United States 

Department of 

Agriculture

Forest Service

Pacific Southwest 

Research Station

General Technical 

Report 

PSW-GTR-237

March 2012

DEPAR TMENT OF AGRICULT URE

Managing Sierra Nevada Forests
Editor

Malcolm North is a research ecologist, Pacific Southwest Research Station, 

1731 Research Park Dr., Davis, CA 95618.

Cover photographs: (top) mixed-conifer forest with an active fire regime, by 

Marc Meyer; (middle, from left) regeneration in a forest gap, by Malcolm North; 

chipmunk on a log surrounded by shrub cover, by Brian Oakley; waterfall and 

pool in Sierra Nevada granite, by Malcolm North; (bottom) prescribed fire at 

Blodgett Experimental Forest, by Kevin Krasnow.

The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of 

multiple use management of the Nation’s forest resources for sustained yields of wood, 

water, forage, wildlife, and recreation. Through forestry research, cooperation with the 

States and private forest owners, and management of the National Forests and National 

Grasslands, it strives—as directed by Congress—to provide increasingly greater service 

to a growing Nation.

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opportunity provider and employer.
Managing Sierra Nevada Forests

Malcolm North, Editor

U.S. Department of Agriculture, Forest Service

Pacific Southwest Research Station

Albany, California

General Technical Report PSW-GTR-237

March 2012
Abstract

North, Malcolm, ed. 2012. Managing Sierra Nevada forests. Gen. Tech. Rep. 

PSW-GTR-237. Albany, CA: U.S. Department of Agriculture, Forest Service, 

Pacific Southwest Research Station. 184 p. 

There has been widespread interest in applying new forest practices based on 

concepts presented in U.S. Forest Service General Technical Report PSW-GTR-220, 

“An Ecosystem Management Strategy for Sierran Mixed-Conifer Forests.” This 

collection of papers (PSW-GTR-237) summarizes the state of the science in 

some topics relevant to this forest management approach, presents case studies 

of collaborative planning efforts and field implementation of these new practices, 

and clarifies some of the concepts presented in GTR 220. It also describes a 

method for assessing forest heterogeneity at the stand level using the Forest 

Vegetation Simulator and a new geographic information system tool for projectlevel planning that classifies a landscape into different topographic categories. 

While this collection of papers presents information and applications relevant to 

implementation, it does not offer standards and prescriptions. Forest management 

should be flexible to adapt to local forest conditions and stakeholder interests. 

This report does, however, strive to clarify concepts and present examples that 

may improve communication with stakeholders and help build common ground 

for collaborative forest management.

Keywords: Ecosystem restoration, forest resilience, heterogeneity, 

stakeholder collaboration.
Preface

Public forest-land management policy in the Sierra Nevada has gone through 

substantial changes over the last 20 to 30 years. Policies have tried to incorporate 

and adapt to public concerns on such issues as sensitive wildlife, high-severity 

wildfire, and changing climate conditions. Through the 1990s and first decade of 

the 21st century, Sierra Nevada forest management focused on either mechanical 

fuels reduction or minimal entry into and maintenance of California spotted owl 

(Strix occidentalis occidentalis) habitat. Recently, many of the 10 national forests 

in the Sierra Nevada began using concepts found in U.S. Forest Service General 

Technical Report PSW-GTR-220, “An Ecosystem Management Strategy for 

Sierran Mixed-Conifer Forests”1

 (hereafter GTR 220) as a foundation to plan and 

implement projects. Summarizing recent scientific research, GTR 220 suggested 

revising management practices to actively integrate the provision of wildlife habitat 

and ecosystem restoration with fuels reduction. The GTR emphasized increasing 

forest heterogeneity at fine (within-stand) and large (across-landscapes) scales using 

topography as a guide for varying treatments. It also emphasized the ecological 

importance of fire, the need to retain suitable structures for sensitive wildlife, and 

locations where ecosystem restoration might involve thinning intermediate-sized 

trees. In the initial GTR, the focus was on developing the concepts of ecosystem 

management for the Sierra Nevada. A second edition of the GTR published in 

2010 added an addendum addressing some of the issues frequently raised by 

forest managers. 

Translating GTR 220’s concepts into management practices required innovation 

in collaboration, planning, and implementation. Over the course of many field visits 

to projects implementing GTR 220 concepts, it became clear that some information 

gaps still persist, including science summaries of typically problematic topics most 

projects need to address, conditions that fostered successful stakeholder collaboration, tools for assessing forest heterogeneity, and project examples of GTR 220 

implementation and marking options. This GTR is an effort to respond to those 

needs. 

The first section provides a summary of recent research in areas that managers 

have requested and addresses a specific suite of topics that affect fuels and forest 

restoration treatments and wildlife habitat in lower and mid-elevation Sierra Nevada 

forests. Topics include (1) fire and fuels reduction and whether current fire models 

1 North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An ecosystem management strategy for Sierran mixed-conifer forests. 2nd ed. with addendum. Gen. Tech. Rep. 

PSW-GTR-220. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific 

Southwest Research Station. 49 p.
can simulate fire response to the fine-scale heterogeneity suggested by GTR 220; 

(2) bark beetle dynamics—their potential response to different stand structures 

and how beetles may respond to increased variability in stem density and species 

composition; and (3) current and future impacts of climate change on Sierra Nevada 

forests and how important it is to understand the processes shaping historical 

forests to better manage ecosystems in an uncertain future. 

The second section focuses on aspects of wildlife management affecting Sierra 

Nevada forests. It includes (4) the latest research about two species of concern in 

lower and mid-elevation forests—fisher and marten; (5) a summary of California 

spotted owl research that has accumulated since Verner et al. (1992); and (6) some 

principles of managing for wildlife communities with variable scales, different preferred habitat conditions, and often-unknown responses to management practices. 

The next section examines tools that can aid project implementation such as (7) 

building collaboration and (8) stakeholder involvement. Also addressed are (9) tools 

for increasing forest heterogeneity at the stand level with general marking guidelines and using the Forest Vegetation Simulator to assess structural heterogeneity in 

treated stands; and (10) at the landscape level using a geographic information system (GIS) tool developed to classify project landscapes into different topographic 

categories, which might merit different forest treatments. 

The next section focuses on implementation, presenting case studies of projects 

that have used GTR 220 concepts. It details how the concepts in GTR 220 were (11) 

translated into project design and marking in the Dinkey North and South project 

on the Sierra National Forest; were (12) similar to the variable density thinning 

study at Stanislaus-Tuolumne Experimental Forest; and (13) used in drier eastern 

Sierra forests on the Sagehen Experimental Forest to meet fuels reduction, forest 

restoration, and marten habitat improvement objectives.

The final summary sections clarify some GTR 220 concepts and address topics 

that appear to currently limit management options. Chapter 14 addresses under 

what conditions GTR 220 concepts apply; what characteristics identify “defect” 

trees with wildlife value; how canopy conditions can be more accurately assessed 

given the current standards and guides emphasis on canopy cover targets; and how 

heterogeneity may influence forest resilience and how it might be assessed. The 

final chapter (15) suggests changes that may be needed to insure that progress made 

with GTR 220 continues. Reflecting on lessons learned from field project visits and 

from these compiled chapters, this last chapter discusses how silviculture practices 

can adopt principles of heterogeneity, economic constraints and the scale of treatments, and the scientific merit and collaborative importance of committing to 

question-driven monitoring. 
Forest Service managers in the Sierra Nevada have repeatedly mentioned two 

concerns with GTR 220. The first is an apprehension that practices suggested in the 

ecosystem management strategy are too time consuming, expensive to implement, 

difficult for marking crews to interpret, and involve lengthy and costly forums 

for public involvement. The examples in these chapters suggest that such hurdles 

appear larger than they really are. With any new forest management strategy, 

initial implementation will be slower and more complex than current practices. 

This approach, however, offers a set of ecological restoration principles that are 

grounded in the latest research findings. Adoption of these principles may help 

build the trust and transparency necessary before more streamlined projects are 

attempted. Future workshops and information exchange could help managers communicate what worked and what did not, and avoid each project having to “reinvent 

the wheel.” I hope that what is presented in these chapters will help shorten the 

learning curve for all of us. 

A second concern is balancing the need to clarify concepts while retaining 

management flexibility. Although managers have requested more detailed definition 

of GTR 220’s concepts, there is also wariness that this detail will lead to prescriptive guidelines that could constrain management practices. This collection of 

papers, however, is not a prescriptive guide or a set of standards for ecosystem management. Rather it provides examples and information on lessons learned so far, as 

well as relevant science summaries. Each manager will need to find their own route 

to implementation that responds to the forest conditions and public constituencies 

they have. Best management practices require a flexible response to local conditions 

and needs. Helping to return that flexibility and “art” back to forestry is the essential hope of this second GTR. For stakeholders to support this flexibility, however, 

there needs to be a common conceptual foundation for understanding how management decisions will be made and how we subsequently learn from the attempts to 

implement these new approaches. This collection of papers attempts to clarify that 

conceptual foundation and provide tools and examples of GTR 220 implementation. 

There is an apprehension that practices 

suggested in the 

ecosystem management 

strategy are too time 

consuming, expensive 

to implement, difficult 

for marking crews to 

interpret, and involve 

lengthy and costly 

forums for public 

involvement. The 

examples in these 

chapters suggest 

that such hurdles 

appear larger than 

they really are. 
Contents

1 Chapter 1: Fire and Fuels Reduction

 B.M. Collins and S.L. Stephens

1 Introduction

1 Modeling Considerations

4 Landscape Fuel Treatment Design

7 Mixed Fire Severity Across Landscapes

9 Literature Cited

13 Chapter 2: Forest Health and Bark Beetles

C.J. Fettig

13 Introduction

13 Host Tree and Bark Beetle Dynamics

14 Factors Associated With Bark Beetle Infestations

15 Managing Stand Density to Reduce Susceptibility to Bark Beetle Infestations 

16 Implications of Climate Change on Bark Beetle Dynamics 

18 Forest Heterogeneity and Bark Beetles

19 References

23 Chapter 3: Climate Change and the Relevance of Historical Forest Conditions

 H.D. Safford, M. North, and M.D. Meyer

23 Introduction

25 Recent Trends in Climate and Climate-Driven Processes in the Sierra Nevada

31 Projected Trends in Climate and Climate-Driven Processes 

37 Is History Still Relevant?

39 References

47 Chapter 4: Fishers and American Martens

 K.L. Purcell, C.M. Thompson, and W.J. Zielinski

47 Introduction

47 Habitat Preferences

50 Forest Condition and Management Effects

51 New Analysis Tools

52 Potential Implications of Climate Change

54 Unknowns

56 References

61 Chapter 5: California Spotted Owls

 S. Roberts and M. North

61 Introduction

61 Population Trends

62 Barred Owl

62 Climate Change Effects

63 Spotted Owl Nesting and Foraging Habitat Characteristics

64 Spotted Owls and Fire

66 References
73 Chapter 6: Managing Forests for Wildlife Communities

M. North and P. Manley

73 Introduction

73 Multispecies Habitat Management

74 Vertebrate Conservation and Fuels Reduction

77 Multiscale Monitoring

78 References

81 Chapter 7: Developing Collaboration and Cooperation

 G. Bartlett

81 Introduction

81 Dinkey Project History

83 Mediator’s Role

84 Five Stages of Collaboration 

84 Steps That Facilitated Collaboration for the Dinkey Project

87 Additional Steps for Successful Collaboration and Cooperation

88 References

89 Chapter 8: Using GTR 220 to Build Stakeholder Collaboration

 C. Thomas

89 Introduction

89 Improved Communication

90 Sustainability

91 Perceived Problems

91 Challenges

91 Future Directions

92 References

95 Chapter 9: Marking and Assessing Forest Heterogeneity

 M. North and J. Sherlock

95 Introduction

96 General Marking Suggestions

97 Stand Visualization Simulator Examples

101 Using FVS to Assess Heterogeneity

104 References

107 Chapter 10: Geographic Information System Landscape Analysis 

Using GTR 220 Concepts

M. North, R.M. Boynton, P.A. Stine, K.F. Shipley, E.C. Underwood, 

N.E. Roth, J.H. Viers, and J.F. Quinn

107 Introduction

108 Foundations for the GIS Tool

109 Background and Description of the GIS Tool

114 Chapter Summary

114 Literature Cited

117 Chapter 11: Dinkey North and South Project

M. North and R. Rojas

117 Introduction
118 Context

118 Information Used

120 Implementation

121 Lessons Learned

124 References

127 Chapter 12: The Variable-Density Thinning Study at Stanislaus-Tuolumne 

Experimental Forest 

E. Knapp, M. North, M. Benech, and B. Estes

127 Introduction 

129 Context 

129 Information Used

132 Implementation

135 Lessons Learned

138 References

141 Chapter 13: Applying GTR 220 Concepts on the Sagehen Experimental Forest

 P. Stine and S. Conway

141 Introduction

141 Context

143 Information Used

144 Implementation

144 Lessons Learned

147 References

149 Chapter 14: Clarifying Concepts 

 M. North and P. Stine

149 Introduction

150 Forest Types and Landscapes Where GTR 220 Concepts Apply

151 Defect Trees

152 Canopy Cover and Closure

156 Heterogeneity and Resilience

159 References

165 Chapter 15: A Desired Future Condition for Sierra Nevada Forests 

 M. North 

165 Introduction

165 The Limitations of Stand-Level Averages

167 Economics and Treatment Scale

169 Monitoring

172 Chapter Summary

172 References

176 Metric Equivalents

176 Acknowledgments

177 Appendix: Examples of Forest Structures That May Provide Wildlife Habitat

D. Walsh and M. North
1

Managing Sierra Nevada Forests

B.M. Collins1 and S.L. Stephens2

Introduction

Fire will continue to be a major management challenge in mixed-conifer forests 

in the Sierra Nevada. Fire is a fundamental ecosystem process in these forests 

that was largely eliminated in the 20th century. Fire reintroduction is a critical 

goal but is subject to constraints such as smoke production, risk of fire moving 

outside designated boundaries, the expanding wildland-urban interface, and lack of 

experience in burning large areas of forest. Recent fire and fuels research relevant 

to planning and implementing forest/fuels treatments revolve around three main 

topics: (1) potential limitations in the widely used Fire and Fuels Extension (FFE) 

module of the Forest Vegetation Simulator (FVS), (2) designing effective fuels 

treatment placement in landscapes under real world constraints, and (3) the size of 

high-severity burn patches in a landscape with an active mixed-severity fire regime. 

Although it currently may be difficult to model fire behavior in forests treated for 

the fine-scale structural and fuel heterogeneity suggested in U.S. Forest Service 

General Technical Report PSW-GTR-220, “An Ecosystem Management Strategy 

of Sierran Mixed-Conifer Forests” (hereafter GTR 220) (North et al. 2009a) 

collectively, the ideas presented may improve fuel treatment implementation 

and forecasting of wildfire effects on Sierran forests.

Modeling Considerations

Fire behavior predictions from FFE are critical in the evaluation of forest/fuel 

treatments (North et al. 2009a). These predictions rely heavily on the characterization of surface fuels. It is difficult, however, to both accurately measure all of the 

key characteristics affecting surface fuel pools (loads by size class, fuel bed depth, 

surface area to volume ratios by size class, heat content, etc.) and calibrate these 

values based on observed fire behavior. Therefore, fuels are often represented by 

established fuel models (Anderson 1982, Scott and Burgan 2005) that contain the 

collection of fuel properties needed to run the Rothermel surface fire spread model 

(Rothermel 1972), the basis for much of the fire behavior modeling done in the 

United States (Andrews et al. 2003; Finney 1998, 2006). Fuel models are determined internally in FFE based on forest structural characteristics, species composition, and, in some cases, site productivity (Rebain 2009, Reinhardt and Crookston 

2003). Recent studies have identified some inadequacies with this internal fuel 

Chapter 1: Fire and Fuels Reduction

1 Postdoctoral research fire ecologist, U.S. Department of Agriculture, Forest Service, 

Pacific Southwest Research Station, 1731 Research Park Dr., Davis, CA 95618.

2 Associate professor, Mulford Hall, University of California, Berkeley, CA 94720.
2

GENERAL TECHNICAL REPORT PSW-GTR-237

Summary of Findings

1. Potential limitations in the widely-used Fire and Fuels Extension 

(FFE) module of the Forest Vegetation Simulator (FVS). We discuss 

three limitations: (1) FFE’s internal fuel model selection based on forest structure, which can lead to underestimation of fire behavior and 

crown fire potential; (2) problems with FVS’s regeneration module, which 

produces higher live crown base heights over time that may incorrectly 

reduce torching potential; and (3) FFE’s calculation of single stand-level 

inputs for fire behavior modeling, which may not capture variable fire 

effects in forests with fine-scale heterogeneity such as those proposed in 

GTR 220.

2. Designing effective fuels treatment placement in landscapes under 

real world constraints. Past research has provided a theoretical framework in the design of strategically placed landscape fuel treatments, but 

such designs are constrained by real landscapes. Two recent Sierran landscape fuel treatment projects were evaluated where treatment arrangement 

was based more on local knowledge than on intensive modeling. Results 

indicate that such treatments can be quite effective at reducing potential 

fire behavior.

3. The size of high-severity burn patches in a landscape with an active 

mixed-severity fire regime. Mixed-conifer fire regimes have commonly 

been characterized as frequent, low-moderate intensity before the onset 

of fire exclusion. Recent research has identified patches of high-severity 

fire as integral components of these regimes, but the vast majority of such 

patches were small. In upper mixed-conifer forests that have been subjected to over 30 years of burning by lightning fires, the median highseverity patch size was about 5 ac, while large patches, those >150 ac, 

made up <5 percent of the total patches by frequency. Some wildfires 

today are creating high-severity patches at much larger scales than are 

desirable to ecologists, managers, and the public.
3

Managing Sierra Nevada Forests

model logic, particularly when incorporating the 40 Scott and Burgan (2005) fuel 

models (Collins et al. 2011a, Seli et al. 2008). Collins et al. (2011a) reported that 

the inclusion of FFE-selected fuel models when simulating fire across their study 

landscape resulted in a substantial underrepresentation of crown fire potential when 

modeling under 95th percentile wind and moisture conditions. This assessment of 

crown fire potential was based on a comparison between modeled crowning within 

their study area and observed crowning in two nearby wildfires, both of which 

occurred under wind and moisture conditions similar to those modeled. In a recent 

study, Cruz and Alexander (2010) pointed out inherent problems in our current fire 

modeling approaches, whether using FFE or other models such as NEXUS, that lead 

to the underprediction of crown fire potential. Regardless, model users should critically evaluate both the FFE-chosen fuel model(s) and the fire behavior output from 

FFE before finalizing modeling results. In instances where predicted fire behavior is 

noticeably different from observed fire behavior for similar stands/fuel complexes, 

overriding the FFE fuel model selection with a user-input fuel model is probably 

necessary.

Another potential problem with FFE model outputs of future fire behavior can 

result from limitations in the regeneration module in FVS. The FVS variants other 

than western Montana, central and northern Idaho, and coastal Alaska do not have 

the “full” regeneration establishment model (Dixon 2002). Consequently, most FVS 

variants do not model natural regeneration or ingrowth. In the absence of ingrowth, 

modeled development of undisturbed stands generally results in larger and taller 

trees with higher stand-level canopy base height. These conditions are modeled to 

produce self-pruning of the trees’ lower limbs. The net effect of this increase in 

canopy base height over time is reduced crown fire potential. This may or may not 

reflect reality. For example, Stephens and Moghaddas (2005) reported that 80 to 

100-year-old mixed-conifer stands in the central Sierra Nevada, which regenerated 

naturally after early railroad logging and were subjected to minimal or no silvicultural treatments throughout their development (except full fire suppression), had high 

canopy base heights, and as a result, low potential for crown fire. Stands with similar 

structure and management history, however, may be rare in the Sierra Nevada. Many 

stands managed with either even- or uneven-age systems have higher potential for 

torching, mainly driven by lower canopy base heights (Stephens and Moghaddas 

2005). The user-defined regeneration option in FVS is one way to manipulate the 

progression of canopy base height over time. The FVS user may need to experiment 

with different levels of regeneration in FVS to insure that model results are consistent 

with observational data from the actual stands that are modeled. A more comprehensive solution would be to collect and summarize long-term forest inventory data to 

support development of a full regeneration module for the western Sierra variant.
4

GENERAL TECHNICAL REPORT PSW-GTR-237

Finally, the FFE module may have difficulty predicting fire behavior in forests 

with fine-scale structure and fuels variability that might be created using GTR 

220 concepts. The FFE stand-level fire behavior predictions are based on a single 

value for each of the fuel/stand structure inputs: fuel model, canopy cover, canopy 

top height, canopy base height, and canopy bulk density. There can be substantial 

heterogeneity within many forest stands, whether driven by variability in underlying edaphic conditions or variability induced by management (Collins et al. 2011b, 

North et al. 2009a). Consequently, the fire behavior predictions may not completely 

reflect actual fire potential. For example, a stand composed of relatively dense tree 

clumps with sparser tree spacing between clumps may be predicted to support an 

active crown fire, when in an actual wildfire, only individual tree and small group 

torching may occur because of the canopy separations between the tree clumps. A 

relatively new output from FFE called P-Torch may help users capture some variability in predicted fire behavior (Rebain 2009, app. A). P-Torch is an index that 

estimates the probability of finding torching of small areas (33 by 33 ft) within a 

stand. Because it is a probability, which is based on fire behavior calculated for 

numerous random subplots as opposed to a threshold windspeed value (e.g., torching index), P-Torch may be better able to represent heterogeneous forest stands.

When more standard fire behavior outputs are required (e.g., flame length, 

fireline intensity), little can be done to correct for the modeling homogenization 

within FVS-FFE short of acquiring more detailed fuel/stand structure data and 

modeling at the substand level. A recent study using a detailed network of sensors 

found significant differences in microclimate, fuel moisture, and fire danger rating 

with fine-scale, topographically-induced weather variation (Holden and Jolly 2011). 

The increased acquisition of light detection and ranging (LiDAR) data may aid in 

capturing fine-scale variability in stand structure. However, these data are expensive, both for acquisition and for processing, and often cannot produce reliable 

information on surface fuels. Further, it is unclear how much, if any, improvement 

there is in fire behavior predictions when using higher spatial resolutions (e.g., 

5- or 1-m pixels [3.3- or 16.4-ft]) vegetation/fuel inputs.

Landscape Fuel Treatment Design

The occurrence of increasingly large fires from warming climates and fuel accumulations (Miller et al. 2009, Westerling et al. 2006) warrants large planning scales for 

fuel and restoration treatment projects. In addition, the effort required for planning 

and analysis of alternatives tends to force larger project areas. However, infrastructure and funding limitations, combined with land management and operational 

constraints, limit the extent to which fuel and restoration treatments can be impleThe FFE module 

may have difficulty 

predicting fire behavior 

in forests with finescale structure and 

fuels variability that 

might be created using 

GTR 220 concepts. 

... A relatively new 

output from FFE called 

P-Torch may help 

users capture some 

variability in predicted 

fire behavior. 
5

Managing Sierra Nevada Forests

mented across landscapes (Collins et al. 2010). As such, managers are forced to 

make choices about how to arrange discrete treatment units to collectively limit the 

spread of high-intensity wildfire across a landscape. Owing to the complexity of 

modeling fire and fuels treatments across landscapes (data acquisition, data processing, model execution, etc.), fuel treatment project design is often based on local 

knowledge of both the project area and past fire patterns. 

Two recent studies in the northern Sierra Nevada suggest that such landscape 

fuel treatment projects (i.e., treatment arrangement was based more on local 

knowledge than on intensive modeling) can be quite effective at reducing potential 

fire behavior at the landscape scale (Collins et al. 2011a, Moghaddas et al. 2010). 

Reductions in potential fire behavior in two U.S. Forest Service projects were 

largely attributed to treatment unit arrangement relative to the dominant highwind directions that typically occur throughout the fire season in each project area 

(fig. 1-1). In the Meadow Valley study area (Moghaddas et al. 2010), treatment 

units were arranged in a somewhat linear fashion with multiple “layers” across the 

landscape (fig. 1-1, left panel). These “layers” tended to be orthogonal to the “problem” wind direction in that area, which increases the potential for modeled fires to 

intersect treated areas. This orientation, combined with the multiple layers of treatments, resulted in reductions in modeled fire spread and intensity for “problem” 

wind-driven fires, which reduced the probability of high-intensity fire across much 

of the landscape. Aside from predictable reductions in intensity within treatment 

units, there were also pronounced effects on the downwind or lee side of treatments 

(fig. 1-1, left panel). 

Treatment units in the Last Chance study area (Collins et al. 2011a) were much 

more clumped and centered about the long axis of the study area. In addition, 

the treatments were slightly shifted toward the upwind side of the study area (fig. 

1-1, right panel). This treatment arrangement was quite different from that for the 

Meadow Valley area, but very effective at reducing the probability of high-intensity 

fire (fig. 1-1). Unlike Meadow Valley, Last Chance had multiple “problem” wind 

directions. By having relatively large, centralized treatment blocks that were placed 

more toward the upwind edge, Last Chance treatments may have been a good 

safeguard against modeled wind-driven fires spreading from multiple directions.

Accelerating the rate and extent of fuels reduction is needed because longer fire 

seasons and warmer temperatures associated with a changing climate (Westerling 

et al. 2006) may increase the potential for high-severity fire in Sierra Nevada 

mixed-conifer forests (Miller et al. 2009). Stand- and landscape-level reductions 

in hazardous fire occurrence can be achieved while incorporating heterogeneity into stand prescriptions (North et al. 2009a). Recent papers found most fuels 

Landscape fuel 

treatment projects 

based more on local 

knowledge than on 

intensive modeling 

can be quite effective 

at reducing potential 

fire behavior at the 

landscape scale.
6

GENERAL TECHNICAL REPORT PSW-GTR-237

Figure 1-1—Posttreatment minus pretreatment difference in modeled conditional burn probabilities for two landscape fuel treatment 

projects in the northern Sierra Nevada. Conditional burn probabilities are based on 5,000 randomly placed ignitions simulated using 

RANDIG. Reported burn probabilities are for flame lengths that are consistent with crown fire initiation (see Collins et al. 2010a for 

explanation). The arrows represent the modeled “problem” wind direction(s) for each project. Note the different scales for the two 

projects; the approximate sizes of the study area are Meadow Valley 45,700 ac (18 500 ha); Last Chance 10,600 ac (4300 ha). NF = 

national forest.

treatments did not adversely affect many ecosystem services (Stephens et al. 2011) 

and had minimal impact on forest microclimate (Bigelow and North 2011) suggesting treatments may not compound warming trends. Forest resiliency at landscape 

scales (Collins et al. 2010) needs to be increased before changing fire regimes create 

conditions that managers and the public find unacceptable. The next one to three 

decades are a critical period in mixed-conifer forest management and conservation 

in the Sierra Nevada.
7

Managing Sierra Nevada Forests

Mixed Fire Severity Across Landscapes

One of the concepts presented in GTR 220 is the ecological importance of fire 

in Sierran mixed-conifer forest (North et al. 2009a) as it applies to stand-level 

processes and structures, as well as landscapes. There are numerous studies documenting the historical occurrence of frequent, low-severity fires in mixed-conifer 

forests throughout the Sierra Nevada (Beaty and Taylor 2008; North et al. 2005, 

2009b; Scholl and Taylor 2010; Skinner and Chang 1996; Stephens 2001; Stephens 

and Collins 2004; Taylor and Beaty 2005). Collectively, these studies suggest that 

historical forests had a low incidence of high-severity, or stand-replacing fire. However, issues of data availability and data collection associated with these historical 

reconstructions limit the inferences that can be made regarding more fine-grained 

stand-replacing fire effects, particularly when attempting to characterize fire over 

a landscape (Collins and Stephens 2010). These limitations lead to uncertainty in 

characterizing the “natural” role of stand-replacing fire in Sierra Nevada mixedconifer forests. This information is important for determining acceptable levels 

of stand-replacing fire and designing forest/fire management strategies to achieve 

these levels. Areas that have allowed naturally ignited fires to operate on the landscape for multiple decades, such as the Illilouette Creek basin in Yosemite National 

Park and Sugarloaf Creek area in Sequoia and Kings Canyon National Parks, are 

possible points of reference for characterizing more natural forest/fire interactions 

in the Sierra Nevada. This is not to suggest that these long-term natural fire areas 

are a proxy for historical forest/fire interactions because despite having multiple 

decades of natural fire, these areas were affected by fire-exclusion policies for about 

90 years prior to initiation of natural fire programs (Collins and Stephens 2007). 

Although there were noticeable impacts of fire exclusion, these areas represent fire 

regimes that are largely restored, which has particular relevance to current forest 

management given differences between historical and current/projected future 

climates (Collins and Stephens 2010). While both of these long-established natural 

fire areas are characterized as mixed-conifer forests, they are generally at higher 

elevations (6,500 to 8,000 ft) than much of the managed mixed-conifer forests 

throughout the Sierra Nevada. Dominant tree species in these areas are Jeffrey pine 

(Pinus jeffreyi Balf.), white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), 

red fir (A. magnifica A. Murray), lodgepole pine (P. contorta murrayana (Balf.) 

Engelm.), and to a lesser extent, sugar pine (P. lambertiana Douglas).

Collins and Stephens (2010) studied stand-replacing patches within recent 

fires occurring in the upper elevation, mixed-conifer forests of the Illilouette 

basin. These fires were predominantly low to moderate severity, with about 15 

percent of the fire areas classified as high severity (Collins and Stephens 2010). 

Patch sizes ranged from 1.3 to 230 ac (0.53 to 93 ha), with small patches (<10 ac) 
8

GENERAL TECHNICAL REPORT PSW-GTR-237

(4 ha) accounting for more than 60 percent of the total number of patches (fig. 1-2). 

Large patches (>150 ac) (60 ha) made up about 5 percent of the total number of 

patches, but accounted for nearly half the total stand-replacing patch area. Median 

stand-replacing patch size was 5.4 ac (2.2 ha). Perhaps most importantly, Collins 

and Stephens (2010) found that the largest stand-replacing patches in the Illilouette 

basin (200 to 220 ac) (81 to 89 ha) were an order of magnitude or more below those 

that occurred in recent northern Sierra Nevada wildfires (Antelope Complex and 

Moonlight Fire; 2,500 to 6,200 ac [1011 to 2509 ha]). The authors suggested three 

main implications from their study: (1) stand-replacing fire is a component of Sierra 

Nevada mixed-conifer forests (at least in upper elevation mixed conifer similar to 

the Illilouette area), but at relatively low proportions across the landscape (15 percent or less); (2) the distribution of stand-replacing patches consists of many small 

patches and few large patches; and (3) the stand-replacing patch sizes observed in 

recent Sierra Nevada fires (outside of natural fire areas) often greatly exceed the 

range of patch sizes reported for the Illilouette basin (Miller et al. 2009). 

Figure 1-2—Four-acre high-severity burn patch in the Illilouette basin that provides a high light environment for Ceanothus shrubs and 

pine regeneration. 

Malcolm North

Median stand-replacing 

patch size was 5.4 ac 

... the largest standreplacing patches in 

the Illilouette basin 

(200 to 220 ac) were 

an order of magnitude 

or more below those 

that occurred in recent 

northern Sierra Nevada 

wildfires.
9

Managing Sierra Nevada Forests

Literature Cited

Anderson, H.E. 1982. Aids to determining fuel models for estimating fire 

behavior. Gen. Tech. Rep. INT-122. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Intermountain Forest and Range Experiment Station. 22 p.

Andrews, P.L.; Bevins, C.D.; Seli, R.C. 2003. BehavePlus fire modeling 

system, version 2.0. Gen. Tech. Rep. RMRS-GTR-106WWW. Ogden, UT: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research 

Station. 132 p.

Beaty, R.M.; Taylor, A.H. 2008. Fire history and the structure and dynamics of 

a mixed conifer forest landscape in the northern Sierra Nevada, Lake Tahoe 

Basin, California, USA. Forest Ecology and Management. 255(3–4): 707–719.

Bigelow, S.W.; North, M.P. 2011. Effects of fuels-reduction and group-selection 

silviculture on understory microclimate in Sierran mixed-conifer forest. Forest 

Ecology and Management. 264: 51–59.

Collins, B.M.; Everett, R.G.; Stephens, S.L. 2011b. Impacts of fire exclusion and 

managed fire on forest structure in an old growth Sierra Nevada mixed-conifer 

forest. Ecosphere. 2(4): art 51.

Collins, B.M.; Stephens, S.L. 2007. Managing natural wildfires in Sierra Nevada 

wilderness areas. Frontiers in Ecology and the Environment. 5(10): 523–527.

Collins, B.M.; Stephens, S.L. 2010. Stand-replacing patches within a mixed 

severity fire regime: quantitative characterization using recent fires in a longestablished natural fire area. Landscape Ecology. 25(6): 927–939.

Collins, B.M.; Stephens, S.L.; Moghaddas, J.J.; Battles, J. 2010. Challenges and 

approaches in planning fuel treatments across fire-excluded forested landscapes. 

Journal of Forestry. 108(1): 24–31.

Collins, B.M.; Stephens, S.L.; Roller, G.B.; Battles, J.J. 2011a. Simulating fire 

and forest dynamics for a landscape fuel treatment project in the Sierra Nevada. 

Forest Science. 57(2): 77–88.

Cruz, M.G.; Alexander, M.E. 2010. Assessing crown fire potential in coniferous 

forests of western North America: a critique of current approaches and recent 

simulation studies. International Journal of Wildland Fire. 19(4): 377–398.

Dixon, G.E. 2002. Essential FVS: a user’s guide to the Forest Vegetation Simulator. 

Internal Rep. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 209 p.
10

GENERAL TECHNICAL REPORT PSW-GTR-237

Finney, M.A. 1998. FARSITE: fire area simulator—model development and 

evaluation. Revised. Res. Pap. RMRS-RP-4. Missoula, MT: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station. 47 p.

Finney, M.A. 2006. An overview of FlamMap modeling capabilities. In: Andrews, 

P.L.; Butler, B.W., eds. Fuels management—how to measure success. Gen. Tech. 

Rep. RMRS-P-41. Portland, OR: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station: 213–220.

Holden, Z.A.; Jolly, W.M. 2011. Modeling topographic influences on fuel moisture 

and fire danger in complex terrain to improve wildland fire management decision 

support. Forest Ecology and Management. 262: 2133–2141.

Miller, J.D.; Safford, H.D.; Crimmins, M.; Thode, A.E. 2009. Quantitative 

evidence for increasing forest fire severity in the Sierra Nevada and southern 

Cascade Mountains, California and Nevada, USA. Ecosystems. 12: 16–32.

Moghaddas, J.J.; Collins, B.M.; Menning, K.; Moghaddas, E.E.Y.; Stephens, 

S.L. 2010. Fuel treatment effects on modeled landscape level fire behavior in the 

northern Sierra Nevada. Canadian Journal of Forest Research. 40(9): 1751–1765.

North, M.; Hurteau, M.; Fiegener, R.; Barbour, M. 2005. Influence of fire and El 

Niño on tree recruitment varies by species in Sierran mixed conifer forest. Forest 

Science. 51(3): 187–197.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009a. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

North, M.P.; Van de Water, K.M.; Stephens, S.L.; Collins, B.M. 2009b. 

Climate, rain shadow, and human-use influences on fire regimes in the eastern 

Sierra Nevada, California, USA. Fire Ecology. 5(3): 20–34.

Rebain, S.A. 2009. The Fire and Fuels Extension to the Forest Vegetation 

Simulator. Gen. Tech. Rep. RMRS-GTR-116: Addendum. Ogden, UT: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station. 

262 p.

Reinhardt, E.; Crookston, N.L. 2003. The Fire and Fuels Extension to the Forest 

Vegetation Simulator. Gen. Tech. Rep. RMRS-GTR-116. Ogden, UT: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station. 

209 p.
11

Managing Sierra Nevada Forests

Rothermel, R.C. 1972. A mathematical model for predicting fire spread in 

wildland fuels. Res. pap. INT-115. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Intermountain Forest and Range Experiment Station. 40 p.

Scholl, A.E.; Taylor, A.H. 2010. Fire regimes, forest change, and self-organization 

in an old-growth mixed-conifer forest, Yosemite National Park, USA. Ecological 

Applications. 20(2): 362–380.

Scott, J.H.; Burgan, R.E. 2005. Standard fire behavior models: a comprehensive 

set for use with Rothermel’s surface fire spread model. Gen. Tech. Rep. RMRSGTR-153. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 72 p.

Seli, R.C.; Ager, A.A.; Crookston, N.L.; Finney, M.A.; Bahro, B.; Agee, J.K.; 

McHugh, C.W. 2008. Incorporating landscape fuel treatment modeling into 

the Forest Vegetation Simulator. In: Havis, R.N.; Crookston, N.L., eds. Third 

Forest Vegetation Simulator conference. RMRS-P-54. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station: 

27–39.

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. Wildland Resources Center Report No. 37. 

Davis, CA: University of California, Centers for Water and Wildlands Resources: 

1041–1069.

Stephens, S.L. 2001. Fire history differences in adjacent Jeffrey pine and upper 

montane forests in the eastern Sierra Nevada. International Journal of Wildland 

Fire. 10(2): 161–167.

Stephens, S.L.; Collins, B.M. 2004. Fire regimes of mixed conifer forests in 

the north-central Sierra Nevada at multiple spatial scales. Northwest Science. 

78(1): 12–23.

Stephens, S.L.; McIver J.D.; Boerner, R.E.J.; Fettig, C.J.; Fontaine, J.B.; 

Hartsough, B.R.; Kennedy, P.; and Schwilk, D.W. [In press]. Effects of forest 

fuel reduction treatments in the United States. BioScience.

Stephens, S.L.; Moghaddas, J.J. 2005. Silvicultural and reserve impacts on 

potential fire behavior and forest conservation: twenty-five years of experience 

from Sierra Nevada mixed conifer forests. Biological Conservation. 125(3): 

369–379.
12

GENERAL TECHNICAL REPORT PSW-GTR-237

Taylor, A.H.; Beaty, R.M. 2005. Climatic influences on fire regimes in the 

northern Sierra Nevada Mountains, Lake Tahoe Basin, Nevada, USA. Journal 

of Biogeography. 32(3): 425–438.

Westerling, A.L.; Hidalgo, H.; Cayan, D.R.; Swetnam, T. 2006. Warming 

and earlier spring increases western U.S. forest wildfire activity. Science. 

313: 940–943.
13

Managing Sierra Nevada Forests

C.J. Fettig1

Introduction

In recent years, bark beetles have caused significant tree mortality in the Sierra Nevada (http://

www.fs.fed.us/r5/spf/publications/pestconditions/

index.shtml), rivaling mortality caused by wildfire 

in some locations. This chapter addresses two 

important questions: How can managers prepare 

for and influence levels of bark beetle-caused 

tree mortality given current forest conditions and 

future climate uncertainties? and How would the 

variable forest conditions suggested by U.S. 

Forest Service General Technical Report PSWGTR-220, “An Ecosystem Management Strategy 

for Sierran Mixed-Conifer Forests” (hereafter 

GTR 220) (North et al. 2009), influence these 

dynamics?

Host Tree and Bark 

Beetle Dynamics

Colonization of living hosts by bark beetles 

requires recruitment of a critical minimum 

number of beetles to initiate mass attack and 

overcome host tree defenses (Franceschi et al. 

2005). This threshold differs with host tree vigor 

(i.e., the more “healthy” the tree, the more beetles 

required to overcome tree defenses) as beetles that 

initiate host selection are often killed by drowning or immobilization in resin, especially when 

adequate flow and oleoresin exudation pressure 

exist (Raffa and Berryman 1983, Vité and Wood 

1961). Depending on the bark beetle species and 

numerous other factors (Fettig et al. 2007), levels 

of tree mortality attributed to bark beetle attack 

may be limited to small spatial scales (e.g., single 

Chapter 2: Forest Health and Bark Beetles

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

1731 Research Park Dr., Davis, CA 95618.

Summary of Findings

1. Bark beetles are an essential component of 

forest ecosystems and an important influence 

on stand dynamics. Sierra Nevada forests are 

well recognized for the diversity of tree-killing 

bark beetle species inhabiting them (table 2-1).

2. In the absence of frequent understory fire, 

increases in stand density and tree competition have made many forests more susceptible 

to bark beetle attack. Microclimatic influences 

associated with dense stand conditions may 

increase beetle success in finding host trees and 

beetle fecundity and fitness. In addition, drought 

is one of the more important abiotic factors influencing tree susceptibility in the Sierra Nevada, 

suggesting changing climatic conditions could 

significantly alter the amount and distribution of 

bark beetle-caused tree mortality, particularly in 

dense stands.

3. Reductions in stand density are the most effective treatment for reducing bark beetle-caused 

tree mortality. Reducing competition improves 

tree growth and defensive mechanisms while 

often disrupting pheromone plumes, thus negatively affecting the beetle’s ability to locate and 

successfully mass attack host trees.

4. Increases in stand- and landscape-level heterogeneity may reduce the occurrence of high levels of bark beetle-caused tree mortality while 

maintaining endemic (low) levels. In contrast, 

forested landscapes that contain little heterogeneity promote the creation of large contiguous areas 

susceptible to bark beetle outbreaks.
14

GENERAL TECHNICAL REPORT PSW-GTR-237

trees or small groups of trees) or may affect large areas. When favorable stand and 

climatic conditions coincide, significant tree mortality may occur. While bark beetle 

infestations may affect timber and fiber production, water quality and quantity, fuel 

loadings, fish and wildlife habitat and populations, recreation, grazing capacity, real 

estate values, biodiversity, carbon storage, endangered species, cultural resources, 

and other resources (Coulson and Stephen 2006), bark beetles also play a critical 

role in the functioning of forests.

Factors Associated With Bark Beetle Infestations

After an indepth review of tree and stand factors associated with bark beetle infestations, Fettig et al. (2007) discussed the effectiveness of reducing stand density for 

preventing bark beetle infestations. Most work has concentrated on forests dominated by ponderosa pine (Pinus ponderosa Lawson & C. Lawson) or lodgepole pine 

(Pinus contorta Douglas ex Loud var.). Starting with the earliest research studies, 

factors such as stand density, tree diameter, and host density have been identified as 

primary attributes associated with bark beetle infestations. For example, Craighead 

(1925) and Miller (1926) were among the first to demonstrate that slower growing 

ponderosa pines were more susceptible to bark beetle attack, specifically by the 

western pine beetle, a species of primary importance in the Sierra Nevada. Working 

in the Pacific Northwest, Sartwell (1971) examined the relationship between radial 

growth and mountain pine beetle attack, another species of concern in the Sierra 

Nevada. He reported that nearly all trees killed by mountain pine beetle had crown 

Table 2-1—Bark beetle species that cause significant amounts of tree mortality in the Sierra Nevada 

Common name Scientific name Primary hosts in the Sierra

California fivespined ips Ips paraconfusus Ponderosa pine (Pinus ponderosa Laws.), lodgepole pine (Pinus 

contorta Loud.), sugar pine (Pinus lambertiana Douglas), 

Jeffrey pine (Pinus jeffreyi Grev. & Balf.), and others

Fir engraver Scolytus ventralis White fir (Abies concolor (Gordon & Glend.) Lindl. ex Hildebr.), 

California red fir (Abies magnifica A. Murray bis)

Jeffrey pine beetle Dendroctonus jeffreyi Jeffrey pine

Mountain pine beetle Dendroctonus ponderosae Ponderosa pine, lodgepole pine, sugar pine, white bark pine 

(Pinus albicaulis Engelm.), limber pine (Pinus flexilis James),

western white pine (Pinus monticola Douglas ex D. Don), 

and others

Pine engraver Ips pini Ponderosa pine, lodgepole pine, sugar pine, Jeffrey pine, 

and others

Piñon ips Ips confusus Singleleaf piñon (Pinus monophylla Torr. & Frem.) and others

Western pine beetle Dendroctonus brevicomis Ponderosa pine
15

Managing Sierra Nevada Forests

ratios (the ratio of crown length to total tree height) of ≤ 30 percent, suggesting that 

greater tree competition and slow growth rates increase the likelihood of mountain 

pine beetle attack. In general, less productive sites experienced higher levels of 

mountain pine beetle-caused tree mortality than did high-quality sites of similar 

stocking, a relationship that seems to hold for many bark beetle species. 

Hayes et al. (2009) reported that stand density, measured as basal area or stand 

density index (SDI) (based on the number of trees per unit area and quadratic mean 

diameter [diameter at breast height of the tree of average basal area]), is the most 

important predictor of western pine beetle-caused tree mortality at large spatial 

scales in California. Areas with the highest stand densities experienced the highest 

levels of tree mortality on both an absolute (trees/ha) and proportion (percentage 

of mortality) basis. Surprisingly, host density had less predictive power than other 

measures of stand density, suggesting that tree competition is more important than 

host tree availability. Because SDI is an indicator of the amount of growing space 

available (Reineke 1933), and thus well correlated with tree growth, it is not surprising that SDI would be useful in predicting levels of bark beetle-caused tree mortality. Oliver (1995) reported that maximum SDI for even-aged ponderosa pine stands 

in northern California was regulated by mountain pine beetle and western pine 

beetle infestations. An SDI value of 230 defined a threshold for a zone of imminent 

bark beetle-caused tree mortality within which endemic populations kill a few trees 

but net growth is positive. Maximum (limiting) SDI was defined at 365. Modeling 

by Hayes et al. (2009) supports these observations and suggests that it might be 

appropriate to consider lower SDI thresholds under some conditions (e.g., during 

elevated bark beetle populations as associated with extended drought). 

Managing Stand Density to Reduce Susceptibility to 

Bark Beetle Infestations 

Thinning has long been advocated as a preventive measure to alleviate or reduce the 

amount of bark beetle-caused tree mortality (Fettig et al. 2007). However, thinning 

prescriptions differ widely, and much of the research concerning the effects of thinning on stand susceptibility to bark beetles has been conducted in stands thinned 

to achieve other specific objectives (e.g., to reduce wildfire severity). Thinning may 

have functionally different responses on the abundance and distribution of preferred 

hosts in the residual stand. Furthermore, thinnings conducted in a careless manner may also result in physical damage to residual trees. Although thinning may 

reduce stand susceptibility to bark beetle attack, there may be greater potential for 

increases in subcortical insects and root pathogens (Witcosky et al. 1986). In some 

cases, root diseases have been shown to increase the susceptibility of trees to bark 

[Tree] host density had 

less predictive power 

than other measures 

of stand density, 

suggesting that tree 

competition is more 

important than host 

tree availability.
16

GENERAL TECHNICAL REPORT PSW-GTR-237

beetle attack in the Sierra Nevada (Goheen and Cobb 1980). Furthermore, several 

bark beetle species (e.g., engraver beetles) are attracted to slash created during thinning operations. Effective guidelines, however, are available to reduce associated 

risks through proper slash management (DeGomez et al. 2008). 

