United States Department

of Agriculture

Forest Service

Rocky Mountain Research Station

General Technical Report RMRS-GTR-231

January 2010 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
Elliot, William J.; Miller, Ina Sue; Audin, Lisa. Eds. 2010. Cumulative watershed 

effects of fuel management in the western United States. Gen. Tech. Rep. 

RMRS-GTR-231. Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station. 299 p.

Abstract

Fire suppression in the last century has resulted in forests with excessive amounts 

of biomass, leading to more severe wildfires, covering greater areas, requiring more 

resources for suppression and mitigation, and causing increased onsite and offsite 

damage to forests and watersheds. Forest managers are now attempting to reduce 

this accumulated biomass by thinning, prescribed fire, and other management 

activities. These activities will impact watershed health, particularly as larger areas 

are treated and treatment activities become more widespread in space and in time. 

Management needs, laws, social pressures, and legal findings have underscored a 

need to synthesize what we know about the cumulative watershed effects of fuel 

management activities. To meet this need, a workshop was held in Provo, Utah, 

on April, 2005, with 45 scientists and watershed managers from throughout the 

United States. At that meeting, it was decided that two syntheses on the cumulative 

watershed effects of fuel management would be developed, one for the eastern 

United States, and one for the western United States. For the western synthesis, 

14 chapters were defined covering fire and forests, machinery, erosion processes, 

water yield and quality, soil and riparian impacts, aquatic and landscape effects, 

and predictive tools and procedures. We believe these chapters provide an 

overview of our current understanding of the cumulative watershed effects of fuel 

management in the western United States.

Keywords: cumulative effects, watershed, wildfire, fuel management, water 

quality, soil erosion

You may order additional copies of this publication by sending your 

mailing information in label form through one of the following media. 

Please specify the publication title and series number.

Fort Collins Service Center

Telephone (970) 498-1392

FAX (970) 498-1122

E-mail rschneider@fs.fed.us

Web site http://www.fs.fed.us/rm/publications

Mailing address Publications Distribution

Rocky Mountain Research Station

240 West Prospect Road

Fort Collins, CO 80526

Rocky Mountain Research Station

240 W. Prospect Road

Fort Collins, Colorado 80526
Foreword

This document is the result of a major interdisciplinary effort to synthesize our 

understanding of the cumulative watershed effects of fuel management. This 

document is the product of more than 20 authors and 40 reviewers including 

scientists from four Forest Service Research Stations and numerous universities. 

Chapter outlines and contents were first reviewed at a workshop in April 2005. 

Authors then drafted chapters that were peer-reviewed over the next two years. 

We edited all chapters twice before submitting them for a third round of editing by 

RMRS publication specialists. Chapter topics include overviews of the effects of fuel 

management on both terrestrial and aquatic watershed processes. The other editors 

and I are grateful to all authors and reviewers for their considerable efforts in the 

development of this document over the past four years. We wish to acknowledge 

the Stream Team and the National Fire Plan for financial assistance. As with all 

syntheses, science will continue to generate new knowledge, which will in time 

supersede the contents of this document. Readers are encouraged to seek updated 

and locally derived information to supplement the contents of this document. My 

personal thanks go to all the authors, reviewers, my coeditors and RMRS publishing 

staff for the considerable effort necessary to develop and publish this synthesis.

William J. Elliot, PE, PhD

Supervisory Research Engineer
Contents

Foreword i

Chapter 1. Introduction to Synthesis of Current Science 1

Regarding Cumulative Watershed Effects of Fuel 

Reduction Treatments

Douglas F. Ryan

Chapter 2. Fire Regimes and Ecoregions 7

Robert G. Bailey

Chapter 3. Fuel Management in Forests of the Inland West 19

Russell T. Graham, Theresa B. Jain, Susan Matthews

Chapter 4. Tools for Fuel Management 69

Bob Rummer

Chapter 5. Fuel Management and Erosion 79

Pete R. Robichaud, Lee H. MacDonald, Randy B. Foltz

Chapter 6. Cumulative Effects of Fuel Treatments on 101

Channel Erosion and Mass Wasting

Leslie M. Reid

Chapter 7. Fuel Management and Water Yield 126

Charles A. Troendle, Lee H. MacDonald, Charles H. Luce, 

I.J. Larsen

Chapter 8. Effects of Fuel Management Practices on 149

Water Quality

John D. Stednick

Chapter 9. Cumulative Effects of Fuel Treatments on 164

Soil Productivity

Deborah S. Page-Dumroese, Martin F. Jurgensen, 

Michael P. Curran, Sharon M. DeHart

Chapter 10. Potential Effects of Fuel Management 175

Activities on Riparian Areas

Kathleen A. Dwire, Charles C. Rhoades, Michael K. Young,

ii
Chapter 11. Biological Responses to Stressors in 206

Aquatic Ecosystems in Western North 

America: Cumulative Watershed Effects of Fuel 

Treatments, Wildfire, and Post-Fire Remediation

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner

Chapter 12. Landscape Scale Effects of Fuel Management 234

or Fire on Water Resources: The Future of 

Cumulative Effects Analysis?

Charles H. Luce, Bruce E. Rieman

Chapter 13. Tools for Analysis 246

William Elliot, Kevin Hyde, Lee MacDonald, James McKean

Chapter 14. Understanding and Evaluating Cumulative 277

Watershed Impacts

Leslie M. Reid

Appendix. Workshop Participants and First Round 

Reviewers (2006) 299

iii
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USDA Forest Service RMRS-GTR-231. 2010. 1

Chapter 1.

Introduction to Synthesis of Current Science 

Regarding Cumulative Watershed Effects of 

Fuel Reduction Treatments

Douglas F. Ryan, Aquatic and Land Interaction Program, Pacific Northwest Research Station, 

USDA Forest Service, Olympia, WA

Introduction

This report was produced by a group of scientists who were invited by the U.S. 

Forest Service to synthesize the current scientific literature to answer an important question facing the managers of federal and private lands in many parts of the country. The 

question was: What potential cumulative environmental effects at the watershed scale 

might be caused by implementing land management activities that reduce forest fuels on 

large scales? The main body of this report is a compilation of what they found, including 

both what can and cannot be concluded from the current science.

The scientific principles reviewed in this report are intended to be general. The 

examples of fire environments, land management practices, and vegetation types are 

drawn primarily from the western continental United States, roughly the region west of 

100o W longitude. A follow-up report is planned to address the same question but with a 

focus on examples from the Eastern section of the continental United States (Lafayette 

and others, under review).

In this chapter, I broadly describe fuel reduction treatments on wildlands and the 

concept of analyzing cumulative watershed effects. For perspective, I have referred to 

some of the primary legislative and policy direction that influences the way that federal 

land managers apply fuel reduction treatments and analyze cumulative effects.

Fuel Reductions Treatments and Policies and 

Laws Related to Them

Fuel reduction treatments are land management actions taken to reduce the threat 

posed by severe and/or intense wildland fire by manipulating live and dead vegetation to 

reduce the loading of fuel on the landscape that can support wildland fire. Fuel reduction 

can be accomplished in a number of ways with the most common involving mechanical removal of fuel material (usually brush or trees) and/or consumption of fuel using 

prescribed fire. These two types of treatments may be applied alone, sequentially, or in 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
2 USDA Forest Service RMRS-GTR-231. 2010.

various combinations. Treatment of wildlands to reduce fuel was given a national mandate when Congress passed the Healthy Forests Restoration Act of 2003 (P.L. 108-148) 

(HFRA). Efforts to reduce the risk of severe wildland fire may receive additional impetus from studies that attribute recent increases in the frequency of large wildland fires 

to changing climate (Westerling and others 2006), raising the possibility that this threat 

may further increase in western forests with expected climate changes in future years.

To effectively reduce the risk of wildland fires, fuel reduction treatments will need 

to be applied to large areas of federal lands each year in the form of mechanical fuel 

removal and/or prescribed fire. In most cases, vegetation can regrow after treatments, 

meaning that, in many areas, maintaining low fuel stocking will require repeated 

treatments to reduce fuel stocking at intervals ranging from several years to a few decades. Where they are well designed and implemented, fuel reduction treatments will 

probably create a relatively low intensity of disturbance, for example, by disturbing 

only a small amount of surface soil per acre. However, because they will be carried 

out over many acres each year and entail return treatments at regular intervals, there 

remains the possibility that local, project-level impacts of fuel reduction treatments 

may add up to significant impacts at larger watershed scales and thus result in cumulative effects. These cumulative effects on watersheds might be caused by activities 

directly related to removing fuels (for example, felling, skidding, and/or chipping to 

mechanically remove fuel and/or prescribed fire to consume it). Cumulative effects 

might also include impacts of operations or infrastructure that support fuels reduction that may occur in areas at some distance from the actual site of fuel reduction. 

Examples of these supporting functions could include the movement from logging, 

fire control, and other vehicles used in fuel management. Examples of supporting 

infrastructure could include roads that provide access to large areas of the landscape 

where fuel management activities take place and the drainage ditches, culverts, and 

stream crossings associated with roads.

In recognition of the critical role of wildland fire in forest ecosystems and the 

risk that high fuel loads pose in forests, Congress and the Forest Service have taken several actions to accelerate fuel reduction treatments. Several policy initiatives 

by the Forest Service and other federal agencies (Federal Wildland Fire Policy of 

1995, the Cohesive Fire Strategy of 2000, National Fire Plan of 2000, and Ten-year 

Comprehensive Strategy and Implementation Plan of 2001/2002) were strengthen 

when the President announced the Healthy Forest Initiative (HFI) (White House 

2002). HFI streamlined administrative procedures required to implement fuel reduction treatments, including approval for using the Categorical Exclusion for fuel 

reduction treatments, a process for complying with the National Environmental 

Policy Act of 1969 (P. L. 91-190) (NEPA) that reduces the documentation required 

for planning these activities. In addition, HFRA reduced the number of alternatives 

that must be considered in NEPA analysis and added specific public involvement and 

collaboration requirements. Although these initiates streamlined consideration of fuel 

reduction treatments under NEPA, they did not exempt these treatments from the 

requirements of the Act.

What Are Cumulative Watershed Effects?

When a federal agency proposes a land management action, its potential cumulative 

environmental effects must be considered, along with direct and indirect effects, and 

documented in a public report that the proposing agency prepares to comply with the 

NEPA. This report may be an Environmental Impact Statement (EIS), Environmental 

Assessment (EA), or Categorical Exclusion (CE), depending on the nature of the action and the likelihood of significant effects. Thus, to comply with NEPA, cumulative 

effects are among the environmental impacts of proposed major federal actions and 

any alternative actions that federal agencies must present for public review.

The basic concept of a cumulative effects analysis is to identify and consider the 

total effects of actions that overlap temporally or spatially and might be missed by 

Chapter 1. Introduction to Synthesis of Current Science Regarding Cumulative Watershed Effects of Fuel Reduction Treatments
USDA Forest Service RMRS-GTR-231. 2010. 3

evaluating each action individually. The goal of cumulative effects analysis is to provide government decision makers and the public considering proposed federal projects 

with comprehensive information about “the impact on the environment which results 

from the incremental impact of the action when added to other past, present and reasonably foreseeable future actions”(40 CFR 1508.7). In general terms, cumulative 

effects may arise from single or multiple actions that may result in additive, interactive, direct, or indirect effects. Cumulative watershed effects are the net impact on 

watersheds of multiple management activities that may coincide geographically and 

temporally.

Although cumulative effects are defined by NEPA, concepts related to cumulative watershed effects also come into play in the application of other more restricted 

environmental laws. The Clean Water Act of 1972 (P.L. 92-500) (CWA) requires that 

both point sources (in other words, having a readily identifiable origin) and nonpoint 

sources (such as, lacking a readily identifiable origin) of water pollution be controlled, 

especially in waters that have been designated by states as not meeting water quality 

standards under section 303b of CWA. A common reason that nonpoint sources are 

not easily attributable to distinct locations is that they are spatially and/or temporally 

dispersed and thus may be the result of cumulative watershed effects. In addition, 

the Endangered Species Act of 1973 (P.L. 93-205) (ESA) protects species that are at 

risk of extinction (listed under the Act as “threatened” or “endangered”) from actions 

by federal agencies that could reduce the number of these organisms or their habitat. 

Where species listed under ESA dwell in aquatic or riparian habitats, these species 

or their habitat may be at risk from multiple management activities occurring at a 

watersheds scale, that is, as a result of cumulative watershed effects. These examples 

are not exhaustive. Laws such as the Clean Air Act of 1970 (P.L. 91-604), National 

Historic Preservation Act of 1966 (P. L. 89-665, section 106), and others have requirements of their own that, under some conditions, may call for a cumulative effects 

analysis. If, for a given landscape, the consideration of cumulative watershed effects 

for complying with multiple laws becomes an issue for fuel reduction treatments or 

other land management practices, a more comprehensive watershed-scale analysis 

that meets the requirement of all these laws simultaneously might be warranted. This 

synthesis could provide a scientific basis for developing such a comprehensive watershed analysis to address multiple laws should federal land managers find it necessary.

Evidence of Cumulative Watershed Effects

Implementation of fuel reduction treatments at large scales has only begun recently 

so direct evidence of its cumulative watershed effects is likely to be scarce. However, 

cumulative effects of other land management activities have been measured at watershed scales. A classic example comes from a study of fish habitat in streams from 

across the Columbia River Basin (McIntosh and others 2000). In this study, habitat 

for anadromous fish in 122 streams that had been originally surveyed in the 1930s and 

1940s was remeasured in the 1980s and 1990s. With the exception of streams in roadless watersheds, the prime habitat features in these streams showed significant losses 

over the intervening 60 years (for example “large pools” decreased by 24% and “deep 

pools” decreased 65%). An analysis of land management practices in these watersheds showed that no single practice or project was clearly responsible for the loss of 

habitat in these watersheds. Instead, they found that a wide spectrum of land uses had 

occurred within the watersheds of the degraded streams, including forestry, grazing, 

urbanization and road construction. It was the aggregate impact of all these practices, 

that is, the cumulative effect of all the land uses that had caused the habitat loss. By 

comparison, in watersheds with little or no change in land use over the period (which 

the authors represented by examining watersheds with no roads), aquatic habitat condition had remained constant or improved, reinforcing the conclusion that cumulative 

effects of multiple land management activities had caused the degradation. The lesson 

from this study for large-scale fuel management is that wide-spread land management 

Douglas F. Ryan Cumulative Watershed Effects of Fuel Management in the Western United States
4 USDA Forest Service RMRS-GTR-231. 2010.

activities have the potential to cause significant, real impacts on aquatic systems even 

where the impacts of individual local projects may be small or difficult to measure.

Considering Cumulative Watershed Effects in 

Fuel Management

It is critical that cumulative watershed effects be considered early as part of planning 

and implementing fuel reduction treatments in the current legal and policy environment. 

Under HFI and HFRA, NEPA analysis is not waived. HFRA streamlined NEPA analysis 

by reducing the number of alternatives that must be considered and added requirements 

for public collaboration, but did not exempt or waive any projects from NEPA analysis. 

While HFI included Categorical Exclusions for fuel reductions treatments, the intent was 

to use an approach that more efficiently complies with NEPA requirements and likewise 

does not waive consideration under NEPA. Although a brief discussion of NEPA requirements follows, it is the purpose of this synthesis to assess what valid scientific information 

is available to assess the cumulative watershed effects of fuels reduction treatments, rather 

than explain in detail the legal requirements for documenting these effects. Planning teams 

may use information in this report to produce environmental documents at the appropriate 

level.

On National Forest lands, the forest planning rule approved in 2008 required that forest 

plans be written at a broad strategic scale. The Forest Service has determined that, at this 

broad scale, forest plans do not have environmental effects. Therefore, forest plans qualify 

for a Categorical Exclusion and do not require documentation in an EIS. As has been 

previously true, NEPA analysis will continue to be done for individual projects that are 

on the scale at which ground-disturbing activities are analyzed. In determining the scope 

of a proposed action, and the level of NEPA analysis needed, it is the responsible public 

official who is required to consider the action’s environmental effects, including direct, 

indirect, and cumulative impacts (see 40 CFR 1508.25). In other words, the responsible 

public official decides the appropriate level of detail for the cumulative watershed effects analysis for the fuels reduction project(s) in question. Under the 2008 planning rule, 

site-specific actions are required to comply with NEPA, and cumulative watershed assessments will be a key part of the strategic resource decisions on these forests in the future.

The Council on Environmental Quality (CEQ) gave guidance on when to include cumulative effects in NEPA analysis (CEQ 1997). A recent memo (CEQ 2005) stated that 

“except in extraordinary circumstances, proposed actions that are categorically excluded 

from NEPA analysis do not involve cumulative effects analysis.” This means that to be categorically excluded, a project must fit within specifically defined categories and must not 

involve extraordinary circumstances. For the Forest Service, extraordinary circumstances 

are defined as the degree of environmental impact to seven specific resource conditions 

listed in the Forest Service Handbook 1909.15, chapter 30, section 30.3. Fuel reductions 

treatments that meet these requirements may not have to undergo detailed cumulative 

watershed effects analyses.

Ultimately, it is the responsibility of the leadership and employees of the agency to find 

a balance between the broad set of laws and policies designed to produce the intended 

effect of protecting the public from wildland fire, while at the same time complying with 

other sets of laws intended to protect natural resources and the environment. If members 

of the public disagree with the balance that is struck, they have the right to challenge these 

management decisions through administrative procedures in the courts where these differences will be resolved.

Within this changing legal and policy arena, tools for analyzing cumulative watershed 

effects are likely to remain important for managers of natural resources. Cumulative effects are real, and sustaining multiple natural resources over the long run will require that 

they be considered. Streamlining requirements for analysis under NEPA or other rules 

assumes that these practices have impacts that are either insignificant or small compared 

to the long-term benefits from the proposed action. Courts and public opinion will likely 

Chapter 1. Introduction to Synthesis of Current Science Regarding Cumulative Watershed Effects of Fuel Reduction Treatments
USDA Forest Service RMRS-GTR-231. 2010. 5

place the burden on land managers to demonstrate that those assumptions are valid. The 

standard for showing that kind of validity usually requires predictions that are supported 

by the current science.

The Need for Science-Based Decisions

The unprecedented scope and scale of fuels reduction treatments being undertaken by 

Federal land managers also makes a strong argument for developing available and scientifically based tools to estimate their potential cumulative effects. A recent, tragic example 

illustrates the vital role that tools play in bringing scientific information to bear on large 

scale problems. An analysis of the structural failure that caused the collapse of the World 

Trade Center Towers (WTCT) on September 11, 2001 was presented on Public Television 

(PBS, 2002). Paradoxically, the analysis showed that the buildings were not brought down 

by the physical impact of the airplanes that crashed into them. Instead, the buildings failed 

because of damage caused by the heat of the subsequent fires that were fueled primarily 

by the contents of the building themselves and not by the aircraft fuel that had only served 

to start the fire.

In an interview, the lead engineer who designed the buildings pointed out with some 

pride that at the time they were designed, the WTCT were not only the tallest buildings 

ever constructed but were also the first designed to withstand the physical impact of a large 

airplane. His design had succeeded to the degree that the initial impacts had not brought 

the buildings down. When asked why the buildings had failed to survive the effects of the 

subsequent fire, the engineer admitted that he was not able to consider the effects of such 

a fire in the buildings’ design. At the time, there were no models available of how a fire of 

that magnitude would affect the structure of such a large building. In effect, the science of 

building fires was not available in the form and format (that is as a useful tool) that would 

permit practitioners to use it to evaluate this critical question at the scale of the problem 

they faced. The lesson from this example is that when decision makers must tackle projects outside of the previous scope and scale that they have experienced, the relevant body 

of science, where it exists, may be of little practical use if it has not been interpreted and 

articulated as tools that are directly useful for addressing problems at the proper scale.

Applying this lesson to fuels reduction treatments, land managers are planning these 

treatments at unprecedented geographic and temporal scales. If tools based on current science are not available, it is possible that planners and managers may not be able to include 

cumulative watershed effects in a meaningful way in designing and implementing fuel 

reduction treatments. Alternatively, if courts decide that fuel reduction treatments cannot 

proceed unless adequate cumulative watershed effects analysis are part of their planning, 

these treatments may be delayed until useful tools are developed that incorporate the latest 

science. In either case, developing tools that predict cumulative watershed effects of fuels 

reductions based on current science will be important.

Potential Uses of This Synthesis

This synthesis of the current literature on cumulative watershed effects is a first step 

toward developing useful tools for managers to consider these effects when planning 

and implementing fuel reduction treatments. It assembles in one place the current state 

of thinking that was previously scattered across many outlets in the scientific literature. 

At the minimum, it should provide managers, planners, and policy makers with a place 

to start when they have questions about this topic.

This synthesis, however, goes beyond being a central source of scientific information 

on this subject. Although cataloguing and summarizing the literature are useful, this report 

tries to go further to anticipate questions that are likely to be posed by managers, planners 

and policy makers by asking them of the literature. By doing this, the audience can be 

informed about what relevant questions the current science can and cannot answer. The 

Douglas F. Ryan Cumulative Watershed Effects of Fuel Management in the Western United States
6 USDA Forest Service RMRS-GTR-231. 2010.

“science gaps” are at least as important as the current knowledge because it is in these gaps 

that management and policy may lack science for guidance. These are areas in which managers and policy makers should be cautious because the outcomes of their actions in these 

areas may not be reliably predicted with a scientific basis, produce unforeseen outcomes, 

or be vulnerable to legal challenges. Identifying critical knowledge gaps also performs 

an important function for the science community. Future research and development that 

fill these gaps could potentially have a high payoff for managers and policy makers. This 

science synthesis may only be a first step toward providing useful tools. If managers, 

planners, or policy makers find that they need more detailed or explicit tools, the peerreviewed knowledge gathered in a synthesis can provide an information base from which 

to start developing tools that meet those further needs.

The value of this synthesis will depend strongly on how well it reinterprets existing 

knowledge in the face of a new question. While it is true that a synthesis of the current 

literature may be a reworking of existing information, asking new questions of old data 

often casts them in new light. When done thoughtfully, new questions may suggest new 

insights that have not previously been considered. The questions considered here are 

indeed new because they involve the implications of a new management practice being 

imposed on the landscape at unprecedented scales of space and time.

Conclusion

In the end, this synthesis will be judged by its usefulness to future policy and management decision makers and as a starting point for future researchers and tools developers. 

We will leave it to you, our readers, to decide how well this document meets your particular needs. As you use this document, if you find other pressing questions that we did 

not anticipate or address, we urge you to ask the science community to answer them. 

If this report is used in these ways, it will have served its purpose to advance the state 

of land management and policy making and set the stage for future research and tools 

development.

References

Council on Environmental Quality [CEQ]. 2005. Guidance on the consideration of past actions 

in cumulative effects analysis, James L. Connaughton, Chairman. Memo dated June 24, 2005.

Council on Environmental Quality [CEQ]. 1997. Considering cumulative effects under the 

National Environmental Policy Act. Council on Environmental quality. Executive Office of 

the President. TD194.65 C65 1997 Washington, DC. 62 p.

McIntosh, B.A.; Sedell, J.R.; Thurow, R.F.; Clarke, S.E.; Chandler, G. 2000. Historical changes in 

pool habitats in the Columbia River Basin. Ecological Applications 10(5) 1478-1496.

Public Broadcasting Service [PBS]. 2002. “Why the Towers Fell.” Airdate April 30, 2002. 

[Online]. http://www.pbs.org/wgbh/nova/transcripts/2907_wtc.html [July 2009]

Lafayette, R.; Brooks, M.T.; Potyondy, R.P.; Audin, L.; Krieger, S.; Trettin, C.C. [Eds.]. (In 

review.) Cumulative watershed effects of fuel management in the Eastern United States. Gen. 

Tech. Rep. Asheville, NC. U.S. Department of Agriculture, Forest Service, Southern Research 

Station.

Westerling, A.L.; Hidalgo, H.G.; Cayan, D.R.; Swetnam, T.W. 2006. Warming and earlier 

spring increases. Western U.S. Forest Wildfire Activity. ScienceXpress [Online]. http://www.

newforestry.org/shfsc/fireplan/pdfs/regional/Westerling-07-07-06.pdf [August 2009]

White House. 2002. Healthy Forest Initiative. [Online]. http://georgewbush-whitehouse.archives.

gov/infocus/healthyforests/ [July 2009].

Chapter 1. Introduction to Synthesis of Current Science Regarding Cumulative Watershed Effects of Fuel Reduction Treatments
USDA Forest Service RMRS-GTR-231. 2010. 7

Chapter 2.

Fire Regimes and Ecoregions1

Robert G. Bailey2, Rocky Mountain Research Station, USDA Forest Service, 

Fort Collins, CO

Introduction

The public land management agencies are phasing in a radically new approach to 

land management. They are shifting from their focus on individual resources to a more 

holistic approach of managing whole ecosystems. Fire-excluded systems are prone to 

changes in composition and density and are susceptible to catastrophic fire and invasion 

by non-native species. The cause of the problem in many areas includes more than a 

century of fire exclusion and suppression along with increased human development at 

the wildland-urban interface. Grazing and logging have also contributed to this problem.

To correct this problem, fire and land management must return ecosystems to a 

healthier, sustainable condition. One way to do this is to modify the current structure of 

ecosystems to mimic natural structures (Bailey 2002).

Ecosystem Structure and Process

Ecosystem structure and process are related. For example, riparian forests evolved 

with flooding, and fire-adapted forests evolved with fire of varying frequency and intensity. For ecosystems to be able to sustain natural structures, they will need to experience 

the same kinds of processes in which they evolved (Allen and others 2002; Savage 2003).

Range of Variation

Restoration works best if ecosystems are returned to within a “natural range of variation” (Landres and others 1999). Ecosystems, for example, have variability not only 

through time because of climate change, but across the landscape and the nation because 

of disturbance events, successional processes, and natural climatic variation in addition to 

climate change. From forests, to desert, to steppe, the continent’s ecosystems vary vastly. 

It is not possible to reconstruct how each system looked in the past. Instead, we can reset 

altered ecosystems back to within a range of natural variability. As Melissa Savage (2003) 

puts it, “If we can restore the natural processes, the natural structure should follow.”

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States

1 This chapter is derived from a presentation at the annual meeting of the Association of American Geographers, Denver, Colorado USA, held 

April 5 through 9, 2005. 2 Formerly with the Inventory and Monitoring Institute, USDA Forest Service, Fort Collins, Colorado.
8 USDA Forest Service RMRS-GTR-231. 2010.

Climate, Ecoregions, and Fire Regimes

To restore altered systems and to understand how and why they are distributed, we 

must understand the processes of how they form. Climate largely determines ecosystem 

differences. As it varies, the other components vary in response. As a result, ecosystems 

of different climates differ significantly (Bailey 1996).

The most important climatic factor in determining the distribution of ecosystems is 

the climatic regime, defined as the daily and seasonal fluxes of energy and moisture. 

For example, tropical rainforest climates lack seasonal periodicity, whereas midlatitude steppes have pronounced seasons. As the climatic regime changes, so does the 

hydrologic cycle, as reflected in the streamflow of rivers located in different climatic 

regions. For example, no water flows in creeks located in the warm, dry summer region of California during summer and fall, but in winter and early spring, groundwater 

contributes to streamflow. Climate profoundly affects landforms and erosion cycles. 

Such effects are evident when we contrast the angularity of arid land topography of the 

Colorado Plateau with the rounded slopes of the humid Blue Ridge Mountains. Plants 

and animals have adjusted their life patterns to the basic environmental cycles produced 

by the climate. Whenever a marked annual variation occurs in temperature and precipitation, a corresponding annual variation occurs in the life cycle of the flora and fauna. 

Climate also determines the distribution, frequency, and density of natural ignitions.

Controls over the climatic effect change with scale. At the macroscale, ecosystem 

patterns are controlled by macroclimate (in other words, the climate that lies above 

the local modifying effects of landform and vegetation). Based on macroclimatic conditions, I subdivided the continents into ecoclimatic zones, also known as ecosystem 

regions, or ecoregions. They were mapped at a scale of 1:30,000,000 (Bailey 1989). 

Three hierarchical levels of macroclimatic differentiation are shown (in order that reflect finer scale climatic differences: domain, division, and province). The domains and 

divisions are based largely on the climatic zones of Köppen (1931) as modified by 

Trewartha (1968). While the Köppen-Trewartha system is based on climate, there is 

good correspondence between its climatic types and the natural climax vegetation types 

and soils within them (Bailey 1996)3

. Because of this, it was considered a logical basis 

for ecological zoning. A major advantage to using the system is it is based on quantitative definitions and as such, can be applied to any part of the Earth where climatic data 

are available4. The zoning was made hierarchical using Köppen-Trewartha’s climatic 

groups and climatic types as ecoregion domains and divisions, respectively, (table 1). At 

the second level (division), further differentiation was made according to landform—

distinguishing mountains with altitudinal zonation from lowland plains.

The climate is not completely uniform within level 2 (division), so a further subdivision was undertaken. Within the dry climates, for example, there is a wide range of 

degree of aridity, ranging from very dry deserts through transitional levels of aridity in 

the direction of adjacent moist climates. We refer to these as climate subtypes. The subtypes largely correspond to major plant formations (for example, broadleaved forest), 

which are delimited on the basis of macro features of the vegetation by concentrating on 

the life-form of the plants. They form the basis for subdividing ecoregion divisions into 

provinces, and are based on a number of sources, including a world map of landscape 

types (Milanova and Kushlin 1993). Of course, not all the space is taken up by the formation, because the nature of the topography will allow the differentiation into many 

habitats. One ignores these local variations in mapping climatic regions (and therefore 

ecoregions).

3 This is largely because Köppen derived his climate classes from observations on the distribution of vegetation types on various continents.

4 Others have followed this precedent for using Köppen-Trewartha in global ecological zoning. One good example was carried out by the 

United Nation’s Foreign Agricultural Organization (FAO), who developed an ecological zone map for the Forest Resource Assessment 2000 

(FAO 2001) using a combination of vegetation characteristics and Köppen-Trewartha.

Chapter 2. Fire Regimes and Ecoregions
USDA Forest Service RMRS-GTR-231. 2010. 9

I also used this approach to construct a 1:7,500,000-scale map of ecoregions for 

the United States (Bailey 1976, revised 1995). A simplified, reduced-scale map of the 

second highest of three hierarchical levels (division) appears in (fig. 1). They were delineated using both macroclimate data and a map of existing climax or potential vegetation 

by Küchler (1967). More information on the rationale I used for identifying ecoregion boundaries on maps of the United States and the world’s continents is presented 

elsewhere (Bailey 2005). In 1993, as part of the National Hierarchical Framework of 

Ecological Units (Cleland and others 1997), the Forest Service adopted the ecoregion 

classification system for use in ecosystem management.

It seems reasonable that regions that differ substantially in background climate 

should have different fire regimes. In fact, fires burn with more or less regular rhythms. 

The simplest means to reveal a fire regime is to consider the distribution of water within 

an ecosystem. If they are too wet, they won’t burn. The ecosystem’s moisture changes 

with the daily and seasonal fluxes of the moisture of air masses as they move through 

the region. Long-term fire records around the Pacific Ocean trace nicely the pulses of 

the Pacific Decadal Oscillation. In this oscillation, the Pacific alternates from warm to 

cool phases and causes wet and dry periods on the adjacent North American continent. 

These wet-dry rhythms set the ecological cadence for fire regimes.

Table 1. Ecoregion global framework.

Ecoregion Level 1 – Domain Ecoregion Level 2 – Division

Criteria Criteria

(equivalent to Köppen- (approximate equivalent KöppenTrewarthaa Trewarthaa types, in combination

Name climatic groups) Name Code with vegetation physiognomy)

Polar No more than 3 months Icecap 11 All months below 0 oC. Perpetual snow

over 10 oC and ice.

Tundra 12 All months below 10 oC. Vegetation 

physiognomy: tundra.

Subarctic 13 Up to 3 months over 10 oC. Vegetation 

physiognomy: dense coniferous forest 

dominant.

Humid Eight months or Warm continental 21 Same as 220, warmest below 22 oC.

Temperate less over 10 oC Hot continental 22 4-7 months over 10 oC, coldest month 

below 0 oC, warmest above 22 oC.

Subtropical 23 Same as 260, no dry season.

Marine 24 4-7 months above 10 oC, coldest month 

over 0 oC.

Prairieb 25 Sub-humid. Vegetation physiognomy: 

grasslands.

Mediterranean 26 8 months over 10 oC, coldest below 

18 oC, dry summer.

Dry Evaporation > Tropical/subtropical steppe 31 Semi-arid: all months above 0 oC.

precipitation

Tropical/subtropical desert 32 Arid: 1⁄2 precipitation of steppes, all 

months above 0 oC.

Temperate steppe 33 Semi-arid: cold month below 0 oC.

Temperate desert 34 Arid: All months dry, cold month 

below 0 oC.

Humid All months without frost: Savanna 41 Same as 420, with 2 months dryc in winter

Tropical in marine areas over 

18 oC Rainforest 42 Wet: no dry season

a Köppen (1931), as modified by Trewartha (1968)

b Köppen (1931) did not recognize the prairie as distinct climatic type. Geographer’s recognition of the prairie climate (Borchert 1950) has 

been incorporated into the system presented here. The ecoregion classification system represents it at the arid side of the 210, 220, 

and 230 types. c

 A dry month is defined as the month in which the total precipitation, P, expressed in millimeters, is equal to less than twice the mean 

temperature (oC).

Robert G. Bailey Cumulative Watershed Effects of Fuel Management in the Western United States
10 USDA Forest Service RMRS-GTR-231. 2010.

Different Ecoregions, Different Fire Regimes

Different ecoregions produce different fire regimes. There are several studies that 

have looked at variation in fire regimes at the ecoregion scale. We will examine three 

of them.

Pre-Colonial Fire Regimes (Vale)

Pre-colonial fire regimes for different vegetation types in North America have been 

determined by analyzing fire scars. In areas lacking trees, the development of vegetation 

after recent fires and early journal accounts and diaries have been used to make inferences about fire regimes. Vale (1982) synthesized this information in his book, Plants 

and People.

Vale analyzed “natural” vegetation types based on ecoregions. He characterized fire 

regimes from 45 published studies of fire regimes or from his estimates of the fire regimes based on the fire ecology of the plant species in the areas mapped. He found that 

fire regimes varied by ecoregion (fig. 2). In the northern coniferous forest and woodland 

(boreal forest), for example, infrequent large-magnitude fires carried the flames in the 

Figure 1. Approximate boundaries of ecoregion divisions, conterminous United States from Bailey 1996.

Chapter 2. Fire Regimes and Ecoregions
USDA Forest Service RMRS-GTR-231. 2010. 11

canopy of the vegetation, killing most of the forest. Such fires are called “crown fires” 

because they burn in the upper foliage or crown of the trees.

Other environments, such as the deciduous forests of the east, probably had infrequent crown or severe surface fires. These areas are typically cool or wet and consist of 

vegetation that inhibits the start or spread of fire.

In mountainous regions, fire frequency is related to altitude, or elevation. The 

lower-elevation forests in the western United States had a regime of frequent, smallmagnitude, surface fires. Here, the burning was restricted to the forest floor and most 

mature trees survived. Ponderosa pine (Pinus ponderosa) forests are good examples of 

this kind of forest.

Fire Regime Types (The Nature Conservancy)

The Nature Conservancy (2004), working in cooperation with the World Wildlife 

Fund and the International Union for Conservation of Nature, has recently completed 

a global assessment of fire regime alteration on an ecoregional basis. The assessment 

identified three broad fire regime types (fig. 3). The report reveals that, among globally 

important ecoregions for conservation, 84 percent of the area is at risk from altered 

fire regimes. Almost half of priority conservation ecoregions can be classified as “firedependent” (shown in reddish brown).

In fire-dependent systems, fires are fundamental to sustaining native plants and animals. Many of the world’s ecosystems, from taiga forest to chaparral shrublands to the 

savanna, have evolved with fires. What characterizes all of these ecosystems is resilience and recovery following exposure to fires. In the case of chaparral, fire does not kill 

most of the shrub layer, they sprout back from root crowns.

Figure 2. Pre-colonial fire 

regimes of broad vegetation 

types (based on ecoregions) 

in North America. Only 

major divisions of the 

ecoregion map are shown 

(from Vale (1982); reprinted 

with permission of the 

Association of American 

Geographers).

Robert G. Bailey Cumulative Watershed Effects of Fuel Management in the Western United States
12 USDA Forest Service RMRS-GTR-231. 2010.

Thirty-six percent of these important ecoregions are fire-sensitive. In these regions, 

frequent, large and intense fires were, until recently, rare events. In these systems, plants 

lack adaptations to allow them to rapidly rebound from fire. These areas are typically 

cool or wet and consist of vegetation that inhibits the start or spread of fire. Examples 

include the tropical moist broadleaf forest and temperate rainforests.

Eighteen percent are classified as fire-independent ecosystems. Here, fires are largely 

absent because of a lack of vegetation or ignition sources, such as in Africa’s Namibian 

Desert or in tundra ecosystems in the arctic.

According to The Nature Conservancy (2004), fire regimes are degraded in over 

80 percent of globally important ecoregions. The majority of North American forests 

and grasslands are adapted to fire of varying frequencies and intensities. Fire-excluded 

systems are prone to changes in composition and density, and are susceptible to catastrophic fire and invasion by non-native species. Fire-loving invasive alien plants can 

drastically change the fire regimes of both fire-dependent and fire-sensitive ecosystems 

(fig. 4).

Characterizing U.S.A. wildfire regimes (Malamud, Millington, and Perry)

Researcher Bruce Malamud and colleagues report that the spread of wildfires and 

their severity patterns show distinct regional styles across the United States (Malamud 

and others 2005). Using high-resolution Forest Service wildfire statistics, this study was 

based on 31 years (1970-2000) of wildfire data consisting of 88,916 fires ≥1 acre on the 

National Forest System. To allow spatial analysis with regard to the biophysical factors 

that drive wildfire regimes, the researchers classified the wildfire data into ecoregion 

divisions (areas of common climate, vegetation, and elevation). In each ecoregion, they 

asked: What is the frequency-area distribution of wildfires? The study compared area 

Figure 3. Dominant fire regimes in priority ecoregions for biodiversity conservation. Reddish brown areas are fire dependent; 

green areas are fire sensitive; and gray areas are fire independent (Copyright, The Nature Conservancy; reproduced with 

permission).

Chapter 2. Fire Regimes and Ecoregions
USDA Forest Service RMRS-GTR-231. 2010. 13

burned, number of fires, and the wildfire recurrence interval. These parameters were 

calculated at the ecoregion division level (fig. 5). The study created maps to display 

wildfire patterns and risk for the entire continental United States.

The authors found that the ratio of large to small wildfires decreases from east to west 

(fig. 6B). There is a relatively higher proportion of large fires in the west compared to 

the east. This may be due to greater population density and increased forest fragmentation. Alternatively, the observed gradient may be due to natural drivers, with climate, 

vegetation, and topography producing conditions more conducive to large wildfires.

Figure 4. Nonnative cheatgrass 

(Bromus tectorum) 

is invading 

sagebrush steppe 

in the western 

United States 

(photograph 

copyright, 

The Nature 

Conservancy; 

reproduced with 

permission).

Figure 5. Ecoregion 

divisions and U.S. 

Forest Service 

lands.

Robert G. Bailey Cumulative Watershed Effects of Fuel Management in the Western United States
14 USDA Forest Service RMRS-GTR-231. 2010.

The fire recurrence interval differs markedly between ecoregions. For example, the 

fire cycle values ranged from 13 years for the Mediterranean Mountains Ecoregion to 

203 years for the Warm Continental Ecoregion (fig. 6B). Note the term “fire cycle” does 

not mean that a fire will occur “every” 13 years, or “every” 203 years. It is a probabilistic hazard. For example, a recurrence interval of 100 years would mean that in ANY 

year, we have a 1 in 100 chance of a fire of a given size.

Other Studies

In other studies, gradients similar to those observed by Malamud and others (2005) 

have been described and related to climate and vegetation. Turner and Romme (1994) 

describe wildfire occurrence gradients as a function of altitude and latitude. They attribute these gradients to broad climatic variation and note western and central regions tend 

to have frequent fires with forest stand structures dominated by younger trees, whereas 

the eastern region experiences longer inter-fire intervals and older stand structures. A 

Figure 6. Maps of wildfire patterns across the 

conterminous United States for years 1970 

to 2000 for U.S. Forest Service wildfires 

classified by ecoregion division. (A) Ratio 

of large to small wildfires. The darker the 

color, the greater the number of large fires. 

(B) Fire recurrence interval. The legend 

goes from dark red to white, representing 

“high” to “low” hazard (from Malamud 

and others 2005).

Chapter 2. Fire Regimes and Ecoregions
USDA Forest Service RMRS-GTR-231. 2010. 15

statistical forecast methodology developed by Westerling and others (2002) exploits 

these gradients to predict area burned by western United States wildfires, by ecoregion, 

a season in advance.

Littell et al. (2009) found that climate drivers of synchronous fire differ regionally. 

They identified four distinct geographic patterns of ecoregion provinces (ecoprovinces) across the West, each associated with a unique set of climate drivers of annual 

area burned by wildfire. For example, in northern mountain ecoprovinces, dry, warm 

conditions in the seasons leading up to and including the fire season are associated 

with increased area burned, suggesting that fuel condition that is dry vs. wet, was the 

key determinant of regionally synchronous fires. In contrast, in the southwestern dry 

ecoprovinces, moist conditions the seasons prior to the fire season are more important 

than warmer temperatures or drought conditions in the year of the fire, suggesting that 

fuel abundance determined large fire years.

Use of Fire Regime at the Ecoregion Scale

The results of these studies can be used to assess burn probabilities across the nation to identify areas with high risk. This helps government agencies to better plan for 

wildfire hazards. They can also be used as a baseline from which to assess natural fire 

regimes, which can be used to abate the threat of fire exclusion and restore fire-adapted 

ecosystems. In fact, these baseline reference conditions are currently being developed 

as part of the LANDFIRE project (http://www.landfire.gov) by the United States Forest 

Service (Missoula Fire Sciences Laboratory), the U.S. Geological Survey (EROS Data 

Center), and The Nature Conservancy for all biophysical systems across the United 

States. In addition, an understanding of fire regimes at the ecoregion scale can provide 

valuable insights important for designing fuel treatments by helping to identify high 

from low hazard situations.

Finally, what can be done to reduce the risk of fire? Savage (2003) and Allen and 

others (2002) suggest several principles to guide the implementation of ecologically 

justifiable restoration projects. Two of the most important principles are:

1. Restoration of natural fire regimes (for example, in southwestern ponderosa pine 

forests to reduce the widespread risk of crown fires by return to low-intensity surface 

fire);

2. Pay attention to both structure and process (for example, thinning young trees to reduce 

the fuel load may not work unless low-intensity surface fires are also reintroduced).

Recent data from the Forest Service reflects the scale of the challenge. Schmidt and 

others (2002) mapped fire regime condition class (FRCC), which is an ecological metric 

used by federal agencies, The Nature Conservancy (2004), and others to determine the 

degree to which the vegetation and fire regimes of a given area have changed compared 

to reference conditions. As shown on the Schmidt and others (2002) map (fig. 7), fire 

management has significantly changed the fuel levels of many forests, and concurrently, 

the frequency and intensity of fire. About 30 percent of all ownerships (except those 

related to agricultural, barren, and urban land) are in high risk categories (shown in yellow and red). In many ecoregions, this percentage is much higher. For example, in the 

mountains of the southwest, as much as 83 percent is moderately to severely altered5

.

5 Finer resolution and more accurate FRCC maps are being produced by the LANDFIRE project. For more information, see

http://www.landfire.gov.

Robert G. Bailey Cumulative Watershed Effects of Fuel Management in the Western United States
16 USDA Forest Service RMRS-GTR-231. 2010.

Why Ecoregions Are Needed

The same forest type can occur in different ecoregion divisions. For example, ponderosa pine forests occur in the northern Rockies and the Southwest. This does not 

imply that the climate, topography, soil, and fire regime are necessarily the same. In the 

Southwest, the historical fire regime is of frequent, low-intensity surface fires that tend 

to maintain open, multi-age forests. Farther to the north in the Rockies, cooler conditions mean moister forests in which fires burn less readily. This distinction is important 

because fire management strategies and restoration protocols are often applicable only 

to the region in which they were developed. Therefore, management strategies planned 

to address the fire and fuel issue, such as those documented in the interagency National 

Fire Plan, should take into consideration ecoregional variation in fire regimes. This 10-

year comprehensive strategy can be viewed online at: http://www.fireplan.gov.

Use of Ecosystem Patterns Within Ecoregions

Macroclimate accounts for the largest share of systematic environmental variation at 

the macroscale or ecoregion level. At the mesoscale level, physiography (geology and 

landform) modifies the macroclimate and exerts the major control over ecosystem patterns and processes within climatic zones. With this in mind, Bailey and others (1994) 

used physiographic factors to subdivide the ecoregion provinces of the United States 

into subregional areas, or sections that have different landform characteristics6

. These 

differences are important because the character of the landform with different geology 

will vary in the climatic zone. In the same climatic zone, different geologies, such as 

granitic mountains or volcanic plateaus, will weather and erode differently forming different landform relief. Where this occurs, the spread of a disturbance such as wildfire 

may differ among landforms. Swanson and others (1990) hypothesized that in forested, 

steep-mountain landforms along the northwest coast of the United States, where landform relief does not exceed several tree heights (for example, Coast Ranges), disturbance 

agents such as fire and wind can readily move through the forest with little regard for topography. Landforms may have a greater effect on the spread of disturbance and mosaic 

6 Cleland and others (2005) developed another approximation of section boundaries as shown on a revised version of the 

ecological subregions map.

Figure 7. Fire regime condition class 

(as mapped by Schmidt and others 

2002) with ecoregion division 

boundaries (thick black lines). Green 

areas (condition class 1) are largely 

intact and functioning; yellow areas 

(condition class 2) are moderately 

altered; red areas (condition class 3) 

are significantly altered; and gray 

areas are non-vegetated, agricultural, 

or urban.

Chapter 2. Fire Regimes and Ecoregions
USDA Forest Service RMRS-GTR-231. 2010. 17

structure where relief substantially exceeds tree height (for example, Cascade Range). 

The classification and mapping of physiography, as was done to delineate ecological 

subregions at the section level, should provide an important means of discriminating 

broad areas with differing fire regimes within a particular ecoregion.

 At finer scales, one finds considerable variation in fire regimes in response to local 

topography, vegetation, and microclimate (Cleland and others 2004). As we have seen, 

local ecosystems occur in predictable patterns within a particular ecoregion. Similar fire 

regimes occur on similar sites within an ecoregion. Knowledge about fire regimes on 

similar sites allows ecological restoration so as to incorporate the natural variability of 

fire regimes across the ecoregion.

Future Range of Variation

The range of variation concept is a useful starting point, but it is limited for a number 

of reasons. First, many systems have been fragmented because of human disturbance. 

Because of this, fires will not carry the way they did historically. Second, the introduction of non-native species (for example, cheatgrass) has made permanent changes in 

fire frequencies. Third, fire size and intensity of the past are clearly not acceptable in 

developed areas. And fourth, system boundaries and fire regimes will change as the climate changes (McKenzie and others 1996). Therefore, only where possible, we need to 

restore the natural range of variation. We must also determine our feasible alternatives 

for the “Future Range of Variation.”

References

Allen, C.D.; Savage, M.; Falk, D.A.; Suckling, K.F.; Swetnam, T.W.; Schulke, T.; Stacey, P.B.; 

Morgan, P.; Hoffman, M.; Klingel, J.T. 2002. Ecological restoration of southwestern ponderosa 

pine ecosystems: A broad perspective. Ecological Applications. 12(5):1418-1433.

Bailey, R.G. 1976. Map. Ecoregions of the United States. Ogden, Utah. USDA Forest Service. 

Intermountain Region. Scale 1:7,500,000.

Bailey, R.G. 1989. Ecoregions of the continents—scale 1:30,000,000. Supplement in 

Environmental Conservation. 16(4): 307-309.

Bailey, R.G. 1995. Description of the ecoregions of the United States, 2nd ed. Misc. Pub. No. 1391 

(rev.). Washington, DC. USDA Forest Service. With separate map at 1:7,500,000.

Bailey, R.G. 1996. Ecosystem geography. New York. Springer Verlag. 204 p.

Bailey, R.G. 2002. Ecoregion-based design for sustainability. New York. Springer Verlag. 222 p.

Bailey, R.G. 2005. Identifying ecoregion boundaries. Environmental Conservation. 34 Suppl. 1, 

S14-S26.

Bailey, R.G.; Avers, P.E.; King, T.; McNab, W.H. [Eds.]. 1994. Map. Ecoregions and subregions of 

the United States. Washington, DC. U.S. Geological Survey. Scale 1:7,500,000. Accompanied 

by supplementary table of map unit descriptions compiled and edited by W.H. McNab and 

R.G. Bailey.

Borchert, J.F. 1950. The climate of the central North American grassland. Annals of the Association 

of American Geographers. 40: 1-39.

Cleland, D.T.; Avers, P.E.; McNab, W.H.; Jensen, M.E.; Bailey, R.G.; King, T.; Russell, W.E. 

1997. National hierarchical framework of ecological units. In: Boyce, M.S.; Haney, A. [Eds.]. 

Ecosystem management: Applications for sustainable forest and wildlife resources. New 

Haven, Connecticut. Yale University Press: 181-200.

Cleland, D.T.; Crow, T.R.; Saunders, S.C.; Dickmann, D.I.; Maclean, A.L.; Jordan, J.K.; Watson, 

R.L.; Sloan, A.M.; Brosofske, K.D. 2004. Characterizing historical and modern fire regimes in 

Michigan (USA): A landscape ecosystem approach. Landscape Ecology. 19: 311-325.

Cleland, D.T.; Freeouf, J.A.; Keys, Jr., J.E.; Nowacki, G.J.; Carpenter, C.A.; McNab, W.H. 2005. 

Map. Ecological subregions: Sections and subsections of the conterminous United States. CDROM. Washington, DC. USDA Forest Service. Scale 1:3,500,000. [Online]. http://svinetfc4.

fs.fed.us/research/section/index.html. [July 2009].

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18 USDA Forest Service RMRS-GTR-231. 2010.

Foreign Agriculture Organization (FAO) of the United Nations. 2001. Global ecological zoning 

for the Forest Resources Assessment 2000. Rome, Italy. FAO. Forestry Department. [Online]. 

http://www.fao.org/docrep/006/ad652e/ad652e00.htm [July 2009].

Köppen, W. 1931. Grundriss der klimakunde. Berlin: Walter de Gruyter. 388 p.

Küchler, A.W. 1967. Potential natural vegetation of the United States. Washington, DC. U.S. 

Geological Survey, National Atlas: 89-90.

Landres, P.B; Morgan, P.; Swanson, F.J. 1999. Overview of the use of natural variability concepts 

in managing ecological systems. Ecological Applications. 9(4): 1179-1188.

Littell, J.S.; McKenzie, D.; Peterson, D.L.; Westerling, A.L. 2009. Climate and wildfire area 

burned in western US ecoprovinces, 1916-2003. Ecological Applications. 19(4): 1003-1021.

Malamud, B.D.; Millington, J.D.A.; Perry, G.W. 2005. Characterizing wildfire regimes in the 

United States. Proceedings National Academy of Sciences. 102: 4694-4699.

McKenzie, D.; Peterson, D.L.; Alvarado, E. 1996. Predicting the effect of fire on large-scale 

vegetation patterns in North America. Res. Paper PNW-RP-489. Portland, OR. USDA Forest 

Service. Pacific Northwest Research Station. 38 p.

Milanova, E.V.; Kushlin, A.V., [Eds.]. 1993. World map of present-day landscapes: An explanatory 

note. Moscow, Russia. Moscow State University. Separate map at 1:15,000,000. 33 p.

Nature Conservancy, The. 2004. Fire, ecosystems and people. Tallahassee, FL. Global Fire 

Initiative. 9 p.

Savage, M. 2003. Restoring natural systems through natural processes. Quivera Coalition 

Newsletter. 6(2): 1, 20-27.

Schmidt, K.M.; Menakis, J.P.; Hardy, C.C.; Hann, W.J.; Bunnell, D.L. 2002. Development of 

coarse-scale spatial data for wildland fire and fuel management. RMRS GTR-87. Fort Collins, 

CO. USDA Forest Service. Rocky Mountain Research Station. 41 p.

Swanson, F.J.; Franklin, J.F.; Sedell, J.R. 1990. Landscape patterns, disturbance, and management 

in the Pacific Northwest, USA. In: Zonneveld, I.S.; Forman, R.T. [Eds.]. Changing landscapes: 

An ecological perspective. New York. Springer Verlag: 191-213.

Trewartha, G.T. 1968. An introduction to climate, 4th ed. New York. McGraw-Hill. 

408 p.

Turner, M.G.; Romme, W.H. 1994. Landscape dynamics in crown fire ecosystems. Landscape 

Ecology. 9(1): 59-77.

Vale, T.R. 1982. Plants and people. Washington, DC. Association of American Geographers. 88 p.

Westerling, A.L.; Gershunov, A.; Cayon, D.R.; Barnett, T.P. 2002. Long-lead statistical forecasts 

of area burned in western U.S. wildfires by ecosystem province. International Journal of 

Wildland Fire. 11: 257-266.

Chapter 2. Fire Regimes and Ecoregions
USDA Forest Service RMRS-GTR-231. 2010. 19

Chapter 3.

Fuel Management in Forests of the 

Inland West

Russell T. Graham, Rocky Mountain Research Station, USDA Forest Service, Moscow, ID

Theresa B. Jain

Susan Matthews, National Forests in Florida, USDA Forest Service, Tallahassee, FL

Introduction

Recent estimates indicate that nearly 40.5 million ha (100 million ac) of forest lands 

that were historically burned by frequent surface fires in the western United States may 

benefit from the restoration of surface fire. An additional 4.5 million ha (11 million ac) 

of forests need to be treated to protect communities from wildfire (Aplet and Wilmer 

2003). Rummer and others (2003) estimate that over 26.7 million ha (66 million ac) of 

forestlands could benefit from fuel reduction. Even with uncertainties in these estimates 

and arguments as to their precision and accuracy, they clearly illustrate the staggering 

number of hectares (acres) that need fuel treatments in order to modify fire behavior 

and burn severity. Access and operability issues further limit the options available on a 

large portion of western forests. Costs and lack of industrial infrastructure to use small 

diameter material are other critical factors influencing treatment possibilities. We, the 

authors, recognize that theoretically, all forests of the western United States could be 

treated in one way or another to modify wildfire behavior and burn severity. Many of 

the principles and concepts we discuss are relevant for fuel treatments within other forests and locales; however, we will emphasize forest treatments applicable for use in the 

cold, dry, and moist forests of the inland western United States. We will discuss forest 

treatments that influence watershed processes, defined as those that occur when water 

transports sediment, woody debris, chemicals, heat, flora, or fauna away from a site and 

deposits it on another site. We define a cumulative effect as one that results from the 

incremental effects of an event when added to other past, present, and reasonable projected future effects regardless of the triggering action or event (Reid 1988). 

Forests of the Inland Western United States

Major river drainages dissect the Rocky, Bitterroot, Salmon, and other mountain ranges along with the Colorado Plateau within the inland western United States. Maritime, 

continental, and Gulf of Mexico air masses converge and intermingle across this rugged 

topography with its wide diversity of geologies, soils, and climates that give rise to a 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
20 USDA Forest Service RMRS-GTR-231. 2010.

plethora of biophysical settings. As the names of the forest classifications infer, what differentiates these forests is their respective differences in climate and biophysical settings 

and the resulting suite of forest vegetation. Moreover, the biophysical setting, combined 

with the vegetation composition and structure, result in different disturbances with varying intensities and severities that lead to a variety of interactions and subsequent effects. 

Fire, grazing, insects, diseases, weather, and timber harvesting, along with vegetation 

establishment, growth, and succession, interact to create fine (less than 0.1 ha, 0.25 ac) 

to large (greater than 500 ha, 1,235 ac) mosaics distributed across landscapes. These dynamics occur on some of the most majestic and rugged topography in the world, ranging 

from less than 300 m (984 ft) above sea level on settings along the Clearwater and Snake 

Rivers in Idaho to over 3,600 m (11,811 ft) in the mountains of Colorado. There are approximately 147 million ha (363 million ac) of forests within the western United States. 

About 101 million ha (258 million ac) of these lands are administrated by federal, state, 

or other public agencies (USDA Forest Service 2001). The forests occupying these lands 

have a variety of dominant vegetation, ranging from the woodland communities such as 

chaparral (for example chamise, Adenostoma fasciculatum; manzanita, Arctostaphylos

spp.; Ceanothus spp.) in California and pinyon-juniper (Pinus edulis/Juniperus spp.) in 

Arizona, New Mexico, and Utah to forests that can be classified as dry, cold, or moist 

(Hann and others 1997). Dry forests are typically dominated by ponderosa pine (Pinus 

ponderosa) and Douglas-fir (Pseudotsuga menziesii), moist forests are dominated by 

grand fir (Abies grandis), western redcedar (Thuja plicata), or western hemlock (Tsuga 

heterophylla), and cold forests are dominated by Engelmann spruce (Picea engelmannii), 

subalpine fir (Abies lasiocarpa), or lodgepole pine (Pinus contorta). To refine this broad 

characterization, potential vegetation type (PVT) is often used. Potential vegetation type 

is a classification system based on the abundance and presence of the potential vegetation 

(or sometimes called indicator species) that may grow in a particular area in the absence 

of disturbance. Since not all vegetation can grow in all places because of limitations in 

water, soils, etc., this vegetation presence and abundance reflects the physical and biological environment (Daubenmire and Daubenmire 1968; Hann and others 1997; Smith 

and Arno 1999). Classifications usually offer insight into the type of seral or climax vegetation (ground level and canopy) and the different seral stages that can develop within a 

particular PVT (Cooper and others 1991; Pfister and others1977). In addition, these classifications provide insight into their expected response to disturbance, how they interact 

with fire, and the distribution of different species. 

Moist Forests 

Moist forests of the inland western United States occur in the eastern Cascade 

Mountains (east of the Cascade Crest in Washington and Oregon) and the northern Rocky 

Mountains (northeastern Washington and Oregon, northern Idaho, and the western portion of Montana) (fig. 1). They grow at elevations ranging from sea level to 2,300 m 

(7,550 ft) (Foiles and others 1990; Graham 1990; Hann and others 1997; Packee 1990; 

Schmidt and Shearer 1990). The topography is usually steep and broken with V-shaped 

and round-bottomed valleys. In the northern Rocky Mountains and eastern Cascades, 

total precipitation averages from 500 to 1,520 mm (28 to 60 in) and is influenced by a 

maritime climate that tends to favor wet winters and dry summers. Most precipitation 

occurs during November through May with amounts ranging from 508 mm to 2,280 mm 

(20 to 90 in) (Foiles and others 1990; Graham 1990; Packee 1990; Schmidt and Shearer 

1990). Precipitation comes as snow in the Inland West, often accompanied by cloudiness, fog, and high humidity. Rain-on-snow events are common January through March 

in the northern Rocky Mountains along with a distinct warm and sunny drought period 

occurring in July and August with rainfall in some places averaging less than 25 mm 

(1.0 in) per month. Throughout these forests, the soils are quite diverse and can include 

sedimentary, metamorphic, and igneous parent materials. Soil orders include, but are not 

limited to, Spodosols, Ultisols, Entisols, Histosols, Inceptisols, and Alfisols. A defining 

characteristic of the northern Rocky Mountains is the layer of fine-textured decomposed 

ash (up to 64 cm, 25 in thick) that caps the residual soils. The combination of climate, 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 21

Figure 1. (A) The extent of the cold forests is 

represented by the range of subalpine fir, 

(B) the extent of the moist forests is represented 

by the range of western redcedar, and (C) the 

extent of the dry forests is represented by the 

range of ponderosa pine. 

Cold Moist

Dry

A

B

C

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
22 USDA Forest Service RMRS-GTR-231. 2010.

topography, parent material, soils, weathering, and ash depth creates the most productive 

of all forests occurring within the inland western United States. 

Vegetation 

The vegetation complexes of the moist forests range from early- to late-seral and 

occur within landscape mosaics possessing all possible combinations of species, seral 

stages, and structural stages (Cooper and others 1991; Oliver and Larsen 1990). The 

PVTs in the moist forests of the northern Rocky Mountains include western redcedar 

(Thuja plicata), western hemlock (Tsuga heterophylla), and grand fir (Abies grandis). 

Western white pine (Pinus monticola), western larch (Larix occidentalis), lodgepole pine 

(Pinus contorta), Douglas-fir, and ponderosa pine occur as the early- and mid-seral species (Daubenmire and Daubenmire 1968; Hann and others 1997). The eastern Cascades 

and Pacific coast PVTs include western redcedar, western hemlock, grand fir, white fir 

(Abies concolor), Pacific silver fir (Abies amabilis), Port-Oxford-cedar (Chamaecyparis 

lawsoniana), incense cedar (Libocedrus decurrens), and noble fir (Abies procera). On 

these PVTs, the early- and mid-seral species include lodgepole pine, Douglas-fir, Sitka 

spruce (Picea sitchensis), and ponderosa pine. While less abundant than in the northern 

Rocky Mountain moist forests, western white pine and western larch do occur as earlyand mid-seral species (Franklin and Dyrness 1973; Lillybridge and others 1995). Lush, 

ground-level vegetation is the norm in the moist forests. The vegetation complexes are 

similar to those occurring on the west side of the Cascade Mountains and in some Pacific 

coastal areas. Tall shrubs include vine maple, (Acer circinatum), Rocky Mountain maple 

(Acer glabrum), Sitka alder (Alnus sinuata), devils club (Oplopanax horridum), rose 

(Rosa spp.), gooseberry (Ribes spp.), huckleberry (Vaccinium spp.), and willow (Salix

spp.). Forbs include baneberry (Actaea rubra), pathfinder (Adenocaulon bicolor), wild 

ginger (Asarum caudatum), queencub beadlilly (Clintonia uniflora), bunchberry dogwood (Cornus Canadensis), and golden thread (Coptis occidentalis).

Soil Surface Characteristics and Coarse Woody Debris

Moist forests tend to accumulate large amounts of coarse woody debris (CWD) (fig. 2). 

Depending on forest age, surface organic layers can contain deep pockets of rotten wood, 

sometimes representing up to 60 percent of the surface organic horizons (Graham and 

others 1994; Reinhardt and others 1991). Old forests (greater than 200 years) can have 

deep (30 cm, 12 in) layers of surface organics and large amounts of CWD ranging between 35 to 72 Mg/ha (15 to 32 tons/ac) (Brown and See 1981; Graham and others 1994).

Cold Forests

Within inland western North America, cold forests generally occur at high elevations (relative to surrounding landscapes) and extend throughout the western United 

States and into Alberta and British Columbia, Canada (fig. 1). At their northern extent, 

they occasionally occur at or near sea level and, in southern forests, their range extends 

to elevations exceeding 3,658 m (12,000 ft) (Lotan and Critchfield 1990). Within the 

Inland Northwest, they occur primarily in northern Idaho, central Idaho, and the northern 

Cascades Mountains of Washington (fig. 1). Growing seasons in cold forests are short, 

ranging from approximately 90 days at low elevations to just a few weeks at the high elevations with frosts occurring any time during the year. These forests are limited by poorly 

developed soils and, in some areas, by moisture. Nearly all (99 percent) of the cold forests within the inland northwestern United States occur over 1,220 m (4,000 ft), but cold 

air drainage allows some of them to extend below this elevation (Hann and others 1997; 

Steele and others 1981). On subalpine fir PVTs, mean annual temperatures range from 

3.8 to 4.4 o

C (25 to 40 oF) with the majority of the precipitation falling as snow and sleet, 

coming early in the season and staying late. Annual snow fall easily exceeds 1,300 cm 

(512 in) in the cold forests of the Cascade Mountains with lesser amounts falling where 

lodgepole pine persists (central Oregon and central Idaho) (Alexander and others 1990). 

Cold forests have a wide precipitation range with generally less precipitation in southern 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 23

cold forests, such as those occurring in New Mexico compared to those in Washington 

and Idaho. For example, precipitation in the cold forests of the Cascades of Washington 

ranges from 610 to 2,540 mm (24 to 100 in). Precipitation within the northern Rocky 

Mountains ranges from 610 to 1,520 mm (24 to 60 in). The central Rocky Mountains 

receive an average of 610 to 1,400 mm (24 to 55 in) of precipitation and the southern 

Rocky Mountains receive from 61 to 1,020 mm (24 to 40 in) of precipitation (Alexander 

and others 1990; Steele and others 1981). Cold forests occurring in southwestern Oregon 

and California are cool and moist or cold and moist with summer temperatures rarely 

exceeding 29 oC (85 oF) and winter temperatures rarely dipping below -29 oC (20 oF). 

Unique to this area is a 4- to 5-month dry spell between April or May through October 

where precipitation from thunderstorms is rare. Most precipitation occurs during other 

months, primarily in the form of snow. The snow pack can exceed 4 m (13 ft) in the cold 

forests of the Sierra Nevada Mountains of California and in the cold forests of southwestern Oregon and northwestern California, up to 2 m (7 ft) of snow often accumulates. In 

general, the total precipitation of these California and Oregon cold forests ranges from 

750 to 1,500 mm (30 to 60 in). The soils supporting the cold forest are relatively young, 

often shallow, and poorly developed. Mountain glaciers extensively covered these forests 

during the Pleistocene and have generally been free of ice less than 12,000 years. Most 

soil parent material is alluvium or glacial tills, but soil surfaces range from very weakly 

weathered (rocky with no organic layers) to thick soils composed primarily of organic 

materials. The soil orders common to the cold forests include the Entisols, Inceptisols, 

Alfisols, and Spodosols (Laacke 1990). 

Vegetation

The potential vegetation types dominating the cold forests include subalpine fir (with 

and without Engelmann spruce) and mountain hemlock (Tsuga mertensiana). These 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States

Figure 2. A typical mid-aged and 

mid-seral moist forest containing 

abundant layers of vegetation 

and a robust covering on 

the forest floor consisting of 

vegetation and coarse woody 

debris.
24 USDA Forest Service RMRS-GTR-231. 2010.

PVTs occur at the highest elevations within the Rocky and Cascade Mountains. Western 

larch and lodgepole pine are early-seral species in the subalpine fir/Engelmann spruce 

PVT, Douglas-fir and western white pine are mid-seral species, and western redcedar, 

grand fir, Engelmann spruce, and subalpine fir are late-seral. The species composition 

that occurs in the subalpine fir/Engelmann PVT is highly dependent on elevation, associated climate, and disturbance frequency and type. In California, the PVT’s dominating 

the cold forests include red fir, white fir (Abies concolor), and noble fir (Abies procera), 

which are also the dominant late-seral species. Lodgepole pine, western white pine, 

incense-cedar, Brewer spruce (Picea breweriana), and Jeffery pine (Pinus jefferei) are 

common early-seral species (Laacke 1990). 

Like the moist forests, lush ground-level vegetation is the norm for most settings 

in the cold forests. Tall shrubs include false huckleberry (Menziesia ferruginea) and 

Sitka alder, and the dominant medium and low shrubs are often huckleberries. Pinegrass 

(Calamagrostis rubescens), bluejoint reedgrass (Calamagrostis canadensis), and elk 

sedge (Carex geyeri) typify the graminoids occurring in the cold forests. Some of the 

most commonly occurring forbs include beargrass (Xerophyllum tenax), round-leaved 

violet (Viola orbiculata), and queencup beadlilly (Clintonia uniflora) (Cooper and others 1991). 

Medium sized shrubs include species such as gooseberry (Ribes spp.), pinemat manzanita (Arctostaphylos nevadensis), mahala mat (Ceonothus prstratus), mountain pride 

(Penstemon newberryi), and mountain whitethorn (Ceonothus cordulatus). Areas with 

deep soils often contain bush chinquapin (Chrysolepis sempervirens) or greenleaf manzanita (Arctosstaphylos partula). Small upland meadows are common in these forests 

and provide habitats for a wide variety of sedges, grasses, and forbs (Laacke 1990). 

Soil Surface Characteristics and Coarse Woody Debris

In cold forests, such as along the Continental Divide in central Montana, slow decomposition causes needles and other surface litter to accumulate and create dense 

organic mats from 2 to 8 cm (0.75 to 3.0 in) thick intermixed with large boulders in 

some areas (fig. 3). Coarse woody debris amounts vary depending on forest age. In 

mature subalpine forests in Idaho and Montana, CWD can range from 22 to 55 Mg/ha 

(13 to 25 tons/ac) (Brown and See 1981; Graham and others 1994). In young forests 

where lodgepole pine dominates the site as an early-seral species, up to 40 percent of the 

soil surface can be composed of CWD and rotten wood (Brown and See 1981; Harmon 

and others 1986) (fig. 3). 

Dry Forests

Dry forests are typically dominated by ponderosa pine and/or Douglas-fir and can 

occur throughout the western United States, southern Canada, and northern Mexico 

(fig. 1) (Little 1971). Their greatest extent is in the inland northwestern United States 

and in northern California. These forests also occur in the Black Hills of South Dakota 

and Wyoming, along the Front Range of the Rocky Mountains in Colorado, and along 

the Mogollon Rim in Arizona, the rugged escarpment that forms the southern limit of 

the Colorado Plateau. Elevations range from sea level to 3,281 m (10,000 ft) depending 

on latitude (Oliver and Ryker 1990). 

The topography of the dry forests is highly variable and dependent on the region 

where they occur. East of the Continental divide in central Montana, South Dakota, eastern Wyoming, and central Nebraska, the dry forests tend to occur within discontinuous 

mountainous regions, plateaus, and canyons intermixed with the plains. Large expanses 

of dry forests dominated by ponderosa pine occur in the Black Hills of South Dakota 

and Wyoming, which is largely an isolated mountain range (fig. 4). In the southwestern 

Rocky Mountains (Colorado, New Mexico, Arizona, Utah), dry forests can occur on 

flat plateaus to steep mountain slopes and often populate all slope aspects depending on 

location (Boldt and Van Deusen 1974; Oliver and Ryker 1990). 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 25

Figure 3. (A) Mature lodgepole pine growing on a subalpine potential 

vegetation type typifying much of the cold forests. (B) The inset shows a 

large accumulation of brown rotten wood that is often present in many cold 

forests. 

A

B

Figure 4. The Black Hills 

of western South 

Dakota are dominated 

by late-seral ponderosa 

pine forests. 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
26 USDA Forest Service RMRS-GTR-231. 2010.

Average annual temperatures in dry forests range between 5 and 10 oC (41 and 50 oF), 

and July and August temperatures average between 17 and 21 oC (62 and 70 oF). The 

number of frost-free days ranges from 90 to 154 in eastern Montana and South Dakota 

and to more than 200 days in central California (Oliver and Ryker 1990). Soil moisture 

influences growth and development of these forests and is highly variable depending on 

location. In the southwestern United States, Colorado Rockies, Black Hills, and Utah 

forests, summer rains often occur although little precipitation occurs in May and June. 

In eastern Oregon and Washington, July through September is usually dry with precipitation amounts in Montana and east of the Continental divide averaging from 280 to 

430 mm (11 to 17 in), with approximately half of it occurring from May to August. In 

the dry forests of eastern Oregon, Washington, and Idaho, precipitation in general averages from 355 to 760 mm (14 to 30 in) with much of it falling in the form of snow. In 

these forests, July to September are generally dry with precipitation averaging less than 

25 mm (1 in). The dry forests growing on the west slope of the Sierra Nevada Mountains 

in northern California receive on the average 1,750 mm (69 in) of precipitation with 

very little moisture falling in July and August. 

Parent material supporting the dry forests comes from a variety of substrates including 

igneous, metamorphic, and sedimentary rocks, and they often include quartzite, argillite, schist, shale, basalt, andesite, granite, cinders, pumice, limestone, and sandstone. 

The soils derived from these materials are most often included in the orders Entisols, 

Inceptisols, Mollisols, Alfisols, and Ultisols. The vegetation distribution within the dry 

forests is a function of available moisture, with soil texture and depth influencing the 

availability. 

Vegetation

Ponderosa pine is the primary conifer that defines the dry forests throughout much of 

the western United States, southern Canada, and northern Mexico (fig.1) (Little 1971). 

It is the principle species on over 27 million acres and, for every 2.8 ha (7 ac) that it 

dominates, it is present on an additional 1.4 ha (3.5 ac) (fig. 5). Within the western 

United States, California alone contains the greatest concentrations of ponderosa pine 

(2.07 million ha, 5 million ac) closely followed by Oregon (1.9 million ha, 4.7 million 

ac). When combined, Arizona and New Mexico contain an additional 2.5 million ha 

(6 million ac) of ponderosa pine (Van Hooser and Keegan 1988). The species occupies 

sites with elevations ranging from sea level to 3,050 m (10,000 ft) depending on latitude 

(Oliver and Ryker 1990). In terms of area occupied, it is second only to Douglas-fir. 

In the southern and extreme eastern portion of the range, ponderosa pine grows primarily on ponderosa pine PVTs. On these settings, quaking aspen (Populus tremuloides) 

is the most frequent early-seral tree species (Huffman and Alexander 1987; Youngblood 

and Mauk 1985). Ground-level vegetation includes grasses (for example Festuca spp. 

Agropyron spp.) and shrubs such as snowberry (Symphorcarpus spp.), spirea (Spirea

spp.), and russet buffaloberry (Shepherdia canadensis ) (fig. 5). 

With increasing moisture, ponderosa pine occurs as a mid-seral species and Douglasfir becomes the late-seral species. Quaking aspen and lodgepole pine are early-seral 

associates of ponderosa pine on these Douglas-fir PVTs (Mauk and Henderson 1984). 

These ponderosa pine forests occur in the Rocky Mountains along the Front Range of 

Colorado, in Utah, and in southern Idaho. They also occur along the western slopes of 

the Sierra Nevada Mountains in California and the eastern slopes of the Cascades in 

Oregon (Franklin and Fites-Kaufman 1996; Hann and others 1997). On these settings, 

ground-level vegetation includes ninebark, elk sedge, and pine grass. These species, in 

particular, exemplify aggressive survivors after disturbance (for example, fire, mechanical site preparation) and can colonize a site quickly after disturbance (Baumgartner and 

others 1986). 

In several locales, dry grand fir and/or white fir PVTs represent the dry forests (Hann 

and others 1997). On such settings, ponderosa pine and Douglas-fir occur but are succeeded by late-seral grand fir and/or white fir in the absence of disturbance (Bradley and 

others 1992a) (fig. 6). Additional trees that can occur in such forests include juniper, 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 27

Figure 5. Ponderosa pine growing in central Oregon. (A) Note the open 

understories and high crown base heights of these mature trees and 

the forest floor covered by a layer of needles. This needle layer 

does not readily decompose and provides a highly flammable fuel. 

(B) The inset shows lush ground-level vegetation developing after a 

ponderosa pine timber harvest on a Douglas-fir potential vegetation A type in central Idaho.

B

Figure 6. On the Douglas fir and grand fir 

potential vegetation types, ponderosa pine 

is readily succeeded by these species in 

the absence of disturbance (for example 

fire, harvesting). This succession results in 

abundant fuel layers and nutrient rich crowns 

that extend to the soil surface making them 

highly susceptible to loss during fires. 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
28 USDA Forest Service RMRS-GTR-231. 2010.

pinyon pine, sugar pine (Pinus lambertiana), incense-cedar (Libocedrus decurrens), 

western larch, Jeffrey pine, and lodgepole pine. Pine grass and ninebark (Physocarpus 

malvaceus) are frequent associates, but tall shrubs such as Rocky Mountain maple often 

occur. 

Soil Surface Characteristics and Coarse Woody Debris

In the dry forests, needle shed from long needle pines is a major component of the 

surface litter (fig. 5). Without fire, these layers can quickly accumulate, often minimizing the amount of grasses, forbs, and shrubs that were more prevalent on these 

sites when fire maintained smaller amounts of these litter layers. Coarse woody debris 

(CWD) is relatively scarce when compared to moist and cold forests (figs. 2 and 5). 

However, the more productive dry forests tend to accumulate relatively high amounts 

of CWD, especially in the absence of fire. For example, on grand fir and Douglas-fir 

PVTs in Montana and Idaho, CWD ranges from 10 to 30 Mg/ha (5 to 20 tons/ac). In 

contrast, on ponderosa pine PVTs in Arizona, CWD can range from 10 to 20 Mg/ha 

(5 to 10 tons/ac) but can quickly accumulate where white fir are the late-seral species, 

as exemplified by the 10 to 30 Mg/ha (5 to 15 tons/acre) reported by Graham and others 

(1994) for these PVTs. 

Forest Change

Most forest conditions of the western United States have changed from those that 

occurred historically (pre-1900). In particular, many of these changes relate to both the 

decrease in fire occurrence and the increase in the size and severity of how the wildfires 

burned. The changes in how fires burn, often because of successful fire exclusion, combined with timber harvesting and climate cycles resulted in changes in the abundance, 

composition, and distribution of tree, ground level vegetation, and forest floor components within the three-forest types (Graham and others 2004; Jain and Graham 2005). 

These changes include shifts in species composition, volume, and density, thus creating 

situations such as altering vegetative chemistry and the biological and chemical composition of the forest floor (Harvey and others 1999a) (fig. 6). 

For the most part, western forests of the late 1800s and the first half of the 20th 

century produced timber crops for expanding local and national economies. Thus, the 

forests were aggressively protected from damaging animals, insects, diseases, and fire 

(Graham and Jain 2004). The species harvested included western white pine, western 

redcedar, western larch, ponderosa pine, and Douglas-fir that produced diverse products 

such as toothpicks, matches, ship masts, railroad ties, fuel, and building material. At this 

time, many tree and shrub species were considered weeds (for example, western hemlock and grand fir) and were removed (slashed and burned) to provide growing space 

for product producing species. In many locales throughout the western United States, 

this product centric forest management continued into the 1950s and early 1980s (Davis 

1942; Graham and others 2005; Steen1976). 

Two large fire events, the Peshtigo fires that burned in northern Wisconsin in October 

of 1871 and the wildfires that burned in northern Idaho, eastern Washington, and western 

Montana in August of 1910, burned millions of forested hectares (acres) and towns and 

caused loss of life (Gess and Lutz 2002; Pyne 2001) (fig. 7). These destructive events were 

the catalyst that cemented the mission of the newly formed Forest Service to protect the 

valuable forestlands of the United States from damaging agents (Steen 1976). The result 

was a significant decrease in the number of fires burning and the amount of area burned in 

western forests. The effectiveness of fire exclusion increased dramatically especially with 

the use of airplanes and smoke jumpers to aerially combat fires and the development of 

access roads (Graham and others 2004; Graham and Jain 2004). Although fire exclusion 

and timber harvesting influenced the moist and cold forests, the dry forests had the most 

noticeable changes (Covington and Moore 1994; Hann and others 1997). 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 29

Since the dry years of the 1930s, the climate of the western United States has been 

relatively moist, facilitating the regeneration and development of large amounts of forest vegetation (Haig and others 1941; Pearson 1950). Historically, native insects (for 

example, pine beetle [Dendroctonus spp.]), diseases (for example, root rots [Armillaria

spp.]), and mistletoe (Arceuthobium spp.) infected and killed the very old or stressed 

individuals, which tended to diversify vegetation communities (Hessburg and others 

1994). However, in present forests, changes in vegetation have facilitated development 

of unprecedented epidemic levels of these insects and diseases in many locales (fig. 8). 

These disturbance agents were often encouraged by weather events such as ice storms, 

windstorms, and periodic droughts. In addition, the movement of Europeans into the 

Figure 7. The wildfires that burned in the 

northern Rocky Mountains in 1910 

consumed over 1. 2 million ha (3 million 

acres) and burned communities, 

reinforcing the need to protect forests from 

disturbances and fire in particular.

Figure 8. Lodgepole pine 

killed by mountain 

pine beetle in Colorado 

(photo by William 

M. Ciesla, Forest 

Health Management 

International, 

Bugwood.org). 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
30 USDA Forest Service RMRS-GTR-231. 2010.

western United States resulted in the intentional and inadvertent introduction of both 

exotic plant and animal species that often displaced native species. Non-native insects 

and diseases often found no natural checks or balances, enabling them to invade western 

forest ecosystems unimpeded. In concert, these and allied events have facilitated the 

development of abundant amounts of forest vegetation and, in some settings, a different 

suite of vegetation, insects, and diseases than those that occurred prior to 1900. 

