relations, species mixes, wildlife relations, coarse woody debris relations, site 

productivity estimates, and vegetation simulations (Bradley and others 1992a, 1992b, 

Cooper and others 1991, Graham and others 1994, Graham and others 1999b, Pfister 

and others 1977, Smith and Fischer 1997, Wykoff and others 1982). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 5 
Ponderosa pine ecosystems—Graham and Jain 

Figure 2—Possible successional pathways for a Douglas-fir potential vegetation type 

in response to fire as the only disturbance (Smith and Fisher 1997). Note the many

different vegetative and structural combinations that can occur on one of the simpler 

potential vegetation types. PIPO=ponderosa pine, PSME=Douglas-fir. 

Vegetative Complexes 

In the southern and extreme eastern portion of the range, ponderosa pine grows 

primarily on ponderosa pine PVTs. On these settings, quaking aspen is the most 

frequent early-seral tree species (Hoffman and Alexander 1987, Youngblood and

Mauk 1985). Ground-level vegetation includes oaks (Quercus spp.), grasses (Festuca

and Agropyron spp.), and low shrubs (e.g., snowberry (Symphorcarpus spp.) and

spirea (Spirea spp.). Russet buffaloberry (Shepherdia canadensis (L.) Nutt.), a 

frequent shrub in these forests, stands out for its nitrogen fixing properties which is

the process of making elemental nitrogen in the atmosphere available to plants

(Jurgensen and others 1991). 

With increasing moisture, ponderosa pine occurs as a mid-seral species and 

Douglas-fir becomes the late-seral species (fig. 2). Quaking aspen and lodgepole pine

are early-seral associates of ponderosa pine on these Douglas-fir PVTs (Mauk and 

Henderson 1984). These ponderosa pine forests occur in the Rocky Mountains along 

the Front Range of Colorado, in Utah, and in southern Idaho. They also occur along

the western slopes of the Sierra Nevadas in California and the eastern slopes of the 

Cascades in Oregon (Franklin and Fites-Kaufman 1996, Hann and others 1997, 

Steele and others 1983). Ground-level vegetation includes ninebark, elk sedge (Carex 

geyeri Boott), and pine grass (Calamagrostis rubescens Buckl.). These species, in 

particular, exemplify aggressive survivors after disturbance (e.g., fire, mechanical

6 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

site preparation) and are strong competitors for light and nutrients which compete 

with ponderosa pine seedlings (Baumgartner and others 1986). 

In several locales, dry grand fir and white fir PVTs represent the dry forests

(Hann and others 1997). On such settings, ponderosa pine and Douglas-fir occur but

are succeeded by late-seral grand fir and/or white fir in the absence of disturbance

(Bradley and others 1992b). Additional trees that can occur in such forests include 

juniper (Juniperus spp.), pinyon pine (Pinus edulis Engelm.), sugar pine (Pinus 

lambertiana Dougl.), incense-cedar (Calocedrus decurrens (Torr.) Florin), western

larch, Jeffrey pine (Pinus jeffreyi Grev. & Balf.), and lodgepole pine. Pine grass and 

ninebark are frequent associates but tall shrubs such as Rocky Mountain maple (Acer

glabrum Torr.) often occur.

The wettest forests where ponderosa pine occurs are the wet grand fir and/or 

white fir PVTs and the driest western redcedar PVTs. Such forests occur in the 

interior northwestern United States and in southern British Columbia (Cooper and 

others 1991, Daubenmire and Daubenmire 1968, Hann and others 1997). The western

redcedar PVT is by far the most productive type on which ponderosa pine occurs, and

lush and complex vegetation mixes may develop. Western white pine is a frequent 

associate of ponderosa pine with an occasional paper birch (Betula papyrifera

Marsh.). A rich understory of shrubs, grasses, and forbs occur in these forests. Early 

seral-species such as redstem ceanothus (Ceanothus sanguineus Pursh), snowbrush 

ceanothus (Ceanothus velutinus Dougl. ex Hook.) and Sitka alder (Alnus viridis

(Vill.) Lam. & DC. ssp. sinuata (Regel A. & D. Löve) rapidly colonize sites after

disturbance and are also active nitrogen fixers (Jurgensen and others 1991, Smith and

Fischer 1997). Mid-seral shrubs include Rocky Mountain maple which readily

survives disturbances and is joined by late-seral species such as huckleberry

(Vaccinium spp.) and false huckleberry (Menziesia ferruginea Smith). The latter 

readily survives disturbances but is an aggressive colonizer. Probably one of the 

greatest competitors and survivors after disturbance of any ground-level species 

occurring with ponderosa pine is pine grass. This ground-level vegetation can play

critical roles in forests such as providing wildlife habitat, stabilizing soil, and 

capturing nutrients after disturbance. Fireweed, (Chamerion angustifolium (L.) 

Holub), for example, rapidly regenerates after fire and captures and recycles nitrogen 

(Baumgartner and others 1986, Cooper and others 1991, Daubenmire and 

Daubenmire 1968, Reynolds and others 1992, Smith and Fischer 1997). Because of

the range of species that can occur with ponderosa pine and their wide range of 

tolerance (e.g., shade, competition, fire) along with how they interact with 

disturbances a plethora of vegetative compositions and structures can occur within 

ponderosa pine forests arranged and interspersed in a variety of mosaics. 

Wildfire and Ponderosa Pine Forests 

Before successful fire exclusion, temperature and precipitation patterns

combined with natural and human ignitions allowed fires to burn the dry forests at

relatively frequent (e.g., < 40 years) intervals (Agee 1993, Hann and others 1997). 

Cultural burning by Native Americans augmented and even dominated burning in

several locations (Barrett and Arno 1982, Stewart 1951). In the northern Rocky 

Mountains of Idaho and western Montana, dry settings (ponderosa pine and/or 

Douglas fir PVTs) historically burned by non-lethal (low severity surface fires that 

did not kill or kill few overstory trees) wildfires at 15 to 23 year mean return intervals 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 7 
Ponderosa pine ecosystems—Graham and Jain 

(Smith and Fischer 1997). Mesic forests containing ponderosa pine (grand fir and/or 

Douglas-fir PVTs) were burned frequently by lethal fires (i.e. fires that kill the 

majority of the dominant and codominant canopy layers) or mixed fires (a

combination of lethal and non-lethal fires), at mean return intervals extending to over 

60 years (Smith and Fischer 1997). In the central and southern Rockies (ponderosa 

pine and/or Douglas-fir PVT’s), although non-lethal fires dominated, mixed fires also 

occurred, especially along the Front Range of the Rocky Mountains in Colorado

(Bradley and others 1992a, 1992b, Fulè and others 1997, Kaufmann and others 

2001). On the driest settings, (ponderosa pine and/or woodlands), because of

discontinuous surface fuels, fires tended to be few (Bradley and others 1992b). In 

contrast to other locales dominated by late-seral ponderosa pine, the forests of the 

Black Hills possibly experienced greater extents of lethal fires (Shepperd and 

Battaglia 2002, Shinnen and Baker 1997). Nevertheless, historical wildfires most 

likely burned through most ponderosa pine forests leaving in their wake a wide

variety of species compositions and vegetative structures. 

Other Disturbances 

In the western United States domestic livestock grazing and harvesting of

ponderosa pine forests was occurring by the mid 1800s (Cooper 1960, Rasmussen

1941). Ponderosa pine was extensively harvested, altering both forest composition 

and structure (Barrett 1979, Pearson 1950,Van Hooser and Keegan 1988). In mesic 

forests, grand fir and/or white fir and Douglas-fir rapidly colonized these sites when

ponderosa pine was harvested. Especially on the ponderosa pine PVT, grass cover

tended to decrease ponderosa pine seedling establishment and survival (Brawn and 

Balda 1988). However, when heavy livestock grazing ceased in the early 1900s in the 

southwestern United States, dense stands of ponderosa pine seedlings became 

established. Because of fire exclusion, climate changes, and other factors these trees

readily developed into dense stands (Covington and Moore 1994, Pearson 1950, Stein 

1988). 

The dense stands that developed increased the abundance of insect and disease 

epidemics, and when combined with fire exclusion, significantly altered the 

composition and structure of these forests (Harvey and others 2000). Historically 

western pine beetle (Dendroctonus brevicomis LeConte), pine engraver (Ips spp.), fir

engraver (Scolytus ventralis LeConte), Douglas-fir tussock moth (Orgyia 

psudotsugata McDunnough) were insects associated with regularly burned areas 

(Hessburg and others 1994). In most years bark beetles occurred at endemic levels in

ponderosa pine, Douglas-fir, and grand fir killing large and weakened trees that were 

struck by lightning, infected by root disease (Armellaria spp.), or too old to resist 

attack (Williams and others 1986, Wu and others 1996). Pine engraver and fir

engraver beetles attacked young, densely stocked ponderosa pine or removed trees 

scorched by low-intensity surface fires and/or trees severely infected with disease.

Sometimes disease and insect infestations increased during droughts when trees were

stressed. 

Since fire exclusion in some settings, these same insects have occurred at

epidemic levels (Hedden and others 1981, Gardner and others 1997, Schmid and 

Mata 1992). Today (2005) ponderosa pine continues to be susceptible to the western 

pine beetle and mountain pine beetle often kills ponderosa pine on Douglas-fir and 

grand fir/white fir PVTs. The pine engraver beetle is more abundant and destructive 

today with some of the severest outbreaks occurring on low-elevation ponderosa pine 

8 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

PVTs (Hessburg and others 1994). Pandora moth (Coloradia pondora Blake)

defoliates ponderosa pine and scattered outbreaks have occurred in Arizona, 

California, Colorado, and Oregon during the 20th century. The larvae prefer loose 

soils created by weathered granites or pumice where they burrow and pupate (Speer 

and others 2001). In addition to ponderosa pine being damaged by insects, dense 

stands of Douglas-fir and grand fir or white fir that developed on many settings are 

very susceptible to both defoliators and root diseases.

Weather, another formidable disturbance, in the form of snow, ice, or wind often

creates variable sized canopy openings ranging to 16 ha (40 ac.) (Boldt and Van

Deusen 1974, Shepperd and Battaglia 2002). The crowns of seral species (ponderosa 

pine, western larch, and western white pine) tend to shed snow thereby minimizing 

crown breakage. However, as the snow sloughed from tree crowns it could damage

trees occurring in the lower layers. Often these mid- and late-seral species (e.g., 

grand fir, Douglas-fir) would break, creating canopy gaps, decreasing stand densities, 

and altering species composition (Jain and Graham 2005). In addition to being 

susceptible to weather damage when occurring in the lower canopy layers these same

species when in the overstory are susceptible to the accumulation of snow and ice,

which in turn often results in limb and bole damage, which in turn can increase the 

risk of bark beetle infestations (Jain and Graham 2005). 

When combining forest succession, potential vegetation, disturbance, weather,

and physical setting, it becomes obvious that ponderosa pine forests can be very

complex. Depending on the combination of these components, multiple tree species 

can occur within stands and across landscapes, as can multiple shrub and forb species 

(fig. 2). This vegetation varies in arrangement, amounts, and juxtapositions that are 

continually changing, in response to the occurrence, extent, and severity of both 

natural and human caused disturbances. 

Ponderosa Pine Stand Structure 

Historically, the development and maintenance of ponderosa pine forests was

favored by non-lethal fires ignited by both humans and lightning. The continued fire 

presence in the drier potential vegetation types (PVTs), limited the regeneration and

existence of fire intolerant species. These fires burned heterogeneously and isolated 

areas existed where ponderosa pine regenerated (i.e., old rotten logs) (Covington and 

Moore 1994, Everett and others 2000). As a result ponderosa pine (more than any 

other) trees were often clumped into small groups (fig. 3). For example, on the Boise

Basin Experimental Forest located in southern Idaho, five to 15 tree clumps per 

hectare (2 to 6 per ac.) of mature ponderosa pine trees were observed with clumps

ranging in size from 0.0004 to 0.02 ha (0.001 to 0.05 ac.) (fig. 4) (Graham and Jain 

2005). The density of trees within these clumps ranged from 21.6 m2

 ha-1 to 430 m2

ha-1 (94 to 1871 ft2 per ac.) of basal area (fig. 5). However, on a stand basis, the basal

area averaged 16 m2

 ha-1 (70 ft2 per acre) of basal area with 5.7 m2 ha-1 (25 ft2 per ac.)

occurring within clumps of trees and 10.3 m2

 ha-1 (45 ft2 per ac.) attributed to trees 

outside of the clumps (fig. 6). Pearson (1950) observed a similar clumpy nature on 

the Fort Valley Experimental Forest in Arizona and Youngblood and others (2004) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 9 
Ponderosa pine ecosystems—Graham and Jain 

Figure 3—Mature ponderosa pine growing in clumps on the Pringle Falls 

Experimental Forest in central Oregon.

10 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

0.000

0.010

0.020

0.030

0.040

0.050

0.060

1 2 3 4 5 6 7 8 9 X

Randomly located one-acre plots

Tr

e

e cl

u

mp size (

Ac)

F

and their respective means occurring in a mature stand of ponderosa pine growing 

on the Boise Basin Experimental Forest in southern Idaho and the number of clump

occurring per acre. These values are displayed for nine randomly located plots as are

the means ( X ̄ ) of the nine plots (Graham and Jain 2005). 

within clumps tend to have fewer limbs and be smaller in diameter while trees on the 

clump perimeters tend to be larger and lean away from the clump center (fig. 3). Even 

though it appears that space between clumps is not occupied, the root systems of trees 

within the clump most often occupy this space (Pearson 1950) (fig. 7). 

Not only do ponderosa pine forests exhibit variation in the

ture, but they also exhibit considerable variation in the amount of coarse woody 

debris (CWD) that is associated with soil productivity. For example, on ponderosa 

pine PVTs of Arizona, CWD associated with soil productivity range from 11 to 29 

Mg ha-1 (5 to 13 tons ac-1). In contrast on Douglas-fir PVTs in Montana, CWD 

associated with soil productivity ranged from 10 to 55 Mg ha-1 (5 to 25 tons ac-1) 

(Graham and others 1994) (fig. 8). In general, ponderosa pine forests in which fires 

were frequent tended to maintain and use less CWD than those with less frequent 

fires. This open, clumpy forest structure along with the presence of some CWD 

benefits many wildlife species and are relatively resistant to stand replacing fire 

events (Graham and others 2004, Long and Smith 2000, Reynolds and others 1992)

(figs. 4, 5, 6, 7, 8). 

Number of tree clumps/Ac

5 

6

6

5

3

7

3 2 5

5 

igure 4—The maximum, mean, and minimum size of ponderosa pine tree clumps 

s

observed similar distributions in California and Oregon (also see White 1985). Trees 

standing tree 

struc

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 11 
Ponderosa pine ecosystems—Graham and Jain 

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4 5 6 7 8 9 X

 Randomly located one-acre plots

B

asal area (ft

2 ac-1)

F

trees occurring in clumps defined by trees with overlapping crowns growing on the 

Boise Basin Experimental Forest in Southern Idaho. These values are displayed for

nine randomly located plots as are the means ( X ̄ ) of the nine plots (Graham and

Jain 2005).

igure 5—The maximum, mean, and minimum basal area of mature ponderosa pine 

12 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 X

Randomly located one acre plots

B

a

s

al area (ft

2 ac-1)

Clump Isolated

F

defined by trees with overlapping crowns and among trees not associated with 

clumps (Isolated) growing on the Boise Basin Experimental Forest in southern Idaho.

These values are displayed for nine randomly located plots as are the means ( X ̄ ) of

the nine plots. The bar represents the standard error of the mean for the total mean 

basal area (Graham and Jain 2005). 

P

Another way to characterize forest structure and composition is

rent forest components interact and influence fire intensity and severity. For

example, forest structure can be divided into fuel bed strata where each level 

differentially influences combustion, fire propagation and spread, and fire effects (fig. 

9). Canopy fuels (tree crowns), ladder fuels (midstory trees) and shrub layers

contribute to crown fires. Low vegetation (low shrubs and grasses), down woody 

material (tree branches, boles), and ground fuel (needles, leaves, rotten wood, and 

litter on the forest floor) contribute to surface fires. Forests composed of mature 

ponderosa trees are susceptible to the accumulation of large amounts of organic 

material at the base of trees from both needle fall and bark slough (fig. 3). Also,

woody material covering the forest floor, which is less than 7.6 cm (3.0 in.) in 

diameter, is the greatest contributor to the spread of surface fires while large wood (>

7.6 cm, 3.0 in.) and ground fuels tend to favor smoldering fires (Graham and others 

2004, Peterson and others 2005). When burning, the intensity (flame length) of these

fires determines the potential for the tree canopy to be ignited and most often 

determines if crown fires would likely be sustained (Graham and others 2004,

Peterson and others 2005).

igure 6—The basal area of mature ponderosa pine occurring within clumps (Clump) 

onderosa Pine Forests as Fuel For Wildfires

to describe how

diffe

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 13 
Ponderosa pine ecosystems—Graham and Jain 

1

The size of the tree clumps and the

basal area within the clumps

6 0.054 152

5 0.034 116

4 0.004 366

3 0.010 261

2 0.032 315

1 0.030 406

Basal Area

(Ft

2 Ac-1)

Size

(Ac)

Clump

2

3

4

5

6

Figure 7—A map showing an example of the spatial distribution of mature ponderosa 

pine growing on the Boise Basin Experimental Forest in southern Idaho (■ = trees in 

clumps defined by trees with overlapping crowns, ♦ = isolated trees). The circle 

represents a randomly located one-acre plot (Graham and Jain 2005).

14 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

0 5 10 15 20 25 30 35

Grand fir/Spirea -ID

Grand fir/Mt. Maple-ID

S. Alpine fir/Huckleberry-ID

D.fir/Ninebark-ID

Grand fir/Beargrass-MT

S.alpine fir/Beargrass-MT

D.fir/Pine grass-MT

S.alpine fire/Twin flower

S.alpine fir/Dwarf huckleberry-MT

Hemlock/Beadlilly-ID

D.fir/Ninebark-ID

D.fir/Inegrass-ID

P.pine/Fescue-AZ

P.pine/Oak-AZ

W.fir-AZ-NM

Tons/Acre

Figure 8—The amount of coarse woody debris recommended by Graham and others 

(1994) for maintaining soil productivity after disturbance for selected potential

vegetation types of the Rocky Mountains. The solid bars represent types in which

ponderosa pine is well represented. NM=New Mexico, AZ=Arizona, ID=Idaho, and

MT=Montana). 

Changes in Ponderosa Pine Forests 

With the advent of fire exclusion, animal grazing, timber harvest, and climate

cycles on the moist potential vegetation types (e.g. grand/white fir), ponderosa pine is 

being succeeded by Douglas-fir, grand fir and/or white fir (figs. 10, 11) (Graham and 

others 2004, Gruell and others 1982, Smith and Arno 1999). The accumulation of fire 

intolerant vegetation, dense forest canopies, with homogenous and continuous 

horizontal and vertical structures are developing thus creating forests favoring crown 

fires rather than low intensity surface fires that historically occurred (fig. 9) (Arno 

and Brown 1991, Dodge 1972, Peterson and others 2005, Van Wagner 1977). Within

the Inland Northwest, the extent of mid-seral (e.g., Douglas-fir) vegetation has 

increased by nearly 3.2 million ha (8 million acre) and the extent of single storied 

mature vegetation (e.g., ponderosa pine) has decreased by over 1.6 million ha (4

million ac.) (Hann and others 1997). Another way to view these changes is that the

successional processes in some locations have been compressed by a factor of at least 

10. For example, ponderosa pine may or may not be succeeded by Douglas-fir in 300 

to 400 years within forests historically burned by frequent fires but in many locations 

Douglas-fir has succeeded ponderosa pine in less than 50 years (fig. 2) (Hann and 

others 1997, Harvey and others 1999, Smith and Arno 1999). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 15 
Ponderosa pine ecosystems—Graham and Jain 

The structural and compositional changes occurring over the last 100 years in

the dry forests are most noticeable within the tree and shrub component or the 

increase of canopy and ladder fuels (figs. 9, 10, 11). In addition; to noticeable 

changes in plant composition and structure, the soils (surface and mineral) in many 

settings have also changed considerably during the last century (fig. 12). The

accumulation of organic materials on the soil surface and the frequent changes in 

their composition (e.g., ponderosa pine litter to true fir litter) can alter 

ectomycorrhizae habitat and water holding properties (Harvey and others 1999, 

Harvey and others 2000). For example, when the species within a forest shifts from 

being dominated by ponderosa pine to being dominated by Douglas-fir and/or true 

firs, the vertical distribution of ectomycorrhizal short roots is compressed

dramatically (figs. 10, 11) (Harvey and others 1986). Ectomycorrhizal activities occur 

deeper in mineral soil of forests dominated by ponderosa pine compared to sites 

dominated by true firs; on these sites ectomycorrhizal activities occur in shallow

organic horizons. In ponderosa pine dominated forests, ectomycorrhizal-mediated 

nutrient acquisition and turnover are relatively well protected from wildfire damage. 

However, when fires burn in forests with uncharacteristically deep organic layers on 

the surface they can have a detrimental impact on ectomycorrhizal activities and the

post-fire acquisition and cycling of nutrients (Harvey and others 1999, Harvey and 

others 2000, Neary and others 1999) (figs. 9, 10, 11, 12). These changes in soil 

microbial activities may increase the likelihood of uncoupling any continuity

between current and preceding vegetative communities (Amaranthus and Perry 

1994). 

Another soil-based change in pine compared to the fir forests is the type and 

distribution of substrates important for nutrient storage and cycling. There is a 

gradual shift in the proportion of soil nitrogen reserves and organic matter from 

mineral layers in pine forests to surface organic layers in fir forests (figs. 10, 11).

Accumulation of both above-and below-ground biomass from roots, needles, and 

boles in fir forests accelerates activities of decomposers by increasing and changing

the basic substrate they utilize. Because biological decomposition in ponderosa pine 

forests is more limited than biological production, accumulation of organic material

is inevitable, especially in the absence of fire (figs. 11B, 12) (Harvey 1994). The 

result can be accumulations of materials that differ substantially from those occurring 

in historical pine forests (fig. 11). Associated with these changes in litter type and

quantity is a likely change in soil surface chemistry, including the presence of 

allopathic substances with the potential to alter a variety of microbial activities (Rose 

and others 1983). Forests dominated by ponderosa pine develop brown cubical rotten

wood products that are deposited on the forest floor and subsequently are 

incorporated into the mineral soil. These products can persist in soils for hundreds of

years and during that time provide soil structural and nutritional benefits. In contrast, 

grand fir/white fir develop white rotten wood products that are dispersed in soil 

relatively rapidly (decades) shortening their contribution to soil productivity (Harvey 

and others 1987, Larsen and others 1979). 

16 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

Figure 9—Fuelbed strata have different implications for combustion environment, fire 

propagation and spread, and fire effects. The canopy (A), ladder fuels (B) and shrub 

layers (C) contribute to crown fires. Low vegetation (D), woody fuel (E), and ground 

fuel (F) contribute to surface fires. Woody fuel (E) and ground fuels (F) are most often 

associated with smoldering fires and residual combustion that can transfer large 

amounts of heat deep into the soil (Sandburg and others 2001, Graham and others 

2004).

F 

C E D

D 

E 

B 

A

A 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 17 
Ponderosa pine ecosystems—Graham and Jain 

Figure 10—Forest development on the Bitterroot National Forest in Montana in a

ponderosa pine stand after harvest (1909) in which fire was excluded since 1895. 

Note the changes in vertical arrangement and horizontal continuity in forest stand

structure. In general many of today’s ponderosa pine forests contain higher densities 

of fire-intolerant species and suppressed trees than historical forests (Gruell and 

others 1982, Smith and Arno 1999, Graham and others 2004).

1989 

1948

1909

18 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

Fi

Utah in which harvesting removed much of the ponderosa pine and fire has been 

excluded allowing abundant white fir trees to develop. Photograph B shows a 

ponderosa pine stand in which fire has been excluded, the development of multipl

canopy layers, and a deep layer of needles and other organic material covering the 

forest floor (Graham 2003).

to

Figure 12—When fires are excluded from ponderosa pine forests organic layers tend 

concentrate in these layers. Note the contrast between the amount of organic 

material on the forest floor when General Custer came through the Back Hills in 1874 

and the amount that has accumulated around the rocks in the photo in 2000. P

courtesy of Paul Horsted/custertrail.com (Grafe and Horsted 2002).

A B

gure 11—Photograph A shows the multiple canopy layers developed in a stand in 

e

accumulate and tree roots, ectomycorrhizae, and nutrients also tend to 

hotos 

Tree crowns

Roots, ectomycorrhizae, nutrients 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 19 
Ponderosa pine ecosystems—Graham and Jain 

Forests dominated by grand fir or white fir tend to concentrate both nitrogen and

potassium in their foliage which often extends to the soil surface (fi

re 1990, Moore and others 1991). In general, the combination of a low canopy 

structure with nutrients and microbial activities concentrated in or near the soil

surface make both of these critical ecological resources susceptible to both

mechanical and fire destruction (fig. 11). Shifting from a few large stems of

ponderosa pine to many Douglas-fir stems will maintain brown rotten wood in the 

system, but these conditions tend to sequester substantial nutrient resources in

recalcitrant organic material which is slow to release, thus making these resources

susceptible to loss from wildfire or timber harvest activities (Jurgensen and others 

1997) (fig. 10). 

In general, historical ponderosa pine forests were likely well matched to soil

resources, relativ

te and short-term climate variation, subject to modest (largely beneficial) insect

and pathogen mortality, and could be considered long-lived and relatively stable (fig. 

10). In contrast, forests that were dominated by ponderosa pine and are now

dominated by Douglas-fir, grand fir or white fir are probably not well matched to soil 

resources and are also not likely resistant to the wide range of site and climate

variation found within the dry forests (figs. 10, 11). In turn, they are often subject to

high insect and pathogen mortality and can not be considered either long-lived or 

stable (Harvey and others 1999). 

E

The introduction of

species and pollinators

ologic processes (Chong and others 2003, Galley and Wilson 2001). Within the 

dry forests, some of the more notable invasive species include cheatgrass (Bromus 

tectorum L.), leafy spurge (Euphorbia esula L.), Canada thistle (Cirsium arvense (L.)

Scop.), and spotted knapweed (Centaurea biebersteinii DC.) (Hann and others 1997).

Cheatgrass aggressively colonizes and invades exposed soil in the dry forests and

tends to rapidly develop in the spring and then quickly dry. Annually, the continuous 

and dense covers of dead grass provide extremely flammable fuels that facilitate 

more frequent and severe wildfires than those that occurred historically. Because of

its interaction with fire, cheatgrass has made some of the successional pathways in

the dry forests of the western United States indeterminate (Bradley and others 1992b,

Everett 1987, Graham and others 1999b). Cheatgrass is palatable during a portion of 

its annual development; subsequently it is not always considered a noxious weed. 

Therefore, even though mulch used in vegetation seeding programs (such as after

wildfires) may be weed free, it may contain cheatgrass seed, thereby inadvertently 

spreading this exotic (Chong and others 2003, Robichaud and others 2003). Exotic 

plant species have readily spread throughout the Inland West. All 97 counties in the 

interior Columbia Basin contain cheatgrass and Canada thistle (even some of the 

most remote locations in central Idaho), 92 counties contain spotted knapweed, and 

72 counties contain leafy spurge (Hann and others 1997). 

g. 11) (Mika and

Moo

ely resistant to detrimental fire effects, well adapted to wide ranges 

of si

xotic Species

 non-native plant species can cause the decline of native 

, alter fire regimes, disturb nutrient cycling, and disrupt

hydr

20 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

W

Ponderosa pine forests appear to have evolved with fire and m

suggested that their composition and structure are dependent on the vegetation’s 

relations with fire (Covington and Moore 1994, Everett and others 2000, Hann and

others 1997, Harvey et al 1999). However, when wildfires burn altered ponderosa 

pine forests, the extent or area burned is similar to historical times but they tend to 

burn more severe (Graham 2003, Graham and others 2004, Hann and others 1997,

Kaufmann and others 2001). They often kill large continuous expanses of vegetation, 

consume the forest floor, volatilize nutrients, provide for exotic species introductions, 

increase soil erosion, and, in general, create forest conditions that may not be

favorable to society (fig. 13). The long-term consequences are not well understood

for issues such as water quality and wildlife habitat. Nor will the sense of place that

forests often provide which, in some cases, will not be replaced for many generations 

(Galliano and Loeffler 1999, Kent and others 2003, Schroeder 2002). 

Some of the notable recent wildfires that burned the dry forests

res that burned in the Bitterroot Valley of western Montana in 2000, the Hayman 

Fire along the Front Range of the Rocky Mountains in Colorado in 2002, the RodeoChediski Fire in Arizona in 2002, and the Biscuit Fire in Oregon in 2002 (USDA 

2000, Graham 2003, Graham and others 2004). All of these wildfires exemplified 

large (≈40,000 to 200,000 ha) and severe events. The Rodeo-Chediski fire in Arizona 

severely burned over 6,000 ha (15,000 acre) in 15 minutes and moved on a broad

front at over 6.4 kph (4 mph). The Hayman Fire severely burned over 19,000 ha 

(47,000 acre), much of it in one day (fig. 14) (Finney and others 2003, Robichaud 

2003). Both of these fires burned in ponderosa pine forests that were accustomed to 

non-lethal or mixed fires. Also, what is striking about all of the fires occurring in the 

dry forests in recent years (2000-2004), is the large impact they had on real property 

by burning homes and businesses along with impacting municipal watersheds and the 

tourism industry (Graham and others 2004, Kent and others 2003, Robichaud and

others 2003). The fires occurring in the dry forests and the hazard they pose to human 

values influenced the development of the Healthy Forests Initiative and the passing 

of the Healthy Forests Restoration Act (USDA 2004).

 Forest Treatments 

Dry forests, particularly those

elevations and along rivers and travel ways, resulting in some of the earliest 

silvicultural practices being developed and used in these forests (Meyer 1934, 

Pearson 1950). This long history of treatment application and the knowledge gained

through these practices can be applied and adapted to meet present and evolving

management objectives. Severe crown fires are often considered the primary threat to

these forests (Graham and others 2004). Because of the many changes that have 

occurred in the dry forests, even low intensity surface fires can now damage soils, 

weaken or kill overstory trees, and provide an ignition source for homes and other 

property (Cohen and Stratton 2003, Hungerford and others 1991). 

ildfires in Current Ponderosa Pine Forests

any authors have 

include at least 

16 fi

Dry

containing ponderosa pine, tend to occur at low 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 21 
Ponderosa pine ecosystems—Graham and Jain 

Figure 13—A photograph of the intense and severe Rodeo-Chediski Fire that burned

in Arizona in 2002. This ponderosa pine forest was historically burned by low 

intensity surface fires but singly and in combination fire exclusion, timber harvest, 

climate change, and livestock stock grazing contributed to forest changes that 

facilitated this uncharacteristically severe fire. 

The current understanding of fire behavior in dry forests indicates that a crown

fire begins with a transition from a surface fire to the ignition of the canopy (figs. 9, 

13, 14) (Finney and others 2003). Therefore, management activities can target 

specific fuel strata to disrupt the continuity of fuels from the soil surface to the crown 

and also target the horizontal arrangement of trees to disrupt the progression of fires

especially from tree crown to tree crown (Graham and others 1999a, Scott and

Reinhardt 2001) (fig 9). In the dry forest it appears the most effective strategy for 

reducing crown fire intensity and severity is (1) reduce surface fuels, (2) increase

crown base heights, (3) reduce canopy bulk density, and (4) reduce continuity of the 

forest canopy (Graham and others 1999a, Cruz and others 2003, Scott and Reinhardt 

2001, Van Wagner 1977). Generally, fuel treatments are beneficial for modifying

both fire behavior and fire severity under normal weather conditions (Albini 1976).

However, under extreme weather conditions (e.g., low humidity, high winds) fires 

can overwhelm most fuel treatments resulting in intense and severe fires (Finney and 

others 2003). Also, there is no guarantee that the combination of canopy and surface

fuel treatments will reduce the risk of intense wildfires or immunize property losses 

when a fire does occur. Nevertheless there is the potential that treated areas will

experience lower burn severity than untreated areas (Finney and others 2003, Graham

and others 2004) (fig. 14). 

22 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

Figure 14—This photograph shows a ponderosa pine forest that was thinned in 2001 

reducing the continuity and bulk density of the tree canopy. The surface fuels were in 

place when the Hayman Fire burned (moving from the left to the right in the photo) 

the area in on June 9, 2002. Even though the trees were killed the brown needles will 

mulch the forest floor when they fall reducing soil erosion compared to the areas in 

which all of the needles were consumed in the fire (Finney and others 2003, Pannkuk 

and Robichaud 2003). 

Prescribed fire has long been used in the dry forests for cleaning the forest floor, 

increasing canopy base heights, and preparing seed beds for regeneration (Barrett

1979, Pearson 1950, Weaver 1943). Fire can alter multiple fuelbed characteristics by 

decreasing ground and surface fuels and decreasing ladder fuels (fig. 9) (Graham and

others 2004, Peterson and others 2005). Mechanically thinning trees can also modify

ladder fuels and decrease or alter the continuity of canopy fuels. Mechanical 

treatments offer more control in creating the desired forest structures than prescribed 

fire and they are less uncertain because of the inherent risk of prescribed fires

escaping (Graham and others 1999a, Scott and Reinhardt 2001, Peterson and others 

2005). However, if surface fuels created by mechanical treatments are not removed 

or treated they can exacerbate both the risk and hazard associated with fuel 

treatments (Brown and others 1977). This was exemplified on a portion of the 

Hayman Fire where the canopy bulk density and continuity had been greatly reduced 

within a treatment area, but because the surface fuels were not treated, the area 

burned intensely (fig. 14), yet the tree severity of the fire was less, as indicated by the 

presence of brown needles, compared to areas that were not thinned, where all 

needles were consumed leaving black branches. What is significant about this 

treatment is that when these brown ponderosa pine needles fall they will mulch the 

forest floor reducing soil erosion (interrill) by 60 percent compared to bare mineral 

soil. If they had been Douglas-fir needles, erosion would have been reduced by 80

percent (Pannkuk and Robichaud 2003).

Thinned N

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 23 
Ponderosa pine ecosystems—Graham and Jain 

Forests continue to regenerate, develop, and die, meaning that depending on

how fast these processes occur, fuel treatments aimed at remediation of wildfire fire

hazard need to be continued and/or maintained. For example, surface fuel treatments

occurring within a year prior to the Hayman Fire in Colorado had a significant impact 

on the fire’s progression. In contrast, areas with fuel treatments conducted seven

years prior were intensely and severely burned (Finney and others 2003). As shown

by the large fires that have occurred in the western United States during the last few 

years, most fuel treatments have local impacts on a fire’s intensity and severity but

for the most part made little impact on the overall outcome of the fire (Finney and 

others 2003). Strategically placed fuel treatments may have greater potential for

altering the spread of large wildfires than randomly placed fuel treatments. Fuel 

treatments are most effective if they are encountered by a wildfire early in its 

development (Finney 2001, 2003, Finney and others 2003). 

Conclusions 

Because of its wide distribution, ponderosa pine occurs in many diverse forests 

and it has been studied and managed for over a century (Barrett 1979, Meyer 1934,

Pearson 1950, Shepperd and Battaglia 2002). Even though ponderosa pine forests are 

often considered simple in terms of species and structure they can be rather complex. 

The species grows on a variety of biophysical settings ranging from those where 

ponderosa pine is the late seral species and the only conifer species possible to those 

where western redcedar is the late seral species and over seven conifer species can

occur (Cooper and others 1991). With the interaction of wind, snow, ice, diseases, 

insects, and fire, an abundance of successional pathways are possible (Bradley and 

others 1992a, Smith and Fischer 1997). The resulting species and structural mosaics 

can be rather intricate occurring within spatial scales as small as those defined by tree

groups to large ones defined by landscapes. Similarly, temporal scales associated

with the disturbance, regeneration, and development ponderosa pine forests can range 

from months to centuries (Hann and others 1997, Long and Smith 2000, Reynolds

and others 1992). 

Through the advent of fire exclusion, climate cycles, grazing, and harvesting 

ponderosa pine forests have changed (e.g., species composition, soil characteristics, 

horizontal and vertical structure) significantly during the last 100 years (Covington

and Moore 1994, Hann and others 1997). Nevertheless, even with these changes there 

are tremendous opportunities for restoring these forests to their structure and 

composition reminiscent of historical conditions (Graham and Jain 2005, Jain and 

Graham 2005, Long and Smith 2000). Some key treatments such as reducing the 

quantity and continuity of surface fuels, increasing crown base heights, and

decreasing crown continuity and density can lessen the risk of loss from extreme

wildfire events (Graham 2003, Graham and others 2004, Peterson and others 2005

Scott and Reinhardt 2001). Both prescribed fire and mechanical techniques can be 

used to change the forest structure and encourage the regeneration and development 

of ponderosa pine, especially as an early seral species, within interspersed mosaics. If 

the structure were changed, such forests may be resistant and resilient to native 

insects and diseases, uncharacteristically severe wildfires, and be beneficial to many 

wildlife species (Graham and others 1999a, Graham and others 1999b, Graham and 

others 2004, Long and Smith 2000, Reynolds and others 1992). 

24 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

Ponderosa pine forests extend throughout the western United States and Canada 

and they contain some of the most prized scenery and special paces in the West. The 

presence and existence of ponderosa pine reinforces these special qualities (Grafe and 

Horsted 2002, Gruell and others 1982, Smith and Arno 1999). Forests that contain

large trees with yellow bark and emit that unique and pleasant odor on a warm

summer day only attributable to ponderosa pine, provide the essence of being in or 

part of a forest. These attributes and the wildlife they support bring people solace and

enjoyment when visiting or living in these settings. Because of these and other values

to society, ponderosa pine forests often evoke strong feelings in people as to their

management and conservation. 

References 

Agee, James K. 1993. Fire ecology of Pacific Northwest forests. Washington, DC: Island 

Press. 493 p. 

Amaranthus, M.P. and Perry, D.A. 1994. The functioning of ectomycorrhizal fungi in the

field: linkages in space and time. Plant and Soil 159: 133-140. 

Arno, S.F.; Brown, J.K. 1991. Overcoming the paradox in managing wildland fire.

Western Wildlands 171: 40-46. 

Arno, S.F.; Sneck, K.M. 1977. A method for determining fire history in coniferous forests

of the Mountain West. Gen. Tech. Rep. INT-42. Ogden, UT: Intermountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 28 p. 

Barrett, James W. 1979. Silviculture of ponderosa pine in the Pacific Northwest: the state

of our knowledge. Gen. Tech. Rep. PNW-97. Portland, OR: Pacific Northwest Forest

and Range Experiment Station, Forest Service U.S. Department of Agriculture; 106 p. 

Barrett, S.W.; Arno, S.F. 1982. Indian fires as an ecological influence in the Northern 

Rockies. Journal of Forestry 80 (10): 647-651. 

Baumgartner, D.M.; Boyd, R.J.; Breuer, D.W.; Miller, D.L. 1986. Weed control for forest 

productivity in the Interior West. Pullman, WA: Cooperative Extension, Washington 

State University; 148 p. 

Boldt, Charles E. ;Van Deusen, James L. 1974. Silviculture of ponderosa pine in the Black

Hills: the status of our knowledge. Res. Pap. RM-124. Fort Collins, CO: Rocky

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 45 p.

Bradley, Anne F.; Fischer, William C.; Noste, Nonan V. 1992a. Fire ecology of the forest

habitat types of eastern Idaho and western Wyoming. Gen. Tech. Rep. INT-290. 

Ogden, UT: Intermountain Forest and Range Experiment Station, Forest Service, U.S.

Department of Agriculture; 92 p. 

Bradley, Anne F.; Noste, Nonan V.; Fischer, William C. 1992b. Fire ecology of forests and 

woodlands in Utah. Gen. Tech. Rep. INT-287. Ogden, UT: Intermountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 128 p. 

Brawn, J.D.; Balda, R.P. 1988. The influence of silvicultural activity on ponderosa pine

forest bird communities in the southwestern United States. In: Jackson, J. A., ed. 

Bird conservation 3. Madison, WI: The University of Wisconsin Press: The International

Council for Bird Preservation, United States Section, 3-21. 

Chong, Geneva; Stohlgren, Tom; Crosier, Catherine; Simonson, Sara; Newman, Greg;

Peterson, Eric. 2003. Key invasive nonnative plants. In: Graham, Russell T. tech. ed. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 25 
Ponderosa pine ecosystems—Graham and Jain 

Hayman Fire Case Study. Gen. Tech. Rep. RMRS-GTR-114. Ogden, UT, Rocky 

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 244-249. 

Cohen, Jack; Stratton, Rick. 2003. Home destruction within the Hayman Fire perimeter.

In : Graham, Russell T. tech. ed. Hayman Fire Case Study. Gen. Tech. Rep. RMRSGTR-114. Ogden, UT: Rocky Mountain Research Station, Forest Service, U.S. 

Department of Agriculture; 263-292.

Cooper, C.F. 1960. Changes in vegetation, structure, and growth of southwest pine 

forests since white settlement. Ecological Monographs 30: 129-164. 

Cooper, S.V.; Neiman, K.E.; Roberts, D. W. 1991. Forest habitat types of northern Idaho:

a second approximation. Gen. Tech. Rep. INT-236. Ogden, UT: Intermountain 

Research Station, Forest Service, U.S. Department of Agriculture; 143 p.

Covington, W.W.; Moore, M.M. 1994. Postsettlement changes in natural fire regimes and 

forest structure: Ecological restoration of old-growth ponderosa pine forests. In: 

Sampson, R. Neil; Adams, David L., eds. Assessing forest ecosystem health in the 

Inland West. New York: The Haworth Press Inc.; 153-181.

Cruz, M. G.; Alexander, M. E.; Wakimoto, R. H. 2002. Definition of a fire behavior model

evaluation protocol: a case study application to crown fire behavior models. In: 

Omi, Philip N.; Joyce, Linda. Tech. Eds. Fire, fuel treatments, and ecological 

restoration: conference proceedings. 2002, 16-18 April, Fort Collins, CO. Proceedings . 

RMRS-P-29. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. 

Department of Agriculture, 49-68. 

Daubenmire, R.; Daubenmire, J. B. 1968. Forest vegetation of eastern Washington and 

northern Idaho. Tech. Bull. 60. Pullman, WA: Washington Agricultural Experiment

Station; 104 p.

Dodge, Marvin. 1972. Forest fuel accumulation. Science 177: 139-142.

Dunning, Duncan. 1928. Tree classification for the selection forests of the Sierra Nevada.

Journal of Agricultural Research 36: 755-771. 

Everett, R. L.; Schellhaas, R.; Keenum, D.; Spurbeck, D.; Olson, P. 2000. Fire history in the

ponderosa pine/Douglas-fir forests on the east slope of the Washington Cascades.

Forest Ecology and Management 129: 207-225. 

Everett, Richard L. 1987. Plant responses to fire in the pinyon/juniper zone. In: Everett, 

Richard L. compiler. Proceedings: pinyon juniper conference. Gen. Tech. Rep. INT-215. 

Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department of

Agriculture; 152-157. 

Finney, M. A. 2001. Design of regular landscape fuel treatment patterns for modifying 

fire growth and behavior. Forest Science 47: 219-228. 

Finney, M. A. 2003. Calculating fire spread rates across random landscapes. International

Journal of Wildland Fire 12(2): 167-174. 

Finney, Mark A.; Bartlette, Roberta Bradshaw; Larry; Close, Kelly; Collins, Brandon M.;

Gleason, Paul; Hao, Wei Min; Langowski, Paul; McGinely, John; McHugh, Charles W.; 

Martinson, Erik; Omi, Phillip N.; Shepperd, Wayne; Zeller, Karl. 2003. Fire behavior,

fuel treatments, and fire suppression on the Hayman Fire. In : Graham, Russell T., 

tech. ed. Hayman Fire case study. Gen. Tech. Rep. RMRS-GTR-114. Ogden, UT: Rocky 

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 33-180. 

Franklin, Jerry F.; Fites-Kaufman, Jo Ann. 1996. Assessment of late successional forests of

the Sierra Nevada. In: Sierra Nevada ecosystem project, final report to Congress, Vol. 

II, assessments and scientific basis for management options. Davis, CA: University of

California, Centers for Water and Wildland Resources; 627-662. 

26 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

Franklin, Jerry F.; Spies, Thomas A.; Van Pelt, Robert; Carey, Andrew B.; Thornburgh, Dale 

A.; Rae Berg, Dean; Lindenmayer, David B.; Harmon, Mark E.; Keeton, William S.; 

Shaw, David C.; Bible, Ken; Jiquan, Chen. 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.

Fulé, Peter Z.; Covington, Wallace; Moore, Margaret M. 1997. Determining reference 

conditions for ecosystem management of southwestern ponderosa pine forests.

Ecological Applications 7(3): 895-908.

Galley, Krista E. M.; Wilson, Tyron P., eds. 2001. Proceedings of the invasive species 

workshop: The role of fire in the control and spread of invasive species. Tall

Timbers Research Station; Tallahassee, FL: 146 p. 

Galliano, Steven J. and Loeffler, Gary M. 1999. Place assessment: how people define

ecosystems. Gen. Tech. Rep. PNW-GTR-462. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 31 p. 

Gardner, B. and Mocettini P.; Halsey, D. 1997. Forest, insect, and disease conditions. Ogden,

UT: Intermountain Region, Forest Service, U.S. Department of Agriculture; 27 p. 

Grafe, Ernest; Horsted, Paul. 2002. Exploring with Custer: The 1874 Black Hills 

Expedition. Custer, SD: Golden Valley Press; 285 p. 

Graham, Russell T.; Jain, Theresa B. 2005. Application of free selection in mixed forests of 

the inland northwest United States. Forest Ecology and Management 209: 131-145. 

Graham, Russell T.; Harvey, Alan. E.; Jain, Theresa B.; Tonn, Jonalea R. 1999a. The effects 

of thinning and similar stand treatments on fire behavior in western forests. Gen.

Tech. Rep. PNW-GTR-463. Portland, OR: Pacific Northwest Research Station, Forest

Service, U.S. Department of Agriculture; 27 p. 

Graham, Russell T.; Harvey, Alan E.; Jurgensen, Martin F.; Jain Theresa B.; Tonn, Jonalea

R.; Page-Dumroese, Deborah S. 1994. Managing coarse woody debris in forests of

the Rocky Mountains. Res. Pap. INT-RP-477. Ogden, UT: Intermountain Research

Station, Forest Service, U.S. Department of Agriculture; 13 p. 

Graham, Russell T.; Rodriguez, Ronald L.; Paulin, Kathleen L.; Player, Rodney L.; Heap, 

Arlene P.; Williams, Richard. 1999b. The northern goshawk in Utah: habitat 

assessment and management recommendations. Gen. Tech. Rep. RMRS-GTR-22.

Ogden, UT: Rocky Mountain Research Station, Forest Service, U.S. Department of 

Agriculture; 48 p.

Graham, Russell T.; Tonn, Jonalea R.; Jain, Theresa B. 1995. Cone and seed production of 

western larch in response to girdling and nitrogen fertilization--an update. In:

Schmidt, W. C.; McDonald, K. J., comps. Proceedings of a symposium on ecology and 

management of Larix forests: a look ahead. Gen. Tech. Rep. GTR-INT-319. Ogden, UT:

Intermountain Research Station, Forest Service, U.S. Department of Agriculture; 204-

208.

Graham, Russell T.; McCaffrey Sarah; Jain Theresa B. tech. eds. 2004. Science basis for

changing forest structure to modify wildfire behavior and severity. Gen. Tech. Rep.

RMRS-GTR-120. Fort Collins, CO: Rocky Mountain Research Station; Forest Service, 

U.S. Department of Agriculture; 43 p. 

Graham, Russell T., tech. ed. 2003. Hayman Fire case study. Gen. Tech. Rep. RMRS-GTR114. Ogden, UT: Rocky Mountain Research Station, Forest Service, U.S. Department of

Agriculture; 400 p. 

Gruell, G.E.; Schmidt, W.C.; Arno, S.F.; Reich, W.J. 1982. Seventy years of vegetative 

change in managed ponderosa pine forest in western Montana: Implications for

resource management. Gen. Tech. Rep. GTR-INT-130. Ogden, UT: Intermountain

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 27 
Ponderosa pine ecosystems—Graham and Jain 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture;

42 p.

Haig, I.T.; Davis, K.P.; Weidman, R.H. 1941. Natural regeneration in the western white 

pine type. Tech. Bull. 767. Washington, DC: U.S. Department of Agriculture; 99 p. 

Hann, Wendel J; Jones, Jeffrey L.; Karl, Michael G. Sherm; Hessburg, Paul F.; Keane, Robert

E.; Long, Donald G.; Menakis, James P.; McNicoll, Cecilia H.; Leonard, Stephen G.; 

Gravenmier, Rebecca A.; Smith Bradley G. 1997. Landscape dynamics of the Basin.

In: Quigley, Thomas M.; Arbelbide, Sylvia J. tech.eds. An assessment of ecosystem

components in the interior Columbia Basin and portions of the Klamath and Great

Basins: Volume II. Gen. Tech. Rep. PNW-GTR-405. Portland, OR: Pacific Northwest

Research Station, Forest Service, U.S. Department of Agriculture; 338-1055. 

Harlow William M.; Harrar, Ellwood S. 1968. Textbook of dendrology. New York: 

McGraw-Hill; 512 p.

Harvey, A. E. 1994. Integrated roles for insects, diseases, and decomposers in fire 

dominated forests of the Inland Western United States: Past present and future 

forest health. Journal of Sustainable Forestry 2: 211-220. 

Harvey, A.E.; Jurgensen, M.F.; Larsen, M.J.; Schleicher, J.A. 1986. Distribution of active 

ectomycorrhizal short roots in forest soils of the Inland Northwest: effects of site 

and disturbance. Res. Paper. INT-374. Ogden, UT: Intermountain Research Station,

Forest Service, U.S. Department of Agriculture; 8 p. 

Harvey, Alan E.; Graham, Russell T.; McDonald, Geral I. 1999. Tree species composition 

change: forest soil organism interaction: potential effects of nutrient cycling and 

conservation processes in interior forests. In: Meurisse, Robert T.; Ypsllantis, William 

G.; Seybold, Cathy. tech. eds. Proceedings: Pacific Northwest forest and rangeland soil 

organism symposium. Gen. Tech. Rep. PNW-GTR-461. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 137-145. 

Harvey, Alan E.; Graham, Russell T.; McDonald, Geral I.; Larsen, Michael J. 2000. 

Fire/decay: managing codependent processes across the landscape. In: 

Neuenschwander, Leon F.; Ryan, Kevin C., tech. eds. Crossing the Millennium:

Integrating spatial technologies and ecological principles for a new age in fire

management, Joint fire science conference and workshop. Spokane, WA: International

Association of Wildland Fire. 179-189. 

Harvey, Alan E.; Jurgensen, Martin F.; Larsen, Michael J.; Graham, Russell T. 1987. 

Decaying organic materials and soil quality in the inland northwest: a management

opportunity. Gen. Tech. Rep. INT-225. Ogden, UT: Intermountain Research Station,

Forest Service, U.S. Department of Agriculture; 15 p. 

Hedden, R.; Barras, S.; Coster, J. 1981. Hazard-rating system in forest insect pest

management. Gen. Tech. Rep. GTR-WO-27. Washington, DC: Forest Service, U.S.

Department of Agriculture; 166 p. 

Hessburg, Paul F.; Mitchell, Russel G.; Filip Gregory M. 1994. Historical and current roles 

of insects and pathogens in eastern Oregon and Washington forested landscapes.

Gen. Tech. Rept. PNW-GTR-327. Portland, OR: Pacific Northwest Research Station, 

Forest Service, U.S. Department of Agriculture; 72 p. 

Hoffman, G.R.; Alexander, R.R. 1987. Forest vegetation of the Black Hills National Forest 

of South Dakota and Wyoming: a habitat type classification. Res. Pap. RM-276. Fort

Collins, CO: Rocky Mountain Forest and Range Experiment Station; Forest Service, 

U.S. Department of Agriculture; 48 p. 

Hungerford, R.D.; Harrington, M.G.; Frandsen, W.H.; Ryan, K.C.; Niehoff, G.J. 1991. 

Influence of fire on factors that affect site productivity. In: Harvey, A.E.;

Neuenschwander, F.L., comp. Proceedings--Management and productivity of western28 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

montane forest soils. Gen. Tech. Rep. INT-280. Ogden, UT: Intermountain Research

Station, Forest Service, U.S. Department of Agriculture; 32-50.

Hutchison, S.B.; Winters R.K. 1942. Northern Idaho forest resources and industries.

Washington, DC: US Department of Agriculture; 75 p. 

Jain, Theresa B.; Graham, Russell T. 2005. Restoring dry and moist forests of the inland 

northwestern U.S. In: Stanturf, John A.; Madsen, Palle., eds. Restoration of boreal and 

temperate forests. Boca Raton, FL: CRC Press; 463-480.

Jurgensen, M.F.; Harvey, A.E.; Graham, R.T.; Page-Dumroese, D.S.; Tonn, J.R.; Larsen, 

M.J.; Jain, T.B. 1997. Impacts of timber harvesting on soil organic matter, nitrogen, 

productivity, and health of Inland Northwest forests. Forest Science 43(2): 234-251.

Jurgensen, Martin F.; Tonn, Jonalea T.; Graham, Russell T.; Harvey, Alan E.; Geier-Hayes, 

Kathleen. 1991. Nitrogen fixation in forest soils of the inland northwest. In: Harvey,

A. E., ed. Proceedings of the symposium management and productivity of westernMontana forest soils. Gen. Tech. Rep. INT-280. Ogden, UT: Intermountain Research

Station, Forest Service, U.S. Department of Agriculture; 101-109.

Kaufmann, M.R.; Fornwalt, P.J.; Huckaby, L.S.; Stoker, J.M. 2001. Cheesman Lake a 

historical ponderosa pine landscape guiding restoration in the South Platte 

watershed of the Colorado Front Range. In: Vance, R. K.; Edminster, C. B.; 

Covington, W. W.; Blake, J.A., comps. Ponderosa pine ecosystems restoration and

conservation: steps toward stewardship. Proc. RMRS-P-22. Fort Collins, CO: Rocky

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 9-18.

Keen, F. P. 1936. Relative susceptibility of ponderosa pines to bark-beetle attack. Journal 

of Forestry 34: 919-927.

Keen, F. P. 1943. Ponderosa pine tree classes redefined. Journal of Forestry 41: 249-253.

Kent, Brian; Gebert, Krista; McCaffrey, Sarah; Wade; Calkin, David; Martin, Ingrid;

Schuster, Ervin; Martin, Wise Holly Bender; Alward, Greg; Kumagai, Yoshitaka; Cohn,

Patricia J.; Carroll, Matt; Williams, Dan; Ekarius Carol. 2003. Social and economic

issues of the Hayman Fire. In: Graham, Russell T., tech. ed. Hayman Fire case study. 

Gen. Tech. Rep. RMRS-GTR-114. Ogden, UT: Rocky Mountain Research Station, 

Forest Service, U.S. Department of Agriculture; 315-396. 

Larsen, M.J.; Harvey, A.E.; Jurgensen, M.F. 1979. Residue decay processes and associated 

environmental functions in northern Rocky Mountain forests. In: Proceedings of the

symposium on environmental consequences of timber harvesting in Rocky Mountain

coniferous forests. Gen. Tech. Rep. INT-90. Ogden, UT: Intermountain Forest and

Range Experiment Station, Forest Service, U. S. Department of Agriculture; 157-174. 

Little, Elbert. L., Jr. 1971. Atlas of United States trees, volume 1: conifers and important 

hardwoods. Misc. Publ. 1146. Washington, DC: U.S. Department of Agriculture; 9 p. 

313 maps. 

Little, Elbert. L. Jr. 1979. Checklist of United States trees. Agric. Handbk. 541. Washington, 

DC: U.S. Department of Agriculture; 375 p. 

Long, James N.; Smith, Frederick W. 2000. Restructuring the forest: Goshawks and

restoration of southwestern ponderosa pine. Journal of Forestry: 98: 25-30. 

Mauk, R.L.; Henderson, J.A. 1984. Coniferous forest habitat types of northern Utah. Gen. 

Tech. Rep. GTR-INT-170. Ogden, UT: Intermountain Forest and Range Experiment

Station, Forest Service, U.S. Department of Agriculture; 89 p. 

Meyer, W. H. 1934. Growth in selectively cut ponderosa pine forests of the Pacific 

Northwest. Tech. Bull. 407. Washington, DC: U.S. Department of Agriculture; 64 p. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 29 
Ponderosa pine ecosystems—Graham and Jain 

Mika, P. G.; Moore, J. A. 1990. Foliar potassium explains Douglas-fir response to 

fertilization in the Inland Northwest. Water, Air and Soil Pollution 54: 477-491.

Minore, D. 1979. Comparative autecological characteristics of northwestern tree species; 

A literature review. Gen. Tech. Report PNW-87. Portland, OR: Pacific Northwest 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture;

72 p.

Moore, J.A.; Mika, P.G.; Vanderploeg, J.L. 1991. Nitrogen fertilization fertilizer response

of Rocky Mountain Douglas-fir by geographic area across the Inland Northwest.

Western Journal of Applied Forestry 64: 94-98.

Neary, Daniel G.; Klopatek, Carole C.; DeBano, Leonard F.; Ffolliott, Peter F. 1999. Fire 

effects on belowground sustainability: A review and synthesis. Forest Ecology and 

Management 122:51-71.

Oliver, William. W.; Ryker, Russell A. 1990. Silvics of ponderosa pine. In: Burns, R.M.; 

Honkala, B. H., tech. coords. Silvics of North America, Volume 1, Conifers. Agric.

Handbk. 654. Washington, DC: Forest Service, U.S. Department of Agriculture; 413-

424.

Pannkuk, C.D. and Robichaud, P.R. 2003. Effectiveness of needle cast reducing erosion 

after forest fires. Water Resource Res. 39(12): 1333, doi:10.1029/2003WR002318. 

Peterson, David L; Johnson, Morris C.; Agee, James K; Jain, Theresa B; McKenzie, Donald;

Reinhardt, Elizabeth D. 2005. Forest Structure and Fire Hazard in dry forests of the 

western United States. Gen. Tech. Rept. PNW-GTR-628. Portland, OR: Pacific

Northwest Research Station. Forest Service, U.S. Department of Agriculture; 30 p. 

Pearson, G.A. 1950. Management of ponderosa pine in the southwest as developed by 

research and experimental practices. Agriculture Monograph 6. Washington, D.C:

Forest Service, U.S. Department of Agriculture; 218 p. 

Pfister, R.D.; Kovalchik, B.L.; Arno, S.F.; Presby, R.C. 1977. Forest habitat types of

Montana. Gen. Tech. Rep. INT-34. Ogden, UT: Intermountain Forest and Range

Experiment Station, Forest Service, U.S. Department of Agriculture; 174 p. 

Rasmussen, D. Irvin. 1941. Biotic communities of the Kaibab plateau, Arizona. Ecological

Monographs 11(3): 229-275.

Rehfeldt, G.E. 1994. Microevolution of forest trees in cedar-hemlock forests. In: 

Baumgartner, David M.; Lotan, James E.; Tonn, Jonalea R., comps. Proceedings of he

symposium on interior cedar-hemlock-white pine forests: Ecology and management. 

Spokane, WA. Pullman, WA: Department of Natural Resources, Washington State 

University; 92-100. 

Reynolds, Richard T.; Graham, Russell T.; Reiser, M.H.; Bassett, Richard L.; Kennedy, 

Patricia L.; Boyce, Douglas A.; Goodwin Greg; Smith, Randall; Fisher, E. Leon. 1992. 

Management recommendations for the northern goshawk in the southwestern

United States. Gen. Tech. Rep. 217. Fort Collins, CO: Rocky Mountain Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 90 p. 

Robichaud, Pete; MacDonald, L.; Freeouf, J.; Neary, D.; Martin, D.; Ashmun, Louise. 2003.

Postfire reehabilitation of the Hayman Fire. In : Graham, Russell T., tech. ed. 

Hayman Fire case study. Gen. Tech. Rep. RMRS-GTR-114. Ogden, UT: Rocky 

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 293-313. 

Rose, S.L.; Perry, D.A., Pilz, D.; Schoeneberger, M.M. 1983. Allelopathic effects of litter on 

growth and colonization of mycorrizal fungi. Journal of Chemical Ecology 9: 1153-

1162. 

Sandburg, D.V.; Ottmar, R.D.; Carlson, G.H. 2001. Characterizing fuels in the 21st 

century. International Journal of Wildland Fire 10: 381-387. 

30 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa pine ecosystems—Graham and Jain 

Schmid, J. M.; Mata S. A., 1992. Stand density and mountain pine beetle-caused tree

mortality in ponderosa stands. Gen. Tech. Rep. RM-GTR-275. Fort Collins, CO:

Rocky Mountain Forest and Range Experimental Station, Forest Service, U.S.

Department of Agriculture; 14 p. 

Schroeder, Herbert. 2002. Experiencing nature in special places: surveys in the north 

central region. Journal of Forestry 100(5): 8-14. 

Schubert, Gilbert H.; Adams, Ronald S. 1971. Reforestation practices for conifers in

California. Sacramento, CA: Division of Forestry, Department of Conservation, State of

California; 359 p. 

Scott, Joe H.; Reinhardt, Elizabeth D. 2001. Assessing crown fire potential by linking 

models of surface and crown fire behavior. Res. Pap. RMRS-RP-29. Fort Collins, CO:

Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture; 59 p.

Shepperd, Wayne D. and Battaglia, Michael A. 2002. Ecology, silviculture, and 

management of Black Hills ponderosa pine. Gen. Tech. Rep. RMRS-GTR-97. Fort

Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. Department of

Agriculture; 112 p. 

Shinnen, D.J.; Baker, W.L. 1997. Non equilibrium dynamics between catastrophic 

disturbances and old-growth forests in ponderosa pine landscapes of the Black

Hills. Conservation Biology 11(6): 1276-1288. 

Smith, Helen Y.; Arno, Stephen F., eds. 1999. Eighty-eight years of change in a managed

ponderosa pine forest. Gen. Tech. Rep. RMRS-GTR-23. Ogden, UT: Rocky Mountain

Research Station, Forest Service, U.S. Department of Agriculture; 55 p. 

Smith, Jane Kapler and Fischer, William C. 1997. Fire ecology of the forest habitat types of

northern Idaho. Gen. Tech. Rep. INT-GTR-363. Ogden, UT: Intermountain Research

Station, Forest Service, U.S. Department of Agriculture; 142 p. 

Speer, James H.; Swetnam, Thomas W.; Wickman, Boyd E.; Youngblood, Andrew. 2001. 

Changes in pandora moth outbreak dynamics during the past 622 years. Ecology 

82 (3): 679-697. 

Steele, R.; Cooper, S.V.; Ondov, D.M.; Roberts, D.W.; Pfister, R.D. 1983. Forest habitat

types of eastern Idaho-western Wyoming. Gen. Tech. Rep. INT-144. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 122 p. 

Stein, S.J. 1988. Explanations of imbalanced age structure and scattered distribution of 

ponderosa pine within a high-elevation mixed coniferous forest. Forest Ecology and 

Management 25: 139-153. 

Stewart, O.C. 1951. Burning and natural vegetation in the United States. Geographical 

Review 41: 317-320. 

Thomas, J.W., ed. 1979. Wildlife habitats in managed forests, the Blue Mountains of

Oregon and Washington. Agric. Handb. 553. Washington, DC: Forest Service, U.S. 

Department of Agriculture; 512 p. 

USDA Forest Service. 2000. Bitterroot Fires 2000, an overview of the events, effects on 

people and resources, and post-fire recovery priorities. Hamilton, MT: Region One, 

Forest Service, U.S. Department of Agriculture; 108 p. 

USDA Forest Service. 2004. The healthy forests initiative and healthy forests restoration 

act: interim field guide. FS-799. Washington, DC: Forest Service, U.S. Department of

Agriculture; and U.S. Department of Interior, Bureau of Land Management; 58 p. 

Van Hooser, Dwane; Keegan, Charles E., III. 1988. Distributions and volumes of 

ponderosa pine forests. In: Baumgartner, D.M.; Lotan, J.E., eds. Proceedings of the

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 31 
Ponderosa pine ecosystems—Graham and Jain 

symposium on ponderosa pine: the species and its management. Pullman, WA:

Washington State University; 1-6. 

Van Wagner, C.E. 1977. Conditions for the start and spread of crown fire. Canadian 

Journal of Forest Research 7: 23-24.

Weaver, H. 1943. Fire as an ecological and silvicultural factor in the ponderosa pine

region of the Pacific slope. Journal of Forestry 41: 7-14. 

White, Alan S. 1985. Presettlement regeneration patterns in a southwestern ponderosa

pine stand. Ecology 66(2): 589-594.

Williams, R.E.; Shaw, C.G. III; Wargo, P. M.; Sites, W. H. 1986. Forest insect and disease.

leaflet 78. Washington, DC: Forest Service, U.S. Department of Agriculture; 9 p.

Wu, Y.; Johnson, D.W.; Angwin, P. A. 1996. Identification of Armillaria species in Rocky

Mountain Region. Rep. R2-58. Golden, CO: Rocky Mountain Region, Forest Service,

U.S. Department of Agriculture; 26 p. 

Wykoff, W.R.; Crookston, N.L.; Stage, A.R. 1982. User's guide to the Stand Prognosis

Model. Gen. Tech. Rep. INT-133. Ogden, UT: Intermountain Forest and Range

Experiment Station, Forest Service, U.S. Department of Agriculture; 112 p. 

Youngblood, A.P.; Mauk, R.L. 1985. Coniferous forest habitat types of central and 

southern Utah. Gen. Tech. Rep. GTR-INT-187. Ogden, UT: Intermountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 89 p. 

Youngblood, Andrew; Max, Timothy; Coe, Kent. 2004. Stand structure in eastside oldgrowth ponderosa pine forests of Oregon and northern California. Forest Ecology

and Management 199: 191-217. 

32 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
An Overview of Key Silvicultural 

Information for Ponderosa Pine1 

John Fiske2 and John Tappeiner3 

Abstract 

This paper provides a selected list of classical references for the important silvicultural 

findings for ponderosa pine, and categorizes some of the key current literature, as well as 

some of the older, lesser known but important literature. The paper also provides some 

history of scientific developments, and sources of further information. 

Introduction 

In this paper we review what we consider to be the key silvicultural information 

for ponderosa pine (Pinus ponderosa P. & C. Lawson). Our experience with 

ponderosa pine and consequently much of our information comes from Oregon and 

California. We did not attempt to examine the entire literature on this species, which 

is enormous! Rather, we focused on what we think is the most important information 

in fifteen categories. We included older information that is often overlooked, 

probably because it is not in bibliographic electronic databases. Also, proceedings of 

at least two symposia that are devoted primarily to ponderosa pine (Baumgartner and 

Lotan 1988 and Robson and Standiford 1983) and summaries of ponderosa pine 

silvics (Barrett 1979 and Oliver and Ryker 1990) and silvicultural systems (Schubert 

1974, Oliver and others 1983, Ryker and Losensky 1983, and Boldt and others 1983), 

Ronco and Ready (1983) include very helpful information. Syntheses of regeneration 

practices are also very important (Schubert and Adams 1971, Cleary and others 1978, 

Hobbs and others 1992) 

Our review is divided into categories under the twin headings Reforestation 

and Timber Stand Improvement and Stand Growth, and we provide an abstract 

summarizing the main points in these parts of the literature. The categories overlap. 

For example, information on bark beetles occurs under stand growth and density as 

well as under insects, pathogens, animal, and snow damage. 

Undoubtedly we omitted important information that ought to be included. 

Perhaps this review can be considered a work in progress. 

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues,

Trends, and Management, October 18-21, 2004, Klamath Falls, Oregon.

2 Regional Program Manager, Reforestation and Timber Stand Improvement, Retired, USDA Forest

Service, Pacific Southwest Region, Vallejo, CA., 717 Acacia Drive, Burlingame, CA 94010, (e-mail:

jnfiske@yahoo.com).

3

 Professor Emeritus, Oregon State University, Forest Resources Dept., Corvallis, OR 97331 (email:

john.tappeiner@oregonstate.edu).

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 33 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Regeneration and Timber Stand Improvement 

Fully recognizing that regeneration and timber stand improvement (TSI) are best 

thought of as a complete system, and that failure occurs if any single component 

fails, for the purposes of this presentation, we divided “regeneration” and “TSI” into 

five categories: natural regeneration, seed collection and handling, nursery practices, 

site preparation and release, and precommercial thinning. 

Natural Regeneration. 

Natural regeneration, with seed-tree or shelterwood systems, has been used 

effectively in many parts of ponderosa pine’s natural range (for example, Heidmann 

1988, McDonald 1976a, 1976b, 1976c, McDonald and Abbot 1994, Muelder and 

others 1963, Roy 1983, Shearer and Schmidt 1970, 1971), especially if sites are wellprepared, include rodent control, and coincide with good seed crops. Pearson (1923) 

was the earliest example of the rich scientific literature we found. Advanced 

regeneration can also be considered as natural regeneration. 

Seed Collection and Handling 

In contrast to the other major western conifer species, proper collection and seed 

handling methods for artificial regeneration of ponderosa pine were comparatively 

easy to determine and are well established (Fowells and Schubert 1956). Early work 

(in the 1940’s and 1950’s) focused on germination and cold storage. The most 

significant single development was the establishment of seed zones, elevational 

bands, and seed transfer guidelines, beginning in the 1940’s in California (Fowells 

1946, Buck and others 1970), later elsewhere (for example, starting in the 1950’s in 

Oregon, Roy 1955). 

Nursery Practices 

Volumes have been written over the last 5 decades about culturing ponderosa 

pine seedlings, a subject that now is very well understood and practiced. We focus on 

just three key developments. The first was the development of fumigation (initially 

primarily methyl bromide) to control root diseases in bare-root seedlings (Bega and 

Smith 1960, Smith and Bega, 1966). Although ponderosa pine is somewhat resistant 

to seedling root diseases compared to most other commercial western conifers, 

fumigation use significantly improved production efficiencies for ponderosa pine. 

The second key development was the concept of how nursery practices and seed 

source (genetics) affect the potential for growing new roots upon out-planting (root 

growth capacity or root regeneration potential) and lifting windows (Jenkinson 1980, 

Stone 1955, Stone and Benseler 1962, Stone and Schubert 1959a 1959b, and Stone 

and others 1963). The third key set of developments was the enormously successful 

technology of container nurseries, starting in the 1960’s (Tinus and McDonald 1979, 

Tinus and others 1974). This technology is best summarized in The Container Tree 

Nursery Manual (Landis and others 1989, 1990a, 1990b, 1992, 1995). Container 

nursery technology continues to improve in the western United States and Canada, 

primarily by private nurseries, often in cooperatives. 

34 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Site Preparation and Release. 

There is considerable literature on the theory and practice of controlling 

unwanted vegetation (for example the Proceedings of the Annual Forest Vegetation 

Management Conference, starting in 1981, and Walstad and Kuch 1987). The 

scientific basis for predicting ponderosa pine responses to effective control of 

competing vegetation is well established. Practices have undergone continual 

development, in part to reduce unit costs, and to reduce controversies over herbicide 

use. Just about every conceivable alternative to herbicide use has been tried 

somewhere during the last three decades (including dynamite for site preparation!). 

We focus on three key aspects: the development and application of herbicides, 

the USDA Forest Service National Administrative Study, and the scientific 

understanding of the interaction between site quality and tradeoffs between release 

vs. precommercial thinning. 

Herbicide use started in the 1950’s with adaptation of agricultural aerial 

application techniques of the phenoxy herbicides. Later, appropriate use of a much 

broader range of herbicides was established on a scientific basis, including human 

health and ecological risk considerations. Additions to the scientific literature 

continue, and (in part because of legal challenges) comprehensive risk assessments 

are scheduled for almost continuous updating. The current risk assessments for 

hexazinone, sulfometuron methyl (OUST), imazapyr (Arsenal®, Chopper®, and 

Stalker®4 formulations), glyphosate, and triclopyr are available online (SERA 1997, 

1998a, 1998b, 2003a, 2003b). 

The National Administrative Study focused on release in northern California (a 

20-year-plus study), and continues to establish much of the long-term scientific basis 

for herbicide and non-herbicide treatments (Fiddler and McDonald 1984). 

Comparable long-term study results for site preparation and release are becoming 

available elsewhere in California and in Oregon. 

Our third focus is on the relationship between determining needs for release vs. 

precommercial thinning, as influenced by site quality. Numerous studies have 

quantified effects of shrub competition and release treatment on conifer growth 

(Baron 1962, Crouch 1971, 1979, Doescher and others 1989, Fiddler and McDonald 

1984, Lanini and Radosevich 1986, Tappeiner and Radosevich 1982, White and 

Newton 1989). When investment funds are limited, and only one kind of treatment 

can be done, which treatment should receive priority, and how does site quality affect 

the decision? Bill Oliver compared results of both kinds of treatments on a highquality and a low-quality site in northern California (McDonald and Oliver 1984), 

and established the important principle that on low-quality sites, inter-tree 

competition in ponderosa pine plantations is insignificant, compared to competition 

between the trees and shrubs. That is, precommercial thinning is a wasted investment 

unless the thinning follows, or is done concurrently with, effective release treatments 

to control shrubs. On such sites, lack of effective release treatments can result in 

unacceptably high tree mortality rates. In contrast, on high-quality sites, inter-tree 

competition can be greater than tree-shrub competition, so a single precommercial 

thinning treatment can yield a better investment return compared to a single release 

treatment. 

4

 The use of trade or firm names in this publication is for the reader information and does not 

imply endorsement by the U.S. Department of Agriculture of any product or service. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 35 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Precommercial Thinning 

Practical experience with early ponderosa pine plantations (early part of the 20th 

century) and widely-distributed spacing studies led to commonly-used residual 

stocking levels of approximately 100 to 250 trees per acre, depending on site quality, 

management objectives (including wood quality), and other factors. Two significant 

quantitative models for predicting growth of pre-commercial-sized ponderosa pine in 

plantations have been developed. Oliver and Powers (1978) developed the first 

quantitative model for spacings of 6, 8, 10, and 12 feet, respectively, for a range of 

site qualities in northern California. Powers and others (1989) and Ritchie and 

Powers (1993) described the first quantitative model (SYSTUM-1) to include the 

effects of shrub competition (also at different tree spacings), based largely on 

ponderosa pine and Douglas-fir plantation data from southwestern Oregon and 

northern California. 

Stand Growth 

Genetics, Autecology. 

Conkle (1973) reported on the ponderosa pine elevational study from the Sierra 

Nevada. In this study, trees from low-, mid and high-elevation seed sources were 

reciprocally planted at these elevations. Ponderosa pine height growth varied by 

elevation. Trees from high elevation seed sources grew slower than those from other 

elevations, and had lower height-to-diameter ratios. Trees from mid-elevation sources 

appeared to be most productive and can be moved more readily than those from low 

and high elevations, but they were susceptible to snow damage when planted at high 

elevations. 

Ponderosa pine has the ability to grow roots into rock fissures in the 

unweathered soil horizons and extract water stored there. Shrubs that grow on the 

same sites have the same ability; however, Douglas-fir is much less able to use water 

stored in rock fissures (Zwieniecki and Newton 1994, 1995, 1996). 

Growth and Yield 

Much early research on this species was focused on growth and yield, and was 

presented in tabular form. Examples of published yield tables include: Dunning and 

Reineke (1933), Meyer (1934, 1938), Oliver and Powers (1978). More recently, 

growth and yield information usually takes the form of computer simulators (e.g. 

DeMars and Barrett 1987, Hann 1981, Hann 2003, Ritchie and Powers 1993, Wensel 

and Koehler 1986). 

Site productivity, traditionally reflected in site index curves have been 

developed for many regions within the range of ponderosa pine (Barrett 1978, Biging 

1985, Dunning 1942, Lynch 1958, Oliver 1972, Powers and Oliver 1978, Hann and 

Scrivani 1987, Verdyla and Fischer 1989). 

Tree Growth and Stand Density (tree and shrub)—Thinning 

Several studies on thinning response and the growth of ponderosa pine at a 

range of stand densities have been reported in the last several decades. These studies 

indicate that young, even-age ponderosa pine stands respond to thinning like most 

36 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

other conifer species. Thinning increases diameter growth, and maintains crown 

lengths (Barrett 1982, Cochran and Barrett 1993, Fiddler and others 1989, McDonald 

and others 1992, Oliver 1984, 1997). Heavy thinning tended to decrease volume yield 

per unit area, but at high densities or with light thinning net volume yield was low 

because of mortality from bark beetles. Mechanical treatments may impact soil 

characteristics and site productivity (Busse and others 1996, Helms and Hipkin 1986, 

Helms and others 1986). 

These studies indicate that western pine beetles may determine the upper levels 

of stand density (Oliver 1995). Also snow breakage is another important cause of 

mortality at high densities. On dry sites shrubs (Ceanothus and Manzanita sp.), may 

reduce ponderosa pine growth during stand establishment and reduce or delay it even 

after the ponderosa pine has overtopped the shrubs (Gordon 1962, McDonald and 

Oliver 1984, Oliver 1984, 1990, Powers and others 2005, Shainsky and Radosevich 

1986). It appears that eventually the pines may shade out the shrubs and increase 

their growth rates. 

Fertilization, Stand Growth Effects of Shrubs 

Ponderosa pine responds to fertilizers but only after shrub control. Where shrub 

density is high, control of shrubs appears necessary to provide the water needed for 

fertilizers to be effective. Under combined shrub control-fertilization, most growth 

response resulted from removal of shrubs; the direct effect of fertilizers is secondary 

(Powers and Jackson 1978, Powers and Ferrell 1996, Powers and others 1988, 

Walker 1999a, 2002, White and Newton 1989). 

Measures of Stand Density 

Measures of density for stands in the pine region have been developed around 

stand density index (Reineke 1933). Stockability, (the potential stand density for a 

site) can be adjusted for specific sites (Dunning and Reineke 1933, Cochran 1992, 

Cochran and others 1994; Hall 1983, Peterson and Hibbs 1989). 

Uneven Age Management 

Techniques for developing stocking guidelines for uneven aged stands are based 

on distributing the desired residual SDI (possibly half of maximum) throughout 

several diameter classes, resulting in a large variety of possible stand structures. The 

resulting distribution can be evaluated by calculating the numbers of trees and basal 

area by diameter class. Shifting different amounts of SDI into various diameter 

classes can modify the distribution. Thus the method is quite flexible and a large 

number of structures are possible (Cochran 1992, McDonald and Abbott 1994, 

Lillieholm and others 1990, O’Hara 1996, O’Hara and Gersonde 2004, Olson and 

Helms 1996). 

Insects, Pathogens, Animal, and Snow Damage 

Drought, diseases, bark beetles, and high stand densities, all influence ponderosa 

pine mortality (Barrett and Roth 1985). Root diseases (Heterobasidium) and 

mistletoes, and high density weaken trees and make them susceptible to bark beetles 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 37 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

(Dendroctonus) especially during periods of drought and also to damage by heavy, 

wet snow (Hawksworth and Wiens 1996, Filip 1986, Filip and others 1989, 1999, 

Megahan and Steele 1987, Miller and Keen 1960, Scharpf and Bega 1981, Schmid 

and others 1994, Smith 1982). Bark beetle attacks may indicate trees under stress 

(Storm and Halvorson 1967, Stoszek 1973). 

Old Stand and Tree Management 

Early work has provided tree classification systems for determining the vigor of 

ponderosa pine and its susceptibility to insects (Dunning 1928 and Keen 1936, 1943). 

Recent work has shown that older ponderosa pine stands and trees can respond to 

thinning. For example a sustained 1.5 to 2.0 percent increase in tree basal area growth 

was common for trees (+200yr) in stands previously thinned 15 to 30 years earlier 

(Dolph and others 1995). Removal of understory trees established after fire cessation 

in the early to mid 1900s may improve the vigor of old ponderosa pine as well as 

protect them from fire (Latham and Tappeiner 2002, McDowell and others 2003, 

Biondi 1996). 

Understory Vegetation and Stand Density 

Recent studies have documented the interactions between overstory density and 

understory development (Riegel and others 1992, 1995). At higher levels of overstory 

density, understory is “shaded out” and its density is reduced in response to scarce 

water and light. Understory vegetation, however can increase organic matter and 

nutrients in the forest floor (Busse and others 1996, Harris and Covington 1982). 

Fire History and Use of Prescribed Fire/Thinning 

The history of fire in ponderosa pine has been studied extensively, and 

prescribed fire and thinning are being increasingly used to reduce the risk and 

intensity of fire in ponderosa pine stands (Covington and Sacket 1984, 1986; 

Covington and Moore 1994; Harris and Covington 1982, Hall 1976, 1983; McNeil 

and Zobel 1980, Bork 1985). Some important emerging issues include the effect of 

fire on mortality of large trees, minimization of slash/dead trees after initial 

prescribed fire, and the effects of fire in stimulating germination of buried seed and 

vegetative buds (Mutch and Parsons 1998; Parsons and DeBenedetti 1979, Weaver 

1959, 1961, White and others 1973). More research and practical experience is 

needed on the use of fire, and mechanical methods in commercial and precommercial 

thinning and combinations of treatments to achieve fuel reduction. 

References 

Baron, F.J. 1962. Effects of different grasses on ponderosa pine seedling establishment. 

Res. Note PSW-199. Berkeley CA: Pacific Southwest Forest and Range Experiment 

Station, Forest Service, U.S. Department of Agriculture. 

Barrett, J.W. 1978. Height growth and site index curves for managed even-aged stands of 

ponderosa pine in the Pacific Northwest. Res. Paper PNW-232. Portland OR: Pacific 

Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 14 p. 

38 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Barrett, J.W. 1979. Silviculture of ponderosa pine in the Pacific Northwest: the state of 

our knowledge. Gen. Tech. Rep. PNW-97. Portland OR: Pacific Northwest Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 106 p. 

Barrett, J.W. 1982. Twenty-year growth of ponderosa pine thinned to five spacings in 

central Oregon. Res. Paper PNW-301. Portland OR: Pacific Northwest Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Barrett, J.W.; Roth, L.F. 1985. Response of dwarf mistletoe-infested ponderosa pine to 

thinning. Res. Paper PNW-330. Portland OR: Pacific Northwest Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture. 

Baumgartner, D.M.; Lotan, J.E. 1988. Ponderosa Pine, The Species and Its Management. 

Pullman WA: Washington St. Univ. Cooperative Extension Symposium Proceedings. 

281p. 

Bega, R.V.; Smith, R.S. 1960. Diseases threaten forest nurseries. PSW Misc. Paper No. 52. 

Berkeley CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture; 3p. 

Biging, G.S. 1985. Improved estimates of site index curves using a varying-parameter 

model. Forest Science 31:248-259 

Biondi, F. 1996. Decadal-scale dynamics at the Gus Pearson Natural Area: evidence for 

inverse (a)symetric competition. Canadian Journal of Forest Research 26:1397-1406. 

Boldt, Charles E.; Alexander, R.R.; Larson, M.J. 1983. Interior Ponderosa Pine. In: Burns, 

R.M., Tech. Compiler. Silvicultural Systems for the Major Forest Types of the United 

States. Ag. Handbook 445. Washington D.C.: Forest Service, U.S. Department of 

Agriculture; 80-83. 

Bork, J. 1985. Fire history in three vegetation types on the eastside of the Oregon 

Cascades. Corvallis OR: Oregon State University; Ph.D. dissertation. 

Buck, J.M.; Adams, R.S.; Cone, J.; Conkle, M.T.; Libby, W.J.; Eden, C.J.; Knight, M.J. 1970. 

California Seed Zones. USDA For. Serv. Calif. Region and Calif. Resources Agency, 

Dept. of Conservation, Division. of Forestry. 

Busse, M.D.; Cochran, P.H.; Barrett, J.W. 1996. Changes in ponderosa pine site 

productivity following removal of understory vegetation. Soil Science Society of 

America Journal. 60:614-62. 

Cleary, B.D.; Greaves, R.D.; Owston, P.W. 1978. Regenerating Oregon’s Forests. Corvallis 

OR: Oregon State University, College of Forestry, Extension. Service. 286 p. 

Cochran, P.H. 1992. Stocking levels and underlying assumptions for uneven-aged 

ponderosa pine stands. Res. Note PNW-RN-509. Portland OR: Pacific Northwest 

Research Station, U.S. Department of Agriculture; 10 p. 

Cochran, P.H.; Hopkins, W.E. 1990. Does fire exclusion increase productivity of 

ponderosa pine? In: Harvey, A.E.; Neuenschwander, L.F., compilers. Management and 

Productivity of Western Montane Soils; 1990, April 10-12, Boise, Idaho. Gen. Tech. 

Rep. GTR-INT-280. Ogden UT: Intermountain Research Station, Forest Service, U.S. 

Department of Agriculture. 

Cochran, P.H.; Barrett J.W. 1993. Long-term response of planted ponderosa pine to 

thinning on Oregon's Blue Mountains. Western Journal of Applied Forestry 8:126-

132. 