Research suggests that posttreatment tree density may be the best predictor of 

subsequent levels of bark beetle-caused tree mortality. For example, Fettig et al. 

(2010) reported significant positive correlations between the percentage of pines 

killed by bark beetles (several species) and trees/ha, basal area (ft2

/ac), and SDI in 

the southern Cascades, California. Of these three metrics, trees/ha was the best 

predictor of levels of tree mortality following fuel reduction and forest restoration 

treatments (fig. 2-1). Thinning not only affects the vigor of residual trees influencing 

resin chemistry, flow, and oleoresin exudation pressure, but also the physical 

environment within treated stands. Increased windspeeds (Bigelow and North 2011) 

and temperatures are common within thinned stands, and these factors influence 

bark beetle fecundity, fitness, and survivorship in a variety of ways (Fettig et al. 

2007). Thinning also increases wind turbulences that disrupt pheromone plumes 

used for recruiting conspecifics during initial phases of host tree colonization 

(Thistle et al. 2004). Low-density stands result in unstable layers and multidirectional traces that dilute pheromone concentrations and could result in 

reductions in beetle aggregation on individual trees. 

Recent work conducted on the Tahoe National Forest, California to determine 

the impact of thinning on bark beetle infestations in Jeffrey pine (Pinus jeffreyi

Balf.) forests provides further support for managing stand density to reduce stand 

susceptibility (Fettig et al. 2012). Treatments included thinning from below (i.e., 

initiating in the smallest diameter classes) to different residual target basal areas 

(80.1, 120.2, and 179.9 ft2/ac [18.4, 27.6, and 41.3 m2/ha], and an untreated control) . 

Throughout the study, bark beetles killed no pines during the 10-year period in the 

lowest density treatment. Significantly fewer trees (ac/yr) were killed in the lowdensity thin than in the high-density thin or untreated control. 

Implications of Climate Change on 

Bark Beetle Dynamics 

Climatic changes will significantly affect forest productivity and distribution. For 

example, Rehfeldt et al. (2006) estimated that by the end of this century, 48 percent 

of the Western U.S. landscape will have climate profiles incompatible with their 

current coniferous vegetation. These changes will likely have significant impacts 

on the frequency and severity of disturbances, such as bark beetle outbreaks, that 

shape these ecosystems. Bark beetle population success is influenced directly by 

Posttreatment tree 

density may be the 

best predictor of 

subsequent levels of 

bark beetle-caused 

tree mortality.

Bark beetle species 

indigenous to the 

Southwestern United 

States and Mexico 

have the potential to 

move northward with 

climate change.
17

Managing Sierra Nevada Forests

Figure 2-1—Relationship between (A) basal area (m2/ha) (multiply by 4.36 

to get ft2/ac), (B) numbers of trees per hectare (trees/ha) (divide by 2.47 to 

get trees/ac), (C) stand density index and percentage of pines killed by bark 

beetles pooled across treatments on the Klamath National Forest, California. (Adapted from Fettig et al. 2010.) 

temperature effects on developmental timing (Powell and Logan 2005) and mortality 

(Régnière and Bentz 2007). Warming may 

allow some species to complete extra generations per year, and adult emergence and flight 

activity could occur earlier and last longer. 

Cold-induced mortality during winter may 

also decrease. Effects of climate change on 

community associates and host tree vigor will 

also influence population success indirectly, 

although little information is available to 

quantify these relationships. Furthermore, 

climate-induced changes in carbon assimilation 

can alter the within-plant allocation of carbohydrates (Grulke et al. 2001) affecting the production of chemical defenses (Herms and Mattson 

1992) and a tree’s ability to prevent bark beetle 

colonization. 

Based on projected changes in climate, 

Bentz et al. (2010) suggested that future 

thermal regimes may be particularly favorable 

for mountain pine beetle populations, although 

considerable spatial and temporal variability 

was modeled. These predictions suggested a 

movement of temperature suitability to higher 

latitudes and elevations (e.g., as currently 

witnessed in whitebark pine (Pinus albicaulis

Engelm.) in the Sierra Nevada) and identified 

regions with a high potential for bark beetle 

outbreaks and associated tree mortality in the 

coming century. Furthermore, Bentz et al. 

(2010) expressed a concern that bark beetle 

species indigenous to the Southwestern United 

States (e.g., Arizona) and Mexico have the 

potential to move northward with climate 

change following range expansions of their 

current hosts or adaptation to novel hosts.

14

12

10

8

6

4

2

0

Percentage of Pinus 

killed by bark beetles

r 2 = 0.46, P = 0.016

Basal area (m2/ha)

10 20 30 40 50 60 70

A

14

12

10

8

6

4

2

0

Percentage of Pinus 

killed by bark beetles

r 2 = 0.76, P = 0.001

Trees per hectare

0 200 400 600 800 1,000 2,000

B

14

12

10

8

6

4

2

0

Percentage of Pinus 

killed by bark beetles

r 2 = 0.59, P = 0.0031

Stand density index

0 100 200 300 400 500

C
18

GENERAL TECHNICAL REPORT PSW-GTR-237

Forest Heterogeneity and Bark Beetles

In the absence of frequent understory fire, bark beetles have become one of the 

principle agents of tree mortality in the Sierra Nevada and a strong influence on 

ecosystem processes. Although bark beetle infestations affect timber and fiber 

production, and indirectly a range of ecosystem services (Coulson and Stephen 

2006), in the past, mortality of individual or small groups of overstory trees may 

have been a significant influence on the fine-scale spatial heterogeneity characteristic of mixed-conifer forests in California (Savage 1994). Beetles often inflict 

density-dependent mortality (Smith et al. 2005), and consequently maintain a mix 

of tree species, ages, sizes, and spatial heterogeneity in these forests. This is accomplished through the opening of canopy gaps that allow for differential reproduction 

of overstory species. 

Tree mortality is often highly episodic (Franklin et al. 1987) making it difficult 

to determine when rates of beetle-induced tree mortality are uncharacteristically 

“high.” At the Teakettle Experimental Forest, California, cumulative levels of tree 

mortality (i.e., from all causes, not just bark beetles), as measured by standing 

dead trees ≥2 in (5 cm) d.b.h., was 8.7 percent, (range 5.3 to 13.1 percent) (Smith 

et al. 2005) compared to 14.0 percent (range 3 to 33 percent) in mixed-conifer, 

old-growth forests of the Lake Tahoe Basin (Barbour et al. 2002). In the Sierra San 

Pedro del Martir National Park of Baja, Mexico, where little fire suppression has 

occurred, cumulative tree mortality in mixed-conifer, old-growth forests was found 

to be 12.7 percent (range 4 to 15 percent) (Maloney and Rizzo 2002). Ansley and 

Battles (1998) reported an annual mortality rate of 0.6 percent per year in a Sierran old-growth, fire-suppressed forest, compared to only 0.162 percent per year in 

an active-fire, old-growth forest in the Sierra San Pedro del Martir (Maloney and 

Rizzo 2002). Rates in excess of the upper end of these ranges might be considered 

indicative of “high” levels of tree mortality in mixed-conifer forests.

 The forest heterogeneity suggested in GTR 220 is likely to reduce beetlecaused tree mortality below current levels in most fire-suppressed forests. If 

treatments differ with topography, higher stem densities will be left in the most 

mesic (and presumably productive) sites that can support these conditions without 

incurring high levels of tree mortality. Heavier thinning on more xeric sites may be 

appropriate to reduce competition in areas most prone to drought stress and associated bark beetle attacks. Although measures of density and SDI are usually standlevel means, SDI and potential competitive stress should be assessed at a fine scale 

(see chapter 9) in areas where microtopography may create localized differences in 

productivity. 
19

Managing Sierra Nevada Forests

At the landscape scale, the maintenance of a mosaic of different stand 

structures, densities, and compositions, as suggested in GTR 220, may reduce 

the frequency and extent of bark beetle outbreaks. Larger scale beetle outbreaks 

are often associated with more homogeneous forest conditions (i.e., less species 

diversity and more uniform stem densities). Management that increases spatial 

diversity of forest conditions with variable tree density, species diversity and 

growth rates may retain the ecological benefits of chronic bark beetle impacts 

without facilitating episodic, large-scale tree mortality that historically may have 

been rare in much of the Sierra Nevada. 

In general, bark beetle abundance is a good indicator of tree stress. As climate 

conditions change and high stem densities increase with fire suppression, beetle 

mortality can provide some measure of ecosystem response. If patterns change 

from low-level chronic mortality of scattered individual trees to persistently higher 

rates, particularly of large clusters, ecosystem resistance and resilience may be 

compromised. 

References

Ansley, J.S.; Battles, J.J. 1998. Forest composition, structure, and change in an 

old-growth mixed conifer forest in the northern Sierra Nevada. Journal of the 

Torrey Botanical Society. 125: 297–308.

Barbour, M.; Kelley, E.; Maloney, P.; Rizzo, D.; Royce, E.; Fites-Kaufmann, 

J. 2002. Present and past old-growth forests of the Lake Tahoe Basin, Sierra 

Nevada, US. Journal of Vegetation Science. 13: 461–472.

Bentz, B.J.; Régnière, J.; Fettig, C.J.; Hansen, E.M.; Hayes, J.L.; Hicke, J.A.; 

Kelsey, R.G.; Negrón, J.F.; Seybold, S.J. 2010. Climate change and bark 

beetles of the western U.S. and Canada: direct and indirect effects. Bioscience. 

60: 602–613.

Bigelow, S.W.; North, M.P. 2011. Effects of fuels-reduction and group-selection 

silviculture on understory microclimate in Sierran mixed-conifer forest. Forest 

Ecology and Management. 264: 51–59.

Coulson, R.N.; Stephen, F.M. 2006. Impacts of insects in forest landscapes: 

implications for forest health management. In: Payne, T.D., ed. Invasive 

forest insects, introduced forest trees, and altered ecosystems: ecological pest 

management in global forests of a changing world. New York: Springer-Verlag: 

101–126.

As climate conditions 

change and high stem 

densities increase with 

fire suppression, beetle 

mortality can provide 

some measure of 

ecosystem response.
20

GENERAL TECHNICAL REPORT PSW-GTR-237

Craighead, F.C. 1925. The Dendroctonus problems. Journal of Forestry. 

23: 340–354.

DeGomez, T.; Fettig, C.J.; McMillin, J.D.; Anhold, J.A.; Hayes, C.J. 2008. 

Managing slash to minimize colonization of residual leave trees by Ips and other 

bark beetle species following thinning in southwestern ponderosa pine. AZ1448. 

Tucson, AZ: University of Arizona, College of Agriculture and Life Sciences 

Bulletin. 21 p.

Fettig, C.J.; Borys, R.R.; Dabney, C.P. 2010. Effects of fire and fire surrogate 

treatments on bark beetle-caused tree mortality in the Southern Cascades, 

California. Forest Science. 56: 60–73.

Fettig, C.J.; Hayes, C.J.; Jones, K.J.; McKelvey, S.R.; Mori, S.L.; Smith, 

S.L. 2012. Thinning Jeffrey pine stands to reduce susceptibility to bark 

beetle infestations in California, U.S.A. Agricultural and Forest Entomology. 

14(1): 111–117.

Fettig, C.J.; Klepzig, K.D.; Billings, R.F.; Munson, A.S.; Nebeker, T.E.; 

Negrón, J.F.; Nowak, J.T. 2007. The effectiveness of vegetation management 

practices for prevention and control of bark beetle outbreaks in coniferous forests 

of the western and southern United States. Forest Ecology and Management. 

238: 24–53.

Franceschi, V.R.; Krokene, P.; Christiansen, E.; Krekling, T. 2005. Anatomical 

and chemical defenses of conifer bark against bark beetles and other pests. New 

Phytologist. 167: 353–376.

Franklin, J.F.; Shugart, H.H.; Harmon, M.E. 1987. Tree death as an ecological 

process. Bioscience. 37: 550–556.

Goheen, D.J.; Cobb, F.W., Jr. 1980. Infestation of Ceratocystis wageneri-infected 

ponderosa pine by bark beetles (Coleoptera: Scolytidae) in the central Sierra 

Nevada. The Canadian Entomologist. 112: 725–730.

Grulke, N.E.; Andersen, C.P.; Hogsett, W.E. 2001. Seasonal changes in carbohydrate pools of ponderosa pine in stands under differing environmental stress. 

Tree Physiology. 21: 173–184.

Hayes, C.J.; Fettig, C.J.; Merrill, L.D. 2009. Evaluation of multiple funnel 

traps and stand characteristics for estimating western pine beetle-caused tree 

mortality. Journal of Economic Entomology. 102: 2170–2182.
21

Managing Sierra Nevada Forests

Herms, D.A.; Mattson, W.J. 1992. The dilemma of plants: to grow or defend. The 

Quarterly Review of Biology. 67: 283–335.

Maloney, P.E.; Rizzo, D.M. 2002. Pathogens and insects in a pristine forest 

ecosystem: the Sierra San Pedro Martir, Baja, Mexico. Canadian Journal of 

Forest Research. 32: 488–457.

Miller, J.M. 1926. The western pine beetle control problem. Journal of Forestry. 

24: 897–910.

North, M.; Stine, P.; O'Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Oliver, W.W. 1995. Is self-thinning in ponderosa pine ruled by Dendroctonus bark 

beetles? In: Proceedings of the 1995 national silviculture workshop. Gen. Tech. 

Rep. GTR-RM-267. Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station: 213–218.

Powell, J.A.; Logan, J.A. 2005. Insect seasonality: circle map analysis of 

temperature-driven life cycles. Theoretical Population Biology. 67: 161–179.

Raffa, K.F.; Berryman, A.A. 1983. The role of host plant resistance in the 

colonization behavior and ecology of bark beetles (Coleoptera: Scolytidae). 

Ecological Monographs. 53: 27–49.

Régnière, J.; Bentz, B. 2007. Modeling cold tolerance in the mountain pine beetle, 

Dendroctonus ponderosae. Journal of Insect Physiology. 53: 559–572.

Rehfeldt, G.E.; Crookston, N.L.; Warwell, M.V.; Evans, J.S. 2006. Empirical 

analyses of plant climate relationships for the western United States. 

International Journal of Plant Science. 167: 1123–1150.

Reineke, L.H. 1933. Perfecting a stand-density index for even-aged forests. 

Journal of Agricultural Research. 46: 627–638.

Sartwell, C. 1971. Thinning ponderosa pine to prevent outbreaks of mountain 

pine beetle. In: Baumgartner, D.M., ed. Precommercial thinning of coastal and 

intermountain forests in the Pacific Northwest. Pullman, OR: Washington State 

University: 41–52.

Savage, M. 1994. Anthropogenic and natural disturbance and patterns of mortality 

in a mixed-conifer forest in California. Canadian Journal of Forest Research. 

24: 1149–1159.
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Smith, T.; Rizzo, D.; North, M. 2005. Patterns of mortality in an old-growth 

mixed-conifer forest of the southern Sierra Nevada, California. Forest Science. 

51: 266–275.

Thistle, H.W.; Peterson, H.; Allwine, G.; Lamb, B.K.; Strand, T.; Holsten, 

E.H.; Shea, P.J. 2004. Surrogate pheromone plumes in three forest trunk spaces: 

composite statistics and case studies. Forest Science. 50: 610–625.

Vité, J.P.; Wood, D.L. 1961. A study on the applicability of the measurement of 

oleoresin exudation pressure in determining susceptibility of second growth 

ponderosa pine to bark beetle infestations. Contributions of Boyce Thompson 

Institute. 21: 67–78.

Witcosky, J.J.; Schowalter, T.D.; Hansen, E.M. 1986. Hylastes nigrinus 

(Coleoptera: Scolytidae), Pissodes fasciatus, and Steremnius carinatus

(Coleoptera: Curculionidae) as vectors of black-stain root disease of 

Douglas-fir. Environmental Entomology. 15: 1090–1095.
23

Managing Sierra Nevada Forests

H.D. Safford,1 M. North,2 and M.D. Meyer3

Introduction

Increasing human emissions of greenhouse gases are modifying the Earth’s climate. 

According to the Intergovernmental Panel on Climate Change (IPCC), “Warming of the climate system is unequivocal, as is now evident from observation of 

increases in average air and ocean temperatures, widespread melting of snow and 

ice, and rising global average sea level” (IPCC 2007). The atmospheric content 

of carbon dioxide (CO2) is at its highest level in more than 650,000 years and 

continues to rise. Mean annual surface air temperatures in California are predicted 

to increase by as much as 10 °F (5.6 °C) in the next century, creating climatic 

conditions unprecedented in at least the last 2 million years (IPCC 2007, Moser et 

al. 2009). Yet climate change is by no means the only stress on forest ecosystems. 

Growing human populations and economies are dramatically reducing the extent of 

the Earth’s natural habitats. Land use change has reduced the availability of suitable 

habitat for native plants and wildlife, and, in many places, fragmentation of habitat 

has led to highly disconnected natural landscapes that are only weakly connected 

via dispersal and migration. Biotic response to climate and land use change is 

further complicated by other anthropogenic stressors, including exotic invasives, 

altered disturbance regimes, air and water pollution, and atmospheric deposition 

(Noss 2001, Sanderson et al. 2002). 

Traditionally, restoration and ecosystem management practices depend on the 

characterization of “properly functioning” reference states, which may constitute 

targets or desired conditions for management activities. Because human-caused 

modifications to ecosystems have been so pervasive, fully functional contemporary reference ecosystems are difficult to find, and reference states must often be 

defined from historical conditions. One of the implicit assumptions of restoration 

ecology and ecosystem management is the notion that the historical range of 

variation (HRV) represents a reasonable set of bounds within which contemporary 

ecosystems should be managed. The basic premise is that the ecological conditions 

most likely to preserve native species or conserve natural resources are those that 

Chapter 3: Climate Change and the 

Relevance of Historical Forest Conditions

1 Regional ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Region, 1323 Club Dr., Vallejo, CA 94592.

2 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 1731 Research Park Dr., Davis, CA 95618.

3 Ecologist, U.S. Department of Agriculture, Forest Service, Southern Sierra Province, 

Sierra National Forest, 1600 Tollhouse Rd., Clovis, CA 93611.
24

GENERAL TECHNICAL REPORT PSW-GTR-237

Summary of Findings

1. Effects of climate change are already apparent in rising minimum temperatures, earlier snowpack melting, changing stream 

hydrology, and increased frequency of large, severe wildfires.

Tree mortality rates are increasing in lower and mid-elevation forests but may be decreasing for some subalpine species as well. Some 

animal species are changing their geographic ranges in response to 

climatic shifts.

2. Over the next century, average temperature is predicted to 

increase by 2 to 4 °F (1.1 to 2.2 °C) in the winter and 4 to 8 °F 

(2.2 to 4.4 °C) in the summer in the Sierra Nevada. Changes in 

precipitation are more difficult to model and may differ between 

northern and southern California. Models suggest that snowpack in 

the Sierra Nevada could decrease by 20 to 90 percent. The annual 

summer drought in California may become more pronounced in its 

direct and indirect impacts on biota. Changing disturbance regimes 

(e.g., increases in fire frequency and burned area, and, in some forest types, fire severity) are likely to be the most significant influence 

on changes in vegetation types and distributions. 

3. In preparing forests for changing climatic conditions, the value 

of historical ecology is the insight it provides into “the way 

things work” rather than “the ways things were.” This suggests 

a management focused on ecological processes (e.g., fire, hydrology, 

etc.) rather than forest structure. It may be necessary to begin by 

restoring forest conditions and fuel loadings, but that should not be 

construed as the final goal.

4. Management practices may enhance ecosystem resilience 

and sustainability by removing or reducing other, nonclimate 

stressors. A key management focus should be restoration of heterogeneity in forest conditions. In low- and mid-elevation Sierra 

Nevada forests, such general practices might include reductions of 

stem densities of smaller fire-intolerant trees and increased use of 

wildland fire (prescribed fire and managed wildfire).
25

Managing Sierra Nevada Forests

sustained them in the past, when ecosystems were less affected by people (Egan 

and Howell 2001; Manley et al. 1995; Wiens et al., in press). However, rapid and 

profound changes in climate and land use (as well as other anthropogenic stressors) 

raise questions about the use of historical information in resource management. In 

the last decade, as the scale and pace of climate change have become more apparent, many scientists have questioned the uncritical application of historical reference conditions to contemporary and future resource management (e.g., Craig 2010, 

Harris et al. 2006, Millar et al. 2007, Stephenson et al. 2010, White and Walker 

1997). What role can historical ecology still play in a world where the environmental baseline is shifting so rapidly?

In this chapter, we review the nature of climate change in the Sierra Nevada, 

focusing on recent, current, and likely future patterns in climates and climatedriven ecological processes. We then discuss the value of historical reference conditions to restoration and ecosystem management in a rapidly changing world. The 

climate trend portion of this chapter is drawn from a series of climate change trend 

summaries that were conducted for the California national forests by the U.S. Forest 

Service, Pacific Southwest Region Ecology Program in 2010 and 2011 (available at 

http://fsweb.r5.fs.fed.us/program/ecology/). The historical ecology portion is based 

on work the first author contributed to Wiens et al. (in press), especially Safford et 

al. (in press a and b). 

Recent Trends in Climate and Climate-Driven 

Processes in the Sierra Nevada

Climate

The Western United States is warming at a faster rate than any other part of the 

country (Saunders et al. 2008). In the Sierra Nevada, mean annual temperatures 

have generally increased by around 1 to 2.5 °F (0.5 to 1.4 °C) over the last 75 to 100 

years, although some areas of the northern Sierra have experienced slight decreases 

in temperature (fig. 3-1). Warming temperatures are mostly driven by increases in 

nighttime minima over the last two to four decades. Over the same period, most 

weather stations do not show an appreciable increase in mean daily maximum 

temperatures. At higher elevations, the annual number of days with below-freezing 

temperatures is dropping, and at lower elevations, there has been an increase in the 

number of extreme heat days (Moser et al. 2009).

The Sierra Nevada (together with northwestern California) is one of the few 

places in the Western United States with a positive water balance (precipitation 

minus potential evapotranspiration) over the last half century. Precipitation has 

What role can historical 

ecology still play in 

a world where the 

environmental baseline 

is shifting so rapidly?
26

GENERAL TECHNICAL REPORT PSW-GTR-237

been steady or increasing over much of the area (fig. 3-1), although year-to-year 

variability in annual precipitation (i.e., higher highs and lower lows) is also increasing at many stations. At higher elevations, the proportion of precipitation falling as 

rain (vs. snow) is increasing. Over the last 50 years, spring snowpack has decreased 

by 70 to 120 percent across most of the northern Sierra Nevada, but snowpack is up 

in much of the southern Sierra Nevada, owing to the combination of higher precipitation and the terrain’s higher elevation (fig. 3-2).

Figure 3-1—Differences in mean annual temperature (A), and mean annual precipitation (B) between the 1930s and 2000s, as derived 

by the PRISM climate model. Temperatures have risen across most of the Sierra Nevada (with some local areas of decrease), while 

precipitation has increased along most of the west slope. (Graphic courtesy of S. Dobrowksi, University of Montana.)

Hydrology

Stewart et al. (2005) showed that the onset of spring thaw in most major streams in 

the central Sierra Nevada occurred 5 to 30 days earlier in 2002 than in 1948, and 

peak streamflow (measured as the center of mass annual flow) occurred 5 to 15 days 

earlier. During the same period, March flows in the studied streams were mostly 

higher by 5 to 20 percent, but June flows were mostly lower by the same amount. 

Overall spring and early summer streamflow was down in most studied streams. 

Rising winter and spring temperatures appear to be the primary driver of these 

patterns (Stewart et al. 2005).
27

Managing Sierra Nevada Forests

Figure 3-2—Trends in the amount of water contained in the snowpack (“snow water equivalent”) on 

April 1, for the period 1950–1997. Red circles indicate percentage of decrease in snow water; blue 

circles indicate increase in snow water. (Redrawn from Moser et al. 2009.)
28

GENERAL TECHNICAL REPORT PSW-GTR-237

Forest Fires

Data on forest fire frequency, size, total area burned, and severity all show increases 

in the Sierra Nevada over the last two to three decades. Westerling et al. (2006) 

found that increasing frequencies of large fires (>1,000 ac) (405 ha) across the Western United States since the 1980s were strongly linked to increasing temperatures 

and earlier spring snowmelt. The Sierra Nevada was one of two geographic areas 

of especially increased fire activity, which Westerling et al. (2006) ascribed to an 

interaction between climate and increased fuels owing to fire suppression. Westerling et al. (2006) also identified the Sierra Nevada as being one of the geographic 

regions most likely to see further increases in fire activity on account of future 

increases in temperature. Miller et al. (2009) showed that mean and maximum fire 

size, and total burned area in the Sierra Nevada, have increased strongly between 

the early 1980s and 2007. Climatic variables explain very little of the pattern in 

fire size and area in the early 20th century. In contrast, over the last 25 years, 35 

to 50 percent of the pattern in fire size and area can now be explained by spring 

climate variables (spring precipitation and minimum temperature). The mean size 

of escaped fires in the Sierra Nevada was about 750 ac (304 ha) until the late 1970s, 

but the most recent 10-year average has climbed to about 1,100 ac (445 ha). Miller 

et al. (2009) also showed that forest fire severity (a measure of the effect of fire on 

vegetation) rose strongly during the period 1984 to 2007, with the pattern concentrated in middle-elevation conifer forests. Fires at the beginning of the record 

burned at an average of about 17 percent high (stand-replacing) severity, while the 

average for the last 10-year period was 30 percent. Miller et al. (2009) found that 

both climate change and increasing forest fuels were necessary to explain the patterns they analyzed.

Forest Structure

Fire suppression has been practiced as a general federal policy since the 1920s. 

Pre-Euro-American fire frequencies in high-elevation forests such as red fir (Abies 

magnifica (Gordon & Glend.) Lindl. ex Hildebr.) (>40 to 50 years in many places) 

and subalpine forest (>100 years) were long enough that fire suppression has had 

little or no impact on ecological patterns or processes (Miller et al. 2009, Van de 

Water and Safford 2011). Higher elevation forests are also much more remote, less 

likely to have economic uses, and often protected in wilderness areas and national 

parks, so impacts from logging or recreation use are generally minimal. Subalpine 

tree growth is strongly influenced by higher precipitation and warm summers 

(Graumlich 1991). Long-term changes in stand structure in higher elevation forests 

are thus more likely to represent responses to changes in exogenous factors like 

climate. 

Mean and maximum 

fire size, and total 

burned area in the 

Sierra Nevada, have 

increased strongly 

between the early 

1980s and 2007.

Thirty five to 50 percent 

of the pattern in fire 

size and area can now 

be explained by spring 

climate variables.

Fires at the beginning 

of the record burned at 

an average of about 17 

percent high severity, 

while the average for 

the last 10-year period 

was 30 percent.
29

Managing Sierra Nevada Forests

In the early 1930s, the Forest Service mapped vegetation on national forest 

lands in the Sierra Nevada and sampled thousands of vegetation plots (Wieslander 

1935). Bouldin (1999) compared the 1930s plots with the modern Forest Inventory 

and Analysis plots and described changes in forest structure for the Sierra Nevada 

from Yosemite National Park to the Plumas National Forest, that is, primarily north 

of the Sierra National Forest. In red fir forest, Bouldin (1999) found that densities of 

young trees had increased by about 40 percent between 1935 and 1992, but densities 

of large trees had decreased by 50 percent during the same period. In old-growth 

stands, overall densities and basal areas were higher, and the number of plots in the 

red fir zone dominated by shade-tolerant species increased at the expense of species like Jeffrey pine (Pinus jeffreyi Balf.) and western white pine (Pinus monticola 

Douglas ex. D. Don). In old-growth subalpine forests, Bouldin (1999) found that 

young mountain hemlock (Tsuga mertensiana (Bong.) Carriere), a shade-tolerant 

species, was increasing in density and basal area while larger western white pine 

was decreasing. In whitebark pine stands, overall density was increasing owing to 

increased recruitment of young trees, but species composition had not changed. 

Lodgepole pine (Pinus contorta Douglas ex. Louden) appears to be responding 

favorably to increased warming or increased precipitation throughout the subalpine 

forest.

Bouldin (1999) also studied mortality patterns in the 1935 and 1992 data sets. 

He found that mortality rates had increased in red fir (Abies magnifica A. Murray 

bis), with the greatest increases in the smaller size classes. At the same time, in 

subalpine forests, lodgepole pine, western white pine, and mountain hemlock all 

showed decreases in mortality. The subalpine zone was the only forest type Bouldin 

(1999) studied in which mortality had not greatly increased since the 1935 inventory. This suggests that climate change (warming, plus higher precipitation in some 

cases) is actually making conditions better for some tree species in this stressful 

environment. Dolanc et al. (2012) recently completed a study that resampled the 

1930s Forest Service (Wieslander) plots in the subalpine zone between Yosemite 

National Park and the Lake Tahoe Basin. Corroborating Bouldin (1999), they found 

that growing conditions in the subalpine zone were probably better today than in the 

1930s, as the density of small trees of almost all species had increased greatly in the 

75-year period. Dolanc et al.’s (2012) direct plot-to-plot comparison also found that 

mortality of large trees had decreased the density of the subalpine forest canopy, 

but the overall trend was for denser forests with no apparent change in relative tree 

species abundances. 

Van Mantgem et al. (2009) recently documented widespread increases in tree 

mortality in old-growth forests across the Western United States, including in the 
30

GENERAL TECHNICAL REPORT PSW-GTR-237

Sierra Nevada. Their plots had not experienced increases in density or basal area 

during the 15- to 40-year period between first and last census. The highest mortality 

rates were documented in the Sierra Nevada, and in middle-elevation forests (3,300 

to 6,700 ft) (1006 to 2042 m). Higher elevation forests (>6,700 ft) (2042 m) showed 

the lowest mortality rates, corroborating the Bouldin (1999) findings. Van Mantgem et al. (2009) ascribed the mortality patterns they analyzed to regional climate 

warming and associated drought stress. 

Comparisons of the 1930s Forest Service vegetation inventories and map with 

modern vegetation maps and inventories show changes in the distribution of many 

Sierra Nevada vegetation types over the last 70 to 80 years (Bouldin 1999, Moser 

et al. 2009). The principal trends are (1) loss of yellow pine-dominated forest, (2) 

increase in the area of forest dominated by shade-tolerant conifers (especially fir 

species), (3) loss of blue oak woodland, (4) increase in hardwood-dominated forests, 

(5) loss of subalpine and alpine vegetation, and (6) expansion of subalpine trees into 

previous permanent snowfields. Trends four through six appear to have a strong 

connection to climate warming, while trends one through three are mostly the 

product of human management choices, including logging, fire suppression, and 

urban expansion.

Wildlife

Between 1914 and 1920, the Museum of Vertebrate Zoology (MVZ) at the University of California Berkeley surveyed the terrestrial vertebrate fauna at 41 sites along 

a transect that extended from the western slope of Yosemite National Park to an 

area near Mono Lake (Grinnell and Storer 1924). In the past decade, MVZ resurveyed the Yosemite transect to evaluate the near century-long changes in Yosemite’s vertebrate fauna across this elevation gradient, stretching across numerous 

vegetation types (Moritz et al. 2008). By comparing earlier and recent MVZ small 

mammal surveys, Moritz et al. (2008) came to several conclusions: (1) the elevation 

limits of geographic ranges shifted primarily upward, (2) several high-elevation 

species (e.g., alpine chipmunk [Tamias alpinus]) exhibited range contraction (shifted 

their lower range limit upslope), while several low-elevation species expanded their 

range upslope, (3) many species showed no change in their elevational range, (4) 

elevational range shifts resulted in minor changes in species richness and composition at varying spatial scales, (5) closely related species responded idiosyncratically 

to changes in climate and vegetation, and (6) most upward range shifts for highelevation species are consistent with predicted climate warming, but changes in 

most lower to mid-elevation species’ ranges are likely the result of landscape-level 

vegetation dynamics related primarily to changes in fire regimes. 

Closely related 

species responded 

idiosyncratically to 

changes in climate 

and vegetation.
31

Managing Sierra Nevada Forests

Similar distribution patterns have been observed for other faunal taxa throughout the Sierra Nevada. Forister et al. (2010) tracked 159 species of butterflies over 

35 years in the central Sierra Nevada and observed upward shifts in the elevational 

range of species, a pattern consistent with a warming climate. Tingley et al. (2009) 

resurveyed bird distributions along the Grinnell transects in the entire Sierra 

Nevada and concluded that 91 percent of species distributions shifted with changes 

in temperature or precipitation over time and 26 percent of species tracked both 

temperature and precipitation. This suggests that birds move in response to changing climates in order to maintain environmental associations to which they are 

adapted. The authors also suggested that combining climate and niche models may 

be useful for predicting future changes in regional bird distributions (Tingley et 

al. 2009). In contrast with other faunal studies, Drost and Fellers (1996) found that 

most frog and toad species in Yosemite exhibited widespread decline over the past 

several decades, regardless of elevation. Primary factors that may contribute to this 

faunal collapse throughout the Sierra Nevada include introduced predators, a fungal 

pathogen, pesticides, and climate change (Wake and Vredenburg 2008).

Projected Trends in Climate and 

Climate-Driven Processes 

Climate

Currently, no published climate change or vegetation change modeling has been 

carried out for the Sierra Nevada alone. Indeed, few future-climate modeling efforts 

have treated areas as restricted as the state of California. The principal limiting 

factor is the spatial scale of the General Circulation Models (GCMs) that are used 

to simulate future climate scenarios. Most GCMs produce raster outputs with pixels 

that are 10,000s of square acres in area. To be used at finer scales, these outputs 

must be downscaled by using a series of algorithms and assumptions—these finer 

scale secondary products currently provide the most credible sources we have for 

estimating potential outcomes of long-term climate change for California. Another 

complication is the extent to which GCMs disagree with respect to the probable 

outcomes of climate change. For example, a recent comparison of 21 published 

GCM outputs that included California found that estimates of future precipitation 

ranged from a 26 percent increase per 1.8 °F (1 oC) increase in temperature to an 

8 percent decrease (Gutowski et al. 2000, Hakkarinen and Smith 2003). That said, 

there was some broad consensus. All of the reviewed GCMs predicted warming 

temperatures for California, and 13 of 21 (62 percent) predicted higher precipitation 

(three showed no change, and five predicted decreases). According to Dettinger 

(2005), the most common prediction among the most recent models (which are 
32

GENERAL TECHNICAL REPORT PSW-GTR-237

considerably more complex and, ideally, more credible) is temperature warming by 

about 9 °F (5 °C) by 2100, with precipitation remaining similar or slightly reduced 

compared to today. Most models agreed that summers will be drier than they are 

currently, regardless of levels of annual precipitation.

The most widely cited of the recent modeling efforts is probably Hayhoe et al. 

(2004). They used two contrasting GCMs (much warmer and wetter, vs. somewhat 

warmer and drier) under low and high greenhouse gas emission scenarios to make 

projections of climate change impacts for California over the next century. By 2100, 

under all GCM-emissions scenarios, April 1 snowpack was down by 22 percent to 

93 percent in the 6,700- to 10,000-ft (2042 to 3048 m) elevation belt, and the date 

of peak snowmelt was projected to occur from 3 to 24 days earlier in the season. 

Average temperatures were projected to increase by 2 to 4 °F (1.1 to 2.2 °C) in the 

winter and 4 to 8 °F (2.2 to 4.4 °C) in the summer. Finally, three of the four GCMemissions scenarios employed by Hayhoe et al. (2004) predicted strong decreases 

in annual precipitation by 2100, ranging from 91 to 157 percent; the remaining 

scenario predicted a 38 percent increase. Although the southern Sierra Nevada 

snowpack has generally remained steady (or risen) over the past half-century (fig. 

3-2) (Moser et al. 2009), continued warming is likely to erode the temperature 

buffer that is currently observed in the high southern Sierra Nevada. Most modeling 

projects a continuous increase in the rain:snow ratio and earlier runoff dates for the 

next century, with decreased snowpack (late winter snow accumulation decreases 

by 50 percent by 2100) and growing-season streamflow even in the higher elevation 

river basins (Miller et al. 2003, Moser et al. 2009).

Hydrology

Miller et al. (2003) modeled future hydrological changes in California as a function 

of two contrasting GCMs (the same GCMs used in Hayhoe et al. [2005] and Lenihan et al. [2003; see below]) and a variety of scenarios intermediate to the GCMs. 

Miller et al. (2003) found that annual streamflow volumes were strongly dependent 

on the precipitation scenario, but changes in seasonal runoff were more complex. 

Predicted spring and summer runoff was lower in all of the California river basins 

they modeled, except where precipitation was greatly increased, in which case 

runoff was unchanged from today (Miller et al. 2003). Runoff in the winter and 

early spring was predicted to be higher under most of the climate scenarios because 

higher temperatures cause snow to melt earlier. In California rivers that are fed 

principally by snowmelt (i.e., higher elevation streams), flood potential was predicted to increase under all scenarios of climate change, principally owing to earlier 

dates of peak daily flows and the increase in the proportion of precipitation falling 

as rain. These increases in peak daily flows are predicted under all climate change 

Most modeling projects 

a continuous increase 

in the rain:snow ratio 

and earlier runoff 

dates for the next 

century, with decreased snowpack.
33

Managing Sierra Nevada Forests

scenarios, including those assuming reduced precipitation (Miller et al. 2003). The 

predicted increase in peak flow was most pronounced in higher elevation river 

basins, owing to the greater reliance on snowmelt. If precipitation does increase, 

streamflow volumes during peak runoff could greatly increase. Under the wettest 

climate scenario modeled by Miller et al. (2003), by 2100 the volume of flow during 

the highest flow days could more than double in many Sierra Nevada rivers. This 

would result in a substantial increase in flood risk in flood-prone areas in the Central Valley. According to Miller et al. (2003), increased flood risk is highly probable 

under current climate change trends, because temperature, not precipitation, is the 

main driver of higher peak runoff. If climate change leads not only to an increase 

in average precipitation but also a shift to more extreme precipitation events, then 

peak flows would be expected to increase dramatically.

Fire

The combination of warmer climate and increased fuel production (owing to 

higher CO2 fertilization) will likely cause more frequent and more extensive fires 

throughout western North America (Flannigan et al. 2000, Price and Rind 1994). 

Fire responds rapidly to changes in climate and will likely overshadow the direct 

effects of climate change on tree species distributions and migrations (Dale et al. 

2001, Flannigan et al. 2000, National Research Council 2011). A temporal pattern of 

climate-driven increases in fire activity is already apparent in the Western United 

States (Westerling et al. 2006). Modeling studies specific to California expect 

increased fire activity to persist and possibly accelerate under most future climate 

scenarios, owing to increased production of fuels under higher CO2 (and in some 

cases, precipitation), decreased fuel moistures from warmer dry season temperatures, and possibly increased thundercell activity (Lenihan et al. 2003, 2008; Miller 

and Urban 1999; Price and Rind 1994; Westerling and Bryant 2006). By 2100, 

Lenihan et al.’s (2003, 2008) simulations suggest about a 5 to 8 percent increase in 

annual burned area across California, depending on the climate scenario. Increased 

frequencies or intensities of fire in coniferous forest in California will almost 

certainly drive changes in tree species compositions (Lenihan et al. 2003, 2008), 

and will likely reduce the size and extent of late-successional refugia (McKenzie et 

al. 2004, USDAFS and USDI 1994). Thus, if fire becomes more active under future 

climates, there may be significant repercussions for old-growth forest and oldgrowth-dependent flora and fauna.

A key question is to what extent future fire regimes in montane California 

will be characterized by either more or less severe fire than is currently (or was 

historically) the case. Fire regimes are driven principally by the effects of weather/

climate and fuel type and availability (Bond and van Wilgen 1996). Seventy years 

If fire becomes more 

active under future 

climates, there 

may be significant 

repercussions for 

old-growth forest and 

old-growth-dependent 

flora and fauna.
34

GENERAL TECHNICAL REPORT PSW-GTR-237

of effective fire suppression in the semiarid American West have led to fuel-rich 

conditions that are conducive to intense forest fires that remove significant amounts 

of biomass (Arno and Fiedler 2005, McKelvey et al. 1996, Miller et al. 2009). Most 

future climate modeling predicts climatic conditions that will likely exacerbate 

these conditions. Basing their analysis on two GCMs under the conditions of 

doubled atmospheric CO2 and increased annual precipitation, Flannigan et al. 

(2000) predicted that mean fire severity in California (measured by difficulty of 

control) would increase by about 10 percent averaged across the state. Vegetation 

growth models that incorporate rising atmospheric CO2 show an expansion of 

woody vegetation on many Western landscapes (Hayhoe et al. 2004; Lenihan et al. 

2003, 2008), which could feed back into increased fuel biomass and connectivity 

and more intense (and thus more severe) fires. Use of paleoecological analogies also 

suggests that parts of the Pacific Northwest (including northern California) could 

experience more severe fire conditions under warmer, more CO2-rich climates 

(Whitlock et al. 2003). Fire frequency and severity (or size) are usually assumed 

to be inversely related (Pickett and White 1985), and a number of researchers 

have demonstrated this relationship for Sierra Nevada forests (e.g. Miller and 

Urban 1999, Swetnam 1993). However, if fuels grow more rapidly and dry more 

rapidly—as is predicted under many future climate scenarios—then both severity 

and frequency may increase, at least in the short term. In this scenario, profound 

vegetation-type conversion is likely. Lenihan et al.’s (2003, 2008) results for fire 

intensity predict that large proportions of the Sierra Nevada landscape may see 

mean fire intensities increase over current conditions by the end of the century, 

with the actual change in intensity depending on future precipitation patterns.

Vegetation

Lenihan et al. (2003, 2008) used a dynamic ecosystem model (“MC1”) that estimates the distribution and productivity of terrestrial ecosystems such as forests, 

grasslands, and deserts across a grid of 100 km2

 (38.6 mi2) cells. To date, this is 

the highest resolution at which a model of this kind has been applied in California. 

Based on their modeling results, Lenihan et al. (2003, 2008) projected that forest 

types and other vegetation dominated by woody plants in California would migrate 

to higher elevations as warmer temperatures make those areas suitable for colonization and survival. For example, with higher temperatures and a longer growing 

season, the area occupied by subalpine and alpine vegetation was predicted to 

decrease as evergreen conifer forests and shrublands migrate to higher altitudes (fig. 

3-3). Under their “wetter” future scenarios (i.e., slightly wetter or similar to today), 

Lenihan et al. (2003, 2008) projected a general expansion of forests in the Sierra 

Nevada, especially in the north and at higher elevations. With higher rainfall and 
35

Managing Sierra Nevada Forests

Figure 3-3—MC1 outputs for the Sierra Nevada (A) and Sierra Nevada Foothills (B) ecological sections, current vs. future projections 

of vegetation extent. These ecological sections include most of the Sierra Nevada west slope. The PCM-A2 scenario = similar precipitation to today, with <5.5 °F (<3.1 °C) temperature increase; GFDL-B1 = moderately drier than today, with a moderate temperature 

increase (<5.5 °F) (<3.1 °C); GFDL-A2 = much drier than today and much warmer (>7.2 °F) (>4 °C). All scenarios project significant 

loss of subalpine and alpine vegetation. Most scenarios project lower cover of shrubland (including west-side chaparral and east-side 

sagebrush), resulting principally from increasing frequencies and extent of fire. Large increases in the hardwood component of forests 

are projected in all scenarios except for the hot-dry scenario in the foothills. Large increases in cover of grassland are projected for 

the Sierra Nevada section. The drier scenarios project moderate expansion of arid lands. In the Sierra Nevada section, conifer forest 

decreases in cover under all scenarios. (Graphic developed using data from Lenihan et al. 2008.)

Subalpine forest and alpine

Evergreen conifer forest

Mixed forest

Mixed woodland

Shrubland

Grassland

Arid lands

35

30

25

20

15

10

5

0

Percentage of landscape

Current 

(1961–1990)

PCM-A2 

(2071–2100)

GFDL-B1 

(2071–2100)

GFDL-A2 

(2071–2100)

35

30

25

20

15

10

5

0

Evergreen conifer forest

Mixed forest

Mixed woodland

Shrubland

Grassland

Arid lands

Percentage of landscape

Current 

(1961–1990)

PCM-A2 

(2071–2100)

GFDL-B1 

(2071–2100)

GFDL-A2 

(2071–2100)

70

60

50

40

30

20

10

0

A

B

Forest vegetation type

Forest vegetation type
36

GENERAL TECHNICAL REPORT PSW-GTR-237

higher nighttime minimum temperatures, broadleaf trees (especially oak species) 

were predicted to replace conifer-dominated forests in many parts of the low- and 

middle-elevation Sierra Nevada. Under their drier future scenarios, Lenihan et 

al. (2003, 2008) predicted that grasslands would expand, and that increases in the 

extent of tree-dominated vegetation would be minimal. An expansion of shrublands 

into conifer types was also predicted, owing to drought and increases in fire frequency and severity, but increasing fire frequency in the Sierra Nevada may replace 

much low- to middle-elevation shrubland with grassland (fig. 3-3). Hayhoe et al. 

(2004) also used the MC1 ecosystem model to predict vegetation and ecosystem 

changes under a number of different future greenhouse gas emissions scenarios. 

Their results were qualitatively similar to the Lenihan et al. (2003, 2008) results.

Wildlife

Projected changes in California’s terrestrial fauna and flora are expected over the 

next century. Stralberg et al. (2009) developed current and future species distribution models for 60 focal bird species and found that novel avian assemblages with 

no modern analogy could occupy over half of California. This implies a dramatic 

reshuffling of avian communities and altered pattern of species interactions, even 

in the upper elevations of the Sierra Nevada, where only a modest proportion of 

novel avian communities were projected. Using species distribution modeling, the 

California Avian Data Center (2011) projected that approximately 60 percent of 

coniferous forest bird species in the Sierra Nevada will exhibit substantial range 

reductions within the next 40 to 90 years (using 21 focal avian species). Based on 

bioclimatic models, Lawler et al. (2009a,b) projected high (>50 percent) turnover 

and vulnerability of California’s amphibian fauna and moderate (10 to 40 percent) 

turnover in California’s mammalian fauna under a high greenhouse gas emissions 

scenario by the end of the century. In a similar study, Loarie et al. (2008) projected 

that 66 percent of California’s native flora will experience >80 percent reduction in 

range size within a century. Their study identified the southern Sierra Nevada and 

the coastal mountains of northwest California as climate change refugia, defined 

as areas projected to harbor species with shrinking ranges (presumably retaining 

subsets of regional species assemblages over time). Authors from these studies 

recommended novel adaptive management approaches and large-scale planning 

efforts that promote landscape/regional habitat connectivity. Loarie et al. (2008) 

also recommended serious consideration of human-assisted dispersal of California’s 

flora and prioritization of climate change refugia for conservation and restoration. 