Fire Regimes

Fires, in concert with other disturbances, create mosaics of forest composition and 

structure within and among stands and across landscapes. These mosaics can occur 

over relatively fine spatial scales (in other words, less than 0.5 ha, 1.2 ac) to rather large 

mosaics exceeding hundreds of hectares (acres). Wildfires historically burned the cold, 

moist, and dry forests at various intensities and frequencies giving rise to a wide variety 

of burn severities and producing a variety of vegetative successional pathways and a 

diversity of vegetation and forest floor conditions. A fire regime is a generalized description of the role fire plays in a forest and is related to a fire’s frequency, severity, and 

intensity (Agee 1993). While multiple fire regime classifications are available, we find 

that for describing fires occurring in the dry, cold, and moist forests, a system containing 

three classes—stand replacing fires (lethal), mixed fires, and low intensity surface fires 

(non-lethal)—is most useful (Hann and others 1997; Schmidt and others 2002). 

The most extreme fire regime, the stand replacing (lethal) regime, kills all canopy 

layers across stands or relatively large areas (in other words, areas larger than ~2 ha, 

5 ac). In general, these fires kill the standing vegetation and could be classified as intense (all black stems), but some moderately severe (brown needles present) burning 

may exist in numerous areas. Within forests containing burned and blackened trees, the 

level of soil burn severity can be highly variable, ranging from light to highly severe 

depending on the state of the ground-level vegetation, surface fuels, forest floor, and 

burning conditions during the fire.

Low intensity surface fire (non-lethal) regimes clean the forest floor of vegetation 

and accumulated woody debris but yet leave the majority of the high forest cover alive. 

These non-lethal fires rarely kill dominant trees, but soil burn severity can range from 

nothing to highly severe depending on the amount, condition, and extent of the surface 

fuels and the heat and residence time of the fire.

Mixed severity fires combine lethal and non-lethal fires, killing small to medium sized 

groups of dominant trees, burning surface fuels in other areas while leaving the dominant trees alive. Mixed fire spatial extents can range from small patches of vegetation to 

rather large landscapes that burned for days to weeks. By their nature, fires described by 

this regime leave compositionally and structurally fine scale mosaics of forest vegetation 

and simple to complex burn patterns. With the advent of successful fire exclusion, these 

mixed severity fires were frequently extinguished preventing them from modifying many 

forested landscapes. Historically, all three fire regimes occurred in all three forest types 

allowing fire suppression activities, to some degree, to impact all three forest types.

Moist Forest Changes

Fire exclusion, insects, diseases, and weather interacted with climate change (climate 

cycles) to alter the moist forests from one dominated by early-and mid-seral species 

to one dominated by mid-to late-seral species. Historically, wildfires burning the moist 

forests were highly variable. Estimates suggest that nonlethal surface fires occurred at 

relatively frequent intervals (15 to 25 years) within 25 percent of the moist forests. Lethal 

crown fires burned about 25 percent of the moist forests every 20 to 150 years but occasionally extended to 300-year intervals. The mixed fire regime burned across about 50 

percent of the moist forests at 20- to 150-year intervals with some lethal events occurring at 300-year intervals. Fires typically started burning in July and were usually out 

by early September with the change in weather. Most fires were small, but occasionally, 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 31

large fires did occur with 74 percent of fires killing a portion of the canopy (Hann and 

others 1997; Pyne 2001) (fig. 7). Because of fire exclusion, surface fires now burn 10 

percent of the moist forests, mixed fires burn 30 percent, and crown fires burn 60 percent 

of the moist forests. Although fire exclusion played a role in altering the moist forests in 

the western United States, introduction of a European stem rust, white pine blister rust 

(Cronartium ribicola), was a greater factor in causing change in these forests (fig. 9) 

(Jain and Graham 2005). The disease attacked and killed western white pine, a primary 

commercial species. Upon introduction of blister rust, a massive effort was initiated to 

control the disease by removing currant (Ribes spp.) bushes (the alternate host). During 

the Civilian Conservation Corp days of the 1930s, workers pulled, sprayed, and grubbed 

Ribes bushes throughout the northern Rocky Mountains. Hutchison and Winters (1942) 

described the effort “like bailing the ocean with a teacup” and efforts to control the 

disease proved futile. By 1968, the western white pine blister rust program and management of the species was “realigned,” resulting in the accelerated removal of naturally 

occurring western white pine before they supposedly succumbed to the rust (Ketcham 

and others 1968).

Harvesting of ponderosa pine and western larch, other high value timber species, exacerbated the forest changes resulting from the introduction of blister rust. The partial 

and intermittent canopy removal and minimal soil surface disturbance caused by both 

tree harvest and western white pine mortality were ideal situations for grand fir and western hemlock to establish and aggressively encroach. In the eastern Cascades, the effect 

of blister rust on forest composition and structure was less severe since western white 

pine was not as dominant, thus fire exclusion and harvesting were more important change 

agents in these forests. Grand fir and Douglas-fir readily filled the niches western white 

pine, ponderosa pine, and western larch once held.

Figure 9. Blister rust, an introduced Eurasian disease, significantly reduced the abundance of western white pine 

from much of its historical range.

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
32 USDA Forest Service RMRS-GTR-231. 2010.

Since 1991 native insect and pathogen activity in the moist forests far exceed those 

of the past. The Douglas-fir beetle (Dendroctonus pseudotsugae), mountain pine bee-

tle (Dendroctonus ponderosae), spruce budworm (Choristoneura occidentalis), and 

tussock moth (Orgyia pseudotsugata) that were historically endemic are now often 

epidemic. Similarly, the root diseases Armillaria spp. and Phellinus weirii that were 

historically endemic are now common in the current fir-dominated forests (Hann and 

others 1997; Hessburg and others 1994).

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

ates a variety of canopy openings ranging from gaps to large openings (~16 ha, 40 ac). 

In early-seral dominated species (ponderosa pine, western larch, western white pine) 

forests, snow will often slip from the trees, minimizing breakage, while other species 

in the intermediate crown classes (grand fir, Douglas-fir) will break, creating gaps and 

openings, decreasing forest densities, and altering species composition. Today, species 

that dominate many sites, such as grand fir and Douglas-fir, have dense crowns that hold 

snow and tend to break more readily compared to western larch or western white pine, 

which shed the snow (Graham and Jain 2005; Jain and Graham 2005). 

Disturbances in the moist forests, singularly or in combination, or the lack thereof, 

have culminated in the current distribution of successional-stage, forest structure, spe-

cies composition, and disturbance regimes that differ from historical conditions (1850 

to 1900) (Hann and others 1997). In some settings, the mixed-fire regime maintained 

closed canopy conditions that allowed the mid-seral stage to develop into late-seral, 

multi-story stages (Hann and others 1997). The late-seral, multi-story structure, which 

typically developed in cool, moist bottoms and basins, has decreased by about half in 

the last century. The early-seral, single-story stands that once occupied an estimated 

25 to 30 percent of the area now occupy only 9 to 10 percent, except in the northern 

Cascades (Washington) where they increased in abundance. The mid-seral stages have 

generally increased in abundance in the northern Rocky Mountains and, to a lesser de-

gree, in the eastern Cascades.

Because of fire, weather, disease, and insect interactions, species composition has 

shifted in the moist forests of the northern Rocky Mountains (Fins and others 2001; 

Hann and others 1997; Neuenschwander and others 1999). For example, before 1900, 

western white pine (early-to mid-seral species) dominated many settings, often repre-

senting 15 to 80 percent of the trees within stands (Fins and others 2001). Western larch 

and ponderosa pine also occurred in the early-and mid-seral structures but declined 

along with western white pine and were succeeded by grand fir, Douglas-fir, and west-

ern hemlock (Atkins and others 1999; Hann and others 1997). The eastern Cascades had 

limited amounts of western white pine and western larch; therefore, ponderosa pine, 

lodgepole pine, and Douglas-fir played more of a role in occupying the early-to midseral successional stages.

Western white pine, ponderosa pine, and western larch-dominated forests are gener-

ally tall and self-pruning, even in moderately dense stands. They have large branches 

high in the crowns and the base of the crowns is well above surface fuels. In general, 

this crown architecture protects the nutrients stored in the canopy from surface fires. In 

contrast, young- to mid-aged (less than 150 years) western hemlock and grand fir/white 

fir generally do not self prune. Forests dominated by grand fir tend to concentrate both 

nitrogen and potassium in their foliage, which often extends to the soil surface. In gen-

eral, low canopy structure, combined with nutrient and microbial activities concentrated 

in or near the soil surface, makes these two critical ecological resources susceptible 

to mechanical and fire destruction (Harvey and others 1999a; Mika and Moore 1990; 

Minore 1979; Moore and others 1991).

A positive change in the moist forests is the introduction of western white pines that 

are resistant to blister rust (Bingham 1983). Tree improvement programs that began in 

earnest in the 1950s started yielding rust-resistant seedlings for use in reforestation. By 

2005, millions of rust resistant seedlings have been planted throughout the moist forests. 

In addition, some native resistance to the disease remained in non-harvested residual 

western white pines. As a result, western white pine has many opportunities to play both 

significant ecological and commercial roles in the moist forests (Graham and Jain 2005). 

Chapter 3.  FuelManagement inForests oftheInland West
USDA Forest Service RMRS-GTR-231. 2010. 33

Cold Forest Changes

Depending on the physical setting, estimates suggest that the cold forests of the inland northwestern United States historically (1850 to 1900) burned in the range of 25 

to 100 year intervals. Non-lethal surface fires burned approximately 10 percent of these 

forests, every 30 to 100 years. Lethal crown fires burned 25 to 30 percent of the cold 

forests every 30 to 100 years with the longer intervals occurring in moist areas. During 

the short fire season (~60 days), a mixed fire regime burned about 60 percent of the 

cold forests at 25- to 100-year intervals, with occasional large fires occurring every 100 

years (Hann and others 1997). It is estimated that the proportions of the cold forests 

burned by non-lethal (10 percent), mixed fires (60 percent) and lethal fires (30 percent) 

is similar to the proportions historically burned by the different fire regimes. Therefore, 

fire exclusion has had minimal influence on these forests. However, local impacts on 

forest composition and structure are very likely the result of fire exclusion, as are the 

locations where the different fire regimes likely burned. In turn, the vegetative mosaic 

and its texture (size, shape, and location of vegetation patches) most likely differ from 

the historical characteristics of these forests (Bradley and others 1992a).

In the subalpine fir PVT, fire maintained 23 percent of the cold forest in early-seral 

vegetation primarily dominated by lodgepole pine. In these areas, lethal fires created 

ideal conditions (for example, ~10 acre openings and larger, burned-over and mineral 

soil surfaces) for the regeneration of lodgepole pine. Extremely dense stands of lodgepole pine would develop and, without subsequent disturbance, dominate settings for 

decades. Similarly, in some of the drier and colder portions of the cold forests, a single 

canopy of lodgepole pine could persist for over a hundred years.

Historically, mid-seral structures occupied about 53 percent of the cold forests (Hann 

and others 1997). A mixed fire regime in these forests, along with periodic wind, floods, 

snow, and other small-scale disturbances, allowed uneven-aged and patchy stands to 

develop. Engelmann spruce, western redcedar, grand fir, mountain hemlock, and subalpine fir would readily regenerate in a variety of canopy conditions (gaps), giving rise to 

dense stands with many canopy layers. In the absence of lethal fires, the warmer forest 

settings containing lodgepole pine were readily succeeded by Engelmann spruce and 

subalpine fir.

Prior to 1900, late seral, multi-storied forests occupied 15 percent of the cold forests 

(Hann and others 1997), and subalpine fir and Engelmann spruce dominated these forests with lodgepole pine and Douglas-fir as intermittent associates. Forest densities were 

often high (exceeding 29,000 trees/ha, 11,733 trees/ac) and dominated by subalpine fir 

and Engelmann spruce but, occasionally, a few large, fire resistant Douglas-firs would 

be interspersed throughout these multi-storied forests (Franklin and Mitchell 1967). 

Non-lethal surface fires would encourage single canopies of subalpine fir, Engelmann 

spruce, or lodgepole pine to develop over approximately 8 percent of the cold forests. 

Due mainly to harvesting, and to a lesser degree lethal fires, the greatest vegetative 

changes occurring in cold forests over the last 100 years is the increase in the extent of 

early-seral structures consisting primarily of lodgepole pine. Large (100s to 1,000s of 

ha) expanses of lodgepole pine forests, especially those with large (greater than 20-cm, 

8-in) diameters, are often killed by mountain pine beetle (fig. 8). Also Douglas-fir beetle, spruce budworm, tussock moth, and spruce bark beetle (Dendroctonus rufipennes) 

appear to be defoliating and killing trees more readily in the cold forests than they did 

historically. Singly, and in combination, the defoliation and mortality caused by these 

insects can provide large amounts of dead fuel for future fire events (Hann and others 

1997) (fig. 8).

Dry Forest Changes

In the western United States, domestic livestock grazing and harvesting of ponderosa 

pine forests was occurring by the mid 1800s (Barrett 1979; Cooper 1960; Pearson 1950; 

Rasmussen 1941;Van Hooser and Keegan 1988). In mesic forests, grand fir and/or white 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
34 USDA Forest Service RMRS-GTR-231. 2010.

fir and Douglas-fir rapidly colonized these sites when ponderosa pine was harvested. 

Grass cover tended to decrease ponderosa pine seedling establishment and survival, 

especially on the ponderosa pine PVT (Brawn and Balda 1988). However, in the early 

1900s in the southwestern United States when heavy livestock grazing ceased (thus 

eliminating seedling damage), abundant ponderosa pine seedlings became established. 

Because of fire exclusion, climate changes, and other factors, these trees readily devel-

oped into dense stands (Covington and Moore 1994; Pearson 1950; Stein 1988). 

Before successful fire exclusion, temperature and precipitation patterns combined 

with natural and human ignitions that allowed fires to burn the dry forests at relatively fre-

quent (for example, less than 40 years) intervals. Cultural burning by Native Americans 

augmented and even dominated burning in several locations (Barrett and Arno 1982; 

Stewart 1951). In the northern Rocky Mountains of Idaho and western Montana, dry 

settings (ponderosa pine and/or Douglas-fir PVTs) were historically burned by nonlethal wildfires at 15- to 23-year mean return intervals. These fires could be quite large 

often burning for weeks to months (Weaver 1943). Mixed fires frequently burned mesic 

forests containing ponderosa pine (grand fir and/or Douglas-fir PVTs) at mean return 

intervals extending to over 60 years. Non-lethal fires dominated the central and south-

ern Rockies (ponderosa pine and/or Douglas-fir PVTs), although mixed severity fires 

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

(Bradley and others 1992a; 1992b; Fulé and others 1997; Kaufmann and others 2001). 

Fires tended to be few on the driest settings (ponderosa pine and/or woodlands) because 

of discontinuous surface fuels (Bradley and others 1992a). In contrast to other locales 

dominated by late-seral ponderosa pine, the forests of the Black Hills of Wyoming and 

South Dakota possibly experienced greater extents of lethal fires because of the abun-

dant ponderosa pine regeneration that normally occurred (Shepperd and Battaglia 2002; 

Shinnen and Baker 1997). Nevertheless, historical wildfires likely burned through most 

ponderosa pine forests leaving in their wake a wide variety of species compositions and 

vegetative structures arranged in a variety of mosaics.

Within the dry forests, dense conditions often develop and are exacerbated by fire 

exclusion, increasing the abundance of insect and disease epidemics, which significant-

ly altered the composition, and structure of these forests (Harvey and others 2000). 

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

fir engraver (Scolytus ventralis), and Douglas-fir tussock moth were insects associated 

with regularly burned areas (Hessburg and others 1994). In most years, bark beetles 

occurred at endemic levels in ponderosa pine, Douglas-fir, and grand fir, killing large 

weakened trees that were struck by lightning, infected by root disease (Armellaria spp.), 

or too old to resist attack (Williams and others 1986; Wu and others 1996). Pine en-

graver and fir engraver beetles attacked young, densely stocked ponderosa pine, killing 

trees scorched by low-intensity surface fires and severely infected trees containing root 

rot or dwarf mistletoe.

Because of forest change, these same insects have reached epidemic levels in many 

forests (Gardner and others 1997; Hedden and others 1981). Today, ponderosa pine 

continues to be susceptible to the western pine beetle, and the mountain pine beetle is 

prevalent on Douglas-fir and grand fir PVTs. The pine engraver beetle is more abundant 

and destructive now with some of the severest outbreaks occurring on low-elevation 

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

defoliates ponderosa pine and scattered outbreaks have occurred in Arizona, California, 

Colorado, and Oregon during the 20th century (Speer and others 2001). Dense stands 

of Douglas-fir and grand fir that developed on many grand fir and Douglas-fir PVTs are 

very susceptible to both defoliators and root diseases.

Harvesting western larch and ponderosa pine precipitated the regeneration and 

growth of grand fir/white fir and Douglas-fir in the dry forests, which subsequently 

facilitated the accumulation of both above-and below-ground biomass and associate 

nutrients close to the soil surface (Harvey and others 1986) (fig. 6). As a result, even 

low-intensity surface fires often consume the surface organic layers, killing tree cam-

biums and/or fine roots, volatilizing nutrients, killing trees, and increasing soil erosion 

potential (Debano 1991; Hungerford and others 1991; Robichaud and others 2000; Ryan 

Chapter 3.  FuelManagement inForests oftheInland West
USDA Forest Service RMRS-GTR-231. 2010. 35

and Amman 1996). In addition, the abundant fir in the understory creates nutrient-rich 

ladder fuels that facilitate crown-fire initiation, increasing the likelihood of nutrient loss 

(Harvey and others 1999a; Minore 1979; Van Wagner 1977). The risk of nutrient loss is 

greater on infertile sites because dense stands of late-seral species are more demanding 

of nutrients and water than the historical stands dominated by widely spaced early-seral 

species (Harvey and others 1999a; Minore 1979) (see Chapter 9).

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

on the moist potential vegetation types (for example grand/white fir), ponderosa pine is 

being succeeded by Douglas-fir, grand fir, and/or white fir (fig. 6) (Arno and others 1997; 

Graham and others 2004; Gruell and others 1982). Fire intolerant vegetation, dense forest canopies, and homogenous and continuous horizontal and vertical structures are 

developing, thus creating forests favoring crown fires rather than low intensity surface 

fires that historically occurred in these forests (Arno and Brown 1991; Dodge 1972; 

Peterson and others 2005; Van Wagner 1977). Within the Inland Northwest, the extent 

of mid-seral (for example, Douglas-fir) vegetation has increased by nearly 3.2 million ha (8 million ac) and the extent of single storied mature vegetation (for example, 

ponderosa pine) has decreased by over 1.6 million ha (4 million ac) (Hann and others 

1997). Another way to view these changes is that the successional processes (movement from one successional stage to another) in some locations have been shortened 

by a factor of at least 10. For example, ponderosa pine may or may not be succeeded 

by Douglas-fir in 300 to 400 years within forests historically burned by frequent fires, 

but in many locations Douglas-fir has succeeded ponderosa pine in less than 50 years 

(fig. 6) (Hann and others 1997; Harvey and others 1999a; Smith and Arno 1999).

Forest Floor Changes

The shift in species composition from western white pine, western larch, and/or 

ponderosa pine to Douglas-fir, grand fir/white fir, and/or western hemlock dominated 

forests (including the shrub and forb components) has changed litter (soil surface) type 

and quantity from that which occurred historically. In addition, the accumulation of 

both above- and below-ground biomass from roots, needles, and boles in fir forests is 

accelerating activities of decomposers by increasing and changing the basic substrate 

they use (Harvey 1994). Associated with these changes in litter type and quantity is a 

likely change in ectomycorrhizal relationships and soil surface chemistry, including allelopathic substances, with the potential to alter a variety of microbial activities (Rose 

and others 1983). In addition, fire exclusion, timber harvesting, and animal grazing 

have exacerbated these forest floor alterations in many locales singly, or in combination, by soil compaction and displacement. For example, decomposed true firs create 

white rotten wood, which rapidly disperses into the soil and is quickly consumed by 

decomposers. In contrast, decomposed ponderosa pine, western white pine, and western larch create brown rotten wood, which can persist in soil for centuries and in this 

condition, can retain nutrients and hold water (Harvey and others 1988; Larsen and others 1980). Western larch and ponderosa pine tend to be deep-rooted, in contrast to the 

relatively shallow-rooted western hemlock and grand fir, which have abundant feeder 

roots and ectomycorrhizae in the shallow soil organic layers (Harvey and others 1987; 

Minore 1979). The soil microbial activities in fir-dominated forests compared to pinedominated forests may diminish the post-fire acquisition and cycling of nutrients (Neary 

and others 1999). Moreover, these changes in soil microbial activities may increase the 

likelihood of uncoupling any continuity between current and preceding vegetative communities (Amarnathus and Perry 1994).

In the dry forests, biological decomposition is more limited than biological production. When fire return intervals reflected historical fire frequencies, the accumulation of 

thick organic layers was minimized and nutrient storage and nutrients were dispersed 

in the mineral soils (Harvey and others 1999b). In the absence of fire, bark slough, 

needles, twigs, and small branches can accumulate on the forest floor and when these 

layers are continuously moist, ectomycorrhizae and fine roots of all species tend to concentrate in the surface mineral soil and thick organic layers, making them vulnerable 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
36 USDA Forest Service RMRS-GTR-231. 2010.

to disturbances (Harvey and others 1994). In addition, historical ponderosa pine forests 

were likely well matched to soil resources, relatively resistant to detrimental fire effects, 

well adapted to wide ranges of site and short-term climate variation, subject to modest 

(largely beneficial) insect and pathogen mortality, and could be considered long-lived 

and relatively stable. In contrast, forests that were dominated by ponderosa pine and 

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

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

variations found within the dry forests (fig. 6). In turn, they are often subject to high 

insect and pathogen mortality and are no longer considered either long-lived or stable 

(Harvey and others 1999a).

Forests as Fuel

Fire behavior and burn severity depend on the properties of the various fuel (live 

and dead vegetation and detritus) strata and the continuity of those fuel strata, horizontally as well as vertically. The fire hazard for any particular forest stand or landscape 

relates to its potential for the fuels to cause specific types of fire behavior and effects. 

Understanding the structure of fuelbeds and their role in the initiation and propagation 

of fire is the key to developing effective fuel management strategies. Fuelbeds are classified in six strata: 

1. tree canopy, 

2. shrubs/small trees, 

3. low vegetation, 

4. woody fuels, 

5. moss, lichens, and litter, and 

6. ground fuels (in other words, humus, fermentation layer, surface and partially buried 

rotted wood, etc. (Sandberg and others 2001) (fig. 10). 

Modification of any fuel stratum has implications for fire behavior, suppression, and 

burn severity. 

Ground Fuels 

Ground fuels consist of duff (organic soil horizons), roots, and buried woody material 

(fig.10) (Sandberg and others 2001). Often, needle fall and bark slough will accumulate 

at the base of trees and eventually create deep organic layers in which fine roots and ectomycorrhizae of trees and ground level vegetation may accumulate (Graham and others 

2000). Ground fuels typically burn by smoldering and may burn for many hours, days, 

or even weeks if initial moisture contents are high (Frandsen 1991; Hungerford and others 1991) (fig. 11). This long duration smoldering can often lead to soil damage, tree 

mortality (high severity), and smoke (Ryan and Noste 1983; Ryan and Reinhardt 1988; 

Wells and others 1979). Rotten material on the ground surface is particularly ignitable by 

firebrands (small twig segments or bark flakes supporting glowing combustion) falling 

ahead of an advancing fire front and increases the success of spotting. 

Surface Fuels and Ladder Fuels 

Surface fuels consist of grasses, shrubs, litter, and woody material lying on, or in 

contact with, the ground surface (fig.10) (Sandberg and others 2001). The bulk density 

(weight within a given volume) of surface fuels and size class distribution of fine fuels 

(sticks less than 7.62 cm (3.0 in) are critical to frontal surface fire behavior (spread rate 

and intensity) compared to fuel loading (weight per unit area) alone. Other characteristics of surface fuels that determine surface fire behavior are fuel depth, continuity, and 

chemistry. Surface fires burn in both flaming and postfrontal (smoldering or glowing) 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 37

Figure 10. Fuelbed strata have different 

implications for combustion 

environment, fire propagation and 

spread, and fire effects. (A) The canopy, 

(B) ladder fuels and (C) shrub layers 

contribute to crown fires. (D) Low 

vegetation, (E) woody fuel, and 

(F) ground fuel contribute to surface 

fires. (E) Woody fuel and (F) ground 

fuels are most often associated 

with smoldering fires and residual 

combustion that can transfer large 

amounts of heat deep into the soil 

(Graham and others 2004; Sandburg 

and others 2001). 

Figure 11. Large amounts of 

smoke can be produced from 

smoldering ground fuels after 

flames have subsided and 

large amounts of heat can be 

transferred to the soil.

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
38 USDA Forest Service RMRS-GTR-231. 2010.

phases (fig. 11). High-energy release rates occur during the relatively short flaming phase 

when fine fuels are consumed. Low energy release rates occur over longer periods by 

smoldering and glowing phases that consume larger (greater than 7.62 cm, 3 in diameter) 

fuels. Surface fuel complexes with high loadings of large material, such as slash left after timber harvesting or precommercial thinning operations (fig. 12), have long flaming 

residence times compared to fine fuels such as needles, shrubs, or grasses (fig. 5). High 

surface fire intensity usually increases the likelihood for igniting overstory canopy fuels, 

but surface fires with long residence times can contribute to drying aerial fuels that can 

lead to torching (when a tree or group of trees’ foliage ignites and flares up, usually from 

bottom to top) (Alexander 1988). 

Even in the dry forests, shrub and small tree regeneration can be abundant and frequent creating dense and robust layers of vegetation covering the forest floor (Pearson 

1950) (fig. 5). In the moist and cold forests, tolerant tree and shrub regeneration is common even in forests with continuous canopy cover (Cooper and others 1991) (figs. 2 

and 3). How these ground vegetative layers develop into mid-canopy layers depends on 

disturbance and how species differentiate as they develop based on their competitive and 

successional abilities (Oliver and Larson 1990). Stem differentiation can occur in evenaged, single species forests as stands self-thin because of inter-tree competition often 

in association with disturbances such as fires, diseases, and insects. Most often, these 

mid-canopy layers constitute the majority of the ladder fuels (Sandberg and others 2001).

Canopy Fuels

Crown fuels (also referred to as canopy fuels or aerial fuels) are those suspended 

above the ground in trees or vegetation (for example, vines, mosses, needles, branches 

etc.) (fig. 10). These fuels tend to consist mostly of live and fine materials less than 0.635 

cm (0.25 in) in diameter. Crown fuels are the biomass available for a crown fire, which 

can ignite from a surface fire via understory shrubs and trees (ladder fuels) or from crown 

to crown. The shrub/small tree stratum is also involved in facilitating crown fires by 

increasing surface fireline intensity and serving as ladder fuels that provide continuity 

from the surface fuels to canopy fuels. These essentially bridge the vertical gap between 

surface and crown strata. The size of this gap is critical to ignition of crown fire from a 

surface fire below (Van Wagner 1977). Van Wagner (1977) identified two thresholds of 

crown fire activity: (1) crowns are ignited after the surface fire reaches critical fireline 

intensity relative to the height of the base of the aerial fuels in the crown; (2) crown 

ignition can become an “active” crown fire if its spread rate is high enough to surpass 

Figure 12. Large amounts of 

fine fuels can be created 

when reducing canopy 

fuels. Without treatment, 

these fuels can increase the 

risk of unwanted wildfires 

and increase burn severity 

to both the high forest 

canopy and forest floor 

during prescribed fires and 

wildfires. Mechanical fuel 

treatments (for example 

piling and mastication) are 

often used to treat these fuel 

conditions.

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 39

the second threshold based on the crown density (often referred as canopy bulk density, 

canopy weight for a given volume). Aerial fuels separated from surface fuels by large 

gaps are more difficult to ignite because of the distance above the surface fire, thus requiring higher intensity surface fires, surface fires of longer duration that dry the canopy 

before ignition, or mass ignition from spotting over a wide area (Byram 1966). However, 

once ignited, high-density canopy fuels are more likely to result in a spreading crown fire 

(active crown fire) than are low-density canopies (fig. 13).

The upper canopy is composed of leaves, branches, and boles of trees. Again, depending on the forest, its setting, and inherent disturbances, these layers may be simple and 

uniform such as those that occur in young (30 to 50 years) to mid-aged (80 to 120 years) 

early-seral species such as lodgepole pine and western larch. In contrast, dense and highly complex upper canopy layers often occur in late-seral, moist forests in which over five 

conifer species may occur (Haig and others 1941).

Wildfire

Several terms and concepts describe a wildfire, including fire intensity, fire behavior, 

fire severity, fire line intensity, burn severity, and fire effects (Scott and Reinhardt 2001; 

Peterson and others 2005). However, several of these terms are often used interchangeably 

Figure 13. Fires can progress from torching individual 

and groups of trees (A) until entire hillsides are a 

blaze (B) (K. Watenmaker photograph). 

A

B

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
40 USDA Forest Service RMRS-GTR-231. 2010.

and mean different things to different individuals and disciplines. Therefore, to further 

the understanding of wildfires and their effects, we suggest the circumstances concerning 

a wildfire be described as a continuum, beginning with the pre-fire environment, then fire 

environment, and finishing with the post-fire environment (Jain and others 2004).

Pre-Fire Environment

The pre-fire environment describes the condition of the forest before a fire occurs. 

It includes, but is not limited to, such descriptors as physical setting (for example, location, geology, soils, topography, landform, etc.), current vegetation, seral stage of 

vegetation, structure of vegetation, and fuel moisture content. Other information, such 

as the time since fuel treatment and time of year may also be included (Peterson and 

others 2005; Jain and Graham 2007) (figs. 4 through 6).

Fire Environment

The fire environment includes the state of the fuel, physical setting, weather (shortand long-term), and their interactions (Graham and others 2004; Jain and others 2004; 

Peterson and others 2005; Rothermel 1983). Weather characteristics, such as wind 

speed and direction, relative humidity, temperature, and atmospheric stability interact 

with physical attributes such as aspect, slope angle, topographic position, and landscape 

orientation. In turn these characteristics interact with the presence or absence of fuel 

(in other words, canopy, surface, or even buildings), their moisture contents, composition, and structure (for example, multiple canopies of conifers and deciduous trees and 

shake-roofed homes). As such, how a fire ultimately burns, and its effects are predicated 

on weather, and how the fuels are arranged within the physical setting (Finney 2001; 

Graham and others 2004; Peterson and others 2005; Scott and Reinhardt 2001) (fig. 10). 

Fire intensity (fire line intensity) describes how a fire burns and the amount of energy 

it produces. Flame length, rate of spread, amount and location of torching, and spotting 

distance are frequently used to describe fire intensity (Jain and others 2004). The direct 

effects of a fire are often referred to as fire severity and/or as first-order fire effects. Fire 

severity is a function of how much heat a fire produces and the resulting consumption 

of plants and forest floor, heating of soils (which can volatize nutrients, create water repellent soils, distill organic matter, etc.), smoke production, and in some circumstances, 

the burning of homes (Cohen and Stratton 2003; Jain and others 2004; Ryan and Noste 

1983; Turner and others 1999; Ulery and Graham 1993). For example, tree fire severity describes the amount of pre-fire tree crowns consumed, charred, or scorched, and 

the proportion of the tree cambium killed (Ryan and Reinhardt 1988). Similarly, how 

a community responds (for example, supportive, angry, frustrated) to fire suppression 

activities or smoke could also be a direct fire effect (Kent and others 2003).

Post-Fire Environment

The post-fire environment describes conditions when all the flames, smoldering, and 

heat are gone, or in simpler terms, what is left after the fire is out (fig. 14) (Jain and others 2004). Descriptors of the post-fire environment include, but are not limited to, the 

amount and condition of live and dead vegetation, condition of the forest floor and soils, 

and the state of the homes and buildings impacted by the fire (Cohen and Stratton 2003; 

Jain and others 2004; Peterson and Arbaugh 1986; Ryan and Noste 1983; Ryan and 

Reinhardt 1988; Skinner and Weatherspoon 1996). However, the post-fire environment 

does not describe what was consumed, nor does it describe the influence of the fire alone 

(Jain and others 2004). Instead it assumes that the pre-fire environment, fire environment, and combustion processes all contributed to creating the post-fire environment or 

burn severity (figs. 14 and 15).

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 41

Figure 14. A ponderosa 

pine stand burned 

by the highly intense 

Rodeo-Chediski Fire in 

Arizona that resulted in 

high tree burn severity 

(level 5) (Jain and 

Graham 2007). 

Figure 15. Ground fires (especially 

those with long residence times) 

can severely burn soils, removing 

organic matter, volatilizing nutrients, 

killing tree roots, and creating water 

impermeable layers (soil burn severity 

level 6) (Jain and Graham 2007).

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States

Burn Severity

How an ecosystem responds in the post-fire environment is often referred to as indirect or second-order fire effects (Reinhardt and others 2001). These effects include 

characteristics such as soil erosion and sedimentation of streams, the opening of serotinus lodgepole pine cones, colonization of a burned forest by woodpeckers, and the 

introduction of exotic plants. Burn severity may also include homeowners’ response 

to burned houses or community reaction to post-fire rehabilitation activities (Kent and 

others 2003). These biological, physical, social, and economic responses to a fire vary 
42 USDA Forest Service RMRS-GTR-231. 2010.

over time and space and are interdependent. Therefore, we suggest the term burn severity best describes the post-fire environment because for a given fire intensity (behavior), 

depending on the pre-fire environment, a fire can create a variety of post-fire characteristics (Cohen and Stratton 2003; Graham and others 2000; Hungerford and others 

1991; Reinhardt and others 1991; Robichaud and others 2003). For example, an intense 

canopy consuming wildfire can severely burn tree crowns but minimally affect the forest floor and surface soils. This wildfire outcome frequently occurs when the surface 

organic layers are too moist to burn, resulting in low soil burn severity. Similarly, a low 

intensity surface fire with long residence times can produce large amounts of heat that 

can alter mineral soil, kill vegetation, and predispose trees to insect attacks (figs. 11 and 

15). As such, a low intensity fire can result in high burn severity. To this end, we have 

found that the relation between soil burn severity and tree burn severity is inconsistent. 

For example, tree death can be a function of soil burn severity, tree burn severity, or both 

severities combined. In addition, it appears that forest structure and composition can 

differentially influence both soil burn severity and tree burn severity.

Soil Burn Severity 

We use six levels to classify soil burn severity that link fire intensity to the physical 

and biological responses to the fire (Jain and Graham 2007). The factors we chose to 

define the levels include: proportion of surface organic layers, mineral soil, and exposed 

rock present after a fire and the dominant char class defined as unburned and black char 

specific to both litter and mineral soil, and grey and orange char specific to mineral soil. 

Level 1 soil burn severity occurs when surface organic horizons (litter, humus, rotten wood) cover approximately ≥85 percent of the forest floor after a fire, either in 

an unburned state or showing some evidence of black char (Debano and others 1998; 

Ryan and Noste 1983; Ulery and Graham 1993). This ≥85 percent threshold for organic horizons followed the soil quality standards used in Forest Service Regions 1, 2, 

4, and 6 that define a 15 percent loss of soil organic horizons as detrimental to forest 

productivity (Page-Dumroese and others 2000). Not only do unburned surface organic 

layers maintain productivity they also provide refugia for microbes and other organisms (Hungerford and others 1991; Neary and others 1999).

Level 2 soil burn severity occurs when surface organic horizon cover is ≥40 and 

<85 percent of the forest floor, indicating minimal consumption occurred (Wells and 

others 1979). However, much of the mineral soil could be covered by black charcoal, 

and small and isolated gray to orange colored mineral soils may be present. Soils exhibiting this burn severity would contain nutrients in the surface horizons and microbes 

would be living in the humus and/or mineral soil layers (Hungerford and others 1991). 

Level 3 soil burn severity occurs when forest floor conditions exhibit less than 

40 percent surface organic horizons and black char dominates the site. Little or no areas are unburned, but a considerable amount of black, charred litter exists (Hungerford 

and others 1991; Neary and others 1999). Although some volatilization of soil nutrients 

would occur when large logs burned, many nutrients remain in the upper mineral soil 

and residual surface organic materials (organic cover tends toward 40 percent rather 

than 5 percent). If the pre-fire environment favors soil erosion (for example, slope 

angle, soil texture, parent material, etc.), this level of soil burn severity would indicate 

the potential for rill erosion; however, soil heating and duration may be insufficient to 

create hydrophobic soils (Debano 2000; Johansen and others 2001; Wondzell and King 

2003). 

Level 4 soil burn severity occurs when organic layers comprise less than 40 percent 

of the forest floor and gray or orange colored char dominates the mineral soil. The 

organic layers covering the site would be dispersed, and isolated amounts of surface 

organics and nitrogen volatilization would most likely occur. Refugia for organisms 

would be absent except in isolated areas, water repellent soil could exist, all areas 

would show some evidence of fire, and temperatures that create these types of conditions would have ranged from 20 to 400 o

C (Debano 2000).

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 43

Level 5 soil burn severity occurs when no litter is present and black soil dominates 

the area. Depending on the site, potential soil erosion could be high and nitrogen in 

the surface organic horizons would likely be volatized, but nutrients in the mineral soil 

would likely remain (Hungerford and others 1991).

Level 6 soil burn severity describes a forest floor condition where no surface organics are present and gray to orange char dominates the mineral soil appearance. This soil 

burn severity indicates that minimal or if any nutrients or microorganisms are present 

in the soil surface (Debano 2000). Soil erosion and water repellent soils are possible 

and the abundance and presence of exposed rock may influence overland water flow 

(fig. 15).

Tree Burn Severity

Tree burn severity can be characterized two ways (Jain and Graham 2007). The first 

describes the vertical distribution of post-fire tree condition and is typically used to 

estimate post-fire tree mortality (Peterson 1985; Peterson and Arbough 1986; Wyant 

and others 1986). For example, ponderosa pines with 30 percent green crown have 

a 0.38 probability of dying after a fire and grand firs with similar crowns have a 0.87 

probability of dying (Ryan and Reinhardt 1988). Secondly, we define horizontal tree 

burn severity as the proportion of trees and their condition remaining in a patch, stand, 

or landscape after a fire (Broncano and Retana 2004; Turner and others 1999) (fig. 14). 

We identified five levels of tree burn severity. Because in most wildfires there are 

areas that do not burn, we defined a level 0 in our tree burn severity, as did several other 

authors (for example, Hutto 1995; Pollet and Omi 2002; Weatherspoon and Skinner 

1995). Level 1 tree burn severity is defined as trees having greater than 60 percent of 

the residual crown remaining green. Defined horizontally, level 1 burn severity would 

have all trees within an aerial extent containing trees with greater than 60 percent green 

crowns. Mixed green burn severity (level 2) is highly variable with trees containing 

<30 percent green crowns to those having over 60 percent residual green crowns. 

Completely brown (scorched) trees can be present within level 2, but no trees with 

completely black crowns can occur. Typically, the site is dominated by trees containing 

some green crowns (Hutto 1995; Pausas and others 2003; Skinner and Weatherspoon 

1996). Mixed brown crown severity (level 3) also contains green trees; however, trees 

with black crowns (needles consumed by the fire) occur as well as some trees with 

partially consumed crowns (brown needles and no needles present). In this situation, 

the abundance of green trees tends to be much less when compared to the abundance of 

completely dead trees (black or brown trees).

Level 4 tree burn severity occurs when the entire spatial extent contains trees without 

green needles and the majority are brown. However, within a given patch, some trees 

could be black (all needles consumed). When brown needles fall, they can decrease 

inter-rill and rill soil erosion, and because of the organic matter input, soil productivity 

can be enhanced (Harvey and others 1987; Pannkuk and Robichaud 2003). Level 5 tree 

burn severity occurs when an intense crown fire consumes all foliage (needles), leaving 

black branches, stems, and boles (figs. 13 and 14).

The tree and soil burn severity levels we defined are a series of classes that partition a 

continuum from everything remaining after a wildfire (as in the pre-fire state), to where 

all of the foliage and forest floor are consumed leaving blackened boles and bare soil. As 

such, the soil and tree burn severity we present is highly flexible allowing for the severity levels to be combined or kept separate depending on the data resolution required to 

meet a particular purpose or need.

Fuel Treatments 

Crown fires are generally considered the primary threat to forests and human values; however; low intensity surface fires can degrade forest soils, kill trees, and burn 

domestic structures (Cohen and Stratton 2003; Graham 2003; Graham and others 2004) 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
44 USDA Forest Service RMRS-GTR-231. 2010.

(fig. 11). In the moist, cold, and dry forests, crown fires are also the primary challenge 

for fire management. Our current understanding of fire behavior in most forests indicate that a crown fire begins with a transition from a surface fire to the ignition of the 

canopy. Therefore, crown fire development depends on the sequence of available fuels 

beginning with surface fuels, followed, in order, by woody fuel, low vegetation, shrubs, 

ladder fuels, and canopy fuels (figs. 5, 6 and 10). 

There is a wide range of treatments that can be used to modify forest fuels (vegetation) that in turn influence both fire intensity (behavior) and burn severity (what is left). 

As a result, fuel treatments not only influence how a fire burns, but they can also influence how a fire affects water quality, timber quantities, wildlife habitat, scenery, and 

other forest elements that society values. Treating forests to produce commodities and 

values that society favors is not a new endeavor. Forest treatments that produced desired 

conditions over time existed by the mid-1600s (Evelyn 1664). These treatments have 

been improved over the years, especially the last 100 years, with continued research and 

experience in the practice and art of silviculture (Nyland 2002; Smith and others 1997). 

In general, silviculture is the art and science of controlling the establishment, growth, 

competition, health, and quality of forests and woodlands to meet the diverse needs and 

values of landowners and society on a sustainable basis (Helms 1998). The plan and execution of forest and fuel treatments over time fall under the umbrella of a silvicultural 

system. There are not two or three systems, but rather an infinite number that can be 

developed and implemented over time and space integrating biology, management, and 

economic knowledge to treat forest fuels (Nyland 2002; Schlich 1906; Smith and others 

1997). Even though silvicultural methods historically stressed the production of wood 

crops, treatments can be designed to create and maintain a variety of forest compositions and structures relevant and effective for modifying fire intensity and burn severity. 

The challenge is to develop systems to manage forests as fuel yet create variable and 

complex forest structures and compositions that address other values such as maintaining the sense of place or maintaining wildlife habitat (Graham and Jain 2004). 

The most effective strategy for reducing crown fire occurrence and tree and soil burn 

severity is to: 

1. reduce surface fuels, 

2. increase height to live crown, 

3. reduce continuity of the forest canopy, and 

4. reduce canopy bulk density (Cruz and others 2002; Graham and others 1999a; Scott 

and Reinhardt 2001; Van Wagner 1977) (fig. 10). 

The documentation of treatments in a fuel treatment strategy is written in a silvicultural 

prescription that describes the treatments and the resulting composition and structure of 

dead and live vegetation through time. 

Forest Floor Treatments 

Forest floor treatments, possibly more than any other, influence how forest vegetation 

establishes and develops and are major determinants of both fire intensity and burn 

severity. No matter what method is used to treat the forest floor, a key to treatment success is ensuring that highly diverse (for example, diverse amounts of CWD, bare soil, 

litter depths and compositions etc.) forest floor conditions remain after a treatment to 

facilitate forest recovery after a wildfire. By doing so, a fire burning these fuels would 

burn heterogeneously and result in soil burn severity dominated by levels 1 through 4. 

Mechanical Treatments 

Machines through their proper use can create and maintain desired forest floor conditions in many forest settings. However, if not used properly they can compact and/or 

displace mineral soils and reduce soil organic content (Harvey and others 1996; PageDumroese and others 1997). As such, they are usually limited to operating on gentle 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 45

slopes (approximately <40 percent). Machines capable of separating slash of different 

sizes, often called grapple machines, displace less soil than rakes attached to the front of 

tractors, which in turn conserve and protect the soil surface layers (fig. 16). After piling 

the slash, although usually burned, piles can also be chipped, used for bioenergy, or used 

for domestic firewood. 

Machines can rearrange, compact, chip, masticate, or otherwise change the fire hazard without reducing the fuel loads (fig. 17). The effects such mastication and similar 

machines have depends on the size, composition, and location of the residual fuels they 

leave (Graham and others 2000). For example, thin layers of wood chips spread on the 

forest floor tend to dry and rewet readily, and deep layers of chips and chip piles may 

have insufficient air circulation creating poor decomposition conditions. In addition, 

these layers of small woody material on the forest floor can insulate the soils and when 

decomposition does occur, the decomposing organisms utilize large amounts of nitrogen, which reduces its availability to plants. Therefore, use of any of these crushing, 

chipping, or mulching treatments needs to consider the impact on the decomposition 

processes and the potential contribution to smoldering fires. 

Figure 16. Grapple machines have the 

ability to separate coarse from fine 

fuels more readily than tractors and 

tend to displace and compact soils 

less than tractors. 

Figure 17. Masticator used 

to treat ladder and 

surface fuels in the moist 

forests near Lake Tahoe, 

California.

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
46 USDA Forest Service RMRS-GTR-231. 2010.

Prescribed Fire 

Prescribed fire is commonly used to treat and manage forest floor conditions 

throughout the western United States. Fire can reduce fine fuels, reduce ground-level 

vegetation, preserve surface organic layers, and maintain appropriate amounts of coarse 

woody debris (fig. 18). However, unless fuel and weather conditions at the time of ignition are appropriate, fire can also create conditions adverse to vegetative development 

and impair soil productivity (Debano 1991; Hungerford and others 1991). The amount 

of forest floor consumed by a fire is dependent on its moisture content, particularly in 

the lower humus and fermentation layers. Within the Inland West, when the moisture 

content of these lower layers exceeds 100 percent when a fire occurs, the majority of 

these layers are generally conserved (Ryan 1982). When burning occurs under these 

conditions, nutrients (P, N, K) in the litter and fine fuels (≤7.6 cm, 3 in) have the opportunity to condense in the lower layers (for example humus) and, therefore, are not lost 

from the site (Harvey and others 1989) (soil burn severity less than or equal to level 3). 

Figure 18. (A) Fire being used to 

decrease the amount of organic 

material that developed, most 

likely because of fire exclusion, at 

the base of this large ponderosa 

pine located in southern Idaho. 

Fire was applied early in the 

spring when the temperature 

of the lower organic layers was 

below 4.4 oC (40 oF) (when fine 

root activity is minimal) and 

when their moisture contents 

exceeded 100 percent. (B) The 

application of a low intensity 

prescribed fire treating the entire 

free selection area after three 

spring “snow well” treatments 

used to reduce the organic layers 

at the base of the trees. B

A

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 47

Some ground-level vegetation responds vigorously to heat, such as Ceanothus spp., 

which has seeds buried in the forest floor. In addition, many ground-level species sprout 

aggressively in response to fire (fig. 19). The amount, kind, season, and type of fire used 

to treat the forest floor can create a particular soil burn severity. Therefore, the relation 

between the desired soil burn severity and the expected response of vegetation for a 

given forest, PVT, and biophysical setting can be highly variable (Baumgartner and others 1986, 1989; Bradley and others 1992a, 1992b). 

Prescribed fire can reduce horizontal fuel continuity (shrub, low vegetation, woody 

fuel strata), which in turn disrupts growth of surface fires, limits their intensity, and 

reduces the potential of spot fire ignition. In addition, by reducing fine fuels, duff, large 

woody fuels, and rotten material, their continuity changes the fuel energy stored on the 

site and potentially reduces both fire intensity and burn severity (figs. 13, 14 and 15). 

Also, prescribed fire can directly consume low ladder fuels (shrubs, dead trees, needle 

drape, and small trees) and scorch and kill the lower branches of overstory trees, effectively raising the live crown above the ground surface. 

Prescribed fire is an excellent tool for treating the forest floor; however, there are 

also considerable risks and uncertainties with its use (Biswell and others 1973; Cooper 

1960; Fernandes and Botelho 2003; Weaver 1955, 1957). For example, fire cannot readily create precise stand structures and compositions compared to controlled mechanical 

treatments. Climatic and fuel moisture conditions can severely restrict when fire can 

be used, especially in forests with large amounts of fuel or located in areas sensitive to 

smoke production. Also, fires may escape and cause unintended resource and economic 

damage. Even with these short-comings, prescribed fire, by influencing multiple fuels, 

can effectively modify both fire behavior and burn severity. 

Ladder Fuel Treatments 

Precommercial thinning and other intermediate forest treatments can be designed to 

target specific fuel strata and disrupt, (1) the vertical progression of fire from surface 

Figure 19. Ponderosa pine saplings growing among ceanothus, a ground-level shrub that responds aggressively in 

response to fire. The clearcut is located on a grand fir potential vegetation type in eastern Oregon. 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
48 USDA Forest Service RMRS-GTR-231. 2010.

fuels to ladder fuels to canopy fuels and (2) the horizontal progression of fire through 

individual fuel strata. These treatments can be designed and applied to reduce both the 

continuity and density of shrubs and trees and disrupt fire spread, and prevent the fire 

from producing sufficient heat to detrimentally affect the surface soils (Biswell 1960; 

Biswell and others 1973; Cooper 1960; Fisher 1988; Martin and others 1989; Pollet and 

Omi 2002; Scott 1998a; 1998b; Scott and Reinhardt 2001; Weaver 1955). Depending 

on the forest and its condition, these tending activities can occur at a variety of time 

intervals and intensities, thereby creating an infinite number of stand structures and 

compositions (Graham and others 1999a) (figs. 17 and 20). 

Treatments emphasizing the smaller trees and shrubs (ladder fuels) can effectively 

reduce vertical fuel continuity that fosters crown fire initiation (fig. 21). During this 

period in the life of a forest, the structure and composition are the most plastic (in 

other words, responsive to treatments) and future stand dynamics are largely determined 

(Graham 1988; Haig and others 1941; Pearson 1950). In addition, thinning small material and pruning branches are more precise methods than prescribed fire for targeting 

ladder fuels and specific fuel components in the ladder-fuel stratum. The net effect of 

removing ladder fuels is that surface fires burning through treated stands are less likely 

to produce enough energy to ignite the overstory fuels. 

The issue in many forests is excessive regeneration, which makes weeding and 

cleaning young stands essential to develop fire resilient forests (Helms 1998; Smith and 

others 1997). For example, in the ponderosa pine forests of the Black Hills (northeastern 

Wyoming and western South Dakota), ponderosa pine regeneration is often prolific, 

creating a fire hazard and compromising stand development (Shepperd and Battaglia 

2002) (fig. 22). Similarly, in both the cold and moist forests, abundant regeneration is 

often the norm; again requiring tending operations to develop stand characteristics that 

reduce fire intensity and burn severity (Deitschman and Pfister 1973; Graham 1988; 

Haig and others 1941; Johnstone 1985; Johnstone and Cole 1988) (fig. 23). Such ladder 

fuel treatments can be most often accomplished mechanically and, in rare situations, fire 

can be used (Saveland and Neuenschwander 1988). 

Canopy Treatments 

Classically, the term thinning was applied to stand treatments aimed at redistributing growth on remaining stems, but often, any kind of partial cutting (tending) such as 

Figure 20. A thinned mixed 

conifer stand located in 

northern Idaho.

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 49

Figure 21. The first entry of a 

free selection system being 

accomplished using a masticator. 

Depending on stand conditions, 

the majority of the ladder fuels and 

small trees (less than 20 cm, 8 in) 

were chunked, leaving a clumpy 

high forest canopy. The objective of 

the system is to create and maintain 

a wildfire resilient ponderosa pine 

forest located in southern Idaho, 

similar to those that occurred 

historically. 

Figure 22. Ponderosa pines in the 

Black Hills of western South 

Dakota tend to regenerate 

prolifically using shelterwood 

regeneration methods. 

Figure 23. In moist forests, western 

hemlock (a late-seral species) 

readily regenerates in relatively 

closed canopy conditions to 

create multiple fuel layers. 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
50 USDA Forest Service RMRS-GTR-231. 2010.

liberation, preparatory, improvement, sanitation, and selection cuttings could be termed 

thinning (Graham and others 1999a). Thinnings can be designed to affect canopy bulk 

density, which in turn determines whether a crown fire could be sustained. 

Low thinning occurs when trees are removed from the lower canopy, leaving large 

trees to occupy the site. This method mimics mortality caused by inter-tree competition 

or surface fires, and primarily removes small and suppressed trees (ladder fuels). Crown 

and selection thinnings can be used to reduce canopy density and continuity within the 

main forest canopy and alter forest composition (Nyland 2002) (fig. 20). Usually, different tree species have characteristic development rates that result in individual species 

dominating specific canopy layers. For example, in many dry forests, ponderosa pine 

primarily occupies the dominant canopy layers, whereas shade-tolerant grand fir, white 

fir, or Douglas-fir occupy the intermediate and suppressed layers (fig. 6). In this situation, low thinning favors the development of the dominant and codominant ponderosa 

pine, often a desirable forest fuel condition. Thinnings can remove few to many trees and 

need not create regularly spaced forests, but the number, clumping, and juxtaposition of 

residual trees can be varied (Long and Smith 2000; Nyland 2002; Reynolds and others 

1992). As such, thinnings can precisely create targeted stand structures and compositions 

that will influence both fire intensity and burn severity (Agee and others 2000; Miller and 

Urban 2000; Stephens 1998; van Wagtendonk 1996; Weatherspoon and Skinner 1996).

A clearcut may be an appropriate fuel treatment, especially for fuel breaks or in other 

areas in which the spatial continuity of fuels needs to be drastically decreased (Agee and 

others 2000; Graham and others 2004). Disposal of hazard fuels (in other words, activity fuels, tree limbs, and boles less than 7.6 cm, 3 in diameter etc.) can occur by using 

prescribed fire and/or mechanical means. This amount of canopy and fuel removal will 

have the greatest impact on watershed, wildlife, and wildfire responses. Clearcuts can be 

modified by not removing all trees but retaining a few to many. Traditionally for timber 

production, seed-tree and shelterwood regeneration methods created such conditions. 

This condition might be similar to those created by a mixed severity fire (Graham and 

Jain 2005; Graham and others 2005). The retained trees will modify a site’s environment, 

influencing fuel moistures and how fires would burn. The number, location, juxtaposition, disposition (longevity), and species of the residual trees can be specified. By doing 

so, a variety of forest structures and compositions and landscapes can be developed 

(Long and Smith 2000; Reynolds and others 1992).

Selection systems are another set of forest treatments that have applicability for treating all forest (fuel) layers (Graham and Jain 2005; Graham and others 1999b; Graham 

and Smith 1983; Long and Smith 2000; Marquis 1978; Nyland 2002; Reynolds and others 1992; Smith and others 1997). Depending on the design, they can maintain high 

forest cover, which is an important component to many current management objectives. 

Individual tree, group, and free (irregular) selection systems have been described. As traditionally applied, they maintain uneven-aged (diameter distributions) forest structures 

by planning for and executing frequent (in other words, 10- to 20-year) entries (treatments). However, by varying the opening sizes, canopy gaps, tree clumping, species 

preferences, and their juxtapositions, highly heterogeneous forest structures and compositions can be created and maintained (Jain and others 2008). An integral part of all 

selection systems is the tending of all canopy (fuel) layers over time and space to ensure 

the desired conditions are created and maintained (Graham 1990; Graham and others 

1999b). This is of particular importance in treating the ladder fuels and multiple canopies using selection systems. Canopy gaps, highly variable tree arrangements, and forest 

floor treatments can be used in concert, as to ensure the lethal fire risk is not exacerbated 

(Graham and Jain 2005) (fig. 18).

Fuel treatments can increase the probability of modifying fire behavior and burn severity during most weather conditions. However, extreme weather conditions (low fuel 

moisture contents, low humidity, high winds) can create fire behavior that can burn 

through or breach most fuel treatments (Finney and others 2003) (fig. 24). A realistic 

objective of fuel treatments is to reduce the likelihood of crown fire and severely burned 

soils that would lead to a loss in value or undesirable future conditions and not necessarily guarantee crown fire elimination.

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 51

Canopy Treatments Combined With Forest Floor Treatments

The most effective and appropriate sequence of fuel treatments depends on the 

amount of surface fuel present; the density of understory and mid-canopy trees 

(Fitzgerald 2002); long-term potential effects of fuel treatments on vegetation, soils, 

and wildlife; and short-term potential effects on smoke production (Huff and others 

1995). In forests that have not experienced fire for many decades, multiple fuel treatments are often required to achieve the desired fuel conditions. Canopy treatments, 

followed by prescribed burning, reduce canopy, ladder, and surface fuels, thereby providing maximum protection from intense fires in the future (Peterson and others 2005). 

Potential fire intensity and/or burn severity in treated stands is significantly reduced 

only if canopy treatments are accompanied by reducing the surface fuels (woody fuel 

stratum) created from the thinning operations (Alexander and Yancik 1977; Graham 

and others 1999a) (fig. 18). Given current accumulations of fuels in some stands, multiple prescribed fires—as the sole treatment or in combination with thinning—may 

initially be needed, followed by long-term maintenance burning or other fuel reduction 

(for example, mowing, mastication, scarification, etc.) to reduce crown fire hazard and 

the likelihood of high burn severity (Jain and Graham 2004; Peterson and others 2005). 

(see Chapter 4).

The most appropriate fuel treatment strategy is often thinning (removing ladder fuels 

and decreasing tree crown density), followed by prescribed fire, piling and burning, 

mastication of fuels, or other mechanical treatments that reduce surface fuel amounts 

and often promote decomposition (figs. 18 and 21). This approach reduces canopy, ladder, and surface fuels, thereby reducing both the intensity and burn severity of potential 

wildfires. Restoring forests to a condition in which fire alone can maintain the desired 

conditions will take time (fig. 18). Wildland fire use (that is, allowing certain wildfires 

to burn under certain conditions and locations) offers some hope once homes, communities, and key resources are protected through thinning, prescribed fires, or other 

treatments. 

Figure 24. The intense Rodeo-Chediski Fire that burned in Arizona in 2002. This ponderosa pine forest 

was historically burned by low intensity surface fires, but singly and in combination, fire exclusion, 

timber harvest, climate change, and livestock grazing contributed to forest changes that facilitated this 

uncharacteristically intense fire. Often, fuel treatments will locally impact such fires but most treatments 

are readily breached. 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
52 USDA Forest Service RMRS-GTR-231. 2010.

Post Treatment Environment 

Thinning and prescribed fires can modify understory microclimate that was previously buffered by overstory vegetation (Scott and Reinhardt 2001; Pollet and Omi 2002; 

Weatherspoon 1996). Thinned stands (open tree canopies) allow incoming solar radiation to penetrate to the forest floor increasing surface temperatures, decreasing fine fuel 

moisture, and decreasing relative humidity compared to unthinned stands—conditions 

that facilitate intense fires (Countryman 1955; Pollet and Omi 2002). An increase in surface fire intensity may increase the probability of a fire exceeding the critical threshold 

needed to initiate a crown fire (Van Wagner 1977). Therefore, it is important that the 

gap between the surface and crown fuels is increased by either prescribed fire or pruning (fig. 18) so if a fire should occur, the potential for crown fire initiation is minimized. 

Rothermel (1983) found significant differences in fire behavior between a closed stand 

(no harvest) and an open stand (thinned). Changing stand structure, while ignoring surface fuels, will only affect the likelihood of active crown fires—it will not necessarily 

reduce the likelihood of surface fires intense enough to damage soils or cause significant 

overstory mortality. For example, figure 25 illustrates the build-up of organic layers as a 

function of fire exclusion. If only ladder and crown fuels are treated ignoring the ground 

fuels, in this situation, a fire would most likely lead to high soil burn severity and killing 

of trees through cambium kill. Moreover, surface fire intensity may be greater in thinned 

stands compared to untreated stands depending on whether the thinning activity adds to 

the surface fuels (Alexander and Yancik 1977; van Wagtendonk 1996; Stephens 1998). 

Therefore, it cannot be emphasized enough that all fuel layers need to be managed (over 

time and space) to minimize the unwanted consequences of wildfires (fig. 10). 

Treatment Longevity 

Very few specific experiments have evaluated the longevity of treatments and their 

effectiveness in altering fire behavior and burn severity. However, there is considerable 

information on forest growth and development, and this information is useful in providing estimates on the longevity of potential treatments. There are good models available 

(Reinhardt and Crookston 2003; Wykoff and others 1982) that predict vegetation development over time and provide estimates of treatment longevity. 

Figure 25. When fires are 

excluded from ponderosa pine 

forests, organic layers tend to 

accumulate and tree roots, 

ectomycorrhizae, and nutrients 

also tend to concentrate in 

these layers. Note the contrast 

between the amount of 

organic material on the forest 

floor when General Custer 

came through the Back Hills 

in 1874 and the amount that 

has accumulated around the 

rocks in the photo in 2000. 

Photograph courtesy of Paul 

Horsted/custertrail.com (Grafe 

and Horsted 2002). 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 53

There are limited amounts of information on the relation between canopy structure 

and ground-level vegetation, or the relation between vegetation development and fuel 

moisture. For short time periods (months) after treatment, fuel changes can produce 

dramatic differences in fire behavior. Biswell and others (1973) showed that the effectiveness of prescribed fire treatments in maintaining desired fuel conditions decreased 

significantly over 2 decades in a ponderosa pine forest. Van Wagtendonk and Sydoriak 

(1987) directly examined fuel accumulation following prescribed burning and found 

that fuel amounts reached 67 percent of their pre-burn loading after 7 years. Many of the 

prescribed fires they used were the first fuel treatments that occurred in these stands in 

decades and would potentially kill many small trees that would contribute to the woody 

fuel load. Repeated burns were not studied, but the elimination of small trees using a 

series of burns would be expected to retard fuel accumulation compared to the amounts 

they reported. Van Wagtendonk and Sydoriak (1987) concluded that prescribed burning 

would be required at least every 11 years to maintain fuel loads below their preburn 

condition. Van Wagtendonk (1995) also reported reductions in fire spread and intensity 

of fires up to 14 years after previous burns within the mosaic of large fires in the mixedconifer forests of Yosemite National Park. 

The duration of treatment effectiveness will vary with climate, PVT, soils, and other factors that influence productivity and the nature of the fuel treatments (Keyes and 

O’Hara 2002). For example, the longevity of thinning slash is greater on drier sites, 

particularly for finer woody material compared to fine fuels occurring in wetter forests 

(Christiansen and Pickford 1991). Treatment effects will likely last longer in areas in 

which vegetation development is slower than in highly productive areas where vegetation development is more rapid and lush (Weatherspoon and Skinner 1996). Few data 

exist, but inferences from fire history research and modeling show that the length of 

treatment effectiveness will vary with forest type (general fuel characteristics) and fire 

regime (Heyerdahl and others 2001; Miller and Urban 1999; Taylor and Skinner 1998; 

Taylor and Skinner 2003). 

Fuel Treatment on Landscapes 

The spatial patterns of fuel treatments in landscapes will most likely determine their 

effectiveness in modifying wildfire behavior (Hessburg and others 2000), because multiple stands and fuel conditions are involved in large fires (Finney 2001). Fire behavior 

under extreme fire weather may involve large areas of fuels, multiple fires, and spotting, 

so a “firesafe” landscape needs to populate hundreds to thousands of hectares (acres) 

with strategically located fuel treatments (Finney 2003). Treating small or isolated 

stands without assessing the broader landscape will most likely be ineffective in reducing wildfire extent and severity. 

There are limited examples of how fuel treatments have altered subsequent fire behavior and burn severity (Helms 1979; Martin and others 1989; Pollet and Omi 2002). 

However, despite small-scale modification of fire behavior, none of these studies demonstrated that spread or behavior of a large fire was significantly altered, probably 

because the units were relatively small and were surrounded by areas containing vegetation favoring continued fire growth. In the mixed-conifer forests of northern California, 

fire intensity varied with dominance of short-needle or long-needle conifers in the same 

fire regime (frequent, low-moderately intense surface fires). Under similar burning conditions in a retrospective study of the widespread fires of 1987, stands dominated by 

Douglas-fir sustained significantly less damage than did stands dominated by ponderosa 

pine (Weatherspoon and Skinner 1995). Given current fuel accumulations across the 

Interior West, small areas (unknown threshold) favoring low intensity fires will probably be irrelevant to fire behavior (Dunn 1989; Salazar and Gonzalez-Caban 1987). 

Therefore, treatments that alter vegetation to favor low intensity fires must consider 

spatial arrangement of fuel structures to alter wildfire behavior. 

Large-scale, frequent mosaic burning may maintain many portions of some landscapes in a treated condition and disrupt growth of the inevitable wildfire (Brackebusch 

1973). Evidence that mosaic patterns reduce fire spread comes from natural fire patterns 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
54 USDA Forest Service RMRS-GTR-231. 2010.

that have fragmented fuels across landscapes. This spatial pattern produces self-limiting 

fire growth and behavior by management of natural ignitions, as shown in Yosemite 

National Park and Sequoia National Park (van Wagtendonk 1995, 1996). The spatial 

arrangement of vegetation influences the growth of large fires (Brackebusch 1973; 

Finney 2001). Patches of vegetation that burn relatively slower or less intensely than 

surrounding patches may force the fire to move around them by flanking (at a lower intensity), which locally delays the forward progress of the fire. Such strategically placed 

treatments create landscape fuel patterns that collectively slow fire growth and modify 

behavior while minimizing the amount of treated area required (Finney 2001) (fig. 26). 

The importance of spatial pattern is emphasized by findings that random fuel treatment 

arrangements (Finney 2003) are extremely inefficient in changing fire behavior (fig. 

26)—requiring perhaps 50 to 60 percent of the area to be treated compared to 20 percent 

in a strategic fashion (Finney 2001). If fuel treatments are to be effective at changing 

the growth of large fires, then strategic placement of treatment areas must incorporate 

land ownership, endangered species, riparian buffers, and other concerns. The costs and 

maintenance levels needed to maintain this forest pattern would vary depending on forest type, PVT, access, and public acceptance. 

An alternative to a landscape approach to altering fuels is to create fuel breaks, which 

modify easily accessible portions of the vegetation in strategic locations across a landscape (Agee and others 2000; Weatherspoon and Skinner 1996). The purpose of fuel 

breaks, which are typically placed in defensible locations like a ridge, is to aid suppression efforts of firefighters to stop fire spread (Green 1977). The benefits of a fuel break 

are successful only if the fire suppression activities anchored to the fuel break limit the 

size or perimeter of the fire. If fire suppression does not occur, a fire can continue to 

burn through the fuel break with little or no effect on fire size. Moreover, fuel breaks 

(clearcuts) most often require long-term maintenance and repeated treatments. 

Treatment Efficacy 

Fire behavior and burn severity (see section on burn severity, page 42) are strongly 

influenced by stand structure as it relates to live and dead fuel loadings and ladder fuels. 

The type and abundance of surface fuels have an effect on the abundance of falling embers, which can ignite distant fuels and spread, thus influencing fire behavior. Reducing 

both ladder fuels and surface fuels is essential to effectively change fire behavior and 

burn severity (Graham and others 1999a; Omi and Kalabokidis 1991; Pollet and Omi 

2002). Examples from the Hayman Fire in Colorado illustrate these interactions (Finney 

and others 2003). The Polhemus prescribed burn in November 2001 removed most surface fuels and pruned lower live branches from trees in a ponderosa pine forest but did 

Figure 26. Comparison of large 

fire growth rate among 

different spatial fuel patterns 

(Finney 2003).

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 55

not significantly reduce overstory density (tree burn severity less than or equal to level 

2). These changes were sufficient to stop the Hayman Fire when it burned into the area 

in June 2002 even though intense fire behavior was present, facilitated by high winds 

(48 kmph, 30 mph and greater) and low relative humidities (near or below 10 percent). 

This treatment was applied within a few months of the fire, thus decreasing the surface 

fuels substantially (soil burn severity less than or equal to level 3). In this case, the time 

since treatment, plus the treatment contributed to the change in fire behavior and subsequent burn severity. On the Manitou Experimental Forest (Hayman Fire), mechanical 

harvesting (selection silvicultural system) reduced the density of all sizes of trees in a 

pure ponderosa pine forest and concentrated logging slash in large piles. These actions 

resulted in an easily suppressed surface fire when the Hayman Fire burned into the 

area. On the other hand, all trees were killed in the Sheepnose Fuels Reduction Project 

(shelterwood) within the Hayman Fire. Although the stand was heavily thinned from 

below, heavy surface fuels from non-merchantable logging slash allowed the fire to burn 

intensely through this stand, potentially damaging the soils and scorching and killing 

the trees left after the treatment (Finney and others 2003) (fig. 27). 

Another example of fuel treatment effectiveness is the Cone Fire (September 2002) 

in northern California that burned into the Blacks Mountain Experimental Forest. The 

fire burned approximately 809 ha (2,000 ac) of a study area that was designed to evaluate 

the effect of varying forest structures (thinnings) on wildlife. When the fire encountered 

forest structures in which the surface fuels had been burned and the canopy density was 

reduced, the fire dropped from a crown to a surface fire within the first few yards of 

entering the treatment units. In areas where the surface fuels were not treated, the fire 

continued through the unit as a surface fire with variable intensity. There was considerable crown scorch and bark charring in these treatment units with areas of up to 1 ha 

(2.47 ac) where all trees were dead (Graham and others 2004). These examples show 

that variability in weather, physical setting, and forest fuels (composition, structure, 

Figure 27. A thinned 

ponderosa pine stand in 

which the surface fuels 

remained after harvest, 

which resulted in an 

intense surface fire (tree 

burn severity level 4) and 

high soil burn severity 

(level 5 to 6) (Jain and 

Graham 2007) when the 

Hayman Fire burned near 

Colorado Springs, CO, in 

2003.

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
56 USDA Forest Service RMRS-GTR-231. 2010.

etc.), influences fire behavior and effects, making it difficult to generalize the effects of 

treating forests to alter fire behavior and burn severity. However, a key point from these 

examples is that in many cases, particularly if combined with fire suppression efforts, 

reduced surface fuels and thinning can significantly limit fire spread and influence burn 

severity to both vegetation and soils. 

Fuel Treatments and Cumulative Watershed Effects 

The cumulative effects (either positive or negative) of a fuel treatment are the environmental consequences of the activity when added to the existing landscape condition 

and any reasonably foreseeable future actions or disturbances. An environmental consequence has both spatial and temporal dimensions and short-term and long-term effects 

(Reid 1988). Fuel treatments should cumulatively influence vegetation (forest composition and structure function) and be considered as wildfire fuel (Finney 2003; Graham 

and others 1999a; Graham and others 2004). The cumulative impacts that fuel treatments have on burn severity and fire behavior can range from local to the landscape 

and watershed levels. As Finney (2003) suggests, fuel treatments can be strategically 

located and designed for disrupting a fire’s progression as it burns through watersheds 

and landscapes. The cumulative impact of such treatments on potential fire behavior and 

burn severity would depend on how much of a watershed or landscape was treated, the 

treatment locations, the timing of the treatments, the kind and intensity of the treatment, 

and the length of time before both dead and live vegetation would return to pretreatment 

conditions (for example, the longevity of the fuel treatments and their impact on the fuels 

complex). In addition, the physical character of the watershed (in other words, slopes, 

aspect, geology, soils, orientation, and elevation), forest type, PVT, structural stages, 

seral stages, and patch sizes and juxtapositions would interact with current, planned, and 

continued maintenance fuel treatments to influence wildfire intensity and burn severity. 

Similar to targeting the vertical distribution of fuels to modify fire outcomes, treating 

different fuel strata would most likely differentially affect an array of wildlife species that 

are dependent on the vertical forest strata for habitat or habitats of their prey (Reynolds 

and others 1992; Theobald and others1997; Thomas 1979). Fuel treatments that affect 

the accumulation and disposition of snags and coarse woody debris, and the retention, 

disposition, juxtaposition, size, and amount of canopy cover, seral stages, and structural 

stages occurring on a site, would most likely impact wildlife (Reynolds and others 1992; 

Thomas and others 1979). These wildlife implications would be important to current 

planning and the execution of fuel treatments, but future and maintenance treatments 

would need to include their potential impact on wildlife. Also, depending on the wildlife 

species and the extent, number, and location of fuel treatment, their effects would most 

likely be cumulative and could encompass watersheds and large landscapes (Thera and 

Wildman 2001). Canopy cover also affects water relations within and across watersheds 

similarly to the potential impacts it has on wildlife. Through evapotransporation, shading, snow interception, snow retention, and other watershed impacts, canopy cover can 

affect watershed stability (Ziemer and Lisle 1998). 

Canopy cover can influence watershed processes (for example, sedimentation and 

peak flow) through altering rainfall intensity on established snow packs and raindrop 

intensity on the forest floor; however, these effects must be placed with the context of 

the soil type, geology, and other biophysical characteristics to understand the cumulative 

impacts to water quality and quantity. Even though they are not part of fuel treatments, 

present and future roads are integral to forest management actions. Their location and 

use for managing fuels inherently affects watersheds and the cumulative effects of fuel 

treatments on watersheds (Berg 1989; Elliot 2000) (see Chapter 5). 

The effect fuel treatments have on visual quality is often an important component 

of a cumulative effects analysis. Fuel treatment appearance and juxtaposition within a 

landscape are integral to their visual effects (Bergen and others 1995). The visual quality of a watershed is highly intertwined with the road network along with the character 

(in other words, prescribed fire, piling slash, timber harvest, etc.) of the treatments and 

Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 57

their visual quality. Canopy closure—its shape, location, size, and other attributes—has 

significant impact on visual quality, both in the short- and long-term, and the cumulative 

visual impact of such treatments (Brown and Daniel 1986). In addition, the visual quality 

attributes of a fuel treatment are predicated by whether the treatments are viewed from 

the foreground, middle ground, or the background. 

Fuel treatments should treat forests using silvicultural systems. The silvicultural system documented in a silviculture prescription can disclose the cumulative effects fuel 

treatments have on vegetation regeneration and development. In particular, silvicultural 

systems designed for treating fuels should integrate the cumulative and interactive role 

that insects, diseases, and wildfires play in forest development. Moreover, by designing 

a silvicultural system and documenting it in a silvicultural prescription, the prescription 

could display the dynamics of a forest and all of its components over time, which can facilitate the understanding of the cumulative effects of fuel treatments among a wide array 

of disciplines and stakeholders. By disclosing the effects in a prescription, the effects of 

fuel treatments on the sustainability of a forest, along with their risks and uncertainties, 

are identified and documented. In addition, silvicultural systems and their documentation provide a framework for understanding cumulative watershed effects and can be 

developed into visualizations and other communication tools applicable to a wide range 

of disciplines and stakeholders. 

Conclusion 

The cold, moist, and dry forests are all inherently different (figs. 1 through 5). Each 

forest has a unique suite of forest vegetation, seral and structural stages, and compositions. With this uniqueness comes distinctiveness in where wildfires burn, what they 

burn, and the effects they have as well as the effect and latitude of forest treatments 

that modify fire behavior and burn severity. The fuels that wildfires burn range from 

high canopy fuels to those located on and below the soil surface (fig. 10). Fires can be 

rather short-lived (minutes), producing little heat to long-lived (months), producing large 

amounts of heat. The spatial extent of fires can be small (a few m2, ft2) to large (100s km2, 

mi2). The burn severity within these extents can range from homogeneous to extremely 

heterogeneous, leaving a wide variety of vegetation and soil conditions in the after fire 

(figs. 11, 14, and 15). 

Lethal fires (stand replacing), non-lethal (low intensity and severity) surface fires, 

mixed fires, or a combination, burn through the moist, cold, and dry forests at various 

intervals and intensities resulting in a variety of burn severities. Fire exclusion has affected all forests, but in general, it has had the largest impact on the dry ponderosa pine/

Douglas-fir forests by changing species compositions, structures, and forest floor constituents in many locales. Fire regimes have minimally changed in the moist and cold 

forests because of fire exclusion but they have greatly altered dry forests. 

White pine blister rust (an exotic stem disease) has altered the moist forests by killing 

western white pine and is progressing to severely alter the cold forests by killing white 

bark pine (Pinus albicalus) (fig. 9). In addition, because of the uniformity of age and size 

of lodgepole pine and Engelmann spruce in many cold forests, bark beetles are killing 

millions of trees (fig. 8). 

Forests that were once dominated by vegetative structures and compositions relatively resilient to native insects, diseases, and fire regimes are now (2009) more prone 

to epidemics of insects and diseases and uncharacteristically large and severe wildfires. 

The changes in forests occurred through a variety of components, ranging from ground 

level vegetation to high forest canopies and the forest floor and mineral soil that support 

the vegetation. In addition, all forest vegetative components—live, dead, and in various stages of decay—are part of the fuel matrix, and their composition, development, 

structure, and juxtaposition at both fine and broad temporal and spatial scales influence 

how fires burn. These forest characteristics, in concert with physical setting and weather 

(observable both at fine and broad spatial and temporal scales), ultimately determine fire 

behavior and burn severity. 

Russell T. Graham, Theresa B. Jain, Susan Matthews Cumulative Watershed Effects of Fuel Management in the Western United States
58 USDA Forest Service RMRS-GTR-231. 2010.

The final item influencing the scope and impact of wildfires is the efficiency of suppression activities that, in concert with locale, fuels, and weather, determine the extent 

and severity of wildfires. Fuel treatments are the only management activity that can 

influence fire behavior and burn severity. In addition, depending on forest development 

and values at risk, the frequency of treatments to maintain desired fuel conditions could 

occur often. It is recommended that surface fuels be treated first, followed by ladder and 

crown base height treatments and canopy treatments. 

Fuel treatments that affect canopy openings most likely impact the amount of water 

produced within a watershed, and treatments that disturb the forest floor subsequently 

influence water sedimentation. Also, the location, number, size, age, intensity, and vegetative and forest floor recovery (development) will determine the cumulative effects 

of fuel treatments within and among watersheds. Because they tend to occupy locales 

at the higher elevations relative to the surrounding landscapes, cold forests would contain more headwater stream locations. Both the dry and moist forests occupy the lower 

elevations and often the dry forests border grass and/or shrublands, especially in the 

central and southern Rocky Mountains. Therefore, the affects that fuel treatments would 

cumulatively have on watersheds is highly variable among forest types and highly variable depending on the location and juxtaposition of the forests and treatments within 

and among watersheds. 

Forests die, regenerate, and develop in response to disturbances or the lack thereof. 

Fuel treatments are yet another disturbance that influences how wildfires behave and 

the subsequent outcomes they produce (figs. 17, 18 and 21). Along with influencing 

wildfires, such treatments influence both the physical (soils, water, and air) and vegetative properties of a setting. Cumulatively fuel treatments affect many forest attributes, 

including wildlife habitat, sense of place, invasive species, cultural resources, sensitive 

plants, and ecosystem services (air and water quality, water quantity, and soil productivity). Moreover, forests are dynamic and, therefore, fuel treatments should change over 

time and space. We suggest that it is very useful to display fuel treatments and associated outcomes spatially and temporally in addition to identifying the associated risks 

and uncertainties. At a minimum, these silvicultural systems should demonstrate their 

cumulative impacts over time on both wildfires and the soil and water resources within 

and among watersheds. This is the essence of silvicultural systems and forest planning. 

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Chapter 3. Fuel Management in Forests of the Inland West
USDA Forest Service RMRS-GTR-231. 2010. 69

Chapter 4.

Tools for Fuel Management

Bob Rummer, Southern Research Station, USDA Forest Service, Auburn, AL

Introduction

Fuels management is an active term. It is an intentional, planned activity defined by 

consideration of fire behavior, silvicultural principles, ecological constraints, and the 

economic and technical limitations of the tools selected to implement the treatment. 

A forest operation is a tool used to manipulate vegetation or site condition in order to 

achieve some desired management objectives. Given the wide range of forest operations that can be employed to treat forest fuel, it is imperative to employ a tool that is 

well-matched to both operational needs and treatment constraints. Selecting a poorly 

suited tool increases costs and reduces the effectiveness of the operation in achieving 

the desired outcomes. The selection of a forest operation also plays a critical role in 

determining the amount and type of cumulative effects associated with the treatment. 