Cochran, P.H.; Geist, J.M.; Clemens, D.L.; Clausnitzer, R.R.; Powell, D.C. 1994. Suggested 

stocking levels for forest stands in northeastern Oregon and southeastern 

Washington. Res. Note PNW-RN-513. Portland OR: Pacific Northwest Research 

Station, Forest Service, U.S. Department of Agriculture. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 39 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Conkle, T. 1973. Growth data for 29 years from the California elevational transect of 

ponderosa pine. Forest Science 19:31-39. 

Covington, W.W.; Moore, M.M. 1994. Southwestern ponderosa pine forest structure: 

Changes since Euro-American settlement. Journal of Forestry 92(1):39-47. 

Covington, W.W.; Sacket, S.S. 1984. The effect of a prescribed burn in southwestern 

ponderosa pine on organic matter and nutrients in woody debris and forest floor. 

Forest Science 30:183-192. 

Covington, W.W.; Sacket, S.S. 1986. Effect of periodic burning on soil nitrogen 

concentrations in ponderosa pine. Soil Science Society of America Journal. 50:452-

457. 

Crouch, G.L. 1971. Susceptibility of ponderosa pine and lodgepole pine to pocket 

gophers. Northwest Science 45:252-256. 

Crouch, G.L. 1979. Atrazine improves survival and growth of ponderosa pine threatened 

by vegetative competition and pocket gophers. Forest Science 25:99-111. 

DeMars, D.J.; Barrett, J.W. 1987. Ponderosa pine managed-yield simulator: PPSIM user’s 

guide. Gen. Tech. Rep. PNW-GTR-203. Portland, OR: Pacific Northwest Forest and 

Range Experiment Station. Forest Service, U.S. Department of Agriculture. 

Doescher, P.S.; Tesch, S.D.; Drewien, W.E. 1989. Water relations and growth of conifer 

seedlings during three years of cattle grazing on a southwest Oregon plantation. 

Northwest Science 63:232-240. 

Dolph, K.L.; Mori, S.R.; Oliver, W.W. 1995. Long-term response of old-growth stands to 

varying levels of partial cutting in the eastside pine type. Western Journal of Applied 

Forestry 10:101-108. 

Dunning, D. 1928. A tree classification for the selection forests of the Sierra Nevada. 

Journal of Agriculture Research 36:755-771. 

Dunning, D. 1942. A site classification for the mixed conifer selection forests of the Sierra 

Nevada. Res. Note 28. Berkeley, CA: California Forest and Range Experiment Station, 

Forest Service, U.S. Department of Agriculture. 

Dunning, D.; Reineke, L.H. 1933. Preliminary yield tables for second-growth stands in the 

California pine region. Technical Bulletin 354. Washington D.C.: U.S. Department of 

Agriculture. 

Fiddler, G.O.; McDonald, P.M. 1984. Alternatives to Herbicides in Vegetation 

Management. In: Proceedings, Fifth Annual Forest Vegetation Management 

Conference. 1983, Nov. 2-3, Sacramento CA; 115-126. 

Fiddler, G.O.; Fiddler, T.A.; Hart, D.R.; McDonald, P.M. 1989. Thinning decreases 

mortality and increases growth of ponderosa pine in northeastern California. Res. 

Paper PSW-194. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, 

Forest Service, U.S. Department of Agriculture, 6p. 

Filip, G.M. 1986. Symptom expression of root diseased trees in mixed conifer stands in 

central Washington. Western Journal of Applied Forestry 1:46-48. 

Filip, G. M.; Goheen, D. J.; Johnson D.W. 1989. Precommercial thinning in a ponderosa 

pine stand affected by Armillaria root disease: 20 years of growth and mortality in 

central Oregon. Western Journal of Applied Forestry 4:58-59. 

Filip, G. M.; Fitzgerald, S. A.; Ganio, L. 1999. Precommercial thinning in a ponderosa 

pine stand affected by Armillaria root disease: 30 years of growth and mortality. 

Western Journal of Applied Forestry 14:144-148. 

40 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Fowells, H.A. 1946. Forest tree seed collection zones of California. Res. Note 51. Berkeley 

CA: California Forest and Range Experiment Station, Forest Service, U.S. Department 

of Agriculture. 

Fowells, H.A.; Schubert, G. 1956. Seed crops of forest trees in the pine region of 

California. Tech. Bulletin 1150. Washington D.C.: U.S. Department of Agriculture; 

48p. 

Gordon, D.T. 1962. Growth response of eastside pine poles to removal of low vegetation. 

Res. Note 209. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, 

Forest Service, U.S. Department of Agriculture; 3p. 

Hall, F.C. 1973. Plant communities of the Blue Mountains of eastern Oregon and 

southeastern Washington. Region 6 Area Guide 3-1. Portland OR: Forest Service, U.S. 

Department of Agriculture; 62p. 

Hall, F.C. 1976. Fire and vegetation in the Blue Mountains: Implications for land 

managers. Tall Timbers Fire Ecology Conference Proceedings. 15:155-170. 

Hall, F.C. 1983. Growth basal area: A field guide for appraising forest site potential for 

stockability. Canadian Journal of Forest Research. 13:70-77. 

Hann, D.W. 1981. Development of an even and uneven-aged ponderosa pine/Arizona 

fescue stand simulator. Gen. Tech. Report RP-267. Ogden, UT: Intermountain Forest 

and Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Hann, D.W. 2003. ORGANON User’s Manual Edition 7.0. College of Forestry, Oregon 

State University, Corvallis; 135 p. 

Hann, D.W.; Scrivani, J.A. 1987. Dominant-height-growth and site-index equations for 

Douglas-fir and ponderosa pine in southwest Oregon. Research Bulletin 56. 

Corvallis, OR: College of Forestry, Forest Research Laboratory, Oregon State 

University. 

Harris, G.R.; Covington, W.W. 1982. The effect of a prescribed fire on nutrient 

concentration and standing crop of understory vegetation in ponderosa pine. 

Canadian Journal of Forest Research 501-507. 

Hawksworth, F.G.; Wiens, D. 1996. Dwarf mistletoes: Biology, pathology, and 

systematics. Agricultural Handbook 709. Washington, D.C.: Forest Service, U.S. 

Department of Agriculture. 410p. 

Helms, J.A.; Hipkin, C. 1986. Effects of soil compaction on tree volume in a California 

ponderosa pine plantation. Western Journal of Applied Forestry 1:121-124. 

Helms, J.A.; Hipkin, C.; Alexander, E.B. 1986. Effects of soil compaction on height 

growth of a California ponderosa pine plantation. Western Journal of Applied 

Forestry 1:104-107. 

Heidmann, L.J. 1988. Regeneration strategies for ponderosa pine. In: Baumgartner, D. and 

Lotan, J.E., editors. Proceedings, Ponderosa Pine The Species and Its Management. 

Symposium 1987, Sept. 29–Oct. 1, Spokane WA. Washington St. Univ. Cooperative 

Extension; 227-233. 

Hobbs, S.D.; Tesch, S.D.; Owston, P.W.; Stewart, R.E.; Tappeiner, J.C.; Wells, G.E. 1992. 

Reforestation practices in southwestern Oregon and northern California. Forest 

Research Laboratory, Oregon State University, Corvallis OR. 

Jenkinson J.L. 1980. Improving plantation establishment by optimizing root growth 

capacity and planting time of western yellow pine. Res. Paper PSW-154. Berkeley, 

CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. 

Department of Agriculture; 22 p. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 41 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Keen, F.P. 1936. Relative susceptibility of ponderosa pine to bark-beetle attack. Journal 

of Forestry 34:919-927. 

Keen, F.P. 1943. Ponderosa pine tree classes redefined. Journal of Forestry 41:854-848. 

Keen, F.P. 1958. Cone and seed insects of western forests. Technical Bulletin 1169. 

Washington D.C.: Forest Service, U.S. Department of Agriculture. 

Landis, Thomas D.; Tinus, Richard W.; McDonald, Stephen E.; Barnett, James P. 1989. The 

Container Tree Nursery Manual, Volume Four, Seedling Nutrition and Irrigation. 

Agriculture Handbook 674. Washington D.C.: Forest Service, U.S. Department of 

Agriculture. 

Landis, Thomas D.; Tinus, Richard W.; McDonald, Stephen E.; Barnett, James P. 1990a. 

The Container Tree Nursery Manual, Volume Two, Containers and Growing 

Media. Agriculture Handbook 674. Washington D.C.: Forest Service, U.S. Department 

of Agriculture. 

Landis, Thomas D.; Tinus, Richard W.; McDonald, Stephen E.; Barnett, James P. 1990b. 

The Container Tree Nursery Manual, Volume Five, Nursery Pests and 

Mycorrhizae. Agriculture Handbook 674. Washington D.C.: Forest Service, U.S. 

Department of Agriculture. 

Landis, Thomas D.; Tinus, Richard W.; McDonald, Stephen E.; Barnett, James P. 1992. The 

Container Tree Nursery Manual, Volume Three, Atmospheric Environment. 

Agriculture Handbook 674. Washington D.C.: Forest Service, U.S. Department of 

Agriculture. 

Landis, Thomas D.; Tinus, Richard W.; McDonald, Stephen E.; Barnett, James P. 1995. The 

Container Tree Nursery Manual, Volume One, Nursery Planning, Development, 

and Management. Agriculture Handbook 674. Washington D.C.: Forest Service, U.S. 

Department of Agriculture. 

Lanini W. T.; Radosevich, S.R. 1986. Response of three conifer species to site preparation 

and shrub control. Forest Science 32:61-77. 

Latham, P.; Tappeiner, J.C. 2002. Response of old-growth conifers to reduction in stand 

density in western Oregon forests. Tree Physiology 22:137-146. 

Lilieholm, R.J.; Davis, L.S.; Heald, R.C.; Holman, S.P. 1990. Effects of single-tree selection 

harvests on stand structure, species composition, and understory tree growth in a 

Sierra mixed conifer forest. Western Journal of Applied Forestry 4:43-47. 

Lynch, Donald W. 1958. Effects of stocking on site measurement and yield of secondgrowth ponderosa pine in the inland empire. Res. Paper No. 56. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 36 p. 

McDonald P.M. 1976a. Forest regeneration and seedling growth from five major cutting 

methods in north-central California. Res. Paper PSW-RP-115. Berkeley, CA: Pacific 

Southwest Forest and Range Experiment Station. Forest Service, U.S. Department of 

Agriculture. 

McDonald P.M. 1976b. Inhibiting effect of ponderosa pine seed trees on seedling growth. 

Journal of Forestry 74:220-224. 

McDonald P.M. 1976c. Shelterwood cutting in a young-growth mixed conifer stands in 

north-central California. Res. Paper PSW-RP-117. Berkeley, CA: Pacific Southwest 

Forest and Range Experiment Station. Forest Service, U.S. Department of Agriculture. 

McDonald, P.M.; Abbott, C.S. 1994. Seed fall regeneration and seedling development in 

group selection openings. Res. Paper PSW-220. Berkeley, CA: Pacific Southwest 

Forest and Range Experiment Station. Forest Service, U.S. Department of Agriculture. 

42 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

McDonald, Philip M.; Oliver, William W. 1984. Woody shrubs retard growth of 

ponderosa pine seedlings and saplings. In Proc. Fifth Ann. For. Vegetation 

Management Conf., Nov. 2-3, 1983, Sacramento, CA. pp 65-89. 

McDonald, P.M.; Skinner, C.; Fiddler, G.O. 1992. Ponderosa pine needle length: an early 

indicator of release treatment effectiveness. Canadian Journal of Forest Research 

22:761-764. 

McDowell, N.; Brooks, J.R.; Fitzgerald, S.A.; Bond, B.J. 2003. Carbon isotope 

discrimination and growth response of old Pinus ponderosa trees to stand density 

reduction. Plant Cell and Environment 26: 631-644. 

McNeil, R.C.; Zobel, D.B. 1980. Vegetation and fire history of ponderosa pine-white fir 

forest in Crater Lake National Park. Northwest Science 54:30-46. 

Megahan, W.F.; Steele, R. 1987. An approach for predicting snow damage to ponderosa 

pine plantations. Forest Science 33:485-503. 

Meyer, W.H. 1934. Growth in selectively cut ponderosa pine forests of the Pacific 

Northwest. Tech. Bulletin 407. Washington D.C.: U.S. Department of Agriculture; 64 p. 

Meyer, W.H. 1938. Yield of even-age stands of ponderosa pine. Tech. Bulletin 630. 

Washington D.C.: U.S. Department of Agriculture; 59 p. 

Miller, J.M.; Keen, F.P. 1960. Biology and control of the western Pine beetle. 

Miscellaneous Publication 800. Washington D.C.: Forest Service, U.S. Department of 

Agriculture. 

Muelder D.W.; Hall, D.O.; Skolman, R.G. 1963. Root growth and first-year survival of 

Pinus ponderosa seedlings in second-growth stands in the Sierra Nevada. 

Publication 32. University of California Forestry and Forest Products. 

Mutch, L. S.; Parsons, D. 1998. Mixed conifer forest mortality and establishment before 

and after prescribed fire in Sequoia National Park, California. Forest Science 

44:341-355. 

O'Hara, K.L.; Gersonde, R.F. 2004. Stocking control concepts in uneven-aged silviculture. 

Forestry Chronicle 77:131-143. 

O'Hara, K.L. 1996. Dynamics and stocking-level relationships of multi-aged ponderosa 

pine stands. Forest Science Monograph 33. 

Oliver, W.W. 1972. Height intercept for estimating site index in young ponderosa pine 

plantations and natural stands. Res. Paper PSW-276. Berkeley, CA: Pacific 

Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture. 

Oliver, W.W. 1984. Brush reduces growth of thinned ponderosa pine in northern 

California. Res. Paper PSW-RP-172. Berkeley, CA: Pacific Southwest Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Oliver W.W. 1990. Spacing and shrub competition influence 20-year development of 

planted ponderosa pine. Western Journal of Applied Forestry 5:79-82. 

Oliver W.W. 1995. Is self-thinning in ponderosa pine ruled by Dendroctonous bark 

beetles? Lane G. Eskew, editor. Forest Health Through Silviculture; Mescalero, NM. 

Gen Tech. Report. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, 

U.S. Department of Agriculture. 

Oliver, W.W. 1997. Twenty-five-year growth and mortality of planted ponderosa pine 

repeatedly thinned to different stand densities in northern California. Western 

Journal of Applied Forestry 12:122-130. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 43 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Oliver, W.W.; Powers, R.F. 1978. Growth models for ponderosa pine I. Yield of 

unthinned plantations in northern California. Res. Paper PSW-128. Berkeley, CA: 

Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. 

Department of Agriculture. 

Oliver, W.W.; Powers, R.F.; Fiske, J.N. 1983. Pacific Ponderosa Pine. In Burns, Russell M., 

technical. compiler. Silvicultural Systems for the Major Forest Types of the United 

States. Agriculture. Handbook 445. Washington D.C.: U.S. Department of Agriculture. 

pp 48-52. 

Oliver, W.W.; Ryker, R.A. 1990. Pinus ponderosa Dougl. Ex Laws. In Burns, Russell M.; 

Honkala, Barbara H., technical coordinators. Silvics of North America, Volume 1. 

Conifers. Agriculture Handbook 654. Washington D.C.: U.S. Department of 

Agriculture. pp 413-424. 

Olson, C.M.; Helms, J.A. 1996. Forest Growth and stand structure at Blodgett Forest 

Research Station. In. Sierra Nevada Ecosystem Research Project: Final Report to 

Congress. Centers for Water and Wildland Resources, University of California, Davis, 

pp. 681-632. 

Parsons, D.J.; DeBenedetti, S. H. 1979. Impact of fire suppression on a mixed-conifer 

forest. Forest Ecology and Management 2:23-33. 

Pearson G.A. 1923. Natural reproduction of western yellow pine in the southwest. Tech. 

Bulletin 1105. Washington D.C.: U.S. Department of Agriculture. 

Peterson, W. C.; Hibbs, D.E. 1989. Adjusting stand density management guides for stands 

with low stocking potential. Western Journal of Applied Forestry 4:62-65. 

Powers R.F.; Jackson, G. 1978. Ponderosa pine response to fertilizer: influence of brush 

removal and soil type. Res. Paper PSW-RP-132. Berkeley, CA: Pacific Southwest 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Powers, R.F.; Ferrell, G.T. 1996. Moisture, nutrient, and insect constraints on plantation 

growth: the "Garden of Eden" study. New Zealand Journal of Forestry Science 

26:126-144. 

Powers, R.F.; Oliver, W.W. 1978. Site Classification of ponderosa pine stands under 

stocking control. Res. Paper PSW-RP-128. Berkeley, CA: Pacific Southwest Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Powers, R.F.; Ritchie, M.W.; Ticknor, L.O. 1989. SYSTUM-1: simulating the growth of 

young conifers under management. In Proc. Fifth Ann. For. Vegetation Management 

Conf., Nov. 1-3, 1988, Eureka, CA. 101-115. 

Powers, R.F.; Webster, S.R.; Cochran, P.H. 1988. Estimating response of ponderosa pine to 

fertilizer. Gen. Tech. Report INT-243. Ogden, UT: Intermountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture. 

Powers, R.F.; Young, D.H.; Fiddler, G.O.; Spear, T.H. 2005. Balderston plantation 

revisited: A tale of two sites 25 years after early treatments. In: Proc. 25th Ann. For. 

Vegetation Management Conf. U.C. Cooperative Extension. 

Riegel, G.M.; Miller, R.F.; Krueger, W.C. 1992. Competition for resources between 

understory vegetation and overstory Pinus ponderosa in northeastern Oregon. 

Ecological Applications 2:71-85. 

Riegel, G.M.; Miller, R.F.; Krueger, W.C. 1995. The effects of aboveground and 

belowground competition on understory species composition in a Pinus ponderosa 

forest. Forest Science 41:864-889. 

Reineke, L.H. 1933. Perfecting a stand-density index for even-aged forests. Journal of 

Agricultural Research 46:627-638. 

44 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Ritchie, M.W.; Powers, R.F. 1993. User’s guide for SYSTUM-1 (Version 2.0): A simulator 

of growth trends in young stands under management in California and Oregon. 

Gen. Tech. Report PSW-GTR-147. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; 45 p. 

Robson, Thomas F.; Standiford, Richard B., editors. 1983. Management of the Eastside 

Pine Type in Northeastern California – Proceedings of a Symposium. SAF 83-06, 

Northern California Society of American Foresters. 

Ronco F.; Ready, Kenneth L. 1983. Southwestern Ponderosa Pine. In Burns, Russell M. 

technical compiler. Silvicultural Systems for the Major Forest Types of the United 

States. Agriculture Handbook 445. Washington D.C.: U.S. Department of Agriculture. 

70-72. 

Roy, Douglas F. 1955. Oregon limits of California tree seed collection zones. Res. Note 

No. 93. Berkeley CA: California Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture; 3p. 

Roy, Douglas F. 1983. Natural regeneration. In Robson, T.F.; Standiford, R.B. (eds.) 

Management of the Eastside Pine Type in Northeastern California. Proceedings of a 

Symposium. SAF 83-06, Northern California Society of American Foresters; pp 87-102. 

Ryker, Russell A.; Losensky, Jack. 1983. Ponderosa Pine and Rocky Mountain Douglasfir. In Burns, Russell M. technical compiler. Silvicultural Systems for the Major Forest 

Types of the United States. Agriculture Handbook 445. Washington D.C.: U.S. 

Department of Agriculture; 53-55. 

Scharpf, R.F.; Bega, R.V. 1981. Elytroderma disease reduces growth and vigor and, 

increases mortality of Jeffrey pines at Lake Tahoe Basin. Res. Paper PSW-155. 

Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture. 

Schmid, J.M.; Mata, S.A.; Obedzinski, R.A. 1994. Hazard rating ponderosa pine stands for 

mountain pine beetles in the Black Hills. Res. Note RM-529. Fort Collins, CO: 

Forest Service, U.S. Department of Agriculture; 4p. 

Schubert G.H.; Adams, R.S. 1971. Reforestation practices for conifers in California. 

California State Board of Forestry; 359p. 

Schubert, G.H. 1974. Silviculture of southwestern ponderosa pine: the status of our 

knowledge. Res. Paper. RM-123. Fort Collins, CO: Rocky Mountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 71p. 

SERA (Syracuse Environmental Research Associates, Inc.). 1997. Selected Commercial 

Formulations of Hexazinone – Human Health and Ecological Risk Assessment. 

Final Draft. SERA TR 95-21-04-01b. March 4, 1997. Fayetteville, New York; 161 p. 

SERA (Syracuse Environmental Research Associates, Inc.). 1998a. Sulfometuron Methyl 

(OUST) – Final Report. SERA TR 98-21-09-02d. September 11, 1998. Fayetteville, 

New York; 211 p. 

SERA (Syracuse Environmental Research Associates, Inc.). 1998b. Imazapyr (Arsenal, 

Chopper, and Stalker Formulations) – Final Report. SERA TR 98-21-14-01b. May 

6, 1999. Fayetteville, New York; 202 p. 

SERA (Syracuse Environmental Research Associates, Inc.). 2003a. Glyphosate – Human 

Health and Ecological Risk Assessment – Final Report. SERA TR 02-43-09-04a. 

March 1, 2003. Fayetteville, New York; 281 p. 

SERA (Syracuse Environmental Research Associates, Inc.). 2003b. Triclopyr – Revised 

Human Health and Ecological Risk Assessment – Final Report. SERA TR 02-43-13-

03b. March 15, 2003. Fayetteville, New York; 264 p. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 45 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Shainsky, L.J.; Radosevich, S.R. 1986. Growth and water relationships of Pinus ponderosa 

seedlings in competetive regimes with Arctostaphylos patula seedlings. Journal of 

Applied Ecology 23:957-966. 

Shearer, Raymond C.; Schmidt, Wyman C. 1970. Natural regeneration in ponderosa pine 

forests of western Montana. Res. Paper INT-86. Ogden, UT: Intermountain Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 19p. 

Shearer, R.C.; Schmidt. W.C. 1971. Ponderosa pine cone and seed losses. Journal of 

Forestry 69:370-372. 

Smith, G.W. 1982. Habitat use by porcupines in a ponderosa pine/Douglas-fir forest in 

northeastern Oregon. Northwest Science 56:236-24 

Smith, R.S. Jr.; Bega, R.B. 1966. Root disease control by fumigation in forest nurseries. 

Plant Disease Reporter, 48. 

Stone, Edward C. 1955. Poor survival and the physiological condition of planting stock. 

Forest Science. 1:90-94. 

Stone, Edward C.; Benseler, Rolf W. 1962. Planting ponderosa pine in the California pine 

region. Journal of Forestry 60:462-466. 

Stone, Edward C.; Schubert, Gilbert H. 1959a. Root regeneration by ponderosa pine lifted 

at different times of the year. Forest Science. 5:322-332. 

Stone, Edward C.; Schubert, Gilbert H. 1959b. The physiological condition of ponderosa 

pine (Pinus ponderosa Laws.) planting stock as it affects survival after cold storage. 

Journal of Forestry 57:837-841. 

Stone, Edward C.; Schubert, Gilbert H.; Benseler, Rolf W.; Baron, Frank J.; Krugman, 

Stanley L. 1963. Variation in the root regeneration potentials of ponderosa pine 

from four California nurseries. Forest Science 9:217-225. 

Storm, G.L. and C.H. Halvorson. 1967. Effect of injury by porcupine on radial growth of 

ponderosa pine. Journal of Forestry 65:740-743. 

Stoszek, K.J. 1973. Damage to ponderosa pine plantations by the western pine-shoot 

borer. Journal of Forestry 71:701-705. 

Tappeiner J.C.; Radosevich S.R. 1982. Effect of bearmat (Chamaebatia foliosa) on soil 

moisture and ponderosa pine (Pinus ponderosa) growth. Weed Science 30:98-101. 

Tinus, Richard W.; McDonald, Stephen E. 1979. How to grow tree seedlings in containers 

in greenhouses. Gen. Tech. Report RM-60. Fort Collins, CO: Rocky Mountain Forest 

and Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Tinus, Richard W.; Stein, William I.; Balmer, William E. (eds.). 1974. Proceedings of the 

North American. Containerized Forest Tree Seedling Symposium. August 26-29, 

1974, Denver, Colorado. Great Plains Agricultural Council Publication No. 68; 444 pp. 

Verdyla, D.; Fischer. R.F. 1989. Ponderosa pine habitat types as indicators of site quality 

in the Dixie Natiuonal Forest, Utah. Western Journal of Applied Forestry. 4:52-54. 

Walker, R.F. 1999a. Artificial regeneration of Jeffrey pine in the Sierra Nevada: Growth, 

nutrition, and water relations as influenced by controlled release fertilization and 

solar protection. Journal of Sustainable Forestry 9:23-37. 

Walker R.F. 2002. Response of Jeffrey pine on a surface mine site to fertilizer and lime. 

Restoration Ecology 10:204-212. 

Walstad, John D.; Kuch, Peter J. (eds.). 1987. Forest Vegetation Management for Conifer 

Production. John Wiley & Sons, NY, 480 p. 

46 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Key Silvicultural Information for Ponderosa Pine—Fiske and Tappeiner 

Weaver, H. 1959. Ecological changes in the ponderosa pine forest of the Warm Springs 

Indian Reservation. Journal of Forestry 57:15-20. 

Weaver, H. 1961. Ecological changes in the ponderosa pine forest of Cedar Valley in 

southern Washington. Ecology 42:416-420. 

Wensel, L.C.; Koehler, J.R. 1986. A tree growth projection system for northern California 

coniferous forests. Res. Note 12. Northern California Growth and Yield Cooperative. 

University of California, Berkeley; 30 p. 

White D.E.; Newton, M. 1989. Competitive interactions of white leaf manzanita, herbs, 

Douglas-fir and ponderosa pine in southwestern Oregon. Canadian Journal of Forest 

Research 19:232-238. 

White, E.W.; Thompson, W.; Gartner, F.R. 1973. Heat effect on nutrient release from soils 

under ponderosa pine. Journal of Range Management 26:22-24. 

Zwieniecki, M.A.; Newton, M. 1994. Root distribution of 12-year-old forests at rocky sites 

in southwestern Oregon. Canadian Journal of Forest Research 24:1791-1796. 

Zwieniecki, M. A.; Newton, M. 1995. Roots growing in rock fissures: Their morphological 

adaptation. Plant and Soil 172:181-187. 

Zwieniecki, M.A.; Newton, M. 1996. Seasonal patterns of water depletion from soil/rock 

by selected ecosystems in a Mediterranean climate. Canadian Journal of Forest 

Research 26:1346-1352. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 47 

Silvicultural Systems for Managing 

Ponderosa Pine1

Andrew Youngblood2

Abstract 

Silviculturists have primarily relied on classical even-aged silvicultural systems (the planned 

series of treatments for tending, harvesting, and re-establishing a stand) for ponderosa pine,

with uneven-aged systems used to a lesser degree. Current management practices involve

greater innovation because of conflicting management objectives. Silvicultural systems used

in the foreseeable future will likely meld traditional systems with greater reliance on variation 

across the landscape because of differing values and desired outputs. Significant changes in 

the management of ponderosa pine are reviewed; issues that likely will affect the future 

management of ponderosa pine systems are listed; and critical gaps in our understanding of

ponderosa pine silviculture that may affect our management in the near term are identified.

Introduction 

Ponderosa pine (Pinus ponderosa P. & C. Lawson) is one of the most widely

distributed pines in western North America (Oliver and Ryker 1990). It occurs from 

southern British Columbia in Canada into Mexico, and from the Pacific Coast along 

the California-Oregon border as far east as western Nebraska and Oklahoma. Two

subspecies are recognized; Pacific ponderosa pine (var. ponderosa) ranges along the

flanks of the Cascade and Sierra Nevada Ranges as far south as Riverside County in

southern California, while Rocky Mountain ponderosa pine (var. scopulorum

Engelm.) occurs in Idaho, Montana, Utah, and east of the continental divide (USDA

2004).

Ponderosa pine is a major component of three forest cover types (Eyre 1980). 

The Interior Ponderosa Pine cover type (Society of American Foresters Type 237),

the most widespread pine type in the western United States, is composed of pure or

mixed stands east of the Cascade-Sierra Nevada crest in northern California, east of

the Cascade Range crest in Oregon and Washington, and eastward into the Plains 

States: Pacific Ponderosa Pine-Douglas-fir cover type (Society of American Foresters 

Type 244) is composed of mixed stands on eastern slopes of the Coast Range and 

western slopes of the Cascades in Oregon, extending southward through the Klamath 

Mountains into northern California. The Pacific Ponderosa Pine Type (Society of 

American Foresters Type 245) is essentially pure stands of ponderosa pine in the 

Klamath Mountains of Oregon and Washington, extending southward along the 

Sierra Nevada into central California. Ponderosa pine also occurs as a minor 

component in at least 23 other cover types. 

Of all the North American forest types, ponderosa pine forests offer the greatest

opportunity for meeting multiple objectives such as water, minerals, timber, forage, 

1

 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Research Forester, USDA Forest Service, PNW Research Station, 1401 Gekeler Lane, LaGrande, OR 

97850 (e-mail: ayoungblood@fs.fed.us) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 49 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

wildlife habitat, recreation, subsistence or spiritual purposes, firewood, homesites,

and scenic beauty (Morgan 1988). Given that ponderosa occurs across diverse 

landscapes with broad ecological amplitude, and the relative ease in accessibility at

lower elevations has led to greater intensity of management activities for multiple 

objectives compared to cover types occurring at higher elevations, it is not surprising

that numerous silvicultural systems for stand management on public lands have been

applied. In this paper, the traditional or conventional silvicultural systems 

recommended for managing ponderosa pine on public lands are summarized, recent 

changes in ponderosa pine silviculture and the underlying causes for the change are 

examined, future management actions and their effect on ponderosa pine sites are 

hypothesized, and the critical gaps in our understanding of ponderosa pine

silviculture are identified. 

Traditional Silvicultural Systems 

Graham and Jain (2004) traced the role of silviculturists from the late 1800s 

with the transfer of public lands into homesteads, through the rapid expansion

westward of railroads, the creation of national forests, and the advent of timber 

management and fire suppression for the growth and protection of cities and town 

during in the late 1800s and early 1900s, into the era of multiple use beginning in the 

1960s. Ponderosa pine stands figured prominently in these events because they were

relatively easy to access and they yielded high quality timber. With passage of the 

National Forest Management Act of 1976, silvicultural systems that emphasized

multiple values of ponderosa pine stand became increasingly important. 

Traditional or conventional silvicultural systems (the planned series of

treatments for tending, harvesting, and re-establishing a stand) used for managing 

ponderosa pine stands include clearcutting, seed tree, shelterwood, single tree 

selection, and group selection. These systems, named after the regeneration method, 

are fully defined in Helms (1998). Clearcutting is the method of cutting essentially all

existing trees, producing a fully exposed microsite for the development of a new age 

class, with regeneration from either natural seeding, direct seeding, or planted 

seedlings. A variant is overstory removal, when the presence of advance regeneration 

is sufficient to warrant no additional action other than the complete harvesting of the 

overstory. The seed tree method is the cutting of all trees except for a limited number

of widely dispersed trees retained for seed production. The shelterwood method is the 

cutting of most trees, leaving only those needed to produce sufficient shade or 

insulation from temperature extremes to produce a new age class in a moderated

microenvironment. Variants are based on the distribution of the residual trees left for 

shading. Selection methods involve the removal of some trees in all size classes 

either singly (single tree selection) or in groups (group selection), with regeneration 

occurring in the resulting gaps and continued growth of all remaining trees.

Clearcutting, seed tree, and shelterwood methods result in the establishment of evenaged stands while selection methods maintain uneven-aged stands. The coppice

method may be used for species that sprout from the stump or produce root suckers, 

thus is not applicable for managing ponderosa pine.

Ponderosa pine stands have been managed to provide a wide range of outputs 

and values by using these silvicultural systems, including timber, habitat for large

game and avian species, protection of wildland resources from damaging insects,

disease, or wildfire, quality forage for domestic ungulates, and water. Traditional or

50 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

conventional silvicultural systems commonly recommended for managing ponderosa 

pine are summarized (table 1) for four regions: 1) northern Rocky Mountains, 

including western Montana, northern Idaho, and extreme northeastern Washington; 

2) Pacific Northwest, including eastside forests of Washington and Oregon; 3)

westside California, including southwest Oregon; and 4) eastside California. 

In general, the even-aged silvicultural system based on clearcutting was 

frequently recommended for use across all four regions through the early 1980s. This 

recommendation likely was in response to a general preference for managing 

ponderosa pine stands with a primary emphasis on timber production that featured 

conversion of old stands to more vigorously growing young stands. Other even-aged

systems, including seed tree and shelterwood methods, were clearly secondary in

preference. A special variant of even-aged management practices in the Blue 

Mountains of northeastern Oregon and southeastern Washington was either a 

complete or partial overstory removal of old-growth ponderosa pine followed by

management of the advance regeneration that developed after decades of fire 

exclusion or suppression. This practice had at least three underpinnings: 1) the

overstory ponderosa pine was growing slowly and had high susceptibility to bark

beetles; 2) the overstory ponderosa pine had very high value and revenue that was 

generated could be used for other land management projects within the timber sale 

area; and 3) management of the advanced regeneration avoided the high cost of tree 

planting, it maintained a green, forested setting thus avoided the visual impacts 

associated with clearcutting, and it capitalized on the initial growth of the understory 

trees (Powell 1994). Selection systems were restricted in application to special areas

such as high visibility stands surrounding recreation areas. 

Clearcutting and other even-aged methods continued to be the preferred means 

of managing ponderosa pine stands into the early 1990s, except in the Blue 

Mountains where overstory removals prevailed. Clearcutting and planting was 

recommended when timber management was the primary objective because it 

required less sale administration, resulted in lower costs of wood production, and

probably had higher wood productivity because of fewer difficulties in controlling 

tree density compared to uneven-aged management (Helms and Lotan 1988). At the 

same time, uneven-aged systems became increasingly popular in the northern Rocky

Mountains and the Pacific Northwest for protecting visuals, for managing recreation

sites, and for providing wildlife habitat. The advisability of uneven-aged systems for 

ponderosa pine remained in question throughout California. 

More recently, uneven-aged silvicultural systems for managing ponderosa pine 

were frequently suggested, with emphasis on group selection. A further refinement is

termed “free selection”, described as the combination of group and single tree

selection systems with reserve trees left in all structural stages, and recommended for 

creating clumpy and irregular stand structure that is preferred for species such as the 

northern goshawk (Accipiter gentiles) (Graham and Jain 2004). Even-aged systems, 

especially seed tree or shelterwood systems with retention of some overstory into the 

next rotation, also were recommended because they ensured some high structure, had

greater visual appeal, and accommodated the needs of more cavity-dependent avian 

species. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 51 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

Table 1—Recommended silvicultural systems for ponderosa pine forests in the 

northern Rocky Mountains, Pacific Northwest, eastside California, and westside 

California.

Region Recommended silvicultural system Source 

Northern Rocky Mountains Clearcutting with planting on dry sites, with 

limited use of seed tree or shelterwood 

methods; clearcutting with planting on 

moist sites, with limited use of group

selection or seed tree methods 

Foiles and 

Curtis 1973

Pacific Northwest Clearcutting, limited use of shelterwood

method; selection systems used for special

areas 

Barrett 1977 

Northern Rocky Mountains Clearcutting or shelterwood methods; 

selection systems used for special areas 

Adams 1980

Pacific Northwest Overstory removal followed by shelterwood 

or clearcutting method 

Scott 1980 

Eastside California Clearcutting method with planting Helms 1980

Westside California Clearcutting or seed tree method, and group

selection

Helms 1980 

Northern Rocky Mountains Clearcutting and planting on sites with

infections of dwarf mistletoe; single tree or

group selection on dry sites where natural 

regeneration is difficult to obtain; group

selection or shelterwood on more moist 

sites 

Ryker and 

Losensky 1983 

Pacific Northwest Both even-aged and uneven-aged systems; 

uneven-aged systems sometimes preferred

for visuals, in recreations, and for wildlife 

habitat 

Barrett and 

others 1983

Westside California Clearcutting, seed tree, or shelterwood

methods; uneven-aged systems are 

impractical 

Oliver and 

others 1983

Westside California Seed tree, shelterwood, and group selection 

methods 

Minore and 

Kingsley 1983 

Northern Rocky Mountains Group selection, seed tree, or shelterwood 

systems with increasing emphasis on greentree retention

Adams 1994

Pacific Northwest Multiple-entry management using either 

long-rotation even-aged systems or unevenaged system; some type of group selection 

likely to be most successful 

Tesch 1994

Eastside California Group selection with regeneration best

achieved by planting 

Helms 1994 

Westside California Clearcutting or seed-tree well-suited where 

wood production is the primary objective; 

group selection preferable to single-tree 

selection because of overstory competition 

constraints 

Helms 1994 

52 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

Silvicultural Systems Currently In Use

Currently, the full array of silvicultural systems, ranging from clearcutting to 

single and group selection, are found applied to ponderosa pine management on 

public lands from the northern Rocky Mountains to California. All the variations

applied in specific situations probably are adequately defined and described as

deviations within a more formally defined general system. 

Perhaps the greatest change in management of ponderosa pine is the prominence 

of intermediate cuttings which have no expectation or objective of natural 

regeneration, especially improvement cuttings designed to remove less desirable trees

in order to meet stand composition or vertical structure objectives. The emphasis of

improvement cutting is on improving the stand structure rather than removal of any

particular size stem. Many density-reduction treatments on dry sites in the Blue 

Mountains are improvement cuttings rather than strict thinning treatments because 

they have a strong species composition and tree quality component to them. 

At least six recent social, political, and legal changes may appreciably influence 

the application of silvicultural prescriptions designed to implement silvicultural

systems for managing ponderosa pine ecosystems: 

• The USDA Forest Service adopted in 1992 a new policy limiting the use of 

clearcutting on national forests. The clearcutting regeneration method

currently may be used only under specific circumstances such as to maintain 

habitat for threatened, endangered, or sensitive species; to enhance wildlife 

habitat; to rehabilitate lands adversely impacted by natural disturbances, or to

rehabilitate lands due to past management practices. 

• The Regional Forester amended the forest plans of National Forests in 

Oregon and Washington east of the crest of the Cascade Range in Oregon 

and Washington to include three “Eastside Screens”, one of which

established a policy restricting the harvesting of trees greater than 53

centimeters (21 inches) in diameter at breast height for areas where stand 

structural characteristics of late and old successional stages were found to be 

deficient. This policy currently protects the larger and presumably older 

ponderosa pine, but it also limits management activities designed to reduce, 

for example, the spread of western dwarf mistletoe (Arceuthobium

campylopodum Engelm.), western pine beetle (Dendroctonus brevicomis

LeConte), or mountain pine beetle (D. ponderosae Hopk.). 

• Interim Riparian Habitat Conservation Areas on federal lands, established

under PACFISH (USDA Forest Service and USDI Bureau of Land

Management 1994) and Inland Native Fish (USDA Forest Service 1995),

established a buffer on either side of the active stream channel of fishbearing streams, within which timber harvesting, including fuelwood cutting 

is prohibited except where silvicultural practices are needed to attain desired 

vegetation characteristics to meet riparian management objectives. 

• Across the four regions, forest density management— silvicultural activities 

designed to improve stand conditions by concentrating tree growth on fewer 

stems, reduce fire risk and improve forest health, encourage undergrowth 

vegetation and wildlife forage, and promote patch- and landscape-scale 

diversity— has shifted to include a primary focus on reducing the number of 

small-diameter trees. In the Pacific Northwest Region of the Forest Service,

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 53 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

the forest density management program of work has not kept pace with the 

programmed need, and the backlog continues to increase at about 200 square 

kilometers (50,000 acres) each year (Powell and others 2001). The policy

restricting the size of trees that are harvested also may already limit the 

amount of thinning in some ponderosa pine stands, especially stands that

have grown near or beyond the 53-centimeter diameter limit. Growth rates in

these stands may decline without thinning and the stands will become more

susceptible to bark beetle attack. 

• A new emphasis on fuel reduction to lessen the risk and severity of wildfire, 

especially in low elevation forests that have developed under natural 

disturbance regimes dominated by high frequency, low-severity fires, is

focusing much of the silvicultural activity within the wildland/urban 

interface. The wildland/urban interface in eastern Washington near Spokane, 

in central Oregon near Bend, and in eastern California in the Tahoe Basin are 

examples of rapidly expanding wildland/urban interface where fuel 

reductions treatments are being applied to protect people and homes. Fuel 

reduction activities commonly used in these areas, such as underburning or 

mowing, usually result in short term decreases in available browse that may

be important for wild ungulates during winter months. 

• Implementation of National Fire Plan objectives for reducing fuels is limited

because of challenges for the efficient disposal and/or utilization of 

significant quantities of small trees, especially the large numbers of lowvolume stems less than 10 centimeters (4 inches) in diameter. A recent

analysis of potential yields from fuel reduction projects in western states

indicated the potential size of the manufacturing infrastructure needed to 

process material from fuel reduction treatments is large (USDA Forest

Service 2003). For example, to process the merchantable volume from only

the western states where fire regimes have been significantly altered and 

there is a high risk of losing key ecosystem components in a wildfire (Class 

3), fuel reduction treatments will require the capacity of about 75 averagesized conventional sawmills for 30 years. Loss of processing mills, however,

has eliminated much of the infrastructure necessary to conduct these fuel

reduction treatments across much of the four regions. As a result, many fuel

reduction projects now require financial subsidies, resulting in smaller areas

being treated. Adding to the problem is the concern that many even-aged 

stands of ponderosa pine that were precommercially thinned are approaching

the target diameter (about 20 centimeters (8 inches)), previously projected for 

the first commercial thinning. The market and demand for these small trees 

do not currently exist. 

While these changes tend to directly affect management of ponderosa pine 

ecosystems, they also have an effect on the management of other forest types, 

especially those forest types at mid elevations that may contain small amounts of 

ponderosa pine. 

54 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

Issues Affecting Future Application of Silvicultural 

Prescriptions 

Given the broad array of silvicultural systems that can be use to manage

ponderosa pine, it is unlikely that silvicultural activities occurring in the near term

(the next 10 years) will not readily fit into the existing framework of planned 

treatments. What is likely to occur, however, is that increasingly complex resource

values associated with ponderosa pine ecosystems will require silviculturists to

consider a wider array of treatments within the context of ponderosa pine silviculture.

One common context for management is emulation of natural disturbance regimes. 

Silviculturists likely will be asked to design treatments that are closer analogues or

surrogates for a specific disturbance event. Manipulations of stand structure with the

objective of reducing fuels will become an increasingly common management action

on landscapes supporting ponderosa pine. Fuel reduction treatments involving either

mechanical manipulation of fuels, the use of fire, or a combination of the two can 

result in changes in the horizontal and vertical distribution of trees, their composition, 

and the number, size, and distribution of gaps or canopy openings. It is likely that 

federal, state, and private resources devoted to fire suppression will continue to battle 

wildfires, many of which will occur in ponderosa pine ecosystems. Density 

management activities will continue to the degree that funding allows projects to be 

implemented. If these activities continue to be generally restricted to small-diameter

trees only, it is likely that little effort will be devoted to creating complex stand

structures through spatial and structural diversity. At the same time, fuels will 

continue to accumulate across landscapes until treated or burned by wildfire. There is 

a possibility that our collective focus on reducing fire risk will overshadow the need

to consider other disturbance factors in the context of long-term forest health. For 

example, failing to address the increase in dwarf mistletoe in overstory trees now will

probably result in greater numbers of infected understory trees in the future. 

Similarly, failing to consider fully the risk of bark beetle outbreaks may limit our 

management options and lead to greater reliance on clearcutting in severely infested 

areas to restore healthy stands. 

What are the critical gaps in our understanding of ponderosa pine silviculture 

that may affect our management in the near-term and beyond? We must first

recognize that essentially all of our knowledge base for managing ponderosa pine

ecosystems is derived from studies conducted in even-aged stands. While existing 

work compares the various methods of regeneration after harvests, there are few if 

any empirical comparisons of even- and uneven-aged systems for the management of 

ponderosa pine across any full suite of treatments (Helms and Lotan 1988). 

Current amounts of old-growth ponderosa pine forest in the northern Rocky 

Mountains, the Pacific Northwest, and both eastside and westside California are 

estimated at 3 to 15 percent of pre-Euro-American settlement levels (Bolsinger and

Waddell 1993; Beardsley and others 1999). Increasingly, managers are attempting to 

restore the frequency and intensity of disturbances within existing old-growth stands

and thus the resulting periods of stability through various fuel reduction treatments 

designed to ultimately prevent stand-replacement fires (Conard and others 2001;

Oliver 2001). Land managers may lack the knowledge of how disturbance agents, 

both natural and human-caused, interact with each other and how they interact across

multiple scales to cause changes that may affect ecosystem integrity. Methods to 

protect remnant old-growth ponderosa pine stands and individual trees during 

implementation of prescribed fire as well as protocols to ensure variability in

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 55 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

thinning density to mimic the spatial distribution of stems in old-growth stands 

(Youngblood and others 2004) are largely unknown or unavailable. At the same time, 

little is known of methods for developing future old-growth structure in young 

uneven-aged or even-aged stands, and forecasting the productivity of these multiaged stands. Tools such as the Ponderosa Pine-Multi-aged Stocking Assessment

Model (O’Hara and others 2003) are promising steps toward this goal. 

Finally, it is clear that much of the recent changes in the management of 

ponderosa pine ecosystems on public lands are the result of changes in the way

society— either the individual living in the wildland/urban interface, the local

community, the special interest groups that represent user groups, or national and 

international organizations— values these forests. Perhaps our most challenging 

unknown is how the various components of society will value these forests in the

future. If processes were readily available for predicting the range of commodity and 

amenity values, and thus the structure, that society will desire in ponderosa pine 

forests of the future, management could begin to develop that structure today.

Regardless of these knowledge gaps, the role of the silviculturist in guiding the 

development of ponderosa pine stands will remain exciting. 

References 

Adams, D.L. 1980. The Northern Rocky Mountain Region. In: Barrett, J.W., editor. 

Regional silviculture of the United States. New York: John Wiley and Sons; 341-390. 

Adams, D.L. 1980. The Northern Rocky Mountain Region. In: Barrett, J.W., editor. 

Regional silviculture of the United States. New York: John Wiley and Sons; 387-440. 

Barrett, J.W. 1979. Silviculture of ponderosa pine in the Pacific Northwest: The state of 

knowledge. Gen. Tech. Rep. PNW-97. Portland, OR: Pacific Northwest Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 106 p. 

Barrett, J.W.; Martin, R.E.; Wood, D.C. 1983. Northwest ponderosa pine and associated 

species. In: Burns, R.M., technical compiler. Silvicultural systems for the major forest 

types of the United States. Agric. Handb. 445. Washington, DC: U.S. Department of

Agriculture; 16-18. 

Beardsley, D.; Bolsinger, C.; Warbington, R. 1999. Old-growth forests in the Sierra 

Nevada: by type in 1945 and 1993 and ownership in 1993. Res. Pap. PNW-RP-516. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of

Agriculture; 46 p.

Bolsinger, C.L.; Waddell, K.L. 1993. Area of old-growth forests in California, Oregon,

and Washington. Resource Bulletin PNW-RB-107. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 26 p. 

Conard, S.G.; Hartzell, T.; Hilbruner, M.W.; Zimmerman, G.T. 2001. Changing fuel

management strategies—the challenge of meeting new information and analysis 

needs. Intern. J. Wildland Fire 10: 267–275. 

Eyre, F.H., ed. 1980. Forest cover types of the United States and Canada. Washington, 

DC: Society of American Foresters; 148 p. 

Foiles, M.W.; Curtis, J.D. 1973. Regeneration of ponderosa pine in the northern Rocky 

Mountain-Intermountain Region. Res. Paper INT-145. Ogden, UT: Intermountain

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture;

44 p.

56 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

Graham, R.T.; Jain, T.B. 2004. Past, present, and future role of silviculture in forest 

management. In: Shepperd, W.D.; Eskew, L.G., compilers. Silviculture in special

places: proceedings of the national silviculture workshop; 2003 September 8-11; 

Granby, CO. Proceedings RMRS-P-34. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture; 1-14. 

Helms, J.A. 1980. The California region. In: Barrett, J.W., editor. Regional silviculture of

the United States. New York: John Wiley and Sons; 391-440. 

Helms, J.A. 1994. The California region. In: Barrett, J.W., editor. Regional silviculture of

the United States. New York: John Wiley and Sons; 441-487. 

Helms, J.A., ed. 1998. The dictionary of forestry. Bethesda, MD: Society of American 

foresters; 210 p. 

Helms, J.A.; Lotan, J.E. 1988. Selecting silvicultural systems for timber. In: Baumgartner,

D.M.; Lotan, J.E., editors. Proceedings of a symposium on ponderosa pine—the species

and its management. Pullman, WA: Washington State University; 221-225. 

Minore, D.; Kingsley, D. 1983. Mixed conifers of southwestern Oregon. In: Burns, R.M., 

technical coordinator. Silvicultural systems for the major forest types of the United

States. Agric. Handb. 445. Washington, DC: U.S. Department of Agriculture; 23-25. 

Morgan, P. 1988. Managing ponderosa pine forests for multiple objectives. In:

Baumgartner, D.M.; Lotan, J.E., editors. Proceedings of a symposium on ponderosa

pine—the species and its management. Pullman, WA: Washington State University; 

161-164. 

O’Hara, K.L; Valappil, N.I.; Nagel, L.M. 2003. Stocking control procedures for multiaged 

ponderosa pine stands in the inland northwest. Western Journal Applied Forestry

18(1): 5-14. 

Oliver, W.W.; Ryker, R.A. 1990. Pinus ponderosa. In: Burns, R.M.; Honkala, B.H., 

technical coordinators. Silvics of North America: Volume 1, Conifers. Agric. Handb.

654. Washington, DC: U.S. Department of Agriculture; 413-424.

Oliver, W.W.; Powers, R.F.; Fiske, J.N. 1983. Pacific ponderosa pine. In: Burns, R.M., 

technical coordinator. Silvicultural systems for the major forest types of the United

States. Agric. Handb. 445. Washington, DC: U.S. Department of Agriculture; 48-52. 

Oliver, W.W. 2001. Can we create and sustain late successional attributes in interior

ponderosa pine stands? Large-scale ecological research studies in northeastern

California. In: Vance, R.K.; Edminster, C.B.; Covington, W.W.; Blake, J.A., compilers. 

Proceedings of the ponderosa pine ecosystems restoration and conservation: steps 

toward stewardship; 2000 April 25–27; Flagstaff, AZ. RMRS-P-22. Ogden, UT: Rocky 

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 99–103. 

Powell, D.C. 1994. Effects of the 1980s western spruce budworm outbreak on the

Malheur National Forest in northeastern Oregon. Tech. Publ. R6-FI&D-TP-12-94.

Portland, OR: Pacific Northwest Region, Forest Service, U.S. Department of

Agriculture; 176 p. 

Powell, D.C.; Rockwell, V.A.; Townsey, J.J.; Booser, J.; Bulkin, S.P.; Martin, T.H.; 

Obedzinski, B.; Zensen, F. 2001. Forest density management: recent history and 

trends for the Pacific Northwest Region. Tech. Publ. R6-NR-TP-05-01. Portland, OR: 

Pacific Northwest Region, Forest Service, U.S. Department of Agriculture; 22 p. 

Ryker, R.A.; Losensky, J. 1983. Ponderosa pine and Rocky Mountain Douglas-fir. In: 

Burns, R.M., technical coordinator. Silvicultural systems for the major forest types of 

the United States. Agric. Handb. 445. Washington, DC: U.S. Department of Agriculture;

53-55.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 57 
Silvicultural Systems for Managing Ponderosa Pine—Youngblood 

Scott, D.R.M. 1980. The Pacific Northwest Region. In: Barrett, J.W., editor. Regional

silviculture of the United States. New York: John Wiley and Sons; 487-489. 

Tesch, S.D. 1994. The Pacific Northwest Region. In: Barrett, J.W., editor. Regional 

silviculture of the United States. New York: John Wiley and Sons; 499-558. 

U.S. Department of Agriculture, Forest Service. 1995. Inland native fish strategy. U.S.

Department of Agriculture, Forest Service and U.S. Department of Interior, Fish and 

Wildlife Service. Washington, DC; 17 p. plus appendices. 

U.S. Department of Agriculture, Forest Service; U.S. Department of Interior, Bureau of Land

Management. 1994. Environmental assessment for the implementation of interim

strategies for managing anadromous fish-producing watersheds in eastern Oregon 

and Washington, Idaho, and portions of California (PACFISH). Washington, DC; 

68 p

U.S. Department of Agriculture, Forest Service. 2003. A strategic assessment of forest 

biomass and fuel reduction treatments in western states. Washington, DC; 18 p.

U.S. Department of Agriculture, Natural Resources Conservation Service. 2004. The

PLANTS Database, Version 3.5 (http://plants.usda.gov). National Plant Data Center,

Baton Rouge, LA 70874-4490 USA.

Youngblood, A.; Max, T.; Coe, K. 2004. Stand structure in eastside old-growth ponderosa

pine forests of Oregon and northern California. Forest Ecology and Management

199: 191-217. 

58 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Multiaged Silviculture of Ponderosa Pine1

Kevin L. O’Hara2

Abstract 

Ponderosa pine (Pinus ponderosa P. & C. Lawson) is highly suitable for management using

multiaged systems. This suitability is primarily the result of a frequent, low severity 

disturbance regime, but also because it naturally occurs at low densities and has a long history 

of management to promote multiple age classes. Several different stocking control tools are

available for ponderosa pine including the q-factor, allocation of stand density index, and

allocation of growing space represented by leaf area. These methods are applicable to pure or 

mixed stands. The productivity of multiaged ponderosa pine is shown to be comparable to 

even-aged stands. Trends in multiaged management have included shorter cutting cycles and

lighter harvest treatments. Multiaged silviculture in ponderosa pine is highly suitable for 

achieving a variety of objectives including timber production, aesthetics, and restoring

presettlement stand structures. 

Introduction 

Ponderosa pine (Pinus ponderosa P. & C. Lawson) has a long history of

management to retain multiple age classes within a single stand. This is primarily the 

result of the disturbance regimes that affect regeneration, mortality, stand density,

and other ecosystem processes. The result – prior to European settlement – was an

abundance of unmanaged stands with multiple age classes of trees. Much of the early

management of this forest type perpetuated this structure and many of our multiaged

stands today are more the result of previous management than prehistoric disturbance 

regimes. As a result there is an abundance of stand structures that are multiaged and

an increasing desire to maintain this complex structure with future management.

This paper will provide an overview of the silviculture of stands with two or more 

age classes. These stands will be referred to as multiaged in contrast to the term 

uneven-aged that has traditionally denoted stands with three or more age classes

(Helms 1998). 

Fire is the primary disturbance agent, but insects, wind, and pathogens are also

important. Although fire regimes are highly variable across the entire range of

ponderosa pine, a low severity, high frequency regime is common in most areas with 

pure pine. As species composition becomes more complex at higher elevations or on 

moister sites, the fire regime becomes one of higher severity and lower frequency. In

pure stands, the disturbance regime often results in multiaged stands. These areas 

represent an ideal situation for multiaged silviculture. In the mixed stands, managing 

for multiaged ponderosa pine is more difficult because ponderosa pine is usually less 

1

 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21 2004, Klamath Falls, Oregon. 2

 Professor, Department of Environmental Science, Policy and Management, 137 Mulford Hall, 

University of California, Berkeley, CA 94720-3114 (email: ohara@nature.berkeley.edu) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 59 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

shade tolerant than its associates. In these situations, the conditions for regeneration

and early growth favor other species and ponderosa pine may decline. In this paper, I

will generally discuss mixtures and pure ponderosa pine stands separately.

Disturbance Ecology and Regeneration Patterns 

Ponderosa pine may have the highest fire frequency of any tree species in

western North America. Frequencies vary throughout the range: studies have 

documented fire return intervals as low as one year in pure stands and 40 or more

years in mixtures (Arno 1980, Agee 1993, Weaver 1959). These fires had mixed 

effects: small trees were very susceptible whereas larger trees were largely

unaffected. These events often gave rise to new age classes or cohorts of trees and

resulted in highly variable multiaged stands. Patterns of regeneration were variable 

across the range of ponderosa pine. Some researchers have described groups of 

distinct age classes (Arno and others 1995, Cooper 1960, West 1969) while others

have found heterogeneous patterns of age at the group level (White 1985). The 

former might resemble stands regenerated with a group selection system, the latter 

with single tree selection. Both patterns likely occurred at small scales.

Generalizations are difficult at larger scales because the great heterogeneity over the

entire range of ponderosa pine in soils, topography, elevation, associated species, and 

genetic variation in ponderosa pine. Another feature of older presettlement ponderosa 

pine forests was their open, park-like structure as was noted in many early

descriptions of these forests. Later descriptions estimated crown closure at less than

30 percent (Covington and Moore 1994) and overstory tree densities of 40 – 60 stems 

ha-1 (Arno and others 1995, Covington and Moore 1994, Youngblood and others 

2004).

Historical Management of Multiaged Stands

Much of the early history of timber harvest in ponderosa pine forests consisted

of partial harvests that perpetuated multiaged stand structures. Initially these harvests 

were to support mines, railroads, farms, and towns. Later, as commercial harvests 

began in the late 1800s, they focused on private lands. These early cuttings were 

primarily heavy partial cuts that removed 75 to 90 percent of the volume but 

generally did not have a silvicultural objective (Mowat 1961). Following formation

of the national forests, cutting of ponderosa pine on these lands followed similar

patterns. One of the first published references to multiaged silviculture in ponderosa 

pine on national forests was by Clapp (1912). He described systems of very heavy 

removals of approximately two-thirds of the volume and cutting cycles from 40 to 60

years. Dunning (1928) developed tree classifications to aid in selecting trees that

were overmature or low in vigor. Keen (1943) developed a more detailed tree 

classification system specific to ponderosa pine that became a key component of

many multiaged systems for decades. Meyer’s (1934) yield tables for selectively cut 

stands in the Pacific Northwest were one of the first references to quantitative criteria 

for multiaged management of ponderosa pine. Meyer proposed periodic cuttings of 

up to about 85 percent of board foot volume at intervals of greater than 40 years. 

Munger et al. (1936) developed a “maturity selection system” in the interior Pacific

Northwest that emphasized the financial maturity of individual trees. This differed

from diameter-limit cutting or zero-margin selection cutting (Smith et al. 1997) by 

also considering the tree’s biological maturity in assessing whether to leave or cut. In 

60 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

the southwest, Pearson (1942) developed a procedure called “improvement selection” 

that attempted to upgrade the amount and quality of the growing stock. 

Munger and Pearson debated the relative merits of “maturity selection” and

“improvement selection” in the Journal of Forestry (see letters and responses 

following Pearson 1942). O’Hara (2002) concluded that the differences between the

approaches were likely the result of differences in the current state of ponderosa pine

forests of the interior Northwest and the southwest US: the forests of the southwest

were probably more degraded from heavy cutting, grazing, an abundance of stocking

from the 1919 regeneration year, and had a greater need for improvement than the

forests of the interior Northwest. 

Another trend in these early treatments that has carried forward to more recent 

multiaged silviculture is the decline in severity of harvest over time. Mowat (1961) 

noted this trend and described current practices around 1960 as removing 25-65 

percent of volume. There are a number of factors that have contributed to this trend 

including greater stumpage values and the availability of the crawler tractor that

made less severe harvest economically and operationally feasible. There was also a 

developing recognition that lighter cuttings produced greater yields (Brandstrom

1937, Roe 1947) because the stand response to partial harvests was greatest in the 

first decade or two after cutting (Mowat 1961, Roe 1952). Later descriptions of

multiaged silviculture in ponderosa pine described cutting cycles of 20 to 30 years 

(Alexander and Edminster 1977, Shepperd and Battaglia 2002). 

Contemporary Stocking Procedures 

Stocking control is central to multiaged systems because through stocking the

silviculturist affects stand structure, the potential for regeneration, and the 

sustainability of the stand. There are a variety of stocking control procedures for 

multiaged stands managed with single tree selection systems. O’Hara and Gersonde 

(2004) discussed the development of these systems over time. The most common 

stocking control procedure for ponderosa pine has been the q-factor approach that

uses a reverse-J diameter frequency distribution. The traditional interpretation of the 

q-factor was as a constant diminution quotient where the number of trees in a 

diameter class is a constant ratio of the tree number in the next larger class (fig. 1). 

For example, a q-factor of 1.2 applied to a 25-30 cm diameter class with 50 trees ha-1

would result in 60 trees ha-1 in the 20-25 trees ha-1cm class and 72 trees ha-1 in the 15-

20 cm class. This diameter distribution may represent the post-harvest stand target. 

Using this method, a stand is marked to conform to the target diameter distribution at 

the end of each cutting cycle. During each cutting cycle the stand will experience 

growth in most diameter classes and the diameter distribution moves away from the

target. Alexander (1986) and Fiedler and others (1988) provide more details on this 

approach. This approach has also been described as the BDq approach where B

represents the total basal area, D the maximum diameter class, and q the q-factor of 

the target structure (see Guldin 1991). 

Stand regulation with the q-factor approach is achieved through harvest or 

thinning treatments that reset the stand to the target structure at the end of each

cutting cycle. Stands managed to meet a particular q-factor diameter distribution have 

been described as “balanced” (Meyer 1943, 1952, Nyland 2002, Smith et al. 1997)

because they were assumed to have constant volume production over time and equal 

space occupancy by each size and age class. The balanced stand therefore resembles

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 61 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

a forest under area control regulation but at a smaller scale. O’Hara (1996)

questioned these assumptions and concluded that management to maintain these

“balanced” stands resulted in lower yields for ponderosa pine and didn’t guarantee 

sustainability. In practice, segmented q-factors can be used so some parts of the

diameter distribution have a different q-factor than other parts. This helps avoid the

common drawback of this approach where large numbers of small trees occupy a 

greater share of growing space than necessary for most management objectives. 

Stand density index (SDI) can also be allocated among diameter classes or 

groups of classes as a means of allocating growing space in multiaged stands. Long 

and Daniel (1990) demonstrated this approach with examples for ponderosa pine (fig. 

1). SDI can be calculated for groups of diameter classes and then added to obtain a 

stand-level total. Their assumption was that even-aged density management zones for 

even-aged stands could also be applied to multiaged stands. Long and Daniel (1990) 

demonstrated how the approach could be applied to design stands that deviated from 

the traditional reverse-J diameter distribution with a constant diminution coefficient. 

This approach has also been applied to ponderosa pine stands with presettlement

structures (Cochran 1992) and two-aged stands (Long 1996). 

Diameter class midpoints (cm)

0 1 2 3 4 5

Basal area (

m2 ha-1) and SDI

0

20

40

60

80

100

120

140

160

Number of trees ha-1

0

100

200

300

400

500

600

basal area

SDI

number of trees

10 25 40 55

Figure 1— A diameter distribution, stand density index, and basal area for a

ponderosa pine stand with a q-factor of 1.5 using metric units. Note the unequal 

distribution of SDI and basal area on a diameter distribution that was assumed to be 

"balanced" (Modified from Long and Daniel 1990 and O'Hara and Gersonde 2004). 

All stocking control procedures are essentially tools for allocating growing 

space. This was explicit in the leaf area or growing space allocation tool developed 

for multiaged ponderosa pine (O’Hara 1996, 1998; O’Hara and others 2003; O’Hara 

62 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

and Nagel 2004). The growing space allocation method is distinguished from other

methods because: 1) trees are divided into two to four stand components such as 

canopy strata or age classes rather than diameter size classes; and 2) growing space

occupancy is represented by leaf area index (LAI - ratio of leaf surface area per unit 

of ground area covered). A user of the system divides growing space among

components so as to meet management objectives. The target structure might 

therefore have the most growing space allocated to larger trees or perhaps to smaller

trees. This flexibility is an asset of this method and allows the design of stand 

structures such as two-aged stands and presettlement structures with large or old 

trees. 

A spreadsheet-based model is used for growing space allocation in this 

procedure. This model, called PP-MASAM, has been calibrated for pure ponderosa 

pine stands from three regions: central Oregon, western Montana, and the Black Hills 

in South Dakota and Wyoming (O’Hara and others 2003; O’Hara and Nagel 2004) 

and is available online at cnr.berkeley.edu/~ohara/downloads/. Table 1 shows a threeage ponderosa pine stand using the Montana version of PP-MASAM. A four-age 

stand is described in Table 2 using the PP-MASAM from Montana. The model 

projects volume increment, and calculates estimates of basal area, tree vigor, and 

SDI. It is flexible for designing stands that are two-aged, stands with high or low

stand densities, or designing stand structures where harvest of presettlement trees 

above a certain diameter is avoided. 

Table 1 — Three-aged ponderosa pine stand designed with the PP-MASAM model from

Montana (from O'Hara et al. 2003). Bold text are values provided by the user: the others are 

model output. 

USER-SPECIFIED VARIABLES

TOTAL Leaf Area Index (LAI) 6 

Cohort 1 Cohort 2 Cohort 3 Cohort 4 TOTAL 

Number of Trees/Cohort/Hectare 60 100 140 0 300 

Percent of LAI/Cohort 50 35 15 0 100 

DIAGNOSTIC INFORMATION

Cohort 1 Cohort 2 Cohort 3 Cohort 4 TOTAL 

Leaf Area Index/Cohort ECC 3.0 2.1 0.9 0.0 6.0 

Leaf Area Index/Cohort BCC 1.3 0.6 0.0 1.9

Leaf Area/Tree (m2

) ECC 500.0 210.0 64.3 0.0

BA/Cohort (m2

/ha) ECC 15.0 9.7 3.8 0.0 28.5

BA/Cohort (m2

/ac) BCC 5.8 2.7 0.0 8.5

Avg. Vol. Increment/Tree (m3

/yr) ECC 0.04 0.01 0.01 0.00

Avg. Vol. Increment/CC (m3

/ha/yr) 1.7 1.0 0.4 0.0 3.1 

Quadratic Mean DBH/Cohort (cm) ECC 50.1 31.1 16.5 0.0 

Tree Vigor (cm3

/m2/yr) 76.988 79.069 91.604 0.000

Stand Density Index ECC 182.2 141.9 72.3 0.0 396.3 

Stand Density Index BCC 85.1 51.6 0.0 136.8

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 63 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

Table 2 — A four-aged ponderosa pine stand designed with the PP-MASAM model from

Montana. Bold text are values provided by the user: the others are model output. The PPMASAM model is also available in English units (from O'Hara et al. 2003). 

USER-SPECIFIED VARIABLES

TOTAL Leaf Area Index (LAI) 6 

Cohort 1 Cohort 2 Cohort 3 Cohort 4 TOTAL 

Number of Trees/Cohort/Hectare 45 60 74 89 268 

Percent of LAI/Cohort 40 30 20 10 100 

DIAGNOSTIC INFORMATION

Cohort 1 Cohort 2 Cohort 3 Cohort 4 TOTAL 

Leaf Area Index/Cohort ECC 2.4 1.8 1.2 0.6 6.0 

Leaf Area Index/Cohort BCC 1.4 1.0 0.5 2.8

Leaf Area/Tree (m2

) ECC 533.3 300.0 162.2 67.4

BA/Cohort (m2

/ha) ECC 12.1 8.3 5.1 2.5 28.1

BA/Cohort (m2

/ac) BCC 6.3 4.2 2.1 12.5 

Avg. Vol. Increment/Tree (m3

/yr) ECC 0.05 0.02 0.02 0.00

Avg. Vol. Increment/CC (m3

/ha/yr) 1.5 1.1 0.7 0.1 3.4 

Quadratic Mean DBH/Cohort (cm) ECC 51.8 37.3 26.3 16.8 

Tree Vigor (cm3

/m2/yr) 77.885 80.591 71.188 46.368

Stand Density Index ECC 144.4 113.8 80.4 47.2 385.8 

Stand Density Index BCC 85.4 65.2 39.3 189.8

Group Selection 

Another highly appropriate form of multiaged silviculture for ponderosa pine is

group selection. These groups provide openings with sufficient light to allow shade 

intolerant species to germinate and be competitive in mixed-species stands. Another

advantage of group selection is the operational efficiencies that arise from harvesting 

in larger gaps than single tree selection systems. 

For stand regulation, group selection operates on an "area control" basis where

openings are moved throughout a stand and each opening cycles back for a second 

treatment after a period of time analogous to an even-aged rotation. In one of these 

"rotations", the entire stand would be treated with equal areas harvested in each

cutting cycle. Although there is very little experience with more than one "rotation"

with group selection systems, a number of areas in the ponderosa pine region are 

through several cutting cycles. A key planning strategy when first establishing a 

group selection system is to organize openings so that all are accessible through all

cutting cycles. There are also advantages to how openings are oriented with respect

to shading each other. For example, there may be significant advantages to having a 

younger and shorter group of trees on the south side of a new opening to maximize 

light availability. 

Although group selection openings provide open growing conditions for 

developing trees, this open condition occurs primarily in the center or north side of

openings in the ponderosa pine region and declines toward the group edges. In

mixed-species forests – that often have greater crown closure and higher LAI – group 

sizes must therefore be sufficiently large to provide conditions where ponderosa pine 

has an advantage. York and others (2004) documented the edge effect for six conifer 

64 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

species in the Sierra Nevada where the greatest growth was from seedlings in the

center and north of center within group openings. For ponderosa pine, mean height 

of seedlings after five years was greatest in the largest opening sampled (1 ha). They

also measured growth of trees outside but bordering the group opening and found 

increased growth after group establishment suggesting a positive productivity effect

that might compensate for the growth losses of edge seedlings in the opening. 

Mixed-Species Applications 

Mixed stands that include ponderosa pine also have the potential for

management with multiaged systems. However, with the exception of western larch 

(Larix occidentalis Nutt.) in the inland Northwest and the Northern Rocky 

Mountains, ponderosa pine is less shade tolerant than all of its major competitors in 

mixed-species stands. This provides a competitive disadvantage for ponderosa pine 

in multiaged systems in these mixed species types. Without management

intervention, the regeneration success of ponderosa pine will decline leading to 

greater dominance by more shade tolerant species. Whereas these mixed-species

stands are desirable for a variety of management objectives, the decline in numbers

of shade intolerant species like ponderosa pine often leads to a number of insect and

pathogen problems and may leave the stand more susceptible to fire. 

Several studies have examined multiaged stand management in the Sierra 

Nevada. Lilieholm et al. (1990) documented trends in diameter distributions and

species composition after several decades of selection harvests in stands that were

even-aged but with irregular stocking. They found all five major conifer species –

including ponderosa pine – were able to regenerate although the more shade tolerant 

species comprised the bulk of the regeneration. They also noted that the diameter

distributions after 20-28 years of harvest treatments were moving towards the target

reverse-J distributions. Guldin (1991) applied the BDq method to the Sierra Nevada 

mixed-conifer forests. He concluded that a form of group selection was needed to 

insure regeneration of shade intolerant species and advocated the BDq procedure for

these stands. Gersonde and others (2004) used a light model to identify locations 

where shade intolerant species were most likely to be successful in mixed-conifer

stands in the Sierra Nevada. 

In other parts of the ponderosa pine range, similar problems exist. For example, 

interior Douglas-fir (Pseudotsuga menziesii var. glauca (Mirb.) Franco) and several 

other species compete with ponderosa pine on many sites in the inland Northwest and 

northern Rocky Mountains. In these forests, mechanical control of Douglas-fir or use 

of understory burning are necessary to give ponderosa pine an advantage and

maintain its presence. 

Other Issues with Multiaged Stands

The Cutting Cycle 

In a fully regulated multiaged system, the length of the cutting cycle is a 

function of the severity of the harvests (O’Hara and Valappil 1999). Heavy harvest

treatments would necessitate longer cutting cycles to rebuild pretreatment stocking 

levels. Lighter harvest treatments would have the opposite effect: shorter cutting 

cycles. Many of the earliest multiaged systems in ponderosa pine used very heavy

removals (Meyer 1934) whereas more recent systems used light cuttings and short 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 65 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

cutting cycles (Becker 1995, Shepperd and Battaglia 2002). O’Hara and Valappil 

(1999) described a tradeoff between the probability of obtaining regeneration and 

volume increment with shorter cutting cycles/lighter harvests resulting in greater 

volume increment and a lower probability of obtaining natural regeneration because

of heavier competition. The opposite would be true for longer cutting cycles/heavier 

harvests. The trend to shorter cutting cycles and with lighter harvests in ponderosa

pine may favor greater stand growth but less regeneration. In mixed stands, longer 

cutting cycles would be more likely to produce ponderosa pine regeneration and give

this species a competitive advantage. 

Theoretically the target multiaged stand is best met at only one point in time

during a cutting cycle. Otherwise, the stand is either growing towards or away from 

the target. Longer cutting cycles would therefore deviate more from the target than

shorter cutting cycles. Another consideration is the q-factor and SDI approaches 

generally design target structures for the beginning of the cutting cycle. The PPMASAM designs end-of-cutting cycle structures but also provides data on stand 

characteristics at the beginning of the cutting cycle. When designing a cutting cycle 

it is more important to recognize the tradeoffs between cutting cycle length and 

harvest levels and how to achieve the target stand structure for as long as possible. 

Productivity 

The relative productivity of multiaged stands to other stand structures, 

particularly even-aged stands, is a point of great interest for most foresters. There is

no empirical evidence for ponderosa pine that indicates multiaged stands are more or 

less productive than other structures. O’Hara (1996) compared increment in evenaged and multiaged ponderosa pine stands in central Oregon and western Montana. 

Cubic volume increment was slightly higher for multiaged stands in both study areas 

but differences were not significant (Table 3). Since LAI was slightly higher in evenaged stands, these results suggest higher efficiencies of growing space occupancy in

the multiaged stands. Similar results were obtained in the Black Hills although only 

one even-aged stand was sampled (Table 3 – O’Hara and Nagel 2004). Additional

studies found greater water pressure deficits in even-aged stands during the growing 

season suggesting differences in water availability may contribute to lower

productivity in even-aged stands (Nagel and O’Hara 2002). A review on multiaged 

productivity3

 concluded that any productivity differences that might exist between

even-aged and multiaged stands were small and probably less significant than

differences in operational effects on growth and volume recovery [(O’Hara and Nagel

2006)].

3

 O’Hara, K.L. and L.M. Nagel. 2006. A functional comparison of productivity in even-aged

and multiaged stands: A synthesis for Pinus ponderosa. Forest Science (in press).

66 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

Table 3 — Mean (+ SE) volume increment, leaf area index (LAI), and growing space

efficiency (GSE) for even-aged and multiaged ponderosa from three study areas. Only the

GSE means for central Oregon were significantly different of these results. Data are from 

O’Hara (1996) and O’Hara and Nagel (2004). 

Location Age

Structure 

Vol. Increment 

+SE 

m3

 ha-1 yr-1 LAI +SE 

Stand GSE 

+SE 

m3

 m-2

Western Montana 

Western Montana 

Even-aged 5.0 +0.3 7.2 +0.47 0.72 +0.04

Multiaged 5.4 +0.3 6.8 +0.31 0.80 +0.03

Central Oregon

Central Oregon

Even-aged 4.8 +0.4 6.9 +0.41 0.70 +0.04

Multiaged 4.7 +0.3 6.1 +0.29 0.81 +0.03

South Dakota

1

South Dakota 

Even-aged 5.8 7.8 0.73

Multiaged 5.2 +0.2 6.9 +0.043 0.77 +0.04

1

One even-aged stand was sampled in South Dakota so a comparison of means was not

possible for these data. 

Slash and Fuel Treatments 

The variation in tree sizes in multiaged stands has the potential to form fuel

ladders that increase the potential for crown fire development. In pure ponderosa 

pine, stands can be maintained at low densities so fuels are not continuous. In

mixtures, this problem is more significant and may preclude multiaged stands in 

some locations such as fuel breaks or near structures. Prescribed understory burning 

may also be more difficult in multiaged stands because some small trees would 

always be present. Slash disposal may also be problematic as broadcast burning is

not possible and residual trees may limit equipment options for piling. These are 

additional limitations on operations beyond those related to the removal of trees from

multiaged stands and may require additional expenses to provide comparable fire 

protection as in older even-aged stands. 

Site Quality

A long-standing shortcoming of multiaged systems is the inability to estimate 

site quality using site index. Because a requirement of site trees is that they be free 

growing trees throughout their development, any tree developing in a multiaged 

system is unsuitable. Managers are therefore forced towards finding similar sites

with free-growing even-aged trees, using soil-site relationships, or vegetation

analyses such as plant associations. These latter methods often provide only wide

ranges of site productivity values and are ultimately tied to site index relationships 

from even-aged stands. There have been attempts to determine site index from the 

free-growing period of development for a multiaged tree, but this is an area that could 

use more research. 

Summary

Ponderosa pine has a rich history in both the research and practice of multiaged 

silviculture. A variety of different methods have been used and many have had some

success. Much of this success is because ponderosa pine, particularly when growing 

in pure stands, is a highly suitable species for multiaged management. This is due to 

several factors including the low stand densities of many ponderosa pine stands that 

can permit regeneration and development of several age classes. Another important 

factor is the disturbance regime dominated by high frequency, low intensity fire in

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 67 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

much of the ponderosa pine range. These disturbances often produce new age classes 

resulting in multiage stands that can be easily emulated by management. On moister 

sites, where ponderosa pine often grows with more shade tolerant species, multiaged 

silviculture can be more difficult, particularly on sites where fire exclusion has 

already altered the species composition of these stands. On these sites, multiaged

silviculture can also be successful, but will required additional treatments to control 

undesirable species and to reduce fire hazards. 

One of the truly great assets of the pure ponderosa pine ecosystem is the wide 

range of management practices that can be successful. This includes multiaged as 

well as even-aged silviculture. For multiaged systems, land managers can usually

choose between regimes with short or long cutting cycles, high or low levels of 

residual stocking, and many to just a few age classes or cohorts. Flexibility to

accommodate a wide variety of regimes is therefore an important component of any 

management tool. Multiaged silviculture can therefore be used to meet a wide variety

of objectives in an ecosystem management context. These objectives can include

providing stand structures for wildlife habitat, timber production, enhancing

aesthetics, or restoration of presettlement stand structures. 

References 

Agee, J.K. 1993. Fire ecology of Pacific Northwest forests. Island Press, Washington, 

D.C. 

Alexander, R.R. 1986. Silvicultural systems and cutting methods for ponderosa pine 

forests in the front range of the central Rocky Mountains. Gen. Tech. Report RM128. Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest

Service, U.S. Department of Agriculture. 

Alexander, R.R.; Edminster, C.B. 1977. Regulation and control of cut under uneven-aged 

management. Res. Paper RM-182. Fort Collins, CO: Rocky Mountain Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture. 

Arno, S.F. 1980. Forest fire history in the northern Rockies. Journal of Forestry 78: 460-

465. 

Arno, S.F.; Scott, J.H.; Hartwell, M.G. 1995. Age-class structure of old growth ponderosa

pine/Douglas-fir stands and its relationship to fire history. Res. Paper INT-RP-481 

Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department of

Agriculture..

Becker, R. 1995. Operational considerations of implementing uneven-aged

management. In: O’Hara, K. L., editor. Uneven-aged Management: Opportunities, 

Constraints and Methodologies. University of Montana, Montana Forest and 

Conservation Experiment Station. Misc. Rep. No. 56; 67-81. 

Brandstrom, A.J.F. 1937. The role of selective cutting in promoting sustained yield with 

special reference to ponderosa pine. Journal of Forestry 35: 142-147. 

Clapp, E.H. 1912. Silvicultural systems for western yellow pine. Proceedings of the

Society of American Foresters, Volume 7: 168-176. 

Cochran, P.H. 1992. Stocking levels and underlying assumptions for uneven-aged 

ponderosa pine stands. Res. Note PNW-RN-509. Portland, OR: Pacific Northwest

Research Station, Forest Service, U.S. Department of Agriculture; 10 p. 

Cooper, C.F. 1960. Changes in vegetation, structure, and growth of southwestern pine

forests since white settlement. Ecological Monographs 30: 129-164. 

68 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

Covington, W.W.; Moore, M.M. 1994. Southwestern ponderosa forest structure: 

Changes since Euro-American settlement. Journal of Forestry 92(1): 39-47. 

Dunning, D. 1928. A tree classification for the selection forests of the Sierra Nevada.

Journal of Agricultural Research 36: 755-771. 

Fiedler, C.; Becker, R.; Haglund, S. 1988. Preliminary guidelines for uneven-aged 

silvicultural prescriptions in ponderosa pine. In: Baumgartner, D. M.; Lotan, J. E., 

editors. Ponderosa pine: the species and its management. Washington State University

Cooperative Extension, Pullman; 235-242. 

Gersonde, R.; Battles, J.J.; O’Hara, K.L. 2004. Characterizing the light environment in 

Sierra Nevada mixed-conifer forests using a spatially explicit light model. Canadian

Journal of Forest Research 24: 1332-1342. 

Guldin, J.M. 1991. Uneven-aged BDq regulation of Sierra Nevada mixed conifers.

Western Journal of Applied Forestry 6: 27-32. 

Helms, J.A. (Editor). 1998. The Dictionary of Forestry. Society of American Foresters,

Bethesda, MD. 

Keen, F.P. 1943. Ponderosa pine tree classes redefined. Journal of Forestry 41: 249-253. 

Lilieholm, R.J.; Davis, L.S.; Heald, R.C.; Holmen, S.P. 1990. Effects of single tree

selection harvests on stand structure, species composition, and understory tree

growth in a Sierra mixed conifer forest. Western Journal of Applied Forestry 5: 43-

47. 

Long, J.N. 1996. A technique for the control of stocking in two-storied stands. Western

Journal of Applied Forestry 11(2): 59-61.

Long, J.N.; Daniel, T.W. 1990. Assessment of growing stock in uneven-aged stands. 

Western Journal of Applied Forestry 5: 93-96. 

Meyer, H.A. 1943. Management without rotation. Journal of Forestry 41: 126-132. 

Meyer, H.A. 1952. Structure, growth, and drain in balanced uneven-aged forests.

Journal of Forestry 50: 85-92. 

Meyer, W.H. 1934. Growth in selectively cut ponderosa pine forests of the Pacific 

Northwest. Technical Bulletin no. 407. Washington D.C.: U.S. Department of 

Agriculture; 64 p.

Mowat, E.L. 1961. Growth after partial cutting of ponderosa pine on permanent sample 

plots in eastern Oregon. Res. Paper 44. Portland, OR: Pacific Northwest Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture.

Munger, T. T.; Brandstrom, A. J. F.; Kolbe, E. L. 1936. Maturity selection system applied

to ponderosa pine. West Coast Lumberman 63: 33, 44. 

Nagel, L.M.; O’Hara, K.L. 2002. Diurnal fluctuations of gas exchange and water 

potential in different stand structures of Pinus ponderosa. Trees: Structure and 

Function 16: 281-290.

Nyland, R.D. 2002. Silviculture: Concepts and Applications. McGraw Hill, New York. 

O'Hara, K.L. 1996. Dynamics and stocking-level relationships of multi-aged ponderosa

pine stands. Forest Science 42, Monograph 33. 34 p.

O’Hara, K.L. 1998. Silviculture for structural diversity: A new look at multiaged 

systems. Journal of Forestry 96(7): 4-10. 

O’Hara, K.L. 1998. Leaf area allocation: How does it work? Journal of Forestry 96(7):

11. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 69 
Multiaged Silviculture of Ponderosa Pine—O’Hara 

O'Hara, K.L. 2001. The silviculture of transformation: a commentary. Forest Ecology

and Management 151(1-3): 81-86. 

O'Hara, K.L. 2002. The historical development of uneven-aged silviculture in North 

America. Forestry 75(4): 339-346.

O'Hara, K.L.; Gersonde, R.F. 2004. Stocking control concepts in uneven-aged 

silviculture. Forestry 77(2): 131-143. 

O'Hara, K.L., Nagel, L.M. 2004. A multiaged stocking model for Black Hills ponderosa 

pine. Western Journal of Applied Forestry 19: 242-244.

O’Hara, K.L.; Valappil, N.I. 1999. MASAM – A flexible stand density management 

model for meeting diverse structural objectives in multiaged stands. Forest Ecology

and Management 118(1-3): 57-71. 

O'Hara, K.L.; Valappil, N.I. ; Nagel, L.M. 2003. Stocking control procedures for

multiaged ponderosa pine stands in the Inland Northwest. Western Journal of

Applied Forestry 18(1): 5-14.

Pearson, G.A. 1942. Improvement selection cutting in ponderosa pine. Journal of

Forestry 40: 753-766. 

Roe, A.L. 1947. What is the right cutting cycle for ponderosa pine? Research Note No. 

57. Missoula, MT: Northern Rocky Mountain Forest and Range Experiment Station, 

Forest Service, U.S. Department of Agriculture.

Roe, A.L. 1952. Growth of selectively cut ponderosa pine stands in the upper Columbia 

Basin. Handbook No. 39. Washington, D.C.: U.S. Department of Agriculture; 29 p. 

Shepperd, W.D.; Battaglia, M.A. 2002. Ecology, silviculture, and management of Black 

Hills ponderosa pine. Gen. Tech. Report RMRS-GTR-97. Fort Collins, CO: Rocky

Mountain Research Station, Forest Service, U.S. Department of Agriculture. 