Loarie et al. (2008) 

projected that 66 

percent of California’s 

native flora will 

experience >80 

percent reduction in 

range size within a 

century. Their study 

identified the southern 

Sierra Nevada and the 

coastal mountains of 

northwest California as 

climate change refugia.
37

Managing Sierra Nevada Forests

Is History Still Relevant?

In the Sierra Nevada, much has been made of the drastic ecosystem changes 

wrought by Euro-Americans since their arrival en masse in California in the 

mid-19th century. Numerous scientific studies have documented these changes, 

which result from—among other things—changed fire regimes, logging, livestock 

grazing, mining, agriculture, hunting, growing human populations and their 

infrastructure, air and water pollution, species introductions, water diversion, and, 

most recently, climate warming. In lower and middle-elevation forests of the Sierra 

Nevada, the combined impacts of these human influences have resulted in significant habitat loss in some forest types (oak woodlands and low-elevation riparian 

forests, for example), and major changes in forest composition and structure in 

others (e.g., in many conifer-dominated forest types at lower and middle elevations, 

especially yellow pine [ponderosa and Jeffrey pine] and mixed-conifer forests). 

Higher elevation forests, especially in the subalpine zone, have suffered much less 

from human impacts.

In the face of this ecosystem degradation, there is an understandable tendency 

to “get back to the good old days.” In this school of thought, ecosystem status before 

the arrival of Euro-Americans is assumed to be optimal, while current conditions 

are impaired. The goal then is to return the ecosystem to its historical state, trajectory, or range of variation (HRV) before Euro-Americans arrived. This approach 

has been a foundation for conservation, preservation, and restoration management 

in the United States, but rapidly and profoundly shifting environmental baselines 

threaten our ability to continue this approach (Craig 2010; Harris et al. 2006; Millar 

et al. 2007; Stephenson et al. 2010; White and Walker 1997; Wiens et al., in press).

The major concern is that intrinsic assumptions of environmental “stationarity” 

that pervade traditional conservation, preservation, and restoration practices are no 

longer valid (if they really ever were) (Craig 2010; Milly et al. 2008; Wiens et al., in 

press). “Stationarity” is the idea that:

“...the long-term mean is more or less invariant and the range of past conditions encompasses current and future conditions as well. The reasoning is 

that, although true environmental stationarity may not exist over the long 

term, the periodicity or rate of change may be slow enough compared to 

human experience to permit the useful assumption of stationarity” (Safford 

et al., in press).

With environmental conditions changing as rapidly and as extensively as they 

are, critics question the relevance of applying historically based targets in environments that are fundamentally different from what they were in the past. 
38

GENERAL TECHNICAL REPORT PSW-GTR-237

Given all of this change, are historical forest conditions irrelevant? Absolutely 

not! However, the way that history is used in ecosystem management, restoration 

or conservation should change. For example, the HRV concept was developed to 

ensure that ecosystem functions, especially disturbance processes, were incorporated into management (Landres et al. 1999, Morgan et al. 1994). However, 

as currently practiced, conservation and resource management often focuses on 

preservation of specific species, species assemblages, or a relatively static notion 

of the habitat required to maintain populations. In light of rapid global change, an 

alternative perspective is developing, one that is more focused on management of 

ecosystem structure and process rather than specific species or their habitat (Harris 

et al. 2006, Hunter et al. 1988, Stephenson et al. 2010). This perspective emphasizes 

the ecological function or ecological integrity of a site, and is less concerned with 

the identities, numbers, or arrangements of biota. 

In this changed management environment, the role of historical ecology is to 

inform a management response to global change rather than resisting global change. 

Historical ecology can, among other things, identify important broad-scale and 

long-term processes that influence local ecological outcomes under different climate conditions or disturbance regimes. Historical conditions also can provide clues 

to mechanisms underlying ecosystem dynamics and resilience (i.e., Why have some 

systems persisted through climatic changes in the past?), guide the development 

and validation of predictive models, suggest appropriate future trajectories, define 

parameters by which we will recognize “properly functioning” ecosystems, help 

us to operationally define concepts like “ecological integrity” and “resilience,” 

allow us to determine expected levels of ecosystem services, and inform us if current conditions are anomalous and worthy of management intervention (Landres 

et al. 1999; Millar and Woolfenden 1999; Safford et al., in press a and b; Swetnam 

et al. 1999). In essence, historical ecology represents our clearest window into 

ecological patterns and processes that occur at temporal scales beyond the scope 

of human observation. 

Forest Heterogeneity and Climate Change

Given the uncertainties associated with climate change, focusing on the reduction 

or removal of nonclimate stressors can be prudent management. Historical conditions in active-fire forests suggest burning created fine- and large-scale heterogeneity in stand structure, wildlife habitat, fuel loads, and understory conditions. 

Human management of Sierra Nevada forests over the last century and a half has 

greatly reduced this heterogeneity. It is difficult to quantify forest heterogeneity 

from limited historical data, and unlikely that frequent fire would reproduce the 

Conservation and 

resource management 

often focuses on 

preservation of specific species, species 

assemblages, or a 

relatively static notion 

of the habitat required 

to maintain populations. In light of rapid 

global change, an 

alternative perspective 

is developing, one that 

is more focused on 

management of ecosystem structure and 

process rather than 

specific species or 

their habitat.
39

Managing Sierra Nevada Forests

same forest structure under current conditions. However, management practices following those in U.S. Forest Service General Technical Report PSW-GTR-220 that 

increase variation in forest conditions may help increase forest resilience to changes 

in climate and climate-related processes such as fire. For example, variation in stem 

density and fuel loads can limit the extent and severity of drought stress and highseverity fire, such that resulting mortality contributes to forest heterogeneity. Many 

fire-suppressed forests are now in an “alternative stable state” where disturbance, 

whether a result of beetle, drought, or fire mortality, tends to reinforce current 

structural and compositional homogeneity. Such uniform conditions promote low 

resilience to disturbances and projected changes in climate. A goal of current 

management could be to alter forest conditions past a threshold where disturbance 

processes act to increase rather than reduce forest heterogeneity. Heterogeneity in 

structure, function, and composition can provide ecosystems with the ecological 

“flexibility” (Holling 1973) to withstand and persist through both expected and 

unexpected environmental stresses.

References

Arno, S.F.; Fiedler, C.E. 2005. Mimicking nature’s fire: restoring fire-prone 

forests in the West. Washington, DC: Island Press. 256 p.

Bond, W.J.; van Wilgen, B.W. 1996. Fire and plants. London, England: Chapman 

and Hall. 263 p.

Bouldin, J. 1999. Twentieth-century changes in forests of the Sierra Nevada, 

California. Davis, CA: University of California, Davis. 222 p. Ph.D. dissertation. 

California Avian Data Center. 2011. Modeling bird distribution responses 

to climate change: a mapping tool to assist land managers and scientists in 

California. Data obtained from California Avian Data Center, http://data.prbo.

org/cadc2/ (November 22, 2011).

Craig, R.K. 2010. “Stationarity is dead”—long live transformation: five 

principles for climate change adaptation law. Harvard Environmental Law 

Review. 34: 9–75.

Dale, V.H.; Joyce, L.A.; McNulty, S.; Neilson, R.P.; Ayres, M.P.; Flannigan, 

M.D.; Hanson, P.J.; Irland, L.C.; Lugo, A.E.; Peterson, C.J.; Simberloff, 

D.; Swanson, F.J.; Stocks, B.J.; Wotton, B.W. 2001. Climate change and 

forest disturbances. BioScience. 51: 723–734.
40

GENERAL TECHNICAL REPORT PSW-GTR-237

Dettinger, M.D. [N.d.]. From climate-change spaghetti to climate-change 

distributions for 21st century California. San Francisco Estuary and Watershed 

Science. 3(1): Article 4. http://repositories.cdlib.org/jmie/sfews/vol3/iss1/art4.

Dolanc, C.R.; Thorne, J.H.; Safford, H.D. 2012. Widespread shifts in the 

demographic structure of Sierra Nevada subalpine forests over the last 80 years. 

Global Ecology and Biogeography. DOI: 10.1111/j.1466-8238.2011.00748.x.

Drost, C.A.; Fellers, G.M. 1996. Collapse of a regional frog fauna in the Yosemite 

Area of the California Sierra Nevada, USA. Conservation Biology. 10: 414–425.

Egan, D.; Howell, E.A., eds. 2001. The historical ecology handbook: a 

restorationist’s guide to reference ecosystems. Washington, DC: Island 

Press. 457 p.

Flannigan, M.D.; Stocks, B.J.; Wotton, B.M. 2000. Climate change and forest 

fires. Science of the Total Environment. 262: 221–229.

Forister, M.L.; McCall, A.C.; Sanders, N.J.; Fordyce, J.A.; Thorne, J.H.; 

O’Brien, J.; Waetjen, D.P.; Shapiro, A.M. 2010. Compounded effects of 

climate change and habitat alteration shift patterns of butterfly diversity. 

Proceedings of the National Academy of Sciences. 107: 2088–2092.

Graumlich, L.J. 1991. Subalpine tree growth, climate, and increasing CO2: 

an assessment of recent growth trends. Ecology. 72: 1–11.

Grinnell, J.; Storer, T. 1924. Animal life in the Yosemite. Berkeley, CA: 

University of California Press. [Not paged].

Gutowski, W.J.; Pan, Z.; Anderson, C.A.; Arritt, R.W.; Otieno, F.; Takle, E.S.; 

Christensen, J.H.; Christensen, O.B. 2000. What RCM data are available for 

California impacts modeling? Sacramento, CA: California Energy Commission 

workshop on climate change scenarios for California. California Energy 

Commission.

Hakkarinen, C.; Smith, J. 2003. Appendix I: Climate scenarios for a California 

Energy Commission study of the potential effects of climate change on 

California: summary of a workshop. In: Global climate change and California: 

potential implications for ecosystems, health, and the economy. Palo Alto, CA: 

Electric Power Research Institute. 38 p.

Harris, J.A.; Hobbs, R.J.; Higgs, E.; Aronson, J. 2006. Ecological restoration 

and global climate change. Restoration Ecology. 14: 170–176.
41

Managing Sierra Nevada Forests

Hayhoe, K.; Cayan, D.; Field, C.B.; Frumhoff, P.C.; Maurer, E.P.; Miller, N.L.; 

Moser, S.C.; Schneider, S.H.; Cahill, K.N.; Cleland, E.E.; Dale, L.; Drapek, 

R.; Hanemann, R.M.; Kalstein, L.S.; Leniahn, J.; Lunch, C.K.; Neilson, 

R.P.; Sheridan, S.C.; Verville, J.H. 2004. Emissions pathways, climate change, 

and impacts on California. Proceedings of the National Academy of Sciences. 

101: 12422–12427.

Holling, C.S. 1973. Resilience and stability of ecological systems. Annual Review 

of Ecology and Systematics. 4: 1–23.

Hunter, M.L., Jr.; Jacobson, G.L., Jr.; Webb, T., III. 1988. Paleoecology and the 

coarse-filter approach to maintaining biological diversity. Conservation Biology. 

2: 375–385.

Intergovernmental Panel on Climate Change [IPCC]. 2007. Climate change 

2007: synthesis report. Contribution of working groups I, II and III to the 

Fourth Assessment Report of the Intergovernmental Panel on Climate Change. 

[Pachauri, R.K; Reisinger, A., eds.]. Geneva, Switzerland: 104 p.

Landres, P.B.; Morgan, P.; Swanson, F.J. 1999. Overview of the use of natural 

variability concepts in managing ecological systems. Ecological Applications. 9: 

1179–1188.

Lawler, J.J.; Shafer, S.L.; Bancroft, B.A.; Blaustein, A.R.. 2009a. Projected 

climate impacts for the amphibians of the Western Hemisphere. Conservation 

Biology. 24: 38–50.

Lawler, J.J.; Shafer, S.L.; White, D.; Kareiva, P.; Maurer, E.P.; Blaustein, 

A.R.; Bartlein, P.J. 2009b. Projected climate-induced faunal change in the 

Western Hemisphere. Ecology. 90: 588–597.

Lenihan, J.M.; Bachelet, D.; Neilson, R.P.; Drapek, R. 2008. Response of 

vegetation distribution, ecosystem productivity, and fire to climate change 

scenarios for California. Climate Change. 87(Suppl. 1): S215–S230.

Lenihan, J.M.; Drapek, R.; Bachelet, D.; Neilson, R.P. 2003. Climate change 

effects on vegetation distribution, carbon, and fire in California. Ecological 

Applications. 13: 1667–1681.

Loarie, S.R.; Carter, B.E.; Hayhoe, K.; McMahon, S.; Moe, R.; Knight, C.A.; 

Ackerly, D.D. 2008. Climate change and the future of California’s endemic flora. 

PLoS One. 3(6): e2502: 1–10.
42

GENERAL TECHNICAL REPORT PSW-GTR-237

Manley, P.N.; Brogan, G.E.; Cook, C.; Flores, M.E.; Fullmer, D.G.; Husari, 

S.; Jimerson, T.M.; Lux, L.M.; McCain, M.E.; Rose, J.A.; Schmitt, G.; 

Schuyler, J.C.; Skinner, M.J. 1995. Sustaining ecosystems: a conceptual 

framework. Publ. R5-EM-TP-001. San Francisco, CA: U.S. Department of 

Agriculture, Forest Service, Pacific Southwest Region. 216 p. 

McKelvey, K.S.; Skinner, C.N.; Chang, C.; Erman, D.C.; Husari, S.J.; Parsons, 

D.J.; van Wagtendonk, J.W.; Weatherspoon, C.W. 1996. An overview of 

fire in the Sierra Nevada. In: Sierra Nevada Ecosystem Project: final report to 

Congress. Vol. II, Assessments and scientific basis for management options. 

Davis, CA: University of California, Centers for Water and Wildland Resources: 

1033–1040.

McKenzie, D.; Gedalof, Z.; Peterson, D.L.; Mote, P. 2004. Climatic change, 

wildfire, and conservation. Conservation Biology. 18: 890–902.

Millar, C.I.; Stephenson, N.L.; Stephens, S.L. 2007. Climate change and forests 

of the future: managing in the face of uncertainty. Ecological Applications. 

17: 2145–2151.

Millar, C.I.; Woolfenden, W.B. 1999. The role of climate change in interpreting 

historical variability. Ecological Applications. 9: 1207–1216. 

Miller, C.; Urban, D. 1999. Forest pattern, fire and climatic change in the Sierra 

Nevada. Ecosystems. 2: 76–87.

Miller, J.D.; Safford, H.D.; Crimmins, M.; Thode, A.E. 2009. Quantitative 

evidence for increasing forest fire severity in the Sierra Nevada and southern 

Cascade Mountains, California and Nevada, USA. Ecosystems. 12: 16–32.

Miller, N.L.; Bashford, K.E.; Strem, E. 2003. Potential impacts of climate change 

on California hydrology. Journal of the American Water Resources Association. 

39: 771–784.

Milly, P.C.D.; Betancourt, J.; Falkenmark, M.; Hirsch, R.M.; Kundzewicz, 

Z.W.; Lettenmaier, D.P.; Stouffer, R.J. 2008. Stationarity is dead: whither 

water management? Science. 319: 573–574.

Morgan, P.; Aplet, G.H.; Haufler, J.B.; Humphries, H.C.; Moore, M.M.; 

Wilson, W.D. 1994. Historical range of variability: a useful tool for evaluating 

ecosystem change. Journal of Sustainable Forestry. 2: 87–111. 

Moritz, C.; Patton, J.L.; Conroy, C.J.; Parra, J.L.; White, G.C.; Beissinger, 

S.R. 2008. Impact of a century of climate change of small-mammal communities 

in Yosemite National Park, USA. Science. 322: 261–264.
43

Managing Sierra Nevada Forests

Moser, S.; Franco, G.; Pittiglio, S.; Chou, W.; Cayan, D. 2009. The future is 

now: an update on climate change science impacts and response options for 

California. California Climate Change Center Report CEC-500-2008-071. 

Sacramento, CA: California Energy Commission. 91 p.

National Research Council. 2011. Climate stabilization targets: emissions, 

concentrations, and impacts over decades to millennia. Washington, DC: 

The National Academies Press. 298 p.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Noss, R.F. 2001. Beyond Kyoto: forest management in a time of rapid climate 

change. Conservation Biology. 15: 578–590. 

Pickett, S.T.A.; White, P.S. 1985. The ecology of natural disturbance and patch 

dynamics. New York, NY: Academic Press. 472 p.

Price, C.; Rind, D. 1994. The impact of a 2 × CO2 climate on lightning-caused 

fires. Journal of Climate. 7: 1484–1494.

Safford, H.D.; Hayward, G.; Heller, N.; Wiens, J.A. [In press a]. Climate 

change and historical ecology: can the past still inform the future? In: Wiens, 

J.A.; Hayward, G.; Safford, H.D.; Giffen, C. eds. Historical environmental 

variation in conservation and natural resource management: past, present and 

future. New York, NY: John Wiley and Sons.

Safford, H.D.; Wiens, J.A.; Hayward, G. [In press b]. Conclusion: the growing 

importance of the past in managing ecosystems of the future. In: Wiens, J.A.; 

Hayward, G.; Safford, H.D.; Giffen, C. eds. Historical environmental variation 

in conservation and natural resource management: past, present and future. New 

York, NY: John Wiley and Sons.

Sanderson, E.W.; Jaiteh, M.; Levy, M.A.; Redford, K.H.; Wannebo, A.V.; 

Woolmer, G. 2002. The human footprint and the last of the wild. BioScience. 

52: 891–904.

Saunders, S.; Montgomery, C.; Easley, T.; Spencer, T. 2008. Hotter and drier. 

The West’s changed climate. New York, NY: The Rocky Mountain Climate 

Organization and the Natural Resources Defense Council. 54 p.
44

GENERAL TECHNICAL REPORT PSW-GTR-237

Stahlberg, D.; Jongsomjit, D.; Howell, C.A.; Snyder, M.A.; Alexander, J.D.; 

Wiens, J.A.; Root, T.L. 2009. Re-shuffling of species with climate disruption: 

a no-analog future for California birds. PLoS One. 4(9) e6825: 1–8.

Stephenson, N.L.; Millar, C.I.; Cole, D.N. 2010. Shifting environmental 

foundations: the unprecedented and unpredictable future. In: Cole, D.N.; 

Yung, L., eds. Beyond naturalness: rethinking park and wilderness stewardship 

in an era of rapid change. Washington, DC: Island Press: 50–66.

Stewart, I.T.; Cayan, D.R.; Dettinger, M.D. 2005. Changes toward earlier 

streamflow timing across western North America. Journal of Climate. 

18: 1136–1155.

Swetnam, T.W. 1993. Fire history and climate change in giant sequoia groves. 

Science. 262: 885–889.

Swetnam, T.W.; Allen, C.D.; Betancourt, J.L. 1999. Applied historical ecology: 

using the past to manage for the future. Ecological Applications. 9: 1189–1206.

Tingley, M.W.; Monahan, W.B.; Beissinger, S.R.; Moritz, C. 2009. Birds track 

their Grinnellian niche through a century of climate change. Proceedings of the 

National Academy of Sciences. 106: 19367–19643.

U.S. Department of Agriculture, Forest Service and U.S. Department of the 

Interior, Bureau of Land Management [USDA and USDI]. 1994. Record of 

decision for amendment to Forest Service and Bureau of Land Management 

planning documents within the range of the northern spotted owl. [Place of 

publication unknown]. 74 p. (plus attachment A: standards and guidelines].

Van de Water, K.M.; Safford, H.D. 2011. A summary of fire frequency estimates 

for California vegetation before Euroamerican settlement. Fire Ecology. 7: 26–58. 

Van Mantgem, P.J.; Stephenson, N.L.; Byrne, J.C.; Daniels, L.D.; Franklin, 

J.F.; Fulé, P.Z.; Harmon, M.E.; Larson, A.J.; Smith, J.M.; Taylor, A.H.; 

Veblen, T.T. 2009. Widespread increase of tree mortality rates in the western 

United States. Science. 323: 521–524.

Wake, D.B.; Vrendenburg, V.T. 2008. Are we in the midst of the sixth mass 

extinction? A view from the world of amphibians. Proceedings of the National 

Academy of Sciences. 105: 11466–11473.

Westerling, A.L.; Bryant, B. 2006. Climate change and wildfire in and around 

California: fire modeling and loss modeling. Report from the California Climate 

Change Center to the California Energy Commission. CEC-500-2006-190-SF. 

Sacramento, CA, California Energy Commission publishing. 28 p.
45

Managing Sierra Nevada Forests

Westerling, A.L.; Hidalgo, H.; Cayan, D.R.; Swetnam, T. 2006. Warming 

and earlier spring increases western U.S. forest wildfire activity. Science. 

313: 940–943.

White, P.S.; Walker, J.L. 1997. Approximating nature’s variation: selecting and 

using reference information in restoration ecology. Restoration Ecology. 

5: 338–349.

Whitlock, C.; Shafer, S.L.; Marlon, J. 2003. The role of vegetation change in 

shaping past and future fire regimes in the northwest U.S. and the implications 

for ecosystem management. Forest Ecology and Management. 178: 5–21.

Wiens, J.A.; Hayward, G.; Safford, H.D., Giffen, C., eds. [In press]. Historical 

environmental variation in conservation and natural resource management: past, 

present and future. New York, NY: John Wiley and Sons.

Wieslander, A.E. 1935. A vegetation type map of California. Madroño. 3: 140–144.

Western Regional Climate Center. 2010. California climate data archive. Western 

Regional Climate Center. http://www.calclim.dri.edu/ccacoop.html. (21 May 

2010).
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47

Managing Sierra Nevada Forests

K.L Purcell,1 C.M. Thompson,2 and W.J. Zielinski 3

Introduction

Fishers (Martes pennanti) and American martens (M. americana) are carnivorous 

mustelids associated with late-successional forests. The distributions of both species have decreased in the Sierra Nevada and southern Cascade region (Zielinski 

et al. 2005). Fishers occur primarily in lower elevation (3,500 to 7,000 ft) (1067 to 

3134 m) Sierran mixed-conifer and ponderosa pine forests, while marten distribution overlaps that of fishers but extends to much higher elevation (4,500 to 10,000 

ft) (1372 to 3048 m) red fir and lodgepole pine forests. Fishers and martens have 

disproportionately large home ranges for their body sizes. Home ranges for male 

and female fishers average 9,960 ac (4031 ha) and 2,456 ac (994 ha), respectively. 

Martens have home ranges that average 1,413 ac (572 ha) and 877 ac (355 ha) for 

males and females, respectively. 

Habitat Preferences

Habitat selection occurs at multiple spatial scales. For martens, the strength of 

habitat selection varies with scale (Minta et al. 1999); selection appears to be 

strongest at the microhabitat (e.g., resting and denning sites [generally 0.1 to 1 ac] 

[0.04 to 0.4 ha]) and the landscape scales (> 2,000 ac (809 ha). Fishers are expected 

to show similar patterns at larger scales, relative to their larger home ranges; 

however, documentation is lacking. Resting and denning structures are likely the 

most limiting habitat elements (Martin and Barrett 1991, Porter et al. 2005, Purcell 

et al. 2009, Spencer et al. 1983, Zielinski et al. 2004), and understanding resting 

habitat characteristics may be particularly important for conserving both species. 

The majority of fisher resting sites are cavities or platforms in live trees or snags, 

whereas martens more often use snags, logs, and stumps (Martin and Barrett 1991, 

Purcell et al. 2009, Spencer 1987, Zielinski et al. 2004). Trees and snags used as 

rest sites are typically among the largest available, often >35 in diameter at breast 

height (d.b.h.) (range 13 to 71 in) (89 cm; range 34 to 180 cm) (Martin and Barrett 

1991, Purcell et al. 2009, Spencer 1987, Zielinski et al. 2004). Live trees used by 

fishers are often of declining health, with resting locations found in cavities caused 

by heartwood decay or platforms resulting from diseases such as mistletoe and 

Chapter 4: Fishers and American Martens

1 Research wildlife biologist, U.S. Department of Agriculture, Forest Service, Pacific 

Southwest Research Station, 2081 E. Sierra Ave., Fresno, CA 93710. 

2 Postdoctoral research wildlife ecologist, U.S. Department of Agriculture, Forest Service, 

Pacific Southwest Research Station, 2081 E Sierra Ave., Fresno, CA 93710.

3 Research wildlife biologist, U.S. Department of Agriculture, Forest Service, Pacific 

Southwest Research Station, 1700 Bayview Dr., Arcata, CA 95521.
48

GENERAL TECHNICAL REPORT PSW-GTR-237

Summary of Findings

1. The distributions of American martens and fishers in the Sierra 

Nevada and southern Cascade region have decreased, and both species are expected to suffer additional habitat loss under changing 

climatic conditions. Habitat selection by both species occurs at multiple 

spatial scales, ranging from microsite conditions to landscape configuration.

2. Resting and denning structures are probably the most limiting habitat element for fishers and martens. Because fishers and martens are 

nomadic within defined ranges (i.e., they move between rest sites on a 

daily basis outside the denning season), they require resting structures 

and resting habitat that are well distributed across the landscape and are 

sensitive to changes in landscape configuration. 

3. High canopy cover and large trees and snags are important components in both fisher and marten resting habitat. Results suggest a minimum canopy cover target of approximately 60 percent for fishers and 30 

percent for martens. Fishers prefer shade-intolerant species such as oaks 

and pines while martens use firs and lodgepole pines. Both species select 

sites characterized by complex vertical and horizontal structure.

4. Recent findings support recommendations for focusing habitat 

management for fishers and martens in areas where fire would have 

burned less frequently historically, such as north-facing slopes, canyon bottoms, and riparian areas. 

5. Two new analysis tools may be helpful for predicting management impacts on fisher populations. One tool allows the quantitative 

evaluation of proposed treatments on fisher resting habitat using FIA 

data (Zielinski et al. 2006, 2010). A second analysis tool uses growth 

and disturbance models, combined with landscape trajectory analysis, to provide a visual, intuitive representation of the predicted risk 

of potential management actions on fisher habitat at the home-range 

scale (Thompson et al. 2011). 
49

Managing Sierra Nevada Forests

rust brooms. The use of both live trees and snags by these species suggests that, if 

sufficient numbers of large trees are present over the landscape, requirements for 

large snags will likely also be met over time (Smith et al. 2005). These findings 

are consistent with North et al. (2009) regarding the importance of large trees and 

snags, especially those with defects such as disease or damage. Suitable structures 

need to be well-distributed throughout their home ranges because reuse of resting 

sites is typically low. Research shows that fishers prefer to rest in shade-intolerant 

trees such as pines and oaks (Purcell et al. 2009), which are now less abundant than 

they were historically (McDonald 1990, Minnich et al. 1995, Roy and Vankat 1999). 

The North et al. (2009) approach encouraged the retention of oaks and pines, and 

stressed the importance of hardwoods, especially California black oaks (Quercus 

kelloggii Newberry). Black oaks require openings for regeneration (McDonald 

1990), suggesting that the creation of small openings around mature productive 

trees would aid establishment of young trees needed to replace dying oaks. This 

should be balanced with retaining smaller trees around oaks that are potential dens 

for hiding cover. Fishers seldom use oak snags for resting. Most oaks used by fishers are live trees, although dead portions of otherwise healthy trees are important. 

In the northern Sierra Nevada, martens frequently use large red firs (Abies magnifica Andr. Murray), white firs (Abies concolor (Gordon & Glend.) Lindley) and 

lodgepole pines (Pinus contorta Douglas ex. Loudon) for resting (Spencer 1987).

Habitat conditions in the immediate vicinity of resting structures (resting 

sites) are characterized by complex vertical and horizontal structure, dense canopy 

cover, large trees, and snags (Purcell et al. 2009, Spencer et al. 1983, Zielinski et 

al. 2004). Canopy cover is consistently the most important variable distinguishing 

resting sites from available sites for fishers, with results suggesting a minimum 

canopy cover target of approximately 60 percent (Purcell et al. 2009). Cover is also 

influential for martens, which generally do not occur in areas where canopy cover is 

less than 30 percent (Spencer et al. 1983). The typically high diversity of tree sizes 

surrounding fisher resting sites suggests the need for complex vertical structure, 

but may be an artifact of past logging practices and fire suppression, which altered 

forest conditions from stands dominated by large trees and snags to dense stands 

with size class distributions that include more small stems and fewer large stems 

(Goforth and Minnich 2008, Minnich et al. 1995). Smaller trees may provide the 

requisite canopy cover, if a suitably large resting structure is available (Poole et al. 

2004, Purcell et al. 2009). The small-diameter tree component of canopy cover may 

explain why the basal area of small-diameter trees is an important predictor for 

fisher resting sites (Zielinski et al. 2004).

Habitat conditions in 

the immediate vicinity 

of resting structures 

are characterized by 

complex vertical and 

horizontal structure, 

dense canopy cover, 

large trees, and snags.
50

GENERAL TECHNICAL REPORT PSW-GTR-237

Forest Condition and Management Effects

Recent research findings support the validity of the North et al. (2009) recommendations for focusing habitat management for fishers and martens in areas where, 

historically, fires would have burned less frequently, such as north-facing slopes, 

canyon bottoms, and riparian areas. Resting sites are often found close to streams 

and on relatively steep slopes (Bull et al. 2001, Purcell et al. 2009, Zielinski et al. 

2004), and fisher telemetry locations include more observations in canyons and 

fewer observations on ridges than expected (Underwood et al. 2010). Marten habitat 

typically occurs at elevations where natural fire-return rates are low (e.g., red fir 

forest) compared to the elevations where fishers occur (McKelvey et al. 1996); 

consequently, there is generally less need for fuels treatment in marten habitat.

Our knowledge of habitat needs of fishers and martens at larger spatial scales 

is based largely on studies of martens conducted in other regions. At the landscape 

scale, martens’ preference for mature forest has been well established. Martens 

rarely occupy landscapes where 25 to 30 percent of mature forests have been 

removed (Bissonette et al. 1997, Chapin et al. 1998, Hargis et al. 1999, Potvin et 

al. 1999). In Oregon, Bull et al. (2001) showed that martens preferentially selected 

unharvested stands compared to stands subjected to regeneration, partial, or 

selection cuts. Buskirk and Ruggiero (1994) reviewed marten responses to anthropogenic habitat alteration, and found that martens made little use of regenerating 

clearcuts for several decades after harvest, and that marten populations declined 

after clearcut logging. Thompson (1994) documented that martens in uncut forests 

had significantly higher density, survival, and reproduction than in surrounding 

logged, regenerating forests. These responses may also be occurring in the Sierra 

Nevada, where a long-term study site in the Tahoe National Forest has documented 

a significant decline in marten abundance during the last few decades, possibly 

because of the cumulative effects of timber harvests on forest landscape configuration (e.g., decreases in patch size of mature forest with an increase in interpatch 

distance) (Moriarty et al. 2011). These studies reinforce the sensitivity of martens, 

and presumably fishers, to changes in landscape composition and configuration.

At the same time, martens are known to inhabit younger or managed forests as 

long as some of the structural elements found in older forests remain, particularly 

those required for resting and denning. In British Columbia, Porter et al. (2005) 

reported that martens were capable of persisting in a young, manipulated forest 

as long as structural features characteristic of older forests were retained. On the 

Lassen National Forest, martens preferentially used shelterwood stands during the 

summer, when chipmunks and ground squirrels were available in these relatively 
51

Managing Sierra Nevada Forests

open areas; however, females showed strong year-round selection for old-growth 

stands (Ellis 1998). Habitat conditions for martens appear best in old-growth stands, 

particularly red fir and lodgepole pine in proximity to meadows or riparian areas 

(Simon 1980, Spencer et al. 1983).

New Analysis Tools

A research need identified in North et al. (2009) was an assessment of proposed 

treatments on wildlife habitat features of interest. For fisher resting habitat, these 

predictive models would use either a predictive microhabitat model or a habitat 

model based on Forest Inventory and Analysis (FIA) data. The effects of forest 

practices on fisher resting habitat can now be quantitatively evaluated with the 

development of a model for the southern Sierra Nevada that predicts resting habitat 

value from plot data (Zielinski et al. 2006, 2010). The model can use FIA data 

or other types of fixed-area plot data and the Forest Vegetation Simulator (FVS) 

to forecast future effects of proposed activities on fisher resting habitat. Similar 

models have not yet been developed for martens.

In general, we still know little about the risks associated with different forest 

management actions, particularly for fishers. A specific research need identified in 

North et al. (2009) entailed examination of potential outcomes of proposed forest 

treatments based on modeling habitat in female fisher home ranges. This shortcoming has been partially addressed through the recent development of an analytical 

tool that predicts the relative impacts of management actions on fisher habitat 

(Thompson et al. 2011). Lacking more explicit information, this approach is essentially a form of ecological risk management. We quantified the range of variation 

in currently occupied female fisher home ranges and assumed that, if we managed 

landscapes to resemble those occupied home ranges, there is a high likelihood the 

landscape will remain functional fisher habitat and minimize the risk of negative 

population impacts. By following the trajectory of the landscape through time, we 

demonstrate how certain management prescriptions, including “no action,” may 

involve greater risk to fishers owing to the greater divergence from the reference 

conditions. Results also indicate that female fishers use landscapes with relatively 

high proportions of large trees and snags, and where patches of high-quality habitat 

are connected in a heterogeneous mix of forest ages and conditions. This suggests 

that some level of management to reduce fire risk may be consistent with the maintenance of landscapes capable of supporting fishers as long as sufficient resting/denning structures are retained. This finding is in agreement with results from other 

recent efforts that modeled the effects of wildfires and fuels management on fisher 

Certain management 

prescriptions, including 

“no action,” may involve 

greater risk to fishers 

owing to the greater 

divergence from the 

reference conditions.

Management to 

reduce fire risk may 

be consistent with 

the maintenance of 

landscapes capable 

of supporting fishers 

as long as sufficient 

resting/denning 

structures are retained.
52

GENERAL TECHNICAL REPORT PSW-GTR-237

populations (Scheller et al. 2011, Spencer et al. 2008). These studies found that, 

although fuels treatments had direct negative effects on habitat suitability, those 

effects were mitigated by the potential benefits of reducing the likelihood of large 

wildfires that would eliminate or severely degrade available fisher habitat. This may 

especially be true if future fire regimes prove to be more extreme than past regimes 

(Carroll et al., in press; Spencer et al. 2008).

Potential Implications of Climate Change

Climate change is expected to have profound effects on the distributions of animal 

and plant species. In general, we expect upward shifts in latitude and elevation as 

warming occurs and species move to areas that suit their metabolic temperature 

tolerances (Root et al. 2003). Climate change will lead directly to shifts in the 

abundance and distribution of plant species, which could take decades to centuries 

to unfold (Davis 1990). Although the potential impacts of climate change have not 

been evaluated quantitatively in the southern Sierra Nevada, they are likely to alter 

species and structural composition. Overall, the extent of forested landscape is not 

expected to change appreciably during the 21st century, but the biggest predicted 

change is the reduction in area of conifer-dominated forest types, which are generally replaced by mixed woodland and hardwood-dominated forest types. (Lawler et 

al., in press; Lenihan et al. 2003). Because oaks, especially California black oaks, 

are a key component of fisher habitat, floristic changes may benefit fishers as long 

as temperature effects do not result in upward range shifts. 

Lawler et al. (in press) recently published a study investigating the possible 

direct and indirect effects of climate change on selected species of the genus 

Martes. They found that macroclimate conditions closely correlated with Pacific 

fisher presence in California were likely to change greatly over the next century, 

resulting in a possibly pronounced loss of suitable habitat. Their results suggested 

that martens and fishers will be highly sensitive to climate change, and would 

probably experience the largest climate impacts at their southernmost latitudes 

(i.e., in the southern Sierra Nevada). The authors noted that fisher habitat is driven 

to a great extent by mesotopographic and local vegetation features that could not 

be incorporated into their climatic models. However, since fire occurrence and 

behavior have substantial effects on local vegetation and these factors are driven 

to a large extent by climate/weather, they also looked at stand-level implications 

of fire under a series of future fire scenarios. Lawler et al. (in press) recommended 

protecting fisher habitat through targeted forest-fuel treatment, and applying more 
53

Managing Sierra Nevada Forests

liberal fire-management policies to naturally ignited fires during moderate weather 

conditions.

Interactions between climate and fire generate further changes in projected 

vegetation (see Safford et al. this volume). Climate-driven changes in fire regimes 

are projected to include increases in fire frequency, area, and intensity (Flannigan 

et al. 2000). Changes in fire regimes are expected to result in loss of late-seral 

habitat, increasing the probability of local extinction of species—such as fishers and 

martens—associated with these habitats (McKenzie et al. 2004). Decreases in the 

density of large conifer and hardwood trees and canopy cover are projected as fire 

severity increases. As these factors are closely related to fisher rest site and home 

range use in the southern Sierra Nevada (Purcell et al. 2009; Zielinski et al. 2004, 

2005), the expectation is for an overall decrease in the availability of fisher habitat. 

Other indirect, complex, interacting, and largely unpredictable effects may also 

play important roles. Predator-prey relationships may be altered if shifts in prey do 

not track those of martens and fishers. Reductions in snowpack could alter competitive relationships between martens and fishers, as snow potentially mitigates 

competitive interactions between the species (Krohn et al. 1997). Increased overlap 

between martens and fishers is expected to lead to increased competition between 

the two species, with fishers the likely beneficiary. 

For martens, a shift in distribution to higher elevations would drive them 

toward the limit of forested habitats, which could limit their distribution and lead 

to decreases in population size. The marten range in the Cascades of California 

may already be demonstrating such effects (Kirk and Zielinski 2009, Zielinski et 

al. 2005). At high elevations, martens currently occupy areas with small trees and 

reduced forest cover (Green 2007), and have also been documented to use boulder 

fields, talus slopes, and rock slides (Green 2007, Grinnell et al. 1937). While use 

of these habitats may be more than transitory, they may not provide for year-round 

habitat needs (Green 2007).

Perhaps the biggest challenge related to climate change lies not simply in the 

changes per se, but in the rate of increase. Change is expected to occur at a rate and 

order of magnitude greater than rates of change experienced previously, and beyond 

the capability of species to adaptation through evolutionary responses (Root and 

Schneider 1993, Root et al. 2003). Although predictions based on various model 

projections differ, taken as a whole, martens and fishers are expected to be highly 

sensitive to climate change. 

Martens and fishers 

are expected to be 

highly sensitive to 

climate change.
54

GENERAL TECHNICAL REPORT PSW-GTR-237

Unknowns

At present there is a great deal of uncertainty around predicting impacts on marten 

and fisher habitat, particularly cumulative effects. This is largely because our 

knowledge of how habitat change influences survival and reproduction is limited, 

and because we do not yet understand the importance of landscape heterogeneity to 

these species. Owing in part to the large home ranges of fishers and martens, multiple spatial scales must be considered in forest management planning. In particular, 

managers should consider the extent and connectivity of older forest patches, 

and the heterogeneity and composition of the remaining landscape. For fishers in 

particular, maintaining habitat in riparian areas and on topographic positions that 

normally did not burn frequently or severely (North et al. 2009) may help provide 

connectivity without significantly reducing the effectiveness of fuel reduction 

efforts. New analytical tools (i.e., Thompson et al. 2011, Zielinski et al. 2010) should 

be evaluated to assess projected effects at home range and landscape scales. 

We still lack important information about reproductive site characteristics for 

these species, including their requirements for den trees and denning habitat at 

multiple spatial scales. As suggested in North et al. (2009), one way to help ensure 

the retention of key forest structures would be to provide a list of attributes and representative photos of resting and denning structures for use by marking crews (fig. 

4-1) (see Lofroth et al. 2010 for descriptions of the specific types of structures used 

by fishers for resting and denning). Because most disturbances in fisher and marten 

habitat will be the result of treatments to reduce fuels and control forest pathogens, 

it is important to conduct rigorous studies on the effects of fuel treatments on fishers, martens, and their prey. Also, we know very little about the effects of management activities on important fisher and marten prey species or foraging behavior 

(Martin 1987). Addressing these information needs will lead to better informed 

management decisions and a greater likelihood that forest managers can provide the 

habitat conditions needed to support viable fisher and marten populations. 
55

Managing Sierra Nevada Forests

Figure 4-1—Examples of structures used as resting and denning sites by fishers in the Sierra National Forest, California. (A) 

cedar log (rest), (B) cavity in the base of a black oak (rest), (C) mistletoe broom in a sugar pine (Pinus lambertiana Dougl.) 

(rest), (D) deformity in a white fir (rest), (E) cedar snag with fisher looking out (rest), (F) cedar snag (rest), (G) woodpecker 

hole in a live ponderosa pine (den), and (H) cavity entrance in a black oak (den). 

A B

C D E

F G H

All photographs on this page by Rebecca Green
56

GENERAL TECHNICAL REPORT PSW-GTR-237

References

Bissonette, J.A.; Harrison, D.J.; Hargis, C.D.; Chapin, T.G. 1997. The influence 

of spatial scale and scale-sensitive properties on habitat selection by American 

marten. In: Bissonette, J.A., ed. Wildlife and landscape ecology. New York: 

Springer-Verlag: 368–385.

Bull, E.L.; Aubry, K.B.; Wales, B.C. 2001. Effects of disturbance on forest 

carnivores of conservation concern in eastern Oregon and Washington. 

Northwest Science. 75: 180–184.

Buskirk, S.W.; Ruggiero, L.F. 1994. American marten. In: Ruggiero, L.F.; Aubry, 

K.B.; Buskirk, S.W.; Lyon, L.J.; Zielinski, W.J., tech. eds. The scientific basis for 

conserving forest carnivores: American marten, fisher, lynx, and wolverine in 

the Western United States. Gen. Tech. Rep. RM-GTR-254. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station: 

38–73. 

Carroll, C.; Spencer, W.; Lewis, J. [In press]. Use of habitat and viability models 

in Martes conservation and restoration. In: Aubry, K.; Zielinski, W.; Raphael, 

M.; Proulx, G.; Buskirk, S., eds. Biology and conservation of martens, sables, 

and fishers: a new synthesis. Ithaca, NY: Cornell University Press.

Chapin, T.G.; Harrison, D.J.; Katnik, D.D. 1998. Influence of landscape pattern 

on habitat use by American marten in an industrial forest. Conservation Biology. 

12: 96–227.

Davis, M.B. 1990. Climatic change and the survival of forest species. In: 

Woodwell, G.M., ed. The earth in transition: patterns and processes of biotic 

impoverishment. Cambridge, England: Cambridge University Press: 99–110.

Ellis, L.M. 1998. Habitat use pattern of the American marten in the southern 

Cascade mountains of California. Arcata, CA: Humboldt State University. 95 p. 

M.S. thesis.

Flannigan, M.D.; Stocks, B.J.; Wottom, B.M. 2000. Climate change and forest 

fires. Science of the Total Environment. 262: 221–229.

Green, R.E. 2007. Distribution and habitat associations of forest carnivores and an 

evaluation of the California wildlife habitat relationships model for American 

marten in Sequoia and Kings Canyon National Parks. Arcata, CA: Humboldt 

State University. 90 p. M.S. thesis. 
57

Managing Sierra Nevada Forests

Grinnell, J.; Dixon, J.S.; Linsdale, J.M. 1937. Fur-bearing mammals of 

California: their natural history, systematic status, and relations to man. 

Volumes 1, 2. Berkeley, CA: University of California. 265 p.

Goforth, B.R.; Minnich, R.A. 2008. Densification, stand-replacement wildfire, 

and extirpation of mixed conifer forest in Cuyamaca Rancho State Park, southern 

California. Forest Ecology and Management. 256: 36–45.

Hargis, C.D.; Bissonette, J.A.; Turner, D.L. 1999. The influence of forest 

fragmentation and landscape pattern on American martens. Journal of Applied 

Ecology. 36: 157–172. 

Kirk, T.A.; Zielinski, W.J. 2009. Developing and testing a landscape habitat 

suitability model for the American marten (Martes americana) in the Cascades 

mountains of California. Landscape Ecology. 24: 759–773.

Krohn, W.B.; Zielinski, W.J.; Boone, R.B. 1997. Relations among fishers, 

snow, and martens in California: results from small-scale spatial comparisons. 

In: Proulx, G.; Bryant, H.N.; Woodard, P.M., eds. Martes: taxonomy, ecology, 

techniques, and management. Edmonton, AB: Provincial Museum of Alberta: 

211–232.

Lawler, J.J.; Safford, J.D.; Girvetz, E.H. [In press]. Martens and fishers in a 

changing climate. In: Aubry, K.; Zielinski, W.; Raphael, M.; Proulx, G.; Buskirk, 

S., eds. Biology and conservation of martens, sables, and fishers: a new synthesis. 

Ithaca, NY: Cornell University Press.

Lenihan, J.M.; Drapek, R.; Bachelet, D.; Neilson, R.P. 2003. Climate change 

effects on vegetation distribution, carbon, and fire in California. Ecological 

Applications. 13: 1667–1681. 

Lofroth, E.C.; Raley, C.M.; Higley, J.M.; Truex, R.L.; Yaeger, J.S.; Lewis, 

J.C.; Happe, P.J.; Finley, L.L.; Naney, R.H.; Hale, L.J.; Krause, A.L.; 

Livingston, S.A.; Myers, A.M.; Brown, R.N. 2010. Conservation of fishers 

(Martes pennanti) in south-central British Columbia, western Washington, 

western Oregon, and California. Volume I: Conservation assessment. Denver, 

CO: U.S. Department of the Interior, Bureau of Land Management. 163 p. 

Martin, S.K. 1987. The ecology of the pine marten (Martes americana) at 

Sagehen Creek, California. Berkeley, CA: University of California. 223 p. 

Ph.D. dissertation.

Martin, S.K.; Barrett, R.H. 1991. Rest site selection by marten at Sagehen 

Creek, California. Northwestern Naturalist. 72: 37–42.
58

GENERAL TECHNICAL REPORT PSW-GTR-237

McDonald, P.M. 1990. Quercus kelloggii Newb. California black oak. In: Burns, 

R.M.; Honkala, B.H., tech. coords. Silvics of North America. Volume 2. Agric. 

Handb. 654. Washington, DC: U.S. Department of Agriculture: 661–671.

McKelvey, K.L.; Skinner, C.N.; Chang, C.; Erman, D.C.; Husari, S.J.; Parsons, 

D.J.; van Wagtendonk, J.W.; Weatherspoon, C.P. 1996. An overview of fire in 

the Sierra Nevada. Sierra Nevada Ecosystem Project: Final report to Congress. 

Volume II: assessments and scientific basis for management options. Water and 

Resources Center Report No. 37. Davis, CA: Centers for Water and Wildland 

Resources, University of California, Davis: 1033–1040.

McKenzie, D.; Gedalof, Z.; Peterson, D.L.; Mote, P. 2004. Climate change, 

wildfire, and conservation. Conservation Biology. 18: 890–902.