A tool that is not matched to the terrain or job requirements will likely produce more 

undesirable impacts.

The purpose of this chapter is to give a basic overview of forest operations for 

fuel treatments along with information to guide selection of appropriate technologies. 

Terminology is also important in this discussion. In the biological sciences we have 

learned that it is important to use scientific names of organisms, rather than common 

names, to avoid confusion. Unfortunately, many forest operations acquire common 

names that are contradictory, regionally limited, or non-specific. When someone speaks 

of a “hydro-ax” treatment, for example, they could mean a vertical-shaft brushcutter, 

horizontal-shaft masticator, shear feller-buncher, or sawhead feller-buncher. These possible meanings represent very different costs, capabilities, and fuel treatment outcomes. 

The reference listing at the end of this chapter provides some standard definitions.

Forest Operations for Fuel Treatment

The objective of fuel treatment is to alter fire behavior and severity by modifying 

properties of various fuel strata in a stand (Graham and others 2004). Treating one 

strata may improve fire behavior in one respect, but aggravate it in another. For example, activity fuel resulting from a thinning may reduce crown fuel but increase surface 

fuel loading. A clear fuel treatment prescription should consider effects on the total 

fire behavior response and clearly specify acceptable treatment outcomes. The primary 

challenge of selecting appropriate operations, then, is to match the task requirements 

specified by the fuel prescription to equipment capabilities within constraints of terrain 

and cost.

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
70 USDA Forest Service RMRS-GTR-231. 2010.

Because it should deal with all fuel strata, not just merchantable trees, a fuel treatment 

operation may involve activities, such as mastication or raking, that have different types 

of disturbance than conventional forest harvesting. The disturbance effects can be direct 

(scraping soil to reduce fine surface fuel, for example) or indirect (dozer piling resulting in high temperature burning with resulting hydrophobic soils and poor herbaceous 

regeneration). The selection of an operation will affect the spatial pattern and total extent 

of disturbance. The interaction between the type of operation and the sensitivity of the 

site affects the severity of disturbance and thus the temporal pattern of recovery or effect.

Forest operations for fuel treatment can be broadly divided into two types—in-situ 

treatment where no biomass or product removal occurs and removal treatments that extract some amount of fuel loading for utilization or disposal outside of the stand. In-situ 

treatments are selected when there are no economically viable markets for biomass material and it is technically feasible to meet the fuel reduction goals with the material 

left in place. Removal treatments are selected when it is possible to recover additional 

value from the treated material or when it is not feasible to treat the fuel in the stand. 

Resource managers in the western United States have often faced a lack of biomass 

markets resulting in extensive in-situ piling and burning treatments. More recently however, growing restrictions on burning have motivated efforts to find economically viable 

removal treatments.

In-Situ Treatments

Fuels treatment can be accomplished within the stand by performing two basic functional tasks: (1) killing selected vegetation and (2) reducing the resulting activity fuel 

loading to acceptable fire behavior conditions. The selection of an in-situ treatment is 

probably limited more by the second function than any other factor. Simply rearranging 

high fuel loading in the stand may not be sufficient to lower fire risk. In fact, shifting 

fuel loading from ladder fuel or crown strata to surface fuel can significantly aggravate 

some aspects of fire behavior. Thus most in-situ treatments combine an initial vegetation 

cutting treatment with a follow-on burn to reduce the volume of activity fuel in piles or 

scattered slash under controlled burning conditions.

Generally the least expensive in-situ treatment is prescribed fire. Cleaves and others 

(2000) found that average prescribed burning costs ranged from $22.80 to $121.00/acre 

(1994 dollars, excluding Region 5). Slash burning was generally about twice as expensive as management burning. Prescribed fire mimics many of the ecological functions 

of natural wildfire. However, the use of this tool has significant limitations. The pattern 

of vegetative mortality is difficult to control, air quality is adversely impacted, there is 

risk of escape, and acceptable burning conditions may only occur in limited windows of 

opportunity. Perhaps the largest limitation to the use of prescribed fire is fuel loading. 

Many forest areas in the western United States have such high fuel loading that fire is not 

acceptable without some initial pre-treatment (definition of Condition Class 3).

Chopping, or drum chopping, is a pre-treatment to knock down brush and small trees 

before broadcast burning. A large steel drum with cutting knives mounted on the face of 

the drum is rolled across a site (fig. 1). The drums can range in size from 8 to 12-ft wide 

and can be loaded with water for additional weight. The drum can be towed behind a 

wheeled or tracked tractor or it can be pulled on a winch cable. As the drum rolls over 

vegetation, the knives break limbs and stems into shorter pieces. Some trees may even be 

uprooted in the process. Chopping increases surface roughness by incorporating organic 

material into the soil; however, there is little soil displacement associated with the treatment. When the drum is towed by a winch line, this treatment can be used on steep slopes 

with little soil impact.

After several months of drying, the chopped material can be burned. Chopping lowers 

the fuel bed depth, which reduces flame height. It also increases surface fuel density and 

continuity, which can make it easier to carry prescribed fire across a site. While this treatment is most often used for residue treatment after clearcut harvesting, it has also been 

Chapter 4. Tools for Fuel Management
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Bob Rummer Cumulative Watershed Effects of Fuel Management in the Western United States

used effectively for fuel treatment in brush fields, understory control in open pine stands, 

and as treatment for wildlife habitat improvement.

Chaining is similar to chopping, although it is strictly a clearcut or open field brush 

fuel treatment. A long, heavy chain, often anchor chain, is connected between two tractors. As the tractors drive forward, the chain knocks over or uproots the brush and trees 

between the machines. Soil disturbance results from uprooting and the movement of 

debris with the chain. However, Farmer and others (1999) showed that chaining for 

pinyon-juniper restoration actually reduced runoff and erosion when compared to untreated areas. A variation of chaining uses a single tractor towing a heavy steel ball 

connected to the end of the chain. Operating cross-slope on hilly land, the heavy ball 

pulls the chain downhill and serves as the second anchor. Depending on the fuel loading, 

chained sites can be burned or left to decompose over time.

Grubbing also kills vegetation by uprooting and breaking plant vegetation to reduce 

growth. It is principally applied to hard-to-control species that will resprout from cut 

stumps (for example, salt cedar [Tamarix sp.] or alligator juniper [Juniperus deppeana]). 

Grubbing attachments vary from subsoil cutting blades to specially designed grasping 

attachments for excavators. Extracted plants are piled for disposal or removal. A grubbing treatment creates more severe soil disruption in the areas where plants have been 

removed, but this soil disturbance is discontinuous compared to a chaining treatment. 

Grubbing is often the alternative to herbicide treatment.

Manual lopping is another pre-treatment for in-situ fuel management. Chainsaws, 

brush saws or manual loppers can be used to fell small trees and brush. Lopping may 

require slashing to reduce piece sizes to specified length or height. Depending on fuel 

loading, lopping can be combined with scattering (spreading activity fuel across the 

stand) or handpiling. Generally, lighter fuel loads would be treated by scattering, while 

heavier loading would necessitate concentrating the slash into piles for burning. Manual 

lopping results in minimal site impact and can be used on steep slopes. The primary 

disadvantages of this operation are safety concerns associated with chainsaws and the 

significant labor requirements to achieve modest production rates. Manual operations are 

also limited by piece size and stems per acre.

An alternative to manual lopping is to use a swing machine with a brushcutter or 

sawhead attachment. The approach is to cut small stems quickly and leave them scattered 

on the site. Feller-bunchers have been used in such applications, but the head is generally not designed to cut or grasp small stems effectively. Mechanical lopping has very 

little impact on the site. The machine cuts material to the front and drives on the felled 

mat of slash. This treatment can be applied on a wide range of slopes depending on the 

capabilities of the base machine. Self-leveling feller-bunchers, for example, are able to 

operate on 50 percent slopes. Non-leveling swing machines should be limited to gentler 

Figure 1. Drum chopper 

pulled by a bulldozer.
72 USDA Forest Service RMRS-GTR-231. 2010.

slopes. Site disturbance is further reduced because a swing machine can access a 60-ft 

wide swath from one position.

Lopped material can also be mechanically piled using either a brush rake or a grapple. 

Brush rakes mount on the front of a wheeled or tracked machine to facilitate pushing 

debris. The rake teeth on the lower edge of the blade catch residues while minimizing 

the amount of soil displacement that occurs. However, dozer or tractor piling still causes 

significant soil disturbance from debris movement. Fuel loading and pile size constraints 

will determine the number of piles per acre and the required amount of trafficking. 

Grapple piling is an alternative method that uses a swing machine, either a knuckleboom 

log loader or a modified hydraulic excavator, to grasp and pile residues. Because grapple 

piling lifts the material rather than pushing it, soil disturbance is negligible. The resulting piles have very little soil and rock and can be built higher than tractor or hand piles.

Chopping, lopping, and piling are all pre-treatment activities that require subsequent 

burning to reduce fuel loading. If burning is not possible, however, there are still two 

options for in-situ fuel treatment—chipping and mastication. Both of these mechanical 

treatments convert existing fuel into smaller size classes with the objective of removing 

forest fuel through decomposition. Chipped or masticated material is spread on the forest 

floor and, as a result of more direct soil contact, has significantly different fuel moisture 

and burning characteristics than typical forest fuel. It may be possible to use chipping 

or mastication as a tool to reduce fuel loading prior to a prescribed burn, but more commonly these techniques are used in lieu of burning.

Mobile chippers can be self-propelled or towed machines that reduce trees into chips 

through slicing. The chips are relatively uniformly sized due to the process and are projected into the stand through a discharge spout. Chippers are fed by a loader and will be 

most productive if the felled material has been pre-bunched. Towed chippers are typically limited to roadside processing, while self-propelled tracked chippers can operate 

in the stand. Chipping would be a good alternative to burning if piles had already been 

constructed.

The direct impacts of chipping include trafficking by the machine and the direct impact of spreading material on the soil surface. Trafficking effects are limited since most 

of the undercarriage systems produce a ground pressure of less than 7 psi. The effects of 

the chipped material on soils and water quality are more uncertain. Given the density of 

wood chips, 20 bone dry tons spread across an acre would be a layer about 1-inch deep. 

Chips could exclude herbaceous regrowth, alter soil moisture regimes, and change nutrient cycling processes. Chips may also reduce soil exposure to rainfall and thus reduce 

erosion.

Mastication equipment shreds, rather than chips, standing trees and brush. Unlike 

mobile chippers, masticators are generally able to fell material. Windell and Bradshaw 

(2000) provide a thorough review of the range of machines that can be used. There are 

two basic types of attachments—vertical shaft and horizontal shaft (fig. 2). Either of 

Figure 2. Horizontal drum 

masticator mounted on a 

tracked tractor.

Chapter 4. Tools for Fuel Management
USDA Forest Service RMRS-GTR-231. 2010. 73

Bob Rummer Cumulative Watershed Effects of Fuel Management in the Western United States

these can be equipped with pivoting flail-type cutters or rigidly mounted cutting teeth. 

Masticators can be mounted on nearly every form of base machine including tracked 

machines, wheeled machines, swing machines, agricultural tractors, or even walking 

excavators. Johnson (1993) described the use of a walking excavator to masticate material on the Olympic National Forest in areas with slopes exceeding 60 percent. While 

the shredded material is highly variable given the range of attachments, it is generally 

coarser and more irregular in shape than chips.

The principle impact of mastication will result from the trafficking of the base machine and the work area defined by the attachment configuration. Direct-mount cutters 

must traverse nearly the entire stand to implement a treatment. This would approximate 

the extent of trafficking by a feller-buncher in a clearcut harvest. Boom-mounted cutters, on the other hand, have limited trafficking and soil impact. The type of trafficking 

disturbance is also a function of the type and size of tire or track that is used. A wheeled 

machine with wide tires may actually have lower ground pressure than a tracked machine 

with standard tracks. Careful consideration should be given to the specification of appropriate base equipment for particular soil conditions.

Removal Treatments

If the activity fuel loading from a particular treatment is going to exceed acceptable 

levels, or if there are marketable products that can be recovered, a removal fuel treatment 

may be required rather than an in-situ treatment. Like conventional forest harvesting, 

a removal treatment will involve felling and extraction. However, the type of material 

removed in a fuel treatment may make the operation radically different in terms of effects and cost than traditional product recovery. For example, skidder load sizes could 

be smaller and the total number of trips into the stand may be greater when removing 

small-diameter thinnings. In a fuel treatment, material may be brought out of the stand 

simply for roadside disposal without the need for product merchandizing that would occur in a sawlog harvest. 

Felling for removal can use chainsaws, feller-bunchers, or harvesters. Manual felling 

is effective for a wide range of tree size and terrain. However, as the number of stems per 

acre increases, mechanical options become more desirable. Mechanized felling can also 

move felled material into concentrated bunches for more effective extraction. It is also 

easier to control the direction of fall and minimize residual stand damage with machines. 

Like other forest operations, the type of carrier (wheeled or tracked) and the type of attachment mounting (drive-to-tree or swing-to-tree) will determine the primary impacts 

of felling. Swing machines can operate on steeper slopes and can access a larger area 

with minimal traffic. Drive-to-tree machines are generally more appropriate for flatter 

terrain (fig. 3).

Figure 3. Wheeled fellerbuncher thinning a 

ponderosa pine stand.
74 USDA Forest Service RMRS-GTR-231. 2010.

Felled material can be removed from the stand using skidders, forwarders, cable systems, or helicopters. A basic functional difference among these methods is how the load 

is moved—skidders drag one end of the load, forwarders carry the load on a wheeled 

frame, cable systems drag the load but without wheel traffic, and helicopters lift the load 

completely above the ground. Cost per ton removed increases with increasing extraction 

distance. This cost-distance curve is a function of load size, operating costs, and travel 

speed. Skidders will generally be used for distances less than 400 ft; forwarders and cable 

systems can work effectively at distances of 800 to 1,000 ft; while helicopters can move 

material several miles.

With any extraction system where repeated cycles are necessary to remove material, 

the cost per acre is strongly influenced by load size. Collection and removal of slash and 

brush is particularly challenging because small pieces make it hard to get full payloads. 

A forwarder load of biomass limbs and tops is about one-third the bulk of a load of logs 

(fig. 4). If the fuel reduction treatment requires slash removal, the least expensive approach is skidding whole trees. By taking limbs and tops to a roadside attached to the 

main stem, activity fuel are minimized and the number of trips into the stand to accomplish the treatment is reduced.

Cut-to-length (CTL) systems are considered the lowest impact ground-based harvesting system (fig. 5) and require special consideration. In CTL, trees are felled and 

processed at the stump using a harvester, and each tree is cut into log lengths that are 

Figure 4. Forwarder 

carrying thinning 

residues to roadside.

Figure 5. Wheeled 

harvester performing a 

fuel reduction thinning.

Chapter 4. Tools for Fuel Management
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Bob Rummer Cumulative Watershed Effects of Fuel Management in the Western United States

piled by product. The forwarding function then collects the logs and carries them to 

roadside. In some CTL operations, trees may be processed in front of the harvester, 

creating a mat of slash for the machines to travel on. The slash mat, coupled with forwarding, significantly reduces soil disturbance and compaction with CTL. Harvesters 

also minimize soil impacts by using a boom-mounted attachment to cut and process 

the trees. In small-diameter treatments, special harvester heads may be needed to effectively handle material.

Material brought to roadside may be separated into product classes in a process 

called merchandizing. Various log categories can be bucked into specified lengths; pulpwood logs may be debarked and chipped; and fuelwood and residues may be processed 

through a grinder. Non-merchantable residues can be disposed of at roadside by piling 

and open burning or with an air curtain incinerator. Roadside merchandizing increases 

the area of landings and heavy traffic. The more product options involved, the larger the 

area required for loading, processing, stacking, and transporting. Processing operations 

also create additional disposal problems—sawdust, bark, butt cuts, and other miscellaneous forms of biomass. Depending on site constraints and the amount of this material, 

it may be spread on-site or collected for trucking to off-site disposal.

Roadside processing operations can be limited by available area, road access, or 

the total volume brought to individual landings. If this occurs, trees and biomass can 

be directly loaded onto a variety of truck types and hauled to a concentration point 

or woodyard for processing. This “two-stage” hauling can improve operational efficiency by increasing volume and minimizing setup times. Woodyards also reduce 

in-woods impacts associated with erosion and soil disturbance. If the processed volume 

is high enough, measures such as gravel surfacing and stormwater management may be 

warranted.

The final function in removal treatments for fuel management is transportation. 

Forest roads are recognized as a primary contributor to the water quality impacts associated with forest management. Some type of road access is necessary for all of the 

operations discussed in this chapter. In-situ treatments are possible with a minimal 

amount of roading and lower standard roads. Removal treatments impose additional 

constraints on road spacing and standard. Road spacing affects, or is affected by, the 

type of extraction system. Skidding requires closer roads, while helicopters can operate 

at longer distances. The type of product and processing operation determines requirements for road standard. Chipping and grinding produce low-density products that 

necessitate large transport containers. Right corners or steep grades may exclude this 

kind of transportation system and thus limit treatment options. The important point to 

keep in mind is that the road system is part of the forest operation. Transport and access 

have to match the type of in-woods operation and the impacts of the total system must 

be considered.

Conclusions

There are many options for forest fuel treatment. Specifications of the prescription, 

particularly slope requirements and treated material size, may easily exclude some 

operations from consideration. However, there will generally be a range of feasible 

alternatives for the resource manager to review. As a project develops, a manager must 

know:

1. all feasible alternatives that are under consideration (are any options missing),

2. the performance attributes of each option,

3. the tradeoffs among alternatives, and

4. the treatment cost associated with each option.

In general, cost considerations dictate treating fuel as close to the stump as possible. Removal must be justified by fire risk considerations or product values. Forest 

operations for fuel treatment must satisfy the often conflicting demands of ecological 
76 USDA Forest Service RMRS-GTR-231. 2010.

compatibility and economic viability. Minimal impact can be achieved but nearly always 

at higher cost. Project managers need to balance anticipated impacts of the operation 

against estimated impacts of the “no treatment” alternative as they select appropriate 

tools for fuel treatment.

References

Cleaves, D.; Martinez, J.; Haines, T. 2000. Influences on prescribed burning activity and costs in 

the National Forest System. SRS-GTR-37. Asheville, NC. USDA Forest Service. Southern 

Research Station. 34 p.

Farmer, M.E.; Harper, K.T.; Davis, J.N. 1999. The influence of anchor-chaining on watershed 

health in a juniper-pinyon woodland in central Utah. In: Proceedings, ecology and management 

of pinyon-juniper communities within the Interior West. Proceedings RMRS-P-9. Ogden, UT. 

USDA Forest Service. Rocky Mountain Research Station: 299-301.

Graham, Russell T.; McCaffery, Sarah; Jain, Theresa B. [Tech Eds.]. 2004. Science basis for 

changing forest structure to modify wildfire behavior and severity. RMRS-GTR-120. Fort 

Collins, CO. USDA Forest Service. Rocky Mountain Research Station. 43 p.

International Organization for Standardization. 1999. Machinery for forestry—mobile and selfpropelled machinery—terms, definitions and classification. International Standard 6814. 

Geneva International Organization for Standardization. 7 p.

Johnson, Roy E. 1993. Shred, don’t burn—an alternative for treating slash on steep terrain. Fire 

Management Notes. 53-54(4):14-16.

Stokes, Bryce J.; Ashmore, Colin; Rawlins, Cynthia; Sirois, Don. 1989. Glossary of terms used in 

timber harvesting and forest engineering. Gen. Tech. Rep. SO-73. New Orleans, LA. USDA 

Forest Service. Southern Forest Experiment Station. 33 p.

Windell, Keith; Bradshaw, Sunni. 2000. Understory biomass reduction methods and equipment 

catalog. Tech. Rep. 0051-2826-MTDC. Missoula, MT. USDA Forest Service. Missoula 

Technology Development Center. 156 p.

Terminology

As described in ISO 6814 (ISO 1999), forest machines are defined primarily by the 

function performed (for example, skidder), then by additional adjectives defining mode 

of operation (e.g., grapple skidder) and mobility method (that is a tracked grapple skidder). Some of the following terms are from Stokes and others (1989).

Air curtain—a machine that uses forced air to improve combustion of wood in a fire pit or fire 

box

Bone dry ton—a quantity of wood or biomass weighing 2,000 lbs at zero percent moisture 

content (also called ovendry ton). This is the typical basis for defining forest fuel loading.

Brush rake—a blade for a skidder or crawler tractor with teeth extending down from the bottom 

edge

Cable system—an arrangement of winches, rigging, and wire rope used to pull trees or parts of 

trees from the stand

Chaining—the process of knocking over brush and small trees by dragging a length of heavy 

chain between two tractors or using a tractor and a heavy weight

Chipping—the process of reducing trees into uniformly dimensioned pieces by slicing

Chopping—the process of knocking down and rolling over brush and small trees with a heavy 

towed drum that has blades mounted across the face of the drum

Clambunk skidder—a machine that drags trees or parts of trees from the woods to a landing by 

grasping the load in a large inverted grapple (fig. 6) on the back of the machine (a specialized 

form of a grapple skidder)

Chapter 4. Tools for Fuel Management
USDA Forest Service RMRS-GTR-231. 2010. 77

Bob Rummer Cumulative Watershed Effects of Fuel Management in the Western United States

Clean chips—chips with very low bark content, generally produced by chipping debarked logs, 

that are marketable for pulp production or high-quality pellet fuel

Cut-to-length—a harvesting system that fells trees, processes in the woods into product lengths, 

and uses a forwarder rather than a skidder to move wood to roadside

Dirty chips—chips produced by chipping whole trees (also called whole-tree chips)

Dozer piling—the process of pushing residues or felled stems into a pile with a crawler tractor 

that may be equipped with a straight blade, brush blade or a brush rake

Feller-buncher—a machine that fells trees and accumulates the felled stems into a pile using 

either a shear head or a sawhead attachment

Forwarder—a machine that carries trees or parts of trees from the woods to a landing

Grapple piling—the process of placing residues or felled stems into a pile with a knuckleboom 

loader or hydraulic excavator

Green ton—a quantity of wood or biomass weighing 2,000 lbs at field moisture content

Grinder—a machine that coarsely reduces wood or biomass through a shredding action

Grubbing—the process of pushing or pulling to extract most of a plant’s root system from the 

ground

Harvester—a forest machine that fells, delimbs, and bucks trees

Harwarder—a machine that combines the functions of a harvester and forwarder

Hog fuel—coarsely reduced wood material that is intended for direct combustion use

Horizontal grinder—a grinder with a horizontal infeed table

Hotsaw—a high-speed continuous rotation sawhead that is attached to feller-bunchers

Knuckleboom log loader—a swing machine with a hydraulically operated boom and a log 

grapple attachment to lift and position trees or parts of trees (fig. 7)

Lopping—felling stems to leave them laying on the ground

Mastication—the process of reducing standing trees and brush by shredding or grinding

Merchandizing—the process of separating trees or parts of trees into specified product categories 

by sizing and sorting

Mobile chipper—a towed machine that reduces trees or parts of trees by chipping

Processor—a machine that takes a felled tree and delimbs and bucks it

Raking—the process of pushing slash or residues into piles, generally windrows, with a brush 

rake or a towed rake implement

Figure 6. Clambunk 

skidder.
78 USDA Forest Service RMRS-GTR-231. 2010.

Figure 9. Tub grinder (Source: http://www.collectiblereviews.net/).

Self-propelled chipper—a tracked chipping machine that can move from place to place

Skidder—a machine that drags trees or parts of trees from the woods to a landing, using either 

cables or a grapple to grasp the load

Strokeboom delimber—a machine that processes trees into delimbed lengths using delimbing 

knives and a sliding boom (fig. 8)

Tub grinder—a grinder with a circular rotating top-loaded infeed tub (fig. 9)

Figure 7. Knuckleboom loader (Source: http://

www.collectiblereviews.net/).

Figure 8. Strokeboom delimber.

Chapter 4. Tools for Fuel Management
USDA Forest Service RMRS-GTR-231. 2010. 79

Chapter 5.

Fuel Management and Erosion

Pete R. Robichaud, Rocky Mountain Research Station, USDA Forest Service, Moscow, ID

Lee H. MacDonald, Watershed Science Program, Colorado State University, Fort Collins, CO

Randy B. Foltz, Rocky Mountain Research Station, USDA Forest Service, Moscow, ID

Introduction

As the severity and extent of wildfires increase, efforts to reduce forest densities on 

public lands by thinning and prescribed burning also are increasing. The intentional suppression of fires in the western United States, beginning in the early 1900s, has altered 

the extent, frequency, and severity of wildfires (Agee 1993; Baker 1993). Reductions 

in timber harvest and in grazing, when combined with the suppression of wildfires, 

have resulted in higher fuel loadings, which increase the risk of high severity wildfires 

(Norris 1990). Changes in the fire regime may also cause vegetation changes, such as 

increases in tree stand density, spread of noxious weeds, and tree invasion into grasslands (Arno and Gruell 1986). Any increase in high severity wildfires is of considerable 

concern because of the potential damage to life and property and the adverse effects on 

water quality, fish habitat, and other aquatic resources (Keane and others 2002). The 

goal of most fuel management efforts is to reduce the potential adverse effects due to 

increased frequency of large, high severity wildfires. Although forest managers attempt 

to minimize impacts of fuel management activities, the removal of vegetation and the 

alteration of soil properties due to logging, road building, and prescribed fire may affect 

site conditions, forest runoff, and water quality (Lindeburgh 1990; Lousier 1990; Rice 

and Datzman 1981; Tiedemann and others 1979).

Undisturbed forests are an important source of the clean water that is necessary for 

ecosystem health as well as urban and agricultural uses. Forest vegetation and litter 

promote high infiltration rates and low levels of overland flow and protect the soil from 

rainsplash and erosive forces due to overland flow (Baker 1990; Robichaud 2000). This 

results in high quality runoff, low erosion rates, and low sediment yields (Binkley and 

Brown 1993; Buckhouse and Gaither 1982; MacDonald and Stednick 2003). Reported 

sediment yields from undisturbed forests in the western United States are typically 

around 0.003 t ac-1 (0.007 Mg ha-1) (Mg = 106

 grams or 1 metric tonne), but values 

up to 11 t ac-1 (25 Mg ha-1) have been measured (Stednick 2000). Sediment yields are 

dependent on several factors such as climate, topography, soil type, vegetation, historic 

land use, and the dominant erosion processes (Stednick 2000). By altering infiltration 

rates, evapotranspiration rates, and disturbing the soil, forest management activities—

including road construction, timber harvesting, site preparation, and fuel reduction—

can greatly increase overland flow rates and sediment yields.

This chapter reviews the effects of roads, thinning operations, and prescribed fire on 

runoff and erosion, and discusses the current understanding of the cumulative effects of 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
80 USDA Forest Service RMRS-GTR-231. 2010.

these activities on water yield, stream flow, and sediment production at the watershed 

scale. Much of the relevant research has been done at the plot, or occasionally, the hillslope scale; however, simply “scaling up” or summing the measured small-scale effects 

will not necessarily provide an accurate estimation of cumulative watershed effects. In 

addition, relatively few studies have specifically measured the effects of fuel treatments. 

Thus, this review includes the results from selective timber harvest studies and low severity wildfires, as these studies provide the data needed to estimate the likely effects of 

different fuel treatment activities. The effects of roads, forest thinning, and prescribed 

fire on runoff and erosion in the western United States are discussed in separate sections, even though many fuel management programs will require more than one of these 

activities. The final section discusses the cumulative effects of these fuel management 

activities, as well as the potential cumulative effects at the watershed scale.

Effects of Forest Roads for Fuel Management

Roads are ubiquitous in the forest environment. Forest roads are needed for economical removal of forest products, resource management activities, recreation activities, 

and public access. From a fuel management perspective, forest roads are needed to conduct prescribed burning, thinning, and timber harvest operations. The majority of forest 

roads are unpaved. These compacted road surfaces typically have very low infiltration 

rates and, as a result, generate large amounts of surface runoff (Luce and Cundy 1992; 

Reid and Dunne 1984; Vincent 1979). Road surfaces are subjected to rainsplash, and 

the combination of rainsplash with large amounts of surface runoff results in surface 

erosion rates that are several orders of magnitude higher than the adjacent undisturbed 

forest (for example, MacDonald and others 2004; Megahan 1978). Research has consistently shown that roads have the greatest effect on erosion of all practices associated 

with forest management (Megahan and King 2004). Although other forest management activities usually occur on a larger proportion of the landscape, the erosion rates 

on roads are the dominant source of sediment in most managed forests (Brown and 

MacDonald 2005).

Forest road effects have been summarized in Forest Roads: A Synthesis of Scientific 

Information (Gucinski and others 2001) and Roads Analysis: Informing Decisions About 

Managing the National Forest Transportation System (Bisson and others 1999). The 

former compiles current knowledge about the direct physical and ecological effects, 

indirect and landscape-scale effects, and direct and indirect socio-economic effects of 

forest roads. Roads Analysis is a six-step planning tool designed to evaluate, mostly in 

qualitative terms, the ecological, social, and economic effects of existing and future forest roads. Thus, only relevant studies addressing runoff and sediment yield from roads 

used for fuel management are presented.

Effects of Forest Roads on Runoff and Erosion

Effects of roads as structures

Infiltration rates in undisturbed forests are typically at least 1.5 to 3 in h-1 (40 to 

80 mm h-1) (Robichaud 2000); therefore, few rainstorms or snowmelt events initiate 

infiltration-excess (Horton) overland flow. In comparison, road components (cut slope, 

ditch, running surface, and fill slope) have infiltration rates from 0.004 to 0.4 in h-1 (0.1 

to 10 mm h-1), which frequently results in overland flow.

The flow paths of overland flow depend on road geometry. On insloped roads, water 

from the cut slope flows to the ditch and reaches the forest floor via a culvert (fig. 1A), 

and runoff from the fill slope flows onto the forest floor. On outsloped roads, runoff from 

the cut slope and running surface flows across the road and fill slope to the adjacent forest floor (fig. 1B). The benefits of insloped roads include: 

1. the ability to control and direct the concentrated flow; 

Chapter 5. Fuel Management and Erosion
USDA Forest Service RMRS-GTR-231. 2010. 81

P.R. Robichaud, L.H. MacDonald, R.B. Foltz Cumulative Watershed Effects of Fuel Management in the Western United States

2. the absence of concentrated flow on the structurally weaker fill slope; and 

3. lower risk that a vehicle will slide off the road in wet conditions. 

The benefits of outsloped roads include: 

1. less concentrated flow because surface runoff immediately drains off the road prism; 

2. less undercutting of the hillslope because flow is not concentrated parallel to the 

hillslope; 

3. fewer culverts are used, reducing culvert maintenance and road damage due to 

culvert failure; and 

4. reduced delivery of concentrated flow. 

Proper road maintenance is needed to attain the benefits of both insloped and outsloped 

roads. In particular, if wheel ruts form on the running surface or grading results in a 

small berm at the edge of the road surface, runoff will be concentrated on the running 

surface (fig. 1C). On insloped roads, concentrated road surface runoff may result in 

bypassed relief culverts, while on outsloped roads, road runoff will drain off the road 

prism as concentrated flow rather than dispersed sheet flow (Foltz 2003).

Effects of road use

Runoff can detach and transport the fine material available on unpaved road surfaces. Without vehicle traffic, the sediment concentration in the road runoff decreases 

over time. However, vehicle traffic, especially heavy trucks, can crush road surface 

aggregate material and this generates more fine particles that are available for transport 

by runoff. In addition, the pressure of vehicular tires on saturated road aggregate can 

force fine particles from below the surface to move to the surface (Bilby and others 

1989; Truebe and Evans 1994). In western Oregon, 20 percent of the material finer than 

0.003 in (0.075 mm) diameter was eroded over 3 months from a structurally weak road 

aggregate that was subjected to 26 in (660 mm) of rainfall and 884 logging truck trips 

(Foltz and Truebe 1995). The authors concluded that truck traffic generated 11 tons of 

fines per acre of road surface (24 Mg ha-1).

Road erosion rates generally increase with increased traffic, and heavy vehicles 

tend to cause more erosion than light vehicles (Megahan 1974; Reid and Dunne 1984). 

Higher use also is associated with more frequent maintenance operations, and grading 

Figure 1. Typical forest road prism structure. 

(A) insloped road with ditch; (B) outsloped 

road; and (C) road with wheel ruts.
82 USDA Forest Service RMRS-GTR-231. 2010.

increases the amount of available sediment and road erosion rates (Luce and Black 

1999). Bilby and others (1989) measured sediment production from two forest roads in 

southwestern Washington—one mainline road with high traffic and one secondary road 

with little traffic. Routine maintenance was performed on the mainline road once or 

twice per week while maintenance was done on the secondary road every 7 to 8 weeks. 

Sediment production over the 23-week study period was 2.5 times greater for the mainline road (46 t mi-1, 26 Mg km-1) than for the secondary road (18 t mi-1, 10 Mg km-1).

Many techniques used to estimate road sediment production assume factors that influence it (for example, rainfall, traffic, roadway material, etc.) are additive. For example, 

in the Washington Forest Practices (1995) analysis method, sediment production estimates are independently modified by factors for traffic and surface material. However, 

a recent study in western Oregon found little difference in sediment production between 

road plots that were subjected to traffic and those that were recently graded but had no 

traffic (Luce and Black 2001). They concluded that applying adjustment factors independently overestimated the effect of traffic on new roads or recently maintained roads.

Mitigation of road use effects

The impacts of traffic on sediment production can be mitigated through the use of 

Best Management Practices (BMP) such as slash filter windrows, rocking the road surface, and ditch armouring (Burroughs and King 1989; Megahan and others 1992). On 

the Eldorado National Forest, rocking reduced road sediment production by approximately one order of magnitude (MacDonald and others 2004). A comparison of 20 road 

surface aggregates showed that sediment production was directly proportional to the 

amount of aggregate finer than 0.24 in (0.60 mm) (Foltz and Truebe 2003). However, 

some fines are needed to prevent the aggregate from rolling under vehicle tires and 

being ‘kicked’ off the road by traffic. More recent BMPs include practices such as reducing truck tire inflation pressures, which reduces the contact pressure on the road 

surface and traffic-induced sediment production. For example, Foltz and Elliot (1996) 

found that reducing tire pressure from 90 psi (620 kPa) (highway pressure) to 70 psi 

(480 kPa) reduced sediment production by 45 percent, and a further reduction to 50 psi 

(350 kPa) reduced sediment production by 80 percent.

Use of low-use, brushed-in roads for fuel management activities

On many miles of low-use forest roads, vegetation has been allowed to grow on the 

running surface to reduce road-generated sediment. Although no formal assessment has 

been done, observations of these “brushed-in” roads indicate that sediment production 

rates are a tenth of the rates for bare roads with traffic. Forest access for fuel management activities will likely require that these brushed-in roads be reopened by scraping 

the vegetation off the running surface and, to some degree, the cut and fill slopes. In 

many cases, the increased road availability and use for fuel management activities will 

also attract additional recreational traffic, including off-highway vehicles (OHV). While 

OHVs, particularly all-terrain vehicles (ATVs), are lighter than trucks or automobiles, 

they loosen and move road surface material laterally making it available for subsequent 

transport (Iverson 1980).

Road Obliteration Effects on Runoff and Erosion

The type and frequency of fuel management activities must be factored into forest 

transportation plans, as this may affect both road construction and road removal. The removal of forest roads from service, or “decommissioning,” is usually accomplished by 

blocking the road entrance and restoring the road prism to a more natural state (USDA 

Forest Service 2000). Road obliteration is the most complete form of decommissioning, 

and this involves ripping the road surface, removing culverts, re-establishing stream 

channels, reshaping the roadbed to match the hillside contour, and planting vegetation.

Like road construction, road obliteration typically causes a spike in sediment production that decreases rapidly after the activity ends. Brown (2002) measured the sediment 

Chapter 5. Fuel Management and Erosion
USDA Forest Service RMRS-GTR-231. 2010. 83

generated during road obliteration at five stream crossings with wooden culverts in 

central Idaho. Peak suspended sediment concentrations ranged from 2.9 to 68,400 mg 

L-1, depending on the number of straw bales placed in the stream and the flow diversion channel. Foltz and Yanosek (2005) reported sediment yields of 4.4 to 375 lb (2 

to 170 kg) from the removal of each of three corrugated metal pipe culverts in central 

Idaho. The removal of these culverts did cause the instantaneous turbidity levels to 

exceed the 50 NTU standard for aquatic habitat (IDEQ 1994) immediately below the 

culverts, but this standard was not violated 0.5 miles (0.7 km) downstream. The 10-day 

criteria of 25 NTU (IDEQ 1994) was not exceeded at any of the three crossings, as the 

peaks in turbidity caused by mechanical activity in the stream typically decreased by an 

order of magnitude within 2 hours.

Forest Road Effects at the Watershed Scale

The watershed-scale effects of forest roads are much more difficult to detect than 

the effects at the site or road segment scale for several reasons. First, forest roads rarely 

exist without some accompanying timber harvest activities. In some watershed studies, 

the road network was installed 1 or more years prior to logging to identify the effects 

of the roads on runoff, sediment yields, or water quality (for example, Lewis 1998; 

Troendle and others 2001). However, only 1 to 3 years of data were collected before 

timber harvest began, and this short time period made it difficult to detect a distinct 

impact for small- to moderate-sized rain events (Bunte and MacDonald 1999; Loftis 

and others 2001).

Three studies, conducted in snowmelt-dominated climates where the roaded area was 

only 2 to 4 percent of the watershed area, were able to isolate forest roads and measure 

the impact on watershed runoff rates. Two paired-catchment studies in Colorado have 

shown no detectable change in runoff due to just the roads (MacDonald and Stednick 

2003). Similarly, in the third study, the road system did not alter annual water yield or 

peak stream flows from a 4,035-ac (1,633-ha) watershed in central Idaho (King 1994).

A second issue is the connectivity of roads to the stream network. Reported road erosion rates for the western United States vary from negligible amounts to 1,400 t mi-2 yr-1

(500 Mg km-2 yr-1) (table 1). However, road erosion rates measured at the plot or roadsegment scale cannot be directly extrapolated to the watershed scale (in other words, 

tens to thousands of acres [hectares]) because not all of the runoff and sediment may 

be delivered into and through the stream network (MacDonald 2000). For roads immediately adjacent to a stream, much of the road-generated sediment is delivered directly 

to streams. However, when a sufficient forest buffer is located between the road and 

the stream, much of the sediment may be deposited on the forest floor (Megahan and 

Ketcheson 1996). Recent multi-agency management agreements (PACFISH to protect 

anadromous fish and INFISH to protect inland native fish) require a 300-ft (90-m) forest 

buffer between roads and fish-bearing streams. This buffer width reflects a “consensus” 

opinion among scientists and managers, and it is designed to minimize the delivery of 

runoff and sediment to the stream network.

In addition to road location, road-stream connectivity can be increased because the 

concentrated runoff from roads can increase the drainage density (Croke and Mockler 

2001; Montgomery 1994; Wemple and others 1996). Wemple (1994) reported that 

nearly 60 percent of the road network was hydrologically connected to the stream network in two adjacent 5th order basins in western Oregon (mean precipitation is 89 in 

or 2,260 mm per year). On the Olympic peninsula of Washington, the average annual 

precipitation is 153 in (3,890 mm), and 75 percent of the roads were reported to be connected to the stream network (Reid and Dunne 1984). Bilby and others (1989) found 

that 34 percent of the roads were connected to the streams in southwestern Washington 

(precipitation amounts not reported). In western Oregon, the road-stream connectivity 

was reported to be 23 to 47 percent in areas with a mean annual precipitation of 20 to 

100 in (500 to 2,540 mm) (Skaugset and Allen 1998). The study sites in the Wemple, 

Reid, and Bilby studies were roads that had been constructed between the 1950s and 

1970s, while the roads examined in the Skaugset study were constructed in the 1980s 

P.R. Robichaud, L.H. MacDonald, R.B. Foltz Cumulative Watershed Effects of Fuel Management in the Western United States
84 USDA Forest Service RMRS-GTR-231. 2010.

Table 1. Road erosion rates from selected studies in the western United States (after MacDonald and Stednick 2003 and Elliot and Foltz 2001).

Traffic, slope,	 Erosion rate	 Sediment yield

Reference State running surface reported* (lb ft-2-yr-1) (kg m-2-yr-1)

Road surfaces

Megahan and Kidd 1972 ID Variable use, slopes 51 t mi-2-yr-1 1.5 7.3

Megahan 1975 ID 20 Mg ha-2-yr-1 0.41 2.0

Wald 1975 WA Moderate traffic, 6.4% 44.2 t mi-2-yr-1 1.4 6.6

Low traffic, 3.0% 3.4 t mi-2-yr-1 0.1 0.5

Bunkhouse and Gaither 1982 OR 0-7 Mg ha-2-yr-1 0.0-1.4 0-7

Reid and Dunne 1984 WA Heavy traffic, 10% 500 Mg km-2-yr-1 20 100

Moderate, 10% 42 Mg km-2-yr-1 1.7 8.5

Light, 10% 3.8 Mg km-2-yr-1 0.16 0.77

Abandoned, 10% 0.51 Mg km-2-yr-1 0.020 0.1

Bilby 1985 WA Mostly high use, 1% 0.0052 Mg m-2-yr-1 1.1 5.2

Vincent 1979 ID Light use, 6.3-13.4% 9.3-31 t ac-yr-1 0.47-1.6 2.3-7.6

Foltz 1996 OR Heavy, 12%, good aggregate 18 Mg ha-1 **

Heavy, 12%, marginal aggregate 132 Mg ha-1 **

Luce and Black 1999 OR Aggregate 30-99 Mg ha-1 **

Luce and Black 2001 OR Aggregate and ditch maintenance 0.05-4.8 Mg ha-1 **

Cutslopes

Wilson 1963 OR 6- to 7-yr old cutslopes 153 Mg ha-2-yr-1 3.1 15

new cutslopes 370 Mg ha-2-yr-1 7.6 37

Dyrness 1970, 1975 OR 5-yr old cutslopes 0.5 cm yr-1 1.5 7.5

1-yr old cutslopes 0.7 cm yr-1 2.3 11

Megahan 1980 ID 45-yr old cutslopes, soil 0.01 m3 m-2-yr-1 3.1 15

45-yr old cutslopes, granite 0.011 m3 m-2-yr-1 3.5 17

Megahan and others 1983 ID 11 mm yr-1 3.3 16

Megahan and others 2001 ID Cover 0.1-89%; gradient 55-104% 0.1-250 Mg ha-2-yr-1 0.0020-5.1 0.01-25

Fillslope

Bethlahmy and Kidd 1966 ID Unvegetated fillslope 94 Mg ha-2 for 10 mo 2.3 11

Megahan 1978 ID 12-yr old fillslope 12 Mg km-2-yr-1 0.25 1.2

* Mg = 106 grams or 1 metric tonne

** Short measurement period precludes extrapolation to annual yield.

to 1990s when forest road design was more of an issue. In general, the connectivity of 

the road network to streams will be a function of the precipitation regime, road design, 

and road maintenance.

Effects of Forest Thinning for Fuel Management

Numerous studies have evaluated the effects of timber harvest on runoff, water 

quality, erosion, and sediment yields (Binkley and Brown 1993; Stednick 2000). Most 

studies have focused on commercial harvests using relatively severe treatments such as 

clearcuts, patch cuts, or heavy selective cuts, while few studies have focused on forest 

thinning operations. Fuel management treatments are more similar to thinning operations, such as selective single tree selection or group cuts, rather than patch or clearcuts. 

This means that the observations and conclusions presented here are based partly on 

inference and extrapolation from studies of more intensive forest harvest operations, 

and to the extent possible, on the limited data from thinning studies that more closely 

correspond to the amount of disturbance that might be expected from fuel reduction 

treatments.

Chapter 5. Fuel Management and Erosion
USDA Forest Service RMRS-GTR-231. 2010. 85

Effects of Forest Thinning on Runoff

Changes in annual water yields

The removal of forest cover decreases interception and transpiration, and in wetter areas, this generally increases annual water yields (Bosch and Hewlett 1982; MacDonald 

and Stednick 2003). The increases in annual water yield following forest harvest are 

usually assumed to be proportional to the amount of forest cover removed, but at least 

15 to 20 percent of the trees must be removed to produce a statistically detectable effect 

(MacDonald and Stednick 2003). In areas where the annual precipitation is less than 

18 to 20 in (450 to 500 mm), removal of the forest canopy is unlikely to significantly 

increase annual water yields (Bosch and Hewlett 1982). In drier areas, the decrease in 

interception and transpiration is generally offset by the increase in soil evaporation, and 

there is no net change in runoff as long as there is no change in the underlying runoff 

processes (for example, a shift from subsurface stormflow to overland flow due to soil 

compaction) (MacDonald and Stednick 2003). For example, removing 100 percent of 

the forest cover in a snow-dominated area with a mean annual precipitation of 21 in 

(530 mm) resulted in an initial water yield increase of 1.1 in yr-1 (28 mm yr-1) (Bates 

and Henry 1928), while a 24 percent reduction in forest cover in a snow-dominated 

area with a mean annual precipitation of 34 in (871 mm) caused an initial water yield 

increase of 3 in yr-1 (76 mm yr-1) (Troendle and others 2001). In wetter environments, 

the combination of clearcutting and roads may increase annual water yields by 20 in 

(500 mm) or more.

Extrapolating from these and other results suggest that relatively heavy thinning 

operations can increase annual water yields in wetter environments. No measurable 

increase in runoff can be expected from thinning operations that remove less than 15 

percent of the forest cover or in areas with less than 18 in (450 mm) of annual precipitation. Since evapotranspiration rapidly recovers with vegetative regrowth in partially 

thinned areas, any increase in runoff due to thinning operations is likely to persist for no 

more than 5 to 10 years.

Runoff timing and peakflows

The timing of the increase in runoff due to forest harvest is important because of 

the potential impact on water supplies, sediment transport capacity, bank erosion, and 

aquatic ecosystems. If forest harvest only increases low or moderate flows, one would 

expect little or no change in channel erosion or sediment yields. An increase in larger flows provides a mechanism for increasing annual sediment yields (Lewis 1998; 

Schumm 1971).

The timing of the increased runoff due to harvesting will vary with the hydrologic/

physiographic characteristics and climate regime. If the climate is dry in summer and 

rainy during the winter, the largest increase in runoff will occur in the fall to early 

winter. This is due to the increase in soil moisture in late summer after forest harvest 

and the resulting increase in runoff efficiency because less precipitation is needed for 

soil moisture recharge. Runoff rates also will increase throughout the winter due to the 

reduction in interception.

In snow-dominated environments, nearly all of the increase in runoff will occur in 

early spring. As in rain-dominated environments, forest harvest reduces summer evapotranspiration and increases the amount of soil moisture carryover. Less snowmelt is 

needed for soil moisture recharge, so more of the early season melt is converted into 

runoff. The reduction in forest canopy also increases the amount of solar radiation that 

reaches the surface of the snowpack and the transfer of advective heat, and these changes increase the rate of snowmelt and may slightly accelerate the timing of peak runoff 

(for example, MacDonald and Stednick 2003; Troendle and King 1985).

An analysis of the changes in flow duration curves due to forest harvest indicates that 

low flows generally experience the largest percentage change, while the higher flows 

experience the largest absolute change. In other words, most of the additional water 

P.R. Robichaud, L.H. MacDonald, R.B. Foltz Cumulative Watershed Effects of Fuel Management in the Western United States
86 USDA Forest Service RMRS-GTR-231. 2010.

comes during the higher flows (Austin 1999). In rain-dominated areas, the percent increase in high flows is generally much less than the percent increase in low flows. For 

example, Austin (1999) reported that in rain-dominated areas, the combination of roads 

and intensive forest harvest increased the larger daily flows by about 10 to15 percent. 

Studies in the cold snow zone in the Rocky Mountains indicate that 100 percent harvest will generally increase the size of the annual maximum flow by about 40 percent 

(MacDonald and Stednick 2003). If less than 100 percent of the vegetation is removed, 

the increase in the size of the annual maximum flow is roughly proportional to the percent of forest cover removed (MacDonald and Stednick 2003). For example, peak flows 

increased by 20 to 28 percent after removing 30 to 50 percent of the forest canopy in 

northern Arizona, while peak flows increased by 90 percent after removing 77 percent 

of the canopy and 170 percent in a clearcut watershed (Brown and others 1974). In areas 

dominated by snowmelt, there may be little change in low flows (Bates and Henry 1928; 

Troendle and King 1985).

Several studies indicate that the increase in runoff due to forest management can 

increase suspended sediment concentrations and annual sediment yields. Suspended 

sediment loads increased after harvesting 10 sub-watersheds in the North Fork of 

Casper Creek in northwestern California. This increase was attributed to the increase 

in channel shear stress and transport capacity as a result of the increase in runoff (total 

flow volume), as the harvest units, roads, and landings were restricted to upslope locations (Lewis 1998). On the Fraser Experimental Forest in Colorado, the harvest-induced 

increases in high flows can account for most of the observed increases in annual sediment yields (Troendle and Olsen 1993). These results suggest that flow increases due 

to forest harvest can increase in-channel erosion and can be the dominant cause of an 

increase in sediment production, particularly when the amount of ground disturbance is 

kept to a minimum.

Effects of Forest Thinning on Erosion

Types of timber management activities used for thinning

The effects of forest harvest activities on erosion and sediment yields depend on 

techniques used, site characteristics, storm event of concern, and skills of the equipment 

operators. In decreasing order of disturbed area, some common forest harvest practices 

are clear-cutting, seed tree and shelterwood harvests, single tree selection, and group 

selection. Light or moderate thinning operations typically cause much less ground disturbance than clear-cuts or shelterwood cuts. On the other hand, a relatively intense 

thinning operation may require access to more of a stand than a harvest using patch 

cuts or group selection even though a smaller volume of timber is being cut (Haupt 

and Kidd 1965). Erosion rates tend to be positively correlated with percent bare soil 

and the amount of surface disturbance, and these two factors generally are proportional 

to the number of trees being harvested (Haupt and Kidd 1965). In general, erosion 

rates are acceptably low when the proportion of bare soil is less than 30 to 40 percent 

(Benavides-Solorio and MacDonald 2005; Gary 1975; Swank and others 1989).

Like other forest management practices, thinning generally requires road access. The 

amount of roads needed for commercial thinning will vary with the spatial distribution 

of the tress being thinned and the yarding techniques used. Non-commercial thinning 

may require fewer roads than most other forest harvest activities because yarding is not 

necessary. When evaluating the effects of thinning relative to unmanaged forests, it is 

essential to consider the effects of the road network—including new road construction, 

changes to existing roads, and the increase in traffic—in addition to the effects of the 

thinning activities.

Effects of felling on erosion

Felling is the action of cutting down a tree by machine or hand. Mechanized fellers 

cut a tree down with a saw blade and then de-limb the tree. Some machines are designed 

Chapter 5. Fuel Management and Erosion
USDA Forest Service RMRS-GTR-231. 2010. 87

to collect the trees using a specialized attachment (feller-buncher). Mechanized felling 

is faster and less hazardous than hand-felling, but the trees need to be under a certain 

diameter and the area has to be machine accessible. Mechanized fellers can disturb 

and compact the soil, and the use of these machines is a potential source of erosion. 

However, because they do not drag the logs on the ground, they often generate less erosion than log skidders.

The effects of felling on erosion generally have not been studied independent of 

yarding. Hand felling can be accomplished by one person with a chainsaw, and the 

amount of soil disturbance from this activity generally is considered negligible. A comparison of clearcut and thinned plots to control plots showed that hand-felling without 

mechanized yarding caused minimal surface disturbance and no increase in erosion 

(McClurkin and others 1987).

Non-commercial thinning to reduce fuel loads is being done on an increasingly large 

scale using masticating machines. These machines are usually large, rubber-tired or 

tracked skidders with a mulching or wood grinding attachment such as a Hydro-Ax or 

a Bull-Hog. Some machines are designed to masticate standing trees, while others fell 

the trees before masticating the material. Like mechanized fellers, the movement of 

masticating machines can disturb or compact the soil and thereby increase the potential 

for erosion. The shredded wood that remains after these operations may increase the 

amount of ground cover and reduce the erosion potential. The effects of these treatments, including impacts on vegetation, have not been rigorously evaluated.

Effects of yarding on erosion

The amount of disturbed area and bare soil due to thinning and forest harvest will depend largely on the amount and type of yarding activities. Ground-based tractor-yarding 

generally necessitates an extensive network of skid trails and roads, while full suspension cable yarding will cause much less ground disturbance and generally requires a 

less dense road network. Tractor yarding generally produces the greatest amount of site 

disturbance, followed by jammer, high lead cable, skyline, and helicopter yarding (Rice 

and others 1972; Stednick 1987). This list is slightly misleading in that the amount of 

disturbance due to logging was not separated from the disturbance due to roads. In some 

situations, jammer logging (cut trees are cable yarded using a truck-mounted boom) can 

result in up to 29 percent more road area than tractor-logging (Rice and others 1972), and 

the higher road density can greatly increase the total erosion rate from the project area. 

In a northwestern California study, a categorical variable to represent the type of yarding 

helped to more accurately predict post-harvest erosion rates (Rice and Furbish 1981).

Although thinning a stand of trees to a desired density requires access to the entire 

stand, non-commercial thinning generally requires little or no yarding and can be one of 

the least disturbing forest management practices. Commercial thinning requires yarding 

methods appropriate for smaller trees, such as small skylines with light cables and short 

towers, small crawler tractors, rubber-tired skidders, horses, tractor-mounted winches, 

or specialty yarding machines (Small Woodlands Program of BC 2002). The amount of 

disturbance caused by yarding will depend on the site characteristics, timing of yarding, 

and the percent of the stand that is being thinned. In most cases, the amount of disturbance from commercial thinning will be similar to selective harvest techniques.

Review and integration of erosion rates from managed watersheds

Several recent studies have summarized erosion and sediment yields from managed 

and unmanaged forests. These include a summary of erosion and sediment production 

data from different site preparation and timber harvest activities in the United States 

(Stednick 2000) and suspended sediment data from areas subjected to forest harvest and 

road construction (Binkley and Brown 1993). These reviews indicate a general lack of 

data for non-commercial thinning operations (table 2) and a relatively rapid decline in 

surface erosion rates after timber harvest activities. For example, in central Idaho, 90 

percent of the erosion from skyline and jammer logging occurred within the first 2 years 

after harvest (Megahan 1975).

P.R. Robichaud, L.H. MacDonald, R.B. Foltz Cumulative Watershed Effects of Fuel Management in the Western United States
88 USDA Forest Service RMRS-GTR-231. 2010. Table 2. Changes in sediment and streamflow due to forest management activities. Data are restricted to studies in the western United States. Yarding Plot size Harvest Reference	 Location	 Type of logging	 method	 or area	 percent	 Sediment response	 Streamflow response Lewis 1998 South Casper Selective cut Tractor 424 ha 65% Suspended sediment increased NA Creek, CA for 1 yr after road building (335%) and in the 6 yrs following harvest there was a 212% increase in sediment load Lewis 1998 North Casper, CA Clearcut 80% cable ~30-473 ha 48% 89% increase in sediment NA yarded load after treatment Lopes and others 2001 Beaver Creek, AZ Ponderosa pine clearcut/ Bulldozer 184 ha 100% Where: Suspended Sediment 30% increase in annual windrowed and burned = k a (Streamflow Discharge) b+1, water yield the a and b coefficients were increased by 440 and 54% respectively Lopes and others 2001 Beaver Creek, AZ Ponderosa pine cut Bulldozer 546 ha 40% Where: Suspended Sediment 20% increase in annual into irregular strips = k a (Streamflow Discharge) b+1, water yield and 25% of the a and b coefficients were residual thinned increased by 97 and 44% respectively Lopes and others 2001 Beaver Creek, AZ Large pinon-junipers Bulldozer 131 ha 100% Where: Suspended Sediment No significant increase were pulled out with = k a (Streamflow Discharge) b+1, in annual water yield bulldozer the a and b coefficients were increased by 44 and 21% respectively Lopes and others 2001 Beaver Creek, AZ Herbicide on pinon- None 147 ha 100% Where: Suspended Sediment 160% increase in annual juniper = k a (Streamflow Discharge) b+1, water yield the a and b coefficients were increased by 58 and 27% respectively Heede 1987 S. Fork Thomas Patch cuts and group Crawler 0.01 - 0.06 ha NA Sediment delivery was Overland flow was 89% higher Creek, AZ selection (moderately Tractors 10.8 kg ha-1 yr-1 compared than 1.31 mm yr-1 control disturbed) to 8.05 in control Heede 1987 S. Fork Thomas Patch cuts and group Crawler 0.01 - 0.06 ha NA Sediment delivery was Overland flow 240% higher Creek, AZ selection (severely Tractors 31.8 kg ha-1 yr-1 compared to than 1.31 mm yr-1 control disturbed) 8.05 in control Williams and Ag. Research Cut to stand density of Rubber tired 1 by 5 m plot NA No sediment No runoff (up to 39 mm hr-1 Buckhouse 1993 Center, OR 1 stem per 69 m2 skidders rain intensity) Williams and Ag. Research Cut to stand density of Rubber tired 1 by 5 m plot NA No sediment No runoff (up to 39 mm hr-1 Buckhouse 1993 Center, OR 1 stem per 132 m2 skidders rain intensity) Megahan 1975 Horse Creek, ID Clearcut Skyline 12 ac total 100% Sediment rate was NA 33 yd3 yr-1 mi-2 compared to 21 yd3 yr-1 mi-2 Megahan 1975 Horse Creek, ID Clearcut Jammer 10 ac total 100% Sediment rate was 33 yd3 yr-1 mi-2 NA compared to 21 yd3 yr-1 mi-2 Madrid unpublished Lincoln National Pre-commercial thinning None 10-1 m2 plots Low Dry simulation = 102% No significant change Forest, NM with slash piled intensity increase in sediment yield in runoff from 1.12 to 2.26 kg ha-1; Wet simulation = 200% increase from 0.43 to 1.28 kg ha-1 Madrid unpublished Lincoln National Pre-commercial thinning None 10-1 m2 plots Low Dry simulation = 59% increase from No significant change Forest, NM with slash scattered intensity 1.12 to 1.77 kg ha-1; Wet simulation = in runoff 123% increase from 0.427 to 0.951 kg ha-1 Brown and MacDonald Upper South Pre-commercial thinning None from 0.094 25% No sediment in control NA unpublished Platte, CO to 0.65 ha or thinned swales Chapter 5. Fuel Management and Erosion
USDA Forest Service RMRS-GTR-231. 2010. 89

An ongoing hillslope-scale study is comparing ground cover and erosion rates from 

intensively thinned areas to undisturbed areas in ponderosa pine forests in the Colorado 

Front Range. In the treated stands, the use of a Hydro-Ax redistributed existing litter and 

scattered wood chips over 21 percent of the surface area (Brown and MacDonald 2005; 

Brown and others 2005). The mean surface cover of wood increased from 3 to 6 percent, 

but the thinning did not significantly affect the proportion of litter, rock, or live vegetation cover. Percent bare soil increased from 9 to 15 percent, but this was only marginally 

significant (p = 0.08). The 48 plot-years of data from 2003 to 2005 show no evidence 

of surface runoff or hillslope erosion from either the thinned or the control plots, even 

though the steepest plots (>50 percent slope) were subjected to a 1.6 in (42 mm) storm 

with a maximum 30-minute intensity of 2.4 in h-1 (61 mm h-1) (Brown and MacDonald 

2005; Brown and others 2005).

In northern New Mexico, a series of rainfall simulations (6 in h-1 or 150 mm h-1 for 

1 hour on successive days) was done on control plots, lightly thinned plots with the 

slash piled, and lightly thinned plots where the slash was scattered (Madrid 2005). The 

results show that thinning had no effect on runoff or the amount of bare soil, but the 

mean sediment yields from the second (wet) simulation on the thinned plots was two to 

three times higher than the mean sediment yield of 1.8 t ac-1 (4 Mg ha-1) from the control 

plots (Madrid 2005).

The spatial pattern and location of the harvest activities relative to the stream network influences the amount of sediment that is delivered from severely disturbed areas. 

Forest management activities often generate a mosaic of severely disturbed areas 

(clearcuts, skid trails, and landings) and relatively undisturbed areas (streamside management zones). The former usually are considered sediment source areas and the latter 

usually serve as sediment sinks. If the runoff and sediment yields from the source areas 

are less than the absorption capacity of the downslope sediment sinks, it follows that 

there will be little or no change in runoff and sediment yields at the watershed scale. 

It is important to recognize that watershed-scale changes in sediment yields tend to be 

correlated with the amount of disturbance in a watershed, but a high level of disturbance 

does not always mean that there will be a detectable change in sediment yields at the 

watershed scale (Haupt and Kidd 1965).

Effects of Prescribed Burning

Prescribed burning is the controlled use of fire to achieve specific forest management 

objectives (Walstad and others 1990). Prescribed fires are often used after timber harvest operations to dispose of flammable residues and reduce the wildfire risk. Prescribed 

fires are also used to facilitate tree planting by removing logging slash, debris, and 

undesirable vegetation; reduce the risk of destructive insect infestation; create suitable 

environmental conditions for the establishment and growth of desired tree species; manipulate secondary plant succession to favor the development of preferred species; and 

increase production of understory vegetation for wildlife (Walstad and Seidel 1990). 

Prescribed burning is increasingly being used to reduce fuel loads in forests.

Fire Effects on Forest Floor

The major factor that determines the effects of burning on runoff and erosion is the 

amount of disturbance to the surface organic material (commonly referred to as duff or 

forest floor) that protects the underlying mineral soil. The effects of burning can vary 

from merely removing some of the litter (low burn severity) to totally consuming the 

duff layer and organic matter in the upper soil layers (high burn severity). If the duff is 

completely consumed by a fire, the mineral soil is exposed to rain splash and overland 

flow (Soto and others 1994; Wells and others 1979). Any loss of organic matter in the 

uppermost layers of the mineral soil will alter the structure of the surface soil, and the 

resultant disaggregation of the soil particles can greatly increase its susceptibility to 

P.R. Robichaud, L.H. MacDonald, R.B. Foltz Cumulative Watershed Effects of Fuel Management in the Western United States
90 USDA Forest Service RMRS-GTR-231. 2010.

erosion (Brown and others 1985; DeBano and others 1998; Robichaud and Waldrop 

1994; Ryan 2002; Wells and others 1979). In some vegetation types, a moderate or 

high severity fire can change or induce water repellent soil conditions at or near the soil 

surface (DeBano 1981; Huffman and others 2001; Robichaud and Hungerford 2000). 

The fire-induced soil water repellency and disaggregation of soil particles will reduce 

the infiltration rate of the mineral soil, and the loss of organic material reduces the water 

storage capacity above and in the mineral soil. These changes result in increased runoff, 

especially from short duration, high intensity rain events (Baker 1990). Prescribed fires 

are generally designed to leave some residual duff to protect the mineral soil and maintain high infiltration rates, which minimizes potential erosion (table 3).

The amount of duff consumption during prescribed fires is controlled primarily by 

the thickness and water content of the duff prior to burning (Brown and others 1985; 

Frandsen 1997; McNabb and Swanson 1990; Reinhardt and others 1991; Wells and others 1979). For example, the First Order Fire Effects Model (FOFEM) uses 22 different 

algorithms to predict percent duff consumption, depth of duff consumed, and percent 

of mineral soil exposed, and all but one use pre-burn duff thickness and duff moisture 

content as input variables (FOFEM, version 5.0). Fire managers use models such as 

FOFEM to help design prescribed burns that will consume much of the fuel load while 

leaving a protective duff layer over the mineral soil.

Fire Effects on Runoff and Erosion

Prescribed fire

Prescribed fires create a highly variable mosaic of burn severity, duff consumption, 

and unburned area (Robichaud 2000; Robichaud and Miller 1999). This spatial variability in postfire surface conditions results in spatially varying runoff and erosion rates. 

Post-prescribed fire variations in runoff and erosion have been assessed by conducting 

rainfall simulation on small plots. For example, high infiltrations rates and low sediment yields were reported after a spring season, low burn severity prescribed fire in 

northern Idaho (Robichaud and others 1994) (table 4). In another study, two low burn 

severity prescribed fires were conducted after timber harvest—one in Idaho (Hermada) 

and one in Montana (Slate Point), and postfire assessments indicated that only 5 percent 

of the Hermada site and 15 percent of the Slate Point site had burned at high severity 

(Robichaud 1996; Robichaud 2000). As expected, the initial infiltration rates in the high 

burn severity were lower than in the unburned and undisturbed areas. More importantly, 

Table 3. Published first-year sediment losses after prescribed fires (after Robichaud and others 2000).

Dominant plant, Sediment loss

location Treatment (t ac-1) (Mg ha-1) Reference

Ponderosa pine, CA Control <0.0005 <0.001 Biswell and Schultz 1965 

Prescribed fire <0.0005 <0.001

Chaparral, CA Control, steep slope 0.0009 0.002 DeBano and Conrad 1976 

Prescribed fire, steep slope 3 7

Control, gentle slope 0 0

Prescribed fire, gentle slope 1 3

Chaparral, AZ Control 0 0 Pase and Lindenmuth 1971 

Prescribed fire 2 4

Larch/Douglas-fir, MT Control <0.0004 <0.001 DeByle and Packer 1972

Slash burn 0.07 0.2

Ponderosa pine, CO Low severity 0.16 0.37 Benavides-Solorio 2003 

Moderate severity 0.058 0.13

High severity 0.36 0.81

Ponderosa pine, CO Low severity 0.30 0.67 Benavides-Solorio 2003

Moderate severity 0.49 1.1

Chapter 5. Fuel Management and Erosion
USDA Forest Service RMRS-GTR-231. 2010. 91

the initial infiltration rates in the areas burned at low severity (which comprised the largest proportion of the prescribed burn area) fell within the upper end of the range from 

the areas left unburned and undisturbed areas (Robichaud 2000). The total sediment 

yields from the three 30-minute rainfall simulations on the plots burned at low severity 

were an order of magnitude smaller than the values from the plots burned at high severity (table 4) (Robichaud 1996). Similar differences in sediment yields were reported by 

Benavides-Solorio and MacDonald (2005).

Runoff and sediment yields were also measured from natural rainfall events at the 

catchment-scale (17 to 22 ac, 7 to 9 ha) after the same prescribed burns at both Slate Point 

and Hermada. At both sites, the runoff and sediment yields were generally low from the 

catchments subjected to both timber harvest and prescribed burning (table 5) (Covert 

and others 2005). The low runoff and sediment yields were most likely due to the generally low burn severity and the averaging of fire effects (Covert 2003; Robichaud 1996).

Earlier work also noted that erosion after prescribed fires occurred primarily in areas 

where the fires were locally severe or there was extensive disturbance due to forest 

harvesting (McNabb and Swanson 1990). A study of 200 permanent 11 ft2 (1-m2) plots 

in northern Idaho have a pre-harvest erosion of 0.04 t ac-1 (0.09 Mg ha-1). Prior to any 

activities, the litter coverage was 83 percent, and this decreased by just 8 percent 1 year 

after helicopter-logging and broadcast burning. One year after broadcast burning, the 

total erosion was 0.8 t ac-1 (1.9 Mg ha-1); 40 percent of this was attributed to the mechanical disturbance from logging and 32 percent to the broadcast burning (Clayton 1981).

Another study in northern Idaho measured erosion rates of 67.2 yd3 ac-1 yr-1 (127 m3 

ha-1 yr-1) from a clearcut area that was then burned by a high severity wildfire (Megahan 

and Molitor 1975). No erosion was measured from an uncut watershed that burned in 

the same wildfire. Erosion pin data suggested a net soil loss of 0.43 in (11 mm) on the 

clearcut and burned watershed as compared to a net gain of 0.20 in (5 mm) on the uncut 

watershed. Rill erosion was observed within 30 days after the fire on the clearcut watershed, while on the uncut watershed, there was some soil movement from rainsplash but 

there was no evidence of rilling (Megahan and Molitor 1975).

Wildfire

The effects of high severity wildfires on runoff and erosion are generally much more 

severe than the effects of prescribed fires. High severity fires are of particular concern 

Table 4. Sediment yields from rainfall simulation studies on low severity burned plots (after Benavides-Solorio and MacDonald 2001; Johansen 

and others 2001; Robichaud 2000).

Rainfall intensity

Slope	 [Rainfall duration] Sediment yield

Dominant plant	 [Time since burn]	 (in h-1) (mm h-1)

type, location (%) [(min)]	 [(min)]	 (t ac-1 in-1) (kg ha-1 mm-1) Reference

Sagebrush-juniper, CA — 2.6 65 0.034-0.083 3.0-7.3 Simanton and others 1986 

[1 year] [30-60] [30-60]

Mixed conifer, ID 13-27 2.0 50 0.028-0.12 2.5-11.0 Robichaud and others 1994

[within days] [30] [30]

Pinon-juniper, NV 5-8 3.3 84 0.045-0.11 4.0-9.7 Roundy and others 1978 

coppice [1-2 months] [60] [60] 0.035-0.15 3.1-12.8

Pinon-juniper, NV [1 year] 0.090-0.29 7.9-26.0

interspace 0.13-0.36 11.9-32.0

Ponderosa pine, CO 21-22 3.1 80 0.056-0.092 4.9-8.1 Benavides-Solorio 

[1-2 months] [60] [60] and MacDonald 2001

Douglas-fir, MT 30-70 3.7 94 0.094 8.3 Robichaud 1996

[within days] [90] [90]

Douglas-fir, ID 40-75 3.7 94

[within days] [90] [90] 0.41 35

P.R. Robichaud, L.H. MacDonald, R.B. Foltz Cumulative Watershed Effects of Fuel Management in the Western United States
92 USDA Forest Service RMRS-GTR-231. 2010.

Table 5. Mean annual rainfall, runoff, and sediment yield for two catchments that were logged and broadcast burned at low burn 

severity. Hermada was burned 3 years after harvesting; Slate Point was burned 1 year after harvesting; and Round-Up was 

burned 2 years after harvesting (Covert 2003; Covert and others 2005; Robichaud 1996).

Catchment name	 --------------Hermada-------------	 ---------------Slate Point---------------	 ---------Round-Up--------

size (ac, ha) 22, 9 17, 7 5, 2

Year since Rx burn 1 yr 2 yr 3 yr 4 yr 1 yr 2 yr 3 yr 4 yr 1 yr 2 yr 3 yr

ground cover (%) 95 98 99 99 98 99 100 100 92 96 98

Annual rainfall

(in) 34.3 26.5 47.1 18.7 22.4 20.4 28.1 9.53 11.8 21.1 10.4

(mm) 870 673 1196 474 568 519 714 242 300 537 265

Annual runoff

(in) 3.1 3.5 13 7.1 1.7 2.1 3.8 1.3 2.0 0.51 1.3

(mm) 78 89 320 180 43 53 97 33 51 13 32

Annual sediment yield

(t ac-1) 0.00 0.00 0.00 0.00 0.0015 0.016 0.0052 0.00 0.045 0.045 0.045

(t ha-1) 0.00 0.00 0.00 0.00 0.0033 0.036 0.012 0.00 0.10 0.10 0.10

because the loss of protective cover and fire-induced soil water repellency can induce 

severe flooding and erosion even after moderate rain events (DeBano and others 1998; 

Neary and others 2005). In severely burned areas, high intensity, short duration rain 

events have increased peakflows from 2 to 2,000 times (DeBano and others 1998; Neary 

and others 1999, 2005). Published sediment yields after high severity wildfires range 

from 0.004 to 49 t ac-1 yr-1 (0.01 to over 110 Mg ha-1 yr-1) in the first year after burning (Benavides-Solorio and MacDonald 2005; Moody and Martin 2001; Robichaud 

and others 2000). In most cases, the decline in soil water repellency and vegetative 

regrowth means that these large increases in runoff and erosion diminish quite rapidly. 

Most long-term studies show no detectable increase in erosion by about the fourth year 

after burning (Benavides-Solorio and MacDonald 2005; Robichaud and Brown 2000).

Watershed Effects of Fuel Management

It is much more difficult to quantify the effects of roads, timber harvest, and fuel 

treatments on stream flow and sedimentation at the watershed scale than at the plot scale 

because of the inherent complexity of the underlying processes and the variability over 

time. For example, Jones and Grant (1996) tried to determine the changes in stream flow 

caused by roads and timber harvesting on six watersheds in western Oregon that varied 

in size from 150 ac to 230 mi2 (60 ha to 600 km2). They concluded that: 

1. forest harvesting increased peak discharges by as much as 50 percent in small basins 

and 100 percent in the three large basins; 

2. increases in drainage efficiency were due to the connectivity of the road system to 

the stream channel network; and 

3. the entire population of peak discharges was shifted upward by clear-cutting and 

roads.

Using the same data set, Thomas and Megahan (1998) were unable to detect any effect of cutting on peak flows in one of the large basins and determined that the data were 

inconclusive for two large basins. They found that the timber management activities had 

altered stream flows for smaller events on the small watersheds, but there were no detectable differences for the larger events (2-year return interval or greater). The effects 

of roads and forest harvest decreased over time, but they were still detectable after 20 

years on the clear-cut watershed and for 10 years on the patch-cut and roaded watershed 

(Thomas and Megahan 1998).

Chapter 5. Fuel Management and Erosion
USDA Forest Service RMRS-GTR-231. 2010. 93

Beschta and others (2000) also analyzed the same data set as Jones and Grant (1996) 

and they concluded that the increases in peakflows after harvest operations (including road building, clearcutting, cable logging, and site preparation) depended on the 

peakflow magnitude. Peakflow increases averaged approximately 13 to 16 percent after 

treatment for events with a recurrence interval of 1 year, and by 6 to 9 percent for storms 

with a recurrence interval of 5 years.

These different interpretations of the same data set reflect the challenges of assessing 

and understanding the effects of forest management activities at the watershed scale. 

The differences in site conditions, climatic regime, and treatment intensity mean that 

different studies have found very different results, and a study can be found to support almost any point of view. For example, 11 watershed studies from sites in British 

Columbia to California can be cited to show that logging can increase, decrease, or have 

no effect on the size of peak flows (Harr 1979). Accurate predictions of the effects of 

fuel treatments are only possible if there is a simultaneous understanding of the underlying processes and how the different effects might be transmitted and aggregated at the 

watershed scale.

Conclusions

Fuel management in forested areas can involve a number of activities, including the 

construction, maintenance, and use of forest access roads; timber cutting and removal; 

non-commercial thinning or mastication; and prescribed fire. The following conclusions reflect our current understanding of the effects of fuel treatments at the plot and 

watershed scales:

1. Roads greatly increase runoff and erosion rates at the plot and road segment scale. 

The effect of these increases at the watershed scale depends on the connectivity of the 

road and stream networks, but several studies have indicated that roads have minimal 

effect on runoff at larger spatial scales. More studies have shown that unpaved forest 

roads are chronic sediment sources and that roads can significantly increase sediment 

yields on small to moderate-sized catchments. Road building, maintenance, and 

obliteration can generate significant short-term increases in runoff and sediment. 

The effects of forest roads on runoff and sediment yields can be greatly reduced by 

improved road placement, road designs that dissipate runoff and direct it away from 

streams, and the widespread use of erosion mitigation techniques.

2. Non-commercial thinning operations (without yarding) have small, short-lived 

impacts on runoff and sediment production, even when operations extend over large 

areas.

3. Commercial thinning and yarding has a greater potential to increase runoff, erosion, 

and sediment yields because of the more extensive removal of the forest canopy; 

greater ground disturbance due to skid trails, cable rows, and landings; greater 

ground disturbance due to more intensive harvest; need for extensive road access; 

and increase in heavy truck traffic. The potential increases in erosion and sediment 

yield can be minimized by reducing the area and amount of soil disturbance, 

establishing buffer strips along stream channels, and minimizing overland flow by 

restoring severely disturbed areas.

4. High severity wildfires increase runoff and erosion rates by two or more orders of 

magnitude, while low and moderate severity burns have much smaller effects on 

runoff and sediment yields. If areas are burned at low severity, the potential for 

increasing peak flows and erosion rates is relatively small. However, if prescribed 

fires are conducted under dry duff moisture conditions and larger areas are burned 

at high severity, there is a much greater risk for significantly increasing runoff and 

erosion rates. The natural regrowth on severely burned areas means that overland 

flow rates and sediment yields generally return to pre-burn levels in approximately 4 

years. Water yields may remain elevated for a longer period due to the time required 

for interception and transpiration rates to return to pre-burn levels.

P.R. Robichaud, L.H. MacDonald, R.B. Foltz Cumulative Watershed Effects of Fuel Management in the Western United States
94 USDA Forest Service RMRS-GTR-231. 2010.

5. Vegetative recovery after fuel treatments is generally very rapid, with erosion rates 

typically dropping to pre-fire levels within 1 to 2 years. Hydrologic recovery after 

fuel treatments also tends to be more rapid than after clearcutting or high burn 

severity fires because a smaller proportion of the forest canopy is being removed.

6. Fuel management treatments generally are needed every 10 to 20 years and the 

associated cumulative effects occur during each access and treatment cycle. Although 

hillslope erosion rates recover quickly, the road system, which is typically used and 

maintained between treatment activities, is a chronic source of sediment. Sediment 

yields from high severity wildfires are much greater than the increase in sediment 

yields due to fuel management activities, but the recurrence interval of such wildfires 

can be hundreds of years. Over longer time scales, the cumulative impacts of fuel 

treatments, repeated at 10 to 20 year intervals, when combined with the impacts 

of continuous road maintenance and use, may be similar to the pulse impact from 

wildfires.

The cumulative effect of fuel management activities is related to their location and 

concentration within a given watershed as well as the degree and frequency of disturbance for each activity. The watershed-scale impacts of any fuel management activity 

must consider the associated activities of road use, road maintenance, increased traffic, 

and multiple entries with various types of equipment as well as the combined effects 

of all the fuel treatments being applied. However, these effects are complex and interrelated. Few studies have examined the role of different controlling factors, much less 

the effects and interactions of the different activities on runoff and erosion at the watershed scale. Identifying the cumulative effects of timber harvest activities is a continuing 

challenge, as it is almost impossible to quantify the relative contribution of each activity 

at each location. It follows that determining the cumulative effects of fuel treatments, 

which generally cause less disturbance than timber harvesting, will be even more of a 

challenge.

Knowledge Gaps

Additional research is needed to understand the cumulative effects of fuel treatments 

at the watershed scale. Research to date has identified and quantified some of the key 

factors relevant to fuel treatment operations, but the combined effects of these variables 

are not well understood. In particular, studies are needed in the following areas to determine the

1. change in peak flows, soil moisture, and sediment yields from repeated entries into the 

forest for fuel management operations on various soil types, precipitation regimes, 

and scales—both time and area;

2. extent to which roads, burned areas, and timber harvest units are connected to 

stream networks and how this connectivity changes over time as a function of the 

precipitation regime and site conditions; and

3. changes in runoff and sediment yields due to reopening brushed-in, low-use forest 

roads for fuel management activities.

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USDA Forest Service RMRS-GTR-231. 2010. 101

Chapter 6.

Cumulative Effects of Fuel Treatments on 

Channel Erosion and Mass Wasting

Leslie M. Reid, Redwood Sciences Laboratory, Pacific Southwest Research Station, 

USDA Forest Service, Arcata, CA

Introduction

Controversy over fuel treatments on public forestlands often focuses on the potential 

for such treatments to contribute to cumulative watershed impacts. If a fuel treatment 

project modifies the production or transport of water, sediment, or woody debris through 

a channel network, downstream habitats and aquatic resources may respond adversely 

to the changes. If these changes augment impacts from previous or on-going activities, 

the fuel treatment project will have increased the overall level of impact—the cumulative impact—to downstream resources.

As currently applied, “fuel treatments” include a variety of practices, such as prescribed burning, removal of sub-canopy “ladder fuel” and downed wood, thinning of 

canopy trees, thinning of understory trees, conversion of fire-susceptible stands, clearing of shaded fuel breaks, post-fire salvage logging, and logging of insect-damaged or 

at-risk stands. Many of these activities are not economically self-supporting, so they are 

often bundled with standard timber sales to offset costs. Such projects tend to be subjected to particularly intense public scrutiny, and questions are often raised concerning 

the extent to which fuel treatments influence erosion.