Smith, D.M.; Larson, B.C.; Kelty, M.J.; Ashton, P.M.S. 1997. The Practice of Silviculture: 

Applied Forest Ecology, Ninth Edition. John Wiley. New York. 

Weaver, H. 1959. Ecological changes in the ponderosa pine forests of the Warm Springs

Indian Reservation in Oregon. Journal of Forestry 57: 15-20. 

West, N.E. 1969. Tree patterns in central Oregon ponderosa pine forests. American 

Midland Naturalist 81: 584-590. 

White, A.S. 1985. Presettlement regeneration patterns in a southwestern ponderosa

pine stand. Ecology 66: 589-594. 

York, R.A.; Heald, R.C.; Battles, J.J.; York, J.D. 2004. Group selection management in

conifer forests: relationships between opening size and tree growth. Canadian

Journal of Forest Research 34: 630-641.

Youngblood, A.; Max, T.; Coe, K. 2004. Stand structure of eastside old-growth 

ponderosa pine forests of Oregon and northern California. Forest Ecology and

Management 199: 191-217. 

70 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
The West-Wide Ponderosa Pine Levels-ofGrowing-Stock Study at Age 401

William W. Oliver2

Abstract 

In the 1960s a series of levels-of-growing-stock studies was established in young, even-aged 

stands throughout the range of ponderosa pine in the western United States. Using a common 

study plan, installations were begun in the Black Hills of South Dakota, eastern and central

Oregon, the Coconino Plateau of Arizona and the west slope of the Sierra Nevada in

California. Innovative features for the time were tests of a wide range of stand densities from

open-grown to densities high enough to jeopardize stand health, and to periodic rethinning of

the plots back to the stand density level originally assigned. Perhaps the major reason for the 

longevity of this west-wide study was the foresight of the original planners in testing a range

of stand densities far beyond those practiced at the time. Establishment of this range provided 

a demonstration of the long-term stand development of even-aged ponderosa pine applicable

to many current management objectives. 

Introduction 

Ponderosa pine (Pinus ponderosa P. & C. Lawson) is one of the most widely

distributed conifers in North America. It occurs in 15 western states, extending from

the western Great Plains to the Pacific Coast and from southern British Columbia, 

Canada, to Baja California, Mexico. Ponderosa pine is found at elevations ranging

from sea level in the northern part of its range to 10,000 ft in the southwestern United 

States (Oliver and Ryker 1990). Throughout this vast area ponderosa pine is one of

the most valued tree species. Recognized initially for the quality of its wood yields 

and as a major source of forage for cattle, ponderosa pine forests are now recognized 

as vital wildlife habitat, and they provide abundant recreational opportunities. As a 

result, ponderosa pine forests have a long history of intensive management. 

In the mid 20th century, however, management of young growth ponderosa pine

forests was in its infancy. Results from studies conducted in one area (Gaines and 

Kotok 1954; Mowat 1953; Myers 1958) seemed to have limited use in another area. 

Dissimilar experimental designs and measurements that were incomplete or based on 

specific products further restricted comparability. Also, these early studies did not 

test the low reserve densities that may be desired for today’s multi-resource 

management. 

In the mid 20th century, however, management of young growth ponderosa pine

forests was in its infancy. Results from studies conducted in one area (Gaines and 

Kotok 1954; Mowat 1953; Myers 1958) seemed to have limited use in another area. 

1

 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine:

Issues, Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Principal Silviculturist, Emeritus, Pacific Southwest Research Station, Redding Silviculture 

Laboratory, 3644 Avtech Parkway, Redding, CA 96002, (email: boliver@fs.fed.us)

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 71 
West wide L-O-G-S Study at Age 40—Oliver 

Dissimilar experimental designs and measurements that were incomplete or based on 

specific products further restricted comparability. Also, these early studies did not 

test the low reserve densities that may be desired for today’s multi-resource 

management. 

Consequently, growth information was needed over a wide range of stand and

site conditions and with a minimum of operational restrictions to provide useful 

guides for a variety of management objectives. To fill this need three western

Research Stations of the U.S. Department of Agriculture, Forest Service, cooperated 

on a large scale levels-of-growing-stock study through the use of a common study

plan (Myers 1967).

Many reports have been published on individual installations (table 1) of this

west-wide study and two reports combining data from most of the installations were 

published more than 15 years ago (Oliver and Edminster 1986; Edminster 1988).

This paper reports on the present status of the six installations after about 40 years. It

describes the development of the stands, their value in demonstrating the influence of

low reserve stocking, and the opportunities for satellite studies. 

Original Study Plan 

Five regions within the range of ponderosa pine in the western United States

were arbitrarily selected for study and assigned to the participating Research Stations. 

These five “provinces” differ in many respects. Physiography ranges from the uplift 

of the Black Hills of South Dakota to the Coconino Plateau of Arizona, the Blue 

Mountains and Cascade Range of Oregon, and Sierra Nevada of California. Two

varieties of ponderosa pine are recognized (Pinus ponderosa P. & C. Lawson var. 

ponderosa and Pinus ponderosa P. & C. Lawson var. scopulorum) (Conkle and 

Critchfield 1988). Some provinces are without summer precipitation; other provinces 

receive most of their annual precipitation during the growing season. Within each

province, combinations of four tree-size classes from small saplings to large poles on 

areas of three site qualities of high, medium, and low were to be sampled, as 

available, in even-aged stands. 

The initial plan specified that each study installation would consist of three 

replications of plots thinned to five or six different stand densities. Plots were to be at

least 0.25 to 0.5 acre in size with 20-ft isolation strips for small saplings, and 0.5 to 

1.0 acre with 30-ft isolation strips for the larger size classes. One plot in each

replication was to be thinned to the density considered best for that site quality, based 

on past experience. Two or three plots were to be thinned to lower, and two or three 

plots to higher stand densities. The highest stand density would be chosen such that 

the production of merchantable material would be reduced below that of lower 

densities. And the lowest density level would be chosen such that cubic-foot volume 

production would be lower than that at higher densities. 

Stand densities to be retained after thinning were specified as a series of

growing stock levels (GSLs) (Myers 1967). These levels were defined by

relationships between basal area and average stand diameter. Numerical designation 

of the level assigned to a plot was the basal area per acre that would remain after 

thinning when mean stand diameter was 10 inches or more. Stands with trees smaller 

than 10 inches when thinned would contain residual basal areas that were less than

the designated GSL. 

72 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005 
West wide L-O-G-S Study at Age 40—Oliver 

Table 1— Installations in the west-wide levels-of-growing-stock study fore even-aged 

ponderosa pine. 

Geomorphic 

Province 

Name 

& Year 

Site

Index1

Size

class 

Growing 

stock levels 

Periods 

analyzed 

References

Black Hills 

South Dakota 

Black Hills 

Saplings 

1964 

55 large

saplings 

20,40,60, 

80,100, 120 

7 Boldt and Van

Deusen 1974 

Black Hills 

South Dakota 

Black Hills 

Poles 

1964 

55 small

poles 

20,40,60, 

80,100, 120 

7 Boldt and Van

Deusen 1974 

Coconino 

Plateau 

Arizona 

Taylor Woods 

1962 

62 small

poles 

30,60,80, 

100,120, 150 

7 Ronco and

others 1982 

Schubert 1971 

Blue Mts.

Oregon 

Crawford 

Creek 

1967 

60 small

poles 

30,60,80, 

100,120, 140 

6 Cochran and

Barrett 1995 

East-side

Cascade Range 

Oregon 

Lookout Mt. 

1966 

92 large poles 30,60,80,

100,120, 150 

7 Barrett 1983

Cochran and 

Barrett 1999 

West-side Sierra

Nevada 

California 

Elliot Ranch 

1969 

140 Small

poles 

40,70,100, 

130,160 

6 Oliver 1979

Oliver 1997 

1 feet at 100 yrs (Meyer 1938).

Thinning was to be from below, primarily, with the smallest trees and rough 

dominants removed first. Each installation was scheduled to run for 20 years, with

measurements at 5-year intervals. At the end of 10 years, plots were to be rethinned

to the specified GSLs. 

Before the growing season following initial thinning, all trees were to be tagged

and measured for diameter at breast height (dbh) to the nearest 0.1 inch. Tree damage

and diseases were to be noted. Various sampling schemes could be used to select

trees for total height and height to the living crown, measured to the nearest 1 ft. 

Total stem volume was obtained either by the use of local volume tables or by an 

optical dendrometer. All measurements were to be repeated on the same trees after

each 5-year period. 

The Installations 

The study as envisioned was ambitious, requiring prodigious amounts of land, 

labor, and money. Cooperators experienced difficulty both in finding sufficient areas 

of uniform site and stand conditions, and in allocating sufficient resources to sample

but a few of the province/size/site combinations. Although many fewer than planned, 

the five installations established in naturally regenerated stands and the one 

installation established in a plantation (Elliot Ranch) nearly spanned the geographic 

range of ponderosa pine (table 1). 

During the planned 20-year life of the study, the six installations were 

established and maintained in general conformance with the plan except as follows:

(1) two rethinnings were performed at Elliot Ranch at five-year intervals rather than 

ten-year intervals because of rapid growth (fig. 1); (2) only one rethinning was 

performed in the lowest GSL plots at Lookout Mountain because a second rethinning

would have resulted in too few trees for a sufficient sample; (3) only one rethinning 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 73 
West wide L-O-G-S Study at Age 40—Oliver 

has been performed in both of the Black Hills installations; (4) the controlling 

measure of stand density was changed to stand density index (SDI; Reineke 1933) at 

Lookout Mountain, Crawford Creek and Elliot Ranch Because basal area (GSL for

mean stand diameters above 10 inches) as a measure of stand density is not 

independent of tree size and age. Remarkably, all installation have been continuously

maintained and remeasured for twice as long originally envisioned, albeit not always

on a rigid 5-year interval. 

Figure 1—Net basal area development of the Growing Stock Level (GSL) treatments 

at six installations of the west-wide ponderosa pine levels-of-growing-stock study. 

74 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005 
West wide L-O-G-S Study at Age 40—Oliver 

Results and Discussion 

Treatment Effects on Stand Growth

An unthinned stand treatment was not included in the original plan. Neither is 

information available on the stand before thinning. Presuming that the stands before 

treatment were similar to those of normal density (Meyer 1938), the thinning

treatments created a uniform array of stand densities ranging from those containing 

essentially open-grown trees to those retaining about half of the original basal area

after light thinning. 

Mortality (primarily in the higher reserve densities) tended to blur this uniform 

array. Mortality from mountain and western pine beetle was especially prevalent 10 

to 20 years after initial thinning in the GSLs above 100 at Elliot Ranch. Mortality 

from mountain pine beetles was also high at Crawford Creek and breakage from a 

heavy wet snow was so severe at Taylor Woods that the two highest GSLs at these 

two installations differed little in actual density for the first 10 years. Mortality by all

agents has declined over the years. Except for recent killing by mountain pine beetles 

at the highest GSL at Lookout Mountain, the treatments are now distinctly different

in stand density. 

Stand Structure Changes 

Thinning, especially heavy thinning, has had a profound influence on the 

structure of the plots (fig. 2a, 2b). In general, maintaining plots at the highest reserve 

densities, GSLs 120 to 160 has over the period of observation transformed the 

diameter distribution from one resembling a reverse “J’ shape to one resembling a

normal distribution. Heavy thinning, in contrast, immediately created a normal

distribution that has been maintained for 40 or more years.

Opportunities for Satellite Studies 

Studies continuously maintained for 40 years are rare in forestry. Research 

interests and priorities can change over such a long time and make such long-term 

studies obsolete. Nevertheless, silvicultural studies in which vegetation is

manipulated in a statistically valid field design and with well-documented treatment 

responses afford many opportunities for studies never anticipated by the original

researchers. Such is the case in this west-wide levels-of-growing-stock study. This

study has already answered many of the questions for which it was first designed. 

The wide range of stand densities created under carefully controlled manipulations, 

however, provides opportunities for many satellite studies. One example has been a 

study demonstrating the efficacy of low reserve densities in maintaining stand health. 

Because most tree mortality, whether it is caused by biotic or abiotic factors, is

episodic, evaluations of forest health are meaningful only if reserve stand densities 

are maintained over a long period of time. Another use of the overall data is in the 

construction of growth models for even-aged ponderosa pine stands. The database for 

these models is restricted to remeasured permanent plots, of which the data from the

west-wide levels-of-growing-stock study is a critical part. Some examples of these 

studies follow. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 75 
West wide L-O-G-S Study at Age 40—Oliver 

Figure 2a—Diameter distributions for the extreme Growing Stock Level (GSL) 

treatments after initial thinning and 30 or more years later for three installations 

(Black Hills Poles, Black Hills Saplings and Taylor Woods) in the west-side 

ponderosa pine levels-of-growing-stock study. 

76 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005 
West wide L-O-G-S Study at Age 40—Oliver 

Figure 2b—Diameter distributions for the extreme Growing Stock Level (GSL) 

treatments after initial thinning and 30 or more years later for three installations 

(Crawford Creek, Lookout Mountain and Elliot Ranch) in the west-side ponderosa

pine levels-of-growing-stock study. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 77 
West wide L-O-G-S Study at Age 40—Oliver 

Elliot Ranch 

• Influence of overstory stand density on amount and availability of deerbrush 

(Ceanothus integerrimus Hook. & Arn.) browse for cattle and deer. 

• Influence of overstory shade on growth of five species of conifer seedlings 

(Oliver and Dolph 1992). 

• Influence of Dendroctonus bark beetles on maximum stand density for 

ponderosa pine (Oliver 1995). 

• Demonstration of how to create complex species and stand structures in a 

mono-specific plantation. This has been of particular interest to visitors 

because of the abundant regeneration of mixed conifers and the interest in 

speeding development of more “natural” appearing forests. Unfortunately, 

leaving this advance regeneration unchecked would jeopardize the original 

study objectives. 

Taylor Woods 

• Forage production under different overstory stand densities 

• Testing differences in canopy cover as measured by spherical densiometer 

and moosehorn. 

• Contribution to database for simulating potential production for various 

combinations of stand density, site index, age and thinning schedule

(Alexander and Edminster 1980). 

Black Hills 

• Forage production under different overstory stand densities (Severson and 

Boldt 1977) 

• Influence of stand density on wood quality (Markstrom and others 1983) 

• Costs and returns from pruning stands thinned to various stand densities 

(Smith and others 1988) 

• Contribution to database for simulating potential production for 

various combinations of stand density, site index, age and thinning 

schedule (Myers 1966; Alexander and Edminster 1980). 

Conclusions 

Although the scientists involved in establishing the installations have retired

(four scientists from the Rocky Mountain Research Station have been responsible for

Taylor Woods throughout their careers) and the Pacific Northwest Research Station

has officially abandoned Lookout Mountain and Crawford Creek, the commitment to 

maintain the study remains firm. The Rocky Mountain Research Station continues to

maintain Taylor Woods and the two Black Hills installations. The Pacific Southwest

Research Station has assumed responsibility for Crawford Creek and, with the 

assistance of Oregon State University, Lookout Mountain. 

Early in the life of the study, meetings were held periodically to exchange 

information and coordinate activities. Several decades have elapsed since the last

such meeting. Now may be time for another meeting. It has been evident for some

time that another rethinning of the lower reserve densities is no longer possible in

most installations. Increasing tree size would result in reducing the number of trees 

on the half-acre plots below the 12 to 15 considered to be the minimum needed to

78 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005 
West wide L-O-G-S Study at Age 40—Oliver 

characterize growth response. A restructuring of the array of treatments might be 

discussed as well as an exploration of satellite studies that could be undertaken on 

more than one installation. 

Perhaps the major reason for the longevity of this west-wide study is the

foresight of the original planners in testing a range of stand densities far beyond those 

practiced at the time, thus providing a demonstration of the long-term stand 

development of even-aged ponderosa pine applicable to many current management

objectives. 

References 

Alexander, Robert R.; Edminster, Carleton B. 1980. Management of ponderosa pine in 

even-aged stands in the Southwest. Res. Pap. RM-225. Fort Collins, CO: Rocky

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 11 p.

Alexander, Robert R.; Edminster, Carleton B. 1981. Management of ponderosa pine in 

even-aged stands in the Black Hills. Res. Pap. RM-228. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 10 p.

Barrett, James W. 1983. Growth of ponderosa pine poles thinned to different stocking 

levels in central Oregon. Res. Pap. PNW-311. Portland, OR: Pacific Northwest Forest

and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 9 p.

Boldt, Charles E.; Van Deusen, James L. 1974. Silviculture of ponderosa pine in the Black

Hills: The status of our knowledge. Res. Pap. RM-124. Fort Collins, CO: Rocky

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 45 p.

Cochran, P.H.; Barrett, James W. 1995. Growth and mortality of ponderosa pine thinned 

to various densities in the Blue Mountains of Oregon. Res. Pap. PNW-RP-483 .

Portland, OR: Pacific Northwest Forest and Range Experiment Station, Forest Service,

U.S. Department of Agriculture; 27 p. 

Cochran, P.H.; Barrett, James W. 1999. Growth of ponderosa pine thinned to different 

stocking levels in central Oregon: 30-year results. Res. Pap. PNW-RP-508. Portland, 

OR: Pacific Northwest Research Station, Forest Service, U.S. Department of 

Agriculture; 27 p.

Conkle, M. Thompson; Critchfield, William B. 1988. Genetic variation and hybridization

of ponderosa pine. In: Baumgartner, David M.; Lotan, James E., compilers and editors. 

Proceedings of the symposium on ponderosa pine: the species and its management. 

Pullman, WA: Cooperative Extension, Washington State University; 27-43. 

Edminster, Carleton B. 1988. Stand density and stocking in even-aged ponderosa pine 

stands. In: In: Baumgartner, David M.; Lotan, James E., compilers and editors. 

Proceedings of the symposium on ponderosa pine: the species and its management. 

Pullman, WA: Cooperative Extension, Washington State University; 253-260. 

Gaines, Edward M.; Kotok, E.S. 1954. Thinning ponderosa pine in the Southwest. Sta. Pap. 

17. Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest

Service, U.S. Department of Agriculture; 20 p. 

Markstrom, Donald C.; Troxell, Harry E.; Boldt, Charles E. 1983. Wood properties of 

immature ponderosa pine after thinning. Forest Products Journal 33(4): 33-36. 

Meyer, Walter H. 1938 (Rev. 1961). Yield of even-aged stands of ponderosa pine. Tech. 

Bull. 630; Washington, DC: U.S. Department of Agriculture, 59 p.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 79 
West wide L-O-G-S Study at Age 40—Oliver 

Mowat, Edwin L. 1953. Thinning ponderosa pine in the Pacific Northwest. Res. Pap. 5.

Portland, OR: Pacific Northwest Forest and Range Experiment Station, Forest Service,

U.S. Department of Agriculture; 24 p. 

Myers, Clifford A. 1958. Thinning improves development of young stands of ponderosa

pine in the Black hills. Journal of Forestry 56(9): 656-659. 

Myers, Clifford A. 1966. Yield tables for managed stands with special reference to the 

Black Hills. Res. Pap. RM-21. Fort Collins, CO: Rocky Mountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 20 p.

Myers, Clifford A. 1967. Growing stock levels in even-aged ponderosa pine. Res. Pap.

RM-33. Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 8 p. 

Oliver, William W. 1979. Growth of planted ponderosa pine thinned to different stocking 

levels in northern California. Res. Pap. PSW-147. Berkeley, CA: Pacific Southwest 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture;

11 p.

Oliver, William W. 1997. Twenty-five-year growth and mortality of planted ponderosa

pine repeatedly thinned to different stand densities in northern California. Western

Journal of Applied Forestry 12(4): 122-130.

Oliver, William W.; Dolph, K. Leroy. 1992. Mixed-conifer seedling growth varies in

response to overstory release. Forest Ecology and Management 48: 179-183. 

Oliver, William W. 1995. Is self-thinning of ponderosa pine ruled by Dendroctonus bark

beetles? In: Eskew, Lane G., compiler. Proceedings of the 1995 national silviculture 

workshop of forest health through silviculture. Gen. Tech. Rep. RM-GTR-267. Fort

Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture; 213-218. 

Oliver, William W.; Edminster, Carleton B. 1986. Growth of ponderosa pine thinned to 

different stocking levels in the western United States. In: Schmidt, Wyman C., 

compiler. Proceedings - Future forests of the Mountain West. Gen. Tech. Rep. INT-243. 

Ogden UT: Intermountain Research Station, Forest Service, U.S. Department of 

Agriculture; 153-159. 

Oliver, William W.; Ryker, Russell. 1990. Pinus ponderosa Dougl. ex Laws. Ponderosa

pine. In: Burns, Russell M.; Honkala Barbara H., tech. coord. Silvics of North America

Volume 1, Conifers. Agric. Handb. 654. Washington, DC: U.S. Department of 

Agriculture; 413-424. 

Reineke, L.H. 1933. Perfecting a stand-density index for even-aged forests. Journal of

Agricultural Research 46: 627-638. 

Ronco, Frank, Jr.; Edminster, Carleton B.; Trujillo, David P. 1985. Growth of ponderosa

pine thinned to different stocking levels in northern Arizona. Res. Pap. RM-262. 

Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest

Service, U.S. Department of Agriculture; 15 p. 

Severson, Kieth E.; Boldt, Charles E. 1977. Options for Black Hills forest owners: timber, 

forage, or both. Rangeman’s Journal 4(1):13-15. 

Schubert, Gilbert H. 1971. Growth response of even-aged ponderosa pines related to 

stand density levels. Journal of Forestry 69: 857-860.

Smith, Richard C.; Kurtz, William B.; Johnson, Thomas E. 1988. Cost efficiency of pruning 

Black Hills ponderosa pine. Western Journal of Applied Forestry 3(1): 10-14.

80 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005 
Accelerating Development of LateSuccessional Features in Second-Growth 

Pine Stands of the Goosenest Adaptive 

Management Area1

Martin W. Ritchie2 and Kathleen A. Harcksen3

Abstract 

This paper describes implementation and early results of a large-scale, interdisciplinary 

experiment in the Goosenest Adaptive Management Area in northeastern California. The 

study is designed to investigate development of late-successional forest attributes in secondgrowth ponderosa pine stands. The experiment has four treatments replicated five times and

encompasses 1600 hectares, including controls. Complete treatment implementation took five

years, including application of prescribed fire. Initial post-treatment measurements were 

conducted in 2002. Change in quadratic mean diameter averaged 12.5 cm among thinned

stands. Initial estimates of post-treatment growth from remeasured diameters indicate little

immediate impact of treatments on individual tree growth. However increment cores from

dominant trees showed an increase in diameter growth by 11 to 14 percent in the treated plots

during the first three years after treatment. Quadratic mean diameter in thinned stands was

still well below that reported in reference old-growth stands. Among those stands treated with 

a targeted change in species composition, the mean treatment effect was an increase of 16 

percent in proportion of pine basal area, with a range from 6 to 29 percent. The control

treatment and thin from below treatment showed no significant change in species 

composition. The initial application of prescribed fire resulted in little mortality (less than 1

percent for large trees) and had no immediate impact on the diameter distribution. Logging 

damage observed on residual trees varied between 2 and 6 percent, depending on treatment 

and tree size. 

Introduction 

The Northwest Forest Plan (USDA and USDI 1994a) ushered in a new era for 

forest management on federal land in the Pacific Northwest. Intended to implement

management strategies that would be more favorable to the meet the habitat 

requirements of the northern spotted owl (Strix occidentalis caurina), the Plan

changed management emphasis for millions of acres of forests in Washington, 

Oregon and northern California. One requirement of the Record of Decision (USDA 

and USDI 1994b) of the Northwest Forest Plan was to establish a network of 

1

 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends, and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Biometrician, Pacific Southwest Research Station, Redding Silviculture Laboratory, 3644 Avtech

Parkway, Redding CA 96002, (email: mritchie@fs.fed.us) 3

 Silviculturist, Parashant National Monument, Arizona Strip BLM, 345 East Riverside Drive, St. 

George UT 84790, (email: harcksen@blm.gov) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 81 
Goosenest AMA—Ritchie and Harcksen 

Adaptive Management Areas, thus providing managers opportunities to develop and 

test innovative strategies to meet management objectives. 

The Goosenest Adaptive Management Area is located in northern California on

the Klamath National Forest. One of the primary objectives of the Goosenest AMA

is to evaluate “...the development of ecosystem management approaches, including

the use of prescribed burning and other silvicultural techniques for management of

pine forest including objectives related to forest health, production and maintenance 

of late-successional forest and riparian habitat, and commercial timber production” 

(USDA and USDI 1994b; Page D-13). 

Harvesting in the early 1930s removed the largest and most valuable pines and

most of the larger white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.). The 

land was transferred to the Klamath National Forest in the 1950s. Subsequently,

some of the area received precommercial thinning and sanitation/salvage treatments. 

The historic fire return interval in these stands created an environment favoring 

ponderosa pine (Pinus ponderosa P. & C. Lawson), a long-lived species well adapted 

to frequent low-intensity fires (Skinner and Chang 1996). The harvest of overstory

pine trees and the elimination of fire from the ecosystem have significantly changed 

the size and species distributions of trees throughout the AMA. 

Forests in this area are naturally regenerated second-growth stands with

ponderosa pine and white fir as the primary tree species. There are lesser amounts of

sugar pine (Pinus lambertiana Dougl.), incense-cedar (Calocedrus decurrens (Torr.) 

Florin) and red fir (Abies magnifica A. Murr.) at the higher elevations. Historically

this area featured open park-like stands dominated by large ponderosa pine trees. 

Measured in 2004, breast-height age of dominant, site quality, pine averages 64 years 

with a range from 49 to 85. There is a component of 200+ year old trees scattered

through the overstory, however the heights indicate that these were subdominant

(intermediate crown class) trees in 1930, and released by the initial harvests. These 

trees have diameters and heights very similar to those of the trees that regenerated 

after overstory removal. 

In 1995, the Klamath National Forest and the Pacific Southwest Research

Station entered into a partnership to establish a study on the AMA to address key 

issues stated in the Record of Decision. An interdisciplinary research team, engaged

in work at Blacks Mountain Experimental Forest (Oliver and Powers 1998, Oliver 

2000), began working with managers from the Goosenest Ranger District to

investigate problems and potential treatments to evaluate on the AMA. The research

team considered a range of issues relating to development of late-successional forest 

conditions. The resulting project is a long-term study geared to evaluating the effects 

of large-scale treatments designed to accelerate tree growth, create more open stand

conditions and re-introduce fire to the system (Ritchie and Harcksen 1999, Ritchie 

2005). Our study will provide information to managers and researchers seeking a 

better understanding of the consequences of various management strategies in stands 

with a similar treatment history and species composition. 

This paper describes treatment implementation and presents some early

treatment effects on vegetation and coarse woody debris. 

82 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Goosenest AMA—Ritchie and Harcksen 

Methods

Study Design 

The research team focused on three key factors in designing this study: species

composition, distribution of trees by diameter class, and the role of fire in this

system. In order to accelerate late successional stand attributes we wish to create

stands with (1) a higher proportion of ponderosa pine, (2) more open conditions with 

larger trees, and (3) fire as a functioning component of the system. The study was 

designed to evaluate combinations of these three factors. 

The AMA is located at 41.5 N latitude and 121.9 W longitude. The elevational 

range for the study site is 1,480 to 1,780 m (4,860 to 5,840 ft). The forest type (Eyre

1980) is predominantly Interior Ponderosa Pine (Society of American Foresters Type

237). Slopes are gentle, generally with a northwest aspect. Soils in the study area are 

sandy loams or loams derived from volcanic ash. A 20 to 36 cm (8 to 14 in) pumice 

overburden is common in the area. Site productivity is difficult to estimate in this 

area because current site quality trees are from two separate age cohorts, and many 

have not been truly free-to-grow. Based on the second-generation stand (trees with a 

breast height age < 70 years) site index (Barrett 1978) is 37 m (120 ft) at a base age 

of 100. Converted to a base age of 50 years, site index is 25 m (82 ft). This converts 

to a Forest Service Region 5 site class of 3. 

In 1996, a sample of 20 stands in the area was selected to evaluate stand 

structure, species composition, and appropriateness for inclusion in the study (table 

1). This represents pre-treatment conditions for stands within the study area. Units 

with recent sanitation and salvage entries tended to be more open than those without 

recent treatment history. Reineke’s (1933) Stand Density Index (SDI) exceeded 570 

(230 trees ac-1), the zone of imminent mortality reported by Oliver (1995), in over 

half of these stands. 

Table 1—Summaries of pre-treatment quadratic mean diameter (QMD), basal area (BA),

stand density index (SDI), stem density (N), and percentage of basal area in pine for stands of

the Goosenest Adaptive Management Area. Units are metric with English equivalents in 

parentheses. 

QMD BA SDI N Pine BA 

cm 

(in) 

m2 ha-1

(ft

2

 ac-1) 

trees ha-1

(trees ac-1) 

trees ha-1

(trees ac-1) percent 

Minimum 24.6 ( 9.7) 26.6 (116) 474 (192) 217 ( 88) 15 

1st Quartile 28.2 (11.1) 30.3 (132) 523 (212) 385 (156) 31

Median 29.0 (11.4) 37.0 (161) 689 (279) 568 (230) 43 

3rd Quartile 39.4 (15.5) 42.9 (187) 822 (333) 778 (315) 60

Maximum 41.1 (16.2) 58.3 (254) 1084 (439) 902 (365) 73 

There were four treatments: Pine Emphasis, Pine Emphasis with Fire, Large

Tree, and a Control treatment. Each treatment was replicated five times in a

completely randomized design (fig. 1). Each treatment unit was 40 ha (100 ac), with 

an additional buffer of approximately 100 m (328 ft). This experimental unit size was 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 83 
Goosenest AMA—Ritchie and Harcksen 

considered to be sufficient to encompass the range of small mammals and passerine 

birds (although this aspect of the study is not presented here). The number of 

replicates and variety of treatments was restricted by our ability to locate units of 

sufficient size with fairly uniform conditions. 

Figure 1—Map of the treatments at the Goosenest Adaptive Management Area. 

The Pine Emphasis treatment was intended to accelerate growth of trees and 

modify species distribution by moving stands toward ponderosa pine dominance. The 

prescription called for a thinning from below with required retention of all dominant 

and co-dominant ponderosa pine and sugar pine, regardless of spacing (Ritchie 

2005). Spacing for fir and intermediate or suppressed pine was determined by tree 

size with larger leave trees having a greater spacing than smaller trees. Because of the

“must leave” requirement for ponderosa pine and sugar pine dominant and codominant trees, the resulting spacing was not uniform. Small aggregates of closely

spaced trees were left scattered through the stand. Because artificial regeneration was 

the only effective means for changing species composition in areas with very dense

white fir, small openings, totaling 15 percent of the area, were created in each unit 

and planted with ponderosa pine seedlings. The openings were deep-tilled to 

penetrate the pumice overburden and planted with 2-0 ponderosa pine seedlings. 

The Pine Emphasis with Fire treatment began with the same thinning

prescription and artificial regeneration as the Pine Emphasis. The thinning was then

followed with application of prescribed fire. The application of prescribed fire took 

place after planting for some of the units, however fire did not carry through the 

plantations because the sub-soiling treatment buried surface fuels and exposed 

mineral soil. 

84 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Goosenest AMA—Ritchie and Harcksen 

The prescription called for stands to be burned repeatedly over time in a manner 

consistent with both the historic fire frequency, and fuel loadings sufficient to carry

fire. Stands are to be re-evaluated periodically for the potential to carry fire in 

subsequent prescribed burns. A study is currently underway to document the historic

fire frequency of the Goosenest AMA. 

The Large Tree treatment was intended to address only the size distribution of

trees in the stand. The prescription was a thinning from below with no regard for 

species. The intent was to create more large trees as quickly as possible by removing

the smaller diameter trees. Since species distribution was not relevant to this

treatment, there is no regeneration component. The prescription called for a sizedependent spacing guide (Ritchie 2005). The spacing varied from about 5 m to 9 m 

(16 to 30 ft), with larger leave trees being more widely spaced. This prescription 

tended to create a more uniform spacing than the Pine Emphasis treatment because

there was no restriction on cutting dominant and co-dominant pine trees. 

The Control treatment was consistent with custodial management. No thinning,

prescribed burning, or salvage was conducted in the Controls. By comparing our 

treated units with Control units, we can quantify the impact of our prescriptions on a 

variety of treatment response variables.

All units have a 100 m (328 ft) grid of permanently monumented sample points;

UTM coordinates for these points have an error of less than 15 cm (6 in). All data 

were spatially referenced to these grid points to facilitate integration of results from 

different disciplines (Oliver 2000). 

Treatment Implementation 

The Goosenest Ranger District completed the NEPA process, signed the Finding 

of No Significant Impact, and offered the timber for bid in 1997. Total revenue for 

the timber sale was $5.474 million. Scaling was done by weight; removals totaled

92,669 metric tons (green weight) of sawlogs and peelers, and 62,004 metric tons of 

chips from saplings, limbs, and tops. 

To ensure conclusions would be based on the effects of the treatments, not on

how the treatments were implemented, the control of all activities within the 

treatment units was important. To this end, the entire project was offered as one 

timber sale, knowing full well it would take at least three years to complete. 

Harvesting started in July 1998 and was completed in October 2000. In the first 

season, one complete replicate was thinned. In each of the two following years, two 

replicates were completed. All treatments were “leave-tree” marked, and all landings

were located outside the treatment units. Two natural openings became the 

processing landings” Skid trails were pre-designated at approximately 60 m (200 ft) 

spacing. Operators were required to place (with feller-bunchers) or fall all trees to 

lead. Grapple skidders were restricted to the designated skid trails. Operations were 

authorized only when the soil was adequately drained to prevent compaction, and

was neither frozen nor covered with snow. 

First, the feller-bunchers cut and placed next to skid trails all trees from 10 cm to

45 cm (4 to 18 in). As the operation progressed across the unit, the skidders followed, 

dragging the bundles of trees to a “hot landing.” A heal-boom loader was used to sort 

the trees by size and species and load them onto a hay-rack (fig. 2). All limbs and 

tops accumulating at the landing were redistributed along skid trails by the grapple 

skidders. Finally, the fallers hand-felled trees greater than 45 cm (18 in) DBH. These

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 85 
Goosenest AMA—Ritchie and Harcksen 

trees were limbed, topped and skidded to the hot landing where they were loaded

onto the hay-rack and hauled to the processing landing. 

At the processing landings, trees were sorted by size and species. Ponderosa 

pine was processed for saw logs and white fir was processed as peelers. Trees larger

than 20 cm (8 in) were limbed, topped, and cut to length by a stroke delimber. 

Saplings between 10 and 20 cm (4 and 8 in) were processed as clean chips for paper. 

Remaining saplings, tops and limbs were then processed for hog fuel. 

After harvesting, the openings in the Pine Emphasis treatment units were deeptilled and then planted. 

Figure 2—Trees being transported from the hot landing to the processing site at the

Goosenest Adaptive Management Area. 

To minimize damage to fine roots and active cambium, fall burning was used in 

application of prescribed fire. The initial burns were conducted in October 2001 to all

five of the Pine Emphasis with Fire units. Burning of each unit took up to three days. 

Although Forest Service crews typically use a strip burning technique, tree centered 

firing was widely used when possible (Weatherspoon and others 1989).

Vegetation Sampling Methods 

Each treatment unit has approximately 36 grid points, at 100 m (328 ft) spacing, 

depending on orientation of unit boundaries. The number is slightly less than 40 due

to restrictions on grid point establishment near the plot boundary. Every other grid 

point was selected for vegetation sampling, such that the sampled grid points are 

spaced at 141 m (463 ft) intervals. 

The initial post-treatment vegetation sample was conducted in 2002, the season 

following completion of all harvesting and the initial application of prescribed fire.

Typically such sampling would be done after the end of the growing season.

However, due to the scale of this study, that was not possible. We may have to adjust 

growth to account for the period lengths between subsequent remeasurements 

(Flewelling and Peters 1997). The initial vegetation sampling and permanent plot

establishment took two three-person crews the entire summer to complete. 

At each sampled grid point, three nested fixed-area plots were established. Trees 

> 29.2 cm (11.5 in) breast-height diameter were sampled on a 0.81 ha (0.2 acre) plot 

86 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Goosenest AMA—Ritchie and Harcksen 

centered on the grid point. Trees from 9.1 to 29.2 cm (3.6 to 11.5 in) diameter at 

breast height were sampled on a 0.020 ha (0.05 acre) plot, also centered on the grid 

point. Trees < 9.1 cm (3.6 in) diameter were tallied by 2.5 cm (1-inch) diameter

classes on 0.004 ha (0.01 ac) plots. 

Species, height, diameter, and height to crown base were recorded for each tree. 

We also recorded damage, with particular emphasis on damage related to treatment 

implementation. Damage was primarily bole scars from either skidding or fire scorch. 

In order to evaluate growth on dominant (site-quality) trees, we sampled 36 site 

quality trees (Barrett 1978) on three treatment units. Increment cores were obtained 

from each tree and radial growth rates (periodic annual increment) were observed for

the 2-yr period immediately before and after treatment. We conducted a paired t-test 

on pre and post treatment growth for each of the treatment units. 

Coarse woody debris was sampled on a 100 m (328 ft) transect using the 

methods described by Brown (1978). Transects were centered on every grid point

where trees were sampled. Material was identified as being either decay class 1

(recent material), class 2 (some decay but still structurally intact), or class 3 

(advanced decay with no structure). 

Results 

The study was designed to evaluate responses over a 50-year time line. 

However, initial results can indicate something of the potential for effectiveness over 

the long-term as well as provide an indication of short-term changes in stand 

structure and habitat. 

Stand Structure 

The initial entry increased the proportion of pine for both Pine Emphasis and 

Large-Tree treatments, although the increase tended to be greater for the Pine 

Emphasis units. Large-Tree units showed a small increase in pine because a thin from 

below, with a dominance of fir in the understory, necessarily produces a reduction in 

fir (fig. 3). As the pine plantations develop, this change in proportion of pine should 

become more pronounced in the Pine Emphasis units. 

Figure 3—Change in species composition for four treatments in the Goosenest

Adaptive Management Area (error bars = standard error). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 87 
Goosenest AMA—Ritchie and Harcksen 

A comparison of pre- and post-treatment diameter distributions, averaged across

treatment units (fig. 4), shows that the skewed pre-treatment size distribution has

been modified to a more symmetric distribution. There were very few trees above 60

cm (24 in) in diameter throughout the study (generally less than 15 trees per ha or 6

trees per acre). The Pine Emphasis units appear to have a higher proportion of pine,

particularly in the middle diameter classes. 

Figure 4 — Diameter distributions before (1996) and after (2002) treatment, 

averaged across experimental units, for the treatments (excluding Controls) in the

Goosenest Adaptive Management Area. 

88 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Goosenest AMA—Ritchie and Harcksen 

Because treatments targeted the lower diameter classes, there is a pronounced

“chainsaw effect” on QMD. QMD increased in treated units an average of 12.5 cm

(4.9 in), ranging from 2.3 to 19.3 cm (0.9 to 7.6 in); QMD is substantially higher than 

in controls, as seen in the following tabulation. 

Control Large Tree Pine Emphasis Pine Emphasis with Fire 

30.8 cm ± 1.5 43.5 cm ± 1.4 45.1 cm ± 1.6 43.6 cm ±1.6

The shape of the current diameter distribution in these stands is more consistent

with hypothesized late-successional forest structure, where frequent low-intensity 

fires maintained a more open understory. 

Number of large trees, defined as those > 60 cm (24 in) in diameter, varies 

across all treatments (fig. 5) from 5 to 35 trees ha-1 (2 to 14 trees ac-1). Basal area was

reduced an average of 29 percent for Pine Emphasis plots and 35 percent for Large 

Tree units. Stand density index (Reineke 1933) now ranges between 356 (143 ac-1) 

and 453 (182 ac-1) for the five Large Tree units and between 326 (131 ac-1) and 572

(230 ac-1) for the five Pine Emphasis Units. 

Figure 5 — Post-treatment (2002) proportion of pine, and number of large trees,

defined as those > 60 cm ( 24 in) DBH, for treatment units in the Goosenest Adaptive

Management Area.

Mortality and Damage 

Initial mortality rates are low, indicating little damage to residual stands 

immediately after harvest and application of prescribed fire. Logging damage was

also generally low (estimated below 6 percent) regardless of treatment and tree size.

Damage was significantly less (P=0.001) among trees > 50 cm (20 in) in the Large 

Tree treatment when compared with the Pine Emphasis treatments (fig.6). This 

difference may be attributable to a more clumpy distribution of trees in the Pine 

Emphasis units. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 89 
Goosenest AMA—Ritchie and Harcksen 

Burn damage to residual trees in the units receiving prescribed fire was also low. 

Initial mortality among trees > 29 cm (11.5 in) diameter was less than 1 percent. Firerelated mortality among trees between 9 and 29 cm (3.5 and 11.5 in) DBH averaged 

3.5 percent. This mortality rate is probably an underestimate because it only includes 

those trees killed within the first year after burning and does not reflect any 

secondary mortality that may occur over the next several years (Ryan and others 

1988). 

Initial Growth Response 

Thinning in ponderosa pine generally increases growth on residual trees 

(Cochran and Barrett 1995, Cochran and Barrett 1999). A preliminary analysis of 

two-year thinning response, using a sample of trees from three different treatment 

units, revealed no significant change in tree growth in response to thinning. However, 

this may be due to high variability within treatments or because it may take several

years for trees to build sufficient crown and roots to take advantage of the increase in 

available resources. The only evidence of accelerated growth was among small trees.

Because most of the smaller trees were removed, there are very few residual trees

less than 30 cm (12 in) in the treated units, so sample size was limited. 

The treated plot with the greatest gain in diameter increment was the Pine Emphasis 

plot, with an increase of 14+12 percent (+90 percent confidence interval). In the 

Large Tree and Pine Emphasis with Fire Treatments we observed approximately 11+ 

23 and 11+22 percent radial growth increase respectively. Note that the confidence 

interval includes zero for both the Large Tree and Pine Emphasis with Fire 

Treatments. 

Figure 6 — Percentage of damaged trees by diameter class for Large Tree and Pine

Emphasis Treatments (error bars = 1 standard error).

Woody Debris 

The primary treatment impact on woody debris was from fire. There was no

detectable difference between mechanical treatments. However a comparison of Pine

Emphasis units and Pine Emphasis with Fire units showed a significant reduction in

volume. Debris in a more advanced state of decay is substantially (73 percent by

volume) reduced by fire (P=0.013). Material in a less advanced state of decay was 

90 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Goosenest AMA—Ritchie and Harcksen 

reduced about 43 percent on average (P=0.120). Differences between burned (Pine 

Emphasis with Fire) and unburned (Pine Emphasis) was limited to smaller diameter 

class material (table 2). 

Table 2 — Post-treatment means (with standard error) for number of woody debris pieces 

 ha-1 for Pine Emphasis (no burn) and Pine Emphasis with Fire (burn), by size class.

Length 

Diameter < 2m 2 – 4 m 4 – 6 m 

burn no burn burn no burn burn no burn 

< 25 cm 171 (16) 697 (186) 49 (8) 227 (65) 16 (6) 81 (20) 

25-50 cm 75 (18) 175 (37) 48 (15) 81 (29) 14 (9) 34 (11) 

50-75 cm 19 (4) 18 (4) 6 (3) 6 (3) 6 (3) 18 (8) 

> 75 cm 3 (3) 6 (4) 3 (3) 3 (3) 0 (0) 1 (1) 

Discussion 

Observations of changes in growth rate are small at this point, primarily because 

it takes a few years for trees to develop leaves and roots to exploit the increased

availability of resources. The growth rate increase observed for dominant trees 

appears to be less than that for stands with similar levels of growing stock observed

by Cochran and Barrett (1999) who found that diameter growth increased by

approximately 40 percent. However Cochran and Barrett (1999) had 30 years of

observations. The results suggest that growth rates in the prescribed fire units are

slightly less than those in Pine Emphasis units. This is consistent with research

showing that diameter growth was suppressed, in the short term, following

application of prescribed fire (Busse and others 2000). 

Differences in diameter distribution are fairly subtle, except for the obvious 

difference between harvested and control units. Mortality processes initiated by fire 

and insects may take an extended period to significantly impact the dynamics of these

stands. The expected distribution of large trees in late successional pine stands is

difficult to ascertain. One of the few un-disturbed sites left in California averaged 17 

trees ha-1 in trees > 60 cm (7 trees ac-1 >24 in) DBH, with a QMD of 53 cm (21 in)

(Beaver Creek Pinery, data on file PSW Research Station, Redding CA). Treated unit 

QMD ranges from 36 to 48 cm (14.0 to 18.7 in). Youngblood and others (2004)

found QMD of 60 cm in (24 in) old-growth ponderosa pine stands and density of

overstory trees ranging from 15 to 53 ha-1 (6 to 21 ac

-1). With current growth rates, it

could take a decade or more to increase stand diameter another 10 cm (4 in). 

As one would expect, there were no discernable trends with regard to the 

number of trees > 60 cm (24 in) in the 2002 post treatment data. If any treatment

effect is observed, it may take decades to detect. 

The snag retention in units with prescribed fire is not consistent with published 

guidelines that range from 2-10 snags ha-1 (5 to 25 ac

-1)(Bunnell and others 2002;

USDA and USDI 1994b; USDA 2004). Maintenance of snags with frequent lowintensity fires is difficult because fire-induced mortality is low while many existing 

snags are consumed. 

The rate of consumption of down material by fire at this site suggests that, with 

frequent application of prescribed fire, there will be very little coarse woody debris 

present, particularly with regard to material in an advanced state of decay. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 91 
Goosenest AMA—Ritchie and Harcksen 

Mortality and damage resulting from thinning was kept at low levels by laying

out all skid trails in advance, marking all leave trees, and closely supervising

operators. 

Acknowledgements 

This paper is contribution number 11 of the Goosenest Adaptive Management

Area Ecological Research Project. Supplemental data collection and analyses were

completed by Nick Vaughn, Todd Hamilton, and Brian Wing. 

References 

Barrett, J.W. 1978. Height growth and site index curves for managed even-aged stands of

ponderosa pine in the Pacific Northwest. Res. Pap. PNW-232. Portland, OR: Pacific 

Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 14 p.

Brown, J.K. 1974. Handbook for inventorying downed woody material. Gen. Tech. Rep. 

INT-16. Ogden, UT: Intermountain Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 24 p. 

Bunnell, F.L.; Boyland, M.; Wind, E. 2002. How should we spatially distribute dying and

dead wood? In: Laudenslayer, W.F., P.J. Shea, B.E. Valentine, C.P. Weatherspoon and 

T.E. Lisle (Tech. Coordinators). Proceedings of the symposium on the Ecology and 

Management of Dead Wood in Western Forests. 1999 November 2-4; Reno, NV. Gen.

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; 739-752.

Busse, M.D.; Simon, S.A.; Riegel, G.M. 2000. Tree growth and understory responses to 

low-severity prescribed burning in thinned Pinus ponderosa forests of central

Oregon. Forest Science. 46: 258-268. 

Cochran, P.H.; Barrett, J.W. 1995. Growth and mortality of ponderosa pine poles thinned 

to various densities in the Blue Mountains of Oregon. Res. Pap. PNW-RP-483. 

Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department of

Agriculture; 27 p.

Cochran, P.H.; Barrett, J.W. 1999. Growth of ponderosa pine thinned to different stocking 

levels in Central Oregon: 30 year results. Res. Pap. PNW-RP-512. Portland, OR:

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 28

p. 

Eyre, F.H., ed. 1980. Forest cover types of the United States and Canada. Washington, 

DC: Society of American Foresters; 148 p. 

Flewelling, J.; Peters, R. 1997. Calculation of periodic annual increment (PAI) on 

permanent plots using within-growing-season measurements. In Ortega, A.; Gezan,

S., editors. Modeling growth of fast grown tree species. Proceedings, IUFRO Conf.;

Sept. 5-7, 1997; Valdivia, Chile; Universidad Austral de Chile; 110-116. 

Oliver, W.W. 1995. Is self-thinning of ponderosa pine ruled by Dendroctonus bark

beetles? In: Eskew, L.G., editor. Forest Health through Silviculture. Proceedings 1995 

National Silviculture Workshop. Gen. Tech. Rep. RM-GTR-267. Fort Collins, CO:

Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture; 213-

218. 

Oliver, W.W. 2000. Ecological research at the Blacks Mountain Experimental Forest in 

northeastern California. Gen. Tech. Rep. PSW-GTR-179. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 66 p. 

Oliver W.W.; Powers, R.F. 1998. Blacks Mountain California: Interdisciplinary field 

research in ponderosa pine. Journal of Forestry 96(8): 4-9. 

92 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Goosenest AMA—Ritchie and Harcksen 

Reineke, L.H. 1933. Perfecting a stand-density index for even-aged forests. Journal of

Agricultural Research 46: 627-638. 

Ritchie, M.W. 2005. Ecological Research at the Goosenest Adaptive Management Area in

Northeastern California. Gen. Tech. Rep. PSW-GTR-192. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 119 p. 

Ritchie, M.W.; Harcksen, K.A. 1999. Long-term interdisciplinary research on the 

Goosenest Adaptive Management Area, Klamath National Forest, California.

Forestry Chronicle 75(3): 453-456. 

Ryan, K.C.; Peterson, D.L.; Reinhardt, E.D. 1988. Modeling long-term fire-caused 

mortality in Douglas-fir. Forest Science 34(1): 190-199. 

Skinner, C.N.; Chang, C.-R.. 1996. Fire regimes, past and present. P. 1041-1069 in Sierra

Nevada Ecosystem Project: Final Report to Congress, Volume II. Assessments and 

scientific basis for management options. University of California, Davis. 

U.S. Department of Agriculture, Forest Service; U.S. Department of Interior, Bureau of Land

Management. 1994a. Final supplemental environmental impact statement on

management of habitat for late-successional and old growth forest related species

within the range of the northern spotted owl. Volume1. Washington, D.C.: U.S.

Forest Service, Department of Agriculture and U.S. Bureau of Land Management. 

U.S. Department of Agriculture, Forest Service; U.S. Department of Interior, Bureau of Land

Management. 1994b. Record of decision for amendments of forest service and 

bureau of land management planning documents within the range of the northern 

spotted owl. Washington, D.C.: Forest Service, U.S. Department of Agriculture and

U.S. Bureau of Land Management. 

U.S. Department of Agriculture. 2004. Sierra Nevada Forest Plan Amendment, Record of 

Decision. Washington, D.C.: Forest Service, U.S. Department of Agriculture.

Weatherspoon, C.P.; Almond, G.A.; Skinner, C.N. 1989. Tree-centered spot firing – a 

technique for prescribed burning beneath standing trees. Western Journal of Applied

Forestry. 4(1):29-31. 

Youngblood, A.; Max, T.; Coe, K. 2004. Stand structure in eastside old-growth ponderosa

pine forests of Oregon and northern California. Forest Ecology and Management. 

199:191-217. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 93 

Positive Seedling-Shrub Relationships in 

Natural Regeneration of Ponderosa Pine1

Christopher R. Keyes2 and Douglas A. Maguire3

Abstract 

An understanding of natural regeneration processes, and the stand structural features that

influence those processes, is vital to attaining goals associated with natural regeneration. This 

paper discusses natural regeneration concepts and the interactions that occur between shrubs

and natural regeneration of ponderosa pine. The interactions observed recently in a series of 

related seedling recruitment studies in central Oregon are summarized. Evidence suggests a 

positive relationship between shrubs and the occurrence of ponderosa pine seedlings during

the first two years of the seedling establishment phase. The vast majority of germinant 

mortality occurs during summer months, and especially the weeks immediately after 

emergence. Shrubs do not enhance emergence rates, but do enhance overall recruitment rates 

by reducing rates of first-summer mortality. The mechanism driving these patterns appears to

be microenvironmental amelioration by shrubs, abating germinant moisture stress and 

desiccation. The manifestation of this relationship is a positive spatial relationship between

shrubs and small seedlings during this establishment phase. 

Introduction 

For most forest management objectives, the recruitment of a cohort of seedlings

is the first and most critical process following regeneration harvest or stand-replacing 

disturbance. The spatial and temporal patterns of seedling recruitment set the stage 

for all subsequent stand development patterns; hence, the seedling recruitment stage 

is the first step in determining future stand structures, habitat conditions,

susceptibility to disturbances, and silvicultural options. An understanding of the

natural regeneration processes in forests of ponderosa pine (Pinus ponderosa P. & C. 

Lawson), and the stand structural features that have bearing on those processes, is

vital to manipulating controllable factors in order to successfully secure natural

regeneration. This subject is particularly relevant under the current Forest Service 

paradigm of ecosystem management, wherein reliance upon natural processes in

natural systems management is stressed, and funds for reforestation are scarce. 

An understanding of regeneration processes is equally important for those 

management objectives wherein regeneration is undesirable. For example, managers

may wish to maintain crown fire resistance by promoting ponderosa pine stands with

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2 Assistant Professor, Department of Forestry and Watershed Management, Humboldt State University, 

Arcata, California 95521 (e-mail: Christopher.Keyes@humboldt.edu) 3

 Associate Professor, Department of Forest Science, Oregon State University, Corvallis, OR 97331

95521 (e-mail: Doug.Maguire@oregonstate.edu)

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 95 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

open-understory structures that are free of ladder fuels. Currently, management and

research in this region is directed toward dealing with the existing condition of dense 

ponderosa pine stands. However, it is worthwhile to analyze the processes that have 

contributed to the development of these dense stands in the era of fire suppression

and exclusion. It is reasonable to theorize that the effects of fire exclusion on 

ponderosa pine regeneration have been both direct and indirect. If the relationship of

shrubs to seedling recruitment is positive, for example, it then follows that one effect

of fire exclusion may have been the indirect proliferation of pine seedlings by

enabling dense shrub understories to establish and persist. An understanding of these 

and other potential indirect effects of fire exclusion on pine proliferation is essential 

to prescribing practices that will create and sustain stands with crown fire resistance. 

Despite an abundance of previous research on the subject, the effects of shrubs 

on processes of ponderosa pine natural regeneration are still poorly understood. 

Research efforts have been geographically limited, short in duration, and restricted to 

a single stage of regeneration, a situation that is typical of regeneration research in 

other species and regions as well (Clark and others 1999). The result has been 

sometimes-conflicting and often-confusing advice for forest managers dealing with 

regeneration objectives. This paper addresses the relationship of shrubs to the

establishment of ponderosa pine regeneration with a discussion of shrub effects 

within the context of recent conceptual models of facilitation and competition that

have been applied in similarly xeric ecosystems. We also offer evidence of positive 

seedling-shrub relationships in a summary of the results of three integrated 

establishment-phase regeneration studies that were recently conducted in central

Oregon. 

Constraints on Regeneration 

Several ubiquitous biological and physical factors are capable of limiting 

seedling recruitment in ponderosa pine forests, and often do so (table 1). Many of

these factors may occur simultaneously during any given year, thus severely

curtailing opportunities for regenerating ponderosa pine without human intervention.

Among those factors, moisture stress represents the most significant of practicably 

controllable factors. The potential roles of phytotoxins as chemical regeneration 

inhibitors have also been investigated (Kelsey and Harrington 1979), but were 

revealed to be absent. 

In previous reviews of ponderosa pine regeneration processes, Heidmann (1992) 

and Barrett (1979) both identified aspects of climate having greatest influence on the 

establishment of seedlings from seedfall. Heidmann (1992) opened his review article, 

Regeneration Strategies for Ponderosa Pine, with the bluntly succinct statement,

“Regenerating ponderosa pine (Pinus ponderosa) is difficult.” He elaborated that, 

The primary obstacle to regeneration of this species throughout its 

natural range is drought... Annual precipitation in the western and 

southwestern United States is generally adequate for tree growth but 

erratic distribution during the year makes seedling establishment

difficult. 

96 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

Table 1—Factors that potentially limit ponderosa pine regeneration, the affected

regeneration stages, and relevant literature specific to ponderosa pine (references not

specific to ponderosa pine are denoted by parentheses). 

Factor Regeneration stage Sample reference

Seed deficiency flower, seed Pearson 1923 

Fowells and Schubert 1956 

Daubenmire 1960 

Curtis and Foiles 1961

Shearer and Schmidt 1970 

Foiles and Curtis 1973

Dahms and Barrett 1975 

Barrett 1979 

McDonald 1992

Molds seed Fowells and Schubert 1951 

Wagg 1958

Roth 1970

Predation seed, germinant,

seedling 

Pearson 1913

Eastman 1960 

Hooven 1966

Cochran 1970

Blake and others 1986

Blake and others 1989

Shearer and Schmidt 1971 

Damping-off fungi germinant Wagg and Hermann 1962

Roth 1970

Unfavorable forest floor substrate germinant Larsen 1924

Foiles and Curtis 1965

Litterfall burial germinant (Koroleff 1954) 

(Tappeiner and Helms 1971) 

Excessive heat germinant Baker 1929 

Larson 1967 

Moisture stress, drought germinant, seedling Pearson 1923

Hermann 1968 

Larson and Schubert 1969 

Cleary 1970

Djavanshir and Reid 1974

Frost heaving germinant, seedling Heidmann 1976

Summer frosts germinant, seedling Cochran 1972 

Cochran 1984

Excessive shade germinant, seedling Pearson 1936 

Atzet and Waring 1970 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 97 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

In his report, Silviculture of Ponderosa Pine the Pacific Northwest, Barrett 

(1979) summarized the primary constraints on ponderosa pine regeneration with the

observations: 

Prolonged moisture for germination, growth, and life during the 

critical heat of July and August is critical... Germination usually 

occurs in early spring, but rapid drying of the germinating medium

often causes death of the seedling... Because summers are usually 

dry, conservation of moisture is critical. 

In the Pacific Northwest, ponderosa pine forests experience a harsh climate with

cold winters and hot, dry summers. Annual precipitation is limited, and a regular 

period of drought occurs throughout much of the growing season (fig. 1). On the east 

slope of the Cascade Range, these climatic conditions are exacerbated by the 

presence of relatively young, poorly developed, mineral deficient, and highly porous 

volcanic soil types that dominate the region. These climatic and edaphic conditions 

present, through the moisture stress they induce, significant environmental challenges 

to tree regeneration, survival, and growth. 

Precipitation (m

m)

0

10

20

30

40

50

Precipitation

Mean temperature

JAN FEB MAR APR MAY JUN JUL AUG S

Figure 1—Climatic conditions in the central Oregon area illustrating the annual 

coincidence of high temperatures with low precipitation (1928-2004 mean values

from National Climate Data Center cooperative station no. 350694 at Bend, Oregon). 

Given these constraints, the microenvironments most favorable for seedling 

establishment will be those where moisture stress is abated. Moisture stress may be 

abated by a reduction in solar radiation, wind, soil temperature or ambient 

Mean tem

perature (degrees celsius)

-2

0

2

4

6

8

10

12

14

16

18

20

EP OCT NOV DEC

98 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

temperature; by an increase in relative humidity; and by retention of soil moisture 

near the forest floor surface further into the summer months. 

Shrub Influences on Regeneration 

This challenging regeneration environment suggests the potential for positive 

effects of shrubs on ponderosa pine seedling recruitment by their microenvironmental

influences and attendant effects on germinant and seedling moisture stress. Past

observations of regeneration have provided indications of numerous influences of

shrubs on ponderosa pine recruitment processes, both positive and negative (table 2). 

Table 2—Potential influences of shrubs on ponderosa pine seedling regeneration. 

Positive influences Negative influences 

Enhanced soil fertility via N fixation Accelerated soil moisture depletion 

Extended soil moisture retention via shading Excessive shade 

Lower ambient temperatures via shading Reduced seedling growth

Physical browse interference Enhanced seed-predating mammal habitat 

Enhanced soil moisture via hydraulic lift Burial by litterfall 

Improved seedling form Consumption by fire (via fuelbed continuity) 

Reduced thermal flux and frost heaving 

But in some cases these influences are conflicting. On balance, do shrubs 

promote or disfavor tree regeneration? Do they facilitate seedling survival by

ameliorating the harsh climate, or are they important competitors for the highlyrestricted below-ground resources? Moreover, do their effects change over the course 

of seedling establishment and growth? The situation is likely characteristic of the socalled ‘seed-seedling’ conflict described by Schupp (1995). Schupp determined that 

inter-specific conflicts and intra-specific conflicts had been well addressed in 

ecological literature, but that intra-individual conflicts had received considerably less 

attention. For trees, intra-individual conflicts occur when the conditions favorable for 

growth are diametrical to those favorable for establishment (fig. 2).

Such conflicts have been recognized for centuries by silviculturists and have 

been addressed operationally in the utilization of shelterwood regeneration systems.

Shelterwood systems, which have been employed as formal systems since at least the 

18th century (Kostler 1956), were developed to balance the requirements for seedling

establishment with those for seedling growth. Under these systems, partial live tree

overstories are retained at harvest in order to facilitate regeneration by providing a

seed supply and a shaded forest floor (ameliorated microenvironment); once an

understory cohort has become established, the overstory is removed to maximize 

growth of the new cohort (Matthews 1989, Smith and others 1997). Although this

concept is well known and understood by foresters, other potential intra-individual

conflicts have not been widely recognized by foresters or adequately investigated by 

researchers. For ponderosa pine, investigations into seed-seedling conflicts during the 

periods of germinant emergence and establishment are absent. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 99 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

Figure 2—Illustration of intra-individual regeneration conflicts. Above, germinants 

recruited beneath partial live overstories have greater initial survival potential, but 

survivors of the establishment phase have reduced growth potential. Below, 

seedlings establishing in the open or beneath a sparse overstory have reduced

survival potential, but survivors have greater growth potential. 

In ecosystems where plants are similarly subjected to severe environmental

stresses, evidence is mounting that positive interactions (facilitations) are common.

Positive interactions and facilitated recruitment in vascular plants are most often 

observed in those natural communities where either physical stress is great or

consumer pressure is intense (Bertness and Callaway 1994). For example, in many 

ecosystems where severe desiccating conditions are typical – including grasslands, 

tundra, sand dunes, deserts, salt marshes – positive interactions frequently occur 

(Holmgren and others 1997). All observed plant interactions can be generalized as 

100 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

the net result of co-occurring facilitation and competition (Callaway and Walker 

1997). In xeric plant systems, facilitation is the dominant force when the costs 

associated with reduced light levels are more than offset by improved water relations 

(Holmgren and others 1997). This balance of competition and facilitation is 

dependent upon plant life stages, so the relationship between individuals may differ 

over time. Adapting these concepts to ponderosa pine systems, it is reasonable to 

theorize that ponderosa pine germinants may benefit from shrub presence during the 

establishment phase in a facilitative relationship that becomes competitive once 

seedlings become established and increase their demands for growth resources. 

Regeneration Field Studies 

The relation of shrubs to ponderosa pine seedling regeneration was recently 

analyzed in a series of related field studies located in central Oregon (Keyes 2002,

Keyes and Maguire 2000). The goal of the project comprising the studies was to

quantify the relative effect of stand structural features on the earliest phases of 

seedling recruitment. An objective of each study was to determine whether the 

relationship of shrubs to seedlings was one of attraction (positive spatial association) 

or repulsion (negative spatial association). A summary of the relevant findings of the 

three field studies is presented here. 

The first of these is a case study of regeneration in an old-growth ponderosa pine 

stand. The second is an observational study of ponderosa pine germinant emergence 

and 1-2 season survival, and the relationship of those processes to the presence of 

shrubs. The third is a seed-sowing experiment relating the presence of shrub cover to 

ponderosa pine germinant emergence and 1-season survival rates. 

Each of the studies presented here was conducted in pure ponderosa pine stands 

on the lower east slope of the Cascade Range in central Oregon. All stands were at 

sites that were flat or nearly so. The case study was conducted in one undisturbed 

stand at the Metolius Research Natural Area, located 22 km northwest of the town of

Sisters. The observational study was conducted in four stands at the eastern edge of

the Deschutes National Forest southeast of the city of Bend. The experiment was

conducted in four stands of the Deschutes National Forest; two were located on the 

forest’s eastern edge, and two were located on the forest’s western half, near the

Pringle Falls Experimental Forest. The stands in the observational study and

experiment had been subjected to operational regeneration harvests performed within 

the past 20 years, but retained partial overstories. The stands in the observational

study had not been cut within the previous decade; the stands in the experiment had 

been cut more recently. 

Case Study: Regeneration in an Old-Growth Stand 

In the first study, an analysis was conducted of the spatial relationships between 

ponderosa pine small seedlings (≤10 cm tall), large seedlings (10.1-140 cm tall), 

saplings (0.1-10 cm dbh), overstory trees (≥10 cm dbh), and shrubs (Keyes and 

others 2001). The study was conducted in a multi-cohort old-growth stand containing 

a range of tree sizes (including 4 or more trees in each 10-cm dbh class from 0-100 

cm) and was virtually pure in ponderosa pine. A grid of 28 2-meter radius 

regeneration plots was installed within a 4.5-hectare study area. A tally was made of 

the number of seedlings and saplings in each plot. Percent shrub cover (primarily

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 101 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

antelope bitterbrush; Purshia tridentata Pursh DC.) was visually estimated to the 

nearest five percent from illustrations of shrub cover drawn in the field. Local 

overstory basal area was calculated within a 5-m radius of each plot center. Simple

and multiple Poisson regressions were used to identify significant relationships

between seedling or sapling density (stems per hectare) and percent shrub cover. It 

was theorized that positive or negative spatial associations would be suggestive of 

facilitative attraction or competitive repulsion. 

The analysis revealed that small seedlings were negatively related to local

overstory basal area (P=0.0007) and sapling density (P=0.0029). Large seedlings

were also negatively related to local overstory basal area (P=0.0043) and sapling

density (P=0.0269). Shrub cover, however, was negatively related to saplings 

(P=0.0003), had no statistically-significant relationship to large seedlings 

(P=0.0888), and was positively related to small seedlings (P=0.0141). Consistent 

with these results, when local overstory basal area was included in two-factor 

models, positive relationships of shrubs to small seedlings (P=0.0005) and large 

seedlings (P=0.0070) were observed. These spatial associations suggest a facilitative 

relationship between shrubs and seedlings that yields to a competitive relationship

between shrubs and saplings. They also suggest that the presence of shrubs benefits

seedlings in a way that saplings and overstory trees do not. 

Observational Study: Patterns of Recruitment 

In the observational study, the temporal patterns of seedling emergence and 

survival over two seasons (one winter) were addressed. All fresh germinants from 

natural seedfall were identified in 64 10-m2

 circular regeneration plots systematically 

located in grids within 1-hectare study areas in four stands. Germinants were labeled 

as shaded by live local vegetation, shaded by dead local vegetation, or unshaded. 

Shrubs were antelope bitterbrush and greenleaf manzanita (Arctostaphylos patula

Greene). Two cohorts of germinants were tracked over the course of 1-2 years for 

patterns of mortality.

Only about 3 percent of viable seed resulted in emergents. A small fraction of

emergents survived their first summer. Overall, most mortality occurred immediately 

after emergence, and nearly all mortality occurred during the summer months. Local

shade did not improve emergence rates. Most germinants (72.4 % in 1999, 57.8% in 

2000) emerged without understory shading, and in fact the proportion of shaded 

emergents during 1999 (27.6%) was significantly lower than the expected proportion

assuming random germination and survival, and based on estimates of percent shrub 

cover (34.5%) (Fisher’s Exact Test; P=0.0138). But although most new germinants 

were unshaded, few of those survived their first summer (0.8% in 1999, 4.4% in

2000). Most germinants surviving the first summer received local shade, and the only

survivors of two summers were shaded germinants. During both years, the proportion

of survivors within shade was significantly greater than the expected proportion 

(Fisher’s Exact Test; P<0.0001 during 1999, P=0.0005 during 2000). This positive 

effect of shrubs on germinant survival were quantified in cumulative mortality 

distributions that differed significantly (at α=0.05) among the three conditions of 

shading, with mortality extended furthest into the summer by live shade, and 

secondarily by dead shade. 

102 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

Experimental Study: Shrub Effects on Recruitment 

The experimental study was a seed-sowing experiment consisting of ponderosa 

pine seed sown under controlled conditions to test for differences in germination and 

survival rates among shrub-shaded and unshaded locations. Shrubs were antelope 

bitterbrush, greenleaf manzanita, and snowbrush ceanothus (Ceanothus velutinus

Dougl. ex Hook.). Survival was monitored over one summer under conditions

controlled by the split-plot design of the experiment. Whole plots tested caching and

substrate treatments. Because mechanisms driving the germination and survival

patterns were of interest in this experiment, measurements were taken to assess

whether differences in relative humidity, air temperature, soil temperature, and light

intensity existed between shrub-shaded and unshaded treatments. 

Less than 30 percent of all seed sown in fall resulted in live germinants the 

following spring, and just 5 percent resulted in live germinants by the following fall. 

Shrubs had no effect on germinant emergence rates (P=0.349). However, mortality to

germinants under shrubs occurred at a slower rate than germinants in the open, and

hence establishment rates were higher (P=0.032). At unshaded sites, the mortality

rate was greatest immediately after germination, whereas the rate remained relatively 

constant throughout the summer at shrub-shaded sites. As a result, by midsummer the 

survival rate among shaded germinants was 2.2 times the survival rate of unshaded 

germinants; by November, nearly 4 out of every 5 germinants were shaded by shrubs. 

Shrub-sheltered germinants received about one-half to one-third the solar radiation 

received by adjacent unshaded germinants (data collected 31 July to 1 August 2000). 

This shading was not reflected in relative humidity or air temperature differences, but 

did result in cooler soil temperatures, especially during the hottest parts of the day

(P<0.05). 

Summary of Study Findings 

The studies described above focused on establishment-phase regeneration 

processes during the first two growing seasons after emergence. They provide 

additional evidence supporting moisture stress as a major factor in ponderosa pine 

seedling recruitment. For this early phase of regeneration, the relationship of shrub 

presence to germinant recruitment is a positive one. Results from these studies can be 

summarized as follows: 

• Seedling spatial patterns are positively associated with shrub cover and 

negatively associated with sapling and overstory tree density, suggesting that 

shrubs benefit seedlings in ways that saplings and overstory trees in the same

stand do not.

• The positive spatial association of shrubs to regeneration does not persist once 

seedlings achieve sapling proportions (taller than 140cm). Adopting the 

conceptual model of Callaway and Walker (1997), this suggests that the

relationship transitions from one of facilitation to one of competition between 

the seedling and sapling stages. 

• Local shade increases recruitment rates over unshaded sites by reducing rates 

of germinant mortality. Desiccation is the primary source of mortality, and 

nearly all mortality occurs during summer (most during the first summer). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 103 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

• Probability of germinant survival is high if desiccation can be avoided during 

the first weeks after germination. The germinant survival rate in the second 

season is higher than survival rate in the first season. 

• Shrub cover is not associated with greater emergence rates but greatly 

improves germinant survival. Establishment from seeds sowed beneath shrubs 

was several times that from seeds sowed in the open. 

• Shrub cover appears to indirectly reduce moisture stress in germinants. The

specific mechanism by which shrub cover affects germinants may be by 

reducing soil temperature or by reducing solar radiation. 

Taken together, these findings indicate that the objective of securing natural

regeneration in this region will be best served by the retention of understory shrubs. 

They also indicate that by enabling dense shrub understories to establish and persist, 

the practice of fire suppression has had an additional (indirect) effect on the 

development of dense ponderosa pine stands in this region during the past century. 

Dense shrub understories are likely to continue contributing to the development of 

ladder fuels by their positive effect on seedling recruitment. Therefore, understory

shrub structure should be taken into consideration by managers responsible for 

prescribing long-term silvicultural treatments to minimize fire behavior. 

The time frame encompassed by these studies represents the period when natural

regeneration is most strongly influenced by stand structural features, but the studies 

should be regarded as a foundation for further research into ponderosa pine 

regeneration processes. Monitoring of seedlings from germination onward is

necessary to identify the long-term influences of shrubs on regeneration. This would 

serve to clarify the role of shrubs on survival of new seedlings beyond the first two

seasons, as well as the effects of shrubs on seedling growth. It will probably be useful 

to analyze shrub cover as a quantitative variable (such as distance from dripline or 

distance from shrub center) to describe the range of conditions for seedling 

regeneration within the area of shrub crowns. Differences in regeneration effects

among different species of shrubs common in ponderosa pine forests – including

antelope bitterbrush, greenleaf manzanita, and snowbrush ceanothus – should be

determined, if these differences can be assessed without being confounded by site 

quality.

Acknowledgements 

The authors wish to express their appreciation to Andy Hackethorn, Meg 

McAndrews Cowden, Sean Garber, Eric Watrud, Doug Mainwaring, John Tappeiner, 

Bob Powers, Greg Filip, and Everett Hansen for their contributions to the field 

studies summarized in this paper. Thanks are due to Jo Booser of the Deschutes

National Forest for facilitating access to field sites, and to the Pacific Northwest

Research Station of the U.S. Forest Service for use of the indispensable bunkhouse 

and facilities of the Pringle Falls Experimental Forest. Thanks also to Andrew 

Youngblood for comments that helped improve this manuscript. 

104 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

References 

Atzet, T.; Waring, R.H. 1970. Selective filtering of light by coniferous forests and 

minimum light requirements for regeneration. Canadian Journal of Botany 48: 2163-

2167. 

Baker, F.S. 1929. Effect of excessively high temperatures on coniferous reproduction. 

Journal of Forestry 27: 949-975. 

Barrett, J.W. 1979. Silviculture of ponderosa pine in the Pacific Northwest: the state of

our knowledge. Gen. Tech. Rep. PNW-GTR-97. Portland, OR: Pacific Northwest 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture;

106 p. 

Bertness, M.D.; R. Callaway. 1994. Positive interactions in communities. Tree 9(5): 191-

193. 

Blake, E.A.; Wagner, M.R.; Koerber, T.W. 1986. Insects destructive to ponderosa pine 

cone crops in northern Arizona. In: R.C. Shearer, compiler. Conifer tree seed in the 

inland Mountain West, proceedings of the symposium; 1985 August 5-6; Missoula, MT.

Gen. Tech. Rep. INT-GTR-203. Ogden, UT: Intermountain Research Station, Forest

Service, U.S. Department of Agriculture; 238-242.

Blake, E.A.; Wagner, M.R.; Koerber, T.W. 1989. Relative effect of seed and cone insects on

ponderosa pine in northern Arizona. Journal of Economic Entomology 82(6): 1691-

1694. 

Callaway, R.M.; Walker, L.R. 1997. Competition and facilitation: a synthetic approach to 

interactions in plant communities. Ecology 78: 1958-1965. 

Clark, J.S.; Beckage, B.; Camill, P.; Cleveland, B.; HilleRisLambers, J.; Lichter, J.;

McLachlan, J.; Mohan, J.; Wyckoff, P. 1999. Interpreting recruitment limitation in 

forests. American Journal of Botany 86(1): 1-16. 

Cleary, B.D. 1970. The role of moisture stress and temperature in the growth of 

seedlings. In: Hermann, R.K., ed. Regeneration of ponderosa pine: Proceedings of the

symposium; 1969 September 11-12; Corvallis, OR. Corvallis, OR: Oregon State

University; 64-68. 

Cochran, P.H. 1970. Seeding ponderosa pine. In: Hermann, R.K., ed. Regeneration of

ponderosa pine: Proceedings of the symposium; 1969 September 11-12; Corvallis, OR. 

Corvallis, OR: Oregon State University; 28-35. 

Cochran, P.H. 1972. Temperature and soil fertility affect lodgepole and ponderosa pine 

seedling growth. Forest Science 18(2): 132-134. 

Cochran, P.H. 1984. Should ponderosa pine be planted on lodgepole pine sites? Res. Note 

PNW-RN-419. Portland, OR: Pacific Northwest Forest and Range Experiment Station,

U.S. Department of Agriculture; 6 p.

Curtis. J.D.; Foiles, M.W. 1961. Ponderosa pine seed dissemination into group

clearcuttings. Journal of Forestry 59: 766-767. 

Dahms, W.G.; Barrett, J.W. 1975. Seed production of central Oregon ponderosa pines

and lodgepole pines. Res. Paper PNW-RP-191. Portland, OR: Pacific Northwest Forest

and Range Experiment Station, U.S. Department of Agriculture; 13 p. 

Daubenmire, R. 1960. A seven-year study of cone production as related to xylem layers

and temperature in Pinus ponderosa. American Midland Naturalist 64(1): 187-193. 

Djavanshir, K.; Reid, C.P.P. 1974. Effect of moisture stress on germination and radicle

development of Pinus eldarica Medw. and Pinus ponderosa Laws. Canadian Journal

of Forest Research 5: 80-83 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 105 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

Eastman, W.R. Jr. 1960. Eating of tree seeds by birds of central Oregon. Research Note 42. 

Corvallis, OR: Oregon State University; 24 p.

Foiles, M.W.; Curtis, J.D. 1965. Natural regeneration of ponderosa pine on scarified

group cuttings in central Idaho. Journal of Forestry 63: 530-535. 

Foiles, M.W.; Curtis, J.D. 1973. Regeneration of ponderosa pine in the northern Rocky 

Mountain – Intermountain Region. Res. Paper INT-RP-145. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 44 p.

Fowells, H.A.; Schubert, G.H. 1951. Recent direct seeding trials in the pine region of

California. Res. Note PSW-RN-78. Berkeley, CA: California Forest and Range

Experiment Station, Forest Service, U.S. Department of Agriculture; 9 p.

Fowells, H.A.; Schubert, G.H. 1956. Seed crops of forest trees in the pine region of 

California. Technical Bulletin 1150. Washington, DC: U.S. Department of Agriculture; 

48 p.

Heidmann, L.J. 1976. Frost heaving of tree seedlings: a literature review of causes and 

possible control. Gen. Tech. Rep. RM-GTR-21. Fort Collins, CO: Rocky Mountain

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture;

10 p.

Heidmann, L.J. 1992. Regeneration strategies for ponderosa pine. In: Baumgartner, D.M.;

Lotan, J.E., eds. Ponderosa pine: the species and its management: Proceedings of the

symposium; 1987 September 29 – October 1; Spokane, WA. Pullman, WA: Washington

State University Press; 227-233. 

Hermann, R.K. 1968. A watering experiment with sown ponderosa pine in central

Oregon. Northwest Science 42(2): 47-52.

Holmgren, M.; Scheffer, M.; Huston, M.A. 1997. The interplay of facilitation and 

competition in plant communities. Ecology 78: 1966-1975. 

Hooven, E.F. 1966. Pine regeneration in Oregon – habits and control of seed-eating 

mammals. Research Note 5. Corvallis, OR: Oregon State University; 24 p.

Kelsey, R.G.; Harrington, M.G. 1979. A search for phytotoxins influencing germination 

and early growth of ponderosa pine. Res. Paper INT-RP-216. Ogden, UT:

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 22 p.

Keyes, C.R. 2002. Recruitment of ponderosa pine seedlings beneath partial overstories. 

Corvallis, OR: Oregon State University; 193 p. Ph.D. dissertation.

Keyes, C.R.; Maguire, D.A. 2000. A long-term study of ponderosa pine seedling 

recruitment and growth under partial overstories. In: Proceedings of the 1999 

Society of American Foresters national convention; Portland, OR. Bethesda, MD: 

Society of American Foresters; 560-561. 

Keyes, C.R.; Acker, S.A.; Greene, S.E. 2001. Overstory and shrub influences on seedling 

recruitment patterns in an old-growth ponderosa pine stand. Northwest Science

75(3): 204-210. 

Koroleff, A. 1954. Leaf litter as a killer. Journal of Forestry 52(3): 178-182.

Kostler, J. 1956. Silviculture (translated from Waldbau by M.L. Anderson). London: Oliver 

and Boyd; 416 p.

Larsen, J.A. 1924. Some factors affecting reproduction after logging in northern Idaho. 

Journal of Agricultural Research 28: 1149-1157. 

106 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Positive Seedling-Shrub Relationships—Keyes and Maguire 

Larson, M.M. 1967. Effect of temperature on initial development of ponderosa pine 

seedlings from three sources. Forest Science 13(3): 286-294. 

Larson, M.M.; Schubert, G.H. 1969. Effect of osmotic water stress on germination and 

initial development of ponderosa pine seedlings. Forest Science 15(1): 30-36.

Matthews, J.D. 1989. Silvicultural systems. Oxford: Oxford University Press; 284 p. 

McDonald, P.M. 1992. Estimating seed crops of conifer and hardwood species. Canadian

Journal of Forest Research 22: 832-838.

Pearson, G.A. 1913. Methods of combating seed destroying animals. Review of Forest

Service Investigations 2: 82-85.

Pearson, G.A. 1923. Natural reproduction of western yellow pine in the Southwest. 

Bulletin 1105. Washington, DC: U.S. Department of Agriculture; 144 p.

Pearson, G.A. 1936. Some observations on the reaction of pine seedlings to shade. 

Ecology 17: 270-276. 

Roth, L.F. 1970. Disease as a factor in regeneration of ponderosa pine. In: Hermann, R.K.,

ed. Regeneration of ponderosa pine: Proceedings of the symposium; 1969 September

11-12; Corvallis, OR. Corvallis, OR: Oregon State University; 89-93.

Schupp, E.W. 1995. Seed-seedling conflicts, habitat choice, and patterns of plant 

recruitment. American Journal of Botany 82(3): 399-409. 

Shearer, R.C.; Schmidt, W.C. 1970. Natural regeneration in ponderosa pine of western

Montana. Res. Paper INT-RP-86. Ogden, UT: Intermountain Forest and Range

Experiment Station, Forest Service, U.S. Department of Agriculture; 19 p.

Shearer, R.C.; Schmidt, W.C. 1971. Ponderosa pine cone and seed losses. Journal of

Forestry 69: 370-372. 

Smith, D.M.; Larson, B.C.; Kelty, M.J.; Ashton, P.M.S. 1997. The practice of silviculture: 

applied forest ecology. 9th ed. New York: John Wiley and Sons; 537 p.

Tappeiner, J.C.; Helms, J.A. 1971. Natural regeneration of Douglas-fir and white fir on 

exposed sites in the Sierra Nevada of California. The American Midland Naturalist 

86(2): 358-370. 

Wagg, J.W.B. 1958. Spot seeding ponderosa and Jeffrey pine. Research Note 35. Corvallis,

OR: Oregon State University; 19 p. 

Wagg, J.W.B.; Hermann, R.K. 1962. Artificial seeding of pine in central Oregon. Research 

Note 47. Corvallis, OR: Oregon State University; 47 p.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 107 

Managing Ponderosa Pine Forests in 

Central Oregon: Who Will Speak for the 

Soil?1

Matt D. Busse2

 and Gregg M. Riegel3

Abstract 

The soils of the central Oregon pumice plateau are relatively young and infertile, yet support 

an array of plant diversity and growth in the region’s pine forests. Whether these coarsetextured, pumice and ash soils are resilient to forest disturbance is not well understood. We 

present results from a long-term experiment that examined changes in soil quality in response 

to combinations of thinning and repeated prescribed fire. Soil quality was generally

unaffected in fifteen years following pre-commercial thinning. The soils were also resilient to

fire with the exception of the loss of nearly 25 percent of the ecosystem’s total nitrogen due to 

burning in 1991 and 2002. Natural replacement of N by N-fixing shrubs such as snowbrush

ceanothus (Ceanothus velutinus Dougl. ex Hook.) and antelope bitterbrush (Purshia 

tridentata (Pursh.) DC.) is an important means to offset N losses, along with careful planning

of burn prescriptions to limit forest floor N consumption. 

Introduction 

How can the 

non-farmer jet-set bureaucrats 

Speak for the green of the leaf? Speak for the soil?

Gary Synder, 1974 

Soil is cursed. This complex medium that covers much of the surface of our 

planet and helps ensure the survival of the human race suffers from an unavoidable 

fact: it is terminally boring. It just sits there with little aesthetic value, unable to

attract attention by changing colors, growing, or communicating. Adding insult to

injury, soil is known synonymously as dirt, the common irritant found under 

fingernails and on pant legs. This is not to suggest that the value of soil is lost upon

society, however. Far from it. Both historic and contemporary examples of degraded 

soils and the human hardships that often follow (Lal and others 2004) provide a 

constant reminder that soil is (1) an indispensable natural resource, (2) generally 

nonrenewable in our lifetime, and (3) susceptible to disturbance and mismanagement.

Thus, preventing soil degradation is a common-sense requirement for managing 

forest lands, regardless of the desired social or economic product, a requirement of

both legal and ethical proportions for federal land managers as directed by the United 

States Congress. 

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 USDA Forest Service, Pacific Southwest Research Station, 3644 Avtech Parkway, Redding CA 96002. 

mbusse@fs.fed.us 

3

USDA Forest Service, Pacific Northwest Region, Area Ecology Program, Bend, OR, 97701. 

griegel@fs.fed.us 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 109 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Have the soils of central Oregon avoided productivity losses during the past 

century of unprecedented changes in forestry practices (fire suppression, railroad 

logging, and aggressive fuel reduction)? Or, are there clear examples of irreversible 

soil damage? Unfortunately, no archived soil collection exists from the pre-fire 

suppression era, and, thus, a true evaluation of soil changes is not possible. As a 

substitute, we present results from a forest manipulation experiment (the Black Bark

Study) that tracks recent trends in soil quality associated with forest management 

practices. Changes in soil quality and plant growth in 15 years following a

combination of prescribed fire, thinning, and nutrient additions are explored. In 

particular, we discuss the potential loss of soil quality associated with repeated

prescribed burning. 