Minnich, R.A.; Barbour, M.G.; Burk, J.H.; Fernau, R.F. 1995. Sixty years 

of change in Californian conifer forests of the San Bernardino Mountains. 

Conservation Biology. 9: 902–914.

Minta, S.C.; Kareiva, P.M.; Peyton, A.C. 1999. Carnivore research and 

conservation: learning from history and theory. In: Clark, T.W.; Peyton Curlee, 

A.; Minta, S.C.; Kareiva, P.M., eds. Carnivores in ecosystems: The Yellowstone 

experience. New Haven, CT: Yale University Press: 323–404.

Moriarty, K.M.; Zielinski, W.J.; Forsman, E. 2011. Decline in American 

marten occupancy rates at Sagehen Experimental Forest, California. Journal 

of Wildlife Management. 75: 1774–1787.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Poole, K.G.; Porter, A.D.; de Vries, A.; Maundrel, C.; Grindal, S.G.; St. 

Clair, C.C. 2004. Suitability of a young deciduous-dominated forest for 

American marten and the effects of forest removal. Canadian Journal of 

Zoology. 82: 423–435.

Porter, A.D.; St. Clair, C.C.; de Vries, A. 2005. Fine-scale selection by marten 

during winter in a young deciduous forest. Canadian Journal of Forest Research. 

35: 901–909.

Potvin, F.; Belanger, L.; Lowell, K. 1999. Marten habitat selection in a clearcut 

boreal landscape. Conservation Biology. 14: 844–857.
59

Managing Sierra Nevada Forests

Purcell, K.L.; Mazzoni, A.K.; Mori, S.; Boroski, B.B. 2009. Resting structures 

and resting habitat of fishers in the southern Sierra Nevada, CA. Forest Ecology 

and Management. 258: 2696–2706.

Root, T.L.; Schneider, S.H. 1993. Can large-scale climatic models be linked with 

multiscale ecological studies? Conservation Biology. 7: 256–270.

Root, T.L.; Price, J.T.; Hall, K.R.; Schneider, S.H.; Rosenzweig, C.; Pounds, 

J.A. 2003. Fingerprints of global warming on wild animals and plants. Nature. 

421: 57–60.

Roy, D.G.; Vankat, J.L. 1999. Reversal of human-induced vegetation changes 

in Sequoia National Park, California. Canadian Journal of Forest Research. 

29: 399–412.

Scheller, R.M.; Spencer, W.D.; Rustigian-Romsos, H.; Syphard, A.D.; Ward, 

B.C.; Strittholt, J.R. 2011. Using stochastic simulation to evaluate competing 

risks of wildfires and fuels management on an isolated forest carnivore. 

Landscape Ecology. 26: 1491–1504.

Simon, T.L. 1980. An ecological study of the pine marten in the Tahoe National 

Forest. Sacramento, CA: California State University. 143 p. M.S. thesis. 

Smith, T.F.; Rizzo, D.M.; North, M. 2005. Patterns of mortality in an old-growth 

mixed-conifer forest of the Southern Sierra Nevada, California. Forest Science. 

51: 266–275.

Spencer, W.D.; Barrett, R.H.; Zielinski, W.J. 1983. Marten habitat preferences in 

the northern Sierra Nevada. Journal of Wildlife Management. 47: 1181–1186.

Spencer, W.D. 1987. Seasonal rest-site preferences of pine martens in the northern 

Sierra Nevada. Journal of Wildlife Management. 51: 616–621.

Spencer, W.D.; Rustigian, H.L.; Scheller, R.M.; Syphard, A.; Strittholt, J.; 

Ward, B. 2008. Baseline evaluation of fisher habitat and population status and 

effects of fires and fuels management on fishers in the southern Sierra Nevada. 

Unpublished report. http://consbio.org/products/reports/4. (February 8, 2012.)

Thompson, I.D. 1994. Marten populations in uncut and logged boreal forests in 

Ontario. Journal of Wildlife Management. 58: 272–280.

Thompson, C.M.; Zielinski, W.J.; Purcell, K.L. 2011. The use of landscape 

trajectory analysis to evaluate management risks: a case study with the 

Pacific fisher in the Sierra National Forest. Journal of Wildlife Management. 

75: 1164–1176. 
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Underwood, E.C.; Viers, J.H.; Quinn, J.F.; North, M. 2010. Using topography 

to meet wildlife and fuels treatment objectives in fire-suppressed landscapes. 

Environmental Management. 46: 809–819.

Zielinski, W.J.; Truex, R.L.; Schmidt, G.A.; Schlexer, F.V.; Schmidt, K.N.; 

Barrett, R.H. 2004. Resting habitat selection by fishers in California. Journal of 

Wildlife Management. 68: 475–492.

Zielinski, W.J.; Truex, R.L.; Schlexer, F.V.; Campbell, L.A.; Carroll, C. 2005. 

Historical and contemporary distributions of carnivores in forests of the Sierra 

Nevada, California, USA. Journal of Biogeography. 32: 1385–1407. 

Zielinski, W.J.; Truex, R.L.; Dunk, J.R.; Gaman, T. 2006. Using forest 

inventory data to assess fisher resting habitat suitability in California. Ecological 

Applications. 16: 1010–1025.

Zielinski, W.J.; Gray, A.; Dunk, J.R.; Keyser, C.; Sherlock, J.; Dixon, G. 

2010. Using Forest Inventory and Analysis (FIA) data and the Forest Vegetation 

Simulator (FVS) to predict wildlife habitat suitability: resting habitat for the 

fisher (Martes pennanti). Gen. Tech. Rep. PSW-GTR-232. Albany, CA: U.S. 

Department of Agriculture, Forest Service, Pacific Southwest Research Station. 

31 p. 
61

Managing Sierra Nevada Forests

S. Roberts1 and M. North2

Introduction

California spotted owls (Strix occidentalis occidentalis) 

are habitat specialists that are strongly associated with 

late-successional forests. For nesting and roosting, 

they require large trees and snags embedded in a stand 

with a complex forest structure (Blakesley et al. 2005, 

Gutiérrez et al. 1992, Verner et al. 1992b). In mixedconifer forests of the Sierra Nevada, California spotted 

owls typically nest and roost in stands with high canopy 

closure (≥75 percent) [Note: when citing studies, we 

use terminology consistent with Jennings et al. (1999), 

however, not all studies properly distinguish between 

canopy cover and closure and often use the terms 

interchangeably (see chapter 14 for clarification)] and 

an abundance of large trees (>24 in (60 cm) diameter 

at breast height [d.b.h.]) (Bias and Gutiérrez 1992, 

Gutiérrez et al. 1992, LaHaye et al. 1997, Moen and 

Gutiérrez 1997, Verner et al. 1992a). The California 

spotted owl guidelines (Verner et al. 1992b) effectively 

summarized much of the information about nesting 

and roosting habitat. Since that report, research on the 

California spotted owl has continued with much of the 

new information concentrated in five areas: population trends, barred owl (Strix varia) invasion, climate 

effects, foraging habitat, and owl response to fire. 

Population Trends

A rangewide investigation from 1990 to 2005 into 

the population dynamics of the California spotted 

owl showed that subpopulations at four studied locations were declining or remaining steady (mean λ = 

1.007, 95 percent confidence interval (CI) = 0.952 to 

Chapter 5: California Spotted Owls

1 Wildlife ecologist, U.S. Geological Survey, Western Ecological Research Center, 

Yosemite Field Station, 7799 Chilnualna Falls Rd., Box 2163, Wawona, CA 95389.

2 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 1731 Research Park Dr., Davis, CA 95618.

Summary of Findings

1. Spotted owls select habitat at multiple 

scales, with less flexibility in the nesting and 

roosting habitat requirements, and more

flexibility in the foraging habitat.

2. Foraging habitat appears to have more 

moderate canopy closure and is still associated with large trees, possibly because of 

their importance as nest sites for northern 

flying squirrels, an important prey species for 

spotted owls in mesic Sierra Nevada forests.

3. Low- to moderate-severity fire does not 

reduce the probability of spotted owl occupancy if numerous large trees and areas of 

high canopy closure remain after a fire.

4. Dense understory of regenerating trees 

can interfere with owl foraging. Low- to 

moderate-severity fire reduces the density of 

small trees and may improve the habitat quality of spotted owl nesting or foraging habitat.

5. Forest heterogeneity, with various vegetation communities or fire severities infused 

into late-successional forest, may improve 

spotted owl fitness.

6. Fire effects on foraging habitat are not well 

understood, and future research needs to be 

directed toward owl foraging use patterns in 

a burned landscape.
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GENERAL TECHNICAL REPORT PSW-GTR-237

1.066) (Blakesley et al. 2010). Apparent survival was similar between the sexes 

and increased with owl age. The subpopulation residing in the only national park 

included in the meta-analysis, Sequoia-Kings Canyon (SEKI), showed the highest 

survival rates. Mean annual reproductive output (number of young fledged per 

territorial female) ranged from 0.988 (± 0.154) in the El Dorado National Forest to 

0.555 (± 0.110) in SEKI. El Dorado showed the highest annual variation, with higher 

reproduction every second year, while SEKI had low annual variation. Although 

reproductive output varied between the four subpopulations, the El Dorado showed 

a declining trend. This declining trend is probably related to recent low annual 

reproduction and a consistent decrease in recruitment in the El Dorado. The high 

annual variation and decreasing trend observed in the El Dorado subpopulation 

indicate that habitat quality is not stable and probably decreasing over time. As with 

the northern spotted owl, reproductive output was highest with adults, followed by 

second-year subadults, and then first-year subadults. Population viability analyses 

indicated that the probability of a >10 percent decline in 7 years was lowest at 0.41 

(95 percent CI = 0.09 to 0.78) for the Sierra National Forest subpopulation and 

highest at 0.64 (95 percent CI= 0.27 to 0.94) for the Lassen National Forest, and 

inconclusive for the El Dorado and SEKI (Blakesley et al. 2010). 

Barred Owl

The barred owl, an aggressive competitor, has invaded the Sierra Nevada from 

the north and started reproducing as far south as the El Dorado National Forest 

(Keane 2007). This invasion appears to be a natural biogeographical process (Dark 

et al. 1998). Once barred owls establish a population adjacent to spotted owls, 

there are negative effects on spotted owl metapopulation dynamics (Olson et al. 

2005). Barred owls are habitat and diet generalists (Livezey 2007) and appear to 

outcompete spotted owls during the breeding season, displacing spotted owls from 

territories that they occupy (Hamer et al. 2007). Ishak et al. (2008) found that many 

spotted owls had a blood parasite not found in barred owls, which may further 

reduce spotted owl competiveness with the recent invader. In the Pacific Northwest, 

scientists and managers are currently trying to rapidly formulate methods for reducing the barred owls’ negative impacts on spotted owls (Buchanan et al. 2007). 

Climate Change Effects

In the Pacific Northwest, Glenn et al. (2010) showed that the rate of population 

change (λ) for the northern spotted owl was positively influenced by wetter-thannormal growing seasons, which they speculated improved owl prey availability. 

However, cold, wet winter and spring (early nesting season), as well as the number 
63

Managing Sierra Nevada Forests

of hot summer days, negatively affected the rate of population change. The influence of climate data on the rate of population change (λ) was highly variable, 

explaining 3 to 85 percent of the total variability seen in λ, across six different 

study areas. Adult survival, which was closely related to regional climate conditions, had a stronger influence on the rate of population change than recruitment, 

which was associated with local weather. As climate change models project warmer 

winters with higher variability in winter precipitation, and hotter, drier summers 

across the Pacific Northwest and northern California, climate could potentially 

have a rangewide negative effect on spotted owl survival, recruitment, and population growth rates. North et al. (2000) suggested that regional weather during the 

nesting season influenced reproductive success and nest-site canopy structure was 

important in mitigating the effects of detrimental weather. Carroll (2010) advised 

that models used for spotted owl conservation planning should incorporate habitat 

variables along with climate information.

Spotted Owl Nesting and Foraging 

Habitat Characteristics

Generally, spotted owl survival increases with increasing area of late-successional 

forest (Dugger et al. 2005, Franklin et al. 2000, Olson et al. 2004) and decreases 

with increasing area of early successional forests (Dugger et al. 2005). However, 

because owls use a variety of habitats for foraging and nesting, forest heterogeneity 

across the landscape can improve spotted owl viability. Spotted owl survival and 

reproductive rates were higher in owl territories that included a mosaic of vegetation types infused within late-successional forest (Franklin et al. 2000), presumably 

because there was a greater diversity or abundance of prey within this mosaic 

(Ward et al. 1998, Zabel et al. 1995).

Spotted owls select habitat at multiple spatial and temporal scales, with less 

flexibility in nesting and roosting habitat requirements than foraging habitat. 

Blakesley et al. (2005) used remote sensing vegetation data to investigate the importance of spatial scale for spotted owl occupancy on a landscape scale. Between the 

two scales (500 and 2,000 ac) (202 to 809 ha) they found that the forest structure at 

the 500-ac (202-ha) scale was the most important. Within that scale, studies agree 

that both high overstory canopy closure and cover and an abundance of large trees 

are major influences in owl habitat selection (Bias and Gutiérrez 1992, Blakesley et 

al. 2005, Gutiérrez et al. 1992, LaHaye et al. 1997, Moen and Gutiérrez 1997, Roberts et al. 2011, Verner et al. 1992a). Reproduction can be associated with foraging 

habitat quality, because owls appear to fledge young more often as prey availability 

increases (Carey et al. 1992, Rosenberg et al. 2003). In northeastern California, 

Because owls use a 

variety of habitats for 

foraging and nesting, 

forest heterogeneity 

across the landscape 

can improve spotted 

owl viability.
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GENERAL TECHNICAL REPORT PSW-GTR-237

spotted owl reproduction was negatively correlated to nonforested areas and forest 

types not used for nesting or foraging within the nest area (500 acres) (Blakesley et 

al. 2005). 

While foraging has been better studied for the northern spotted owl (Strix occidentalis caurina ex. Forsman et al. 2004), there are several emerging patterns applicable to California spotted owl foraging. For example, northern spotted owls may 

forage in or near edge habitat (Clark 2007, Folliard et al. 2000, Ward et al. 1998), 

but California spotted owls did not locate their nests close to edges (Phillips et al. 

2010). For California spotted owls, foraging habitat appears to be more open (≥40 

percent) than nesting habitat (≥70 percent) with respect to canopy closure (Call et 

al. 1992, Zabel et al. 1992), basal area (Roberts et al. 2011), and stand density (Irwin 

et al. 2007). Additionally, spotted owl foraging habitat is associated with large 

trees, possibly because of their importance as nest sites for northern flying squirrels 

(Glaucomys sabrinus) (Meyer et al. 2005, Waters and Zabel 1995), an important 

prey species for spotted owls in mesic or closed-canopied Sierra Nevada forests 

(Williams et al. 1992). Irwin et al. (2007) found owl foraging associated with forests 

in proximity to nest sites and small streams. In an analysis of owl locations including many foraging locations in the southern Sierra Nevada, owls used canyon/

stream bottoms significantly more than expected (Underwood et al. 2010). Riparian 

area use may be related to preferred forest structural conditions (i.e., large trees 

and high canopy closure) or possibly higher abundance of northern flying squirrels 

(Meyer et al. 2005, 2007). In northern Sierra Nevada mixed-conifer forests, Innes 

et al. (2007) found higher densities of dusky-footed woodrats (Neotoma fuscipes), 

another preferred owl prey species, in areas with large black oaks (Quercus kelloggii Newberry). In general, these studies suggest that foraging habitat is (1) more 

open (less vegetation biomass) than nesting habitat, (2) often located close to nest 

sites, (3) associated with large trees and snags, and (4) infused with other vegetation 

types (e.g., riparian forests, black oak-dominated patches). 

Spotted Owls and Fire

The late-successional, and often dense, forests favored by spotted owls for nesting 

and roosting are at risk to stand-replacing fires because of heavy fuel loading (Agee 

et al. 2000). Accumulated dead biomass and down woody debris can carry fire 

horizontally through the forest and vertically into the upper canopy (Tappeiner and 

McDonald 1996, Weatherspoon and Skinner 1995). Such high fuel loading and 

vertically continuous ladder fuels put structurally complex, mature forests at greater 

risk of stand-replacing fire (Agee, 1993, North and Hurteau 2011, Weatherspoon 

et al. 1992). However, forest landscapes exposed to repeated burning are often 
65

Managing Sierra Nevada Forests

buffered from the effects of future wildfires and characterized by a mosaic of forest 

patches with high structural heterogeneity at multiple spatial scales (Collins et al. 

2009, Stephens et al. 2008). This heterogeneity can improve spotted owl persistence 

by protecting late-successional patches from stand-replacing fire and potentially 

enhancing the abundance or diversity of prey species within an individual territory 

(resulting from greater habitat diversity) (fig. 5-1).

High fuel loading and ladder fuels can reduce foraging or nesting habitat 

quality for California spotted owls in Sierra Nevada forests. In a fire-suppressed 

forest, Blakesley et al. (2005) found that increasing the proportion of smaller trees 

(<23 in d.b.h.) (<60 cm) around the nest, even with high overstory canopy cover 

(>70 percent), can negatively influence owl occupancy. Decades of fire suppression 

created a dense understory of regenerating white fir (Abies concolor (Gordon & 

Glend.) Lindley), and these thickets of young trees could interfere with owl foraging in high-use areas. Roberts et al. (2011) found that scattered small trees did 

not negatively affect owl occupancy in forests where managers allowed low- to 

moderate-severity fire to periodically clear out these thickets and leave behind 

large, live trees while retaining high overstory canopy closure. Scattered pockets 

of small- and medium-diameter trees (4 to 20 in d.b.h.) (10 to 50 cm) can contribute 

to a multilayered canopy that may allow for efficient thermoregulation for spotted 

owls, which are not well adapted to heat exposure (Barrows 1981, Weathers et al. 

2001). In contrast, Clark (2007) showed that northern spotted owl occupancy and 

annual survival rates declined (Clark et al. 2011), and annual home range and local 

extinction increased immediately following (1 to 4 years) wildfire. Clark (2007) 

also found that annual home range size increased with increasing amount of hard 

edge (e.g., logging or fire boundaries) within the home range, suggesting lower 

Figure 5-1—A California spotted owl nest in a mixed-conifer forest that burned in a prescribed fire with mixed fire severity in 1997 in 

Yosemite National Park. Note the nest (shown by arrow) is in an area that burned at low severity and has high canopy closure. The nest is 

adjacent (<50 ft away) (<15.2 m) to an area (left one third of the photo) with lower closure that experienced moderate fire severity.

Stephanie Eyes

Scattered pockets 

of small- and 

medium-diameter 

trees can contribute 

to a multilayered 

canopy that may 

allow for efficient 

thermoregulation 

for spotted owls.
66

GENERAL TECHNICAL REPORT PSW-GTR-237

quality habitat within fragmented sites. Postfire salvage logging and large areas of 

early-seral forests in his study area, however, may have confounded his observed 

occupancy rates.

Fire effects on foraging habitat are not well understood. Clark (2007) observed 

23 northern spotted owls using all types of fire severity in southern Oregon. However, within burned areas, owls strongly selected low-severity or unburned areas 

with minimal overstory canopy mortality. In this burned landscape, owl high-use 

areas were characterized by lower fire severity and greater structural diversity. 

Clark (2007) also found that postfire salvage logging reduced owl habitat quality. 

In contrast, Bond et al. (2009) followed seven owls (three pairs and an individual) 

using a 4-year-old burned forest in southern Sierra Nevada and found higher than 

expected owl foraging in high-severity burn areas. The study, however, is limited 

by its small sample size, brief period of study (12 weeks), and nonrandom owl 

selection. Additionally, studies of deer mice (Peromyscus maniculatus) and other 

spotted owl prey in Yosemite National Park indicate that deer mouse abundance 

was negatively associated with increasing fire severity (Roberts et al. 2011). Collectively, these studies suggest the presence of large trees and high overstory canopy 

closure are the most important pre- and postfire conditions associated with spotted 

owl occupancy. 

References

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

Island Press. 505 p. 

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 fuel breaks in 

landscape fire management. Forest Ecology and Management. 127: 55–66.

Barrows, C.W. 1981. Roost selection by spotted owls: an adaptation to heat stress. 

The Condor. 83: 302–309.

Bias, M.A.; Gutiérrez, R.J. 1992. Habitat association of California spotted owls in 

the central Sierra Nevada. Journal of Wildlife Management. 56: 584–595.

Blakesley, J.A.; Noon, B.R.; Anderson, D.R. 2005. Site occupancy, apparent 

survival, and reproduction of California spotted owls in relation to forest stand 

characteristics. Journal of Wildlife Management. 69: 1554–1654.
67

Managing Sierra Nevada Forests

Blakesley, J.A.; Seamans, M.E.; Conner, M.M.; Franklin, A.B.; White, G.C.; 

Gutiérrez, R.J.; Hines, J.E.; Nichols, J.D.; Munton, T.E.; Shaw, D.W.H.; 

Keane, J.J.; Steger, G.N.; McDonald, T.L. 2010. Population dynamics of 

spotted owls in the Sierra Nevada, California. Wildlife Monographs. 174: 1–36.

Bond, M.L.; Lee, D.E.; Siegel, R.B.; Ward, J.P. 2009. Habitat use and selection 

by California spotted owls in a postfire landscape. Journal of Wildlife 

Management. 73: 1116–1124.

Buchanan, J.B.; Gutiérrez, R.J.; Anthony, R.G.; Cullinan, T.; Diller, L.V.; 

Forsman, E.D.; Franklin, A.B. 2007. A synopsis of suggested approaches to 

address potential competitive interactions between barred owls (Strix varia) and 

spotted owls (S. occidentalis). Biological Invasions. 6: 679–691.

Call, D.R.; Gutiérrez, R.J.; Verner, J. 1992. Foraging habitat and home-range 

characteristics of California spotted owls in the Sierra Nevada. Condor. 

94: 880–888.

Carey, A.B.; Horton, S.P.; Biswell, B.L. 1992. Northern spotted owls: influence 

of prey base and landscape character. Ecological Monographs. 62: 223–250.

Carroll, C. 2010. Role of climatic niche models in focal-species-based conservation 

planning: assessing potential effects of climate change on northern spotted owl 

in the Pacific Northwest, USA. Biological Conservation. 143: 1432–1437.

Clark, D.A. 2007. Demography and habitat selection of northern spotted owls 

in post-fire landscapes of southwestern Oregon. Corvallis, OR: Oregon State 

University. 202 p. M.S. thesis. 

Clark, D.A.; Anthony, R.G.; Andrews, L.S. 2011. Survival rates of northern 

spotted owls in post-fire landscapes of southwest Oregon. Journal of Raptor 

Research. 45: 38–47.

Collins, B.M.; Miller, J.D.; Thode, A.E.; Kelly, M.; van Wagtendonk, J.W.; 

Stephens, S.L. 2009. Interactions among wildland fires in a long-established 

Sierra Nevada natural fire area. Ecosystems. 12: 114–128.

Dark, S.J.; Gutiérrez, R.J.; Gould, G.I., Jr. 1998. The barred owl (Strix varia) 

invasion in California. The Auk. 115: 50–56.

Dugger, K.M.; Wagner, F.; Anthony, R.G.; Olson, G.S. 2005. The relationship 

between habitat characteristics and demographic performance of northern 

spotted owls in southern Oregon. Condor. 107: 863–878.
68

GENERAL TECHNICAL REPORT PSW-GTR-237

Folliard, L.B.; Reese, K.; Diller, L.V. 2000. Landscape characteristics of northern 

spotted owl nest sites in northwestern California. Journal of Raptor Research. 

34: 75–84.

Forsman, E.D.; Anthony, R.G.; Meslow, E.C.; Zabel, C.J. 2004. Diet and 

foraging behavior of northern spotted owls in Oregon. Journal of Raptor 

Research. 38: 214–230.

Franklin, A.B.; Gutiérrez, R.J.; Burnham, K.P. 2000. Climate, habitat 

quality, and fitness in northern spotted owl populatoin in northwest California. 

Ecological Monographs. 70: 539–590.

Glenn, E.M.; Anthony, R.G.; Forsman, E.D. 2010. Population trends in northern 

spotted owls: associations with climate in the Pacific Northwest. Biological 

Conservation. 143: 2543–2552.

Gutiérrez, R.J.; Verner, J.; McKelvey, K.S.; Noon, B.R.; Steger, G.N.; Call, 

D.R.; LaHaye, W.S.; Bingham, B.B.; Senser, J.S. 1992. Habitat relations of the 

California spotted owl. In: Verner, J.; McKelvey, K.S.; Noon, B.R.; Gutiérrez, 

R.J.; Gould, G.I., Jr.; Beck, T.W., tech. coords. The California spotted owl: 

a technical assessment of its current status. Gen. Tech. Rep. PSW-GTR-133. 

Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station: 79–98.

Hamer, T.E.; Forsman, E.D.; Glenn, E.M.; Elizabeth, M. 2007. Home range 

attributes and habitat selection of barred owls and spotted owls in an area of 

sympatry. The Condor. 109: 750–768. 

Innes, R.J.; Van Vuren, D.H.; Kelt, D.A.; Johnson, M.L.; Wilson, J.A.; Stine, 

P.A. 2007. Habitat associations of dusky-footed woodrats (Neotonia fuscipes) in 

mixed-conifer forest of the northern Sierra Nevada. Journal of Mammalogy. 

88: 1523–1531. 

Irwin, L.L.; Clark, L.A.; Rock, D.C.; Rock, S.L. 2007. Modeling foraging 

habitat of California spotted owls. Journal of Wildlife Management. 

71: 1183–1191.

Ishak, H.D.; Dumbacher, J.P.; Anderson, N.L.; Keane, J.J.; Valkiunas, G.; 

Haig, S.M.; Tell, L.A.; Sehgal, R.N.M. 2008. Blood parasites in owls with 

conservation implications for the spotted owl (Strix occidentalis). PLOS One. 

3: e2304.
69

Managing Sierra Nevada Forests

Keane, J. 2007. Personal communication. Research wildlife biologist, U.S. 

Department of Agriculture, Forest Service, Pacific Southwest Research Station, 

1731 Research Park Dr., Davis, CA 95618. 

LaHaye, W.S.; Gutiérrez, R.J.; Call, D.R. 1997. Nest-site selection and 

reproductive success of California spotted owls. Wilson Bulletin. 109: 42–51.

Livezey, K.B. 2007. Barred owl habitat and prey: a review and synthesis of the 

literature. Journal of Raptor Research. 41: 177–201. 

Meyer, M.D.; Kelt, D.A.; North, M.P. 2005. Nest trees of northern flying squirrels 

in the Sierra Nevada. Journal of Mammalogy. 86: 275–280.

Meyer, M.D.; Kelt, D.A.; North, M.P. 2007. Microhabitat associations of northern 

flying squirrels in burned and thinned forest stands of the Sierra Nevada. 

American Midland Naturalist. 157: 202–211.

Moen, C.A.; Gutiérrez, R.J. 1997. California spotted owl habitat selection in the 

central Sierra Nevada. Journal of Wildlife Management. 61: 1281–1287.

North, M.P.; Steger, G.N.; Denton, R.; Eberlein, G.; Munton, T.E.; Johnson, K. 

2000. Association of weather and nest-site structure with reproductive success in 

California spotted owls. Journal of Wildlife Management. 64: 797–807.

North, M.P.; Hurteau, M.D. 2011. High-severity wildfire effects on carbon 

stocks and emissions in fuels treated and untreated forest. Forest Ecology and 

Management. 261: 1115–1120.

Olson, G.S.; Glenn, E.M.; Anthony, R.G.; Forsman, E.D.; Reid, J.A.; 

Loschl, P.J.; Ripple, W.J. 2004. Modeling of demographic performance of 

northern spotted owls relative to forest habitat in Oregon. Journal of Wildlife 

Management. 68: 1039–1053.

Olson, G.S.; Anthony, R.G.; Forsman, E.D.; Ackers, S.H.; Loschl, P.J.; Reid, 

J.A.; Dugger, K.M.; Glenn, E.M.; Ripple, W.J. 2005. Modeling of site 

occupancy dynamics for northern spotted owls, with emphasis on the effects of 

barred owls. Journal of Wildlife Management. 69: 918–932.

Phillips, C.E.; Tempel, D.J.; Gutiérrez, R.J. 2010. Do California spotted owls 

select nest trees close to forest edges? Journal of Raptor Research. 44: 311–314.

Roberts, S.L.; van Wagtendonk, J.W.; Miles, A.K.; Kelt, D.A. 2011. Effects 

of fire on spotted owl site occupancy in a late-successional forest. Biological 

Conservation. 144: 610–619.
70

GENERAL TECHNICAL REPORT PSW-GTR-237

Rosenberg, D.K.; Swindle, K.A.; Anthony, R.G. 2003. Influence of prey 

abundance on spotted owl reproductive success in western Oregon. Canadian 

Journal of Zoology. 81: 1715–1725.

Stephens, S.L.; Fry, D.; Franco-Vizcano, E. 2008. Wildfire and forests in 

northwestern Mexico: the United States wishes it had similar fire problems. 

Ecology and Society. 13: 10.

Tappeiner, J.C.; McDonald, P.M. 1996. Regeneration of Sierra Nevada forests. In: 

Sierra Nevada Ecosystem Project; final report to Congress. Vol. II: Assessments 

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

Center for Water and Wildland Resources: 501–512.

Underwood, E.C.; Viers, J.H.; Quinn, J.F.; North, M.P. 2010. Using topography 

to meet wildlife and fuels treatment objectives in fire-suppressed landscapes. 

Journal of Environmental Management. 46: 809–819.

Verner, J.; Gutiérrez, R.J.; Gould, G.I., Jr. 1992a. The California spotted owl: 

general biology and ecological relations. In: Verner, J.; McKelvey, K.S.; Noon, 

B.R.; Gutiérrez, R.J.; Gould, G.I., Jr.; Beck, T.W., tech. coords. The California 

spotted owl: a technical assessment of its current status. Gen. Tech. Rep. PSWGTR-133. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific 

Southwest Research Station: 55–77.

Verner, J.; McKelvey, K.S.; Noon, B.R.; Gutiérrez, R.J.; Gould, G.I., Jr.; Beck, 

T.W. 1992b. Assessment of the current status of the California spotted owl, with 

recommendations for management. In: Verner, J.; McKelvey, K.S.; Noon, B.R.; 

Gutiérrez, R.J.; Gould, G.I., Jr.; Beck, T.W., tech. coords. The California spotted 

owl: a technical assessment of its current status. Gen. Tech. Rep. PSW-GTR-133. 

Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station: 3–26.

Ward, J.P., Jr.; Gutiérrez, R.J.; Noon, B.R. 1998. Habitat selection by northern 

spotted owls: the consequences of prey selection and distribution. The Condor. 

100: 79–92.

Waters, J.R.; Zabel, C.J. 1995. Northern flying squirrel densities in fir forests of 

northeastern California. Journal of Wildlife Management. 59: 858–866.

Weathers, W.W.; Hodum, P.J.; Blakesley, J.A. 2001. Thermal ecology and 

ecological energetics of California spotted owls. The Condor. 103: 678–690.
71

Managing Sierra Nevada Forests

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.; Gutiérrez, R.J.; 

Gould, G.I., Jr.; Beck, T.W., tech. coords. The California spotted owl: a technical 

assessment of its current status. Gen. Tech. Rep. PSW-GTR-133. Albany, CA: 

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

Station: 247–260.

Weatherspoon, C.P.; Skinner, C.N. 1995. An assessment of factors associated 

with damage to tree crowns from the 1987 wildfires in northern California. 

Forest Science. 41: 430–451.

Williams, D.F.; Verner, J.; Sakai, H.F.; Waters, J.R. 1992. General biology of 

prey species of the California spotted owl. In: Verner, J.; McKelvey, K.S.; Noon, 

B.R.; Gutiérrez, R.J.; Gould, G.I., Jr.; Beck, T.W., tech. coords. The California 

spotted owl: a technical assessment of its current status. Gen. Tech. Rep. PSWGTR-133. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific 

Southwest Research Station: 207–221.

Zabel, C.J.; Steger, G.N.; McKelvey, K.S.; Eberlein, G.P.; Noon, B.R.; Verner, 

J. 1992. Home-range size and habitat-use patterns of California spotted owls in 

the Sierra Nevada. In: Verner, J.; McKelvey, K.S.; Noon, B.R.; Gutiérrez, R.J.; 

Gould, G.I., Jr.; Beck, T.W., tech. coords. The California spotted owl: a technical 

assessment of its current status. Gen. Tech. Rep. PSW-GTR-133. Albany, CA: 

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

Station: 149–163.

Zabel, C.J.; McKelvey, K.S.; Ward, J.P., Jr. 1995. Influence of primary prey 

on home-range size and habitat-use patterns of northern spotted owls (Strix 

occidentalis caurina). Canadian Journal of Zoology. 73: 433–439.
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73

Managing Sierra Nevada Forests

M. North1 and P. Manley2

Introduction

Forest management to maintain native wildlife communities is an important, yet complex objective. The 

complexities stem from two primary sources: habitat 

requirements for native species are diverse and span 

multiple spatial scales and seral stages, and habitat is a 

species-specific concept making multispecies community response difficult to predict. Given these uncertainties, restoration objectives frequently lack target 

conditions for the multitude of species that comprise the 

various vertebrate communities, and monitoring plans 

fail to integrate across multiple scales and habitats. 

Multispecies Habitat Management 

Habitat can be defined as the environmental conditions 

needed to support essential food, resting, and breeding 

requirements of an individual species (Morrison et al. 

2006). Habitat suitability is a function of the degree 

to which an environment can support these requirements. Detailed habitat requirements are not known for 

many vertebrate species associated with Sierra Nevada 

forests. Most habitat models are limited to species of 

conservation concern, which are often habitat specialists associated with forest conditions that are uncommon or declining in extent. The California spotted owl 

(Strix occidentalis occidentalis), northern goshawk 

(Accipiter gentilis), and Pacific fisher (Martes pennanti) are among the highest profile species of concern 

in the Sierra Nevada, and they are all associated with 

old-forest elements or structural conditions, such as 

large trees, snags, and logs, and some areas with high 

Chapter 6: Managing Forests for Wildlife Communities

1 Research ecologist, U.S. Department of Agriculture, Forest 

Service, Pacific Southwest Research Station, 1731 Research 

Park Dr., Davis, CA 95618.

2 Program manager, U.S. Department of Agriculture, Forest 

Service, Pacific Southwest Research Station, 60 Nowelo St., 

Hilo, HI 96720.

Summary of Findings

1. It is difficult to predict the effects of forest 

management on multiple species, which have 

different habitat requirements and respond to 

forest conditions at different scales. Current 

models for assessing wildlife habitat, such 

as the California Wildlife-Habitat Relations, should be viewed with caution as 

they generally fail to account for the different 

spatial and temporal scales at which species 

may respond to forest conditions or assess 

habitat features other than large trees and 

canopy cover.

2. For a few species of interest, there is standlevel information on habitat associations, 

but little information on how to optimize the 

spatial arrangement of different forest conditions, or how to “knit” the pieces together at 

the landscape level. In the absence of better 

information, a cautious approach is to 

increase habitat that is currently rare, or 

underrepresented compared to active-fire 

forest conditions, avoid creating forest 

conditions that do not have a historical 

analog, and emulate the spatial heterogeneity 

of forest conditions that would have been 

created by topography’s influence on fire 

frequency and intensity.

3. Monitoring may be the best means of 

overcoming some of these limitations, if it 

is rigorously designed and leverages existing 

inventory and sampling effort. 
74

GENERAL TECHNICAL REPORT PSW-GTR-237

canopy closure. To provide habitat for a broad array of species, managers will 

need to consider other seral conditions and forest structures. For example, some 

songbirds are strongly associated with shrub patches (Burnett et al. 2009) that have 

become increasingly rare in the low-light understory of fire-suppressed forests. In 

addition to old-forest conditions, some habitats (e.g., aspen stands, meadows, open 

large pine-dominated forests, shrub fields) and some “special habitat elements” 

(e.g., “defect” trees, downed logs, large snags) have clearly declined in abundance 

(Bouldin 1999). In the absence of better information, managers may examine what 

forest conditions currently are rare compared to historical active-fire conditions, 

and then treat stands to increase underrepresented habitat conditions.

A second concern is that many wildlife species respond to forest conditions 

at multiple spatial and temporal scales. This suggests that management practices 

should be based on careful consideration of the amounts and configurations of 

current and target habitat conditions within landscapes. In many cases, however, 

potential management impacts on wildlife are examined only at the stand scale 

or over relatively short timeframes. Temporal considerations can be particularly 

important because decades of stand development may be needed to create some 

desired habitat conditions. Management plans should be explicit about maintaining 

current high-value habitat in sufficient amounts and distribution while at the same 

time treating other areas more heavily to accelerate development of desired future 

habitat conditions. For large-scale assessments of landscapes, it is often difficult 

to determine the optimal size and distribution of different forest conditions that 

would improve current and future habitat conditions for the local vertebrate community. There are few reference landscapes with active fire regimes, and the spatial 

configuration of habitat conditions in such landscapes has yet to be examined (fig. 

6-1). While research can suggest general principles for landscape-scale wildlife 

management, such as providing for connectivity and a mosaic of forest conditions 

(Hilty et al. 2006, Lindenmayer and Fisher 2006, Lindenmayer et al. 2008), specifics are generally lacking and will differ with different species and existing forest 

conditions. Lacking better information, a prudent approach may be to emulate the 

variation in forest conditions that could be expected to occur given the influence of 

local topographic conditions on fire frequency and intensity (North et al. 2010). 

Vertebrate Conservation and Fuels Reduction

Fuels reduction commonly focuses on reducing the amount and connectivity of 

woody material on the forest floor, from the forest floor to the canopy, and across 

the canopy. Two of the primary challenges associated with reducing the risk of 

high-intensity wildfire and maintaining native vertebrate species are (1) inadequate 

Managers may 

examine what forest 

conditions currently 

are rare compared to 

historical active-fire 

conditions, and then 

treat stands to increase 

underrepresented 

habitat conditions
75

Managing Sierra Nevada Forests

tools for characterizing wildlife habitat relationships and assessing impacts of fuels 

treatments to these habitats, and (2) the inherent conflict between maintaining existing species while changing forest structure and composition. 

Currently, models for assessing how different types of treatments affect the 

wildlife community lack precision. The California Wildlife-Habitat Relationships 

(CWHR) database is often used to approximate how treatments will alter habitat 

based on general changes in tree size and canopy cover (Mayer and Laudenslayer 

1988). The forest is broadly categorized using the dominant tree size class, and 

canopy cover is approximated through interpretation of aerial photographs or 

modeled indirectly with the Forest Vegetation Simulator into broad cover classes 

(see limitations of this approach in chapter 14 under “Canopy Cover and Closure”). 

These are rough estimates of a forest’s habitat taken at a fixed point in time and do 

not consider features such as snags, down wood, or understory diversity that are 

often linked to wildlife use. The CWHR is a set of broad-scale habitat associations 

and general life history traits for the 694 species in its database that is based largely 

on expert opinion. Consequently, the use of CWHR for making reliable, projectlevel predictions on the potential habitat impacts of forest management activities on 

a wildlife community is limited. In addition, CWHR does not account for area size 

and landscape context in its habitat designations (George and Zack 2001). Furthermore, tests of CWHR (Block et al. 1994, Laymon 1989, Laymon and Halterman 

Figure 6-1—Illilouette Basin, Yosemite National Park, which has burned several times since being designated a wildland-fire use area in 

the 1970s. Note the diversity and complexity of different forest types and conditions resulting in part from different fire severity patterns 

and changes in edaphic conditions.

Marc Meyer
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GENERAL TECHNICAL REPORT PSW-GTR-237

1989, Purcell et al. 1992) have found high rates of omission (species detected but 

not listed in CWHR) and commission (species predicted but not present), prompting 

the authors of one study (Block et al. 1994) to suggest that CWHR not be used “as 

the sole source of information in land-use decisions.” Variation in forest community 

types (e.g., CALVEG) has also been used to estimate landscape-scale biodiversity, 

but research suggests it may fail to explain variation in species abundances or 

account for spatial variability (Cushman et al. 2008, Noon et al. 2003). For some 

sensitive wildlife species, quantitative models have been developed to examine how 

treatments may impact habitat quality more explicitly (e.g., Thompson et al. 2011). 

However, the use of such models to infer impacts on the entire vertebrate community should be viewed with caution. Recent assessments of the effectiveness of 

“keystone,” “umbrella,” “indicator,” “top predator,” and “flagship” species suggest 

that management activities that are based on such surrogate species generally fail to 

capture the needs of the ecosystem’s broader array of species (Caro 2010, Sergio et 

al. 2008). 

Fuels treatments alter habitat conditions for wildlife species that currently 

occupy the treatment area, benefiting some but reducing habitat quality for others 

(Stephens et al., in press). Managers should be cautious when applying prescriptions 

that result in the simplification and homogenization of stand structures, creating relatively novel habitat conditions to which few native vertebrate species are 

adapted. These include significantly reducing or eliminating crown overlap, vertical 

canopy complexity, and small tree and understory cover (fig. 6-2). Fuels reduction 

that removes all understory cover, sometimes called “clearcutting from below,” 

Figure 6-2—Example 

of a fuels treatment that 

removes all understory and 

ladder fuels, a condition 

sometimes referred to as a 

“clearcut from below.”

Pat Manley

Assessments of the 

effectiveness of 

“keystone,” “umbrella,” 

“indicator,” “top 

predator,” and 

“flagship” species 

suggest that management activities that 

are based on such 

surrogate species 

generally fail to capture 

the needs of the 

ecosystem’s broader 

array of species.
77

Managing Sierra Nevada Forests

may eliminate habitat for many species of the vertebrate community. For example, 

a diverse array of understory shrubs may serve a variety of ecological functions 

including the provision of wildlife forage and protective cover, soil stabilization, 

nitrogen fixation, barriers to invasive plant establishment, and sources of nectar 

for pollinators. Yet because of their potential role as a fuel and their competition 

with tree seedlings, some treatments specifically strive to dramatically reduce or 

eliminate shrub cover. Eliminating these conditions probably moderately increases 

forest resistance to crown fire and may have value close to communities and in 

strategic locations. However models suggest retaining these stand features may 

not significantly increase high-severity fire risk if care is taken to create vertical 

diversity in vegetation cover without creating ladder fuels. An alternative approach 

in fuels reduction projects would be to manage for wildlife habitat heterogeneity: (1) 

increase the frequency of underrepresented habitat conditions (e.g., late-seral structures, canopy gaps, open, low-density forests, rare or uncommon tree and shrub 

species), (2) promote variable forest conditions based on natural topography and fire 

regimes, and (3) facilitate both overstory and understory vegetation diversity.

Multiscale Monitoring

Effective monitoring is needed to understand the complex response of wildlife communities to forest management. There is a perception that resources and expertise 

are too limited to initiate a multispecies, multiscale monitoring program. Manley 

et al. (2006), however, introduced a protocol to serve as a consistent and efficient 

method for obtaining basic presence/absence and habitat data for several species at 

sites using a probabilistic sample. The Multiple Species Inventory and Monitoring 

(MSIM) protocol is designed to be implemented in association with Forest Inventory and Analysis grid points. The protocol uses a base monitoring approach on 

which national forests can build to meet their specific monitoring needs with the 

greatest efficiency of effort and cost. The MSIM protocol could be used as a basis 

for developing plans to monitor treatments following U.S. Forest Service General 

Technical Report PSW-GTR 220 “An Ecosystem Management Strategy for Sierran 

Mixed-Conifer Forests” (North et al. 2009) concepts and to assess how management strategies may better meet desired conditions.
78

GENERAL TECHNICAL REPORT PSW-GTR-237

References

Block, W.M.; Morrison, M.L.; Verner, J.; Manley, P.N. 1994. Assessing 

wildlife-habitat-relationships models: a case study with California oak 

woodlands. Wildlife Society Bulletin. 22: 549–561.

Bouldin, J. 1999. Twentieth-century changes in forests of the Sierra Nevada, 

California. Davis, CA: University of California, Davis. 222 p. Ph.D. dissertation. 

Burnett, R.; Jongsomjit, D.; Stralberg, D. 2009. Avian monitoring in the Lassen 

and Plumas National Forest: 2008 annual report. Point Reyes Bird Observatory 

Contribution. 1684: 104–186.

Caro, T. 2010. Conservation by proxy: indicator, umbrella, keystone, flagship, and 

other surrogate species. Washington, DC: Island Press. 374 p.

Cushman, S.A.; McKelvey, K.S.; Flather, C.H.; McGarigal, K. 2008. Do forest 

community types provide a sufficient basis to evaluate biological diversity? 

Frontiers in Ecology and the Environment. 6: 13–17. 

George, T.L.; Zack, S. 2001. Spatial and temporal considerations in restoring 

habitat for wildlife. Restoration Ecology. 9: 272–279.

Hilty, J.; Lidicker, W.Z., Jr.; Merenlender, A.; Dobson, A.P. 2006. Corridor 

ecology: the science and practice of linking landscapes for biodiversity 

conservation. Washington, DC: Island Press. 344 p.

Laymon, S.A. 1989. A test of the California wildlife-habitat relationship system 

for breeding birds in valley-foothill riparian habitat. In: Abell, D.L., tech. 

coord. Proceedings of the California riparian systems conference: protection, 

management, and restoration for the 1990s. Gen. Tech. Rep. PSW-GTR-110. 

Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Forest and Range Experiment Station: 307–313.

Laymon, S.A.; Halterman, M.D. 1989. A proposed habitat management plan for 

yellow-billed cuckoos in California. In: Abell, D.L., tech. coord. Proceedings 

of the California riparian systems conference: protection, management, and 

restoration for the 1990s. Gen. Tech. Rep. PSW-GTR-110. Berkeley, CA: U.S. 

Department of Agriculture, Forest Service, Pacific Southwest Forest and Range 

Experiment Station: 272–277.

Lindenmayer, D.B.; Fischer, J. 2006. Landscape change and habitat 

fragmentation. Washington, DC: Island Press. 352 p.
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Managing Sierra Nevada Forests

Lindenmayer, D.; Hobbs, R.J.; Montague–Drake, R.; Alexandra, J., Bennett, 

A.; Burgman, M.; Cale, P.; Calhoun, A.; Cramer, V.; Cullen, P.; Driscoll, 

D.; Fahrig, L.; Fisher, J.; Franklin, J.; Haila, Y.; Hunter, M.; Gibbons, 

P.; Lake, S.; Luck, G.; MacGregor, C.; McIntyre, S.; Mac Nally, R.; 

Manning, A.; Miller, J.; Mooney, H.; Noss, R.; Possingham, H.; Saunders, 

D.; Schmiegelow, F.; Scott, M.; Simberloff, D.; Sisk, T.; Tabor, G.; Walker, 

B.; Wiens, J.; Woinarski, J.; Zavaleta, E. 2008. A checklist for ecological 

management of landscapes for conservation. Ecology Letters. 11: 78–91.