Considerable research has been carried out on channel erosion and mass-wasting 

processes, but few studies explore the effects of fuel treatments on such processes. 

Wondzell (2001) reviewed the literature available as of 2001. However, the scarcity 

of literature that specifically addresses the issue is not a critical problem. Fuel treatments influence factors controlling process rates in ways similar to activities (such as 

logging) and events (such as wildfires) that have been more widely studied. If erosion process mechanisms are understood, a large body of literature becomes applicable 

to the problem. This chapter describes characteristics of channel erosion and masswasting processes, describes the environmental factors that most strongly influence erosion processes, discusses the mechanisms by which fuel treatments can influence those 

controlling factors, outlines strategies for determining whether such influences will occur, and describes how erosion evaluations might be incorporated into a cumulative 

impact analysis. The erosion processes discussed here include channel-bank erosion, 

gullying, soil creep, landsliding, and related processes. Sheetwash erosion is considered 

in chapters 5, 8, and 13.

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
102 USDA Forest Service RMRS-GTR-231. 2010.

Characteristics of Erosion Processes

The erosion processes considered in this chapter often occur downstream or 

downslope of the triggering land use activities. Consequently, they not only can contribute to off-site cumulative watershed impacts, but also can themselves be influenced 

by multiple upslope or upstream activities. The potential influences of each process on 

downstream environments can be inferred through an understanding of 

1. the factors affecting the distribution and rates of these erosion processes, 

2. the kinds of sediment likely to be produced by each, and 

3. the likely distribution of sediment inputs in time and space.

Channel-Bank Erosion

Bank erosion generally occurs by direct tractive erosion of a raw bank face or by undercutting and toppling or slumping. At sites where activities impinge on banks, direct 

disruption can also be important. The rate, mode, and distribution of channel-bank erosion are strongly influenced by bank materials, vegetation on the bank, pore pressures in 

the bank, channel flows, near-bank activities, and in-channel deflections. Hooke (1979), 

Thorne and Tovey (1981), and Couper and Maddock (2001) describe processes of bank 

erosion and evaluate factors that control the erosion rate.

Tractive erosion is most active on sparsely vegetated banks formed of non-cohesive 

materials such as sand and gravel. Repeated wetting and drying or freezing and thawing 

of bank materials can reduce their cohesion, contributing to “dry ravel” of the banks and 

increasing their susceptibility to tractive erosion. Banks formed from cohesive clays are 

more resistant to tractive erosion but can spall off in sheets when subjected to wet/dry 

or freeze/thaw cycles. Tractive erosion usually is negligible on bedrock banks unless the 

rock is poorly indurated. Bank erosion rates at a site generally increase if the duration 

of inundation increases, and more of the bank face is susceptible to tractive erosion for 

longer periods if hydrologic changes lead to increased channel flows.

Tractive erosion sources generally are distributed along the channel network—rarely 

is input dominated by erosion at a single site. Potential rates of tractive erosion are expected to increase downstream with increasing discharge and increasing prevalence of 

fine-grained bank materials. However, this general downstream trend may be reversed 

in low-gradient, lowland rivers with banks formed of cohesive materials (Lawler and 

others 1999). At a reach scale, erosion tends to be most rapid at the downstream outer 

edge of bends, where high-velocity flow impinges on banks. Often, erodible banks are 

inundated for only a small fraction of the year, so sediment inputs may be restricted to 

high-flow events.

Tractive erosion generally produces fine-grained sediment that remains mobile after 

entering the stream (table 1). Larger clasts are also contributed to the extent that they 

are present in the bank, but they are usually dislodged by undermining rather than by 

traction.

Bank failures are often triggered by undercutting, so rates of bank erosion by toppling 

and slumping depend in part on rates of tractive erosion. Toppling is most pronounced 

where floodplain- or terrace-surface deposits are cohesive. Roots increase cohesion 

even in inherently non-cohesive materials, and banks along incised grassland channels 

are often characterized by toppling failures.

In contrast to tractive erosion, bank failures tend to occur as high flows recede 

because 

1. the susceptible material is then at its highest bulk density due to saturation, 

2. pore pressures in the bank are high, and 

3. the undercut soil mass is no longer partially supported by the hydrostatic force from 

inundation (Thorne and Tovey 1981). 

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 103

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States

Because bank failures often produce blocks of cohesive sediment and often occur after 

the flow peak, the sediment introduced may remain close to its source. Tractive erosion 

during lower flows then gradually mines away the sediment. In forested areas, bank 

failures often contribute woody debris to channels.

Undercutting can also trigger large streamside landslides that affect more than just 

bank materials. Such slides can be found wherever channels encroach on valley walls, 

and they frequently occur along the “inner gorges” (Kelsey 1988) characteristic of many 

tectonically active areas. Although undercutting usually contributes to the instability, 

these failures are also susceptible to the same kinds of influences as other landslides. 

Some streamside landslides initiate at the toe of a slope and propagate upslope over 

time, while others fail as a single unit.

Streamside landslides can produce large quantities of extremely coarse sediment. 

Their deposits may remain in place for long periods and can modify the course and 

character of the channel both upstream and downstream. Where slide deposits deflect 

channel flows, additional landslides can be triggered by undercutting of new sites, 

thereby propagating the impacts even farther downstream. The largest slides may create 

temporary dams, sometimes resulting in dam-release floods capable of scouring and 

widening channels for long distances downstream.

Direct disruption of channel banks and beds can occur through trampling by animals 

or people and by land use activities that impinge on stream channels, such as in-stream 

mining and yarding of logs across channels. The distribution and rates of erosion from 

direct disruption depend strongly on animal and human use patterns and on the original 

morphology of the banks. Sites where banks are low, for example, tend to be selected 

as crossing points. Initial sediment inputs from these sources usually occur during lowflow seasons, when disruptive activity levels are often highest. But because the resulting 

channel modifications tend to be unstable during higher flows, storm flows usually mobilize additional sediment as they rework the unstable deposits.

Inputs from direct bank disruption are often relatively fine-grained and can be an 

important source of turbidity during low-flow periods, when natural turbidity levels 

Table 1. Selected characteristics of major channel erosion and mass-wasting processes.

Erosion process	 Grain size	 Sediment input timing	 Location	 Potential influences a

Bank erosion fine to medium high flows of most concern in altered woody debris

after high flows moderate to large altered riparian vegetation

channels altered channel form 

increased channel migration

Gully erosion fine to medium periods of runoff hillslopes altered site productivity

early season flows small to medium lowered water table

channels accelerated runoff 

below diversions more hillslope sediment delivery 

increased bank erosion 

altered channel form 

reduced floodplain connectivity

Soil creep fine to medium chronic pervasive increased bank erosion

Shallow slides fine to coarse high-intensity rain inner gorges altered site productivity

onto wet ground hillslope swales flow deflection

undercut banks altered woody debris 

certain bedrocks

Debris flows fine to coarse high-intensity rain steep swales altered channel roughness

onto wet ground certain bedrocks flow deflection

altered woody debris 

channel blockage

Deep-seated slides fine to very coarse very wet seasons certain bedrocks flow deflection

Earthflows fine to very coarse very wet seasons certain bedrocks flow deflection

altered site productivity

a All erosion processes can also contribute to aggradation, turbidity, altered bed material, and altered bed stability.
104 USDA Forest Service RMRS-GTR-231. 2010.

are low. Such unseasonal sediment inputs can be disproportionately important if they 

contribute to additional stress on organisms already challenged by low flows or high 

temperatures.

If a channel reach is not aggrading, incising, or changing form, bank erosion rates 

along the reach are expected to be roughly equivalent to rates of sediment resupply to 

those banks (Dietrich and Dunne 1978). Channels can supply fine sediment to banks 

through overbank deposition, while coarser channel-bed sediments can be incorporated 

into banks through bar accretion and associated channel migration. Where channels 

abut hillsides, hillslope sediment transport processes, such as soil creep and landsliding, 

also can contribute sediment to channel margins. Over a long period, slight imbalances 

in rates of erosion and deposition lead to the gradual down-wasting of the landscape, 

while over a short period, larger imbalances lead to temporary, localized changes in 

channel and bank form. Over an intermediate period, however, conditions tend to average out in most undisturbed settings. An undisturbed headwater channel is expected to 

look much the same today as it did a hundred years ago, despite relatively continuous 

bank erosion along the channel.

Under some conditions, bank erosion can occur quite rapidly and may lead to extreme changes in channel character. Major floods or debris flows can significantly widen 

channels, and sudden or episodically high inputs of sediment can fill channels, leaving 

flow to spread across the valley bottom in multiple “braided” flow strands. If the aggraded sediment is erodible, each strand then mines the new deposits, gradually shifting 

the load downstream. Braided channels are typical of glacial outwash plains and alluvial 

fans.

Unless sediment input remains high or a channel is freely migrating, accelerated bank 

erosion is usually self-limiting. Banks begin to stabilize once a channel has widened 

enough that flow becomes too shallow—or impinges on banks too infrequently—to 

remove eroded sediment.

Gully Erosion

Gully erosion is a particular kind of rapid channel erosion that forms incised, steepwalled channels. Rapidly incised channels small enough to be eliminated by plowing 

are referred to as “rills,” which are considered a component of sheetwash erosion. In 

forested settings in North America, gullies are usually of most concern along headwater channels and in meadows. In the semi-arid west, gullying is also important farther 

downstream, where incision of gullies known as “arroyos” has strongly altered valleybottom conditions over the past 150 years (Cooke and Reeves 1976). Factors expected 

to influence susceptibility to gullying include channel gradient, substrate, vegetation 

cover, and peak-flow regimes. Bull and Kirkby (1997) and Oostwoud Wijdenes and 

Bryan (2001) discuss gully erosion processes and factors that influence rates of gully 

erosion.

Gullies can form in unchanneled settings by upslope migration of channel heads, 

collapse of subsurface soil pipes, or incision of scour holes along previously stable 

drainageways. Generalized incision or headcut migration can also form gullies along 

existing channels. Widespread gullying is most often associated with anthropogenic 

changes, such as introduction of cultivation or livestock. However, gullying can also 

be triggered by natural events that reduce vegetation cover (such as wildfires), deposit 

erodible material (such as volcanic eruptions), or generate extreme surface runoff (such 

as intense thunderstorms). Stratigraphy of valley-bottom deposits in the southwestern 

United States suggests that climatic shifts have triggered several episodes of arroyo 

formation over the past 4,000 years (Waters and Haynes 2001).

Gullies commonly grow by upstream retreat of a near-vertical headwall. Water falling over the headwall excavates a plungepool at its base, undercutting the headcut 

and sidewalls. Undercutting promotes toppling failures, allowing the gully to widen 

and to progress upstream. Seepage at the base of a headcut can also increase rates of 

undercutting and in some areas can be the dominant mechanism for headcut retreat 

(Higgins and others 1990). A depositional lip typically forms at the downstream end 

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 105

of the plungepool, and the channel downstream is often graded to the level of the lip. 

Channel-fill sediment downstream of a migrating headcut and its associated plungepool 

may thus represent the upstream progress of deposition on the plungepool lip.

Gully cross sections are modified by the types of bank erosion processes described 

in the previous section. Often, gully width increases and wall gradient decreases as a 

function of the distance downstream of a headcut, reflecting progressively longer periods of recovery since passage of the headcut. Upstream headcut migration may halt if a 

headcut encounters non-erodible material or if the contributing area becomes too small 

to generate erosive flows.

Gullying most commonly forms intermittent or ephemeral channels, where “intermittent” refers to channels that carry water seasonally, while “ephemeral” usually implies 

that water is present only during storms. Sediment often accumulates in gullies during 

dry periods through trampling, dry ravel, and spalling of banks. The first flows after a dry 

period may then carry particularly high sediment loads as the accumulated sediment is 

flushed out (Crouch 1990). Gullying tends to be suppressed where soils contain coarse 

sediment because the coarse clasts can armor the bed and banks and restrict further erosion. Consequently, gullying is generally associated with fine-grained substrates, and 

sediment produced by gullying usually is readily transportable by channel flows.

Some areas of steep terrain and poorly consolidated bedrock are susceptible to rapid 

formation of gullies large enough and steep enough that gully-wall failures begin to 

generate debris flows. At this point, expansion no longer depends on channel flow, and 

the gully network can form an amphitheater-shaped basin that extends to the ridgeline. 

These gully-landslide complexes are referred to as “gully slips” in New Zealand, where 

they formed after conversion of forest to pasture in some regions (Betts and others 

2003). Reforestation of gullied watersheds has halted the growth of many New Zealand 

gully slips, although the forms remain present.

Recovery from a gullying episode tends to be slow, and evidence of gullying may 

persist for centuries in the form of terraces. Gullies may continue to produce sediment 

from headcut retreat and wall erosion long after the conditions that initially triggered 

gully formation have been reversed. Sediment redeposited downstream of actively incising reaches may remain in storage for long periods. Moody and Martin (2001), for 

example, expect that much of the sediment produced by channel incision after a fire in 

Colorado will remain in the watershed for several hundred years.

Soil Creep

Soil creep is a gradual mass wasting process that occurs within the soil mantle on 

most hillslopes. Transport can occur through plastic deformation of the soil mass in 

some clay-rich soils, but more common is transport by displacement of individual soil 

particles through root growth, animal burrowing, wetting and drying, and freezing 

and thawing. These soil disturbances tend to move particles preferentially downslope 

because of the influence of gravity, and incremental transport of individual particles 

combines to gradually displace the entire soil profile. Saunders and Young (1983) provide a tabulation of measured creep rates. More recent work (such as Heimsath and 

others 2002) adds to the measurement record and provides further discussion of creep 

mechanisms.

Although rates of soil creep are slow, the process is influential because it occurs 

over most of the landscape. The nature of the motion and its slow rate make measurement difficult, so transport rates are generally estimated by other means. In many 

quasi-steady-state systems, soil creep is the major source of sediment resupply to stream 

banks abutting hillslopes, so long-term measurements of bank erosion can provide estimates of creep rates.

Creep rates are expected to depend on hillslope gradient, soil texture, soil moisture, 

biological activity within the soil, and vegetation, but little is known about the relative 

influences of these factors because measurement is difficult. Changes in hillslope conditions that increase soil moisture or soil disturbance are likely to increase creep rates, but 

such effects have not yet been documented in a controlled setting.

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
106 USDA Forest Service RMRS-GTR-231. 2010.

Shallow Landsliding

“Shallow landsliding” is a commonly used term that is not recognized in the widely 

adopted landslide classification system presented by Cruden and Varnes (1996). Some 

apply the term to any slide that involves only colluvial material, thus corresponding 

to the “debris” material category of Cruden and Varnes (1996). Others use the term to 

indicate that the depth to the failure plane is markedly less than the length or width of 

the slide, corresponding roughly to the “translational” motion category of Cruden and 

Varnes. Under this second usage, a 5-m deep slide might be considered “shallow” if 

it is 50 m long or “deep-seated” if it is only 10 m long. When used in forestry related 

literature, “shallow landsliding” appears to most commonly refer to translational slides. 

Although these often consist primarily of surficial deposits, some may include significant bedrock. Saunders and Young (1983) compiled measurements of landsliding rates, 

and many more recent studies provide additional measurements.

Shallow failures generally occur during periods of high-intensity rain that falls onto 

already wet soils. Relations between slide occurrence and various measures of rainfall 

intensity have been developed at many sites (for example, Crosta 1998; Crozier 1999; 

Finlay and others 1997; Nilsen and others 1976; Reid and Page 2003). Slide frequencies are also influenced by hillslope gradient, root cohesion, soil moisture, lateral slope 

convergence, bedrock type, soil depth, and soil texture. Shallow slides occur most frequently on steep portions of the landscape into which subsurface flow is concentrated, 

such as headwater swales and inner-gorge slopes. Failure planes of small slides are 

often within the rooting depth of forest vegetation. Increased landsliding rates are sometimes noted several years after logging, after dead roots have decayed but before new 

roots have matured (Bishop and Stevens 1964; Swanston 1969). A variety of analytical 

tools have been developed to identify sites susceptible to shallow sliding (for example, 

Montgomery and Dietrich 1994).

Shallow slides often mobilize both soil and partially weathered bedrock, so most 

slide deposits contain a wide range of grain sizes. In forests, deposits usually include 

woody debris. The proportion of landslide debris reaching a channel tends to decrease 

with increasing distance between the landslide scar and the stream. However, even distant slides may contribute sediment where slopes are steep or when slides are generated 

by intense storms. At such times, overland flow generated from the new slide scar can 

act as a temporary extension to the downstream channel, allowing sediment delivery 

directly to the stream. Shallow landslides generally occur during periods of intense rain 

and high flow, so some portion of the landslide sediment reaching a channel is usually 

transported downstream during the triggering storm.

Once a shallow slide has occurred, the bared scar continues to contribute sediment 

through surface erosion and gullying until vegetation regrows (Larsen and others 1999). 

Sediment inputs can be further prolonged as streams rework temporarily stored landslide deposits, contributing both suspended sediment and bedload (Sutherland and 

others 2002). Because of the relatively slow transport rates for bed material, decades 

may be required before debris from a major landslide-generating storm is fully evacuated from a moderate-sized channel (Madej and Ozaki 1996). Meanwhile, aggradation 

from the downstream transport of landslide debris can deflect stream flow into banks, 

causing secondary failures at downstream sites.

Debris Flows

Shallow failures often displace saturated material, and pore pressures at some failure 

sites are high enough that landslide debris can lose all cohesion and flow as a liquid. 

If debris moves as a fluid, the event is referred to as a “debris flow.” Field evidence 

suggests that some debris flows can initiate within channel deposits, and flows have 

occasionally been found to originate high on slopes without evidence of an initiating 

landslide (J. McKean, personal communication).

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 107

Debris flows in steep forestland channels can entrain large volumes of channel deposits and woody debris (May 2002). Wood-bearing debris flows often come to rest 

where the wood becomes jammed or the channel gradient decreases to the point that 

material can no longer flow. These conditions are often present where an affected tributary joins the mainstem channel (Benda and Cundy 1990), so landscapes characterized 

by debris flows commonly exhibit debris fans at tributary mouths. Debris flow deposits 

are recognized as unstratified mixtures of diverse grain sizes.

Debris flows and less dense, sediment-laden “hyperconcentrated flows” can also 

form through rapid incision and entrainment of in-channel deposits (Cannon and others 

2001; Cannon and Reneau 2000). In some areas, such flows are common after highintensity fires that generate hydrophobic soil layers. After a debris flow has occurred, 

the scoured channel and debris deposits remain subject to accelerated erosion until they 

are revegetated or become armored by coarse sediment. Log jams formed by debris 

flows at tributary junctions can accumulate considerable volumes of bed material from 

both the affected tributary and the mainstem. When the jam eventually fails, a portion 

of the trapped sediment is released to resume its downstream transport.

Deep-Seated Landsliding and Earthflows

The term “deep-seated landslide” is also not recognized by the Cruden and Varnes 

(1996) classification system. The term is variously used to refer to landslides having 

failure surfaces within bedrock or to slides that are deep relative to their length and so 

have moved by rotation along a curved failure plane (slumps). In the forestry literature, 

the term is used primarily for rotational slides, though it also often encompasses nonrotational bedrock failures if they seem unlikely to have been influenced by near-surface 

pore pressures.

Large, deep-seated landslides tend to be more responsive than shallow slides to seasonally high rainfall accumulations and respond less to high-intensity rain bursts or 

individual storms. The failure surface is often deep enough that root cohesion is inconsequential. The largest features remain visible on the landscape for millennia, and only 

ancient examples are present in many areas. Controversy persists over the extent to 

which long-stabilized slides can be reactivated by land management activities.

Once mobilized, large deep-seated slides can remain active for decades or longer. 

Slide surfaces are often irregular and hummocky, and a depression or sag-pond may 

be present at the base of the headwall scarp. In some cases, the progressive motion is 

slow enough that it is most readily recognized by haphazard orientations of mature tree 

trunks, disruption of road surfaces, or distortion of fences. In other cases, the entire failure may occur over minutes or days, with subsequent activity limited to erosion of the 

disrupted slide mass and bared scarp. The toes of old slumps often form over-steepened 

slopes that are now susceptible to shallow landsliding. Sediment contributed by deepseated slides can include grain sizes ranging from weathered clays to large blocks of 

intact bedrock.

In some terrains, materials initially mobilized by deep-seated slumps continue to 

move downslope as earthflows. Earthflows are plastically deforming masses of unconsolidated material that remain active over long periods, ordinarily moving from several 

centimeters to tens of meters each year. More rapid flows that occur as discrete events 

are termed “mudflows” or “debris flows.” Earthflows generally occur in areas of clayrich, mechanically weak bedrock, such as shale or argillite. In areas susceptible to 

earthflows, evidence of past activity is often visible as hummocky terrain, and active 

earthflows may appear as patches of grassland in otherwise forested areas.

Earthflows are most active during seasonally wet periods. Activity may cease during 

the dry season or in years with low rainfall and resume when water tables have again 

risen to a threshold level. On large flows, variations in velocity generally are not associated with individual storms. Flageollet and others (2000) describe the three-dimensional 

structure of a major earthflow, and Iverson and Major (1987) describe patterns of motion for a similar flow over a 3-year period.

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
108 USDA Forest Service RMRS-GTR-231. 2010.

Many large earthflows are bounded by streams at their toes. Activity of the slide can 

then strongly control the form and sediment load of the stream channel, while channel 

erosion, in turn, repeatedly undercuts and reactivates the slide mass. A year of rapid 

motion may constrict the stream, while years of lesser activity may allow the stream to 

reexcavate its characteristic channel.

Earthflow toes are often the site of intensive surface erosion and shallow landsliding. Consequently, periods of high sediment production are associated with individual 

storms even though motion of the earthflow itself often is not. Earthflow surfaces often 

support gullied drainage networks that contribute additional sediment during storms. 

Because earthflows generally form in areas with weak, clay-rich bedrock, even the 

coarser blocks tend to be rapidly broken down once introduced to a channel. The largest 

sediment blocks remain stranded in channels until worn away, while finer sediments can 

contribute to chronically high suspended sediment loads.

Related Erosion Processes

A variety of other channel erosion and mass-wasting processes can be strongly influenced by fuel management activities and may be important in some settings even though 

they rarely dominate the sediment supply. Of particular note for forested areas are subsurface channel erosion (tunnel erosion or piping; Jones 1981; Uchida and others 2001), tree 

throw (Schaetzl and others 1989), and animal burrowing (Gabet and others 2003). Several 

other processes, such as dry ravel and sheetwash erosion, frequently occur on sites bared 

by channel erosion and mass-wasting processes and prolong sediment inputs from the 

primary sources.

Tunnel erosion is common in unchanneled swales in many areas, though its presence 

is often unnoticed. The process can usually be detected by examining channel heads for 

soil pipe outlets. Pipeflow is generated primarily by subsurface drainage during storms, 

though some pipe networks can continue to flow long into the dry season. Pipeflow 

tends to remain relatively clear of sediment even during storms. Surficial erosion processes do not contribute directly to pipeflow sediment loads unless the pipe’s roof is 

breached upslope. Instead, most tunnel erosion sediment is generated by bank erosion 

processes and tractive erosion within the pipe. Tractive erosion of the pipe circumference increases with increasing discharge.

Piping is often present in unchanneled swales that are subject to periodic debris slides. 

In a quasi-steady-state system, soil-creep input of sediment to these swales is largely 

balanced by the combined activity of tunnel erosion and landsliding. At a smaller scale, 

pipe diameters are expected to remain relatively constant over time, so erosion of sediment from pipe walls evidently keeps pace with the tendency for pipes to constrict due 

to soil creep. Tree throw or cave-ins can unroof pipes, temporarily increasing sediment 

loads and diverting flow to the surface. It is likely that pipe roofs can be reestablished 

by bridging with forest floor litter and small woody debris, though descriptions of the 

recovery process have not been published.

Tree throw can contribute appreciable sediment to streams where forested banks or 

valley walls are steep. At such sites, it may be difficult to distinguish tree-throw events 

from landsliding because both contribute a mixture of woody debris and sediment and 

leave similar scars. The distinction rests on the cause of the failure: did a landslide 

topple the trees, or did falling trees destabilize adjacent soils?

Tree throw is most prevalent during high winds that occur while soils are saturated and 

trees are in full foliage. Although blowdown of snags is common after fires, such falls often occur by stem breakage and thus do not contribute directly to sediment loads. Whether 

a tree is likely to break or uproot also varies by species (Veblen and others 2001).

Under most conditions, animal burrowing is an implicit component of soil creep, 

so creep rate estimates generally account for displacement by burrowing. However, 

burrowing can also influence sediment production by exposing unvegetated soils to 

overland flow or by directly contributing sediment to streams where burrow tailings are 

deposited within the high-flow stream margin. In the Pacific Northwest, for example, 

mountain beaver burrows often are associated with headwater streams. Populations of 

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 109

burrowing animals vary with stand age, and young stands may provide food sources to 

support large populations of burrowing rodents.

“Dry ravel” of surface sediments occurs when grains are transported downslope in 

the absence of flow. Cohensionless particles can be dislodged downslope by even minor 

disturbances, so dry ravel is common on landslide scars and eroding banks of noncohesive sediments. Particles on a bare surface can be loosened by cycles of wetting 

and drying or freezing and thawing, and fire often promotes dry ravel by baring mineral 

soils and by burning out small woody debris that has trapped sediment on stream banks 

and hillslopes. After fires, ravel can be an important source of sediment delivery to 

low-order streams, where the accumulated sediment can then be easily remobilized by 

wet-season flows (Roering and Gerber 2005).

Factors Influencing Erosion Processes

Although many environmental characteristics can affect erosion processes, several 

are particularly influential for multiple processes. The distribution of erosion processes, 

their rates of sediment production, and the timing of sediment inputs are largely controlled by topographic setting, materials, surface conditions, hydrologic conditions, and 

vegetation. Each of these factors also exerts influence on the others. An understanding 

of these controlling factors and of how they may be influenced by management activities provides the link needed to evaluate the effects of specific land use activities on 

erosion processes.

Topography

The susceptibility of a site to various erosion processes can often be inferred from its 

topographic setting. On hillslopes, local gradient, lateral convergence, and distance from 

the ridge-top strongly influence which erosion processes will be active. Once processes 

are activated, their influence depends in part on how far the mobilized sediment travels. 

Topographic conditions downslope of an eroding site strongly affect the proportion of 

the mobilized sediment that reaches a channel. Particularly influential are gradient and 

lateral convergence downslope, presence of topographic irregularities along the travel 

path, and distance to the stream.

In channels, local topography strongly influences the shear stress imparted by flows 

on the bed and banks. Deep, high velocity flows on steep slopes develop the highest 

shear stresses—these are the sites most likely to incise. Along a channel, variations in 

gradient and channel width can control the distribution of aggradation and incision.

Topographic setting is also important because management-related topographic changes can trigger a variety of erosion processes. On forested hillslopes, most 

topographic modifications are associated with road construction. Excavation of oversteepened road-cuts, emplacement of fills, construction of stream crossings, excavation 

of road-side ditches, and deposition of unstable side-cast material can all contribute to 

increased erosion risk.

Topographic modifications in channels also often result from road construction. 

Banks may be realigned and armored to protect riparian roads, and levees are sometimes constructed to reduce flooding. Bridges or culverts modify channel cross sections, 

sometimes restricting passage of woody debris or coarse sediment. Stream crossings 

on steep slopes are particularly vulnerable to failure because drainage structures can be 

blocked by woody debris, allowing flow to pond behind the unconsolidated road fill. 

Overtopping can then lead to rapid gullying, while increased pore pressures within the 

fill can trigger landslides. At some sites, in-stream structures have been built to divert 

flow for low-head hydroelectric power generation or to pond water for livestock. Such 

changes can alter sediment delivery and channel erosion rates downstream. At a larger 

scale, dams are major controls on downstream channel forms and processes and can 

strongly influence the effects of upstream activities on downstream environments.

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
110 USDA Forest Service RMRS-GTR-231. 2010.

Materials and Surface Conditions

Material characteristics—particularly grain size and cohesion—also influence which 

processes are likely to be active and how far eroded sediment can move. Coarse-grained 

sediment tends to have low cohesion and thus is susceptible to dry ravel, but bedrock 

that weathers to coarse material is not likely to support earthflows. Clays, in contrast, 

are extremely fine-grained and cohesive. Earthflows usually occur in areas with clayrich bedrock, but cohesive clay soils are resistant to tractive erosion and ravel. Coarse 

sediment requires high shear stress for in-stream transport and so may be mobile only 

during high flows. Coarse sands, gravel, and cobbles thus generally form the bed material in upland streams, while clays and silts are readily transported in suspension and 

contribute little to the bed material.

Surface characteristics can strongly influence the susceptibility of hillslope or channel materials to erosion. Removal of readily transported fine-grained sediment often 

leaves a lag of coarse sediment that armors hillslopes or stream beds, impeding further 

erosion. Soil surface characteristics change radically after fires. Erodible mineral soils 

are often exposed when protective organic material is burned off. At some sites, fire 

can generate a surficial hydrophobic layer (DeBano 2000a, b), resulting in rapid runoff 

and increased surface erosion during subsequent rains. The increased runoff may trigger debris flows, gullying, and increased bank erosion downstream. Ground-disturbing 

activities can also modify the susceptibility of swales to gully incision by exposing 

erodible soils.

Hydrologic Conditions

Water affects most types of erosion and sediment transport on hillslopes, and the 

largest sediment inputs usually occur during major storms. The occurrence of shallow 

landslides is particularly responsive to the timing and spatial distribution of high pore 

pressures, which in turn are influenced by soil surface topography, bedrock surface topography, subsurface drainage paths, location along a slope, hydraulic conductivity of 

soils and bedrock, and the amount of water contributed to the site by precipitation or 

surface and subsurface drainage. These factors generally control the routing of water 

down hillslopes and so influence the distribution of gullying, tunnel erosion, debris 

flows, deep-seated slides, and earthflows.

Shear stress at a channel cross section increases with discharge, thus increasing rates 

of sediment transport and channel erosion. Because of this dependence, and because 

sediment inputs from hillslopes also respond to water, most of a stream’s annual sediment transport may occur during a few major storms. Changes in the timing, amount, 

and duration of runoff change the timing, amount, and duration of in-channel erosion, 

sediment transport, and aggradation.

Land use activities or natural events that modify hillslope hydrology can influence 

rates of shallow landsliding. Hillslopes may become wetter after logging or wildfire due 

to decreased transpiration and rainfall interception. The presence of roads often influences hillslope hydrology by rerouting shallow subsurface flows and by diverting road 

drainage onto hillsides.

Vegetation

Vegetation strongly affects erosion processes by influencing soil strength, surface 

materials, and hydrology. Root networks in both forest (Schmidt and others 2001) and 

grassland (Preston and Crozier 1999) can provide additional cohesion to soils of low 

inherent strength. In some areas, the distribution of shallow landslides reflects this influence. Roering and others (2003), for example, found that slides in their study area were 

located at some distance from the nearest trees.

Forest-floor litter strongly affects the characteristics of near-surface soil horizons. 

Organic-rich horizons often have relatively open textures, resulting in high infiltration 

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 111

rates and high moisture storage capacities. Overland flow is uncommon where deep 

litter has accumulated, and litter shields mineral soils from surface erosion and gully 

initiation. Removal of a litter layer through mechanical disruption or fire can increase 

the incidence of overland flow, thus increasing rates of downstream channel erosion.

Channel erosion rates can be particularly sensitive to vegetation changes because of 

the influence of vegetation on hydrology. Plants use large quantities of water, drawing it 

from the soil through their root systems and transpiring it into the atmosphere through 

their leaves. Conversion of vegetation to a community with lower water use increases 

runoff (Bosch and Hewlett 1982), thereby increasing the potential for channel erosion. 

Plants also trap rain and snow on foliage, increasing the evaporative loss of water during 

and after storms (Calder 1990). In areas where cold-season storms can include either 

rain or snow, warm rainstorms falling onto well-developed snowpacks can generate 

large flood flows that are often associated with significant in-channel erosion. In these 

settings, snow accumulations are highest and melt most rapidly in cleared areas, so presence of a forest cover moderates the runoff rate (Marks and others 1998).

Forest stand characteristics in the western United States are changing in response 

to earlier fire management strategies and on-going global climate change. Given the 

strong influence of vegetation on erosion processes, erosion regimes are expected to 

change in response. But even though vegetation change can strongly influence shortterm sediment yields, influences on sediment yield over the long term may not be as 

great because the long-term average soil erosion rate must balance the long-term average soil formation rate if soil depths do not perpetually increase. The soil formation rate, 

in turn, is influenced by soil depth, erosion processes, and vegetation, and soil depths are 

controlled by erosion processes and soil formation rates. Because these factors are interdependent and all are influenced by vegetation, a vegetation change alters the balance 

between them. Where forest was converted to grassland in parts of the East Cape region 

of New Zealand, for example, deep forest soils are being removed by widespread shallow landsliding (Reid and Page 2003). Over time, a transition to shallower soils typical 

of grasslands is likely at these sites. The net erosion rate might eventually be nearly 

the same as before the vegetation change as erosion once again becomes constrained 

by soil formation rates, but the transition period is characterized by extreme erosion 

as the volume of sediment stored on hillslopes is rapidly reduced (see also Gabet and 

Dunne 2003). Such short-term readjustments on hillsides can lead to profound longterm changes downstream, where channels may be choked and floodplains inundated by 

the sudden influx of new sediment.

Potential Influences of Fuel Treatments on Erosion Processes

Once the factors controlling erosion process rates are understood, the potential influences of various fuel treatments can be inferred by examining their effects on the 

controlling factors. Forest fuel treatments can be grouped into four categories on the 

basis of their potential effects on hillslope and channel erosion processes: managed 

burning, mechanical treatments, logging, and strategic stand design. These activities are 

supported by the transportation infrastructure and, in some cases, require modification 

of existing road networks. General patterns of influence are summarized in table 2.

Managed Burning

Fire can be used to reduce ground fuel over wide areas at relatively low cost, whether 

it is applied through prescribed burning or by allowing wildfires to burn unhindered in 

particular areas. Activities associated with managed burning often include road use and 

construction of fire breaks. A small proportion of managed burns escape control or burn 

more severely than planned, leading to erosional conditions typical of more intense 

wildfires. Many publications describe the effects of wildfire on erosion processes (for 

example, Wondzell and King 2003).

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
112 USDA Forest Service RMRS-GTR-231. 2010.

Burning strongly affects soil surface characteristics, ground-cover vegetation, and 

organic debris on the forest floor, while construction of associated roads and firebreaks 

mechanically disrupts soils. Depending on the soil type, vegetation type, and burn intensity, burning may induce hydrophobicity in soils (DeBano 2000a, b; Huffman and 

others 2001; Robichaud 2000). Rain falling on hydrophobic soil may run off as overland 

flow instead of infiltrating, increasing the likelihood of gully erosion, channel incision, 

channel-bank erosion, and in-channel debris flows. These processes are also accelerated by burning of soil-surface litter and in-channel woody debris, and by removal of 

ground-cover vegetation. Canfield and others (2005) describe channel incision after a 

fire, and Istanbulluoglu and others (2003) describe post-fire gullying. In general, the potential for accelerated erosion is expected to increase with burn intensity (Wondzell and 

King 2003). Hillslopes may be particularly susceptible to other influences after burning. 

In one case, for example, trafficking after a low-intensity burn triggered incipient gullying (Saynor and others 2004).

Burning of ground-cover and understory vegetation may reduce transpiration and 

increase soil moisture. However, these vegetation components usually have shallower 

Table 2. Potential influences on major channel erosion and mass-wasting processes.

Treatmenta

Process	 Influential attributes	 Mechanisms of change	 Brn	 MT	 Log	 Sal	 Rd

Bank erosion, peakflow, runoff interception, transpiration + ++

gullying “ road, skid trail drainage + + + ++

 “ hydrophobicity ++ 

 “ compaction + + + ++

direct disruption trampling, trafficking + + + ++

soil-pipe collapse trampling, trafficking + + + ++

rooting density trampling, trafficking + + +

 “ canopy removal + 

 “ burning of groundcover ++ 

surface armoring burning of litter ++ 

 “ less ground-cover vegetation ++ + + 

Soil creep soil moisture interception, transpiration + ++ 

soil disturbance trampling, trafficking + + + +

rooting change burning of groundcover + 

 “ canopy removal + 

Shallow slides, antecedent wetness interception, transpiration + ++ 

debris flows increased drainage road, skid trail drainage + + + ++

 “ hydrophobicity ++ 

 “ compaction + + + ++

 “ interception, transpiration + ++ 

undercut toe disruption + + + ++

undercut by flow road, skid trail drainage + + + ++

 “ hydrophobicity ++ 

 “ compaction + + + ++

material emplaced fill ++

 “ less woody debris + ++ ++

root cohesion canopy removal + 

Slumps, seasonal wetness interception, transpiration + ++ 

earthflows “ road, skid trail drainage + + + ++

root cohesion canopy removal + 

undercut toe disruption + + + ++

undercut by flow road, skid trail drainage + + + ++

 “ hydrophobicity ++ 

 “ compaction + + + ++

+ indicates a likely influence, and ++ indicates that the influence is likely to be strong.

a Treatments and associated activities: Brn = Managed burning; MT = Mechanical treatment; Log = Green-tree thinning; Sal = Salvage 

logging; Rd = Road construction or use.

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 113

roots than overstory vegetation, so the effect is expected to be insignificant by the end of 

the dry season in areas characterized by seasonal drought. Similarly, changes in rainfall 

interception would be small unless a significant proportion of the vegetation burns.

If large portions of a landscape are treated, managed fire will burn through small 

channels and riparian zones. In-channel erosion rates are likely to increase where channels have burned. Sediment in low-order channels is often held in place by small pieces 

of woody debris. When these burn, trapped sediments are free to move downstream 

Loss of protective litter in unchanneled swales may allow gullying to progress at these 

sites, and burning of bank vegetation can increase susceptibility to bank erosion. It may 

be possible to burn during seasons when naturally high moisture levels might deflect 

burns from riparian areas or moderate their intensity, but unseasonal burns may defeat 

faunal strategies for coping with typical wildfires. Spring burns, for example, may disproportionately impact amphibians that are seasonally dispersed across the landscape 

(Pilliod and others 2003).

Mechanical Treatments

Accumulations of dead wood on the forest floor can be removed mechanically, along 

with sub-canopy trees that form “ladder fuel” capable of carrying a ground fire to the 

forest canopy. Dense understories of suppressed conifers form ladder fuel at many sites. 

Such wood usually is not merchantable and may be treated on site by chipping or chunking, with the pieces then spread as mulch. Alternatively, debris may be piled and burned 

or marketed for wood chips. Occasionally, logging of the smaller trees (thinning from 

below) produces stems large enough to be marketable as saw logs or fence posts. In each 

case, associated activities include road use and may involve road construction.

The primary erosional influences of mechanical understory treatments are likely to 

be associated with direct disruption to soils through yarding or by high-intensity fire 

effects under burn piles. Effects are particularly likely where these activities impinge 

on unchanneled swales or low-order channels. Spreading of chipped materials as mulch 

may promote infiltration on hillslopes, reducing the potential for increased erosion in 

swales.

Mechanical treatments are expected to influence hydrology primarily by compaction 

and disruption of soils due to yarding or other trafficking. Increased surface runoff from 

compaction may increase the potential for gullying, both in previously unchanneled 

swales and in downstream channels. Changes in live vegetation density are unlikely 

to be large enough to significantly influence transpiration or interception unless a high 

density of green ladder fuel is removed.

Logging

A number of timber sales recently have been categorized as fuel treatments, either 

because they accomplish canopy thinning (thus reducing the likelihood of spread of 

a crown fire) or because they remove dead or at-risk stems after wildfires or insect 

outbreaks. In the case of green-tree removal, such activities entail the same types of erosional consequences as ordinary timber sales, and such effects have been widely studied 

(for example, Chamberlin and others 1991). McIver and Starr (2000) summarize literature on the effects of post-fire logging on erosion.

After logging, decreased transpiration and interception may lead to increased pore 

pressures and reduce slope stability. Reduced interception is likely to be the more important of the two mechanisms in the coastal Pacific Northwest, where high interception 

rates have been measured even during the high-intensity winter rainstorms that generate 

most sediment in the region (Reid and Lewis 2007). Reduced interception increases 

effective rainfall, directly increasing the geomorphic impact of individual storms as 

well as contributing to increased seasonal groundwater levels. In contrast, transpiration 

changes are most influential during the growing season and so may be most important 

in areas where the major sediment-producing storms do not occur in winter. Decreased 

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
114 USDA Forest Service RMRS-GTR-231. 2010.

transpiration does not directly increase effective storm rainfall but can augment pore 

pressures by slowing the reduction of soil moisture and groundwater levels after storms 

so that antecedent conditions are wetter than usual at the onset of the next storm. Reduced 

interception and transpiration can thus increase both the activity of deep-seated slides 

and the risk of shallow landslides and debris flows.

The risk of shallow sliding is further enhanced by reduced root cohesion after greentree logging. Debris flows may be more mobile if the entrained woody debris does not 

include boles, which are most likely to lodge in channels and halt the flow. Logging 

has also been associated with increased activity of existing deep-seated landslides 

(Swanston and others 1987), and earthflow velocities under forest vegetation in New 

Zealand were found to be several orders of magnitude lower than in deforested terrain 

(Zhang and others 1993). Such differences may reflect changes in both hillslope hydrology (Reid and Lewis 2007) and the mechanical behavior of the root-laden soil (Zhang 

and others 1993). Each of these effects will vary in importance with the proportion of 

trees logged. Miller and Sias (1998) modeled the effect of altered forest canopy on the 

stability of a deep-seated landslide.

In areas where rain-on-snow flooding occurs, clearcut logging can increase flood 

frequencies and magnitudes by allowing deeper snow accumulation and increasing the 

melt rates. Selective logging is expected to have a lesser effect. At sites where logging 

has been extensive enough to modify runoff characteristics, small channels with erodible beds and banks are likely to adjust to altered flow regimes through bank erosion, 

incision, and downstream aggradation. The extent of the adjustment depends in part on 

the magnitude and persistence of flow changes.

Assessment of the erosional consequences of salvage logging requires consideration 

of two issues that are not relevent for green-tree logging. First, erosion processes reflect 

interactions between the salvage logging and conditions left by the disturbance because 

a site’s sensitivity to logging-related impacts may have increased due to the initial disturbance. Hillsides and small channels can become more susceptible to erosion if the 

litter layer and small organic debris have burned or if surface runoff has increased due 

to burn-induced hydrophobicity.

Second, removal of dead or dying trees modifies the erosional response to the initial disturbance. Fires and other stand-killing disturbances themselves increase erosion 

rates. Landslide rates may increase due to reduced transpiration, interception, and root 

cohesion, and surface erosion increases where mineral soil is exposed. But after disturbance, newly downed wood can trap eroded sediment by adding roughness to slopes and 

channels, and woody debris may reduce landslide debris mobility by promoting debris 

jams. Downed wood also can provide soil moisture reservoirs that hasten regrowth. To 

the extent that post-disturbance management reduces the supply of woody debris, these 

inherent recovery mechanisms may be impaired relative to an unmanaged condition.

Strategic Stand Design

A fourth fuel reduction approach employs landscape-level design of forest stand distributions to restrict the spread of individual wildfires or to modify fire intensity in 

critical areas (Graham and others 1999). This strategy arose because there is far more atrisk forest present than can be treated in the near future using the approaches described 

above. However, if such approaches are used strategically to control future fire behavior 

at specific locations, the areal extent or overall effects of wildfires might be controllable. 

For example, one of the methods previously described might be used to establish strips 

of fire-resistant forests, called “shaded fuel breaks,” along ridgelines. Fires originating 

within a watershed would then be more likely to go to ground upon reaching the fuel 

break and thus be more readily managed.

Similar strategic planning can be used to protect at-risk structures and communities 

by concentrating fuel management activities around the area to be protected. Because 

these approaches are limited in scope, they are less likely to entail widespread erosional 

consequences than is a more extensive implementation of fuel treatments.

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 115

Use of strategic stand design introduces a need to understand the implications of 

landscape-scale distributions of erosion processes. Local effects can be evaluated on the 

basis of the particular practices used, while the broader-scale effects reflect the distribution of treatments (in time and space) and the nature of process interactions within and 

downstream of particular watersheds. At this scale, an understanding of in-stream sediment transport becomes particularly important.

Other Activities Associated with Fuel Treatment

Each fuel treatment approach described above is associated with additional activities 

such as road use and, in some cases, road construction. Roads are often a major source 

of management-related sediment through road surface erosion, gullying, landslides, and 

stream crossing failures. Effects of roads on erosion are described in Chapter 5.

Maintenance of an extensive, functioning road network is sometimes justified in part 

by the need for ongoing fuel treatment. To the extent that a road network supports fuel 

treatment, a sediment budget would associate the road-related sediment production with 

the fuel treatment efforts. For example, if 50 percent of the erosion-generating activity 

on a road is in support of fuel treatment, then 50 percent of the road-related sediment 

can be attributed to fuel treatment activities.

Strategies for Evaluating Influences

The previous sections describe how various fuel treatments could influence erosion 

processes. Whether such influences are likely to occur in a particular instance depends 

on the setting, treatment, and weather. Evaluation of the potential for erosion usually 

entails 

1. examining the landscape to be treated to identify erosion processes already active at 

the site, 

2. examining similar sites over a broader area to identify the less common processes 

that might occur, and 

3. examining similar areas that have undergone similar treatments to identify the types 

of changes likely.

The questions to be addressed for each erosion process are 

1. In what settings can the process occur? and 

2. Under what conditions is it likely to occur in those settings? 

Different erosion processes need different strategies for evaluation, require examination of different portions of the landscape, and are most usefully addressed at different 

spatial and temporal scales. Strategies are described here for evaluating channel-bank 

erosion, gullying, shallow landsliding, and deep-seated sliding. Similar strategies would 

be used to evaluate other channel erosion and mass-wasting processes if they are of 

concern at a project site.

Channel-Bank Erosion and Gullying

Evaluation of in-channel and gully erosion relies on information obtained by examining channel systems at several spatial scales. First, the types of channels and settings 

at and downstream of the project site are described. This work identifies past and current 

styles of channel behavior to answer the questions:

• Is there evidence of recent or older changes in channel plan-form?

• Is there evidence of recent or older channel aggradation or incision?

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
116 USDA Forest Service RMRS-GTR-231. 2010.

• Is there evidence of recent or older gully activity upslope of the current channel 

heads?

• Do banks show evidence of recent or older erosion?

If such evidence is found, the spatial and temporal patterns of the occurrences would 

be identified. Evidence of past episodes of gullying might take the form of bank-like 

scarps upstream of channel heads in otherwise unchanneled swales, uncharacteristically 

low width-to-depth ratios along small streams, or the presence of exposed tree roots in 

banks. If gullying was active in the past, the stream network may be particularly sensitive to small changes in factors promoting channel incision.

The next scale of inquiry examines sites outside of the project area that (1) are likely 

to be most susceptible to increased channel or gully erosion because of their history or 

setting and (2) have bedrock and topography similar to those of the project area. For 

in-channel erosion, these might include channels downstream of road drainage inputs 

or sites downstream of pervasively logged watersheds. Off-site examinations for gully 

erosion might focus on burned swales or sites where unprotected ditch-relief culverts 

empty into steep swales or headwater channels.

This portion of the evaluation describes potential mechanisms of influence on the 

processes, defines the tolerance of the landscape to change, and identifies the changes 

in controlling variables to which local erosion processes are sensitive. For example, if 

channels appear stable at the project site, but similar channels show extensive bank erosion below road surface drainage inputs, the effects of the proposed activities on runoff 

become a concern. Interpretation of the field observations requires evaluation of the 

storm history in the area. If no large storms have occurred since a road was constructed, 

lack of evidence for downstream destabilization cannot be considered evidence that 

destabilization is unlikely.

Field examination next turns to sites at which the proposed activities—or similar 

activities—have already been carried out. Here, too, evidence of channel destabilization 

and gullying is sought, as is evidence for influences on the controlling factors found to 

be important elsewhere. For example, if gullying was found at sensitive sites, treated 

sites would be examined for evidence of changes in swale-surface erodibility and surface runoff. In this case, too, sites for which challenging events have not occurred are 

not particularly useful.

The series of observations described above is intended to document the logic trail 

needed to support a diagnosis. Information presented might include:

1. descriptions of channel types in the area and downstream,

2. observations of those channel types in potentially erosive settings,

3. discussion of likely destabilization mechanisms at sites where erosion was observed,

4. description of channels and of any evidence for disruption at sites of analogous 

activities, and

5. description of evidence for the effects of the analogous management activities on 

conditions likely to influence the mechanisms in (3).

If evidence for an effect is found, or if information from elsewhere suggests that influences are possible, those effects would be further analyzed for the project site. Likely 

changes in runoff might be estimated through modeling, for example, and this change 

could then be compared to that present at sites where road drainage has destabilized 

channels. Particularly important issues for channel and gully erosion often include altered runoff, woody debris, and surface conditions.

In some cases, the weather conditions that provoke erosion may not have occurred 

recently enough to provide evidence of potential changes. Most channel changes occur 

during large floods, so conclusions will be weak if a geomorphically significant flood 

has not occurred in the past decade or so. Similarly, if the combination of disturbances 

and fuel treatment prescriptions are unprecedented for an area, evidence from past landscape behavior provides a weaker conclusion than it would had analogous conditions 

existed in the past.

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 117

Landsliding

Analysis of shallow landsliding requires special care because

1. such landslides often occur at sites where no evidence of previous destabilization is 

visible,

2. significant landsliding often occurs only with major storms,

3. the areal density of landslides is usually low even after landslide-generating storms, 

4. even a few landslides can cause major impacts in downstream channels, and

5. the process is often of great public concern because it is frequently the most visible 

erosion process associated with land management activities.

Shallow landslides associated with forest management usually occur because management activities modify conditions at previously stable sites, destabilizing them. 

Consequently, site inspections cannot reliably reveal whether specific sites will become 

unstable after activities occur. The diagnosis instead must be made by identifying the 

site types present at the proposed activity site, assessing the inherent susceptibility of 

those site types to landsliding, and determining whether the proposed activities will 

increase that susceptibility. This strategy is essentially the same as that described for 

assessing susceptibility to channel-bank and gully erosion.

Shallow landsliding is generally associated with particular landscape features such 

as inner gorges and steep hillslope swales. Such associations simplify the analysis by 

allowing efficient stratification of the landscape into landslide-prone and stable areas. 

Analysis is also simplified because, in contrast to gullying and channel erosion, large 

slides are often visible on aerial photographs. Analysis usually begins with a broadscale, air-photo-based evaluation of landslide distribution across the landscape using 

photos that pre-and post-date a major landslide-generating storm. Associations between 

landslide distribution and landform are first evaluated, then areal landslide densities are 

calculated for each landform type in areas that had undergone different types or ages 

of management activities at the time of the storm. Comparison between these values 

for different management activities provides estimates of the relative influence of the 

activities on landsliding for particular landforms.

In the hypothetical example shown in table 3, recent logging is associated with an 

overall landslide frequency 2.5 times that of unlogged areas, and most of the increase 

results from destabilization of headwater swales. Data for the same 1994 to 1997 storms 

for older logging suggest that the older sites are largely restabilized, showing only a 

22 percent increase relative to unlogged sites. In most locales, the area of remaining old 

growth forest is too small to allow comparison between unlogged and logged areas, so 

changes relative to naturally occurring rates cannot be directly calculated. In such cases, 

definition of the recovery trend as a function of disturbance age can provide an estimate 

of the minimum change likely, or a simple comparison of rates in older and younger stands (such as the comparison between less than 15-year stands and greater than 

15-year stands in table 3) might indicate a minimum likely change if management practices did not differ greatly between the periods.

Susceptibility to shallow sliding can be strongly influenced by hydrologic changes, 

and such changes can be generated by activities occurring upslope from potentially 

unstable sites. For example, concentration of road drainage onto a hillside can trigger 

failures downslope. It may thus be useful to test for relationships between downslope 

landslide frequencies and upslope activities.

Human activities can also influence characteristic landslide size, and landslides of 

different sizes often have different effects on impacted resources. If management activities increase landslide frequency and decrease landslide size, for example, biological 

responses may be important due to the altered spatial and temporal distribution of impacts even if the average rate of sediment input is unchanged (Chapter 12).

Once the association of landslides with particular landforms is defined and the 

relative susceptibility of those landforms to destabilization is understood, the project 

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
118 USDA Forest Service RMRS-GTR-231. 2010.

area—and areas downslope—can be examined for presence of the types of landforms 

found to be most important. The change in susceptibility can be estimated as the ratio 

between rates per unit area of the given landform on forested and treated sites (for 

example, table 3). The level of concern would be particularly high if the landforms of 

interest already show evidence of destabilization.

Examination of sites that have undergone analogous treatments is primarily intended 

to evaluate the types of influences the planned activities may have on controlling variables. Rarely would the sample area be large enough, and the storm history suitable 

enough, that influences on landslide frequency could be directly estimated on the basis 

of a site examination.

As with shallow landsliding, it is useful to begin an analysis of deep-seated landsliding with a broad-scale air-photo survey to identify patterns in the distribution of 

the process. If deep-seated slides are not already present in settings with bedrock and 

topography similar to those at the project site, they are not likely to be of concern unless 

significant earthwork is planned.

If deep-seated slumps and earthflows are present in similar settings, the broad-scale 

survey can be used to detect patterns in their activity levels. In particular, evidence can 

be sought to determine whether existing features can be reactivated or accelerated by 

management activities occurring on or upslope of the features. Remobilization of a 

dormant slump might be recognized by opening of new tension cracks at the base of the 

headscarp or by increased rates of shallow sliding from the toe. Temporal variations in 

activity level for earthflows can often be detected by using sequential aerial photographs 

to track the displacement of surficial features such as trees or roads.

The project site itself is then examined to determine whether deep-seated slumps 

or earthflows are present and evaluate their current activity levels. If either active or 

dormant features are present, activities that increase water inputs to the features would 

tend to increase their activity level. Evaluation of deep-seated features must usually be 

qualitative rather than quantitative.

Table 3. Hypothetical example of a rate calculation for shallow landsliding

Area of landform Number of slidesa Rate Ratio to Ratio to

Landform (ha) 1994-97 (slides/km2) unlogged >15 yr logging

Unlogged

Planar slope 1900 3 0.16 1 0.83

Headwater swale 210 2 0.95 1 0.69

Inner gorge 430 4 0.93 1 0.62

Other b 450 1 0.22 1 --

Total 2990 10 0.33 1 0.82

Logged within 15 years

Planar slope 6300 19 0.30 1.91 1.59

Headwater swale 510 23 4.51 4.74 3.27

Inner gorge 1410 36 2.55 2.74 1.69

Other b 1510 3 0.20 0.89 --

Total 9730 81 0.83 2.49 2.04

Logged before 15 years ago

Planar slope 3700 7 0.19 1.20 1

Headwater swale 290 4 1.38 1.45 1

Inner gorge 730 11 1.51 1.62 1

Other b 680 0 0 0 --

Total 5400 22 0.41 1.22 1

Grand total 18120 113

a Only slides greater than 100 m2 are tabulated to provide uniform resolution in different vegetation types. b “Other” includes inherently stable sites such as ridge-tops and floodplains.

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 119

Evaluating Cumulative Impacts

The preceding sections focused on understanding and evaluating the influences 

of fuel treatments on the distribution and rates of channel erosion and mass-wasting 

processes. Such analyses can provide estimates of the extent to which management 

activities might increase the erosion risk. However, increased erosion is of concern only 

if an increased risk of erosion is accompanied by an increased hazard to a resource or 

entity of concern. It is at this point that evaluation of the cumulative impacts of altered 

erosion becomes necessary.

From the point of view of an impacted resource, the effects of a land use activity on 

individual processes are not nearly as important as the overall effect of changes caused 

by the full distribution of activities through time and across the landscape. These cumulative effects are important to understand in two respects. First, the combined influences 

on a particular process must be understood if the net change in process rate is to be 

evaluated. For example, rates of shallow landsliding might increase because of both decreased rainfall interception and decreased root cohesion after canopy thinning. Second, 

the combined effects of all influences on a potentially impacted resource must be understood if the actual severity of the impact is to be evaluated. For example, increased 

flood damage caused by heightened rain-on-snow runoff may be further augmented by 

reduced channel conveyance due to landslide-related aggradation.

The Council on Environmental Quality (CEQ) has provided guidance (CEQ 1997) 

for preparation of cumulative impact analyses for documents prepared under the 

National Environmental Policy Act (NEPA), and federal courts have clarified standards 

for analysis through their opinions on cases involving such analyses (Chapter 14). Both 

the CEQ and the courts indicate that analysis is intended to evaluate the net impacts on 

particular resources. Consequently, a cumulative impact analysis for a fuel treatment 

project would need to assess the extent to which erosion rates influenced by the project 

might affect the nature and severity of impacts on specific resources.

The CEQ (1997) describes the analytical steps useful for cumulative impact analysis 

(table 1, Chapter 14), and these are readily applied to analysis for cumulative impacts 

associated with channel erosion and mass wasting. The procedure first defines impacted 

resources of potential concern in the area, as well as the resources, values, or issues of 

importance in the area that may not yet show impacts (step 1). Issues that might necessitate evaluation of erosion processes could include concerns over salmonid populations, 

downstream flooding, water quality, reservoir sedimentation, or any other impact that 

can be affected by altered sediment load or channel form.

For each entity of concern, the mechanisms through which impacts might occur are 

then identified. Potential interactions between impacts and sediment load may begin to 

become evident at this stage, though identified mechanisms need not directly involve 

erosion processes. Because the analysis is of cumulative effects, the broader context in 

which sediment-related influences occur must be evaluated. In the case of concerns over 

increased downstream flooding, for example, potential mechanisms of interest that are 

not directly related to a project’s sediment inputs might include increased peakflows, 

reduced channel conveyance due to vegetation encroachment, changes in reservoir 

management strategies due to increased irrigation demands, and increased residential 

development on floodplains. Sediment-related mechanisms could include reservoir sedimentation and reduced channel conveyance due to aggradation.

An understanding of the distribution of the resources of interest and of the nature of 

relevant impact mechanisms then allows definition of the spatial and temporal scales 

needed to analyze impacts on each resource (steps 2 and 3). Because different impacts 

are expressed at different sites and over different time scales, analysis scales will differ 

for each kind of impact, and sometimes for each impact mechanism. For example, most 

influences on flood hazard need to be evaluated over the watershed upstream of sites 

susceptible to flooding, but prediction of the contribution of changes in reservoir management strategy to flood hazard requires consideration of socio-economic influences 

over a much broader scale.

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
120 USDA Forest Service RMRS-GTR-231. 2010.

At this point, a general overview is useful of the types of activities that have occurred 

in each relevant analysis area and that may affect the resources of concern (step 4). 

Evaluation of the nature and timing of past changes is facilitated if the distribution and 

timing of past agents of change are known. An assessment of cumulative impacts on 

flood hazard, for example, might evaluate the history of vegetation change in the upstream watershed and assess the timing and distribution of activities that can influence 

rates of sediment production.

Examination of recent legal opinions suggests that defining the significance of environmental changes is particularly challenging (Chapter 14), and the next analysis steps 

outline a strategy for addressing this problem. First, the types of coping strategies or 

responses to each potential impact are described for each resource (step 5). This information provides a basis for evaluating how much of a change is tolerable before 

a resource becomes impaired. Impacts on some issues of concern, such as municipal 

water supplies or transportation infrastructure, can be assigned economic values. In 

other cases, regulations may have established particular thresholds of significance. At 

this stage, examination of natural disturbance patterns can be very useful. Many resources of concern (such as endangered species) developed in the context of the spatial 

and temporal variations in conditions that occurred before Euro-American settlement. 

For these, deviations from the natural patterns define the levels of stress currently experienced (step 6). In some cases, attempts have been made to place current conditions 

in the context of very-long-term averages for sediment inputs obtained by cosmogenic 

isotope work. However, if the “range of natural variability” is found to have included 

an extreme sediment-generating event 2,000 years ago, that event did not occur in the 

context of the other changes that are present today. If such major events are found to 

have occurred naturally, the impact assessment would need to evaluate the cumulative 

effect of the modern land use activities on the ability of impacted resources to recover 

from such an event.

The CEQ then suggests that baseline conditions be described (step 7), and explains 

that “the baseline condition of the resource of concern should include a description 

of how conditions have changed over time and how they are likely to change in the 

future without the proposed action” (CEQ 1997, p. 41). In this context, establishing the 

baseline requires description of the pre-Euro-American conditions, comparison of those 

to today’s conditions, and description of the current trajectory of conditions. Of these 

tasks, description of the pre-Euro-American conditions is usually the most challenging 

because undisturbed conditions are rarely available for comparison. Instead, those conditions generally must be inferred from (1) observation of sites with relatively undisturbed 

conditions, (2) an understanding of the history of change in an area (step 4 above), and 

(3) historical evidence, including old snapshots, early aerial photographs, oral histories, 

and so on. For the flood hazard example, baseline conditions would be established for 

flood frequencies at susceptible sites as well as for the conditions influencing those 

frequencies. Baseline channel conveyance, for example, might be established by using 

historical aerial photographs to evaluate changes in channel form and bank vegetation, 

and old surveyed cross sections may be available from bridge construction sites.

At step 8, the cause-and-effect relations between human activities and impacts are 

identified. For increased flooding, anthropogenic effects on peakflows and channel conveyance would be evaluated at this stage. Most impacts are influenced by a variety of 

mechanisms, many of which do not involve sediment production. Anthropogenic effects 

on channel conveyance, for example, might include vegetation management on channel 

banks or construction of levees.

Past and on-going land use activities would then be evaluated to determine the extent 

to which they influence conditions that affect impact levels. The existing cumulative 

impact on a resource is the overall impairment caused by the combined mechanisms 

(step 9). At this stage, the potential influences of a proposed activity would be examined 

to determine whether they could contribute to the identified impacts. The first eight 

analysis steps outlined potential impact mechanisms relevant to the particular setting, 

thus narrowing the scope of the portion of the analysis relating specifically to erosion 

processes. It now becomes possible to match the potential changes likely to be associated 

Chapter 6. Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting
USDA Forest Service RMRS-GTR-231. 2010. 121

with altered erosion (for example, column 5 in table 1) with the types of changes relevant to the impacts of concern. Many potential influences would be discarded at this 

stage if they are found not to be relevant in the particular system being evaluated.

To evaluate impacts associated with erosion processes, the proposed activities would 

first be analyzed to identify their potential influences on particular processes (table 2). 

Each of the impact mechanisms identified for flood hazard, for example, could then 

be evaluated to determine whether the potential influences from the relevant erosion 

processes (table 1, column 5) can affect the impact mechanism. For example, a project 

involving road construction for salvage logging in steep terrain might be expected to 

generate shallow landsliding (table 2), which could contribute to aggradation (table 1). 

If analysis has suggested that reduced channel conveyance is of concern, for example, potential changes in aggradation could contribute to a cumulative impact on flood 

hazard.

The final steps outlined by the CEQ allow for use of the analysis to redesign or mitigate the project (step 10) and for monitoring and modification of the project after it is 

implemented (step 11). The preceding analysis steps provide much of the information 

needed to design efficient and effective mitigations and monitoring projects.

Impact analysis under NEPA also requires analysis of the cumulative impacts associated with the “no action” alternative. In the case of salvage activities, such analysis 

would ordinarily consider impacts of the disturbance event and any rehabilitation work 

associated with the event. Analysis of the project’s effects on channel erosion and mass 

wasting would need to address how changes from the project would modify the effects of the event on those processes in the absence of the project. At some sites, for 

example, woody debris contributed to small streams by a fire might trap large volumes 

of sediment eroded from burned slopes, and salvage of the wood could increase the 

downstream sediment flux relative to the effect of the fire alone. In addition, if EuroAmerican management practices influenced the extent or character of the infestation 

or fire, some aspects of the initial disturbance are themselves anthropogenic, and those 

influences would need to be evaluated as a component of cumulative impacts.

Analysis of the role of fuel treatment projects in cumulative impact generation will 

also be required during impact evaluation for future projects of other kinds. At that time, 

the erosional consequences of past fuel treatment projects—even if carried out under 

categorical exclusions under NEPA—would need to be evaluated since they will have 

become “past projects” that provide the context for newly planned projects.

Cumulative impact analysis is necessarily an interdisciplinary exercise. Here we 

consider effects on mass-wasting and channel erosion processes, but similar analyses 

would be carried out for effects on hydrology, vegetation, wildlife, and so on. In the 

real world, all of these influences interact. As analysis proceeds for each of these environmental components, linkages between components are identified and incorporated 

into the analysis. For example, when likely hydrological changes are identified, their 

influences on erosion processes can be evaluated. Influences on the impact mechanisms 

from other previous and potential future activities would also be analyzed using a similar approach. In particular, implications of the combined influence of past and proposed 

activities in prolonging the duration and spatial extent of the impacts would need to 

be considered. Interdisciplinary analysis is also important because a change in erosion 

rate is of interest in cumulative impact analysis only insofar as it influences an impact 

of concern, so evaluation of the significance of erosional changes may require an understanding of fisheries biology, riparian ecology, structural engineering, or any of a 

number of other fields.

As in many areas of human endeavor, forest management decisions must be made 

even though knowledge of the likely outcomes of those decisions is incomplete. Even if 

knowledge of erosion processes were perfect, precise outcomes could not be predicted 

because future weather conditions are unknown. The challenge for cumulative impact 

analysts is to use knowledge from a broad range of disciplines as effectively as possible 

to allow adequately informed decision-making.

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
122 USDA Forest Service RMRS-GTR-231. 2010.

Conclusions

The broad range of potential fuel treatment practices can influence channel erosion 

and mass-wasting processes in a variety of ways, so the erosional outcome from a particular project depends strongly on the nature and setting of the project. Thus, each 

application must be evaluated in its own right to assess potential impacts. Even though 

the effects of particular fuel treatment activities on erosion rates have not been widely 

studied, information from a variety of other studies is applicable to the problem if the 

factors controlling the distribution and rates of erosion processes are understood and 

the effects of particular fuel treatment practices on those factors can be determined. 

In general, fuel treatment activities that modify soil conditions, hydrologic conditions, 

vegetation, or hillslope or channel morphology are likely to influence the rates and distribution of channel erosion and mass-wasting processes.

If the resulting influences adversely affect an entity that is experiencing impacts from 

other sources as well, the fuel treatment project will have contributed to the cumulative 

impact on that entity. If the relevant impact mechanisms are understood, the potential 

effect of erosion from a planned fuel treatment project on the cumulative impact can be 

evaluated by determining the extent to which the types of erosion that are likely to be 

associated with the project will influence those impact mechanisms.

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Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
126 USDA Forest Service RMRS-GTR-231. 2010.

Chapter 7.

Fuel Management and Water Yield

Charles A. Troendle, METI Corporation, Fort Collins, CO

Lee H. MacDonald, Watershed Science Program, Colorado State University, Fort Collins, CO

Charles H. Luce, Rocky Mountain Research Station, USDA Forest Service, Boise, ID

I.J. Larsen, Department of Earth and Space Sciences, University of Washington, 

Seattle, WA

Introduction

There have been numerous studies worldwide demonstrating that changes in forest 

density can cause a change in water yield. Bosch and Hewlett (1982), Hibbert (1967), 

Stednick (1996) and Troendle and Leaf (1980) have summarized the findings from most 

of these studies. In general, as Hibbert (1967) observed, reducing forest cover increases 

water yield; establishing forest cover on sparsely vegetated land decreases water yield; 

and response to treatment is highly variable and, for the most part, unpredictable.

Although the first two of these conclusions are still accepted, the hydrologic response to changes in forest cover, although variable, is more predictable than Hibbert 

(1967) concluded (Bosch and Hewlett 1982; Stednick 1996; Troendle and Leaf 1980). 

This change in thinking results from the increased number of observations available 

with each successive review and an improved understanding of the factors influencing streamflow response. Streamflow response to a change in forest cover is strongly 

related to climate, species composition, and the percentage change in vegetation density (fig. 1). The data from 95 watershed experiments conducted in the United States 

show that, on average, annual runoff increases by nearly 2.5 mm for each 1 percent of 

watershed area harvested (Stednick 1996). Because runoff is quite variable from year 

Figure 1. The relationship between 

reduction in vegetation cover 

and increases in stream flow for 

three vegetation types (redrawn 

from Bosch and Hewlett 1982).

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
USDA Forest Service RMRS-GTR-231. 2010. 127

to year, the general conclusion is that approximately 20 percent of the basal area of the 

vegetation must be removed before a statistically significant change in annual runoff 

can be detected (Bosch and Hewlett 1982; Hibbert 1967; Stednick 1996). However, as 

Bosch and Hewlett (1982) suggest, reductions in forest cover of less than 20 percent 

(fig. 1), particularly in more humid areas, may well produce statistically non-significant 

increases in streamflow that would presumably decrease to zero increase in streamflow 

at zero reduction in forest cover.

Much of our understanding about the effects of forest disturbance on water yield has 

come from paired watershed experiments. Unfortunately, very few of these catchmentscale experiments provide data on the hydrologic response to fuel reduction since the 

vast majority of the treatments imposed a partial or complete clearcutting of the mature 

trees rather than a partial cut or thinning (Stednick 1996). Hence, much of our understanding of the hydrologic impacts of thinning and prescribed fire comes from inference 

supported by various plot and process studies.

Objectives

This chapter has three objectives pertaining to the effects of fuel management on 

water yield:

1. Determine whether regionalization can help reduce the variability in treatment 

response that made streamflow change unpredictable according to Hibbert (1967).

2. Assess the effect of forest disturbance on each component of the water balance—

interception and evaporation, transpiration, infiltration, and storage—and use this to 

help infer how fuel reduction treatments may impact annual water yields as well as 

peak and low flows.

3. Identify tools that can help hydrologists and land managers predict both the on-site 

and cumulative changes in water yield that may result from vegetative treatments.

Hydrologic Impact of Forest Disturbance on 

Streamflow Characteristics

Regionalization of Hydrologic Response

The hydrologic cycle represents the processes and pathways involved in the circulation of water from land and water bodies to the atmosphere and back again. An 

understanding of the hydrologic cycle is fundamental to understanding the effects of different forest practices on key components of the water balance, including soil moisture 

and streamflow. The hydrologic cycle is often expressed in the form of a water balance 

or continuity equation:

Runoff = Precipitation – (Evaporation + Transpiration Loss + Change in Storage) (1)

Precipitation can be in the form of rainfall, snowmelt, or fog drip; evaporation includes 

evaporation from both the soil and the surface of plant canopy and litter (interception 

loss); and change in storage includes soil moisture and groundwater. Evaporation and 

transpiration are usually regarded as losses and reduce the amount of precipitation that 

is transformed into runoff. Changes in storage can be very important over short time 

periods (in other words, seasonal or less than 1 year), but are generally assumed to be 

zero over long periods unless there is continuing groundwater extraction.

Although the components of the hydrologic cycle are always the same, the relative importance of each component can vary considerably with geographical location 

and from season to season. The complex interactions between climate and vegetation 

C.A. Troendle, L.H. MacDonald, C.H. Luce, I.J. Larsen Cumulative Watershed Effects of Fuel Management in the Western United States
128 USDA Forest Service RMRS-GTR-231. 2010.

control the role that the individual components play in the water balance and the influence that forest disturbance has on the water balance.

In the mid-1970s, Bailey (1976, revised 1994) developed an ecoregion map of the 

United States that depicted the relationship between vegetation patterns, climate, and 

landscape or topography (fig. 2). Vegetation types with similar moisture and energy 

requirements were found to be present in reoccurring patterns within and between ecoregions for given site conditions. Differences in vegetation patterns between ecoregions 

were primarily influenced by differences in the amount and seasonal distribution of 

water and energy. Precipitation and energy are largely controlled by elevation, latitude, 

aspect, topography, prevailing wind direction, and proximity to oceans, and the balance 

between precipitation and energy are the primary controls on streamflow. The concepts 

used in developing the ecoregion classification for the United States (Bailey 1976) have 

been successfully applied to North America (Bailey and Cushwa 1981) and the rest 

of the world (Bailey 1998). Ecoregion classification provides a useful framework for 

stratifying hydrologic response and predicting the effects of vegetation manipulation 

on water yield.

In the late 1970s, the ecoregion concept (Bailey 1976) was used to stratify the United 

States into seven hydrologic regions (fig. 3) in order to better predict the effects of 

silvicultural activities on non-point source pollution (EPA 1980). The resulting handbook, An Approach to Water Resources Evaluation of Non-Point Silvicultural Sources, 

is commonly referred to as WRENSS. This contained graphical procedures, stratified by 

region, to predict the effects of forest disturbance on streamflow, erosion, temperature, 

and nutrients. The same hydrologic regionalization is being used here to help understand and predict the effects of forest disturbance, including fuel reduction treatments, 

on annual water yield, peak flows, and low flows.

This chapter will emphasize the hydrologic effects of fuel reduction treatments 

in the Rocky Mountain region (WRENSS Hydrologic Region 4 in fig. 3) for the following reasons. First, this synthesis focuses on the western United States. Second, 

more than 50 percent of all National Forest System lands are contained within the 

Rocky Mountain region, and excessive fuel loadings and departures from historical 

ecological conditions are particularly severe (Romme and others 2003). These factors 

mean that fuel reduction programs are most likely to be concentrated in this region. 

Figure 2. Ecoregion classification 

based on Bailey (1994).

Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 129

Figure 3.The United States divided 

into seven hydrologic regions 

(see Troendle and Leaf 1980).

In addition, the hydrologic effects of fuel treatments are potentially more important 

in this region because possible changes in water yield may be more important and 

longer-lived than in other regions. From a process standpoint, the Rocky Mountain 

region provides examples of how vegetation management strongly influences snowpack accumulation and melt as well as summer evaporation and transpiration. This 

means that the processes being discussed here will cover the key processes for nearly 

all forested areas in the United States, even though the relative magnitude will vary 

by region. This chapter first discusses and explains the observed variations in the 

hydrologic responses to forest disturbance in the Rocky Mountain region, uses these 

observations to predict the likely effects on fuel reduction treatments, and then compares these responses to the potential hydrologic responses that may occur in other 

ecoregions in the western United States.

Water Yield

Numerous publications have quantified the effects of forest disturbance on streamflow in different regions of the United States (for example, Brown and others 1974; 

Debano and others 2004; Douglas 1983; Gary 1975; Harr 1983; Hornbeck and others 1997; Kattleman and Ice 2004; Keppeler and Zeimer 1990; NRC 2008; Reinhart 

and others 1964; Troendle and Leaf 1980; Troendle 1983). These studies have shown 

that the magnitude of change in water yield is most strongly related to the amount 

of precipitation and the proportion of forest cover that is removed. The increases in 

flow following forest disturbance can be quite large in the humid southeast, northeast, 

north central, and northwest regions of the United States. In contrast, increases in water yield due to removing woody vegetation are an order of magnitude smaller in drier 

areas such as the Southwest. The effect of a decrease in forest density on water yield 

can occur regardless of whether this is due to disturbance from fire, insects, disease, 

or timber harvest. Afforestation or an increase in forest density generally has the opposite effect on water yield than does forest removal.

The magnitude of the hydrologic response to disturbance between years will depend on the summed effect of the changes in processes as indicated by equation 1. 

These include the degree to which the management activity alters net precipitation 

to the soil by altering interception losses and infiltration characteristics and the soil 

moisture evaporation and transpiration. The timing of a change in streamflow within a 

year depends on when precipitation or snowmelt exceeds both evapotranspiration demand and soil moisture recharge requirements. Hence, any effort to predict the effect 

of forest disturbance on water yield requires an understanding of how the disturbance 

affects the water balance with respect to the amount and timing of precipitation inputs 

(whether there are changes in flow pathways) and the degree to which soil moisture 

C.A. Troendle, L.H. MacDonald, C.H. Luce, I.J. Larsen Cumulative Watershed Effects of Fuel Management in the Western United States
130 USDA Forest Service RMRS-GTR-231. 2010.

storage and recharge requirements have been altered as a result of changes in evaporation and transpiration.

Rocky Mountain Region

The Rocky Mountain region is fortunate to have a long series of carefully controlled 

paired watershed experiments to evaluate the effects of forest harvest on water yield. 

Worldwide, the first such experiment was conducted at Wagon Wheel Gap in southcentral Colorado on the headwaters of the Colorado River (Bates and Henry 1928; 

Troendle and King 1987; Van Haveren 1988). This study was followed by a series of 

watershed studies in the region (Hoover and Leaf 1967; Stednick and Troendle 2004; 

Troendle and King 1985, 1987; Troendle and Leaf 1981), but the longest running and 

most detailed study has been conducted on the Fool Creek watershed on the Fraser 

Experimental Forest in central Colorado (Hoover and Leaf 1967; Troendle and King 

1985).

The results of the Fool Creek study are presented in more detail because this is 

the longest and most comprehensive study in the Rocky Mountain region, and the 

process-based understanding developed at Fool Creek applies throughout the snowmelt 

dominated Rocky Mountain region. Mean annual precipitation at Fool Creek is about 

760 mm per year while annual evapotranspiration ranges from 450 to 570 mm per year 

(Troendle and King 1985). At a nearby study site, the average annual evapotranspiration (ET) is directly proportional to precipitation once precipitation exceeds 462 mm 

(18.2 inches) (Troendle and Reuss 1997).This relationship can be expressed by:

ETmm = 462mm + 0.284 (Precipitationmm – 462mm) (2)

Annual water yields from the Fool Creek watershed were calibrated against East St. 

Louis Creek for a 15-year period. From 1954 to 1956, approximately 40 percent of the 

Fool Creek watershed, or 50 percent on the commercially forested area, was clearcut 

in alternating cut and leave strips. Comparison of the mean annual hydrographs for the 

15-year calibration period and the first 15 years after harvest clearly shows that, on 

average, forest harvest increased both annual and peak flows (fig. 4). Numerous other 

studies have shown that the changes in runoff shown in figure 4 are typical of the effect 

of forest disturbance in the cold snowmelt region typical of the Rocky Mountains (Bates 

Figure 4.The average 

hydrograph from the Fool 

Creek Watershed for the 

15-year period both before 

and after treatment.

Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 131

and Henry 1928; Swanson and Hillman 1977; Swanson and others 1986; Troendle and 

Bevenger 1996; Troendle and King 1987; Troendle and Reuss 1997).

Within the first 15 post-treatment years, the observed increases in annual water yield 

have ranged from a high of 16.2 cm in the wettest year to a low of 3.6 cm in the driest 

year. The “average” first-year response to the treatment on Fool Creek was equivalent 

to a 10.0 cm increase in seasonal water yield (Troendle and King 1985). During the 

1956 to 1983 post treatment period, on average, these increases are due to the 50 percent reduction in the annual ET that would have occurred on the clearcut portion of the 

watershed (Troendle and King 1985; Troendle and Reuss 1997). By 1983, 28 years after 

harvest, regrowth in the clearcuts was causing a significant decline in the average annual 

water yields.

A month-by-month analysis showed that significant increases in flow occurred primarily in May with only an occasionally significant increase in June. No detectable 

impact has been documented on flows from July to October (Troendle and King 1985). 

There is little opportunity for measurable increases in water yield to occur during most 

of the growing season because summer evapotranspiration is limited by the amount 

of available water. The high summer water deficit explains why, on average, less than 

5 percent of summer rainfall is transformed into streamflow (Bevenger and Troendle 

1987; Garstka and others 1958; Troendle and King 1985) and the reduction in summer 

evapotranspiration does not detectably increase summer or fall streamflow.

The observed changes in the cold snow zone’s water yield after forest removal are 

due to both a decrease in winter interception and a reduction in growing season soil 

moisture depletion (Dietrich and Meiman 1974; Goodell and Wilm 1955; Potts 1984b; 

Troendle 1987, 1988; Troendle and Meiman 1986; Troendle and Reuss 1997; Wilm and 

Dunford 1948). In the cold snow zone, such as at Fool Creek, precipitation accumulates 

over the winter as snow pack, with minimal melt over this accumulation period. When 

the snowpack begins to melt in spring, the melt water first recharges the soil by replacing the water that was depleted during the previous growing season. Once soil moisture 

storage is filled, the excess meltwater is available to become streamflow. At Fool Creek, 

which is comprised mostly of east- and west-facing slopes, approximately 30 percent of 

the increase in water yield can be attributed to the decrease in interception and resultant 

increase in the amount of water contained in the snowpack. The reduced evapotranspiration during the previous summer also reduces the amount of meltwater needed for soil 

moisture recharge in the clearcut. This process accounts for approximately 50 percent 

of the increase in water yield. The remaining 20 percent of the observed increase in 

water yield results from the reduction in evapotranspiration losses during April and May 

(Troendle and King 1985).