Soil Quality 

Soil quality is a fairly new term to the discipline of soil science. Thus, a brief 

discussion of its origin, definition, and application to forestry is appropriate before 

examining possible implications for central Oregon soils. 

Coined by agricultural soil scientists in the early 1990s (Doran and Parkin

1994), soil quality is a holistic, feel-good concept derived from its cousin and 

predecessor, soil productivity. Consider the definition of these two terms from the

Soil Science Society of America (http://www.soils.org/sssagloss):

Soil productivity: the capacity of a soil to produce a certain yield of crops or 

other plants with a specified system of management. 

Soil quality: the capacity of a soil to function within ecosystem boundaries to 

sustain biological productivity, maintain environmental quality, and 

promote plant and animal health. 

The language used in defining soil quality is key; terms like function,

ecosystem, sustain, environmental quality, and health are pleasing to our 21st-century

ears. As a result, soil quality is politically correct, in vogue. Soil productivity, 

although often used synonymously with soil quality, is a plant-centric term perhaps

more fitting for agricultural soils, where farmers can track annual crop yields and 

examine short-term (5 to 10 year) productivity trends. Translating the concept of soil 

productivity to forestry is troublesome, however, given the dynamics of stand 

development, changing management systems within a forest rotation, and the 

Herculean effort required to measure total vegetative growth. Equally telling, the 

term productivity is stigmatized in many public circles with respect to managing

public lands. 

Soil quality is admittedly in its infancy as a practicable and reliable indicator of 

the soil condition. Lacking is a scientifically-accepted set of indices that reflect

disturbance-related changes in soil properties. Proposed indices encompass a

combination of soil physical (e.g. water infiltration, erosion, soil strength, aeration), 

chemical (e.g. pH, organic matter, total C, total N, salinity, cation exchange 

capacity), and biological (e.g. microbial biomass, respiration, N mineralization) 

properties (Doran and Parkin 1994). Difficulty in selecting indices that are both 

insightful and affordable is a stumbling block and a common theme discussed in

several review articles (Burger and Kelting 1999; Page-Dumroese and others 2000;

Powers and others 1998). As Page-Dumroese and others (2000) state, “efforts to 

110 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

construct definitive soil quality/sustainability standards and guidelines are still in 

their infancy..... because of the diversity of soil properties to be measured, appraisal

techniques, and soil uses.” 

Regardless of any technical ambiguities, soil quality has gained strong support 

among land resource managers and the scientific community as a conceptual and

communicative tool. If told there is a substantial decline in soil quality due to forestry

practices, resource managers will likely listen (even if they don’t know exactly what

it means). From there, the door is open for professional soil scientists to identify the

soil properties that fail to meet forest guidelines, and to propose ameliorative 

treatments when needed. 

Soils of Central Oregon 

Central Oregon offers a beautiful landscape, starting with the high mountain

peaks of the Cascades to the west, and traversing across mixed-conifer forests, to

ponderosa pine (Pinus ponderosa P. & C. Lawson) and lodgepole pine (Pinus

contorta Dougl. ex Loud.) forests at lower elevations, and finally to the high desert

plateau to the east. The soils are diverse and reflect a geomorphically-complex 

landscape, which includes 5 of the 8 geomorphic provinces found in Oregon. Soils 

supporting ponderosa pine growth, in contrast, are fairly uniform, and are primarily

derived from wind deposits of pumice and ash from the eruption of Mt. Mazama 

(Crater Lake). Smaller volcanic activity scattered across the plateau has added 

subordinate parent material diversity.

In general, the soils are poorly developed Andisols with loamy sand and sandy

loam textures. The benchmark soil (Lapine series), for example, has a 6 to 10 cm (2.4 

to 4 inch) surface horizon (A horizon) above a 12 to 24 cm (5 to 10 inch) transition 

horizon (AC) and an undeveloped C horizon (see http://www.nrcs.usda.gov for 

details). The depth to the buried soil (itself a poorly developed, infertile soil) is 60 to 

100 cm (24 to 39 inch), and generally declines with increasing distance from Crater

Lake. Clay contents are 8 percent or less throughout the profile. Other dominant soil 

characteristics include (1) low fertility, and (2) unusually high porosity and waterholding capacity for a sandy soil. Poor fertility is a function both of the young parent

material and the semi-arid conditions on the pumice plateau (30 to 75 cm annual 

precipitation), which limits plant growth and, ultimately, soil organic matter input.

The soils have impressively low N concentrations beneath the A horizon (Dyrness 

and Youngberg 1966; Youngberg and Dyrness 1963). 

The Black Bark Study 

The Black Bark study began in the 1980s as a collaborative project between the 

Deschutes National Forest and the Pacific Northwest Research Station (Bend

Silviculture Laboratory) to better understand the ecology of central Oregon

ponderosa pine forests. With a wide array of silvicultural treatments replicated across 

a productivity gradient of pine forests, the study provides an interesting insight to the 

resilience of the area’s soils. 

The study concept was prompted by a large-scale mountain pine beetle 

infestation in the lodgepole pine forests south of Bend, OR. Whether the insect

population would migrate into ponderosa pine stands was unclear and, consequently, 

of immense concern to the Deschutes National Forest. Prior evidence suggested that 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 111 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

thinning of overstocked pine stands was the most successful means to prevent further

insect damage (Mitchell and Preisler 1991). As a result, the Deschutes National 

Forest adopted an aggressive thinning program in its second-growth ponderosa pine

stands. The targeted area included approximately 100,000 hectares (247,000 acres) of 

“black bark” ponderosa pine, considered at the time the most productive secondgrowth pine forests in central Oregon. 

The management objective of the study (as conceived by Pat Cochran, retired

PNW Soil Scientist, Bill Hopkins, retired Area Ecologist, and Don Peterson, retired 

Timber Staff Officer) was to evaluate ecological changes following partial overstory 

harvesting, and thus contribute to the monitoring needs of the Forest’s thinning

program. From a scientific standpoint, the objective was expanded greatly to evaluate 

soil and plant responses to manipulation of site organic matter. Sixteen treatments

were selected which created a gradient of surface organic matter retention following 

combinations of thinning and prescribed fire (table 1). 

Three study sites were selected along a west-to-east transect on the Bend-Fort 

Rock District. Swede Ridge, the most productive site, is proximal to the Cascade 

crest, and thus receives considerably more annual precipitation than the other sites; 

Sugar Cast, the middle site, is near the heart of the pumice plateau on the Lava Cast

forest near Sunriver, OR; and East Fort Rock, the poorest site, is on the eastern edge

of the ponderosa pine forests, within 5 km of the desert fringe. Additional site 

characteristics are presented in table 2. All treatments were replicated at each site 

(block) on 0.4 ha plots in a randomized complete block experimental design. 

Thinning to a target basal area of 13.7 m2

 ha-1 (60 ft2 ac-1) was completed in 

1989, and the prescribed burns were conducted in spring 1991 and repeated in spring

2002. The burns were generally low to moderate intensity (0.5 to 1.2 m (1.6 to 4 ft)

average flame lengths) with 45 to 50 percent duff reduction. Details of the 1991

burns, including fuel loading, consumption, and soil heating, are presented by Shea

(1993). Fertilizer (224 kg ha-1 N; 112 kg ha-1 P; 37 kg ha-1 S, or the equivalent of 200

lb ac-1 N; 100 lb ac-1 P; 33 lb ac-1 S) was applied in the fall of 1991 and again in 1996. 

Table 1—Treatment design of the Black Bark study. Treatments are ranked generally from

the lowest to highest level of organic matter retention. 

Treatment rank Thinning method Additional treatment

1 Whole-tree harvest Fire

2 Whole-tree harvest Fire + fertilize 

3 Whole-tree harvest Fertilize

4 Whole-tree harvest None

5 Bole-only harvest Fire

6 Bole-only harvest Fire + fertilize 

7 Bole-only harvest Fertilize

8 Bole-only harvest None

9 Thin, leave trees on site Fire 

10 Thin, leave trees on site Fire + fertilize 

11 Thin, leave trees on site Fertilize 

12 Thin, leave trees on site None

13 No thin Fire

14 No thin Fire + fertilize 

15 No thin Fertilize

16 No thin None

112 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Table 2—Characteristics of the three Black Bark study sites prior to treatment in 1988.

Site characteristic Swede Ridge Sugar Cast East Fort Rock

Relative site quality High Medium Low 

Site index (m; Barrett 1978) 35 31 25 

Age (yr) 40 49 56 

Density (trees ha-1) 783 707 495

Basal area (m2 ha-1) 39 33 28

Dominant understory

vegetation 

Snowbrush ceanothus, 

antelope bitterbrush

Antelope bitterbrush, 

greenleaf manzanita 

Antelope bitterbrush, 

greenleaf manzanita 

Elevation (m) 1,520 1,398 1,554 

Precipitation (cm) 65 50 38 

Mean July temperature (

o

C) 15 18 18

Soil nutrients, wood decay, tree height and volume, diameter at breast height, and 

fuel loading were measured on a 5-year cycle. Herbaceous production was measured

annually by clipping all vegetation within ten 0.25 m2

 (2.7 ft2) frames in each plot.

Shrub cover was determined every third year by measuring the canopy size of all

plants within three 100 m2

 (1076 ft2) belt transects per plot. Percent shrub cover was

converted to a dry weight basis using site-specific biomass equations. Additional soil

quality measurements (microbial biomass, respiration, surface CO2 efflux, C

utilization, litter decay, phospholipid fatty acid content) were made periodically 

between 1989 and 2005. 

Results 

No trends in chemical or biological indices of soil quality were detected in the

initial 15 years following thinning. In contrast, substantial increases in tree vigor and 

production of wildlife browse were evident. The periodic annual increment for 

diameter growth increased 60 percent, while shrub cover increased more than 200

percent due to thinning (fig. 1). Antelope bitterbrush (Purshia tridentata (Pursh.) 

DC.; hereafter bitterbrush), in particular, responded to thinning: average cover was 7 

percent on unthinned plots compared to 25 percent on thinned plots by 2002. 

Maximum bitterbrush cover on thinned plots reached 50 percent. Herbaceous 

production also increased due to thinning, although this result is tempered by the fact 

that biomass production was extremely small regardless of treatment (14 kg ha-1 for 

thinned plots versus 4 kg ha-1 for unthinned plots). Plant diversity (number of

species) was low regardless of treatment, and declined slightly due to thinning. 

Whether thinning has improved forest health and resistance to insect attack can only 

be assumed, since no insect-related mortality has been identified on thinned or 

unthinned plots. 

Differences in soil quality or vegetation growth due to the method of thinning

(whole-tree harvest; bole-only harvest; thin, leave trees on site) were slight. Thus, the 

gradient of organic matter retention associated with pre-commercial thinning appears

to have little short-term effect in these pine ecosystems. Whether this will change 

with time as the larger organics decompose and their products become incorporated

in the soil is unclear. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 113 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Figure 1—Thinning effects in central Oregon pine stands. Bars represent mean

percentage plus standard error (n=3) of Whole-tree harvest (treatment 4) plots 

relative to No thin (treatment 16) controls (e.g. thinned and unthinned treatments are

equivalent at 100 percent). Tree growth is the 10-year diameter increment. Soil C and

N values include forest floor plus mineral soil to a depth of 60 cm. 

The strongest ecosystem-level response to date has been to nutrient additions.

Soil C and N, microbial biomass and activity, tree growth, and herbaceous production 

and diversity are among the numerous measures that increased substantially 

following fertilizer applications in 1991 and 1996 (fig. 2). Only shrub growth failed

to respond positively, indicative of the poor competitive ability of shrubs relative to 

other vegetative lifeforms in acquiring and utilizing available nutrients. Our results 

not only support previous findings from central Oregon of soil nutrient limitations to 

tree growth (Cochran 1978; Cochran 1979; Youngberg and Dyrness 1965), but 

extend the results to include other important lifeforms and processes. Does this mean 

that the Deschutes National Forest should consider applying fertilizers in its secondgrowth pine forests? There is an important message from our finding, but it has little

to do with the economic benefits of applying fertilizer. The results show soil-plant

processes in central Oregon are not just controlled by moisture limitations; they are 

also nutrient limited. Forest practices that conserve (or even increase) total nutrient 

pools while meeting the primary ecological, social, or economic objectives should be 

emphasized. 

The effects of prescribed fire have generally been benign to date. Strong 

declines in soil N content and shrub cover are the only exceptions. Soil N content

was more than 20 percent lower on burn plots compared to controls as a direct result 

of consumption of forest floor organics (fig. 3). No changes in mineral soil N (total or 

available) were detected following either burn, nor were changes evident in mineral 

soil C, pH, extractable phosphorus, cation exchange capacity, C utilization or 

phospholipid fatty acid composition. Only an inconsistent decline in microbial 

biomass was found between 1991 and 2003 in the surface mineral soil of burned 

plots. 

114 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Figure 2—Nutrient limitations in central Oregon pine stands. Bars represent mean

plus standard error (n=3) of fertilized plots (treatment 3) relative to unfertilized 

controls (treatment 4). Mean value for herbaceous biomass is 845 percent. 

Figure 3—Fire effects in central Oregon pine stands. Bars represent mean values 

plus standard error (n=3) of burned plots (treatment 1) relative to unburned controls

(treatment 4).

Bitterbrush cover was severely reduced after the initial burn, although post-fire

seed germination led to partial recovery in the following eleven years. By 2001, 

bitterbrush cover on burned plots averaged 13 percent compared to 25 percent on 

unburned plots. After the second round of burns, however, bitterbrush was virtually 

eliminated from the stands, with little sign of basal stem sprouting or seed

germination noted by the end of the second growing season. 

Tree growth between 1991 and 2001 was slightly higher on burned plots 

compared to controls, which contradicts previous studies in central Oregon showing

tree growth declines associated with burning (Busse and others 2000; Cochran and

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 115 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Hopkins 1991; Landsberg 1993). We suspect the increase in tree growth was a result

of a small pulse of available N following burning in combination with reduced 

understory competition for water and nutrients. It remains to be seen whether these 5 

to 10-year changes in tree growth have long-term implications to stand growth. 

Fire and Soil Nitrogen

Our planet and atmosphere are loaded with N. It’s in the air, in the soil and 

ground water, and rising in exhaust emissions. Nitrogen is everywhere. So, there 

should be more than enough for every living organism to thrive, right? Then why is 

N generally considered the most limiting of all nutrients for plant growth on a global

scale? And what role does fire play in altering plant-available N?

At the heart of the N conundrum is the fact that most organisms primarily

assimilate inorganic N (ammonium and nitrate), which, in turn, comprises a

miniscule fraction of the total N pool (Paul and Clark 1996). The great majority of

soil N, for example, is found in organic complexes, and is released as inorganic forms 

in a slow bottleneck process by soil microorganisms. Nitrogen-fixing legumes and 

actinorhizal plants (e.g., snowbrush ceanothus (Ceanothus velutinus Dougl. ex 

Hook.; hereafter snowbrush) and bitterbrush) that convert atmospheric N directly into 

plant-available N are the main exceptions to the rule. Accentuating this problem is 

the fact that N is not distributed evenly in terrestrial ecosystems either at micro- or 

macro-scales. Dry environments, such as those found in central Oregon, are 

characteristically on the low end of the N distribution scale. Comparing the N content

of forest ecosystems in central Oregon versus those in moist western Oregon

provides a good example of this inequity. As much as three to ten times more total 

ecosystem N is found west of the Cascade crest than in central Oregon (fig. 4).

Nitrogen conservation, therefore, is vital to the integrity of central Oregon forests. 

Any N disruptions, additions, or subtractions will have a much greater ecological 

effect in these poorly-buffered forests than in N “rich” forests west of the Cascade 

crest. As an example, a loss of 350 kg N ha-1 would result in a 15 percent reduction of

total N in central Oregon, but only a 3 percent reduction of site N in western Oregon. 

Fire plays a major role in determining total and available N in forests of the

interior west by consuming organic matter, altering rates of soil N processes, and 

modifying post-fire plant community composition and growth. Total ecosystem N is 

reduced during burning primarily as a result of volatilization losses from forest floor 

material. Temperatures in the mineral soil, in contrast, rarely exceed the critical range 

for N volatilization of 300 to 500o

C (Hungerford and others 1991), and thus N loss 

from the mineral fraction is generally of little concern. The absolute quantity of N 

lost during burning is difficult to predict, and depends on factors such as pre-burn 

fuel loading, fuel moisture, fuel continuity, and fire severity. Estimates of N loss 

range from 20 to 400 kg ha

-1 in central Oregon studies (table 3). On the positive side,

fire typically results in an abundant release of plant-available N, as volatilization 

losses to the atmosphere are usually incomplete. This often-reported flush of 

inorganic N (Covington and Sackett 1986, 1992) can result in short-term increases in

plant growth. Therefore, fire wields a double-edged sword: providing a short-term

flush of plant-available N, while reducing the total ecosystem N pool. 

116 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

An impressive quantity of forest floor N was lost during repeated burning in 

thinned and unthinned plots on the Black Bark study: the combined loss for the 1991

0

2000

4000

6000

8000

10000

12000

14000

Western OR Central OR

T

otal N (kg/ha)

Vegetation

Forest floor

Mineral soil

Figure 4—Comparison of total ecosystem N in a mesic-climate forest of western

Oregon and a semi-arid ponderosa pine forest in central Oregon. Data for western

Oregon is from R. Zasoski1 and for central Oregon is from the Black Bark study2

. 

Table 3—Estimated N losses from prescribed fire studies conducted in central Oregon

ponderosa pine stands. 

Source Fire intensity N loss (kg ha-1) 

Landsberg (1993) Severe 280 

Shea (1993) Moderate (1991) 366 to 397 

Black Bark study Moderate (2002) 126 to 183 

Simon1 Low to moderate 100 

Nissley and others (1980) Low 20 to 260 

1 Data on file, Deschutes National Forest, Bend, OR

Table 4—Forest floor nitrogen (kg ha-1) before and after repeated prescribed fires in secondgrowth ponderosa pine stands in central Oregon. N=6 in 1991, n=3 in 2002. 

Initial burns in 19911 Repeated burns in 2002

Treatment Preburn Postburn N loss Preburn Postburn N loss Total N loss 

Thinned 756 359 397 287 161 126 523

Unthinned 764 398 366 301 118 183 549

1 Data for 1991 burns are from Shea (1994).

and 2002 burns was more than 500 kg ha

-1 (table 4). Unfortunately, the post-fire flush 

of inorganic N was not quantified, although circumstantial evidence suggests that the 

amount released was inconsequential. Specifically, measurements taken 18 months

after burning showed no differences in available soil N between burned and unburned 

plots. Also, herbaceous production did not increase following fire as might be 

expected with a flush of N, as was seen on fertilized plots. 

1

 Personal communication, data on file, Deschutes National Forest, Bend, OR 2 Data on file, Deschutes National Forest, Bend, OR

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 117 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Table 5—Estimated N losses due to silvicultural practices in central Oregon pine stands from

the Black Bark study. Total ecosystem N includes all vegetation, downed woody material,

forest floor, and mineral soil through the C1 horizon, and averaged 2467 kg ha-1 for the three 

study sites (Little and Shainsky 1995).

Stand treatment Estimated N loss (kg ha-1) Percentage of ecosystem N 

Prescribed fire (1991+2002) 

Thinned 523 21 

Unthinned 549 22 

Pre-commercial thinning 

Bole-only 36 1

Whole tree 94 4 

Just how important is the loss of 500 kg N ha-1 to the sustainability of these pine 

forests? Certainly no detrimental effects to vegetation growth have been expressed so 

far in the study, indicative of a nutritionally resilient system. Forest productivity, 

therefore, has not declined. On the other hand, 500 kg N ha-1 represents a loss of

nearly one-fourth of the total ecosystem N pool (table 5), indicating that soil quality

was compromised. As a comparison of alternative methods to reduce fire risk, precommercial thinning had a relatively innocuous effect on ecosystem N, while 

mowing of shrubs, although not measured, would have minimal affect on total N. 

Interestingly, the practice of slash retention (bole-only harvest) as a means to 

conserve site organic matter resulted in little improvement in site N compared to 

whole-tree harvest. 

Taking the concept of repeated fire in eastside pine forests one step further, 

Johnson and others (1998) estimated total N losses during a 100-year period for a 

range of fire-return intervals (1, 3, 5, 10, or 20 burns in 100 years). Assuming that 

each fire consumed 50 percent of the forest floor N, and given the natural rate of litter

input and decay for their site, they found that burning every five years resulted in a 

loss of nearly 1500 kg ha

-1 of N (fig. 5). Burning every 10 years resulted in a 50 

percent reduction in total N by the end of 100 years. Admittedly their model is 

simplistic and does not account for changes in stand structure, litterfall, or burn

prescriptions during the 100-year rotation. Nevertheless, the potential loss of soil 

quality is daunting. 

This exercise in predicting N losses during 100 years brings up an interesting

question. If repeated burning results in near-catastrophic losses of soil N, and if the

pine forests in central Oregon burned on a 4 to 24 year interval prior to the era of fire 

suppression (Bork 1984), then why didn’t the forests run completely out of N a few 

centuries ago? Several possible explanations come to mind: (1) the forests actually 

ran out of N; (2) N input from atmospheric deposition and N-fixing plants was 

sufficient to offset N losses; (3) the model of Johnson and others (1998) and the 

results from the Black Bark study over-predict N loss in forests prior to fire 

suppression. Of course, explanation (1) is nonsensical, and explanation (2) is highly 

unlikely since fewer N-fixing shrubs were present in the understory of ponderosa

pine forests prior to the 20th century (Cochran and Hopkins 1990). The third

explanation is intuitively acceptable (although unproven) if we acknowledge that the 

earlier forests had open, park-like structure with less litterfall and forest floor 

accumulation, which led to lighter burns and, consequently, less N volatilized per 

burn. 

118 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

0

300

600

900

1200

1500

kg/ha

100 30 20 10 5

Fire-return interval (yr)

Figure 5—Predicted N losses during a 100-year rotation due to repeated prescribed

burning at differing fire intervals. Data are from Johnson and others (1998) for stands 

of Jeffrey pine (Pinus jeffreyi Grev. & Balf.). 

Can N Be Replaced By Natural Processes? 

Maybe so. Nitrogen fixation–the conversion of atmospheric N into biologicallyavailable forms via atmospheric deposition, lightning, symbiotic N fixation, and nonsymbiotic N fixation–can partially or completely counter N losses due to fire. 

Symbiotic N fixation, in particular, is an energy efficient and productive means of 

replacing N losses. 

Bitterbrush and ceanothus are the most common N-fixing plants in central

Oregon. Bitterbrush is found on mid- to low-elevation pine sites, while snowbrush is 

found at comparatively higher elevations. N-fixation rates range from 0.5 to 2 kg ha-1

yr-1 for bitterbrush and from 4 to 16 kg ha-1 yr-1 for snowbrush in central Oregon

(Busse 2000). These are not large quantities of fixed N, like is common in pure 

stands of agricultural legumes. Thus, replacing N losses after fire is a long-term

venture (table 6), and, in the case of bitterbrush, will never be complete. Snowbrush, 

by comparison, can replenish the total N pool in 25 years following a single 

prescribed fire. 

Table 6—Estimated time require to replace N losses (kg ha-1) from prescribed burning. 

Years required to replenish lost N3

Fire N loss Snowbrush Bitterbrush

Single 2801 25 140

Repeated 5232 48 262 1

 From Landsberg (1993) 2

 Black Bark study, data on file, Deschutes National Forest, Bend, OR 3 Nitrogen-fixation rates, based on the results of Busse (2000), are 10 kg ha-1 yr-1 for

snowbrush; 1 kg ha-1 yr-1 for bitterbrush; and 1 kg ha

-1 yr-1 for atmospheric deposition

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 119 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Management Considerations 

Let’s face it, soils are boring to the masses. If soil was only impervious to 

disturbance, we wouldn’t have to give it much thought. Then we would accept 

Kimmins (1994) statement “it is neither possible nor is it necessary to consider all of 

the processes and components in order to make useful predictions about the longterm consequences of forest management” as appropriate for forest soils. Alas, the

misfortune of past civilizations that failed to respect their soils or those exposed to 

catastrophic events leaves a lasting imprint of the need to revere soil. 

Obviously, the results from the Black Bark study in central Oregon pine forests 

paint a far less stunning picture of soil devastation compared to images from the Dust

Bowl or from hydraulic mining in the Sierra Nevada mountains. Most soil 

characteristics and processes, in fact, were unaffected by combinations of thinning

and fire. Repeated burning, however, resulted in a loss of soil quality due to reduced

total N. Continued burning on the plots may only accentuate this problem. 

We offer the following suggestions to avoid similar fire-induced losses in soil

quality in central Oregon ponderosa pine forests: 

• Prescribe low severity burns, particularly in stands lacking previous

prescribed fire entry. Prescriptions that leave 75 percent or more of the 

duff layer intact will help conserve N. 

• Reduce fire frequency. Soil N loss increases with increasing fire 

frequency.

• Incorporate mechanical treatments (thinning and mowing) to reduce fire

risk. Little N is removed by these methods compared to burning. 

• Value N-fixing understory plants. Nitrogen can be restored on burned

sites, particularly at higher elevations where snowbrush is present. 

Forest management does not revolve around protecting soil N pools. Instead, 

this is the era of wildfire risk reduction, threatened and endangered species 

protection, wildlife habitat restoration, and recreation use. Long-term changes in soil 

quality, however, need not occur in central Oregon if simple precautions are taken 

such as conserving soil N. Most importantly, they will be avoided if all that work

(and play) in the forests speak for the soil. 

References 

Barrett, J.W. 1978. Height growth and site index curves for managed, even-aged stands of 

ponderosa pine in the Pacific Northwest. Res. Pap. PNW-232. Portland, OR: Pacific 

Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 14 p.

Bork, J.L. 1984. Fire history in three vegetation types on the east side of the Oregon 

Cascades. Corvallis: Oregon State University; 94 p. Ph.D. dissertation.

Burger, J.A.; Kelting, D.L. 1999. Using soil quality indicators to assess forest stand 

management. Forest Ecology and Management 122: 155-166. 

Busse, M.D. 2000. Suitability and use of 15N-isotope dilution method to estimate 

nitrogen fixation by actinorhizal shrubs. Forest Ecology and Management 136: 85-95. 

120 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Busse, M.D.; Simon, S.A.; Riegel, G.M. 2000. Tree-growth and understory responses to 

low-severity prescribed burning in thinned Pinus ponderosa forests of central

Oregon. Forest Science 46: 258-268. 

Cochran, P.H. 1978. Response of pole-sized ponderosa pine stand to nitrogen, 

phosphorus, and sulfur. Res. Note PNW-319. Portland, OR: Pacific Northwest 

Research Station, Forest Service, U.S. Department of Agriculture; 8 p.

Cochran, P.H. 1979. Response of thinned ponderosa pine to fertilization. Res. Note PNW

339. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department 

of Agriculture; 8 p. 

Cochran, P.H.; Hopkins, W.E. 1991. Does fire exclusion increase productivity of 

ponderosa pine? In: Harvey, A.E.; Neuenschwander, L.F., compilers. Proceedings:

Management and productivity of western montane forest soils. Gen. Tech. Report. INTGTR-280. Intermountain Research Station, Forest Service, U.S. Department of 

Agriculture; 224-228. 

Covington, W.W.; Sackett, S.S. 1986. Effect of periodic burning on soil nitrogen 

concentrations in ponderosa pine. Soil Science Society of America Journal 50: 452-

457. 

Covington, W.W.; Sackett, S.S. 1992. Soil mineral nitrogen changes following prescribed 

burning in ponderosa pine. Forest Ecology and Management 54: 175-191. 

Doran, J.W.; Parkin, T.B. 1994. Defining and assessing soil quality. In: Doran, J. W.; 

Coleman, D.C.; Bezdicek, D.F.; Steward, B.A., editors. Defining soil quality for a 

sustainable environment. Soil Science Society of America Special Publication No. 35. 

Madison, WI: Soil Science Society of America; 3-21 

Dyrness, C.T.; Youngberg, C.T. 1966. Soil-vegetation relationships within the ponderosa 

pine type in the central Oregon pumice region. Ecology 47: 122-138. 

Hungerford, R.D.; Harrington M.G.; Frandsen W.H.; Ryan K.C.; Niehoff G.J. 1991. 

Influence of fire on factors that affect site productivity. In: Harvey, A.E.;

Neuenschwander, L.F., compilers. Proceedings: Management and productivity of

western montane forest soils. Gen. Tech. Report. INT-GTR-280. Ogden, UT: 

Intermountain Research Station, Forest Service, U.S. Department of Agriculture; 32-50.

Johnson, D.W.; Susfalk, R.B.; Dahlgren, R.A.; Klopatek, J.M. 1998. Fire is more important 

than water for nitrogen fluxes in semi-arid forests. Environmental Science and Policy 

1: 79-86. 

Kimmins, J.P. 1994. Identifying key processes affecting long-term site productivity. In: 

Dyck, W.J.; Cole, D.W.; Comerford, N.B., editors. Impacts of forest harvesting on longterm site productivity. New York: Chapman and Hall: 119-150. 

Lal, R; Sobecki, T.M.; Iivari, T.; Kimble, J.M. 2004. Soil degradation in the United States: 

extent, severity, and trends. Boca Raton, FL: Lewis Publishers; 204 p.

Landsberg, J.D. 1993. Response of ponderosa pine forests in central Oregon to prescribed

underburning. Corvallis: Oregon State University; 302 p. Ph.D. dissertation. 

Little, S.N.; Shainsky, L.J. 1995. Biomass and nutrient distributions in central Oregon 

second-growth ponderosa pine ecosystems. Res. Paper PNW-RP-481. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 17

p. 

Mitchell, R.G.; Preisler, H.K. 1991. Analysis of spatial patterns of lodgepole pine attacked 

by outbreak populations of the mountain pine beetle. Forest Science 37: 1390-1408. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 121 
Managing ponderosa pine forests in central Oregon – Busse and Riegel 

Nissley, S.D.; Zasoski, R.J.; Martin, R.E. 1980. Nutrient changes after prescribed surface

burning of Oregon ponderosa pine stand. In: Proceedings of the Sixth Conference on

Fire and Forest Meteorology. Society of American Foresters. 

Page-Dumroese, D.; Jurgensen, M.; Elliot, W.; Rice, T.; Nesser, J.; Collins, T.; Meurisse, R.

2000. Soil quality standards and guidelines for forest sustainability in northwestern 

North America. Forest Ecology and Management. 138: 445-462. 

Paul, E.A.; Clark, F.E. 1996. Soil microbiology and biochemistry. San Diego, CA: 

Academic Press; 340 p. 

Powers, R.F.; Tiarks A.E.; Boyle, J.R. 1998. Assessing soil quality: practicable standards

for sustainable forest productivity in the United States of America. In: Adams, M. B,

Ramakrishna, K., Davidson, E.A., editors. The contribution of soil science to the 

development of criteria and indicators of sustainable forest management. Soil Science 

Society of America Special Publication No. 53. Madison, WI: Soil Science Society of 

America; 53-80. 

Shea, R.W. 1993. Effects of prescribed fire and silvicultural activities on fuel mass and 

nitrogen redistribution in Pinus ponderosa ecosystems of central Oregon. Corvallis:

Oregon State University; 132 p. M.S. thesis. 

Snyder, G. 1974. Turtle Island. Alexandria, VA: Chadwyck-Healey; 114 p. 

Youngberg, C.T.; Dyrness, C.T. 1963. Some physical and chemical properties of pumice 

soils in Oregon. Soil Science 97: 391-399. 

Youngberg C.T.; Dyrness, C.T. 1965. Biological assay of pumice soil fertility. Soil Science 

Society of America Proceedings 29: 182-187. 

122 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of Ponderosa Pine Nutrition 

Through Fertilization 1 

Mariann T. Garrison-Johnston2, Terry M. Shaw2, Peter G. Mika2 and 

Leonard R. Johnson3 

Abstract 

The results of a series of replicated fertilization trials established throughout the Inland 

Northwest were reviewed for information specific to ponderosa pine (Pinus ponderosa P. and C. 

Lawson) nutrition. Ponderosa pine nitrogen (N) status was often better than the N-status of other 

Inland Northwest species, and therefore growth response to N fertilization was often lower than 

that of other species. Fertilization of ponderosa pine with N alone sometimes appeared to cause 

increased tree susceptibility to mortality by insect, disease and perhaps abiotic stresses. Growth 

and mortality response to N fertilization appeared to be related to foliage potassium (K)/N ratio 

in some cases. The application of K and micronutrients in combination with N may have 

protected the trees from N-related mortality while stimulating a growth response. Sulfur 

fertilization was not found to evoke a growth response in ponderosa pine, and may have 

increased mortality rates slightly. On certain rock types and vegetation series, ponderosa pine 

showed high growth response to macronutrient plus micronutrient fertilization as well as 

herbicide treatment. Ponderosa pine generally did not show a strong growth response to N 

fertilization, except on ‘good’ rock types on moist sites. Multinutrient (macro- plus 

micronutrient) fertilization combined with an herbicide treatment often provided a better 

response than N alone on moderate to dry sites and/or ‘bad’ rock types. Other species in mixedconifer stands, particularly grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), often showed a 

better growth response to fertilization than ponderosa pine. The nutritional ecology of ponderosa 

pine is unique among Inland forest tree species and should be considered when evaluating 

nutrient management options. 

Introduction 

Since its inception in 1980, the Intermountain Forest Tree Nutrition Cooperative 

(IFTNC) has established numerous studies of forest tree response to various fertilization 

treatments throughout the inland portion of the northwestern United States (table 1). 

The initial studies, established in Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) 

and ponderosa pine (Pinus ponderosa P. and C. Lawson) stands, tested various rates of 

nitrogen (N) fertilizer, while subsequent studies incorporated potassium (K). During the 

establishment of the Forest Health and Nutrition study in the mid-1990’s, rock type was 

implicated in plantation success and stand health, leading to the establishment of a 

region-wide Seedling Establishment study (Moore and Mika 1997, Garrison and others 

1 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, Trends 

and Management, October 18-21, 2004, Klamath Falls, Oregon. 

2 Research Scientists and 3

Interim Director of the Intermountain Forest Tree Nutrition Cooperative, Forest 

Resources Department, College of Natural Resources, University of Idaho, Moscow, Idaho, 83844-1133 

(email: marianng@uidaho.edu, tshaw@uidaho.edu, pmika@uidaho.edu,

 ljohnson@uidaho.edu) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 123 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

1997, Garrison and Shaw 1998). A series of individual tree screening trials in ponderosa 

pine and other tree species tested growth response to various combinations of fertilizer 

and herbicide4

. More recently, unfertilized foliage nutrient concentrations of four tree 

species, including ponderosa pine, were compiled to identify suggested sample sizes for 

nutrient testing, as well as to identify natural ranges of nutrient variability (Moore and 

others 2004). The objective of this paper is to summarize the implications of these 

studies for ponderosa pine nutrition. Changes in nutrient concentration and growth rate 

after fertilization or herbicide application will be addressed in detail. 

Tree nutrition may be assessed by comparing foliage nutrient concentrations to 

published critical levels (table 2). Average concentrations of both unfertilized and 

fertilized ponderosa pine foliage from several IFTNC studies were measured one year 

after treatment (table 3). If the measured foliage concentration was below the critical 

level for ponderosa pine, the trees were considered deficient in that element, and the 

element was considered growth limiting. A yield response to fertilization with the 

deficient element was therefore expected. If a nutrient concentration was at or above the 

critical level, the trees were considered to have a sufficient quantity of that element for 

growth, and the element was considered non-limiting; thus, no yield response was 

expected. 

Critical levels are based on traditional yield curves, and therefore provide a direct, 

species-specific and biologically significant technique for assessing the effects of 

nutrient amendments on tree growth and yield. A related method of nutrient assessment 

involves the use of optimum nutrient proportions (nutrient ratios). This technique is 

based on the hypothesis that for a given amount of one element, usually N, a certain 

proportion of other elements is required to maintain an optimum nutrient balance within 

the plant (Powers 1983, Blake and others 1990, Ingestad 1971). The optimum 

concentration of other elements therefore varies based on the N concentration. Several 

of the critical levels proposed in table 2 were derived using optimum ratios in 

conjunction with the established critical N level for ponderosa pine. Because nutrient 

ratios are not tied to a yield expectation, they provide a useful assessment of internal 

plant nutritional balances, and are suited to assessment of forest stands for general 

nutritional status even in the absence of fertilization. Because one of the primary 

research directives of the IFTNC is to increase forest yield through improved tree 

nutrition, the critical level method is more commonly referenced throughout this paper. 

Several terms used throughout this paper require some additional explanation. The 

terms ‘rock type’, ‘underlying geology’ and similar references to the dominant geology 

underlying forest stands is used intentionally, rather than the more common terms 

‘parent material’ or ‘soil type.’ Forested sites are often underlain by several parent 

materials, including bedrock and one or more surficial deposits. The underlying 

geologic formation often dominates soil properties, and has been a useful variable in 

explaining forest nutrition and fertilization response during IFTNC research. Therefore, 

references to the underlying geologic formation are used as such throughout this paper. 

The term ‘vegetation series’ refers to a grouping of habitat types or plant associations 

named after a tree species that is expected to become 

4

 Unpublished data on file, Intermountain Forest Tree Nutrition Cooperative, University of Idaho, 

Moscow, Idaho 

124 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Table 1—List of selected fertilization and herbicide studies established by the Intermountain Forest Tree Nutrition Cooperative between 1980 and 2000. 

Regions refer to northeastern Oregon (NE OR), central Washington (C WA), northeastern Washington (NE WA), central Idaho (C ID), northern Idaho (N ID) 

and western Montana (W MT). 

Trial name No. Year(s) Stand Region Treatments and rates1 

of estab- composition 

sites lished 

Douglas-fir trials 90 1980- Douglas-fir C ID, C WA, NE control; 224 kg N; 448 kg N 

1982 WA, NE OR, N ID, 

W MT 

Ponderosa pine 10 1985 Ponderosa pine NE OR, C WA control; 224 kg N; 448 kg N 

Montana ponderosa pine 6 1987 Ponderosa pine W MT control; 224 kg N; 224 kg N + 190 kg K 

Umatilla mixed conifer 8 1991 Mixed conifer NE OR control; 224 kg N; 224 kg N + 112 kg S 

Okanogan mixed conifer 8 1993 Mixed conifer C WA control; 224 kg N; 224 kg N + 190 kg K 

Forest health and 31 1994- Mixed conifer C ID, C WA, NE 1994 (12 sites): control; 336 kg N; 190 kg K; 336 kg N + 190 kg K 

nutrition 1996 WA, NE OR, N ID 1995 (12 sites): control; 336 kg N; 190 kg K; 336 kg N + 190 kg K; 

336 kg N + 190 kg K + 112 kg S 

1996 (7 sites): control; 336 kg N; 190 kg K; 336 kg N + 190 kg K; 

336 kg N + 190 kg K + 112 kg S + 5.6 kg B + 11.2 kg Cu 

+11.2 kg Zn + 0.1 kg Mo 

All years: Additional N+K combinations ranging from 0 kg N and 0 

kg K to 672 kg N and 574 kg K, per experimental design 

Seedling establishment 12 1998 Douglas-fir and C ID, C WA, NE control; 16 g N; 16 g N + 4.8 g S; 16 g N + 12 g K; 16 g N + 12 g 

ponderosa pine WA, NE OR, N ID K+ 4.8 g S; 16 g N + 12 g K + 4.8 g S + 4.1 g P + 0.61 g Mg 

+ 0.01 g B + 0.03 g Cu + 0.26 g Fe + 0.04 g Mn + 0.01 g Mo 

Screening trials 29 1999- Ponderosa pine C ID, C WA, NE control; 224 kg N; 224 kg N + 190 kg K + 101 kg S + 1.1 kg Mg + 

2000 WA, NE OR 1.1 kg Cu + 3.4 kg B + 1.1 kg Zn + 3.4 kg Fe (multinutrient); 

3.4 kg hexazinone; multinutrient + 3.4 g hexazinone 1

 Rates in kg ha-1 as broadcast application, except for seedling establishment study for which the rate is g seedling-1 as a subsurface (dibble) application. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 125 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

dominant under late successional conditions (Cooper and others 1991, Lillybridge and 

others 1995).Vegetation series are used as a proxy for site moisture regimes by the 

IFTNC, with the more common series in the IFTNC study region ranging from dry to 

moist in the order of ponderosa pine, Douglas-fir, grand fir, western red cedar (Thuja 

plicata Donn ex. D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.). The 

habitat types or plant associations comprising each vegetation series are based on 

understory vegetation and also show a gradual progression from dry to moist. The term 

‘plant association’ is more commonly used in Oregon and Washington, while the term 

‘habitat type’ is more commonly used in Idaho and Montana. Both terms are used on 

occasion in this paper to refer to relative moisture regimes within a vegetation series. 

Results from eight replicated studies were reviewed for this paper. Analysis of 

variance was used to detect treatment effects, and results were considered significant at 

or below a level of p=0.10. 

Table 2—Critical nutrient concentrations for current, upper-crown ponderosa pine foliage in 

the northwestern United States. 

Nutrient Concentration1 

Nitrogen (N; pct) 1.103 

Phosphorus (P; pct) 0.083 

Potassium (K; pct) 0.482 

Sulfur (S; pct) 0.08 

Calcium (Ca; pct) 0.052 

Magnesium (Mg; pct) 0.052 

Manganese ( Mn; ppm) 603 

Iron ( Fe; ppm) 503 

Zinc (Zn; ppm) 303 

Copper (Cu; ppm) 33 

Boron (B; ppm) 203 

1 Value for N from Powers and others (1985), values for P, K, Ca and Mg from Powers (1983) and Powers 

and others (1985). Critical S value derived for this paper using an N/S ratio of 14.7 with the critical N value 

(Turner and Lambert 1979, Blake and others 1990). Micronutrients from Boyer (1984, personal 

communication). 

2

 Derived by cited author(s) using optimal proportions 

3

 Derived by cited author(s) experimentally 

Nutrition of mature, second-growth stands 

Nitrogen and potassium 

Nitrogen is probably the most common fertilizer element utilized in forest 

management applications in the western United States (Moore and others 1991, Mitchell 

and others 1996, Peterson and others 1984, Shumway and Chappell 1995, Tiedemann 

and others 1998, Chappell and others 1999, Carter and others 1998). In the Inland 

Northwest, N has traditionally been applied towards the end of the rotation, when the 

cost of application can be recouped through increased growth during the final few years. 

Fertilization with N typically results in increased foliage N concentrations the first year 

after fertilization (table 3), with concentrations in ponderosa pine foliage collected one 

year after fertilization typically well-correlated with N application rate. For example, 

increasing rate of N fertilization during the Forest Health and Nutrition Study resulted in 

an almost linear increase in foliage N concentrations of about 60 percent over the 

unfertilized control trees at 600 lb ac

-1 N, with the K fertilizer having no notable effect 

on the foliage N response (fig. 1). 

126 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

Table 3—Average nutrient concentrations of current-year, upper-crown ponderosa pine foliage 

measured one year after application of various fertilization treatments for several Intermountain 

Forest Tree Nutrition Cooperative studies. 

Average foliage N concentrations (pct) 

Control N1 N+K N+S N+K+S Multi-nutrient2 

Treatment 

Study 

Montana ponderosa pine 1.24 1.46 1.48 

Umatilla/Okanogan mixed 1.27 1.63 1.56 1.44 

conifer 

Forest health and nutrition 1.15 1.57 1.71 1.65 1.66 

Seedling establishment 1.44 1.65 1.61 1.71 1.73 

Average foliage K concentrations (pct) 

Control N1 N+K N+S N+K+S Multi-nutrient2 

Treatment 

Study 

Montana ponderosa pine 0.75 0.72 0.79 

Umatilla/Okanogan mixed 0.81 0.74 0.79 0.81 

conifer 

Forest health and nutrition 0.89 0.90 0.89 0.99 0.92 

Seedling establishment 0.65 0.56 0.64 0.62 0.64 

Average foliage S concentrations (pct) 

Control N1 N+K N+S N+K+S Multi-nutrient2 

Treatment 

Study 

Umatilla/Okanogan mixed 0.06 0.06 0.06 

conifer 

Forest health and nutrition 0.09 0.07 0.07 0.08 0.08 

Seedling establishment 0.10 0.10 0.12 0.12 0.12 1 For treatment rates see table 1 

2

 Multinutrient fertilization consisted of some combination of macronutrient and micronutrient 

fertilization and varied depending on the study (table 1). 

Nitrogen leads to increased tree growth by building tree foliage, which in turns leads to 

increased rates of photosynthesis and growth response (Miller 1981, Cole and Gessel 

1992, Ballard and Carter 1985). An increase in ponderosa pine needle weight typically 

accompanies increased N-application rate. For example, needle weights in the same 

study also increased with increasing N fertilization rates, leveling off at around 400 lb N 

ac

-1 with an increase of over 2 g 100 needles-1 

over the unfertilized needles (fig. 2). 

Potassium fertilization resulted in somewhat decreased needle sizes at application rates 

greater than 200 lb K ac-1 when applied in the absence of N fertilizer. 

While IFTNC studies have shown that foliage N concentrations increase after N 

fertilization in ponderosa pine, these studies have also shown that (1) ponderosa pine 

generally has higher foliage N concentrations than other common Inland Northwest 

forest species, and (2) other species are more often N-deficient and generally show 

greater increases in N concentration and needle weight following N fertilization. The 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 127 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

Figure 1—Percent difference between fertilized and unfertilized ponderosa pine foliage 

nitrogen (N) concentration one year after application of nitrogen (N) and potassium (K) 

fertilizer during the Forest Health and Nutrition study, for all rock types and vegetation 

series combined. 

Figure 2—Difference between fertilized and unfertilized ponderosa pine needle weight 

(g 100 fascicles-1) one year after application of nitrogen (N) and potassium (K) fertilizer 

during the Intermountain Forest Tree Nutrition Cooperative’s Forest Health and Nutrition 

study, for all rock types and vegetation series combined. 

128 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0.8 

0.9 

1.0 

Relative Cumulative Frequency

Ponderosa 

Pine 

Grand Fir 

Douglas-fir 

Lodgepole 

Pine 

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 

Nitrogen Concentration (pct) 

Figure 3—Cumulative frequency distribution of nitrogen (N) concentrations in 

unfertilized ponderosa pine, lodgepole pine, Douglas-fir and grand fir trees in the Inland 

Northwest. From Moore and others (2004). 

first point was illustrated graphically in frequency distributions of foliage N in 

unfertilized ponderosa pine trees from 37 sites, Douglas-fir from 130 sites, grand fir 

(Abies grandis (Dougl. ex D. Don) Lindl.) from 14 sites and lodgepole pine (Pinus 

contorta Dougl. ex. Loud.) from nine sites across the Inland Northwest (fig. 3) (Moore 

and others 2004). The vertical axis of this graph is the proportion of all sites with foliage 

concentrations less than or equal to a particular value on the horizontal axis. Ponderosa 

pine foliage N concentrations were significantly higher than the other three species, 

which were all similar to each other. Critical nutrient concentrations were also evaluated 

using this distribution. For example, trees on about 97 percent of the Douglas-fir sites 

were below the critical foliage N concentration of 1.40 percent. 

Most of the lodgepole and grand fir trees were also below their respective critical 

levels (1.20 and 1.15 percent, respectively). However, only about 15 percent of 

ponderosa pine N concentrations were below the critical level of 1.10 percent (table 2). 

Furthermore, foliage N response of ponderosa pine was usually of lower magnitude and 

showed more variation than Douglas-fir, grand fir or lodgepole pine on the same or 

similar sites. Correspondingly, volume growth response to N fertilization was typically 

lower for ponderosa pine than other species (Garrison and others 2000, Moore and 

others 1998). These results suggest that the critical level of 1.10 percent for N in 

ponderosa pine foliage may be somewhat low. A foliage N concentration of 1.20 

percent (approximately the 35th percentile in the foliage N distribution) may be a more 

reasonable critical level for Inland Northwest ponderosa pine, based on positive fouryear growth responses to 224 kg ha-1 N fertilization of ponderosa pine with N 

concentrations ranging from 1.18 to 1.24 percent (IFTNC 1992a, IFTNC 1992b). 

Positive growth responses of ponderosa pine to 448 kg ha-1 N fertilizer have been 

obtained with foliage N concentrations as high as 1.47 percent. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 129 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

Conventional wisdom has generally held that growth response of ponderosa pine 

and other forest species will increase linearly with increased rates of N application. 

Studies by the IFTNC have shown that under ideal growth conditions, this is often the 

case (Mika and VanderPloeg 1991, Moore and others 1994). However, growth response 

of ponderosa pine to N fertilization appears to depend on several factors, including 

moisture regime, underlying rock type, and the availability of other nutrients on the site. 

These relationships were first illustrated during the initial ponderosa pine study 

established by the IFTNC in 1985, comprised of a series of N rate trials located in ten 

ponderosa pine stands in northeastern Oregon and central Washington. The stands were 

predominantly mature, second-growth, managed stands, and N was applied at the rate of 

0, 224 and 448 kg ha-1 

as urea. Growth response was measured as the difference 

between treated and control plots at each site, and results were adjusted to a common 

initial basal area. Growth response was expected to increase proportionately with 

increased N rate. However, the six-year results of this study showed that gross basal 

area response after adding 448 kg ha-1 

was not different than after adding 224 kg ha-1. 

Both responses were greater than the untreated controls (IFTNC 1992a, IFTNC 1992b). 

Net basal area response for the same time period was insignificant for both fertilization 

treatments. The difference between the gross and net results was due to mortality. 

Mortality was greater on N-fertilized plots than on the control plots during the first four 

years, particularly for the 448 kg treatment on the northeast Oregon sites, though 

mortality diminished during subsequent measurement periods (IFTNC 1992b). Growth 

and mortality were related to vegetation series, with lower growth and higher mortality 

occurring on the relatively drier Douglas-fir series compared to the grand fir series. 

Growth and mortality were also related to parent material, with lower growth and higher 

mortality occurring on basaltic sites, and higher growth response with less mortality 

occurring on sandstones. Also of interest during this study was the finding that, based on 

two-year periodic response analysis during the first six years, growth rates were the 

same for all three two-year periods, suggesting that response to fertilization was not 

declining and continued to be positive six years after fertilization. 

Potassium was implicated in tree mortality following the 1985 ponderosa pine trials 

and an earlier series of Douglas-fir trials testing the same N treatments. Potassium status 

on all sites was assessed using a foliage K/N ratio (Ingestad 1971). Foliage K/N ratio of 

0.50 is considered critical, and a ratio of 0.65 or higher is considered sufficient. The 

nutrient ratio method is a useful means of assessing K status, as K does not typically 

show a significant change in foliage concentration following fertilizer application (table 

3). Foliage K/N ratios were examined in unfertilized trees on the IFTNC ponderosa pine 

and Douglas-fir trial sites. Those sites with unfertilized foliage K/N ratios greater than 

0.65 appeared to have less mortality and greater growth response to the 448 kg ha-1 N 

treatment. In contrast, those sites with unfertilized foliage K/N ratios less than 0.50 

experienced high mortality, particularly in response to the 448 kg N treatment. Thus, as 

foliage K status appeared likely related to mortality rates after N fertilization, K was 

incorporated into most subsequent IFTNC studies. An N+K combination treatment was 

first included in a study established in six ponderosa pine stands in western Montana in 

1987. On these sites, the 448 kg treatment was dropped, and a treatment consisting of 

224 kg ha-1 N plus 190 kg ha-1 K was substituted. This same series of treatments 

(unfertilized control, 224 kg N and 224 kg N+190 kg K ha-1) was applied in eight mixed 

conifer stands on the Okanogan National Forest in 1993. A series of N+K treatments in 

a response surface design was also applied to 31 mixed conifer stands during the Forest 

Health and Nutrition study in the mid-1990’s (table 1). 

Foliage K concentrations in treated plots one year after fertilization did not show 

significant differences from control plots during any of these studies (table 3). 

130 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

Potassium concentrations occasionally decreased slightly following N-only fertilization, 

due to an effect known as nutrient dilution. Nutrient dilution refers to a decrease in 

nutrient concentration due to an increase in foliage biomass that is not matched by 

accelerated uptake of a nutrient (Jarrel and Beverly 1981). In most cases, the combined 

N+K treatment restored foliage K concentrations to unfertilized levels, suggesting 

uptake of applied K. 

Interestingly, foliage K levels occasionally appeared to increase as a result of S 

fertilization, as shown during a study established in 1991 in mixed conifer stands on the 

Umatilla National Forest (tables 1 and 3). This study did not include K fertilization, but 

did include an N+S combination, with the S and some N applied as ammonium sulfate, 

and the remainder of the N as urea. Foliage K concentrations were above critical levels 

for all treatments, with no significant differences among the controls and any treatment. 

Examination of total K content (K concentration multiplied by foliage biomass of 100 

fascicles) indicated that the N+S treatment produced greater total K content than the 

controls (Garrison and others 2000). This K response to N+S fertilization may be 

explained in part by the chemical properties of ammonium sulfate, particularly when 

applied to soils high in clay such as those derived from basalts. The influx of NH4

+ ions 

from ammonium-based fertilizers has been shown to compete with K+ ions for sites on 

the soil exchange complex (Liu and others 1997, Chen and Mackenzie 1992). In our 

study, this appears to have resulted in an increase in exchangeable K available for plant 

uptake. 

The 10-year results from the Montana ponderosa pine study supported the 

hypothesis that N+K application would decrease tree mortality compared to N-only 

fertilization (IFTNC 1998). While neither fertilization treatment increased net basal area 

growth over control plot growth, the N+K treatment did increase gross basal area 

growth. The difference between gross and net responses was due to mortality, with the 

N+K treatment showing positive growth response (10.4 percent gross basal area 

response) and low mortality (3.1 percent of gross basal area), and the N treatment 

showing low growth response (1.9 percent gross basal area response) and high mortality 

(7.2 percent of gross basal area) compared to the control plots (1.1 percent mortality; 

fig. 4). In other words, N+K fertilization appeared to protect the trees from mortality 

while allowing them to respond to N fertilization. Notably, most of the mortality during 

this study was caused by mountain pine beetle. The IFTNC hypothesized that beetles 

were responding to some physiological or chemical differences in the trees that were 

fertilized with N alone (Mika and others 1993). Alternatively, K provided in the N+K 

treatment may have enabled some protective mechanisms in those trees, allowing them 

to withstand beetle attack. Similar results occurred during the Douglas-fir trials 

established in the early 1980’s, though the mortality agents were different (Mika and 

Moore 1991). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 131 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

0 

1 

2 

3 

4 

5 

6 

7 

8 

Mortality (pct)

Other 

Beetles 

Control N N + K 

Fertilization 

Figure 4— Mortality response and cause of mortality of ponderosa pine ten years after 

224 kg ha-1 nitrogen (N) and 224 kg ha-1 nitrogen plus 190 kg ha-1 potassium (N+K) 

fertilization during the Intermountain Forest Tree Nutrition Cooperative’s Montana 

ponderosa pine fertilization trials. 

Relative volume growth response (four-year volume growth on fertilized plots 

relative to unfertilized plots) for ponderosa pine in the Okanogan and Umatilla mixed 

conifer studies was marginally greater for the N+K treatment compared to the controls 

(Garrison and others 2000). None of the other treatments applied during those studies (N 

or N+S) differed from each other or from the controls. These results were similar to 

those of the Montana ponderosa pine study. However, six-year basal area growth 

response during the Forest Health and Nutrition study confirmed the expected growth 

increase with increasing N rate5

. Basal area increased by as much as 30 percent at the 

higher rates of N application and decreased somewhat with increasing K application to a 

low of almost 20 percent lower lasal area growth on the fertilized compared to control 

trees at the 0 lb N ac

-1 rate (fig. 5). As suggested by the results of the earlier fertilization 

trials, variation in N response was likely related to moisture regime and perhaps rock 

type. The Montana and Okanogan studies were installed on relatively dry sites 

supporting Douglas-fir series and some drier habitat types and plant associations within 

the grand fir series. In contrast, the Forest Health and Nutrition study incorporated 

moister habitat types and plant associations within the grand fir series, as well as sites in 

the western red cedar and western hemlock series. While several of the Montana sites 

were on nutritionally poor metasedimentary rocks, the Okanogan and many of the 

Forest Health and Nutrition sites were on nutritionally better granitic and basaltic rock 

types. These factors likely interact, with higher response by ponderosa pine to N 

fertilization occurring on moister sites and better rock types. This pattern also holds true 

for Douglas-fir and grand fir, although these species performed better on the drier sites 

compared to ponderosa pine. On the relatively drier Okanogan and Umatilla study sites, 

Douglas-fir showed a strong growth response to N fertilization, while ponderosa pine 

5

 Unpublished data on file, Intermountain Forest Tree Nutrition Cooperative, University of 

Idaho, Moscow, Idaho 

132 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

did not. During the Forest Health and Nutrition study, both species responded at about 

the same rates due to inclusion of moister sites. 

Figure 5—Relative basal area (BA) response of ponderosa pine on fertilized plots 

relative to unfertilized plots six years after application of nitrogen (N) and potassium (K) 

fertilizer during the Intermountain Forest Tree Nutrition Cooperative’s Forest Health and 

Nutrition study, for all rock types and vegetation series combined. 

Table 4—Cumulative frequency distributions of foliage weight and nutrient concentrations for 

unfertilized ponderosa pine from 37 sites across the Inland Northwestern United States. Modified 

from Moore and others (2004). 

Percentile Weight1 N P K S Ca Mg B Cu 

(g) (pct) (pct) (pct) (pct) (pct) (pct) (ppm) (ppm) 

5 10.2 1.045 0.135 0.534 0.037 0.052 0.068 12.8 1.64 

10 12.5 1.083 0.148 0.572 0.046 0.061 0.072 14.7 1.88 

20 15.4 1.135 0.165 0.624 0.056 0.073 0.077 16.8 2.21 

30 17.5 1.176 0.176 0.663 0.064 0.083 0.081 18.4 2.48 

40 19.4 1.213 0.186 0.699 0.071 0.092 0.085 19.6 2.72 

50 21.1 1.248 0.194 0.733 0.078 0.101 0.088 20.7 2.96 

60 22.8 1.283 0.202 0.767 0.084 0.110 0.092 21.8 3.20 

70 24.6 1.322 0.210 0.804 0.091 0.120 0.096 23.0 3.47 

80 26.7 1.368 0.220 0.848 0.099 0.132 0.101 24.2 3.78 

90 29.5 1.432 0.232 0.908 0.109 0.149 0.108 25.9 4.23 

95 31.8 1.484 0.241 0.958 0.118 0.164 0.114 27.2 4.60 1

 Foliage weight for 100 needle fascicles and sheaths. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 133 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

The cumulative frequency distribution of unfertilized plots by foliar K (table 4) 

suggests that the critical K level of 0.48 percent for ponderosa pine (table 2) may be 

reasonable, particularly given the generally low growth response (gross and net 

responses by both basal area and cubic foot volume) to K fertilization demonstrated in 

the various studies. Specifically, K availability in the Okanogan, Umatilla and Forest 

Health and Nutrition studies seemed adequate based on both initial K concentrations (all 

greater than 0.48 percent) and the low response of foliage K to fertilization. In the 

Forest Health and Nutrition study, while mortality of ponderosa pine appeared to 

increase with increasing N rate to almost 2 percent 6 years after fertilization at the 

highest N application rates, mortality decreased with increasing K rate to less than 1 

percent at the highest K rates in the absence of N fertilization (fig. 6). Thus, K 

fertilization alone did not increase growth rates in this study (and may have slightly 

decreased growth rates), but appeared to decrease mortality rates. Results of this study 

were consistent with those of the Montana study, underscoring the importance of K in 

eliciting an N response by decreasing mortality. As with growth response, effects of N 

and K fertilization on mortality appeared related to rock type and moisture regime, with 

higher mortality rates occurring on drier sites and nutritionally poorer rock types 

following N-only fertilization, and lower mortality rates on moister sites and 

nutritionally better rock types. Potassium fertilization may mitigate mortality 

acceleration of N fertilization, as demonstrated in the Montana ponderosa pine study 

and the region-wide Forest Health and Nutrition study. However, it is important to note 

that K fertilization does not always have this effect, and that rock type (which affects 

soil characteristics), moisture regime and K fertilization all interact to determine growth 

and mortality response to N fertilization. 

Figure 6—Ponderosa pine mortality as percent of gross basal area (BA) six years after 

application of nitrogen (N) and potassium (K) fertilizer during the Intermountain Tree 

Nutrition Cooperative’s Forest Health and Nutrition study, for all rock types and 

vegetation series combined. 

134 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

Sulfur and micronutrients 

Sulfur (S) was first tested by the IFTNC in 1991 during the Umatilla study 

(Garrison and others 2000), and again as a treatment applied to several sites during the 

Forest Health and Nutrition study in 1995 and 19966

. In both studies, foliage S 

concentrations for ponderosa pine were deficient on most of the control plots, and were 

above critical level following N+S fertilization. Grand fir and Douglas-fir in both 

studies were also S-deficient on unfertilized plots. While grand fir S concentrations 

increased to above-critical levels on most plots following S fertilization, most Douglasfir S concentrations remained deficient. Thus, ponderosa pine behaved more like grand 

fir in terms of foliage response. Examination of ponderosa pine total foliage S content 

(S concentration times foliage biomass of 100 fascicles) in the Umatilla study showed 

that S contents (g 100 fascicles-1) increased on the N+S treatments, providing evidence 

for S uptake by ponderosa pine. However, in neither study did S appreciably stimulate 

volume growth for ponderosa pine. Grand fir growing in the same stands with 

ponderosa pine in the Forest Health and Nutrition study showed positive responses to S 

fertilization, as did Douglas-fir to a lesser extent. During the Umatilla study, neither 

grand fir nor Douglas-fir responded particularly strongly to S fertilization, though 

Douglas-fir showed a marginally positive response, and both species responded better 

than ponderosa pine. 

The cumulative frequency distribution of foliage S concentrations of ponderosa 

pine across the Inland Northwest (table 4) suggests that about half of the ponderosa pine 

stands in the Inland Northwest are S-deficient (critical S level = 0.08 percent, table 2). 

However the lack of growth response to S fertilization during various IFTNC studies 

suggests that this may not be the case. Reasons for the lack of growth response to S 

fertilization in ponderosa pine, particularly on apparently S-limited sites, are not entirely 

clear. A slight decrease in foliage weight for N+K+S treatment compared to N+K did 

occur during the Forest Health and Nutrition study, and when viewed together with the 

increase in foliage S concentration, might suggest S toxicity. A more reasonable 

hypothesis, however, was that some other element besides S might be limiting growth 

response on those sites. 

The inclusion of several micronutrients in a multinutrient fertilization treatment 

during the 1996 Forest Health and Nutrition trials provided one of the first opportunities 

to test growth response to those elements in mature, second-growth mixed conifer 

stands in the Inland Northwest7

. The multinutrient treatment included N, K, S, boron 

(B), copper (Cu), zinc (Zn) and molybdenum (Mo). Foliage nutrient characteristics 

measured one year after fertilization showed that ponderosa pine B concentrations 

increased from 16 to 39 ppm following micronutrient fertilization, raising foliage B 

levels from deficient (below critical level) to adequate (above critical level). While B 

concentrations also increased for Douglas-fir and grand fir, neither species was Bdeficient in unfertilized trees. Ponderosa pine foliage Cu concentrations increased 

slightly from 2.6 to 2.9 ppm following fertilization, but remained below the critical level 

of 3.0 ppm. Grand fir and Douglas-fir Cu concentrations were both adequate following 

Cu fertilization. Ponderosa pine Zn concentrations increased from 28 to 60 ppm 

following micronutrient fertilization, raising Zn concentrations to adequate. Douglas-fir 

and grand fir Zn concentrations were adequate in unfertilized trees, and did not change 

following fertilization. Molybdenum concentrations increased from 0.3 to 0.5 ppm in 

ponderosa pine. Neither Douglas-fir nor grand fir showed foliage Mo responses to Mo 

6,7 Unpublished data on file, Intermountain Forest Tree Nutrition Cooperative, University of 

Idaho, Moscow, Idaho 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 135 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

fertilization. Ponderosa pine needle weights increased from 27 g 100 needles-1 following 

N+K+S fertilization to 33 g 100 needles-1 following N+K+S+micronutrient fertilization, 

an increase attributable to the micronutrients. Grand fir and Douglas-fir needle weights 

did not differ between the same two treatments. 

The increases in ponderosa pine foliage nutrient concentrations and needle weights 

following fertilization with N+K+S+micronutrients suggest that a growth response to 

that treatment might be expected. In fact, six-year gross basal area growth was 41 

percent greater on those plots than the controls. Comparison of that response to the 

N+K+S response indicated that 8 percent of the growth response was due to Cu, Zn, Mo 

and B fertilization, demonstrating the potential importance of these less-studied 

elements. The rest of the growth response was due to N, but not to K or S. Because the 

micronutrient elements were applied in combination, it was not possible to determine 

which particular element(s) caused the growth response, but this finding did provide 

evidence that ponderosa pine may respond to micronutrient fertilization. In the same 

study, Douglas-fir and grand fir growing in mixed conifer stands did not show positive 

growth responses to micronutrient fertilization, though they did respond to S 

fertilization (though only marginally so for Douglas-fir). Sulfur fertilization increased 

six-year mortality in ponderosa pine and Douglas-fir, while S led to decreased mortality 

in grand fir. In contrast, micronutrients led to decreased mortality in ponderosa pine and 

Douglas-fir, but did not affect grand fir mortality. Disease, insect and weather-related 

death were the leading causes of mortality in all species. 

Growth and mortality responses indicated that in mixed conifer stands, grand fir 

responded best to S fertilization but not to micronutrients. Douglas-fir responded 

marginally in growth to S and showed a slight decrease in mortality (but no change in 

growth) due to micronutrients. Ponderosa pine did not respond to S fertilization, but did 

respond in both increased growth and decreased mortality to micronutrients. Thus, 

stands dominated by grand fir might respond better to N, K and S fertilization, while 

those dominated by ponderosa pine might respond better to a combination of N, K and 

micronutrients. Douglas-fir should respond well to N and perhaps N+K fertilization 

(where site K limitations exist), but may respond only marginally to S fertilization, and 

not at all to micronutrient application. 

Notably, these results at least partially disproved the previous hypothesis that 

another element might be limiting growth response to S fertilization in ponderosa pine. 

Even in the presence of positive foliage and growth responses to four important 

micronutrients, no S response was observed in ponderosa pine. Some additional 

experimentation with other elements may be warranted; however, possible S-toxicity 

suggested by foliage analysis also merits further consideration. 

Nutrition of outplanted seedlings 

While the various IFTNC studies provided new information on the growth and 

nutrition of ponderosa pine following various fertilization treatments, an additional 

factor affecting forest health became apparent during the site selection process for the 

Forest Health and Nutrition study. The study design included three sites each in a four 

by three sampling matrix based on four rock types (metasedimentary, granitic, basaltic 

and mixed) and three moisture regimes (Douglas-fir, grand fir and western red 

cedar/western hemlock vegetation series). Despite extensive review of numerous 

candidate sites, no suitable stands were found on metasedimentary rock types in the 

Douglas-fir series. Furthermore, only two sites were found on this rock type in the grand 

fir series, one of which was subsequently found to overlay granitics on about half the 

136 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

plots. The importance of rock type had been evident in previous studies; however, the 

difficulty of finding stands on metasedimentary rocks in the Forest Health and Nutrition 

study design further implicated underlying geology as an important component of stand 

health. Therefore, the Seedling Establishment study was designed with to compare 

establishment of seedlings on ‘good’ and ‘bad’ rocks. 

The overall intent of this study was to determine whether fertilization could 

mitigate the perceived rock type effect detected during the Forest Health and Nutrition 

study. The study design called for selecting pairs of sites on differing rock types, with 

all other site characteristics being matched as closely as possible (IFTNC 1997). Six 

paired sites were selected throughout Idaho, Oregon and Washington. The rocks 

underlying the sites in each pair were rated as ‘good’ or ‘bad’ relative to each other 

(table 5). At each site, four blocks of six plots each were established. In the spring of 

1998, two blocks each were planted with Douglas-fir and ponderosa pine, with species 

randomly assigned to the four blocks. Immediately after planting, fertilizer was applied 

as a subsurface treatment next to each seedling (table 1). The six fertilization treatments 

were randomly assigned to the six plots within each block. In 1999, a second 

fertilization was applied to the seedlings, using the same fertilizer treatments as 

previously applied on each plot, but doubling the rate and applying the treatment as a 

spot broadcast rather than subsurface. In 2000 a third fertilization was applied to a 

subset of sites. This consisted of a block-wide broadcast application of multiple 

nutrients plus hexazinone herbicide to one of the two blocks per species per site. 

Table 5—Relative rating of rock types as ‘good’ or ‘bad’ for paired study established at six 

locations in five regions during the Intermountain Forest Tree Nutrition Cooperative’s Seedling 

Establishment study. 

Region ‘Good’ rock ‘Bad’ rock 

Northeastern Washington Quartz monzonite Sericite schist 

Central Washington Teanaway pyroclastic Roslyn formation sandstone 

Central Washington Basalt of Camas Prairie Andesite of Laurel 

North Idaho Basalt of Onaway Striped Peak quartzite 

Central Idaho Columbia River basalt Quartz diorite gneiss 

Northeastern Oregon Ferro-basaltic andesite Andesite 

Seedling caliper and height were measured every year following establishment. 

Three-year volume growth was heavily affected by rock type. For ponderosa pine, those 

sites associated with ‘good’ rocks showed higher growth response and somewhat lower 

mortality than those associated with ‘bad’ rocks. Furthermore, only the multinutrient 

plus hexazinone treatment on good rocks produced positive growth increases over the 

controls. As in the Forest Health and Nutrition study, micronutrients seemed key for 

eliciting a ponderosa pine growth response, this time for seedlings. Furthermore, the 

importance of herbicide as a tool to reduce competition and increase availability of 

resources for seedlings was underscored. While Douglas-fir showed stronger growth 

responses than ponderosa pine, the pattern of better response on ‘good’ rocks was 

similar. 

Treatments that included N increased Douglas-fir mortality on ‘bad’ rocks relative 

to the same treatments on ‘good’ rocks. For ponderosa pine, similar trends were evident, 

though not all treatments with N increased mortality. Moisture deficit patterns were 

examined for all sites during these three years, to determine whether moisture deficit, 

rather than rock type, might have affected the results. Patterns were similar for all three 

years, with about half the regions showing higher moisture deficit on the good rocks, 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 137 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

and half showing higher moisture deficit on the bad rocks. Moisture deficit patterns 

therefore did not vary consistently with respect to ‘good’ or ‘bad’ rock, and did not 

explain the growth response results. In contrast, response did appear to be affected by 

rock type. 

Foliage nutrient concentrations the first year after planting were affected by the 

nutrient-loading that occurred at the nursery. Some nursery effect was still present after 

the second fertilization treatment, though during both years effects of field fertilization 

were also evident in the foliage chemistry. The most significant finding of foliage 

analysis was a notable B deficiency. Boron concentrations on all plots following the first 

two treatments, and on the control plots following the third treatment, were at or below 

the recommended minimum of 20 ppm for both species. However, with application of 

the third multinutrient treatment, which included a higher B rate than the previous two 

fertilization treatments, B concentrations were well above critical levels, and notably 

higher than previous foliage B levels. The results suggested that B application rates 

applied in previous treatments were below levels required for Douglas-fir and ponderosa 

pine response. 

The seedling establishment study has been followed on only four of the original 12 

sites, largely because mortality due to vegetative competition and browsing resulted in 

too few live trees to continue the study with statistical reliability. However, initial 

results of growth response (caliper and volume) on all 12 sites as well as the continued 

growth response on the four remaining sites suggest that (1) a significant rock type 

effect exists and (2) boron was initially deficient in these seedlings and remained 

deficient after the first two fertilization treatments, likely hindering growth response to 

other applied elements. Mitigation of rock type effects through fertilization remains 

inconclusive, in part because of the apparent growth-limiting effect of B on seedling 

fertilization response during this study. 

Nutrition of young plantations 

A series of individual tree screening trials were established to test the effects of 

herbicide and various nutrients on tree growth. Screening trials provide a means of 

assessing a variety of fertilization and herbicide treatments within a relatively small area 

and short time frame. Treatments that provide the greatest short-term response are then 

selected for long-term plot-based trials. Between 1999 and 2000, 29 ponderosa pine 

screening trials were established in young (15 to 30 year-old) plantations (table 1), all of 

which contained ponderosa pine as a significant component. Each screening trial 

included up to nine treatments incorporating various combinations of fertilizer and 

herbicide. Five treatments common to all sites were an unfertilized control, N only, a 

multinutrient blend, herbicide only, and herbicide plus the multinutrient blend. The 

multinutrient blend included N, K, S, magnesium (Mg), Cu, B, Zn and iron (Fe) (table 

1). The trials were located on sites with three moisture regimes, classified by Douglasfir, grand fir and western red cedar series; and four rock types, classified as 

metasedimentary, mixed (principally glacial deposits), granitic and basaltic. While sites 

did not occur on all combinations of rock type and vegetation series, several 

comparisons of response across rock types and vegetation series were possible. 

138 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

Two-year basal area increment (cm2 tree-1) 

100

90

80

70

Douglas-fir Grand fir Western red 

cedar 

Vegetation series 

Control 

60 N-only 

50 Multinutrient 

40 Hexazinone 

Hexazinone + 30 

Multinutrient 20

10

0

Figure 7—Two-year basal area increment of ponderosa pine trees from three 

vegetation series on granitic substrates following five fertilization and herbicide 

treatments during the Screening Trial study. 

Trials on all three vegetation series on granitic rocks showed the positive effect of 

increased moisture on response to fertilization and/or herbicide (fig. 7). In the absence 

of fertilizer or herbicide, two-year basal area growth of ponderosa pine was significantly 

greater on western red cedar series than on Douglas-fir series, with grand fir series 

intermediate between the two. In the absence of herbicide, basal area growth was greater 

following both the N-only and multinutrient treatments on western red cedar series 

compared to Douglas-fir or grand fir. When herbicide was applied, alone or in 

combination with fertilizer, two year basal area growth on the grand fir series was 

greater than on the Douglas-fir series, but was not different from the western red cedar 

series. In other words, the addition of fertilizer alone increased the growth response on 

the moister sites compared to the moderate or drier sites, while the addition of herbicide, 

alone or in combination with fertilizer, increased the growth response on moderate sites 

over that of drier sites. Thus, management recommendations for enhanced basal area 

growth on granitic sites might include fertilizer alone on moist sites, herbicide plus 

fertilizer on moderate sites, and no fertilizer or herbicide on dry sites 

Ponderosa pine response was compared between mixed, granitic and basaltic rock 

types within the grand fir series, and between metasedimentary, mixed and granitic rock 

types within the western red cedar series. Across the grand fir series, rock type did not 

have a great effect on basal area growth (fig. 8). Herbicide plus multinutrient fertilizer 

did produce a positive growth response on mixed rocks, but no other treatments showed 

growth responses. In contrast, rock type did seem to affect ponderosa pine growth on the 

western red cedar series (fig. 9). This finding in itself was interesting because it 

suggested that as moisture became less limiting, the rock type effect became more 

apparent. Of those sites on the red cedar series, unfertilized trees on metasedimentary 

rock types had lower absolute two-year basal area growth than unfertilized trees on 

granitic rocks, while unfertilized trees on mixed rocks were intermediate between the 

two. Application of fertilizer alone, whether N-only or multinutrient, resulted in greater 

absolute two-year basal area growth on granitic rocks compared to mixed rocks and 

metasedimentary rocks. However, herbicide applied with or without fertilizer resulted in 

greater absolute two-year basal area growth on mixed and metasedimentary rocks 

compared to granitic rocks. Thus, the lower growth rates on metasedimentary and mixed 

rocks appeared to be mitigated by the application of herbicide, whereas fertilizer alone 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 139 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

produced the best response on the granitic sites. These findings suggested that while 

ponderosa pine growing on ‘good’ rock types and high moisture regime sites may 

benefit from multinutrient fertilization alone, ponderosa pine on most rock types and 

moisture regimes should benefit from the application of herbicide in combination with 

multinutrient fertilization. 

Two-year basal area increment (cm2 tree-1) 

100

90

80

70

Mixed Granite Basalt 

Rock types 

Control 

60 N-only 

50 Multinutrient 

40 Hexazinone 

Hexazinone + 30 

Multinutrient 20

10

0

Figure 8—Two-year basal area (BA) increment of ponderosa pine trees on three rock 

types on grand fir series following five fertilization and herbicide treatments during the 

Screening Trial study. 

Two-year basal area increment (cm2 tree-1 ) 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

Control 

N-only 

Multinutrient 

Hexazinone 

Hexazinone + 

Multinutrient 

Metasedi - Mixed Granite 

mentary 

Rock types 

Figure 9—Two-year basal area (BA) increment of ponderosa pine trees on three rock 

types on western red cedar series following five fertilization and herbicide treatments 

during the Screening Trial study. 

Conclusions 

Nitrogen nutrition of unfertilized ponderosa pine in the Inland Northwest is 

generally better than that of its close associates, even when growing with those other 

species in mixed-conifer stands. Consequently, growth response to N fertilizer is 

somewhat lower for ponderosa pine compared to other species. While K fertilization 

does not usually elicit either a foliage K response or a growth response in any of these 

species, some evidence does exist that K fertilization can lead to decreased mortality in 

ponderosa pine. Sulfur fertilization has not been overly successful in increasing growth 

140 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

rates in ponderosa pine, and is probably not a cost-effective addition to operational 

fertilization regimes, unless other more responsive species such as grand fir are present. 

The most promising results for ponderosa pine growth response have occurred 

following fertilization with a combination of N, K and micronutrients, particularly B, 

Cu, Zn and Mo. Additional research into micronutrient and perhaps additional 

macronutrient fertilization of ponderosa pine is warranted. Also promising are results 

related to herbicide application, particularly on drier sites where competition for 

available moisture may be significant. Rock type appears to interact with moisture in 

determining tree growth response to herbicide application, such that tree growth on 

moist sites with ‘bad’ rock substrates may also benefit from herbicide plus multinutrient 

fertilization. 

Ponderosa pine responds differently to fertilization than grand fir, and somewhat 

differently than Douglas-fir. Because ponderosa pine and Douglas-fir commonly occur 

together in stands, the two species could be considered for similar fertilization regimes. 

Fertilization blends containing N, micronutrients and perhaps K (on K-limited sites) 

should suffice for these species. For stands containing grand fir, the addition of S to the 

fertilization regime may elicit a growth response in that species and in Douglas-fir, but 

not ponderosa pine. Average fertilizer response is greater on moister sites such as the 

western red cedar series, western hemlock series and moister habitat types and plant 

associations within the grand fir series, compared to drier sites such as the Douglas-fir 

series and drier habitat types and plant associations within the grand fir series. 

Acknowledgements 

The authors acknowledge and thank all current and past members of the 

Intermountain Forest Tree Nutrition Cooperative, whose collective direction and support 

during the last 24 years have contributed tremendously to the current state of knowledge 

regarding Inland Northwest forest tree nutrition. Thanks also to the two technical 

reviewers of this manuscript, whose comments and suggestions greatly improved the 

clarity and content of this paper. 

References 

Ballard, T. M.; Carter, R. E. 1985. Evaluating forest stand nutrient status. BC Ministry of 

Forests Land Management Report No. 20. Victoria, B.C.: British Columbia Ministry of 

Forests; 60 p. 

Blake, J. I.; Chappell, H. N.; Bennett, W. S.; Webster, S. R.; Gessel, S. P. 1990. Douglas-fir 

growth and foliar nutrient responses to nitrogen and sulfur fertilization. Soil Science 

Society of America Journal 54: 257-262. 

Carter, R. E.; McWilliams, E. R. G.; Klinka, K. 1998. Predicting response of coastal Douglasfir to fertilizer treatments. Forest Ecology and Management 107: 275-289. 

Chappell, H. N.; Prescott, C. E.; Vesterdal, L. 1999. Long-term effects of nitrogen fertilization 

on nitrogen availability in coastal Douglas-fir forest floors. Soil Science Society of 

America Journal 63(5): 1448-1454. 

Chen, J. S.; Mackenzie, A. F. 1992. Fixed ammonium and potassium as affected by added 

nitrogen and potassium in three Quebec soils. Communications in Soil Science and Plant 

Analysis 12 (11&12): 1145-1159. 

Cole, D. W.; Gessel, S. P. 1992. Fundamentals of tree nutrition. In: Chappell, H. N.; 

Weetman, G. F.; Miller, R. E., editors. Proceedings of conference on forest fertilization: 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 141 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

sustaining and improving nutrition and growth of western forests, Institute of Forest 

Resources Contribution No. 73. Seattle, WA: University of Washington; 7-16. 

Cooper, S. V.; Neiman, K. E.; Roberts, D. W. 1991. Forest habitat types of northern Idaho: a 

second approximation. Gen. Tech. Rep. GTR-INT-236. Ogden, UT: Intermountain 

Research Station, Forest Service, U.S. Department of Agriculture; 143 p. 

Garrison, M. T.; Moore, J. A.; Shaw, T. M.; Mika, P. G. 2000. Foliar nutrient and tree growth 

response of mixed-conifer stands to three fertilization treatments in northeast Oregon 

and north central Washington. Forest Ecology and Management 132: 183-198. 

Garrison, M. T.; Shaw, T. M. 1998. Seedling establishment/nutrition study establishment 

report. Moscow, ID: Intermountain Forest Tree Nutrition Cooperative, University of 

Idaho; 7 p. 

Garrison, M. T.; Shaw, T. M.; Moore, J. A.; Mika, P. G. 1997. Forest health and nutrition 

study establishment report. Moscow, ID: Intermountain Forest Tree Nutrition 

Cooperative, University of Idaho; 104 p. 

IFTNC. 1992a. 1992 Technical Documentation Report. Moscow ID: Intermountain Forest 

Tree Nutrition Cooperative, University of Idaho. 

IFTNC. 1992b. Ponderosa pine response to nitrogen or nitrogen plus potassium 

fertilization: Part I. Moscow, ID: Intermountain Forest Tree Nutrition Cooperative, 

University of Idaho; 14p. 

IFTNC. 1997. Field design, methods and establishment: seedling establishment/nutrition 

study. Moscow, ID: Intermountain Forest Tree Nutrition Cooperative, University of Idaho. 

IFTNC. 1998. 1998 Annual Report: Ponderosa pine response to nitrogen or nitrogen plus 

potassium fertilization. Moscow, ID: Intermountain Forest Tree Nutrition Cooperative, 

University of Idaho; 13 p. 

Ingestad, T. 1971. A definition of optimum nutrient requirements in birch seedlings II. 

Physiology of Plants 24: 118-125. 

Jarrel, W. M.; Beverly, R. B. 1981. In Brady, editor. Advances in Agronomy 34. New York, 

NY: Academic Press; 147-224. 

Lillybridge, T. R.; Kovalchik, B. L.; Williams, C. K.; Smith, B. G. 1995. Field guide for 

forested plant associations of the Wenatchee National Forest. Gen. Tech. Rep. GTRPNW-359. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. 

Department of Agriculture; 337 p. 

Liu, Y. J.; Laird, D. A.; Barak, P. 1997. Release and fixation of ammonium and potassium 

under long-term fertility management. Soil Science Society of America Journal 61: 310-

314. 

Mika, P. G.; Moore, J. A. 1991. Foliar potassium status explains Douglas-fir response to 

nitrogen fertilization in the inland northwest, USA. Water, Air and Soil Pollution 54: 

477-491. 

Mika, P. G.; Moore, J. A.; Mandzak, J. D. 1993. Beetle-caused mortality in ponderosa pine: 

induced by nitrogen fertilization but prevented by potassium amendment. Moscow, 

ID: Intermountain Forest Tree Nutrition Cooperative, University of Idaho. 

Mika, P. G.; VanderPloeg, J. L. 1991. Six year fertilizer response of managed second-growth 

Douglas-fir stands in the inland northwest. In: Proceedings of Interior Douglas-fir: the 

species and its management. Pullman, WA: Department of Natural Resource Science, 

Washington State University. 

Miller, H. G. 1981. Forest fertilization: some guiding concepts. Forestry 54(2): 157-167. 

142 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Management of ponderosa pine nutrition—Garrison-Johnston, Shaw, Mika and Johnson 

Mitchell, A. K.; Barclay, H. J.; Brix, H.; Pollard, D. F. W.; Benton, R.; DeJong, R. 1996. 

Biomass and nutrient element dynamics in Douglas-fir: effects of thinning and 

nitrogen fertilization over 18 years. Canadian Journal of Forest Research 26(3): 376-388. 

Moore, J. A.; Hanley, H. N.; Shumway, J. S.; Mandzak, J. M. 1998. Fertilizing eastern 

Washington coniferous forests: a guide for nonindustrial private forest landowners. 