Manley, P.N.; Van Horne, B.; Roth, J.K.; Zielinski, W.J.; McKenzie, M.M.; 

Weller, T.J.; Weckerly, F.W.; Vojta, C. 2006. Multiple species inventory and 

monitoring technical guide. Gen. Tech. Rep. WO-73. Washington, DC: U.S. 

Department of Agriculture, Forest Service, Washington Office. 204 p.

Mayer, K.E.; Laudenslayer, W.F. 1988. Guide to wildlife habitats of California. 

Sacramento, CA: State of California, Resources Agency, Department of Fish and 

Game. 166 p.

Morrison, M.; Marcot B.G.; Mannan, R.W. 2006. Wildlife-habitat relationships: 

concepts and applications. Washington, DC: Island Press. 435 p.

Noon, B.; Murphy, D.; Beissinger, S.; Shaffer, M.; Dellasala, D. 2003. 

Conservation planning for U.S. national forests: conducting comprehensive 

biodiversity assessments. Bioscience. 53.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

North, M.; Stine, P.; Zielinski, W.; O’Hara, K.; Stephens, S. 2010. 

Harnessing fire for wildlife. The Wildlife Professional. 4: 30–33.

Purcell, K.L.; Hejl, S.J.; Larson, T.A. 1992. Evaluating avian-habitat 

relationships models in mixed-conifer forests of the Sierra Nevada. 

Transactions of the Western Section of the Wildlife Society. 28: 120–136.

Stephens, S.L.; McIver, J.D.; Boerner, R.E.J.; Fettig, C.J; Fontaine, J.B.; 

Hartsough, B.R.; Kennedy, P.; Schwilk, D.W. [In press]. Effects of forest 

fuel reduction treatments in the United States. BioScience.
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Sergio, F.; Caro, T.; Brown, D.; Clucas, B.; Hunter, J.; Ketchum, J.; 

McHugh, K.; Hiraldo, F. 2008. Top predators as conservation tools: 

ecological rationale, assumptions and efficacy. Annual Review of Ecology, 

Evolution, and Systematics. 39: 1–19.

Thompson, C.M.; Zielinski, W.J.; Purcel, K.L. 2011. The use of landscape 

trajectory analysis to evaluate management risks: a case study with the 

Pacific fisher in the Sierra National Forest. Journal of Wildlife Management. 

75: 1164–1176. 
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Managing Sierra Nevada Forests

Chapter 7: Developing Collaboration and Cooperation

G. Bartlett1

Introduction

Good forestry practices require onsite flexibility. A core concept in U.S. Forest 

Service General Technical Report PSW-GTR-220 “An Ecosystem Management 

Strategy for Sierran Mixed-Conifer Forests” (North et al. 2009) is that management 

treatments and thinning intensity should differ depending on local forest conditions 

and topographic location. In the absence of restricted forestry practices (e.g., stream 

exclusion zones, upper diameters for thinning, etc.), managers have to effectively 

communicate where and how different treatment decisions will be made. Using 

GTR 220 concepts requires effective outreach and project transparency. No single 

blueprint exists to achieve cooperation and trust as social context differs between 

projects, national forests, and stakeholders involved. 

The objective of this chapter is to provide an example and analysis of a successful collaboration that may help projects find their own path to building public 

cooperation. Other forest management projects many not need professional mediation, yet some of the principles discussed here may be of value in any project 

involving public outreach. This chapter’s example is a summary of how mediation 

and group collaboration led to settlement of one of the more litigated forest management projects in the Sierra Nevada—fuels treatments around the Dinkey Creek area 

on the Sierra National Forest. 

For 15 years, conflict and litigation had stalled management practices on the 

Kings River project, which contains habitat used by a subpopulation of fisher. In 

2009, with the help of an outside mediator, the Sierra National Forest Project Planning Forum successfully developed a proposed 5,000-ac (2023-ha) project—Dinkey 

Creek North and South based on GTR 220’s conceptual framework. Subsequent to 

the successful project collaboration, the Sierra National Forest received significant 

Collaborative Forest Landscape Restoration funding. Currently, the Sierra National 

Forest is proceeding with the environmental analysis, and is expanding the collaborative group’s membership and project area.

Dinkey Project History

In 2007, the Center for Collaborative Policy, a program of California State University, Sacramento, that provides impartial mediation services, conducted an assessment of the mediation potential of several forest management projects, including 

1 Staff mediator, Center for Collaborative Policy, 815 S Street., 1st floor, Sacramento State 

University, Sacramento, CA 95811.
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GENERAL TECHNICAL REPORT PSW-GTR-237

Kings River, in the Southern Sierra Nevada. At that time, the center did not recommend the parties meet to resolve project issues because the conditions necessary for 

success were not present. The center did, however, make some recommendations 

to correct these conditions. The first recommendation was for the parties to engage 

in joint factfinding to establish consensus on the scientific foundations from which 

projects could be developed. Joint factfinding is a process in which stakeholders 

engage with scientific experts to frame research questions and interpret research 

results (Ehrman and Stinson 1999, Karl et al. 2007). In the southern Sierra projects, 

stakeholders often cited conflicting studies to justify their proposed management 

Summary of Findings

1. Collaboration involves five stages: assessment, organization, education, negotiation, and implementation: Assessing the issues, organizing 

the collaborative group, and educating stakeholders about each other’s 

interests and technical issues lay the foundation for negotiation. During 

negotiation, the parties work through all the issues, building agreements 

over time. Stakeholders then monitor the project and adapt during implementation.

2. Early engagement of a broad range of participants is essential to 

robust agreements: For stakeholders to have meaningful dialogue and 

an effect on issues, stakeholders need to engage early in project planning. 

Engaging a broad range of stakeholder participants can create a project 

that balances fire, wildlife, and silviculture perspectives, making final 

agreements more robust. 

3. Site visits support decisionmaking and agreements: Site visits illustrate 

existing variability and contribute to clarifying project objectives. Site 

visits help ground stakeholder discussion over desired conditions, providing a specific context in which decisions need to be made rather than a 

principled argument over management practices.

4. An impartial mediator can promote trust and problemsolving: 

The mediator’s essential role is to organize the process, create trust, 

normalize conflict, develop a problemsolving environment, manage the 

timeframe, and orient the group to reach outcomes. A key element to trust 

building is the mediator’s independence and ability to speak to all parties 

confidentially.
83

Managing Sierra Nevada Forests

recommendations. As a result, the Forest was “paralyzed by science.” The center 

also recommended that the Sierra National Forest engage the public early in any 

project development. During the assessment, stakeholders complained that they 

only learned about projects once they were in such late stages of development that 

the Forest Service did not have flexibility to modify or significantly change the 

project because of the professional and resource investment, which had already 

occurred.

Between the 2007 assessment and March 2009, a group of Forest Service and 

university scientists developed GTR 220 (North et al. 2009) summarizing recent 

research on forest and fire ecology, ecosystem restoration, silviculture, and wildlife 

species (particularly the Pacific fisher) (Martes pennanti) in the Sierra Nevada. 

There was substantial research relevant to forest management that had been completed since the last major summary of Sierra Nevada science (SNEP 1996), but 

much of it was technical and scattered among many different journals. Using the 

North et al. (2009) paper as a starting point for finding scientific common ground, 

the U.S. Institute for Environmental Conflict Resolution invited the Center for Collaborative Policy to speak with the parties and consider organizing a collaborative 

effort to develop a project. 

Mediator’s Role

The center appointed a mediator to the project with the assigned task of facilitating 

meetings and being impartial to the substance or content of outcomes. The mediator’s essential role was to organize the process, create trust, normalize the conflict, 

develop a problemsolving environment, manage the timeframe, and orient the 

group to reach outcomes. A key element to building trust was the condition that the 

mediator had the planning forum’s permission to speak confidentially with all of the 

participants to discuss their interests, concerns, and negotiation strategies. In turn, 

participants were able to call the mediator when they were upset or worried about 

something. This trust helped the parties overcome hurdles and allowed the mediator to reframe conflict as a problem to be solved. For example, early in the process, 

during the development of one of the signature documents, the mediator was able 

to combine significant comments from several stakeholders into one document, 

getting permission from several key parties to share it as a straw proposal for group 

consideration. She never disclosed who submitted comments, and one person’s contribution might have been viewed as controversial within the person’s organization. 

However, this version was substantially better and the parties’ accepted it without 

question, largely because the draft better reflected the intent they wanted to convey. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

Five Stages of Collaboration 

As practiced by the center, collaborative policymaking typically involves five 

stages: assessment, organization, education, negotiation, and implementation (table 

7-1). The Dinkey collaborative went through these stages and is now in the implementation process. The first three stages lay the foundation for getting to negotiation. In the assessment stage, the mediator meets with the parties to determine 

whether they would like to negotiate and if they have enough interests in common 

to support a negotiated outcome. In this stage, it is important to identify participants 

willing to collaborate and consider others’ perspectives. Next the organizational 

structure is developed. The mediator works with the parties to set the agenda and 

a decisionmaking rule for the collaborative process, and to define how agreements 

and outcomes will link to agency decisionmaking. In the third stage, education, the 

parties develop a common understanding of the project’s scientific and technical 

issues, and also the interests and goals of each of the interest groups.

During negotiations, the parties first identify all the key issues that need to 

be addressed. Then the group works through the issues, building agreements over 

time. The parties’ interests are used to develop criteria for decisionmaking. As 

areas of potential disagreement emerge, they are put on the table and treated as 

issues that the parties need to resolve. During implementation, stakeholders initiate 

and monitor the project, modifying the approach as data indicate. 

Steps That Facilitated Collaboration for the 

Dinkey Project

• Include a broad range of participants. The initial inclination was for the 

Forest Service to meet with a singular environmental organization that had 

engaged on the original larger Kings River project. However, the success of the 

process was ultimately rooted in having a diversity of perspectives represented. 

For each “small” agreement, stakeholders had to grapple with balancing fire, 

wildlife, and silviculture perspectives, a process that made final agreements 

more robust. Expanding participation diffused tensions that had developed over 

the long history of the conflict and litigation. Additional parties brought expertise, problemsolving, and humor.

• Establish a conceptual framework, purpose and need, and long-term 

desired condition. There is often a tendency to immediately start evaluating the project without first finding common ground on current forest conditions and long-term objectives. General Technical Report 220 helped establish 

a conceptual framework around which the purpose and need was developed. 

The parties first 

identify all the key 

issues that need to 

be addressed. The 

parties’ interests are 

used to develop criteria 

for decisionmaking. 

As areas of potential 

disagreement emerge, 

they are put on the 

table and treated as 

issues that the parties 

need to resolve. 
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Managing Sierra Nevada Forests

Table 7-1—Progressive steps in collaborative decisionmaking

Five stages of collaborative decisionmaking on public issues

 Negotiation/

Assessment/planning Organization Education resolution Implementation

Conflict analysis 

and assessment

• Do the parties want 

to negotiate?

• Are the issues negotiable?

Can the parties get a 

better deal elsewhere?

What are the chances 

for success?

Identify:

• What is the problem

• Mission goals

• Range of issues to be 

addressed

• Preliminary process 

design

Representation issues 

(stakeholder analysis):

• Who are the dealmakers 

and dealbreakers?

• What groups should 

be represented?

• Who can legitimately 

speak for each group?

Assess adequacy of staffing:

• Process

• Policy

• Administrative

Assess adequacy of 

commitment:

• Time

• Financial resources

Training in interest-based

collaboration

Meeting logistics and 

schedule

Settle representation issue

Settle mission goals

Develop ground rules:

• Decisionmaking

• Press/observers

• Roles/responsibilities

• Other

Dealbreaker analysis

Determine ongoing 

communication and 

accountability systems 

with:

• Constituents

• Elected/appointed boards

• General public

• Other important players

Agenda setting for 

education phase:

• Initial discussion 

of issues

• Initial issue 

framework

Finalize process design

Review history, context, 

and legal/statutory 

framework

Develop common 

understanding of 

problem and issues

Thorough understanding 

of one’s interests and 

adversaries’ interests

Thorough understanding 

of most likely alternatives 

to a negotiated agreement

Develop common 

information base:

• What information do 

we have?

• What portion of that 

information is accepted 

by all?

• What new information 

is needed and how to 

get it (data gaps)

Educate constituency to 

issues and interests

Develop framework for 

negotiation, including 

range and order of 

issues to be addressed

Turn interests into 

decisionmaking 

criteria

Option generation/

brainstorming 

Inventing without 

deciding

Developing/refining 

trial balloons

Linking and 

packaging 

agreements

Agreements in 

principle

Agreements in detail

If get stuck:

• Revisit underlying 

interests

• Revisit alternatives 

to a negotiated 

agreeement

Constant feedback 

from one’s 

constituency

Develop agreements 

with:

• Quid pro quo 

linkages

• Assurances for 

mutual commitments

Linking agreements to 

external 

decisionmaking

Monitoring 

implementation 

to assure compliance and 

respond to 

changing 

conditions

Can problem be successfully addressed through 

negotiation?

Not excluding any party 

that could undermine 

negotiated agreements

Key challenges by stage

Determining how group 

makes its decisions

Agreeing to devote 

sufficient time to

this stage

Postponing judgment to 

learn about other 

parties’ interests

Reconciling conflicting interests

Bringing constituents along

Development of

assurances

A test of how well

implementation

was integrated

into the agreement
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GENERAL TECHNICAL REPORT PSW-GTR-237

Determining desired future conditions involved evaluating current conditions 

using forest measurement data, discussion, and selection of desired future conditions, and developing management practices to get there. Given the time commitment and expertise required, a subcommittee was formed and tasked with 

developing recommendations to bring back to the full group. 

• Scientific experts served as technical resources during meetings. In the 

organization phase, the mediator vetted scientists with relevant expertise with 

each of the stakeholders who were going to participate in the collaborative 

planning forum. The planning forum participants essentially approved each 

technical expert. The technical experts participated in most planning forum 

meetings: they were able to answer scientific questions immediately, keeping 

the workflow and dialogue moving. This proved invaluable to moving forward 

and reaching agreements. In cases where questions arose requiring analytical 

work, the scientists were able to clarify the analytical questions first hand and 

then conduct analytical work or provide data with a clear understanding of what 

was needed. 

• Some intractable issues moved forward without complete consensus. For 

example, the parties were unable to reach agreement on the definition of forest 

health because they had different philosophical approaches to forest management. However, the parties were still able to negotiate the details of the Dinkey 

project by dealing with the specifics of the particular project rather than the 

philosophy or values around forest health. The negotiations forced parties to 

evolve from individuals challenging each other to a collaborative team seeking 

solutions.

• Site visits used to develop decision priorities and the initial mark. The subcommittee went out into the field and looked at parts of the project area. After 

the site visit, the group developed a set of decision priorities to clarify how project objectives varied with location (e.g., forest in defense zones versus riparian 

areas). This priorities document continued to evolve and serve as the repository 

for agreements. Working with the silviculturists, the group developed targets 

that were translated into preliminary marking guidelines. After stands in different priority zones were marked, the group and the GTR authors visited the sites 

and discussed the mark and the reasoning used to make decisions. This field 

visit was particularly useful for grounding discussions over desired conditions, 

providing a specific context in which decisions needed to be made rather than a 

principled argument over management practices. 

The parties were 

unable to reach 

agreement on the 

definition of forest 

health... [However, 

they] were still able 

to negotiate the 

details of the Dinkey 

project by dealing 

with the specifics 

of the particular 

project rather than the 

philosophy or values 

around forest health.
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Managing Sierra Nevada Forests

Additional Steps for Successful Collaboration 

and Cooperation

• Timely engagement. For stakeholders to have meaningful dialogue and an 

effect on issues, the Forest Service needs to engage potential participants 

early in project planning. While stakeholders can be nimble, in cases of 

low trust and high conflict, having adequate time is essential for conflict 

resolution. Working with a stakeholder group, a deliberative initial pace 

can be frustrating, but is often needed to build the foundation for long-term 

collaboration and may potentially reduce project approval time during the 

environmental analysis and review. 

• Building trust. Many issues can come up to derail collaboration, but one 

of the most common is starting off with the most difficult and contentious 

issues first. In the long-term it may be more productive to first build general 

agreement on ecological principles. For example, does the group agree that 

low-intensity fire is a critical ecological process that management actions 

should attempt to mimic where possible? General agreements on ecological principles tied to topographic feature can help determine if the parties 

share concepts for current and future desired conditions for the planning 

landscape. If there is conceptual agreement, do the parties also understand 

and trust the data being used to examine treatment levels and impacts to 

resources. Information used to understand the landscape, descriptions of 

existing conditions, historical reference conditions, and estimates of effects 

of actions (alternatives, no action) taken to achieve desired conditions need 

to be supported by the group. Next, where possible (i.e., outside defense 

zones), the planning process and marking prescriptions should balance and 

move multiple objectives forward (e.g., fuels reduction, ecosystem restoration, and provision of wildlife habitat) rather than using single or primary 

objectives for different landscape locations. Finally, project monitoring is 

essential to demonstrating a commitment to understanding what worked 

and what did not. Greater management flexibility will only improve forest conditions if it commits to assessing and adapting from what it learns. 

As climate changes, all management practices will be experimental. 

Monitoring is essential to building trust in an uncertain future. 

Many issues can 

come up to derail 

collaboration, but one 

of the most common 

is starting off with 

the most difficult and 

contentious issues 

first. In the longterm it may be more 

productive to first build 

general agreement on 

ecological principles.
88

GENERAL TECHNICAL REPORT PSW-GTR-237

• Testing implementation. Heterogeneity marking is less about right or 

wrong and more about moving in a new direction. Sharing ideas, trying 

different approaches, and making mistakes will be part of developing a new 

approach. The marking crew leader and crews should understand the design 

features and preliminarily mark several acres to test design measures as 

they are transferred to the ground. The collaborative group should review 

this phase with the Forest Service since the marking crews are the people 

who will actually cover all the ground in the project area. 

• Patience. These collaborative projects may initially require more time and 

resources before a particular method or “tool box” application is developed. One potential benefit would be to try GTR 220-based collaboration 

in several more areas and then analyze commonalities across all the projects. This would help fine tune procedures and provide insights that could 

streamline project development efforts and develop a set of tools that might 

be applicable in other landscapes. 

References

Ehrman, J.R.; Stinson, B.L. 1999. Joint fact-finding and the use of technical 

experts. In: Susskind, L.; McKearnan, S.; Thomas-Larmer, J., eds. The 

Consensus Building Handbook. Thousand Oaks, CA: Sage Publications: 

375–398.

Karl, H.A.; Susskind, L.E.; Wallace, K.H. 2007. A dialogue, not a diatribe: 

effective integration of science and policy through joint fact finding. 

Environment. 49: 20–34.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Sierra Nevada Ecosystem Project [SNEP]. 1996. Sierra Nevada Ecosystem 

Project: final report to Congress. Davis, CA: University of California, Davis 

Centers for Water and Wildland Resources. Volumes 1–4. 
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Managing Sierra Nevada Forests

Chapter 8: Using GTR 220 to Build

Stakeholder Collaboration

Summary of Findings

1. GTR 220 provides a conceptual 

model to use as a starting point 

for new dialog about forest management. Exploring the principles 

of GTR 220 in a collaborative 

setting provides the basis for joint 

fact finding and mutual learning.

2. Future applications of GTR 

220 should strive to more fully 

address wildlife ecology at the 

microsite, stand, home range and 

landscape scales.

3. Successful GTR 220 application 

may require capacity changes

such as organized information 

exchange, standardized short- and 

long-term monitoring, and facilitating stakeholder group participation. 

C. Thomas1

Introduction

Since 2008, Sierra Forest Legacy, a nonprofit conservation 

organization, has increased its participation in the design of 

projects on national forest lands in the Sierra Nevada. Our 

interest has been to engage scientists, managers, and other 

stakeholders in the design of projects that integrate the best 

available scientific information. Our second interest has been 

to explore the possibilities for “up-front” collaboration between 

these parties to bridge disagreements over the scope of natural 

resource impacts. We have observed, and, in some cases, 

actively participated in, the application of principles outlined 

in U.S. Forest Service General Technical Report GTR 220, “An 

Ecosystem Management Strategy for Sierran Mixed-Conifer 

Forests,” (North et al. 2009) in approximately 12 project-level 

planning efforts since its 2009 publication. These projects 

included various levels of collaborative efforts between land 

managers, scientists, and stakeholders grounded in GTR 220 

principles. Previously, questions about “whose science,” where 

to take risks, and with what resources have sometimes been 

settled in the courtroom. The value of GTR 220 for all groups is 

its provision of a conceptual model to use as a starting point for 

fresh dialog after a decade of conflict.

Improved Communication

Because GTR 220 is not prescriptive, practitioners have shared ideas, mostly in 

field settings, about how to identify, mark, and describe desired microsite and 

project-level heterogeneity. This information exchange has been crucial as the flow 

of new research on fisher (Martes pennanti) rest sites, fire ecology, topographical 

influences, climate change effects, carbon storage, and pest dynamics has significantly accelerated. Through collaborative factfinding, diverse interests can explore 

and expand a communal knowledge base and support adaptive management and 

incorporation of new information while conducting ongoing restoration efforts.

1 Executive Director, Sierra Forest Legacy, P.O. Box 244, Garden Valley, CA 95633.
90

GENERAL TECHNICAL REPORT PSW-GTR-237

The social implications of using GTR 220 are also significant. There is now 

more emphasis on interdisciplinary team integration, stakeholder involvement, 

and collaboration in project design. In project planning, where GTR 220 is a 

centerpiece, it is not uncommon to find conservation groups, scientists, mill owners, Forest Service staff, and others discussing protection of wildlife trees, clumping strategies and variable density, snag retention, oak structural decadence, the 

importance of shrub species, and size of openings for pine regeneration. There is 

a marked improvement in project planning that is building stronger relationships, 

more trust, and improved projects. While the GTR 220 approach is still a work in 

progress with no pat formulas for success and little to judge yet in terms of monitored outcomes, it suggests intensive, science-based collaboration has a future in 

project and landscape planning. There is a growing body of scientific knowledge, 

significant experience, and a deep interest in restoring the Sierra mixed-conifer 

forests that is driving a stronger concept of sustainability. 

Sustainability

Questions regarding the sustainability of natural resources have been at the core 

of these conflicts in a period where stakeholders and managers debated the relative 

merits of proposed treatments affecting fire behavior, forest health, and wildlife 

in the Sierra Nevada. Sustainability has often been conceived as a “three-legged 

stool” (fig. 8-1) suggesting that social and economic issues exist outside of an 

ecological foundation (e.g., Dawe and Ryan 2003). Weak sustainability can result 

in local economy boom-and-bust cycles, weakened social structures, and damaged 

landscapes. In contrast, strong sustainability (Hart 1998) defines a much closer connection between our socioeconomic activities and the environment—a vision where 

Figure 8-1—Schematics of weak and strong sustainability concepts. (Adapted from Hart 1998.) 

Triple Bottom Line

Interconnected and Interdependent Benefits

Environment Economy

Society

Economy

Society

Environment

Weak Sustainability Stong Sustainability

There is a marked 

improvement in 

project planning that 

is building stronger 

relationships, more 

trust, and improved 

projects. 
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Managing Sierra Nevada Forests

economic activities, communities and society are based within and supported by 

the environment. Callicott and Mumford (1998) further refined the connection 

between human use of resources and the ecosystem by defining ecological sustainability “as meeting human needs without compromising the health of ecosystems.” 

General Technical Report 220 provides a foundation for discussing the ecological 

needs of a healthy mixed-conifer ecosystem and our sustainable interaction with 

this environment. 

Perceived Problems

One objection to the use of GTR 220 is the additional time and costs associated 

with designing and marking ecologically appropriate and more complicated 

prescriptions. When taking a holistic approach, the success rate of cooperatively 

designed projects in achieving agreed-upon goals should be tracked over time so 

this monitoring can support improved approaches. While these projects do develop 

slowly, they may still come out ahead when compared to projects that are appealed 

or litigated. 

Challenges

We believe wildlife ecology, in a broad sense, should be expanded in future applications of GTR 220. Concerns about wildlife need to be extended beyond Pacific 

fisher to include principles for sustaining the whole wildlife community in these 

landscapes through ongoing restoration efforts. Designing projects that sustain key 

attributes associated with occupancy was identified as a future research need in the 

2009 publication (North et al., p. 32) and represents a fundamental aspect of wildlife conservation. Biodiversity protection and ecological resilience are at the heart 

of Sierra Nevada restoration. This linkage is supported in a recent synthesis on 

forests and climate change by the United Nations’ Convention on Biodiversity and 

co-authored by the U.S. Forest Service: “The available scientific evidence strongly 

supports the conclusion that the capacity of forests to resist change, or to recover 

from disturbance, is dependent on biodiversity at multiple scales” (Thompson et 

al. 2009). Key concepts that foster biodiversity, including promoting landscape 

connectivity, heterogeneity, and reducing human impacts, need to be addressed in 

landscape- and project-level planning. 

Future Directions

For successful collaboration to continue in the Sierra Nevada, we believe three 

principle capacity issues need to be addressed: organized information exchange, 

standardized short- and long-term monitoring, and stakeholder group capacity to 
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GENERAL TECHNICAL REPORT PSW-GTR-237

meaningfully participate. At present, there are multiple projects based on GTR 

220 concepts, yet no centralized forum for exchanging information and learning 

from other projects. The region might consider establishing a Web site, newsletter, 

or workshops to support expanded use of GTR 220 in planning and design efforts 

across the Sierra Nevada. Another approach might be a Web-based “living” seminar to support information exchange for practitioners. 

A second concern is the need for monitoring to understand the impacts of 

these new management practices on species and ecosystems. Monitoring of forest 

stands is necessary to understand how the treatments alter stand conditions and 

how wildlife responds. Monitoring protocols that build on existing inventory and 

assessment approaches (i.e., Manley et al. 2006) may be the most efficient means to 

develop monitoring plans. Effective monitoring plans need to integrate the results 

from multiple scales and should feed into a decision-support framework for implementing adaptive management in a transparent and collaborative manner. 

The third concern can be best addressed by Forest Service support for ongoing facilitation services, collaboration with the University of California, and other 

institutions that can offer scientific expertise and exploring foundation interest in 

capacity building within stakeholder groups. 

For many of the GTR 220 principles to be fully implemented, fire will have to 

become more widely used as an ecological tool. We encourage establishing regional 

direction that promotes returning fire as a key component of forest restoration. This 

would include appropriate staffing at the forest and district levels, public education, 

collaboration with air quality regulators, and strong commitments to the use of 

managed fire. 

References

Callicott, J.B.; Mumford, K. 1997. Ecological sustainability as a conservation 

concept. Conservation Biology. 11: 32–40. 

Dawe, N.K.; Ryan, K.L. 2003. The faulty three-legged-stool model of sustainable 

development. Conservation Biology. 17: 1458–1460.

Hart, M. 1998. Triple bottom line sustainability graphic. From Sustainable 

Community Indicators Trainer’s Workshop, Courtesy of Maureen Hart, Hart 

Environmental Data, and U.S. Environmental Protection Agency Office of 

Sustainable Ecosystems and Communities. http://www.sustainablemeasures.com. 

(September 15, 2011).

At present, there are 

multiple projects based 

on GTR 220 concepts, 

yet no centralized 

forum for exchanging 

information and 

learning from other 

projects.
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Managing Sierra Nevada Forests

Manley, P.N.; Van Horne, B.; Roth, J.K.; Zielinski, W.J.; McKenzie, M.M.; 

Weller, T.J.; Weckerly, F.W.; Vojta, C. 2006. Multiple species inventory and 

monitoring technical guide. Gen. Tech. Rep. WO-73. Washington, DC: U.S. 

Department of Agriculture, Forest Service, Washington Office. 204 p.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Thompson, I.; Mackey, B.; McNulty, S.; Mosseler, A. 2009. Forest resilience, 

biodiversity, and climate change. A synthesis of the biodiversity/resilience/

stability relationship in forest ecosystems. Secretariat of the Convention on 

Biological Diversity, Montreal. Technical Series no. 43. 67 p.
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GENERAL TECHNICAL REPORT PSW-GTR-237
95

Managing Sierra Nevada Forests

M. North1 and J. Sherlock 2

Introduction

Marking guidelines commonly use stocking level, crown 

class, and species preferences to meet management 

objectives. Traditionally, these guidelines were applied 

across the extent of the stand. Current marking guidelines 

are more flexible, responding to within-stand variability 

with different stocking level, crown class, and species 

preference guidelines in response to fine-scale variability 

in forest structure and composition. By varying marking 

guidelines within stands, managers can meet potentially 

conflicting prescription objectives such as reducing 

crown bulk density while maintaining an average target 

canopy cover (Sherlock 2007). In this chapter, we discuss 

marking guidelines that may help explicitly implement a 

fine-scale response to within-stand variability and provide 

ways of measuring and assessing posttreatment heterogeneity. The emphasis in U.S. Forest Service General 

Technical Report PSW-GTR-220 “An Ecosystem Management Strategy for Sierran Mixed-Conifer Forests” (North 

et al. 2009) is still on using topography to help vary 

treatments, but silviculturists also need to respond to the 

stand conditions they have to work with. 

In forests with frequent, low-intensity fire regimes, 

fine-scale heterogeneity makes it difficult to identify 

and demarcate stands (“group(s) of trees and associated 

vegetation having similar structures and growing under 

similar soil and climatic conditions” [Oliver and Larson 

1996]). Structure analysis at the Teakettle Experimental 

Forest found that mixed conifer was made up of three 

Chapter 9: Marking and Assessing

Forest Heterogeneity

1 Research ecologist, U.S. Department of Agriculture, Forest 

Service, Pacific Southwest Research Station, 1731 Research Park 

Dr., Davis, CA 95618.

2 Assistant regional silviculturist, U.S. Department of Agriculture, 

Forest Service, Pacific Southwest Region, 1323 Club Dr., Vallejo, 

CA 94592.

Summary of Findings

1. GTR 220 suggests creating three 

general patch conditions: tree groups, 

gaps, and a matrix with a low density 

of large, preferably pine, trees. The 

relative proportion of these three patch 

conditions may change with topographic 

position and in response to the forest 

conditions managers have to work with. 

2. It may help marking crews to first 

identify tree groups and gaps as 

anchor points around which to mark 

the remainder of the treatment area.

Reconstruction studies suggest most 

tree groups and gaps were 0.1 to 0.5 ac 

(0.04 to 0.2 ha). It may be most difficult to develop prescriptions and mark 

stands lacking large legacy trees or that 

have fairly uniform spacing. 

3. The Forest Vegetation Simulator 

(FVS) and stand exam plots may be 

used to assess forest heterogeneity by 

classing plots by patch type, using the 

“process plots as stands” option and 

then comparing the mean and coefficient 

of variation between all plots and plots 

by patch type. Details are provided on 

using “Suppose” within FVS to model 

current and future conditions, and outputting results to Excel® to calculate 

the coefficient of variation. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

dominant vegetation conditions: tree groups, gaps, and shrub patches. An average 

“stand” in Teakettle’s mixed-conifer forest supports about 70 percent of the stand 

area in tree groups or scattered large trees, 16 percent in gaps, and 14 percent 

in shrub patches (North et al. 2002). Teakettle studies also found that ecological 

processes were best understood at this patch scale, before and after fuels reduction 

treatments were applied (Ma et al. 2010, North and Chen 2005, Wayman and North 

2007, Zald et al. 2008). These patches differed in size but most were between 0.02 

to 0.3 ac, fitting the general patch size pattern noted by Knapp et al. (chapter 12). 

For ecological restoration and the provision of habitat and microclimate variability, 

marking and measuring forest structure at finer patch scales may be an important 

complement to stand average assessments.

General Marking Suggestions

Within stands, GTR 220 describes three general conditions: (1) high-density, 

closed-canopy groups of trees; (2) open gaps; and (3) a matrix of low-density areas 

dominated by large, preferably pine, trees. These three conditions were also found 

in a recent meta-analysis of all studies of tree patterns in fire-frequent forests of 

western North America (Larson and Churchill 2012). With these conditions, one 

approach to marking might be to start with the areas that most easily fit either a 

group or gap as anchor points. Both groups and gaps could have a range of sizes 

anywhere from 0.1 to 1.0 ac (0.04 to 0.4 ha), but reconstructions suggest that before 

fire suppression, size more commonly ranged from 0.1 to 0.5 ac (0.04 to 0.2 ha). 

If a stand lacks gaps, the goal in creating them is to produce a high-light 

environment favoring both regeneration of shade-intolerant trees and some shrub 

patches. Areas currently lacking pine, and fir groups with evidence of root disease, 

could be recognized as priority locations for gaps. Some gaps may be created by 

enlarging existing openings or low-density areas, particularly if the higher light 

environment may benefit a struggling shade-intolerant such as a remnant black oak 

(Quercus kelloggii Newberry). Gaps may occasionally include a large pine that 

would act as a seed source. If a tree were left in a gap, it would ideally be located 

near the edge or the northern end of the opening to maximize the amount of light 

available to regenerating pines in the remaining area. To increase light, the gap edge 

may also be “feathered” by thinning trees, particularly those on the gap’s southern 

edge. Groups of tree may be identified by focusing on the attributes that make them 

potential wildlife habitat such as the presence of large, old trees and higher levels 

of canopy closure. Particular priority for retaining a group is when it has additional 

attributes that may enhance habitat value such as broken stems, evidence of heart 

rot organisms, mistletoe brooms, etc. (see defect tree section in chapter 14 and 

Within stands, GTR 220 

describes three general 

conditions: (1) highdensity, closed-canopy 

groups of trees; (2) 

open gaps; and (3) a 

matrix of low-density 

areas dominated by 

large, preferably 

pine, trees.
97

Managing Sierra Nevada Forests

the appendix). The size and shape of groups should depend on obvious breaks in 

composition or size of trees in the existing stand. 

After groups and gaps are identified, low-density areas may be marked with 

the intent of restoring a more open, pine-dominated forest condition in topographic 

locations where historical fire would have produced these conditions (see Stand 

Visualization System examples below). Most leave trees would be selected based 

on size, species, and vigor, but also on important habitat features.

As the climate changes and temperatures increase, water stress will increase 

on trees. If trees are left in groups, will they experience increased water stress and 

a higher rate of mortality? Any increase in tree density will increase competition 

for resources and generally reduce growth. However, it is clear in all reconstruction studies in the Sierra Nevada that large trees have historically been clumped, 

and this pattern existed even during past periods of extended drought. We do not 

know the exact reasons for this drought resilience but one consideration may be the 

broader environment that the clump exists within. Recognizing the opportunistic 

nature of root growth, gaps adjacent to tree clumps may have provided greater 

resource availability to sustain large trees during drought periods. 

An important concern, then, is the stem density of areas adjacent to the group. 

Historically, low-density areas or gaps surrounded clumps, and these openings may 

have increased resource availability for trees in the clump. With fire suppression, 

many of these areas are now filled with shade-tolerant trees, which may increase 

stress within the large tree clump. This suggests that, when emphasizing the large 

tree clump, thinning around clumps may be warranted, in place of the more traditional radial release thinning where much of the clump is thinned to increase the 

growth of one leave tree. 

Stand Visualization Simulator Examples

Using the Stand Visualization Simulator, we constructed representative stands of 

common Sierra Nevada forest conditions. These images were then edited to demonstrate how treatments might increase heterogeneity in tree spacing and canopy 

layering, while reducing standwide fuel ladders. 

A thinning following GTR 220 concepts might be based on producing different 

groups of trees and leave-tree densities. In most treated stands, the largest trees are 

left, regardless of their relative height in the overall stand, and suppressed trees, 

which may act as ladder fuels, are removed (e.g., left and right sides of fig. 9-1). 

However, in tree groups valued for potential wildlife habitat, understory trees (the 

intermediate and suppressed crown class) can be important clump components (e.g., 

central clump in fig. 9-1). While these suppressed trees provide understory cover in 
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GENERAL TECHNICAL REPORT PSW-GTR-237

tree groups with high habitat potential, they also increase the hazard of crown fire, 

as they can provide fuel ladders into the upper canopy. If the tree group is burned, 

fire may cause some level of overstory mortality, but gaps and low-density areas 

surrounding the tree group may reduce the risk of further crown fire spread. While 

potentially reducing the numbers of larger trees within the area, high postfire mortality in the tree group would contribute to large snag and down log recruitment. 

Over time, as other locations in the area develop into new groups, landscape-level 

conditions would be expected to compensate for the short-term loss of live large 

trees. 

In fire-suppressed forests, current stand structure conditions may not significantly differ with slope position. After treatments designed to increase landscape 

heterogeneity have been completed, valley bottom, midslope and ridgetop stands 

would have different tree densities and resultant canopy cover levels (figs. 9-2 to 

9-4). In general, upslope changes in slope position often correspond with reduced 

soil moisture availability and lower productivity. Parker (1982) developed the 

topographic relative moisture index (TRMI) to provide a relative measure of xeric 

(TRMI value of 0) to mesic (maximum value of 60) conditions that has been found 

to correspond with historical differences in stand structure (Taylor 2004, 2010). 

Historically, slope position also may have corresponded with increasing fire intensity that would have also affected stand density and canopy cover.

Figure 9-1—Stand Visualization Simulator image of a hypothetical stand treated following U.S. Forest Service General 

Technical Report 220 concepts producing a high-density tree group, a gap, and lower density matrix (North et al. 2009).
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Managing Sierra Nevada Forests

Figure 9-2—Valley bottom stand (A) before and (B) after treatment.

Figure 9-3—Mid-slope stand (A) before and (B) after treatment.

Figure 9-4—Ridgetop stand (A) before and (B) after treatment.

A B

A B

A B
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GENERAL TECHNICAL REPORT PSW-GTR-237

Forests lacking large trees, or that have uniform spatial distributions, may be 

the most difficult to mark when keying off of existing conditions. Following GTR 

220 concepts, microsite and landscape topography can be used to vary treatments. 

However many forests affected by early 1900s railroad logging and pre-1980s timber management plans have little topographic variation and few, if any, large legacy 

trees to anchor the location of tree groups (fig. 9-5). In most of these stands, however, there are differences in stem densities and sizes that can be used to increase 

the variability in tree distributions. Even in fairly homogeneous second growth, 

some trees are larger, and these may serve to identify leave-tree groups (fig. 9-5).

Younger planted forests with little crown class differentiation can be very 

difficult to shift toward higher levels of spatial heterogeneity because of relatively 

uniform distribution and tree size (fig. 9-6). In this case, thinning that enhances 

large tree development may take priority over creating spatial heterogeneity. 

Although the primary management objective might be tree density reduction to 

increase growth rates, even in plantations there are often opportunities to favor 

natural regeneration and to increase heterogeneity in both species composition 

and tree arrangements. 

Figure 9-5—Second-growth stand with few older legacy structures (A) before and (B) after treatment.

A B

Figure 9-6—Pine plantation (A) before and (B) after treatment.

A B

Forests lacking 

large trees, or that 

have uniform spatial 

distributions, may be 

the most difficult to 

mark when keying off 

of existing conditions.
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Managing Sierra Nevada Forests

Using FVS to Assess Heterogeneity

With a slight modification, both Common Stand Exam (CSE) data and the Forest 

Vegetation Simulator (FVS) can be used to assess whether treatments have 

increased forest heterogeneity. Here we present an approach that provides an 

effective estimation of the mean and variation in stand-level and within-stand 

forest attributes.

In practice, variable-radius sample plots are small. For example, using a 

20-basal area factor (BAF) prism, sample area differs with target tree diameter, 

yet even for a 30-in (76-cm) diameter at breast height (d.b.h.) tree the sample area 

will be 0.24 ac (0.1 ha). This plot size falls within the range of tree group and gap 

sizes found in many reconstruction studies. This is important because statistical 

analyses can only detect patterns of variability at scales equal to or larger than the 

plot size. 

The Field Sampled Vegetation (FSVeg), CSE, and FVS can be customized 

to annotate plots and assess different stand conditions such as high-density, lowdensity, and gap areas. For example with CSE-protocol stand exams, the Plot User 

field can be used to categorize the “type” of forest condition sampled such as highdensity (HD tree cluster), low-density (LD matrix), and Gap. 

After using FSVeg to create an FVS-ready Access database, an FVS_PlotInit 

table is available to simulate plots as stands. To enable this option, Suppose preferences must be set to “Process plots as stands” (fig. 9-7). Plots can then be grouped 

for simulation in the Select Stands process step. For example, if 15 plots are sampled in an analysis area, field technicians may have indicated that plots 1, 5, 12, and 

14 are HD (tree cluster) plots in the Plot User field. These four plots are selected and 

“grown” or “treated” in the simulation together to provide information on HD tree 

group response. Several methods exist to summarize the results of this within-stand 

simulation approach. The use of the Average Summary Table post processor is one 

option (fig. 9-8). Continuing with our example, the same analysis can be completed 

for the LD, and Gap condition plots within the stand, and also completed for the 

entire set of plots to yield a stand-level average. 

The creation of a table to compare variation between the entire sample and the 

posttreatment patches is simplified by using Suppose and Excel together. Within 

Suppose, specify an output database, in this case an Excel file, to capture the forest 

structural variable of interest. After each simulation, copy and paste the output for 

that variable into an Excel worksheet. Using Excel’s statistical functions, the mean 

and coefficient of variation for stand- and patch-level attributes can be calculated 

using all plots and plots by patch type, respectively. By dividing a population’s standard deviation by its mean, the coefficient of variation (CV) permits a comparison 
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GENERAL TECHNICAL REPORT PSW-GTR-237

Figure 9-7—Screen capture image of the preferences menu in the Suppose module of the Forest 

Vegetation Simulator.

Figure 9-8—Screen capture image of the Average Summary Table post processor in the Forest Vegetation Simulator.
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Managing Sierra Nevada Forests

of relative variability about different-sized means. In effect, CV, often expressed as 

a percentage, standardizes variability around the mean of the sample population. 

In the example provided (fig. 9-9), basal area per acre was selected from each 

plot for a common year. After pasting the data into Excel, the program’s statistical 

functions SDEV and AVERAGE are used. After these values are calculated, enter a 

user-defined formula for the CV (coefficient of variation = SDEV/AVERAGE).

A highly heterogeneous stand, after treatment, should have a large CV when 

all plots are pooled. This is because some plots will have sampled tree groups with 

high basal area, stand density index, and canopy cover, and other plots will sample 

gaps and the LD matrix, which will have much lower values. For each patch type, 

means should be significantly different from each other and be widely varied compared to the all-plots mean. The CVs for each patch type should be smaller than the 

CV for all plots combined. As a rule of thumb, higher stand-level CV and greater 

differences between the patch-type means will usually be associated with increased 

structural heterogeneity. 

Figure 9-9—Screen capture image of 

an Excel spreadsheet where the mean 

(average), standard deviation (SDEV) 

and coefficient of variation (CV) have 

been calculated for data pasted from 

the Forest Vegetation Simulator’s Suppose module. HD = high density tree 

cluster; LD = low density matrix.

As a rule of thumb, 

higher stand-level 

CV [coefficient of 

variation] and greater 

differences between 

the patch-type 

means will usually 

be associated with 

increased structural 

heterogeneity. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

If sample plots are arranged on a systematic grid covering the treatment area, 

the percentage of plots in each patch type will also indicate the project’s overall 

ratio of HD tree groups, gaps, and LD areas. Recording plot locations with a 

global positioning system receiver allows the data to be easily incorporated into 

geographic information system software and facilitates plot relocation for future 

repeated sampling. This type of analysis has the advantage of providing both mean 

and CV for the entire sample stand and the finer scale, patch type variability that 

creates within-stand structural heterogeneity. 

References

Larson, A.J.; Churchill, D. 2012. Tree spatial patterns in fire-frequent forests 

of western North America, including mechanisms of pattern formation and 

implications for designing fuel reduction and restoration treatments. Forest 

Ecology and Management. 267: 74–92.

Ma, S.; Concilio, A.; Oakley, B.; North, M.; Chen, J. 2010. Spatial variability 

in microclimate in a mixed-conifer forest before and after thinning and burning 

treatments. Forest Ecology and Management. 259: 904–915. 

North, M.; Chen, J. 2005. Introduction to the Teakettle Special Issue. Forest 

Science. 51: 185–186.

North, M.; Oakley, B.; Chen, J.; Erickson, H.; Gray, A.; Izzo, A.; Johnson, D.; 

Ma, S.; Marra, J.; Meyer, M.; Purcell, K.; Rambo, T.; Roath, B.; Rizzo, D.; 

Schowalter, T. 2002. Vegetation and ecological characteristics of mixed-conifer 

and red-fir forests at the Teakettle Experimental Forest. Gen. Tech. Rep. PSWGTR-186. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific 

Southwest Research Station. 52 p.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. Gen. Tech. 

Rep. PSW-GTR-220. 2nd printing with addendum. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Oliver, C.D.; Larson, B.C. 1996. Forest stand dynamics. Updated edition. New 

York, NY: John Wiley and Sons, Inc. 520 p.

Parker, A.J. 1982. The topographic relative moisture index: an approach to soil 

moisture assessment in mountain terrain. Physical Geography. 3: 160–168.
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Managing Sierra Nevada Forests

Sherlock, J.W. 2007. Integrating stand density management with fuel reduction. 

In: Powers, R.F., tech. ed. Restoring fire-adapted ecosystems: proceedings of the 

2005 national silviculture workshop. Gen. Tech. Rep. PSW-GTR-203. Albany, 

CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research 

Station: 55–66.

Taylor, A.H. 2004. Identifying forest reference conditions on early cut-over lands, 

Lake Tahoe Basin, USA. Ecological Applications. 14: 1903–1920.

Taylor, A.H. 2010. Fire disturbance and the structure and dynamics of an 

old-growth P. ponderosa forest in the southern Cascades, USA. Journal of 

Vegetation Science. 21: 561–572.

Wayman, R.; North, M. 2007. Initial response of a mixed-conifer understory 

plant community to burning and thinning restoration treatments. Forest Ecology 

and Management. 239: 32–44.

Zald, H.; Gray, A.; North, M.; Kern, R. 2008. Initial regeneration responses 

to fire and thinning treatments in a Sierra Nevada mixed-conifer forest, USA. 

Forest Ecology and Management. 256: 168–179.
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107

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Chapter 10: Geographic Information System

Landscape Analysis Using GTR 220 Concepts

1 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 1731 Research Park Dr., Davis, CA 95618.

2 Information Center for the Environment, Department of Environmental Science and 

Policy, One Shields Ave., University of California, Davis, Davis, CA 95616.

3 National coordinator for experimental forests and ranges, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, The John Muir Institute, One 

Shields Ave., University of California, Davis, CA 95616.