On north-facing slopes, the reduction in winter interception losses can account for 

more than 50 percent of the increase in annual water yield after forest harvest (Troendle 

and King 1987; Troendle and Meiman 1986). In contrast, on south-facing slopes, the 

reduction in winter interception may account for only 20 percent of the observed change 

in annual water yield. This difference in the role of winter interception is because the 

snow remains in the canopy almost continuously from November to May on northfacing slopes. The tremendous surface area of exposed snow allows a great deal of 

evaporative loss to occur despite the lower incoming solar radiation compared to southfacing slopes, and this can be attributed to the low relative humidity and relatively 

strong vapor pressure deficit. On south-facing slopes, the forest canopy is less dense and 

intercepts less snow, and the intercepted snow is more likely to melt and fall out of the 

canopy, thus allowing less time for interception losses to occur. Surprisingly, the 13- to 

19-cm change in summer evapotranspiration appears to be independent of aspect and 

varies primarily with the amount of annual precipitation (Troendle 1987, 1988).

A similar hydrologic response to Fool Creek has been documented following forest 

harvest for other watershed studies in the Rocky Mountain region, and these include 

Wagon Wheel Gap in south-central Colorado (Bates and Henry 1928), Dead Horse 

Creek in central Colorado (Troendle and King 1987), Coon Creek in southern Wyoming 

(Troendle and others 2001), thinning in South Dakota (Anderson 1980), tree mortality 

due to insect attacks in northwestern Colorado (Love 1955), beetle kill in southwestern 

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132 USDA Forest Service RMRS-GTR-231. 2010.

Montana (Potts, 1984a), and wildfire in northern Wyoming (Troendle and Bevenger 

1996). It should be noted that the forest cover at Wagon Wheel Gap was predominantly 

aspen as compared to mostly conifers in all of the other watersheds.

At lower elevations in the Rockies, there is less snow, summers are hotter and drier, 

and the dominant tree species are ponderosa pine and Douglas-fir. The fire regimes in 

the ponderosa pine and mixed Douglas-fir/ponderosa pine forests have been severely 

affected by fire suppression. It is within these forest types that most of the thinning 

and prescribed fire treatments are being proposed or taking place. A comparison of the 

potential water yield changes from these sites to the more extensively studied changes 

in the cold snow zone helps illustrate the magnitude and causes of the variations that 

confounded Hibbert in 1967.

Studies in southwestern Idaho indicate that forest harvest causes smaller and less 

persistent increases in annual water yields than at Fool Creek. The observed changes in 

water yield are strongly influenced by aspect. At Boise Basin, 42 percent of the area was 

logged or burned in 1929 and 1930. Ten years later the increase in annual water yield 

was only 7.6 mm (Rosa 1961). At Silver Creek, 23 percent of the basin was clearcut, 

primarily on south-facing slopes, and there was no detectable increase in water yield. 

In contrast, a clearcut and prescribed fire on a nearby 1-ha catchment with a northerly 

aspect doubled the subsurface flow during spring runoff. This doubling in runoff was 

due to a 5- to 8-cm decrease in on-site evapotranspiration. As in the cold snow zone, 

these increases in water yield were smaller when there was less precipitation and greater 

energy input. These results indicate that the general lessons learned from the cold snow 

zone apply to lower elevation sites in the Rocky Mountain region, but the predicted 

increases in water yield from lower elevations must take into account the lower precipitation and greater differences by aspect.

Equation 1 and the results from the Rocky Mountain region show that the increased 

runoff after forest disturbance is the integrated response to the amount and timing 

of precipitation and snowmelt inputs, soil moisture recharge requirements, and the 

evapotranspirational demands at the time of soil moisture recharge. In the humid, raindominated regions in the eastern United States, the maximum increases in flow can be 

as much as 300 or 400 mm per year following clearcutting (Hornbeck and others 1997; 

Stednick 1996). Unlike the cold snow zone, these increases in streamflow often occur 

in the late summer and early fall because that is when precipitation begins to exceed 

the reduced amount of soil moisture recharge in the harvested areas. Once soil moisture recharge is satisfied in the harvested and unharvested areas, the only difference in 

winter water yield and peak discharges will be due to the difference in rainfall interception losses between the harvested and unharvested areas. In the snow-dominated areas, 

the timing of the water yield increase would include a spring component similar to the 

Rocky Mountain region, although there would also be an increase in growing season 

flows if there is sufficient precipitation. Overall, the magnitude of the changes in annual 

water yield do not differ greatly between the Northeast (Hydrologic Region 1, fig. 3) 

and the Rocky Mountain region (Hydrologic Region 4, fig. 3) for a similar reduction in 

basal area. However, the increases in water yield tend to be less persistent because of 

the relatively rapid vegetative regrowth after forest harvest, and some long-term studies 

indicate a decrease in summer and annual streamflow 25 to 35 years after harvest. A 

plot of the data from the Northeast also suggests that a detectable change in water yield 

can occur after removing only 10 to 12 percent of the basal area (Hornbeck and others 

1997), and this can be attributed to the wetter conditions during the summer growing 

season.

The effect of timber harvest on water yield from the “warm” snow and rain-on-snow 

zones of the Cascades of Oregon and Washington (Hydrologic Region 5, fig. 3) and the 

Sierra Nevada of California (Hydrologic Region 7, fig. 3) have both similarities and 

differences in response compared to that of the cold snow zone of the Rocky Mountain 

region (Kattleman and Ice 2004; Rice and others 2004). Snowpacks are generally at 

or near 0 o

C, so snowmelt can occur during the winter and precipitation can occur as 

snow, rain, or a mixture of snow and rain at any time throughout the winter. Nearly all 

forests are coniferous, so winter interception losses are higher than in the deciduous 

Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 133

forests of the east, but less than the interception losses in the cold snow zone in the 

Rocky Mountain region because the snow rapidly melts out of the canopy in all but the 

highest elevation zones. Forest harvest in areas with high annual precipitation and high 

soil moisture storage capacity can cause a greater reduction in summer evapotranspiration than in the cold snow zone forests like Fool Creek, and this can lead to more soil 

moisture carryover relative to uncut sites. This difference in soil moisture carryover can 

lead to larger increases in annual water yields, such as in the first-year values of 300 to 

400 mm that have been observed from paired watershed studies in Oregon (Jones and 

Post 2004; Stednick 1996). As in the eastern United States, the relatively rapid regrowth 

means that the water yield increases due to forest harvest are typically eliminated in a 

much shorter time than at Fool Creek, and the rapid regrowth can lead to a decrease in 

summer and annual water yields within 1 to 3 decades after harvest.

Precipitation and Interception

Throughout much of the Rocky Mountain hydrologic region, the annual hydrograph 

is dominated by the melting of the winter snowpack. In snow dominated areas of the 

western United States, the amount of water present in the snowpack on 1 April can 

explain from 60 to 90 percent of the variation in annual runoff (Bevenger and Troendle 

1987; Garstka and others 1958; Troendle and King 1985). Overall, as much as 95 percent of the total annual streamflow in the cold snow zone originates as melting snow, 

while only 3 to 5 percent of the rainfall becomes stormflow. In contrast, up to 24 percent 

of the rainfall can be returned as stormflow in some of the more humid areas in the 

eastern United States, and this can approach 70 percent for some rainstorms under exceptionally wet antecedent conditions (Hewlett and others 1977; Woodruff and Hewlett 

1970).

In the cold snow zone of the Rocky Mountains, virtually any reduction in stand 

density will increase snowpack accumulation (for example, Gary and Troendle 1982; 

Haupt 1979; Meiman 1970, 1987; Packer1962; Troendle and Kaufmann 1987; Wilm 

and Dunford 1948). In the higher elevation lodgepole pine and spruce-fir forests, the 

increase in the snowpack on partially cut stands is directly proportional to the percent 

of basal area removed and the increases observed in clearcuts (Goodell 1952; Love 

1953; Troendle and Meiman 1984; Wilm and Dunford 1948). As noted previously, the 

increases in peak snow water equivalent in the cold snow zone after forest disturbance 

Figure 5. Percent of gross precipitation reaching the forest floor in the Central and Northern Rocky 

Mountains as stand density increases from 0 (opening) to 100-percent of the maximum basal area for 

the site (from Troendle and others 2003).

C.A. Troendle, L.H. MacDonald, C.H. Luce, I.J. Larsen Cumulative Watershed Effects of Fuel Management in the Western United States
134 USDA Forest Service RMRS-GTR-231. 2010.

are greatest on north-facing slopes and smallest on south-facing slopes. Increases on 

east- and west-facing slopes are intermediate (Troendle and others 2003, 2005; fig. 5). 

In drier ponderosa pine forests, a reduction in basal area did not detectably increase the 

snow water equivalent on south, east, and west aspects, but did substantially increase 

the snow water equivalent on north-facing slopes (Haupt 1979).

The amount of interception loss during and after individual snowfall events varies 

significantly with storm size, storm intensity, wind speed, and location (in the case of 

small clearings). In coniferous forests in the cold snow zone, one generally can expect that 25 to 35 percent of the winter snowpack will be intercepted and lost to the 

atmosphere by some combination of sublimation and evaporation. Timber harvest in a 

deciduous forest, such as an aspen forest, will also increase peak snow water equivalent, 

but the much smaller amount of canopy reduces winter interception losses to about 10 

to 12 percent. Process-based studies have shown that the observed increases in the winter snowpack after forest harvest result from the reduction in interception losses rather 

than a redistribution of snow during or after a storm event (Schmidt and Troendle 1989, 

1992; Troendle and King 1987).

The magnitude and significance of interception losses by forest vegetation to the 

overall water balance have been documented by Kittredge (1948), Coleman (1953), and 

others. Interception losses may account for 25 to 35 percent of the annual precipitation, 

depending on the amount, type, and intensity of precipitation and the type and density of 

forest vegetation. In the cold snow zone, the effect of a reduction in winter interception 

on water yield is particularly important because the storm-based changes in interception 

accumulate over the course of the winter and can represent a significant increase in water inputs during spring melt. The snow interception losses measured in the cold snow 

zone of the Rocky Mountain region are surprisingly consistent with values from other 

cold snow regions in the United States (Troendle and Leaf 1980). The increase in net 

precipitation resulting from forest removal is proportional to the reduction in stand density and can range up to 15 to 30 percent for individual storm events (Kittredge 1948). 

Soil Moisture and Summer Evapotranspiration

The effects of a change in stand density or leaf area index on summer evaporation, 

and especially transpiration, are not as linear as the changes in snowpack accumulation. 

Clearcutting in the Central Rocky Mountains reduces on-site soil moisture depletion 

by 13 to 19 cm during the growing season, regardless of aspect (Dietrich and Meiman 

1974; Troendle 1987, 1988; Troendle and Kaufman 1987; Troendle and Meiman 1984; 

Figure 6. Daily ET (soil water 

depletion) per unit of leaf area 

as a function of basal area (from 

Troendle 1987).

Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 135

Wilm and Dunford 1948). However, thinning can have very little effect on summer 

evapotranspiration rates as the residual trees can capture some or all of the savings in 

soil water by increasing water use (MacDonald 1986; Troendle 1987). The variations in 

the relationship between leaf area index and daily evapotranspiration (fig. 6) illustrates 

the ability of trees to adjust their water use in accordance with soil moisture availability 

as well as other factors. This means that the relationship between stand density and soil 

water depletion is statistically significant in wet years when there is less competition for 

soil water, while in dry years, there may be no correlation between basal area and soil 

water depletion because evapotranspiration from the residual stand may use all of the 

available water, regardless of the reduction in stand density (Troendle 1987). Hence, the 

potential for thinning to reduce summer transpiration and increase water yields depends 

on the amount of precipitation. If the sum of the water stored in the soil and summer 

precipitation exceeds potential evapotranspiration, thinning may increase the amount 

of water available for streamflow because of the reduction in summer evapotranspiration. If the sum of the stored water and summer precipitation are less than the potential 

evapotranspiration, any reduction in evapotranspiration due to thinning or forest harvest 

will be lost to evaporation from the soil and transpiration by the residual vegetation. If 

there is not a reduction in summer evapotranspiration there will not be any reduction in 

the amount of water needed for soil moisture recharge. In water limited systems, such 

as most of the Rocky Mountain hydrologic region, summer precipitation is low and soil 

water reserves are often depleted on all aspects and across a wide range of stand densities and forest types. Therefore, it is unlikely that most fuel reduction treatments will 

sufficiently decrease soil water depletion to cause an increase in annual water yields 

unless precipitation amounts exceed evaporative demand. In most areas, the only mechanism for fuel treatments to increase water yields is to (1) reduce interception losses 

and thereby increase rainfall runoff during the winter when soils are relatively wet or 

(2) increase the snow water equivalent and increase runoff during the spring melt period.

Peak Flows

The effect of forest disturbance on the size of peak flows can be predicted by the 

changes in the dominant controlling factors, which include:

1. the change in peak snowmelt rates;

2. the change in rainfall interception, particularly when the soils are relatively wet;

3. the degree to which roads and other disturbances intercept water and alter the pathway 

that water takes to the stream channel,

4. alteration of the infiltration rate to the extent that runoff pathways are changed, and

5. changes in soil moisture content and storage capacity (Anderson and others 1976).

With respect to the change in peak snowmelt rates, the magnitude of the effect of 

forest disturbance (other than fire) on peak discharges in the cold snow zone is similar 

to the observed changes in annual water yields. In the case of Fool Creek, peak flow 

increased by an average of about 20 percent (fig. 4); however, the three largest peaks of 

the post treatment period, from 1967 to 1998, were not significantly increased (Laurie 

Porth, personal communication). During those years when snow packs are greater and 

more long lasting, melt rates in the clearings appear similar to those in the forest and differences in soil moisture resulting from timber harvest are eliminated before the peak, 

thus diminishing the effects of forest removal on peak discharge for those largest events. 

Other studies in the cold snow zone have shown a 20 to 50 percent increase in the average peak flows due to clearcutting, but these have also shown no significant increase 

in the largest peaks of record (Troendle and Bevenger 1996; Troendle and King 1985; 

Troendle and others 2001).

A comparison of pre- and post-harvest flow duration curves indicates that the flows 

most affected by forest harvest are those that exceed the lowest 40 percent of the 

discharges but do not exceed the 90th percentile. However, the duration of bankfull discharge at Fool Creek, which is assumed to equal the 1.5-year instantaneous discharge, 

C.A. Troendle, L.H. MacDonald, C.H. Luce, I.J. Larsen Cumulative Watershed Effects of Fuel Management in the Western United States
136 USDA Forest Service RMRS-GTR-231. 2010.

increased from 3.5 days to 7 days per year after the timber harvest (Troendle and Olsen 

1994). The longer duration of bankfull flows was presumed to increase channel scour as 

indicated by the observed increases in annual sediment yields after patch clearcutting on 

the North Fork of Deadhorse Creek (Troendle and King 1987).

There has been considerably more debate over the effect of forest harvest on peak 

flows in the maritime snow climates of the Pacific Northwest and Continental/Maritime 

hydrologic regions (Grant and others 2008; Jones and Grant 1996; Thomas and Megahan 

1998). This debate is due in part to the fact that the largest peak flows are typically due 

to mid-winter rain-on-snow events, and forest harvest can affect a series of processes 

that control the amount of snow in the canopy and on the ground, as well as the amount 

of heat that is available to melt the snowpack. These additional processes, when combined with the variability in climatic conditions during a storm and within a watershed, 

can make it very difficult to determine exactly how forest harvest affects peak flows 

from a given event.

Plot-scale studies have shown that rain-on-snow events accompanied by high winds 

can dramatically increase snowmelt rates in forest openings (Beaudry and Golding 1983; 

Berris and Harr 1987; Christner and Harr 1982; Harr 1986; Marks and others 1998; 

Storck and others 1998, 1999). This increase in melt rates is due to the increased condensation of moist air on the snowpack driven by the high winds and the resulting transfer of 

heat to the snowpack (Berris and Harr 1987; Harr 1986; Marks and others 1998; Storck 

and others 1999). Much less research has been done on how thinning affects this process, 

but basic research on turbulence theory suggests that even widely spaced cylinders (for 

example, trees) can be effective in reducing turbulence at the bottom surface (Poggi and 

others 2004a, b). This would suggest that thinning may have little effect on peak snowmelt rates during rain-on-snow events in the transient snow zone.

Forest roads, whether paved or unpaved, typically have very low infiltration rates 

and, therefore, convert nearly all of the rainfall or snowmelt into overland flow. When 

they are cut into the hillslopes, they also can intercept the slower moving subsurface 

flow. Depending on their connectivity with the stream network, roads may deliver this 

water directly to the channel. The increase in runoff and faster flow velocities act together to increase the size of peak flows (LaMarche and Lettenmaier 2001; Luce 2002; 

Megahan 1972; Wemple and Jones 2003; Wemple and others 1996) as well as total 

runoff. Skid trails can also generate surface runoff because of their lower infiltration 

rates, but generally these are not deeply incised to the hillslopes and, therefore, do not 

intercept subsurface stormflow. A compilation of published data indicates that the proportion of roads that are connected to the stream network is proportional to mean annual 

precipitation, as this tends to increase the number of streams and road crossings, which 

are a primary source of road-stream connectivity. The effect of roads on the size of 

peak flows can be minimized by outsloping and reducing their density and proximity to 

stream channels.

As a result of tracked or wheeled vehicles, soil compaction can reduce infiltration 

rates to the point that overland flow is generated during storm or snowmelt events. 

Again, this will increase the amount and velocity of runoff and thereby increase the 

size of peak flows. As with roads, best management practices are usually implemented 

during mechanical operations to reduce or eliminate this problem, including avoiding 

operations, such as minimizing high traffic areas during wet weather when the soils are 

more susceptible to compaction.

Other mechanisms that increase the size of peak flows in rain-dominated areas include the post-harvest increases in soil moisture and rainfall interception. Wetter soils 

allow a greater percentage of the precipitation to become streamflow, and the reduction in summer evapotranspiration generally results in wetter soils through the growing 

season. This would cause an increase in the runoff response in the first fall rainstorms. 

However, once the soil moisture in uncut areas has been fully recharged, there would 

be minimal differences in soil moisture between the cut (or thinned) and uncut areas 

and the initial soil moisture effect would be largely eliminated. Since the largest runoff 

events occur under wet conditions, the change in soil moisture due to timber harvest is 

unlikely to affect the size of the largest peak flows (Troendle 1987).

Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 137

Forest harvest or forest thinning will also reduce the amount of rainfall interception 

by reducing the total leaf area. Any reduction in interception will effectively increase 

the amount of precipitation reaching the mineral soil, and this change should increase 

the size of peak flows. Again, this change will be most important in the smaller storms 

and less in the larger, more intense storms as the forest canopy can generally capture 

only a few millimeters of water and evaporation rates during large storms are relatively 

small due to the small amounts of incoming solar radiation and high relative humidity.

A recent review on the effects of forest harvest on peak flows in western Oregon 

supports these basic principles (Grant and others 2008). First, data from a variety of 

paired watershed experiments shows that forest harvest has a progressively smaller 

effect on peak flows as recurrence interval increases, and this is consistent with our 

general understanding of runoff processes and results from the Rocky Mountain region. 

The observed changes in the size of peak flows varied by watershed, but the peak flow 

increases ranged from 0 to 40 percent in the rain and transient snow zones and from 0 to 

50 percent in the snow zone. The observed increases in peak flows generally approach 

the limit of detectability (about a 10 percent change) at a recurrence interval of approximately 6 years (Grant and others 2008). The largest increases in the size of peak flows 

occur in the fall because of the higher soil moisture carryover in harvested areas. The 

timing of the largest increases is consistent with equation 1 and the observed changes in 

the cold snow zone where the runoff increase occurs almost entirely on the rising limb 

of the snowmelt hydrograph because of the soil moisture carryover from the previous 

summer and corresponding reduction in the amount of water needed for soil moisture 

recharge in the following spring.

As in the cold snow zone, the magnitude of the observed changes in the size of 

peak flows in western Oregon is generally linear with respect to the proportion of the 

watershed that has been harvested (Grant and others 2008). The effect of roads cannot 

be clearly disentangled or quantified relative to the effect of timber harvest, although 

the data and modeling studies suggest that roads can increase the size of peak flows 

(for example, Bowling and others 2000; Grant and others 2008; Jones 2000). Using the 

mean response lines from different watershed studies, thinning less than 40 percent of 

a watershed is unlikely to cause a detectable change in the size of peak flows in raindominated areas and would result in only a 14 percent increase in the size of peak flows 

in the transient snow zone (Grant and others 2008).

In conclusion, both the available data and our understanding of hydrologic processes 

indicate that thinning should generally have little or no effect on the size of peak flows. 

In general, the changes in the size of peak flows due to forest management are small 

relative to the interannual variability in the size of the largest runoff events, and this 

again makes it difficult to link thinning with statistically significant hydrologic, geomorphic, or ecological changes.

Hydrologic Recovery

The longevity of hydrologic response following timber harvest appears to be unique 

in the cold snow zone of the Rocky Mountain region relative to other hydrologic regions, and this includes both the changes in water yield and snowpack accumulation. 

At Fool Creek the “average” 10-cm first-year increase in flow had declined by only 

28 percent over the first 28 years following timber harvest (Troendle and King 1985). 

Recent streamflow data suggest that full hydrologic recovery will require 60 or more 

years (Laurie Porth, personal communication).

The duration of hydrologic recovery is more speculative when the silvicultural practice is a thinning or individual tree removal as compared to clearcutting strips, patches, 

or entire watersheds. It is generally assumed that the residual trees will very quickly 

occupy the site and use the soil moisture savings. However, the significant increases in 

snow pack accumulation persisted for at least 20 years after a partial cut that removed 

40 percent of the basal area at Deadhorse Creek (Laurie Porth, personal communication; 

Troendle and King 1987). The persistent increase in the snowpack after partial cutting 

C.A. Troendle, L.H. MacDonald, C.H. Luce, I.J. Larsen Cumulative Watershed Effects of Fuel Management in the Western United States
138 USDA Forest Service RMRS-GTR-231. 2010.

implies that at least a portion of the associated increase in annual water yields and peak 

flows would also be long lasting in the cold snow zone.

In contrast to the cold snow zone, the hydrologic response to clearcutting and thinning is relatively short-lived throughout the balance of the United States (Beasley 

and others 2004; Brown and others 1974; Douglass 1983; Harr 1983; Hornbeck and 

Kockenderfer 2004; Hornbeck and others 1997; Jackson and others 2004; Jones and 

Post 2004; Kattleman and Ice 2004; Keppeler and Zeimer 1990; Troendle and Leaf 

1980). The shorter duration is due to the much more rapid rate of vegetative regrowth, 

which is due largely to the warmer temperatures and greater availability of water. 

Paired watershed studies suggest that the increase in annual water yields resulting 

from clearcutting will drop to zero within 30 years, and there may then be a period of 

a net decrease in water yields as a result of the active regrowth and changes in species 

composition (Jones and Post 2004). The persistence of any increase in annual water 

yields due to thinning or partial cuts will be much shorter due to the tendency for the 

residual vegetation to uptake any savings, and these are likely to disappear within 5 

or possibly 10 years. When this occurs, any increase in low flows is also likely to be 

very short-lived.

Hydrologic Effects of Prescribed Fire

Prescribed burning is the controlled use of fire to achieve specific management 

objectives (Walstad and others 1990), and it is commonly used to reduce fuel buildup 

and the associated risk of severe wildfire (Norris 1990). Between 1998 and 2007, 6.7 

million hectares managed by federal agencies in the United States were treated with 

prescribed fire (NIFC 2008). Relative to wildfires and forest harvest, the effects of 

prescribed burning have received little study until recently.

The hydrologic effects of prescribed burning are largely a function of fire severity 

and area burned. High severity burns that consume protective litter and expose mineral soil generally increase runoff and sediment yields, whereas low severity burns that 

only consume the upper litter layers have much less hydrologic impact (BenavidesSolorio and MacDonald 2001, 2005; Tiedemann and others 1979). Because prescribed 

fires are typically intentionally set during times when flame lengths are expected to 

be low, fire residence times are expected to be short, soil heating is expected to be 

low, and the effects of prescribed fires on soil properties are limited in severity and 

extent. The percent exposed mineral soil following low severity prescribed burns is 

generally between 5 and 30 percent, whereas values ranging from 35 to 95 percent 

have been reported following high severity prescribed burns or wildfires (BenavidesSolorio and MacDonald 2001, 2005; Cooper 1961; Robichaud and others 1993; Swift 

and others 1993; Robichaud and Waldrop 1994; Van Lear and Kapeluck 1989). The 

occurrence of surface runoff and erosion after fires is highly dependent on the amount 

of ground cover. Most studies indicate that little overland flow or surface erosion 

occurs when there is less than 35 to 40 percent bare mineral soil (Benavides-Solorio 

and MacDonald 2005; Robichaud and Brown 1999). This may be a useful first-order 

threshold for predicting whether there is likely to be a significant increase in surface 

runoff, but the hydrologic effects of fire depend on many other factors beyond burn 

severity and percent bare soil. These include the amount of vegetation that is killed by 

the fire, proportion of a watershed that is burned, location of the areas burned within a 

watershed, soil type, rate of vegetation recovery, and precipitation regime after burning (Luce 2005).

On-Site Effects

The surface condition after a prescribed fire is typically a mosaic-like pattern of 

low severity, high severity, and unburned patches (Robichaud 2000). The connectivity 

of runoff producing patches imparts a strong control on water and sediment yields to 

Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 139

the stream channel (Doerr and Moody 2004; Luce 2005; Shakesby and others 2000). 

The patchiness of burn severity allows unburned and low severity patches to infiltrate 

runoff and trap sediment that is generated on adjacent high severity patches (Biswell 

and Schultz 1957; Cooper 1961; Swift and others 1993). The patterns of burn severity help control the spatial scale at which the effects of prescribed burning can be 

detected. For example, strong soil water repellency in high severity patches may have 

little effect at the watershed scale if only a small percentage of the watershed burns at 

high severity, or if there are intervening low severity or unburned patches (Huffman 

and others 2001).

Effects on Streamflow

Since low severity prescribed fires do not cause a high degree of tree mortality or 

litter combustion, the effects on evapotranspiration and forest floor water storage are 

generally too small to change watershed-scale water yields. For example, the 1 to 

10 percent basal area mortality reported following low severity prescribed burns in 

ponderosa pine is below the 20 percent threshold at which changes in streamflow are 

usually detectable (Gottfried and DeBano 1990). The reduction in forest floor water 

storage due to prescribed burning varies, but the lower-most litter layer must be modified or removed before the water holding capacity of the forest floor is significantly 

reduced (Agee 1973; Brender and Cooper 1968; Clary and Ffolliot 1969; Cooper 

1961). Therefore, prescribed fire is unlikely to increase watershed-scale runoff unless 

a large proportion of the watershed burns at high severity.

As evidence, water yields did not increase following a prescribed fire that burned 

43 percent of an Arizona ponderosa pine watershed (Gottfried and DeBano 1990). The 

lack of a significant increase in flow was likely due to the fact that the fire killed only 

1 percent of the pre-burn basal area and left most of the litter intact (Gottfried and 

DeBano 1990). Two successive prescribed fires that completely burned four loblolly 

pine watersheds in South Carolina had no detectable effect on streamflow (Douglass 

and Van Lear 1983). Similarly, prescribed fires in giant sequoia-incense cedar forests 

in Sequoia National Park in California had no effect on streamflow in a 100-ha watershed where 60 percent of the area was burned, and in a 20,000-ha watershed where 

eight fires burned 11 percent of the watershed over a 7-year period (Heard 2005). 

The absence of any change in water yield was attributed to the low severity burn 

in the 100-ha watershed and the small proportion that was burned in the 20,000-ha 

watershed. In contrast, a different prescribed fire in Sequoia National Park did cause 

streamflow to increase (Williams and Melack 1997). The fire was more severe than 

the low severity burn described by Heard (2005) and killed most of the younger trees 

and understory vegetation and consumed the majority of the forest litter (Williams 

and Melack 1997).

The effects of prescribed fire can vary by cover type. When the cover type is chaparral, the relative intensity of the burn may be greater, a greater percentage of the 

vegetation is consumed, and a greater percentage of the soils become water repellent. 

In two chaparral watersheds, burning 80 to 90 percent of the area by moderate and 

high severity fires increased water yields by 4 and 14 times, respectively, relative to 

unburned areas (Riggan and others 1994).

These results confirm that light to moderate prescribed fire has little effect on 

streamflow. This is largely because only a small percentage of the vegetation is affected and net changes in infiltration characteristics are minimal. Since the major 

components of the water balance are not substantially altered, there is little or no effect on streamflow.

In some vegetation types, particularly chaparral, there is a much greater propensity 

for prescribed fires to burn at higher severity. In these areas, the use of prescribed fire 

as a fuel reduction treatment may have a greater hydrologic effect. In each case, the 

integrated hydrologic response to successive prescribed fires must be compared to the 

hydrologic response resulting from the likely frequency and severity of a wildfire.

C.A. Troendle, L.H. MacDonald, C.H. Luce, I.J. Larsen Cumulative Watershed Effects of Fuel Management in the Western United States
140 USDA Forest Service RMRS-GTR-231. 2010.

Predicting Changes in Water Yield

The 1980 WRENSS Handbook includes a set of graphical procedures that have 

proven useful for estimating the hydrologic impacts of various silvicultural activities on 

water yield and water quality (EPA 1980). The hydrology chapter has regional evapotranspiration estimates based on the hydrologic regions in figure 3. Regionalized curves 

and modifier functions are then provided to estimate the changes in actual evapotranspiration in response to changes in stand density and stand condition (Troendle and Leaf 

1980). The predicted changes in evapotranspiration were assumed to affect the amount 

of water available for stream flow. For snowmelt-dominated areas, the changes in forest 

cover alter net precipitation and the amount of evapotranspiration. In rain-dominated 

areas, the precipitation is not adjusted to reflect stand conditions and the change in 

evapotranspiration is estimated directly.

The understanding of hydrologic processes in the cold snow zone has evolved significantly since WRENSS was developed, and a new version of the model, WinWrnsHyd, 

has been produced (Swanson 2004). One of the most significant changes is how this 

program simulates the effects of forest harvest on snow accumulation. The revised 

snowpack sublimation and scour routines are more sensitive to wind speed, surface 

roughness, and opening size. These changes allow one to better link the changes in wind 

speeds due to removing some or the entire forest canopy to changes in snow accumulation, and to more accurately predict the effects of leaving or removing slash or other 

forms of roughness on snowpack accumulation. The net effect is to make the model 

more sensitive and more accurate with respect to the effects of partial cuts and thinning 

on water yields (Shepperd and others 1992).

WinWrnsHyd is programmed in Microsoft Access and uses database tables as input 

so that different harvesting scenarios can be created using GIS or other forest planning tools. Data reflecting stand conditions can be input as a series of “snapshots.” 

Alternatively, if growth curves are available, the data for one or more silvicultural prescriptions, occurring simultaneously or at different time intervals, can be input to the 

model and the effects of regrowth on hydrologic response can be simulated as a time 

series. The WinWrnsHyd program can also estimate the likely changes in peak flows 

following forest disturbance. These procedures and updates are particularly relevant because, as noted earlier, the cold snow zone is of tremendous importance for water supply 

purposes, and fuel reduction treatments in this zone are more likely to affect runoff for 

a longer period than similar treatments in other ecoregions.

Cumulative Watershed Effects

The concern over cumulative effects arises because the effect of a single activity may 

not be significant, but the effect may be significant when combined with the effect of 

other management activities. A cumulative effect can occur spatially, such as the effect 

of multiple management activities within a basin, or over time, such as the hydrologic 

effect of one activity persists and the residual effect is superimposed on the effect of a 

second activity on the same site (MacDonald 2000).

The potential for generating a cumulative effect in space depends on the magnitude 

of each effect, their persistence over time, and the extent that the effect is delivered to 

the downstream location. In the case of fuel management activities, the hydrologic effect of a given activity is likely to be relatively small because only some of the forest 

canopy is being removed. As noted earlier, it has been generally accepted that at least 20 

percent of the basal area in a forested watershed must be removed to obtain a detectable 

change in stream flow. As watershed size increases, it is increasingly unlikely that forest 

management will affect more than 20 percent of the basal area in a watershed before 

hydrologic recovery eliminates the hydrologic change due to some of the management 

actions. The implication is that the hydrologic effect of a fuel management activity is 

most likely to be detectable immediately below the activity, and the rate of hydrologic 

recovery will make it difficult to detect the effect of multiple activities over time and 

Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 141

space, especially in larger watersheds (MacDonald 2000). As an example, clearcutting 

36 percent of the North Fork of Deadhorse Creek sub-basin in the Fraser Experimental 

Forest in central Colorado caused a significant increase in streamflow. However, this 

change was not detectable a few hundred meters downstream at the main stream gauge 

on Deadhorse Creek, as the harvest in the North Fork watershed affected less than 6 percent of the area in the Deadhorse Creek watershed (Troendle and King 1987).

The potential for cumulative watershed effects due to fuel management will also be 

limited because most of the fuel management activities in the western United States 

will be concentrated in the drier forest types that have the greatest risk of high severity 

wildfires. As noted earlier, most studies have shown that forest harvest will not result 

in a detectable change in streamflow when mean annual precipitation is less than 18 

to 20 inches. In contrast, thinning has been demonstrated to cause moderate increases 

in streamflow in the central Appalachians where precipitation greatly exceeds 18 to 

20 inches (Reinhart and others 1964). But in humid areas, the hydrologic recovery is 

quite rapid (Hornbeck and others 1997). In general, the absolute changes in runoff due 

to fuel reduction activities in the drier forest types will be small or undetectable relative 

to the potential changes in more humid areas. The potential for cumulative hydrologic 

effects is further limited because the persistence of a hydrologic change due to thinning 

or a partial cut will generally be relatively short everywhere except in the cold snow 

zone, but these forest types are less likely to be the focus of fuel reduction treatments 

(Romme and others 2003).

Another issue in assessing the potential cumulative hydrologic effect is whether a 

given change in flow will be transmitted downstream to the location of interest. In most 

mountainous areas, any change in flow generated by forest harvest or fuel management activities should not be substantially altered by downstream transmission losses. 

However, seepage losses may become significant when streams and rivers flow onto 

broad, semi-arid alluvial plains. In such areas, the streams are likely to be losing water 

to the underlying alluvial aquifer during at least the drier portions of the year. In other 

words, the increase in streamflow may be “lost” to groundwater storage. The potential 

for transmission losses will be a function of the scale of the analysis, relative and absolute magnitude of the changes in flow, and specific watershed characteristics.

In most cases, the measurement and detection issues mean that the magnitude of 

a potential cumulative hydrologic effect will have to be assessed by modeling. As an 

example, Troendle and Nankervis (2000) and Troendle and others (2003) estimated the 

changes in average annual water yield resulting from long-term vegetation changes in 

the North Platte River Basin (table 1). Current vegetative conditions in the river basin 

were extrapolated backwards in time from United States Forest Service stand condition records, and water yields under the different forest conditions from 1860 to 2000 

were simulated using the WRENSS model. The results suggested that streamflow from 

National Forest System lands has decreased 3 inches (76 mm) from 1860 to 2000 as 

the result of an increase in forest density (table 1). Although these decreases are difficult to detect using the existing streamflow records on the North Platte River, they are 

considered real and significant by water users and planners in the Platte River Basin. A 

separate study using a combination of precipitation, snowpack, and streamflow records 

reached similar conclusions (Leaf 1999).

Table 1. Water yield from National Forest land in the North Platte River 

basin from 1860 to 2000.

Year Area (ha) Predicted water yield (mm)

1860 448,418 376

1880 448,418 343

1900 448,418 366

1920 448,418 340

1940 448,418 307

1960 448,418 302

1980 448,418 307

2000 448,418 300

C.A. Troendle, L.H. MacDonald, C.H. Luce, I.J. Larsen Cumulative Watershed Effects of Fuel Management in the Western United States
142 USDA Forest Service RMRS-GTR-231. 2010.

In a more recent assessment, Troendle and others (2007) used the WRENSS 

Hydrologic Model to predict the changes in water yield resulting from proposed fuel 

management treatments in the Upper Feather River watershed in the Sierra Nevada of 

California. Because proposed treatments influenced only a small percentage of the total 

vegetation on the entire study area, the cumulative impact on water yield was minimal. 

However, the GIS-based modeling was useful for demonstrating that the treatments 

could have an on-site or local affect on annual water yields.

Conclusions

One can conclude that fuel reduction treatments in forested watersheds will probably have little detectable impact on water yields either on-site or downstream. Most 

prescriptions are not likely to remove the 20 percent of basal area that is needed 

in most areas to generate a detectable change in flow. As Bosch and Hewlet (1982) 

concluded and subsequent data (Hornbeck and others 1997) and modeling (Troendle 

and others 2003, 2007) support, removing less than 20 percent of the basal area may 

also result in a change in flow, but this change will not be detectable. In cases where 

there is a detectable hydrologic response to fuel management treatments, the observed 

response will be greatest in wet years and smallest or non-detectable in dry years. 

Fuel reduction treatments that are carefully implemented and do not induce overland flow as a result of skid trails or compaction should generally have little or no 

detectable effect on peak discharges. With the exception of the cold snow zone in the 

Rocky Mountain region, any change in flow due to fuel reduction treatments will be 

short-lived.

Prescribed fires, when designed and used as a fuel reduction tool, are probably less 

likely to influence water yield than mechanical treatments because of the smaller reduction in basal area and lack of ground disturbance by heavy machinery. Prescribed 

fires that kill a significant proportion of the mature canopy or expose more than 35 to 

50 percent of the mineral soil may have a significant, detectable effect on annual water 

yields or storm runoff.

Simple models are available to simulate the on-site and cumulative hydrologic impacts of virtually any individual or combination of forest disturbance scenarios. The 

use of these models should be a required component of the planning process in order 

to assess both on-site and cumulative impacts over time.

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Chapter 7. Fuel Management and Water Yield
USDA Forest Service RMRS-GTR-231. 2010. 149

Chapter 8.

Effects of Fuel Management Practices on 

Water Quality

John D. Stednick, Department of Forest, Rangeland, and Watershed Stewardship, Colorado 

State University, Fort Collins, CO

Introduction

Fuel management practices in the Rocky Mountain region may include prescribed 

fire, timber harvesting (patch cuts, thinning, high-grading, or selective logging), mechanical treatments (mulching, chipping or chunking), chemical treatments, or grazing 

to reduce undesirable species (Chapter 4). The application of any of these treatments 

has the potential to affect water quality. Understanding the effects of land use practices 

on hydrologic processes is of primary importance when assessing water quality effects. 

Unlike agriculture where there are often many activities each year, fuel managements 

practices occur once every year to once over several decades. Fuel management activities should be implemented with best management practices (BMPs) to minimize or 

prevent water quality changes or nonpoint source pollution.

Fire

Research has largely focused on the effects of wildfire on water quality. Few address 

prescribed or controlled fires as smaller watershed level effects are expected. In general, 

wildfires are more intense (EPA 2005) and more extensive in area than prescribed fires, 

resulting in potentially greater effects on watershed processes. Watershed effects from 

fire depend on several variables, including fire size, fire severity, soils, watershed slope, 

vegetation, vegetation regrowth, precipitation, physical location on the watershed, and 

proportion of watershed burned.

Temperature

Soil heating may occur following the removal of cover (vegetation, litter and duff, 

and organic material) by fire (Wells and others 1979). The magnitude of heat pulse into 

the soil depends on fuel loading, fuel moisture content, fuel distribution, rate of combustion, soil texture, and soil moisture content (Chapter 9). The movement of heat into the 

soil is not only dependent upon the maximum temperature reached, but the length of 

time and the heat source that is present. Because fuel is not evenly distributed, a mosaic 

of heating occurs. The highest soil temperatures are associated with areas of greatest 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
150 USDA Forest Service RMRS-GTR-231. 2010.

fuel consumption and longest duration of burning. In forested areas, high subsurface 

soil temperatures usually occur beneath fuel accumulations, with the highest temperatures most likely found in association with consumption of large piles of harvest residue 

or windrow or very thick duff layers.

Rangelands have lighter fuel loadings, resulting in fires of shorter duration and less 

subsurface heating. The greatest subsurface heating likely occurs where thick, dry litter 

layers are consumed beneath shrubs and isolated trees. The soil heat pulse, including 

both amount and duration, is instrumental in eventual effects of fire on plants (DeBano 

and others 1998). Excessive soil heating can kill plants and decrease vegetative cover 

and influence stream temperature from loss of riparian cover to soil water heating.

Exposure of small streams to direct solar radiation is the dominant process responsible for stream temperature increases (Tiedemann and others 1978). Other mechanisms 

include increased air temperature, channel widening, soil water temperature increases, 

and streamflow modification (Ice 1999). Streams with smaller surface areas may be 

more susceptible to heating, but usually return to expected temperature within 500 ft 

(150 m) downstream (Andrus and Froehlich 1991). Maintaining shade in riparian zones 

can be used to avoid most temperature increases in small streams. As stream width 

increases, more of the water surface is exposed to sunlight, consequently reducing the 

influence of riparian canopy on stream temperature.

The ability of a forest fire to change the temperature of any particular watercourse 

or water body depends on the amount of water subject to heating. More precisely, it 

depends on the affected unit’s surface-area-to-volume ratio. In essence, this means that 

temperatures rise faster in smaller and shallower water bodies than in larger and deeper 

ones. All else equal, the magnitude of any temperature change depends on both the 

amount of heat directed at the water surface per unit time and the duration of heating. 

As fire burns in surrounding vegetation and woody debris, it can raise the temperature of 

water in forest streams (Amaranthus and others 1989; Cushing and Olson 1963; Feller 

1981; Hall and Lantz 1969; Helvey 1972; Levno and Rothacher 1969; Spencer and 

Hauer 1991; Swift and Messer 1971).

The best management practices for prescribed fire are to schedule burning when 

the soil moisture conditions will minimize heat conductivity into the soils. Streamside 

management zones or buffers along stream channels can provide shade for stream 

temperatures and provide filter strips for sediment and nutrients as described later. 

Streamside buffers are often difficult to exclude from a prescribed burn, but the soil and 

vegetation are usually moist and do not burn.

Sediment

Watershed responses to prescribed fire may include changes in runoff characteristics, 

sediment yield, and water chemistry. Under pre-fire conditions, grasses, brush, and the 

forest canopy intercept precipitation and release it as throughfall, supporting infiltration. 

Infiltration reduces direct overland flow from precipitation. Runoff is generated through 

the variable source area concept where infiltration exceeds the saturation potential of 

soils. As the erosive potential of overland flow is minimized, nutrients and sediments 

are retained on site. In the absence of vegetative cover, runoff becomes flashier as more 

streamflow is generated by overland flow, resulting in sharper, higher peak flows and 

often lower baseflows. With less infiltration, vegetative uptake and retention of water, 

total water yields from burned watersheds are higher. Once runoff begins, loose soils 

and ash are quickly removed from steeper slopes. Fire-associated debris is swiftly delivered directly to streams in large quantities. The first storm of the year may produce 

a ‘rolling black’ that is a storm event high in suspended sediment and ash. Suspended 

concentrations over 40,000 mg/L were measured in the first storm event after the 2000 

Bobcat fire in Colorado (Kunze and Stednick 2005).

Organic compounds in litter, probably aliphatic hydrocarbons, are volatilized during combustion, migrate into the soil profile, and condense on soil particles, forming a 

water repellant layer (DeBano and others 1998). The phenomenon is more evident in 

dry, coarse textured (sandy) soils. It also appears that high temperatures, above 550 °F, 

Chapter 8. Effects of Fuel Management Practices on Water Quality
USDA Forest Service RMRS-GTR-231. 2010. 151

John D. Stednick Cumulative Watershed Effects of Fuel Management in the Western United States

destroy the compounds responsible for water repellency. These data suggest fires that 

heat soils to an intermediate range of temperature (400 to 500 °F) are more likely to 

cause the formation of a non-wettable layer than fires that heat only the soil surface or 

those that cause deep penetration of high temperatures. In addition, certain plant communities, such as those containing chaparral species, are more likely to be affected. It 

is important to recognize that hydrophobicity occurs naturally (DeBano 1981) and may 

develop under prescribed fire conditions (Huffman and others 2001); however, the effect is not long-lived. Repeated measurements of hydrophobicity after fire suggested the 

phenomenon lasted up to 22 months in forest soils of the Colorado Front Range, but is 

usually gone after less than 1 year (Huffman and others 2001).

Suspended sediment is the major nonpoint-source pollution problem in forests, most 

often associated with forest roads (MacDonald and Stednick 2003). Sediment and turbidity are the most significant water quality responses associated with fire (Beschta 

1990). Erosion resulting from prescribed burning is generally less than that resulting 

from roads, skid trails, and site preparation techniques that cause soil disturbance, which 

are often a necessary component of prescribed burn projects (EPA 2005).

A controlled burn is usually designed to modify a vegetation type (Chapter 3), while 

uncontrolled wildfires are less selective in modifying vegetation type or age class. 

Erosion rates following fires may increase from decreased vegetative cover and/or 

modified soil properties, including decreased infiltration, hydrophobicity and movement of ash or debris and increased rill erosion from hillslopes directly to the stream 

channel. Soil erosion may cause decreases in soil nutrients, but unless soil erosion rates 

are excessive, more nutrients are usually “lost” through the consumption of vegetative 

fuel. Actual soil erosion and nutrient loss varies by site as a function of vegetation type 

and recovery, soil type, fire severity, topography, slope position in relation to surface 

waters, and climate. Significant climate modification has been linked to large area fires. 

For example, the Bobcat Fire was severe and subsequent storms that occurred had low 

recurrence intervals, resulting in higher frequency peakflows and higher soil erosion 

rates (Kunze and Stednick 2005).

Burned areas are sometimes seeded to rapidly establish plants or are given physical treatments to quickly stabilize the soil (Moench and Fusaro 2004). Following 

severe wildfire, the Forest Service and other land managers may implement Burn Area 

Emergency Rehabilitation (BAER) treatments to reduce the risk of high runoff and sediment flows. The effectiveness of the most widely used BAER practice, contour-felled 

log barriers, has not been systematically studied (Robichaud and others 2000). The second most used BAER practice, postfire broadcast seeding with grasses, has been studied 

and the majority of studies found that this treatment did not significantly reduce erosion 

during the critical first 2 years after fire (Robichaud and others 2000). Research on the 

effectiveness of other watershed restoration treatments is ongoing.

Reseeding with grasses is not a reliable technique for erosion control after severe 

wildfire. Additionally, when an area is seeded with nonnative grass species, native 

plant species may be effectively excluded leading to questions about long-term stability. Firelines, particularly those that are created by bulldozers, are potential areas of 

increased soil erosion and establishment of non-native plants. Firelines may be difficult 

to stabilize with vegetation because much of the nutrient-rich surface soil is cast aside. 

Hence, they are likely to be slow to revegetate with perennial vegetation. Application of 

native seed and fertilizer is an effective way to protect firelines (Klock and others 1975; 

Tiedemann and others 1979).

Nutrients

There are regional differences in the effects of fire on water quality. Of the few 

studies available for the southeastern United States, results have shown either no effect 

or small increases in stream nutrients following fires (Richter and others 1982). This 

contrasts with regions in the western United States where fires have a notably larger 

effect on water quality (Gresswell 1999; Neary and others 2005; Spencer and others 

2003; Stednick 2000). Dissolved nutrients in streamflow are derived primarily from 
152 USDA Forest Service RMRS-GTR-231. 2010.

weathering, decomposition of plant material, and anthropogenic sources. Vegetative 

communities accumulate and cycle large quantities of nutrients (Tiedemann and oth-

ers 1979). Fire can disrupt this cycle and cause nutrient leaching, volatilization, and 

transformation.

The concentrations of inorganic ions often increase in streams after a fire (DeBano 

and others 1998). Studies indicate that changes in chemistry and flow conditions after 

forest fires are temporary, usually lasting less than 5 years (Chorover and others 1994; 

Covington and Wallace 1992; Fredriksen 1971; Hauer and Spencer 1998; Ice and others 

2004). Early reestablishment of vegetative ground cover after a wildfire is an important 

factor controlling the recovery.

Water from forested watersheds is typically lower in nutrients than water draining 

from other land uses. Forest management activities, such as forest cutting and harvest-

ing, may increase annual water yields (Bosch and Hewlett 1982; Stednick 1996) and 

disrupt the natural cycling of nutrients (Stednick 2000). Several chemical constituents 

are likely to increase after forest and rangeland burning. The primary constituents of 

concern are nitrate (NO

3

-

), phosphate (PO

4

3-), calcium (Ca2+), magnesium (Mg2+) and 

potassium (K

+). Nitrate is a mobile ion and easily leached from burned areas. Stream 

nitrate responses to prescribed fire are generally lower than for wildfire (Stednick 2000). 

Conversely, phosphorus binds readily to sediment and is thus predominately trans-

ported with soil erosion. The bulk of phosphorus transport is as total phosphorus, and 

orthophosphate concentrations are low (Stednick and others 1982). Changes in concen-

trations of sulfate, pH, total dissolved solids, chloride, iron, and other constituents have 

been measured. If organic compounds leach into surface waters, water color, taste, and 

smell may be affected.

Nitrate-nitrogen (NO

3

-N) concentrations are usually quite low (0.002 to 1.0 mg/L) 

in streams draining undisturbed forest watersheds (Binkley and Brown 1993a,b). 

Concentrations are low because nitrogen is rapidly used by ecosystem biota, and nitrate 

formation (nitrification) is relatively slow in forest soils. Slow rates of organic matter 

decomposition, acid soil conditions common in forest environments, and bacterial al-

lelopathy all decrease rates of nitrification. Organic matter and anaerobic conditions in 

saturated riparian soils allow for denitrification, the reduction of nitrate to nitrogen gas, 

which may be lost to the atmosphere.

Often, fires will create soil environmental conditions that are favorable for increased 

microbial activity (Ballard 2000). These include near neutral pH, increased soil mois-

ture (because there are no interception or evapotranspirational losses), a food or carbon 

source, and soil temperatures. The increased microbial activity often results in a shortterm increase in nitrogen availability. Depending on the monitoring frequency and site 

specifics, an ammonium pulse may be seen, but usually a pulse of nitrate is measured. 

The short increase in nitrogen availability helps new or existing vegetation become es-

tablished. Increased nitrogen mineralization rates persisted for 1 year in range grassland 

and up to 2 years in a shrub community (Hobbs and Schimel 1984).

If vegetation is quickly reestablished, nutrient exports are short-lived and usually do 

not represent a threat to water quality or site productivity. There are a couple of possible 

exceptions. Nitrogen deposition can accumulate in forest soils over time, especially 

in areas with air quality concerns (Riggan and others 1985; Silsbee and Larson 1982). 

If timber harvesting occurs in these areas, mobilization of accumulated soil nitrogen 

may result in higher nitrate concentrations and outputs in the streamwater. Values for 

nitrate generally increased after fire but not to a level of concern, except in nitrogensaturated areas. Nitrogen-saturated areas are where the atmospheric inputs of nitrogen 

compounds from precipitation and dryfall exceed the plant uptake requirement, and 

thus, excess nitrogen moves through the system. The most striking response of nitrate 

concentration in streamflow after wildfire was observed east of Los Angeles in southern 

California (Riggan and others 1994).

Immediately after a fire, stream pH may be affected by direct ash deposition as oxides 

form from the volatilization of metallic cations. In the first year after fire, increased soil 

pH may also contribute to increased streamwater pH (Wells and others 1979). In most 

studies, pH values were little changed by fire and fire-associated events (Landsberg 

Chapter 8.  Effects ofFuelManagement Practices on Water Quality
USDA Forest Service RMRS-GTR-231. 2010. 153

and Tiedemann 2000). Transient pH values up to 9.5 were measured 8 months after the 

Entiat fires in eastern Washington (Tiedemann 1973, 1981).

Measures that reduce on-site soil erosion and stream vegetative buffers, such as riparian areas, will minimize effects of fire on water quality.

Timber Harvesting

Timber harvest, whether marketable or not, is often used as a tool in fuel management (Chapter 4). The effects of timber harvesting on water quantity and quality are 

well known. Most water quality studies are conducted at small watershed levels in order 

to decipher treatment effects from variability in water quality data. The effects of timber 

harvesting as a thinning, selective cut, or other partial canopy removal treatment, will 

have less of an effect than complete canopy removal. Less site disturbance will result in 

less erosion potential and remaining vegetation will quickly utilize increased available 

nutrients and water from evapotranspiration savings.

Temperature

Surprisingly, few recent studies have been published on the effects of silvicultural 

practices on water temperature, and most of these were conducted in the 1970s. These 

studies include harvesting with and without streamside vegetation buffers (Beschta and 

others 1987; Binkley and Brown 1993a; Swank and Johnson 1994).

Literature on the effects of timber harvesting on stream temperatures shows daily 

maximum stream temperature increases from 1.5 to 8 °C in eastern forests and 0.6 to 

10 °C in western forests. The range in temperature increases reflects a range in streamside vegetation buffers from no buffer to a 100-m buffer. Changes in minimum nighttime 

stream temperatures (during the winter or dormant season) range from no change to less 

than 1 °C in the East and from zero to less than 2 °C in the West (Stednick 2000).

Temperatures in small streams may increase when the streamside vegetation canopy 

is removed. Providing streamside buffers or management zones can mitigate this effect. 

Several studies have reported temperature increases with streamside buffers, but the 

increases are much smaller than those of fully exposed streams. The lack of documentation on buffer characteristics makes extrapolation difficult. Different measurements of 

stream temperature also make direct comparisons difficult. Attributes needed to estimate the contribution of forest overstory to stream surface shade include stream width, 

distance from vegetation to stream, stream orientation, height and density of vegetation, 

crown or canopy measurement, latitude, date, and time (Quigley 1981).

Generally, forest practices that open small stream channels to direct solar radiation 

increase stream temperatures. Retention of streamside vegetation appears to mitigate 

potential temperature changes, especially temperature extremes. These principles are 

well documented by research throughout the country. Streamside canopy removal may 

also decrease winter stream water temperatures, since radiation losses may be increased. 

For small streams, temperature returns to expected levels within a short distance downstream of where canopy shade is reestablished (Andrus and Froehlich 1991). In general, 

removal of streamside vegetation cover has the potential to increase streamwater temperatures during the day in the summer. In certain settings, the vegetation removal 

may allow for decreased nighttime temperatures, especially in the winter. Temperature 

changes return to pretreatment levels as the streamside vegetation reestablishes. The 

maintainence of streamside vegetation as a thermal cover is key to maintaining stream 

temperatures at existing levels.

Sediment

Fuel management practices that result in soil disturbances may increase soil erosion. Soil erosion is the detachment and movement of soil particles, measured as 

John D. Stednick Cumulative Watershed Effects of Fuel Management in the Western United States
154 USDA Forest Service RMRS-GTR-231. 2010.

tons/acre/year (Mg/ha/yr). Suspended sediment is eroded soil material transported in 

the water column of a stream. It is measured as a concentration such as mg/L or as 

turbidity, an optical measurement of the water’s ability to diffract light expressed as 

Nephelometric Turbidity Units (NTU) (Stednick 1991).

Site properties that affect erosional processes include vegetative cover, soil texture, 

soil moisture, and slope (Falletti 1977; Renfro 1975). The sediment load of streams 

(both suspended and bedload) is determined by characteristics of the drainage basin 

such as geology, vegetation, precipitation, topography, and land use. Sediment enters 

the stream system through erosional processes, often as pulse events during storms. To 

achieve stream stability, an equilibrium must be maintained between sediment enter-

ing the stream and sediment transported through the channel, thus resulting in a stream 

profile that neither aggrades or degrades over time. A land use activity that significant-

ly changes sediment load can upset this balance and result in physical and biological 

changes to the stream system (State of Idaho 1987).

Undisturbed forest watersheds usually have erosion rates from near 0 to 0.25 

tons/acre/year (0.57 Mg/ha/yr) (Binkley and Brown 1993a). Erosion rates have been 

estimated as less than 0.1 tons/acre/year (0.2 Mg/ha/yr) for three-quarters of eastern 

and interior western forests (Patric and others 1984). Typical timber harvesting and 

road construction activities may increase erosion rates to 0.05 to 0.25 tons/acre/year 

(0.11 to 0.57 Mg/ha/yr). More intensive site preparation treatments, such as slash wind-

rowing, stump shearing, or roller chopping, may increase soil erosion rates by up to 

5 tons/acre/year (11.2 Mg/ha/yr). Soil erosion from a single precipitation event from a 

wildfire burned watershed was 0.42 tons/ac (0.95 Mg/ha) and accounted for 90 percent 

of the estimated annual erosion (Kunze and Stednick 2005). Erosion from unpaved road 

and trail surfaces may be higher.

Numerous studies have been done on the effects of different forest management 

practices on erosion rates or sediment production. In general, increased site disturbance 

will result in increased soil erosion and subsequent sediment production. The type and 

magnitude of erosion depend on the amount of soil exposed by management practices, 

the kind of soil, steepness of the slope, weather conditions, and any treatments after the 

disturbance (Swank and others 1989).

Logs are moved (skidded) from the stump to a landing by tractor, cable, aerial sys-

tems, or animals. Tractor skidders may be either crawler or wheeled units, both of which 

are frequently equipped with arches for reducing the extent of contact between log and 

ground. Site disturbance will vary greatly with the type of skidding or yarding sys-

tem. Crawler tractors generally cause the greatest amount of site disturbance, followed 

closely by wheeled skidders. On some sites, use of wheeled skidders can result in more 

compaction than crawler tractors. One method of decreasing the amount of soil dis-

turbed by crawler tractors or wheeled skidders is through careful layout of skid trails. 

Location of skid roads away from the stream channel and off steep slopes can greatly 

decrease the impact of tractor logging. Logging slash placement on used skid trails 

increases surface roughness and may decrease soil and water runoff. Cable logging 

systems will result in less site disturbance because yarding trails are established to the 

yarding tower machinery, which is restricted to road surfaces. Cable systems can be 

ranked in order of decreasing soil disturbance as follows: single drum jammer, high lead 

cable, skyline, and balloon (Stone 1973). Helicopters and balloons will likely result in 

minimum site disturbance, but both are costly and subject to operational constraints.

Unlike many other land uses that disturb soil for long periods, any increase in sedi-

ment yields from timber management activities is usually short-lived. Surface soil 

disturbances provide a sediment supply, but once the finer materials are transported and 

revegetation occurs, the site is less apt to continue eroding. Sediment yields or mea-

sured suspended sediment concentrations decrease over time as a negative exponential 

(Beschta 1978; Leaf 1974; NCASI 1999). This time factor should be considered when 

assessing watersheds for effects on water quality (Stednick 1987).

Most timbering operations will involve the use of forest roads for site access and 

removal of wood products. Roads are recognized as a potential source of erosion and 

sediment. BMPs related to roads include road location, road design, time of use, road 

Chapter 8.  Effects ofFuelManagement Practices on Water Quality
USDA Forest Service RMRS-GTR-231. 2010. 155

construction and maintenance, and road obliteration. Roads are addressed by Luce and 

Reiman in Chapter 12.

Streamside vegetation or filter strips have been used to prevent overland flow and 

soil erosion from reaching surface waters. The filter strip, or equivalent, decreases the 

velocity of the overland flow by creating surface roughness. The decreased velocity 

allows sediment to settle out and overland flows to infiltrate into the undisturbed soils. 

The streamside vegetation filters were originally used to control or limit road-derived 

sediment from reaching forest streams. The filter had a recommended width of 10 to 

100 m and was dependent on hill slope. These filter strips are effective in sediment 

removal unless an extreme precipitation or overland flow event exceeds the sediment 

detention/retention capacity. The characteristics that determine filter strip efficiency include width, vegetative and litter cover, surface roughness, and microtopography.

Fuel management by forest thinning is a relatively new practice and few studies have 

been conducted to assess the influence of these practices on water quantity and quality. 

A recent study in New Mexico on thinning in pinyon-juniper forests showed that water 

yield increased more on slash piled plots than scattered plots, when compared to a control. Similarly, sediment yields were higher on the slash piled plots than scattered plots. 

When slash was scattered, erosion was lower than the control plots (Madrid 2005).

Nutrients

Cutting vegetation disrupts the nutrient cycle and may accelerate dissolved nutrient 

leaching and loss via streamflow. Exposing sites to direct sunlight may increase the 

rate of nitrogen mineralization. Phosphorus is commonly associated with eroded soil 

particles and sediment and may be lost from the site (Swank and others 1989). Usually, 

there is minimal opportunity for a buildup of these nutrients in the stream system after 

a timber harvest because of the normally brief period of increased nutrient flux to the 

stream (Currier 1980). Throughout the United States, studies have found that nutrient 

losses from silvicultural activities are minimal and water quality (in terms of nutrients) 

was not affected (Aubertin and Patric 1972; Chamberlain and others 1991; Hornbeck 

and Federer 1975; Reuss and others 1997; Sopper 1975; Stednick 2000).

Catchment studies have produced a large body of information on streamwater nutrient 

responses, particularly from clearcutting. Changes in streamwater nutrient concentrations vary substantially among localities, even within a physiographic region. In central 

and southern Appalachian forests, nitrate-nitrogen (NO3-N), potassium (K+), and other 

constituents increased after harvesting, but the changes were small and did not affect 

downstream uses (Swank and others 1989). Clearcutting in northern hardwood forests 

may result in large increases in concentrations of some nutrients (Hornbeck and others 

1987). Research on catchments has identified some of the reasons for varied ecosystem 

response to disturbance (Swank and Johnson 1994).

In general, nutrient mobility from disturbed forests follows the order: nitrogen 

> potassium > calcium and magnesium > phosphorus (Stednick 2000). Thus, forest 

harvesting or other disturbances, such as fire, generally produce larger differences in 

nitrogen concentrations in streamwater than in other constituents. Possible exceptions 

are the loss of calcium and potassium documented in the northeast United States when 

precipitation inputs had greater acidity from fossil fuel combustion (Federer and others 

1989). Phosphorus is often associated with sediments and increased sediment inputs to 

the stream may increase phosphorus concentrations.

If vegetation is reestablished quickly, nutrient exports are short-lived and do not 

represent a threat to water quality or site productivity. Minimization of site disturbance 

areas will reduce potential soil erosion and allow for quick vegetation establishment. 

Use of streamside vegetation zones or buffers are effective in removing sediment from 

upslope overland flows and nutrients from surface and subsurface flows.

John D. Stednick Cumulative Watershed Effects of Fuel Management in the Western United States
156 USDA Forest Service RMRS-GTR-231. 2010.

Fertilization

As noted earlier, there are some instances where site restoration or revegetation may 

require fertilization. The most common fertilizer used in wildland management is nitrogen, usually in the form of urea. Urea fertilizer is highly soluble in water and readily 

moves into the forest floor and soil with any appreciable amount of precipitation. Under 

normal conditions, urea is rapidly hydrolyzed (4 to 7 days) to the ammonium ion (NH4). 

When moisture is limited, urea may be slowly hydrolyzed on the forest floor. Fertilizer 

is usually applied in the spring or fall to take advantage of seasonal low intensity and 

short duration precipitation events (Stednick 2000). If the fertilizer stays dry, the soil 

surface pH favors formation of ammonia (NH3), which is lost by volatilization. These 

losses may be significant, and ammonia absorption by surface water is minimal (USDA 

Forest Service 1980).

The reported effects of forest fertilization on water quality, particularly nutrient concentrations in streams are variable (reviews by Binkley and Brown 1993b; Binkley and 

others 1999; Fredriksen and others 1975). Nutrient retention by forest soils is excellent 

and nutrient concentrations in surface waters after forest fertilization are usually low. 

Fertilizers may enter surface water by several routes. Direct application of chemicals 

to exposed surface water is the most significant. Identification of surface water bodies 

prior to the application essentially eliminates this entry mode.

The effects of forest fertilization on water quality, particularly nutrient concentrations 

in streams are variable (reviews by Binkley and Brown 1993b; Binkley and others 1999; 

Fredriksen and others 1975). Nutrient retention by forest soils is excellent and nutrient concentrations in surface waters after forest fertilization are usually low. Fertilizers 

may enter surface water by direct application of chemicals to exposed surface waters. 

Identification of surface water bodies prior to the application essentially eliminates 

this entry mode. Any ammonium concentrations in surface waters are rapidly reduced 

through aquatic organism uptake and stream sediment sorption. Streamside vegetation 

zones that are not fertilized are generally protective of surface waters.

Nitrate concentrations, if measured in surface waters, usually peak 2 to 4 days after 

fertilizer application (USDA Forest Service 1980). The magnitude of the peak concentration may depend on the presence and width of streamside buffers and the density of 

smaller tributaries to the streams. Peak nitrate-nitrogen concentrations usually decrease 

rapidly, but may remain above pretreatment levels for 6 to 8 weeks. Winter storms may 

also result in peak nitrate-nitrogen concentrations, but these peaks usually decrease over 

successive storms and concentrations decrease quickly between storms (Stednick 2000).

Careful delineation of application areas will avoid direct stream inputs of fertilizer. 

Fertilizer application should be timed to avoid high precipitation periods as fertilizer 

might be moved directly to surface waters. When fertilizer is properly applied at a rate 

and time when vegetation can benefit, fertilizers do not adversely affect surface waters. 

Streamside vegetation is an effective nutrient removal system and any increase in nutrient concentrations in surface waters from fertilizer applications is usually short-lived.

Mechanical Treatments

When vegetation is too thin for prescribed fire, logging is not economical, or fire is 

not acceptable, mechanical treatments can be effective in fuel management (Chapter 4). 

Properly used, mechanical treatments reduce fire hazards, increase plant diversity, control noxious weeds, and improve the quality and quantity of vegetation for wildlife and 

livestock (Zachman 2003). Treatment increases ground cover, which often results in 

increased infiltration rates and decreased surface runoff and soil erosion.

Roller chopping is a mechanical treatment that is frequently applied to mountain 

shrub types and pinyon-juniper stands with stem diameters up to 20 cm. The method 

is effective for knocking down brush and trees and chopping up the slash. Roller chopping can be done when the soil is firm and dry enough to support the heavy equipment. 

Chapter 8. Effects of Fuel Management Practices on Water Quality
USDA Forest Service RMRS-GTR-231. 2010. 157

Low-pressure tires or tracked vehicles can be used on soils that may be subject to 

compaction.

A cylindrical roller or drum, equipped with several full-length blades, is towed behind a crawler-type tractor or “cat.” The roller chopper may be pulled straight or at a 

diagonal to increase the chopping action. Two roller choppers are sometimes towed in 

tandem and at slightly contrasting angles. The cat will usually have its blade positioned 

low to the ground to push over trees and brush. The heavy weight of the roller chopper 

crushes the trees and brush, while the blades chop them and help roughen the ground 

surface (Zachman 2003). The increase of litter and the increased soil surface roughness 

will increase infiltration and decrease soil erosion.

The use of a Hydro-axe is a mechanical treatment that is frequently applied to mountain shrub types and pinyon-juniper stands. This method is effective for knocking down 

brush and trees and chopping up the slash. A Hydro-axe, also known as a Hydro-mower, 

is an articulated tractor with a mower-mulcher mounted on the front of the machine. The 

Hydro-axe has rubber flotation-type tires that cause little disturbance to the surface of 

the ground. The machine can move around trees to treat selected areas (Zachman 2003).

The vegetation/soil litter following this treatment is much finer than that resulting 

from other mechanical treatments. The Hydro-axe allows the operator to be precise in 

the areas and vegetation treated. The mulch creates a protective vegetal layer for the 

rubber tire tractor to travel over, thus reducing surface disturbance. Large safety zones 

are required when using the machine since materials of varying size are frequently 

thrown from the machine

Depending on the fuel load, other site conditions, and the effectiveness of the chipper 

or mulcher, woody material is reduced to an organic layer of various thicknesses. Some 

of these organic horizons have been observed to be up to 30 cm in depth. Any increase in 

the organic horizon will reduce overland flow potential and hence erosion, but the deep 

layer may decrease soil temperatures and decrease vegetation establishment (USDA 

Forest Service 1979). To avoid the potential decrease in soil temperatures and to allow 

organic matter to decompose over a longer time period, some land mangers are using 

“chunking.” Chunking is the mechanical breakdown of woody materials to larger sizes 

rather than the less than 3 cm on a side. Some operations produce woody debris from 

15 to 30 cm on a side.

Mechanical treatments are new as a fuel management practice, and few studies are 

completed that determine their effect on water resources. Nonetheless, best professional 

judgment would suggest that if soil disturbance is minimized by limiting the number 

of tractor passes, avoiding steep slopes (greater than 35 percent), and scattering the 

woody material, overland flow and soil erosion will not be a problem. Vegetative cover 

reduction will temporarily increase on-site water quantity, which can be utilized by the 

remaining vegetation. If sufficient watershed area is treated, channels with intermittent 

flows may become perennial.

Grazing

Grazing animals can be used to remove vegetation. The management objective may 

be to remove understory vegetation or reduce noxious weeds. The effects of the grazing practices on water quality would be expected to be minimal if best management 

practices are followed. Most grazing lands are in ponderosa pine or pinyon-juniper type 

communities.

The ponderosa pine range is the most extensive forested range in the western United 

States. It occupies the low elevations of the mountains and foothills in many areas, but 

mixes with other tree species at moderate elevations. This type of community is associated with an understory of bunchgrasses and shrubs. As the tree density increases, 

there is generally a curvilinear decrease in understory production. This range commonly 

serves as spring, summer, and fall range for cattle. Both rest-rotation and deferredrotation grazing systems, under proper stocking rates, benefit these forested ranges 

John D. Stednick Cumulative Watershed Effects of Fuel Management in the Western United States
158 USDA Forest Service RMRS-GTR-231. 2010.

in terms of maintaining vegetative cover and precipitation infiltration (Leininger and 

Stednick 2002).

The pinyon-juniper range is located between the ponderosa pine forest and desert 

shrub or grassland. The pinyon-juniper range generally occurs on rocky, poorly developed soils, and in many locations it alternates with big sagebrush, which occupies 

deeper soils. Cattle and sheep frequently graze this range in spring before moving to 

higher-elevation summer ranges and again in fall as they return to their wintering areas.

Fire suppression and overgrazing by livestock have allowed woodlands to expand 

both upslope and downslope over the past 100+ years (Gruell 1999). Prescribed burns 

and mechanical removal of pinyon and juniper trees by chaining—large tractors pulling anchor chains or cables over the land—are frequently used to reduce this invasion. 

Desirable grasses are also commonly seeded into recently treated areas to increase forage for livestock and wildlife.

The most important deleterious effect of improper range management on water quality is soil erosion and the subsequent suspended sediment production. Vegetative cover 

and soil properties determine the infiltration rates of precipitation water and the amount 

of streamflow that occurs on grazed lands. Vegetative cover is the dominant factor in 

controlling runoff and water erosion from agricultural lands and rangelands. Livestock 

grazing may alter the natural infiltration-runoff relationships by reducing vegetative 

cover, reducing and scattering litter, and compacting the soil through trampling. The 

magnitude of these changes is determined by topography, climate, vegetation, stocking 

rate, and animal species.

This reduction in vegetative cover may in turn increase the occurrence of overland 

flow and contribute to the desertification of marginal rangelands. Water yield due to 

overland flow may be increased by decreased infiltration rates and capacities due to 

soil compaction. As use of an area increases, so does the probability of soil compaction. Animal bedding grounds, stock trails, watering locations, and salt licks are areas 

of potential soil compaction. Soil texture, moisture, and the amount of organic matter 

influence the degree of compaction. Soil compaction may also reduce plant growth or 

range productivity through changes in soil aeration and soil moisture.

Animal activity along stream channels or other open waters may change the chemical and bacterial quality of water. Specifically, animal feces may contaminate waters 

with bacteria or act as sources of nitrate and phosphate. Studies of two adjacent pastures 

along Trout Creek in central Colorado indicated only minor chemical effects of cattle 

grazing on water quality. The bacterial contamination of the water by fecal matter, however, increased significantly. After the cattle were removed, bacterial counts quickly 

dropped to background levels (Johnson and others 1978).

The removal of plant cover by grazing may increase the impact of raindrops, decrease 

the amount of organic matter in the soil, increase surface crusting (puddling), decrease 

infiltration rates, and increase erosion. Increased overland flow, reduced soil moisture, 

and increased erosion translate into greater concentrations of suspended sediment. 

Other water quality concerns, such as increased bacterial and nutrient concentrations, 

do not appear to be a problem with grazing systems, except perhaps in riparian zones. 

The impact of livestock grazing on watersheds has recently become a resource management issue of national proportions. Research project data have often been evaluated 

emotionally or according to the political advantages offered rather than by scientific and 

objective thinking. Recent interest in federal grazing practices, particularly grazing allotments, may bring a reevaluation of the environmental and economic implications of 

grazing systems on watershed resources (Leininger and Stednick 2002).

Changes in the chemical quality of water due to grazing activities are generally not 

significant or long-lasting unless animals and their waste products are concentrated in 

one area. Grazing under best management practices does not adversely affect water 

quality (Leininger and Stednick 2002).

Best management practices for grazing include vegetation monitoring. Most water 

quality related problems result from loss of vegetative cover. Other practices include 

off-channel water sources, salting, and pasture or allotment rotation.

Chapter 8. Effects of Fuel Management Practices on Water Quality
USDA Forest Service RMRS-GTR-231. 2010. 159

Pesticides

Vegetation management usually refers to the treatment of competing vegetation to 

allow the release of the desired species, for example, spraying of hardwoods to release 

conifer regeneration or growth. Vegetation control or removal by herbicides can be considered a fuel management practice when the target vegetation represents a contribution 

to the site fuel load. Similarly, removal of noxious species by herbicides may improve 

the existing vegetation used by grazing. Noxious weeds control is often accomplished 

with herbicides. Noxious weeds are usually nonnative species that, lacking natural 

controls, spread quickly and take over or reduce habitat for native species. Vegetation 

management often includes the protection of desired vegetation from pathogens, competing vegetation, insects, and animals (Michael 2000). Pesticides provide management 

with an effective and often inexpensive method to achieve these goals. The Federal 

Insecticide, Fungicide, and Rodenticide Act as amended (PL92-516) provides for the 

registration of pesticides in the United States. An integral part of protecting public health 

and environmental values is the requirement that pesticides must be applied according 

to directions approved by the U.S. Environmental Protection Agency and on the label of 

every registered pesticide. The USDA Forest Service requires training of personnel who 

recommend and use pesticides, applicator certification, and safety plans to assure the 

safety of personnel and the protection of environmental values (Michael 2000).

In most situations, herbicide applications are infrequent and often may be a one-time 

treatment. Monitoring for chemicals in water bodies depends on the type of pesticide, 

rate of application, area soils, and precipitation events following the application. Water 

quality monitoring for chemicals after pesticide application using best management 

practices shows that little to no chemicals are detected in water bodies. Studies of the 

effects of forest herbicide use (applied under regulatory guidelines) on streamwater 

element concentrations revealed that no levels were high enough to warrant concern 

(Binkley and Brown 1993b; Michael 2000). In general, when pesticides were detected 

in surface waters after their application, concentrations were well below the threshold 

of concern.

Today’s more commonly used pesticides rapidly degrade in the natural environment, 

often a half-life of days. Degradation of pesticides includes biological, hydrolytic, and 

phtolytic processes that occur in the soil and water. Probably the most important process 

is the breakdown of organic chemicals by soil microorganisms. Most pesticides have a 

high affinity for clay and organic matter and may be removed from the soil water as they 

are bound to soil particles. Once bound, pesticides are often difficult to desorb (MacKay 

1992; Michael 2000).

When pesticides are applied to wildlands near surface waters, a buffer zone is usually 

left between the application area and the water resources. The width of the buffer varies 

with site conditions, site sensitivity, and state or local regulations. Little research has 

been done on the buffer width necessary on forested landscapes; more work has been 

done on agricultural lands.

Hand application of pesticides is easily controlled and site personnel can be advised to avoid streams or other sensitive areas. Pesticide analysis is expensive and any 

monitoring program can use surrogate assessments. Spray cards can be used to assess 

pesticide coverage and drift. Often the pesticide carrier (diesel) can be looked for in 

water quality samples to determine if overspray or drift resulted in pesticides entering 

surface waters.

Conclusions

A variety of fuel management practices are available to decrease fuel load or improve forest heath condition. These treatments have the potential to affect water quality, 

but the implementation of best management practices (BMPs) will minimize or eliminate potential water quality effects. There is a relationship between the amount of area 

John D. Stednick Cumulative Watershed Effects of Fuel Management in the Western United States
160 USDA Forest Service RMRS-GTR-231. 2010.

disturbed and the amount of potential erosion, thus the amount of disturbed area should 

be minimized. Streamside management zones or streamside buffers are effective in 

capturing overland flows, removing sediment and nutrients, and aiding in maintaining 

stream temperature.

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John D. Stednick Cumulative Watershed Effects of Fuel Management in the Western United States
164 USDA Forest Service RMRS-GTR-231. 2010.

Chapter 9.

Cumulative Effects of Fuel Treatments on 

Soil Productivity

Deborah S. Page-Dumroese, Rocky Mountain Research Station, USDA Forest Service, 

Moscow, ID

Martin F. Jurgensen, School of Forestry and Environmental Sciences, Michigan Technological 

University, Houghton, MI

Michael P. Curran, British Columbia Ministry of Forests and Range, Nelson, British Columbia

Sharon M. DeHart, Forest Service Job Corps, Lakewood, CO, (formerly Region 1 Soil 

Program Manager)

Introduction

Soil quality, function, and productivity potential are interrelated concepts that cover 

the range of soil properties and their associated ecological processes. Since the passage of the National Forest Management Act in 1976 (NFMA) and related legislation, 

management of National Forest lands must be done is such a way as to maintain their 

productive potential as demonstrated through implementation, effectiveness, and validation (research) monitoring. However, the concept of site productivity is not well 

defined, and the impacts of timber removal or fire on soil productive potential are not 

well understood or easily measured (Powers 2006). Two main factors make it difficult 

to define: (1) the variability in soil and climatic conditions across forest sites and (2) the 

length of time it takes for trees to reach a predictive age. If tree (or vegetative) growth 

is used as an indicator of productivity, it may take more than 20 years before the consequences of various management practices in many North American ecosystems can be 

evaluated (Morris and Miller 1994).

In response to this problem, a number of soil-based indices have been proposed as 

indirect measures of forest site productive potential. For example, Burger and Kelting 

(1998) suggest that soil monitoring should vary by soil, site, and management practice. 

Powers and others (1998) recommend establishing a baseline from a soil survey, then 

use one physical (soil strength), one chemical (anaerobically mineralized nitrogen N), 

and one biological (soil fauna activity) index to monitor changes in soil properties. 

Other soil measures of site productivity have been proposed (Burger 1996; Curran and 

others 2005a; Herrick 2000; Powers and others 1990), but the link between soil indices 

and site productivity are not conclusive (Curran and others 2005b; Powers and others 

1990, 2004). The data from these studies show that soil compaction and organic matter 

(OM) removal are important drivers in many ecosystem processes, and the maintenance 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
USDA Forest Service RMRS-GTR-231. 2010. 165

of adequate soil porosity and OM content is important for continued site productivity 

and ecological function (Jurgensen and others 1997; Powers and others 2004).

Active fire suppression in the western United States during the 20th century has led to 

OM accumulation in many forest stands that historically supported a regular fire return 

interval (Oliver and others 1994; Page-Dumroese and others 2003). Forest stands high 

in OM levels are usually undesirable because of the increased risk from high intensity 

wildfires and slower OM decomposition rates (Covington and Sackett 1984). These accumulations of woody residue and surface OM from fire suppression activities are likely 

above the range of natural variability for these ecosystems and would be susceptible to a 

correspondingly higher loss during a wildfire (Mutch 1995; Page-Dumroese and others 

2003). However, previous human disturbances make it difficult to determine baseline, 

stand level OM values. Fire suppression has also altered tree density, growth, vigor, 

and susceptibility to diseases and pests (Kilgore 1981), but the effects of this practice 

on soil properties are unclear (Monleon and others 1997). For instance, fire suppression 

can result in stagnant nutrient cycles and, therefore, decreased nutrient availability and 

tree growth (Biswell 1973; Covington and Sackett 1990). Conversely, current growth 

of ponderosa pine trees on some sites is higher than growth predicted from yield tables 

developed shortly after fire exclusion (Cochran and Hopkins 1991), which is attributed 

to a negative impact of fire on soil productivity.