Bulleting EB 1874. Pullman WA: Washington State University Cooperative Extension 

Service, Washington State University, 18 p. 

Moore, J. A. and Mika, P. G. 1997. Influence of soil parent material on the nutrition and 

health of established conifer stands in the inland northwest. In: Haase D.L. and Rose R., 

editors. Proceedings of conference on forest seedling nutrition from the nursery to the field; 

Oct 28-29, 1997, Corvallis, OR. Corvallis, OR: Nursery Technology Cooperative, Oregon 

State University; 144-153. 

Moore, J. A.; Mika, P. G.; Schwandt, J. W.; Shaw, T. M. 1994. Nutrition and forest health. In: 

Proceedings of conference on interior cedar-hemlock-white pine forest: ecology and 

management. Pullman WA: Department of Natural Resource Science, Washington State 

University; 173-176. 

Moore, J. A.; Mika, P. G.; Shaw, T. M.; Garrison-Johnston, M. T. 2004. Foliar nutrient 

characteristics of four conifer species in the interior northwest United States. Western 

Journal of Applied Forestry 19(1): 13-24. 

Moore, J. A.; Mika, P. G.; VanderPloeg, J. L. 1991. Nitrogen fertilizer response of Rocky 

Mountain Douglas-fir by geographic area across the inland northwest. Western Journal 

of Applied Forestry 6(4): 94-98. 

Peterson, C. E.; Ryan, P. J.; Gessel, S. P. 1984. Response of northwest Douglas-fir stands to 

urea: correlations with forest soil properties. Soil Science Society of America Journal 

48: 162-169. 

Powers, R. F. 1983. Forest fertilization research in California. In: Ballard, R.; S.P. Gessel, 

editors. Proceedings of IUFRO symposium on forest site and continuous productivity. Gen. 

Tech. Rep. GTR-PNW-163. Portland, OR: Pacific Northwest Research Station, Forest 

Service, U.S. Department of Agriculture; 388-397. 

Powers, R. F.; Webster, S. R.; Cochran, P. H. 1985. Estimating the response of ponderosa pine 

forests to fertilization. In: Schmidt, W. C., editor. Proceedings of future forests of the 

mountain west: a stand culture symposium. Gen. Tech. Rep. INT-GTR-243. Missoula MT: 

Intermountain Research Station, Forest Service, U.S. Department of Agriculture; 219-225. 

Shumway, J. S.; Chappell, H. N. 1995. Preliminary DRIS norms for coastal Douglas-fir soils 

in Washington and Oregon. Canadian Journal of Forest Research 25: 208-214. 

Tiedemann, A. R.; Mason, R. R.; Wickman, B. E. 1998. Forest floor and soil nutrients five 

years after urea fertlization in a grand fir forest. Northwest Science 72(2): 88-95. 

Turner, J.; Lambert, M. J. 1979. Sulfur nutrition of conifers in relation to response to 

fertilizer nitrogen, to fungal infections and to soil parent materials. In: C.T. Youngberg, 

editor. Proceedings of conference on forest soils and land use, fifth North American forest 

soils conference. Ft. Collins, CO: Colorado State University; 546-564. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 143 

Ungulate Ecology of Ponderosa Pine 

Ecosystems in the Northwest1

Martin Vavra2, Kenric Walburger3 and Timothy DelCurto3

Abstract 

Ponderosa pine ecosystems provide important foraging habitats for both wild and domestic

ungulates. Livestock typically graze ponderosa pine ecosystems from May through October. 

Mule deer and elk may utilize these habitats on a yearlong basis in some areas. Stand density

has a significant effect on understory production. Competition for soil moisture and nitrogen

limit understory production. Since these systems typically exist at lower elevations, south 

aspects and on rather shallow soils, soil moisture is usually unavailable to understory species 

by mid summer. Optimal forage quality, therefore, occurs from late spring through midsummer. Livestock use for optimal production should occur during this time frame. Herbivory

by both native and wild ungulates can influence the structure and composition of understory 

vegetation. Ungulates, through the act of selective foraging influence the competitive ability

of understory plants utilized. Ungulates can by considered agents of change in ecosystems by

three processes: the regulation of process rates, modification of spatial mosaics, and action as 

switches controlling transitions between alternative ecosystem states. These understory 

composition and structure changes may have important implications to such diverse attributes

as nutrient cycling, energy flow, biodiversity, stand density, fire type and interval, forest

productivity, and ungulate productivity. Key Words: habitat, deer, elk, herbivory, fire, and

nutrition. 

Introduction 

Ponderosa pine (Pinus ponderosa P.& C. Lawson) ecosystems are the most

extensive and valuable grazed forestlands in North America (Skovlin and others 

1976). In Oregon and Washington 4.5 million hectares (11 million acres) of 

ponderosa pine-bunchgrass type exists (Skovlin and others 1976), and in the fourstate region of Colorado, New Mexico, Arizona and Utah there exists 10.5 million 

hectares (26 million acres) (Lowe and others 1978). These ecosystems additionally 

provide valuable habitat for wild ungulates (primarily mule deer and elk) (Skovlin

and others 1976, Urness and others 1975). Specific habitat provided varies greatly

with stand density, and may provide primarily foraging habitat at lower densities and

security cover at higher densities. Habitat quality for both wild and domestic

ungulates is often a function of past management practices such as logging and fire 

exclusion or natural disturbances such as fire and insect outbreaks. Herbivory, by 

both wild and domestic ungulates, can act as a chronic form of disturbance 

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends, and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Range Scientist, PNW Research Station, USDA, Forest Service, 1401 Gekeler Lane, La Grande, OR 

97850 (mvavra@fs.fed.us) 

3

 Graduate Research Assistant and Associate Professor and Superintendent, Eastern Oregon Agricultural 

Research Center, P.O. Box E, Union OR 97883 (walburgk@onid.orst.edu; 

Tim.DelCurto@oregonstate.edu)

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 145 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

interacting with periodic disturbances (logging, fire) to develop alternative steady

states of understory succession, which, in turn, may confound restoration efforts 

(Riggs and others 2000). Weigand and others (1993) related that ungulate herbivory 

could have substantial impacts on site productivity when used in conjunction with

prescribed fire, stocking control, and species selection. 

Habitat Characteristics 

Ponderosa pine communities may be used by mule deer and elk on a year round

basis (Skovlin and Vavra 1979), depending on elevation and snow conditions. Cattle 

use of these ranges is usually in summer and early fall (Skovlin and others 1976). 

Depending on stocking density, ponderosa pine communities have the potential to

provide security cover and foraging habitat to ungulates. Certainly site specific

variables such as aspect, soil depth, and annual precipitation have an influence on 

understory production of ponderosa pine communities. The principal variable, 

however, is probably stand density. Competition for nitrogen and water between the 

overstory and understory vegetation limits understory development (Riegel and 

others 1991). 

Ponderosa pine stands in the western U. S. have long been recognized as 

overstocked and not at potential for producing forage for ungulates (McConnell and

Smith 1970, Weaver 1951). However, with the passage of the Healthy Forest

Restoration Act in 2003, increases in forage production can be expected (Germaine 

and others 2004). Germaine and others (2004) went on to caution that, if large 

treatment blocks are initiated, then use by mule deer could be precluded if all 

resource needs are not met within the treated area. The same can be hypothesized for 

elk. Manipulation of ponderosa pine communities has the potential to impact

understory productivity and diversity, forage nutritional quality, and microhabitat 

characteristics. Post-manipulation management, e.g. road access, also has the

potential to affect use of treated areas at least by wild ungulates. 

Understory productivity

Of primary concern to domestic and wild ungulates is meeting nutritional needs. 

Herbivores commonly seek foraging areas that are high in understory production 

(DelCurto and others 2000). Understory productivity is controlled to a large extent by

the density of the overstory (Riegel and others 1991). With fire exclusion and the 

resultant regeneration and ingrowth of trees (Germaine and others 2004), and the near

cessation of public land timber harvest, ponderosa pine forests now provide much

less forage than they did historically. Rehabilitation treatments will focus on 

reduction of basal area, overstory canopy cover, and stem density (Germaine and

others 2004).

Previous research on thinning and understory production effects provides an 

indication of the increases in forage that can be expected. McConnell and Smith

(1970) thinned 48-year-old overstocked pine sapling stands to 625, 330, and 165

trees per hectare (253, 134, and 67 trees per acre) while maintaining control stands at

6,916 trees per hectare (2,800 trees per acre). The authors reported a 10 kilogram per

hectare (9 pounds per acre) increase in grass yield and a 2.2 kilogram per hectare (2 

pounds per acre) increase in shrub yield for each 30.8 cm (one foot) increase in pine 

spacing. Total understory production varied from 112 kilograms per hectare (100 

pounds per acre) for controls to 384 kilograms per hectare (342 pounds per acre) for 

146 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

the165 trees per hectare (67 trees per acre) thinning. Gibbs and others (2004) 

working in South Dakota found that heavily thinned stands of ponderosa pine

exhibited a standing biomass 2.9 times greater in shrubs, 6.1 times greater in

graminoids, and 13.0 times greater in forbs than standing biomass of unthinned

stands. Moderately thinned stands had a biomass 3.4 times greater in shrubs, 3.4 

times greater in graminoids, and 4.9 times greater in forbs than did unthinned stands. 

Walburger and others (2005) reported on a long term data set collected after 

a commercial thinning in ponderosa pine stands. Tree density was reduced from 346 

to 148 trees per hectare (140 to 60 trees per acre) and canopy cover reduced from 61

to 29 percent. The study area was logged in 1985. Total understory production was 

twice as high in the thinned stands compared to controls in 1989 but the difference 

declined since this initial response (fig. 1). The site potential for understory 

production of ponderosa pine communities is excellently portrayed by these studies. 

Busse and others (2000), however, remarked that central Oregon ponderosa pine 

stands had six-fold lower understory production than did comparable stands in 

northeastern Oregon. Bennett and others (1987) found herbage yields similar among

a gradient of soil types with dense canopy covers. However, with open canopies, soil 

production potentials were fully expressed with the more productive soils producing 

3 times the herbage of the least productive at 10 percent canopy cover. 

0

200

400

600

800

1000

1200

1400

1600

1989 1992 1995 2003

Year

Understory Production (kg/ha)

Thinned

Control

Figure 1— The effects of timber harvest through commercial thinning (Thinned) vs. 

no harvest (Control), on understory production (kg/ha) in a Ponderosa pine habitat

type in northeastern Oregon. Bars with differing letters, within year, differ at α = 0.05, 

and bars with differing numbers differ at α = 0.05. 

Fire may also have dramatic influences on forage production. Fire that reduces 

canopy cover may have the same stimulatory effect on understory production as 

overstory thinning. Busse and others (2000) provided citations of research that 

reported inconsistent understory response with application of low-severity understory 

burns. Their reasoning for lack of response was that low-severity fires did not reduce 

tree canopy and therefore competition for soil nitrogen and water remained nearly the

same. Their research did not reveal any significant differences in grass or forb 

 b,1 

a,2 

 b,1 

b,1,2 a,2

a,1 

a,3 

 b,2 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 147 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

productivity as a result of fire, but shrub cover (principally Purshia tridentata ) was 

reduced 50 percent compared to controls. 

Wildfires that are typically stand replacing in nature usually occur on areas 

where extensive fuels have built up over time. In this situation the suggested benefits 

of fire-reduced competition for soil resources, reduced litter, and increased nutrient 

availability (Busse and others 2000) may increase understory productivity. Lowe and

others (1978) generalized expected responses of grasses and forbs to wildfire (fig. 2). 

The frequency of the principal shrub in their studies, Ceanothus fendleri, dropped to 

zero as a result of the fire then increased by three to four times the pre-fire condition. 

The initial response of the understory may be typical across the western U.S. 

Persistence of improved understory biomass is, however, dependent on the rapidity

and increasing density of the regenerating overstory. 

Understory productivity can be enhanced by a disturbance or management

practice that reduces canopy cover. Fire treatments may lead to an increase or 

decrease in the shrub component over time depending on species composition. Low 

intensity fires that do not cause mortality in the overstory will probably provide an 

inconsistent response in understory vegetation. 

Figure 2— Time-trend response curves for basal area of forbs and grasses (Lowe

and others 1978). 

Forage nutritional quality

Meeting nutritional needs is not just a case of adequate forage productivity; the 

animal must obtain forage of sufficient quality to satisfy physiological requirements 

(lactation, growth). Management manipulations and natural disturbances may

improve the quantity of forage present but can in some cases result in a decline in 

forage quality compared to untreated stands (Svejcar and Vavra 1985). 

The results of several studies are available that provide information on forage

quality of individual plant species important to ungulates (Hickman 1975, Skovlin 

1967) and quality of actual cattle diets, (Holechek and others 1981, Vavra and

148 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

Phillips 1979). Generally, in ponderosa pine ecosystems with summer drought, a

decline in herbaceous forage quality occurs as plants mature and senesce, and 

nutrients are translocated into the roots. The rate of decline is affected by annual 

precipitation (Holechek and Vavra 1983). 

Management manipulations that decrease canopy cover may accelerate the 

decline in nutritional quality of forage. Svejcar and Vavra (1985) speculated that 

decreasing canopy cover allows more sunlight to reach the soil surface which warms

the soil more rapidly in the spring and dries it more rapidly in the summer, 

accelerating plant phenology. Low biomass productivity sites can also be expected to 

lose forage nutritional quality more rapidly as the summer progresses due to limited

soil moisture and competition for that supply (Busse and others 2000). In 

northeastern Oregon, nutritional quality of ponderosa pine ranges deteriorates below 

required levels by mid- to late-August. Declining herbaceous forage quality can be 

mitigated in animal diets by the presence and consumption of palatable understory

shrubs. It is generally accepted that mule deer and elk employ this dietary strategy

(Ganskopp and others 1999). Typically on forested ranges, cattle will also increase 

their consumption of shrubs as herbaceous forage quality declines (Holechek and 

others 1982). Therefore management strategies that promote development of a

diversity of understory species should provide adequate nutritional quality to 

ungulates later in the season. Problems of grazing distribution might, however, 

develop late in the gazing season in regard to concentration of animals around 

riparian areas. Typically, upland water dries up or has stagnated in late season, and 

upland forage is mature and dry. Both of these factors contribute to increased

utilization of riparian vegetation. 

Cover 

Much of today’s ponderosa pine ecosystems are densely stocked, with closed

canopies and provide no concern for lack of cover. With the implementation of the

Healthy Forest Restoration Act, however, concern may develop if large blocks are 

uniformly treated. Additionally, silvicultural activities during restoration may disrupt

mule deer and elk behavior (Edge and Marcum 1985, Ward 1976). Elk appear to be

more affected by the act of timber harvest and concomitant activities like road

building and resultant traffic (Leege 1976, Ward 1976, Wisdom and others 2004). 

From a review of the literature, Lyon and Christensen (2002) found elk could be 

displaced from habitats by as much as five miles. Most often, however, the distance

moved appeared to be the minimum required to avoid contact with equipment and 

people. Continual timber harvest within an individual watershed for five consecutive 

years can impose learned behavior that delays return to previously used habitats 

(Lyon 1979). Edge and others (1985) did report that home ranges of individual 

animals were not altered when areas of extensive cover remained available within 

their home range. The authors speculated that where cover becomes limited, harvest

activity may increase home-range size and reduce home-range fidelity. 

If timber harvest activities decrease or increase human access to an area, elk 

distributions can be expected to shift, with elk avoiding areas with increased access,

and selecting areas with little or no access (Wisdom and others 2004). Specifically, 

road density and traffic rates in areas open to vehicular travel negatively influence elk

distribution; elk avoid habitats near roads open to traffic (Rowland and others 2000,

Wisdom and others 2004). The influence is not demonstrably linear, however, with 

roads having no apparent influence at zero or very low traffic rates. Cole and others 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 149 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

(1997) found that road management areas where access was restricted to

administrative uses reduced Roosevelt elk home range size. Additionally, Lyon 

(1976) found that elk used habitats with greater canopy closure in areas of higher 

road density.

Mule deer security cover and bed sites may be compromised (Germaine and 

others 2004) as a result of restoration activities. These authors found that, in a 

ponderosa pine landscape treated under a typical restoration prescription, mule deer

day-bed (security) microhabitat was reduced 50-100 percent, while available foraging 

microhabitat was increased 30-60 percent compared to untreated forest. The authors

went on to suggest that stands of saplings and pole-sized trees having greater than 40 

percent midstory canopy closure should be retained in patches of at least 0.04 

hectares (0.1 ac) during restoration efforts. Thomas and others (1979) suggested that 

an optimal landscape for mule deer and elk would be comprised of 40 percent cover 

and 60 percent foraging habitat. Clary (1972) prescribed timber basal areas of 9.1 to 

18.3 square meters per hectare (40 to 80 square feet per acre) to improve big game

habitats in ponderosa pine forests. Additionally, one pine sapling thicket per 40 

hectares (100 acres) was recommended for big game bedding cover. Hillis and others 

(1991) defined a security area for elk as a 101 hectare (250 acre) block that was nonlinear in shape and at least one-half mile from roads. Such areas should compose at

least 30 percent of a watershed. Gibbs and others (2004) felt that unthinned stands 

that provide essential thermal and hiding cover could become more important where

availability of these habitats is more limited. 

In contrast to these conclusions, Wisdom and others (2004) noted changes in elk 

spatial distribution during timber harvest but found no loss of animal performance 

attributable to that change. During harvest activities elk traveled over areas twice as

large as areas covered prior to harvest indicating disturbance to the animals (Edge

and others 1985). After harvest animal spatial distribution decreased from the levels 

occurring during harvest but was still higher than pre-cut levels. 

No major changes in cattle spatial distribution during a timber harvest operation 

due to harvest activities are expected since cattle are domesticated animals, so are

familiar with and tolerate human activity. After harvest, however, the physical

changes in the grazing environment related to harvest may redistribute cattle. Harris 

(1954) reported that cattle seldom use dense overstory canopies except in conditions

of extreme heat or intense insect harassment. Hedrick and others (1968) found it

more difficult to obtain moderate or heavy utilization under dense overstory canopies 

than under low-density canopies. Following timber harvest and the concomitant 

decrease in overstory canopy a release of understory production usually occurs. This

release may vary from two to eight times pre-harvest forage production (Svejcar and 

Vavra 1985) depending on intensity of the cut, site potential, and soil disturbance 

(Hedrick and others 1968). Miller and Krueger (1976) reported that 60 percent of the 

forage consumed in a given pasture by cattle was from areas logged and reseeded. 

Road construction to facilitate harvest also provides improved distribution of cattle 

by improving access (Hedrick and others 1968). Restoration efforts therefore, should 

provide new grazing areas for cattle. 

Stand replacement wildfires that are unusually intense due to long-term fire 

exclusion and unnaturally high stand densities create landscapes usually devoid of

cover. In these cases effects on ungulates are similar to severe canopy reduction from 

timber harvest, so the same mitigating management options should be considered.

Forage is not a limiting factor but cover may be. Increased vulnerability to hunting, 

150 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

distribution alteration due to open roads, and increased vulnerability to predators are

possible. 

Ungulate use of large burns is usually a function of forage availability, but may

be influenced by other factors like livestock grazing (Lowe and others 1978, fig. 3). 

For example, elk summer fall use declined after introduction of sheep grazing in

summer on a 20-year burn (fig. 3). 

Herbivory Effects 

Following disturbances like large fires or fuels reduction treatments, secondary 

succession of the understory and regeneration of conifers are initiated. These areas 

often become focal points of ungulate herbivory for two reasons: 1) vegetation 

developing after disturbance is often more palatable to ungulates relative to that 

available on undisturbed sites; and 2) surrounding untreated or unburned forest 

communities with dense canopies contain limited forage in the understory. Large 

herbivores are attracted to areas that are characterized by relatively high biomass of

palatable food resources, and thus can be expected to focus foraging activity in 

recently disturbed areas. 

Figure 3 —Time-trend response curves for deer and elk use as a ratio of burn use to 

control use (Lowe and others 1978). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 151 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

Only rudimentary data exist (Riggs and others 2000), but ungulate herbivory is 

strongly implicated as a significant agent in altering successional trajectories 

following disturbance (fire, logging, fuels reduction) in the Blue Mountains. Raedeke 

(1988) related that selective feeding of forest animals can result in complete changes 

in the structure, composition, and productivity of the forest. In general, plant 

communities within exclosures are more diverse than the surrounding forest 

community subjected to continual herbivory (Raedeke 1988). Recent literature 

reviews (Augustine and McNaughton 1998, Hobbs 1996) clearly indicate the 

important role of herbivory not only in modifying the composition of plant

communities, but also of other biotic communities in the ecosystem. Ungulates are 

important agents of change in ecosystems by three processes: regulation of process

rates, modification of spatial mosaics, and action as switches controlling transitions 

between alternative ecosystem states (Hobbs 1996). In the Blue Mountains herbivory

has long been recognized to be a competitive factor in ungulate relationships (Cliff 

1939, Pickford and Reid 1943) and in understory shrub suppression (Mitchell 1951). 

However, the role of herbivory is not well recognized in the predominant 

management paradigms, either in the Blue Mountains or any other forest ecosystem 

of the western U. S., and knowledge is more anecdotal than predictive (Riggs and 

others 2000). 

Jones (2000) reviewed the effects of cattle grazing and reported that cover of 

grasses and shrubs, as well as total vegetation biomass often was reduced. Riggs and 

others (2000) reported that, in the Blue and Wallowa Mountains of eastern Oregon, 

understory biomass in ungulate exclosures was 2.1 times greater inside than outside

enclosures, and forest-floor biomass was 1.5 times greater inside than outside. Shrub 

biomass was influenced more by ungulates than was grass or forb biomass. 

Mazancourt and Loreau (2000) stated that herbivory, in general, could lead to species 

replacement in plant communities. Augustine and McNaughton (1998), stated that 

species composition of plants can be dramatically altered by selective foraging of

ungulates and that this phenomenon is a trademark of plant-ungulate relations. The

authors noted that by altering the competitive relations among plants, differential 

defoliation tolerances to grazing of co-occurring plant species appear to be important 

determinants of how woody and herbaceous plant communities respond to herbivory.

Augustine and McNaughton (1998) went on to include effects on overstory 

species as well, and listed several species of coniferous and deciduous trees that were

reported as herbivory intolerant. Healy (1997) found that white-tailed deer 

interrupted the sequence of stand development and simplified understories in eastern

oak forests. Likewise, Alverson and Waller (1997) found that white-tailed deer 

abundance reduced the size and number of hemlock seedlings and explained the

widespread regenerative failure of eastern hemlock. The literature review of Alverson

and Waller (1997) also indicated that white-tailed deer substantially altered tree, 

shrub and herbaceous components of plant communities. 

Ungulate herbivory shapes vegetation pattern in coniferous forests of the 

Northwestern U.S.(Schreiner and others 1996, Woodward and others 1994). Research

by these authors indicated that ungulates maintained a reduced standing crop, 

increased species richness of forbs, and determined the distribution, morphology, and 

reproductive performance of several species of shrubs. Woodward and others (1994) 

stated that the extent to which herbivores can change forest ecosystem processes

might depend on the scale and magnitude of other disturbances. All of the

observations are consistent with available information in interior forests. 

152 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

With ungulates, attraction to and therefore selectivity for areas of lower canopy 

cover and greater forage production may create a chronic disturbance effect after 

timber harvest. Walburger and others (2005) reported that timber harvest had a 

greater effect on understory vegetation than did herbivory, but many species were 

affected by the interaction of timber harvest and herbivory (fig. 4). Plant production

was measured as peak standing crop in the absence of cattle grazing the year 

measured. However, herbivory affected production and presence of grasses, forbs

and shrubs. Total understory production was 124 kilograms per hectare (110 pounds

per acre) lower in cattle grazed pastures than in exclosures. Production of pinegrass 

and elk sedge was also reduced by cattle grazing; whereas, Kentucky bluegrass and

other perennial grass production was not affected by grazing. The total production of

forbs was not affected by herbivory; however, there were varying species effects. 

Walburger and others (2005) also reported that shrub production was moderately 

affected by herbivory and that species diversity was not affected by either timber 

harvest or herbivory. This lack of response of species diversity and shrub production

to herbivory may be due to years of fire exclusion or to prior management. 

Forest succession is a function of edaphic factors, the density and viability of 

seed and sprouting rootstocks, episodic disturbance regimes, and herbivores (Riggs 

and others 2000). Herbivory alters the utilization profile of a plant community

(palatable versus unpalatable plants) and thus can alter its successional trajectory. 

Herbivores influence growth, recruitment, and mortality rates of plants and may do

so in ways correlated with plant density, frequency, or other neighborhood traits, or 

with competitive abilities (Huntly 1991). Moreover, herbivory may increase, offset, 

or generate reciprocal negative interactions among plants (Huntly 1991). Herbivory is 

highly variable in space and in time, and these spatial and temporal patterns of

herbivory can generate heterogeneity in plant population structure, the existence of

which strongly influences community dynamics. 

Management Implications 

Ponderosa pine ecosystems have been modified by fire exclusion for most of the 

twentieth century. Consequently, ungulate habitat provided by these ecosystems has

changed dramatically. In the coming years, resources will be directed to the 

rehabilitation of these ecosystems to restore some target structure and functionality. 

If ungulate habitat is a priority then certain considerations are in order for improving

effectiveness of rehabilitation treatments and follow-up management. 

In order to persist in an environment, wild ungulates, must utilize food that 

results in a given level of fitness, allowing persistence or growth of their population 

in that environment (Belovsky and others 1999). Likewise, utilization of that food 

must occur with minimum risk to the individuals (predation avoidance). Therefore, in 

the management of ungulates, forage resources and cover are considerations. The 

current condition of most ponderosa pine ecosystems is such that cover is not

limiting. As fuel reduction treatments are implemented, however, cover may become 

a limiting factor. Uncut or unburned cover patches should be considered where 

treatment patches are large. Topography plays a mitigating role, so that in landscapes 

with irregular topography, cover patches can be fewer and strategically placed. 

Cover provides for predator avoidance, both human and animal. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 153 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

Figure 4 — Influence of herbivory, A) big game (elk and deer) and cattle exclosure,

B) grazed by big game and cattle and C) grazed by big game only, on a commercially 

thinned Ponderosa pine site in northeastern Oregon. 

Once areas have been treated, the roads developed to gain entry also allow easy

access for hunters, increasing animal vulnerability to harvest. Open roads that 

provide both easy access and decreased tree density after thinning may result in 

animal harvests above desired levels. Road closures not only limit hunter access, but

in the case of elk, prevent compression of available habitats because of their aversion

to road traffic. 

With a reduction in overstory canopy cover, increased forage production is

possible. The degree to which it occurs will be dependent on site factors and the 

remaining tree density. Late summer forage nutritional quality, however, may be 

impacted by the fuels reduction/thinning process because maturation and senescence

of herbaceous plants may occur earlier in the summer in thinned areas (Svejcar and 

Vavra 1985). Livestock should, where possible, utilize ponderosa pine communities 

early in the summer to optimize the capture of plant nutritional value (Vavra 1983). 

Problems of over-utilization of riparian vegetation likely will occur in late summer. 

The development of prescribed fire intervals for ponderosa pine ecosystems 

poses questions for ungulate nutritional ecology. Frequent return interval prescribed 

burning may result in decreased productivity of forbs and shrubs (Tiedemann and

others 2000). These two forage components are important in optimizing quality of 

ungulate diets. Shrubs play a particularly important role in late summer and fall when

grasses have senesced and declined in nutritional quality (Vavra 1983). Tiedemann 

and others (2000) note that the issue was not whether to burn, but rather, defining the 

minimum interval to burn without unacceptable risks to productivity. 

154 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

Herbivory by wild and domestic ungulates has the potential to impact vegetation 

dynamics following rehabilitation efforts on ponderosa pine ecosystems. In 

ponderosa pine stands Walburger and others (2004) did not note the large differences 

due to herbivory on grand fir associations observed by Riggs and others (2000).

Changes to productivity and structure may be the most pronounced herbivory effects 

on ponderosa pine ecosystems. Within a given watershed, size and number of 

rehabilitation units, as well as anticipated ungulate (wild and domestic) utilization are 

important considerations if management goals include specific levels of understory

plant community productivity, diversity and structure. 

Ponderosa pine ecosystems are important to ungulates throughout the western

U.S. These diverse and wide-spread ecosystems have been recognized to be

undergoing alterations attributable to fire exclusion for more than half a century

(Weaver 1951). Also, unregulated historic livestock grazing has played a role in the 

alteration process (Belsky and Blumenthal 1997). Rehabilitation efforts in the next

few years will begin to drastically change the composition and structure of these 

ecosystems. Ungulate habitat will continue to be a critical product of these 

ecosystems, although specific use at a given location may change (security cover 

converted to foraging habitat). 

References 

Alverson, W.S.; Waller, D.M. 1997. The white tailed deer: a keystone herbivore. Wildlife 

Society Bulletin 25:217-226. 

Augustine, David J.; McNaughton, S.J. 1998. Ungulate effects on the functional species 

composition of plant communities: Herbivore selectivity and plant tolerance.

Journal of Wildlife Management 62(4):1165-1183. 

Belovsky, G.E.; Fryxell, J.; Schmitz, O.J. 1999. Natural selection and herbivore nutrition: 

Optimal foraging theory and what it tells us about the structure of ecological

communities. In: Jung, Hans-Joachim G.; Fahey, George C; (eds.) Nutritional ecology

of herbivores. American Society of Animal Science, Savoy, IL; 1-70. 

Belsky, A.J.; Blumenthal, D.M. 1997. Effects of livestock grazing on stand dynamics and

soils in upland forests of the interior West. Conservation Biology 11:315-327. 

Bennett, D.L.; Lemme, G.D.; Evenson, P.D. 1987. Understory herbage production of 

major soils within the Black Hills of South Dakota. Journal of Range Management; 

40(2):166-169. 

Busse, Matt D.; Simon, Steven A.; Riegel, Gregg M. 2000. Tree-growth and understory

responses to low-severity prescribed burning in thinned Pinus ponderosa forests of 

Central Oregon. Forest Science 46(2):258-268. 

Clary, Warren P. 1972. A treatment prescription for improving big game habitat in

ponderosa pine forests. In: Proceedings of the 16th Annual Arizona Watershed 

Symposium, Sept. 20, 1972; Phoenix, AZ: Arizona Water Commission Report 2:25-28.

Cliff, Edward P. 1939. Relationship between elk and mule deer in the Blue Mountains of

Oregon. In: Proceedings of the Fourth North American Wildlife Conference. Portland, 

OR: USDA Forest Service, 560-569. 

Cole, E.K.; Pope, M.D.; Anthony, R.G. 1997. Effects of road management on movement 

and survival of Roosevelt elk. Journal of Wildlife Management 61(4):1115-1126. 

DelCurto, T.; Johnson, B.K.; Vavra, M.; Ager, A.A.; Coe, P.K. 2000. The Influence of 

season on distribution patterns relative to water and resource use by cattle grazing 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 155 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

mixed forested rangelands. In: Proceedings of the Western Section American Society 

of Animal Science; June 21-22, 2000; Davis, CA; 51:171-175.

Edge, W.D.; Marcum, C.L. 1985. Movements of elk in relation to logging disturbances.

Journal of Wildlife Management 49(4):1115-1126. 

Edge, W.D.; Marcum, C.L.; Olson, S.L. 1985. Effects of logging activities on home-range

fidelity of elk. Journal of Wildlife Management. 49(3):741-744. 

Ganskopp, Dave; Svejcar, Tony; Taylor, Fred; Farstvedt, J.; Paintner, K. 1999. Seasonal

cattle management in 3 to 5 year old bitterbrush stands. Journal of Range 

Management 52:166-173. 

Germaine, Stephen S.; Germaine, Heather L.; Boe, Susan R. 2004. Characteristics of mule 

deer day-bed and forage sites in current-condition and restoration-treated 

ponderosa pine forest. Wildlife Society Bulletin 32 (2):554-564. 

Gibbs, Mary C.; Jenks, Jonathan A.; Deperno, Christopher S.; Sowell, Bok F.; Jenkins, Kurt J. 

2004. Cervid forage utilization in noncommercially thinned ponderosa pine forests.

Journal of Range Management 57:435-441. 

Harris, Robert W. 1954. Fluctuations in forage utilization on ponderosa pine ranges in 

eastern Oregon. Journal of Range Management 7(6):250-255. 

Healy, W.M. 1997. Influence of deer on the structure and composition of oak forests in 

central Massachusetts. In: McShea, W.J.; Underwood, H.B.; Rappole, J.H. (eds); The 

science of overabundance: deer ecology and population management. Smithsonian

Institution Press, Washington D.C.; 249-266. 

Hedrick, D.W.; Young, J.A.; McArthur, J.A.B.; Kenistor, R.F. 1968. Effects of forest and

grazing practices on mixed coniferous forests in northeastern Oregon. Technical

Bulletin 103; Corvallis, OR: Agricultural Experiment Station; Oregon State University; 

1-24. 

Hickman, O.E. 1975. Seasonal trends in the nutritive content of important range forage 

species near Silver Lake, Oregon. Res. Paper PNW-RP-187. Portland, OR: Pacific

Northwest Forest and Range Experiment Station, USDA Forest Service; 33 p.

Hillis, J.M.; Thompson, M.J.; Canfield, J.E.; Lyon, L.J.; Marcum, C.L.; Dolan, P.M.;

McCleery, D.W. 1991. Defining elk security: the Hillis paradigm. In: Christensen, 

A.G.; Lyon, L.J.; Lonner, T.N.; compilers. In: Proceedings, elk vulnerability 

symposium. Bozeman, MT: Montana State University; p. 38-43. 

Hobbs, N.T. 1996. Modification of ecosystems by ungulates. Journal of Wildlife 

Management 60(4):695-713. 

Holechek, J.L.; Vavra, M.; Skovlin, J. 1981. Diet quality and performance of cattle on 

forest and grassland range. Journal of Animal Science 53:291-298. 

Holechek, J.L.; Vavra, M.; Skovlin, J.; Krueger, W.C. 1982. Cattle diets in the Blue 

Mountains of Oregon II: Forests. Journal of Range Management 35(2):239-242.

Holechek, J.L.; Vavra, M. 1983. Drought effects on diet and weight gains of yearling

heifers in northeastern Oregon. Journal of Range Management 36(2):227-231. 

Huntly, N. 1991. Herbivores and the dynamics of communities and ecosystems. Annual

Revue of Ecological Systems 22:477-503.

Jones, A. 2000. Effects of cattle grazing on North American arid ecosystems: a 

quantitative review. Western North American Naturalist 60(2):155-164. 

Leege, T.A. 1976. Relationship of logging to decline of Pete King elk herd. In: Proceedings

of the Elk-Logging-Roads Symposium; Moscow, ID: University of Idaho; 6-10. 

156 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

Lowe, P.; Ffolliott, P.F.; Dieterich, J.H.; Patton, D.R. 1978. Determining potential wildlife

benefits from wildlife in Arizona ponderosa pine forests. Gen. Tech. Rep. RM-52. Ft.

Collins, CO: Rocky Mountain Forest and Range Experiment Station, USDA Forest 

Service; 1-12. 

Lyon, L.J. 1976. Elk use as related to characteristics of clearcuts in western Montana. In:

Proceedings of the Elk-Logging-Roads Symposium; Moscow, ID: University of Idaho; 

69-72.

Lyon, L.J. 1979. Influences of logging and weather on elk distribution in western 

Montana. Res. Paper INT-RP-236. Ogden, UT: Intermountain Forest and Range 

Experiment Station, USDA Forest Service; 12 p.

Lyon, L.J.; Christensen, A.G. 2002. Elk and land management. In: Toweill. D.E.; Thomas,

J.W.; (eds). North American Elk Ecology and Management; Smithsonian Institution 

Press, WA; 557-582. 

Mazancourt, C.; Loreau, M. 2000. Effect of herbivory and plant species replacement on 

primary production. American Naturalist 155:735-754. 

McConnell, Burt R.; Smith, Justin G. 1970. Response of understory vegetation to

ponderosa pine thinning in eastern Washington. Journal of Range Management 

23(3):208-212. 

Miller, R.; Krueger, W. 1976. Cattle use on summer foothill rangelands in northeastern

Oregon. Journal of Range Management 29:367-371. 

Mitchell, G.E. 1951. Status of browse on ranges of eastern Oregon and eastern 

Washington. Journal of Range Management 4:249-253. 

Pickford, G.; Reid, E. 1943. Competition of elk and domestic livestock for summer range

forage. Journal of Wildlife Management 7:328-332. 

Raedeke, K.J. 1988. Forest management and wildlife in the pacific northwest. Journal of

Northwest Environments 4:263-278. 

Riegel, Gregg M.; Miller, Richard, F.; Krueger, William. C. 1991. Understory vegetation

response to increasing water and nitrogen levels in a Pinus ponderosa forest in 

northeastern Oregon. Northwest Science 65(1):10-15. 

Riggs, Robert A.; Tiedemann, Arthur R.; Cook, John G.; Ballard, Teena M.; Edgerton, Paul

J.; Vavra, Martin; Krueger, William C.; Hall, Frederick C.; Bryant, Larry D.; Irwin,

Larry L; DelCurto, Timothy. 2000. Modification of mixed-conifer forests by 

ruminant herbivores in the Blue Mountains ecological province. Res. Pap. PNW-RP527. Portland, OR: Pacific Northwest Forest and Range Experiment Station, USDA

Forest Service; 77 p. 

Rowland, M.M.; Wisdom, M.J.; Johnson, B.K.; Kie, J.G. 2000. Elk distribution and

modeling in relation to roads. Journal of Wildlife Management 64(3):672-684. 

Schreiner, E.G.; Krueger, K.A.; Happe, P.J.; Houston, D.B. 1996. Understory patch 

dynamics and ungulate herbivory in old-growth forests of Olympic National Park, 

Washington. Canadian Journal of Forest Research 26:255-265. 

Skovlin, J. M. 1967. Fluctuations in forage quality on summer range in the Blue

Mountains. Res. Paper PNW-44. Portland, OR: Pacific Northwest Forest and Range

Experiment Station, USDA Forest Service; 20 p.

Skovlin, J.M.; Harris, R.W.; Strickler, G.S.; Garrison, G.A. 1976. Effects of cattle grazing 

methods on ponderosa pine-bunchgrass range in the Pacific Northwest. Technical 

Bulletin No. 1531. Portland, OR: Pacific Northwest Forest and Range Experiment

Station, USDA Forest Service; 44 p. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 157 
Ungulate Ecology of Ponderosa Pine Ecosystems — Vavra and others 

Skovlin, Jon; Vavra, Martin. 1979. Winter diets of elk and deer in the Blue Mountains, 

Oregon. Res. Paper PNW-RP-260. Portland, OR: Pacific Northwest Forest and Range

Experiment Station, USDA Forest Service; 23 p.

Svejcar, Tony; Vavra, Martin. 1985. The influence of several range improvements on 

estimated carrying capacity and potential beef production. Journal of Range 

Management 38(5):395-399. 

Thomas, J.W.; Black, H., Jr.; Scherzinger, R.J.; Pedersen, R.J. 1979. Deer and elk. In:

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

Handbook No. 553. Portland, OR: Pacific Northwest Forest and Range Experiment

Station, USDA Forest Service; 124-137. 

Tiedemann, Arthur R.;Klemmedson, James O.; Bull, Evelyn L. 2000. Solution of forest

health problems with prescribed fire: are forest productivity and wildlife at risk?

Forest Ecology and Management 127:1-18. 

Urness, P.J.; Neff, D.J.; Watkins, R.K. 1975. Nutritive value of mule deer forages on 

ponderosa pine summer range in Arizona. Res. Note RM-304. Ft. Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, USDA Forest Service; 6 p. 

Vavra, Martin. 1983. Managing grazing animal response to forestland vegetation. In: Ben 

F. Roche, Jr. and David M. Baumgartner (eds); Forestland grazing proceedings of a

symposium held Spokane, WA: Feb. 23-25, 1983; 43-51. 

Vavra, M.; Phillips, R.L. 1979. Diet quality and cattle performance on forested rangeland 

in Northeastern Oregon. In: Proceedings of the Western Section American Society of 

Animal Science; July 28-Aug. 1, 1979; Tucson, AZ. Vol. 30:170-173. 

Walburger, K.J.; DelCurto, T.; Vavra, M. 2005. The effects of domestic and wild ungulate

herbivory and timber harvest on the understory vegetation structure and 

composition in a Ponderosa pine (Pinus ponderosa) habitat in northeastern Oregon

[abstract]. In: Abstracts for the 58th Annual Meeting of the Society for Range

Management; Ft. Worth, TX: Feb. 5-11, 2005. 

Walburger, Kenric; DelCurto, Tim; Vavra, Martin. 2004. The effects of cattle and big game 

herbivory and logging on the understory vegetation structure and composition in a 

grand fir (Abies grandis) habitat in northeastern Oregon [abstract]. In: Abstracts for

the 57th Annual Meeting of the Society for Range Management; Salt Lake City, Utah:

January 24-30 2004; #379. 

Ward, A.L. 1976. Elk behavior in relation to timber harvest operations and traffic on the 

Medicine Bow Range in South-Central Wyoming. In: Proceedings of the ElkLogging-Roads Symposium; Moscow, ID: University of Idaho; 32-43.

Weaver, H. 1951. Fire as an ecological factor in the southwestern ponderosa pine forests.

Journal of Forestry 49:93-98. 

Weigand, James F.; Haynes, Richard W.; Tiedemann, Art R.; Riggs, Robert A.; Quigley,

Thomas M. 1993. Economic assessment of ungulate herbivory in commercial forests 

of eastern Oregon and Washington, USA. Forest Ecology and Management 61:137-

155.

Wisdom, Michael J.; Johnson, Bruce K.; Vavra, Martin; Boyd, Jennifer M.; Coe, Priscilla K.;

Kie, John G.; Ager, Alan A.; Cimon, Norman J. 2004. Cattle and elk response to 

intensive timber harvest. In: Transactions of the North American wildlife and natural

resources conference. March 20, 2004; Spokane, WA; 727-758. 

Woodward, A.; Schreiner, E.G.; Houston, D.B.; Moorhead, B.B. 1994. Ungulate-forest 

relationships in Olympic National Park: Retrospective exclosure studies. Northwest 

Science 68(2):97-110. 

158 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
A Comparison of Bird Species Composition 

and Abundance Between Late- and Midseral Ponderosa Pine Forests1

T. Luke George2, Steve Zack3, and William F. Laudenslayer, Jr.4

Abstract 

We compared the relative abundance of bird species between two ponderosa pine (Pinus

ponderosa) forests in northeastern California: one with a canopy of large old-growth trees 

present (Blacks Mountain Experimental Forest, BMEF) and the other with large trees 

essentially absent (Goosenest Adaptive Management Area, GAMA). We surveyed 24 units at

BMEF and 20 at GAMA using point counts and compared the relative abundance of bird

species detected at the two locations using Wilcoxon-rank tests. Overall bird species 

composition was similar at the two locations. Of the 51 species detected at both locations, 29

were detected at both GAMA and BMEF, 14 were only detected at BMEF and 8 were only

detected at GAMA. Most of the species that were detected at only one site were rare at the site 

where they were observed. Plot diversity (the number of bird species detected on a plot) did 

not differ between the two locations. Bird species were lumped into four foraging guilds, 

woodpeckers, bark gleaners, foliage gleaners, and flycatchers, to examine if foraging ecology

predicted differences in abundance between the two sites. Woodpeckers, bark gleaners, and

flycatchers were more abundant at BMEF while foliage gleaners were more abundant at

GAMA. Differences in the abundances of individual species were generally consistent with 

the overall guild differences. For instance, Williamson’s Sapsuckers (Sphyrapicus

thyroideus), Hairy and White-headed Woodpeckers (Picoides villosus and P. albolarvatus),

and Northern Flickers (Colaptes auratus) were all significantly more abundant at BMEF than 

GAMA. The only species whose abundance was not consistent with the difference in guild

abundance was the Red-breasted Nuthatch (Sitta canadensis), a bark gleaner, which was more 

abundant at GAMA. These results are consistent with other studies suggesting that 

woodpeckers and bark gleaners are strongly associated with large trees and snags. The dense

canopy of small to medium sized trees at GAMA relative to BMEF may account for the 

higher density of foliage gleaners at GAMA. 

Introduction 

Ponderosa pine (Pinus ponderosa P. & C. Lawson) and related Jeffrey pine (P.

jeffreyi Grev. & Balf.) forests which occur from Baja California to British Columbia, 

and from the Cascade and Sierra Nevada Mountains eastward to the Rocky

Mountains, have perhaps changed more in the last century than any other forest type

in western North America (Covington and Moore 1994). Two major changes have 

occurred in these forests: a decrease in the mean diameter of the trees and a change in

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Department of Wildlife, Humboldt State University, Arcata, CA 95521 3

 Wildlife Conservation Society, Portland Office, North America Program, 219 SW Stark Street, Suite 

200, Portland, OR 97204 

4 Research Wildlife Ecologist, USDA Forest Service, Sierra Nevada Research Center, Pacific Southwest 

Research Station, Fresno, CA 93710

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 159 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

the relative proportion of tree species. Many forest stands that had been composed

almost exclusively of ponderosa pine are now numerically dominated by white fir

(Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), Douglas-fir (Pseudotsuga 

menziesii (Mirbel) Franco), and grand fir (Abies grandis (Dougl. ex D. Don) Lindl.). 

The change in the mean diameter of the trees is a result of extensive logging of

ponderosa pine forests over the last century while the change in species composition 

is due to the exclusion of fire and possibly other factors over the last several decades

(Agee 1993, Mohr and others 2000, Odion and others 2004, Perry and others 2004,

Skinner and Chang 1996).

Although there has been more focus on effects of logging on wildlife in wetter 

forests of the western United States (e.g., Hejl 1994, Morrison 1992, Sallabanks and 

others 2000, Zarnowitz and Manuel 1985), there nonetheless are several studies that

have examined the effects of logging on wildlife in ponderosa pine forests (Blake 

1982, Brawn and Balda 1988, Mannan and Meslow 1998, Szaro and Balda 1979a). 

From the literature, it appears that the presence of large-diameter trees is critical to 

some species of wildlife (Brawn and Balda 1988, Finch and others 1997, Weikel and

Hayes 1999), but there is a general paucity of good controls or in multi-year 

replication in such evaluations (Sallabanks and others 2000). 

This paper is the part of a series of evaluations of ponderosa pine wildlife and 

wildlife interactions in eastside pine forests of northern California (Farris and others 

2002, Farris and others 2004, Liebezeit and George 2002, Zack and others 2002). We 

participated in the design and implementation treatments at two sites (George and 

Zack 2001, Zack and others 1999): Blacks Mountain Experimental Forest (BMEF) 

(Oliver and Powers 1998) in Lassen National Forest, and Goosenest Adaptive 

Management Area (GAMA) (Ritchie and Harcksen 1999) in the eastern part of 

Klamath National Forest. In brief, the treatments are large-scale (at least 40 hectares),

replicated, with different thinning alternatives and with and without prescribed fire. 

Here we provide a baseline and comparative basis for understanding the 

avifaunas at BMEF and GAMA prior to such treatments. BMEF was designated as an

experimental forest in the 1930s, and our plots had an outstanding legacy of large and

old ponderosa and Jeffrey pines (Oliver 2000). In contrast, GAMA was clearcut in 

the early 1900s (Ritchie and Harcksen 1999) and has had little logging activity since, 

making it typical of many western ponderosa pine forests. Thus, we have an 

opportunity to compare the avifauna between a relatively intact forest of large 

diameter trees (BMEF) with a mid-seral forest of medium-diameter trees (GAMA).

Both sites prior to treatments had considerable encroachment of white fir and high 

densities of small trees and shrubs in the understory, all typical effects of fire

exclusion. 

Methods

Study Sites 

Blacks Mountain Experimental Forest (lat. 40°40’N., long. 121°10’W.) is

located 56 km NW of Susanville, Lassen County, California. Ponderosa pine is the 

principal tree species with small numbers of Jeffrey pine and incense cedar 

(Calocedrus decurrens (Torr.) Florin). White fir becomes increasingly prevalent at

higher elevations. BMEF has two major diameter classes of trees—a scattered

overstory of large 300-700 year-old pines and incense cedar and a dense understory 

160 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

of pines and white fir that is thought to have originated after wild fire exclusion

(Oliver and Powers 1998). Although some logging was conducted at BMEF during

the 1938-1947 as part of the Methods of Cutting study (Dolph and others 1995), 

much of the area was never logged making it an ideal location to examine the 

avifauna of a late-seral ponderosa pine forest. The elevation ranges from 

approximately 1700-1950 m. In 1995, 12 treatment units (each divided into two splitplots) were established at BMEF to examine the effects of different silvicultural 

treatments on the flora and fauna (Oliver and Powers 1998).

Goosenest Adaptive Management Area (lat. 41°34’N., long. 121°41’W.) is

located in Siskiyou County, 2 km SE of Tennant, CA. The vegetation at GAMA is 

predominantly 80-year-old, second growth ponderosa pine forest. The dominant tree 

species are ponderosa pine and white fir. Incense cedar and sugar pine (Pinus 

lambertiana Dougl.) are also common on the northwestern portion of the site. The 

understory is dominated by greenleaf manzanita (Arctostaphylos patula Greene),

snowbrush ceanothus (Ceanothus velutinus Dougl. ex Hook.), and white fir saplings.

The topography is relatively flat with no perennial streams. Elevations range from

1500 to 1645 m. Mean annual precipitation ranges from 38 to 51 cm, with most 

precipitation falling as snow (Anonymous 1996). The average summer and winter 

temperatures are 15° C and -2° C respectively (Oregon Climate Service 2000). In

1996, 20 40-ha units were established within the GAMA to test different methods of

accelerating the development of late-seral ponderosa pine forest structure (Ritchie 

and Harcksen 1999). 

Point Counts 

We estimated the relative abundance of birds on the experimental units at BMEF

and GAMA using point counts. Surveys were conducted at BMEF from 20 June-24

July 1995, and at GAMA from 7 June-2 July 1996, prior to the implementation of 

silvicultural treatments at each site. All experimental units were surveyed at GAMA

and both split plots of each of the 12 experimental units were surveyed at BMEF. 

Because the point count surveys on each split plot at BMEF were sufficiently far 

apart to avoid overlap, the surveys were analyzed separately. Thus there were 24 

survey units at BMEF (split plots at BMEF are hereafter referred to as units). Eight

points were surveyed on each unit at GAMA and BMEF. Each survey point was at

least 100 m from the unit’s edge and 200 m from other point count locations. At each

site, each unit was surveyed two times by different observers. 

Point count surveys started within 15 min of sunrise and continued until all

points on a plot were surveyed (generally 2 hrs). Count duration was 8 min and

started upon arrival at the point. The horizontal distance to each bird was estimated in

10 m bands to 50 m, 51-75 m, 76-100 m, and > 100 m. To reduce the chance of 

double counting, only birds detected within 100 m of the observer were used in

analyses. Also excluded from analyses were birds detected flying over but not 

utilizing the unit. We computed an index of abundance for each bird species on each 

unit by dividing the number of detections on a unit by the number of surveys (2) on 

each unit. Species richness was computed for each unit by totaling all of the species

that were detected in each unit during the two surveys. Bird species were grouped

into four guilds based on their foraging behavior (appendix 1). We compared the 

relative abundance of bird species detected at the two locations using Wilcoxon-rank

tests and a significance level of 0.05. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 161 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

Results 

The overall bird species composition was similar at the two locations. Of the 51

species detected at both locations, 29 were detected at both GAMA and BMEF, 14 

were only detected at BMEF and 8 were only detected at GAMA (table 1). Most of 

the species that were detected at only one site were rare at the site where they were

observed. When rare species (<1 detection/10 surveys) are excluded, 5 species were

observed only at BMEF and 5 species were observed only at GAMA and 25 species 

were observed at both sites. The number of species detected on each unit did not 

differ between the two sites (table 1). 

The relative abundance of woodpeckers, bark gleaners, and flycatchers was 

higher at BMEF while foliage gleaners were more abundant at GAMA (table 2). 

Differences in abundance of individual species were generally consistent with the 

differences in the abundance of guilds at the sites. Hairy Woodpeckers, Williamson’s

Sapsuckers, and White-headed Woodpeckers (see appendix 1 for scientific names of

bird species) were more abundant at BMEF than GAMA. In addition, Downy

Woodpeckers were only detected at BMEF. Thus, both the density and diversity of 

woodpeckers was higher at BMEF than GAMA. Among the bark gleaners, Mountain

Chickadees, White-breasted Nuthatches, Pygmy Nuthatches, and Brown Creepers

were all more abundant at BMEF. Of the foliage gleaners, Cassin’s Vireos, Warbling

Vireos, Golden-crowned Kinglets, Hermit Warblers, and Western Tanagers were all

more abundant at GAMA. The only species whose abundance pattern differed 

significantly from the overall trend in its guild was the Red-breasted Nuthatch that 

was more abundant at GAMA than BMEF. 

Discussion 

The songbird and woodpecker communities at BMEF and the GAMA were 

similar to other ponderosa pine avifaunas, especially when only considering the 

common species (Hall and others 1997, Laudenslayer and Balda 1976, Szaro and

Balda 1979a, 1979b, Rosenstock 1996, Szaro and Balda 1986, Thomas and others 

1979). These core species include Hairy Woodpecker, Steller’s Jay, Mountain 

Chickadee, White-breasted Nuthatch, Red-breasted Nuthatch, Brown Creeper, 

American Robin, Townsend’s Solitaire, Hermit Thrush, Western Bluebird, Cassin’s

Vireo, Yellow-rumped Warbler, Brown-headed Cowbird, Western Tanager, Darkeyed Junco, Cassin’s Finch, and Pine Siskin. All of these species occur at both BMEF

and GAMA. Many of these species, in turn, occur widely throughout many western

forest types (e.g., Chambers and others 1989, Raphael and others 1987). 

Although the core group of common species was similar at BMEF and GAMA, 

there were five species that were relatively common at one site and absent at the

other. The common species present at BMEF and absent at GAMA were the Whiteheaded Woodpecker, Olive-sided Flycatcher, Western Wood-Pewee, Gray

Flycatcher, and Fox Sparrow. The White-headed Woodpecker has been found to be 

associated with large diameter trees (Booth 1991, Dixon 1995), while the Olive-sided 

Flycatcher and Western Wood-Pewee are associated with a high density of large 

snags and forest openings (Hutto and others 1992). Thus the absence of these species 

from GAMA is consistent with the absence of large trees and snags at the GAMA

site. Gray Flycatchers occur at the low elevation units at BMEF and are associated 

with sagebrush (Artemisia spp.) which was absent at GAMA (Sterling 1999). Fox 

162 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

Table 1—Number of birds detected (mean ± SE) on point counts (detections/survey) at Blacks 

Mountain Experimental Forest (BMEF) and Goosenest Adaptive Management Area (GAMA)

in northeastern California. P values are given for those comparisons where P<0.05. 

Scientific names of birds are provided in appendix 1.

Species BMEF GAMA P 

Sharp-shinned Hawk 0.04±0.03 0 

Cooper’s Hawk 0.08±0.05 0 

Northern Goshawk 0.10±0.07 0 

Red-tailed Hawk 0.10±0.07 0.03±0.03 

Unknown Raptor 0 0.05±0.03 

Mountain Quail 0.02±0.02 0.03±0.03 

Mourning dove 0.06±0.05 0

Great Horned Owl 0.02±0.02 0 

Unknown Owl 0 0.03±0.03 

Common Nighthawk 0.06±0.05 0 

Calliope Hummingbird 0.02±0.02 0 

Unknown Hummingbird 0.29±0.09 0 0.0026 

Williamson’s Sapsucker 1.27±0.25 0.15±0.06 0.0002

Downy Woodpecker 0.04±0.03 0 

Hairy Woodpecker 0.98±0.15 0.53±0.13 0.0300

White-headed Woodpecker 0.19±0.07 0 0.0094

Black-backed Woodpecker 0.10±0.06 0.03±0.03 

Northern Flicker 0.88±0.16 0.43±0.11 0.0386 

Pileated Woodpecker 0.10±0.05 0.05±0.05 

Unknown Woodpecker 1.33±0.24 0.95±0.18 

Olive-sided Flycatcher 0.19±0.10 0 

Western Wood-Pewee 0.25±0.15 0

Hammond’s Flycatcher 0.52±0.22 0.73±0.26 

Gray Flycatcher 0.23±0.18 0 

Dusky Flycatcher 4.69±0.55 3.88±0.91 

Unknown Empidonax Flycatcher 6.94±0.74 2.23±0.57 <0.0001

Cassin’s Vireo 1.96±0.40 3.35±0.67 

Warbling Vireo 0 0.43±0.19 0.0044 

Gray Jay 0 0.45±0.22 0.0233

Steller’s Jay 0.33±0.13 0.30±0.11 

Common Raven 0.60±0.20 0.23±0.13 

Mountain Chickadee 12.98±0.82 8.18±0.62 <0.0001

Red-breasted Nuthatch 5.79±0.56 7.98±0.62 0.0199

White-breasted Nuthatch 1.25±0.25 0.08±0.04 <0.0001

Pygmy Nuthatch 0.88±0.31 0.05±0.05 0.0102

Brown Creeper 3.75±0.36 0.63±0.19 <0.0001

Golden-crowned Kinglet 1.58±0.31 3.55±0.53 0.0045

Townsend’s Solitaire 0.90±0.16 1.00±0.19

Hermit Thrush 4.58±0.66 6.73±0.68 0.0486

American Robin 2.10±0.37 0.05±0.03 <0.0001

Nashville Warbler 0 6.10±0.76 <0.0001

Yellow-rumped Warbler 8.10±0.55 7.00±0.76 

Hermit Warbler 0 3.68±0.61 <0.0001

Western Tanager 1.94±0.37 5.13±0.67 0.0003

Green-tailed Towhee 0 0.08±0.05 

Chipping Sparrow 2.50±0.49 2.25±0.41 

Fox Sparrow 0.25±0.13 0 0.0177 

Dark-eyed Junco 7.83±0.67 4.05±0.53 0.0002 

Brewer’s Blackbird 0 0.05±0.05 

Brown-headed Cowbird 0.08±0.05 0.43±0.14 0.0275 

Purple Finch 0.71±0.31 0.03±0.03 0.0049 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 163 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

Species BMEF GAMA P 

Cassin’s Finch 0.42±0.20 0.18±0.10 

Red Crossbill 0.06±0.06 0.38±0.17 0.0228

Unknown Carpodacus finch 0.88±0.30 0.65±0.25 

Pine Siskin 0.08±0.07 0 

Evening Grosbeak 0 0.28±0.13 0.0044

Black-headed Grosbeak 0 0.03±0.03 

Unknown 1.33±0.30 0.18±0.07 0.0013

Species Richness 18.88±0.56 18.05±0.47

Table 2—Number of birds (mean ± SE) in different foraging guilds detected on point counts 

(detections/survey) at Black’s Mountain Experimental Forest (BMEF) and Goosenest

Adaptive Management Area (GAMA) in northeastern California. P values are given for those

comparisons where P<0.05. 

Guild BMEF GAMA P

Flycatchers 12.81±0.70 6.83±1.33 0.0014

Foliage 13.58±1.06 23.15±1.25 0.0001

Bark Gleaners 11.67±0.77 8.73±0.70 0.0049

Woodpeckers 4.90±0.54 7.00±0.76 <0.0001

Sparrows are more common at elevations higher than those found at GAMA 

(Weckstein and others 2002). 

Three of the common species present at GAMA but absent at BMEF were

species that are generally associated with denser, more closed canopy forest. These

include the Warbling Vireo, Gray Jay, and Hermit Warbler. The other two species

either occur erratically across the landscape (Evening Grosbeak) or are associated

with extensive shrub patches (Nashville Warblers) that were not present at BMEF. 

Despite differences in the species composition of the bird communities at the 

two sites, bird species richness did not differ. Thus, the presence of species

associated with large-diameter trees at BMEF and those associated with a more

closed forest canopy at GAMA resulted in no difference in the number of species 

detected on units at the two locations. Thus, the presence of large trees and an 

associated more open canopy does not lead to an increase in the number of bird 

species. This underscores the point that bird species richness (or diversity) at a 

particular site should not be used as a measure of the success of restoration efforts in

ponderosa pine ecosystems. 

One of the most consistent differences in the bird communities between BMEF 

and GAMA was the greater abundance of woodpeckers and bark gleaners at BMEF. 

Woodpeckers as a group and several species individually were more common at 

BMEF including the Williamson’s Sapsucker, Hairy, and White-headed

Woodpeckers, and the Northern Flicker. White-breasted Nuthatch, Pygmy Nuthatch, 

and Brown Creeper, all bark gleaners, were more common at BMEF than they were 

at GAMA. Mountain Chickadees, which do feed as bark gleaners, but also in the 

foliage of trees, were also more common at BMEF. A strong exception to the above 

pattern is found with the Red-breasted Nuthatch, which is more common at GAMA.

Red-breasted Nuthatches rarely feed on the tree bole, in contrast to the other bark 

gleaners in this guild (e.g., Adams and Morrison 1993). In addition, Red-breasted 

Nuthatches typically fed on medium-diameter, not large-diameter trees in the Sierra

164 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

Nevada (Airola and Barrett 1985) but the opposite was found in coastal Douglas-fir 

forests (Weikel and Hayes 1999).

Other species were more common at BMEF included hummingbirds (often

unidentified to species), American Robins, Dark-eyed Juncos, and Purple Finches. 

Robins and Juncos, both ground foragers, seemingly take advantage of the generally 

more open forest structure at BMEF. 

Foliage gleaners were consistently more abundant at GAMA than BMEF. 

Warbling Vireos, Golden-crowned Kinglets, Hermit Warblers, and Western 

Tanagers, all foliage gleaners, were more abundant at GAMA. Foliage gleaners may

be favored at GAMA because of the high encroachment of white fir and associated

high canopy cover and foliage volume at the site (Ritchie and Harcksen 1999). Other 

species that were more abundant at GAMA relative to BMEF include the Hermit 

Thrush, Brown-headed Cowbird and Red Crossbill. Hermit Thrushes are generally 

associated with higher elevation fir forests (Hejl and Verner 1988) and may also be 

responding to the high level of white fir encroachment at GAMA. Higher densities of 

Brown-headed Cowbirds at GAMA may be related to the higher densities of potential 

hosts for this brood parasite, particularly among warbler species. Red Crossbills are 

highly erratic in time and space across all forest types, and so may not indicate any

real differences between sites. 

The greater abundance of flycatchers at BMEF is difficult to explain because 

many of the flycatchers could not be identified to species at both sites (table 1). It is 

clear, however, that the species richness of flycatchers was much higher at BMEF as

3 of the 5 species were only detected there. Olive-sided Flycatchers responded 

strongly to differences in the abundance of flying arthropods between burned and

unburned sites in north central California (Meehan and George 2003). Furthermore, 

the abundance of flying arthropods was positively associated with the cover of 

ground vegetation, down wood, and shrubs and saplings. It would be interesting to

examine whether differences in ground vegetation, down wood and the associated 

arthropod fauna between BMEF and GAMA explains differences in flycatcher

abundance between the two sites. 

Despite the differences in abundance in some species between the two sites, it is

important to recognize that several common species occur at similar densities. For 

example, Chipping Sparrow, Yellow-rumped Warbler and Cassin’s Finches are

similarly common at both sites. Chipping Sparrows are ground-feeding birds, while

Cassin’s Finches are often detected in the high canopy feeding on cones. Yellowrumped Warblers are primarily foliage gleaners and therefore the lack of difference

in abundance between the two sites is not consistent with overall greater abundance 

of foliage gleaners at GAMA. 

The main differences between the ponderosa pine forest sites are the higher

densities of bark gleaners at BMEF in comparison to the higher densities of foliage 

gleaners at GAMA. Large-diameter trees at BMEF mean more trunk surface to

forage upon. Hairy and Black-backed Woodpeckers at BMEF often feed on larval 

bark beetles in snags, while White-headed Woodpeckers mostly feed on large living 

ponderosa pines (Hughes 2000). Large-diameter trees were preferred foraging

substrates for Hairy Woodpeckers and Chestnut-backed Chickadees (P. rufescens) by

Weikel and Hayes (1999) in their coastal study noted above. Further, they found that 

Brown Creepers selected trees with deeper furrows in the bark (Weikel and Hayes

1999). We have no measured bark furrow depth. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 165 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

The forest at GAMA includes many small- and medium-diameter white fir, and

this may provide a basis for the high densities of leaf gleaners. Brawn and Balda 

(1988) proposed that high densities of foliage gleaning warblers and tanagers in 

ponderosa pine forests was due to more productive foliage of intermediate-aged trees. 

Airola and Barrett (1985) followed insect gleaning birds in Sierra Nevada mixedconifer forests (with oak) and found that Hermit Warblers preferred pine, whereas

Golden-crowned Kinglets, Yellow Warrblers, and Western Tanagers preferred white

fir. Cassin’s Vireo showed no such preference. 

Finally, we should also note that bark gleaners are cavity nesters, and foliage

gleaners are cup nesters. Thus, it is possible that the driving difference between 

BMEF and GAMA bird densities is not tree diameter but rather is cavity availability.

We have found that cavities, and occupied cavities, are much more common at

BMEF compared to GAMA (Zack and others 2002), but we have no way to measure 

whether substrate for cup nesters is higher at GAMA. Brawn and Balda (1988)

consider the paucity of snags with cavities to be a major reason for the hypothesized

declines in chickadee, nuthatch and bluebird (Sialia spp.) populations. 

This comparison of bird communities at our two sites provides a baseline for 

understanding the ongoing experimental treatments at both BMEF and GAMA. 

Sallabanks and others (2000), in a review of bird response to timber harvest, noted

that only a minority of studies were the result of experimental treatments and most

were not long term. The result is that most studies do not truly address cause and 

effect issues nor do they address the relationships of birds to treatments as the 

vegetation develops and changes following treatment. This study is indeed 

correlational, and only a comparison of patterns from one year at each site. But it is a 

foundation of ongoing evaluation of these avifaunas with experimental silvicultural

treatments. While the details of the treatments differ (see Zack and others 1999, 

Ritchie and Harcksen 1999), both sites have plots that were thinned, and plots that 

were burned. Monitoring avifauna use after these treatments will allow us to more

clearly understand broad differences in the responses of both bark gleaners and 

foliage gleaners. 

Acknowledgments 

We thank Christian Buckley, Shay Childress, Mike Van Hatten, and Joe

Liebezeit for their diligence in conducting point counts at the two sites. Kerry Farris 

provided help with the logistics at Blacks Mountain and many insightful discussions 

over the years. Staff at the Goosenest Ranger District, Klamath National Forest

provided logistical support at Goosenest Adaptive Management Area. Steve Zack has 

been supported by the Wildlife Conservation Society since 1998. The members of the

interdisciplinary research team at the Pacific Southwest Research Station provided

many helpful comments and suggestions during the planning and implementation of

this research. This is contribution no. 21 of the Blacks Mountain Ecological Research

Project and no. 12 of the Goosenest Adapative Management Area Ecological 

Research Project 

166 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

References 

Adams, E. M.; Morrison, M. L. 1993. Effects of forest stand structure and composition on

red-breasted nuthatches and brown creepers. Journal of Wildlife Management 57:

616-629. 

Agee, J. K. 1993. Fire ecology of Pacific Northwest forests. Washington, D.C.: Island Press;

493 p. 

Airola, D. A.; Barrett, R. H. 1985. Foraging and habitat relationships of insect-gleaning 

birds in a Sierra Nevada mixed-conifer forest. Condor 87: 203-216. 

Anonymous. 1996. Goosenest adaptive management area: Ecosystem analysis. Klamath

National Forest, Goosenest Ranger District, Forest Service. U.S. Department of

Agriculture; 40 p.

Blake, J. G. 1982. Influence of fire and logging on nonbreeding bird communities of 

ponderosa pine forests. Journal of Wildlife Management 46: 404-415. 

Booth, D. E. 1991. Estimating prelogging old-growth in the Pacific Northwest. Journal of

Forestry 89: 25-29. 

Brawn, J. D.; Balda, R. P. 1988. The influence of silvicultural activity on ponderosa pine 

forest bird communities in the southwestern United States. Bird Conservation 3: 3-

21. 

Chambers, C. L.; McComb, W. C.; Tappeiner, J. C. II. 1989. Breeding bird responses to 

three silvicultural treatments in the Oregon coast range. Ecological Applications 9:

171-185. 

Covington, W. W.; Moore, M. M. 1994. Southwestern ponderosa forest structure, changes

since Euro-American settlement. Journal of Forestry 92: 39-47.

Dixon, R. D. 1995. Ecology of White-headed Woodpeckers in the central Oregon 

Cascades. Moscow: University of Idaho; 148 p. Master’s thesis. 

Dolph, K. L., Mori, S. R., and Oliver, W. W. 1995. Long-term response of old-growth 

stands to varying levels of partial cutting in the eastside pine type. Western Journal

of Applied Forestry 10: 101-108. 

Farris, K. L.; Garton, E. O.; Heglund, P. J.; Zack, S.; Shea, P. J. 2002. Woodpecker foraging 

and the successional decay of ponderosa pine. In: Laudenslayer, W. F., Jr.; Shea, P. J.; 

Valentine, B. E.; Weatherspoon, C. P.; Lisle, T. E., technical coordinators. Proceedings

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

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

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 237-246. 

Farris, K. L.; Huss, M. J.; Zack, S. 2004. The role of foraging woodpeckers in

decomposition of ponderosa pine snags. Condor 106: 50-59.

Finch, D.; Ganey, J. L.; Yong, W..; Kimball, R. T.; Sallabanks, R. 1997. Effects and

interactions of fire, logging and grazing. In: Block, W. M.; Finch, D. M., technical 

coordinators. Songbird ecology in southwestern ponderosa pine forests: a literature

review. Gen. Tech. Rep. RM-GTR-292. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture; 103-136.

George, T. L.; Zack, S. 2001. Spatial and temporal considerations in restoring habitat for

wildlife. Restoration Ecology 9: 272-279. 

Hall, L. S.; Morrison, M. L.; Block, W. M. 1997. Songbird status and roles. In: Block, W. 

M.; Finch, D. M., technical coordinators. Songbird ecology in southwestern ponderosa 

pine forests: a literature review. Gen. Tech. Rep. RM-GTR-292. Fort Collins, CO: 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 167 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture; 69-

88. 

Hejl, S. J.; Verner, J. 1988. Evaluating avian-habitat relationships in red fir forests of the 

Sierra Nevada. Transactions of the Western Section Wildlife Society 24: 121-134.

Hejl, S. J. 1994. Human-induced changes in bird populations in coniferous forests in 

western North American during the past 100 years. In: Jehl, J. R.; Johnson, N. K. 

editors. A century of avifaunal changes in western North America. Study in Avian 

Biology 15: 232-246. 

Hughes, K. 2000. The foraging ecology of picoides woodpeckers in relation to ponderosa

pine decay dynamics. Moscow: University of Idaho; M.S. thesis. 

Hutto, R. L.; Hejl, S. J.; Preston, C. R.; Finch, D. M. 1992. Effects of silvicultural

treatments on forest birds in the Rocky Mountains: implications and management 

recommendations. In: Finch, D. M.; Stangel, P. W., editors. Status and management of 

Neotropical migratory birds. Gen. Tech. Rep. RM-GTR-229. Fort Collins, CO: Rocky 

Mountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agriculture; 386-391. 

Laudenslayer, W. F., Jr.; Balda, R. P. 1976. Breeding bird use of a pinyon-juniper 

ponderosa pine ecotone. Auk 93: 571-586. 

Liebezeit, J. R.; George, T. L. 2002. Nest predators, nest-site selection, and nesting success

of the Dusky Flycatcher in a managed ponderosa pine forest. Condor 104: 507-517. 

Mannan, W. R.; Meslow, E. C. 1984. Bird populations and vegetation characteristics in

managed and old-growth forest, northeastern Oregon. Journal of Wildlife 

Management 48: 1219-1238. 

Meehan, T.; George, T. L. 2003. Short-term effects of wildfire on the site selection and

habitat quality of a disturbance-dependent flycatcher. Auk 120: 1102-1113. 

Mohr, J. A.; Whitlock, C.; Skinner, C. N. 2000. Postglacial vegetation and fire history,

eastern Klamath Mountains, California. Holocene 10: 587-601.

Morrison, M. L. 1992. Bird abundance in forests managed for timber and wildlife 

resources. Biological Conservation 60: 127-134. 

Odion, D. C.; Frost, E. J.; Strittholt, J. R.; Jiang, H..; Dellasala, D. A.; Moritz, M. A. 2004. 

Patterns of fire severity and forest conditions in the western Klamath Mountains, 

California. Conservation Biology 18: 927-936. 

Oliver, W. W. 2000. Ecological research at the Blacks Mountain Experimental Forest in 

northeastern California. Gen. Tech. Rep. PSW-GTR-179. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 66 p. 

Oliver, W. W.; Powers, R. F. 1998. Blacks Mountain, California: Interdisciplinary field 

research in ponderosa pine. Journal of Forestry 96: 4-9.

Oregon Climate Service. 2000. Oregon State University, Corvallis, OR. 

Perry, D. A.; Jing, H.; Youngblood, A.; Oetter, Doug R. 2004. Forest structure and fire 

susceptibility in volcanic landscapes of the eastern High Cascades, Oregon.

Conservation Biology 18: 913-926. 

Raphael, M. G.; Morrison, M. L.; Yoder-Williams, M. P. 1987. Breeding bird populations

during twenty-five years of postfire succession in the Sierra Nevada. Condor 89:

614-626. 

Ritchie, M. W.; Harcksen, K. A. 1999. Long-term interdisciplinary research on the

Goosenest Adaptive Management Area, Klamath National Forest, California.

Forestry Chronicle 75: 453-456. 

168 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bird Species Composition and Abundance in Ponderosa Pine—George, Zack, and Laudenslayer

Rosenstock, S. S. 1996. Habitat relationships of breeding birds in northern Arizona 

ponderosa pine and pin-oak forests. Phoenix: Arizona Game & Fish Department, 

Technical Report 23. 53 p. 

Sallabanks, R.; Arnett, E. B.; Marzluff, J. M. 2000. An evaluation of research on the effects 

of timber harvest on bird populations. Wildlife Society Bulletin 28: 1144-1155. 

Skinner, C. N.; Chang C. R. 1996. Fire regimes, past and present. In: Sierra Nevada

Ecosystem Project: Final report to Congress, Vol. II. Assessments and scientific basis 

for management options. Davis: Centers for Water and Wildland Resources, University

of California, Davis; 1041-1069. 

Sterling, J. C. 1999. Gray Flycatcher (Empidonax wrightii). In: Poole, A.; Gill F., editors. 

The Birds of North America, No. 458. The Birds of North America, Inc., Philadelphia, 

PA. 16 p.

Szaro, R. C.; Balda, R. P. 1979a. Effects of harvesting ponderosa pine on nongame bird

populations. Res. Paper RM-RP-212. Fort Collins, CO: Rocky Mountain Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 25 p.

Szaro, R. C.; Balda, R. P. 1979b. Bird community dynamics in a ponderosa pine forest. 

Studies in Avian Biology 3: 1-66. 

Szaro, R. C.; Balda, R. P. 1986. Relationships among weather, habitat structure, and 

ponderosa pine forest birds. Journal of Wildlife Management. 50: 253-260. 

Thomas, J. W.; Anderson, R. G.; Maser, C.; Bull, E. L. 1979. Snags. In: Thomas, J.W., editor.

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

Agriculture Handbook 553. Washington, D.C.: Forest Service, U.S. Department of

Agriculture; 60-77. 

Weckstein, J. D.; Kroodsma, D. E.; Faucett, R. C. 2002. Fox Sparrow (Passerella iliaca). In:

Poole, A. and Gill, F., eds. The Birds of North America, No. 715. Philadelphia, PA. The 

Birds of North America, Inc.; 28 p. 

Weikel, J. M.; Hayes, J. P. 1999. The foraging ecology of cavity-nesting birds in young

forests of the northern coast range of Oregon. Condor 101: 58-66. 

Zack, S.; Laudenslayer, W. F., Jr.; George, T. L.; Skinner, C.; Oliver, W. 1999. A prospectus

on restoring late successional forest structure to eastside in pine ecosystems 

through large-scale, interdisciplinary research. In Cook, J. E.; Oswald, B. P., 

compilers. First biennial North American forest ecology workshop. Bethesda, MD:

Society of American Foresters; 343-355. 

Zack, S.; George, T. L.; Laudenslayer, W. F., Jr. 2002. Are there snags in the system? 

Comparing “snag-rich” and “snag-poor” eastside pine forests. In Laudenslayer,

William F., Jr.; Shea, Patrick J.; Valentine, Bradley E.; Weatherspoon, C. Phillip; Lisle, 

Thomas E., technical coordinators. Proceedings of the symposium on the ecology and

management of dead wood in western forests; 1999 November 2-4; Reno, NV. Gen.

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; 179-192.

Zarnowitz, J. E.; Manuwal, D. A. 1985. The effects of forest management on cavity-nesting 

birds in northwestern Washington. Journal of Wildlife Management 49: 255-263. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 169 

Effects of Site on the Demographics of 

Standing Dead Trees in Eastside Pine 

Forests1

William F. Laudenslayer, Jr.2

Abstract 

In the last several decades there has been a growing awareness of the value of snags in forests. 

Recent work has resulted in management standards and guidelines that set objectives for 

species such as cavity-nesting birds, but the numbers of snags required may not be attainable 

or sustainable across the landscape. Work reported here on snag demography in eastside pine 

forests was initiated in 1989. While snags have been present on most of the sites throughout

the study period, the number of snags and their “life-spans” depends on tree species, tree size, 

soil characteristics, and topography. Snags persisted for longer periods at Lassen Volcanic 

National Park sites where the soils are covered by up to 0.5 m of volcanic ash, but snag

density was less than our other sites because of the low tree density. These findings suggest 

that standards and guidelines for snag management incorporate variation at local scales. 

Introduction 

Availability of standing dead trees, or snags, has long been a management issue 

in forests (Brawn and Balda 1988, Bull and others 1997, Cline and others 1980, 

Raphael and Morrison 1987, Raphael and White 1984, Rosenberg and others 1988,

Swallow and others 1988, Thomas and others 1979, Waters and others 1990, Welsh 

and Capen 1992, Zack and others 2002), particularly in eastside pine forests – those

forests dominated by ponderosa (Pinus ponderosa P. & C. Lawson) or Jeffrey pine 

(P. jeffreyi Grev. & Balf. ) lying east of the crest of the Cascades and Sierra Nevada

in California, Oregon, Washington, and Nevada (Studinski and Ross 1986). These 

concerns have resulted in management standards that are applied across large

landscapes. For example, the Lassen National Forest requires 1.2 snags per acre (3

per ha) between 15 and 24 inches (38-61 cm) diameter at breast height (dbh) and 0.3 

snags per acre (0.7 per ha) in excess of 24 inches (61 cm) dbh and 20 feet (6 m) in

height (Lassen National Forest 1993). 

While these standards may be relevant (but see Oliver 2002), there is such a 

wide variety in landscape variables in eastside pine forests, such as elevation, 

precipitation, soil composition, soil depth, and water holding capacity, as well as 

existing vegetation composition and structure, and historical vegetation trajectories, 

that the standards may not be applicable to certain areas or spatial and temporal

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Research Wildlife Ecologist, Sierra Nevada Research Center, Pacific Southwest Research Station,

Forest Service, U.S. Department of Agriculture, Fresno, Califonia. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 171 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

scales. Gaining an understanding of snag demographics in eastside pine forests that

differ in composition and site conditions is critical to evaluating the efficacy of the 

snag standards and guidelines for these forests. Variation observed should also help 

focus research and management attention to the processes underlying snag

recruitment and loss rather than a forest’s capacity to maintain a specific number of 

snags. 

Eastside pine forests were burned frequently prior to about the turn of the 

beginning of the 20th century. Since then, fire has generally been excluded. Our 

knowledge of snag processes in these forests is from this long fire-free period and is 

unlikely to accurately reflect snag processes under frequent fire regimes. Changes in 

fire management practices coupled with the increased use of prescribed fire as a 

forest management tool will likely influence snag longevity. 

The objectives of this paper are to (1) illustrate some of the variation in snag

recruitment, loss, and occupancy in four relatively undisturbed eastside pine stands

(stands that have not seen wildfire or lost large trees to timber harvest) and (2) 

discuss the ramifications of this variation relative to the snag management standards

that are applicable to eastside pine forests. 

Methods

The study sites discussed in this paper were established during a larger study of 

24 sites (initiated in 1988) to evaluate the responses of birds to snag density and

subsequent snag dynamics in eastside pine forests (see Landram and others 2002, 

Laudenslayer 2002). The four study sites were chosen because they had little historic

management and reflected two different patterns of snag demography. 

Snags on each study site were counted, mapped and their condition evaluated on 

5-ha (12.4-ac), 100 x 500m (328 x 1640 ft) strip plots annually from 1989 to the 

present. All snags greater than 15 cm (6 in) dbh were included in the snag inventory.

For this analysis, snags were divided into two groups. Small snags were those with

diameters between 15 and 38 cm ( 6 and 15 in) dbh and with any height, or greater 

than 38 cm (15 in) dbh but less than 6 m (20 ft) tall. Large snags were those with

diameters greater than 38 cm (15 in) dbh and height greater than 6 m (20 ft). The 

dividing line, 38 cm (15 in), separates those snags targeted by various snag retention 

standards (usually greater than 38 cm [15 in] dbh) from those smaller snags that are 

not generally considered for retention. Snag heights and diameter were also measured

annually. Snags remained in the inventory until they were completely down

(uprooted or broken at ground level) or had less than 1 m of bole remaining. 

Study Sites 

The four study sites chosen for this report were located in northeastern 

California on the Modoc and Lassen National Forests and within Lassen Volcanic 

National Park (fig. 1). All sites were dominated by either ponderosa or Jeffrey pine

and had little to no active management activity except fire exclusion. 

Old Forest

The Old Forest study site was located within Blacks Mountain Experimental 

Forest (within the Lassen National Forest) (lat. 40o

42’45” N, long. 121o9’45” W)

between 1730 and 1740 m (5676 and 5709 ft) in elevation, and was primarily

172 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

ponderosa pine with small numbers of white fir (Abies concolor (Gord. & Glend.) 

Lindl. ex. Hildebr) and incense cedar (Calocedrus decurrens (Torr.) Florin). It is a

rather open forest dominated by small numbers of widely-spaced large diameter trees

(>61 cm [> 24in] dbh). The understory was occupied by grasses, forbs, shrubs, and

small trees. The only manipulations included a thinning and prescribed burn in 1996 

(Oliver and Powers 1998, Oliver 2000).

Figure 1—Four snag study sites in northeastern California: 1 = Old Forest; 2 = 

Research Natural Area; 3 = Hot Rock; and 4 = Soup Creek. 

 Research Natural Area 

The Research Natural Area, also located within Blacks Mountain Experimental 

Forest (lat. 40o

42’30” N, long. 121o8’15” W), was dominated by ponderosa pine and

had a considerable amount of white fir and incense cedar in the understory. It lies 

between 1820 and 1830 m (5971 and 6004 ft) in elevation. White fir likely has been a 

natural component at this site for at least the last century. This site had the greatest 

canopy closure of the four study sites but rarely exceeds 50 percent, except in dense

thickets of fir reproduction. The forest was dominated by relatively large diameter 

trees (>61 cm [>24 in] dbh), snag recruitment is high, and the numbers of large live 

trees is declining. Under the large trees are thickets of small trees, generally white fir

with smaller amounts of incense cedar, and openings occupied by grasses, forbs, and

shrubs. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 173 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

Hot Rock 

Hot Rock is located within Lassen Volcanic National Park (lat. 40o32’15” N, 

long. 121o

29’30” W) and was dominated by Jeffrey pines with a small amount of 

white fir, generally in the understory. The elevation is about 1890 m (6200 ft). This 

site has the most open canopy of the four and the openness of the site increased

through the study period. This site supported a noticeable number of snags that 

diameter appear to have been recruited in the 1970s. The forest was dominated by

large trees (>61 cm [>24 in] dbh) but snag recruitment was high and the numbers of 

large live trees was declining. Generally, few young trees, shrubs, grasses, or forbs 

appeared in the understory, likely because of the thick layer of volcanic ash – up to 

0.5 m in depth in some areas. However, where mass mortality occurred in the mid

1990s abundant fir regeneration has since established. 

Soup Creek 

Soup Creek is located in the Warner Mountains on the Modoc National Forest 

(lat. 41o

18’0” N, long. 120o18’0” W) and is dominated by ponderosa pine with white 

fir both in the overstory and understory. The average elevation is about 1890 m (6200

ft). This site is on a steep slope in a canyon. The site includes several large 

aggregations of boulders, occupying as much as 0.5 ha (1.2 ac) of the site. The forest

is dominated by large diameter trees (>61 cm [>24 in] dbh) but the density of large 

trees declines as one moves upslope. Past timber harvesting occurred on about 10 

percent of the site. 

Results 

Most snags in the overstory were pines, but white fir comprised most of the

snags in the understory of all sites, except Old Forest where firs were nearly absent. 