M. North,1 R.M. Boynton,2 P.A. Stine,3 K.F. Shipley,2 E.C. Underwood,2 

N.E. Roth,2 J.H. Viers,2 and J.F. Quinn2

Introduction

Forest Service General Technical Report “An Ecosystem Management Strategy for 

Sierran Mixed-Conifer Forests” (hereafter GTR 220) (North et al. 2009) emphasizes increasing forest heterogeneity throughout a range of spatial scales including 

within-stand microsites, individual stands, watersheds, and entire landscapes. For 

fuels reduction, various landscape strategies have been proposed and modeled, 

but there are few conceptual models for integrating forest restoration and wildlife 

habitat at larger scales. General Technical Report 220 proposes varying forest 

structure, composition, and fuels based on topographic characteristics, particularly 

slope position and aspect. The concept is an effort to emulate how frequent fire 

might have created landscape-scale forest heterogeneity and by inference increased 

forest resilience and habitat connectivity. In this chapter, we describe a raster-based 

geographic information system (GIS) tool developed to parse a landscape into basic 

topographic categories. The Landscape Management Unit (LMU) tool has two 

versions. An initial version closely follows the methods described in Underwood 

et al. (2010), binning the landscape into three slope positions crossed with three 

aspects (resulting in nine total categories). A second version addresses application considerations that managers have identified within the U.S. Forest Service. 

It condenses some of the topographic categories present in version 1 while adding 

a category based on mechanical operation limitations that usually occur around 

>30 percent slopes, resulting in six total categories. The second version also allows 

for more user modification. The user can change how topographic categories are 

defined, allowing managers to more closely parameterize the GIS tool for a project’s 

particular topographic conditions.
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Summary of Findings

1. Two versions of a GIS tool have been developed for analyzing and 

binning a forested area into landscape management units (LMUs) 

based on topography using DEMs.

2. The first version divides an area into nine LMUs resulting from 

three slope positions (canyon bottom/drainage, midslope, ridge) and 

three slope aspects (Southwest, Northeast, and neutral) following 

earlier published work.

3. A second version divides an area into six LMUs (ridge, canyon 

bottom/drainage, Southwest mid-slope <30 percent, Southwest midslope >30 percent, Northeast mid-slope <30 percent, and Northeast 

mid-slope >30 percent) following feedback from forest managers. 

This version also allows the user to modify three parameters: neighborhood size, minimum-elevation separation, and minimum area of the 

slope position units.

4. The download site for both versions 1 and 2: 

http://ice.ucdavis.edu/project/landscape_management_unit_lmu_tool/. 

Foundations for the GIS Tool 

Historically, frequent low-intensity fire was a strong influence on the structure, 

composition, and ecological functions of mid-elevation Sierra Nevada forests (Skinner and Chang 1996). Aspect, slope position, and slope steepness can influence fire 

frequency and severity, producing different forest structures and species compositions as changes in these topographic variables occur across a landscape (Hessburg 

et al. 2007, Taylor and Skinner 2004). These variables can also influence soil depth, 

microclimate conditions, and soil moisture availability (Ma et al. 2010, Meyer et al. 

2007), affecting tree density, composition, forest productivity, and overall habitat 

characteristics (Parker 1982, Urban et al. 2000). Most reconstruction studies have 

suggested historical Sierra Nevada forests were highly heterogeneous, with forest 

conditions likely varying with fine- and landscape-scale changes in factors such as 

topography and soils. 

Forest heterogeneity may be particularly important for providing a diverse array 

of wildlife habitats. While some species are associated with areas of high canopy 

cover and stem density (e.g., the Pacific fisher (Martes pennanti), northern goshawk 
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Managing Sierra Nevada Forests

(Accipiter gentilis), and California spotted owl (Strix occidentalis occidentalis), 

preferred habitat for others (e.g., some songbirds and small mammals) may be more 

open, xeric forest conditions or shrub patches. Managing for the optimal spatial 

arrangement and connectivity of these different forest conditions is challenging 

because there are few species that have been studied in enough detail to provide 

guidance for management practices. In the absence of better information, a reasonable approach may be to mimic the pattern of forest conditions that might have been 

produced by topographic differences in fire regimes and forest productivity. 

Forest managers are faced with developing project plans that must meet multiple objectives including fuels reduction, ecosystem restoration, increased forest 

resilience, and the provision of a variety of wildlife habitat, especially old-forest 

conditions, which may be at odds with, or are adversative to, fuels objectives. For 

landscape planning, this has sometimes resulted in different areas being managed 

for single objectives (e.g., fuels reduction near the wildland-urban interface, or no 

entry around known sensitive species use areas). There has not been a conceptual 

framework or spatially explicit method for integrating and balancing these different 

objectives across a landscape. The GIS tool described here is an initial attempt to 

analyze and spatially parse forest landscapes into topographic zones with different 

desired forest conditions. Managers may use the tool to develop plans for increasing 

forest heterogeneity while using the conceptual framework to communicate their 

intent to stakeholders and the public. 

Background and Description of the GIS Tool

The first version of the GIS tool, developed by the Information Center for the 

Environment at the University of California, Davis can be downloaded from 

http://ice.ucdavis.edu/project/landscape_management_unit_lmu_tool.

It contains a series of scripts that work in Environmental Systems Research 

Institute ArcMap version 10 (the scripts will not run in earlier versions). The 

essential inputs for the tool are the study area boundary and a digital elevation 

model (DEM) (ideally at 10 m (33 ft) resolution but it will also work on 30-m (98-ft) 

DEMs). The LMU tool contains three toolsets. The first is a preprocessing toolset 

that prepares the data sets, for example, by buffering the study area boundary and 

clipping the DEM by this extent. The main toolset parses the landscape into three 

classes of slope (ridgetop, midslope, canyon/drainage bottoms) and three classes of 

aspect (northerly, southerly, and a neutral class to reflect the amount of solar insolation received), and then recombines these into a total of nine LMUs (see table 10-1). 

Finally, the postprocessing toolset generates summary statistics for either each of 

the nine LMU groups or, alternatively, by the multiple individual units within each 

Managers may use 

the tool to develop 

plans for increasing 

forest heterogeneity 

while using the 

conceptual framework 

to communicate their 

intent to stakeholders 

and the public.
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GENERAL TECHNICAL REPORT PSW-GTR-237

Table 10-1—Classification of landscape management units

Position on slope

Canyon/

Description drainage bottom Slope Ridge

Code 1 2 3

Aspect class:

Neutral (120° to 150° and 300° to 330°) 10 11 12 13

(neutral canyon) (neutral slope) (neutral ridge)

Northerly (centered at 45°) 20 21 22 23 

(northerly canyon) (northerly slope) (northerly ridge)

Southerly (centered at 225°) 30 31 32 33 

(southerly canyon) (southerly slope) (southerly ridge)

LMU type. The summary tables report elevation, slope (in degrees and percentage of rise), aspect, net mean aspect, aspect strength, and wetness index (i.e., the 

amount of water received from upslope in the watershed) (see Underwood et al. 

2010 for details). 

There are a number of options within the tool that can be selected by the user. 

For example, a spatial layer depicting streams or water bodies can be specified if 

the user wants to ensure these are all captured as canyons/drainage bottoms. Also, 

there is an option to simplify the size of the output units within each LMU to 

remove any that are less than 10 ac (4 ha) (see Underwood et al. 2010 for details). 

This size simplification may be useful when the GIS tool is used for planning, but 

users should communicate that prescriptions and marking in the field will differ on 

smaller scales (chapters 9 and 11 through 13). 

Examples: Kings River and Sagehen 

Terrain conditions differ widely across the Sierra Nevada with slope steepness tending to increase in the southern portion of the range. In the first version of the tool, 

thresholds used to determine slope position can be set for either moderate or steep 

slope conditions. We used different thresholds because slope classes are relative. 

A location’s slope position is determined by comparing each cell in a DEM to its 

neighborhood. A slight difference in elevation of the target cell to its neighbors in a 

moderate-terrain landscape may distinguish it as a ridge, whereas the same difference in elevation in a steep-terrain landscape may not. In the steep terrain version, 

the minimum elevation difference between adjacent cells is 25 m (82 ft) for ridges 

and -20 m (-66 ft) for canyons/drainage bottoms. In the moderate terrain version, 

the minimum elevation difference between adjacent cells is 15 m (49 ft) for ridges 

and -14 m (46 ft) for canyons/drainage bottoms (table 10-2). These values were 
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Managing Sierra Nevada Forests

developed iteratively with feedback from field personnel familiar with the two study 

areas presented here. The preprocessing tool will produce a table that gives summary statistics, most importantly mean and standard deviation, for the slope across 

the study area. The user can then use this to help determine whether the moderate 

or steep terrain version should be used in the main toolset analysis. For example, 

a region of steep terrain is the Kings River area in the Sierra National Forest with 

an average slope of 32.1 percent and a standard deviation of 19.6 percent (fig. 10-1). 

In contrast, an area of moderate terrain is the Sagehen Experimental Forest of the 

Tahoe National Forest with an average slope of 19.7 percent and a standard deviation of 14.3 percent (fig. 10-2). 

User Input Version 

The second version of the LMU tool has three adjustments to the basic tool that 

managers may find useful. These adjustments result in six final LMU classes rather 

than nine. This second version can also be downloaded from http://ice.ucdavis.edu/

project/landscape_management_unit_lmu_tool/.

The first adjustment is removal of the aspect categories for the ridge and 

canyon/drainage bottom slope position classes. The tool identifies canyons/drainage 

bottoms and ridges as locations where there is little elevation change between adjacent pixels. Forest managers suggested that, in general, aspect has less influence on 

forest conditions in these two slope position categories because slope steepness is 

minimal. 

A second adjustment is modification of the midslope categories. First we 

removed the neutral category (120 to 150° and 300 to 330°) and adjusted the aspect 

classifications to either southwest (136 to 315°) or northeast (316 to 135°). Managers 

suggested that as a planning tool, the neutral classification was ambiguous and did 

Table 10-2—Thresholds used to determine slope position in “steep” and “moderate” terrain types

Terrain type

Slope position Variable Units Steep Moderate

Ridge Neighborhood Meters 500 500

Minimum separation Meters 25 15

Minimum area Square meters 20,000 20,000

Canyon/drainage bottom Neighborhood Meters 500 500

Minimum separation Meters -20 -14

Minimum area Square meters 40,000 40,000

Slope Any cells not identified 

as ridge or canyon/

drainage bottom
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GENERAL TECHNICAL REPORT PSW-GTR-237

not help identify management scenarios for those areas. In practice, on the ground 

assessments are often used to identify stand aspect and local conditions for these 

areas. We also split the midslope category into two classes, <30 percent and >30 

percent steepness, for two reasons. Mechanical vehicles usually cannot be used on 

slopes steeper than 30 percent, necessitating hand thinning to reduce fuels. This 

limits the removal of cut material, leaving more activity fuel on site. In addition, 

steeper slopes can increase fire intensity particularly when high fuel loads are present, increasing potential tree mortality, and making suppression and containment 

more difficult (Safford et al. 2009). Planning treatments and managing these areas 

requires a different approach than more moderate slope conditions. 

Figure 10-1—Landscape Management Units generated for the Kings River area in the 

Sierra National Forest, California.
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Managing Sierra Nevada Forests

Figure 10-2—Landscape Management Units generated for the Sagehen area in the Tahoe National 

Forest, California.

Version 2 also has a third adjustment that lets the user modify three parameters: neighborhood size, minimum elevation separation, and the minimum area of 

the slope position units created. These adjustments only affect ridge and canyon/

drainage bottoms classification because slope areas are identified as any cells not 

classified as ridge or canyon/drainage bottoms. Neighborhood size determines the 

circular radius around each cell that is used to calculate average elevation and is 

compared to the target cell’s elevation. This will allow users to adjust the grain 

size at which elevation is averaged. Adjusting the minimum elevation separation 

between the cell’s elevation and that of its neighborhood will allow users to alter the 

slope position classifications for the area they are analyzing. Changing minimum 

area will allow users to reduce or increase canyon/drainage bottoms and ridge unit 

size for the scale of analysis that is practical for their planning applications. This 

flexibility may allow managers to adjust the classifications such that final output 

more closely agrees with expert knowledge from field personnel.
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GENERAL TECHNICAL REPORT PSW-GTR-237

Chapter Summary 

The GIS tool is designed to accommodate a range of forest types in the Western 

United States and can be applied to project areas of any size. It is also simple to 

implement requiring easily accessible, basic data inputs such as DEMs and consequently, the units generated are readily interpretable. These units can then provide a 

basis for storing data about each unit within a GIS framework. This foundation can 

be used for further spatial analyses such as calculating the solar radiation associated 

with each unit. It also may be a useful tool for communicating different management scenarios to stakeholders and the public.

All such tools progress through iterative stages of trial, learning, and adjustment. We expect that users of this tool will be able to offer important suggestions 

for improvement once they have had opportunities to test it with real world applications. Technical GIS experts within the agency are well positioned to work with 

managers, making adjustments as experience accumulates and needed improvements become apparent.

Forest Service managers have enormous challenges when contemplating a 

management strategy for any given landscape. They depend on sound science to 

form a foundation from which to build a management strategy. Part of this body of 

defensible scientific knowledge is a set of technical tools that can be used to evaluate ecological conditions and alternative strategies to manage a forested landscape 

toward a desired future condition. We hope the LMU tool is a helpful addition to 

their toolbox, adding analytical power for planning and evaluation of management 

alternatives. 

Literature Cited

Hessburg, P.; Salter, R.; James, K. 2007. Re-examining fire severity relations in 

pre-management era mixed conifer forests: inferences from landscape patterns 

of forest structure. Landscape Ecology. 22: 5–24.

Ma, S.; Concilio, A.; Oakley, B.; North, M.; Chen, J. 2010. Spatial variability 

in microclimate in a mixed-conifer forest before and after thinning and burning 

treatments. Forest Ecology and Management. 259: 904–915. 

Meyer, M.; North, M.; Gray, A.; Zald, H. 2007. Influence of soil thickness on 

stand characteristics in a Sierra Nevada mixed-conifer forest. Plant and Soil. 

294: 113–123.

The GIS tool is designed to accommodate a range of forest 

types in the Western 

United States and can 

be applied to project 

areas of any size. It is 

also simple to implement requiring easily 

accessible, basic data 

inputs such as DEMs.
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North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Parker, A.J. 1982. The topographic relative moisture index: an approach to soil 

moisture assessment in mountain terrain. Physical Geography. 3: 160–168.

Safford, H.D.; Schmidt, D.A.; Carlson, C.H. 2009. Effects of fuel treatments on 

fire severity in an area of wildland-urban interface, Angora Fire, Lake Tahoe 

Basin, California. Forest Ecology and Management. 258: 773–787.

Skinner, C.N.; Chang, C.R. 1996. Fire regimes, past and present, in Sierra 

Nevada Ecosystem Project: final report to congress. Volume 2: Assessments and 

scientific basis for management options. Wildlands Resources Center Report 

No. 37. Davis, CA: University of California, Centers for Water and Wildland 

Resources: 1041–1070.

Taylor, A.H.; Skinner, C.N. 2004. Spatial patterns and controls on historical fire 

regimes and forest structure in the Klamath Mountains. Ecological Applications. 

13: 704–719.

Urban, D.L.; Miller, C.; Halpin, P.N.; Stephenson. N.L. 2000. Forest gradient 

response in Sierran landscapes: the physical template. Landscape Ecology. 

15: 603–620.

Underwood, E.C.; Viers, J.H.; Quinn, J.F.; North, M.P. 2010. Using topography 

to meet wildlife and fuels treatment objectives in fire-suppressed landscapes. 

Journal of Environmental Management. 46: 809–819.
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117

Managing Sierra Nevada Forests

M. North1 and R. Rojas 2

Introduction

Designing and implementing vegetation treatments that can move a forest landscape toward 

a desired future condition is often challenging. Faced with diverse stakeholder interests 

and the unknown effects of changing climate 

conditions, managers need to engage and 

build collaborative projects. One such effort is 

the Dinkey project designed to help restore a 

healthy, diverse, fire-resilient forest structure 

while maintaining and enhancing habitat 

for fisher (Martes pennanti) and California 

spotted owls (Strix occidentalis occidentalis). 

The project retained tree species and size 

classes that are the most drought tolerant; more 

resistant to insects, diseases, and air pollution; 

and have higher rates of postwildfire survival. 

Surface and ladder fuels were decreased to 

reduce the probabilities of crown fire ignition 

and fire severity. Large woody debris and 

higher canopy closure were retained in some areas that may provide suitable habitat 

for sensitive species. Some torching and tree mortality were considered acceptable 

to support cavity nesting and denning structures, and a range of ecosystem functions over time. In areas where a reduction in potential fire intensity was essential, 

treatment included separating tree crowns to reduce the potential for crown-fire 

spread. Forest health and resilience were promoted by increasing the forest’s 

capacity to withstand short-term impacts (e.g., drought) without causing long-term 

changes in the system’s overall function. Mechanical, hand, and prescribed fire 

tools were used to meet these goals. The project was also designed to be conducted 

in an economically efficient manner with minimal outside funding.

1 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 1731 Research Park Dr., Davis, CA 95618.

2 District silviculturist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Region, Sierra National Forest, High Sierra Ranger District, 29688 Auberry Rd., Auberry, 

CA 93651.

Chapter 11: Dinkey North and South Project

Summary of Findings

1. This project, the first to implement GTR 220 concepts, began with discussing and agreeing upon 

a desired future condition for the project area, 

which helped build consensus amongst diverse 

stakeholders.

2. At first, prescription development and marking 

guidelines were difficult to write up, but became 

easier to communicate after they were condensed 

into a series of decision steps.

3. Field visits to test marks with the stakeholders 

allowed grounded discussion of how GTR 220 

concepts were being translated into practice and 

how and why marking decisions were made. 
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Context

The Dinkey North and South project (hereafter the Dinkey project) occurred on 

3,000 ac (1214 ha) of Forest Service land ranging from 5,400 to 6,800 ft (1646 to 

2073 m) in elevation about 30 mi (48 km) northeast of Fresno. Mixed-conifer constitutes most of the forest type (90 percent) with the remainder in ponderosa pine. 

The project area supports known populations of fisher and California spotted 

owls. Monitoring and demographic studies have identified fisher rest sites and 

California spotted owls foraging areas within the project area (North et al. 2000, 

Purcell et al. 2009). Studies in the project area (Spencer et al. 2008) indicated that 

fisher habitat and populations are particularly vulnerable to severe fire. Habitat 

emphasis treatments recognize the importance of late-seral forest structures, home 

range conditions, large trees, and forest heterogeneity.

The project area has a history of fire exclusion that has led to a homogeneous 

landscape of dense conifer forest stands, with prolific establishment of 25- to 

100-year-old, shade-tolerant white fir (Abies concolor (Gordon & Glend.) Lindley) 

and incense cedar (Calocedrus decurrens (Torrey) Florin). Ponderosa (Pinus ponderosa Laws.) and sugar (Pinus lambertiana Douglas) pine, and black oak (Quercus 

kelloggii Newberry) were notably underrepresented in the forest’s current species 

composition. A fire history completed in the adjacent Teakettle Experimental 

Forest found an average fire-return interval of 12 to 17 years for 1700 to 1865, after 

which all fires stopped (North et al. 2005). In addition to fire suppression, past fires 

and mechanical harvest have created large areas dominated by shrubs and dense 

pockets of white fir and incense cedar. High tree density/biomass creates conditions 

that predispose about 50 percent of the landscape to high-severity fire, insect attack, 

and drought-induced mortality.

Information Used

Studies that had reconstructed forest conditions under an active fire regime were 

used to inform general objectives for posttreatment desired conditions. The area has 

lower annual precipitation (about 45 in/yr) (114 cm/yr) than more mesic west-side 

forests, so particular emphasis was given to studies that had been conducted in drier 

mixed-conifer areas such as the eastern side of the Lake Tahoe Basin (Taylor 2004) 

and the nearby Teakettle Experimental Forest (North et al. 2007). The stand density, 

basal area, and species compositions in these studies was used to set lower limits, 

which posttreatment conditions should not fall below. Upper bounds for posttreatment stand conditions were inferred from site capability, landscape zone, and stand 

density index values at which bark beetle mortality may increase (Oliver 1995). 
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Managing Sierra Nevada Forests

The Dinkey project focused on implementing concepts found in U.S. Forest 

Service General Technical Report PSW-GTR-220, “An Ecosystem Management 

Strategy for Sierran Mixed-Conifer Forests” (hereafter GTR 220) (North et al. 

2009). The project’s collaborative group (see chapter 7) developed different prescriptions based on topographic design criteria including a slope position matrix 

(similar to table 10-1). In general, prescriptions were designed to promote heterogeneity by avoiding even spacing of residual trees (fig. 11-1) and protecting unique 

structures including wildlife trees, snags, large logs, clumps of large trees, understory vegetation (including shrubs), and hardwoods (especially black oaks).

A goal of the decision priorities (described below) was to balance the desire 

for a fire resilient, healthy forest with the fisher’s association with areas of 

“maximum biomass” based upon habitat modeling work of the Conservation 

Biology Institute (Spencer et al. 2008). A priority was placed on retaining and 

promoting areas of large-tree-dominated forest sites with high canopy cover 

to benefit the fisher (i.e., 63 percent of its home range had > 60 percent canopy 

cover [Zielinski et al. 2004]) and other rare, old-forest associated species. These 

individual objectives were intended to provide ecological balance to marking 

crews as they implemented prescriptions while working within the overarching 

desire for a healthy, fire-resilient forest. 

Figure 11-1—Variable density left in a white-fir-dominated stand after treatment in the Dinkey project.
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Implementation

The mark was difficult to describe with a simplified written prescription; therefore, a series of sequential steps were followed. The first step was to consider the 

overarching intent of GTR 220 before getting mired in prescription details and 

marking guidelines. A key aspect of GTR 220 is recognizing forest structure at a 

fine scale such as groups of trees and favorable regeneration microsites. While field 

crews have often been trained to recognize individual tree characteristics, they now 

needed to recognize characteristics of several trees in a group including fisher rest 

sites; groups of pine regeneration or potential sites for ponderosa pine regeneration; 

groups of older ponderosa pine; low-quality, even-aged groups of fir; oaks; and 

groups of younger pine. Markers were trained to recognize each microsite or group 

prior to implementing the mark. 

In the second step, markers first focused on groups with high potential for 

being used as fisher rest sites. Visits to known fisher sites and conversations with 

researchers created an emphasis on looking for a particular group structure and 

not just a canopy cover goal. A dense group of trees did not necessarily mean it 

was good fisher habitat. The group also needed to have either large structures (live 

tree, snag, or log) or some “defect” condition. At high-quality fisher rest sites, the 

prescription was to have little, if any, manipulation. These sites were only about 

3 percent of the total area, and therefore did not substantially compromise fuels 

reduction objectives. In moderate-quality fisher rest sites, ladder fuels were targeted 

for reduction but were not completely eliminated in the interest of maintaining 

some understory cover. The lowest quality fisher sites were selected for thinning to 

increase leave-tree size, so as to create better quality fisher habitat in the future.

Next, markers focused on areas of pine regeneration to obtain a working 

knowledge of local soil characteristics amenable to regeneration and the appropriate 

aspect and orientation of openings. The markers were shown examples of successful and unsuccessful shade-intolerant regeneration in small openings. Some collaborative partners were initially uncomfortable with creating holes in the canopy. 

Therefore the first places identified for regeneration were areas where openings 

could be expanded rather than created. Attention was paid to “feathering” the 

gap edge (i.e., reducing foliage density through thinning) and orienting the gap to 

maximize direct sunlight. It took some time to get markers to recognize what is an 

appropriate opening rather than just going to rocky or shallow soil locations. 

In retrospect, it proved more efficient to identify potential regeneration areas 

prior to marking trees. This allowed markers to focus on a single task with unique 

criteria and skills. Depending on forest conditions and the tree markers’ skills, other 

projects may find it easier to identify tree clumps prior to gaps. 

The mark was difficult 

to describe with a 

simplified written 

prescription; therefore, 

a series of sequential 

steps were followed.
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Managing Sierra Nevada Forests

To help markers recognize when to change their mark depending on forest 

conditions and stand location, they were trained to use a stepwise decision tree:

1. What is the emphasis: habitat/restoration or public safety?

2. What type of microsite or group are you in?

a. Is it a high- or moderate-quality potential fisher rest site?

b. If not, does the area provide an opportunity for a regeneration opening?

c. Is tree structure grouped or better for the matrix of low-density large 

pine trees?

3. What landscape zone are you in?

4. What is the basal area retention in this microsite and landscape zone? 

In step 1, the marker decided whether to emphasize ladder fuel reduction or 

canopy cover retention. Step 2 proved to be the most important step because the 

marker needed to identify whether to leave a tree group, create or expand a gap, or 

create more low-density pine-dominated matrix. Steps 3 and 4 required an awareness of aspect and slope position, and the overall basal area target, respectively.

Marking guidelines identified the choices relative to microsites and landscape 

zone in any particular stand. For example, there might be two landscape zones and 

four microsites (priorities) in a stand. Typically a marker would be given a residual 

basal area for pine groups, individual scattered pine, and fir groups. They were also 

told the likeliest location of high-quality fisher rest sites. Pine and fir group residual 

basal area would differ between landscape zones. Residual basal area would remain 

the same for the fisher rest site and lowered for scattered pines. Thus markers would 

use the five-step process in any stand to identify the appropriate residual basal area 

and tree characteristics for retention or removal. Marking guidelines were rarely 

more complex than this example.

Lessons Learned

Three main lessons were learned from the Dinkey project:

1. Move in a stepwise fashion to develop consensus on restoration treatments. 

The Dinkey project focused on a planning process that included the following steps:

a. Clarify the overall strategy contained in GTR 220. Forum members 

needed to agree upon GTR 220 principles of restoration. 

b. Develop desired conditions consistent with GTR 220 and local forest 

processes. The Dinkey collaborative group sought to develop desired 

conditions consistent with the role of frequent fire. These desired conditions allowed collaborative members to identify forest structural components for retention or removal. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

c. Conduct field visits to identify key microsites and groups. Field visits 

with collaborative group members allowed retention priorities to be 

based upon observed rather than assumed stand conditions. 

d. Develop vegetation maps that capture within-stand heterogeneity. Highresolution mapping and subsequent modeling provided a context for 

decisions and end results. 

e. Develop decision priorities that are consistent with retaining key structures. Marking guidelines came only after looking at stand structures 

and discussing small-scale forest heterogeneity.

f. Contract development that carries forward the previous steps. To that 

end, a stewardship contract was developed to implement the removal 

of commercial size trees, and precommercial size material as biomass, 

and treatment of existing and activity-created slash. The contract had 

to be modified to allow for the protection and identification of fisher 

rest sites and the small trees contained within them. The Dinkey project 

used flagging and a map of rest site locations to identify fisher rest 

sites. This proved tedious, underscoring the need for more efficient 

methods to differentiate high-quality fisher rest sites from the surrounding forest matrix. More work with contractors needs to be done to 

use global positioning system or less labor-intensive means of identifying contractually important field areas.

g. Ongoing collaborative monitoring of the implementation and effectiveness of forest restoration treatments provided the opportunity for group 

learning, trust building, and adaptive management.

2. Use language and treatment descriptions consistent with the restoration 

objectives.

a. The scale of restoration treatments required a set of terminology that 

described forest structural components consistently between forum 

members and marking crews. Clumps, groups, openings, gaps, aspect 

zones, rest sites, and microsites were terms used to convey the desired 

conditions both within stands and across the forest landscape. 

b. Retention of vertical within-stand heterogeneity within the context of 

tree density management is difficult to convey on paper. Field visits to 

sample marked areas or key structures proved most helpful. Photos or 

images of these same structures would be helpful in the future.
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Managing Sierra Nevada Forests

c. Focus restoration priorities on retaining forest structures not on eliminating structures. Language in marking guidelines and priorities that 

focused on tree retention proved most helpful in allowing markers and 

collaborative members to visualize end results. Leave tree marking 

proved less practical owing to the great number of trees being retained 

across the project area. Far fewer trees needed to be marked for removal 

than for retention. However, leave tree marking was conducted in 

sample marking areas to aid visualization. 

d. Articulate how the removal or retention of any tree or group moves you 

closer to restoration goals. Collaborative group members were comfortable when removal of intermediate-size trees (20- to 30-in [51 to 76 cm] 

diameter at breast height) was based on meeting the desired conditions 

and ecological restoration objectives.

3. Train crews and keep them for more than one or two seasons. An investment in crew training and the ability of crews to apply marking guidelines 

at a group or gap scale proved essential in applying restoration treatments. 

The application of the restoration guidelines in the Dinkey area was possible because of the experience level and dedication of the marking crew. 

What set the stage in the Dinkey project for building collaboration was first 

getting agreement on the desired future conditions. While the project began with a 

focus on fuels reduction, it transitioned to forest restoration, provision of wildlife 

habitat, and reducing potential wildfire severity. All participants immediately 

agreed that zones adjacent to homes should be prioritized for fuels reduction. 

Outside of those areas, however, the effort was to balance all three objectives by 

increasing forest heterogeneity. Any discussion that started to jump to specific 

locations in the forest or controversial issues (i.e., if, where, and when a larger tree 

might be thinned) was reined back until the collaborative group reached agreement 

on a desired future condition. Sometimes this was difficult, because participants 

were visualizing particular locations or wanted to discuss economic or revenuerelated concerns.

The project design was based on the classification of topographic categories 

and establishment of treatment criteria in each category. This often started with 

suggesting initial prescriptions and working through the details with the collaborative group. After silvicultural and fuels management review, if the treatment did 

not appear to achieve the desired objective, the collaborative group was asked for 

further input. Although the forest staff might have ideas about the next logical 

step, giving the group room to see limitations and propose alternatives allowed for 

Any discussion that 

started to jump to 

specific locations 

in the forest or 

controversial issues 

(i.e., if, where, and 

when a larger tree 

might be thinned) was 

reined back until the 

collaborative group 

reached agreement 

on a desired future 

condition. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

more discovery, creativity, and consensus. For practical purposes, the silviculturist 

insisted that whatever treatment was decided upon, the group had to identify what 

target condition and retained basal area was desired.

At this point, there was enough consensus in the group to start working on 

specifics. We discussed where and when larger trees might be thinned and agreed 

that increasing structural heterogeneity, improving wildlife habitat or ecosystem 

restoration were reasonable criteria for selecting larger trees, rather than focusing 

on project economics. When the group visited stands where some larger trees were 

preliminarily marked for removal, the group often agreed with the mark. In places 

where there was disagreement, the silviculturist and marking crew explained the 

reasoning behind the mark and let the group discuss and revise the mark if desired. 

At this point, the collaborative group was matching the mark to the collective vision 

of the forest’s desired future condition—a more diverse landscape that maintained 

or enhanced wildlife habitat, improved fire resiliency, and shifted structure and 

composition toward a pine-dominated, large-tree condition.

References

North, M.; Hurteau, M.; Fiegener, R.; Barbour, M. 2005. Influence of fire and 

El Niño on tree recruitment varies by species in Sierran mixed conifer. Forest 

Science. 51(3): 187–197.

North, M.; Innes, J.; Zald, H. 2007. Comparison of thinning and prescribed fire 

restoration treatments to Sierran mixed-conifer historic conditions. Canadian 

Journal of Forest Research. 37: 331–342.

North, M.P.; Steger, G.; Denton, R.; Eberlein, G.; Munton, T.; Johnson K. 

2000. Association of weather and nest-site structure with reproductive success 

in California spotted owls. Journal of Wildlife Management. 64: 797–807.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Oliver, W.W. 1995. Is self-thinning in ponderosa pine ruled by Dendroctonus bark 

beetles? In: Eskew, L.G., comp. Forest health through silviculture: proceedings 

of the 1995 national silviculture workshop. Gen. Tech. Rep. RM-GTR-267. Fort 

Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station: 213–218.
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Managing Sierra Nevada Forests

Purcell, K.L.; Mazzoni, A.K.; Mori, S.; Boroski, B.B. 2009. Resting structures 

and resting habitat of fishers in the southern Sierra Nevada, CA. Forest Ecology 

and Management. 258: 2696–2706.

Spencer, W.D.; Rustigian, H.L.; Scheller, R.M.; Syphard, A.; Strittholt, J.; 

Ward, B. 2008. Baseline evaluation of fisher habitat and population status and 

effects of fires and fuels management on fishers in the southern Sierra Nevada. 

Unpublished report. http://consbio.org/products/reports/4/. (February 8, 2012). 

Taylor, A.H. 2004. Identifying forest reference conditions on early cut-over lands, 

Lake Tahoe Basin, USA. Ecological Applications. 14: 1903–1920.

Zielinski, W.J.; Truex, R.L.; Schmidt, G.A.; Schlexer, F.V.; Schmidt, K.N.; 

Barrett, R.H. 2004. Resting habitat selection by fishers in California. Journal 

of Wildlife Management. 68: 475–492.
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127

Managing Sierra Nevada Forests

E. Knapp,1 M. North,2 M. Benech,3 and B. Estes4

Introduction

Prior to historical logging and fire suppression, forests 

of the Sierra Nevada were extremely heterogeneous. 

Frequent low- to moderate-intensity fire was partly 

responsible for this heterogeneity, which in turn helped 

make forests resilient to high-severity stand-replacing 

events. Early observers of forests on the west slope 

of the Sierra Nevada noted the arrangement of large 

trees as grouped or clustered (Dunning 1923, Show 

and Kotok 1924) (fig. 12-1). Show and Kotok (1924) 

described the mixed-conifer forest as “uneven aged, 

or at best even-aged by small groups, and is patchy 

and broken; hence it is fairly immune from extensive 

devastating crown fire.” 

A major emphasis in forest management today is 

improving the resilience of stands to large-scale crown 

fires. To put forests on the path toward resilience after 

a long period of fire exclusion, stands are often first 

mechanically thinned, typically using some variation 

of thinning from below, which targets the smaller trees 

and retains the larger and more fire-resistant dominant 

and codominant individuals. With thinning from below, 

crowns of individual trees are typically separated from 

each other, which can lead to a relatively even forest 

structure. This evenness has sometimes been perceived 

to be in conflict with management of habitat for wildlife 

and other forest species. Thinning that produces a more 

1 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 3644 Avtech Parkway, Redding, CA 96002.

2 Research ecologist, U.S. Department of Agriculture, Pacific Southwest Research Station, 

1731 Research Park Dr., Davis, CA 95618.

3 Resource management program area leader, U.S. Department of Agriculture, Forest 

Service, Stanislaus National Forest, No. 1 Pinecrest Lake Rd., Pinecrest, CA 95364. 

4 Province ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Region, Eldorado National Forest, 100 Forni Rd., Placerville, CA 95667.

Chapter 12: The Variable-Density Thinning Study

at Stanislaus-Tuolumne Experimental Forest

Figure 12-1—Mixed-conifer forest structure in 1929, within 

“methods-of-cutting” study units prior to cutting. These plots are 

located in what today is the Stanislaus-Tuolumne Experimental 

Forest within the Stanislaus National Forest. Note the relatively 

even age/size within groups but uneven age/size among groups, 

along with gaps containing robust understory vegetation. 

Duncan Dunning
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GENERAL TECHNICAL REPORT PSW-GTR-237

grouped arrangement of trees may be one means of creating heterogeneity at a scale 

beneficial for wildlife species that prefer different forest structures for nesting, 

roosting, and foraging, and understory plant species that thrive in different light 

environments, while simultaneously increasing resilience to wildfire. 

The high-variability thinning prescription described in this chapter is part of 

a new variable-density thinning study on the Stanislaus-Tuolumne Experimental 

Forest (STEF) designed to investigate the ecological effects of structural variability 

retained during forest thinning operations (Stanislaus National Forest 2010). Three 

forest structure treatments (high variability, low variability, and an unthinned 

control), all with or without prescribed burning as a followup treatment, are being 

compared. The objective of the high-variability thinning treatment is to produce 

an arrangement of trees and degree of spatial complexity similar to what was once 

found in historical forests prior to logging and fire suppression. The study planning 

predates publication of U.S. Forest Service General Technical Report GTR 220 

(North et al. 2009) and is therefore not among the projects designed specifically to 

implement principles therein. We include it here because the objective of the highvariability treatment is similar to a core concept in GTR 220 of increasing spatial 

heterogeneity and thus provides a useful illustration. 

Summary of Findings

1. The high-variability thinning treatment was designed to produce 

similar spatial heterogeneity to what was noted on detailed maps of 

unlogged stands on the Stanislaus-Tuolumne Experimental Forest in 1929. 

These historical maps show trees arranged in distinct groups of varying 

density, intermixed with small gaps averaging about 0.25 ac (0.1 ha) in 

size (range: 0.1 to 0.5 ac) (0.04 to 0.2 ha).

2. Marking prescriptions initially were difficult to write, but crews in 

the field quickly adopted the approach of first identifying gaps and then 

tree groups using a combination of relative density, average tree size, and 

dominant species.

3. The flexibility of the high-variability thinning treatment made it 

easier to respond to differing topography and forest conditions. In 

addition, after some practice, the rate of marking crew progress began to 

approach the usual rate for more traditional prescriptions.
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Managing Sierra Nevada Forests

Context 

The STEF is located near Pinecrest, California, at elevations ranging from 5,200 

to 6,200 ft (1585 to 1890 m). Precipitation averages about 40 in (102 cm) per year 

with about half falling as snow. January minimum temperatures average 19 °F (-7.2 

°C), and July maximum temperatures average 81 °F (27.2 °C). The vegetation is 

representative of much of the mid-elevation mixed-conifer forest on high-quality 

soils throughout the western slopes of the Sierra Nevada. Based on historical 

data and stem maps produced in 1929, dominant conifer species at that time were 

white fir (Abies concolor (Gordon & Glend.) Lindl. ex Hildebr.), sugar pine (Pinus 

lambertiana Douglas), incense cedar (Calocedrus decurrens Torr. Florin), ponderosa pine (P. ponderosa Laws), and Jeffrey pine (Pinus jeffreyi Balf.), in order of 

abundance. Some of the more important shrubs included bearclover (Chamaebatia 

foliolosa Benth), manzanita (Arctostaphylos patula Greene), and several species of 

Ceanothus (C. cordulatus Kellogg, C. integerrimus Hook & Arn, C. parvifolius (S. 

Watson) Trel.). A recently completed fire history study indicates that the historical 

fire-return interval was between 5 and 8 years, but that the last widespread fire 

occurred in 1889 (Skinner 2011). Therefore, about 15 to 22 cycles of fire have been 

missed. 

The high-variability thinning prescription was applied to stands that were 

originally cut in the 1920s. At that time, most trees of merchantable size were 

removed. The forest that emerged in the years since logging and under a regime of 

fire exclusion contains a greater abundance of fir and incense cedar, and less pine 

than the historical forest (details below). 

Information Used

Data about the historical forest structure that was used to develop the high-variability prescription were obtained from stand maps produced as part of a “methods-ofcutting” (MOC) study installed in 1929, under the direction of Duncan Dunning, 

an early U.S. Forest Service scientist. The study evaluated natural regeneration 

and growth of the residual stand after three different logging treatments that were 

representative of logging in the Sierra Nevada at the time. The MOC studies were 

established at other locations in the Western United States, including other sites 

in the Sierra Nevada, but only at STEF were data for ecological variables other 

than trees collected. In addition, the STEF MOC plots are the only ones known to 

remain intact and undisturbed from additional management activities.

For each of the three 10-ac (4 ha) plots, the well-known surveyor, E.A. 

Wieslander, drew extremely detailed stand maps based on data collected in 1929 

(before and after logging). These maps show the location, species, and diameter of 
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GENERAL TECHNICAL REPORT PSW-GTR-237

all trees >3.6 in (9.1 cm), in addition to the spatial extent of shrubs by species and 

regeneration patches by species, snags, and downed logs. The maps were recently 

digitized and data associated with individual trees were discovered at the National 

Archives in San Bruno, California. All trees within plots were remapped in 2007 

and 2008, using modern survey equipment (laser rangefinder with compass module 

mounted on a tripod and connected to a global positioning system unit). Preliminary analyses show that the number of trees >4 in (10.2 cm) in diameter at breast 

height (d.b.h.), which averaged 142 trees per acre (351 trees per hectare) in 1929 

prior to logging (Hasel et al. 1934), has more than doubled today. The basal area in 

the MOC plots increased from 242 ft 2/ac (55.6 m2/ha) in 1929 to 308 ft2/ac (70.8 

m2

/ha) today. Lack of light on the forest floor has resulted in shrubs declining from 

about 30 percent cover in 1929 to about 2 percent today. The proportion of basal 

area composed of pine species has declined while white fir and incense cedar have 

increased. 

The 1929 prelogging data provide a model for forest structure that the highvariability thinning prescription is based on. These data show that trees were 

arranged in groups of varying density, basal area, and canopy cover, interspersed 

with gaps (fig. 12-2). Some groups consisted of widely spaced large trees, while 

others contained a much higher tree density with interlocking crowns. The 

historical data allowed us to describe some of the variability among tree groups, 

and also to quantify the spatial scale of the groups and gaps. Within these 10-ac 

(4-ha) plots, gaps averaged slightly less than a quarter of an acre (range 0.08 to 

0.51 ac) (0.03 to 0.21 ha), with one gap occurring approximately every 2 acres 

(0.81 ha). 

This gap size is similar to what has been reported in other forests in the 

Western United States with a history of frequent low- to moderate-intensity fire. 

Gaps in giant sequoia/mixed-conifer forest after numerous prescribed burns were 

found to average 0.25 ac (0.1 ha) (Demetry, unpublished data, cited in Stephenson 

[1999]), and a different survey of similar forests showed a large range of gap sizes 

between 0.16 and 2.89 ac (0.06 to 1.17 ha) (Demetry 1995). Most other studies 

have focused on the size of tree groups rather than gaps. Assuming groups of trees 

became established in gaps, group size should be less than the gap size (Stephenson 

1999), because gaps have an edge effect with more light and other resources for 

tree growth in the center of the gap. Bonnickson and Stone (1981) found significant 

clustering of large living and dead trees (together approximating the historical 

stand) in mixed-conifer/giant sequoia forest in Kings Canyon National Park, and 

reported aggregations of trees ranging between 0.07 to 0.40 ac (0.03 to 0.16 ha). 

 Lack of light on 

the forest floor has 

resulted in shrubs 

declining from about 

30 percent cover in 

1929 to about 2 

percent today.
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Managing Sierra Nevada Forests

Using a 1938 stand map from unlogged east-side ponderosa pine at Blacks Mountain (Lassen National Forest), Youngblood et al. (2004) found a random distribution 

of trees at smaller scales (<28 ft) (<8.5 m), but clustering at larger scales up to 79 ft 

(24.1 m). Assuming a circular shape, this would equate to tree group size of 0.11 ac 

(0.04 ha). In a stand reconstruction from old stumps and logs, North et al. (2007) 

determined clustering to occur at a scale up to 197 ft (60 m) [if circular, this would 

be a 0.69-ac area (0.28 ha)] in mixed-conifer forest. These patterns are not limited 

to forests in California. In ponderosa pine forests of Arizona, Cooper (Cooper 1960, 

1961) reported that the size of tree groups ranged between 0.15 and 0.32 ac (0.06 

and 0.13 ha), while White (1985) found a somewhat broader range of group sizes 

(0.05 to 0.72 ac) (0.02 to 0.29 ha), but a very similar average of 0.25 ac (0.1 ha). A 

reconstruction of a ponderosa pine forest in Washington indicated an average group 

size of 0.01 ac (0.004 ha) in more mesic plots to 0.49 ac (0.2 ha) in the driest plots 

Figure 12-2—Stem map from 1929 showing trees >10 in (25.4 cm) diameter in an uncut stand, 

“methods-of-cutting” plot No.10, Stanislaus-Tuolumne Experimental Forest. Gaps and approximate 

groupings of trees of similar size, spatially separated from other groups, were drawn in for illustration. DBH = diameter at breast height.
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GENERAL TECHNICAL REPORT PSW-GTR-237

(Harrod et al. 1999). Graham and Jain (2005) noted the existence of tree groups 

averaging 0.01 to 0.10 ac (0.004 to 0.04 ha) in ponderosa pine forests of southern 

Idaho. An analysis of all western North America studies of tree spatial patterns in 

fire-dependent forests found a common mosaic of three elements usually manifest 

at scales <1 ac (0.4 ha): openings, single trees, and clumps of trees with interlocking 

crowns (Larson and Churchill 2012). 

Implementation

In developing the high-variability thinning prescription, we first examined existing 

published prescriptions designed to increase spatial variability. Graham and Jain 

(2005) introduced a silvicultural concept called “free selection” with the similar 

goal of increasing forest complexity. Free selection is described as a hybrid between 

even-age and uneven-age management, similar in concept to applying an even-age 

system in a fine-scale mosaic. One component of free selection is to include openings to regenerate early successional species. A prescription developed by Harrod 

et al. (1999) helps to define the scale of patchiness. Based on historical forest 

structure data, Harrod et al. (1999) visualized the forest as a series of approximately 

98-ft diameter (0.17 ac) (0.07 ha) circles, each thinned to a varying extent—areas 

with smaller diameter trees thinned to 39 percent to 72 percent of maximum stand 

density index (SDI), depending on average tree diameter, to areas with larger trees 

thinned to 150 percent of maximum SDI. The Harrod et al. (1999) prescription also 

called for leaving the best trees, based on crown form, regardless of spacing. For 

the high-variability prescription at STEF, we used some of the same concepts and 

ideas outlined by Harrod et al. (1999) and Graham and Jain (2005), but refined our 

marking guidelines using data from the nearby 1929 MOC plots. 

The first step in marking the stands was to walk through the entire unit and 

identify locations where gaps would be created. These gaps averaged one quarter of 

an acre (range 0.1 to 0.5 ac) (0.04 to 0.2 ha) and one was placed approximately every 

2 ac (0.81 ha). Gaps varied in shape with dimensions taking into consideration 

shading from adjacent trees so that higher light conditions were produced. Priorities for gaps were areas currently lacking pine, and fir groups with evidence of root 

disease. Some gaps were designed to enlarge existing gaps (e.g., centered around 

remnant black oaks (Quercus kelloggii Newberry)), while others were located in 

more productive areas of the stand to ensure opportunities to grow groups of large 

trees, including pines, in the future. Gap edges were marked with flagging. Gaps 

occasionally included one large pine to provide a seed source. If a tree was left in 

the gap, preference was given to trees located near the northern edge of the opening 

where they would not interfere with the amount of light hitting the forest floor. 