Since the enactment of the Healthy Forest Restoration Act in 2003, forest management decisions to reduce wildfire risk have increasingly relied on partial cuts and 

prescribed fire to remove small diameter trees and surface OM from forest stands. 

Low intensity prescribed underburning, thinning, and combined thinning and burning 

practices are major components of the restoration effort underway in many forests to 

reduce fuel loads and fire hazards (Stephens and Finney 2002). Such repeated burns and 

multiple stand entries by mechanical equipment may have cumulative impacts on ecosystem productivity and sustainability at different scales, such as within a cutting unit 

or an entire watershed (Curran and others 2005a). In this paper, we discuss the effects 

of mechanical thinning and prescribed fire on soil compaction and OM pools and the 

impact this could have on residual fuel loads, soil erosion potential, and long-term site 

productivity (Elliot 2003; Harden and others 2000; Neary and others 2000).

Thinning

Many studies have documented the impacts of clearcut harvesting on soil physical 

properties, especially compaction (Miller and Anderson 2002; Page-Dumroese and others 2006; Powers 2006; Powers and others 2004). Similar harvesting equipment is also 

used in thinning operations and could result in soil compaction on repeatedly trafficked 

areas. Single equipment passes under specific soil moisture and equipment loading conditions (for example, moist soil, fully mechanized harvesting as demonstrated in Curran 

and others 2005a). Compaction increases soil bulk density and strength, decreases water infiltration and aeration porosity, restricts root growth, increases surface runoff and 

erosion, and alters heat flux (Greacen and Sands 1980; Williamson and Neilsen 2000). 

Total pore space is also reduced, especially the volume of large pores (macropores), 

which are usually filled with air (Siegel-Issam and others 2005). Poor aeration due to 

compaction is often cited as a cause of declining root growth (for example, Ruark and 

others 1982; Zaerr 1983). The susceptibility of soil to compaction is a function of soil 

texture and original bulk density (Page-Dumroese and others 2006; Powers and others 

2005; Williamson and Neilson 2000), soil moisture content (Froehlich 1978; Moehring 

and Rawls 1970), soil OM content (Adams 1973; Howard and others 1981), the number of machine passes (Soane 1990), and the type of machine applying the load (Han 

and others 2006). Compaction alters air filled pores, which restricts O2

 movement and 

creates anaerobic conditions (Linn and Doran 1984), causes the accumulation of CO2

(Conlin and van den Driessche 2000), and reduces the physical habitat of soil macroand micro-fauna (Hassink and others 1993).

D.S. Page-Dumroese, M.F. Jurgensen, M.P. Curran, S.M. DeHart Cumulative Watershed Effects of Fuel Management in the Western United States
166 USDA Forest Service RMRS-GTR-231. 2010.

It is assumed that minimizing soil compaction during a timber harvesting operation 

is critical for maintaining the productive capacity of a site (Powers and others 2004). 

While soil compaction can cause substantial declines in tree growth and health in some 

stands (Conlin and van den Driessche 1996; Froehlich and others 1986; Gomez and 

others 2002; Heninger and others 2002), they can have little or no impact on growth 

in others (Powers and others 2004). Growth reductions may occur on both coarse- and 

fine-textured soils (Cochran and Brock 1985; Froehlich and others 1986; Smith and 

Wass 1980); however, the reduction of macropore space on course-textured soils may 

increase soil available water holding capacity and thereby increase tree growth (Gomez 

and others 2002).

Compaction from repeated trafficking on the same plot of land is the most common 

cumulative soil effect of mechanical site treatments (Geist and others 1989). However, 

traffic over many portions of a watershed may also lead to dispersed cumulative impacts 

in the form of lighter compaction affecting a larger area (Curran and others 2005a). 

Thinning method also has a strong influence on the degree and extent of soil compaction. For example, cut-to-length logging, particularly on slopes less than 35 percent, can 

result in spatially dispersed traffic patterns if harvesting machine operators can choose 

their route to a landing. While this type of logging may show fewer surface impacts 

(displacement and visible machine tracks or ruts) than thinning with designated skid 

trails, most compaction occurs in the first few passes and soil damage may be more 

widespread (Curran 1999; Williamson and Neilsen 2000). Log-forwarder impacts occur 

mostly on main trails without slash mat protection or near landings, locations where 

the forwarder makes repeated passes. Using skyline logging systems to thin a stand 

usually results in soil compaction at the landings or is associated with dragging heavy 

logs. In northeastern Oregon, both skyline logging and harvester/forwarding operations 

produced less than 10 percent soil compaction on a number of sites (McIver and others 

2003). This amount of compaction is much lower than that found in other harvesting 

studies from the northwest United States (Allen and others 1999; Froehlich and others 

1986; Geist and others 1989). These variable results could be due to differences in harvesting techniques, which in turn affects the amount of soil compaction. Leaving slash 

from thinning or other harvest activities on skid trails has the potential to help buffer 

machine traffic to lower the impacts on the mineral soil (Han and others 2006), as does 

thinning a stand when the soil is dry (Han and others 2006), frozen (Bock and van Rees 

2002), or has adequate snowpack (Curran 1999). Consequently, managers have a number of options when they need to reduce fuel over large areas.

Another soil disturbance that may occur as a result of compaction and displacement is soil erosion. When surface moisture is impeded from infiltrating it can result in 

increased overland flow that can cause erosion and effect off-site resources and water 

quality. Prudent attention to drainage control and access network planning, construction, and maintenance can help minimize risks associated with erosion. An erosion 

hazard key is discussed later, under planning and monitoring.

Underburning

Underburning is a low intensity prescribed fire that is used to reduce fuel loads 

and fire hazards in overstocked stands (Monleon and others 1997). Since fire suppression caused a shift in forest structure, frequent underburnings are one method used to 

restore stands to pre-European settlement fire regimes (Bork 1985). The impacts of 

prescribed underburning on fuel loads and surface soil conditions can vary considerably depending on fuel characteristics and loading, soil climatic conditions at the time 

of burning, and resulting soil burn severity (Gundale and others 2005). Nitrification and 

N-mineralization showed strong positive correlations with fine fuel consumption after 

underburning in a Montana ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws) 

stand (Gundale and others 2005). In contrast, underburning a ponderosa pine stand in 

central Oregon resulted in a long-term (12 years) decrease in available N, even though 

short-term increases were found in the surface (0 to 5 cm) mineral soil immediately 

Chapter 9. Cumulative Effects of Fuel Treatments on Soil Productivity
USDA Forest Service RMRS-GTR-231. 2010. 167

D.S. Page-Dumroese, M.F. Jurgensen, M.P. Curran, S.M. DeHart Cumulative Watershed Effects of Fuel Management in the Western United States

after the fire (Monleon and others 1997). This lowering of soil N levels and subsequent 

decrease in tree growth after underburning may support the supposition that fire suppression will increase soil fertility (Cochran and Hopkins 1991).

Underburning alone or in combination with thinning can alter microbial communities in a forest stand by increasing the temperature of the post burn soil surface or 

changing the availability of organic substrates (Gundale and others 2005). Many studies 

have shown that soil heating during the burn results in a substantial short-term loss of 

microbial biomass or a shift in community structure (Choromanska and DeLuca 2002; 

Korb and others 2003; Pietikainen and Fritze 1995). These changes, and their duration, 

are the result of the interactions of fuel load, fuel moisture content, weather conditions, landscape position, light-up sequence, and resulting fire behavior and resident 

time combined with heat transfer variability within the soil profile (Busse and others 

2005; Hungerford and others 1991). If a prescribed underburn occurs after a stand is 

thinned, the increased fine fuel load usually results in a higher intensity fire, more OM 

loss, and changes in soil C and N (Pietikainen and others 2000). Total C in the surface 

OM can also be significantly higher after thinning alone as compared to thinning and 

underburning (Gundale and others 2005), but is dependent on the amount of C in the 

undisturbed stand (Page-Dumroese and Jurgensen 2006). The lowering of surface C and 

N pools by underburning is normally short lived, as OM accumulates from the residual 

trees (Gundale and others 2005).

The intent of underburning is to produce a low intensity, fast moving fire that leaves 

much of the humus layer intact (McCandliss 2002) to protect the mineral soil from 

raindrop splash and erosion. However, if large fuel (>7 cm diameter) are dry during 

the underburning, there can be a significant reduction in the amount of coarse wood 

on the soil surface (Youngblood and others 2006), which may affect many species 

of fungi, cryptogams, invertebrates, and vertebrates (Harmon and others 1986). The 

amount of woody residue remaining in a stand after underburning will vary depending 

on fuel load, moisture content, fire intensity, residence time, and suppression activity. Compared to other methods of fuel treatment (thinning, thinning and underburning 

combined), underburning alone usually results in the lowest quantity of residual coarse 

wood. For example, underburning resulted in less than 30 logs/ha, thinned and burned 

stands ~50 logs/ha, thinning alone ~150 logs/ha, and the control stand had larger than 

200 logs/ha (Youngblood and others 2006). Of these residual logs, decay class 5 logs 

(Triska and Cromack 1979) comprised 18 percent of the coarse woody residue in the 

thinned only and control treatments, but were only 7 percent in the underburned and the 

thinned and burned treatment (Youngblood and others 2006).

Planning and Monitoring

The development of a hazard assessment process to determine how sensitive a soil 

may be to mechanical and/or fuel reduction treatments can help minimize risk on forest 

sites and watersheds. For example, the Forest Practices Code of British Columbia, now 

replaced by the Forest and Range Practices Act (Province of BC 2004), defines site hazards as a combination of soil texture, coarse fragment content and soil moisture regime. 

This, in turn, can help guide practitioners in deciding on the appropriate types of equipment to be used, the harvest and maintenance schedule, or type of harvest operation (see 

Erosion Hazard key as an example in table 1, which is based on science and rationale 

presented in Carr and others 1991, with updates based on the research of Commandeur 

1994). The Weyerhaeuser Company assesses risk to site productivity from all types of 

management activities to site productivity for each soil mapping unit, largely based on 

soil physical properties (Heninger and others 1999). The risk ratings are based on modal 

soil characteristics for each soil series and site factors. Principles behind risk rating 

with further examples are discussed in Curran and others (2005b, 2007). Compaction, 

displacement, erosion, and slope stability risks are often interpreted from soil mapping 

(that needs to be verified onsite) or site specific data collected for harvest planning (for 

example, as per Curran and others 2000) and prescribed fire assessments. Harvesting, 
168 USDA Forest Service RMRS-GTR-231. 2010.

thinning, and underburning strategies have been described for meeting soil disturbance 

standards under site conditions in western Washington and Oregon by Heninger and 

others (1997) and for Interior BC by Curran (1999). The objective is to match site 

treatment to site disturbance sensitivity. Ground based equipment may be restricted to 

designated trails or allowed to travel overland depending on the soil and climatic conditions (in other words, dry soil, frozen soil, or snowpack).

Assessing soil changes associated with management is a critical step toward understanding which sites are amenable to trafficking or burning treatments. Generally, 

monitoring after underburning or thinning activities is collected through transect sampling of continuous line or point data (for example, Howes and others 1983; BC Ministry 

of Forests 2001, respectively). However, soil quality evaluations must also assess cumulative management impacts at a landscape scale, which is much harder to accomplish 

than a simple point sampling methodology. When working in larger areas, sampling 

schemes can be stratified (for example, by soil texture, parent material, vegetation type, 

harvest methods, etc.) to improve sampling efficiency and reduce costs (Herrick 2000).

Visual disturbance class indicators (Curran and others 2005b) have been used to 

assess soil displacement or compaction severity after mechanical operations. Such visual class systems are also amenable to the collection of burn severity categories (fire 

caused changes to soil hydrologic function as evidenced by soil characteristics) and 

to visually evaluate the extent of burning into the mineral soil and loss of forest floor 

and surface fuel (Ice and others 2004). The visual assessment of surface OM changes 

after thinning or underburning is often used as a surrogate or proxy for changes in soil 

properties. These properties are associated with loss of soil aggregates and increased 

erosion, which could indicate a loss of site productivity. Placing management impacts in 

the broader context of the range of natural variability observed before harvesting is another appropriate method for evaluating the consequences of thinning and underburning 

(Bock and Van Rees 2002; Grigal and Vance 2000; Landres and others 1999; Pennock 

and van Kessel 1997). Using baseline data from non-harvested stands will help quantify 

the magnitude of variability so that change in a soil property can be gauged against this 

variability and help define the processes that thinning or underburning operations influence (Grigal and Vance 2000; Page-Dumroese and others 2000).

Changes in soil OM can also be used as an indicator of soil biological activity and, 

indirectly, the effect of thinning and underburning on soil quality and site sustainability 

(Weil and others 2003). Weil and others (2003) developed a simple method to measure 

Table 1. Example of a hazard rating system for surface soil erosion within a cutting unit (adapted from the British 

Columbia Ministry of Forests from the Forest Practices Code soil disturbance hazard guidebook, currently 

available in Curran and others 2000).

Degree of contribution of factors

Site factors Low Moderate High Very High

Climate precipitation factor Low Moderate High Very high

(points) 2 4 6 8

Topography

slope gradient (%) 0-10 11-20 21-50 >50

(points) 1 3 6 9

length/uniformity Short broken Short uniform Long broken Long uniform

(points) 1 2 3 4

Depth to water-restricting layer (cm) >90 61-90 30-60 <30

(points) 1 2 3 4

Surface soil detachablity (0-15 cm) SC, C, SiC SiCl, Cl, SCL SL, L Si, SiL, fSL, LS, S

(points) 1 2 4 8

Surface coarse fragments (0-15 cm) >60 31-60 16-30 <16

(points) 1 2 3 4

Subsoil permeability (16-60cm) S, LS, SL, fSL L, SiL, Si Cl, SCl, SiCl SC, SiC

(points) 1 2 3 4

Erosion hazard rating Low Moderate High Very High

(point total) <16 16-22 23-31 >31

Chapter 9. Cumulative Effects of Fuel Treatments on Soil Productivity
USDA Forest Service RMRS-GTR-231. 2010. 169

active soil C and they note that a change in the labile OM fraction can give an early 

indication of soil degradation.

All of the methods listed above need to be applied in an adaptive management 

framework that will allow for changes in methods and procedures as new information or techniques become available (Curran and others 2005c). This adaptive process 

will ensure that the monitoring of thinning and underburning treatments is using best 

management practices, coordinating development of training materials and tools, and 

reporting post treatment evaluations.

Long term research projects are one of the best methods for quantifying the consequences of fuel reduction treatments and evaluation of monitoring strategies. 

Development of effective and practical methods for assessing changes in soil productivity has been the major focus of the North American Long Term Soil Productivity (LTSP) 

study (Powers and others 2004). Although designed to measure the long-term impacts 

of compaction and OM removal after clear-cut timber harvest, this study will also help 

to validate soil quality standards and monitoring changes in soil productivity after fuel 

reduction operations. While the LTSP study did not have a fire component, the Fire and 

Fire Surrogate study was established nationwide to evaluate the ecological impacts of 

thinning and burning treatments on vegetation, fuel, soils, and other ecosystem functions (Weatherspoon 2000).

Conclusions and Management Implications

Restoration treatments used to restore or enhance ecological processes and/or structure to a forest stand usually involve some variations of thinning and burning. Numerous 

soil impacts can occur from these treatments, but the impacts can be quite variable, depending on both manageable factors and inherent site sensitivity factors, which together 

dictate the severity and extent of compaction and burn severity. Manageable factors 

include equipment configuration and use, decisions on fuel arrangement and moisture 

levels, light-up sequence, and resulting fire behavior, all timed to take advantage of 

seasonal soil conditions to minimize impacts. Inherent site sensitivity depends on soil 

texture and mineralogy, coarse fragment content and arrangement, and organic matter 

levels and rooting, among other factors. The impacts of commercial or pre-commercial 

thinning operations (with or without burning) on residual tree growth will have to be 

measured to calibrate (validate) soil disturbance proxies and feed results into practice 

improvements to ensure sustainable productivity. When pre-treatment data is available, 

post-treatment monitoring can use soil disturbance proxies to provide an indirect measure of the impact that a fuel reduction treatment will have on soil properties that are 

currently considered to control productivity and hydrologic function. The results from 

these monitoring studies need to be validated against subsequent tree or stand growth. 

In contrast to clear-cut harvesting, the impacts of thinning operations on changes in soil 

quality can be difficult to quantify. Although the impacts of thinning operations on soil 

properties can be assessed relatively easily, the associated changes in site productivity 

are not documented. Thinning reduces total stand biomass, but can increase the growth 

of individual trees (Karlsson 2006; Liechty and others 1986). If the response of stand 

productivity to thinning is only measured on the residual trees, the negative impacts of 

soil compaction could be masked by the increased growth of the remaining trees.

Increasingly, managers must balance biomass removal to reduce wildfire risk with 

maintaining soil productivity. Thinning and underburning treatments require accurate 

monitoring of soil impacts using proxies that are calibrated against longer term effects 

over time. In the interim, these proxies need to be based on best available science and 

disturbance limits conservatively set to ensure that productivity and hydrologic function 

will be maintained. The wide variability in forest soil properties makes this a challenging task. However, by using risk rating systems, various soil factors affecting site 

sensitivity (response) can be organized and managed during planning and operations. 

The objective is to identify the inherent site sensitivities and/or seasonal soil conditions 

that create vulnerability to negative impacts of the selected fuel reduction treatments. 

D.S. Page-Dumroese, M.F. Jurgensen, M.P. Curran, S.M. DeHart Cumulative Watershed Effects of Fuel Management in the Western United States
170 USDA Forest Service RMRS-GTR-231. 2010.

These include factors such as specific soil texture, rock content, low soil fertility, a high 

proportion of OM pools on the soil surface, or topographic features. Successful fuel 

reduction monitoring protocols must use proxies that integrate the correct combination 

of chemical, physical, and biological properties and are calibrated to demonstrate the 

maintenance of long-term productivity. Use of best management practices (for example, 

site characterization, Curran and others 2000), detailed soil inventory, use of models to 

predict erosion (for instance, WEPP), thinning and underburning strategies to minimize 

disturbance, climatic considerations, soil disturbance monitoring, and prudent use of rehabilitation, all in an adaptive management approach (Curran and others 2005a and b), 

will help limit localized soil damage and reduce the potential of cumulative fuel reduction effects within a watershed. Ultimately, net primary productivity is the measure to 

determine the positive or negative impacts of thinning and underburning treatments and 

will have to be measured in controlled experiments that also calibrate the operational 

disturbance proxies. Consequently, the results from the North American LTSP network, 

the Fire and Fire Surrogate study, and other long-term studies must be an integral part of 

the effort to evaluate both short and long-term impacts of fuel reduction treatments on 

soil productivity and the validation of monitoring protocols and standards.

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Stephens, S.L.; Finney, M.A. 2002. Prescribed fire mortality of Sierra mixed conifer tree species: 

Effects of crown damage and forest floor combustion. For. Ecol. and Manage. 162: 261-271.

Triska, F.J.; Cromack Jr, K. 1979. The role of woody debris in forests and streams. In: Waring, 

R.H. [Ed.]. Forests: Fresh perspectives from ecosystem analysis. Oregon State University 

Press. Corvallis, OR: 171-190.

Weatherspoon, C.P. 2000. A proposed long-term national study of the consequences of fire and 

fire surrogate treatments. In: Neuenschwander, L.F.; Ryan, K.C.; Goldberg, G.E. [Eds.]. 

Proceedings of the Joint Fire Sciences Conference and Workshop. 15-17 June 1999. University 

of Idaho. Moscow, ID: 117-126.

Weil, R.R.; Islam, K.R.; Stine, M.A.; Gruver, J.B.; Samson-Liebig, S.E. 2003. Estimating active 

carbon for soil quality assessment: A simplified method for laboratory and field use. Am. J. of 

Altern. Agric. 18: 3-17.

Williamson, J.R.; Neilsen, W.A. 2000. The influence of forest site on rate and extent of soil 

compaction and profile disturbance of skid trails during ground-based harvesting. Can. J. For. 

Res. 30: 1196-1205.

Youngblood, A.; Metlen, K.L.; Coe, K. 2006. Changes in stand structure and composition after 

restoration treatments in low elevation dry forests of northeastern Oregon. For. Ecol. and 

Manage. 234: 143-163.

Zaerr, J.B. 1983. Short-term flooding and net photosynthesis in seedlings of three conifers. For. 

Sci. 29: 71-78.

Chapter 9. Cumulative Effects of Fuel Treatments on Soil Productivity
USDA Forest Service RMRS-GTR-231. 2010. 175

Chapter 10.

Potential Effects of Fuel Management 

Activities on Riparian Areas

Kathleen A. Dwire, Rocky Mountain Research Station, USDA Forest Service, Fort Collins, CO

Charles C. Rhoades

Michael K. Young, Rocky Mountain Research Station, USDA Forest Service, Missoula, MT

Introduction

A significant increase in fuel management treatments is underway as the Forest 

Service and other natural resource agencies implement the National Fire Plan (USDA 

USDI 2001), the Healthy Forests Restoration Act (GAO 2003; HFRA 2003), and the 

President’s Healthy Forest Initiative (Dombeck and others 2004; Graham and others 2004; Stephens and Ruth 2005). One of the four goals of the National Fire Plan 

Comprehensive Strategy is to reduce hazardous fuel, thus potentially decreasing the risk 

of severe wildfire and modifying fire behavior so that some wildland fires may be more 

readily and safely suppressed (Graham and others 2004; USDA USDI 2002).

The general objective of this report is to provide resource managers and specialists with a summary of existing knowledge that they can use to evaluate the impacts 

of proposed fuel treatment projects, particularly the cumulative effects on watersheds. 

Cumulative watershed effects are defined as “the environmental changes that are affected by more than one land use activity...” (Reid 1998). Cumulative impacts can result 

from individually minor but collectively significant actions that occur over a period 

of time (Belt and others 1992). In other words, the effects may prove to be additive or 

interactive. Riparian areas can act as both moderators and integrators of activities that 

occur within a watershed. Consideration of the potential effects of fuel treatments on 

ecological functions of riparian areas is essential in determining cumulative watershed 

effects.

The objective of this chapter is to synthesize the current state of knowledge about the 

potential impacts of streamside and upland fuel management on the structure and function of riparian areas. Although research is underway, little has been published on these 

topics, and most examples from the literature are derived from studies that investigated 

the effects of forest harvest or wildland fire. Although findings from studies conducted 

throughout the nation are presented in this chapter, the focus is on riparian areas in 

mountainous regions of the western United States The influence of fuel management 

practices on surface water quality and aquatic biota are addressed elsewhere in this 

report (Chapter 8; Chapter 11; Chapter 12).

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
176 USDA Forest Service RMRS-GTR-231. 2010.

Riparian Areas: Definition, Natural Variability, 

and Management

Definition of Riparian Areas

Riparian areas have been ecologically defined as “three dimensional zones of direct physical and biotic interactions between terrestrial and aquatic ecosystems, with 

boundaries extending outward to the limits of flooding and upward into the canopy of 

streamside vegetation” (Gregory and others 1991). The first dimension of riparian areas 

is the longitudinal continuum from headwaters to the mouths of streams and rivers and 

ultimately the oceans (Vannote and others 1980). The second is the vertical dimension 

that extends upward into the vegetation canopy and downward into the subsurface and 

includes hyporheic and belowground interactions for the length of the stream-riparian 

corridor (Edwards 1998; Stanford and Ward 1988). The third dimension is lateral, extending to the limits of flooding on either side of the stream or river (Stanford and Ward 

1993). The vertical and lateral dimensions include the distinct microclimates often associated with riparian areas. In this ecological framework, riparian areas are viewed in 

terms of spatial and temporal patterns of hydrologic and geomorphic processes, terrestrial plant succession, and aquatic ecosystems (Gregory and others 1991; Naiman 

and Decamps 1997). In the scientific literature the terms “riparian habitat,” “riparian 

area,” and “riparian ecosystem” are used somewhat interchangeably, and pertain to the 

ecologically defined area adjacent to streams (Knutson and Naef 1997). In this chapter, 

we use the term “riparian area” when referring to the three dimensional streamside 

zone (Gregory and others 1991). We focus on riparian areas bordering streams, rivers, 

and springs, although much of the information presented in this chapter also pertains to 

vegetated areas surrounding lentic waters such as lakes and wetlands.

To assist in managing riparian areas, numerous administrative definitions have been 

developed along with terms such as “streamside management zones,” “riparian habitat 

areas,” “riparian buffers,” and “riparian management zones”. Most definitions are based 

on attributes that differentiate streamside areas from adjacent uplands (Belt and others 

1992; Knutson and Naef 1997), such as moist soils and occurrence of plant species and 

communities that are adapted to them or may rely on somewhat arbitrary boundaries 

such as a fixed distance on each side of a stream channel (Belt and others 1992). We use 

the term “riparian buffer” when referring to any administratively defined area adjacent 

to flowing or lentic surface water, including those that are specified by a given distance 

from the stream or presence of certain ecological attributes.

As suggested by both ecological and some management definitions, riparian areas 

and influence do not stop at a uniform distance from the stream bank. Instead, they are 

composed of mosaics of land forms, plant communities, and environments that vary 

in width and shape within the larger landscape (Gregory and others 1991; Naiman and 

Decamps 1997) and are not always easily delineated. The Federal Interagency Stream 

Restoration Working Group recognized the following three components of the stream 

corridor: the stream channel, with flowing water at least part of the year; the floodplain, 

a highly variable area on one or both sides of the stream channel that is inundated by 

floodwaters at some interval; and the transitional upland fringe, a portion of the upland 

on one or both sides of the floodplain that serves as a transitional zone or edge between 

the floodplain and the surrounding landscape (Federal Interagency Stream Restoration 

Working Group 1998). In this chapter, we use the term “stream-riparian corridor” when 

referring to the stream channel, adjacent floodplains, and the transitional upland fringe. 

Each of these components should be considered in fuel management because of the linkages and feedbacks that occur among the channel, riparian area, and uplands (Federal 

Interagency Stream Restoration Working Group 1998).

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 177

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States

Natural Variability Among Riparian Areas

Stream-riparian corridors are highly variable and characterized by multidimensional 

spatial gradients. The effects of fuel reduction treatments on riparian areas will depend 

largely on the location of the treatments within a watershed, that is, if they are adjacent 

to the channel or in the uplands or headwaters, middle or lower portion of the drainage, 

and positioned relative to tributaries in the stream network. The factors that vary in different portions of a watershed, including soil characteristics, slope, vegetation cover, 

moisture, and microclimate, also influence the behavior of wildland fire and the potential responses of riparian areas to fuel reduction treatments. Effects will also vary 

considerably depending on the type of treatment. Some treatments in close proximity 

to riparian areas may have little effect, such as a relatively cool prescribed fire with low 

flame length, whereas other treatments may significantly influence riparian areas.

The longitudinal profile of many streams in the western United States can be roughly 

divided into three zones, which are described based on a simple model of dominant 

erosion processes: the steep headwaters, central transfer zone, and low elevation depositional zone (Schumm 1977). Each zone is also characterized by riparian plant species, 

growth forms, and communities that reflect the elevation, geomorphic position, hydrologic and sediment regimes, and past disturbance within a watershed (Carsey and others 

2003; Crowe and Clausnitzer 1997; Youngblood and others 1985). The three-zone 

model is frequently presented for mountain streams; however, the general erosion and 

geomorphic patterns are also applicable to drainages with less topographic relief. Other 

stream classifications based on physical processes also help to explain the interactions 

between the distribution of riparian vegetation and watershed variables and emphasize 

the role of temporal and spatial scales in understanding the interdependence of physical 

and biotic processes (Frissell and others 1986; Montgomery 1999; Montgomery and 

Buffington 1998; Poole 2002; Rosgen 1994; Ward and Stanford 1995).

The diversity of riparian areas is also attributed to the temporal variability in physical 

events and natural disturbances, such as floods, debris flows, landslides, and wildland 

fire along with the subsequent successional changes in riparian plant communities over 

time (Gecy and Wilson 1990; Naiman and others 2005). Fire is a critical disturbance that 

has shaped the structure of forests and rangelands throughout the western United States 

(Agee 1993, 1998; Stephens and Ruth 2005). Although limited research has investigated the role of fire in structuring streamside vegetation, riparian plant communities 

evolved within the ecological context of regional fire regimes (Arno 2000). Studies in 

several parts of the western United States have revealed that historical fire frequencies in uplands and riparian areas were often comparable (Macdonald and others 2004; 

Olson and Agee 2005), whereas in others, riparian fires were less frequent but more 

severe than those in uplands (Arno 1996; Everett and others 2003). Moreover, dendrochronological analyses often detected the same fire events in upland forests and adjacent 

riparian areas. The decline in fire frequencies in both areas corresponded with the onset 

of effective fire suppression (Everett and others 2003). Effects of both wildland fire and 

fire suppression have likely influenced riparian vegetation and functions and should 

be acknowledged during planning and implementation of fuel reduction treatments. 

Predicting the potential impacts of fuel treatments on riparian areas requires consideration of the fire history and natural fire regime along elevation gradients throughout the 

treated watershed and surrounding landscape (Agee 1991, 1993; Arno 2000).

Current attributes and condition of riparian plant communities reflect the historically recent (approximately 100 to 200 years) physical conditions of the landscape as 

well as land management activities (NCASI 2005). Forest harvest, livestock grazing, 

road construction, inadequate road maintenance, flow alteration (dams and diversions), 

and recreation have altered composition and structure of riparian plant communities 

(Kauffman 2004; NCASI 2005). Removal of beaver has changed stream and floodplain 

hydrology in watersheds throughout the western United States and directly and indirectly influenced riparian vegetation and nutrient and organic matter dynamics. Mining 

activities, particularly dredging and hydraulic mining, have left a lasting legacy on the 

geomorphology and hydrology of many western stream riparian corridors (Wohl 2001). 
178 USDA Forest Service RMRS-GTR-231. 2010.

Although portions of many riparian areas along perennial streams are currently protected, the lingering effects of land management prior to the establishment of buffers 

are likely to influence the structure and composition of riparian areas for decades to 

centuries (Young and others 1994). Legacies of past management within watersheds 

could potentially confound responses to fuel reduction treatments.

Best Management Practices and Protection of Riparian Areas

Riparian areas cover a relatively small area, yet they are disproportionately important for maintenance of water quality and quantity (water storage and aquifer recharge), 

habitat for aquatic and terrestrial biota, sediment retention, stream bank building and 

maintenance, and provision of services of economic and social value such as livestock 

grazing and recreation (table 1) (Gregory and others 1991; Naiman and Decamps 1997; 

Naiman and others 2005; Prichard and others 1998). On National Forest lands, protection of riparian areas is often governed by special rules, stated as Standards and 

Guidelines in the Forest Plan for each National Forest, which frequently include sets 

of best management practices (BMPs) (Belt and others 1992; Gregory 1997; Mosley 

and others 1997). BMPs are officially approved practices and techniques that are generally cost effective and practicable means of reducing management impacts on streams, 

valued riparian functions, or ecosystem services (Belt and others 1992; Mosley and others 1997). The management of riparian areas can generally be defined as custodial, in 

which the riparian areas are protected to maintain specific functions (table 1) (Gregory 

1997). The general objective of most BMPs is to protect water quality and habitat along 

streams from timber harvest, road construction, grazing, recreation, and other land use 

activities (Belt and others 1992; Mosley and others 1997) and is often accompanied by 

the designation of riparian buffers (Norris 1993).

Riparian buffers contribute to watershed protection by restricting management activities and other human caused disturbances that alter ecological conditions of stream 

riparian corridors (Norris 1993). Riparian influence decreases with distance from the 

stream channel (fig. 1) (FEMAT 1993). Depending on stream width, location within a 

drainage basin, and management concerns, the required riparian buffer width may vary 

from 5 ft to 300 ft on each side of the stream (Belt and others 1992; Lee and others 

2004). Streams used for domestic water supplies are accorded wider riparian buffers to 

protect downstream reservoirs from non-point pollution resulting from forest management (Belt and others 1992). Many federally listed plant and animal species (frequently 

selected as management indicator species) require riparian areas as habitat. Streams that 

are important for spawning, rearing, or migration of sensitive fish species often receive 

additional protection in the form of wider buffers (USDA 1995). Existence of a riparian 

buffer, however, does not preclude all types of management activities. Lee and others 

(2004) noted that about 80 percent of state and provincial jurisdictions permitted riparian timber harvest. Regulations on public lands are somewhat more restrictive but still 

allow active riparian management.

The effectiveness of BMPs in mitigating the impacts of land management varies 

considerably depending on local conditions, management guidance and practices, 

and the stream or riparian feature of concern (Belt and others 1992; Weller and others 

1998). Implementation of BMPs and establishment of riparian buffers have generally 

decreased the negative effects of forest harvest activities on surface water quality (Belt 

and others 1992; Norris 1993; Osborne and Kovacic 1993). However, less is known regarding BMP effectiveness in protecting other riparian functions (table 1). For example, 

in western Washington, Brosofske and others (1997) found that forest harvest strongly 

affected the riparian microclimate despite designated buffers (mean buffer width, 72 ft; 

range, 40 to 236 ft). Whereas riparian buffers and BMPs will likely assist in mitigating 

some impacts of upland fuel reduction treatments, additional precautions and actions 

may be necessary to protect particular riparian functions. In burned watersheds or areas 

that have experienced insect caused mortality, riparian buffers may consist of mostly 

dead trees, and streamside fuel loads may cause concern about fire risk and potential 

fire behavior. Although the utility of such buffers is questionable for functions such as 

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 179

Table 1. Functions of riparian areas and key relationships to ecological service (modified from NRC 2002; Naiman and others 2005).

Indicators of On-site or off-site Valued goods 

Riparian functions riparian functions effects of functions and services provided

Hydrology and sediment dynamics

Short-term storage of surface Connectivity of floodplain and Attenuates downstream flood Reduces damage from

water stream channel peaks floodwaters

Maintenance of high water table Presence of flood-tolerant, Maintenance of distinct vegetation, Contributes to regional

hydrophytic, & mesic plant particularly in arid climates biodiversity through provision 

species of habitat

Retention and transport of Riffle-pool sequences, point bars, Contributes to fluvial processes Creates predictable yet

sediments; riparian vegetation floodplain terraces, and bank dynamic channel and floodplain

decreases stream bank erosion stability features

Biogeochemistry and nutrient cycling

Riparian vegetation provides Healthy mosaic of riparian Maintenance of aquatic and Supports terrestrial and aquatic

source of organic carbon vegetation terrestrial food webs biodiversity 

(allochthonous inputs to streams; 

organic matter inputs to soils) 

Transformation and retention of Water quality and biotic indicators Interception of nutrients and Improvement and maintenance

nutrients and pollutants toxicants from runoff; water of water quality

quality

Sequestration of carbon in Occurrence, extent, & distribution Contributes to nutrient retention Potentially ameliorates global

riparian soils of organic-rich soils and carbon sequestration warming; provides source of 

dissolved carbon to streams 

via subsurface flow paths

Distinctive terrestrial and aquatic habitat 

Contributes to overall biodiversity High species richness— Provides reservoirs for genetic Supports regional biodiversity 

and biocomplexity plants and animals diversity

Maintenance of streamside Presence of shade-producing Provides shade and thermal Maintains habitat for sensitive 

microclimate canopy; healthy populations of insulation to stream; provides species (amphibians,

native terrestrial and aquatic biota migratory corridors for terrestrial cold-water fishes, others)

and aquatic species

Contribution to aquatic habitat; Aquatic habitat complexity Maintenance of aquatic biota Maintenance of fisheries,

provision of large wood (pool-riffle sequences, debris recreation

(CWD/LWD inputs) dams); maintenance of aquatic 

biota 

Provision of structural diversity Availability of nesting/rearing Maintenance of global biodiversity; Recreation: bird watching,

habitat; presence of appropriate provides migratory corridors for wildlife enjoyment, and game

indicator wildlife species (for terrestrial and aquatic species hunting

example, neotropical migrants) 

100

0

0 .2 .5 1

Coarse wood debris

to stream

Shading

Root

strength

Litter

fall

Distance from channel (tree height)

Cumulative effectiveness (%)

Figure 1. Generalized curves 

indicating cumulative percent 

effectiveness of riparian ecological 

functions occurring with varying 

distance from the stream channel 

(FEMAT 1993).

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
180 USDA Forest Service RMRS-GTR-231. 2010.

maintenance of stream water quality, they may provide critical wildlife habitat and an 

important source of large wood for streams and floodplains. In these cases, as well as for 

prescriptions that are being planned and conducted within riparian areas, managers may 

need to develop and implement additional on-site BMPs and riparian-specific prescriptions to protect streams and valued riparian functions.

Potential Effects of Fuel Management Activities 

on Riparian Areas

Fuel Management Treatments

Fuel reduction treatments are being planned and implemented throughout the western United States (http://www.fireplan.gov). Most treatments have the overall goal of 

decreasing the risk of high severity fire by fragmenting the forest canopy, removing ladder fuel, and reducing the abundance of ground fuel (Peterson and others 2005). Forest 

fuelbeds can be categorized into six strata:

1. forest canopy,

2. small trees and shrubs,

3. low vegetation,

4. dead wood,

5. moss, lichens, and litter, and

6. duff (Sandberg and others 2001).

Fuel reduction treatments typically target crown, ladder, and surface fuel (Peterson and 

others 2003) and include prescribed fire, thinning and other silvicultural operations, 

and chemical and biological treatment (Graham and others 2004). There is considerable 

variation within each treatment type. For example, a controlled burn prescription may 

include different burn intensities and different preparation procedures. Also, various 

combinations of different treatments are used to modify vegetation in each stratum and 

depend on project objectives, targeted fuel, current condition of the vegetation, past 

management, and logistics (Peterson and others 2005) (Chapter 4). Each treatment type 

and combination could have very different individual and cumulative environmental 

effects on ecosystems processes and attributes, ranging from negative to positive to 

benign. Also, fuel reduction projects usually require a sequence of multiple treatments 

staged over a period of time. Discussion of the variation in fuel reduction treatments and 

potential impacts of each type are beyond the scope of this review chapter. However, the 

effectiveness of projects in reducing site specific fire hazard and minimizing negative 

environmental consequences will depend on knowledge of natural fire regimes and existing data on current and historical forest structure and fuel distribution (Peterson and 

others 2005). The current management of natural ignitions or wildland fire use must also 

be integrated into planning for fuel reduction treatments and considered in assessment 

of cumulative impacts.

For most riparian plant communities, few data are available on fuel loads, characteristics, or distribution (Dwire and Kauffman 2003); however, there is a perception 

that current fuel quantities in some riparian areas are hazardous and constitute a fire 

risk. This has likely resulted from the recognition that fire in some riparian areas was 

historically common and that fire suppression has contributed to the accumulation of 

fuel in riparian areas as it has in uplands, particularly in forest types that historically 

supported low intensity, high frequency fire (Everett and others 2003; Olson and Agee 

2005). Given data limitations on historical composition and structure of riparian vegetation, managers are encouraged to consider the natural fire regime and fire history of the 

watersheds to be treated when they define target fuel loads for riparian areas.

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 181

Despite the uncertainty, fuel reduction treatments are underway in riparian areas 

(http://www.fireplan.gov/reports) and for some projects objectives extend beyond 

the reduction of fire risk. For example, prescribed fire has been used to control invasive species along streams and rivers (Tamarix spp. in the Bighorn River Basin, 

Wyoming, Bureau of Land Management Worland Field Office) and enhance wildlife 

habitat through the regeneration of willows (Bridger-Teton National Forest and Grand 

Teton National Park, Wyoming). Mechanical methods have been employed to protect 

structures (for example, restrooms, interpretive displays, and developed campsites) at 

riparian recreational sites such as picnic areas and campgrounds (for example, along the 

Colorado River near Moab, Utah, Bureau of Land Management Moab Field Office). 

These projects are generally quite small (less than 5 acres), and the ecological effects 

are likely to be fairly local. Most projects are being implemented in riparian areas that 

have undergone considerable management and disturbance, including wildfire, infestation by exotic species, timber harvest, and road and recreational development. These 

fuel reduction projects are providing managers with opportunities to reduce fire risk, 

remove invasive species, and restore streamside areas to conditions that support valued 

riparian species.

Riparian Vegetation

Riparian plant communities frequently constitute the most floristically and structurally diverse vegetation in a given region (Naiman and others 1993, 1998, 2005; Pollock 

and others 1998; Tabacchi and others 1998). Because of their transitional location at 

the land water ecotone, riparian plant communities may include upland, riparian, and 

wetland species, and thus maintain high levels of beta and gamma diversity (Pollock 

and others 1998), and a range of life forms and functional groups (NCASI 2005; Pabst 

and Spies 1999). Numerous vascular plant species of concern occur in riparian habitats 

(CNPS 1997; Eastman 1990). Riparian plant species have an array of morphological, 

physiological, and reproductive adaptations for survival in variable and frequently 

disturbed environments. Specific adaptations include those related to flooding, erosion, sediment deposition, seasonally saturated soil environments, physical abrasion, 

and stem breakage. Patterns of riparian plant community development and structure 

are driven by responses to disturbance, hydrologic and geomorphic variables, soil and 

substrate characteristics, and biological attributes related to succession (Baker 1989). 

Characteristics of vegetation structure are similar to those used to categorize fuelbed 

strata (Peterson and others 2005) and include age class, structural type, size, shape, and 

spatial distribution (vertical and horizontal) of vegetation components (Spies 1998).

Limited research has been conducted on the effects of fuel reduction treatments on 

riparian vegetation. However, results from studies of prescribed fire and more extensive forest harvest treatments in upland and riparian areas may be helpful in evaluating 

potential impacts (table 2) (NCASI 2005). Bêche and others (2005) sampled riparian 

vegetation before and after a fall prescribed burn along stream segments in the central 

Sierra Nevada Mountains of California. They found that ground cover taxa richness decreased more in the burned plots than unburned plots, diversity (Simpson’s D) decreased 

in both, and ordination results showed little difference in community composition between burned and unburned riparian plots (table 2) (Bêche and others 2005). Similar 

results have been observed in other locations following prescribed fire (Elliott and others 1999) and may partly be due to patchy burning. In the Oregon Coast Range, riparian 

herbaceous plant diversity did not differ significantly between unharvested riparian 

buffers surrounded by logged uplands and undisturbed riparian forests located in unharvested watersheds (table 2) (Hibbs and Giordano 1996; Hibbs and Bower 2001). In 

forested uplands of the Cascade Mountains (Oregon and Washington), clearcut logging 

and other types of forest harvest have tended to reduce plant diversity initially, although 

most shrub and understory species recover with time as succession proceeds (Halpern 

and others 1992; Halpern and Spies 1995). It should be noted, however, that certain rare 

species have been locally extirpated by forest harvest (Halpern and Spies 1995; Hansen 

and others 1991). As expected, plant cover and structure were dramatically reduced in 

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
182 USDA Forest Service RMRS-GTR-231. 2010.

the first few years following prescribed burning and forest harvest treatments (Bêche 

and others 2005; Halpern and Spies 1995).

Management activities have also increased the vulnerability of riparian areas to invasion by nonnative species (DeFerrari and Naiman 1994; Fleischner 1994; Parks and 

others 2005; Planty-Tabacchi and others 1996). Following forest harvest, the occurrence 

of nonnative species has increased at some sites (Andrus and Froehlich 1988; Halpern 

and Spies 1995). Livestock grazing has led to the introduction of both non-indigenous 

pasture species and noxious range weeds throughout the western United States, including riparian areas (Fleischner 1994; Hessburg and Agee 2003). Many stream valleys 

serve as transportation corridors, and roads and trails—known to be major conduits for 

dispersal of nonnative plants—are frequently located within floodplains (Forman and 

Alexander 1998; Gelbard and Belnap 2003; Trombulak and Frissell 2000). The potential for introduction or increased cover of invasive species is an important consideration 

in the planning and implementation of fuel reduction treatments (Harrod 2001).

Table 2. Effects of wildfire, prescribed burning, and forest harvest treatments on diversity of forest and riparian vegetation.

Time scalea 

Source (years) Treatment and study type Location Findings

Andrus and Froehlich 1988 +2 to + 135 Logging, wildfire, logging + Western hemlock–Douglas Rapid regeneration of shrub and

wildfire; retrospective fir forest type; Oregon Coast herbaceous species; initial

sampling in riparian plots Range (28 streams) increase in exotic species;

overall increase in alder cover/ 

dominance

Nierenberg and Hibbs 2000 + 145 Stand-replacing wildfire; Western hemlock–Douglas Understory shrubs and red alder

retrospective sampling in fir forest type; Oregon dominate initially; eventually

riparian plots Coast Oregon (9 streams) replaced by conifers

Bêche and others 2005 -1 to +1 (with Fall prescribed burn in Mixed-conifer forest type; No clear treatment effects in

unburned riparian plots; experimental Sierra Nevada, CA; riparian community composition;

controls) study diversity decreased in both 

burned and unburned plots

Elliott and others 1999 -1 to +2 Spring prescribed fire on Mixed-oak and pine/ No change in riparian species

hillslope gradient including hardwood forest types; No. composition

riparian cove; experimental Carolina

study

Hibbs and Giordano 1996 +1 to + 32 

(with controls) Unharvested alder- Western hemlock–Douglas No difference in herbaceous

dominated buffers across fir forest type; Oregon Coast species richness, evenness, or

chronosequence of upland Range diversity between buffered and

harvest compared to alder- undisturbed plots 

dominated riparian forests 

undisturbed by upland 

logging; retrospective 

sampling in riparian plots

Hibbs and Bower 2001 +1 to +33 Unharvested riparian buffers Four overstory canopy types: Understory shrub and 

Pabst and Spies 1999 across chronosequence pure conifer (western herbaceous diversity strongly

since upland harvest; hemlock–Douglas fir); conifer correlated with canopy cover

retrospective sampling in dominated; pure hardwood type; no strong differences in

riparian buffers; compared (alder, maple), hardwood shrub and herbaceous cover or

buffer results to those from dominated; Oregon Coast composition between riparian

unmanaged riparian areas Range buffers and undisturbed riparian 

forests.

Halpern and Spies 1995 Varied; for most Clear-cut logging, slash Douglas fir-dominated Temporal trends varied; for most

plots, before (-1) burning, thinning; permanent (young, mature, old-growth); plots, understory richness was

and after (+2 to plot and chronosequence West Cascades, Oregon, reduced following logging, but

+20) logging sampling in managed and and Washington recovered over time 

unmananged upland forests 

a Time scale relative to treatment (year of treatment = 0)

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 183

An immediate goal of most fuel reduction treatments in upland and riparian areas is 

to change vegetative structure, although the longer term changes on plant community 

composition, as well as other ecological consequences, are difficult to predict. In many 

cases, fire managers are able to implement controlled burns by prescription to obtain 

the desired effects (for example, no tree mortality or mortality of certain size classes). 

Reports of successful implementation of prescribed burns are not yet generally available. Monitoring has been minimal and little is known about meeting the longer term 

project objectives, particularly for riparian areas. Many riparian species appear to be 

fairly resilient to disturbance, particularly fire (Dwire and Kauffman 2003). Because of 

the ecological importance of riparian vegetation and the experimental nature of most 

fuel reduction treatments in riparian areas, monitoring before and after treatment to 

evaluate achievement of objectives, including the response of streamside plant communities, will assist in advancing our understanding and avoiding litigation.

Terrestrial and Aquatic Habitat in Stream-Riparian Corridors

Terrestrial Habitat

The critical importance of riparian areas for wildlife, particularly in arid portions of 

the western United States, is well recognized (Kauffman and others 2001; Kelsey and 

West 1998; Raedeke 1988; Thomas and others 1979). Characteristics of stream-riparian 

corridors that are important for wildlife are related to the transitional nature of the interface between upland and aquatic habitats, the resulting microclimates and provision of 

water, food, and cover, and the generally linear shapes with high edge to area ratios that 

serve as routes of seasonal migration for many vertebrate species (table 1) (Kauffman 

and others 2001; Kelsey and West 1998). Structurally and spatially complex riparian 

vegetation provides important habitat for some species, including large and small wood 

on the ground, snags, multiple and diverse vegetative strata and canopy layers (cover), 

and complex branching patterns (Steel and others 1999).

Managers designing fuel reduction treatments need to consider the riparian features 

required by wildlife species of concern as well as potential conditions that might promote increases in undesirable nonnative species (Pilliod and others 2006; Strohmaier 

2000; Tiedemann and others 2000; Wales 2001). Wildlife species that use riparian areas 

are generally divided into riparian obligates, riparian generalists, and exotic species 

(Kelsey and West 1998). Riparian obligates require or depend highly on riparian and 

aquatic resources to the extent that they are likely to be locally extirpated with loss of 

riparian habitat. Such species include some amphibians, reptiles, and small mammals 

and numerous bird species (Kelsey and West 1998). Riparian generalists utilize both 

riparian and upland habitats, and include some salamander species, reptiles, large and 

small mammals (particularly bats), and birds (Kauffman and others 2001; McComb 

and others 1993; Raedeke 1988). Riparian areas support nonnative animal species, such 

as introduced game birds, as well as undesirable exotic wildlife species, such as nutria 

(Myocastor coypus) (Hayes and Jennings 1986). The fragmentation of native riparian 

cover types influences the distribution of certain wildlife species, often favoring opportunistic species over those with more specific habitat requirements (Knopf and others 

1988; Raedeke 1988). In some regions, breaks in riparian corridor continuity can impact 

animal movement (Smith 2000). Narrow corridors that are essentially edge habitat may 

encourage generalist species, nest parasites, and predators (Knopf 1986; Knopf and 

others 1988).

Research on the influence of prescribed fire, wildland fire, and forest harvest on 

wildlife species and habitat has shown mixed results that vary considerably for different 

taxa and by region (table 3) (Raedeke 1988; Smith 2000). Forest management practices 

primarily affect fauna in the ways that they affect habitat, including nesting, rearing, and 

food availability (Lyon and others 2000; Tiedemann and others 2000). Some wildlife 

taxa (or certain life stages of some taxa) may benefit from a particular forest management practice while others may be harmed. For example, certain mammals and birds 

have been shown to increase in species numbers with forest harvest, while reptiles and 

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
184 USDA Forest Service RMRS-GTR-231. 2010.

amphibians have decreased (Raedeke 1988; Salo and Cundy 1987; Thomas and others 

1979). In addition, beneficial effects of forest management on wildlife are sometimes 

difficult to separate from those that are detrimental (Raedeke 1988) and may change 

over successional time. Recent reviews have summarized the general patterns of bird 

responses to fire (Pilliod and others 2006; Saab and Dudley 1998; Saab and Powell 

2005). Our understanding of forest harvest on wildlife species is limited, but even less 

is known about the potential effects of fuel reduction treatments (Bury 2004). Thinning 

and prescribed burning may significantly impact some wildlife by reducing the amount 

of down wood (cover), reducing numbers of older snags (nesting sites), and altering 

the plant species composition of the treated stands (cover and food) (Tiedemann and 

Table 3. Effects of wildfire, prescribed burning and forest harvest treatments on riparian and aquatic habitat and biota.

Source	 Time scalea (years) Treatment and study type Location Findings

Pilliod and others 2003 Review of monitoring Wildland fire, prescribed fire Range of vegetation types, Limited research; declines in

and research results largely conifer or hardwood several amphibian species 

forests; USA and Australia; following wildland and 

prescribed fire

Bury 2004 Review of monitoring Wildland fire, various fuel Mixed conifer; Pacific Limited effects on terrestrial

and research results treatments Northwest forests amphibian species and riparian 

generalists; negative effects on 

riparian obligates

Bury and Corn 1988 Review of monitoring Various forest harvest Mixed conifer; Pacific Declines in amphibian

and research results practices Northwest forests populations following logging; 

severity of decline depended on 

species

Hicks and others 1991 Review of research Removal of trees from Mixed conifer; Pacific Negative impacts on native

results riparian areas and various Northwest forests salmonid species; degradation

upland harvest practices of habitat and reduction in 

number of fish

Smith (ed.) 2000 Review of monitoring Wildland fire, prescribed fire Range of vegetation types, Wildfire and prescribed burning

and research results largely conifer or hardwood affect habitat and food 

forests; USA availability; impacts vary by 

species and with time since fire

Bêche and others 2005 -1 to +1 (with unburned Fall prescribed burn in Mixed-conifer forest type; Periphyton biomass initially

controls) riparian plots; experimental Sierra Nevada, CA lower in the burned stream, but

study exceeded biomass in unburned 

streams within 1 year;

Aquatic macroinvertebrate 

communities showed no 

detectable response

Huntzinger 2003 +1 to +10 Wildland fire, prescribed fire; Mixed-conifer forest types; More butterfly species in burned

experimental study Yosemite National Park, areas (wildfire and prescribed

California; Southern Oregon fire) relative to controls

Hawkins and others +2 to +25 Clearcut logging Mixed conifer; Pacific Initial increases in fish and

1983 Northwest forests salamander populations, 

followed by declines

Brosofske and others -2 to +2 Hillslope clearcut/ harvest Douglas–fir dominated; Harvesting affected riparian

1997 West Cascades, Washington microclimate gradients; 

increased air temperature, 

decreased relative humidity;

riparian environments became 

more similar to uplands

Li and others 1994 Review of multiple Multiple—cumulative effects Range of vegetation types, Cumulative effects of grazing, 

management impacts mostly mixed conifer; forest harvest, water diversions

on aquatic habitat Northeast Oregon result in increased stream 

temperature, degraded fish 

habitat

a Time scale relative to treatment (year of treatment = 0)

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 185

others 2000). However, fuel reduction treatments may also benefit certain species or 

multiple species at certain times. For example, riparian burning and thinning resulted 

in increased butterfly species richness and diversity along streams in the Sierra Nevada 

Mountains of California (table 3) (Huntzinger 2003).

As land managers proceed with fuel reduction prescriptions, wildlife habitat issues 

may be among the most contentious and vulnerable to litigation (Bury 2004). The presence of threatened or endangered wildlife species will likely preclude fuel reduction 

treatments in particular areas, including some riparian areas. However, if goals for treatments include both reduction of fire risk and the return to more historically natural 

conditions that support riparian habitat (Arno 1996), potential impacts to a range of 

wildlife species need to be evaluated. The basic life history traits and riparian habitat 

elements required by rare wildlife species need to be considered at different spatial and 

temporal scales. Wildlife species will likely respond differently to various prescriptions 

and successional changes following fuel reduction treatments, as has been observed 

with other management practices (Bury 2004; Knopf and others 1988; Pilliod and others 

2006; Raedeke 1988). Although there may be short-term risks to some riparian habitat, 

fuel reduction treatments (and the reintroduction of fire to riparian areas) may result in 

a more spatially diverse range of habitat components with long-term benefits for certain 

species. Given limitations of current knowledge on the effects of prescribed fire and 

mechanical treatments on wildlife, monitoring the response of species of concern before 

and after fuel treatments may be essential to avoiding litigation in some locations.

Aquatic Habitat

Streambank stability: Riparian vegetation can directly affect stream channel characteristics, particularly streambank stability (Davies-Colley 1997; Gregory and Gurnell 

1988; Pollen and others 2004; Simon and Collison 2002). Root systems can armor 

stream banks (Stokes and Mattheck 1996; Abernathy and Rutherford 2001) and bind 

bank sediment, thus contributing to bank stabilization, reduction of sediment inputs to 

streams (Dunaway and others 1994), and development and maintenance of undercut 

banks (Sedell and Beschta 1991). Studies have shown marked differences among riparian species and vegetation types in root characteristics and their influence on bank 

stability (Lyons and others 2000; Simon and Collison 2002; Wynn and others 2004). 

Removal of woody riparian vegetation with beneficial rooting characteristics can result 

in erosion of alluvial streambanks. Removal of herbaceous vegetation can decrease retention and accumulation of sediment, possibly influencing floodplain soil development 

(Thorne 1990). Local alterations to riparian vegetation that affect bank stability and 

other geomorphic processes may have effects that extend downstream.

The contribution of woody roots to streambank stabilization was modeled for forested reaches and predicted to extend approximately one-half the average crown diameter 

(fig. 1) (Wu 1986). Trees growing along the banks are important for maintenance of 

streambank stability in most locations, and we suggest that they be retained and protected during mechanical fuel reduction treatments. Prescribed fire may top kill certain 

riparian trees and shrubs but is unlikely to negatively affect belowground structure 

(Dwire and Kauffman 2003). In planning fuel reduction treatments in riparian areas, 

managers need to consider rooting characteristics of the plant species treated and the 

likely replacement species, the nature of streambank sediments, and potential impacts 

on streambank stability.

Aquatic foodwebs: By altering riparian vegetation, fuel reduction treatments have the 

potential to influence stream-riparian organic matter dynamics and aquatic trophic pathways. Autochthonous organic matter is generated through photosynthetic production by 

autotrophic organisms of the aquatic community (vascular plants, bryophytes, algae, 

bacteria, and protists) and is driven by the amount of light reaching the stream surface. 

Removal of riparian vegetation can result in increases in stream temperature and light, 

thus promoting autotrophic production (Bisson and Bilby 1998). In contrast, allochthonous organic matter originates directly from riparian or upland vegetation in the form 

of leaves, twigs, and other fine litter and indirectly as terrestrial invertebrates (Bisson 

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
186 USDA Forest Service RMRS-GTR-231. 2010.

and Bilby 1998). The input, use, retention, and transport of allochthonous organic matter in streams may drive carbon and nutrient dynamics and affect biota (Webster and 

Meyer 1997). For most low order streams in forested watersheds, much of the energy 

for aquatic food webs is derived from allochthonous inputs (Fisher and Likens 1973; 

Sedell and others 1978; Vannote and others 1980; Newbold and others 1982). Different 

plant sources vary widely in nutritional quality, and require different degrees of instream processing and conditioning by microbes and invertebrates (Allen 1995; Webster 

and Benfield 1986). In some areas, seasonal inputs of terrestrial insects from riparian 

areas are an important food source for drift feeding fish species (Young and others 

1997). Such inputs are highest from closed canopy riparian areas dominated by deciduous plant species (Baxter and others 2004, 2005; Edwards and Huryn 1995; Nakano and 

others 1999). For floodplain forests, it has been suggested (FEMAT 1993) that the effectiveness of riparian vegetation in providing allochthonous inputs to streams declines 

at distances greater than approximately one-half a tree height away from the channel 

(fig. 1).

Research from studies on the impacts of fire and forest harvest on aquatic food webs 

have shown mixed results, depending on location, season, and species of interest (Bisson 

and Bilby 1998). Following a streamside prescribed fire in the Sierra Nevada, periphyton biomass was initially lower in the burned stream, but within 1 year of treatment, 

exceeded biomass in the unburned streams. Aquatic macroinvertebrate communities showed no detectable response to prescribed burning (table 3) (Bêche and others 

2005). Significant alteration in the quality or quantity of allochthonous inputs—such as 

those occurring following fire (prescribed fire of wildfire) and forest harvest—has led 

to changes in aquatic trophic pathways that affect fish productivity (Bisson and Bilby 

1998; Bisson and others 2003a; Edwards and Huryn 1996). In forested watersheds of 

the Pacific Northwest, the removal of riparian trees has had negative consequences 

for some native salmonid species (Hicks and others 1991). However, several studies have shown increases in summer biomass of fish species in headwater streams of 

the Pacific Northwest after logging (Bilby and Bisson 1992; Bisson and Sedell 1984). 

In these systems, the fish communities appear to be largely supported by autotrophic 

food pathways, that is, by invertebrate groups that ingest algae and algal conditioned 

organic matter. Increased productivity in summer populations of salmonids have also 

been observed following losses of riparian vegetation caused by other land uses such 

as livestock grazing (Chapman and Knudson 1980). This seasonal increase in fish productivity is attributed to more light reaching the stream, which stimulates autotrophic 

production and supports secondary production of algal dependent invertebrates (Bisson 

and Bilby 1998). In locations where fish bearing streams are management priorities, 

resource managers need to consider potential impacts of fuel reduction prescriptions on 

riparian vegetation that influences aquatic food webs and stream-riparian nutrient and 

organic matter dynamics.

Stream temperature: Fuel reduction treatments could potentially affect water temperature by altering vegetative shade that attenuates the input of solar radiation to streams. 

Direct sunlight warms streams, particularly during periods of low flow. During winter, 

lack of cover can affect stream temperature by permitting radiant cooling to the sky, 

potentially resulting in the formation of anchor ice (Ashton 1989). For many low order streams, riparian shading moderates these thermal fluctuations. Stream temperature 

has tremendous ecological importance for aquatic biota and ecosystem processes such 

as productivity and nutrient cycling (Allan 1995; Sweeney 1992). Water temperature 

strongly influences growth, development, and behavioral patterns of aquatic biota both 

directly and because of its influence on dissolved oxygen concentrations (Sweeney 

1993). Stream temperature is an important factor determining the distribution of fish 

in freshwater streams, and most species of concern have limited temperature tolerances 

(Torgersen and others 1999).

Stream water temperature varies markedly within and among stream systems (Poole 

and Berman 2001). Natural drivers of water temperature include topographic shade, 

upland and riparian vegetation, ambient air temperature and relative humidity, altitude, 

latitude, discharge, water source, and solar angle and radiation (Poole and Berman 

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 187

2001; Sweeney 1993). Streams in different regions and stream segments in different 

parts of a drainage basin vary in response and sensitivity to specific human activities 

that alter these drivers (Poole and Berman 2001). In addition, effectiveness of vegetation in providing stream shade varies with topography, channel size and orientation, 

extent of canopy cover above the channel, and vegetation structure. However, stream 

shading by riparian and upland vegetation is one of the few factors that can be actively managed to achieve stream temperature targets. The curve presented in figure 1 

generalizes the relationship between distance from the channel and shade provided by 

riparian trees. In western Oregon and Washington, riparian buffer width has been designed to correlate with degree of shade (Beschta and others 1987), and riparian buffers 

of 100 ft or more have been reported to provide as much shade as undisturbed late successional/old growth forests (FEMAT 1993). Less is known about the effectiveness of 

buffer widths in providing adequate shade in other regions. In locations where particular 

stream temperature regimes are management goals, the short- and long-term impacts of 

fuel reduction treatments on shade (provided by both upland and riparian vegetation) 

and adequacy of buffer width need to be explicitly addressed.

Large wood dynamics: Fuel reduction treatments could potentially affect aquatic habitat by altering recruitment of large wood to streams. The role of large wood in aquatic 

ecosystems has become increasingly recognized over the last several decades (Bilby and 

Bisson 1998; Gregory and others 2003; Harmon 2002). Large wood affects geomorphic, 

hydrological, and ecological processes in streams and rivers, and its numerous roles link 

aquatic, riparian, and upland portions of watersheds (Gregory 2003; Lienkaemper and 

Swanson 1987). Large wood strongly influences channel form in small streams, creating 

pools and waterfalls and affecting channel width and depth (Montgomery and others 

2003). Many species use pools formed by large wood as habitat and in-stream wood for 

cover (Bilby and Bisson 1998; Dolloff and Warren 2003; Wondzell and Bisson 2003). 

The presence of large wood in streams affects erosion, transport, and deposition of sediment, the creation and growth of gravel bars, and channel and floodplain sedimentation 

(Montgomery and others 2003). Dams formed by accumulations of large wood increase 

channel complexity and facilitate deposition of organic matter, thus providing a food 

source for numerous invertebrate species and contributing to nutrient cycling and retention (Bilby and Bisson 1998; Wondzell and Bisson 2003). Chronic inputs of large wood 

to stream channels occur as a result of bank cutting, windthrow, and mortality of individual trees from adjacent riparian areas (Bragg and Kershner 2004; McDade and others 

1990). Large pulses of wood may originate from near channel sources following fire, 

windthrow, or insect infestations, or be transported from distant sites by debris torrents, 

avalanches, or landslides (Benda and others 2003; Bilby and Bisson 1998; Bragg 2000). 

In forested landscapes, riparian areas are important sources of large wood for streams 

and floodplains. However, riparian forest stands are frequently patchy, and variation 

from all these sources can lead to spatial variability in large wood distribution that is 

often not recognized in management prescriptions for a given amount of large wood per 

unit length of stream (Young and others 2006).

The temporal variation in large wood loads creates additional complexity. Following 

disturbance such as fire, contributions of large wood to channels and riparian areas can 

be very high in the first few decades thereafter, but the storage in each area may differ substantially. In stream channels, peaks in large wood transport may coincide with 

increases in contributions because of declines in stream channel stability and increases 

in discharge following fire, leading to rapid depletion of large wood loads during early 

phases of post disturbance succession. As riparian trees age, they become large enough 

to resist transport and breakage once they fall, and large wood loads can slowly build 

to pre-disturbance levels (Bragg 2000; Minshall and Brock 1991). In riparian areas, the 

decay of fallen trees can be surprisingly swift (Spies and others 1998; Mackensen and 

others 2003). In addition, recurrent fire may consume some riparian large wood (Skinner 

2002) but leave pieces in the stream channel largely unaffected. Because large wood 

dynamics in streams and riparian areas are complex and remain poorly understood, we 

suggest that managers proceed with caution in altering fuel loads near streams, particularly in watersheds that have been logged.

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
188 USDA Forest Service RMRS-GTR-231. 2010.

Land use and management practices have led to marked decreases in the quantity of 

large wood in channels in some forested regions. Historical practices, such as removal 

of wood from rivers for navigation and fish passage, splash damming, tie drives, and 

clearing of riparian trees has resulted in simplification of stream channels and streambanks, reduction in the areal extent of riparian areas, and local decreases in amounts of 

large wood (Sedell and Froggatt 1984; Young and others 1994). More recent research 

has focused on the consequences of streamside logging (table 4). Studies conducted in 

forested portions of the western United States have shown marked long-term reduction 

in recruitment of large wood to streams in basins where forest harvest has been conducted (Lisle 2002). In western Oregon and Washington, the probability that a falling 

tree will enter the stream is low at distances greater than about one tree height away 

from the stream channel (fig. 1) (McDade and others 1990; Van Sickle and Gregory 

1990). Similarly, the effectiveness of upland forests to deliver large wood to riparian areas is expected to decline at distances greater than about one tree height from the upland 

forested edge and depends on steepness of slope. However, timber harvest adjacent to 

riparian buffers eliminates large wood recruitment to the riparian area while increasing 

the potential for windthrow (Grizzel and Wolff 1998). In Montana, researchers also 

found differences in features of large wood in logged and reference streams that provide 

important habitat for bull trout, a federally threatened species (Hauer and others 1999). 

These included difference in ratios of large to small pieces of large wood, the proportion of pieces attached to the stream channel or bank, and the proportion of large wood 

pieces with root wads. The role of large wood is so valuable in structuring aquatic habitat that numerous efforts are underway to restore streams by adding large wood (Bisson 

and others 2003b; Reich and others 2003).

Table 4. Effects of fire and forest harvest on large wood (LW) inputs to streams.

Time scalea

Source	 (years)	 Treatment and study type	 Location	 Findings

Bragg 2000 +10 to +250 Comparative simulation Lodgepole-pine dominated, Overstory removal and slash burning 

study of large wood inputs mixed-conifer, Wyoming reduced long-term large wood

to streams following clear- contributions by 50% relative to

cutting and slash removal, wildfire or beetle kill

relative to wildfire and insectcaused mortality

Bilby and Ward 1991 +5 to +100 Retrospective sampling of Douglas fir dominated mixed Near-stream clearcuts reduced

near-stream areas in conifer, southwest Washington channel large wood counts and size 

clearcuts, second-growth within 5 years of clearcut, relative to 

and old growth old growth

Hauer and others 1999 Not specified Retrospective sampling of Mixed conifer, Flathead Basin, Marked differences between logged

large wood in streams (3-4th northwest Montana and reference streams in ratios of

order) located in unlogged large to small pieces of wood, 

wilderness, and watersheds numbers of unattached and 

that were logged with no unattached pieces, and large wood 

buffers, and logged with pieces with and without root wads. 

buffers

Ralph and others 1994 +3 to +40 Retrospective sampling of Western hemlock-Douglas fir Clear reduction in size of large wood

streams draining watersheds –western red cedar forest in streams, and shift in location of

with unharvested old-growth types, western Washington large wood towards channel margins 

forests, and intensively and in harvested basins relative to 

moderately harvested forests reference (old-growth) streams

Chen and others 2005 +10 to +40 Retrospective sampling of Lodgepole pine dominated – Higher volume (3X), biomass and

streamside areas with mixed conifer; central Interior carbon content of large wood in

harvested riparian forest, British Columbia disturbed (wildfire or harvest) stands

burned riparian forest, and relative to old-growth stands 

undisturbed old-growth 

riparian forest

a Time scale relative to treatment (year of treatment = 0)

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 189

The influence of fuel treatments on large wood is a sensitive issue because of the 

many management actions that have reduced its abundance in stream channels. There is 

little ecological justification for the direct removal of large wood from riparian areas or 

riparian trees or snags that would create it. Prescribed fire, however, will not necessarily 

remove large wood from riparian areas or stream channels. Prescribed burns are typically conducted in spring or fall when fire severity is likely to be low to moderate because 

air temperatures are low and humidities and fuel moisture are relatively high (Knapp 

and others 2005). Under these conditions, large, sound boles of fallen trees do not readily ignite (especially those in and over the stream channel), although rotten pieces are 

consumed (Bêche and others 2005; Brown and others 2003; Stephens and Moghaddas 

2005). Whereas decomposing large wood may contribute to soil formation and provide 

wildlife habitat in riparian areas (Chen and others 2005), only sound pieces are likely to 

resist breakage, promote local erosion and sediment storage, and form habitat in stream 

channels (Montgomery and others 2003). In addition, tree mortality caused by riparian 

prescribed fire is likely to contribute coarse wood in the riparian area and stream channel (Bêche and others 2005; Chen and others 2005).

Given the historical prevalence of fire in montane riparian areas (Everett and others 2003; Macdonald and others 2004), the effects of prescribed burns may emulate 

those of low to moderate severity wildfires that were part of the historical disturbance 

regime that maintained the structural and functional diversity of streams and riparian 

areas (Reeves and others 1995). Nevertheless, the historical interaction between fire, 

forest type, and large wood varied regionally (Agee 2002; Skinner 2002). It is likely 

that the impacts of riparian burning will also vary considerably throughout the western 

United States. Reports on the effects of riparian burning are few (for example, Bêche 

and others 2005), and we urge that these management experiments be widely shared in 

the literature.

Riparian Soils

Chemical, physical, and biological processes occurring within riparian soil profiles have the potential to filter, buffer, degrade, immobilize, and detoxify organic and 

inorganic compounds before they enter streamwater. The likely effects of upland management on down slope hydrologic and biogeochemical fluxes will impact processes 

that regulate nutrient, carbon, and sediment retention within riparian areas (table 5). 

The influence of fuel reduction treatments on compaction and productivity of upland 

soils are described elsewhere in this report (Chapter 9). In this section, we discuss how 

management of upland areas may modify riparian soil processes and contribute to their 

watershed effects.

The intersections of near surface hydrologic flowpaths with carbon and nutrient rich 

soils form “hotspots” of biogeochemical activity in riparian areas (McClain and others 2003; Wagener and others 1998). Riparian soils are frequently moist because of 

their lower landscape position and proximity to streams and shallow water tables. Water 

movement from upslope areas and hyporheic zones controls the flux of nutrients and 

carbon through riparian areas and regulates the soil moisture conditions that influence 

biogeochemical processes (Triska and others 1989). The finer textured soils found in 

many riparian areas have higher water holding capacity and their greater exchange capacity increases nutrient retention relative to upslope landscape positions. Especially 

in arid environments, increased soil moisture availability in riparian areas enhances the 

productivity of streamside vegetation and may support unique or more diverse plant associations as compared to upland areas (Carsey and others 2003). Root production, soil 

nutrient uptake and turnover, and litter production (above and belowground) also tend 

to be higher in streamside plant communities. In lower gradient reaches that are seasonally wet and support productive vegetation, riparian soils may be high in organic matter 

(Crowe and Clausnitzer 1997).

Biogeochemical processes within riparian soils regulate nitrogen transfer from terrestrial to aquatic ecosystems. Groundwater discharge represents the largest source of 

dissolved nitrogen delivered to forest streams (McClain and others 1998), yet plant 

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
190 USDA Forest Service RMRS-GTR-231. 2010.

nutrient uptake and microbial transformations occurring within riparian soils can remove 90 percent of dissolved nitrate from near surface groundwater prior to its release 

into surface water (Gilliam 1994; Haycock and Pinay 1993; Peterjohn and Correll 

1984). Attenuation of nitrate in riparian soils is attributed to a combination of plant uptake and denitrification, the microbially mediated transformation of nitrate to N2

 or N2O 

gas, and subsequent loss to the atmosphere (Groffman and others 1992; Hedin and others 1998; Hill 1996). In contrast to most upland forest soils where denitrification rates 

are low (Groffman and others 1992), frequent saturation of riparian soils provides a 

redox environment that favors denitrification (Lowrance and others 1997; Peterjohn and 

Correll 1984; Vidon and Hill 2004). Denitrying bacteria also requires labile carbon and 

nitrate within the anoxic soil layer. These compounds move along groundwater flowpaths from uplands into riparian soils and denitrification releases significant amounts 

of nitrogen from undisturbed (Duff and Triska 1990; Hussey and others 1985) and disturbed (Davidson and Swank 1987; Rich and Myrold 2004; Waide and others 1988) 

watersheds.

Soil variability regulates groundwater flux and riparian biogeochemical processes. 

In subalpine forest watersheds, greater than 95 percent of snowmelt passes along shallow groundwater flowpaths (Troendle and Reuss 1997) and through riparian areas 

Table 5. Effects of prescribed burning and forest harvest treatments on soil resources and sediment movement.

Source	 Time scalea Treatment Location Comments - Findings

Covington and Sackett 1992 -1 wk to + 1 yr Broadcast burn Ponderosa pine, Ft. Valley Increase in soil NH4-N

Experimental Forest, near immediately after burning,

Flagstaff, Arizona followed by increase in soil NO3

Monleon and Cromack 1996 + 0.3, 5, 12 years Low-intensity Ponderosa pine, Central Burning increased release of N & 

broadcast burn Oregon P from litter & reduced litter 

decomposition rates

Covington and others 1991 1 to 25 years Slash pile burn Pinyon-Juniper, Coconino Increase in soil NH4-N

NF near Flagstaff, Arizona immediately after burning, 

followed by increase in soil NO3.

Each returned to preburn 

conditions in ~ 5 years.

Korb and others 2004 0 to 2 years Slash pile burn Ponderosa pine, Coconino Higher soil pH, NH4 and NO3 and

NF near Flagstaff, Arizona lower total C and N inside burn 

scars

Reuss and others 1997 1 to 10 years Lodgepole pine-dominated Harvest increased soil 

Starr 2004 +20 years Clearcut subalpine forest, Fraser nitrification and cation and nitrate

Experimental Forest, central export. Effect remains significant

Colorado after 20 years

Giardina and Rhoades 2001 5 year after cutting Clearcut + slash Lodgepole pine, Medicine Clearcuts had higher NH4, NO3,

1 year after burning retention; clearcut Bow NF, S. Wyoming net mineralization, and soil

followed by surface moisture than uncut forest. Slash 

fire burning doubled soil N 

availability compared to 

unburned cut.

Swanson and others 1987 Reviews of research and Clearcut Pacific Northwest Increase in suspended sediment

Brown 1983 monitoring results Pacific Northwest concentrations associated with

Binkley and Brown 1993 North America forest roads

Binkley and others 2003 1 year Application of Lodgepole pine-dominated Soil NH4, NO3 declined beneath

chipped harvest subalpine forest, Fraser chips. Soil moisture increased. 

residue Experimental Forest, central

Colorado

Benson 1982 5 years Application of Lodgepole pine, Bridger Surface runoff and soil erosion 

chipped harvest Teton NF, western Wyoming less than residue removal or 

residue undisturbed forest.

aTime scale relative to treatment (year of treatment = 0)

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 191

before entering streams. The depth and seasonal patterns of these flows determine their 

chemical composition and the magnitude of nutrient transformation, retention, or export 

(Simmons and others 1992). Soil texture and porosity control the hydraulic conductivity of near surface groundwater flow paths, exchange with labile nitrogen and carbon 

sources, and rates of denitrification (Hedin and others 1998; Vidon and Hill 2004). 

Riparian soils develop from and upon alluvial, colluvial, and aeolian parent materials and are highly variable. Fine and coarse-textured lenses and buried organic layers 

common to riparian soil profiles (Crowe and Clausnitzer 1997; Youngblood and others 

1985) modify vertical and lateral water and nutrient movement into and through riparian areas (Groffman and others 1992; Jacinthe and others 1998; Simmons and others 

1992). These sources of soil and groundwater heterogeneity form biogeochemically 

reactive zones imbedded within relatively inert regions. Improved ability to identify 

biogeochemical hotspots would help guide efforts to buffer the areas most crucial for 

water quality protection.

Riparian areas are vulnerable to both compaction and physical disturbance during 

ground harvesting operations due to areas of high moisture and low soil strength that 

are common within streamside zones. These concerns, along with riparian and aquatic 

habitat protection, provide the basis for limiting mechanical harvesting activities within 

streamside zones. Beyond designation of riparian buffers, land managers should consider how upland fuel reduction operations may influence nutrient and sediment retention 

in riparian areas and potential water quality impairment. Both vegetation removal and 

the actions of harvesting equipment alter site nutrient and water balances (Bormann 

and Likens 1979; Swank 1988). The linkages between upland management and riparian 

processes depend on a variety of landscape, vegetation, soil, and hydrogeologic factors 

that determine the flux of water, nutrients, and sediment into riparian areas, as well as 

specifics of the fuel management activities.

In subalpine forests of the Fraser Experimental Forest (northern Colorado), clearcutting increased snow accumulation and peak water equivalent by 36 percent and 

increased flow along subsurface flowpaths four-fold (Troendle and Reuss 1997). The 

export of nitrate from undisturbed subalpine forest hillslopes is negligible. In comparison, harvesting increases mineral nitrogen availability (table 5) (Giardina and Rhoades 

2001), leaching (Fahey and Yavitt 1988; Parsons and others 1994), and groundwater 

flux (Reuss and others 1997; Stottlemyer and Troendle 1999). Greater subsurface water 

flux and nitrate concentrations may promote denitrification, if adequate labile carbon 

is available to fuel microbial activity (Groffman and others 1992; Simmons and others 1992). Nutrient and water uptake by riparian and residual upland vegetation will 

also respond to harvesting and may contribute to nutrient retention and water quality 

protection.

Disturbance of organic and mineral soil layers during harvesting operations can alter 

soil structure, infiltration, and bulk density and may lead to channelized runoff and erosion (table 5) (Binkley and Brown 1993; Brown 1983). Overland flow and sheet erosion 

are typically minimal in undisturbed forests, but steep slopes of many forest watersheds 

are susceptible to sediment transport via channelized flow (Megahan and others 1992). 

Loss of surface litter also increases surface runoff and decreases infiltration. Clearcutting 

has been shown to increase suspended sediment yield from Rocky Mountain and Pacific 

Northwest watersheds (Binkley and Brown 1993; Leaf 1966; Swanson and others 1987; 

Wondzell 2001). Similar impacts result from other ground disturbing activities such as 

road and fire break construction associated with fuel management activities (Wondzell 

2001). The potential impact of fuel reduction treatments on the ability of riparian areas 

to retain sediment depends on the geomorphic setting, soil properties of the basin, and 

condition of the riparian vegetation.