Numbers of snags increased substantially in two of these study sites, Research 

Natural Area and Hot Rock, and generally increased slightly in Old Forest and Soup 

Creek. Snag numbers increased starting in the early 1990s and generally ending about 

Figure 2—Numbers of snags greater than 15 cm dbh in each of four 5-ha eastside

pine study sites over a 10-year period: Old Forest = squares; Research Natural Area

= circles; Hot Rock = triangles; and Soup Creek = diamonds. 

174 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

1996. Since then, snag numbers have declined at Old Forest, Research Natural Area, 

and Soup Creek (fig. 2). Numbers of large snags also increased substantially in all 

sites but Old Forest. At Hot Rock, large snag recruitment increased substantially in

1995. Large snag recruitment was greatest in the early 1990s and declined as the 

decade progressed. At the end of the decade, the number of large snags was

beginning to decline in all but Old Forest (fig. 3). 

Figure 3—Numbers of snags greater than 38 cm dbh and 6 m in height in each of

four 5-ha eastside pine study sites over a 10-year period: Old Forest = squares; 

Research Natural Area = circles; Hot Rock = triangles; and Soup Creek = diamonds. 

At Old Forest, recruitment of large snags increased in 1990 and 1996 and 

recruitment of smaller snags was greatest in 1991 and 1997. Many large snags were 

lost in 1994 and 1997, whereas small snag losses were concentrated in 1996 and 

1997. In high recruitment years only 3 - 5 snags were recruited and in high loss years 

5 - 7 snags were lost (fig. 4). As a result, numbers of snags at this site changed little 

during this study period. 

Figure 4—Recruitment and loss of large (greater than 38 cm dbh and greater than 6

m in height) and small snags (15-38 cm dbh and any height, and greater than 38 cm

dbh and less than 6m in height) in the 5-ha study site at Old Forest. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 175 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

At Research Natural Area, the best years for large snag recruitment were 1990 

and 1991, but there was some recruitment from 1994-1996. For small snags, 1995

and to a lesser extent 1994 were high recruitment years. Relatively few large snags

were lost during the observation period, with 1996 having the greatest loss. For small 

snags, however, 1996 and 1997 were high loss years. In contrast to Old Forest,

Research Natural Area gained approximately 4 times as many large snags as it lost in 

a high recruitment year, and perhaps 15 times as many small snags (fig. 5). The trend 

at this site is characterized by high snag recruitment and declining numbers of large 

live trees. 

Figure 5—Recruitment and loss of large (greater than 38 cm dbh and greater than 6

m in height) and small snags (15-38 cm dbh and any height, and greater than 38 cm

dbh and less than 6m in height) in the 5-ha study site at Research Natural Area.

At Hot Rock, the years of highest recruitment for large snags were 1994 and 1995. In

1995, all of the large live trees in approximately 0.05 ha (0.12 ac) died. Recruitment

of small snags was low, with the largest recruitment occurring in 1997. Relatively

few large snags were lost in this decade, and the loss was distributed over a number 

Figure 6—Recruitment and loss of large (greater than 38 cm dbh and greater than 6

m in height) and small snags (15-38 cm dbh and any height, and greater than 38 cm

dbh and less than 6m in height) in the 5-ha study site at Hot Rock. 

176 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

of years (1992-94 and 1996). Losses of small snags were distributed over several

years (1991, 1993, and 1995). Hot Rock recruited the majority of snags, mostly large 

snags, in one year (1995) and without that large pulse of recruitment, the general 

magnitude of recruitment and loss would resemble Old Forest more than Research

Natural Area (fig. 6). 

At Soup Creek, 1992-1995 were high years for large snag recruitment. 

Recruitment of small snags was high in 1995 and 1996. Large snags were lost at a

greater rate in 1995 and 1998. Small snags were lost at a relatively high rate from 

1992 through the rest of the decade (fig. 7). 

Figure 7—Recruitment and loss of large (greater than 38 cm dbh and greater than 6

m in height) and small snags (15-38 cm dbh and any height, and greater than 38 cm

dbh and less than 6m in height) in the 5-ha study site at Soup Creek. 

Discussion 

Historically, management standards and guidelines for snags in eastside pine 

forests were based on numbers of snags with different characteristics. The standards

and guidelines also often specified a certain number of live trees for future snag 

recruitment (Studinski and Ross 1986). The principal purpose for retaining and 

recruiting snags was to provide nesting sites for primary and secondary cavity

nesters. Studies of snag densities in eastside pine forests (Dahms 1949, Keen 1929, 

1955, Landram and others 2002, Zack 2002) suggest that many sites have low 

numbers of snags relative to other forest types, and that even better sites may not be 

able to meet the standards and guidelines for snag numbers in a sustainable manner. 

However, snag density may not be as important to the system as ensuring

recruitment and a continuous flow of snags through time. Picoides woodpeckers 

generally forage for only a few years on dying or freshly dead trees and prey

especially on scolytid, buprestid, and cerambycid larvae (Farris and others 2002, 

Hughes 2000). Insect residence and thus woodpecker foraging occurs early in the life 

of a snag; the half-life of a ponderosa pine snag in northeastern California is between

7 and 10 years (Landram and others 2002). Primary tree-killing bark beetles [e.g., fir 

engraver (Scolytus ventralis LeConte), mountain pine beetle (Dendroctonus

ponderosae Hopkins), and western pine beetle (D. brevicomis LeConte)] generally 

persist in a dying or dead tree for only 60 days to less than a year, depending on the 

time of attack, whereas the longer developing beetles, like California prionus 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 177 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

(Prionus californicus Motschulsky) may be present for 3 to 5 years (Furniss and 

Carolin 1977). 

Tree mortality patterns reported here indicate that even at the relatively fine 

scale of 5 ha (12.4 ac), most plots had a flow of dying and dead trees to replace those 

lost. However, many of the recruited snags were of small diameter (less than 38 cm 

[15 in] dbh), which are unlikely to support the diversity or abundance of beetle larvae 

found in larger diameter snags. The temporal pattern of mortality suggests that much

of the mortality in the early 1990s was related to the drought coupled with bark beetle 

attack. However, beetles may successfully attack trees that are overmature, are

adjacent to windfalls, have root-rot, or are in overstocked or stagnant stands (Cobb 

and others 1974, Furniss and Carolin 1977, Oliver 1995), leading to some constant

rate of background mortality even when moisture is not limiting. 

Tree mortality generally consisted of single trees or small groups of trees 

scattered throughout each site with the exception of the large mortality event at Hot 

Rock. This event was largely confined to an area of about 0.75 ha (1.9 ac), within

which all of the large pine trees died. Oliver (1995) reported that there may be

mortality thresholds related to the basal area present and the growing capability of a 

site, so this mortality event at Hot Rock may have been driven by overstocked 

conditions. Since this site is near Mount Lassen, other less well known causes of

mortality may be responsible, such as excessive carbon dioxide gas in the soil (Sorey 

and others 2000). 

Generally, snag loss occurred in all years, but was punctuated with pulses that 

followed pulses of recruitment. Fall rates for snags in northeastern California vary 

from seven percent per year for ponderosa pine and Jeffrey pine to four percent per 

year for white fir (Landram and others 2002). Snag half-life is related to species and 

diameter. For small (13-38 cm [5-15 in] dbh) ponderosa or Jeffrey pines, half-life 

ranged from five to six years whereas for small white firs, the half-life was seven

years. For larger (greater than 38 cm [15 in] dbh) ponderosa or Jeffrey pines, half-life 

was eight and seven years whereas for larger white firs, half-life was 10 years

(Landram and others 2002). 

Soil characteristics may also be important in controlling tree stocking, snag 

recruitment, and snag longevity. At Old Forest, Research Natural Area, and Soup 

Creek, there were areas greater than 100 m2

 (1076 ft2) in size where trees were not

present because of soil characteristics, soil depths, presence of rock, or some other

factor. At Hot Rock, much of the site was covered by a layer of volcanic ash

averaging about 0.5 m (1.6 ft) in depth (Clynne and others 2000). This thick layer of

ash probably made it more difficult for young trees to get established and may have 

contributed to greater snag longevity by not retaining moisture close to the tree base,

thereby reducing the rate of decay. Within the area experiencing very high mortality

at Hot Rock, there were very few small trees present prior to the event. Following the 

event, a “carpet” of seedlings became established; however, most of the seedlings 

were white fir, suggesting that the tree species composition within this area may be 

shifting toward white fir in the foreseeable future. Further, it will take decades for

these tree cohorts to grow to sufficient size to meet snag guidelines. In the interim,

about 0.75 ha (1.8 ac) will shortly lack snags. However, snags may persist longer on 

these Lassen Volcanic Park sites than the other sites, likely because of the volcanic

ash layer. At Hot Rock, trees that died in the bark beetle outbreak in the mid-1970s

remain standing. 

178 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

Conclusions 

Snag recruitment and loss are likely related to local site characteristics and 

vegetation structure interacting with weather, climate, insects, and disease. 

Considerable variation in recruitment and loss occurs across the landscape even in 

sites that have not been managed or seen wildfire in decades. This variation suggests 

that standards and guidelines for snag retention should incorporate information from 

local scales rather than regional or larger scales. Work reported here suggests that 

processes contributing to snag recruitment and fall down operate at spatial and 

temporal scales that are highly variable. Thus management guidelines may need to 

reflect this variability.

While current numbers of snags are indeed important, managing for a suitable 

population of future snags is more critical to the continued functioning of forests over 

time. If forests are composed of appropriate sizes of living trees, then drought, insect

and disease, and fire will create snags in an appropriate pattern. 

This study focused on forests that have burned frequently under natural 

disturbance regimes. Reintroduction of prescribed fire, and more frequent occurrence 

of wildfire, will substantially alter forest structure, and therefore the snag component 

of forests as well. 

Acknowledgments 

The long-term support from the Modoc and Lassen National Forests, Lassen 

Volcanic National Park, Blacks Mountain Experimental Forest, and the Pacific 

Southwest Research Station Natural Areas Committee has been crucial to the success 

of this study. Some of the key agency people who have supported or are currently 

supporting this study are Jon Arnold, Chris Click, Mary Flores, George Giddings,

Doug Maguire, Ann Mileck, Constance Millar, William W. Oliver, Tom Rickman, 

Martin Ritchie, George Studinski, and Al Vasquez. I especially thank Kerry Farris, 

Christopher Fettig, Thomas Munton, George Steger, Steve Zack, and an anonymous 

editor for their helpful comments on the manuscript. 

References 

Brawn, Jeffrey D.; Balda, Russell P. 1988. Population biology of cavity nesters in northern

Arizona: do nest sites limit breeding densities? The Condor 90: 61-71.

Bull, Evelyn L.; Parks, Catherine G.; Torgersen, Torolf R. 1997. Trees and logs important 

to wildlife in the Interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. 

Portland OR: Pacific Northwest Research Station Forest Service, U.S. Department of

Agriculture; 55 p.

Cline, Steven P.; Berg, Alan B.; Wight, Howard M. 1980. Snag characteristics and

dynamics in Douglas-fir forests in western Oregon. Journal of Wildlife Management 

44: 773-786. 

Clynne, Michael A.; Champion, Duane E.; Trimble, Deborah A.; Hendley, James W. II;

Stauffer, Peter H. 2000. How old is “Cinder Cone”? – Solving a mystery in Lassen 

Volcanic National Park, California. USGS Fact Sheet 023-00. Menlo Park, CA: U.S.

Geological Survey, U.S. Department of Interior; 2 p. 

Cobb, F.W., Jr.; Parmeter, J.R.; Wood, D.L.; Stark, R.W. 1974. Root pathogens as agents

predisposing ponderosa pine and white fir to bark beetles. In: Kuhlman, E. G. (ed). 

Proceedings of the 4th international Fomes annosus conference, International Union of 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 179 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

Forestry Research Organizations. Asheville, NC: Southeastern Forest Research Station,

Forest Service, U.S. Department of Agriculture; 8-15. 

Dahms, W.G. 1949. How long do ponderosa pine snags stand? Research Note PNW-RN57. Portland, OR: Pacific Northwest Forest and Range Experiment Station, Forest 

Service, U.S. Department of Agriculture; 3 p. 

Farris, Kerry L.; Garton, Edward O.; Heglund, Patricia L.; Zack, Steve; Shea, Patrick J. 2002. 

Woodpecker foraging and the successional decay of ponderosa pine. In: 

Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, Brad; Weatherspoon, C. 

Phillip; Lisle, Thomas E. (tech. cords.). Proceedings of the symposium on the ecology 

and management of dead wood in western forests. Gen. Tech. Rep. PSW-GTR-181.

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

Agriculture; 237-246. 

Furniss, R.L.; Carolin, V.M. 1977. Western forest insects. Misc. Publ. 1339. Washington, 

DC: Forest Service, U.S. Department of Agriculture; 654 p.

Hughes, Kerry L. 2000. The foraging ecology of Picoides woodpeckers in relation to 

ponderosa pine decay dynamics. Moscow, ID: University of Idaho; 55 p. M.S. thesis. 

Keen, F.P. 1929. How soon do yellow pine snags fall? Journal of Forestry 27: 735-737.

Keen, F.P. 1955. The rate of natural falling of beetle-killed ponderosa pine snags. Journal 

of Forestry 53: 720-723.

Landram, F. Michael; Laudenslayer, William F., Jr.; Atzet, Thomas. 2002. Demography of

snags in eastside pine forests of California. In: Laudenslayer, William F., Jr.; Shea, 

Patrick J.; Valentine, Brad; Weatherspoon, C. Phillip; Lisle, Thomas E. (tech. cords.). 

Proceedings of the symposium on the ecology and management of dead wood in western 

forests. Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research

Station, Forest Service, U.S. Department of Agriculture; 605-620 

Lassen National Forest. 1993. Lassen National Forest Land and Resources Management 

Plan. Susanville, CA: Lassen National Forest, Forest Service, U.S. Department of

Agriculture; 4-37. 

Laudenslayer, William F., Jr. 2002. Cavity-nesting bird use of snags in eastside pine 

forests of northeastern California. In: Laudenslayer, William F., Jr.; Shea, Patrick J.;

Valentine, Brad; Weatherspoon, C. Phillip; Lisle, Thomas E. (tech. cords.). Proceedings 

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

Gen. Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, 

Forest Service, U.S. Department of Agriculture; 223-236. 

Oliver, William W. 1995. Is self-thinning in ponderosa pine ruled by Dendroctonus bark 

beetles? In: Eskew, Lane G. (compiler). Forest health through silviculture. Proceedings 

of the 1995 national silviculture workshop. Gen. Tech. Rep. RM-GTR-267. Fort Collins, 

CO: Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture; 

213-218. 

Oliver, William W. 2002. Snag frequencies 50 years after partially cutting interior 

ponderosa pine stands. In: Parker, Sharon, and Hummel, Susan Stevens (compilers). 

Beyond 2001: a silvicultural odyssey to sustaining terrestrial and aquatic ecosystems?

Proceedings of the 2001 national silviculture workshop. Gen. Tech. Rep. PNW-GTR546. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S. Department 

of Agriculture; 47-51. 

Oliver, William W. 2000. Ecological Research at the Blacks Mountain Experimental 

Forest in Northeastern California. General Technical Report PSW-GTR-179. Albany,

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

Agriculture; 66 p.

180 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Effects of Site and Scale on Snag Demographics—Laudenslayer 

Oliver, William W.; Powers, Robert F. 1998. Blacks Mountain, California:

Interdisciplinary Field Research in Ponderosa Pine. Journal of Forestry 98(8): 4-9. 

Raphael, Martin G.; Morrison, Michael L. 1987. Decay and dynamics of snags in the Sierra 

Nevada, California. Forest Science 33: 774-783. 

Raphael, Martin G.; White, Marshall. 1984. Use of snags by cavity-nesting birds in the 

Sierra Nevada, California. Wildlife Monographs 86; 66 p.

Rosenberg, Daniel K.; Fraser, James D.; Stauffer, Dean R. 1988. Use and characteristics of 

snags in young and old forest stands in southwest Virginia. Forest Science 34: 224-

228. 

Sorey, Michael L.; Farrar, Christopher D.; Gerlach, Terrance M.; McGee, Kenneth A.; Evans, 

William C.; Colvard, Elizabeth M.; Hill, David P.; Bailey, Roy A.; Rogie, John D.; 

Hendley, James W. II; Stauffer, Peter H. 2000. CO2 gas killing trees at Mammoth 

Mountain, California. USGS Fact Sheet 172-96, Version 2.0. Menlo Park, CA: U.S. 

Geological Survey; 2 p. 

Studinski, George; Ross, Michael. 1986. Modoc National Forest Snags: Analysis of the

Management Situation. Alturas, CA: Modoc National Forest, Forest Service, U.S. 

Department of Agriculture. 

Swallow, Stephen K.; Howard, Ronald A., Jr.; Gutierrez, R.J. 1988. Snag preferences of 

woodpeckers foraging in a northeastern hardwood forest. Wilson Bulletin 100: 236-

246. 

Thomas, J.W.; Anderson, R.G.; Maser, C.; Bull, E.L. 1979. Snags. In: Thomas, J. W. (ed).

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

Agriculture Handbook 553. Washington, DC: Forest Service, U.S. Department of

Agriculture; 60-77. 

Waters, Jeffrey R.; Noon, Barry R.; Verner, Jared. 1990. Lack of nest site limitation in a 

cavity-nesting bird community. Journal of Wildlife Management 54: 239-245. 

Welsh, Christopher J. E.; Capen, David E. 1992. Availability of nesting sites as a limit to 

woodpecker populations. Forest Ecology and Management 48: 31-41.

Zack, Steve; George, T. Luke, Laudenslayer, William F., Jr. 2002. Are there snags in the 

system? Comparing cavity use among nesting birds in “snag-rich” and “snag-poor” 

eastside pine forests. In: Laudenslayer, William F., Jr.; Shea, Patrick J.; Valentine, 

Brad; Weatherspoon, C. Phillip; Lisle, Thomas E. (tech. cords.). Proceedings of the 

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

Tech. Rep. PSW-GTR-181. Albany, CA: Pacific Southwest Research Station, Forest 

Service, U.S. Department of Agriculture; 179-191.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 181 

Woodpecker-snag interactions: an overview 

of current knowledge in ponderosa pine 

systems1

Kerry L. Farris2 and Steve Zack3

Abstract 

Standing dead trees (snags) with cavities are a critical ecological component of western 

coniferous forests. These structures provide foraging, roosting, and nesting habitat for

numerous species of invertebrates, amphibians, reptiles, birds, and mammals. Snags may be

created through a variety of interrelated processes including wildfire, drought, insects and 

disease. However, dead trees containing excavated cavities are primarily the result of nest

excavation by woodpeckers. While the specific factors leading to cavity generation in certain 

snags is not well understood, the manner in which a tree dies likely plays a significant role. 

We provide an overview of woodpecker-snag interactions in relation to the major modes of

tree mortality in ponderosa pine. Of particular interest is the effect of mortality agent on the

temporal patterns of snag decomposition, woodpecker foraging use, and woodpecker cavity

excavation. Generally, snags created by bark beetles, and/or fire decay fastest, and experience 

the greatest foraging and nesting use by woodpeckers. Consideration of these 

interrelationships may aid in snag management. 

Introduction 

Standing dead trees (snags) are important to the structure and function of

western coniferous forests (Bull and others 1997, Harmon and others 1986, Thomas 

and others 1979). These structures provide critical habitat for numerous organisms,

contribute to nutrient cycling, and influence forest productivity (Harmon and others

1986). Dead trees containing excavated cavities are of particular importance to many 

species of snag-dependant wildlife and are a primary focus of forest management

guidelines in the western coniferous forests (Bull and others 1997, Thomas and

others 1997). Snags may be created through a variety of interrelated processes 

including wildfire, drought, insects and disease; however snags containing cavities 

are primarily the result of nest excavation by woodpeckers. Once abandoned, 

woodpecker cavities provide important foraging, roosting, and nesting sites for 

numerous species of birds, mammals, reptiles, amphibians, and invertebrates 

(Thomas and others 1979, Bull and others 1997). 

The factors that determine which snags are selected for cavity excavation by

nesting woodpeckers are complex and poorly understood. Several authors have 

1

 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2 Associate Conservation Scientist, Wildlife Conservation Society, 219 SW Stark Street Suite 200 

Portland, OR 97204 (e-mail: kfarris@wcs.org) 3 Conservation Scientist, Wildlife Conservation Society, 219 SW Stark Street Suite 200 Portland, OR

97204 (e-mail: szack@wcs.org) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 183 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

suggested that the quality of snags, as determined by the size and type of decay, may

be more important than the quantity of snags on the landscape when determining the 

value of habitat for cavity-nesting wildlife (Bull and others 1997, Conner and others 

2001, Jackson 1977, Jackson and Jackson 2004). In ponderosa pine forests, Zack and 

others (2002) found that fewer than 20 percent of pine and fir snags sampled in 

northeastern California contained nest cavities. Additionally, Ganey and Vojta (2004) 

reported that only 17 percent of snags contained cavities in ponderosa pine forests of 

Arizona. These figures suggest current management guidelines which focus solely on 

snag quantity (e.g. snags/hectare) may not adequately reflect habitat requirements of 

nesting woodpeckers. 

Ponderosa pine (Pinus ponderosa P.& C. Lawson) is a particularly important 

snag species for cavity-nesting birds due to its relatively large volume of sapwood,

which often decays quickly and provides suitable sites for nest excavation (Bull and

others 1997). In mixed-conifer stands, ponderosa pine is often preferred over other 

tree species by nesting woodpeckers (Bull and others 1997, Bate 1995, Dixon 1995,

Haggard and Gains 2001, Hutto 1995, Lehmkuhl and others 2003, Zack and others 

2002). Moreover, recent research in ponderosa pine suggests that the foraging 

activity of woodpeckers during the first few years of snag’s life may influence 

subsequent decomposition of the sapwood by promoting decay organisms associated

with nest cavity excavation (Farris and others 2004). While the snag requirements of

nesting woodpeckers have been studied widely, relatively little is known about the

structures associated with foraging (Bull and others 1997, Conner and others 1994,

Steeger and others 1995), which may prove to be instrumental to the creation of

future nesting habitat. Foraging woodpeckers respond to snags originating from 

various modes of mortality, and the manner in which a tree dies likely has a large 

influence on its eventual use by woodpeckers and subsequent wildlife species. 

The objective of this paper is to provide an overview of woodpecker foraging

and nesting behavior as it relates to snags originating from each of the major 

mortality agents in ponderosa pine systems. We will begin with a brief outline of how 

foraging and nesting woodpeckers respond to snags created by wind, lightning, and

diseases. This will be followed by a more detailed discussion of responses of

woodpeckers to fire and bark-beetles, two mortality agents that have been extensively 

studied. Finally, we will discuss woodpecker use of artificially created snags, as these 

structures are becoming a common management tool in some forests. Of particular

interest throughout our discussion is the effect of each mortality agent on the timing 

of woodpecker use and snag attrition. 

Mortality Agents 

There are numerous mortality agents that act to create snags in ponderosa pine

forests. Major agents of tree mortality in forested ecosystems have been outlined by

Harmon and others (1986) and Rose and others (2001) and include: wind, fire, 

insects, diseases, competitive suppression, senescence, flooding, landslides, 

lightening, and volcanic events. Distinguishing between proximate and ultimate 

causes of tree death can be problematic and it is likely that mortality agents rarely act

independently of one another. For example, fires can weaken trees both structurally 

and physiologically leading to windthrow, insect attack, or disease inoculation. For 

the purposes of this review, we will treat each mortality agent independently. 

184 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

Wind 

Wind events can kill trees by uprooting and snapping the bole, or breaking large 

branches. This agent can act on large scales during events such as severe wind storms

or hurricanes, or on a smaller scale by killing single or small clusters of trees. In 

western North America, wind events are typically severe and contribute to a larger

proportion of snag creation on the west side of major mountain ranges such as the 

Cascades or Sierra Nevada, or in coastal forests where as many as 70 percent of the 

stems may be killed (Greene 1984, Harmon and others 1986). In contrast, only 15-20 

percent of trees are killed by wind in interior ponderosa pine forests (Avery and 

others 1976). Depending on the distribution of tree sizes in the affected stand and 

subsequent insect colonization after wind events, the resultant snags and downed logs 

may be useful for woodpeckers as both foraging and nesting sites. Wichmann and 

Ravn (2001) documented large influxes of Scolytid beetles following a windthrow

event in spruce forests. Wickman (1965) reported both foraging and nesting use of 

wind damaged ponderosa pine by Black-backed Woodpeckers (Picoides arcticus

Swainson) foraging on Cerambycid beetles in northeastern California. 

Lightning 

Lightning can kill trees by shattering or exploding the tops or entire boles. It can 

also damage trees, resulting in a narrow furrow of disturbed bark and sapwood

spiraling around the bole from the top to the butt of the tree (Scharpf 1993). This 

often results in dead and decaying wood which may be colonized by insects (Bull and

others 1997), subsequently attracting foraging woodpeckers (Bull and others 1997).

Additionally, these pockets of dead wood can serve as cavity sites for nesting 

woodpeckers (Bull and others 1997). 

Disease 

There are numerous diseases which affect ponderosa pine. Scharpf (1993)

outline 7 major categories: needle diseases; cankers; diebacks and galls; rusts; 

mistletoes; root diseases; and rots. The responses of foraging and nesting 

woodpeckers to trees with these diseases present, or snags created by them, is largely

unknown. From the perspective of woodpecker use perhaps the greatest influence 

these diseases may have is in weakening and/or killing trees which facilitates the 

invasion of bark and/or wood-boring beetles, the major prey of foraging 

woodpeckers. Trees weakened or killed by disease may also provide nesting habitat 

depending on internal decay patterns. 

Insect Mortality 

There are numerous species of bark beetles which act as mortality agents in 

ponderosa pine systems. Most common are members of the genera Dendroctonus and 

Ips. These insects typically attack weakened or suppressed trees, but at epidemic 

levels, they can overcome even healthy trees, resulting in patches of mortality that 

contribute to both vertical and horizontal diversity in forest structure. These beetles

are an important source of prey for many woodpecker species: particularly those of

the genus Picoides. Woodpeckers of this genus respond dramatically to outbreaks of

these insects and have been suggested as control agents for endemic insect 

populations. For instance, Murphy and Lehnhausen (1998) noted a four fold increase 

in Hairy (P. villosus Linnaeus), Three-toed (P. dorsalis Baird), and Black-backed

Woodpeckers (P. arcticus Swainson) following a bark and wood-boring beetle 

outbreak in Alaska. Several authors have suggested that woodpeckers may be 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 185 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

important regulators of bark beetle populations: especially at endemic levels (Kroll 

and Fleet 1979, Kroll and others 1980, Koplin and Baldwin 1970, Koplin 1972). 

Picoides woodpeckers forage most intensively on ponderosa pine infested by

bark-beetles during the first 1 to 3 years after invasion (Farris and others 2002). Bark

beetles of the genus Dendroctonus are the primary prey items of woodpeckers during

the first year following tree death (Farris and others 2002, Shea and others 2002).

During the second and third years following the tree’s demise, phloem and xylem 

consuming insects of the families Buprestidae and Cermabycidae provide additional 

prey for woodpeckers (Farris and others 2002, Shea and others 2002). 

Ponderosa pine killed by bark beetles, once adequately decayed, may also serve 

as nesting sites for woodpeckers. Little information exists examining the nesting 

preferences of woodpeckers in ponderosa snags specifically originating from bark

beetle activity; however it is likely that many of the snags examined in several

studies were influenced by bark beetles. In general, woodpeckers nesting in

ponderosa pine select snags that are larger in diameter and of advanced decay (Bull

and others 1997, Bate 1995, Dixon 1995). 

Recent evidence suggests a potential relationship between nest excavation in

beetle-killed ponderosa pine and previous foraging use by woodpeckers during the 

early stages of snag decay. Zack and others (2002) determined that nest excavation 

was more likely on snags with an extensive history of foraging activity by both

beetles and woodpeckers. Additionally, Farris and others (2004) documented the

influence of foraging woodpeckers on the decomposition of ponderosa pine. Snags 

that were used by foraging woodpeckers experienced significantly greater sapwood 

decay than unused snags. Additionally, more than half the woodpeckers sampled in 

this study carried wood-decaying fungi on their beaks. These findings suggest that 

woodpeckers may influence snag decomposition through their foraging behavior that 

can structurally degrade the wood and passively introduce the wood decaying fungi

required for subsequent nest cavity excavation. 

Snag longevity following insect attack is variable and is likely dependent on

site-specific factors such as soil characteristics, snag size, and local microclimate

(Landram and others 2002; Laudenslayer, this volume). On average, the half-life 

(amount of time it takes for half of the population to fall) of ponderosa and Jeffrey

pine snags in the southern Cascades of California is 5 to 6 years for small (13-36 cm 

[5.2-14.3 in] dbh) snags and 7 to 8 years for large (> 38 cm [15 in] dbh) snags 

(Landram and others 2002). However, the authors don’t distinguish between fall rates 

of snags of various origins (e.g. fire versus beetle kill). Mitchell and Preisler (1998) 

found that the half-life of lodgepole pine killed by the mountain pine beetle in central 

Oregon to be 8 years, with snags falling as early as 3 years after death. 

In summary, the temporal patterns of snag use by woodpeckers following beetle 

kill events are concentrated within the first 1 to 8 years. Foraging is most intense within

the first 1-3 years after tree death, while nesting activity begins around year 5. Snags

begin to fall during this same period and may be an indication that snags killed by

beetles don’t stand long enough to serve as useful nest sites in some instances (fig. 1). 

Fire 

Historically, fire was likely the most common mortality agent in ponderosa pine

forests, and is the most widely studied means of tree death in terms of evaluating 

woodpecker response. Fire can directly kill and weaken trees through crown scorch, 

186 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

cambial girdling, and root damage (Harmon and others 1986). The effects of fire are 

highly variable and typically depend on the type of burn, its intensity, topography,

and forest type. In ponderosa pine forests, fires historically burned at frequent

intervals and low intensities (Agee 1993). However, management activities common 

during most of the 20th century including timber harvest, livestock grazing, and fire 

suppression, have altered both the structure and function of many of today’s forest stands,

resulting in an increase in the number, size, and severity of fires (Allen and others 2002).

Typically woodpeckers respond dramatically to both large and small scale fires where 

they find an abundance of insect prey and decaying snags suitable for nesting. However, 

the specific patterns of woodpecker use are likely dependent upon the severity of the fire

and whether trees are killed directly or experience a prolonged weakening and death from

other associated mortality agents such as bark beetles.

Figure 1—Generalized conceptual model of temporal woodpecker use and attrition 

of snags created by bark beetles in ponderosa pine. Foraging activity is most intense

during the first 3 years following death and corresponds to the insect types active

within the snag. Cavity generation and snag attrition both begin after approximately 5 

years. The shading of the trees in this figure illustrates changes in foliage color from

a healthy green (far left shaded black), fading to yellow (second panel shaded as 

light grey) and dead and shedding red needles (third panel shaded as black with 

gaps of needle loss). Schematic patterned after Steeger and others 1995). 

Foraging woodpeckers, particularly those of the genus Picoides respond 

immediately to post-fire areas where they typically prey on bark and wood boring 

beetles that invade dead and dying trees (Farris and Zack in press, Murphy and 

Lehnhausen 1998). This foraging period is generally brief, lasting only 2-3 years 

after the fire, before most of the beetle prey has been exhausted (Farris and Zack in 

press, Murphy and Lehnhausen 1998). As decay progresses in subsequent years,

insects such as carpenter ants and termites become important prey for other species of

woodpecker, such as the pileated. In general, snags selected by foraging woodpeckers 

within burned areas are typically large in diameter (Kreisel and Stein 1999, Murphy 

and Lehnhausen 1998), and of moderate fire damage (less than 50 percent of the bole

burned) (Murphy and Lehnhausen 1998). However, some studies have demonstrated 

woodpecker use of both small and large diameter snags in post-fire environments 

(Hutto 1995, Horton and Mannan 1988, Haggard and Gains 2001), suggesting that 

other variables, such as fire damage, tree species, bark thickness, timing, and insect

activity may be important factors. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 187 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

Nesting woodpeckers typically use post-fire environs relatively later than 

foraging woodpeckers. For example, models created by Lehmkuhl and others (2003)

for ponderosa pine in the eastern Cascades of Washington predicted nest cavities to

most likely occur between 5 and 25 years post-fire. Note that these were cumulative 

numbers across a chronosequence of wildfires so the exact timing of excavation and

occupancy was unknown. In contrast, the models of Saab and others (2004) predicted

nest occupancy to be highest during the first 5 years, with cavities showing up as 

early as 2 years after the burn. Snags selected as nesting sites are generally larger in

diameter than the average available snag (Bull and others 1997, Lehmkuhl and others 

2003, Saab and Dudley 1998, Saab and others 2004). 

Snag longevity following fires is variable and likely dependent on numerous, 

site-specific factors such as fire severity, soil characteristics, snag size, and local

microclimate (Landram and others 2002; Laudenslayer, this volume). Everett and

others (1999) found that 50 percent of the small (<23 cm [9.1 in] dbh) ponderosa pine 

fell or broke to heights less than 1.5 meters (4.9 feet) during the first 7-12 years 

following fires in the eastern Cascades of Washington. Larger ponderosa pine (>41

cm [16.1 in] dbh) were scarce in their study areas, but of the few present, 79 percent

remained standing 60 years post-fire. In Colorado, Harrington (1996) documented 

ponderosa pine snags falling as early as 3 years following fire. Morrison and Raphael 

(1993) found a 68 percent decline in snags 18 to 23 years following a fire event in the

eastern Sierra Nevada of California, but do not distinguish between pine and fir. In

northeastern California, Laudenslayer (2002) did not observe any snags fall during

the 7 year study period, but did document top breakage after 5 years. Farris and Zack

(in press) found 20 percent of Jeffrey pine snags fell 4 years following a fire event in 

the southern Cascades of California. There is conflicting evidence regarding the 

relative attrition and decay rates of ponderosa compared to other conifers such as 

white-fir. Landram and others (2002), Morrison and Raphael (1993) and Raphael and 

White (1984) all found that both ponderosa and Jeffrey pine fell at more rapid rates 

than white-fir. In contrast, one study in the southern Cascades of California noted 

greater persistence of Jeffrey pine as compared to white-fir following fire (Farris and

Zack in press). Additionally, Lowell (1996) and Farris and Zack (in press) both noted

more pronounced wood decay in white-fir compared to ponderosa and Jeffrey pine 

following fire, which may lead to more rapid attrition. 

Figure 2—Generalized conceptual model of temporal woodpecker use and attrition of snags

created by low to moderate intensity fire in ponderosa pine where most of the trees are

weakened and eventually infested with bark and wood boring beetles. Foraging activity is most 

intense during the first 3 years following fire, while cavity generation can overlap this period

and last for several years following the burn event. Fire-killed trees generally begin to fall about

5 years after death. Schematic adapted after Steeger and others 1995). 

188 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

In summary, the temporal patterns of snag use by woodpeckers following fire 

events are concentrated within the first 1-5 years, but can extend to 15 years 

following wildfire. Foraging is most intense within the first 1-3 years after the burn 

and nesting activity overlaps the later stages of foraging and extends throughout the 

life of the snag. Attrition and advanced decay typically starts around 5 years after the 

burn, but can occur as early as 3 years (fig. 2). These generalizations are for lowmoderate severity fires in which bark and wood-boring beetles play an active role. 

Artificial Creation 

Methods of artificial snag creation are becoming a tool to meet snag 

management guidelines in areas lacking suitable snag densities. Creation methods 

vary and include the use of insect pheromones (Shea and others 2002), mechanical

girdling (Shea and others 2002, Hallett and others 2001), girdling through basal

burning (Parks and others 1999), mechanical topping (Hallet and others 2001), and 

topping using explosives (Bull and others 1981). Typically, the motivation for 

creating snags is to provide nesting habitat, so few studies have evaluated the 

quantitative use of these artificially created structures as foraging substrates. In

ponderosa pine 3 creation methods have been well documented: girdling, topping,

and pheromone baiting. 

In eastern Washington, foraging woodpeckers showed no preference between

topped and girdled snags (Hallet and others 2001). Parks and others (1999) 

documented equal amounts of woodpecker foraging on ponderosa killed by basal

burning and mechanical girdling in New Mexico. Shea and others (2002)

documented a greater use of pheromone-baited trees as compared to girdled trees for

two types of woodpecker foraging strategies aimed at two distinct types of insects. In 

their study, all trees that were baited with western pine beetle pheromone, exhibited 

woodpecker “flaking” (superficial removal of successively thin layers of bark to

procure pupae and emerging adult bark beetles) within a few months after treatment,

while none of the girdled trees showed evidence of flaking; suggesting that bark 

beetles were not present or were too rare to exploit in the girdled snags. In contrast, 

evidence of woodpecker foraging “excavations” (distinct holes created in the bark 

that often penetrate through to the tree’s sapwood created in pursuit of wood-boring

beetles) were recorded on snags in both treatment types, but in much greater densities 

on the pheromone baited snags as compared to the girdled snags; suggesting that 

these structures provided a more productive foraging medium for woodpeckers. 

Nesting woodpeckers tended to prefer topped trees versus girdled trees in

Washington (Hallett and others 2001), while Parks and others (1999) documented

greater nest use in mechanically girdled snags versus trees killed using basal burning 

methods, or a combination of girdling and burning. In the Southern Cascades, 44 

percent of pheromone baited snags contained woodpecker nest cavities 6 years after 

treatment, while none of the girdled trees were used by nesting woodpeckers (Shea 

and others 2002). However, 2 years later, 14 percent of the girdled snags contained

cavities and the use of baited snags increased to 50 percent (Shea unpublished data). 

Decay and attrition of snags created by the three methods are variable and once 

again, likely dependant on local site conditions. Most authors cited “decay” as the

breaking of branches off the bole, the loss of bark, or advancement between the 

standardized decay stages outlined by Thomas and others (1979) or Cline and others 

(1980). Hallet and others (2001) found that topped trees tended to decay slower than 

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Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

girdled trees, but have little data specific to ponderosa pine and do not speculate on 

fall rates. In New Mexico, 97 percent of the girdled trees remained standing while

only 68 percent of the basally burned trees remained standing 4 years after treatment.

After 6 years, standing girdled trees declined to 72 percent, while basally-burned 

trees declined to only 36 percent. In northeastern California, 16 percent of the 

pheromone baited trees had fallen, while only 12 percent of the girdled trees fell or 

broke to heights less than 1.5 meters (4.9 feet) 6 years after treatment (Shea and 

others 2002).

Summary and Implications 

Several factors determine how and when snags are utilized by foraging and 

nesting woodpeckers. These include the mode of mortality, time since tree death, and

snag size. In terms of foraging, woodpecker utilization of snags appears to be most

concentrated within the first three years of tree death, especially on snags originating

from bark-beetles and/or a combination of bark beetles and low/moderate severity

fires. Snags created artificially through girdling or topping are used less intensively

for foraging. Moreover, peak foraging activity in artificially snags typically occurs 

after the first two or three years of snag creation. This disparity is likely due to 

differences in the sequence of insect infestation. Greater insect diversity and 

abundance have been reported in naturally created snags compared to snags created

artificially by girdling (Shea and others 2002). 

In comparison to foraging woodpeckers, snag utilization by nesting 

woodpeckers appears to be concentrated in older snags with some level of decay. 

Importantly, intensive foraging by woodpeckers in young snags may facilitate future 

cavity excavation by promoting wood decomposition through a combination of

structural damage to the wood and the transfer of tree decaying fungi. The manner in 

which a snag is created seems to have an effect on the timing of cavity excavation in 

ponderosa pine. Snags decay to cavity-bearing structures fastest in burned areas, as 

soon as 2 to 3 years after the fire in some cases. Bark beetle killed trees provide 

nesting habitat as early as 5 years after death, while girdled trees can take as long as 6

to 8 years. Snag size is another predictor of cavity generation with larger snags more

likely to eventually contain nest cavities. However, it is important to note, that a very

small fraction of available snags actually contain cavities excavated by woodpeckers;

suggesting the need for more consideration of mortality agent. 

Snag attrition rates are highly variable and tend to depend not only on the mode 

of mortality, but also on local site conditions. In general however, the fastest 

recorded attrition was in instances of fire-killed trees, which fell as early as 4 years 

after the fire. These patterns may be directly related to the severity of fire damage on

individual trees and the history of post-fire beetle use. Generally, snags that 

experience greater use by both bark and wood-beetles attract foraging woodpeckers, 

which serve to further degrade the wood integrity and can lead to faster decay rates

than trees that don’t experience these same use patterns. However, there are instances

where trees that experience extremely severe fire damage stand for extended periods 

of time and are not used by either beetles or woodpeckers. Trees killed by insects,

independent of fire, stand slightly longer than those affected by both fire and insects 

simultaneously. Insect-killed snags begin to fall between 5 to 6 years after death. This 

can be problematic, as these snags may fall before they can provide nesting habitat. 

Snags created artificially by topping or girdling tend to stand longer than either fire 

or insect killed trees. This may be due to the relatively less use of these trees by 

190 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

beetles and woodpeckers, which can contribute to expedited decay of these structures 

(Farris and others 2004). 

These temporal trends in woodpecker use and snag decomposition patters are

paradoxical. Trees killed by bark beetles alone, or in association with fire serve as 

high quality foraging habitat and seem most likely to contain future nest cavities.

However, these same structures are likely to fall more rapidly than snags originating 

from sources of mortality that don’t attract beetles and foraging woodpeckers in 

similar intensities (e.g. artificial creation methods such as mechanical girdling or

topping). 

Classically, snag management has been driven by the objective to provide 

nesting habitat for snag-dependant species such as woodpeckers. Many of the 

strategies have centered on the notion that snags simply needed to be large enough 

and in adequate densities in order to be useful for most wildlife species. As illustrated

through this review, recent information suggests that managing quantity while 

ignoring quality may not be sufficient. In particular the following 5 principles should

be considered: 

1. Snag recruitment and attrition is a dynamic process that is dependent on 

characteristics of individual sites. 

2. Snags are an ephemeral resource on the landscape (e.g. half of all 

ponderosa snags may fall within 8 years of death). 

3. Not all snags are useful to wildlife (a small fraction of standing snags 

are actually used by cavity-nesting wildlife). 

4. The manner in which a tree dies affects its subsequent use by beetles

and woodpeckers. 

5. Foraging use by both beetles and woodpeckers appears to play a 

significant role in the decay dynamics, cavity excavation patterns, and 

standing life span of a snag. These interactions likely influence future 

use by subsequent snag-dependent wildlife species. 

Consideration of these important sources of variability in snag ecology and 

woodpecker use may help improve snag management in ponderosa pine forests. 

Acknowledgements 

This review was funded by the Wildlife Conservation Society and the USDA 

Forest Service, Pacific Southwest Research Station. William Laudenslayer, Patrick

Shea, Doug Maguire, and Martin Ritchie provided helpful comments on earlier 

versions of this manuscript. 

References 

Agee, James K. 1993. Fire ecology of Pacific Northwest forests. Island Press, Washington

D.C. 490 pp. 

Allen, C.D., M. Savage, D.A. Falk, K.F. Suckling, T.W. Swetnam, T. Schulke, P.B. Stacey, P. 

Morgan, M. Hoffman, and J.T. Klingel. 2002. Ecological restoration of southwestern

ponderosa pine ecosystems: a broad perspective. Ecological Applications.

12(5):1418-1433. 

Avery, C.C., F.R. Larson, and G.H. Schubert. 1976. Fifty-year records of virgin stand 

development in southwestern ponderosa pine. General Technical Report RM-GTRUSDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 191 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

22. Fort Collins, CO; Rocky Mountain Forest and Range Experiment Station, Forest

Service, U.S. Department of Agriculture. 

Bate, L.J. 1995. Monitoring woodpecker abundance and habitat in the central Oregon 

Cascades. M.S. Thesis. University of Idaho. Moscow, Idaho. 116pp. 

Bull, E.L., A.D. Partridge, and W.G. Williams. 1981. Creating snags with explosives. 

Research Note PNW-RN-393. Portland, OR. Pacific Northwest Research Station, Forest 

Service, U.S. Department of Agriculture. 4pp.

Bull, E.L., C.G. Parks, and T.R. Torgersen. 1997. Trees and logs important to wildlife in 

the interior Columbia River basin. General Technical Report PNW-GTR-391.

Portland, OR. Pacific Northwest Research Station, Forest Service, U.S. Department of

Agriculture. 

Cline, S.P., A.B. Berg, and H.M. Wight. 1980. Snag characteristics and dynamics in

Douglas-fir forests, Western Oregon. Journal of Wildlife Management 44(4):773-786. 

Conner, R.N., S.D. Jones, and G.D. Jones. 1994. Snag condition and woodpecker foraging

ecology in a bottomland hardwood forest. Wilson Bulletin 106:242–257. 

Conner, R.N., D.C. Rudolph, and J.R. Walters. 2001. The Red-cockaded Woodpecker: 

surviving in a fire maintained ecosystem. University of Texas Press. Austin, TX. 

Dixon, R.D. 1995. Ecology of White-headed Woodpeckers in the central Oregon 

Cascades. M.S. Thesis. University of Idaho. Moscow, Idaho. 148pp. 

Everett, R.,J. Lehmkuhl, R. Schellhaas, P. Ohlson, D. Keenum, H. Riesterer, and D.

Spurbeck. 1999. Snag dynamics in a chronosequence of 26 wildfires on the east slope

of the Cascade range in Washington state, USA. International Journal of Wildland

Fire 9(4):223-234. 

Farris, K. L., E. O. Garton, P. J. Heglund, S. Zack, and P. J. Shea. 2002. Woodpecker

foraging and the successional decay of ponderosa pine. In W. F. Laudenslayer, Jr., P.

J. Shea, B. E. Valentine, P. C. Weatherspoon, and T. E. Lisle [tech coords], Proceedings

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

General Technical Report PSW-GTR-181. Albany, CA; Pacific Southwest Research

Station, Forest Service, U.S. Department of Agriculture; 237–246.

Farris, K.L., M.J. Huss, and S. Zack. 2004. The role of foraging woodpeckers in the

decomposition of ponderosa pine snags. The Condor 106:50-59. 

Farris, K.L. and S. Zack. In press. A comparison of post-burn woodpecker foraging use of

white fir (Abies concolor) and Jeffrey pine (Pinus jeffreyi). In: M.G. Narog (technical 

coordinator). Proceedings of the 2002 fire conference on managing fire and fuels in the

remaining wildlands and open spaces of the Southwestern United States. 2-5 December

2002. San Diego, CA. General Technical Report PSW-GTR-189. Albany, CA; Pacific 

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

Ganey, J.L. and S.C. Vojta. 2004. Characteristics of snags containing excavated cavities in

northern Arizona mixed-conifer and ponderosa pine forests. Forest Ecology and

Management 199:323-332. 

Greene, S.E. 1984. Forest structure and dynamics in an Oregon coast Tsuga heterophylla

– Picea sitchensis forest. Bulletin of the Ecological Society of Amercia 65:207-208. 

Haggard, M. and W.L. Gains. 2001. Effects of stand-replacement fire and salvage logging 

on a cavity-nesting bird community in eastern Cascades. Washington. Northwest

Science 75(4):387-396. 

Hallet, J.G., T. Lopez, M.A. O’Connell, and M.A. Morysewicz. 2001. Decay dynamics and

avian use of artificially created snags. Northwest Science 75(4):378-386. 

192 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

Harrington, M.G. 1996. Fall rates of prescribed fire-killed ponderosa pine. Research Paper 

INT-RP-489. Ogden, UT; Intermountain Research Station, Forest Service, U.S. 

Department of Agriculture. 7pp. 

Harmon, M.E., J.F. Franklin, F.J. Swanson, P. Sollins, S.V. Gregory, J.D. Lattin, N.H.

Anderson, S.P. Cline, N.G. Aumen, J.R. Sedell, G.W. Lienkaemper, K. Cromack,, Jr. 

and K.W. Cummins. 1986. Ecology of course woody debris in temperate ecosystems. 

Advances in Ecological Research 15:133-302. 

Horton, S.P. and R.W. Mannan. 1988. Effects of prescribe fire on snags and cavity-nesting

birds in southeastern Arizona pine forests. Wildlife Society Bulletin 16:37-44.

Hutto, R.L. 1995. Composition of bird communities following stand-replacement fires in

northern Rocky Mountain (U.S.A.) coniferous forests. Conservation Biology

9(5):1041-1058. 

Jackson, J.A. 1977. Red-cockaded Woodpeckers and pine red heart disease. Auk 94:160–

163. 

Jackson, J.A., and B.J.S. Jackson. 2004. Ecological relationships between fungi and

woodpecker cavity sites. Condor 106:37-49. 

Koplin, J.R. 1972. Measuring predator impact of woodpeckers on spruce beetles. Journal

of Wildlife Management 36:308-320. 

Koplin, J.R. and P.H. Baldwin. 1970. Woodpecker predation on endemic population of 

Engelmann spruce beetles. American Midland Naturalist 83:510-15. 

Kreisel, K.J. and S.J. Stein. 1999. Bird use of burned and unburned coniferous forests

during winter. Wilson Bulletin 111(2):243-250.

Kroll, J.C., R.N. Conner, and R.R. Fleet. 1980. Woodpeckers and the southern pine beetle. 

USDA Agriculture Handbook No. 564. Washington D.C. 23pp. 

Kroll, J.C. and R.R. Fleet. 1979. Impact of woodpecker predation on over-wintering

within-tree populations of the southern pine beetle Dendroctonus frontalis. In J.G.

Dickson et al. (Eds). The role of insectivorous birds in forest ecosystems. Academic

Press, New York; 269-282. 

Landram, F.M., W.F. Laudenslayer, and T. Atzet. 2002. Demography of snags in eastside 

pine forests of California. In: W.F. Laudenslayer, Jr., P.J. Shea, B.E. Valentine, P.C.

Weatherspoon, T. E. Lisle [tech cords]. Proceedings of the Symposium on the Ecology 

and Management of Dead Wood in Western Forests. Gen. Tech. Rep. PSW-GTR-181.

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

Agriculture; 605-620. 

Laudenslayer, W.F. Jr. 2002. Effects of prescribed fire on live trees and snags in eastside

pine forests in California. In: N. G. Sugihara, M. E. Morales, and T. J. Morales (eds).

Proceedings of the symposium: fire in California ecosystems: integrating ecology, 

prevention, and management. Misc. Pub. No. 1. Davis, CA; Association for Fire

Ecology; 256-262. 

Laudenslayer, W.F. Jr. 2005. Effects of site on the demographics of standing dead trees in 

Eastside pine forests. In: M.W. Ritchie, A. Youngblood, and D.A. Maguire (Eds).

Proceedings of the Symposium on Ponderosa pine: Management, Issues, and Trends. 

2004 October 19-21; Klamath Falls, OR. Gen. Tech. Rep. PSW-GTR-198. Albany,

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

Agriculture; 171-181. 

Lehmkuhl, J.F., R.L. Everett, R. Schellhass, P. Ohlson, D. Keenum, H. Riesterer, and D.

Spurbeck. 2003. Cavities in snags along a wildfire chronosequence in eastern 

Washington. Journal of Wildlife Mangement 67(1):219-228. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 193 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

Lowell, E.C. 1996. Deterioration of fire-killed timber in southern Oregon and northern 

California. Western Journal of Applied Forestry 11(4):125-131. 

Mitchell, R.G. and H.K. Preisler. 1998. Fall rates of lodgepole pine killed by the mountain 

pine beetle in central Oregon. Western Journal of Applied Forestry 13(1):23-26. 

Morrison, M.L. and M.G. Raphael. 1993. Modeling the dynamics of snags. Ecological

Applications 3(2):322-330. 

Murphy, M.L., and W.A. Lehnhausen. 1998. Density and foraging ecology of woodpeckers 

following a stand replacement fire. Journal of Wildlife Management 62:1359–1372. 

Parks, C.G., D.A. Conklin, L. Bednar, and H. Maffei. 1999. Woodpecker use and fall rates

of snags created by killing ponderosa pine infected with dwarf mistletoe. Research

Paper PNW-PR-515. Portland, OR, Pacific Northwest Research Station, Forest Service,

U.S. Department of Agriculture. 11pp. 

Raphael, M.G., and M. White. 1984. Use of snags by cavity-nesting birds in the Sierra 

Nevada. Wildlife Monograph 86. 

Rose, C.L., B.G. Marcot, T.K. Mellen, J.L. Ohmann, K.L. Waddell, D.L. Lindley, and B. 

Schreiber. 2001. Decaying wood in pacific northwest forests: concepts and tools for

habitat management. In D. H. Johnson and T. A. O’Neil (managing editors). Wildlifehabitat relationships in Oregon and Washington. Corvallis, OR; Oregon State University 

Press; 580-623 

Saab, V.A. and J. Dudley. 1998. Responses of cavity-nesting birds to stand-replacment 

fire and salvage logging in ponderosa pine/Douglas-fir forests of southwestern

Idaho. Research Paper RMRS-RP-11. Ogden, UT; Rocky Mountain Research Station,

Forest Service, U. S. Department of Agriculture.

Saab, V.A., J. Dudley, and W.L. Thompson. 2004. Factors influencing occupancy of nest

cavities in recently burned forests. The Condor 106:20-36. 

Scharpf, R.E. 1993. Diseases of Pacific coast conifers. Agriculture Handbook 521. 

Washington, DC: Forest Service, U.S. Department of Agriculture. 199p. 

Shea, P.J., W.F. Laudenslayer Jr., G. Ferrel, and R. Borys. 2002. Girdled versus bark-beetle

created ponderosa pine snags: utilization by cavity-dependant species and 

differences in decay rate and insect diversity. In W. F. Laudenslayer, Jr., P. J. Shea,

B. E. Valentine, P. C. Weatherspoon, and T. E. Lisle [tech coords.], Proceedings of the

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

Technical Report PSW-GTR-181. Albany, CA; Pacific Southwest Research Station,

Forest Service U.S. Department of Agriculture; 145-153. 

Steeger, C.M. Machmer, and E. Walters. 1995. Ecology and management of woodpeckers

and wildlife trees in British Columbia. British Columbia Wildlife Fact Sheet. Delta, 

BC; Environment Canada..

Thomas, J.W., R.G. Anderson, C. Maser, and E.L. Bull. 1979. Snags. In J. W. Thomas [ed.],

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

Agriculture Handbook No. 553. Portland, OR; U.S. Department of Agriculture; 60–77

Wichmann, L. and H.P. Ravn. 2001. The spread of Ips typographus (L.) (Coleoptera,

Scolytidae) attacks following heavy windthrow in Denmark analyzed using GIS. 

Forest Ecology and Management 148:31-39.

Wickman, B.E. 1965. Black-backed three-toed woodpecker, Picoides articus, predation 

on Monochamus oregonensis. The Pan-Pacific Entomologist 41(3):162-164.

Zack, S., T.L. George, and W.F. Laudenslayer Jr. 2002. Are there snags in the system? 

Comparing cavity use among nesting birds in “snag-rich” and “snag-poor” eastside 

pine forests. In W.F. Laudenslayer, Jr., P.J. Shea, B.E. Valentine, P.C. Weatherspoon, 

194 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Woodpecker-snag interactions: an overview of current knowledge—Farris and Zack 

and T.E. Lisle [tech coords.], Proceedings of the symposium on the ecology and

management of dead wood in western forests. General Technical Report PSW-GTR181. Albany, CA; Pacific Southwest Research Station, Forest Service, U.S. Department

of Agriculture; 179–191. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 195 

Fire Ecology of Ponderosa Pine and the 

Rebuilding of Fire-Resilient Ponderosa Pine 

Ecosystems 1

Stephen A. Fitzgerald2

Abstract 

The ponderosa pine ecosystems of the West have change dramatically since Euro-American

settlement 140 years ago due to past land uses and the curtailment of natural fire. Today, 

ponderosa pine forests contain over abundance of fuel, and stand densities have increased

from a range of 49-124 trees ha

-1 (20-50 trees acre-1) to a range of 1235-2470 trees ha-1 (500

to 1000 stems acre-1). As a result, long-term tree, stand, and landscape health has been

compromised and stand and landscape conditions now promote large, uncharacteristic

wildfires. Reversing this trend is paramount. Improving the fire-resiliency of ponderosa pine 

forests requires understanding the connection between fire behavior and severity and forest

structure and fuels. Restoration treatments (thinning, prescribed fire, mowing and other 

mechanical treatments) that reduce surface, ladder, and crown fuels can reduce fire severity 

and the potential for high-intensity crown fires. Understanding the historical role of fire in

shaping ponderosa pine ecosystems is important for designing restoration treatments.

Without intelligent, ecosystem-based restoration treatments in the near term, forest health and 

wildfire conditions will continue to deteriorate in the long term and the situation is not likely 

to rectify itself. 

Introduction 

Historically, ponderosa pine ecosystems have had an intimate and inseparable 

relationship with fire. No other disturbance has had such a re-occurring influence on

the development and maintenance of ponderosa pine ecosystems. Historically this

relationship with fire varied somewhat across the range of ponderosa pine, and it 

varied temporally in concert with changes in climate. 

Over the last century this relationship has undergone an increasing amount of

strain. Although wildfires continue to burn in ponderosa pine ecosystems, recent 

wildfires tend to be more intense and lethal, and consume large expanses of

ponderosa pine forests. There is an impending need to better understand the role of 

fire and techniques land managers can use to emulate fire to restore fire-resiliency. I 

define fire-resiliency simply as the ability of ponderosa pine forests to survive 

wildfires relatively intact, as typically occurred during presettlement times. 

1

 An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

 Professor and Silviculture and Wildland Fire Education Specialist, Oregon State University Extension 

Forestry Program, Central Oregon Region, 3893 SW Airport Way, Redmond, OR 97756 

(email: stephen.fitzgerald@oregonstate.edu) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 197 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

This paper discusses the ecological role of fire in ponderosa pine ecosystems, 

changes in forest structure and fire behavior over the past century, and strategies for 

rebuilding fire-resilience in ponderosa pine ecosystems in western North America. 

Adaptations and Morphological Characteristics 

Affecting Fire Resistance and Survival 

Various adaptations allow vegetation to survive fire. Adaptations can either

facilitate survival of species (e.g., fire-stimulated flowering, refractory seed buried in 

soils, etc) or individuals (e.g. thick bark, basal sprouting, etc) (Kauffman 1990). 

Ponderosa pine is considered one the most fire resistant conifers in the west, and fire 

resistance increases as the tree matures (Miller 2000). Ponderosa pine is well 

suited to survive low-intensity surface fires primarily due to its bark characteristics. 

Ponderosa pine develops a protective outer corky bark (0.3-0.6 cm) early in life when

saplings reach a basal diameter of 5 cm allowing some young trees to survive very

light-intensity surface fires (Figure 1a) (Hall 1980). Mature ponderosa pine trees 

possess thick, exfoliating bark (Figure 1b), which slough off when the bark is on fire. 

Presumably, this helps “take away” heat as flaming bark flecks flake off, thus 

reducing or preventing heat transfer and minimizing injury to cambial cells; however, 

this mechanism has not been well researched. Ponderosa pine bark on mature trees 

continues to flake off with or without fire, and over long time periods without fire a 

thick mulch layer of bark develops at the base of trees. When ignited, this mulch 

smolders for days, conveying heat directly to and through the bark to the cambial 

layer, often killing or severely stressing the tree. Bark beetles may then attack and 

kill weakened trees. Historically, frequent low-intensity surface fires prevented this 

bark mulch layer from accumulating around mature trees. 

Ponderosa pine also has a deep rooting habit compared to other western conifer 

species (e.g., true firs, Engelmann spruce, and lodgepole pine). Although a surface 

fire may heat the soil and kill some surface roots, deeper roots remain intact and 

allow for continued uptake of water and nutrients. The amount and moisture content

of surface fuels (needles and branches, saplings and herbaceous plant material) along 

with larger woody debris (downed logs) beneath or in contact with the tree affects the 

degree of injury to surface roots. 

Ponderosa pine crown structure, branching pattern, and needle and bud 

characteristics also affect survival during fire. The open crown structure and 

branching pattern of ponderosa pine allows for better mixing of air and dissipation of

heat within stands during a fire, thus reducing the potential for crown scorch. The 

open crown structure may also dampen fire-spread through tree crowns in less 

extreme fire conditions (Flint 1925, Agee 1993). Ponderosa pine has long needles 

with high moisture content that surround terminal buds. Although needles may be 

scorched and killed by heat, they help protect meristematic tissue within the bud, 

allowing branch tips to refoliate. Buds of ponderosa pine have thick outer scales that

also help protect meristematic tissue from heat (Miller 2000). 

198 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198.2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

 A

B

Figure 1—(A) This young ponderosa pine survived a light-intensity surface fire when

the basal diameter was about 3-4 cm. Note that the cambium on approximately half 

the circumference was killed. The sapling recovered and greatly accelerated its 

diameter growth probably as a result of less competition and a flush of nutrients 

following the fire. (B)Typical fire-resistant bark of an old-growth ponderosa pine

showing the platy bark surface. 

Another factor reportedly affecting fire resistance is ponderosa pine’s ability to 

self-prune (gradual shedding of lower branches) (Flint 1925, Starker 1934, Miller

2000), resulting in the clear bole that often characterizes large-diameter old-growth

ponderosa pine. Presumably, this mechanism lifts the lower crown over time and

prevents surface fires from moving up into the tree’s canopy. However, there is no

evidence that ponderosa pine self-prunes on its own. The clear boles are a result of 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198.2005. 199 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

either repeated surface fires, which scorch and kill lower branches when trees are 

young and lower branches have small diameters, and/or death of lower branches from 

competition (shading) from neighboring trees. In both cases, dead branches are shed 

and remaining stubs are grown over after decades or centuries of tree growth. 

Evidence that counters the notion of self-pruning is demonstrated by open-grown 

ponderosa pine in areas where fires were naturally excluded, such as in rocky areas 

where fuels are too scarce to carry fire. Often these trees have branches that are

large, heavy, and located on the lower portions of the bole showing no propensity for

self-pruning.

Fire Regimes in Ponderosa Pine Ecosystems 

Fire regimes are influenced greatly by climate, vegetation types and by

topographic and geologic features that either facilitate or restrict fire spread (Agee 

1993, Camp and others1997, Taylor and Skinner 1998). Fire regimes are 

characterized by their frequency, intensity, severity, extent, and seasonality and have 

a great influence on vegetative recovery, plant succession, and forest and ecosystem 

structure (Agee 1993). 

Frequency

Fire frequency, or the mean fire return interval, is a measure of how often fire 

returns, on average, to an area. There may be a wide range around this mean, which

has important ecological implications for stand development and forest structure 

(Baker and Ehle 2001). The median fire return interval is also used to characterize 

fire return intervals in forest ecosystems.

Within ponderosa pine ecosystems, fire returned approximately every 2-47 years. 

This estimate of fire frequency is based on several studies that date fire scars on

individual trees (point sample) or from several fire-scarred trees in an area

(composite fire interval) (Table 1). The wide range in fire frequency is a reflection of 

current and past regional climate, plant association, aspect and slope, elevation, 

aboriginal burning and other factors. In the Front Range of Colorado, for example, 

ponderosa pine forests were subject to frequent surface fires at lower elevations, 

much like other ponderosa pine forests in the west. At higher elevations (2400 m), 

where ponderosa pine is mixed with Douglas-fir and lodgepole pine (more moist 

conditions), fires were less frequent and were a combination of both surface and 

stand-replacing fire (Veblen and others 2000). In western Montana, Arno and others

(1997) observed the same change in fire frequency from pure ponderosa pine stands

to more mesic mixed stands of ponderosa pine and western larch. Other studies have 

shown a link between regional climate patterns, such as periods of wet and dry 

(drought) conditions and fire occurrence (Swetnam 1988, Touchman and others 

1996, Veblen and others 2000, Grissino-Mayer and others 2004, Wright and Agee 

2004).

Lightning is thought to have been the primary source of presettlement fire 

ignitions. Some geographic areas are more prone to lightning than others due to 

prevailing summer weather patterns and topography. The zone that extends from 

northwest California up through Oregon, northern Idaho and northwest Montana, 

known as “lightning alley,” is a prime example of the relationship between lightning

ignitions and fire frequency in ponderosa pine forests (Figure 2). 

200 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198.2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Aboriginal burning also affected fire occurrence in localized areas. Barrett and 

Arno (1982) compared presettlement fire intervals in forests known to have had

heavy use by Native Americans and compared that to fire intervals on similar sites 

but in more remote areas. Fire intervals were twice as frequent in heavy use areas

(MFI of approximately 5-6 years in heavy-use areas versus 12.5 years in remote areas

for two sites). However, Indian-caused burning may have been much more wide 

spread, as documented by early explorer and pioneer writings, particularly after

Native Americans acquired horses in the early 1700s (Barrett 1980, Barrett and Arno 

1982). 

Figure 2 — Lightning occurrence in the western United States (from Schmidt and 

others 2002). Note the concentration of lightning from northern California extending

northeast through Oregon, Idaho, and northwest Montana. 

Intensity and Severity 

Fire intensity and severity are often used interchangeably, but fire scientist

distinguish between them. Fire intensity is a measure of heat or energy released

(kW) per unit length (m) along the fireline, and can be estimated by measuring flame 

length as the flaming front passes a known point (Rothermal and Deeming 1980). 

Fire severity is determined by either a visual estimate or measured assessment of fire

effects on soils and vegetation. High intensity fires (e.g., long flame lengths), for 

example, result in more consumption and charring of surface fuel, increased exposure 

of soil and alteration of soil properties, and more damage and mortality of trees and

other vegetation. 

Historically, ponderosa pine ecosystems were predominantly subjected to

frequent, low-intensity fire (Agee 1993). These periodic fires would consume 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198.2005. 201 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

accumulated fuels, thin young seedlings and saplings, and consume shrubs and

herbaceous plant material, leaving the large, fire-resistant trees intact. Some

individual large trees or small groups of large trees may have been directly killed or 

stressed by fire and later attacked and kill by bark beetles (Munger 1917).

On more moist sites where ponderosa pine is seral (on Douglas-fir, dry and wet

Grand fir series), fire intensity was often greater and resulted in a more mixedseverity fire regime composed of a combination of underburning (light intensity) and 

patch stand-replacement (high intensity) fire (Agee 1993, Arno and others 1995,

Arno and others 1997, Veblen and others 2000, Baker and Ehle 2001, Wright and 

Agee 2004). In the ponderosa pine forests of the Black Hills of South Dakota, fires 

were of higher intensity and more of mixed-severity (Brown and Sieg 1996,

Shinneman and Baker 1997), most likely because of longer fire intervals and 

abundant regeneration that establishes between successive fires. 

Extent 

The perimeter and extent of presettlement fires is often difficult to ascertain

because fires of very low intensity may not scar trees, or subsequent fires may

destroy fire scars in catfaces or kill and consume fire-scarred trees (Agee 1993). The 

extent of presettlement fires was highly variable and often associated with changes in 

inter-annual weather patterns (Norman and Taylor 2003). In central Washington,

Wright and Agee (2004) found that most fires were small (< 1000 ha (2470 ac)) and 

that large fires (> 4000 ha (9880ac)) occurred every 27 years and were associated

with annual periods of drought (Palmer Drought Severity Index and winter Southern

Oscillation Index (El Nino)). In northern California, Taylor and Skinner (1998) 

found that average burn area was 350 ha, but documented 16 fires between 1627 and 

1992 that were larger than 500 ha. In southwest Colorado, Grissino-Mayer and 

others (2004) found that historic fires in the lower elevation ponderosa pine stands 

were small and quite localized but at higher elevations, where ponderosa pine is 

mixed with other species, fires were less common but larger in size. In central

Colorado and in the Southwest there is an association between large fires and periods 

of wet years that increase dry matter production (fuel), followed by dry spring and

summer months (Swetnam and Baisan 1996, Touchan and others 1996, Veblen and

others 2000, Donnegan and others 2001, Norman and Taylor 2003, Grissino-Mayer 

and others 2004). Norman and Taylor (2003) found that extensive burning of 1000s 

of hectare took place approximately every 20 years in northeastern California.

202 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198.2005. 
Table 1 – Fire return intervals by region and plant series for climax and seral ponderosa pine (adapted from Agee (1994) and Baker and Ehle (20

 _____________________________________________________________________________________________ 

Mean Fire Median Fire Composite (C) or 

Geographic Region Return Interval Return Interval Point (P) Sample Plant Series _______________________________________________________________________________________

Central Washington (E. Cascades) 18.8 15.5 C Douglas-fir  20.6 17.4 C Grand fir (dry)  7 6.7 C Douglas-fir  7-11 -- C Douglas-fir  23.9 20.6 C Grand fir (wet) Northeast Washington 10-24 -- P Douglas-fir -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------Northern Rocky Mountains:  Western Montana 6-11 -- P Ponderosa pine 

7-19 -- P Douglas-fir 

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------South Dakota (Black Hills) 20-23 -- C Ponderosa pine  10-12 -- C Ponderosa pine -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------Central Oregon (E. Cascades) 16-38 -- C Ponderosa pine (dry) 

7-20 -- C Ponderosa pine (mesic) 9-25 -- C White fir 

North-central Oregon (E. Cascades) 11-16 -- P Ponderosa pine 

3-36 -- P Ponderosa pine 

Northeast Oregon (Blue Mts.) 10-43 20 C Ponderosa pine 

10 P Douglas-fir 

 12-53 5-15 C Douglas-fir 

47 -- P White fir 

 13-71 15 C White fir South-central Oregon (Cascades) 9-42 -- C White fir 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
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-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

________________________________________________________________________________________________

Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Table 1 -- continued Northern California (S. Klamath Mts.) 11.5 -- C Ponderosa & limber pine  13.0 --

C 

 Douglas-fir 

 13.0

 -- C 

 Douglas-fir/white fir 

 12.5 --

C 

 Douglas-fir/ponderosa 

 pine/incense-cedar 13.5

 -- C

 Douglas-fir &limber pine 

Northern California (N. Klamath Mts.) 12.0-15.5 -- C Douglas-fir Northern California (S.Cascades Mts.) 21.4 12.0 C Ponderosa pine Central California (Westside Sierras) 9-18 --

C 

 White fir 

Central Rocky Mountains:  San Juan Mts. 6-13 5-9 

C 

 Ponderosa pine 

 19-30 19-29 C Mixed conifer  Northern Front Range 8.3-22.4 6.4-11.61 C Ponderosa pine 

 17.2-18.6 8.1-10.41 C Douglas-fir Southern Rocky Mountains:  North-central Arizona 3.7

 4

 C Ponderosa pine 

 7.4

 6

 C Ponderosa pine 

 8.7

 5

 C Mixed conifer 

 Arizona 4-12

 -- P 

 Ponderosa pine 

 Arizona 1.8

 -- C

 Ponderosa pine 

 Southwest New Mexico 5-8 --

C 

 Ponderosa pine 

1 Weibull median probability interval 

204 USDA Forest Servic
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Seasonality 

Fire in ponderosa pine systems varies somewhat by season and geographic region

within the species range as a result of regional weather patterns. Seasonality of 

presettlement fires can be determined using dendrochronology techniques that

examine the position of each fire scar relative to ring development, such as during 

earlywood and latewood development or after the cessation of latewood growth 

(Baisan and Swetnam 1990). In north-central Washington, Wright and Agee (2004)

found that 80 percent of presettlement fires occurred late in the growing season 

(during late-wood formation) or in early fall (after cambial dormancy) for seral 

ponderosa pine growing on Douglas-fir, dry grand fir, and wet grand fir plant 

association groups (PAGs). Heyerdahl and others (2001) found that in the southern 

Blue Mountains a higher proportion (26 percent) of fires occurred during earlywood 

and latewood formation, while on more mesic sites in the northern Blue Mountains

most fires occurred after cessation of ring growth. In northern California, 93 percent

of fires occurred during the dry midsummer through early fall period (Taylor and 

Skinner 2003). In a study in southwestern ponderosa pine where season could be 

determined, Fulé and others (1997) found that approximately 40 percent of the 

presettlement fires occurred in spring (late April to June) and 60 percent in the 

summer (July to early September). There appears to be a north-south gradient of 

seasonality within the Medeterranean Climate zone of southwestern Oregon 

(Klamath Mountains) to the southern Sierra Nevada in California. Fire scars are 

mostly (>90%) at the ring boundary in the Klamath Mountains, indicating mostly 

late-summer/early-fall fires. In the southern Sierra Nevada, fire scars are mostly 

(>80%) within the rings, indicating many early- to mid-summer fires (Skinner 2002) 

Historic Forest Structure 

Presettlement ponderosa pine forests throughout its range were typified by open,

park-like stands of large-diameter trees with few seedlings and saplings in the 

understory (Langille and others 1903, Munger 1917, Weaver 1943, Morrow 1985,

Arno 1988, Fulé and others 1997, Youngblood and others 2004, Moore and others 

2004). Stands were typically uneven-aged, with many stands containing a few large 

individual trees 400 to 600 years old (Munger 1917, Morrow 1985, Arno and others

1995, Youngblood and others 2004). Historic photos depict the open character of oldgrowth ponderosa pine on the Klamath Indian Reservation in south-central Oregon 

(Figure 3). Other turn-of-the-century photos depict similar forest conditions, although 

historic photos locations are not randomly located. In addition, the understory plant

community may have also been influenced by livestock grazing not readily apparent 

in most historic photos. Many rangelands and adjacent ponderosa pine forests were 

heavily grazed during settlement from the late 1860s through the early 1900s

(Hessburg and Agee 2003). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 205 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Figure 3 -- Harold Weaver standing in an open park-like stand of old-growtth

ponderosa pine on the Klamath Indian Reservation in south central Oregon in the

1930s. Note the open understory. (BIA photo) 

In an early survey of ponderosa pine forests in Oregon, Munger (1917) found 

ponderosa pine forests contained approximately 30-99 (12-40 per acre) largediameter (> 30.5 cm (12 in) DBH) trees per hectare across several sites (Table 2). In 

both a climax ponderosa pine site in central Oregon and a ponderosa pine-dominated 

mixed conifer (dry) site in northeast Oregon very few seedlings and saplings are 

present (Figures 4a,b), and both stands have a relatively low stand density index 

(SDI) (Reineke 1933) compared to ponderosa pine stands today. Even on the more

productive mixed conifer site, there are few seedlings and saplings of ponderosa pine 

and “other” species, which are likely grand fir and Douglas-fir. Because of frequent

fire, presettlement ponderosa pine stands probably had low levels of snags and large 

woody debris (Skinner 2002). The following quote taken from Munger (1917, page 

17) sums up his observations on the historic character of ponderosa pine forests:

“In most of the pure yellow-pine forests of the State the trees are spaced rather 

widely, the ground is fairly free from underbrush and debris, and travel through 

them on foot or horseback is interrupted only by occasional patches of saplings 

and fallen trees.” 

206 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Table 2 -- Historic trees per hectare of trees greater than 30.5 cm DBH for several sites in 

Oregon (from Munger 1917). 

 ________________________________________________ 

Hectares Trees per Hectare 

 Location Surveyed >30.5 cm 

 ______________________________________________________ 

Looking Glass Creek 109 99 

Austin & Whitney 638 77 

Winlock 49 42 

Embody 74 79 

LaPine 99 30 

Klamath Lake 393 86 

 ______________________________________________________ 

Other reconstructive studies have shown similar low stand densities in

presettlement ponderosa pine forests across its range (Weaver 1943, Cooper 1961,

Morrow 1985, Habeck 1985 (cited in Arno 1988), Taylor and Skinner 2003, 

Youngblood and others 2004). 

The stems of trees within ponderosa pine stands also show a distinct spatial

pattern. Historically, many old-growth pine stands had a groupy-patchy stem pattern 

(Munger 1917, Weaver 1943, Cooper 1961, Biswell and others 1973, Habeck 1985

(cited in Arno 1988), Morrison 1985, Arno and others 1995, Kaufmann and others 

2001,Youngblood and others 2004). For example, Youngblood and others (2004) 

examined the spatial stem pattern of mature trees in old-growth ponderosa pine 

stands in central Oregon and northern California and found that trees on 24 out of 27 

large plots were moderately to strongly grouped (Figure 5), most likely the result of 

past fire, insect, and regeneration patterns. The open and groupy nature of oldgrowth ponderosa pine forests affords additional fire resistance because the canopy is 

broken up by gaps between groups of different sizes and ages of trees, leaving the 

overall stand less vulnerable to crown fire. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 207 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

0

2

4

6

8

10

12

14

12.7 33 53.3 73.7 94 107+

Diameter Class (cm)

Trees per

Hectare

PP

0

10

20

30

40

50

60

12.7 33.0 53.3 73.7 94.0 107.0+

Diameter Class (cm)

Trees per

Hectare

Other

PP

B

Figure 4 – (A)Trees per acre by diameter class on a climax ponderosa pine site in 

central Oregon and (B) on a ponderosa pine-dominated mixed-conifer site in 

northeastern Oregon (from Munger 1917).

A 

208 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Figure 5 – (A) Spatial pattern of large (•) and dead (o) trees in the upper canopy of 

old growth plot 23 at Metolius study area and (B) the results of Ripley’s K(d) analysis

on these 99 trees, with empirical cumulative distribution of L(d) shown as a solid line, 

the expected random distribution as a dotted line with mean equal to zero, and pointwise 95% confidence envelop around the expected distribution of complete spatial 

randomness shown by dashed lines (from Youngblood and others 

2004). 

Changes in Forest Structure, Fuels and Fire Regime

Ponderosa pine forests have undergone great ecological change in the last 140 

years since settlement (Hessburg and Agee 2003), and not for the better from a fire 

and forest health perspective. Heavy grazing in the late 1800s and early 1900s,

active fire suppression after 1910, and other land uses have disrupted the natural fire 

regime in ponderosa pine ecosystems. This has allowed succession to proceed 

unchecked resulting in above-normal fuel accumulations and abundant tree 

regeneration. In addition, early selective logging removed the large, fire-resistant 

ponderosa pine, western larch, and Douglas-fir, creating openings that favor the 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 209 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

development of shade-tolerant Douglas-fir and true firs in the understory and midcanopy layers (ladder fuels) on more mesic sites. 

These past land use activities have produced cascading ecological effects that

are manifested today in altered ecological processes (Weatherspoon 1996, Keane and

others 2002). Forest stand structure has changed from open park-like stands 

dominated by large, fire-resistant trees to over-dense even-aged stands (Weaver

1943, Covington and Moore 1994, Moore and others 2004) that are more susceptible

to crown fire (Weatherspoon and others 1992, Skinner and Chang 1996), and contain 

trees that are less likely to survive fire because of their smaller diameter, thinner bark 

and low hanging crowns (Agee 2002). In ponderosa pine stands in the southwest, 

forest density increased from 148 trees (65 ponderosa pine and 80 oaks) per hectare 

in 1883 to 1265 trees per hectare in 1995 (Fulé and others 1997). Similar changes in

stand density have been documented in the northwest and elsewhere (Weaver 1943,

1959, Morrison 1985, Arno 1988, Agee 1993, Adams 1995, Weatherspoon 1996, 

Taylor and Skinner 2003, Youngblood and others 2004). In some cases these 

changes in succession and stand density have been documented from long-term study

plots and time-series photography (Smith and Arno 1999). 

Recent coarse-scale assessments have documented changes in the potential fire

regime from frequent, low-intensity fires confined mostly to the understory to more 

lethal high-intensity fires that have the potential to consume entire stands across large

landscapes (Figure 6) (Quigley and others 1996, Schmidt and others 2002). On more 

mesic sites, forest composition has changed from stands dominated by ponderosa

pine and western larch to those dominated by Douglas-fir and true firs both of which 

are more susceptible to insects, disease, and drought (Filip 2002). 

Remaining old-growth ponderosa pine forests are in jeopardy as well, due to

elevated risk to insect attack, some diseases, and stand-replacement fire (Harrington 

and Sackett 1992, Weatherspoon 1996, Fitzgerald and others 2000, Keane and others 

2002, Moore and others 2004). Management action is needed in these stands to 

maintain this important structure on the landscape for wildlife that depend on mature,

old-growth forest conditions and for human benefits. Because many ponderosa 

pine forests lie adjacent or in close proximity to the wildland-urban interface, homes

and communities are increasingly at risk from high intensity wildfires starting in and 

spilling over from dense, fire-prone forest conditions. Without efforts to restore 

ponderosa pine forests to some semblance of natural forest conditions, large intense 

wildfires will continue, producing detrimental ecological effects and continued

deterioration of forest and watershed health (Wickman 1992, Mutch and others 

1993).

210 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Figure 6 – Historic and current fire regime for the Inland Northwest (from Quigley and 

others 1996). The increase darker grey areas indicate a change to more lethal fire

regimes across the region under current conditions. 

Rebuilding Fire Resilient Ponderosa Pine Ecosystems 

Fire Behavior and Forest Structure 

Fire behavior is affected by the interaction of fuel, weather, and topography,

known as the fire behavior triangle (Figure 7). Aspects of fire behavior that 

managers are primarily interested in include how fast a fire moves (rate of spread),

how hot it burns (intensity), torching of tree crowns (passive crown fire), crowning 

(active crown fire), firewhirls, and spotting. Spotting occurs when fire brands 

(glowing embers) are lofted up and out ahead of the main fire front, igniting spot 

fires that then feed back into the main fire front, creating very extreme (and 

dangerous) fire conditions. A change in any one of these three main factors during 

the course of combustion will influence a fire’s behavior. For example, a surface fire 

will move (spread) faster upslope because flames are tilted toward the slope and more

efficiently dry and preheat fuels in front of the fire. Other topographic features such

as saddles and draws affect wind patterns by funneling air and intensifying fire 

behavior. Weather, too, is a dominant factor in fire behavior. A change in weather 

from hot and dry to cooler and more moist conditions will reduce fire intensity and 

rate of spread. Often firefighters have to wait for a change to cooler and wetter 

weather before they can safely attack a wildfire head on. We have no control over

topography and weather, but fire managers often take advantage of favorable weather

conditions or topographic features to attack and suppress wildfires. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 211 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

 Figure 7 – The fire behavior triangle. 

Fuel comprises the third leg of the fire behavior triangle. How much fuel (fuel

loading in tons per hectare), and its vertical (within stands) and horizontal (across 

landscapes) arrangement affects fire intensity and the ability of surface flames to 

begin torching tree crowns or support active crown fire for a given set of weather and

topographic conditions. Fuels can be comprised of dead biomass (needles, fallen

branches, dried herbaceous material, and coarse woody debris) or of live trees and 

other vegetation, such as shrubs. Some shrubs, such as bitterbrush, contain volatile 

oils and have higher heat content and, because of their air-to-volume ratio, produce 

long flame lengths when ignited, initiating torching. Torching is the movement of

surface flames up into individual tree crowns or into the crowns of tree groups.

Torching is the precursor to active crown fire. 

Fire exclusion over the last century in ponderosa pine forests has allowed fuels 

to build up on the forest floor (surface fuels) and shrub cover and tree regeneration to 

increase. This buildup has created “fuel ladders” where surface fuels are now 

connected to the overstory canopy by dense understory and mid-story saplings and 

medium-sized trees, making it easier for surface fires to move up and torch tree

crowns and, under the right weather conditions and topographic setting, support

active crown-to-crown fire spread. Crown fuels are comprised of needles, twigs, and 

small branches. Crown fuels are quantified by crown bulk density, which is the 

weight of needles, twigs, and small branches in kilograms per cubic meter of crown

volume. Dense, even-aged ponderosa pine stands with crown bulk densities above 

0.10 kg/m3

 are more vulnerable to active crown fire because fire can easily spread 

from tree crown to tree crown under weather and topographic conditions conducive 

to crown fire initiation and spread (Graham and others 1999, Agee and others 2000, 

Graham and others 2004). 

In short, the structure of the forest and the fuels contained within have a major 

influence on fire behavior and severity (Agee and others 2000, Graham and others 

2004, Peterson and others 2005). The amount and arrangement of fuel is the only 

element in the fire behavior triangle that managers have some influence over, and it is 

this concept that drives all fire control efforts from direct fire suppression tactics to 

proactive or pre-fire fuel reduction treatments. 

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Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Treatments to Reduce Fire Intensity and Severity 

Keeping wildfire on the surface is important for reducing fire intensity and 

excessive damage to vegetation and watersheds. Factors that affect a surface fire’s

transition to a crown fire include foliage moisture content, surface flame length, and 

height to the base of the canopy (Agee 1993, Agee and others 2000). Moisture 

content of foliage at the beginning of the summer can be as high as 300 percent in 

new foliage, but declines to less than 100 percent as the summer progresses and is 

more easily ignited by surface flames (Agee and others 2002). In years of drought, 

foliage moisture content declines earlier in the season. We have no influence over 

foliage moisture. 

Surface flame lengths depend on the amount, energy content, and moisture

content of surface fuels. Removing accumulated surface fuels, or targeting the

removal of specific fuels such as bitterbrush because of its high energy content, 

reduces flame lengths making it more difficult to initiate torching of tree crowns. In 

addition, the higher the base of tree crowns, the more difficult it is for surface flames

to combust and torch tree crowns. 

Once a fire begins torching and moving up into the canopy, the rate of spread (a 

function of wind speed) and crown bulk density determine the likelihood for

development of an actively moving crown fire. Increasing the space between tree

crowns reduces the opportunity for fire to spread from tree crown to tree crown, and 

allows a crown fire to transition back to a surface fire. 