An analysis of all 

western North 

America studies of 

tree spatial patterns 

in fire-dependent 

forests found a 

common mosaic of 

three elements usually 

manifest at scales <1 

ac (0.4 ha): openings, 

single trees, and 

clumps of trees with 

interlocking crowns.
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Managing Sierra Nevada Forests

To better visualize the future stand, we used a leave-tree mark. This allowed 

us to also mark to retain patches of regeneration observed during this first walk 

through of the stand. We identified regeneration patches as saplings and young trees 

less than 10 in d.b.h. (25.4 cm), of good health (long crowns) or desired species 

composition (greater than 25 percent of the trees being pine). These regeneration 

patches would normally be removed during the biomass portion of the thinning 

operation. In some cases, the entire regeneration patch was marked for no entry. In 

other cases, just the most desirable young trees were retained at wider spacing. This 

latter situation may eventually lead to portions of the stand with a more open grown 

structure, which may provide important habitat for some wildlife species. 

The second step was to view the portion of the stand not in gaps or regeneration 

patches as a series of continuous groups (similar to methods outlined in Harrod 

et al. 1999), each about a quarter acre, but varying from 0.1 to 0.5 ac (0.04 to 0.2 

ha). The size and shape of groups depended on obvious breaks in composition or 

size of trees in the existing stand. Each group was then marked for thinning to 

either the median basal area target for treed areas (220 ft2/ac; range 170 to 270 ft 2/

ac) (50.5 m2/ha; range 39.0 to 62.0 m2/ha), or to low basal area (120 ft2/ac; range 

70 to 170 ft2/ac) (27.5 m2/ha; range 16.1 to 39.0 m2/ha), or high basal area (320 ft 2/

ac; range 270 to 370 ft2/ac) (73.5 m2/ha; range 62.0 to 85.0 m2/ha). We chose basal 

area as our thinning metric, rather than the SDI proposed by Harrod et al. (1999), 

because we thought it would be easier for a marking crew to visualize. Because 

the historical data suggests that areas of the stand with a higher proportion of pine 

were generally of lower density, fir and cedar were thinned more heavily in groups 

where the largest trees were predominantly pine. In these cases, the existence of 

larger pines within the group determined the basal area category. For the high basal 

area groups, the existing stand was sometimes already at or near the basal area 

target, which resulted in no or few trees being marked for removal. In high basal 

area groups, care was taken in marking so that cut trees were ones that could be 

removed without damaging the residual trees. Each unit within the project ended up 

containing about the same number of each thinning level. However, some parts of 

the unit ended up with more high basal area groups and some parts more low basal 

area groups because the thinning target for each group was dictated by existing 

conditions in the stand rather than being systematically employed.

Within groups, the best trees (generally the largest trees and/or trees with the 

best crown form) were retained regardless of crown spacing. This led to cases 

where leave trees were in closer proximity or farther apart from each other than 

might otherwise occur under standard marking guidelines. Some trees with long 

(deep) crowns were also left to increase canopy cover for wildlife. Because of the 
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GENERAL TECHNICAL REPORT PSW-GTR-237

current lack of pine compared with historical conditions, leave-tree priority among 

conifers was sugar pine > ponderosa/Jeffrey pine > incense cedar > white fir. An 

exception to selection based on size was sometimes made if the group contained 

smaller individuals of the favored pine species mixed with larger firs or cedars. No 

black oaks were cut, but all conifers within the drip line of black oaks were removed 

where damage to the oak could be avoided. Because leave-tree selection was based 

foremost on size and species and secondarily on crown form, some trees with relatively poor vigor (higher probability of mortality in the short term) and other characteristics important for wildlife were maintained. All snags larger than 15 in (38 cm) 

in diameter were retained whenever possible (i.e., when not a safety issue). From a 

starting studywide basal area of approximately 290 ft2

/ac (66.6 m2/ha) (300 ft2/ac 

(68.9 m2

/ha) in the high-variability units), the marking guidelines were designed to 

produce an average postthinning basal area of 200 ft2/ac (45.9 m2/ha) (range 150 to 

250 ft2/ac (34.4 to 57.4 m2/ha)) over the unit (including gaps).

The environmental assessment (EA) for the project was completed by the 

Stanislaus National Forest with the interdisciplinary team consisting of district staff 

and U.S. Forest Service Pacific Southwest Research Station scientists. The decision 

notice was signed in August 2010. Two years of outreach, which became increasingly focused as the research plan and prescriptions evolved, preceded the writing 

of the EA and included tours of the study area by groups representing environmental 

as well as timber industry interests. Thinning commenced in July 2011 (fig. 12-3).

Figure 12-3—Portion of a unit within the “variable-density thinning” study on the StanislausTuolumne Experimental Forest thinned using the high-variability prescription. Photo was taken 

September 14, 2011, shortly after treatment.

Eric Knapp
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Managing Sierra Nevada Forests

Lessons Learned

Importance of Outreach

One of the challenges with writing a prescription to generate a high degree of 

structural variability is describing exactly what will be cut. As noted by Graham et 

al. (2007), complex forest structure defies easy description. Our objective with the 

high-variability prescription was to work with and accentuate residual structure that 

already exists within these second-growth stands. We were interested in what the 

stands will look like after thinning, not what will be removed. Having only stand 

exam data and lacking more detailed information such as complete stand maps, 

it was not possible to accurately describe what will be removed beforehand. We 

purposefully did not include diameter limits in the prescription because diameter 

limits can restrict opportunities for generating structural complexity. However, we 

were also aware of stakeholder concern about the lack of detail provided in metrics, 

such as diameter limits, that are typically stated in thinning prescriptions. Without 

diameter limits, it will be necessary to develop other descriptors that provide a 

sense of accountability to stakeholders. 

We hope that experiments like this one, in which what is removed can be 

quantified after thinning, will provide stakeholders one example of the thinning 

effort required, given the starting conditions, to produce a highly variable structure 

approximating historical stands. Currently, examples are limited. Lacking such 

information, we used historical data and maps to define desired posttreatment stand 

conditions. Field visits with various stakeholder groups were also critical for developing an understanding of objectives and generating some amount of trust. Field 

visits often included walking into the nearby methods-of-cutting plots that were 

established in 1929. Seeing what the stem density, tree arrangement, and understory 

vegetation look like today compared with the 1929 maps provided a powerful visual 

guide. Field visits also included a walk into representative stands targeted for thinning, and discussion about what to cut at different places in the stand to produce the 

desired highly variable structure. On one field visit, tree-marking paint was given to 

participants and, after discussions about objectives, we collectively marked approximately 3 ac (1.2 ha) of a stand. Participants with widely varying backgrounds and 

perspectives came to surprisingly similar conclusions about what trees to leave and 

what trees to remove. 

Training a Marking Crew to Visualize Tree Groups

In standard thinning-from-below prescriptions, marking crews typically make decisions about whether to leave or cut a tree by looking at the health of individual trees 

in relation to immediate neighboring trees. The high-variability prescription takes 

Without diameter 

limits, it will be 

necessary to develop 

other descriptors 

that provide a sense 

of accountability to 

stakeholders. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

a broader view, requiring marking crews to consider a larger patch size (average of 

a quarter-acre group (0.1 ha)), and make decisions not only about how to mark the 

group, but how this group fits with other groups in the stand that are marked differently. This means few black and white decisions and no right or wrong answers, 

which was initially frustrating for some. We found that walking through the stand 

first and finding obvious structures that could be used as anchors helped. These 

included areas with thin soils, root disease pockets, remnant black oaks, and groups 

of larger legacy trees.

On the Stanislaus National Forest, we benefited by having discussions in the 

field and several iterations of sample marks with the district marking crew and 

other forest staff over the course of 3 years as the prescription evolved. In addition 

to members of existing marking crews, the marking crews for the variable-density 

thinning study included personnel with expertise in wildlife, botany, fuels, planning, and silviculture. We spent the first part of the initial days looking over illustrations of stand structure from the 1929 methods-of-cutting plots, which show the 

different types of stand conditions and tree arrangements that once existed. Walking through the stands together and discussing possible structures that could be 

created also helped. Finally, by following the lead of those with the most experience 

implementing this new prescription, those with less experience were able to develop 

a feel for what we were trying to accomplish. Many who helped noted that marking 

stands in this way was a challenge, requiring much more thought than the average 

prescription. However, frequently altering the mark to produce different postthinning structures also encouraged creativity, which was very satisfying to many of 

those involved. 

Metrics for Describing Variability When Marking

We quickly realized that quantifying basal area within each tree group was tedious 

and impractical. In addition, basal area, while easier to visualize and mentally 

calibrate in the field than a percentage of maximum SDI (Harrod et al. 1999), was 

still an imperfect descriptor of the variability created with the prescription. For 

example, a low basal area group could consist of a medium to high density of small 

trees or very widely spaced large trees. In addition, a prism—the common field 

method for estimating basal area—does not cover a defined area and is thus not 

ideal for measurements within discrete tree groups. Therefore, we ended up marking more by “feel” rather than strictly adhering to the basal area targets/ranges for 

each group. We also began to describe groups using a combination of relative 

density (high/medium/low), average tree size (large, medium, small), and dominant 

species (pine, fir, incense cedar), rather than basal area. High-density areas were 

characterized by leave trees with interlocking or closely spaced crowns, while trees 

This means few black 

and white decisions 

and no right or wrong 

answers, which was 

initially frustrating for 

some. 
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Managing Sierra Nevada Forests

in low-density areas generally were relatively widely spaced (though not at a regular 

spacing, in most cases). Medium-density areas were intermediate, approximating 

densities used in standard thinning prescriptions for this forest type. (Note: while 

the tree densities within high, medium, and low groups generally also resulted in 

basal areas within the ranges listed in the prescription, some additional work still 

needs to be done to quantify these structural differences within the marked stands, 

using metrics most relevant to marking crews in the field.) For tree size, large was 

assumed to be leave trees averaging >24 in, (61 cm) medium = 14 to 24 in (36 to 

61 cm), and small = <14 in (36 cm). These tree size categories can readily be 

tailored to the stand conditions at a site. 

Spatial Scale

While we attempted to vary the mark in groups averaging about a quarter acre, 

the actual size of the groups ended up exceeding this value more often than not. 

Perhaps having a larger number of marking crew members working together caused 

the collective broader view. However, obvious boundaries within the stand such 

as changes in tree density, average tree size, or species composition also tend to 

occur at larger spatial scales today. Sometimes crews would continue to mark in one 

type of stand structure until a different type of stand structure was reached rather 

than breaking up areas that are relatively homogeneous today. To mark to produce 

discontinuities at the scale historical forests were structured may therefore require 

frequent recalibration of spatial-scale targets. 

Time/Effort Required

One of the concerns voiced was the extra time, effort, and expertise marking such 

complex prescriptions might require if implemented on a broader scale. Several 

observations suggest that this may not be as big of an obstacle as initially feared. In 

our case, we were more rigid in implementing some aspects of the prescription (e.g., 

requiring five gaps in each 10-ac [4-ha] unit) than needs to be the case outside of 

research. While progress was initially slow until the marking crew became comfortable visualizing the forest in this new way, speed quickly increased throughout 

the 2-week marking period. By the time we finished, a marking crew of three (only 

two carrying paint, while the third produced a hand-drawn map recording what 

was done throughout the stand) was able to mark about 13 to 15 ac (5.3 to 6.1 ha) 

in a day. While still less than a seasoned marking crew can accomplish for simpler 

prescriptions, it is not unreasonable to expect that speed would continue to improve 

with additional experience. This prescription may not lend itself to the traditional 

format of a marking crew of five working in unison and each member taking an 

adjacent strip—a team of two working on a unit together may ultimately be the 

most efficient. 

One of the concerns 

voiced was the extra 

time, effort, and 

expertise marking such 

complex prescriptions 

might require if implemented on a broader 

scale. Several observations suggest that 

this may not be as 

big of an obstacle as 

initially feared.
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GENERAL TECHNICAL REPORT PSW-GTR-237

References

Bonnicksen, T.M.; Stone, E.C. 1981. The giant sequoia-mixed conifer forest 

community characterized through pattern analysis as a mosaic of aggregations. 

Forest Ecology and Management. 3: 307–328.

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

pine forests since white settlement. Journal of Forestry. 92: 39–44.

Cooper, C.F. 1961. Pattern in ponderosa pine forests. Ecology. 42: 493–499.

Demetry, A. 1995. Regeneration patterns within canopy gaps in a giant sequoiamixed conifer forest: implications for forest restoration. Flagstaff, AZ: Northern 

Arizona University. 266 p. M.S. thesis.

Dunning, D. 1923. Some results of cutting in the Sierra forests of California. 

Department Bulletin No. 1176. Washington, DC: U.S. Department of 

Agriculture. 27 p.

Graham, R.T.; Jain, T.B. 2005. Application of free selection in mixed forests of 

the inland northwestern U.S. Forest Ecology and Management. 209: 131–145. 

Graham, R.T.; Jain, T.B.; Sandquist, J. 2007. Free selection: a silvicultural 

option. In: Powers, R.F., ed. 2005 national silviculture workshop: restoring 

fire-adapted ecosystems. Albany, CA: U.S. Department of Agriculture, Forest 

Service, Pacific Southwest Research Station: 121–156. 

Harrod, R.J.; McRae, B.H.; Hartl, W.E. 1999. Historical stand reconstruction in 

ponderosa pine forests to guide silvicultural prescriptions. Forest Ecology and 

Management. 114: 433–446.

Hasel, A.A.; Wohletz, E.; Tallmon, W.B. 1934. Methods of cutting, California 

Forest and Range Experiment Station, Stanislaus Branch, Plots 9, 10, and 11, 

Progress report. On file with: U.S. Department of Agriculture, Forest Service, 

Pacific Southwest Research Station, 3644 Avtech Parkway, Redding, CA 96002.

Larson, A.J.; Churchill, D. 2012. Tree spatial patterns in fire-frequent forests 

of western North American, including mechanisms of pattern formation and 

implications for designing fuel reduction and restoration treatments. Forest 

Ecology and Management. 267: 74–92.

North, M.; Innes, J.; Zald, H. 2007. Comparison of thinning and prescribed fire 

restoration treatments to Sierran mixed-conifer historic conditions. Canadian 

Journal of Forest Research. 37: 331–342.
139

Managing Sierra Nevada Forests

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Show, S.B.; Kotok, E.I. 1924. The role of fire in the California pine forests. 

Bulletin No. 1294. Washington, D.C.: U.S. Department of Agriculture. 80 pp.

Skinner, C. 2011. Personal communication. Geographer, U.S. Department of 

Agriculture, Forest Service, Pacific Southwest Research Station. 3644 Avtech 

Parkway, Redding, CA 96002.

Stanislaus National Forest. 2010. Experimental Forest Research (30298), 

Environmental Assessment. July 2010. 

Stephenson, N.L. 1999. Reference conditions for giant sequoia forest restoration: 

structure, process, and precision. Ecological Applications. 9: 1253–1265.

White, A.S. 1985. Presettlement regeneration patterns in a southwestern ponderosa 

pine stand. Ecology. 66: 589–594.

Youngblood, A.Y.; 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.
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141

Managing Sierra Nevada Forests

Chapter 13: Applying GTR 220 Concepts

on the Sagehen Experimental Forest

Summary of Findings

1. With GIS, the Sagehen fuels reduction project was 

partitioned into subunits based on topographic 

categories, and each subunit was designated with 

an emphasis that established a priority for providing 

habitat, reducing fuels, or restoring forest resilience. 

2. Emphasis areas allow reconciliation of conflicting demands by providing due attention to all of 

the chosen priorities. Different prescriptions were 

developed for each of the different emphases, allowing 

silviculture to be tailored to each area’s priorities. 

3. Field trips and test plots helped ground discussions

so participants could visualize how new prescriptions 

would alter forest conditions.

1 National coordinator for experimental forests and ranges, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, The John Muir Institute, One 

Shields Ave., University of California, Davis, CA 95616.

2 Vegetation management office, U.S. Department of Agriculture, Forest Service, Tahoe 

National Forest, Truckee Ranger District, 10811 Stockrest Springs Rd., Truckee, CA 96161. 

P. Stine 1 and S. Conway2

Introduction

Applying science to the practice of forest 

management is a difficult process. Scientific 

results tend to be expressed in terms such as 

variances, confidence intervals, and probability distributions. Rarely does science 

provide unequivocal information, yet land 

managers must make definitive decisions on 

the ground. The General Technical Report 

“An Ecosystem Management Strategy for 

Sierran Mixed-Conifer Forests,” published 

by the U.S. Forest Service (hereafter GTR 

220) (North et al. 2009) presented some 

important concepts for land managers to 

consider; however, implementation of these 

principles into detailed, site-specific application requires some novel approaches. 

Context

The “Sagehen Fuels Reduction Project” began almost 10 years ago with the goal of 

reducing the risk of a high-severity fire. Over this period, several plans were developed. Early in 2010, the Truckee Ranger District, the Pacific Southwest Research 

Station, the University of California at Berkeley, and copartners in managing the 

experimental forest, agreed to take a step back from the internal planning that had 

been completed to date. In its place, they initiated a collaborative planning process 

to engage all interested public and private parties to thoroughly examine the issues 

pertaining to fuels reduction management. Strong encouragement was offered for 

this idea from Sierra Forest Legacy, a prominent consortium of environmental 

groups concerned with forest management in the Sierra Nevada. A grant was 

obtained from the Sierra Nevada Conservancy to support an independent facilitator, 
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GENERAL TECHNICAL REPORT PSW-GTR-237

and the effort was launched in May 2010. One constraint on this effort was to limit 

planning to the areas covered by previous planning efforts where a suite of survey 

activities had already been completed. These required surveys (e.g., of archeological sites) are expensive and time consuming. Opening up the planning process to 

the entire basin would have added significant costs and time to the project. Thus 

the collaborative planning team (the team) agreed to view this project as a first step 

toward a longer term set of objectives that could be developed and implemented 

over time in the Sagehen basin. 

Sagehen presented an ideal test bed for developing innovative ideas for forest 

management for a number of reasons. Perhaps foremost, almost the entire basin was 

designated as an experimental forest in 2005. There are 80 experimental forests and 

ranges throughout the United States, designated specifically to provide an environment where research can examine new forest management methods. The Sagehen 

basin has also been the home of the Sagehen Creek Field Station of the University 

of California at Berkeley for over 60 years. A wealth of research information and 

monitoring data has been collected in this area. In addition, when Truckee Ranger 

District staff first contemplated some fuels reduction treatments, scientists from 

the University of California developed a research approach to examine the effects 

of Strategically Placed Area Treatments (SPLATs), the principle landscape fuels 

reduction strategy employed by the Forest Service throughout the Sierra Nevada 

(Finney 2001). Research has a prominent role at Sagehen and offers some important 

advantages for trying new management ideas.

The Sagehen basin is a 9,000-ac (3642-ha) watershed at the upper reaches of 

Sagehen Creek, a tributary of the Truckee River just on the east side of the Sierra 

Nevada range, about 10 mi (16 km) north of Truckee, California. The west end 

of the basin begins at the crest of the Sierra Nevada at just over 9,000 ft (2743 m) 

elevation and extends east, ultimately flowing into Stampede Reservoir. Five major 

vegetation cover types can be found in the basin: herbaceous (fen, wet montane 

meadow, and dry montane meadow), montane shrub, mixed conifer, true fir, and 

conifer plantation. The majority of the basin is in mixed conifer (Jeffrey pine 

[Pinus jeffreyi Balf.], incense cedar [Calocedrus decurrens Torr. Florin], white 

fir [Abies concolor (Gordon & Glend.) Lindl. ex Hildebr.]) or a true fir (red fir 

[Abies magnifica A. Murray bis] and white fir) at higher elevations. The basin has 

a Mediterranean type climate with cold, wet winters and warm, dry summers. 

Monthly average maximum temperature ranges from 39 °F (3.9 °C) in December 

to 79 °F (26.1 °C) in July; monthly average minimum temperature ranges from 

14 °F (-10 °C) in January to 37 °F (2.8 °C) in July. Annual precipitation is about 33 
143

Managing Sierra Nevada Forests

in (83 cm); snowfall accounts for greater than 80 percent of the annual precipitation 

and averages over 200 in (508 cm).

The basin is almost entirely national forest land within the Truckee Ranger 

District of the Tahoe National Forest. Portions of the basin have been subject to 

high-severity fire in the past, most notably the Donner Fire that occurred in the fall 

of 1960. Staff on the Truckee Ranger District recognize the risk of another highseverity fire and several fuel reduction plans have been in development. 

Information Used

To our advantage, we had a fairly rich foundation of data with which to work. Key 

data sources included vegetation maps (both recent and from ca. 1980), detailed 

forest stand plot data and stand exam data, American marten (Martes americana) 

survey data (Moriarty et al. 2011), and published research findings and recommendations from several different time periods. Perhaps most important was the 

planning and execution of two test field plots to demonstrate the ideas of spatial 

heterogeneity. These test plots provided both visual examples and quantitative data 

for what dense cover areas and small openings looked like and what the resulting stand composition and structure would be after treatment (fig. 13-1). We even 

included a prescribed burn for one of the two test plots. This proved very effective 

in communicating the anticipated outcomes of treatments to the collaboration team. 

Figure 13-1—Test plot mechanically thinned and prescribe burned at the Sagehen Experimental 

Forest to produce a group and gap structure.
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GENERAL TECHNICAL REPORT PSW-GTR-237

Not all localities have this level of information, but, by the same token, every 

location has limitations in data availability. Even in this situation, as on many 

national forests, we wanted more data. An important feature of this effort was the 

presence of a facilitator. Among many tasks, our facilitator particularly helped 

present a neutral position, kept meetings progressing and the project on pace, and 

organized efforts to gather and assimilate feedback. We also had a technical working group, particularly the professionals on the district staff, who brought a positive, 

problemsolving attitude. We encountered many instances in which we had to adjust 

expectations and address problems, but we always worked within the principle that 

a solution could be found. 

Implementation

Perhaps the biggest challenge was incorporating the concept of landscape heterogeneity at multiple spatial scales into silvicultural prescriptions. As the team 

developed approaches to incorporate heterogeneity at different spatial scales (e.g., 

retention of small patches of dense cover areas embedded within certain emphasis 

areas), we realized that it would be difficult to translate into a prescription and 

to write direction for a marking crew. Implementing these ideas using standard 

silvicultural practices that are grounded in defining and managing toward average 

conditions of a stand will be difficult. Promoting forest heterogeneity, particularly at 

multiple spatial scales, is antithetical to some standard forest management practices 

(e.g., equally spacing between leave trees to maximize growth and resistance to 

crown fire [fig. 6-2]). At present, there are no simple silvicultural tools available 

to operationalize this approach. Yet there are considerable benefits (accompanied 

inevitably with growing pains) to emulating the landscape complexity created by 

an active fire regime.

Lessons Learned 

The innovations that made this project unique and intriguing include some applications that are easily transferable and others that will still need development. The 

lessons learned offer a starting point for other land managers. New tools have been 

developed to assess within-stand heterogeneity (chapter 9) and to divide a forested 

landscape in different topographic categories (chapter 10). Other localities in the 

Sierra Nevada are exploring ways to implement GTR 220 concepts, but there are 

still challenges that need to be addressed.

The process was intended to prepare the Truckee Ranger District to move 

forward with National Environmental Policy Act (NEPA) procedures while providing ample advanced opportunity for satisfying the concerns of all involved parties. 

Perhaps the biggest 

challenge was 

incorporating the 

concept of landscape 

heterogeneity at 

multiple spatial scales 

into silvicultural 

prescriptions.
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Managing Sierra Nevada Forests

The expectation was to apply the concepts of GTR 220 to accomplish an array of 

objectives for a single landscape. By discussing and exploring issues in advance of 

any official NEPA action, the team could collectively reveal and deal with many 

issues prior to crafting and putting forth a proposed action. The key advantages and 

discoveries of this process we implemented and that may be transferable to similar 

forest management planning efforts include:

1. Identify and categorize all potential issues, no matter how small, 

in advance. 

2. Focus attention on the most complex and compelling issues: 

a. Habitat protection and enhancement for a key species of concern, 

American marten (designated as a sensitive species in Forest Service 

Pacific Southwest Region). 

b. Ecological restoration to create more resilient forest stands, capable of 

being sustained through a warming climate, future droughts, and fire.

c. Restoration of fire resiliency; enabling the forest (throughout the basin) 

to be better able to withstand wildfire.

3. Craft objectives to address each of the issues that would be used to direct 

management actions to be taken. The intent was to develop management 

objectives that were achievable, given the current conditions within the 

basin, with an understanding that this was the first of perhaps several treatments that could happen over time. While not achieving everything we 

might strive for, these first treatments would be able to redirect the trajectory of forest structure and composition. 

4. Partition the landscape into subunits using topographic variables (aspect, 

elevation) (chapter 10), one of the key principles in GTR 220, as a determining factor in defining appropriate forest composition and structure, as well 

as other key sources of spatially explicit information, such as the locations 

of high-value marten habitat. Not all areas have equal value (as habitat) 

or have equal ecological potential (for one kind of forest stand or another) 

or generate equal concern (for fire behavior). Partitioning the landscape 

enabled us to explicitly address and provide for the landscape heterogeneity 

that is inherent in this, and most other, project areas. 

5. Formulate “emphasis areas” that dictate which objectives would be given 

priority in a given location (fig. 13-2). Emphasis areas are an important 

innovation that enabled a purposeful differentiation of the landscape to 

promote and manage for the notion of landscape heterogeneity. 

Formulate “emphasis 

areas” that dictate 

which objectives would 

be given priority in a 

given location.
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GENERAL TECHNICAL REPORT PSW-GTR-237

6. Partition the landscape into emphasis areas to better reconcile conflicts and 

provide due attention to all of the chosen priorities. Emphasis areas allowed 

us to apply sound rationale and understand the collective implications of 

these choices at a watershed scale. 

7. Based on these objectives, craft different silvicultural strategies to meet the 

needs of each of the emphasis areas. Some of these silvicultural prescriptions employed relatively conventional approaches, whereas others required 

innovations to achieve the intended outcomes.

Figure 13-2—Sagehen Experimental Forest with treatment areas classified by emphasis area. 

Emphasis areas are (1) high-value marten habitat on north-facing slopes, on ridges, and on higher 

elevation south-facing slopes (above 6,725 ft) (2050 m); (2) drainage bottoms with high-value 

marten habitat; (3) high-value marten habitat on lower elevation (below 6,725 ft) (2050 m) southfacing slopes; (4) drainage bottoms that do not currently support marten habitat; (5) north-facing 

slopes that are not currently marten habitat; (6) vegetation types not identified as marten habitat 

on south-facing slopes; (7) vegetation types not identified as marten habitat on ridges; and (8) 

aspen stands targeted for ecological restoration. NFS = National Forest System.
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Managing Sierra Nevada Forests

A number of details are unresolved, most notably the translation of the written objectives and prescriptions to crews who will mark stands for treatment. This 

step is always a delicate link in the process; more so with the novel strategies 

imbedded in this approach. Plans for handling this process include members of the 

collaborative planning team joining district staff in the exploratory field efforts and 

subsequent training sessions for the crews. However, experiences from the test plots 

suggest a fairly quick learning process for understanding the intentions of variable 

thinning and the other features of this approach. Overall, we see the efforts accomplished to date as a good example of how the principles of GTR 220, combined with 

an open process with ample opportunity for input from all interested parties, can 

lead to well-founded forest management strategies.

References

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

modifying fire growth and behavior. Forest Science. 47: 219–228.

Moriarty, K.M.; Zielinski, W.J.; Forsman, E. 2011. Decline in American marten 

occupancy rates at Sagehen Experimental Forest, California. Journal of Wildlife 

Management. 75: 1774–1787.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. Gen. Tech. 

Rep. PSW-GTR-220. 2nd printing, with addendum. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.
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GENERAL TECHNICAL REPORT PSW-GTR-237
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Managing Sierra Nevada Forests

Chapter 14: Clarifying Concepts

1 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 1731 Research Park Dr., Davis, CA 95618.

2 National coordinator for experimental forests and ranges, U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Research Station, The John Muir 

Institute, One Shields Ave., University of California, Davis, CA 95616.

M. North1 and P. Stine 2

Introduction

There are some topics that continue to be raised by 

managers that were not sufficiently addressed in 

the first and second edition of U.S. Forest Service 

General Technical Report GTR 220 “An Ecosystem 

Management Strategy for Sierran Mixed-Conifer 

Forests.” All of them concern issues about where 

and when GTR 220 concepts apply and how these 

concepts relate to current management practices. 

The first section discusses the appropriate ecological conditions where GTR 220 concepts might be 

applied. The second section attempts to clarify the 

types and potential wildlife uses of defect trees in an 

effort to make them more recognizable in the field. 

The third section defines and distinguishes canopy 

cover and closure, an important distinction because 

some current management practices are focused 

on canopy cover targets. Some aspects of GTR 220 

conditions, particularly localized wildlife habitat, 

may be better assessed with canopy closure. The 

final section examines the link between heterogeneity and ecosystem resilience, a core concept behind 

GTR 220’s emphasis on increasing variability in 

managed forests. General Technical Report 220 is 

a conceptual framework for managing forests and 

intentionally lacks the specificity that practitioners 

might sometimes want. We hope that clarifying the 

following concepts may help elucidate the GTR’s 

intent without constraining management options. 

Summary of Findings

1. GTR 220 concepts could be applied to forest 

types that historically had low-intensity, 

frequent fire regimes in locations with 

topographic relief.

2. “Defect” structures used by wildlife are often 

large live or dead trees with decay, irregular 

bole or crown shapes, broken tops, broomed 

foliage or hollows created by torn branches

(examples in appendix).

3. Canopy closure, the percentage of the sky 

hemisphere obscured by vegetation over a 

point, should be distinguished from canopy 

cover, a measure of canopy porosity averaged 

over a stand. For some wildlife, including 

several sensitive species, high variability in 

canopy closure may be as important as stand 

average canopy cover.

4. Heterogeneity in vegetation structure and 

composition has been strongly linked to 

ecosystem resilience, but direct empirical 

evidence is sparse. Increasing research suggests microclimate variability and refugia from 

temperature extremes may be one mechanism 

linking site and vegetation heterogeneity with 

ecosystem resilience. 
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Forest Types and Landscapes Where 

GTR 220 Concepts Apply

In a broad sense, the GTR 220 strategy could be applied to any low-intensity, 

frequent-fire forest community within the Western United States. These forests generally are the highest priority for fuels reduction and forest restoration treatments 

because of their potential to burn at uncharacteristically high severity in the event 

of a wildfire after decades of fire suppression (Brown et al. 2004). The management 

concepts hinge on mimicking the variable forest conditions that would have been 

created by the effect of topography on fire behavior (North et al. 2009; however, 

see Scholl and Taylor 2010). Areas with no topographic relief may still have experienced variable fire intensities that create a patchy landscape. That variability 

was probably influenced by weather conditions during the burn or small-scale 

differences in fuels, making the pattern of the resulting forest conditions difficult 

to predict. The topographic “roughness” necessary to start directly influencing fire 

intensity has not been studied in the Sierra Nevada. Working with large, widely 

distributed fire scar data, research in eastern Washington mixed-conifer forests 

has started to examine interactions between topography and the scale of fire events 

(Kellogg et al. 2008, Kennedy and McKenzie 2010). These studies suggest modern 

fires are larger than historical burns, overriding topographic features that often 

constrained past wildfires. Contrasts between flatter and more rugged “firesheds” 

suggest that historically, topography did have a bottom-up influence on fire size, 

but the “roughness” at which this occurs has yet to be quantified (Kennedy and 

McKenzie 2010).

In Sierra Nevada landscapes with some topographic relief, forest types with a 

historically frequent, low-intensity fire regime include mixed conifer, ponderosa 

pine (Pinus ponderosa Lawson and C. Lawson), Jeffrey pine (P. jeffreyi Balf.), 

Douglas-fir (Pseudotsuga menziesii Mirbel Franco), giant sequoia (Sequoiadendron 

giganteum (Lindl.) J. Buchholz), and combinations of white fir (Abies concolor

(Gordon & Glend.) Lindl. ex Hildebr), incense cedar (Calocedrus decurrens Torr. 

Florin), California black oak (Quercus kelloggii Newberry), and sugar pine (P. 

lambertiana, Douglas) (Sugihara et al. 2006). Many forests, however, at higher 

elevation or with more mesic conditions such as red fir (A. magnifica A. Murray bis), lodgepole pine (P. contorta Douglas ex Lounden var. Murryana (Balf.) 

Engelm), and western white pine (P. monticola Douglas ex D. Don) have different 

fire regimes (i.e., more infrequent and mixed or high severity), and forest conditions 

may not have been as strongly influenced by topography. The GTR 220 strategy 

also is probably not appropriate for some forests in northern California with a high 

hardwood composition (e.g., >30 percent of basal area) that can occur in forests with 

In a broad sense, the 

GTR 220 strategy 

could be applied to any 

low-intensity, frequentfire forest community 

within the Western 

United States.
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Managing Sierra Nevada Forests

an abundance of tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehder), madrone 

(Arbutus menziesii Pursh), or interior live oak (Q. wislizeni A. DC.) mixed with 

Douglas-fir and ponderosa pine sometimes referred to as mixed evergreen. The low 

densities and gap conditions suggested by GTR 220 for drier conditions might favor 

a transition of treated areas to hardwood dominance unless the area was repeatedly 

treated with mechanical thinning or prescribed fire (Stuart et al. 1993).

Defect Trees

What characteristics make a “defect” tree valuable habitat for wildlife? Although 

this topic is frequently raised, preferred tree structural conditions for many wildlife 

species have not yet been specifically defined in the literature for most species. 

Most of the available research has focused on a few sensitive species such as the 

fisher (Martes pennanti) or spotted owl, or general groups such as bats, small 

mammals, and cavity-nesting songbirds. Furthermore, the number of studies 

that occurred in the Sierra Nevada is limited. There is evidence, however, of the 

preferred use patterns for some well-studied individual and groups of species in 

western coniferous forests.

Several studies have examined the role of legacy trees; large, old individuals 

left in a matrix of younger second growth following a past timber harvest or other 

disturbance. In commercially managed coastal redwoods (Sequoia sempervirens

(Lamb. ex D. Don) Endl.), Mazurek and Zielinski (2004) found significantly higher 

diversity and richness of the wildlife they were surveying (bats, small mammals, 

and birds) in forests that contained some old legacy trees and snags. They suggested 

the higher diversity might result from the structural complexity offered by legacy 

trees, particularly the basal hollows produced by fire scarring. Other animals using 

legacy or old-growth residual trees include northern (Strix occidentalis caurina) 

(Moen and Gutierrez 1997, North et al. 1999) and California spotted owls (S. o. 

occidentalis) (Irwin et al. 2000, North et al. 2000), fisher (Zielinski et al. 2004), 

southern red-backed voles (Clethrionomys gapperi) (Sullivan and Sullivan 2001), 

northern flying squirrels (Glaucomys sabrinus) (Carey 2000), and bats (Pierson 

et al. 2006). Although most of these studies do not quantify the characteristics of 

these legacy trees, they note that the trees were often left during earlier timber 

harvest because of some structural “defect.” The exact habitat value of these trees 

is unknown, but they probably offer some kind of special substrate that can provide 

cover and protection from inclement weather and predators. 

Trees and snags selected by primary cavity nesters, woodpeckers and nuthatches, may be particularly important because once vacated, the cavities are used 

by other birds and mammals (Bull et al. 1997). Several studies have found cavity 
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GENERAL TECHNICAL REPORT PSW-GTR-237

availability can limit the abundance of some of these species in managed forests 

(Carey et al. 1997, 2002; Cockle et al. 2011; Wiebe 2011). A meta-analysis of the 

global distribution of tree cavities found that forest management tends to reduce the 

fungal heart-rots most associated with cavity abundance, thereby increasing reliance 

on primary cavity-nesters for creating suitable cavities (Remm and Lõhmus 2011).

A summary of forest structures favored by wildlife in interior forests of the 

Pacific Northwest focused on five conditions: living trees with decay, hollow trees, 

broomed trees, dead trees, and logs (Bull et al. 1997). The first three conditions 

might have been considered “defects” in past silviculture practices focused on stand 

improvement, and systematically removed. Certainly in some highly managed Sierra 

Nevada forests, these structures may be more rare than large, old trees as a result 

of stand improvement management. Bull et al. (1997) suggested identifying these 

structures by looking for dead and broken tops, large dead branches, wounds, fungal 

fruiting bodies, cavities, bole bends (where a new leader formed after top breakage), 

brooms caused by mistletoe, rust fungi, and Elytroderma disease. Bull et al. (1997) 

also suggested retaining large-diameter, relatively intact (decay classes 1 to 3) snags, 

and large (>15 in [38 cm] in diameter), long, and if available, hollow downed logs. 

Example pictures of some of these conditions are presented in the appendix.

The general pattern across these studies is that wildlife use is associated with 

larger trees that have structural characteristics, which can facilitate a cavity or a 

platform, enabling nesting, denning, roosting, or resting. Examples of these structures include irregular bole (e.g., hollows, forks, etc.) and crown (multiple or broken 

tops, platforms, concentrations of dense foliage) shapes. Care will be needed to identify and maintain these structures during mechanical thinning and prescribed fire 

operations. In some cases where these structures are rare, creating a no-mechanicalentry zone or encircling an area with fire line might be warranted. In some areas, 

management practices, such as prescribed fire, should be encouraged for their role in 

actively recruiting these structures. 

Canopy Cover and Closure

Canopy cover is often cited as an important habitat feature for a number of sensitive 

species associated with old-forest conditions in the Sierra Nevada (Hunsaker et al. 

2002). The standards and guides in the 2004 Sierra Nevada Framework (SNFPA 

2004) have specific minimum canopy cover targets designed to provide suitable 

habitat for sensitive species such as the California spotted owl. Some managers 

concerned that canopy cover would fall below levels in the standards and guides 

have been hesitant to create gaps in treated stands. Creating a gap will lower canopy 

closure (a point measure) over the opening, but may not significantly lower canopy 

[Look] for dead and 

broken tops, large 

dead branches, 

wounds, fungal 

fruiting bodies, 

cavities, bole bends, 

brooms caused by 

mistletoe, rust fungi, 

and Elytroderma 

disease... [as well 

as] large-diameter, 

relatively intact snags, 

and large, long, and 

if available, hollow 

downed logs. 
153

Managing Sierra Nevada Forests

cover (a stand-level average). Canopy closure should be distinguished from canopy 

cover to accurately assess forest canopy conditions and characteristics that matter 

to key wildlife species. This distinction is particularly important because, following 

GTR 220 concepts, treatments are intended to produce tree groups, gaps, and areas 

with a low density of large trees. 

Forest canopies are typically measured at two different scales (i.e., point and 

stand), with different instruments, to distinguish between two different qualities 

of canopy structure that create different wildlife habitat features. Jennings et al. 

(1999) distinguish these two structural qualities by referring to the point measure as 

canopy closure and the stand-level measure as canopy cover (fig. 14-1).

Canopy closure is a measurement of the percentage “of the sky hemisphere

obscured by vegetation when viewed from a single point” (Jennings et al. 1999) 

(emphasis added). Closure measures the canopy hemisphere within an angle of view 

(i.e., a cone) over the sample point. Closure provides valuable information about the 

understory light, microclimate, and microhabitat environment at a specific location 

(Nuttle 1997). It is probably most useful for understanding how available light may 

influence plant composition and growth, and the potential climate conditions and 

vegetative cover over a specific microhabitat site (e.g., nest site cover to discourage predation). Traditionally, canopy closure has been assessed with a spherical 

densiometer, “moosehorn,” or hemispherical photograph. Different methods of 

measurement affect the canopy closure estimation (Paletto and Tosi 2009). As the 

viewing angle (i.e., the width of the observation cone) increases, closure estimates 

increase and within-stand variability between point estimates decreases (Fiala et al. 

2006). Spherical densiometers use a reflective mirror held in front of the observer, 

which produces a large viewing angle and hence high canopy closure estimates. 

Spherical densiometers have large measurement errors at the mid-range of canopy 

closure owing to this large viewing angle (Cook et al. 1995). The moosehorn and 

hemispherical photograph reduce this problem because the image is taken straight 

up and the measurement of canopy closure is typically restricted to 45 to 60° off 

of vertical. Hemispherical photographs have a benefit over other closure estimates 

in that computer programs (e.g., the freeware Gap Light Analyzer) can easily and 

precisely calculate the total direct and diffuse light reaching the point on the forest 

floor over the course of a year. These light levels are highly correlated with surface 

microclimate conditions (Bigelow et al. 2011, Ma et al. 2010). 

In contrast, canopy cover is the percentage “of forest floor covered by the 

vertical projection of the tree crowns” (Jennings et al. 1999). Cover is always 

measured vertically with a very narrow angle of view that approaches a point. 

It is a stand-level measure of canopy porosity (e.g., how much rain falls directly 

Canopy closure should 

be distinguished 

from canopy cover 

to accurately assess 

forest canopy 

conditions and 

characteristics that 

matter to key wildlife 

species. 
154

GENERAL TECHNICAL REPORT PSW-GTR-237

Figure 14-1—The difference between canopy closure and canopy cover in forests treated to produce regular and variable tree spacing. 

Illustration by Steve Oerding.
155

Managing Sierra Nevada Forests

on the forest floor) that indicates how much of the forest floor is vertically 

overtopped with canopy. Canopy cover is usually either directly measured with a 

densitometer (sighting tube) or indirectly estimated from plot data using the Forest 

Vegetation Simulator (FVS).3 Typically, direct densitometer measurements are 

taken at 100 or more points, sampled along a walked grid, in which the observer 

records the percentage of points where the sky directly overhead is obscured. 

Densitometer measurements provide a relatively unbiased estimate of canopy cover 

for the particular area (i.e., the walked grid) assuming that the stand is well sampled 

(Korhonen et al. 2006). 

Indirect estimates of canopy cover are often made by FVS based on stand exam 

and plot data. As an indirect estimate, however, FVS assumes a certain amount of 

crown overlap (Crookston and Stage 1999), but it does not account for spatial variability in tree locations (Christopher and Goodburn 2008). Two stands having the 

same number, species, and size of trees will have the same FVS calculated canopy 

cover even if one has regular spacing and the other is mostly open with the trees 

concentrated in high-density clumps. The FVS will tend to underestimate a stand’s 

actual canopy cover if trees are regularly spaced (i.e., less overlap than the model 

would predict). The FVS will overestimate a stand’s actual canopy cover if trees are 

clumped (i.e., greater overlap than the model assumes). The FVS estimates should 

be viewed with caution because the program is unlikely to accurately estimate 

stand-level canopy cover in stands with a high degree of spatial variability or those 

with complex canopy structure such as those resulting from application of GTR 220 

concepts.

The FVS estimates of stand-level canopy cover do not provide information on 

whether a stand has points of high canopy closure habitat associated with some sensitive species. For example, Purcell et al. (2009) compared FVS estimates of canopy 

cover and measures of canopy closure made with a spherical densiometer and a 

moosehorn in five studies of fisher resting sites. They found substantial differences 

in the estimates between the three methods. In another comparison, Ganey et al. 

(2008) evaluated model estimates of canopy cover developed from stand exam data 

with those derived from in-field densitometer (sighting tube) data at sites used by 

Mexican spotted owls (Strix occidentalis lucida). The model estimates ranged from 

50 to 200 percent of field-based measurements, particularly in mesic mixed-conifer 

forest with multilayered canopies (Ganey et al. 2008). 

3 Two other remotely sensed methods of estimating canopy cover are not addressed in this 

discussion; they include using grid overlaps on aerial photographs and light detection and 

ranging (LiDAR).

FVS estimates should 

be viewed with caution 

because the program is 

unlikely to accurately 

estimate stand-level 

canopy cover in stands 

with a high degree of 

spatial variability.
156

GENERAL TECHNICAL REPORT PSW-GTR-237

Canopy cover measurements alone may not capture aspects of canopy structure 

important to some sensitive species because it is a stand-level average. Historical 

forests can provide some inference about canopy conditions that were suitable 

habitat for these species. A recent study using FVS to derive current and historical 

canopy cover estimated an average cover of only 22 percent in 1911 compared to 

current (2005–2007) cover estimates of 28, 42, and 53 percent for the same area 

in moderate, low, and no fire-severity classes, respectively (Collins et al. 2011). In 

general, FVS estimates of stand-level average canopy cover would likely be very 

low if applied to the consistently low tree densities found in reconstruction studies, 

historical data sets, or photographic records. However, almost all of these sources 

indicate that trees were grouped in clusters, suggesting that active-fire regime 

forests had high-canopy closure at many points. 

Assessing point-level canopy closure within treated stands may improve 

assessment of habitat conditions. Using hemispherical photographs, a moosehorn, 

or a spherical densiometer, closure measurements could be collected with a stratified sampling of gap, low-density, and tree cluster conditions (see suggestions in 

chapter 9 section “Using FVS to Assess Heterogeneity”). With GTR 220’s goal 

of producing variable forest structure across a treated area, point-level canopy 

closure values will be low in gaps and areas with a low density of large trees, and 

high in tree groups. Canopy closure, and its coefficient of variation, can provide an 

assessment of canopy heterogeneity within a stand among microhabitat locations. 

In contrast, canopy cover can provide a mean assessment of stand-level conditions. 

Canopy cover is best assessed with a densitometer in which at least 100 observations are collected in a systematic sample (i.e., a grid) within an area representative 

of the stand’s variability. Distinguishing between cover and closure, and the canopy 

characteristic that each measures and the technique used for canopy estimation, 

may improve assessments of canopy conditions for wildlife species.

Heterogeneity and Resilience

The Forest Service definition of ecological restoration focuses on reestablishing 

the resilience or adaptive capacity of ecosystems. This approach is consistent with 

a recent review of catastrophic shifts in many different ecosystems that suggested 

maintaining resilience was the best strategy for sustainable management (Scheffer 

et al. 2001). How then might heterogeneity increase a forest’s resilience? Although it 

is intuitive that spatial heterogeneity, species diversity, and ecosystem resilience are 

linked, the connection has been difficult to rigorously test. One study examining 

the species-rich littoral forests of Madagascar, did find that forest spatial heterogeneity was associated with the resilience and maintenance of high species diversity 

Although it is intuitive 

that spatial heterogeneity, species diversity, 

and ecosystem resilience are linked, the 

connection has been 

difficult to rigorously 

test.
157

Managing Sierra Nevada Forests

over the last 6,000 years of climatic perturbations (Virah-Sawmy et al. 2009). The 

foundation of the concept, however, is probably more theoretical, based on the 

synthesis of decades of ecosystem research.

Holling (1973) was among the first to define ecological resilience as “the 

capacity of an ecosystem to return to the precondition state following a perturbation, including maintaining its essential characteristics, taxonomic composition, 

structures, ecosystem functions, and process rates.” Definitions of resilience, 

however, evolved as many ecologists moved away from Clements’ ideas that 

ecosystems inherently have a climax or stable state (Clements 1916). A more recent 

definition by Walker et al. (2004) is “the capacity of a system to absorb disturbance 

and reorganize while undergoing change so as to still retain essentially the same 

function, structure, identity, and feedbacks.” In a review of factors associated with 

loss of resilience and regime shifts in ecosystems, altered disturbance regimes was 

cited as a common driver (Folke et al. 2004). Recently, Holling (2010) has suggested 

that there are two aspects to resilience: “the more traditional [engineering] definition concentrates on stability near an equilibrium steady state, where resistance to 

disturbance and speed of return to the equilibrium are used to measure” resilience. 