The impact of upland prescribed burning on the capacity of riparian soils and vegetation to retain nutrients and sediment depends on fire severity and extent and distribution 

within a watershed (DeBano and others 1998; Fisher and Binkley 2000; Neary and others 1999). Low and moderate severity controlled burns have smaller consequences (both 

positive and negative) than high severity wildfires (Wondzell 2001). Fuel consumption and fireline intensity determine nutrient loss and nutrient and sediment movement 

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
192 USDA Forest Service RMRS-GTR-231. 2010.

following combustion. Effects can be comparable between high severity wildfire and 

controlled slash (Feller 1988; Giardina and others 2000) and broadcast burns (Covington 

and Sackett 1992; Knoepp and Swank 1993; Johnson and others 1998; Monleon and others 1997). Combustion of standing or surface fuel coupled with decreased plant uptake 

and fluctuating microbial activity often results in a temporary increase in soil nitrogen 

availability that occurs shortly after broadcast (Covington and Sackett 1992; Giardina 

and Rhoades 2001; Kaye and Hart 1998) and slash pile combustion (Covington and others 1991; Korb and others 2004). Elevated soil nutrient pools can lead to greater nitrate 

and cation leaching (Knoepp and Swank 1993; Trammell and others 2004) and in some 

cases, higher streamwater export (Chorover and others 1994). In uplands, high severity 

prescribed burns can also alter soil structure, porosity, infiltration and water repellency 

(Benavides-Solorio and MacDonald 2001; DeBano 2000; Robichaud 2000) and increase surface runoff and sediment movement. The effects of upland fires on the flux of 

nutrient and sediment into and through riparian areas may be ameliorated by residual 

upland or riparian vegetation and forest floor organic matter (Pannkuk and Robichaud 

2003; Robichaud 2000). The processes determining the outcome of prescribed burning 

conducted within riparian ecosystems are likely to be similar, though we are not aware 

of comparable published results for streamside areas.

Mechanical chipping and mastication operations are being widely prescribed to 

treat hazardous fuel, yet the implications of these practices on riparian and watershed 

conditions are largely unknown. As compared to typical harvesting operations and unharvested stands, these fuel management prescriptions rearrange the amount, size, and 

orientation of surface woody materials. Similar to other upland management activities, 

these mechanical treatments are likely to influence soil processes and nutrient retention 

within riparian areas. A recent review of published findings relating to woody debris 

additions reported that implementation of chipping and mastication treatments varies 

considerably among sites depending on equipment and operational differences (Resh 

and others 2006). The influence of the treatments on soil properties varied as well, although some generalizations emerged. Soil carbon and moisture increased following the 

mechanical fuel reduction operations. Maximum soil temperature and understory vegetation declined. Woody debris additions had variable effects on soil nutrients. In some 

cases, soil nitrogen availability decreased as carbon rich woody material stimulated 

microbial nitrogen immobilization (Binkley and others 2003; Blumfield and Xu 2003; 

Lalande and others 1998). For example, in Colorado lodgepole pine stands, addition 

of wood chips reduced soil nitrogen availability by ~ 65 percent (Binkley and others 

2003). There is some evidence that logging residue and chip additions may depress 

sediment movement (Benson 1982). The potential for upland chipping or mastication to 

significantly alter nutrient and sediment movement into riparian areas partly depends on 

the horizontal continuity and depth of woody material additions. To date, there are no 

completed studies that directly assess the linkages between these new mechanical fuel 

management strategies and riparian processes or watershed conditions.

Cumulative Watershed Effects of Fuel Management Activities 

on Riparian Areas

Most land management activities contribute to cumulative watershed effects, and 

fuel reduction treatments being conducted anywhere within a watershed could potentially influence riparian functions. Because stream-riparian corridors are located at the 

lowest point within drainage basins, they can act as integrators of entire watersheds and 

may be particularly vulnerable to effects of fuel reduction treatments conducted upslope 

and upstream. In the past, undesirable changes in riparian areas have resulted from the 

failure to recognize linkages among streams, riparian areas, and uplands. To minimize 

negative cumulative effects on riparian functions, integrative planning and assessment 

of all management activities, including fuel reduction treatments, grazing, forest harvest, and recreation, should occur at both watershed and larger landscape scales. The 

management of wildfires, including location of back burns, cutting lines and natural 

Chapter 10. Potential Effects of Fuel Management Activities on Riparian Areas
USDA Forest Service RMRS-GTR-231. 2010. 193

ignitions that have been allowed to burn, may have very direct and cumulative effects. 

Wildland fire use (managed wildfire) is increasingly common, and portions of the landscape that have been allowed to burn are likely to be much larger than areas treated with 

prescribed fire and mechanical fuel removal. The management history, hydrologic and 

sediment regimes, and the role of natural disturbance all need to be considered in planning fuel treatments (Chapter 12).

The watershed approach of assessing additive and interactive impacts on riparian 

areas is conceptually simple. However, the actual evaluation of cumulative watershed 

effects on riparian functions is technically difficult because of limited knowledge of 

many biological and physical processes, interactions among processes for which impacts may accumulate through space and time, and time lags in the expression of effects. 

Another limitation is the lack of reference conditions and limited baseline data for comparison and evaluation of environmental changes, including measures of impact severity 

(Reid 1998). Despite these difficulties, an analysis of cumulative watershed effects on 

riparian functions must evaluate potentially important impacts on valued riparian functions, downstream impacts, and impacts accumulating through space and time within 

the watershed using the best available analysis methods and information. Relative risks 

of severe wildfire versus impacts of fuel treatments need to be weighed (O’Laughlin 

2005). In addition, information needs should be acknowledged and monitoring goals 

clearly identified (REO 1995).

Analysis methods for assessment of cumulative effects have been developed to fulfill 

requirements of the National Environmental Policy Act and require a non-traditional approach to information (Reid 1998) (Chapter 14). The ecosystem analysis method used 

on federal lands in much of the Pacific Northwest provides a model that integrates 

background information about ecosystem and landscape interactions that can be used 

for later cumulative effects assessments during project planning (FEMAT 1993; Reid 

1998). In addition, landscape analysis tools, such as Landscape Management System 

(LMS), have been developed to assist in planning of fuel treatments (McCarter and 

others 1998; Peterson and others 2003). These tools display spatial patterns of forest 

structure and fuel across a landscape for current conditions and compare them to patterns produced by various fuel treatment scenarios. When possible, spatial delineation 

of riparian areas should be incorporated into landscape level planning of fuel treatments 

and may contribute to effects analysis as well as integrate riparian protection and management into fuel reduction programs.

Management Implications

1. Riparian areas are spatially diverse and variously defined. Attention to 

ecological context within a drainage basin and the larger landscape is critical, 

as is the connectivity between upslope and upstream management and condition 

of streams and riparian areas. Impacts of fuel treatment activities will vary 

depending on their locations within a watershed, the natural fire regimes, and the fire 

and management history of the treated basins. Stream-riparian corridors are dynamic 

and planning should allow for continuous change, including successional processes 

and natural disturbance.

2. During planning and implementation of fuel reduction treatments, consideration 

of potential impacts on key riparian functions is essential to minimize local 

and immediate effects as well as cumulative, longer term effects. Riparian 

areas provide valued ecological functions (table 1) that have been altered by land 

management (tables 2-5) (Hessburg and Agee 2003). Local and regional issues will 

dictate which riparian functions are priorities for management goals and critical for 

protection.

3. Riparian buffers and BMPs may not protect all riparian functions during fuel 

reduction treatments. Although BMPs and the establishment of riparian buffers 

have mitigated the effects of forest harvest activities on stream water temperature and 

K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
194 USDA Forest Service RMRS-GTR-231. 2010.

quality, current BMPs may not be effective in protecting all valued riparian functions, 

particularly in watersheds that have been recently burned by severe wildfire. With 

multiple fuel reduction treatments (including consecutive entries over time), BMP 

effectiveness may vary and additional conservation practices may be necessary.

4. Objectives for fuel reduction treatments should include the return to fuel 

loads that support ecosystem processes and natural disturbance regimes and 

incorporate short- and long-term targets for the vegetation condition of uplands 

and riparian areas (Rieman and others 2003). Using concepts such as natural or 

historical range of variability (Landres and others 1999), reference areas, and desired 

future condition, the planning and implementation of fuel reduction treatments may 

be regarded as opportunities to restore certain ecological conditions, especially in 

riparian areas (Arno 1996). Fire managers are frequently able to implement fairly 

exact prescriptions, such as reducing certain fuelbeds while retaining others. 

Restoration objectives, in addition to emphasis on fuel management, are encouraged. 

In addition, follow up monitoring for achievement of project objectives (short- and 

long-term) is critical to expand our knowledge of fuel management.

5. Current knowledge on the effects of fuel reduction treatments on riparian areas 

is very limited. Potential environmental effects need to be assessed in a landscape 

context that includes relative influences of all management influences, including 

past fire suppression and current wildland fire use. We have summarized potential 

effects of fuel reduction treatments on riparian vegetation, the provision of terrestrial 

and aquatic habitat (contributions to streambank stability, aquatic food webs, 

maintenance of stream temperature, and large wood dynamics), and the filtering 

and sediment retention capacity of riparian areas (tables 2-5). We emphasize that 

very little is actually known about either specific or cumulative impacts of specific 

fuel reduction treatments. Our understanding of cumulative watershed effects is 

largely derived from a handful of watershed scale studies of past practices (Reid 

1998). Results from these studies are quite variable and confounded by local effects 

of other past and current management activities (Wondzell 2001). Much of the site 

level research cited in this chapter was conducted in the Pacific Northwest and may 

be difficult to extrapolate to other regions in the western United States. Explicit 

recognition of uncertainty is encouraged during planning and implementation of 

treatments, with an adaptive management approach to changing direction if the 

desired outcome is not achieved. We regard each individual fuel reduction project 

as an experiment and emphasize the need for monitoring to track the impacts of 

prescribed burning, tree removal, chipping and mastication, and salvage logging.

6. Research is needed to address the impacts of fuel treatments on watershed 

processes, riparian functions, and aquatic resources. Although studies are 

underway (http://jfsp.nifc.gov/JFSP_Project_Info.htm), we have noted numerous 

research needs throughout this review, as well as regions with limited data (for 

example, many Rocky Mountain ecosystems). Fuel reduction treatments are highly 

variable, and each treatment, sequence, or combination of treatments may have 

significantly different environmental effects. For assessment of cumulative effects, 

research on impacts of multiple stage projects is key, particularly in relation to other 

active management, including that of wildland fire.

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K.A. Dwire, C.C. Rhoades, M.K. Young Cumulative Watershed Effects of Fuel Management in the Western United States
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Chapter 11.

Biological Responses to Stressors in Aquatic 

Ecosystems in Western North America: 

Cumulative Watershed Effects of Fuel Treatments, 

Wildfire, and Post-Fire Remediation

Frank H. McCormick, Rocky Mountain Research Station, USDA Forest Service, Boise, ID

Bruce E. Riemen

Jeffrey L. Kershner, Washington Office, USDA Forest Service, Logan, UT

Introduction

Aquatic communities in North America evolved with disturbance regimes (for example, glaciation, erosion, tectonics, volcanism, fire) that varied in frequency, intensity, 

and severity (Poff 1992; Power and others 1988; Resh and others 1988). Disturbance 

has been recognized for its importance in the organization and maintenance of aquatic 

ecosystems (Reeves and others 1995), in shaping species resilience and persistence 

(Reice and others 1990; Yount and Niemi 1990), and structuring the evolution of aquatic organisms (Lake 2000; Malanson 1984; Schlosser 1990; Sedell and others 1990). 

Disturbances are regarded as having a dominant role in determining the structure of 

stream communities (Palmer and others 1996; Resh and others 1988).

Natural and anthropogenic disturbance regimes are classified as pulse, press, or ramp 

types that vary in their temporal and spatial patterns of impact intensity and duration 

(Lake 2000). Pulse disturbances are short-term and often intense events, whereas press 

types may arise sharply but reach a constant level that is maintained. Ramp disturbances 

arise if the intensity increases over time. In most situations, discrete disturbance regimes 

are unlikely to occur and the system is more likely to be characterized by a mix of disturbance types. For example, the effects of a press disturbance, such as land use change, 

may interact with invasions by exotic species (ramp) and this regime may be affected 

by pulse disturbances in the form of floods that occur unpredictably and with varying 

intensity. However, the life history traits of the longest-lived affected population may 

determine the importance of disturbance in shaping aquatic ecosystem structure and 

function (Benda and others 2003; Bisson and others 1997; Reeves and others 1995; 

1998; Rieman and others 2003).

Catastrophic shifts in ecosystems are often precipitated by stochastic (pulse) events 

such as fire, but the foundation for them lies in the gradual (press-ramp), underlying loss 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
USDA Forest Service RMRS-GTR-231. 2010. 207

of resilience (fragmentation, habitat loss, etc). The real impact of a press disturbance on 

population persistence may only be evident after a pulse disturbance and over relatively 

long time scales. Land use changes constitute a press disturbance that may have a persistent effect on stream community structure and function over the long-term (Harding 

and others 1998). Press disturbances, such as timber harvesting, require longer recovery 

times than pulse disturbances such as floods or droughts (Detenbeck and others 1992). 

When forest management practices affect the stability of in-stream habitats, frequent 

pulse disturbance could result in the local extirpation of refugia-dependent species 

(Parkyn and Collier 2004). Short-term responses in abundance or survival of organisms 

or the physical attributes of streams to cumulative effects are not easily detected because 

suitable habitat features in disturbed landscapes may not provide stable refugia during 

pulse disturbances. These effects may only become evident over long time scales. Thus, 

it may also be important to consider the biological mechanisms (for example, survival, 

growth, dispersal) influencing the responses at different scales (Harvey and others 2006; 

May and Lee 2004). Maintaining a stability domain (sensu Scheffer and others 2001) 

that allows ecosystems to resist disturbance and recover will present significant challenges to resource managers and might be considered in terms of our ability to conserve 

resilient populations, evolutionary legacies, and ecological functions.

Disturbance responses depend on the ability of aquatic organisms to find refugia in 

space and time in heterogeneity of their physical habitat, diversity of life history strategies, 

behavioral adaptations, or connectivity to refugia at various spatial scales (Angermeier 

1995; Poff and Allan 1995; Rieman and others 2000). In the southeastern United States, 

extinction prone aquatic species are typified by a limited geographic range, restricted 

range of habitat sizes, and highly specialized habits (Angermeier 1995; Jelks and others 

2008; Taylor and others 1996; Warren and others 2000). These associations reflected the 

effects of reduced habitat area and increased isolation (insularization), which are also 

important determinants of extinction in terrestrial systems (Angermeier 1995).

Lotic systems, like most natural ecosystems, exhibit extreme heterogeneity in environmental conditions and biotic communities at multiple spatial scales, ranging from 

microhabitats to whole landscapes and ecoregions (Montgomery 1999; Pringle and others 1988; Townsend 1989; Townsend and others 2003; Vannote and others 1980). At 

each scale, variation in environmental conditions affects stream biota (Angermeier and 

Winston 1998; Lake 2000; Poff 1997; Walters and others 2003), leading to high variability in abundance and community structure at multiple spatial scales (Downes and 

others 1993; Li and others 2001; Vinson and Hawkins 1998). Vegetation, geology, hydrology, and land use generally account for differences in community structure among 

river systems (Richards and others 1997; Townsend and others 1997, 2003) but variation 

in species composition is related mainly to local and in-stream factors (Angermeier and 

Winston 1998; Gregory and others 1991; Li and others 2001; Walters and others 2003).

Fire is widely recognized as one of the most important disturbance processes in the 

western United States (Hessburg and Agee 2003). Fire regimes in western North America 

exert strong influences on patterns of forest composition, structure, and successional 

dynamics (Agee 1991; Halpern and Spies 1995) (Chapter 2). During the past century, 

fire suppression has altered fire regimes in some vegetation types, and consequently, 

the probability of large stand replacing fires has increased in those areas. Retrospective 

studies indicate that fire return intervals are longer than prior to European-American 

settlement as fire suppression, landscape conversion, and fragmentation altered fire regimes in much of the western United States (Agee 2003; Hessburg and Agee 2003). 

Fire regimes in riparian areas vary by region and forest type (Chapter 2). In wetter 

forests, riparian fire regimes were more moderate, fire return intervals were longer, 

and fire intensity and severity was lower than in adjacent upland forests (Dwire and 

Kauffman 2003). In drier forest types, fire regimes in riparian and upland forests were 

more similar. Local conditions, governed by microclimate, geomorphology, soils, and 

elevation in riparian areas, contribute to the variability of fire regimes and fire severity 

in riparian areas (Dwire and Kauffman 2003; Whitlock and others 2003). Land management practices, particularly in the western United States, usually conjure landscape 

degradation associated with decreases in vegetation density and cover. The indirect 

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States
208 USDA Forest Service RMRS-GTR-231. 2010.

effects of selective and extensive timber harvest, fire suppression, and grazing practices 

have significantly altered forest structure and fuel loads. Forests that were once mosaics of species, ages, and patterns have been simplified; the area becoming dominated 

by higher density, middle aged stands, thereby reducing their resistance to the effects 

of severe wildfire (Hessburg and Agee 2003; Rieman and Clayton 1997; Rieman and 

others 1997).

The National Environmental Policy Act of 1969, Clean Water Act of 1972, and 

Endangered Species Act of 1973 required greater consideration of the relationships 

among ecosystem components and increased the focus on the effects of land use activities on fish and wildlife resources, especially threatened species (Rinne and Medina 

1995). Fuel reduction and fire suppression are key elements of the National Fire Plan, 

which provides guidance for an interagency approach to fire and fire related management (USDA 2000). In implementing the management goals of the Healthy Forest 

Restoration Act of 2003 (H.R. 1904), it will be important for resource managers to 

understand the effects of fire related management on aquatic and terrestrial ecosystems 

and the tradeoffs between achieving fuel reduction and minimizing the effects of those 

efforts on aquatic and riparian ecosystems. In this paper, we attempt to summarize the 

effects of wildfire and fuel treatment practices on aquatic resources, identify areas of 

uncertainty about the impacts of fuel reduction strategies on the terrestrial-aquatic ecotone, and highlight research needs to better inform resource management.

Disturbance, Fire, and Land Management

The physical and biological effects of wildfire and forest harvest on aquatic ecosystems are not identical. Numerous studies comparing fire and logging disturbance 

regimes confirm the dominant role of the watershed in tempering the aquatic responses 

to terrestrial disturbance and reflect both important similarities and differences in the 

responses to disturbance within the catchment (Carignan and others 2000; Smith and 

others 2003). Both fire and logging exhibit similar stressor characteristics (temporary 

deforestation, sediment and nutrient influx, increased stream temperatures) but have 

important differences in spatial extent, frequency, intensity, and severity of disturbance 

with respect to water quality. Abiotic and biotic elements of a watershed interact to govern the direction and magnitude of change in response to disturbance. Habitat alteration 

probably has the greatest impact on individual organisms and local populations that 

are the least mobile, and reinvasion will be most rapid by aquatic organisms with high 

mobility. Perturbation associated with hydrological processes is probably the primary 

factor influencing post-disturbance persistence of fishes, benthic macroinvertebrates, 

and diatoms in fluvial systems. These effects may be immediate and direct or occur indirectly over long periods of time (Dunham and others 2003; Gresswell 1999; Minshall 

and others 1997). Many aquatic organisms (such as salmonids) have evolved strategies to survive perturbations occurring at the frequency of wildland fires (greater than 

100 years), but this does not prevent extirpations of local populations (Gresswell 1999; 

Rinne 1996).

Physical Effects of Fire and Forest Management Practices

Upland and riparian vegetation interacts with soils, geology, and topology to influence channel form, habitat, flow characteristics, and nutrients (Bisson and others 1987; 

Gregory and others 1991; Montgomery 1999). Where vegetation cover has been disturbed by fire or human activity, terrestrial habitats may experience increased surface 

flows that cause rapid, concentrated surface runoff, accelerated erosion, and increased 

stream peak flows and sediment loads (DeBano and Schmidt 1989; DeBano and others 

1996). Small streams are typically more affected by catchment disturbance than larger 

streams and, as adjacent slopes become steeper, the likelihood of disturbance from instream effects increases (Lee and others 1997; Megahan and Ketcheson 1996). The 

physical effects of fire on aquatic systems depend on the severity of the fire, post-fire 

Chapter 11. Biological Responses to Stressors in Aquatic Ecosystems in Western North America: 

Cumulative Watershed Effects of Fuel Treatments, Wildfire, and Post-Fire Remediation
USDA Forest Service RMRS-GTR-231. 2010. 209

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States

climate, development of soil repellency, and alteration of the hydrologic regime (Benda 

and others 2003; Beschta and others 1987; DeBano and others 1996; Pierson and others 

2001; Tiedemann and others 1979; Wondzell and King 2003). Short-term consequences 

of fire include mobilization of nutrients, soil modification, increased water temperature 

(including direct heating), and changes in hydrology, water chemistry, and geomorphology (Bisson and others 2003; Bozek and Young 1994; Gresswell 1999; Minshall and 

others 1989). Timber harvest activities may accelerate surface erosion and increase sedimentation (Chamberlin and others 1991; FEMAT 1993; MacDonald and others 1991; 

Meehan 1991; Reid 1993; Rhodes and others 1994).

Erosion can be initiated or accelerated by timber harvest and fire management activities including the construction of fire lines, roads, and post-fire rehabilitation efforts 

(Landsberg and Tiedemann 2000; Robichaud and others 2000). Tractors and skidders 

promote soil compaction and may temporarily increase the potential for overland flow but 

reduce interstitial flow through the soil, which may require decades to recover (Backer 

and others 2004; Hartman and others 1996) (Whitson and others 2003; Williamson and 

Neilsen 2000) (Chapter 9). The use of heavy equipment in timber management or restoration may disturb soil integrity, increasing erosion (McIver and Starr 2000; Robichaud 

and others 2000). Burned Area Emergency Restoration (BAER) treatments, including 

felling trees and snags for erosion control, may not reduce storm runoff, erosion, or sedimentation and may cause additional disturbance (McIver and Starr 2000; Robichaud 

and others 2000). The cumulative effects of timber harvest and associated road building 

on aquatic life is exacerbated in forest catchments on steeper, more environmentally 

sensitive terrain (Gucinski and others 2001; Megahan and Hornbeck 2000; Platts and 

Megahan 1975).

Increased fine sediment delivery to streams is usually associated with timber harvesting and road construction (Platts and Megahan 1975; Eaglin and Hubert 1993). The 

majority of sediment from timber harvest activities is related to roads and road construction (Chamberlin and others 1991; Furniss and others 1991; Megahan and Hornbeck 

2000) and associated increased erosion rates (Beschta 1978; Meehan 1991; Reid 1993; 

Rhodes and others 1994; Swanson and Dyrness 1975; Swanston and Swanson 1976). 

Serious degradation of aquatic habitat can result from poorly designed, constructed, 

or maintained roads (Furniss and others 1991; MacDonald and others 1991; Rhodes 

and others 1994). Road networks interact with stream networks and lake basins at the 

landscape scale and affect biological and ecological processes in stream and riparian 

systems. Peak flows and debris flows are influenced by the arrangement of the road 

network relative to the stream network (Swanson and others 1988; Thompson and Lee 

2000, 2002) and they can alter the balance between the intensity of flood peaks and the 

stream network’s resistance to change (Jones and others 2000). Timber harvest activities 

caused increases in lake sedimentation rate and lake productivity in three of four lakes 

studied in western Washington, accelerating the rate of change in the trophic status of 

each lake (Birch and others 1980).

Water Quality

The modification of terrestrial habitats is often accompanied by changes in water 

quality and quantity (Bjornn and Reiser 1991; Chamberlin and others 1991; Rhodes 

and others 1994; Chapter 8) and perturbation of nutrient cycles within aquatic ecosystems (Megahan and Hornbeck 2000; Spencer and others 2003). Timber harvest often 

temporarily increases water yield and alters the timing of the flow, usually seen as an 

increase in low flows. The magnitude and timing of storm and peak flows depend on the 

degree of soil loss, soil compaction or hydrophobicity, and the pattern and schedule of 

harvest. The effects, which vary depending on the prevailing climate, rate of vegetation 

recovery, and type of vegetation, can decrease after initial disturbance but may remain 

above natural levels for many years (Bolstadt and Swank 1997; Hartman and others 

1996; Platts and Megahan 1975; Swanson 1981; Chapter 7). As vegetation recovers, dry 

season minimum flows may be reduced because of enhanced evapotranspiration (Hicks 

and others 1991).
210 USDA Forest Service RMRS-GTR-231. 2010.

Water quality can be altered by timber harvest activities (Bolstad and Swank 1997; 

Chamberlin and others 1991; Chapter 8). Stream temperature may rise following loss 

of streamside shading, disrupted subsurface flows, reduced stream flows, elevated sediments, and morphological shifts toward wider and shallower channels with fewer deep 

pools (Beschta and others 1987; Chamberlin and others 1991; MacDonald and others 

1991; Reid 1993; Rhodes and others 1994; Swank and others 1989). Logging may alter 

temperature as riparian shading is reduced (Hartman and others 1996; Johnson 2004; 

Johnson and Jones 2000; Swank and others 1989). Increased solar input into streams 

may also change the seasonal thermal regimes causing shifts toward earlier and longer 

summers when solar input is at its highest (Hartman and others 1996; Johnson and Jones 

2000; Poole and Berman 2001). Increased stream temperatures can exceed thermal preferences of many species in the PNW and may remain elevated for up to 15 years after 

timber harvest (Johnson and Jones 2000). Dissolved oxygen can be reduced by low 

stream flows, elevated temperatures, and increased fine inorganic and organic materials 

that have infiltrated into stream gravels (Chamberlin and others 1991; Wondzell and 

King 2003).

Nutrients

Stream concentrations of particulate organic matter, phosphorus, nitrogen, and 

ions can increase following forest fires (Bayley and others 1992; Earl and Blinn 2003; 

Spencer and Hauer 1991) and clearcutting (Feller and Kimmins 1984; Hartman and 

others 1996; Likens and others 1970; Webster and others 1990). Nutrient concentrations may increase following logging but generally return quickly to normal levels 

(Chamberlin and others 1991). Increases in total phosphorus and nitrogen concentrations, dissolved organic carbon (DOC), and other trace nutrients appear to be driven by 

higher discharge, which enhances nutrient loading from the watershed and (or) from the 

stream channel (Carignan and others 2000; Prepas and others 2003; Spencer and others 2003). During subsequent years, nutrient concentrations may periodically increase 

in fire impacted sites during spring run-off. Post-fire changes propagated through the 

aquatic food web suggest shifts from reliance on terrestrial and other allochthonous 

sources to a periphyton-based food web following canopy removal and nutrient enrichment. Chlorophyll a concentrations increase, presumably in response to nutrient run-off 

and increased light levels (Allen and others 2003). Some chemical effects on water 

quality diminish with time, but nutrient levels may remain unchanged or continue to increase, suggesting that longer time frames may be necessary for increased nutrient input 

to aquatic ecosystems to return to normal levels (Carignan and others 2000). As a result, 

biotic responses to alterations of water quality may take longer to manifest themselves 

(Brass and others 1996). Paleoecological studies of lake sediments revealed fundamental changes in lake mixing regimes following logging with associated alterations of 

hypolimnetic trophic structure persisting for over 100 years (Scully and others 2000). 

Experimental clearcut logging in some lake catchments produced no significant changes 

in water quality (dissolved organic carbon, chlorophyll a, total nitrogen increased; Ca2+

and Mg2+ decreased), though water clarity decreased (Steedman 2000; Steedman and 

Kushneriuk 2000). The responses, however, varied regionally. In some cases, forest 

harvesting was associated with increases in nutrient and chlorophyll a concentrations, 

cyanobacteria, and net primary production (Prepas and others 2001; Rask and others 

1998). In other cases, differences in nutrient dynamics between logged watershed lakes 

and reference lakes were undetectable (Steedman 2000).

The benefits of the type of fuel management applied (logging, thinning, prescribed 

fire) depend on the frequency and intensity of their application. Presently, the influence 

of disturbance type (logging or fire), time elapsed since the disturbance, and extent of 

natural variation limits our ability to detect the direct effects of fire management activities. Shorter rotations associated with frequent treatments may reduce soil fertility 

(Chapter 9). Low intensity prescribed fires post-harvest may increase short-term productivity but soil nitrogen may be volatilized and lost to the catchment when fire is used 

as a fuel reduction tool. Roads contribute more sediment to streams than any other land 

Chapter 11. Biological Responses to Stressors in Aquatic Ecosystems in Western North America: 

Cumulative Watershed Effects of Fuel Treatments, Wildfire, and Post-Fire Remediation
USDA Forest Service RMRS-GTR-231. 2010. 211

management activity (Gucinski and others 2001; Meehan 1991), but land management 

activities designed to combat wildfires or restore forest conditions depend on roads. 

Natural and anthropogenic disturbances that reduce terrestrial litter inputs to streams 

alter aquatic ecosystem function, highlighting the importance of riparian ecotones in 

sustaining diverse aquatic food webs (England and Rosemond 2004; Wallace and others 

1997). Reduced stream shading, accompanied by increased nutrient input, may contribute to algal blooms.

Habitat

The supply of large woody debris to stream channels is typically a function of the 

size and number of trees in riparian areas, and thus can be profoundly altered by timber 

harvest (Bisson and others 1987; Naiman and others 2000; Robison and Beschta 1990; 

Wood-Smith and Buffington 1996). Shifts in the composition and size of trees within the 

riparian area affect the recruitment potential and longevity of large woody debris within 

the stream channel. Large woody debris influences channel morphology, especially in 

forming pools, slow water refuges, and instream cover, and provides shade, retention 

of nutrients, and storage and buffering of sediment (Robison and Beschta 1990; Rhodes 

and others 1994). In intensively logged watersheds, the size of instream woody debris 

was smaller and pool depths significantly shallower than those found in a relatively 

undisturbed watershed (Overton and others 1993; Ralph and others 1994). All of these 

changes can eventually culminate in the loss of biodiversity within a watershed (Hauer 

and others 1999; Hawkins and others 1997).

Biotic Responses to Watershed Disturbance

Macroinvertebrates

Changes in aquatic invertebrate assemblages have been used for many decades to 

monitor impacts on land and in water. Land and water uses and impacts are reflected in 

species assemblages in streams and lakes. However, the level of detail of most monitoring is not sufficient to track species losses in aquatic invertebrates. Following watershed 

disturbance, the biomass of stream macroinvertebrate communities has been shown to 

increase in some cases (Burton and Ulrich 1994; Haggerty and others 2004; Stone and 

Wallace 1998) but not in others (Minshall and others 1997). Minshall (2003) described 

general patterns of responses of stream macroinvertebrate assemblages to fire, finding 

only minor or no direct effects except in extreme cases of intense heating of the stream 

from severe wildfire. Short-term, post-fire alterations of assemblage structure and decreases in biomass may be associated with changes in riparian vegetation. Most impacts 

were indirect effects on species composition and food web processes that stemmed from 

altered runoff and channel morphology (Minshall and others 2001). Following severe 

wildfire, macroinvertebrate assemblages showed low resistance to spate-induced debris 

flows, and high resilience but low assemblage similarity to pre-fire assemblage structure 

with the post-fire assemblage dominated by generalist taxa (Mihuc and Minshall 1995; 

Vieira and others 2004). In comparative studies of the consequences of timber harvest 

and fire on lake aquatic communities, responses of macroinvertebrate densities varied. 

Generally, invertebrate biomass was greater in lakes from burned catchments than from 

harvested and reference catchments. Scrimgeour and others (2001) found post-wildfire 

nutrient enrichment prompted significant increases in total benthic macroinvertebrate 

biomass in recently burned lake catchments. These analyses suggest that benthic biomasses continue to be elevated for about 15 to 20 years following fire before declining 

to pre-disturbance levels. Under the influence of phosphorus, nitrogen, and chlorophyll 

a, biomass response depended on percent of catchment disturbed (Scrimgeour and others 2000). In some cases, forest harvesting was associated with increases in chlorophyll 

a concentrations and primary production causing moderate increases in zooplankton 

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States
212 USDA Forest Service RMRS-GTR-231. 2010.

density (Rask and others 1998). Biomass increased in burned watershed lakes but declined in logged catchments (Patoine and others 2000; Prepas and others 2001). Changes 

in a food source of such importance as aquatic invertebrates can have repercussions in 

many parts of the food web (Hernandez and others 2005; Spencer and others 2003).

Fish

As with other aquatic organisms, the short-term direct effects of high severity fires on 

fish populations may be minimal (Spina and Tormey 2000) or intense (Bozek and Young 

1994). Intense fires and their subsequent effects on hydrologic regimes, erosion, debris 

flows, woody debris recruitment, and riparian cover can strongly influence the structure 

and function of aquatic systems (Rieman and others 2003; Swanson 1981). Post-fire 

effects may result in fish mortality (Bozek and Young 1994; Minshall and others 1997; 

Rieman and Clayton 1997; Rinne 1996; Spencer and others 2003), but local extirpation 

of fishes is patchy, and recolonization is often rapid (Bisson and others 2003; Gresswell 

1999; Rieman and others 1997, 2003). Subsequent effects associated with the loss of 

vegetation and infiltration capacity of soils may include increased erosion, changes in 

the timing and amount of runoff, elevated stream temperatures, and changes in the structure of stream channels (Benda and others 2003; Rinne and Neary 1996, Swanson 1981; 

Wondzell and King 2003). The nature of these changes depends on the extent, continuity and severity of the fire, and on lithology, landform, and local climate (Rieman and 

Clayton 1997; Swanson and others 1987). Where native fish populations are naturally 

depauperate or have declined and become increasingly isolated because of anthropogenic activities, the effects on fish populations are more pervasive and long lasting (Propst 

and others 1992; Rieman and others 2000; Rinne 1996; Rinne and Minckley 1991). 

Ecological specialists—species with narrow habitat requirements—in highly degraded 

and fragmented systems are likely to be most vulnerable to disturbance (Angermeier 

1995; Angermeier and Winston 1998; Dunham and others 2003; Trebitz and others 

2003). The role of fire in facilitating invasions by non-indigenous aquatic organisms 

is unknown, but must be considered among the indirect effects. Disturbance associated 

with fire may make already vulnerable native populations susceptible to colonization by 

invasive species (Dunham and others 2003). Aquatic systems may not experience shifts 

in assemblage structure, but may exhibit effects at the population level that translate 

into long-term effects (St.-Onge and Magnan 2000; Tonn and others 2003, 2004). This 

illustrates the importance of post-fire monitoring and research at more relevant spatial 

and temporal scales to better understand the natural response regime (Gresswell 1999).

The impacts of timber harvest on fish assemblages are extensions of their effects on 

aquatic ecosystems (Rinne and Neary 2000; Rinne and Stefferud 1999). The extent to 

which hillslope and riparian soils are disturbed and mobilized to the stream channel will 

reduce pool habitats (McIntosh and others 1994, 2000), decrease the survival of incubating salmonid eggs (Reiser and White 1990), and/or increase turbidity (Bolstadt and 

Swank 1997; Lisle and Napolitano 1998). A change in timing or peak flow magnitudes 

may scour redds or embed them. Removal of timber from riparian areas decreases the 

amount of large woody debris available for recruitment into the channel, affecting pool 

formation, sediment storage, and cover availability (Beechie and Sibley 1997; Bilby 

and Ward 1991; Bisson and others 1992; Solazzi and others 2000; Reeves and others 

2002), though the extent of management activity in the catchment may determine the 

severity of the impacts (Reeves and others 1993). Short-term increases in recruitment 

of large woody debris in the channel may benefit fish and amphibian populations but 

the benefits may be transient as the long-term supply of large trees in the riparian zone 

is depleted. Thinning of the riparian canopy increases solar input, stream temperatures, 

and aquatic productivity. Fish populations may exhibit lower abundance or productivity 

resulting from reduced coldwater habitats or increased stream temperatures over time 

spans of decades (Hornbeck and Kochenderfer 2000; VanDusen and others 2005).

Vegetation removal, whether by fire, logging, or other human activity, acts at multiple scales to affect the natural processes that control catchments and stream processes, 

destabilizing flow and thermal regimes, simplifying habitats through siltation, reducing 

Chapter 11. Biological Responses to Stressors in Aquatic Ecosystems in Western North America: 

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USDA Forest Service RMRS-GTR-231. 2010. 213

water quality, and impacting biotic communities (Osborne and Wiley 1988; Rabeni and 

Smale 1995; Snyder and others 2003; Wang and others 1997). Patterns in fish assemblage structure are often attributed to longitudinal changes in stream attributes (Jackson 

and others 2001; Jones and others 1999; Lyons 1996; Rahel and Hubert 1991; Schlosser 

1982) and hydrologic variability (Poff and Allan 1995). Changes in richness, density, 

and species composition are associated with decreased hydrologic disturbance (in other 

words, more stable flows), increases in pool depth and habitat diversity, and local geomorphic conditions and processes that contribute to spatial heterogeneity within the 

stream continuum (Poff and Allan 1995; Schlosser 1990) and may serve to mask responses to anthropogenic disturbance (McCormick and others 2000).

Changing fire regimes and the potential for larger, more destructive fires may threaten 

the loss of aquatic habitat diversity and lead to accelerated extinction of some vulnerable populations (Dunham and others 2003; Gresswell 1999; Minshall 2003; Rieman and 

Clayton 1997; Rieman and others 2003). A simple focus on managing fuel, however, 

may not address the role of fire or the primary threats to the persistence of many species. 

An approach that aims to restore resiliency to fire related disturbances in both terrestrial 

and aquatic ecosystems is needed. Development of predictive models relating physical 

attributes of streams and fish population abundance have shown promise in identifying 

the high priority reaches for restoration (Barnett and others 2003; Latterell and others 2003; Wu and others 2000). This suggests that similar models might be developed 

that would identify stream reaches that would be high priority areas for exclusion of 

treatments.

Amphibians and Reptiles

Amphibians are the most abundant vertebrates in many forests and have the potential to play a significant role in ecosystem dynamics (Wahbe and Bunnell 2003). 

Riparian and upland habitats provide important habitat for amphibians and semi-aquatic 

reptiles that depend on mesic ecotones to forage, aestivate, and reproduce (Burke and 

Gibbons 1995; Castelle and others 1994; Semlitsch 1998). Terrestrial amphibian species 

richness, abundance, and community composition are highly dependent on catchment 

forest cover (Houlahan and Findlay 2003; Wahbe and Bunnell 2003). Intensive harvest 

completely eliminated terrestrial salamanders or reduced them to very low numbers 

when mature forests were clearcut (Knapp and others 2003; Naughton and others 2000; 

Perison and others 1997; Petranka and others 1994) though species may persist where 

large amounts of woody debris are left on the forest floor (Biek and others 2002). At 

larger catchment scales (400 to 4,000 ha), responses of amphibian and reptile species 

to management practices (including clearcutting) varied considerably depending on the 

taxon (Loehle and others 2005; Renken and others 2004). Post-harvest declines in local 

amphibian populations persist for years post-harvest but abundance and species composition may remain relatively stable at larger spatial scales (Babbitt and Tanner 2000; 

Herbeck and Larsen 1999). Selective harvests that create small gaps may have little or 

no effect on amphibians (MacCracken 2005; Messere and Ducey 1998). Reductions in 

litter depth and coarse woody debris contribute to declines in some amphibian populations because of structural changes to forest floor habitats (DeGraaf and Rudis 1990; 

Houlahan and Findlay 2003; Loehle and others 2005; Mitchell and others 1997), but 

studies of forest structure in the Pacific Northwest found no evidence that variation in 

amphibian abundances was strongly influenced by the amount of coarse woody debris 

on the forest floor (Aubry 2000; Bunnell and others 1999). Abundance of stream dwelling amphibians is also reduced following timber harvest (Adams and Bury 2002; Bury 

and others 2002; Corn and Bury 1989).

The vulnerability of amphibian populations to wildfire varies by region, species’ life 

histories, and fire regimes. The coincidence of fire and migration, reproduction, and 

larval periods may determine the vulnerability of amphibian populations to wildfire. 

Studies suggest that direct fire related mortality of adult amphibians is rare, either because of the timing of the fire or because amphibian species were able to exploit refugia 

from fire (for example, burrows, moist ground, ponds, streams; see papers summarized 

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States
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in Pilliod and others 2003). Increases in stream temperature, because of canopy loss, will 

affect species that exhibit strong thermal preferences (Pilliod and others 2003; Welsh 

and others 2001; Welsh and Lind 2002). Sedimentation in streams results in reductions in interstitial spaces that can affect reproductive success in amphibian populations, 

depress growth rates from lost foraging space, and expose individuals to increased predation. Fire may alter conditions along migratory corridors, from terrestrial habitats to 

the aquatic systems where amphibians breed. Preliminary surveys of post-fire amphibian populations in the Klamath-Siskiyou Region suggest no negative effects of wildfire 

on terrestrial amphibians, but stream amphibians decreased following wildfire.

The timing of fuel treatments and prescribed burns may be of critical importance 

to the maintenance of overwintering habitats, post-emergence dispersal, and reproduction of amphibian populations (Thompson and others 2003). In fire driven ecosystems, 

Russell and others (1999) suggested that in the long-term, prescribed burning could help 

maintain amphibians in managed forests by sustaining some of the natural processes of 

ground cover development. Two studies of salamanders in eastern United States plantation forests supported those predictions, although the plantation forests studied were 

young (25 years) and were compared with much older natural origin forest (Bennett and 

others 1980; Pough and others 1987). Prescribed fire and thinning to reduce fuel loads 

will remove large amounts of coarse woody material from forests, which reduces cover 

for amphibians and alters nutrient inputs to streams. Prescribed fire may increase the 

mortality of terrestrial amphibians by fire because prescribed burning usually occurs 

from fall to spring when amphibians in the Northwest are active (Bury 2004). Most reptiles are adapted to open terrain, so fire usually improves their habitat. Reptiles, which 

often exploit open areas for feeding, basking, and display behaviors, tend to increase in 

harvested areas (Moseley and others 2003; Perison and others 1997; Renken and others 

2004; Shipman and others 2004).

While working to restore “healthy” forests and reduce the risk of catastrophic fires, 

forest managers must confront the challenge of maintaining biodiversity in western forests and incorporating the understanding of how fire affects semi-aquatic biota with the 

effects of fuel reduction management on wildlife in western forests (Bury 2004; Olson 

and others 2002). Management implications for forest lands adjacent to aquatic systems 

include effects on terrestrial and semi-aquatic species whose habitat requirements extend beyond the margins of wetlands, streams, and rivers (Houlahan and Findlay 2003; 

Semlitsch and Bodie 2003; Thompson and others 2003). Implementation of an ecosystem management strategy that reverses the current trend of having landscapes dominated 

by early and mid-successional forests would help restore depleted populations to levels 

where salamanders better fulfill their ecological roles as forest floor insectivores. Other 

management techniques that would benefit salamanders include leaving buffers along 

headwater streams (Sheridan and Olson 2003; Stoddard and Hayes 2005) and using 

harvesting techniques that ensure that the basic structure and function of forests remain 

intact following timbering operations.

For purposes of conservation and management, it is important to define core habitats 

used by local breeding populations surrounding aquatic habitats (Houlahan and Findlay 

2003; Semlitsch and Bodie 2003). Semlitsch and Bodie (2003) reviewed studies of riparian habitat use by herpetofauna and found that the mean distances of riparian habitat 

use ranged from 117 m by salamanders to 368 m by frogs with no significant differences 

between mean minimum or mean maximum distances exploited by amphibians and reptiles. The survival of semi-aquatic vertebrate populations may rely on intact terrestrial 

habitats (up to 2 km from aquatic systems) during reproductive seasons, for overwintering, and for maintaining connections among populations (Findlay and Houlahan 1997; 

Houlahan and Findlay 2003; Roe and others 2003).

Houlahan and Findlay (2003) were unable to resolve the interaction between forest 

cover and road density in explaining amphibian species richness, but roads have been 

implicated in reducing amphibian dispersal (Gibbs 1998), increased mortality (Fahrig 

and others 1995), and reduced genetic diversity (Reh and Seitz 1990). Responses to 

habitat alterations associated with management activities suggest that these basins 

Chapter 11. Biological Responses to Stressors in Aquatic Ecosystems in Western North America: 

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USDA Forest Service RMRS-GTR-231. 2010. 215

may be useful as reserves, especially in catchments where timber harvest may not be 

commercially viable (Sheridan and Olson 2003).

Fire Suppression Chemicals, Toxicity, and Mortality in Aquatic Organisms

Toxicity effects of fire suppression chemicals on aquatic organisms have been 

poorly studied (see reviews by Kalabokidis 2000; Gimenez and others 2004). Most 

fire suppression compounds are based on ammonium salts and toxicity is inferred to 

result from ammonium ion concentrations (Hamilton and others 1996). Fish, particularly salmonids, and some invertebrates appeared to be vulnerable to the application 

of these compounds. Boulton and others (2003) observed no short-term effects of fire 

suppressant chemicals on water chemistry and macroinvertebrates in streams following 

wildfire, but Buhl and Hamilton (1998, 2000) reported both laboratory toxicity and fish 

kills associated with fire control compounds.

Fuel Management Activities, Best Management Practices, 

and Cumulative Watershed Effects

Post-Fire Remediation and Logging

In response to the increased risk of runoff and erosion, land managers and technical specialists sometimes apply erosion control efforts (Burned Area Emergency 

Rehabilitation or BAER treatments) to mitigate the effects of fire (Neary and others 

2000). A recent review of BAER practices indicated inadequate scientific evaluation 

of the effectiveness of the treatments (Robichaud and others 2000). Some practices 

contribute to loss of soil integrity, impede the persistence or recovery of native species, 

disrupt riparian functions, and impair water quality (Karr and others 2004; McIver and 

Starr 2000). Postfire logging and road building, undertaken on steep slopes with sensitive soils, exacerbate erosion associated with changes in soil and vegetation structure 

that decrease infiltration and increase overland flow (DeBano and others 1996; McIver 

and Starr 2000). Too little is known about the cumulative effects of site specific responses at the watershed scale, knowledge that is essential if forest management is to be 

linked to aquatic ecosystem integrity (Chapter 14 ). Research at the watershed level that 

integrates terrestrial and aquatic components is needed to inform management about the 

risks and opportunities available in the post-fire landscape. Research and resource management agencies should cooperate to develop the basic tools of experimental design 

that can rapidly evaluate post-fire treatments and reduce the uncertainty of its long-term 

effects. Salvage harvesting policies could be prepared before major disturbances occur 

that would guide the timing and intensity of salvage harvesting.

Natural disturbances are key ecosystem processes that help maintain biodiversity, 

and productivity and support ecosystem restoration by recreating some of the structural 

complexity and heterogeneity lost through intense management of natural resources 

(Beschta and others 2004; Bisson and others 2003; DellaSala and others 2004). Salvage 

harvesting activities undermine many of the ecosystem benefits of major disturbances 

by removing large quantities of “biological legacies” (for example, snags and downed 

trees) that are critical habitat for species and important for the recovery of terrestrial and aquatic systems (Benda and others 2003; Lindenmayer and others 2004; May 

and Gresswell 2003; Swanson 1981; Van Nieuwstadt and others 2001). Effects from 

postfire logging in riparian areas can persist for many decades because of the loss of 

dead trees that would normally become incorporated into stream channels and forest 

floors over several decades or more (Beschta and others 2004; May & Gresswell 2003). 

Similarly, logging large trees from upslope areas prone to landslides would also reduce, 

over time, the recruitment of large wood to riparian and aquatic ecosystems. Fire and 

subsequent hydrologic events can contribute wood and coarse sediment necessary to 

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States
216 USDA Forest Service RMRS-GTR-231. 2010.

create and maintain productive in-stream habitats (Bisson and others 2003; Reeves and 

others 1995) and produce important heterogeneity in channel structure (Benda and others 2003). Natural disturbances interacting with complex terrain has been linked to a 

changing mosaic of habitat conditions in both terrestrial and aquatic systems (Bisson 

and others 2003; Miller and others 2003; Naiman and others 2000; Reeves and others 

1995). Even with mitigation of fuel, large disturbances are inevitable. Only frequency 

and magnitude of individual events can be changed (Istanbulluoglu and others 2004). 

This variation of conditions in space and time may be the key to evolution and maintenance of biological diversity, and ultimately, the resilience and productivity of many 

aquatic populations and communities (Bisson and others 2003; Dunham and Rieman 

1999; Dunham and others 2003; Poff and Ward 1990).

In forested watersheds, valued riparian functions such as stream shading, bank 

stabilization, and large wood recruitment are largely protected by best management 

practices, particularly the establishment of riparian buffers since the influence of most 

riparian features decreases with distance from the stream channel (Beechie and others, 

2000; Van Sickle and Gregory 1990). However, the indirect effects of upland fuel treatments on riparian habitats are poorly understood (Chapter 10). Forest harvest strongly 

affected the riparian microclimate and the riparian environment became more similar 

to upland conditions (Brosofske and others 1997), but the effects do not necessarily 

contribute to increases in stream temperature (Poole and Bermann 2001). The effect of 

fuel reduction activities on drivers of stream temperature needs to be incorporated into 

management and restoration planning.

Hydrological, geomorphological, and ecological processes in streams and rivers are 

affected by the recruitment of large wood from riparian and upland portions of watersheds (Bilby and Bisson 1998; Gregory and others 2003; Lienkaemper and Swanson 

1987; Montgomery and others 2003). Management plans for fuel reduction that could 

affect the recruitment of large wood to stream systems need to consider the importance 

of wood delivery, retention, and transport processes in stream habitats.

Discussion

The widespread decline in forest health has been linked to timber harvest and fire 

suppression (Bisson and others 2003; Brown and others 2004; Hessburg and Agee 

2003). Restoration and management of healthy forest ecosystems must start from the 

realization that they cannot be fireproofed (Agee 1997). Given the goals of ecosystem 

restoration and reduction of the risk of severe wildfire, a comprehensive program of 

pre-fire management, post-treatment monitoring, and adaptive management will be necessary to restore western forests. Effective fuel management will recognize differences 

among fire regimes, forest and landscape types, and departures from natural regimes, 

and incorporate the differences among systems (Hessberg and others 1999a, b). Plans 

must address the importance of spatial pattern of treatments in changing fire behavior 

at the landscape scale and the strategic placement of treatment areas within constraints 

imposed by land ownership, the occurrence of endangered species, and the protection 

of riparian buffers. Resource management strategies that operate under the assumption 

that forest health can be improved simply by managing vegetation through silvicultural 

treatments risk damage to key components of aquatic ecosystems. Repeated fire and 

fuel management programs require knowledge of the cumulative effects of those treatments on aquatic ecosystems.

Restoration efforts based on reestablishing conditions within the range that existed in 

some former sustainable state with an appropriate fire and forest management program 

requires knowledge of historic and current conditions and conditions in reference areas 

(Angermeier 1997; Bisson and others 2003; DellaSala and others 2004; Quigley and 

others 2001; Winston and Angermeier 1995). We lack information about key characteristics of indicators of forest condition that supports management for conservation of 

biodiversity (Lindenmayer and others 2000; McRae and others 2001). Potential indicators that move beyond single species management focus on the composition, complexity, 

Chapter 11. Biological Responses to Stressors in Aquatic Ecosystems in Western North America: 

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USDA Forest Service RMRS-GTR-231. 2010. 217

connectivity, and heterogeneity of forest structure, the same features that characterize 

the resistance and resilience of the aquatic network (Rieman and others 2003). Past 

conditions, including understanding the effects of the frequency, magnitude, and extent 

of disturbance regimes and the conditions they create over time, can be used to provide 

a context for managing ecosystems (Benda and others 2003; Cissel and others 1999; 

Swetnam and others 1999). Among the limitations of applying the “natural disturbance 

regime” to ecosystem management is that the extent of anthropogenic change in a region may have diminished the ability of species to respond to the disturbance (Swanson 

and others 1987, 1994). Silvicultural and prescribed fire management tools can lead to 

the goal of restoring stand structure and composition, but such restoration may have 

mixed implications for restoring other aspects of failing ecosystems such as fishes and 

their habitats. The interrelationships of terrestrial and aquatic disturbance regimes and 

succession processes must be understood if effective land management strategies that 

do not degrade aquatic resources are to be employed (Hessburg and Agee 2003; Lee and 

others 1997; MacDonald 2000; Macdonald and others 2004; Rieman and others 2003).

Natural variability of land use, natural vegetation, species diversity, and interactions 

with inherent disturbance processes needs to be defined at relevant spatial and temporal scales that are climatically, topographically, and biogeographically consistent to 

provide an appropriate geographic scale (Hann and others 1997). Quantifying variability requires knowledge of both the statistical properties of the condition indicator and 

an appreciation of the specific attributes of the indicator being described. Describing 

the “range” of natural variability may be inadequate as the sole descriptor because the 

occurrence of extreme events (pulse disturbances) may be critical in shaping ecosystem characteristics. Incorporating natural variability into management plans as testable 

hypotheses about the mechanisms of ecosystem change will facilitate development of 

future fuel treatment plans. By understanding the variability of natural regimes, using the “natural” state as a template, and modeling the departure of physical systems 

from that distribution of conditions, we will improve our ability to quantify cumulative 

effects of treatments on aquatic systems. Successful adoption of such strategies will 

require explicit statements about the uncertainties involved. Because restoring forest 

health will require repeated applications of treatments, we require better understanding 

of the cumulative effects of repeated disturbances.

Reducing Uncertainty: Knowledge Gaps and Research Opportunities

Effective management of riparian areas would minimize cumulative watershed effects on riparian functions by preserving their dynamic connections to upland areas and 

stream corridors (Reid 1998). Understanding the effects of timber harvest, fuel reduction, and fire requires integration of information about the spatial extent of management 

activities, temporal aspects of natural disturbance regimes (for example, fire return or 

landslide frequencies), and historical human disturbance (Franklin and Agee 2003). 

Anticipating the cumulative watershed effects of fuel treatments on riparian and aquatic ecosystems will be more difficult because of the limited knowledge of the impacts 

of spatially dispersed, temporally intensive, and repeated treatments in the watershed. 

As such, effective experimental design of fuel treatment prescriptions and post-impact 

monitoring will be necessary to increase the available information about the cumulative 

effects of management activities in sensitive areas.

Uncertainty exists over the approaches for incorporating fire and other disturbance 

processes into the management of systems from which it has been excluded. Treatments 

need to be applied as experiments that provide new sources of knowledge that will 

inform future management decisions (Robichaud and others 2000). Restoration of 

forest landscapes that protect aquatic resources requires strategies that identify and protect areas with high ecological integrity and connect them at the catchment level to 

increase the resistance and resilience of ecosystems (Gresswell 1999; Lee and others 

1997; Reiman and others 2000). Status (condition) and trends (changes in condition 

over time) may be tracked at multiple levels of biological organization (from the individual level through population and metapopulation dynamics, assemblage structure, or 

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States
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ecosystem processes). Responses across spatial scales demonstrate the importance of 

designing sampling strategies and analyses capable of discerning differences from local 

to regional scales (Angermeier and Winston 1998; Frissell and Bayles 1996; Gregory 

and others 1991; Li and others 2001; Poff and Allan 1995). Study designs that measure 

abiotic and biotic factors at multiple spatial scales provide important information for 

the monitoring and assessment of stream ecosystems (Kershner and others 2004; Larsen 

and others 2004). Replicating habitats sampled within a stream (as is commonly done 

in an upstream-downstream paired design comparing reference versus impacted sites) 

may not reveal the impact, but only portray the natural background variability of stream 

communities. Both spatially extensive designs with little sampling over time and tempo-

rally extensive designs with little or no spatial sampling may be biased in terms of their 

view of the relative importance of local and landscape factors (Wiley and others 1997). 

Therefore, study designs with temporal and spatial replication that account for assem-

blage variability at a range of spatial scales may improve the likelihood of detecting 

responses of stream ecosystems to wildland fire, fuel treatments, and restoration efforts. 

Studies designed to follow recovery from disturbance over long time scales (decades or 

more) would be necessary if we are to overcome limitations imposed by data collected 

at time scales consistent with more frequent (seasonal or annual) disturbance events. 

Detailed and temporally and spatially intensive monitoring may be necessary to resolve 

the variance components of data collected in lotic systems (McCormick and Peck 2000; 

Minshall and others 2001). Alternatively, paired watershed studies intended to monitor 

post-fire or post-treatment effects could be designed using the comparative approaches 

inherent in treatment versus control and before versus after disturbance studies (BeforeAfter, Control-Impact or BACI designs; Barbour and others 1996; Smith and others 

2003; Underwood 1992; Wiens and Parker 1995).

To be an effective alternative to cumulative effects studies, adaptive management 

requires a commitment to regular monitoring and analysis for subsequent management 

decisions (MacDonald 2000). Forest management and restoration planning require 

data from regional assessments of forest condition that incorporate spatial and tempo-

ral patterns of vegetation, habitats, fuel, and potential fire behavior. Further planning 

should consider the relations between these conditions and a host of issues surrounding 

terrestrial habitats and associated aquatic ecosystem conditions. Before management 

alternatives can be selected and implemented, they must be adequately evaluated for 

their effects on many terrestrial and aquatic ecosystem components. However, because 

post-harvest effects often require decades to dissipate, the long-term experimental study 

of cumulative effects is very costly. In addition, high variance confounds attempt to 

provide integrated assessments of the effects of timber harvest on aquatic habitats and 

biota. There is a need for development of a modeling capability for these processes that 

addresses the large variations in habitat conditions (Benda and others 2004; Davies and 

others 2000; Keane and others 2002; Poole 2002;).

The spatially discontinuous nature of river networks can inform restoration efforts by 

providing a better understanding of variability at different spatial scales (Poole 2002). 

Prioritization of sites for treatment may be based on physical models of fire behav-

ior and response regimes as they relate to key habitats for aquatic populations at risk 

(Rieman and others 2000; Brown and others 2004). Once identified, such high priority 

stream reaches could be reconnected via restored corridors at the landscape level. Large 

scale catchment features successfully predict local scale habitat (Burnett and others 

2003; Davies and others 2000) or process controls (Istanbulluoglu and others 2002, 

2004; Miller and others 2003; Wondzell and Howell 2004). Independent constraints on 

climate and geology strongly influence lower level processes in catchment hierarchies 

and the assemblage responses to the abiotic regime (Burnett and others 2003; Davies 

and others 2000). The refinement of these models to address spatial and temporal varia-

tion in landscape processes supports the emerging capability for modeling catchment 

scale habitat influences on animal populations and characterizes the species specific 

potential of streams to provide habitat for fish (Burnett and others 2003). The develop-

ment of risk assessment models for population and assemblage responses to changes in 

catchment land use will require detailed information (Keane and others 2002). Further 

Chapter 11. BiologicalResponsestoStressors inAquaticEcosystems in WesternNorthAmerica: 

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USDA Forest Service RMRS-GTR-231. 2010. 219

research will contribute to modeling capabilities that assimilate historical conditions 

and predict future conditions under different management scenarios by reducing the 

uncertainty associated with the need to estimate model parameters (Keane and others 

2002; Roloff and others 2005).

Conclusions

Forest resource managers are confronted with two related management challenges. 

Aquatic resources, particularly imperiled salmonid populations, require protection and 

restoration. At the same time, the imperative to reduce the risk of catastrophic wildfires 

requires ecosystem based management that accounts for the inherent linkage between 

aquatic and terrestrial systems and involves processes that are fraught with uncertainties 

(Bisson and others 2003). To ensure the resilience of terrestrial and aquatic ecosystems, 

it is necessary to consider the restoration of terrestrial and aquatic ecosystems simultaneously. A challenge for research will be to integrate the emerging understanding of 

changing vegetation and fire with that of watershed and aquatic ecological processes 

to understand the full implications of the changes made. A challenge for management 

will be to restore ecological processes that support both resilient terrestrial and resilient 

aquatic communities. Research and management need to coordinate their efforts to arrive at a common conceptual model that expresses the uncertainties associated with 

particular courses of management actions and perceived risk to aquatic resources.

The Healthy Forests Restoration Act of 2003 (HFRA; H.R. 1904) increases the 

emphasis on fuel reduction in forest planning. However, the main impact of HFRA is 

largely procedural. It is not a strategy for wildland fire risk management. The prevailing 

conditions in today’s forests developed over a century of fire suppression and cannot 

be dealt with effectively except by long-term adaptive management (Agee and Skinner 

2005; Hessburg and Agee 2003). While restoration may be an appropriate course of 

action, particularly to protect valued aquatic resources, fire disturbance of forests is 

inevitable and even desirable. Restoration efforts must incorporate natural variability, 

which precludes a one size fits all approach to fuel management and post-fire activities 

(Landres and others 1999). The procedural mandates of HFRA will necessitate action 

before such research can inform the decision making process. Adaptive management, 

undertaken with controls (including both unlogged and unburned catchments) and replication, can provide extremely valuable information to resource managers.

Successful fuel management will depend on a strategy that incorporates natural variability in patterns of disturbance and its effects on aquatic resources. Fire management 

is adaptive and requires a long-term commitment to monitoring. Data will be necessary 

to inform the decision making process, either to reduce uncertainty in decision support 

tools or evaluate the results of a management option through effectiveness monitoring. 

Efforts to restore forest condition and maintain the connectivity of terrestrial habitats 

with their aquatic ecosystems will require that we inventory what we know, analyze 

variability in our existing data, express the uncertainty associated with analyses and 

associated predictions, articulate clear goals, design treatments as experiments to test 

specific hypotheses, monitor treatment outcomes, and apply the results in future planning processes.

We can study the natural vegetation and fire patterns of areas designated for treatment and other areas like it and apply knowledge of those patterns to their management. 

Recent bioregional assessment projects (for example, Interior Columbia River Basin 

Ecosystem Management Project and Sierra Nevada Ecosystem Project) provided more 

information about existing forest and rangeland conditions and the state of ecosystems 

and their inhabitants than ever before. Incorporation and integration of this information 

to address interactions between landscape spatial and temporal patterns of vegetation, 

habitats, fuel, and potential fire behavior will provide a basis for adaptive management 

that recognizes the functional attributes of the terrestrial-riparian-aquatic interface. Data 

analyses that characterize variability at different spatial scales will support adaptive 

management and planning. Modeling and simulation tools capable of incorporating 

Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States
220 USDA Forest Service RMRS-GTR-231. 2010.

multidimensional data and examining the effects of management activities on key facets of ecosystems are needed. Ideally, they would also serve as tools for planning and 

evaluating the effects of alternative courses of action on aquatic ecosystems. Modeling 

and predicting potential impacts of forest harvest operations and wildfire on water 

quantity and quality are critical tools for forest managers. To make these predictions, 

the impacts of harvest operations and wildfire on model input parameters must first be 

quantified with measurements. No one knows exactly how to restore healthy forests that 

sustain viable populations of native species in functional habitat networks across space 

and through time. Acknowledging that the inherent complexity and dynamism of ecosystems contributes to uncertainties about outcomes of management practices will be 

necessary if we are to learn from the effects of those practices and incorporate them into 

future management planning. Recognition that risks to aquatic ecosystems may be additive, multiplicative, or synergistic across space and time will not preclude mitigation 

of high fuel loads in forests. Experimental, adaptive approaches to fuel management 

would unite researchers and resource managers in planning, implementing, and monitoring treatments.

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Frank H. McCormick, Bruce E. Riemen, Jeffrey L. Kershner Cumulative Watershed Effects of Fuel Management in the Western United States
234 USDA Forest Service RMRS-GTR-231. 2010.

Chapter 12.

Landscape Scale Effects of Fuel Management 

or Fire on Water Resources: The Future of 

Cumulative Effects Analysis?

Charles H. Luce, Rocky Mountain Research Station, USDA Forest Service, Boise, ID

Bruce E. Rieman

Introduction

Wildfire may pose serious threats to both direct (for example, heating, dissolved toxic gases) and indirect (for instance, post-fire floods, erosion, changing habitat), aquatic 

ecosystems (Dunham and others 2003; Gresswell 1999). There is, however, increasing 

recognition that major flood, erosion, and mass wasting events after fires can also be important to the formation of complex habitats that are beneficial in the long-term (Bisson

and others 2003; Reeves and others 1995).

There is growing interest in restoration of terrestrial vegetation communities that 

have shifted in composition, pattern, and continuity, producing forests that are more 

flammable and more contagious for fire in some parts of the country (Hessburg and 

Agee 2003). Some have noted the potential benefit of restoration to watershed and 

aquatic ecosystem values because the reduction in fuel will mitigate the severity of 

future fires (Graham and others 2004; USDA 2000). Restructuring forests might also 

provide benefits through the restoration of forest-riparian functions that contribute to 

the maintenance of structurally complex and resilient aquatic habitats (Rieman and others 2000, 2005). At present, these benefits are largely hypothetical and others have noted 

that management has not always been benign (Bisson and others 2003; DellaSala and 

Frost 2001; Graham and others 2004). The effects of management can also be fundamentally different than severe fire, which tends to be more chronic than periodic in 

nature (Istanbulluoglu and others 2004; Reeves and others 1995).

An important question stems from this uncertainty: “Which poses a greater risk, 

wildfire or the management intended to reduce its effects?” (Bisson and others 2003; 

Rieman and others 2003). The answer likely depends on context, and the more contentious question is how we objectively evaluate the differences in risk between fire and 

management for a particular area or project. This question has typically been addressed 

in debate or analysis based on the apparent risks associated with the local and shortterm effects of fire and the management intended to mitigate those effects (O’Laughlin 

2005). Ecologically important differences between the two may only be apparent as we 

consider how they might play out over longer time scales (101

 to 102 years) and larger 

spatial scales (103

 to 105 ha). In short, differences in cumulative effects may be recognized at these scales.

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
USDA Forest Service RMRS-GTR-231. 2010. 235

How the relative cumulative effects of fire and management alternatives are analyzed 

is important. Analyses that compare only the absolute sediment or thermal loadings 

accumulated through a watershed will be incomplete and potentially misleading. The 

literature on cumulative effects has already noted that non-linear and synergistic effects 

of activities may be important as well (Dunne and others 2001; MacDonald 2000; Reid 

1993; Sonntag and others 1987). In particular, we argue that synergistic effects related 

to synchrony over several watersheds or sub-populations are an important cumulative 

effect consideration for comparing the effects of fire versus fuel management.

Cumulative Watershed Effects

By strict definition, cumulative effects are expected to manifest only as a result of 

multiple management decisions or projects (CEQ 1997). A more general definition describes cumulative effects as those that occur over larger spatial scales and longer time 

scales and through potentially non-linear interactions of multiple processes (Sonntag

and others 1987). Concern for cumulative effects, resulting largely from the National 

Environmental Policy Act of 1969, has challenged the limits of existing scientific theory 

in many disciplines, and literature has tried to frame an efficient and effective cumulative effects assessment process (Dunne and others 2001; MacDonald 2000; Reid 1993; 

Sonntag and others 1987) (Chapter 12). Because watersheds are a natural accumulator 

of potential pollutants, such as sediment, nutrients, or thermal energy, they have been 

an area of focused development for analysis procedures (Dunne and others 2001; Reid 

1993).

An individual project with ground disturbing activities typically displays watershed 

effects near the stream’s headwaters. Downstream, these effects are diluted (Bisson and 

others 1992). However, when multiple projects are considered over a short time period, 

potential risks to downstream areas may be more apparent because of the accumulated 

effects (Bisson and others 1992; Reeves 1993). Best Management Practices were developed to mitigate the effects of any project; however, even the relatively minor effects of 

many projects, particularly during a short time period, might still substantially change 

downstream habitats. Consequently, most of the concern with respect to forestry in watersheds is with cumulative effects.

This is a well defined problem with a substantial amount of literature providing guidance for the assessment of cumulative watershed effects (CWE) of forest management 

activities. A strong underlying theme is the downstream transport and accumulation of 

watershed materials (water, nutrients, sediment, thermal energy) from multiple land use 

actions (Dunne and others 2001; MacDonald 2000; Reid 1993). The topological context provided by a watershed makes this a natural consideration. In addition, synergies 

between upstream and downstream actions are possible, for example, how the changes 

in gradient and hydraulic geometry along a stream interact with changes in sediment 

and wood supplies and how the downstream reaches can integrate effects from many 

projects in ways that may be more complex than the simple addition and dilution of 

materials.

In contrast to the integration effects over the spatial domain of a watershed, quantitative cumulative effects analyses for forestry often consider the distribution of effects 

across time (Cline and others 1984; Dunne and others 2001; MacDonald 2000; Megahan 

1974; Reid 1993; Washington Forest Practices Board 1995), generally with annual time 

steps. One reason for this approach has been to examine patterns of recovery after anthropogenic disturbances. This approach is in line with the Total Maximum Daily Load 

(TMDL) concept used to regulate cumulative pollutant loads from multiple point and 

non-point source activities (such as silviculture or agriculture) under the Clean Water 

Act. One of the key mitigations for point loading activities is to meter out pollutants 

generated in bulk to allow flow and biological processes to dilute, assimilate, or transform the pollutant. TMDLs are regulatory limits to pollutant loadings that are set using 

state standards and the expected flow at a given point that will dilute the pollutant. 

This approach is easily applied for silvicultural chemical use, but prescribed allowable 

Charles H. Luce, Bruce E. Rieman Cumulative Watershed Effects of Fuel Management in the Western United States
236 USDA Forest Service RMRS-GTR-231. 2010.

loadings for sediment are more commonly based on an average over an unspecified 

multi-annual time scale than on a daily time scale. TMDLs become, in essence, a prescribed limit to CWEs. The goal of many CWE analyses then becomes manipulation of 

various treatments and mitigations to control the distribution of pollutants over time at 

each required point of compliance.

A comparable analysis of the distribution of cumulative effects in space is seldom 

considered. The growing body of work in landscape ecology argues that this is an important issue. In essence, the spatial pattern, structure, and quality of habitats may have 

a profound influence on the resilience, persistence, and diversity of aquatic populations 

and communities (Naiman and others 1992). From a cumulative effects perspective, 

the question becomes not just how much degradation within a watershed could cause 

significant declines in important biological indicators (for instance, abundance or productivity of sensitive species), but how many stream segments within a watershed or 

how many watersheds within a larger river basin might be degraded simultaneously 

(Benda and others 1998; Reeves and others 1995). An example comes from the Oregon 

Coast Range, where substantial work has documented that the downstream accumulation of impacts has degraded habitats and decreased diversity of populations in streams 

with logging (Bisson and others 1992; Reeves 1993). It has been estimated that 86 percent of 5th code watersheds in the Oregon Coast Range have seen reductions in forest 

cover between 1936 and 1996 (Wimberly and Ohmann 2004). This is both a remarkable 

achievement of human engineering and labor and a potentially dangerous ecological 

situation for what was once a large interconnected collection of populations of fishes 

and other organisms. It seems reasonable to suggest that analysis of cumulative effects 

within any of the remaining 14 percent of the coast range watersheds consider the importance of their role within the larger context.

Cumulative effects analysis then may consist of two contrasting approaches—a serial (downstream) cumulative effects technique derived from multiple impacts along 

a single flow path and/or on parallel cumulative effects technique derived from multiple impacts among individual flow paths that do not necessarily flow into one another 

but may share a common ecological context (fig. 1). The serial analysis considers the 

downstream transport or accumulation of many watershed products, for example, water, 

sediment, nutrients, and energy. It also considers non-linear effects from serial contributions with changes in transport capacity and the interactions of multiple constituents. 

Parallel analysis captures effects to watershed products that move both up and downstream (for instance, genetic material, biological populations), and are vulnerable to 

processes that cross boundaries of multiple watersheds. Both have defining scales in 

time and space. With respect to the interpretation of the significance of effects, the 

serial analysis can be thought of as an integrated approach in space, while a parallel approach will be more spatially explicit. In the serial analysis, we may accumulate 

spatially distributed inputs to look at effects at a point. In the parallel analysis, the idea 

is to consider the spatial relationships between affected habitats and sub-population or 

population units. The context of fire and fuel management is particularly relevant for the 

contrast between parallel and serial analyses, precisely because of the large spatial scale 

that fires and proposed fuel management projects may occupy.

The cumulative effect literature has emphasized the point of considering nonlinear, non-additive, or synergistic interactions of multiple actions or processes (Dunne 

and others 2001; MacDonald 2000; Reid 1993; Sonntag and others 1987). The parallel 

analysis is one example of this idea that focuses on geographic interactions. The reason 

we highlight the distinction using the serial-parallel classification is that this particular geographic interaction is a strong example of the synergistic effect; could apply to 

the conservation issues for many sensitive aquatic species populations (for example, 

salmon and trout); may have profound consequences for management and regulation; 

has limited exposure in existing CWE literature; and, as a consequence, has had little 

exposure with watershed management professionals. The general scope of the idea has 

been recognized for decades as being a cornerstone of cumulative effects analysis for 

terrestrial vertebrates (Collinge 1996; Debinski and Holt 2000; Fahrig and Merriam 

1994; Sonntag and others 1987; Wiens 1976; Zavala and Burkey 1997). However, even 

Chapter 12. Landscape Scale Effects of Fuel Management or Fire on Water Resources: The Future of Cumulative Effects Analysis?
USDA Forest Service RMRS-GTR-231. 2010. 237

Charles H. Luce, Bruce E. Rieman Cumulative Watershed Effects of Fuel Management in the Western United States

broad, general discussions of cumulative watershed effects still emphasize the downstream accumulation of water and sediment as the driving factor in cumulative effects 

analysis (Dunne and others 2001; MacDonald 2000; Reid 1993).

When addressing geographic interactions, synchrony or asynchrony of impacts in 

separate populations is the rationale for parallel analysis. This approach tends to require 

larger spatial scales than have traditionally been used for downstream accumulation 

types of analysis. Recent advances in the understanding of scaling in physical and ecological processes provide a foundation for quantitative analysis of effects at larger scales 

and in more complex landscapes than was practical in the past. In light of this growing 

understanding and the need for solutions to problems posed by fire and fuel management decisions, we believe it is important to revisit the utility of parallel cumulative 

watershed analyses of ecologically and operationally relevant effects that are spatial 

scale and pattern dependent.

There are attendant choices in temporal scale to be considered as well. Different 

resources are affected over different time scales. For example, an analysis of concerns 

Figure 1. In serial cumulative watershed 

effects analysis, the effects focus 

on the accumulated contributions 

above a certain point, for example 

the northern watershed (brown) in 

(a). In a parallel cumulative effects 

analysis for the same basin, one 

may need to consider effects to 

populations in neighboring basins 

(green and yellow) linked only 

through a separate waterbody (light 

blue) to which they are tributary “in 

parallel,” such as a large river, lake, 

or ocean. It may also be helpful to 

look within the original basin at 

stream segments (varying segments 

of white to blue) that may be 

affected independently by extreme 

events. We suggest that both types of 

analysis may be useful with respect 

to fire and fuels management.

(a)

(b)
238 USDA Forest Service RMRS-GTR-231. 2010.

about a reservoir filling with sediment could consider information averaged (or summed) 

over a few decades, while analysis of ecological concerns must consider shorter time 

scales consistent with species seasonal habitat use and life cycles (for example, months 

to years). Both biological and physical processes have important seasonal variations 

that may create non-linear interactions. For instance, in climates with summer convective storms, production of fine sediment from roads is introduced to streams when flows 

are too low to transport the sediments away. Because time scales are important ecologically, some have noted the need to not just consider the magnitude of sediment loading, 

temperature, or peak flow changes, but the temporal distributions as well (Poole and 

others 2004). Important aspects of time are frequency or spacing of disturbances, duration and recovery times, and the overall temporal extent. A key concept in the discussion 

of disturbance and population response is that changes in the “predictability” or the timing and frequency of disturbances can have a profound influence on native species that 

evolved under one regime and are now faced with something novel in their evolutionary 

experience (Poff and others 1997). The issues with time and scale are inherent in either 

serial or parallel analyses, but with the latter, the concept of temporal synchrony in disturbance among multiple analysis units represents an important dimension for parallel 

cumulative effects analysis.

Ecological Limitations of Serial CWE Analysis

Serial analysis is most useful for describing processes where thresholds may be exceeded or long-term total loads are important. Reaches that trap substantial sediment 

and wood, for example, reservoirs, lakes, estuaries, and spawning habitat, are points 

where changes to total sediment load may be an important quantity to assess for that 

site. There are similar circumstances where total loads of nutrients such as phosphorous 

or nitrogen would be important to ecosystem processes (Reckhow 1999). Historically, 

there has been a strong reliance on serial cumulative effects for forest management, 

particularly for rigorous process based analyses (Cline and others 1984; examples summarized in Reid 1993; Washington Forest Practices Board 1995).

Modeling of sediment loads has been applied in a general way to the problem of fire 

versus fuel management. Elliot and Miller (2002) provide an example comparing the total loads of sediment derived from surface erosion of roads that might accompany active 

fuel management (for instance, mechanical thinning) over multiple years versus a fire 

event that erodes and recovers. They assumed that one disturbance replaced the other. 

Istanbulluoglu and others (2004) provide another example contrasting the effects of timber harvest and the effects to fire, also assuming that the first could be used to replace the 

latter. The two studies showed very different results. Elliot and Miller (2002) found that 

management produced substantially less sediment overall and Istanbulluoglu and others 

(2004) showed relatively similar values between treatments. The primary differences 

between the models were the slope of the land considered (moderate gradient in the first 

and steep in second) and consequently, the physical processes modeled (surface erosion 

versus mass wasting). The results are consistent with the situations and temporal scales 

assumed in each analysis, and the results of Elliot and Miller (2002) reflect the fact that 

surface erosion from roads is commonly a small part of the total or long-term sediment 

yield in moderate to high relief landscapes (Luce and others 2005).

An important lesson from Istanbulluoglu and others (2004) was that while the total 

load integrated over time was about the same, under a management scenario, the individual landslide events were smaller and the frequency was higher, changing from 

once every few centuries to once every few decades. From an ecological perspective, 

changes on this order could have profound effects on the succession of vegetation and 

the ultimate structure of the channel and availability of habitats. We might anticipate a 

similar result in the temporal distribution of sediments with a pulsed introduction following a fire compared to a smaller but more chronic supply associated with roads. The 

duration, persistence, or frequency of impacts is often more ecologically relevant than 

the magnitude of individual events, so brief high loading events after fire may be less 

Chapter 12. Landscape Scale Effects of Fuel Management or Fire on Water Resources: The Future of Cumulative Effects Analysis?
USDA Forest Service RMRS-GTR-231. 2010. 239

damaging than persistent minor loads from roads (Reeves and others 1995; Rieman and 

others 2003; Yount and Niemi 1990). Although Elliot and Miller (2002) showed that 

total yields may differ substantially, they provide no information that can resolve the 

differences that influence ecological processes through time.

While there are ways we can improve serial CWE analysis, such as being temporally explicit or using regime based (stochastic) standards that better reflect the natural 

history of any basin (Poole and others 2004), there are still limitations to a spatially integrated approach. First, standards or analyses based on natural disturbance regimes are 

problematic because we may have limited understanding of what the “natural” regime 

is and the degree of departure that is biologically important (Reckhow and others 2001), 

and second, the spatial details may be important (Luce and others 2001).

These shortcomings are not just academic in scope but they lead to particular problems from an ecological perspective. First, attempts to meet a specific limit to change 

any single segment or watershed leads to policies spreading impacts over larger areas 

and longer durations. If loading for a particular stream needs to be kept below a particular standard, then disturbance in the basin must be limited within a given time frame, in 

other words, acres or harvest or miles of new road per decade. This means that planning 

to optimize activities on the landscape to produce timber or restore vegetation patterns 

must move activities from basin to basin, metering out the potential for impacts at the 

prescribed level on a continuous basis. Under such a scenario, most watersheds would 

eventually be expected to become compromised to some degree (Reeves and others 

1995; Rieman and McIntyre 1993). Although each would meet the minimum criteria 

defined by typical CWE, few would retain the full productivity characteristic of more 

intact systems.

Second, attempts to identify an optimum or threshold condition of disruption leads 

to poor preparation for major stochastic disturbances. Essentially, major disturbances 

are treated as an exception in serial CWE analyses. Large floods, fires, and debris flows 

are often well beyond the scope of what can be manipulated by human intervention, 

which means that they are not generally considered within a regulatory framework. 

However, they do provide important ecological context within the system being regulated, and they often provide the greatest proportion of the load averaged over time 

(Istanbulluoglu and others 2004; Kirchner and others 2001). When working with a constant standard, a single major disturbance can fill an allocation for a long period, which 

is often not considered a reasonable burden for human interests to bear. Unfortunately, 

a stochastic standard (regime based or range of natural variability) could not provide 

a framework either, since one would need to know the context of that event within the 

distribution of events to know whether the standard had been met. Consequently, major 

disturbance is treated externally to the planning, monitoring, and regulatory (in other 

words, land management) processes. Without clear recognition of these events in the 

planning process, means to mitigate their effects are limited and reactive. Fortunately, 

there are management strategies and practices that can reduce risk from catastrophic 

events with forethought, so it is possible to design ecosystems that are more or less 

resilient to them. These strategies must consider natural adaptations that allowed species persistence through major disturbances (for instance, use of refugia, migration and 

dispersion, variable life histories) and the spatial scope of natural disturbance and management (Dunham and others 2003; Rieman and others 2003).