Following the principles of Agee (2002) (Table 3), four actions will improve 

fire-resilience in ponderosa pine ecosystems: reducing surface fuels, removing ladder 

fuels, leaving large, fire resistant trees, and spacing tree crowns (in that order). These

conditions can be achieved with a variety of methods including prescribed burning, 

mowing, pruning and thinning. 

Prescribed Burning 

Prescribed burning is used in ponderosa pine stands to remove accumulated 

surface fuels, consume slash generated from thinning activities, kill and thin out 

encroaching trees in the understory, and rejuvenate herbaceous plants and shrubs

(Ffolliott and others 1977, Sackett 1980, Walstad and others 1990). Prescribed 

burning also scorches and kills lower branches of trees, which, in the long run, results 

in lifting the canopy much like pruning, increasing the height from the forest floor to 

the lower canopy and increasing fire resistance. Periodic burning can prevent the 

development of ladder fuels and can be used as to maintain stands in a fire-resilient 

condition over time. 

However, in most ponderosa pine stands prescribed burning is limited as a firstentry fuels treatment because of heavy accumulations of surface and ladder fuels. In 

most cases, other mechanical treatments are needed prior to prescribe burning in

order to reduce fuels to a level that prescribed burning can be used in subsequent 

treatments without undue damage to the residual stand. Preparatory treatments, such 

as mowing, pruning, and thinning, improve fire control and safety, reduce the risk of 

escape, reduce damage to residual trees, and significantly reduce the level of smoke 

production and effects on air quality and human health in nearby communities. 

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Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Mowing and Mechanical Fuel Reduction 

Mowing involves using a 4-wheel drive tractor or a tracked-vehicle outfitted 

with a mowing head. The operator essentially mows the understory shrubs and small

trees (< 7 cm (3 in) diameter) reverting back to a grass-dominated understory. 

Mowing cuts and grinds up surface fuels and the smaller ladder fuels to small particle 

sizes, which decay rapidly when in contact with the forest floor. This mechanical 

treatment is limited to gentle topography and has been implemented on the Deschutes 

National Forests near wildland-urban interface areas. Mowing costs are

approximately $40 per acre. Stands to be underburned can be first treated with 

mowing to reduce surface fuels and improve fire safety and control. Because many

shrubs species resprout, mowing is a short-term fuel reduction treatment. 

There are several other mechanical methods for reducing shrubs and small trees. 

These include various kinds of excavators outfitted with a rotating head mounted on a 

hydraulic arm. The operator moves the head back and forth along the ground to

mulch up shrubs or smaller trees (saplings). On larger trees (10 to 20 cm dbh (4 to 8 

inches)) the tree can be ground up by mulching from the top of the tree down to the

base. These treatments can cost up to $350 to $400 per acre, depending on terrain and 

density of shrubs and small trees. However, they cut and mulch all in one pass, thus 

eliminating subsequent costs for piling and burning slash often associated with

manual hand cutting. 

Pruning 

Pruning removes the lower branches of trees and lifts the crown, creating more

distance between potential surface flames and the bottom of the tree canopy. Pruned 

branches need to be piled and burn. This technique is particularly useful in young

stands where crowns are low and close to surface fuels (grass/shrubs). 

Thinning 

Thinning can be used to change stand and fuel characteristics (e.g., ladder and 

crown fuels) and lessen the chance of passive and active crown fires (Graham and 

others 1999, Scott 1998, Agee and others 2000, Fulé and others 2001, Graham and

others 2004, Peterson and others 2005). Thinning from below, also referred to as low 

thinning, removes trees in the subordinate lower crown classes (Figures 8 and 9) 

leaving the larger, more vigorous trees. Thinning from below removes ladder fuels, 

reduces canopy bulk density, and leaves trees that have higher crowns, thicker bark, 

and better ability to survive fire. In mixed conifer stands, thinning should leave the 

most fire resistant species, such as ponderosa pine, western larch, and Douglas-fir. 

Thinning can be done incrementally such that the stand is progressively opened up

over time or, if fire risk is high, thinning more heavily to a wider spacing in one 

operation. The latter situation would be appropriate for ponderosa pine stands 

adjacent to the wildland-urban interface and where the risk of wind throw is low. 

Following thinning, the amount of remaining surface fuel should be assessed 

(Weatherspoon 1996). Where excessive slash is found to exist, slash must be

removed either by piling and burning or with prescribed underburning to prevent

high-severity surface fire (Brown 1980). Wildfire in thinned stands and in stands 

thinned in combination with other fuel treatments experience reduced fire intensity, 

lower rates of spread, less severe tree damage and lower overall fire severity 

214 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

(Graham 2003). However, thinning also opens up the stand and changes the 

microclimate, allowing surface fuels to dry out more completely and within-stand 

wind speeds to increase (Weatherspoon 1996). These changes can increase both the 

rate of spread and intensity of subsequent surface fires. However, the increased

intensity and spread rates are why the original forests had frequent fires. Thinning in 

this manner creates stands similar to pre-settlement conditions. Thus, the reduction in 

fire hazard with thinning generally more than makes up for potential increases in fire 

spread and intensity. This also makes fire suppression, when deemed necessary, more 

efficient. Thus, if heavy fuels are removed, the residence time (or duration) of the fire

is reduced, often resulting in a non-lethal surface fire. 

Figure 8 – Thinning to improve fire resistance. Thinning from below removes 

smaller trees in the stand leaving the larger, more fire resistant trees (adapted from

Graham 1999). 

Figure 9 – A 90-year old ponderosa pine stand thinned from below on the Sun Pass 

State Forest, Oregon. Note the more open canopy and high crowns. The fire

resistance in this stand has been significantly improved. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 215 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Thinning from below can also benefit large, old-growth ponderosa pine trees in

stands that have developed a dense understory and are under increasing competitive 

pressure. Thinning from below not only reduces ladder fuels and the risk of torching, 

but by reducing stand density tree vigor is improved and risk to bark beetle attacked 

reduced (Figure 10) (Fitzgerald and others 2000, Latham and Tappeiner 2002, 

McDowell and others 2003). Because the extent of old-growth ponderosa pine

forests is limited across western North America, thinning from below to restore and 

maintain existing old-growth forests can better insure their survival over the long

term, until other areas develop old-growth conditions and serve as replacement oldgrowth habitat in the future. 

Figure 10 -- This old-growth ponderosa pine stand was thinned from below and later 

underburned to reduce competition and restore a more historic stand structure. 

Thinning ponderosa pine stands (from below) to improve fire resistance typically

involves removing non-commercial trees (<23 cm dbh (9 in)) and trees containing 

small to medium-size sawlogs (25-46 cm dbh (10-18 in)). In most cases the value and

volume removed in small to medium-size sawlogs is not enough to cover all the costs 

of removing non-commercial trees and to conduct follow up treatments. Net costs to 

treat stands have ranged from $247 to $1976 per ha ($100 to $800 per acre). Thus, 

subsidies are needed to accomplish fuel treatments at the landscape level. However, 

some thinning treatments can show a modest profit, depending on stand conditions, 

thinning diameter, basal area limits, and markets (Scott 1998, Barbour and others 

2004, Larson and Mirth 2004). This profit could then be used to offset costs in stands 

that do not produce any net revenues, thus increasing the overall acreage treated.

Although there is resistance to paying for these treatments on federal lands through 

Congressional appropriations, improving fire-resilience in ponderosa pine ecosystems 

through subsidies is far less expensive than the cost of wildfire suppression that can

approach $7410 per ha ($3000 per acre), not to mention the loss in timber value, cost 

of watershed rehabilitation, the risk and loss of homes, and the loss of ecosystem

values and services (Butry and others 2001, Fairbanks and others 2002, Morton and

others 2003, Lynch 2004, Mason and others 2004). 

216 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Table 3 -- Principles for creating fire-resilient forests (after Agee 2002). 

Principle Effect Advantage Concerns

Reduce surface fuels Reduce potential

flame length 

Less torching, 

control easier 

Surface disturbances, 

less with fire than 

with mechanical 

techniques 

Increase height to 

live crown 

Requires longer

flame length to begin 

torching

Less torching, 

control easier 

Opens up understory, 

may allow surface 

winds to increase 

Decrease crown 

density 

Makes tree-to-tree 

crown fire less 

probable

Reduces crown fire 

potential, control 

easier 

Surface wind may 

increase and surface 

fuels may be drier

Keep larger trees Thicker bark and 

higher crowns

Increase the 

survivability of trees 

Removing smaller 

trees is less 

economically 

profitable 

Summary

Over the last 140 years ponderosa pine ecosystems have changed immensely 

and bear little resemblance to their presettlement condition. The original old-growth

ponderosa pine forests were once considered an endless resource to early pioneers 

and settlers, and the vast “yellow pine” forests were utilized to fuel economic growth

and the development of western North America. Past and current land use activities 

along with active fire suppression eliminated natural surface fires from these forests 

and the disturbance patterns that controlled their development and helped sustained

them over the millennia. 

This elimination of fire has profoundly changed the structure of the original

ponderosa pine forests, and not for the better. Today, ponderosa pine forests contain

an overabundance of fuel, high stand densities across large landscapes and few old 

growth trees. These conditions have contributed to declining tree health and have 

helped sustain increases in large, uncharacteristic wildfires across the west. The 

ponderosa pine ecosystems are in trouble, and the problem will not go away or take 

care of itself. In the Pacific Northwest timber stand improvement activities, such as

thinning, are down 60 percent compared to over a decade ago (FY 1988), and the

level of funding for silvicultural treatments has declined over the last decade,

resulting in a huge backlog of forest requiring some level of treatment (Powell and

others 2001). However, doing nothing will result in forests that continue to 

deteriorate over time because wildfire today no longer operates in its historical 

fashion, that of frequent low-intensity surface fires.

Restoration treatments should return ponderosa pine forests to within their

natural range of variation for both stand and landscape structure where possible. 

Ongoing research to determine reference stand conditions (density, tree size, tree 

pattern, gaps, etc) should establish conditions across broader landscapes, which 

would provide a “blueprint” for restoration activities (Covington and Moore 1994, 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 217 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Fulé and others 1997). Restoration also needs to re-introduce processes, like fire, to 

maintain stands and promote the sustainable development of younger ponderosa pine 

stands. 

Craig and others (2002) outline in detail 16 principles to consider for the 

restoration of southwestern ponderosa pine. These same principles could be adapted 

and applied to most ponderosa pine forests of western North America. The first of

these principles, and probably the most important in the near term, “reduce the threat

of crown fire,” is needed to first stop the cycle of uncharacteristic wildfires to prevent 

loosing critical forest structures, important wildlife habitat, and genetic reservoirs, 

like old-growth. Treatments that move stands closer to conditions of pre-European 

settlement (Table 3) are likely to reduce the chance of crown fires and improve fireresiliency. Treatments to reduce fire intensity and severity have been shown to work

(Agee and others 2000, Graham 2003, Martinson and Omi 2003, Graham and others 

2004). To make a real difference at the landscape level, however, will require a suite 

of treatments (prescribed fire, thinning, and combinations) that are prioritized. In 

addition, long-term Congressional investments will be needed to treat the millions of 

acres of ponderosa pine forests on federal lands in need of restoration (U.S. General 

Accounting Office 1999). 

Finally, without intelligent, science-based intervention in the near term to restore

fire-resiliency, we cannot expect ponderosa pine forests of western North America to

continue to produce all the ecological and social values that the public desires in the 

long term. 

References 

Adams, D.L. 1995. The forests of the Inland Northwest. In: Proceedings of forest health

and fire danger in Inland Western forests. September 8-9, 1994, Spokane, Washington,

Harmon Press; 11-14. 

Agee, J.K. 1993. Fire ecology of Pacific Northwest forests. Island Press, Washington, DC. 

493 p.

Agee, J.K. 1994. Fire and weather disturbances in terrestrial ecosystems of the eastern 

Cascades. Gen. Tech. Report PNW-GTR-320. Portland, OR: Pacific Northwest

Research Station, Forest Service, U.S. Department of Agriculture. 52 p. 

Agee, J.K. 2002. Fire behavior and fire-resilient forests. In Fitzgerald, S.A., editor. Fire in 

Oregon’s forests: risks, effects and treatment options. A synthesis of current issues and 

scientific literature. Special Report prepared for the Oregon Forest Resources Institute, 

Portland, OR; 119-126. 

Agee, J.K.; Bahro, B.; Finney, M.A.; Omi, P.N.; Sapsis, D.B.; Skinner, C.N.; van

Wagtendonk, J.W.; Weatherspoon, C.P. 2000. The use of shaded fuelbreaks in 

landscape fire management. Forest Ecology and Management, 127: 55-66.

Agee, J.K.; Wright, C.B.; Williamson, N.; Huff, M.H. 2002. Foliar moisture content of

Pacific Northwest vegetation and its relationship to wildland fire behavior. Forest

Ecology and Management 167: 57-62. 

Arno, S.F. 1976. The historical role of fire on the Bitterroot National Forest. Res. Paper

INT-187. Ogden, UT: Intermountain Forest and Range Experiment Station, Forest

Service, U.S. Department of Agriculture. 29 p. 

Arno, S.F. 1988. Fire ecology and its management implications in ponderosa pine forests.

In Baumgartner, D.M.; Lotan, J.E., editors. Ponderosa pine the species and its

management. Symposium Proceedings. Pullman, WA: Washington State University

Cooperative Extension; 133-139. 

218 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Arno, S.F.; Scott, J.H.; Hartwell, M.C. 1995. Age-class structure of old-growth ponderosa

pine/Douglas- fir stands and its relationship to fire history. Res. Paper INT-RP-481. 

Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department of

Agriculture; 25 p.

Arno, S.F.; Smith, H.Y.; Krebs, M.A. 1997. Old-growth ponderosa pine and western larch

stand structures: Influence of pre-1900 fires and fire exclusion. Res. Paper INT-RP495. Ogden, UT: Intermountain Research Station, Forest Service, U.S. Department of 

Agriculture; 20 p.

Baisan, C.H.; Swetnam, T.W. 1990. Fire history on a desert mountain range: Rinco 

Mountain Wilderness, Arizona, USA. Canadian Journal of Forest Research 20: 1559-

1569. 

Baker, W.L.; Ehle, D. 2001. Uncertainty in surface-fire history: the case of ponderosa

pine forests in the western United States. Canadian Journal of Forest Research 31:

1205-1226. 

Barbour, R.J.; Fight, R.D.; Christensen, G.A.; Pinjuv, G.L.; Nagubadi, R.V. 2004. Thinning 

and prescribed fire and projected trends in wood product potential, financial 

return, and fire hazard in Montana. Gen. Tech. Report PNW-GTR-606. Portland OR:

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 78

p. 

Barrett, S.W. 1980. Indians and fire. Western Wildlands 6(3): 17-21. 

Barrett, S.W.; Arno, S.F. 1982. Indian fires as an ecological influence in the northern 

Rockies. Journal of Forestry 80(10): 647-651. 

Biswell, H.H., Kallander, J.R.; Komarek, R.; Vogl, J.; Weaver, H. 1973. Ponderosa fire 

management. Miscellaneous Publication No. 2. Tall Timbers Research Station, 

Tallahassee, FL; 49 p.

Bork, B.J. 1985. Fire history in three vegetation types on the eastern side of the Oregon

Cascades. Corvallis: Oregon State University; 94 p. Ph.D. dissertation.

Brown, J.K. 1980. Influence of harvesting and residues on fuels and fire management. In: 

Environmental consequences of timber harvesting in Rocky Mountain coniferous 

forests. Symposium Proceedings. Gen. Tech. Report INT-90. Ogden, UT: Intermountain 

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture;

417-432. 

Brown, P.M.; Sieg, C.H. 1996. Fire history in interior ponderosa pine communities of the

Black Hills, South Dakota, USA. International Journal of Wildland Fire, 6:97-105. 

Brown, P.M.,; Sieg, C.H. 1999. Historic variability in fire at the ponderosa pine-northern 

Great Plains prairie ecotone, southeastern Black Hills, South Dakota. Ecoscience, 

6:539-547. 

Butry, D.T.; Mercer, D.E.; Prestemon, J.P.; Pye, J.M.; Holmes, T.P. 2001. What is the price

of catastrophic wildfire? Journal of Forestry, 99(11): 9-17. 

Camp, A.E.; Oliver, C.D; Hessburg, P.F.; Everett, R.L. 1997. Predicting late-successional 

fire refugia from physiography and topography. Forest Ecology and Management 

95: 63-77. 

Cooper, C.F. 1961. Pattern in ponderosa pine forests. Ecology 42(3): 493-499.

Covington, W.W.; Moore, M.M. 1994. Southwestern ponderosa pine forest structure and 

resource conditions: changes since Euro-American settlement. Journal of Forestry,

92(1): 39-47.

Craig, D.A.; Savage, M.; Falk, D.A.; Suckling, K.F.; Swetnam, T.W.; Schulke, T.; Stacey,

P.B.; Morgan, P.; Hoffman, M.; Klingel, J.T. 2002. Ecological restoration of

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 219 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

southwestern ponderosa pine ecosystems: a broad perspective. Ecological 

Applications, 12(5): 1418-1433. 

Dieterich, J. 1980. The composite fire interval – a tool for more accurate interpretation 

of fire history. In: Stokes, M.; Dieterich, J., editors. Proceedings of the fire history

workshop. Gen. Tech. Report RM-GTR- 81. Fort Collins, CO: Rocky Mountain Forest 

and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 8-14. 

Donnegan, J.A.; Veblen, T.T.; Sibold, J.S. 2001. Climatic and human influences on fire 

history in Pike National Forests, central Colorado. Canadian Journal of Forest 

Research, 31: 1526-1539. 

Ffolliott, P.F.; Clary, W.P.; Larson, F.R. 1977. Effects of a prescribed fire in an Arizona 

ponderosa pine forest. Res. Note RM-336. Fort Collins, CO: Rocky Mountain Forest

and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 4 p.

Everett, R.L.; Schellhaas, R; Keenum, D.; Spurbeck, D.; Ohlson, P. 2000. Fire history in the 

ponderosa Pine/Douglas-fir forest on the east slope of the Washington Cascades.

Forest Ecology and Management 129: 207-225. 

Filip, G.M. 2002. Wildfire and forest health. In: Fitzgerald, S.A., editor. Fire in Oregon’s 

forests: risks, effects and treatment options. A synthesis of current issues and scientific

literature. Special Report prepared for the Oregon Forest Resources Institute, Portland, 

OR.; 28-34. 

Finch, R.B. 1984. Fire history of selected sites on the Okanogan National Forests.

Okanogan, WA.: Okanogan National Forest, Forest Service, U.S. Department of

Agriculture; 22 p.

Fitzgerald, S.A.; Emmingham, W.H.; Filip, G.M.; Oester P.T. 2000. Exploring methods for

maintaining old-growth structure in forests with a frequent fire history: a case 

study. In: Moser, W. Keith; Moser, C.F., editors. Fire and forest ecology: innovative 

silviculture and vegetation management. Tall Timbers Fire Ecology Conference

Proceedings, No. 21. Tallahassee, FL.; Tall Timbers Research Station; 199-206. 

Flint, H.R. 1925. Fire resistance of northern Rocky Mountain conifers. Idaho Forester (7):

7-10, 41-43. 

Fairbanks, F.; Hill, E.; Kelly, P; Laverty, L; Mulrooney, K.F.; Philpot, C.; Wise, C. 2002. 

Wildfire suppression: strategies for containing costs. A report by a panel of the 

National Academy of Public Adminsitrtion for the U.S. Congress and the Departments 

of Agriculture and the Interior. Washington, D.C. 65 p.

Fulé, P.Z.; Covington, W.W.; Moore, M.M. 1997. Determining reference conditions for 

ecosystem management of southwestern ponderosa pine forests. Ecological 

Applications 7(3): 895-908. 

Fulé, P.Z., C. McHugh, T.A. Heinlein, W.W. Covington. 2001. Potential fire behavior is

reduced following forest restoration treatments. In: Vance, R.K.; Edminster, C.B; 

Covington, W.W.; Black, J.A., compilers. Ponderosa pine ecosystems restoration and 

conservation: steps toward stewardship. Proceedings RMRS-P-22. Ogden, UT: Rocky 

Mountain Research Station, Forest Service, U.S. Department of Agriculture; 28-35. 

Fulé, P.Z.; Crouse, J.E.; Heinlein, T.A.; Moore, M.M.; Covington, W.W.; Verkamp ,G. 2003. 

Mixed-severity fire regime in a high elevation forest of Grand Canyon, Arizona,

USA. Landscape Ecology 18: 464-486

Graham, R.T. 2003. Hayman Fire case study. Gen. Tech. Report RMRS-GTR-114. Ogden,

UT: Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture;

396 p. 

Graham, R.T.; Harvey, A.E.; Jain, T.B.; Tonn, J.R. 1999. The effects of thinning and

similar stand treatments on fire behavior in western forests. Gen. Tech. Report

220 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

PNW-GRT-463. Portland, OR: Pacific Northwest Research Station, Forest Service, U.S.

Department of Agriculture; 27 p. 

Graham, R.T.; McCaffrey, S.; Jain, T.B. 2004. Science basis for changing forest structure

to modify wildfire behavior and severity. Gen. Tech. Report RMRS-GTR-120. Fort 

Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. Department of

Agriculture; 43 p.

Grissino-Mayer, H.D.; Romme, W.H.; Floyd, M.L.; Hanna, D.D. 2004. Climatic and human 

influences on fire regimes of the southern San Jaun Mountains, Colorado, USA. 

Ecology, 85(6): 1708-1724.

Habeck, J.R. 1985. Changes in stand structure related to fire history in ponderosa

pine/Douglas-fir forests in Pattee Canyon, Missoula County, western Montana.

Contract completion report, USDA Forest Service, Intermountain Fire Science 

Laboratory, Missoula, MT. 

Hall, F.C. 1976. Fire and vegetation in the Blue Mountains – implications for land 

managers. Tall Timbers Fire Ecology Conference Proceedings 15: 155-170.

Hall, F.C. 1980. Fire history—Blue Mountains, Oregon. In: Stokes, M.A.; Dieterich J.H., 

technical editor. Proceedings of the fire history workshop. October 20-24, 1980, Tucson,

Arizona. Gen. Tech. Report RM-81. Fort Collins, CO: Rocky Mountain Forest and

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 75-81. 

Harrington, M.G., Sackett, S.S. 1992. Past and present fire influences on southwestern

ponderosa pine old growth. In: Kaufmann, M.R.; Moir, W.H.; Bassett, R.L., editors. 

Old-growth forest in the Southwest and Rocky Mountain regions. Gen. Tech. Report

RM-213. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, U.S.

Department of Agriculture; 44-55. 

Hessburg, P.F.; Agee, J.K. 2003. An environmental narrative of Inland Northwest United

States forests, 1800-2000. Forest Ecology and Management 178: 23-59. 

Heyerdahl, E.K., Brubaker, L.G.; Agee, J.K. 2001. Spatial controls of historic fire regimes: 

A multiscale example from the interior West, USA. Ecology, 82(3): 660-678. 

Kauffman, J.B. 1990. Ecological relationships of vegetation and fire in Pacific Northwest 

forests. Pages 39-52. In: Walstad, J.D.; Radosevich, S.R.; Sandberg, D.V., editors. 

Natural and prescribed fie in Pacific Northwest forests. Oregon State University Press, 

Corvallis, OR.; 39-52.

Kaufmann, M.R.; Regan, C.M.; Brown, P.M. 2001. Heterogeneity in ponderosa

pine/Douglas-fir forests: age and size structure in unlogged and logged landscapes

of central Colorado. Canadian Journal of Forest Research, 30: 698-711. 

Keane, R.E.; Ryan, K.C.; Veblen, T.T.; Allen, C.D.; Logan, J.; Hawkes, B. 2002. Cascading 

effects of fire exclusion in Rocky Mountain ecosystems: a literature review. Gen.

Tech. Report RMRS-GTR- 91. Fort Collins, CO: Rocky Mountain Research Station,

Forest Service, U.S. Department of Agriculture; 24 p. 

Kilgore, B.M.; Taylor, D. 1979. Fire history of a sequoia-mixed conifer forest. Ecology 

60: 129-142. 

Langille, H.D.; Plummer, F.G.; Dodwell, A.; Rixon, T.F.; Leiberg, J.B. 1903. Forest

conditions in the Cascade Forest Reserve, Oregon. Professional Paper No. 9, Series

H, Forestry 6. Washington Printing Office. 208 p. 

Larson, D.S.; Mirth, R. 2004. A case study on the economics of thinning in the wildland 

urban interface. Western Journal of Applied Forestry 19(1): 60-65.

Latham, P.; Tappeiner J. 2002. Response of old-growth conifers to reduction in stand

density in western Oregon forests. Tree Physiology, 22: 137-146.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 221 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Lynch, D.L. 2004. What do forest fires really cost? Journal of Forestry 102 (6): 42-49.

Martinson, E.J.; Omni, P.N. 2003. Performance of fuel treatments subjected to wildfires.

In: Omni, P.N.; Joyce, L.A., editors. Fire, fuel treatments, and ecological restoration: 

conference proceedings. Proceedings RMRS-P-29. Fort Collins, CO: Rocky Mountain 

Research Station, Forest Service, U.S. Department of Agriculture; 7-13. 

Mason, C.L.; Lippke, B.; Zobrist, K. 2004. Investments in fuel removals to avoid forest

fires results in substantial benefits. RTI Fact Sheet No. 28. Seattle, WA: Rural 

Technology Initiative, College of Forest Resources, University of Washington; 4 p.

McDowell, N.; Brooks, J.R.; Fitzgerald, S.A.; Bond, B.J. 2003. Carbon isotope 

discrimination and growth response of old Pinus ponderosa to stand density 

reductions. Plant, Cell and Environment 26: 631-644. 

McNeil, R.C., Zobel, D.B. 1980. Vegetation and fire history of a ponderosa pine-white fir 

forest in Crater Lake National Park. Northwest Science 54: 30-46. 

Miller, M. 2000. Chapter 2: Fire Autecology. In: Brown, J.K.; Smith, J.K., editors. Wildland

fire in ecosystems: effects of fire on flora. Gen. Tech. Report RMRS-GTR-42- vol. 2.

Ogden, UT: Rocky Mountain Research Station, Forest Service, U.S. Department of 

Agriculture; 9-34. 

Moore, M.M., Huffman, D.W.; Fule, P.Z.; Covington, W.W.; Crouse, J.E. 2004. 

Comparison of historical Contemporary forest structure and composition on

permanent plots in southwestern ponderosa pine forests. Forest Science 50(2): 162-

176. 

Morrow, R.J. 1985. Age structure and spatial pattern of old-growth ponderosa pine in 

Pringle Falls Experimental Forest, central Oregon. Corvallis: Oregon State

University, 80 p. Masters of Science thesis. 

Morton, D.C.; Roessing, M.E.; Camp, A.E.; Tyrell, M.L. 2003. Assessing the

environmental, social and economic impacts of wildfire. GISF Research Paper 001. ,

New Haven, CT: Forest Health Initiative, Global Institute of Sustainable Forestry,

School of Forestry and Environmental Studies, Yale University; 54 p.

Mutch, R.W.; Arno, S.F.; Brown, J.K.; Carlson, C.E.; Ottmar, R.D.; Peterson, J.L. 1993. 

Forest Health in the Blue Mountains: A management strategy for fire-adapted 

ecosystems. Gen. Tech. Report PNW-GTR-3210. Portland, OR: Pacific Northwest

Research Station, Forest Service, U.S. Department of Agriculture; 14 p. 

Munger, T.T. 1917. Western yellow pine in Oregon. Bulletin 418. Washington, D.C.: U.S. 

Department of Agriculture; 48 p. 

Norman, S.P.; Taylor, A.H. 2003. Tropical and north Pacific teleconnections influence fire

regimes in pine-dominated forests of north-eastern California, USA. Journal of 

Biogeography, 30: 1081-1092. 

Peterson, D.L., M.C. Johnson, J.K. Agee, T.B. Jain, D. McKenzie, and E.D. Reinhardt. 2005. 

Forest structure and fire hazard in dry forest of Western United States. Gen. Tech.

Report PNW-GTR-628. USDA Forest Service, Pacific Northwest Research Station, 

Portland, OR. 30 p. 

Powell, D.C.; Rockwell, V.A.; Townsley, J.J.; Booser, J.; Bulkin, S.P; Martin, T.H.; 

Obedzinski, B.; Zensen, F. 2001. Forest density management: Recent history and 

trends for the Pacific Northwest Region. R6-NR-TM-TP-05-01. Portland, OR: Pacific

Northwest Region, Forest Service, U.S. Department of Agriculture; 21 p.

Quigley, T.M.; Haynes, R.W.; Graham, R.T. 1996. Integrated Scientific Assessment for 

ecosystem management in the interior Columbia Basin and portions of the

Klamath and Great Basins. Gen. Tech. Report PNW-GTR-382. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture.

222 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Reineke, L.H. 1933. Perfecting a stand-density index for even-aged forests. Journal of

Agricultural Research 46: 627-638. 

Rothermal, R.C.; Deeming, J.E. 1980. Measuring and interpreting fire behavior for 

correlation with fire effects. Gen. Tech. Report INT-93. Ogden, UT: Intermountain

Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 4

p. 

Sackett, S.S. 1980. Reducing natural ponderosa pine fuels using prescribed fire: two case

studies. Res. Note RM-392. Fort Collins, CO: Rocky Mountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 6 p.

Schmidt, K.M.; Menakis, J.P.; Hardy, C.C.; Hann, W.J.; Bunnell, D.L. 2002. Development of

coarse-scale spatial data for wildland fire and fuel management. Gen. Tech. Report

RMRS-87. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. 

Department of Agiculture; 41 p. 

Scott, J.H. 1998. Fuel reduction in residential and scenic forests: a comparison of three

treatments in a western Montana ponderosa pine stand. Res. Paper RMRS-RP-5.

Fort Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. Department of

Agriculture; 19 p.

Shinneman, D.J.; Baker, W.L. 1997. Nonequilibrium dynamics between catastrophic 

disturbances and old-growth forest in ponderosa pine landscapes of the Black

Hills. Conservation Biology 11: 1276-1288.

Skinner, C.N. 2002. Influence of fire on the dynamics of dead woody material in forests 

of California and southwestern Oregon. In: Laudenslayer, W.F. Jr., Shea, P.J.;

Valentine, B.E.; Weatherspoon, C.P.; Lisle, T.E., Technical Coordinators. Proceedings

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

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

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

445-454. 

Skinner, C.N., Chang, C. 1996. Fire regimes, past and present. In: Sierra Nevada

Ecosystem Project: Final report to Congress, vol. II, Assessments and scientific basis for

management options. University of California, Centers for Water and Wildland

Resources, Davis, CA; 1041-1069. 

Smith, H.Y.; Arno, S.F. 1999. Eighty-years of change in a managed ponderosa pine forest.

Gen. Tech. Report RMRS-GTR-23. Fort Collins, CO: Rocky Mountain Research 

Station, Forest Service, U.S. Department of Agriculture. 

Soeriaatmadja, R.E. 1966. Fire history of the ponderosa pine forests of the Warm Springs

Indian Reservation Oregon. Corvallis: Oregon State University, Ph.D. dissertation.

Oregon State University. 

Starker, T.J. 1934. Fire resistance in the forest. Journal of Forestry 32: 462-467.

Swetnam, T.W. 1988. Fire history and climate in the southwestern United State. In: 

Krammes, J.S., technical coordinator. Effects of fire management of southwestern 

natural resources. Proceedings of the symposium. Gen. Tech. Report RM-191. Fort 

Collins, CO: Rocky Mountain Forest and Range Experiment Station, Forest Service, 

U.S. Department of Agriculture. 

Swetnam, T.W.; Dieterich, J.H. 1985. Fire history of ponderosa pine in the Gila

Wilderness, New Mexico. Pages 390-397. In: Symposium on Wilderness Fire. Gen.

Tech. Report GTR-INT-182. Ogden, UT: Intermountain Forest and Range Experiment

Station, Forest Service, U.S. Department of Agriculture; 390-397.

Swetnam, T.W.; Baisan, C.H. 1996. Historical fire regime patterns in the southwestern 

United States since AD 1700. In: Allen, C.D., editor. Fire Effects in Southwestern

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 223 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Forests: Proceedings of the Second La Mesa Fire Symposium. Gen. Tech. Report RMGTR-286. Fort Collins, CO: Rocky Mountain Research Station, Forest Service, U.S. 

Department of Agriculture; 11-32. 

Taylor, A.H.; Skinner, C.N. 1998. Fire history and landscape dynamics in a latesuccessional reserve, Klamath Mountains, California, USA. Forest Ecology and 

Management, 111: 285-301. 

Taylor, A.H.; Skinner, C.N. 2003. Spatial patterns and controls on historical fire regimes

and forest structure in the Klamath Mountains. Ecological Applications, 13(3): 704-

719. 

Touchman, R., C.D. Allen, and T.W. Swetnam. 1996. Fire history and climatic patterns in 

ponderosa pine and mixed-conifer forests of the Jemez Mountains, northern New 

Mexico. In: Allen, C.D., editor. Fire Effects in Southwestern Forests: Proceedings of the

Second La Mesa Fire Symposium. Gen. Tech. Report RM-GTR-286. Fort Collins, CO:

Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture; 33-

46. 

U.S. General Accounting Office 1999. Western national forests: a cohesive strategy is

needed to address catastrophic wildfire threats. GAO/RCED-99-65. U.S. Printing

Office, Washington, D.C. 60 p. 

Veblen, T.T.; Kitzberger, T.; Donnegan, J. 2000. Climatic and human influences on fire 

regimes in ponderosa pine forests in the Colorado Front Range. Ecological 

Applications 10(4): 1178-1195. 

Walstad, J.D.,; Radosevich, S.R.; Sandberg, D.V. 1990. Natural and prescribed fire in the 

Pacific Northwest forests. Oregon State University Press, Corvallis, OR. 317 p. 

Weatherspoon, C.P. 1996. Fire-silviculture relationships in Sierra forests. In: Sierra

Nevada Ecosystem Project, Final Report to Congress, Volume II: Assessments and

scientific basis for management options. Water Resources Center Report No. 37. Centers 

for Water and Wildland Resources, University of California, Davis ; 1167-1176.

Weatherspoon, C.P.; Husari, S.J.; van Wagtendonk, J.W. 1992. Fire and fuels management 

in relation to owl habitat in forests of the Sierra Nevada and southern California.

In: Verner, J.; McKelvey, K.S.; Noon, B.R.; Gutierrez, R.J.; Gould, G.I. Jr.; Beck, T.W., 

Tech. Coords. The California spotted owl: a technical assessment of its current status.

Gen. Tech. Report PSW-133. Albany, CA: Pacific Southwest Research Station, Forest

Service, U.S. Department of Agriculture; 247-260.

Weaver, H. 1943. Fire as an ecological and silvicultural factor in the ponderosa pine

region of the Pacific Slope. Journal of Forestry 41(1): 7-15. 

Weaver, H. 1951. Fire as an ecological factor in the southwestern ponderosa pine forests. 

Journal of Forestry 49: 93-98. 

Weaver, H. 1959. Ecological changes in ponderosa pine forests of the Warm Springs

Indian Reservation in Oregon. Journal of Forestry 57: 15-20. 

Wickman, B.E. 1993. Forest health in the Blue Mountains: The influence of insects and 

disease. Gen. Tech. Report PNW-GTR-295. Portland, OR: Pacific Northwest Research

Station, Forest Service, U.S. Department of Agriculture; 15 p. 

Wischnofske, M.G.; Anderson, D.W. 1983. The natural role of fire in the Wenatchee

Valley. Wenatchee National Forests, Pacific Northwest Region, Forest Service, 

Wenatchee, WA; 24 p. 

Wright, C.S.; Agee, J.K. 2004. Fire and vegetation history in the eastern Cascades 

Mountains, Washington. Ecological Applications 14(2): 443-459. 

224 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Fire ecology of ponderosa pine – fire resilient ponderosa pine ecosystems -- Fitzgerald 

Youngblood, A., Max, T.; Coe, K. 2004. Stand structure in eastside old-growth ponderosa

pine forest of Oregon and northern California. Forest Ecology and Management 199:

 191-217 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 225 

Diseases as Agents of Disturbance in 

Ponderosa Pine1

Gregory M. Filip2

Abstract 

Several diseases affect the growth and survival of ponderosa pine in the Pacific Northwest

and serve as agents of disturbance. Probably the most widespread and damaging class of

disease agents is dwarf mistletoe, which causes serious growth loss and mortality of

ponderosa pine. Dwarf mistletoes (Arceuthobium spp.) are seed plants that can parasitize all 

age classes of pine. Decades of research and observation have shown that although dwarf 

mistletoes spread slowly within and among trees, their localized effects can be quite

spectacular. Root diseases caused by the fungi Armillaria ostoyae (Romagn.) Herink, 

Heterobasidion annosum (Fr.:Fr.) Bref., and Leptographium wageneri var. ponderosum

(Harrington & Cobb) Harrington & Cobb cause localized mortality resulting in gaps in

affected forests. Root diseases may spread by root contact, airborne spores, or insect vectors 

depending on the species of root disease fungi. Stem decays caused principally by Phellinus

pini (Thore.:Fr.) A. Ames and Fomitopsis officinalis (Villars:Fr.) Bond. & Sing. result in 

single-tree gaps if trees break as a result of advanced decay. Decay fungi infect wounds on 

living trees, and decay may take decades to develop to where tree structural integrity is

compromised. Stem diseases caused by rust fungi such as Cronartium comandrae Peck and 

C. coleosporiodes Arth. can kill the tops of trees or result in whole-tree mortality. Decayed

and cankered trees can serve as habitat for a wide diversity of wildlife. Disturbances in

ponderosa pine forests caused by forest diseases can affect forest succession, insect outbreaks, 

fire frequency and severity, and both animal and plant diversity. 

Introduction 

Diseases caused by fungi and parasitic plants are important fine-scale agents of

disturbance in ponderosa pine ecosystems. In the absence of periodic wildfire, the 

resulting dense stands of ponderosa pine often are attacked by several classes of 

forest diseases including root disease, stem decay, stem disease, foliage disease and

dwarf mistletoe. These diseases have a tremendous effect on the structure and

ecology of ponderosa pine stands. Root diseases increase windthrow of live trees, 

live stem breakage, top-killing, bark beetle attack, tree mortality, down wood, 

wildlife habitat, wildfire, stand opening and regeneration, and shifts in stand 

composition. Stem decays cause hollows in living stems and branches, and increase

tree mortality, amount of down wood, number of hollow logs, diversity of wildlife 

habitat, stem breakage, and intensity and incidence of wildfire. Dwarf mistletoes are

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

Regional Forest Pathologist, USDA Forest Service, Forest Health Protection, PO Box 3623, Portland,

OR 97208-3623 (email: gmfilip@fs.fed.us) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 227 
Diseases as Agents of Disturbance - Filip 

parasitic plants that infect conifers and result in increases in live-crown ratios, 

abnormal branches (witches’ brooms), dead branches, top-killing, branch and stem 

breakage, tree mortality, down wood, wildlife habitat, and intensity of wildfire. Fuel 

ladders caused by dwarf mistletoe make fires more likely to crown. These fine-scale

disturbances created by forest diseases can affect forest succession and alter both 

plant and animal diversity.

Root Diseases of Ponderosa Pine 

Major root diseases of ponderosa pine in the Pacific Northwest include 

Armillaria root disease caused by Armillaria ostoyae (Romagn.) Herink, annosum 

root rot caused by Heterobasidion annosum (Fr.:Fr.) Bref., and black-stain root

disease caused by Leptographium wageneri var. ponderosum (Harrington & Cobb)

Harrington & Cobb. Infection may result in tree growth loss, windthrow, or 

mortality. Root diseases spread primarily by root to root contact between infected

trees or between residual stumps and healthy trees. Root diseases are difficult to 

detect and require removal of soil and bark at root collars to detect signs and 

symptoms of pathogenic root-disease-causing fungi. The preferred tool for examining 

roots is often the pulaski. There is no cure for root disease. Management strategies

include prevention of infection, and favoring tree species that are less susceptible or 

immune to root diseases on the site. 

Armillaria root disease is probably the most common and damaging root disease 

of ponderosa pine in the Pacific Northwest, although pine is considered tolerant to 

Armillaria when compared to white fir (Abies concolor (Gord. & Glend.) Lindl. ex

Hildebr.) or grand fir (A. grandis (Doug. ex D. Don) Lindl.). Major mortality centers 

occur where a particularly virulent clone of the fungus is present or where pine is 

mixed with infected true firs. Some virulent clones of Armillaria are reported to be

very old and cover over 2000 acres of infected forest in northeastern Oregon 

(Ferguson and others 2003). Symptoms of Armillaria root disease include chlorotic 

and shortened leaders and lateral branches, and basal resinosus (pitching), although 

the latter symptom is less common in ponderosa pine. Signs include mycelial fans 

under the bark at the root collar and mushrooms produced at the base of infected trees 

in autumn. Armillaria management involves maintaining good tree health and vigor,

avoiding soil disturbance, and thinning of overstocked young stands. 

Annosum root rot is most damaging in ponderosa pine in southern Oregon and 

northern California, usually on low-quality sites (Schmitt and others 2000). The 

disease is associated with tree harvesting where freshly cut stumps are susceptible to

infection by windborne spores. Infection results in tree mortality or windthrow.

Stumps can be protected from annosus spore infection by treating freshly cut surfaces 

with a boron-containing product with 48 hours of cutting. There are actually two 

types of the fungus: one type infects primarily true firs (S-type) and the other infects 

primarily pine (P-type). Usually only the drier pine sites are seriously affected by 

annosum root rot. 

Black-stain root disease is most common in central and eastern Oregon and in

the Sierras of California. It spreads underground but may also be vectored long

distances by insects. More research is needed to identify the vectors and clarify their 

roles. Best management practices also are being identified, especially the use of 

prescribed fire (Filip 1999). Symptoms and signs of the disease include a basal

resinosus and a black stain in the wood that occurs only in the first few annual rings. 

228 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Diseases as Agents of Disturbance - Filip 

Black-stain root disease management may include thinning or pruning pine in August 

and September to avoid insect flights and disease spread. More research is needed to 

confirm this. There are two types of the fungus: one that infects the 2- or 3-needle 

pines and one that infects Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco). 

Clearcutting of diseased areas and a buffer may help to sanitize black stain-affected

ponderosa pine stands. Any resistant-appearing trees should be retained. Treated

areas can be regenerated immediately since the fungus dies when the trees are cut. 

Prevention strategies are especially important with black stain, since alternative

conifer species are often lacking on sites where this disease occurs. 

Stem Decay of Ponderosa Pine 

Stem decays are less serious in ponderosa pine than in other conifer species

(Filip 2001). Because of the resinous nature of pine wood, most decay-causing fungi

are not able to successfully colonize wound surfaces and deeper tissue. A few 

species, however, such as Phellinus pini (Thore.:Fr.) A. Ames, cause of red ring rot 

or white pocket rot, can infect and decay ponderosa pine. Early stages of decay result 

in reduced wood quality, and advanced decay results in cull logs and loss of 

merchantable material. Hollow logs and decayed trees, however, serve an important

role as wildlife habitat for birds and mammals. Living pines with internal decay may 

stand for centuries and provide habitat longer than dead and decayed trees (Bull and 

others 1997).

Other less common stem decays of ponderosa pine include red-brown butt rot or

velvet top fungus caused by Phaeolus schweinitzii (Fr.:Fr.) Pat., and brown trunk rot

or quinine fungus caused by Fomitopsis officinalis (Villars:Fr.) Bond. & Sing. On

sites with a high incidence of conks, management recommendations include harvest 

rotations less than 150 years and preventing bole wounds that give decay-causing 

fungi easy access for infection, while saving some decayed trees for wildlife. 

Stem Diseases of Ponderosa Pine 

Several species of fungi called rusts cause stem disease of ponderosa pine. The 

most common are western gall rust caused by Endocronartium harknessii (J. P. 

Moore) Y. Hirat., comandra blister rust caused by Cronartium comandrae Peck, and 

stalactiform blister rust caused by Cronartium coleosporiodes Arth. Unlike the wellknown and introduced white pine blister rust (Cronartium ribicola J. C. Fisch.), all of 

the ponderosa pine rusts are native. Rust diseases can cause tree growth loss, top-kill, 

and sometimes tree death. Seedlings, saplings, and mature trees can be affected. Rust 

fungi have complex life cycles that often require two hosts to complete their life 

cycle (Allen and others 1996). Western gall rust, however, does not require an 

alternate host: pine to pine spread can occur. Although more common on lodgepole 

pine (Pinus contorta Dougl. ex Loud.), galls do occur on ponderosa pine, especially 

in riparian communities. Stalactiform blister rust also is more common on lodgepole

than ponderosa pine. Alternate hosts for stalictiform blister rust include several

species of Scrophulariaceae including giant red Indian paintbrush (C. miniata

Dougl.). 

The most damaging rust disease of ponderosa pine is comandra blister rust. It 

gets its common name from its alternate hosts, bastard toadflax (Comandra 

umbellata (L.) Nutt.) and other species in the genus Comandra. The disease can kill

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Diseases as Agents of Disturbance - Filip 

seedlings, but it is most commonly seen as stem cankers on young trees or top-kill on 

older trees. The fungus will girdle the stems of trees resulting in tree mortality or topkilling. If tops are killed, the fungus will grow down the living stem and kill

branches. This is diagnostic and distinguishes top-killing by comandra blister rust 

from top-killing by bark beetles or animals. Management for stem rusts includes 

selective removal of trees with infections, favoring lightly infected trees or diseasefree trees, or pruning of infected branches. 

Foliage Diseases of Ponderosa Pine 

There are three primary diseases of ponderosa pine foliage in the Pacific 

Northwest: Elytroderma needle disease, dothistroma needle blight or red band needle

disease, and diseases caused by several species of fungi that are loosely termed pine

needle diseases. Foliage diseases of ponderosa pine are caused by fungi that cause the 

loss of 2-5-year-old needles. Infection results in some growth loss, but tree mortality

may occur if disease is severe. Infection severity is keyed to proper environmental 

conditions for the fungi and host genetics that regulate infection, colonization, and 

disease expression. Control is usually not warranted in forest settings. 

Elytroderma needle cast or blight is caused by the fungus, Elytroderma

deformans (Weir) Darker. Infection begins in the needle from windborne spores, then

progresses to the twig. Twig infection becomes perennial and results in misshapen 

and upturned branches resembling an “arthritic hand.” Infections in pine resemble

those caused by dwarf mistletoe, but branches with live mistletoe plants present are

green or yellow rather than red or brown as with Elytroderma infections. Severely

infected pines have poor form, experience some growth loss, and can be thinned to

leave alternative conifer species and pines with the least infection. 

Red band needle disease is distinguished by the red or brown banding pattern on 

infected needles rather than the whole needle being discolored. The disease is caused 

by the fungus Mycosphaerella pini Rost. in Munk. Severely infected trees have thin

crowns, and when environmental conditions are favorable for infection, the disease

can spread rapidly. Repeated infections over many years can result in tree death. 

Other pine foliage diseases are caused by several species of fungi including 

Lophodermella concolor (Dearn.) Darker, L. morbida Staley & Bynum, and 

Lophodermium pinastri (Shrad.:Fr.) Chev. These fungi periodically cause 

discoloration of 2-3-year-old needles if environmental conditions are favorable for 

infection. Some tree growth loss occurs. Off-site trees are more severely affected. 

Dwarf Mistletoe of Ponderosa Pine 

Infection by dwarf mistletoe (Arceuthobium campylopodum Engel.) is probably

the most serious disease affecting ponderosa pine in the Pacific Northwest. Dwarf

mistletoes are higher seed plants that have stems, leaves, seeds, and a root system that

colonizes branch and stemwood of living trees. Male and female plants occur with 

pollination in the spring, seed development throughout the summer, and seed 

dispersal in the fall. Seeds are explosively shot from ripe fruit and adhere to needles 

of the same tree or adjacent trees. Infection from overstory to understory trees 

commonly occurs in infested pine stands. Seeds adhere to needles and slide to the 

needle fascicle with fall rains. Seeds then germinate to produce a “penetration 

230 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Diseases as Agents of Disturbance - Filip 

wedge” that enters the bark and subsequently becomes embedded in successive layers

of xylem (Hawksworth and Wiens 1996). Once established, shoots are formed and

then seeds on female plants. The entire life cycle from twig infection to seed

production takes about five years. 

Dwarf mistletoe infection severity (DMR) is rated on a scale from 1 to 6. DMR 

1 trees have light infections only in one third of the crown, whereas DMR 6 trees

have severe infections throughout the entire crown. Tree growth is reduced 

proportional to infection severity. DMR 6 trees can experience growth impacts such

that growth is 20% of similar uninfected pine. Severe infections can cause tree 

mortality especially in sapling to pole-size understory trees. Because dwarf mistletoes 

are obligate parasites (require a living host), once the host tree has died or has been 

killed, the mistletoe also dies. 

The abnormal branches caused by dwarf mistletoe infections (witches’ brooms) 

are used by birds, owls, and mammals for hiding, roosting, and nesting. Although this 

is more common in tree species that form large, dense brooms like Douglas-fir, old

infections in ponderosa pine cause brooms that can serve as wildlife habitat. Girdling 

trees with brooms will kill the tree and prevent mistletoe spread, but the function of 

the broom as wildlife habitat ends earlier than a living tree. 

Although dwarf mistletoe is one of the more damaging diseases of ponderosa 

pine, it is one of the easiest to manage. Silvicultural techniques such as thinning,

sanitation harvesting, and clearcutting have been used for decades to remove infected

trees and reduce the spread of the parasite. In young pine, removing moderately to 

severely infected trees and creating gaps of 18 feet between residual trees have been

shown to significantly reduce spread and impact of dwarf mistletoe (Barrett and Roth 

1985, Roth and Barrett 1985). 

Summary

Several diseases affect the growth and survival of ponderosa pine in the Pacific 

Northwest and serve as agents of disturbance. These include root diseases, stem

decays, stem diseases, foliage diseases, and dwarf mistletoes. Forest diseases serve as 

fine-scale disturbance agents by causing host trees to form structures that are

infrequent in disease-free stands: dead trees, down wood, abnormal branches 

(witches’ brooms), dead branches, dead tops, and broken stems. Disease also

promotes insect attack, diversifies wildlife habitat, and increases risk of wildfire. 

References 

Allen, E. A.; Morrison, D. J.; Wallis. G. W. 1996. Common tree diseases of British 

Columbia. Victoria, BC: Pacific Forestry Centre, Natural Resources Canada/Canadian

Forest Service; 178 p. 

Barrett, J. W.; Roth, L. F. 1985. Response of dwarf mistletoe-infested ponderosa pine to 

thinning: 1. Sapling growth. Res. Paper PNW-330. Portland, OR: Pacific Northwest

Research Station, Forest Service, U.S. Department of Agriculture; 15 p. 

Bull, E. L.; Parks, C. G.; Torgersen, T. R. 1997. Trees and logs important to wildlife in the 

interior Columbia River Basin. Gen. Tech. Rep. PNW-GTR-391. Portland, OR: 

Pacific Northwest Research Station, Forest Service, U.S. Department of Agriculture; 55

p. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 231 
Diseases as Agents of Disturbance - Filip 

Ferguson, B. A.; Dreisbach, T. A.; Parks, C. G.; Filip, G. M.; Schmitt, C. L. 2003. Coarsescale population structure of pathogenic Armillaria species in a mixed-conifer 

forest in the Blue Mountains of northeast Oregon. Canadian Journal of Forest 

Research 33(4): 612-623. 

Filip, G. M. 1999. Ecology, identification, and management of forest root diseases in

Oregon. EC 1512. Corvallis, OR: Oregon State University Extension Service; 11 p.

Filip, G. M. 2001. Managing tree wounding and stem decay in Oregon forests. EC 1519. 

Corvallis, OR: Oregon State University Extension Service; 12 p.

Hawksworth, F. G.; Wiens, D. 1996. Dwarf mistletoes: biology, pathology, and

systematics. Agric. Handb. 709. Washington, DC: Forest Service, U.S. Department of

Agriculture; 410 p. 

Roth, L. F.; Barrett, J. W. 1985. Response of dwarf mistletoe-infested ponderosa pine to 

thinning: 2. Dwarf mistletoe propagation. Res. Pap. PNW-331. Portland, OR: Pacific

Northwest Research Station, Forest Service, U.S. Department of Agriculture; 20 p. 

Schmitt, C. L.; Parmeter, J. R. Jr.; Kliejunas, J. T. 2000. Annosus root disease of western 

conifers. Forest Insect and Disease Leaflet 172. Washington, DC: Forest Service, U.S.

Department of Agriculture; 9 p. 

232 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bugs in the System: Development of Tools 

to Minimize Ponderosa Pine Losses from 

Western Pine Beetle Infestations1

Christopher J. Fettig2

Abstract 

The western pine beetle, Dendroctonus brevicomis LeConte, is a major cause of ponderosa 

pine, Pinus ponderosa Dougl. Ex Laws., mortality in the western USA and particularly in

California. Under certain conditions, the beetle can aggressively attack and kill apparently

healthy trees of all ages and size classes. The average loss is substantial, and has been 

estimated at 1 billion board feet annually. The availability of pest management techniques for 

preventing and suppressing infestations is rather limited. Currently, we are conducting 

several studies on the development of chemical, silvicultural and semiochemical-based

management tactics for minimizing the negative impacts associated with D. brevicomis

infestations. This paper describes the status of four such studies. Efficacy of the insecticide 

bifenthrin for protecting individual, high-value trees, and of the anti-aggregation pheromone 

verbenone for protecting small stands, is described. In a trapping bioaasay, nine nonhost

angiosperm volatiles significantly augmented the effect of two release rates of verbenone, 

reducing trap catches to levels significantly below that of either release rate of verbenone 

alone. These results suggest that the addition of nonhost angiosperm volatiles to verbenone 

could be important for developing successful semiochemical-based management techniques

for D. brevicomis. In another study, we examined and described the effect of mechanical fuel

reduction treatments on the activity of bark beetles in ponderosa pine stands. Many of the

results presented here are preliminary in nature. 

Keywords: western pine beetle, Dendroctonus brevicomis, ponderosa pine, Pinus

ponderosa, insecticides, verbenone, nonhost angiosperm volatiles, semiochemicals, fuel 

reduction, forest health 

Introduction 

The western pine beetle (Dendroctonus brevicomis LeConte) is a major cause of 

ponderosa pine mortality in the western USA and particularly in California. Under 

certain conditions, the beetle can aggressively attack and kill apparently healthy trees 

of all ages and size classes. The total annual loss ranges from 500 million to 3.5 

billion board feet. The average loss is substantial, and has been estimated at

approximately 1 billion board feet annually (Miller and Keen 1960). Much of this 

mortality occurs within the larger diameter classes. Currently, the availability of pest

management techniques for preventing or suppressing infestations is limited to 

prevention thinning or insecticide treatments. 

Severe droughts, such as those occurring in California from 1975 to 1977 and

from 1988 to 1993, are often accompanied by excessive amounts of D. brevicomis1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18-21, 2004, Klamath Falls. 2

 Pacific Southwest Research Station, USDA Forest Service, 1107 Kennedy Place, Suite 8, Davis, CA 

95616 (email: cfettig@fs.fed.us)

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 233 
Bugs in the System—Fettig 

caused tree mortality in both managed and unmanaged stands. High-value trees, such

as those located in residential, recreational, or administrative sites, are particularly 

susceptible to attack as a result of increased amounts of stress associated with

drought, soil compaction, mechanical injury, or vandalism (Haverty and others 

1998). Regardless of landowner objectives, tree losses generally have a catastrophic

impact. For example, the value of a mountain home may be severely reduced by the

mortality of adjacent shade and ornamental trees (McGregor and Cole 1985). The

mortality of trees located in campgrounds or other administrative sites can have 

long-range management impacts. The value of these individual trees, the cost of 

removal, and the loss of aesthetics may justify protecting individual trees with

insecticides until the main thrust of an infestation subsides. This situation 

emphasizes the need for assuring that effective insecticides are available for 

individual tree protection in the future. 

Several formulations of carbaryl have been evaluated and found effective for

protection of individual trees from attack by western bark beetle species (Gibson and 

Bennet 1985, Hall and others 1982, Haverty and others 1985, Shea and McGregor 

1987). These and other studies (McCambridge 1982, Smith and others 1977) led to 

registration of 2 percent Sevimol

® for this use. In 2003, only two formulations of 

carbaryl, permethrin, and injected metasystox-R were registered for protection of 

ponderosa pine from the western pine beetle. Metasystox-R has been shown to be

rather ineffective and is not recommended for use (Haverty and others 1997). Given 

the uncertain future availability of an effective preventative spray, I believe it is 

important to develop alternative insecticides for this important forestry use. 

Verbenone (4,6,6-trimethylbicyclo[3.1.1]-hept-3-en-2-one) is the primary

antiaggregation pheromone of the mountain pine beetle (Dendroctonus ponderosae

Hopkins), southern pine beetle (Dendroctonus frontalis Zimmermann), and western

pine beetle. It was first identified in males of the southern and western pine beetles, 

and subsequently in the hindgut of emergent and feeding female mountain pine

beetles. Verbenone is naturally derived from three sources: (1) the beetles 

themselves, (2) auto-oxidation of α-pinene and subsequently of cis- and transverbenol to verbenone (Lindgren and Borden 1989), and (3) auto-oxidation from cisand trans-verbenol to verbenone by certain microorganisms that are associated with 

bark beetle species. It is assumed that verbenone reduces the negative impacts of

intraspecific competition by reducing the overcrowding of developing brood within 

the host tree. 

In recent years, verbenone has been evaluated as a tool for mitigating stand 

losses due to bark beetle infestations. In the southern USA, verbenone is used once 

an infestation (termed “spot”) has formed to reduce future spot growth (Clarke and

others 1999). In general, by placing elution devices containing synthetic verbenone 

on all freshly attacked trees and a suitable buffer of uninfested trees at the active

margin (termed “head”) of the spot, emerging and reemerging beetles are forced to

disperse in search of unoccupied hosts. Spot growth is often reduced and sometimes

completely suppressed. Verbenone is now available commercially in a slow-release 

polyethylene pouch (Phero Tech Inc., Delta, BC) that has received U. S. 

Environmental Protection Agency (EPA) registration for use in forest stands 

containing southern pines (EPA Reg. No. 56261-CN-1 (1999)).

In the western USA, efforts have concentrated on using verbenone for smallscale stand protection. Most field evaluations have concentrated on D. ponderosae

populations, and results have often been favorable. Verbenone released from multiple

234 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bugs in the System—Fettig 

points in stands of lodgepole pine significantly reduced infestation levels in some 

studies (Amman and others 1989, 1991; Lindgren and others 1989, Gibson and others 

1991, Shea and others 1992, Shore and others 1992, Lindgren and Borden 1993), but 

not others (Gibson and others 1991). In general, the application of verbenone has 

been unsuccessful in reducing the number of D. ponderosae-attacked trees in

ponderosa pine (Bentz and others 1989, Lister and others 1990, Gibson and others

1991). To my knowledge, no studies have been published on the efficacy of

verbenone for prevention or suppression of D. brevicomis infestations in ponderosa 

pine stands. 

Volatile stimuli associated with host and non-host trees are important in 

mediating behavioral responses of phytophagous insects (Visser 1986). Bark beetles 

are believed to use a combination of host kairomones and aggregation pheromones to

locate suitable host material (Borden 1985). Rejection may occur on the basis of 

absence of host cues or presence of non-host cues such as green leaf volatiles or 

angiosperm bark volatiles collectively termed nonhost angiosperm volatiles (NAVs). 

NAVs have been the focus of several recent studies which show that these 

compounds are capable of reducing aggregation in several scolytid species including 

D. frontalis, D. ponderosae, and D. pseudotsugae Hopkins (Zhang and Schylter 

2004). In general, NAVs (except conophthorin) have only been effective for reducing 

aggregation if presented as combinations of two or more volatiles. One study has 

examined the effects of NAVs on D. brevicomis attraction, but was limited in scope 

to green leaf volatiles only (Poland and others 1998). I believe the system has 

promise for prevention and suppression of D. brevicomis infestations in ponderosa 

pine stands, and merits further investigation. 

Under the National Fire Plan, the hazardous fuel treatment program has, and 

likely will, continue to increase in the future. One of the key goals of this program is 

the reduction of hazardous fuels within the wildland urban interface. In FY 2002, the 

goal was to treat 1.0 million hectares, and in consideration of the recent fire activity

throughout the West, the protection of these communities and management of

adjacent fuel loads has become paramount. At present, much of the biomass that has 

been removed is not merchantable as markets have yet to be developed for small 

dimensional timber. On many Forest Service districts in the Southwest, this material 

is chipped, and/or cut and lopped, and distributed on site. As a result increased

amounts of host material (slash), and host volatiles (slash and chips) can attract and 

concentrate bark beetles within these areas. Populations can then reach high enough 

densities to threaten adjacent, apparently healthy trees. Trees that are killed by bark

beetles after fuel reduction treatments increase fuel loads in areas not likely to be retreated for many years. Furthermore, the cost of removal, regeneration, and longterm aesthetic losses justify the development of guidelines to mitigate such losses. 

This paper describes the status of four studies conducted to develop tools for 

mitigating the amount of bark beetle-caused tree mortality in ponderosa pine stands. 

The results presented here are largely preliminary in nature. 

Methods

Insecticide study.

This study was conducted on the eastern slope of the Sierra Nevada between

1400-1700 m elevation in Lassen County, California. Four treatments (insecticides) 

were analyzed for protecting ponderosa pine from D. brevicomis-attack: bifenthrin at 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 235 
Bugs in the System—Fettig 

0.03, 0.06 and 0.12 percent AI (OnyxTM); carbaryl at 2.0 percent AI (Sevin SL®); and 

two separate untreated controls. One control group was used to assess beetle 

pressure during the first summer, and the second used to assess pressure during the 

second summer post-treatment. 

All insecticides were applied in mid-May 2003 using a trailer-mounted

hydraulic sprayer (300 psi), which allowed treatment of the entire bole of each tree, 

until runoff, to a height of >10m (Haverty and others 1983). Two tank samples were 

collected and returned to the laboratory to be analyzed for concentration and purity.

Treatments were applied between 0600 and 1100 when wind speeds are diminished. 

Test trees were located in areas with recent beetle activity and isolated from

other sample trees. Trees selected were 28 to 52cm dbh, and within 75m of an access

road to facilitate treatment. Experimental trees were separated by >160m to ensure 

that a sufficient number of beetles would be in the vicinity of each tree to rigorously 

test the efficacy of these treatments (Shea and others 1984). The surrounding cover

type was Ponderosa-Jeffrey (Yellowpine) Series. Forest composition, in order of

decreasing abundance, was ponderosa pine, Jeffrey pine, Pinus jeffreyi Grev. & Balf., 

white fir, Abies concolor (Gond. and Glend.) Hildebr., and incense-cedar, Calocedrus

decurrens Torr. 

All test trees and the first set of untreated check trees were baited with D. 

brevicomis aggregation pheromone (exo-brevicomin, frontalin, and myrcene; WPB 

Tree Bait®; Phero Tech Inc., Delta, BC) for a period of 4 weeks in August 2003. The 

surviving treated trees in each treatment (if there are no more than 7 killed by the 

bark beetle challenge), and the second set of check trees were baited again in June

2004. Untreated check trees were monitored biweekly until 60 percent exhibit signs 

of successful attack, at which time the baits were removed from all trees. 

Each treatment was randomly allocated to 35 trees (n = 210). The only criterion 

used to determine the effectiveness of the insecticide treatments was whether or not 

individual trees succumbed to attack by western pine beetle. Tree mortality was 

assessed in June 2004 (first baiting) and October 2004 (second baiting). The period 

between pheromone removal and mortality assessment was sufficient for crowns to 

"fade", an irreversible symptom of pending mortality. Treatments were considered to

have sufficient beetle pressure if >60 percent of the untreated control trees die from 

beetle attack. Insecticide treatments were considered efficacious if <7 treated trees

die as a result of bark beetle attack. These criteria were established based on a

sample size of 30-35 trees/treatment and the test of the null hypothesis, Ho:S 

(survival ≥ 90 percent). These parameters provided a conservative binomial test (α = 

0.05) to reject Ho when more than six trees die (Shea and others 1984). 

Verbenone study

This study was conducted over a 3 yr-period. The experimental design was a 

randomized complete block with two treatments (verbenone-treated and untreated) 

and six replicates (3 reps/treatment/block). Plots were 2 ha, square in shape, and

predominately (>60 percent BA) ponderosa pine. Adjacent plots were separated by

>400 m. Three replicates of each treatment were evaluated on the McCloud RD,

Shasta-Trinity National Forest, and three on the Placerville RD, Eldorado National 

Forest. 

236 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bugs in the System—Fettig 

Verbenone pouches (Phero Tech Inc., Delta, BC) were deployed twice annually

on June 1 and July 1 (2002-2004) on a grid, approximately 9.1 by 9.1 m. Individual

pouches were stapled at approximately 2 m in height on the bole of 250 trees per plot. 

Pouches from the June application were removed when the second application was 

made in July. On weekly intervals, one verbenone pouch per plot was removed, and 

stored in a deep freeze for verification of chemical purity and determination of 

release rates. Each pouch that was removed was immediately replaced with a fresh

pouch. Western pine beetle tree baits (Phero Tech Inc., Delta, BC) were placed at the 

center of each plot (verbenone-treated and untreated) to create additional beetle 

pressure and a robust examination of this treatment (Amman and others 1989). 

A 100 percent cruise was conducted pre- and post treatment on each plot in May

and August (2002-2004) for the purpose of locating bark beetle infested trees. For all 

ponderosa pine >15 cm dbh, the number of D. brevicomis-attacked and -unattacked 

trees was recorded. All trees with evidence of bark beetle activity were georeferenced by UTM coordinate. 

Nonhost angiosperm volatile study

Twenty-seven (27) 16-unit multiple-funnel traps were deployed in a ponderosa

pine forest on the McCloud RD, Shasta-Trinity NF, northern California in June 2004. 

Trap locations were separated by >20 m to avoid interference among adjacent

treatments. Traps were hung on 3-m metal poles with collection cups approximately 

1 m from the ground. A 3 x 3-cm time-released insecticidal Prozap Pest Strip (2,2-

dichlorovinyl dimethyl phosphate (DDVP), Loveland Industries Inc., Greely, CO) 

was placed in the trap cup to kill arriving insects. Each trap location was randomly

assigned one of nine treatments: 1) untreated control, 2) frontalin, exo-brevicomin, 

myrcene (WPB bait), 3) verbenone (4 mg/24h) + WPB bait, 4) (E)-2-hexen-1-ol , 

(E)-2-hexenal, (Z)-2-hexen-1-ol (GLV) + WPB bait, 5) GLV + verbenone + WPB 

bait, 6) benzyl alcohol, benzaldehyde, conopthorin, guaiacol, nonanal, 

salicylaldehyde (BV) + WPB bait, 7) BV + verbenone + WPB bait, 8) (E)-2-hexen-1-

ol , (E)-2-hexenal, (Z)-2-hexen-1-ol + benzyl alcohol, benzaldehyde, conopthorin,

guaiacol, nonanal, salicylaldehyde (NAV) + WPB bait, and 9) NAV + verbenone + 

WPB bait (Table 1). Treatment locations (trap and treatments) were re-randomized

daily for 10 consecutive days. 

Specimens were tallied, sexed, and identified using available keys (Wood 1982) 

and voucher specimens. The experimental design was completely randomized with 

nine treatments and 30 replicates per treatment. A test of normality was performed, 

and appropriate transformations were used when the data deviated significantly from 

a normal distribution. We performed a one-way analysis of variance on the pooled

data (exclusive of the untreated control) collected from each trap using α=0.05 

(SigmaStat Version 2.0, SPSS Inc.), and Tukey’s HSD for separation of treatment 

means. 

A second experiment was conducted in August 2004 using similar protocols.

Each trap location was randomly assigned one of 12 treatments: 1) untreated control, 

2) WPB bait, 3) verbenone (4mg/24h) + WPB bait, 4) verbenone (50mg/24h) + WPB 

bait, 5) NAV+C + Verb4 + WPB bait, 6) NAV+C + Verb50 + WPB bait, 7) NAV-C 

+ Verb4 + WPB bait, 8) NAV-C + Verb50 + WPB bait, 9) ALD + Verb4 + WPB 

bait, 10) ALD + Verb50 + WPB bait, 11) ALC + Verb4 + WPB bait and 12) ALC + 

Verb50 + WPB bait (NAV+C includes conophthorin; NAV-C excludes 

conophthorin; ALD (aldehydes); ALC (alcohols)). The NAV alcohols were benzyl

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 237 
Bugs in the System—Fettig 

alcohol, guaiacol, (E)-2-hexen-1-ol, and (Z)-2-hexen-1-ol, and aldehydes were

benzaldehyde, nonanal, salicylaldehyde, (E)-2-hexenal. The experimental design 

was completely randomized with 12 treatments and 30 replicates per treatment. 

Thirty-six (36) 16-unit multiple-funnel traps were used in this experiment.

Table 1— Nonhost angiosperm volatiles used in Experiments 1 and 2. 

Volatile Source Release Device Release (mg/24h) 

benzyl alcohol Fischer Scientific Phero Tech bubblecap 1.3 (20 °C) 

benzylaldehyde Fischer Scientific Phero Tech flexlure 3.5 (20 °C) 

conophthorin Phero Tech 0.4 ml polyethylene vial 3.0 (28 °C) 

guaiacol Sigma Aldrich Phero Tech bubblecap 5.0 (20 °C) 

nonanal Sigma Aldrich Phero Tech flexlure 3.5 (20 °C) 

(E)-2-hexenal Bedoukian Research Phero Tech bubblecap 3.5 (20 °C) 

(E)-2-hexen-1-ol Bedoukian Research Phero Tech bubblecap 3.8 (20 °C) 

(Z)-2-hexen-1-ol Bedoukian Research Phero Tech bubblecap 3.8 (20 °C) 

salicylaldehyde Sigma Aldrich Phero Tech bubblecap 5.0 (20 °C) 

verbenone Phero Tech Phero Tech pouch 50.0 (30 °C)

frontalin

exo-brevicomin 

myrcene 

Phero Tech 250μL Eppendorf vial

250μL Eppendorf vial

1.8 mL X 2 Eppendorf

3.0 (24 °C) 

3.0 (24 °C) 

18.0 (24 °C)

Hazardous fuel reduction study

This study was conducted over a period of two years at three locations, and was 

not limited in scope to D. brevicomis as in the previous three studies. The

experimental design was a randomized complete block with three blocks, six

treatments, and 2 replicates/treatment/block. Blocking occurred on the basis of 

location. Plots were 0.4 ha, square in shape, and predominately (> 60 percent BA) 

ponderosa pine. Adjacent plots were separated by >100 m. Two replicates of each

treatment were evaluated on the Tahoe National Forest, CA, Kaibab National Forest,

AZ, and Prescott National Forest, AZ. 

The following treatments were evaluated: 

1) May chips, randomly dispersed within plot 

2) May chips, raked 2 m from the root collar of all live residual trees 

3) August chips, randomly dispersed within plot 

4) August chips, raked 2 m from root collar of all live residual trees 

5) May slash, scattered according to standard practices 

6) August slash, scattered according to standard practices 

7) Untreated control 

238 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bugs in the System—Fettig 

A 100 percent cruise was conducted on each plot in 2003 and 2004 for the 

purpose of locating all bark beetle infested trees. For all pines >22.8 cm dbh, the 

number of bark beetle-attacked trees was recorded. Any tree containing successful 

bark beetle attacks was tagged, and the species and dbh were recorded. The primary 

variable of interest is the number of bark beetle-attacked trees occurring per unit area

during the two-year period. 

Results and Discussion 

Insecticide study

A rigorous examination of the insecticide treatments occurred during the first 

baiting period as 22 of 35 untreated trees were killed by D. brevicomis attacks. This

mortality rate exceeded the criterion established for a viable experiment (60 percent

or 21 trees). Only the 0.03 percent AI bifenthrin treatment failed to meet the criterion 

for efficacy (12/34). The remaining treatments, specifically 0.06 percent AI

bifenthrin (0/31), 0.12 percent AI bifenthrin (0/29), and 2.0 percent AI carbaryl

(1/34), were effective for protecting ponderosa pine from D. brevicomis attacks

during the first field season. Investigations are continuing to determine if efficacy 

remains during the second field season. This study has led to the registration and 

recommendation of 0.06 percent AI OnyxTM as a preventative spray. 

Verbenone Study

No significant differences were observed between the number of D. brevicomiskilled trees in untreated and verbenone-treated plots, respectively (P = 0.84). In

2002, (mean ± sem) 6.8 ± 2.6 and 9.0 ± 3.3 trees were killed in untreated and 

verbenone-treated plots, respectively (P = 0.84). In 2003, 7.8 ± 2.7 and 4.8 ± 1.2

were killed in untreated and verbenone-treated plots, respectively (P = 0.33).

Analysis of the 2004 data is currently ongoing and not available at this time. At 

present, we must conclude that the high release rate of verbenone (50 mg/24h)

examined here, which represents a 6X increase over conventional release devices,

does not increase the efficacy of this treatment for prevention and suppression of D. 

brevicomis infestations in ponderosa pine. 

Analysis of the 2003 data from Placerville as a separate, completely randomized 

design results in a significant treatment effect (P = 0.07). In fact, 2X more mortality 

occurred on untreated plots than verbenone-treated plots. These data support our 

initial hypothesis that efficacy will likely vary with differences in stand structure, 

composition and topographic features. Forest conditions which include mixed stands 

of susceptible and non-susceptible species (such as Sierra-mixed conifer), increased

crown cover, and vertical stratification will likely result in higher efficacy. 

Nonhost angiosperm volatile study

In Experiment 1, there was no significant interaction between treatment and the 

gender of D. brevicomis (F 7, 464 = 0.52; P = 0.82). A significant treatment effect was

observed (F 7, 232 = 9.35; P < 0.001; Fig. 1), and no significant departures from 

residual normality or equal variance were apparent. Significantly more female than 

male D. brevicomis were collected (paired T-test, P < 0.001). The ratio of males to

females was 0.52. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 239 
Bugs in the System—Fettig 

Figure 1—Disruption of western pine beetle, Dendroctonus brevicomis LeConte,

attraction to baited (frontalin, exo-brevicomin, and myrcene) multiple-funnel traps 

during Experiment 1, McCloud Flats, Shasta-Trinity National Forest, California, June 

2004. Means followed by the same letter are not statistically different (P > 0.05; 

Tukey’s HSD (Honest Significant Difference) for means separation). 

Based on these results, we chose to conduct a second experiment to determine: 

1) if the NAV signal was overwhelmed by higher release rates of verbenone, 2) if

components from the NAV blend could be removed without significantly affecting 

efficacy, and 3) if differences exist in the response of D. brevicomis to the alcohols

and aldehydes in the NAV blend. 

The results from Experiment 2 suggest that conophthorin can be excluded from

the NAV blend without suffering a reduction in efficacy. This result disagrees with

observations by other authors regarding the response of congenerics to NAV blends 

(Fig. 2; Zhang and Schlyter 2004). This observation is extremely important in that 

conophthorin is difficult to procure and is rather costly compared to the other NAVs. 

Future studies are planned to determine the effects of these treatments for protecting 

individual trees. 

Hazardous fuel reduction study

The following results pertain to the Tahoe block specifically. Several bark

beetle species appeared to be preferentially attracted to chipped sites. Most notable

were the red turpentine beetle, D. valens LeConte, D. brevicomis, and Ips

paraconfusus Lanier. Bark beetle activity was greater in chipped plots (19 percent of

residual stems) than chipped and raked plots (12 percent). This was particularly

evident in regard to the spring treatments where we observed a 48 percent reduction 

in tree mortality associated with raking the chips away from the base of residual 

trees. There was relatively little subsequent bark beetle activity in lop and scatter

(3.5 percent) and untreated control (4 percent) plots. Most of the attacks in the 

untreated control were confined to rust-infested sugar pine, P. lambertiana Dougl.

c c

bc 

bc 

bc

bc

b b

ab 

ab 

ab 

ab

ab

ab

a a

Mean trap catch + 1 S.E. 

♂ ♀

60 40 20 0 20 40 60 80 100 120 140

WPB bait alone 

WPB + Lo Verb + NAV 

WPB + Lo Verb + GLV 

WPB + Lo Verb + BV

WPB + Lo Verb

WPB + NAV 

WPB + BV 

WPB + GLV 

Unbaited 

240 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bugs in the System—Fettig 

Our preliminary results suggest that chipping may result in unacceptable levels of 

tree mortality in the Sierra Nevada, particularly when associated with hazardous fuel

reduction treatments in the wildland urban interface. 

Figure 2—Disruption of western pine beetle, Dendroctonus brevicomis LeConte, 

attraction to baited (frontalin, exo-brevicomin, and myrcene) multiple-funnel traps 

during Experiment 2, McCloud Flats, Shasta-Trinity National Forest, California,

August 2004. Final statistical analyses are not yet available. 

Summary

This paper discusses four studies associated with the development of tools to 

reduce undesirable levels of tree mortality. At present, management options are 

rather limited in this regard. It is our hope that continued development and

refinement of these techniques will eventually result in useful products for 

minimizing ponderosa pine losses from western pine beetle infestations. 

Acknowledgments

I thank Robert R. Borys, Christopher Dabney, Stephen R. McKelvey, and L.

Maria Patterson (Pacific Southwest Research Station) for technical assistance. My

collaborators, Michael I. Haverty, Dezene Huber, Steven J. Seybold, Patrick J. Shea

(Pacific Southwest Research Station), Joel McMillin and Sheri L. Smith (Forest 

Health Protection) provided valuable insight. Bayer Inc., FMC Corp., Fruit Grower’s 

Supply Co., Univar Inc., and Sierra Pacific Industries provided valuable resources.

These studies would not have been possible without the help of the Eldorado, Lassen, 

Shasta-Trinity and Tahoe National Forests, California. 

60 40 20 0 20 40 60 80 100 120

♂ ♀

Unbaited 

WPB + NAV – C + Hi Verb 

WPB + NAV + C + Hi Verb 

WPB + NAV + C + Lo Verb 

WPB + NAV – C + Lo Verb 

WPB + ALC + Hi Verb 

WPB + ALC + Lo Verb 

WPB + ALD + Lo Verb 

WPB + ALD + Hi Verb 

WPB + Hi Verb

WPB + Lo Verb

WPB bait alone 

Mean trap catch + SEM

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 241 
Bugs in the System—Fettig 

References 

Amman, G.D.; Thier, R.W.; McGregor, M.D.; Schmitz, R.F. 1989. Efficacy of verbenone

in reducing lodgepole pine mortality by mountain pine beetles in Idaho. Canadian

Journal of Forest Research 19: 60-62.

Amman, G.D.; Thier, R.W.; Weatherby, J.C.; Rasmussen, L.A.; Munson, A.S. 1991.

Optimum dosage of verbenone to reduce infestation of mountain pine beetle in 

lodgepole pine stands of central Idaho. Research Paper INT-RP-446. Ogden, UT: 

Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of 

Agiculture; 5 p. 

Bentz, B.; Lister, C.K.; Schmid, J.M.; Mata, S.A.; Rasmussen, L.A.; Haneman, H. 1989.

Does verbenone reduce mountain pine beetle attacks in susceptible stands of 

ponderosa pine? Research Note RM-RN-495. Fort Collins, CO: Rocky Mountain

Research Station, Forest Service, U.S. Department of Agriculture; 4 p. 

Borden, J.H. 1985. Antiaggregation pheromones. In: Kerkeu, G. A.; Gilbert, L.I., editors. 

Comprehensive insect physiology, biochemistry and pharmacology, Vol. 9. Pergamon 

Press, Oxford, UK; 275-285. 

Clarke, S.R.; Salom, S.M.; Billings, R.F.; Berisford, C.W.; Upton, W.W.; McClellan, Q.C.;

Dalusky, M.J. 1999. A scentsible approach to controlling southern pine beetles –

two new tactics using verbenone. Southern Journal of Applied Forestry 97: 26-31. 

Gibson, K.E.; Bennett, D.D. 1985. Effectiveness of carbaryl in preventing attacks on 

lodgepole pine by the mountain pine beetle. Journal of Forestry 83: 109-112. 

Gibson, K.E.; Schmitz, R.F.; Amman, G.D.; Oakes, R.D. 1991. Mountain pine beetle

response to different verbenone dosages in pine stands of western Montana.

Research Paper INT-RP-444. Ogden, UT: Intermountain Forest and Range Experiment

Station, Forest Service, U.S. Department of Agriculture; 11 p. 

Hall, R.W.; Shea, P.J.; Haverty, M.I. 1982. Effectiveness of carbaryl and chlorpyriphos

for protecting ponderosa pine trees from attack by western pine beetle (Coleoptera: 

Scolytidae). Journal of Economic Entomology 75: 504-508. 

Haverty, M.I.; Shea, P.J.; Hall, R.W. 1985. Effective residual life of carbaryl for 

protecting ponderosa pine from attack by the western pine beetle (Coleoptera:

Scolytidae). Journal of Economic Entomology 78: 197-199. 

Haverty, M.I.; Shea, P.J.; Wenz, J.M. 1997. Metasystox-R, applied in Mauget injectors,

ineffective in protecting individual ponderosa pine from western pine beetles.

Research Note PSW-RN-420. Albany, CA: Pacific Southwest Research Station, Forest

Service, U.S. Department of Agriculture; 7 p. 

Haverty, M.I., Page, M.; Shea, P.J.; Hoy, J.B.; Hall, R.W. 1983. Drift and worker exposure 

resulting from two methods of applying insecticides to pine bark. Bulletin of 

Environmental Contamination Toxicology 30: 223-228. 

Haverty, M.I.; Shea, P.J.; Hoffman, J.T.; Wenz, J.M; Gibson, K.E. 1998. Effectiveness of 

esfenvalerate, cyfluthrin, and carbaryl in protecting individual lodgepole pines and 

ponderosa pines from attack by Dendroctonus spp. Research Paper PSW-RP-237. 

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

Agriculture; 12 p.

Lindgren, B.S.; Borden, J.H. 1989. Semiochemicals of the mountain pine beetle

(Dendroctonus ponderosae Hopkins). In Proceedings: Symposium on the management 

of lodgepole pine to minimize losses to the mountain pine beetle. Gen. Tech. Rep. INTGTR-262. Ogdan, UT: Intermountain Forest and Range Experiment Station, Forest

Service, U.S. Department of Agriculture; 83-89. 

242 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Bugs in the System—Fettig 

Lindgren, B.S.; Borden, J.H. 1993. Displacement and aggregation of mountain pine 

beetle, Dendroctonus ponderosae (Coleoptera: Scolytidae), in response to their

antiaggregation and aggregation pheromones. Canadian Journal of Forest Research 

23: 286-290. 

Lindgren, B.S.; Borden, J.H.; Cushon, G.H.; Chong, L.J.; Higgins, C.J. 1989. Reduction of

mountain pine beetle (Coleoptera: Scolytidae) attacks by verbenone in lodgepole

pine stands in British Columbia. Canadian Journal of Forest Research. 19: 65-68. 

Lister, C.K.; Schmid, J.M.; Mata, S.A.; Haneman, D.; O’Niel, C.; Pasek, J.; Sower, L. 1990. 

Verbenone bubble caps ineffective as a preventative strategy against mountain pine

beetle attacks in ponderosa pine. Research Note RM-RN-501. Fort Collins, CO:

Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture; 3 p.

McCambridge, W.F. 1982. Field tests of insecticides to protect ponderosa pine from the

mountain pine beetle (Coleoptera: Scolytidae). Journal of Economic Entomology 75:

1080-1082. 

McGregor, M.D.; Cole, W.E. 1985. Integrating management strategies for the mountain

pine beetle with multiple resource management of lodgepole pine forests. Gen.

Tech. Rep. INT-GTR-174, Ogden, UT: Intermountain Forest and Range Experiment

Station, Forest Service, U.S. Department of Agriculture; 68 p. 

Miller, J.M.; Keen, F.P. 1960. Biology and control of the western pine beetle. Misc. Publ. 

800. Washington, DC: Forest Service, U.S. Department of Agriculture 381 p. 

Poland, T.M; Borden, J.H.; Stock, A.J.; Chong, L.J. 1998. Green leaf volatiles disrupt 

responses by the spruce beetle, Dendroctonus rufipennis, and the western pine 

beetle, Dendroctonus brevicomis (Coleoptera: Scolytidae) to attractant-baited traps.

Journal of the Entomological Society of British Columbia 95: 17-24. 

Shea, P.J.; McGregor, M.D. 1987. A new formulation and reduced rates of carbaryl for

protecting lodgepole pine from mountain pine beetle attack. Western Journal of

Applied Forestry 2: 114-116. 

Shea, P.J.; Haverty, M.I.; Hall, R.W. 1984. Effectiveness of fenitrothion and permethrin 

for protecting ponderosa pine from attack by western pine beetle. Journal of the

Georgia Entomological Society 19: 427-433.