The more ecological definition emphasizes conditions far from any equilibrium, 

“where instabilities can flip a system into another regime of behavior” and “resilience is the magnitude of disturbance that can be absorbed before the system 

changes its structure by changing the variables and processes that control behavior.” 

Ultimately Holling (2010) suggests that ecological resilience hinges on “designing interrelations between people and resources that are sustainable in the face of 

surprises and the unexpected.”

Beyond its theoretical foundation, empirical plant research has focused on identifying how variable microclimate conditions, driven by topographic heterogeneity, 

are associated with species resilience to changing climate. Some studies, examining 

how plant species persisted during past droughts and glacial advances, have identified variability in microenvironments as important in mediating climate change 

and enhancing species persistence (Suggitt et al. 2011). Microrefugia that support 

lower minimum temperatures may be particularly important for retaining both 

cold-adapted and mesophilous taxa (Dobrowski 2011, Scherrer and Körner 2011). 

The local climate, or topoclimate (Thornthwaite 1953) experienced by individuals 

is affected by regional advection and local terrain. Several studies have found good 

estimates of the lowest minimum temperature in a landscape can be made using 

terrain variables that characterize surface water accumulation (Chung et al. 2002, 

Daly et al. 2010, Dobrowski et al. 2009, Lookingbill and Urban 2003). Slope, aspect, 

Variable microclimate 

conditions, driven 

by topographic 

heterogeneity, are 

associated with 

species resilience to 

changing climate. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

and slope shape are strong influences on local microclimate affecting water balance 

(Dobrowski 2011). These studies support the GTR 220 concept that varying forest 

conditions in response to topography may be consistent with increasing fine-scale 

contrasts in microclimate. Such a strategy may compliment one of the mechanisms 

by which species persist in landscapes as climate conditions change.

In Sierra Nevada forests, resilience, in part, will hinge on the ability of trees to 

persist under future conditions that may include greater or more frequent drought 

stress. A consistent pattern associated with the onset of tree mortality is a drop off 

in annual increment growth. Some studies (Das et al. 2007, 2008; Franklin et al. 

1987) have suggested that these decreases eventually cross a threshold after which 

survival is unlikely. Many studies have documented reductions in tree growth as 

stem density increases. Drought also decreases annual radial increment growth, 

and can increase susceptibility to bark beetle attack. Competition from other trees, 

particularly from high stand density conditions, interact with climate stressors 

increasing the risk of mortality (Hurteau et al. 2007, Linares et al. 2010). Collectively these studies suggest that stand density reduction and variable forest structure 

that provides greater microclimate heterogeneity can make trees more resilient to 

mortality-induced stress. There are still many unknowns in the appropriate scale 

and mechanisms by which heterogeneity may increase ecosystem resilience. 

Measuring Resilience

Ecological resilience is an attractive concept, but often lacks measureable indicators. Quantifying resilience will be critical for identifying thresholds of probable 

concern when adaptively managing forests in the face of climate change (Scheffer 

et al. 2001). Unfortunately, resilience and adaptive capacity are often described as 

theoretical constructs rather than measurable indicators of system response to stress 

or disturbance (Carpenter et al. 2001). Moving from metaphors to measurement of 

ecological resilience requires clearly defining indicators of stress resilience that can 

be adapted to the context-specific conditions of different ecosystems.

If resilience is described in a manner similar to engineering resilience (sensu 

Holling 1973, Gunderson 2000), then (1) resistance can be defined as either no 

reduction or a smaller reduction in ecosystem response to a stress event; (2) recovery is the ability to resume a state relative to the damage experienced during an 

event; and (3) resilience is the capacity to reach pre-event ecosystem condition. A 

recent paper presented a quantitative method for assessing resistance, recovery, 

and resilience (fig. 14-2), in the context of tree radial growth response (Lloret et al. 

2011). This approach may have much wider application for measuring and assessing 

response and resilience of many different ecosystem components (i.e., sensitive 

Moving from 

metaphors to 

measurement of 

ecological resilience 

requires clearly 

defining indicators of 

stress resilience that 

can be adapted to 

the context-specific 

conditions of different 

ecosystems.
159

Managing Sierra Nevada Forests

Figure 14-2—Conceptual diagram of resilience components for tree growth response to a drought 

event (Dr), modified from Lloret et al. (2011). Resistance (Rt), recovery (Rc), resilience (Rs), and 

relative resilience (RRs) are calculated based on tree growth prior to (PreDr), during (Dr), and after 

(PostDr) a drought event.

species reproduction, understory plant diversity, tree mortality rates, etc.). Managers might consider using this approach when monitoring and measuring ecosystem 

response to new forest practices and changing climate conditions. 

References

Bigelow, S.; North, M.; Salk, C. 2011. Using light to predict fuels-reduction and 

group-selection effects on succession in Sierran mixed-conifer forest. Canadian 

Journal of Forest Research. 41: 2051–2063.

Brown, R.T.; Agee, J.K.; Franklin, J.F. 2004. Forest restoration and fire: 

principles in the context of place. Conservation Biology. 18: 903–912.

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: U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Research Station. 55 p.

Carey, A.B. 2000. Effects of new forest management strategies on squirrel 

populations. Ecological Applications. 10: 248–257.

Carey, A.B. 2002. Response of northern flying squirrels to supplementary dens. 

Wildlife Society Bulletin. 30: 547–556. Growth

Time

PreDr

PostDr

Rs

Rt Rc

Dr

Resistance Rt = Dr/PreDr

Recovery Rc = PostDr/Dr

Resilience Rs = PostDr/PreDr

Relative resilience RRs = (PostDr – Dr)/PreDr
160

GENERAL TECHNICAL REPORT PSW-GTR-237

Carey, A.B.; Wilson, T.M.; Maguire, C.C.; Biswell, B.L. 1997. Dens of 

northern flying squirrels in the Pacific Northwest. Journal of Wildlife 

Management. 61: 684–699.

Carpenter, S.; Walker, B.; Anderies, J.M.; Abel, N. 2001. From metaphor to 

measurement: Resilience of what to what? Ecosystems. 4: 765–781.

Christopher, T.A.; Goodburn, J.M. 2008. The effects of spatial patterns on the 

accuracy of Forest Vegetation Simulator (FVS) estimates of forest canopy cover. 

Western Journal of Applied Forestry. 23: 5–11.

Chung, U.; Seo, H.H.; Hwang, K.H.; Hwang, B.S.; Yun, J.I. 2002. Minimum 

temperature mapping in complex terrain based on calculation of cold air 

accumulation. Korean Journal of Agriculture and Forest Meteorology. 

4: 133–140. 

Clements, F.E. 1916. Plant succession: an analysis of the development of 

vegetation. Washington, DC: Carnegie Institution of Washington. 512 p.

Cockle, K.L.; Martin, K.; Wesolowski, T. 2011. Woodpeckers, decay, and the 

future of cavity-nesting vertebrate communities worldwide. Frontiers in Ecology 

and the Environment. 9: 377–382.

Collins, B.M.; Everett, R.G.; Stephens, S.L. 2011. Impacts of fire exclusion and 

recent managed fire on forest structure in old growth Sierra Nevada mixedconifer forests. Ecosphere 2: Article 51.

Cook; J.G.; Stutzman, T.W.; Bowers, C.W.; Brenner, K.A.; Irwin, L.L. 1995. 

Spherical densiometers produce biased estimators of forest canopy cover. 

Wildlife Society Bulletin. 23: 711–727.

Crookston, N.L.; Stage, A.R. 1999. Percent canopy cover and stand structure 

statistics from the Forest Vegetation Simulator. Gen. Tech. Rep. RMRS-GTR-24. 

Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 11 p. 

Daly, C.; Conklin, D.R.; Unsworth, M.H. 2010. Local atmospheric decoupling 

in complex topography alters climate change impacts. International Journal of 

Climatology. 30: 1857–1864.

Das, A; Battles, J.J.; Stephenson, N.L.; van Mantgem, P.J. 2007. The 

relationship between tree growth patterns and likelihood of mortality: a study 

of two tree species in the Sierra Nevada. Canadian Journal of Forest Research. 

37: 580–597. 
161

Managing Sierra Nevada Forests

Das, A; Battles, J.J.; van Mantgem, P.J.; Stephenson, N.L. 2008. Spatial 

elements of mortality risk in old-growth forests. Ecology. 89: 1744–1756. 

Dobrowski, S.Z. 2011. A climatic basis for microrefugia: the influence of terrain 

on climate. Global Change Biology. 17: 1022–1035.

Dobrowski, S.Z.; Abatzoglou, J.; Greenberg, J.A.; Schladow, G. 2009. How 

much influence does landscape-scale physiography have on air temperature in a 

mountain environment? Agricultural and Forest Meteorology. 149: 1751–1758.

Fiala, A.C.S.; Garman, S.L.; Gray, A.N. 2006. Comparison of five canopy cover 

estimation techniques in the western Oregon Cascades. Forest Ecology and 

Management. 231: 188–197.

Folke, C.; Carpenter, S.; Walker, B.; Scheffer, M.; Elmquvist, T.; Gunderson, 

L.; Holling, C.S. 2004. Regime shifts; resilience; and biodiversity in ecosystem 

management. Annual Review of Ecology and Evolution. 35: 557–581.

Franklin, J.F.; Shugart, H.H.; Harmon, M.E. 1987. Tree death as an ecological 

process. BioScience. 37: 550–556.

Ganey, J L.; Cassidy, R.H.; Block, W.M. 2008. Estimating canopy cover in forest 

stands used by Mexican spotted owls: Do stand-exam routines provide estimates 

comparable to field-based techniques? Res. Pap. RMRS-RP-72WWW. Fort 

Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 8 p.

Gunderson, L.H. 2000. Ecological resilience—in theory and application. Annual 

Review of Ecology and Systematics. 31: 425–439.

Holling, C.S. 1973. Resilience and stability of ecosystems. Annual Review of 

Ecological Systems. 4: 1–23.

Holling, C.S. 2010. Engineering resilience versus ecological resilience. In: 

Gunderson, L.H.; Allen, C.R.; Holling, C.S. eds. Foundations of ecological 

resilience. Washington; DC: Island Press. 51–66.

Hunsaker, C.T.; Boroski, B.B.; Steger, G.N. 2002. Relations between canopy 

cover and the occurrence and productivity of California spotted owls. In: Scott, 

J.M.; Heglund, P.J.; Morrison, M.L. eds. Predicting species occurrences: issues 

of accuracy and scale. Covelo, CA: Island Press: 687–700.

Hurteau, M.; Zald, H.; North, M. 2007. Species-specific response to climate 

reconstruction in upper-elevation mixed-conifer forests of the western Sierra 

Nevada, California. Canadian Journal of Forest Research. 37: 1681–1691. 
162

GENERAL TECHNICAL REPORT PSW-GTR-237

Irwin, L.L.; Rock, D.F.; Miller, G.P. 2000. Stand structures used by northern 

spotted owls in managed forests. Journal of Raptor Research. 34: 175–186.

Jennings, S.B.; Brown, N.D.; Sheil, D. 1999. Assessing forest canopies and 

understorey illumination: canopy closure; canopy cover and other measures. 

Forestry. 72: 59–73.

Kellogg, L.K.B.; McKenzie, D.; Peterson, D.L.; Hessl, A.E. 2008. Spatial models 

for inferring topographic controls on historical low-severity fire in the eastern 

Cascade Range of Washington, USA. Landscape Ecology. 23: 227–240. 

Kennedy, M.C.; McKenzie, D. 2010. Using a stochastic model and cross-scale 

analysis to evaluate controls on historical low-severity fire regimes. Landscape 

Ecology. 25: 1561–1573.

Korhonen, L.; Korhonen, K.T.; Rautiainen, M.; Stenberg, P. 2006. Estimation 

of forest canopy cover: a comparison of field measurement techniques. Silva 

Fennica. 40: 577–588.

Linares, J.C.; Camarero, J.J.; Carreira, J.A. 2010. Competition modulates the 

adaptation capacity of forests to climatic stress: insights from recent growth 

decline and death in relict stands of the Mediterranean fir Abies pinsapo. Journal 

of Ecology. 98: 592–603.

Lloret, F.; Keeling, E.G.; Sala, A. 2011. Components of tree resilience: effects 

of successive low-growth episodes in old ponderosa pine forests. Oikos. 

120: 1909–1920.

Lookingbill, T.R.; Urban, D.L. 2003. Spatial estimation of air temperature 

differences for landscape scale studies in montane environments. Agricultural 

and Forest Meteorology. 114: 141–151. 

Ma, S.; Concilio, A.; Oakley, B.; North, M.; Chen, J. 2010. Spatial variability 

in microclimate in a mixed-conifer forest before and after thinning and burning 

treatments. Forest Ecology and Management. 259: 904–915. 

Mazurek, M.J.; Zielinski, W.J. 2004. Individual legacy trees influence 

vertebrate wildlife diversity in commercial forests. Forest Ecology and 

Management. 193: 321–334.

Moen, C.A.; Gutiérrez, R.J. 1997. California spotted owl habitat selection in the 

central Sierra Nevada. Journal of Wildlife Management. 61: 1281–1287.
163

Managing Sierra Nevada Forests

North, M.; Franklin, J.; Carey, A.; Forsman, E.; Hamer, T. 1999. Forest 

structure of the northern spotted owl’s foraging habitat. Forest Science. 

45: 520–527.

North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

North, M.P.; Steger, G.; Denton, R.; Eberlein, G.; Munton, T.; Johnson, K. 

2000. Association of weather and nest-site structure with reproductive success 

in California spotted owls. Journal of Wildlife Management. 64: 797–807.

Nuttle, T. 1997. Densiometer bias? Are we measuring the forest or the trees? 

Wildlife Society Bulletin. 25: 610–611.

Paletto, A.; Tosi, V. 2009. Forest canopy cover and canopy closure: comparison of 

assessment techniques. European Journal of Forest Research. 128: 265–272. 

Pierson, E.D.; Rainey, W.E.; Chow, L.S. 2006. Bat use of the giant sequoia 

groves in Yosemite National Park: a report to Save-the-Redwoods League. 

152 p. Unpublished report. http://www.savetheredwoods.org/media/pdf_pierson.

pdf. (February 8, 2012.)

Purcell, K.L.; Mazzoni, A.K.; Mori, S.R.; Boroski, B.B. 2009. Resting 

structures and resting habitat of fishers in the southern Sierra Nevada, 

California. Forest Ecology and Management. 258: 2696–2706.

Remm, J.; Lõhmus, A. 2011. Tree cavities in forests—the broad distribution 

pattern of a keystone structure for biodiversity. Forest Ecology and Management. 

262: 579–585.

Scheffer, M.; Carpenter, S.; Foley, J.A.; Fole, C.; Walker, B. 2001. Catastrophic 

shifts in ecosystems. Nature. 413: 591–596.

Scherrer, D.; Körner, C. 2011. Topographically controlled thermal-habitat 

differentiation buffers alpine plant diversity against climate warming. Journal 

of Biogeography. 38: 406–416.

Scholl, A.E.; Taylor, A.H. 2010. Fire regimes; forest change; and self-organization 

in an old-growth mixed-conifer forest; Yosemite National Park, USA. Ecological 

Applications. 20: 362–280.
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Sierra Nevada Forest Plan Amendment [SNFPA]. 2004. Sierra Nevada Forest 

Plan Amendment: final supplemental environmental impact statement. R5-

MB-046. Washington, DC: U.S. Department of Agriculture, Forest Service, 

Pacific Southwest Region. 492 p.

Stuart, J.D.; Grifantini, M.C.; Fox, L., III. 1993. Early successional pathways 

following wildfire and subsequent silvicultural treatment in Douglas-fir/

hardwood forests; NW California. Forest Sciences. 39: 561–572.

Suggitt, A.J.; Gillingham, P.K.; Hill, J.K.; Huntley, B.; Kunin, W.E.; Roy, 

D.B.; Thomas, C.D. 2011. Habitat microclimates drive fine-scale variation in 

extreme temperatures. Oikos. 120: 1–8.

Sugihara, N.G.; van Wagtendonk, J.W.; Shaffer, K.E.; Fites-Kaufman, 

J.; Thode, A.E, eds. 2006. Fire in California’s ecosystems. Berkeley, CA: 

University of California Press. 596 p. 

Sullivan, T.P.; Sullivan, D.S. 2001. Influence of variable retention harvests on 

forest ecosystems. II. Diversity and population dynamics of small mammals. 

Journal of Applied Ecology. 38: 1234–1252.

Thornthwaite, C.W. 1953. A charter for climatology. World Meteorological 

Organization Bulletin. 2: 40–46. 

Virah-Sawmy, M.; Gillson, L.; Willis, K.J. 2009. How does spatial heterogeneity

influence resilience to climatic changes? Ecological dynamics in southeast 

Madagascar. Ecological Monographs. 70: 557–574.

Walker, B.; Holling, C.S.; Carpenter, S.R.; Kinzig, A. 2004. Resilience; 

adaptability and transformability in social–ecological systems. Ecology and 

Society. 9: 5.

Wiebe, K.L. 2011. Nest sites as limiting resources for cavity-nesting birds in 

mature forest ecosystems: a review of the evidence. Journal of Field Ornithology. 

82: 239–248.

Zielinski, W.J.; Truex, R.L.; Schmidt, G.A.; Schlexer, F.V.; Schmidt, K.N.; 

Barrett, R.H. 2004. Resting habitat selection by fishers in California. Journal 

of Wildlife Management. 68: 475–492.
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Managing Sierra Nevada Forests

M. North 

Introduction

An unexpected outcome of U.S. Forest Service General 

Technical Report PSW-GTR 220, “An Ecosystem Management Strategy for Sierran Mixed-Conifer Forests” (North et 

al. 2009), was how it generated discussion about a desired 

future condition for Sierra Nevada forests. The paper did not 

convey leading-edge research results or provide an exhaustive literature review. Rather it was an effort to take findings 

generally accepted amongst scientists, and synthesize them 

into a conceptual model for how Sierra Nevada forests might 

be managed. When the GTR has been used in implementing 

projects, the conceptual model often generates discussion 

about a desired endpoint toward which management and treatments could move a forest. Initially that discussion can seem 

removed from the project at hand, but agreement on a desired 

future condition is a foundation for building collaboration. 

Yet in discussions of desired future conditions for Sierra 

Nevada forests there remain some challenges that are more 

fundamental than clarifying GTR 220 concepts or providing more detailed science summaries. During field visits to 

project sites, discussions with managers and through dialogue 

with stakeholders, three areas keep being brought up. Collectively they are issues that may require basic changes in 

how Sierra Nevada forests are managed: changes in the way 

forests are perceived and measured, the scale and economics 

of how forests are managed, and an institutional change in 

management that internalizes science and course correction. 

The Limitations of Stand-Level Averages

Silviculture remains the heart of forest management because it has provided powerful and useful tools for understanding how forest growth responds to manipulation and disturbance. An essential tool in current silviculture applications is the 

Forest Vegetation Simulator (FVS), a model based on hundreds of studies in many 

1 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 1731 Research Park Dr., Davis, CA 95618.

Summary of Findings

1. Silviculture should consider broadening the measures and scales by 

which forests are assessed beyond 

the current focus on averages and 

stands.

2. For practical, ecological, and economic reasons, forest projects 

should be scaled up to treat an 

entire fireshed, and then, where 

safety allows, convert the fireshed’s 

future management to maintenance 

through managed wildfire and 

prescribed fire. Rough calculations 

suggest fuels should be reduced on 

437,000 ac of Forest Service land each 

year to mimic historical fire regimes. 

3. Question-driven, science-based 

monitoring should be integrated 

into management to address uncertainties arising from climate change 

and new forest practices. 

Chapter 15: A Desired Future Condition

for Sierra Nevada Forests
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GENERAL TECHNICAL REPORT PSW-GTR-237

different forest types, which has proved invaluable for forest planning and scenario 

testing for different management practices. Yet silviculture and models of forest 

dynamics are strongly imprinted with treating forests as a collection of stands, “a 

spatially continuous group of trees and associated vegetation having similar structures and growing under similar soil and climatic conditions” (Oliver and Larson 

1996). The concept of the stand can be traced back to European management 

efforts to parse forests into relatively homogenous units that could be efficiently 

managed for more predictable commodity production (Puettmann et al. 2009). The 

stand concept tends to set a scale at which most forest attributes are then evaluated. 

Some attributes such as bark beetle damage are well correlated with stand-level 

measures such as the Stand Density Index (SDI) (chapter 2). However, clearly some 

of the processes that strongly shape forest ecosystems such as fire, climate, and 

edaphic conditions, to name only a few, operate across multiple scales. When those 

processes shape habitat, microclimate, or ecosystem functions at scales other than 

the stand, managing and measuring forests as a collection of stands is unlikely to be 

congruent with those processes or accurately assessed with stand-level metrics (fig. 

15-1). Just within the topics raised in this collection of papers, authors have suggested that stand-level assessments may not accurately capture how forests respond 

to fire and climate change, what forest conditions provide habitat for marten, fisher 

and California spotted owl, or how we measure canopy structure and its influence 

on microclimate and fine-scale wildlife habitat. 

Figure 15-1—A mixed-conifer forest with complex structure created by frequent fire in the Illilouette Basin, Yosemite National 

Park. Identifying “stands” and describing them with averages would probably not accurately represent the forest’s variability across 

different scales.

A second problem with management focused at the stand level is that it can 

lead toward an emphasis on averages. The stand concept is an effort to express 

forest landscape variability by differences between units (i.e., stands) that have 

been delineated as areas with relatively homogenous conditions. Quantifying the 

average of the forest conditions best captures attributes of each unit, because within 

Marc Meyer

Management focused 

at the stand level 

can lead toward an 

emphasis on averages. 
167

Managing Sierra Nevada Forests

the stand, those conditions should be similar. Heterogeneity is then expressed as 

the variability between stands within a landscape. In practice, silviculturists often 

create fine-scale variability within stands by responding to existing forests conditions and accordingly adjusting their treatment. However, with metrics and descriptions of seral development and ecological response that are scaled to the stand, it 

has been difficult to communicate to stakeholders how that finer-scale variability is 

sometimes created. This has hindered support for some management practices by 

suggesting greater uniformity than may actually be present in treated forests. Field 

visits can help overcome this problem but do not change the fact that currently the 

language and metrics of silviculture often fall short of capturing the heterogeneity 

and complexity of forest ecosystems.

A recent critique of silviculture suggested it inherently promotes uniformity 

and discourages variability (Puettmann et al. 2009). Silviculture, however, has 

been tremendously adaptable, as public priorities for a forest’s ecosystem services 

have changed over time. Its tools can be modified (chapter 9) and new avenues of 

research can adapt silviculture practices to a broader range of spatial and temporal 

scales. This could include developing tools and metrics that measure heterogeneity 

at scales relevant to ecological processes of interest.

Economics and Treatment Scale

General Technical Report 220 did not address economics, yet costs often determine whether a project is even viable. It’s difficult to synthesize information about 

the potential economic impacts of revising forest management practices. The 

costs of any particular forest project are highly idiosyncratic depending on many 

factors such as current wood market prices, diesel costs, hauling distances, and 

processing infrastructure. However, current trends in economic conditions are not 

favorable. Many projects require service contracts to remove the noncommercial, 

small-diameter trees, and available revenue for these costs are decreasing as Forest 

Service budgets shrink. Out of necessity many national forests in the Sierra Nevada 

limit projects to areas where the economics are favorable or locations where funds 

for service contracts can be secured. There are good reasons for rethinking this 

approach through changing the scale of projects and specifically planning for and 

linking together areas that can generate revenue with restricted or sensitive areas 

requiring minimal treatment and revenue support. 

How much Sierra Nevada forest would the Forest Service need to treat each 

year to mimic historical patterns of fuel reduction when there was an active (pre1850) fire regime? Acreage that may have historically burned each year was estimated using a Geographic Approach to Planning (GAP) analysis that identified the 

With metrics and 

descriptions of 

seral development 

and ecological 

response that are 

scaled to the stand, 

it has been difficult 

to communicate to 

stakeholders how 

finer-scale variability 

is sometimes created. 

This has hindered 

support for some 

management practices 

by suggesting greater 

uniformity than may 

actually be present in 

treated forests. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

acreage and agency ownership of different forest types in the Sierra Nevada (Davis 

and Stoms 1996) and sources summarizing historical fire regime studies (Stephens 

et al. 2007, Van de Water and Safford 2011, FEIS 2011). Of the Forest Service’s 

4.8 million forested acres (1.9 million ha) (Plumas National Forest south through 

Sequoia National Forest, including Inyo National Forest), approximately 488,000 ac 

(197 000 ha) may have burned each year before the arrival of Europeans. From 1986 

to 2010, on average 51,000 ac/yr (20 600 ha/yr) are burned by wildfire (with great 

annual variability) (Bilyea 2011), leaving 437,000 ac/yr (177 000 ha/yr) that would 

need to be treated to mimic historical fuel reduction levels. Over the last 8 years, 

the Forest Service has averaged 28,600 ac/yr (11 600 ha/yr) of mechanical fuels 

reduction and 8,300 ac/yr (3360 ha/yr) of prescribed burning (Sherlock 2011) for a 

total of 36,900 ac/yr (14 930 ha/yr) treated or about 8.4 percent of the 437,000 ac. 

Despite the best efforts of managers, the current rate of treatment will leave most of 

the forest in high density, high fuel load conditions susceptible to an altered disturbance regime. Even if projects are not slowed by legal or administrative challenges, 

the Forest Service’s current pace and scale of treatments in the Sierra Nevada is an 

order of magnitude less than what is needed to keep up with accumulating fuels 

from forest growth.

Another problem with current fuels treatment practices is that most sensitive 

areas with special value such as threatened and endangered species habitat or 

riparian conservation areas (Van de Water and North 2010, 2011) are excluded from 

projects or have minimal treatment. These areas often have high stem densities, 

moisture stress, and heavy fuels accumulations, decreasing their resilience to wildfire and drought. Yet these areas often are the last to be treated because of increased 

risk of litigation and high cost, because lighter treatments usually do not include 

removing trees with commercial value. Without some change in current practices, 

many of the areas with greatest ecological and habitat value will be prone to high 

overstory mortality and loss of large live trees. 

An additional economic consideration is that in many forests the only potential for generating revenue will be in the first management entry, when some 

intermediate-size trees with commercial value may be thinned. Future treatments 

for maintenance of fuels reduction will probably have expenses that exceed 

any revenue. At current budget levels, it seems unlikely that such extensive and 

expensive treatment can be accomplished for second and future fuels reduction 

entries.

One possible approach to revising management practices within these economic 

constraints is to consider scaling up the size of treatments with an objective, where 

possible, of treating entire firesheds and then converting their future management 

The Forest Service’s 

current pace and scale 

of treatments in the 

Sierra Nevada is an 

order of magnitude 

less than what is 

needed to keep up with 

accumulating fuels 

from forest growth.

[Scale] up the size 

of treatments with 

an objective, where 

possible, of treating 

entire firesheds and 

then converting their 

future management to 

maintenance through 

managed wildfire and 

prescribed fire.
169

Managing Sierra Nevada Forests

to maintenance through managed wildfire and prescribed fire. This approach would 

increase the scale of treatments and provide an opportunity to bundle revenuegenerating areas with lightly treated areas that are revenue sinks. For example, 

across a fireshed, revenue from heavier thinning on upper slopes designed to restore 

low-density large pine conditions, might be used to support hand thinning or prescribed burning that maintains high canopy cover in the parallel track of forest that’s 

in the drainage bottom. Once treatments are completed, the burnshed could largely 

be maintained by allowing it to burn under wildfire or prescribed fire conditions 

determined by local managers. This approach probably cannot be used in areas with 

high home density because of liability from escaped fire. It would, however, restore 

fire and its ecological benefits (Stephens et al., in press) to many forests currently 

degraded by fire exclusion and reduce future maintenance costs. The larger scale 

of treatments and the practical need to spread them out over several years would 

make for a steady, more predictable flow of wood for local mills and potential 

biomass plants. Biomass use of small-diameter fuels holds promise for improving 

the economics of fuels treatments. The lack of consistent biomass supply can limit 

development of processing infrastructure; however, large-scale, long-term treatment planning can overcome some of these limitations (Hampton et al. 2011). Even 

with some firesheds being turned over to maintenance by fire, there would still be a 

substantial need for thinning other firesheds ensuring a continuing supply of wood 

for local communities.

This approach may be criticized as impractical, but at least it could stimulate 

discussions between stakeholders and forest managers about current and future 

economic constraints on management options. Without proactively addressing some 

of these conditions, the status quo will relegate many ecologically important areas to 

continued degradation from fire exclusion.

Monitoring 

Science should become an integral part of forest management, and monitoring may 

be the best means of achieving this inclusion. Monitoring is an important course correction tool particularly as new silvicultural practices are implemented. It is essential 

not only for understanding management impacts on focal wildlife species but also 

for assessing ecosystem response under changing climatic conditions. It is likely 

that some new management practices will not achieve their objectives and will need 

adjustment. Furthermore, we have limited information about how best to increase 

forest resilience under warming conditions, and some trial and error is inevitable. 

Monitoring is a candid admission that all forest management is experimental and 

needs to adapt to uncertain outcomes, changing conditions, and new information. 

Monitoring is a candid 

admission that all 

forest management 

is experimental and 

needs to adapt to 

uncertain outcomes, 

changing conditions, 

and new information. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

Monitoring Policy

There is now a window of opportunity, prompted by the Washington office of the 

Forest Service, to make meaningful improvements in monitoring. The interest 

in establishing an integrated Inventory Monitoring and Assessment Strategy and 

Implementation Plan is driven by several agency initiatives, including the new 

planning rule, the climate change scorecard, the watershed condition framework, 

the ecological integrity index, and a focus on ecosystem restoration. Integrating the 

inventory, monitoring, and assessment components of these ongoing activities will 

improve the consistency and scalability of information and analyses, and hopefully 

enable the Forest Service to capture cost efficiencies. 

Monitoring Implementation

What should be monitored and how will managers know how effective their restoration efforts are? The type of monitoring can determine how informative the data 

are. Passive and mandated monitoring often produces trend observations, whereas 

question-driven monitoring guided by a conceptual model can test à priori predictions (Lindenmayer and Likens 2010). The Society for Ecological Restoration has 

suggested restoration should be assessed in three general areas: species diversity, 

ecological processes, and vegetation structure (Ruiz-Jaen and Aide 2005a, 2005b). 

Monitoring changes in vegetation is fairly common, but assessing changes in species diversity and ecological processes is often viewed as difficult and expensive. 

One approach for species is to target taxa that are more likely to be affected by 

management practices and examine how generalist and specialist species respond 

(Clavel et al. 2011 [e.g., Meyer et al. 2007a, 2007b]). Some ecological processes are 

not difficult to assess using changes in vegetation growth (e.g., tree mortality and 

growth response assessed with increment core samples). National forest system 

ecologists familiar with research methods could help design protocol and have 

study designs peer reviewed. 

Monitoring at the landscape level may not be as daunting as it seems if testable 

hypotheses are well defined. A large-scale restoration project in northern Arizona 

used regularly spaced permanent plots to assess where forest structure and coarse 

woody debris approximated presettlement conditions (Roccaforte et al. 2010). One 

suggestion (DeLuca et al. 2010) has been that monitoring might occur even on limited federal budgets through using a combination of collaborative partnerships, volunteers, prioritized sampling designs (e.g., statistical sampling strategies that focus 

on a limited number of intensively monitored sites), and emerging remote sensing 

technologies. It is important to develop a well-structured monitoring approach that 
171

Managing Sierra Nevada Forests

is founded on the most basic and crucial questions. Initial efforts should probably be 

modest and build success and trust towards a more thorough program over time. 

Monitoring only has value if its information is incorporated using an adaptive 

management approach (Nichols and Williams 2006). Yet adaptive management 

has often become an agency mantra without a well-defined set of implementation 

measures (Allen et al. 2011; Williams 2011a, 2011b). The feedback between learning and decisionmaking needs to be incorporated into management procedures so 

that learning and adjustment actually occurs. Bormann et al. (2007) suggest that 

“adaptive management is less about current decisions than about mutual learning 

that might lead to better future decisions. Mutual learning calls for managers to 

consider learning as a core business and for the science community to improve 

their performance in civic science and their delivery of integrated, science-based 

evidence and tools.” 

Uncertainty, Collaboration and Monitoring

Uncertainty about the effects of climate change could bring about a fundamental 

shift toward adaptive management and active monitoring that has long been proposed; yet rarely implemented. This uncertainty could be viewed as license for 

unending litigation since no environmental assessment will be able to adequately 

present all outcomes. Uncertainty, however, can also be an opportunity for a different approach, one where management practices are tried, evaluated, and modified 

iteratively. Such an approach will require candid acknowledgment of unknowns, 

public participation, and transparent collaborative planning. 

Studies of sustainable resource stewardship suggest that several social, administrative, and economic conditions are needed, with effective management often 

requiring long-term collaboration that builds trust (Dietz et al. 2003, Ostrom 2009). 

In forestry, good management hinges on flexible practices that can respond to 

different onsite conditions. Forest practices restricted with set prescriptions do not 

allow this flexibility, producing predictable treatments often poorly adapted to different ecosystem conditions. Deliberative collaboration, discussed in chapters 7 and 

8, is one means of moving beyond restrictive prescriptions. The pace and cost of 

these efforts may frustrate some, but under the right conditions they can eventually 

allow managers greater flexibility. 

Monitoring can provide the institutional glue for long-term collaboration. 

Often, however, monitoring has not had a clear scientific objective and initial efforts 

fade as funding dwindles. Yet with uncertain forest outcomes, new management 

practices need longitudinal data and an institutional mechanism for incorporating 

Monitoring can provide 

the institutional 

glue for long-term 

collaboration. 
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GENERAL TECHNICAL REPORT PSW-GTR-237

that information into adaptive course correction. Science-based, objective monitoring can build trust. The adage applied to U.S.-Soviet arms treaties, “trust but 

verify,” may be equally apropos to new forest management strategies. 

Chapter Summary

“If we open a quarrel between past and present, we shall find that we 

have lost the future.” (Winston Churchill)

Forestry is an art as well as a science, a creative response to existing forest conditions based on the best silviculture, ecology, and wildlife biology. The challenge has 

always been how to best provide a forest’s multiple ecosystem services with imperfect knowledge of management’s effects. Conflicts over the priority of those ecosystem services (e.g., timber, fuels reduction, wildlife habitat) on public forest lands 

has often resulted in management by restrictive prescription. Yet the best forestry 

has always required flexibility, innovation, and the latitude to respond to ecological 

context. How can forest management in the Sierra Nevada regain its art?

Ironically, the uncertainty of global climate change could be a catalyst for 

restoring flexible management if agencies consider some changes. No one can 

predict exactly how changing climatic conditions may affect forests. All forest 

projects will be experimental, requiring assessment at multiple scales and including 

patterns of variation. Acknowledging this uncertainty, committing to monitoring 

forest response, then adapting management practices as information accumulates, 

would institutionalize flexibility. It would also require managers and stakeholders 

explicitly discuss and develop a desired future condition against which to measure 

forest conditions. The hope of GTR 220 and this collection of papers is that it can 

provide a starting point for that discussion. 

References

Allen, C.R.; Fontaine, J.J.; Pope, K.L.; Garmestani, A.S. 2011. Adaptive 

management for a turbulent future. Journal of Environmental Management. 

92: 1339–1345.

Bilyeu, A. 2011. Personal communication. Natural resource planning specialist, 

U.S. Department of Agriculture, Forest Service, Pacific Southwest Region, Fire, 

Fuels and Aviation Management. 3237 Peacekeeper Way, Suite 101, McClellan, 

CA 95652.

Bormann, B.T.; Hanes, R.W.; Martin, J.R. 2007. Adaptive management of forest 

ecosystems: Did some rubber hit the road? BioScience. 57: 186–191.

The adage applied 

to U.S.-Soviet arms 

treaties, “trust but 

verify,” may be equally 

apropos to new 

forest management 

strategies.
173

Managing Sierra Nevada Forests

Clavel, J.; Julliard, R.; Devictor, V. 2011. Worldwide decline of special species: 

toward a global functional homogenization? Frontiers in Ecology and the 

Environment. 9: 222–228.

Clements 1916. Plant succession: an analysis of the development of vegetation. 

Washington, DC: Carnegie Institution of Washington. 654 p.

Davis, F.W.; Stoms, D.M. 1996. Sierran vegetation: a gap analysis. In: Sierra 

Nevada Ecosystem Project: final report to Congress. Vol. II. Assessments and 

scientific basis for management options. Wildland Resources Center Report 

No. 37. Davis, CA: University of California, Centers for Water and Wildlands 

Resources: 671–690. 

DeLuca, T.H.; Aplet, G.H.; Wilmer, B.; Burchfield, J. 2010. The unknown 

trajectory of forest restoration: a call for ecosystem monitoring. Journal of 

Forestry. 108: 288–295.

Dietz, T.; Ostrom, E.; Stern, P.C. 2003. The struggle to govern the commons. 

Science. 302: 1907–1912. 

Fire Effects Information System [FEIS]. 2011. U.S. Department of Agriculture, 

Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory 

(Producer). Available: http://www.fs.fed.us/database/feis. (December 15, 2011). 

Hampton, H.M.; Sesnie, S.E.; Bailey, J.D.; Snider, G.B. 2011. Estimating 

regional wood supply based on stakeholder consensus for forest restoration in 

northern Arizona. Journal of Forestry. 109: 15–26.

Lindenmayer, D.B.; Likens, G.E. 2010. Effective ecological monitoring. 

Collingwood, Australia: CSIRO Publishing. 184 p.

Meyer; M.; Kelt, D.; North, M. 2007a. Effects of burning and thinning on 

lodgepole chipmunks (Neotamias speciosus) in the Sierra Nevada, California. 

Northwestern Naturalist. 88: 61–72.

Meyer, M.; Kelt, D.; North, M. 2007b. Microhabitat associations of northern 

flying squirrels in burned and thinned stands of the Sierra Nevada. American 

Midland Naturalist. 157: 202–211.

Nichols, J.D.; Williams, B.K. 2006. Monitoring for conservation. Trends in 

Ecology and Evolution. 21: 668–673.
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North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An 

ecosystem management strategy for Sierran mixed-conifer forests. 2nd printing, 

with addendum. Gen. Tech. Rep. PSW-GTR-220. Albany, CA: U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Research Station. 49 p.

Oliver, D.D.; Larson, B.C. 1996. Forest stand dynamics. New York City, NY: 

John Wiley and Sons, Inc. 520 p.

Ostrom, E. 2009. A general framework for analyzing sustainability of socialecological systems. Science. 325: 419–422.

Puettmann, K.J.; Coastes, K.D.; Messier, C. 2009. A critique of silviculture: 

managing for complexity. Washington, DC: Island Press. 189 p.

Roccaforte, J.P.; Fulé, P.Z.; Covington, W.W. 2010. Monitoring landscapescale ponderosa pine restoration treatment implementation and effectiveness. 

Restoration Ecology. 18: 820–833.

Ruiz-Jaen, M.C.; Aide, T.M. 2005a. Restoration success: How is it being 

measured? Restoration Ecology. 13: 569–577.

Ruiz-Jaen, M.C.; Aide, T.M. 2005b. Vegetation structure; species diversity; and 

ecosystem processes as measures of restoration success. Forest Ecology and 

Management. 218: 159–173.

Sherlock, J. 2011. Personal communication. Regional silviculturist, U.S. 

Department of Agriculture, Forest Service, Pacific Southwest Region, 

1323 Club Drive, Vallejo, CA 94592.

Sierra Nevada Forest Plan Amendment [SNFPA]. 2004. Sierra Nevada Forest 

Plan Amendment: final supplemental environmental impact statement. R5-

MB-046. Washington DC: U.S. Department of Agriculture, Forest Service, 

Pacific Southwest Region. 492 p.

Stephens, S.L.; Martin, R.E.; Clinton, N.E. 2007. Prehistoric fire area and 

emissions from California’s forests, woodlands, shrublands, and grasslands. 

Forest Ecology and Management. 251: 205–216.

Stephens, S.L.; McIver, J.D.; Boerner, R.E.J.; Fettig, C.J.; Fontaine, J.B.; 

Hartsough, B.R.; Kennedy, P.; Schwilk, D.W. [In press]. Effects of forest 

fuel reduction treatments in the United States. BioScience.

Van de Water, K.; North, M. 2010. Fire history of coniferous riparian forests 

in the Sierra Nevada. Forest Ecology and Management. 260: 384–395.
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Van de Water, K.; North, M. 2011. Stand structure, fuel loads, and fire behavior 

in riparian and upland forests, Sierra Nevada Mountains, USA; a comparison 

of current and reconstructed conditions. Forest Ecology and Management. 

262: 215–228.

Van de Water, K.M.; Safford, H.D. 2011. A summary of fire frequency estimates 

for California vegetation before Euro-American settlement. Fire Ecology. 

7: 26–58.

Williams, B.K. 2011a. Adaptive management of natural resources—framework 

and issues. Journal of Environmental Management. 92: 1346–1353.

Williams, B.K. 2011b. Passive and active adaptive management: approaches 

and an example. Journal of Environmental Management. 92: 1371–1378.
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Metric Equivalents

When you know: Multiply by: To get:

Inches (in) 25.4 Millimeters

Inches (in) 2.54 Centimeters

Feet (ft) .3048 Meters

Acres (ac) .405 Hectares

Miles (mi) 1.609 Kilometers

Square feet per acre (ft2

/ac) .229 Square meters per hectare

Square miles (mi2

) 2.59 Square kilometers

Degrees Fahrenheit 0.556 (°F – 32) Degrees Celsius

Acknowledgments

We thank the seven reviewers who provided thoughtful and constructive 

reviews of all or part of this collection of papers and Haiganoush Preisler 

for managing the review process. We thank Carolyn Wilson for editing the 

manuscript, and Jamie Shields and Esther Cole for help incorporating edits 

and revisions into the manuscript. We are indebted to Harold Zald for discussing and sharing some of his ideas on resilience. We also thank Steve Oerding 

of IET Academic Technology Service at the University of California, Davis for 

the canopy closure and cover graphic. We are particularly grateful to dozens of 

Forest Service managers and technicians who have shared their knowledge of 

Sierra Nevada forests.
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Managing Sierra Nevada Forests

Appendix: Examples of Forest Structures That May 

Provide Wildlife Habitat

D. Walsh1 and M. North2

The photos in this appendix may help identify some of the unique branching formations or bole characteristics in trees that can make a tree particularly valuable 

for wildlife, either for nesting, roosting, and use as hunting perches, or other uses. 

We have organized these following Bull et al.’s (1997)3

 focus on five conditions: 

live trees with decay, hollows or brooms, snags, and logs. We’ve also included 

in these photos examples of understory areas with vertical diversity and hiding 

cover created by the retention of understory saplings, intermediate-sized trees, 

hardwoods, and brush.

1 Forester, U.S. Department of Agriculture, Forest Service, Pacific Southwest Region, 

Eldorado National Forest, Georgetown ranger district, 7600 Wentworth Spring Rd., 

Georgetown, CA 95634.

2 Research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Research Station, 1731 Research Park Dr., Davis, CA 95618.

3 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. GTR-PNW-391. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 55 p.
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Figure A-3—Live tree with broom structure. The arrow is pointing at a potential 

nesting site formed by an unusual branching pattern most likely associated with an 

old break in the bole of the Douglas-fir 

(Pseudotsuga menziesii (Mirbel) Franco). 

Figure A-4— Live tree with broom structure. A 

relatively young Douglas-fir has a nest associated with its forked top.

Dana Walsh

Dana Walsh

Figure A-1—Live tree with hollow structure. 

The tree has an old dead top with cavity nests 

and a new healthy top leader grown up along 

side, providing some shelter. The tree is healthy 

overall with a high live crown ratio and no ladder 

fuel concern. 

Figure A-2—Live tree with decay. The tree has 

a potential platform nest site that is somewhat 

protected by adjacent trees. This site could be 

used for nesting, or could break and provide a 

platform for nests or for roosting. 

Dana WalshDana Walsh
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Managing Sierra Nevada Forests

Figure A-5— Live tree with broom structure. The tree’s unique forking pattern could easily serve as a nest site for a larger bird. In some 

stands, these types of trees are extremely prevalent, in which case it 

may not be necessary to leave all trees with this characteristic. 

Figure A-6—Live tree with broom structure. A 

medium-size tree with a snag top that may provide 

nesting opportunities, especially when protected by 

surrounding trees.

Figure A-7a—Living tree with decay. Older 

snag-topped trees may provide good nesting 

opportunities or perching locations, and a source 

of wood-boring insects that provide ready food 

sources for woodpeckers or opportunities for 

cavity-nesting species. 

Dana Walsh

Dana Walsh

Dana WalshDana Walsh

Figure A-7b—Closer view of the snag in the 

previous photo.
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Figure A-8—Live tree with hollow. Bayonet top trees, such as the sugar pine (Pinus lambertiana Douglas) in the center, 

can provide roosting and nesting opportunities in the dead top and the “inner platform” of the arm.

Jaime Shields
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Managing Sierra Nevada Forests

Figure A-9—Live tree with hollow. The broken-off large limb on this black oak can provide wildlife habitat.

Jaime Shields
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Figure A-10—Live tree with decay, hollow, and broom structure. Crown reiteration can occur with some broken tops 

providing unique habitat features. 

Jaime Shields
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Managing Sierra Nevada Forests

Figure A-11—A snag with extensive cavities, probably created by 

pileated woodpeckers (Dryocopus pileatus), which may provide 

habitat for secondary cavity users. 

Craig Thomas

Figure A-12—Large logs, even when fairly well decayed, can still provide hiding and resting cover for 

some wildlife. A northern flying squirrel was tracked with radio telemetry to this location.

Malcolm North
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Figure A-14—An example of retaining intermediate-size conifers and protecting hardwoods. 

Around a group of overstory trees, understory mixed hardwoods and intermediate-sized conifers 

were retained to keep an area of diversity within an otherwise relatively uniform stand treatment. 

The trees that have both blue and orange paint are being retained from a size class that would typically have been removed. The orange paint indicates “retention trees” so that the sale administrator 

understands that these trees were intentionally retained. The blue paint under it is from the original 

mark. The Quintette Fuel Reduction Project is on the Georgetown Ranger District, Eldorado 

National Forest.

Figure A-13—Example of retaining understory trees to provide 

wildlife hiding cover and vertical diversity. This retained pocket 

of natural regeneration is on the Sun Dawg Fuels Project, Georgetown Ranger District, Eldorado National Forest. 

Don Errington Don Errington