Shea, P.J.; McGregor, M.D.; Daterman, G.D. 1992. Aerial application of verbenone

reduces attack of lodgepole pine by mountain pine beetle. Canadian Journal of Forest

Research 22: 436-441.

Shore, T.L.; Safranyik, L.; Lindgren, B.S. 1992. The response of mountain pine beetle

(Dendroctonus ponderosae) to lodgepole pine trees baited with verbenone and exobrevicomin. Journal of Chemical Ecology 18: 533-541. 

Smith, R.H.; Trostle, G.C.; McCambridge, W.F. 1977. Protective spray tests on three 

species of bark beetles in the western United States. Journal of Economic 

Entomology 70: 119-125. 

Visser, J.H. 1986. Host odor perception in phytophagous insects. Annual Review of

Entomology. 31: 121-144. 

Wood, S.L. 1982. The bark and ambrosia beetles of North and Central America 

(Coleoptera: Scolytidae), a taxonomic monograph. Great Basin Naturalist Memoirs. 

No. 6 

Zhang, Q.H.; Schlyter, F. 2004. Olfactory recognition and behavioural avoidance of

angiosperm nonhost volatiles by conifer-inhabiting bark beetles. Agricultural and

Forest Entomology 6: 1-19.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 243 

Reintroducing Fire Into the Blacks 

Mountain Research Natural Area: Effects on 

Fire Hazard1

Carl N. Skinner2 

Abstract 

Frequent, low-intensity, surface fires were an integral ecological process in the Blacks

Mountain Experimental Forest (BMEF) prior to the 20th Century. With rare exception, fires

have been successfully excluded from BMEF since the early 1900s. The Blacks Mountain 

Research Natural Area (BMRNA) covers approximately 521 acres of BMEF in 5

compartments of approximately 100 acres each. With the help of the Lassen National Forest, 

we have begun to reintroduce fire to BMRNA using prescribed fire. Two compartments have

been burned – one in fall of 1997, the other in fall of 2000. Stand conditions and responses 

are being compared to two compartments where fire has continued to be excluded. The fifth 

compartment – mostly meadow – is not being studied at this time. Although fire hazard 

reduction was not a primary goal of this project, the usefulness of prescribed fire treatments 

for fire behavior modification is of interest to many. This paper compares the ability of the 

prescribed fire to alter wildfire behavior through computer simulation of expected wildfire

behavior and effects for treated and untreated stands. Though the application of prescribed

fire initially reduced expected fire behavior, expected fire behavior was again quite high

within a few years (~ 4-6 yrs). This is due to ensuing accumulation of dead fuel from the

many small trees killed in the initial burns and the inability of prescribed fire to sufficiently

thin the stands for a more lasting effect. We estimate it may take up to three applications of 

prescribed fire to achieve a level of fire behavior modification that is similar to a single

application of mechanical treatment followed by a single prescribed fire.

Key words: Cascade Range, fire effects, ponderosa pine, prescribed fire, research natural

areas, white fir

Introduction 

Frequent, low-intensity, surface fires were originally an integral ecological

process in the development of relatively open ponderosa pine (Pinus ponderosa

Laws.) and Jeffrey pine (P. jeffreyi Grev. & Balf.) dominated forests of northeastern

California (nomenclature follows Hickman 1993). The frequency of fire occurrence 

varied with the spatial scale of interest. For sites < 100 acres, mean fire intervals 

varied from ~5 to 17 years (Taylor 2000; Norman 2002). In contrast, years of 

widespread fires (10,000+ acres) across broad landscapes occurred with a median fire

interval of 20.5 years (range 7-49) (Norman 2002). 

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends, and Management, October 18-21, 2004, Klamath Falls, Oregon. 2

Geographer and Science Team Leader, USDA Forest Service, Pacific Southwest Research Station,

Silviculture Laboratory, 3644 Avtech Parkway, Redding CA 96002, (email: cskinner@fs.fed.us) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 245 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

The introduction of sheep grazing in the 1800s, followed by fire suppression and 

other forest management activities in the 20th Century (Taylor 2000; Norman 2002), 

led to great changes in the structure of ponderosa pine forests of northeastern 

California, similar to that described for other forests throughout the western USA 

(Agee 1993; Taylor 2000; Norman 2002; Youngblood and others 2004). Higher 

stocking densities and increased fuel accumulations have led to conditions that more 

readily support high-intensity fires than is likely to have been the case historically

(Dolph and others 1995; Taylor 2000; Norman 2002; Youngblood and others 2004). 

Reduced stand density and reduced surface fuel loads often are required to

enhance forest sustainability and ecological function, and to lower the likelihood of 

large, high-intensity wildfires (Weatherspoon and Skinner 1996). Within wilderness 

areas, many parks, and other natural areas intended to be managed primarily for 

natural processes, the tools for achieving these objectives over large areas are largely 

limited to using prescribed fire – either human or lightning ignited. However, after

nearly a century of increasing stand densities and surface fuel loads, reintroducing 

fire to large areas will not be easy nor will it likely mimic the historical fires that 

burned in more open stands with lighter fuel loads. 

Published simulation exercises have suggested that prescribed fire should be

effective at reducing fire hazard (potential for high-intensity wildfire) immediately

following treatment (van Wagtendonk 1996; Stephens 1998). This reduction in fire 

hazard is primarily due to the reduced surface fuels – needles and small woody 

material. There have been few studies on the effectiveness of using prescribed fire

alone to achieve more lasting fire hazard reduction (e.g., Fulé and others 2002;

Fernandes and Botelho 2003). The length of years of effective fire hazard reduction 

will depend not only upon the longevity of reduction in surface fuels, but also on the 

degree to which stand density and canopy conditions have been modified. These 

studies indicate that the care with which prescribed fire must be applied following the 

many years without fire makes it difficult to both restore historical structure and 

reduce fire hazard in an initial application of prescribed fire. 

The Blacks Mountain Research Natural Area (BMRNA), within the Blacks 

Mountain Experimental Forest (BMEF) in the Cascade Range of northeastern

California was set aside to study natural processes in interior ponderosa pine

dominated forests (Cheng 2004). The team of scientists that designed the Blacks

Mountain Interdisciplinary Ecological Research Project included four compartments 

of the BMRNA to study the reintroduction of fire to a forest that had experienced 

many decades of fire suppression and accompanying ecological changes (Oliver 

2001). The goal of treatments in the BMRNA is to achieve a more open stand

condition, dominated by larger trees, where most of the larger trees would survive 

fires burning under typical summer conditions. The team reasoned that the existing 

stand density and surface fuel loads would require that fire be reintroduced in stages

– at least two, and likely three, applications of prescribed fire – before desired

conditions were likely to be achieved. Attempting to achieve desired conditions more 

quickly would likely result in excessive damage to the surviving stands. 

The intent of this paper is to describe the changes in stand density and simulate

the effects on fire hazard resulting from the first application of prescribed fire in the

BMRNA. Additionally, the logic for selection of appropriate fuel models to describe 

expected fire behavior under the different stand conditions is described. 

246 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

Methods

Study Area 

The Blacks Mountain Research Natural Area is made up of five disjunct

compartments of approximately 100-125 acres (40-51 ha) each within the Blacks 

Mountain Experimental Forest and covers a total of 521 acres (211 ha). These 

compartments were set aside to receive no management manipulation shortly after

the BMEF was established in 1934 and were later included in the U.S. Forest 

Service’s Research Natural Area Program (Cheng 2004). 

Elevation varies from 5600 to 6400 ft (~1700-1950 m). The topography is a

gentle volcanic landscape with mostly shallow soils overlaying basalt. There are no 

perennial streams due to rapid percolation of runoff into the porous soils. Average

annual precipitation is 22.55 inches (573 mm), most of which falls as snow in winter. 

Infrequent thunderstorms occur in summer. Temperatures range from – 15 to 85 o

F 

(0.6-29.4 o

C). The lower elevation compartments (A, C, and E) are mostly ponderosa

and Jeffrey pine stands. Compartments B and D at higher elevation have stands 

dominated by ponderosa and Jeffrey pine in association with white fir (Abies 

concolor [Gordon & Glend.] Lindley) and incense-cedar (Calocedrus decurrens

[Torrey] Florin) (Cheng 2004). 

The four mostly forested compartments of the BMRNA were selected for this

study – A, B, C, and D. Compartment E was not included as it is mostly meadow.

Compartments B and C were randomly selected for reintroduction of fire through the

periodic use of prescribed fire. Initial burns were conducted in 1997 (C) and 2000 

(B). Compartments A and D will not be purposely burned and will serve as long-term 

control comparisons to the two burned compartments. 

Data Collection 

Canopy Fuels 

Data to describe stand structural conditions were collected on nested, fixed-area 

plots centered on the established grid points. As part of the Blacks Mountain

Ecological Research Project, the PSW Redding Lab has established a permanently 

monumented 328 x 328 ft (100 x 100 m) grid in each of the four forested

compartments to facilitate interdisciplinary study of spatial relationships of a variety 

of environmental variables (Oliver 2000). Live trees and snags > 11.5 inches (29.2

cm) dbh were measured on .2-acre (.08 ha) plots. Trees 3.5 to 11.5 inches (8.9-29.2 

cm) dbh were measured on .05 acre (.02 ha) plots while seedlings (>.5" [1.3 cm] base 

and <4.5' [1.37 m] high) and saplings (<3.5" [8.9 cm] dbh and >4.5' [1.37 cm] high) 

were tallied on .01 acre (.004 ha) plots (Oliver 2000).

Pre-treatment data were collected in all four compartments to describe existing 

stand conditions. Following application of prescribed fire in B and C, data were again 

collected at the same grid points at post-fire year 1 (both B and C) and post-fire year 

5 (C only). 

Tree height and height to crown base data were not collected in the pretreatment measurements in the BMRNA compartments. Therefore, these values were

estimated by regressing height and height to crown base on diameter using data

collected from compartments A and D that were not burned. Regressions were run

for ponderosa/Jeffrey pine combined, incense-cedar, and white fir. Tree heights were 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 247 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

constrained so that no individual live tree was estimated to be higher at pre-treatment

than it was measured to be post-treatment. 

Surface Fuels

The fuel inventory to describe the <3” diameter surface woody fuel conditions

for fire behavior simulation has not yet been completed for the BMRNA 

compartments. For this paper, surface fuels were estimated by comparing fuel

conditions in the compartments to available photo series (Maxwell and Ward 1980;

Blonski and Schramel 1981) and then subjectively selecting an appropriate standard 

fire behavior fuel model (Anderson 1982; Rothermel 1983). Although there was 

variation in the fuel conditions within and between compartments, fire behavior fuel 

model 10 (Anderson 1982; Rothermel 1983) appeared to be the best fit in all four

compartments for estimating pre-treatment fire behavior. 

Biomass equations supplied by Powers (unpublished data at PSW Silviculture

Lab, Redding, CA) were used to estimate the amount of fuel that has been added to 

the surface fuels from the trees killed by prescribed fire and had fallen by the 5th year 

post-fire measurement in compartment C. 

Data Analysis 

Canopy fuel conditions were estimated using program FUELCALC (Reinhardt 

2004). FUELCALC uses the tree data by plot for each stand and calculates several

variables necessary for estimating crown fire potential and behavior. Output includes 

the following variables: canopy bulk density (CBD, lbs/ft3

), plot averaged canopy base 

height (CBH, ft), plot averaged stand height (SH, ft)2

, total canopy fuel weight (TFW,

tons/acre), plot canopy cover (COV, percent), plot basal area of trees (BA, ft2

/acre),

and trees per unit area (TPA, trees/acre). The 25th percentile of canopy base height 

was used for predicting passive crown-fire behavior (e.g., Fulé and others 2001). 

Fire weather and fuel moisture conditions that existed during a recent wildfire at 

BMEF were used in the fire behavior simulation. Though it did not burn within the 

RNA compartments, the Cone Fire burned nearly 2000 acres of BMEF in September 

of 2002. Fire weather conditions during this fire were as follows, 1-hour fuel

moisture (%) = 1, 10-hour fuel moisture (%) = 2, 100-hour fuel moisture (%) = 2,

wind speed = 15 mph (range 9 – 20) (USDA Forest Service 2002). A wind reduction

factor of 0.3 was used to reduce the 20 ft (6.1 m) measured wind speed to mid-flame 

wind speed to account for the influence of stand structure and canopy on wind. 

Canopy foliage moisture content was estimated to be 75% since the Cone Fire burned

under dry, north wind conditions following the long, dry summer of the area. 

Fire behavior was simulated using the spreadsheet program NEXUS (Scott

1999). NEXUS quantifies fire hazard by coupling existing models of surface and

crown fire behavior to simulate overall fire spread and intensity as described by 

(Scott and Reinhardt 2001). For this study, the NEXUS estimates of Fire Type

(surface fire, passive crown fire, active crown fire), Crown Percent Burned, Rate of

Spread (ROS, chains/hour), Heat/Unit Area (btu/ft

2

), Flame Length (ft), Scorch

Height (ft), Torching Index (wind speed when torching begins), and Crowning Index 

(wind speed when active crown fire begins) were used for comparing pre- and posttreatment fire behavior. Fig. 1 shows the general steps used in providing data to

NEXUS to generate the estimated fire behavior parameters. 

2

 Stand height is the average height of the five tallest trees on each plot (Scott and Reinhardt

2005). 

248 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

Figure 1— Steps used to provide data to NEXUS to estimate fire behavior.

Pre-treatment predictions of fire behavior were made for all four compartments. 

Post-treatment predictions of fire behavior were made for the first year following 

treatment for both of the treated compartments. Because the years of treatments were

staggered, the Cone Fire occurred in the second year following treatment for 

compartment B and the fifth year following treatment for compartment C. Therefore, 

to estimate potential fire behavior had the Cone Fire been able to burn into the two

treated compartments, fire behavior was predicted for the second year following

treatment in compartment B and the fifth year following treatment in compartment C. 

Results 

Pre-treatment Stand Conditions

After many decades without fire, all four compartments had developed relatively 

dense stands with considerable accumulations of duff and litter (table 1, fig. 2). The 

median (25th - 75th percentile) density (trees/acre)[trees/hectare] of seedlings and 

saplings (<3.5” dbh [8.9 cm]) in each compartment were: A=1,050 (625-1,675) [2595 

(1544-4139)], B=1,100 (600-1,800) [2718 (1483-4448)], C=750(450-1225) [1853 

(1112-3027)], and D=1,150 (725-2,075) [2842 (1792-5127)].

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 249 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

Table 1— Pre-treatment median (25th -75th percentile) values of plot-level characteristics for 

trees >3.5” DBH for the Blacks Mountain Experimental Forest RNA compartments. 

Compartment A B C D

Trees/Acre 269.9

(126.2-542.9)

439.9 

(280.0-715.0)

312.4 

(192.6-472.7)

497.4 

(196.3-612.3)

Basal Area (ft2) / 

Acre 

140.3 

(113.6-177.2)

160.0 

(126.5-202.7)

138.6 

(117.9-178.4)

158.5 

(134.12-612.3) 

Canopy Cover % 52.2 

(33.0-60.5) 

64.1 

(57.5-77.4) 

60.4 

(48.7-72.8) 

59.8 

(44.4-67.0) 

Stand Height (ft) 75.5 

(49.2-85.3) 

72.01

(45.0-87.0) 

69.01

(58.5-54.0) 

64.0 

(46.8-86.1) 

Canopy Bulk

Density (lbs/ft3) 

.0021 

(.0017-.0027)

.0034 

(.0022-.0048)

.0018 

(.0011-.0026)

.0036 

(.0022-.0054)

Canopy Base 

Height (ft) 

16.4 

(13.1-32.8) 

13.12

(13.1-16.4) 

16.42

(13.1-16.4) 

13.1 

(7.0-15.6)

Canopy Fuel Load

(tons/acre) 

7.3 

(5.7-9.6) 

8.3 

(5.1-9.6) 

4.3 

(3.7-5.3) 

7.1 

(6.0-10.8) 1

 Post-treatment heights were used since pre-treatment heights were not measured. 2 Canopy base height was estimated by regressing canopy base height against dbh from trees in

compartments A and D for each species. 

After considering the stand conditions and fuel accumulations, fire behavior fuel 

model 10 (Anderson 1982; Rothermel 1983) appeared to be the best fit in all four

compartments. Using the weather and fuel moisture conditions that prevailed during 

the first day of the Cone Fire, the NEXUS simulation predicted passive crown fire in 

all compartments (table 2). 

Figure 2— A typical view of pre-treatment conditions in the Blacks Mountain RNA 

showing dense understory of small trees. (Photo by John Anstead, USDA Forest 

Service). 

250 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

Table 2— Estimates of fire behavior under Cone Fire weather conditions for the Blacks 

Mountain RNA compartments under pre-treatment stand conditions (Wind 15 mph).

Compartment A B C D

Fuel Model 10 10 10 10 

Fire Type Passive 

Crown

Passive 

Crown

Passive 

Crown

Passive 

Crown

Crown % burned 14 36 11 32 

ROS (ch/hr) 24 42 21 27 

H/A (btu/ft2

) 2056 2048 1745 2485

Flame Length (ft) 11 18 10 15 

Scorch Height (ft) 93 139 76 117 

Torching Index (mph) 12 10 12 5 

Crowning Index (mph) 32 22 37 31 

Figure 3 – One year post-treatment. Typical scene showing retention of dead 

needles in standing trees that were killed by the prescribed fire. All trees in the foreand middle-ground are dead. (Photo by Carl Skinner, USDA Forest Service) 

Post-Treatment Stand Conditions

One year following prescribed-fire treatments, tree density had been reduced by 

14.7% in B and 16% in C (fig. 3, table 3). There were corresponding decreases in

basal area, canopy cover, and canopy bulk density. The relatively small proportions 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 251 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

of change are due to mostly small trees being killed by the prescribed fire. Among 

small trees, seedlings and saplings were only partly reduced as can be seen by

comparing the pre- and post-treatment median (25th percentile - 75th percentile) 

density (trees/acre)[trees/hectare] of seedlings and saplings: B was reduced by 55% 

one year post-treatment to 500 (300-1,300)[1236 (741-3212)] and C was reduced by

80% to 150 (75-425)[371 (185-1050)] five years post-treatment. 

Canopy bulk density is reduced in the first year following prescribed fire. Yet, 

canopy fuel load increases in B the first year and in C by the fifth year. This is 

counterintuitive and may be an artifact of having to estimate the pre-treatment tree

heights. 

Table 3–Comparing pre-treatment and post-treament median (25th -75th percentile) values of

plot-level characteristics for trees >3.5” DBH for the Blacks Mountain Experimental Forest 

RNA compartments B and C.

Compartment B B C C C

Time Pre-burn Burn+1yr Pre-burn Burn+1yr Burn+5yrs

Trees/Acre 439.9

(280-715)

375.1 

(230-510)

312.4 

(192.6-

472.7)

262.4 

(162-330)

285.1 

(140-325)

Basal Area 

(ft2) / Acre 

160.0 

(127-203)

149.8 

(110-204)

138.6 

(117.9-

178.4)

125.1 

(103-164)

120.4 

(106-168)

Canopy Cover 

% 

64.1 

(57.5-77.4) 

58.8 

(52.2-71.2) 

60.4 

(48.7-72.8) 

45.3 

(35.4-50.3) 

45.1 

(37.0-49.8) 

Stand Height

(ft) 

72.01

(45.0-87.0) 

68.9 

(49.2-85.3) 

69.01

(58.5-54.0) 

69.01

(58.5-54.0) 

68.9 

(50.9-86.1) 

Canopy Bulk

Density (lbs/ft3

) 

.0034 

(.0022-

.0048)

.0032 

(.0027-

.0043)

.0018 

(.0011-

.0026)

.0012 

(.0008-

.0016)

.0017 

(.0014-

.0023)

Canopy Base 

Height (ft) 

13.12

(13.1-16.4) 

13.1 

(13.1-16.4) 

16.42

(13.1-16.4) 

19.7 

(19.7-25.4) 

19.7 

(19.7-23.8) 

Canopy Fuel

Load (tons/acre) 

5.3 

(3.8-5.8) 

8.3 

(5.2-9.7) 

4.3 

(3.7-5.3) 

2.8 

(2.4-3.8) 

6.3 

(5.7-8.7) 

1

Post-treatment heights were used since pre-treatment heights were not measured. Differences are due

to trees that existed in first measurements that were down by the last measurement. 2 Canopy base height estimated by regressing dbh from trees in compartments A and D for each species. 

Fuel model 8 (Anderson 1982; Rothermel 1983) was used to predict fire 

behavior in the first year following treatment for both compartments because initial 

changes in available fuels were primarily due to reduced amounts of needles and 

small fuels on the surface that easily ignite and carry fire. Fuel model 8 may overpredict fire behavior immediately post-treatment. However, of all of the available 

standard fuel models, model 8 predicts the lowest fire behavior. Additionally, fuel

model 8 was considered appropriate because post-treatment data indicated that 

approximately 60% of the surface was still covered by fairly compact litter and duff, 

even though nearly all of the young, loose, highly flammable needles had been 

consumed. The changes in fuel conditions due to the prescribed-fire treatments 

initially reduced the predicted fire behavior in both treated stands considerably (table 

4). Predicted behavior in both B and C was reduced from a high-intensity, passive

252 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

crown fire to a low-intensity surface fire. Predicted spread rate, energy released,

flame length, scorch height, and potential for passive crown fire (torching index) 

were all reduced in both compartments. However, it is important to note that the 

potential for the stands to carry a crown fire once it is initiated (crowning index) was 

generally not affected. This is because canopy bulk density was not appreciably 

affected by the treatments (table 3). 

Table 4–Comparing estimates of fire behavior under Cone Fire weather conditions pre- and

post-treatment for Blacks Mountain RNA compartments B and C (Wind 15 mph). 

Compartment B B B C C C

Time PreburnBurn+1

yr

Burn+2

yrs 

PreburnBurn+1

yr

Burn+5

yrs 

Fuel Model 10 8 9 10 8 111

Fire Type Passive Surface Surface Passive Surface Surface

Crown % burned 36 0 0 11 0 0

ROS (ch/hr) 42 3 13 21 3 10

H/A (btu/ft2

) 2048 263 536 1745 263 1128

Flame Length (ft) 18 2 4 10 2 5

Scorch Height (ft) 139 2 20 76 2 30

Torching Index (mph) 10 119 24 12 192 35 

Crowning Index (mph) 22 33 33 37 90 53

1

Had fuel model 10 been used here instead of 11, the post-treatment predicted fire behavior would have 

been equal to that of pre-treatment by the fifth year. 

Since the initial reduction in predicted fire behavior was mostly due to the 

reduction of needles and small twigs and not due to significant reduction of stand 

density or raising the canopy base height, fire hazard began to return quickly. Fiveyear re-measurement data were not yet available for compartment B. In order to 

account for changes over time in expected fire behavior due to accumulating needles 

and small twigs, fire behavior model 9 (Anderson 1982; Rothermel 1983) was used

to predict expected fire behavior for two years post-treatment. Two years posttreatment was chosen since few of the small trees that were killed by the prescribed

fire had fallen to become part of the surface fuels and was the condition of 

compartment B in the year of the Cone Fire. The dead, small trees began falling in 

large numbers in year four. Thus, this gives a prediction of the fire behavior that 

would have been expected had the fire been able to burn into compartment B. 

The second year prediction of fire behavior for compartment B suggests that the initial

dramatic reduction in fire behavior will likely not last long. The Torching Index, which is 

most sensitive to the surface fuel load, was reduced from 119 mph (192 km/hr) immediately

following treatment to 24 mph (39 km/hr). The second year figure is close to the maximum 

wind speeds measured during the Cone Fire and suggests that a danger of passive crown fire 

is likely to return as more fuel is added to the surface when the small, dead trees fall. The

stand density was not reduced sufficiently to affect the Crowning Index which is most 

sensitive to canopy bulk density once the crowning phase of the fire has begun. 

Fuel model 11 (light logging slash) was selected for simulating fire behavior for 

the fifth year post-treatment in compartment C for several reasons:

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 253 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

• Model 8 (slow spreading fires in compact litter beds) no longer applied 

due to the accumulation of needle cast and the fallen, small, dead trees. 

• Model 10 (timber stands with large, down, dead fuels and understory 

ladder fuels) did not apply due to the effects of the prescribed fire – a)

the prescribed fire consumed much of the heavy dead, down woody 

fuel, b) broke up continuity of surface fuels, and c) reduced the live, 

woody ladder fuels.

• Model 9 (long needle litter with limited down dead and no live 

understory ladder fuels) was not appropriate because a) fuel continuity

was reduced by the prescribed burn and b) the accumulation of woody 

fuel resulting from the fallen small, dead trees killed by the prescribed 

burn exceeded that appropriate for the model 9. 

• Model 11 (light logging slash) represents a) the accumulation of 

woody fuel over the 5 years since the prescribed burn and b) the

limited number of years of accumulation of litter and needle cast since 

the prescribed burn. Model 11 predicts slower rate of spread but 

higher intensity than model 9. 

Figure 4 – Four years post-treatment. Typical scene showing that many of the 

smaller trees killed by the prescribed fire have fallen and added to the surface fuel 

bed. (Photo by Carl Skinner, USDA Forest Service)

Fire behavior predictions based on using fuel model 11 to represent the fifth 

year post-treatment conditions for compartment C indicate that the initial dramatic

reduction in fire hazard has largely been lost by the fifth year after the first

application of prescribed fire. Several factors contributed to the rapid rebound of fire 

hazard. First, the needles, twigs, and small branches killed (scorched) in the burn 

have mostly dropped to the forest floor by the fifth year. Second, the many live trees 

remaining in the stand continue to annually contribute needles and small twigs to the 

forest floor. Thus, the ability for the fuel bed to ignite and carry fire is quickly

regained. Third, many of the smaller trees killed outright by the prescribed fire had

fallen and become part of the surface fuel load by the fifth year (fig. 4). Thus, an

average of 8 (range 0-33) tons/acre [18 (0-82) Mg/ha] were estimated to have been

254 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

added to the fuel bed. Fourth, stand density was not affected sufficiently to have a 

lasting effect on the potential for crown fire once surface fuels began to rebuild. 

Conclusion 

This simulation exercise indicates that fire hazard (the potential for highintensity wildfire) was immediately reduced following an initial treatment with 

prescribed fire compared to pre-treatment conditions in the Black Mountain Research

Natural Area. However, the reduction in fire hazard from a single burn appears to be 

short-lived for the following reasons: a) the prescribed fire did not appreciably affect

canopy bulk density because only a portion of the smaller trees in the understory 

were killed while most intermediate and larger trees survived, b) though surface fuels 

were initially reduced, the scorched material in dead and living trees and annual 

shedding of needles and small twigs by surviving trees rebuilt the surface fuel bed

within a few years, and c) the small trees that were killed subsequently fell and added 

to the surface fuel bed within five years of treatment. As field data become available

for a more accurate portrayal of surface fuel condition, the results are likely to change 

somewhat. However, the relative differences over time are likely to remain. 

Additional prescribed fires will be necessary to achieve reduction of fire hazard

lasting more than a few years. 

Acknowledgements 

I thank Martin Ritchie and Nick Vaughn for providing tree measurement data 

and Bob Powers for providing unpublished biomass equations. I thank Elizabeth 

Reinhardt for providing program FUELCALC that helped immensely in calculating 

canopy conditions necessary to estimate crown fire potential. I am grateful for the 

comments of Eric Knapp, Doug Maguire, Bob Powers, Martin Ritchie, and Scott

Stephens that helped to improve the manuscript. 

References 

Agee, James K. 1993. Fire ecology of Pacific Northwest forests. Washington, D.C., Island 

Press. 

Anderson, Hal E. 1982. Aids to determining fuel models for estimating fire behavior. Gen.

Tech. Report INT-GTR-122. Ogden, UT: Intermountain Research Station, Forest

Service, U.S. Department of Agriculture. 

Blonski, Kenneth S.; Schramel, John L. 1981. Photo series for quantifying natural forest

residues: Southern Cascades, northern Sierra Nevada. Gen. Tech. Report PSWGTR-56. Berkeley, CA: Pacific Southwest Research Station, Forest Service, U.S.

Department of Agriculture. 

Cheng, Sheauchi, technical editor. 2004. Forest Service Research Natural Areas in 

California. Gen. Tech. Report PSW-GTR-188. Albany, CA: Pacific Southwest

Research Station, Forest Service, U.S. Department of Agriculture. 

Dolph, K. Leroy; Mori, Sylvia R.; Oliver, William W. 1995. Long-term response of oldgrowth stands to varying levels of partial cutting in the eastside pine type. Western 

Journal of Applied Forestry 10:101-108. 

Fernandes, P.M.; Botelho, H.S. 2003. A review of prescribed burning effectiveness in fire 

hazard reduction. International Journal of Wildland Fire 12:117-128. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 255 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

Fulé, Peter Z.; Waltz, Amy E. M.; Covington, W. Wallace; Heinlein, Thomas A. 2001. 

Measuring forest restoration effectiveness in reducing hazardous fuels. Journal of

Forestry 99:24-29. 

Fulé, Peter Z.; Covington, W. Wallace; Smith, H. B.; Springer, Judith D.; Heinlein, Thomas

A.; Huisinga, Kristin D.; Moore, Margaret M. 2002. Comparing ecological restoration 

alternatives: Grand Canyon, Arizona. Forest Ecology and Management 170:19-41. 

Hickman, James C. 1993. The Jepson manual: higher plants of California. Berkeley, 

University of California Press. 

Maxwell, Wayne G.; Ward, Franklin R. 1980. Photo series for quantifying natural forest

residues in common vegetation types of the Pacific Northwest. Portland, OR: Pacific 

Northwest Research Station, Forest Service, U.S. Department of Agriculture.

Norman, Steven Paul. 2002. Legacies of anthropogenic and climate change in fire prone

pine and mixed conifer forests of northeastern California. The Pennsylvania State 

University, State College, PA. Dissertation

Oliver, William W. 2000. Ecological research at the Blacks Mountain Experimental 

Forest in northeastern California. Gen. Tech. Report PSW-GTR-179. Albany, CA:

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

Oliver, William W. 2001. Can we create and sustain late successional attributes in 

interior ponderosa pine stands? Large-scale ecological research studies in

northeastern California. In: Vance, Regina K.; Edminster, Carleton B.; Covington, W.

Wallace; Blake, Julie A., editors. Proceedings - Ponderosa pine ecosystems restoration 

and conservation: steps toward stewardship, April 25-27, 2000, Flagstaff, AZ. 

Proceedings RMRS-p-22. Ogden, UT: Rocky Mountain Research Station, Forest

Service, U.S. Department of Agriculture; 99-103

Reinhardt, Elizabeth D. 2004. FUELCALC. Unpublished program supplied by author. 

Missoula, MT; Rocky Mountain Research Station, Northern Forest Fire Laboratory: 

U.S. Department of Agriculture. 

Rothermel, Richard C. 1983. How to predict the spread and intensity of forest and range

fires. Gen. Tech. Report INT-143. Ogden, UT: Intermountain Research Station, Forest

Service, U.S. Department of Agriculture. 

Scott, Joe H. 1999. NEXUS: a system for assessing crown fire hazard. Fire Management 

Notes 59:20-24. 

Scott, Joe H.; Reinhardt, Elizabeth D. 2001. Assessing crown fire potential by linking 

models of surface and crown fire behavior. Res. Paper RMRS-RP-29. Fort Collins, 

CO: Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture. 

Scott, Joe H.; Reinhardt, Elizabeth D. 2005. Stereo photo guide for estimating canopy fuel

characteristics in conifer stands. Gen. Tech. Report. RMRS-GTR-145. Fort Collins, 

CO: Rocky Mountain Research Station, Forest Service, U.S. Department of 

Agriculture. 

Stephens, Scott Lewis. 1998. Evaluation of the effects of silvicultural and fuels treatments 

on potential fire behavior in Sierra Nevada mixed-conifer forests. Forest Ecology

and Management 105:21-35. 

Taylor, Alan H. 2000. Fire regimes and forest changes along a montane forest gradient,

Lassen Volcanic National Park, southern Cascade Mountains, USA. Journal of 

Biogeography 27:87-104. 

USDA Forest Service 2002. Cone Incident narrative. Unpublished report by the Northern

California Interagency Incident Management Team II to Eagle Lake and Hat Creek

Ranger Districts, Lassen National Forest. 

256 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Projects and Case Studies II—Reintroducing Fire in RNAs—Skinner 

van Wagtendonk, Jan W. 1996. Use of a deterministic fire growth model to test fuel 

treatments. In: Sierra Nevada Ecosystem Project: Final report to Congress. Centers for

Water and Wildland Resources, University of California, Davis: 1155-1165 

Weatherspoon, C. Phillip; Skinner, Carl N. 1996. Landscape-level strategies for forest fuel

management. In: Sierra Nevada Ecosystem Project: Final report to Congress. Centers 

for Water and Wildland Resources, University of California, Davis: 1471-1492

Youngblood, Andrew; Max, Timothy; Coe, Kent. 2004. Stand structure in eastside oldgrowth ponderosa pine forests of Oregon and northern California. Forest Ecology

and Management 199:191-217.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 257 

Three Studies on Ponderosa Pine 

Management on the Warm Springs Indian 

Reservation: Stocking Control in Unevenaged Stands, Forest Products from Firedamage Trees, and Fuels Reduction1

John V. Arena2

Abstract 

Over 60,000 acres of ponderosa pine (Pinus ponderosa P. and C. Lawson) forest on the Warm

Springs Indian Reservation (WSIR) in Oregon are managed using an uneven-age system. 

Three on-going studies on WSIR address current issues in the management of pine forests:

determining levels of growing stock for uneven-age management, fire effects on wood

suitability for engineered wood products, and mechanical forest fuel reduction alternatives. 

To evaluate various levels of growing stock, WSIR installed twelve 1.01-hectare plots in four

areas of the ponderosa pine forest to test three basal area density levels: 8.0 m2

ha-1 (35 ft2ac-1),

11.0 m2ha-1 (48 ft2ac-1) and 14.0 m2ha-1 (61 ft2ac-1). All plots were measured four times over a

fifteen-year period. Preliminary results show the variation in periodic basal area growth. 

Future treatments are planned for 2005 to impose new density levels for the next 20 years. A 

study of fire effects on wood quality was initiated to compare the strength of recently burned

small-diameter ponderosa pine to the strength of unburned, green, small-diameter ponderosa 

pine. Small logs were shipped to Mississippi State University to test their performance as 

engineered wood products. A mechanical forest fuel reduction study was designed to

compare the effectiveness of two methods for reducing understory conifers, shrubs, and

downed fuel. Soil disturbance (both visual classification and soil compaction), machine 

productivity, system cost, and their ability to treat certain various fuel types will be compared

in an 32 ha. (80 ac.) ponderosa pine unit.

Introduction 

The Warm Springs Indian Reservation (WSIR) in Oregon has over 100,000 ha 

(250,000 ac) of commercial forest with approximately 24,000 ha (60,000 ac) of 

ponderosa pine (Pinus ponderosa P. and C. Lawson) type. These forests are managed 

to provide sustainable yield and associated income, as well as wildlife and cultural 

amenities, to the Confederated Tribes of Warm Springs. Timber harvesting and fire 

suppression have changed the structure of these ponderosa pine forests from stands

dominated by large, old ponderosa pine (at least 200 years old) to stands dominated 

by a mixture of scattered old trees and dense groups of young trees (Weaver 1959). 

This new forest structure presents several new challenges: (1) choice of level of 

growing stock and stand structure for uneven-age management; (2) utilization of 

small-diameter ponderosa pine trees; and (3) development of economically efficient 

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues, 

Trends and Management, October 18–21, 2004, Klamath Falls, Oregon 2

 Silviculturist, Bureau of Indian Affairs, Branch of Forestry, PO Box 1239, Warm Springs, OR 97761 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 259 
Ponderosa Pine Management on the Warm Springs Indian Reservation—Arena

methods to reduce the potential of stand-replacement catastrophic fire in ponderosa 

pine forests. 

To begin to address these challenges the following three studies were initiated

on the WSIR in the ponderosa pine forests: determining levels of growing stock for 

uneven-age management, fire effects on wood suitability for engineered wood 

products from small-diameter trees, and mechanical forest reduction alternatives. In 

this paper a brief overview of each study is presented. 

Determining Levels of Growing Stock for Uneven-age 

Management

Early selection harvests in the ponderosa pine forest occurred in the 1950s and

1960s (Logan 1981). These harvests selectively removed the oldest, large-diameter

ponderosa pine of low vigor based on the Keen tree classification (Keen 1943). These 

selection harvests evolved into treating all diameter classes as prescribed in the 

Forest Management Implementation Plan 2002 – 2011 (Arena 2003) to meet the 

target levels of growing stock. These areas are in the ponderosa pine management

group, which includes four plant associations (Marsh and others 1987). 

In 1964 Earle Wilcox with the Bureau of Indian Affairs (BIA) stressed the need 

to determine levels of growing stock for the fully regulated forest under future 

intensive management of ponderosa pine (Wilcox 1964). His focus was on enhancing

growth of young ponderosa pine and improving growth predictions for the allowable 

cut. The focus changed in 1982 from growth rates to optimum levels of growing 

stock for younger ponderosa pine. Wilcox met with forest managers of large 

reservations in the Northwest to determine interest in installing permanent stocking 

study plots (Sassaman 1982). The data from these plots were intended to help 

managers advise the tribes about alternatives for managing their ponderosa pine 

forests. 

In response to this need, the WSIR installed stocking study plots in 1984. Four 

sites were selected (fig.1). Initially, there was some difficulty locating uneven-aged 

stands with three age classes that were less than 120-years-old, as well as areas with 

similar site quality that were disease free. Dwarf mistletoe reconnaissance plots

found infection from western dwarf mistletoe (Arceuthobium campylopodum

Engelmann) scattered through the ponderosa pine forest. Three plots were established 

at each of the four study sites. Each plot was 1.01 ha (2.5 ac) or 100.58 by 100.58 m 

(330 by 330 ft) with an exterior buffer 20.12 m (66 ft) wide. The plots were divided

into 25 square subplots of 20.12 by 20.12 m (66 by 66 ft). Each plot was randomly

assigned a different basal area stocking level yielding three basal area stocking levels

at each site. The levels of basal area per acre were: 8.0 m2

ha-1 (35 ft

2

ac-1), 11.0 m2ha-1

(48 ft2

ac-1) and 14.0 m2ha-1 (61 ft2ac-1). The selection of these levels was based on 

work from the Flathead Indian Reservation, where a similar study was installed in 

1970. Unfortunately, with the exception of the Beachkomb and Upper Tenino plots, 

initial levels of growing stock did not match the planned levels (table 1). 

Warm Springs Forest Products Industries harvested the stocking study plots and 

buffers between the fall of 1984 and the spring of 1985. The logging slash was piled

and burned. The initial measurement was completed in the fall of 1985, and 

subsequent remeasurements were scheduled every 5th year. All trees greater than 1.5 

inch in diameter at breast height (dbh) were tagged and numbered. Tree heights, 5-

260 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa Pine Management on the Warm Springs Indian Reservation—Arena

year dbh growth, age, and growth basal area were recorded for every tree greater than

30 cm (12 in) dbh, every third tree in the 15-25 cm (6-10 in) dbh class, and every

fourth tree in the 5-10 cm (2-4 in) dbh class. Growth basal area (GBA) is the basal

area at which dominant trees grow 2.5 cm (1 in) in diameter per decade at age 100. 

(Hall 1987) 

Figure 1— The location of the stocking study plots on the Warm Springs Indian

Reservation. 

Additional measurement variables that were collected since 1991 included all 

tree heights, height to lowest live limb, tree problem and severity codes, and crown 

class as well as a regeneration plot in the center of all sub-plots. In addition, all 

tagged trees were stem-mapped on each plot. The spatial data were entered into the 

Warm Springs Geographic Information System database. The University of Idaho 

remeasured the plots in 1994 as part of a Global Warming Project with WSIR and the 

Bureau of Indian Affairs Northwest Regional Office. The last remeasurement was 

done in l999-2000. 

In 1991 each plot was classified by plant association (Marsh and others 1987). 

Two of the four study sites were located in areas of relatively high site quality; the

HeHe site was in the ponderosa pine-Douglas-fir/snowberry plant association, and

the Upper Tenino site was in the mixed conifer/snowbrush plant association. In 

contrast, Lower Tenino and Beachkomb sites were of lower site quality and were in

the ponderosa pine/bitterbrush – greenleaf manzanita plant association and ponderosa 

pine/bitterbrush plant association, respectively.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 261 
Ponderosa Pine Management on the Warm Springs Indian Reservation—Arena

Growth monitored over 15 years suggests that periodic rates of basal area

growth differed among plots (table 1). This difference could be seen when comparing 

plot basal area growth at the Beachkomb and Upper Tenino sites, the sites at which 

actual basal areas were closest to the planned targets. At the Beachkomb site, basal 

area periodic annual increments were: 0.243 m2

ha-1 (1.06 ft2ac-1) for plot 1 (residual 

basal area 7.34 m2

ha-1 (32 ft2ac-1)); 0.321 m2ha-1 (1.40 ft2ac-1) for plot 2 (residual

basal area 13.77 m2

ha-1 (60 ft2ac-1)); and 0.259 m2ha-1 (1.13 ft2ac-1) for plot 3 

(residual basal area 10.10 m2ha-1 (44 ft2ac-1)). In contrast, at the Upper Tenino site, 

basal area periodic annual increments were: 0.734 m2

ha-1 (3.20 ft2ac-1) for plot 1 

(residual basal area 8.72 m2

ha-1 (38 ft

2

ac-1)); 0.613 m2ha-1 (2.67 ft2ac-1) for plot 2 

(residual basal area 13.08 m2

ha-1 (57 ft2ac-1)); and 0.659 m2ha-1 (2.87 ft2ac-1) for plot 

3 (residual basal area 15.14 m2

ha-1 (66 ft2ac-1)). 

Table 1—Basal area (ft2 ac-1) of each plot at each remeasurement. Target basal areas are in

the 1982 column.

Plot

Basal area, m2

ha-1 (ft2ac-1) 

1982 1985 1991 1994 2000

Target Actual Actual Actual Actual

HeHe

1 8.0 (35) 9.9 (43) 12.4 (54) 14.0 (61) 17.7 (77)

2 11.0 (48) 9.9 (43) 12.2 (53) 13.8 (60) 17.2 (75)

3 14.0 (61) 9.4 (41) 11.5 (50) 12.6 (55) 14.9 (65)

Upper Tenino

1 8.0 (35) 8.7 (38) 12.4 (54) 15.1 (66) 19.7 (86)

2 11.0 (48) 13.1 (57) 16.1 (70) 17.9 (78) 22.3 (97)

3 14.0 (61) 15.1 (66) 18.4 (80) 20.2 (88) 25.0 (109) 

Lower Tenino

1 14.0 (61) 8.3 (36) 10.3 (45) 11.5 (50) 14.2 (62)

2 8.0 (35) 6.9 (30) 8.3 (36) 8.9 (39) 11.0 (48)

3 11.0 (48) 8.3 (36) 10.1 (44) 11.0 (48) 13.3(58) 

Beachkomb

1 8.0 (35) 7.3 (32) 8.7 (38) 9.6 (42) 11.0 (48)

2 14.0 (61) 13.8 (60) 15.8 (69) 16.8 (73) 18.6 (81)

3 11.0 (48) 10.1 (44) 11.9 (52) 12.6 (55) 14.0 (61)

The next phase of this study will be to remeasure the trees, tag and measure the 

ingrowth, and then harvest the plots and their buffers to the new basal area targets:

8.0 m2

ha-1 (35 ft2ac-1), 11.5 m2ha-1 (50 ft2ac-1) and 14.9 m2ha-1 (65 ft2ac-1). These 

levels are similar to the original targets but will expand the range of densities to test 

the degree of variation in growth by regeneration and merchantable trees, especially

at the higher density. The higher level (14.9 m2

ha-1 (65 ft2ac-1)) is just above the 

prescribed level used in the WSIR Forest Management Implementation Plan 1992 – 

2001 (Donaghu 1993). 

Besides the new density levels, the silvicultural prescription for each plot will 

project a flatter reverse J-shape curve, shifting basal area from the lower 10-cm (4-in) 

dbh classes (sub-merchantable classes) to the small sawlog classes. Using tree data 

formatted for the Forest Vegetation Simulator (FVS) (Wykoff et al. 1982) and the

spatial information from the stem-mapped plots, several marking scenarios can be

262 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa Pine Management on the Warm Springs Indian Reservation—Arena

assessed with respect to how well they meet the planned initial stocking levels, as 

well as establish an expected yield after 20 years. After treatment, the plots will be

remeasured every 5 years and harvested every 20 years. 

Unfortunately, the HeHe plot #3 burned in a wildfire in 1999 and only four trees 

remain in the plot. This plot will be remeasured every 5 years to assess post-fire 

recovery. The number and intensity of recent fires are a major concern on the WSIR

in the ponderosa pine forest and, specifically, the stocking study plots. 

The maintenance and remeasurement of these plots are long-term investments 

by the tribes. As the responses to different stocking levels are analyzed and

compared, the desired stocking levels and stand structure can be prescribed to

ultimately meet the tribal goals and objectives in these ponderosa pine forests. The 

process of remeasurement, harvest and analysis will continue since more questions 

will inevitably arise, as they did in 1964 during Earle Wilcox’s silvicultural

assessments. These plot data when entered into FVS can also be used to calibrate 

growth projections to the Warm Springs Indian Reservation. 

Fire Effects on Wood Suitability for Engineered Wood 

Products from Small-diameter Trees 

Overstocked stands of small-diameter conifer trees in areas that historically 

carried frequent fires have created problems for landowners in central Oregon and on

the WSIR. The cost of thinning and slash treatment necessary to release and protect

these stands is very high. If left untreated, these stands may contribute to and be

consumed by catastrophic wildfires, resulting in subsequent loss of any wood value, 

as well as possible site degradation. The solution to this problem might be to develop

new products or add value to products manufactured from small-diameter trees. At 

present, there are limited markets for either burned or green small-diameter trees.

This study will test samples of recently burned and green small-diameter ponderosa 

pine and lodgepole pine for their utility in manufacturing engineered wood products 

at Mississippi State University (MSU). Eini Lowell and Susan Stevens Hummel from

the USDA Forest Service Pacific Northwest Research Station are the principal 

investigators of this study3

. Both burned and green ponderosa pine samples came 

from the southern portion of the WSIR where the B & B Fire burned in 2003. The 

lodgepole pine samples came from the Deschutes National Forest, Oregon. 

In the fall of 2004, trees were selected, cut, and bucked into 2.4-m (8-ft) lengths 

by two Warm Springs engine crews. Each butt log was tagged, measured, loaded 

onto a trailer and shipped to MSU. The size of the trees ranged from 7.6 to 20.3 cm

(3 to 8 in) dbh. The green trees were selected from a stand near the B & B Fire. 

If engineering wood products from presently submerchantable ponderosa pine 

and lodgepole pine removed in thin-slash-burn treatments meet performance 

standards, forest managers will have new utilization and silvicultural opportunities.

Depending on the cost of extraction and available manufacturing facilities, land 

managers could produce revenue or at least partly offset the cost of treatment, 

enabling them to increase the total area that can be treated. Utilization of this wood 

3 Eini Lowell, Research Scientist, and Susan Stevens Hummel, Research Forester, Pacific Northwest

Research Station, USDA Forest Service, Portland, OR

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 263 
Ponderosa Pine Management on the Warm Springs Indian Reservation—Arena

also creates an opportunity to develop scale-appropriate technology for employment 

through value-added wood products for the WSIR. 

Mechanical Forest Fuel Reduction Alternatives for 

Forest Managers: Non-commercial Component

The ponderosa pine forests of the Warm Springs Indian Reservation are 

overstocked with young trees. The understory is mostly trees of non-commercial size.

This condition predisposes forests to stand-replacement catastrophic wildfire. An

Oregon State University, College of Forestry, research study is assessing mechanical

options for fuels reduction through mulching and masticating small, severely 

suppressed, understory trees and surface fuel. The principal investigators are Chad 

Bolding and Loren Kellogg from the Department of Forest Engineering4

. Two types

of equipment are being studied: (1) a flexible tracked skidding machine with a 

masticating head and, (2) an excavator based swing-boom machine equipped with a 

rotary disk mulching head. 

The objectives of this study were to assess: (1) effects of treatments on the soil,

(2) cost and production rates of the equipment, and (3) apparent efficacy of treatment 

in altering future fire behavior. Visual soil disturbance classification, and soil

strength (compaction) will be compared before and after treatment. The level of

productivity per scheduled machine hour will be evaluated through both shift-level 

and detailed time studies. Productivity observations will determine operating costs 

per unit volume and area for each machine. The study will also attempt to determine 

the type or category of forest fuel that each machine can effectively treat (range of 

dbh classes, dead and down material, shrub component, etc.). The effectiveness of the

machines for implementing the silvicultural prescription will be compared by

simulation evaluating pre- and post-treatment data with the fire and fuels extension 

(FFE) to the forest vegetation simulator (FVS) (Reinhardt and Crookston 2003). 

The 32-ha (80-ac) study area is divided into 16 2-ha (5-ac) subunits in the 

southeast portion of the ponderosa pine forest on the WSIR. Each piece of equipment

will treat approximately 16 ha (40 ac), comprising eight randomly selected subunits. 

The specific silvicultural prescription outlines the density level by diameter class for 

the residual stand, as established in the Warm Springs Forest Management

Implementation Plan 2002-2011 (Arena 2003). Tree groups are scattered throughout

the study area, ranging from patches of old-growth ponderosa pine with an

understory of bitterbrush (Purshia tridentata (Pursh) DC.) and greenleaf manzanita 

(Arctostaphylos patula Greene) to patches of young ponderosa pine within a narrow 

range of diameters. The diameter class of each group will determine the tree spacing 

guideline, but all trees greater than 28 cm (11 in) dbh are designated as leave trees. 

The shrub layer of bitterbrush and greenleaf manzanita will also be treated. Operators 

are not permitted to use any other equipment besides the two being compared to 

complete their specified subunits. 

4

 Chad Bolding, PhD Graduate Student, and Dr. Loren Kellogg, Oregon State University, College of

Forestry, Department of Forest Engineering, Corvallis, OR 

264 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Ponderosa Pine Management on the Warm Springs Indian Reservation—Arena

Summary

These three studies address the need for more information concerning 

management in the ponderosa pine forest. As mentioned earlier, the long-term 

investment in the stocking study plots should yield significant returns in the form of

better stocking guidelines that the WSIR can apply in managing their ponderosa pine

forest. These plots will help the Confederated Tribes identify options that best meet

the diverse needs of their members. Any innovative value-added wood products may

offer potential for both new manufacturing jobs and cost-effective ways to reduce 

overstocking of small-diameter conifer trees. The mechanical fuel reduction study 

examines treatment options and associated soil impacts, productivity, and costs in 

different fuel types, and should thereby help forest managers select the best treatment 

option for various stand and fuel conditions in these ponderosa pine stands. 

References 

Arena, J.V., technical coordinator. 2003. Forest Management Implementation Plan 2002 –

2011. Branch of Forestry, Warm Springs Indian Reservation, Warm Springs, OR: 68-82

Donaghu, W.B., technical coordinator. 1993. Forest Management Implementation Plan 

1992 – 2001. Branch of Forestry, Warm Springs Indian Reservation, Warm Springs,

OR: 33-43 

Hall, F.C. 1987. Growth basal area handbook. R6 – ECOL – 181b – 1984. Portland, OR;

U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 86 p.

Keen, F.P. 1943. Ponderosa pine tree classes redefined. Journal of Forestry. 41(4): 249-253. 

Logan, R. 1981. Historical Perspectives: The Warm Springs Forest through 1980. 37 p.

Marsh, F.; Helliwell, R.; Rodgers, J. 1987. Plant Associations Guide of the Commercial 

Forest of the Warm Springs Indian Reservation. Bureau of Indian Affairs, Branch of

Forestry, Warm Springs Indian Reservation, Warm Springs, OR. 142 p. 

Reinhardt, E.; Crookston, N.L. (tech eds). 2003. The fire and fuels extension to the forest 

vegetation simulator. Gen. Tech. Report RMRS-GTR-116. Ogden, UT: Rocky

Mountain Research Station, Forest Service, U.S. Department of Agriculture, 220 p. 

Sassaman, R.W. 1982 August 19. Letter on file at Branch of Forestry, Warm Springs Indian

Reservation, Warm Springs, OR. 

Weaver, H. 1959. Ecological changes in the ponderosa pine forest of the Warm Springs

Reservation in Oregon. Journal of Forestry: 57(1) 15 – 20. 

Wilcox, E.R. 1964. Growing stock objectives for management of ponderosa pine. 

Unpublished paper, on file, Branch of Forestry, Warm Springs Indian Reservation,

Warm Springs, OR. 

Wykoff, W.R.; N.L. Crookston; Stage, A.R.. 1982. User’s guide to the Stand Prognosis 

Model. Gen. Tech. Report INT-133. Ogden, UT: Intermountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 112 p. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 265 

Lessons Learned on 50,000 acres of 

Plantation in Northern California1

Jeff Webster and Ed Fredrickson2

Abstract 

Many lessons have been learned during reforestation of large wildfires and clearcuts in

interior Northern California, a region of low rainfall and summer drought typical of a 

Mediterranean climate. Challenges appeared from time of establishment right up to

commercial thinning. Establishment issues included procurement of improved seed, site

preparation, soil mitigation, seedling performance, season of planting, and timing of

vegetation management. Important decisions also had to be made with regard to mechanical

vs. hand pre-commercial thinning (PCT), achieving a proper balance between reducing fire

risk and compacting the soil, and prescribing spacing guidelines for thinning operations. On 

some sites damage from Eucosma sonomana (Kearfott) (western pine shoot borer) was a 

factor. 

Introduction 

From 1992 to 2004, Roseburg Resources Company in interior Northern

California accumulated considerable experience while practicing intensive 

silviculture on company lands covering approximately 315,000 ac (128,000 ha) (fig. 

1). Of the approximately 50,000 ac (20,000 ha) of plantation on these lands, twothirds was replanted after wildfire. The remaining plantation acreage was the result of 

a shift in management emphasis over the last decade towards even-age management. 

Northern California has a Mediterranean climate, with hot dry summers that

present numerous silvicultural challenges. The climate also fosters a high fire 

frequency, with historical fire intervals of eight to twelve years (C. Skinner, USDAFS Pacific Southwest Research Station, pers. comm.). The elevation of Roseburg 

Resources property ranges from 1,500 to 7,000 ft (500-2100m), rainfall ranges from 

20 to 100 inches (50-250 cm) per year, and site class ranges from one to five, with 

the average being site 3 (Dunning, 1942). The vast majority of the ownership is

Sierra Mixed Conifer, with smaller areas of Eastside pine, Ponderosa pine, Douglasfir and White fir (Mayer and Laudenslayer, et al., 1988). 

Reforestation practices on private land in Northern California have evolved over 

the last 25 years in response to experience gained on burned over areas. On Roseburg 

ground massive reforestation started with the Pondosa Burn in 1977. Other burns 

included the Day fire (1989), Fern fire (1990), and Finley Fire (1990). The lessons 

learned from these fires were aggressively applied to the Fountain Fire (FF) that

started on August 20, 1992. This fire burned 64,000 ac (26,000 ha), 99 percent on

private property, and included 41,000 acres on industrial ownership (Roseburg, Sierra 

1

An abbreviated version of this paper was presented at the symposium on Ponderosa Pine: Issues,

Trends and Management, October 18-21, 2004, Klamath Falls, Oregon 2 Jeff Webster is Forest Manager for Total Forestry in Anderson, CA 96007 3 Ed Fredrickson is Research Manager for Total Forestry in Anderson, CA 96007 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 267 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

Pacific and Fruit Growers Supply Co.). One percent of the industrial land base in 

California was consumed in the Fountain Fire, and 50,000 ac (20,000 ha) burned in 

two days with an intensity rarely seen before. On Roseburg property, the planting 

mix was 70 percent ponderosa pine (Pinus ponderosa P.& C. Lawson), 20 percent 

Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) and 10 percent White fir (Abies 

concolor (Gord. & Glend.) Lindl. ex Hildebr.). The rest of this paper will describe 

the many lessons learned from these reforestation efforts and subsequent silvicultural 

activities. 

Figure 1—Vicinity map of Roseburg Resources ownership and plantations in

Northern California. 

Planning 

The key to success of any reforestation project is proper planning. The

temptation on large projects is to get started immediately with activities on the

ground. However, the first step should be to break the project up into ecological

units based on soils, aspect, elevation, vegetation type, access, slope, operability, and

other attributes. Defining units of workable size can help focus efforts on achievable

management objectives rather than on the overwhelming size of the undertaking. 

Knowledge of Geographic Information Systems (GIS) and spreadsheet software is

invaluable for managing detailed information. Successful reforestation must be done 

in a series of steps and requires paying much attention to detail. Failing on any one of

these steps often spells failure for the whole effort. 

Units were prioritized on the basis of many factors relevant to maximizing

success. The primary factor was the need for vegetation management. Competing 

vegetation from resprouting woody plants (mostly chinquapin) requires 2-3 years to

268 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

grow sufficient crown volume to absorb enough chemical to completely kill the root 

system. Units with this type of competing vegetation were therefore deferred until the 

end of the reforestation effort. Areas where we could not use herbicides (along any

perennial surface water) were planted immediately to take advantage of the site 

preparation from the fire. Beyond that the priorities were set by operational issues, 

such as timing of logging and a range of elevations to ensure as long a planting

season as possible. 

Planning does not take years; it can be done in a short period of time. Plans were 

completed in a matter of weeks on the Fountain Fire (FF). Logs were rolling into the 

mill by September 9, less than three weeks after the fire started and before the fire 

was even declared under control. It is important to take advantage of the site 

preparation created by the fire rather than see what competing vegetation re-occupies

the site. Where woody vegetation was present before the fire, it will vigorously resprout after the fire. Use of herbicides within stream buffers was limited, so it was 

particularly important to take advantage of the site preparation achieved by the fire

and to reforest without delay. Look for speculation stock in the nurseries that would

be available to plant the following year. 

Even though logging started immediately after the fire, rules set forth in the

California Forest Practices Act (CFPA) provide a set of guidelines that ensure that 

environmental issues are not ignored. Stream buffers were established, archaeological 

surveys were completed, erosion mitigation measures were taken, and approximately

100 miles (160 km) of roads were improved with rock and drainage facilities. 

Although not required by the CFRA, Roseburg prepared Timber Harvest Plans 

(THP’s) to ensure protection of the environment. 

Seed Procurement and Inventory

Large landowners and governmental agencies normally maintain a seed 

inventory for small emergencies and unanticipated management needs. To meet the

demand created by large fires, normal inventories are often inadequate. In this case,

foresters must look on the open market for available seed from the correct seed zones

and elevations. State agencies usually have seed available, as do private cone 

processors. A general rule of thumb is to move seed upon no further than 500 ft (150 

m) up in elevation and 1000 ft (300 m) down, relative to the elevation of origin (J.

Kitzmiller, retired from USDA-FS, pers. comm.). Likewise, seed should not be 

moved any further than the adjacent seed zone within the same series (climate). A 

standard inventory should be enough to reforest 10 percent of your land base, but 

probably more in areas of high fire risk. The more infrequent the cone crops, the

larger should be the maintained reserve. 

Superior seed programs can help reduce the amount of seed maintained in 

inventory. Seed orchards usually produce a more predictable and consistent source of

seed. In addition to the reliability of seed production, improved seed generally has

been developed to increase growth rates. On average, the first generation of improved 

seed is expected to increase growth by 10 to 15 percent, with an additional 10 percent

from the second generation (J. Kitzmiller, retired from USDA-FS, pers. comm.). 

Improved seed is available for small landowners in California from the California 

Department of Forestry and Fire Protection. This state agency is a member of the 

North Sierra Tree Improvement Association (NSTIA), the most successful tree

improvement cooperative on the west coast for ponderosa pine. The seed zones 

covered by the cooperative include 521, 522, 523, 524 and 525, on the west slope of 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 269 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

the Sierra Nevada ranging from the Pit River in the north to the American River in

the south. 

A sufficient seed inventory also must cover the full suite of species required for

potential reforestation projects. Ponderosa pine seed stores for a long time (over 20 

years) as does Douglas-fir, but white fir (and most other Abies species) does not store 

as long (10 years or less). 

Seedlings and Nurseries 

After large fire events, it is important to reserve space in preferred nurseries to 

assure an adequate supply of quality seedlings. Criteria for selection of nurseries 

include the type of seedling desired (bareroot vs. container stock), species, storage,

growing climate, lifting season, and others. 

An effective and clear line of communication with the nursery is vital. Each

nursery has its specialty, and not every nursery is good at growing all species. A solid 

grasp of the physiology of each species is helpful for asking important questions and 

making sure the nursery is growing the correct tree for your needs. Knowing the 

growth cycle of each species is very important. Quiescence is an important

physiological state to understand, and deals with the transition period between

growth and dormancy. The nursery must apply specific cultural practices to ensure 

that the appropriate size and physiological state at the right time. Cultural activities 

will change depending on whether you plant in the fall or spring. It is important to 

visit the nurseries at least once each year, and to communicate regularly by phone to 

emphasize your need for a very specific type of seedling. 

Many important conditions can be observed on your visits. Did you get the 

germination that you planned for? Is the facility organized? How is the irrigation 

working? Is water distributed evenly? How is the fertilizer being calibrated? Do the 

trees look as good as the nursery manager says they are? Are you really going to get

the trees you ordered? If they look poor, then you may want to consider a visit during 

lifting and packing to make sure they are culling weak trees properly. Are your trees

clearly identified? If not, how can you be sure that you are getting your trees?

Showing up and calling shows that you care and will be monitoring the nursery’s 

performance closely.

Another factor to consider when planning reforestation is the number of 

nurseries you order seedlings from. Even the best nurseries can have unexpected

problems, so it is a good rule to have several nurseries growing your seedlings for

any given project. That way, if one nursery has a problem then your whole program 

will not be affected. 

Seedling Trends 

The trend in interior California is toward a higher proportion of container stock. 

Some interesting facts emerge from studies in Douglas-fir and ponderosa pine3

. Three

years after planting, initial stock size had no effect on the seedling volume of 

ponderosa pine or Douglas-fir. However, stock size did affect survival, with larger 

sizes experiencing less mortality. Larger containers result in lower bed densities and, 

hence, yield shorter trees with large caliper and lower limbs. The lower limbs shade

the stem and prevent sun scalding. The same results were obtained for white fir. The

3

 Fredrickson, unpublished data from Roseburg Resources field trials 

270 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

best container sizes for ponderosa pine are stryro 5s or 8s; however; styro 8s and 10s

worked best for Douglas-fir. If ungulate browsing is a potential problem, larger trees 

perform better (stryro 15s and 20s or plug-1 transplants). For surviving the summer 

drought, a relatively high root to shoot ratio (preferably 1:1, max.2:1) is essential, in

contrast to the coastal region where taller stock is preferred. 

The current trend in reforestation is to plant a mix of species. Conventional 

wisdom suggests that monocultures may invite insect problems, but even if they do 

occur the mix of species lowers the risk of total plantation loss. A big challenge in 

mixed species silviculture has been successful establishment of white fir with 

Douglas-fir. Planting the appropriate stock type is critical, and site preparation must 

be done to provide the specific types of microsites that Douglas-fir and white fir 

require. In the early stages of development these species are quite susceptible to sun 

scald and insufficient moisture. Providing dead shade and retaining soil organic 

matter to enhance water holding capacity are very important. The more organic

matter that is retained during site preparation, the better is survival and growth.

Organic matter retention includes minimizing the movement of organic matter across 

the unit. Maximizing organic matter retention, however, must be balanced against 

minimizing fire hazard. 

Frost can be limiting to the success of high-elevation interior plantations. Fir 

planted on flats and low areas are susceptible to frost damage. The fir species are best

planted on slopes (especially north aspect) with good air drainage. 

Harvest Planning 

Combining site preparation with logging activities can save a lot of money. In

recent years our most effective tool has been a pre-harvest application of herbicide 

(mostly Chopper and Round Up, either separately or as a tank mix), preferably a year 

ahead of logging for maximum efficacy and greatest tolerance by conifer seedlings.

We observed a 35 percent reduction in the need for release treatments as a result of 

pre-harvest applications3

. Pre-harvest site-preparation provides more effective control

of tenacious species like tanoak, snowbrush and other evergreen broadleaved shrubs

and trees. Pre-harvest control is more effective in part because crowns and roots of 

undesirable species are not disturbed prior to logging and, allowing for better 

translocation and maximum efficacy of the herbicide. Pre-harvest site preparation 

also offers other benefits: lower labor costs, increased soil moisture retention, greater

tolerance of planted conifers to treatment, and more options on choice of chemicals. 

By spraying competing vegetation prior to logging, the dead material often

disintegrates during felling and yarding. Chipping and removing sub-merchantable

material before or after logging can also eliminate brush. This chipping operation 

adds another opportunity to run over dead woody material and break it down.

Another benefit of chipping is the removal of unmerchantable material and reduction 

in the need to pile, especially if the trees are whole-tree yarded to the landing, where 

tops can be chipped. Even though chipping can be costly, if the market for biomass 

chips is weak, the chipping often is cheaper than piling, and it leaves more forest

floor organic matter distributed across the site. Sub-soiling may be helpful depending

on soil characteristics. 

The importance of proper planning is particularly evident when considering 

access. To mitigate possible adverse effects of roads water quality, fish, and wildlife,

the temptation is to bloc roads off. Closed roads create significant logistical problems

for subsequent silvicultural treatments (planting, spraying, thinning, burning, piling, 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 271 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

etc.). Early coordination of the reforestation effort with the harvesting schedule can

reduce long-term costs of silvicultural activities considerably, but this coordination of 

logging and reforestation activities is too often an after thought. 

Mechanical Site Preparation 

Many more tools are available now for mechanical site preparation than was the

case just a few years ago. The brush rake is still a favorite and is used frequently in

California on slopes up to 30 percent. Ponderosa pine responds well to this type of 

site preparation. With the trend toward more mixed species plantations and reducing

cost, sub-soiling and planting or just planting through the slash is increasingly

common. These practices increase the risk of severe wildfire from the higher fuel 

loadings, and increase the probability of animal damage due to the better habitat that 

down wood provides. In addition, the cost of planting, spraying and thinning 

increases. 

Sub-soiling is often done in combination with tractor piling of logging slash. 

Due to previous logging and site preparation, compaction is often a problem,

especially with clay soils (fig. 2). After clearcutting or stand-replacing fire, the 

opportunity exists to mitigate soil conditions. Subsoiling can also be used to mitigate

soils conditions, including hydrophobic soil resulting from extremely hot wildfires. 

The lower soil strength after subsoiling usually results in cheaper planting costs and

higher quality planting, since the planters do not tire as quickly. Error!

Effecton Soil from Biomass 

Activity

Figure 2—Soil compaction before and after mitigation in the Pondosa Burn.

The design of the shank on subsoiling equipment is important. The wings should 

be essentially flat, because the idea is to lift and fracture the soil, not to plow it. The

shank should have a long leading tip, a sloped and tapered leading edge, and wings 

that feather behind the shank. Accumulation of roots and wood on the shank needs to

be avoided because this accumulation acts as a plow. The operator needs to pay

attention and lift the shank periodically. The target depth to sub-soil is a minimum of 

18 in (46 cm) (R. Powers, UDSA-FS Pacific Southwest Research Station, pers. 

comm.). Due to the irregularities of the ground a target of 24 in (61 cm) is desirable, 

providing a range of treatment from 18 to 24 in (46 to 61 cm). Going deeper only 

slows the operation down and increases the cost. 

272 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

The use of excavators for site preparation is becoming more common in

California. Excavators are the preferred tool west of the Cascades in Oregon and 

Washington because they provide cleaner piles and increase organic matter retention 

(including large woody debris) across the site. However, the greater retention of

organic matter again increases the risk of fire, and the more continuous fuel load

increases the risk of escape from burning piles. An excavator with a 4-ft rake will 

increase the quality of planting and reduce the cost relative to an excavator with 

bucket and thumb. 

The VH Mulcher mounts on an excavator or Timpco frame and works well for 

site preparation in slash or for making mounds. This tool was designed in Canada for 

shallow soils and high water tables. On such sites planting mounds are the preferred

practices, contrary to accepted practices in dry Mediterranean climates. This tool 

works particularly well for making planting spots in slash, eliminating the need for 

piling. The VH Mulcher spins at a relatively high speed, so if the operator is not 

careful the mulcher can throw topsoil out of the hole, leaving only the C horizon to 

plant in. Depending on site conditions and management goals, several alternative 

microsites can be planted in the hole. The thumb on the head is used to move slash,

and the bottom rotates to essentially drill a hole. By working the head back and forth 

you can prevent the removal of soil from the hole to some extent. 

The Spyder is another tool that is relatively new, but is very effective for piling

on steep slopes (fig. 3). This machine essentially walks on four legs, so is capable of 

working on slopes up to 100 percent. The Spyder has been used as an alternative to

broadcast burning. In California, the maximum clearcut size allowed by the CFPA is

40 ac (16 ha), but the operational average is 15 to 20 ac (6 to 8 ha). Broadcast

burning extremely expensive under these conditions. Increasing restrictions on 

burning due smoke management and air quality also limit opportunities for broadcast

burning. Pile burning has a wider range of permissible conditions (larger burning

window) than broadcast burning. A larger window is available for burning piles 

because they can be covered and burned later during wet conditions when risk of

escape is low. The large amount of organic material left behind makes this escape 

risk a serious consideration. 

Figure 3—Spyder is used to prepare sites for planting. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 273 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

As mentioned earlier, chipping is a valuable tool that can be used to reduce the 

need for piling, but opportunities for chipping depend heavily on local demand for

chips, the availability of an infrastructure to process and transport the chips, and a 

price that makes removable of this material economically feasible. The key factor 

determining economic viability is the number of dry tons removed per acre. For 

example, if 10 tons per ac (22 Mg per ha) must be removed, if the market will pay 

$40 per ton ($44 per Mg), and if hauling costs $45 per ton ($50 per Mg), then fuel 

reduction by chipping and removal will cost $50/acre ($132 per ha). 

Masticators are another group of machines that mulch brush very well. One 

disadvantage is that they do nothing to disturb the root system, and another is that the 

machines are expensive. Without some follow up chemical treatment, sprouting

shrubs and hardwoods will return within three to five years. 

To summarize, the predominant trend in mechanical site preparation is to leave

more organic material on site. This increased organic retention is a benefit to

Douglas-fir and white fir survival, but it increases fire risk and drives up the cost of 

subsequent silvicultural treatments. 

Broadcast Burning

The cost of broadcast burning is becoming prohibitive, except as a last resort, 

due to the increasingly small clearcut units in California. Burning is inherently risky

and requires extensive training and experience to implement successfully. 

Increasingly strict smoke management guidelines designed to meet air quality

standards also make it difficult to obtain permits and increases the costs. 

Vegetation Management 

Vegetation management is essential to the establishment of fully stocked 

plantations in northern California and many other regions. Without vegetation

control, many plantations are doomed to failure (fig. 4). Chemical treatment is the

safest and most effective means of ensuring reforestation success. Research in

vegetation management has led to safer chemicals and lower application rates with

the intent to minimize environmental impacts. 

The objectives of vegetation management are: 1) to maximize site resources 

available to planted trees and thereby ensuring survival and enhancing growth, 2) to 

achieve the highest level of control with the least amount of chemical, 3) to obtain 

desired results while protecting and enhancing other resources and 4) to continually 

improve results through research and development. 

Our vegetation management strategy has relied on well-planned initial site 

preparation. The current strategy involves pre-harvest chemical treatment, followed

by logging, mechanical site preparation, and a residual herbicide to control the grass

and forbs. The goal is to maintain a weed-free environment for the first two years to

ensure successful establishment. Release treatments are scheduled as necessary to 

increase growth (fig. 5). Twenty five percent aboveground brush cover equates to

root systems covering 100 percent of the area. 

274 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

Figure 4—A demonstration area in the Pondosa Burn of northeastern California

showing an established ponderosa pine plantation where competing vegetation was 

controlled and a brushfield resulting from no treatment. 

One important key to success is application of the correct product on the target

species, even if that means treating the same unit twice with two different chemicals.

This approach will be cheaper in the long run because it is more difficult to kill the 

unaffected species after one or more growing seasons. Applications of the proper 

chemical will kill the undesirable species rather than simply brown them.. Growth 

regulators should not be mixed with a systemic chemical, e.g., Garlon and Roundup.

The growth regulator destroys the cell structure in the plant before the systemic

chemical gets translocated to the roots. Chemical application beyond the rates and 

volumes needed to kill the target species is a waste. Perhaps the most important

factor is getting a good foreman and crew who will pay attention to the detail 

required to be successful.

Pre-Harvest Site Preparation

The goals of most pre-harvest herbicide applications include: 1) achieving longterm control without re-sprouting, 2) avoiding conifer damage, 3) minimizing 

application costs and 4) eliminating future entries. 

So how do pre-harvest applications achieve these goals? Logging affects how 

the vegetation reacts to chemicals. Often after disturbance the plants go into shock 

and will not absorb chemical well. During logging the root to shoot ratio is increased

by mechanical damage to the shoot; therefore, the remaining crown may not be able 

to absorb enough chemical to kill the root system. By treating before harvest, the root 

to shoot ratio is sufficiently low to ensure effective chemical control. In addition,

plants are usually less able to resist chemical control when light, moisture and

nutrients in the understory limit their sprouting vigor. Pre-harvest herbicide treatment 

is especially effective for schlerophyllous hardwood species that are hard to kill. 

Chopper (imazapyr) and high concentrations (5 to 10 percent) of glyphosate 

(especially with deciduous hardwoods) work well. Pre-harvest application also leads 

to greater success of fall planting due to increased soil moisture (fig. 6). 

Application costs are lower before harvest, assuming that good access is

available. The added benefit is reduced release costs after planting4

. Lower rates of

4

 E. Fredrickson, unpublished data from Roseburg Resources field trials. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 275 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

residual chemicals are required for herbaceous species than for both herbaceous and 

woody species. Also, options for chemicals to apply are much greater before harvest

than after planting because conifer tolerance of the available chemicals varies. 

Figure 5—demonstrating the value of vegetation control, F=fertilization, H=herbicide, 

C=control. (Robert Powers, USDA Forest Service, Pacific Southwest Research

Station, Albany, CA, unpublished results). 

276 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

Keys pieces of advice are: 1) treat at least one year in advance of logging, 2) use 

esterified seed oils or seed oil silicone surfactant combinations to get good 

penetration (usually 5 to 10 percent depending on time of year, with more late in 

year), and 3) providing access is critical - the most common challenge to pre-harvest

site preparation is adequate planning with the logging department to ensure access 

in advance. 

Figure 6—Difference in available moisture three months after planting in units 

receiving competing vegetation control (left) vs. units receiving no control (right). 

Fall Planting

Fall planting is difficult to manage historically gives unpredictable results. So 

why do we continue to pursue it? We found greatest success with fall planting above

5000 ft (1520 m), where snow limits access until after summer drought begins. 

Planting at high elevations can usually be done only at such a late date that little or no 

precipitation typically occurs after planting, and extreme temperatures can still occur 

before the trees develop root systems sufficient for survival. 

So what does it take to be successful? Planting only after receiving early fall 

moisture (preferably 1 to 2 in (2.5 to 5 cm) in September) is critical, although we 

have seen that, in areas with pre-harvest treatment, a half-inch (1.2 cm) has been 

enough for successful reforestation. Choosing the proper sites and planting stock are 

important. Container stock works best due to its flexibility with respect to lifting and 

shipping on short notice. If weather prevents planting, then container stock stores 

well. Having stock that is hardened off enough to deal with the elements is important

to deal with any hot weather in the fall. However, the trees should not be so hardened 

off that they are in dormancy and still capable of growing roots. The ideal is to plant 

at least three weeks before soil temperatures drop below 40 ̊F (4 ̊C), at which time

root growth largely stops (above 5,000 ft (1520m) this usually occurs by November). 

When fall planting; a “hot plant” is essential; that is, the trees should be planted 

within 10 to 14 days of lifting so that they are ready to grow right out of the cooler. 

When storing trees, do not store below 40 degrees, otherwise the trees will be pushed 

into dormancy and will not grow roots after planting. If seedlings are kept longer than 

10 days at 40 ̊F (4 ̊C) or more, there is an increased risk of fungal attack (Botrytis 

spp.). 

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Lessons Learned on 50,000 acres—Webster and Fredrickson 

Biodiversity

The use of herbicides often raises concerns about adverse impacts on 

biodiversity. DiTomaso et al. (1995) conducted a biodiversity study in three different 

fires, the Pondosa burn of 1977 (treated and planted between 1981 and 1988), the 

Tamarack fire of 1985, and the Fountain fire (FF) of 1992. The primary site 

preparation chemical was Velpar (active ingredient is hexanzinone). In the Pondosa

burn and Tamarack fire, stands treated with herbicide showed greater species 

diversity than stands with no treatment; however, the trend over this chronosequence 

of three sites shows that with time the diversity will approach pre-burn species 

diversity in both treated and untreated stands (fig. 7). Untreated stands are rapidly

dominated by a few species of brush, but treated units have greater diversity of 

grasses and forbs. The treatment effect is relatively short lived, so is consistent with 

the goal of setting back the competing vegetation only long enough for successful 

establishment and growth of seedlings. 

Figure 7—Plant species richness for three stand conditions (old growth, young 

plantation with Velpar treatment, young plantation with no Velpar treatment) and

three stand ages (Fountain Fire (1992), Tamarack Fire (1985), and the Pondosa Burn 

(1977).

0

0.2

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Log Species Number

old growth

Velpar

no Velpar

0

0.2

0.4

0.6

0.8

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1.2

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Log Species Area (m)

Log Spe cies N um ber

0

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0.4

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Pre-Commercial Thinning

Most foresters generally leave too many trees after thinning (Webster, 1997), 

often necessitating a second precommercial thinning to avoid stand stagnation and 

excessive mortality. Evaluating stand density using Reineke’s (1933) Stand Density 

Index (SDI=equivalent number of 10-in (25-cm) trees per ac), Oliver and Uzoh 

(1997) have shown that ponderosa pine stands rarely exceed an SDI of 365 (902 25-

cm trees per ha). However, heightened risk of bark beetle mortality begins at an SDI 

of about 230 (568 per ha). Disturbance from snow breakage is confined almost 

exclusively to stand densities of more than 183 SDI (452 per ha). Ensuring that trees 

in the stand get to a commercial size (minimum mean diameter of 14 in (36 cm)) as 

they reach these SDIs requires pre-commercial thinning to approximately 140 trees

per ac (346 tree per ha) or less (Table 1). The stand density bounds for a managed

278 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

depend on the level of risk one is willing to accept under stressful conditions such as 

drought. 

Table 1. Stand density index (SDI) given by four different combinations of tree density 

(trees/ac) and quadratic mean diameter (QMD, in). SDIs are based on a slope of –1.77 for 

the maximum size density limit (Oliver and Powers 1978).

Trees per 

ac (per ha) 

QMD, in 

(cm)

SDI 

(metric)

140 (346) 13 (33.0) 223 (551) 

140 (346) 14 (35.6) 254 (627) 

140 (346) 15 (38.1) 287 (709 

140 (346) 16 (40.6) 322 (795) 

140 (346) 17 (43.2) 358 (884) 

Pre-commercial thinning presents the problem of slash disposal to prevent 

excessive fuel loading and fire risk. Within the public agencies, reducing fuel risk is a 

high priority, so lopping or some type of fuel treatment is required after thinning. In

forest industry, minimizing cost is a higher priority, so lopping is done only along

roads to meet regulatory requirements. This type of fuel creates an elevated fuel 

hazard and after ignition supports longer flame lengths, making fire risk and potential 

severity higher for 5 to 10 years after the thinning. 

Where co-generation plants exist, cutting and hauling the material to the plant 

can reduce other types of fuel. Marketing the biomass of small-diameter material in 

this way can offset the costs of thinning and reducing fuel loads. 

Western Pine Shoot Borer 

The western pine shoot borer (Eucosma sonomana Kearfott) is endemic to the 

interior West and attacks young ponderosa pine. The female attraction pheromone 

was identified in the 1970s. Many studies have explored the use of pheromone for

tree protection. One application technology referred to as microencapsulated, or

MEC, was tested aerially in 2002 and 2004 and worked very well (Gillette and others 

2004). This product was developed by 3M and involves microscopic capsules mixed

in water. Unfortunately, the company has decided to discontinue manufacturing the 

product. Applied Pheromone Technologies in Vancouver, Washington, has just 

registered a hand application product in California (Last Call AK). This product is a 

mating disruptant and an insecticide that together “attract and kill” (AK) the target 

species. Another aerial product consisting of tiny flakes and produced by Hercon is 

being tested in 2005. 

Williams (1989) showed about a five percent increase in volume growth where 

the male pheromone was introduced as a disruptant. In that study a single application 

to a young stand yielded better results than multiple treatments to older stands. 

Recent observations (Webster and Gray, unpublished data) show a doubling of 

damage to the terminal shoot after pre-commercial thinning. Endemic populations of

the western pine shoot borer within the Pondosa Burn of eastern Siskiyou County 

damaged 20 to 40 percent of the trees in 1996. After thinning, damage increased to 

80 to 90 percent of the trees, and it took about five years for damage to return to 

endemic levels. If only a single pheromone treatment was feasible, these observations 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 279 
Lessons Learned on 50,000 acres—Webster and Fredrickson 

suggest that a treatment immediately after pre-commercial thinning may be the best 

strategy. 

Conclusions 

Three main conclusions are worth re-emphasizing: 

• Planning is critical!! 

• Attention to detail is essential!! 

• Research is invaluable!! 

– Increases success 

– Reduces cost in the long term 

– Increases the potential for growth 

– Develops treatments friendlier to the environment 

References 

DiTomaso, J.M.; Marcum, D.B.; Rasmussen, M.S.; Healy, E.A.; Keyser, G.B. 1997. Postfire herbicide spray enhance native plant diversity. California Agriculture 5(1):6-11.

Dunning, D. 1942. A Site Classification for the Mixed Conifer Selection Forests of the 

Sierra Nevada. Res. Note 28. Berkeley, CA: California Forest and Range Experiment

Station, Forest Service, U.S. Department of Agriculture. 

Gillette, N.E.; Owen, D.R.; Webster, J.; Stein, J.D. 2004. Efficacy of microencapsulated

pheromone for mating disruption of western pine shoot borer, Eucosma sonoma. 

Minutes of 53rd Annual Meeting, California Forest Pest Council, November 9, 2004, 

Woodland, CA. 

Mayer, K.E.; Laudenslayer, W.F. Jr. editors. 1988. A Guide to Wildlife Habitats of

California. Sacramento, CA; Department of Fish and Game, Resources Agency, State 

of California; 166 p. 

Oliver, O.W.; Uzoh, U.C.C. 1997. Maximum stand densities for ponderosa pine and red

and white fir in Northern California. Intensive Forest Management. Redding, CA: 

Proceedings of the 18th Annual Forest Vegetation Management Conference, University

of California Cooperative Extension Forestry Program; 57-65. 

Powers, R.F.; Ferrell, G.T. 1996. Moisture, nutrient, and insect constraints on plantation

growth: the “Garden of Eden” experiment. New Zealand Journal of Forestry Science 

26:126-144. 

Powers, R.F.; Alves, T.M.; Spear, T.H. 1999. Soil compaction: Can it be mitigated?

Reporting a work in progress. Healthy Forests for the 21st Century. Redding, CA;

Proceedings of the 20th Annual Forest Vegetation Management Conference, University

of California Cooperative Extension Forestry Program; 47-56. 

Powers, R.F.; Reynolds, P.E. 2000. Intensive management of ponderosa pine plantations:

Sustainable productivity for the 21st Century. Journal of Sustainable Forestry 10: 

249-255. 

Stein, J.D.; Owen, D.R.; Webster, J.N.; Gillette, N.E. 2004. Aerially applied microencapsulated pheromone for mating disruption of western pine shoot borer, 

Eucosma sonomana (Lepidopera: Tortricidae). Forest Diversity and Resistance to 

Native and Exotic Pests Insects. Hanmer Springs, New Zealand: IUFRO meeting, 

Sections 7.03.03, 7.03.05, 7.03.07, and 8.07.02. 

280 USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 
Pacific Southwest Research Station 

PO Box 245 

Berkeley, CA 94701 

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Lessons Learned on 50,000 acres—Webster and Fredrickson 

Webster, J.N. 1997. Pre-commercial Thinning in Plantations: Why, When and How? An 

Industrial Perspective for Interior California. Intensive Forest Management.

Redding, CA; Proceedings of the 18th Annual Forest Vegetation Management

Conference, University of California Cooperative Extension Forestry Program: 83-87. 

Williams, C.B.; Smith, E.L.; Koerber, T.W. 1989. Damage appraisal and management of 

the western pine shoot borer, Eucosma sonomana, in pine plantations in California: 

a case study. In: Alfaro, R.I.; Glover, G. (eds.). Proceedings of the IUFRO working 

group on insects affecting reforestation. Vancouver, B.C.: 18th International Congress of 

Entomology; 110-123.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-198. 2005. 281