Parallel CWE Analysis to Extend Ecological Relevance

Fish and other aquatic species have survived for millennia with disturbances of varying scale and magnitude, some much greater than anything we have seen or created 

through management. A recent example is the aquatic ecosystem recovery from Mt. St. 

Helens’ eruption (Dale and others 2005). Evidence from paleoclimatic studies suggests 

that fires have been severe and even more extensive in the past (Meyer and Pierce 2003; 

Whitlock and others 2003). Sedimentation data reinforces this, where drainages in excess of 100 km2

 show evidence of occasional large disturbances as the major source of 

Charles H. Luce, Bruce E. Rieman Cumulative Watershed Effects of Fuel Management in the Western United States
240 USDA Forest Service RMRS-GTR-231. 2010.

long-term sediment yields (Kirchner and others 2001). Furthermore, as noted earlier, 

there is growing evidence that productive aquatic habitats can benefit or even depend 

on fire related disturbance (Benda and others 2003; Reeves and others 1995). Certainly, 

the evolution of aquatic species in the western United States has been influenced by a 

violent past, and the species and species assemblages have likely evolved in response to 

fire and related disturbances.

Emerging work in population biology and landscape ecology provides some insight 

into how species survive in disturbance prone environments. The expression of migration and the spatial structure of fish populations or networks of populations appear 

key (Rieman and Clayton 1997; Rieman and Dunham 2000). Migration means that 

individuals move among different habitats, generally in response to the availability of 

resources necessary to complete their life cycles. Because different habitats are distributed in space, migration is often variable in timing and extent, and the spatial extent 

and duration of catastrophic events in streams is limited (Miller and others 2003); not 

all members of the population are vulnerable to the same disturbances at the same time. 

Other species, such as amphibians and macroinvertebrates, may have life histories with 

terrestrial components, taking some part of the population out of harm’s way by entirely 

removing them from the stream (Pilliod and others 2003). Spatial structure implies that 

species may exist in a network of habitats linked through dispersal. If fish are lost to 

disturbance in one habitat, for example, it may be recolonized through dispersal from 

others. From an engineering process control point of view, fish populations are using 

spatial and temporal complementation and redundancy to mitigate the risks associated 

with any particular strategy. Both mechanisms require a spatially extensive and interconnected network of habitats.

Forest management interferes with these survival processes by

1. fragmenting habitat with physical or thermal barriers;

2. encroaching on habitat, reducing the quality, number, and size of habitats composing 

the network; and

3. increasing the chances that spatially distinct habitats may be degraded simultaneously.

While serial CWE does not address these issues, parallel analysis can.

If the spatial structure and quality of habitats has an important influence on species 

persistence, then an analysis of CWE in the context of spatial structure and its variability seems important. The range of natural variability has been proposed as a foundation 

to characterize variability, and an important part of the quantification is in geographic 

pattern and spatial structure (Swanson and others 1997). Although the concept is commonly applied at point or reach scales, the range of variability at a given point can often 

be anything from severely disturbed to pristine or simplified to complex, which is uninformative. A more informative approach would be to quantify the spatial distribution of 

habitat conditions in a population of streams or watersheds (Benda and Dunne 1997). 

The goal in the context of CWE would become the maintenance of the total amount, 

grain size, and spacing of conditions that is consistent with the evolutionary past, or 

at least the distribution of conditions that will allow native species and communities 

to persist in the future. While actual disturbances could not be managed, the spatial 

distribution of risk might be. Such an approach simultaneously reduces risks to populations while allowing short-term increases in risks to segments of those populations 

for the long-term benefit of both terrestrial and aquatic ecosystems. With appropriate 

analytical support, managers might consider the frequency distribution of conditions 

in a population of watersheds (Benda and others 1998). For example, simulations of 

historical disturbance indicated that at any point in time, no more than 40 percent of the 

watersheds in the Oregon Coast Range were in a condition of reduced productivity or 

complexity resulting from recent natural disturbance (Reeves and Duncan 2009). This 

level of disruption could become an ecologically defensible standard for spatially explicit cumulative effects. That is, no more than 40 percent of the watersheds in a larger 

basin could be in a degraded condition at any point in time. Ultimately, natural patterns 

of forest succession, disturbance, and watershed recovery would dictate the amount of 

human related disturbance that any basin could support (Swanson and others 1997).

Chapter 12. Landscape Scale Effects of Fuel Management or Fire on Water Resources: The Future of Cumulative Effects Analysis?
USDA Forest Service RMRS-GTR-231. 2010. 241

Many landscapes have been strongly influenced by spatially extensive disruption and 

habitat fragmentation (Hessburg and Agee 2003). Management activities that contribute 

to the restoration of processes that will ultimately lead to a more resilient landscape 

and connected network could be important. Rieman and others (2000) suggested that 

there may be parts of the landscape where terrestrial restoration would not be in conflict 

with aquatic restoration goals even if it did contribute to short-term, local degradation 

of habitats. In particular, they identified that most of the forest in need of structural 

restoration was at relatively low elevations in mixed severity ponderosa pine forests. 

Commonly these are also areas along main stem corridors that have experienced silvicultural manipulations and fire suppression for several decades. These areas are less 

likely to have strong populations of sensitive species, which have gradually become isolated in smaller and higher elevation tributaries, using main stems for migration when 

not blocked. While efforts to restore forests along these main stem corridors would 

likely increase sediment loads and the likelihood of landslides and debris flows from 

steep facing drainages, those loadings and events would be of little immediate ecological consequence since few important populations remain. Even where important 

populations remain, such disturbances could benefit populations if not spatially extensive within a particular habitat patch (Benda and others 2003; Rice and others 2001). If 

these projects break up fuel continuity, reducing the spatial footprint of individual fires 

and related disturbances, and leverage the restoration and reconnection of stream networks that could become productive elements of a larger spatial network in the future, 

the long-term benefits could still be important ecologically.

Challenges to Implementation

While there are some clear benefits to parallel CWE analysis, it represents additional 

effort and a shift in the way of thinking. Acceptance of the additional effort by land 

managers will be needed. In exchange, decisions would be more firmly grounded in 

impacts to ecology, which often increase flexibility for landscape restoration projects. 

Local and temporary disruption to watersheds or streams with little current ecological 

value or vulnerability as a tradeoff for potential long-term benefit would challenge the 

current regulatory framework. Ultimately, however, we believe such an approach is 

more centered on the overall goal of conserving species and their potential for resilience and adaptation in changing environments, not just protection of current habitat 

conditions.

Both managers and regulators will require sound science that demonstrates that the 

geographic relationship of a group of actions is key to the significance of their impact 

on aquatic communities, even across multiple watersheds. They will also need evidence 

that both aquatic and terrestrial ecosystems would benefit from using spatial pattern 

information to make decisions, even with the risk of increased loading. Some of that 

science must explore spatial and temporal scales of disturbance to understand the environment in which current ecosystems evolved. At issue is a need to understand the 

bounds of the physical processes that we would like to influence and emulate (Landres

and others 1999), in other words, what are the limits of disturbance at larger spatial 

scales and longer time scales? Finally, science needs to provide improved and more 

efficient means to inventory aquatic habitat and population conditions over large areas. 

Parallel analysis steps out of traditional monitoring of reaches or watershed outputs and 

into a distributed view of the aquatic landscape. Terrestrial ecologists have been able 

to use aerial photography and satellite imagery for some time for their inventories, and 

similar technology is needed for this type of approach. Many of the scientific challenges 

are being addressed by a range of studies at this time. Agencies will receive the greatest benefit from this research within the conceptual framework of combined serial and 

parallel analysis.

Charles H. Luce, Bruce E. Rieman Cumulative Watershed Effects of Fuel Management in the Western United States
242 USDA Forest Service RMRS-GTR-231. 2010.

Conclusions

Considering spatial patterns in CWE analysis presents some advantages over the spatially lumped approach that has traditionally been used. Aquatic biology has begun to 

incorporate a landscape perspective to better predict population and community dynamics and persistence in the face of major disturbances. The physical sciences supporting 

the relevant analyses of disturbance will also require flexibility in spatial and temporal 

scaling to match ecological process scales, in other words, to explore the spatial pattern 

and timing of landslide and debris flow events across a network of streams under natural 

wildfire regimes compared to a range of managed regimes.

While this portends more effort by management and regulatory agencies, the development of the science has led to automation of GIS tasks for spatially distributing 

impact analysis (Prasad and others 2005). Advances in estimating the local impacts of 

projects and serial cumulative effects as discussed in this book are also directly applicable within a parallel CWE approach.

The subsequent analyses will have a closer tie to ecological outcomes, making them 

more useful and more defensible. In particular, spatially distributed analyses support 

planning that is based on the natural range of variability concept. Although the transition 

from an existing landscape with spatially extensive homogenization and degradation of 

habitat to one where natural disturbances play a more active role is challenging, it is 

likely that the parallel approach can highlight priorities for restoration activities. At the 

same time, it could also highlight where the short-term risks posed by restoration activities might be unacceptably high without advance preparations.

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Charles H. Luce, Bruce E. Rieman Cumulative Watershed Effects of Fuel Management in the Western United States
246 USDA Forest Service RMRS-GTR-231. 2010.

Chapter 13.

Tools for Analysis

William Elliot, Rocky Mountain Research Station, USDA Forest Service, Moscow, ID

Kevin Hyde, Rocky Mountain Research Station, USDA Forest Service, Missoula, MT

Lee MacDonald, Watershed Science Program, Colorado State University, Fort Collins, CO

James McKean, Rocky Mountain Research Station, USDA Forest Service, Boise, ID

Introduction

This chapter presents a synthesis of current computer modeling tools that are, or 

could be, adopted for use in evaluating the cumulative watershed effects of fuel management. The chapter focuses on runoff, soil erosion, and slope stability predictive 

tools. Readers should refer to chapters on soil erosion and stability for more detailed 

information on the physical processes involved.

All cumulative watershed effects (CWE) tools are models of natural processes. A 

“model” is a mathematical or qualitative representation of nature. It includes an understanding of the analysis area including the identification of the important features and 

processes, such as topography, soil properties, and vegetation and climate, as well as 

their interactions. Models provide answers to the question, “What watershed changes 

are anticipated as a result of proposed fuel management activities?”

Getting Started

The first step in modeling cumulative watershed effects (CWE) is to define the 

problems that need to be analyzed. Chapter 14 outlines the qualitative and quantitative 

questions to be answered in a watershed analysis. Briefly, the manager must define:

• values of concern (water resource protection, human welfare, wildlife issues, etc.); 

• predictions needed (peak runoff rates, water yield, upland erosion rates, stream 

sediment delivery rates, etc.); 

• the scale of the analysis (for example project, watershed, landscape);

• the environmental constraints (for example, vegetation, climate, topography);

• the temporal context (single event, average annual, return period analysis);

• requirements of local, state, or federal regulatory agencies; and

• organizational constraints (due dates, available resources, computer capabilities, 

level of analytical and computer skills).

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
USDA Forest Service RMRS-GTR-231. 2010. 247

Once the problem is clearly defined, the watershed manager should review current 

data availability, such as soil surveys, GIS layers, air photo libraries, weather records, 

past watershed disturbance history, and stream flow records for conditions similar to 

those of the watersheds of concern. If it has not already been done as part of other analyses, the manager should conduct a field survey and develop a set of field notes. Typically, 

slope lengths and gradients, vegetation conditions, and relevant soil properties (texture, 

depth, evidence of water logging or erosion, water repellency, etc.) are noted. During 

the field survey, the manager should note current conditions and evidence of past activities contributing to these conditions, such as compaction or evidence of stunted or 

unusually lush vegetation, and if appropriate, evidence of past mass movement.

Impacts of concern

Generally, two public values dominate cumulative watershed effects analyses: impacts on aquatic ecosystems (Chapter 11), and impacts on human resources (for example, 

water supplies, structures in flood plains or on alluvial fans, recreation resources).

In some cases, the values at risk or level of public impact may influence the selection of a more or a less sophisticated modeling approach. For example, a high visibility 

watershed on the edge of a major city may require greater analysis than would a remote 

watershed adjacent to a wilderness area because the potential risk to offsite values is 

much greater.

What needs to be predicted

Before choosing a modeling tool, the manager first must identify the specific predictions that are necessary. Typical predictions include annual water yields, peak runoff 

rates, and related attributes such as runoff duration and time to peak, upland erosion 

rates, and watershed sediment delivery rates. Predictions may be for average values or 

probabilities of exceeding a given value. It is desirable, but not always possible, to use 

the same model to predict both runoff and erosion. Currently, few tools predict both. The 

WATSED suite of models predicts both, but the erosion and sediment delivery are not 

linked to the runoff. The WEPP model predicts both runoff and erosion, and the more 

recent versions of WEPP (Version 6.2 or later) include lateral groundwater flow in watershed runoff (Covert and others 2005; Dun and others 2006). The SWAT and AGNPS 

models predict both runoff and erosion, but do not link the two on the hillslope. The 

runoff is used to route eroded sediment through the stream system with these models.

Table 1. Scales of analysis and dominant processes.

Scale:	 Small	 Medium	 Large

Area < 100 ha 100–500 ha Over 500 ha

(250 acres) (250 acres–2 sq mi) (Over 2 sq mi)

Dominant Runoff Processes Surface runoff from rainfall Surface and shallow lateral Shallow lateral flow and

excess or saturated overland flow groundwater processes

flow

Dominant Sediment Processes Rill and interrill erosion; Rill, ephemeral gully, and Channel erosion and transport

landslides gully erosion; landslides and processes, large deep-seated

debris flows landslides

Dominant Disturbances Wildfire; prescribed fire or Wildfire, stream crossing Large runoff events

road surface erosion failure, large runoff events

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
248 USDA Forest Service RMRS-GTR-231. 2010.

Attributes of Tools

Scales and frameworks for analysis

Within the context of this chapter, watershed impacts of management can be evaluated on a project or hillslope scale (5 to 40 ha) or a small (under 100 ha), medium (100 

to 500 ha), or large (over 500 ha) watershed scale (table 1).

For hillslope scale, onsite surveys coupled with soils and contour maps generally 

provide adequate information for analysis. Analyses are typically carried out with 

hillslope tools, hillslope by hillslope, and results are compiled in summary tables. Air 

photos may be particularly beneficial for mass wasting and road erosion analysis at this 

scale. For mass wasting, photos before and after significant mass wasting events are 

often compared and the features of failure sites are linked to other site conditions, such 

as slope steepness, upslope area, and disturbance history.

For larger area analysis, geographic information systems (GIS) generally are the 

most effective means to compile, integrate, and synthesize data required to describe the 

watershed and to run sediment, water, and stability modeling tools. Although models 

vary in their data needs, managers often access publicly available datasets in their GIS 

(for example, USGS digital elevations, NRCS soils data, and climate files), generate 

derivative datasets from elevation models (such as gradient and aspect data), and delineate watersheds with integrated drainage channels networks. Watershed delineation 

is especially valuable when first starting a project or for smaller watershed modeling 

projects where the limited scale of the analysis does not warrant use of the more detailed 

and labor-intensive modeling systems. Larger watersheds are frequently divided into 

small watersheds or hillslope polygons known as hydrologic response units (HRUs) to 

aid in describing specific areas within a watershed where a given management activity 

is targeted, such as a thinning operation, or a significant disturbance has occurred, such 

as a wildfire. One of the challenges in modeling larger watersheds is in linking the HRU 

runoff and sediment processes to the larger scale (Beighley and others 2005).

Sources of sediment

There are seven typical sources of sediment associated with fuel management 

(table 2): surface erosion from undisturbed and disturbed forest hillsides, runoff and 

erosion from forest road networks, sediment delivered from mass wasting processes, 

and sediment from channel bed and bank erosion. Hillside disturbances tend to be 

ephemeral, lasting 1 to 3 years before the hillslope is recovered, whereas roads can 

be a chronic source of sediment, generating sediment every year. Landslides generally 

generate sediment only during prolonged wet spells when forest hillslopes become saturated or when there are unusually high runoff-initiated debris flows in upland swales. 

Hillside and road erosion processes are described in Chapter 5 and channel and mass 

wasting processes in Chapter 6.

Hillside sources of sediment associated with fuel management are further complicated by wildfire effects. High severity wildfires tend to generate much more sediment 

than do lower severity prescribed fires or wildfires. The impacts of fuel management 

on fire severity and frequency are discussed in Chapter 3. In order to fully evaluate 

Table 2. Typical sources of sediment in a watershed analysis.

Source	 Frequency of occurrence	 Relative erosion amount

Hillslopes following wildfire 20 to 200 years 100

Landslides 5 to 10 years 5

Hillslopes following prescribed fire 5 to 20 years 10

Hillsides following thinning 10 to 40 years 1

Undisturbed hillslopes Yearly 0.1

Road networks Yearly 2-5

Stream channels 5 to 10 years 5-90

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 249

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States

the watershed impacts of fuel treatment activities, the manager also must consider the 

potential for erosion from wildfire. Treatment erosion rates are generally much lower, 

but will likely occur more frequently than wildfire events. Hence, the manager will need 

to carry out a series of analyses comparing erosion from wildfire at the current forest 

condition to erosion from fuel treatment and erosion from a wildfire following fuel 

treatment (table 2).

Sediment production from both roads and hillslopes is largely dependent on the 

weather. Wet years will generate more runoff and sediment. If there is a wet year following a hillside treatment, there is a risk of a high level of erosion, whereas there will 

likely be little to no erosion following fuel treatment in an average to dry year. Roads 

tend to generate sediment even in dry years, but at a much lower rate.

Routing of sediment through a stream system is also highly weather dependent, with 

little sediment being routed most years, and most sediment being routed during years 

with major runoff or flood events. Thus, the stream channel serves as a temporary sediment bank, storing sediment from a disturbance for several years to decades as sediment 

from upland areas is gradually routed through the system.

Many of the nation’s forests are in areas with steep relief and major differences in 

climate. Higher elevations tend to have higher precipitation, but a greater amount of 

that precipitation tends to be snow. Snow melt rates generally are much lower than 

rainfall rates, and so tend to generate less surface runoff and erosion. Snow hydrology processes also are influenced by the presence of trees, with mature forests holding 

significant amounts of snow in the canopy and thinned openings and fringes of open 

areas adjacent to forests being areas of snow accumulation. Large open areas may experience less snow accumulation during times of high wind speeds as the wind scours 

snow from these openings. Open areas with less wind scour could also be areas of 

high snow accumulation due to less canopy interception. Thus the severity of wildfire, 

ephemeral nature of hillside disturbances, chronic nature of road sediments, impacts 

of elevation on climate, effects of forests and wind on snow hydrology, and infrequent 

routing of stream sediments are major challenges to modeling the watershed impacts of 

fuel management activities. The ability of various tools to model these attributes will be 

evaluated in the remainder of this chapter.

Hydrologic considerations

In addition to consideration of the importance of scale and sources of sediment, there 

are a number of hydrologic considerations to consider when selecting cumulative watershed effects tools. The first is the nature of the climate. The hydrology may be driven 

predominantly by thunderstorms in the southwestern or eastern United States, frontal 

storms along the west coast, snowmelt in the higher elevations of the western mountains, or rain-on-snow events in the Interior Northwest. If climates are dominated by 

snowmelt, hydrologic tools developed for rainfall dominated climates will not function 

well. Among these tools are the Universal Soil Loss Equation and NRCS Curve Number 

technologies.

Hydrologic analyses of large area flood events may include the development of runoff hydrographs. Specialist tools are available for such analyses, but are generally best 

done by other agencies, such as the Corp of Engineers, or consultants who have had 

experience with these tools.

Another hydrologic consideration may be the seasonal or long-term distribution of 

runoff. For example, if there is concern about erosion following a chemical brush control operation in July, the manager may wish to estimate the runoff and erosion risk 

during a single month and will need a model that has such a capability. Long-term 

changes in runoff characteristics may be of interest if a long-term fuel management 

plan is envisioned. Such long-term changes may have impacts on changing channel 

morphology if annual peak flows are increased significantly.
250 USDA Forest Service RMRS-GTR-231. 2010.

Environmental constraints

Some of the currently available predictive models were developed by agricultural 

researchers focusing on agricultural conditions. This is particularly true for the USLEbased models and the NRCS Curve Number technology. Some of these tools have 

been further developed for forest conditions, such as the USLE for southeastern forests 

(Dissmeyer and Foster 1981, 1985). Some tools may not be stable for some common 

forest conditions, such as steep slopes.

If the model is empirically based, managers need to be careful if adopting a model 

that was developed for different climates, vegetations, or geologic conditions. For example, the WATSED technologies were originally developed with data from central Idaho. 

Methods have since been developed to adapt this tool for other areas in the Northern 

Rockies, but not for forests elsewhere. The Washington Forest Practices (1997) has extended some of the WATSED technology for application in Washington State.

Local constraints

In some cases, state or local regulations may dictate the model that is selected. For 

example, at one time, the USLE and RUSLE models were considered inappropriate for 

rangeland conditions (NCBA 2003). Numerous city and county codes require that peak 

runoff rates be predicted by a specific method, generally the Rational method or Curve 

Number method, or for some specific design storm. There may be guidelines developed 

by the Forest Service or other agencies for runoff curves based on past experience or 

observations that can be applied locally, although the manager may wish to adjust the 

values based on site characteristics. In these cases, the manager will need to provide 

credible information to support any adjustments made to such guidelines.

Organizational constraints

As new models or new applications of existing models become available, the manager will likely want to compare the new tools to existing methods or observations to be 

confident that the model is providing reasonable predictions. Some of these new models 

may still be under development, in which case the managers may need to work closely 

with the developers in research organizations or universities to make sure that the model 

is correctly applied and the results properly interpreted. As newer models begin to receive more widespread application and acceptance, such collaboration is less critical.

One of the first considerations may be the skills, training, and experience of the manager. Has he/she developed the skills on a given tool or is some training necessary? Is 

such training available?

Depending on the manager’s level of computer expertise, the model interface may be 

crucial. Models requiring high levels of GIS skills may be acceptable to some specialists, whereas others may have limited GIS modeling experience. Some tools are now 

available online, but the assumptions associated with the simplified interfaces may not 

provide the manager with the flexibility needed for some analyses. Some managers may 

not have a high speed Internet connection, which may limit the use of these models.

Additionally, the computer hardware available to the manager may be inadequate for 

some models, lacking the memory or speed required for the tool. Older computers may 

not have the software necessary to run some models, such as recently developed GIS or 

spreadsheet-based models.

Other considerations

There are a number of other attributes that a manager may wish to consider when 

selecting a tool. Is the model under consideration widely used and accepted by the academic, legal, and environmental community? For example, one of the reasons for a legal 

decision against the Forest Service was that the model used for the watershed analysis 

did not predict any variability associated with the estimated means. Another consideration is the availability of the model.

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 251

Obtaining the model may be a problem. Is it online or does it require installation 

from a CD? If it is on a CD, does the manager have the latest version? A few models 

require registration to proceed with immediate download, and less commonly, some tool 

developers require that the user first register and then wait to be sent a download access 

password. One tool reviewed, SedMODL2, charges a fee to cover the cost of burning and shipping software on a CD. Once downloaded, many applications are installed 

through common installation wizards with special computer configuration requirements. 

Some installations may require the manager to get administrative permission to install 

the software. Some models that fall into the research domain, such as DHSVM, require 

the user to compile code and install special system emulators. These installations may 

require assistance from computer support specialists.

To use a tool, a database must be built. This can be one of the biggest challenges in 

operating a given tool. Are data readily available to run the model from either a Forest 

Service database or a public source? For example, some of the more sophisticated hydrologic tools require detailed information on soil depths and properties and properties 

of bedrock, which may not be readily available. In some cases, a database may need 

to be reformatted or certain fields extracted to obtain the necessary information to run 

the model. If online databases are used, it is the user’s responsibility to ensure that the 

data are correct. For example, one online data set contained information from a faulty 

sensor at a SNOTEL site that was only discovered when the model was not performing 

as expected.

Many models include file builders to aid in preparing the data for the model. The 

input file builder may be as straight forward as choosing from selections on drop-down 

lists, as with the FSWEPP online interface. Many tools, especially those designed as distributed, process-based systems, generally running in a GIS, may require large amounts 

of data from multiple data sources. There is a trend to build interfaces that guide the 

user to electronic libraries of public data to simplify data acquisition. This approach is 

especially valuable where users are building models for watersheds for which locationspecific data are incomplete or not available. Alternatively, wizards that interactively 

guide users through each step of the model building process (for example, DHSVM) 

provide a framework to ensure that all components are in place for a model run.

The outputs from a given tool should provide the information the manager requires. 

Some models developed for non-forested conditions may not give the information that 

the user desires or in a satisfactory format. Output files containing more information 

than a user requires may need additional analyses to reformat or synthesize results.

The documentation is an extremely important part of any tool. In some cases, documentation is readily available online and includes many illustrations and examples. In 

other cases, documentation is inadequate, and managers should lobby model developers 

to provide improved, appropriate documentation if the software meets the manager’s 

needs.

The availability of technical assistance is often important, particularly with more 

complex models. Some technical assistance may be built into the model, with help 

screens incorporated into the interface. In some cases, local or regional experts may be 

available to provide such assistance. In others, specialists in other agencies, such as the 

NRCS, Bureau of Reclamation, Army Corp of Engineers, university specialists, federal 

researchers, or consultants, may be available to provide the necessary assistance.

It is unlikely that any watershed tool will meet all of the manager’s needs. Managers 

will have to select from a series of tools that best meet their needs and organization’s 

abilities. Also, not every CWE analysis requires or merits the complexity possible with 

some of the currently available tools. New tools with new features and capabilities 

continue to be developed, and a career as a watershed manager will be one of continued 

learning and evaluation.

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
252 USDA Forest Service RMRS-GTR-231. 2010.

Categories of Models

Cumulative effects models can be categorized into lumped or distributed, conceptual 

or physically based, or deterministic or stochastic.

Lumped vs. Distributed Models

Some models assume that an entire watershed is behaving as a single unit and assume that all of the inputs can be lumped into a single set of variables to describe the 

entire watershed (fig. 1). The outputs are generated as runoff and/or sediment yield at 

the watershed outlet. The Rational Peak runoff method and the Curve Number runoff 

and peak flow models are common examples of lumped models (Ward and Elliot 1995).

Distributed models allow the user to vary model inputs and site characteristics in 

space. There can also be interactions between cells, modeling the “runon-runoff” processes common on disturbed forest hillslopes. Hot spots for sediment sources can be 

identified to focus management, as can environmentally benign areas where management can be more flexible. The GeoWEPP tool is an example of a distributed model 

using hillslope polygons and the DHSVM model is an example of a distributed model 

using grid cells. Many models use combinations of lumping and distributing. For example, soils may be distributed by grid, hillslope topography by polygon, and climate 

may be lumped for the entire area. One common approach to distributed modeling is to 

use hydrologic response units (HRUs) as the smallest unit of discretization. An HRU 

may be a small watershed or a hillslope polygon, depending on the focus of the analysis 

(Beighley and others 2005).

Some form of distributed modeling is essential for estimating sediment detachment 

and delivery. The data needs, however, may be great, and there may not be adequate 

information available to describe variations in soil properties including soil depth and 

surface residue cover. Distributed models are also difficult to calibrate as there are many 

cells that can be adjusted in order to obtain a reasonable prediction. The benefit of 

distributed modeling is that more management options can be evaluated. For example, 

a manager can compare the watershed impacts of thinning only the upper part of hillslopes instead of the entire hillslope or the watershed effects of altering the width of an 

undisturbed forested buffer along stream channels. Management affects on north-facing 

slopes can be compared to those on south-facing slopes. In larger watersheds, it may be 

possible to synchronize or desynchronize hydrographs to obtain desired runoff characteristics. Lumped models would not be as versatile at modeling such spatial variability.

Figure 1. Lumped vs. distributed model. The “lumped” watershed on the left has a single value to describe soil, 

vegetation, and climate conditions in the entire watershed, whereas the “distributed” watershed on the right 

may have different values for each grid cell, or in some cases, individual hillslope polygons.

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 253

A current effort in distributed modeling is to incorporate road networks and their impacts into watershed analysis. This technology has the potential to include the impacts 

of roads as sources of sediment and runoff and also to evaluate the effects of roads on 

fish passage (RMRS 2007).

Conceptual vs. Physically Based Models

Conceptual models are based on the physical processes that drive the watershed responses. Physically based models contain mathematical equations and relationships that 

describe watershed processes. Few models can be labeled as purely conceptual or purely physical, but rather range along a spectrum of complexity from purely conceptual to 

purely physical. The more conceptual or empirical models require less data, but are less 

flexible in the application. The more physically based models can often be applied to a 

greater variety of circumstances, but in order to do this, they will be more computationally intensive and require larger input data sets.

There is often a heavy reliance on empirical data in conceptual models. They tend to 

be lumped or only partially distributed. Because of their reliance on observed data, they 

should not be extrapolated to conditions beyond those that were used in their development. Examples of conceptual models are the Universal Soil Loss Equation (USLE) and 

the Curve Number technology.

Physically based processes may include:

• vegetation growth and senescence; 

• impacts of plant community on evapotranspiration, rainfall and/or snow interception, 

and soil stability; 

• soil water balance and subsurface water movement; 

• sediment detachment, transport, and deposition by raindrop splash, shallow overland 

flow; concentrated rill flow, gullying, and channel processes; and

• mass failure and debris flow processes.

Input parameters for physically based models are generally variables that can be 

measured or derived from measurements of physical or biological processes, such as 

topography, runoff rates, biomass amounts, and surface cover. Physically based models 

are generally more academically acceptable, and can be generally applied to areas other 

than where the original data used for model development were collected. Data needs, 

however, may exceed what is readily available in areas beyond the sites where the models were originally developed. Examples of physically based models include the Water 

Erosion Prediction Project (WEPP) and the DHSVM model.

Deterministic vs. Stochastic Models

A deterministic model will always give the same outputs for the same set of input 

variables. A stochastic model generally has at least one probabilistic input and will give 

a result that describes the risk or likelihood of a given prediction. Examples of stochastic models include the climate generator for the WEPP model or the return period 

analyses associated with peak runoff events from the Curve Number technology.

Lump-Based Runoff Tools

There are two runoff prediction technologies that are generally lump-based: the 

Rational Peak Flow prediction, and the NRCS Curve Number runoff volume and peak 

flow prediction (Ward and Elliot 1995). These technologies are frequently incorporated 

into other higher level hydrologic models and a description of each will be given.

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
254 USDA Forest Service RMRS-GTR-231. 2010.

Rational Peak Flow

The Rational Peak Flow prediction method is (Schwab and others 1993):

q = 0.0028 C i A (1)

where q = design peak runoff rate (m3/s)

C = runoff coefficient

i = rainfall intensity for the design return period and for a duration 

equal to the “time of concentration” of the watershed (mm/h)

A = area of watershed (ha)

The runoff coefficient C is a function of vegetation and rainfall intensity (Schwab 

and others 1993) and for forests, ranges from 6 to 20 (table 3). Users should check with 

local NRCS or state agency users to determine local values. Some typical values are 

presented in table 3. The time of concentration for a given watershed is often estimated 

by the Kirpich equation (Schwab and others 1993):

0 385 .

0 77 .

Tc = L

3077s

(2)

where Tc = time of concentration (h)

L = distance from watershed divide to watershed outlet (m)

s = watershed gradient (m/m)

When applying the Rational method, the time of concentration is frequently a relatively 

small number, typically less than 1 hour. To estimate the peak intensity for the desired 

duration storm, the NOAA Precipitation-Frequency Atlas is often consulted (Bonnin 

and others 2003). There are Internet sites available that aid the user in determining 

the intensities of these shorter duration storms for many states (http://hdsc.nws.noaa.

gov/hdsc/pfds/ ). The Rational method is best suited to watersheds under about 2 mi2. 

For larger watersheds, other runoff methods are recommended. One of the reasons the 

runoff coefficient is so small for forest watersheds is that much of the runoff is shallow 

subsurface lateral flow or groundwater, rather than surface runoff, so peak rates are less 

than would occur on agricultural sites of similar area.

Table 3. Typical values for Runoff Coefficient C in Rational Equation and descriptions of 

hydrologic soil groups (Engel and others 2009).

Hydrologic Soil Group

Land Use, crop and management	 A	 B	 C	 D

Cultivated with crop rotations 

Row crops, poor management 55 65 70 75

Row crops, conservation mgmt 50 55 65 70

Small grains, poor mgmt 35 40 45 50

Small grains, conservation mgmt 20 22 25 30

Meadow 30 35 40 45

Pasture, permanent with moderate grazing 10 20 25 30

Woods, permanent, mature, no grazing 06 13 16 20

Urban residential

30 percent of area impervious 30 40 45 50

70 percent of area impervious 50 60 70 80

Hydrologic Soil Group Descriptions:

A -- Well-drained sand and gravel; high permeability.

B -- Moderate to well-drained; moderately fine to moderately coarse texture; moderate

 permeability. 

C -- Poor to moderately well drained; moderately fine to fine texture; slow permeability. 

D -- Poorly drained, clay soils with high swelling potential, permanent high water table,

 claypan, or shallow soils over nearly impervious layer(s).

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 255

Curve Number Runoff Volume and Peak Flow

The Curve Number runoff technology can be used to predict both runoff volume and 

peak runoff rate (Fangmeier and others 2006). The Curve Number technology was initially developed from a network of small watersheds covering the entire United States. 

Most of these watersheds were in agricultural areas, so data for rangelands and forests 

was limited. The USDA Natural Resource Conservation Service (NRCS) played a leading role in the development of the research technology.

Estimating total storm runoff with curve number

The first step in both total runoff and peak flow is to estimate the total runoff depth Q. 

The Curve Number method uses two foundation equations to estimate Q:

.

. Q I SI S

0 8

0 2

2

= +

^ - h (3)

and

S U CN

1000 = - <a k 10F (4)

where Q = runoff depth (mm or inch)

I = storm depth (mm or inch)

S = maximum potential difference between rainfall and runoff, 

sometimes referred to as surface storage (mm or inch)

U = unit conversion (25.4 mm for metric, 1 inch for English units)

CN = NRCS Curve Number for soil and cover condition (see table 4)

In watersheds with mixed cover, an area weighted average is generally employed to 

estimate the curve number (Fangmeier and others 2006).

Table 4. Some typical Curve Number values for forested conditions (Goodrich and others 2005).

Hydrologic Soil Group

(see table 3 for descriptions)

Ground

Cover type	 cover (%)	 A	 B	 C	 D

Bare 0 77 86 91 94

Fallow 5 76 85 90 93

Shrubland 25 63 77 85 88

Grassland/Herbacious 25 49 69 79 84

Undisturbed Forests

Deciduous & Mixed 50 55 55 75 80

Evergreen 50 45 66 77 83

Forest, Low severity fire

Deciduous & Mixed 43 59 60 78 82

Evergreen 43 49 71 80 85

Shrubland 21 65 79 86 89

Moderate severity fire

Deciduous & Mixed 34 65 65 80 85

Evergreen 34 55 76 82 88

Shrubland 17 68 82 88 90

High severity fire

Deciduous & Mixed 25 70 71 83 87

Evergreen 25 60 82 85 90

Shrubland 12 73 88 91 91

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
256 USDA Forest Service RMRS-GTR-231. 2010.

Estimating peak runoff rates with curve number

From the runoff amount Q, peak runoff can be estimated using the methodology 

developed by the NRCS (2002). This manual method has since been incorporated into 

numerous public and private software programs, several of which are discussed later in 

this chapter. One method that can be readily adapted to local conditions for applying 

the Curve Number technology (Schwab and others 1996) is to first estimate the time of 

concentration with the empirical relationship:

0 8.

T

L CN

1000 9

.

.

c 0 5

0 7

= -

C s

a k (5)

where Tc = time of concentration (hours)

L = length of watershed (m or ft)

CN = NRCS Curve Number

C = constant 441 for metric, 1,140 for English units)

s = average watershed gradient (m/m or ft/ft)

Other methods commonly used to estimate time of concentration generally require 

the user to estimate the runoff velocity overland and in channels, and the lengths and 

slopes of the overland area and the channel. Numerous public and proprietary software 

programs assist in this calculation. Once the time of concentration is estimated, the 

NRCS has developed a series of curves to estimate peak runoff rate as a function of 

total storm runoff. There are numerous software programs that have incorporated these 

curves into the software itself. One relationship between time of concentration, peak 

runoff rate, and total runoff is (Schwab and others 1996):

log(q) = 2.51 – 0.7 log(Tc) – 0.15 (log(Tc))2 + 0.071 (log(Tc))3 (6)

where q is peak runoff rate in cubic feet per second per square mile of watershed area 

per inch of storm runoff. For metric units, multiply this number by 0.0043 to get cubic 

meters per second per square km of watershed area per mm of storm runoff.

Limitations of the Curve Number method

Recent observations of runoff volumes and rates from forests before and after 

wildfire have shown that the runoff volume appears to change little; the time of concentration is generally in the magnitude of days for undisturbed forests and minutes to 

hours for forests following wildfire (Canfield and others 2005). One analysis suggested 

that the Curve Number method was not appropriate for forest or rangeland watersheds, 

and a better estimate of runoff is as a fraction of precipitation based on field observations (Springer and Hawkins 2005). For thinned or prescribed fire conditions, the time 

of concentration is likely to be longer than would normally be estimated for overland 

flow for non-forest conditions as most of the runoff is from subsurface lateral flow. In 

the past, watershed managers often reduced the Curve Number to reduce peak flow rate 

estimates from forests compared to non-forested areas rather than increase the time of 

concentration values. This area warrants further research.

USLE-Based Tools

In the period from 1945 until 1965, a method of estimating soil erosion based on statistical analyses of field plot data from small plots located in many states was developed, 

which resulted in the Universal Soil Loss Equation (USLE) (Wischmeier and Smith 

1978). The USLE was parameterized for some forest hillslope conditions for intensive 

forest management practices in the southeastern United States (Dissmeyer and Foster 

1981). A revised version of the USLE (RUSLE) was later developed as a computer 

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 257

application (Renard and others 1997). When predicting erosion, RUSLE allows a more 

detailed consideration of management practices, rangeland, seasonal variation in soil 

properties, and topography than does the USLE. In 2005, RUSLE2 was released as an 

application for the Windows operating system (Foster and Toy 2003). The basic form of 

the USLE/RUSLE models is:

A = R K L S C P (7)

where A = average annual soil loss (tonnes/ha/year or tons/acre/y)

R = rainfall and runoff erosivity factor for a geographic location

K = soil erodibility factor

L = slope length factor

S = slope steepness factor

C = cover management factor

P = conservation practice factor

The A, R, and K factors are different for English and metric units. To avoid confusion, this chapter will use all English units. Metric units for these three variables can 

be found in Fangmeier and others (2006). The other factors have no units. The L and S 

factors are used in some other models, including the WATSED cumulative effects model 

(USFS 1990).

USLE Factors

R factor

The R factor is based on the rainfall intensity and energy for a given location (Renard 

and others 1997). Figure 2 is the “isoerodent” map for the western United States in 

English units, providing an estimate of the R factor. The west coast and eastern United 

States maps, as well as other methods for estimating R, can be found in Renard and 

others (1997). The R factor is best suited for climates where runoff and erosion are dominated by large storms, not snow melt, whereas much of the area in figure 2 is dominated 

by snow process, making these areas problematic for USLE applications.

K factor

The K factor is generally estimated from soil properties. The equation developed for 

agricultural soils is:

. . . KOM M s p

100

2 1 10 12 # 4 1 14 . 3 25 2 2 5 3 = 7 - ^ - + - + - h ^ h ^ hA (8)

where

K = soil erodibility (English units)

OM = organic matter (percent)

M = particle size fraction in soil between 0.001 and 0.1 mm, or percent silt 

plus percent fine sand (percent)

s = subsoil structure class: 1 – very fine granular

2 – fine granular

3 – med or coarse granular

4 – blocky, platy or massive

p = permeability class: 1 – rapid

2 – moderate to rapid

3 – moderate

4 – slow to moderate

5 – slow

5 – very slow

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
258 USDA Forest Service RMRS-GTR-231. 2010.

Figure 2. Isoerodent map 

of R factor values for the 

western United States. 

(Renard and others 

1997)

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 259

In forest environments, soil erodibility has been found to be a function of not only 

soil properties, as assumed in the USLE technologies, but the vegetation condition. 

Vegetation condition in the USLE technologies is addressed in the C factor. Because of 

this interaction, users should be cautious when applying the USLE to forest conditions 

to ensure that compatible C and K factors are used. It is not advisable to obtain a K factor 

estimate from one source and a C factor estimate from another.

L and S factors

The topographic factors, L and S, adjust the predicted erosion rates to give greater 

erosion rates on longer and/or steeper slopes when compared to the USLE “standard” 

slope steepness of 9 percent and length of 72.6 ft (22 m). In many mountainous conditions, the lengths and steepness values are greater than intended for the L and S factors. 

These factors address the increasing rill erosion rates as more runoff accumulates with 

longer slopes and the hydraulic shear in runoff increases on steeper slopes. The methods 

for estimating L and S factors were modified in RUSLE, and it is advisable to use the 

RUSLE/RUSLE2 method for estimating these topographic factors rather than the USLE 

method.

The RUSLE L factor can be calculated as:

. L l72 6

b

= a k (9)

where L = slope length factor

l = slope length in ft

b = dimensionless exponent

For conditions where rill and interrill erosion are about equal on a 9 percent, 72.6-ft 

long slope

sin sin . .

sin b

0 269 0 05

.0 8

i i

i =

+ ^ h +

(10)

where θ = field slope angle = tan-1(S)

S = slope steepness (ft/ft)

For most conditions where rill erosion is greater than interrill erosion (such as soils 

with a large silt or fine sand content), b should be increased up to 75 percent. Where rill 

erosion is less than interrill erosion (on short slopes), b should be decreased as much as 

50 percent. RUSLE2 makes this calculation internally.

The S factor depends on the length and steepness category of the slope. For slopes 

less than 15 ft long:

S = 3.0 (sin θ)0.8 + 0.56 (11a)

For slopes greater than 15 ft long and steepness less than 9 percent

S = 10.8 sin θ + 0.03 (11b)

For slopes greater than 15 ft long and steepness greater than or equal to 9 percent:

S = 16.8 sin θ - 0.50 (11c)

For the USLE, the slope length is measured from the point where soil erosion begins 

(usually near the top of the ridge) to the outlet channel or a point downslope where deposition begins. RUSLE also considers non-uniform concave or convex slopes. RUSLE2 

considers the entire hillslope, including areas of deposition.

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
260 USDA Forest Service RMRS-GTR-231. 2010.

C factor

The C factor is the cover management factor, sometimes referred to as the cropping 

factor. This factor was originally developed to allow users to specify the cover condition for every 2-week period in a rotation. A rotation may last for several years, and an 

extended calculation is necessary (Ward and Elliot 1995). The RUSLE technologies 

frequently add subfactors to the estimate of C, further complicating this critical calculation. This methodology was developed in order to consider the surface condition 

during any 2-week period in relation to the climate during that same period. In forest 

and rangeland conditions; however, it is much more appropriate to think of the term as 

cover management and consider C as constant for the entire year. Runoff and soil erosion are dominated by ground cover, and when using USLE technology, it is important 

to ensure that the correct term is selected. Wischmeier and Smith (1978) developed 

a set of C factors for forest and rangeland conditions that were a function of canopy 

height and cover and ground cover. For forest management activities in the southeastern 

United States, Dissmeyer and Foster (1981) expanded the Wischmeier set to include site 

preparation tillage practices common in the Southeast. Because tillage is not generally 

associated with fuel management, but ground cover disturbance is, the Wischmeier and 

Smith (1978) C factors are presented in table 5 for forested conditions and table 6 for 

burning. The RUSLE1 technology can calculate a C factor internally from a fixed cover 

condition, and a similar “permanent vegetation” option is available in RUSLE2.

Table 5. USLE C factors for forest conditions (Wischmeier and Smith 1978).

Percent of area covered by canopy Percent of area covered by duff

of trees and undergrowth at least 50 mm (2 in.) C Factor

100 – 75 100 – 90 0.0001 – 0.001

70 – 45 85 – 70 0.002 – 0.004

40 – 20 70 – 40 0.003 – 0.009

Table 6. USLE C factors for burning (Wischmeier and Smith 1978).

Soil condition

Ground cover

(percent) Excellent to good Fair to poor

10 0.23 – 0.24 0.26 – 0.36

20 0.19 0.21 – 0.27

40 0.14 0.15 – 0.17

60 0.08 – 0.09 0.10 – 0.11

80 0.04 – 0.05 0.05 – 0.06

Chapter 13. Tools for Analysis

Recent Variations on the USLE

In the RUSLE2 technology, sediment delivery across buffers is predicted as a function of runoff estimated by the Curve Number method. The C factor in RUSLE is based 

on a weighted average of vegetation cover throughout a growing cycle and takes into 

account prior land use, canopy cover, surface cover, surface roughness, and soil water 

content.

Some variations of the USLE have been developed to make erosion estimates for 

individual storms. This may be done by considering the R factor for an individual storm 

or with the Modified USLE (MUSLE) technology described below.

The factors in RUSLE have generally been developed from, and validated by, 

research studies on tilled agricultural soils. Some rangeland research with RUSLE developed C factors based on surface cover, which give reasonable erosion predictions for 
USDA Forest Service RMRS-GTR-231. 2010. 261

rangeland hillslopes (Elliot 2001). Applications of RUSLE to disturbed forest hillsides 

and roads have been limited.

MUSLE

The modified USLE (MUSLE) replaces the R factor with the product of rainfall 

amount and runoff amount to predict soil erosion for a single storm. Most applications of the MUSLE technology use Curve Number to estimate the runoff. The other 

USLE factors (K, L, S, C, and P) remain unchanged for MUSLE applications. Because 

MUSLE is relatively easy to program, it has been incorporated into numerous soil erosion models in recent years. Its limitations are similar to those of the two technologies 

that drive it.

AGNPS, AnnAGNPS: Agricultural Non-Point Source

The AGNPS erosion model is a distributed parameter tool for moderate- to smallsized agricultural watersheds (Bingner and others 2007; Suttles and others 2003). 

AGNPS and its newer iteration, AnnAGNPS, are well established, actively supported, 

production-ready tools. AGNPS models a single event, simulating a pulse of sediment 

from an individual storm. AnnAGNPS extends the modeling into continuous, annual 

outputs. The system is driven by three core technologies: erosion modeled by RUSLE, 

hydrology by the NRCS Curve Number method, and sediment/contaminant transport 

using CREAMS (Chemicals, Runoff, and Erosion from Agricultural Management 

Systems). Additional AGNPS modules include a channel network evolution model 

(CCHEID) and stream corridor model (CONCEPTS), components that emphasize the 

condition of water within stream channels. Snowmelt is not modeled. Both versions run 

within GIS shells and are challenging to apply. AGNPS is fundamentally an agricultural 

tool with limited utility in forested mountainous environments.

SWAT: Soil and Water Assessment Tool

The SWAT modeling tool predicts the impact of land management practices upon 

water, sediment, and chemical yields in large, complex watersheds (Arnold and others 1998; Di Luzio and others 2002, 2004). SWAT is a distributed model with linked 

modules using both process and empirical logic. Key climate and vegetation simulations are process driven while the core hydrology and sediment modeling includes use 

of an enhanced NRCS Curve Number approach to estimate runoff volume and USLE 

and MUSLE technologies to estimate soil erosion. SWAT has a long development history, strong institutional commitment, and a substantial publishing record based upon 

worldwide application. Comprehensive documentation and ease of access, download, 

and installation permit users to efficiently load and execute the SWAT tool. Although 

originally developed for agricultural applications, the developers have demonstrated a 

commitment to improving mountain hydrology, including implementing advances in 

topographically driven snowmelt processes.

SWAT is a user-friendly, if complex, modeling system that could be a valuable tool 

for CWE analysis. The existing system requires addition of more refined forest practice 

definitions. One of the big challenges when applying SWAT to forested watersheds is 

that SWAT currently estimates all runoff with Curve Number technology. Generally, users will calibrate the Curve Number for SWAT for a given watershed from observations 

from a nearby watershed. As most forest runoff is dominated by lateral flow, and many 

by snowmelt hydrology, this will be a major limitation to applying SWAT for steep 

forested watersheds.

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
262 USDA Forest Service RMRS-GTR-231. 2010.

Rule-Based Tools

R1-WATSED and Derivatives—Water and Sediment Yields

The USDA Forest Service, Region 1 WATSED program is a cumulative watershed 

effects tool designed to model watershed response to multiple management activities 

and disturbances over time (USFS 1990). It estimates and tracks changes in annual 

water and sediment yields, mean monthly flows, delivery of total sediment to a defined 

stream reach, and relative annual changes to sediment delivery within the stream network. WATSED models vegetation and hydrologic recovery, past and assumed future 

activities, background erosion from hillslopes, and surface and mass erosion from activities including roads.

WATSED is an empirical model driven by locally derived and calibrated coefficients 

and recovery response curves. The model assigns lumped parameters to each land area 

modeled (landtype units within watersheds) using a linked table structure. Currently 

there is no GIS interface, but prototypes are under development. Changes to vegetation cover are modeled and expressed as Equivalent Clearcut Areas (ECAs). The ECA 

concept was developed in the 1970s as a method for estimating the change in runoff 

amounts and peak flows associated with a forest practice. It assumes, for example, that 

2 acres of partially cut forest will have the same affect on water yield as 1 acre of clearcut forest. As a forest regrows, the ECA is reduced (Ager and Clifton 2005). WATSED 

has a Windows interface to guide the user through all stages of the model application. 

WATSED spawned several derivatives, each customized for conditions within a given 

national forest, including LoloSED, NezSED, and BoiSED for Lolo, Nez Perce, and 

Boise National Forests, respectively.

State variants of WATSED

Several states, Washington and Idaho in particular, have developed state-specific 

lookup tables to apply to the WATSED technology. Examples are Washington Forest 

Practices and Idaho Cumulative Watershed Effects tools. A computer application of the 

Washington Forest Practices, called WARSEM, has been developed for Washington 

State.

SEDMODL2

SEDMODL2 is a GIS-based road erosion and sediment delivery model designed to 

identify road segments with a high potential for delivering sediment to streams (Dubé 

and McCalmon 2004). The model is based on empirical relationships developed by the 

Washington State Forest Practices manual. SEDMODL2 estimates annual background 

sediment and sediment production by individual road segments, locates road/stream intersections, and estimates delivery of road sediment to streams. Developers provide core 

climate data for several Western States and optional base geology data for Washington, 

Oregon, and Idaho. For most of the variables that define each road segment, users may 

choose default values or define attributes with locally available data. SEDMODL2 has 

an interactive Windows interface and well-written documentation.

Delta-Q and FOREST (FORest Erosion Simulation Tools)

Delta-Q and FOREST are complementary Cumulative Watershed Effects tools. 

These tools are intended to provide managers with estimates of relative cumulative 

changes in forested watershed responses due to multiple management activities over 

time (MacDonald and others 2004). Development of these tools is in part driven by the 

intent to move beyond the basic Equivalent Clearcut Area (ECA) approach. The general 

structure uses GIS-based, two-dimensional spatial representations as an organizing shell 

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 263

to calculate cumulative impacts and watershed recovery across multiple treatment areas. 

Delta-Q uses an empirical approach driven by curves developed from 26 paired watershed datasets to model changes to water yields from disturbed forested areas. FOREST 

predicts changes to sediment regimes from hillslopes and roads in three integrated tools 

that calculate sediment production, delivery, and eventually, in-stream routing. Hillslope 

calculations are based on user-provided data defining hillslope erosion response and recovery rates. Hillslope delivery to streams uses database files derived using the WEPP 

model. The database files are included in the FOREST distribution package and instructions are included so that the user can also use WEPP to customize a file for his or her 

own region. Sediment changes from roads are calculated using one of three user-chosen 

methods: one of two empirical equations or via look-up tables provided with the core 

model or provided by the user. The look-up tables may incorporate local knowledge 

or may be developed using an outside program such as WEPP:Road. Road delivery to 

streams is based on an empirical relationship between percent connectivity and mean 

annual precipitation.

Delta-Q and FOREST provide easy to use, straight-forward, and simple approaches 

to assessing relative cumulative change. The user must adjust basic response settings for 

local conditions. The empirical approach of Delta-Q could limit applicability where the 

area of concern is distant from one of the 26 experimental sites and there is insufficient 

basis to determine which experimental site most closely matches the area of concern. 

In FOREST, model calculations for activity areas and roads are not linked. The spatial 

interface provides a convenient and efficient means to assess possible changes.

WARMF (Watershed Analysis Risk Management Framework)

WARMF is a lumped parameter GIS model that uses USLE-based erosion prediction 

and Curve Number technology for surface runoff. WARMF includes groundwater flow 

and estimates nutrient and bacterial loads. Because of its lumped nature, it does not lend 

itself to project scale management. It also has the limitations of the USLE and Curve 

Number technologies for forest conditions. It is one of the few models available that 

addresses nutrients and bacterial loads (http://www.epa.gov/ATHENS/wwqtsc/html/

warmf.html).

Physically Based Tools

Physically based models predict runoff and/or soil erosion from equations that generally describe the processes that are occurring, such as infiltration, runoff and subsurface 

water flow and soil detachment, transport, and deposition.

WEPP

The Water Erosion Prediction Project (WEPP) model is an interagency physically 

based hydrology and soil erosion model (Flanagan and Livingston 1995). It can be 

run for individual hillslopes or for a small watershed (up to about 2 mi2). The WEPP 

technology includes a Windows interface, a GIS interface, several online interfaces, and 

a stand alone executable program with text file input and output files that can be incorporated into other applications. Most applications of WEPP include databases of soils, 

climates, and vegetation descriptors.

CLIGEN

The CLIGEN weather generator and database of statistics from more than 2,600 

weather stations is part of the WEPP technology. Within the WEPP Windows interface is a feature to allow users to alter the statistics for the climate they have selected 

to match a specific site. Additional climate data can be downloaded from an online 

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
264 USDA Forest Service RMRS-GTR-231. 2010.

web site (http://forest.moscowfsl.wsu.edu/fswepp/) that has a 4-km (2.5-mile) grid of 

monthly precipitation values for the continental United States This site also allows a 

user to modify temperature and precipitation data if local records are available.

WEPP Hillslope version

The Hillslope version of WEPP predicts runoff, onsite erosion, and offsite sediment 

delivery for a hillslope. Interfaces have been developed to run this version from either 

Windows or over the Internet.

WEPP Windows. The WEPP Windows hillslope interface predicts erosion from 

single hillslopes or from lists of hillslopes in project mode. Users may alter any of the 

hundreds of input variables required to run WEPP. This is a highly flexible interface, but 

users seldom have all of the inputs necessary to build input files. Templates are included 

in the interface for a wide range of forest conditions, including those needed for cumulative watershed effects of fuel management.

Internet Suite of Tools. Both the Forest Service and the Agricultural Research Service 

have developed Internet interfaces for the WEPP model (table 7). The Forest Service 

suite of interfaces (FS WEPP) is available for forested hillslope applications (Elliot 

2004), and the ARS interfaces have a greater emphasis on agricultural or rangeland 

conditions.

WEPP FuMe is specifically designed to support fuel management activities. It carries out 12 runs from a single set of inputs. These runs include nine hillslope scenarios: 

undisturbed forest; low, moderate, and high impact thinning; low, moderate, and high 

impact prescribed fire; and low and high intensity wildfire. Additionally, there are three 

road runs for low, moderate, and high levels of traffic. The output page provides tables 

and a narrative of the results of those runs in the context of fuel management activities 

to assist the user in synthesizing the results.

WEPP Watershed Models

WEPP Windows contains a watershed option. WEPP Watershed combines hillslopes, 

channels, and instream structures such as check dams, which it calls “impoundments.” 

The current version predicts peak flow using a variation of the rational equation, which 

limits the size of a watershed to less than 2 mi2 if users desire to consider predictions of 

peak runoff rates.

At the WEPP hillslope scale, only surface runoff is considered, whereas both surface 

runoff and subsurface lateral flow are considered when modeling watersheds. More than 

90 percent of the runoff from many steep forested watersheds is from shallow lateral 

flow or groundwater flow (Conroy and others 2006; Covert and others 2005; Dun and 

others 2006; Zhang 2006).

Table 7. Online WEPP interfaces.

Name Location Features

WEPP:Road http://forest.moscowfsl.wsu.edu/fswepp/ Road erosion and sediment delivery 

from individual segments

WEPP:Road Batch http://forest.moscowfsl.wsu.edu/fswepp/ Multiple road segments for a given 

soil and climate

Disturbed WEPP http://forest.moscowfsl.wsu.edu/fswepp/ Disturbed forest and rangeland 

hillslopes

WEPP FuME http://forest.moscowfsl.wsu.edu/fswepp/ Multiple WEPP runs to support fuel 

management planning

ERMiT http://forest.moscowfsl.wsu.edu/fswepp/ Post wildfire sediment delivery and 

mitigation analysis

WEPP Web Interface http://milford.nserl.purdue.edu/ Agriculture and rangeland erosion, 

detailed graphics

WEPP CAT http://typhoon.tucson.ars.ag.gov/weppcat/index.php Ag, and range Climate Assessment 

Tool including buffers

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 265

WEPP Watershed Windows Interface. The WEPP Watershed Windows interface is 

difficult to use but it allows the user to alter all of the variables necessary to run a 

watershed analysis, including properties of channels and impoundments. Building a 

watershed within WEPP Windows is an arduous task for large landscapes. It is best 

suited to modeling engineered sites, such as ski slopes, parking lots, or agricultural terraces, where dimensions and grades of hillslope planes and channels are generally well 

defined. For natural watersheds, users should use the GeoWEPP technology to build 

watersheds.

GeoWEPP. GeoWEPP is a GIS wizard that builds files to run WEPP Watershed on 

either ArcView or Arc 9.x platforms. Topographic analysis tools build the slope files for 

both hillslope polygons and channels from a Digital Elevation Model (DEM). The same 

soil, climate, and management databases that are used by WEPP Windows are used by 

GeoWEPP. Generally, input files are created, edited, and tested in WEPP Windows so 

they can be accessed by GeoWEPP. GeoWEPP can also read text files that describe the 

soil or vegetation in each grid cell, which may enhance its application for interpreting 

GIS maps of fuel management activities within a watershed.

DHSVM: Distributed Hydrology, Soil, and Vegetation Model

DHSVM is a distributed, physically based hydrologic tool that prepares the data with 

the aid of a GIS and then runs the model using command line codes in a Unix interface. 

Recently, it has incorporated sediment detachment and transport as a function of surface 

runoff. It was developed at the University of Washington in conjunction with the USDA 

Forest Service, Pacific Northwest Research Station. DHSVM was specifically designed 

to address complex hydrologic interactions and variability due to climate and topography. It was originally developed to assess changes in flow resulting from logging at 

relatively large scales. DHSVM (Version 3) models hydrologic processes within vegetation; surface and subsurface flow; management activities; road networks incorporated 

into hillslope and stream channel connections; saturation induced mass wasting and 

redistribution; hillslope erosion driven by saturation excess runoff and rainfall and leaf 

drip detachment; road surface erosion including integration with road side ditches and 

culverts; sediment delivery to stream networks; routing through channels; water discharge accounting for contributions from overland and subsurface flows; and sediment 

deposition, storage, and transport within stream channels based upon channel geometry, 

water flux, and particle sizes of delivered debris.

DHSVM is primarily a research tool relying on an understanding of GIS and UNIX 

command line code. A data assembly wizard assists with preparing input information. 

With further development, DHSVM could provide support for a comprehensive CWE 

analysis. Access further information on-line at: http://www.hydro.washington.edu/

Lettenmaier/Models/DHSVM/.

SMR: Soil Moisture Routing Model

SMR is a physically based distributed hydrologic model that uses simple “map calculation” commands within grid-based GIS software packages (in other words Arc/INFO, 

GRASS) to represent the hydrology of a landscape. The model, originally developed at 

Cornell University (Brooks and others 2007; Frankenberger and others 1999; Johnson 

and others 2003), was designed as a simple management tool to simulate spatially distributed soil water, surface runoff, subsurface lateral flow, and streamflow using publicly 

available data and requiring minimal calibration. Since the program uses commands 

inherent in nearly all available GIS software packages, the source code is a very simple 

batch file or script file (only a few pages long) that is easy to read and modify. Although 

the model does not include many of the complex algorithms in the DHSVM model, 

such as variability in aerodynamic and canopy resistance within multiple layers of the 

canopy and corrections for atmospheric stability to calculate evapotranspiration, the 

fundamental hydrologic mechanisms used to route subsurface lateral flow and generate 

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
266 USDA Forest Service RMRS-GTR-231. 2010.

saturation-excess runoff are very similar to those in the DHSVM model. Despite these 

simplifications, the model has been shown to provide good agreement with distributed 

soil moisture, perched water tables, and snow water equivalent measurements as well as 

stream flow and spatial surface runoff patterns. The model has been used in agricultural 

dominated watersheds to identify critical management zones associated with nutrient 

and pathogen transport. In forestry, SMR applications have helped to identify landslide 

susceptibility (Gorsevski and others 2006b) and quantify the effects of climate change 

on regional water supply and streamflow (Mehta and others 2004). Further information 

is available at: http://soilandwater.bee.cornell.edu/Research/smdr/index.html.

Summary of Watershed Tools

Table 8 provides a summary of currently available tools that have been applied to 

watershed analysis. All of these tools can be run within a GIS framework, some more 

easily than others. Most tools are based on the empirical USLE/Curve Number technologies, with the exception of WEPP and DHSVM. The main differences among the 

empirical models are the spatial detail allowed in the hillslope description and how the 

sediment is routed through the stream system. There are also differences in the availability of databases for forest cumulative watershed effects and other support that is 

available for the model. Currently, WEPP has the best database for modeling cumulative 

watershed effects. The empirical technologies have somewhat easier interfaces to use 

but do not correctly model the dominant forest hydrologic and erosion processes.

Table 8. Summary of currently available watershed modeling tools.

Tool name	 Predicts	 Empirical / process	 Status

AGNPS Runoff and erosion Emp Production

Delta-Q / FOREST Runoff and erosion Emp Production/Beta

DHSVM and SMR Runoff Process Research

Rational Runoff Emp Production

NRCS Curve Number Runoff Emp Production

SedMODL2 Runoff and erosion Emp Production 

from roads

SWAT Runoff and erosion Emp Production

WARMF Runoff and erosion Emp Production

WATSED Runoff and erosion Emp Production

WEPP Runoff and erosion Process Production

Other Modeling Tools Available

These tools are considered separately because, to date, they are commercial experimental research tools and, while they are developed and popular among the water and 

sediment modeling community, their intended uses may vary significantly from CWE 

applications. With many of these models, additional training or consultant support is 

needed before applying the model.

NetMap

NetMap is an integrated suite of numerical models and analysis tools created for three 

purposes: (1) to develop regional scale terrain databases in support of watershed science and resource management, (2) to automate numerous kinds of watershed analyses 

keying on environmental variability for diversifying resource management options, and 

(3) to improve tools and skills for interpreting watershed-level controls on aquatic 

systems, including natural disturbance. Hillslope attributes, such as erosion potential, 

sediment supply, road density, forest age, and fire risk, are aggregated down to the channel 

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 267

habitat scale (20 to 200 m), allowing unique overlap analyses, and they are accumulated 

downstream in networks revealing patterns across multiple scales. Watershed attributes 

are aggregated up to subbasin scales (approximately 10,000 ha), allowing comparative 

analyses across large watersheds and landscapes. Approximately 25 automated tools 

address erosion risk, habitat indices, channel classification, habitat core areas, habitat 

diversity, and sediment and wood supply, among others. Search functions target overlaps 

between specific hillslope and channel conditions and between roads and landslide or 

debris flow potential. To facilitate its use, NetMap contains hyperlinked users’ manuals 

and reference materials, including a library of 50 watershed parameters. NetMap provides decision support for forestry, restoration, monitoring, conservation, and regulation 

(Benda and others 2007). NetMap approaches watershed analysis by stream segment 

reach rather than from DEM grids as in AGNPS and DHSVM or from hillslope polygons as in SWAT and WEPP. Its original intent was to aid in evaluating impacts of land 

management on aquatic ecosystems, but it also shows considerable potential to aid in 

cumulative watershed effects for other watershed services. The 2007 version does not 

predict absolute amounts of hillslope erosion, but rather estimates the erosion risk from 

hillslopes associated with each channel segment. NetMap is not a public domain package, so to apply it, the managers need to obtain the program and the necessary watershed 

information from the developers (http://www.earthsystems.net/).

Hydrologic Engineering Centers (HEC) Tools

The HEC tools were developed by the Army Corps of Engineers. HEC-HMS, 

Hydrologic Modeling System, simulates rainfall-runoff responses and flow accumulation and routing through watersheds. HEC-RAS, River Analysis System, models open 

channel flow through watershed scale stream and river networks. Future versions of HECRAS are expected to model sediment and contaminant transport. HEC-ResSim models 

flow regimes in regulated river systems. In general, the HEC-series tools are thoroughly 

documented with well-written user manuals. For completed HEC modules, ArcView 3.x 

interfaces provide step-by-step assistance with model build, execution, data analysis, 

and graphic display. Through a partnership with The Nature Conservancy, HEC-EFM, 

Ecological Functions Model, proposes to model changes in flow characteristics during 

the year so that users can evaluate the ecological responses to alternative flow regimes. 

For more information on HEC tools access go to http://www.hec.usace.army.mil.

GRAIP: Geomorphic Road Analysis and Inventory Package

GRAIP is a data collection and analysis process and a set of tools for evaluating 

the impacts of roads on forested watersheds (RMRS 2007). GRAIP combines a road 

inventory methodology with a GIS analysis tool set to predict sediment production and 

delivery, risk of mass wasting from gullies and landslides, and ease of fish passage where 

roads cross streams. For further information on the status of this tool go to: http://www.

fs.fed.us/GRAIP/index.shtml.

ArcHydro: GIS for Water Resources

ArcHydro was designed as an organizing framework with which to generate integrated watershed systems linked to relational databases that then port data to and from 

watershed modeling tools (ESRI 2002; Maidment and Djokic 2000). It functions as a 

toolbar plugin in ESRI Arc 8 to 9.x. Required terrain data are extracted from a DEM. 

Channel segments of a network system are linked to drainage areas through node architecture. Nodes associate all watershed metrics into a personal geodatabase structure. 

XML programming language then links the geodatabase to external modeling systems. 

ArcHydro was developed by the Center for Research in Water Resources (CRWR) of the 

University of Texas at Austin and ESRI. Software and documentation are available at 

http://www.crwr.utexas.edu/giswr/.

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
268 USDA Forest Service RMRS-GTR-231. 2010.

Methods of Slope Stability Analysis

Introduction

Landslides may be considered at a variety of spatial scales during analyses of the 

watershed effects of fuel management. At one extreme, the general hazard of slope 

failure is studied over a large, relatively homogeneous portion of a landscape. In this 

case, the analysis applies to the entire polygon and predicts only general susceptibility 

to landslides rather than the likelihood of a particular mass failure. At the other extreme, 

the stability of a particular portion of a single hillslope may be investigated and analyzed intensely. The techniques of stability analysis change considerably over this range 

of scales. Traditionally, stability analyses concern evaluating the likelihood that a slide 

or slides will happen. However, regardless of the spatial scale of investigation, there 

are several other important considerations beyond simple landslide occurrence that can 

affect the choice of stability analysis method. Is it necessary to also assess the size, specific location, timing, frequency, velocity, or travel distance of slides? Do predictions 

need to be made in absolute or relative terms?

The following is a brief review of a complex subject, and all those unfamiliar with 

this subject are strongly encouraged to seek technical assistance from experts within and 

outside the agency before attempting to analyze the mass stability of hillslopes.

Analysis of Individual Landslides or Single Hillslopes

This subject is a well-established core component of the field of geotechnical engineering. In general terms, an analysis is made by calculating both the available static 

forces resisting sliding and the static forces causing sliding. The ratio of resisting to 

sliding forces describes the “Factor of Safety” (FOS) against sliding, and theoretically, 

a slope will not fail if the FOS is greater than 1, in other words, the shear strength available is greater than the strength required to just barely maintain stability. This method is 

sometimes called a limit equilibrium slope stability analysis as it concerns conditions in 

the slope when the balance of forces is just at the limit of equilibrium.

The most simple limit equilibrium formulation, and one that works well on many 

mountainous hillslopes, is the “infinite slope” analysis (fig. 3). Here, the assumption 

is made that the failure along which sliding occurs, the failure surface, is planar and 

generally parallel to the ground surface. This failure surface is often understood to be 

at the soil/bedrock contact, as rock mechanical shear strength is normally much greater 

than that of soil. It is further assumed that the slope is infinitely long, hence the “infinite 

slope” nomenclature, and homogeneous. This means that any single small element of 

Figure 3. Forces involved in a limit 

equilibrium infinite slope stability 

analysis.

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 269

the slope can be analyzed and the stability of that element will be the same as that of the 

whole slope. It also means that the force acting on the upslope face of the element will 

be exactly balanced by the force acting on the downslope face. A further very important 

assumption is that forces acting parallel to the topographic contours (cross-slope forces) 

can be ignored. So, the analysis is purely two-dimensional and involves only the balance of forces along the failure surface on the bottom of the analyzed slope element that 

is normally oriented directly down the line of steepest descent on the slope (fig. 3). If a 

further simplifying assumption is made that the groundwater is unconfined and flowing 

parallel to the slope, the FOS can be calculated as:

sin cos

cos cos tan

FOS

z

c c z s r 2 w z m 2

c b b

c b c b z = + + - ^ h (12)

where cs = soil cohesion

cr = root cohesion

γ = soil unit weight = ρg

where ρ = soil bulk density and g = gravitational acceleration

γw = water unit weight

mz = vertical distance from the failure surface to the groundwater surface

z = vertical soil depth

β = slope angle

ø = angle of shearing resistance of soil (soil “friction angle”)

Of these variables, the FOS is most sensitive to cs, cr, mz, z, and β, and effort should 

be concentrated on their values while reasonable assumptions can often be made about 

the others without introducing undue uncertainty. Equation 12 is the basis for almost all 

mechanistic techniques of slope stability analysis that are currently used at any scale of 

investigation of mountainous hillslopes.

Fuel management potentially affects two parameters in Equation 12: cr and mz. The 

first is due to changes in the three-dimensional spacing, size, and strength of roots in a 

hillslope. The second is a result of changes in the groundwater conditions that may arise 

from variations in the water use by vegetation on the slope. These effects are discussed 

in Chapter 6. In soils that are high in silt, the “apparent” soil cohesion cs can be high 

because of internal water tension at low water content. If fuel management results in 

reduced evapotranspiration, then it is possible that pore water pressure could increase 

and the apparent cohesion decrease, leading to a reduced FOS.

Very simple analyses like that above can be quickly computed on a hand-held calculator. However, computerized analyses also have been developed to evaluate many 

more complicated slope conditions, including those with non-planar failure surfaces, 

confined groundwater situations with excess pore water pressure, variable soil properties, pseudo-static forces from earthquakes, and surcharge loads from concentrated 

masses on the ground surface. When the assumptions of an infinite slope are relaxed, 

automated searches can be made for the minimum FOS for any size of landslide on a 

slope profile. These techniques are discussed in great detail in many references such as 

Graham (1984), Nash (1987), and Duncan (1996).

Equation 12 can be used to predict in absolute terms the FOS of an individual slide at 

a particular location. As we will see later, it can also be implemented in a GIS format to 

map the spatial variability in FOS, either in an absolute or relative sense. If this analysis 

predicts a landslide at a particular location, it can also be used to evaluate the timing and 

frequency of such sliding, although this is not easy. Examination of Equation 12 shows 

that the only parameter that naturally varies strongly in time is the pore water pressure 

(through the variable mz

). This parameter normally fluctuates in response to temporal patterns of precipitation, snow-melt, or rain-on-snow. Changes in mz

 in response to 

variations in moisture input to the hillslope can either be established through empirical 

correlations or by groundwater modeling. If the temporal pattern of other parameters, 

such as the root cohesion, is known, then again the timing and frequency of sliding can 

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
270 USDA Forest Service RMRS-GTR-231. 2010.

be objectively evaluated by repeating the analysis of Equation 12 for those changed 

conditions.

In its two-dimensional form, the simple limit equilibrium stability analysis does not 

predict landslide size: the analyzed element can be of any length along the slope profile. 

Slide size is quite important as it strongly influences other results, such as the slide travel 

distance and the amount of debris likely to be carried into a stream. If the infinite slope 

analysis is extended to three dimensions, then size can be estimated. Currently, the great 

majority of stability analyses, even computer-based techniques, are two-dimensional, 

although there is now a moderate amount of research to develop three-dimensional 

analysis techniques. This is an issue of particular importance to fuel management, as the 

reinforcement from tree roots is truly three-dimensional (cross slope and up/down slope 

as well as vertical). A change in a forest canopy that increases or reduces root reinforcement logically should affect not only the location, but the size of landslides.

If the infinite slope equation is cast in terms of a balance of total forces, it is possible 

to predict the lateral dimensions of a slide according to:

( tan )

sin cos cos tan

z w q c

z

w

c z m

2

1

l ho

b w z 2

v z

c b b c c b z

+ +

- - = -

^ l

^

h

h (13)

where cb = soil + root cohesion on the base of the slide

cl = soil + root cohesion on the sides and head of the slide

w = the width of the slide (cross slope width)

q = the ratio of landslide width/downslope length

vhol = depth-averaged frictional resistance on the sides of the slides

= cos

K

z m 2

o = - ^c c z w zh

Ko = at rest earth pressure coefficient = 1-sin ø

Equation 13 is derived from Equation 16 in Casadei and Dietrich (2003), which includes the lateral soil friction as well as lateral soil and root cohesion.

While predictions of the FOS of some specific location or the width of a slide at a 

site are relatively straight forward, estimates of slide velocity and travel distance are 

difficult. This is an area of very active research, but the prevailing advice at the present 

time is to assume that shallow slides that mobilize into debris flows will move at rates 

on the order of m/s to tens of m/s. In the Oregon Coast Ranges, it has been empirically 

found that shallow land slides (soil thickness 1 m or less) (Dietrich and others 2007) 

tend to stop when the slope angle in the runout zone declines to less than 3.5o or when 

a tributary transporting a debris flow intersects a receiving channel at an angle greater 

than 70o (Benda and Cundy 1990).

Thus far, the discussion has focused on planar failures. In some cases, rotational 

failures can occur. These are more common on uneven terrain or where the surface is 

underlain by uneven bedrock leading to pockets of elevated soil water. Roads frequently 

are subject to rotational failures. These types of failures are more difficult to analyze, 

and generally require iterative solutions. Computer programs such as XSTABL (Sharma 

1994) have been developed to assist for these conditions.

Earth flows may be another source of sediment movement, accelerated by increased 

soil water contents as previously discussed. Their analysis, however, is best carried out 

by geotech specialist as there are no readily available tools for such soil displacement.

Slide Hazard Assessment Over Broad Areas

Landslide inventories

It is commonly observed that landslides often happen in places where they have occurred in the past. Thus, a relatively simple inventory of past landslides may have some 

predictive power about future events. Slide inventories over broad areas are normally 

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USDA Forest Service RMRS-GTR-231. 2010. 271

conducted by stereoscopic examination of air photos with some limited ground verification of results. These inventories often simply identify slide locations, but occasionally 

they are expanded to also map landslide types, sizes, and runout distances. If air photos of multiple ages are available, the time of occurrence and recent state of activity 

can sometimes be estimated. Inventories can be quantified by calculating the spatial 

variation in landslide density to produce what is called a landslide isopleth map (Wright 

and others 1974). The advantage of photo-based inventories is that they are relatively 

inexpensive and can survey large areas rather quickly. It is very difficult, however, to 

determine the size of landslides from air photos and often little is learned of the site conditions that caused sliding. Furthermore, if current or future slope conditions are outside 

those represented by the photographic record of landslides, erroneous predictions of 

existing or future hazard may be produced. Still, this is an extremely useful technique 

and normally a slide inventory map is developed, even if other analysis techniques are 

employed. In many cases, the inventory data are used to calibrate, and validate, the other 

predictive methods (McClelland and others 1999).

GIS multi-factor overlay approaches

An extension of the simple inventory is to map the variables that could reasonably 

affect slope stability, in other words, the parameters in Equation 12. In a GIS environment, these parameter maps are overlaid and examined for combinations of parameters 

that exist at mapped landslide sites. By identifying the same combinations of parameters at other locations, a map of future landslide susceptibility or hazard is produced 

that is based on correlations of slope, aspect, vegetation, geologic materials, and geologic structure with past landslides. In more sophisticated models, the correlations are 

evaluated statistically using discriminate analyses, logistic regression, or Bayesian belief models (Carrara and others 1991; Dai and Lee 2001; Gorsevski and others 2006a; 

Gritzner and others 2001)

These GIS-based analyses are relatively simple to conduct if suitable factor maps are 

available for the pertinent parameters. Again, the assumption is that future conditions 

will be within the range represented by the existing record of landslides. This supposition may be in error if the regional climate changes, or if management, fires, or other 

changes in land use occur that change the vegetation community and thus the root cohesion. GIS analyses do not generally predict landslide size, timing, frequency, velocity 

or runout distance.

Deterministic engineering style analyses

In this approach, mechanistic analyses of the type shown in Equation 12 are performed over large areas represented in a GIS. The result is a distributed, physically 

based model that can predict local slope stability in absolute or relative terms. The great 

advantages are that the technique is objective and can predict location, timing, and frequency of slides. It is also possible to conduct sensitivity analyses and predict landscape 

response to changes in environmental conditions from natural and human causes. These 

conditions may be completely outside the range of those represented in the history of 

observable landslides in an area. For example, it is possible to investigate the effects 

of forest thinning or complete removal on slope stability. At present, almost all models 

of this type employ the two-dimensional infinite slope analysis (Equation 12) and cannot evaluate landslide size (Gorsevski and others 2006b; Montgomery and Dietrich’s 

SHALSTAB model (1994); Ward and others 1982).

A distinct disadvantage of this approach is that the full list of parameters in Equation 

12 must be characterized over large areas. Some, such as soil depth and pore water 

pressure, are very difficult to predict. Pore water pressure, in particular, is a problem 

because it varies in four dimensions—three spatial and a temporal dimension. Pack 

and others (1998) attempted to resolve the problems of parameter uncertainty by describing the probability distribution function (assuming a uniform probability density 

function) of some parameters, rather than using single valued parameters. In their model 

Stability Mapping Index (SINMAP), they then calculate a probability of failure rather 

William Elliot, Kevin Hyde, Lee MacDonald, James McKean Cumulative Watershed Effects of Fuel Management in the Western United States
272 USDA Forest Service RMRS-GTR-231. 2010.

than an FOS. Gorsevski and others (2006b) used a stochastic weather generator and 

a soil water balance model in a GIS approach to predict areas of instability. Wu and 

Sidle (1995) noted that rainfall is a stochastic parameter in their Distributed Shallow 

Landslide Analysis Model (dSLAM). This model uses either an event-based rainfall 

record or theoretical distributions from Monte Carlo simulations to predict the pore 

water pressure, and thus computes either FOS or probability of failure. dSLAM also 

incorporates the time rate of decay of root strength after tree death and the rate of site 

vegetation regrowth, although still only in a two-dimensional model. In their Level one 

Stability Analysis model (LISA), Hammond and others (1992) also employed a Monte 

Carlo analysis with probability density functions for all parameters in Equation 12. 

Rather than calculating the probability of failure directly on the pixels in a DEM, LISA 

first stratifies the landscape into homogeneous units and then evaluates the probability 

of failure for each stratum using a Monte Carlo scheme. This is a subtle but important 

difference, and in the LISA model, a high probability of failure for a stratum gives no 

information about where in a polygon a particular combination of conditions might exist 

that would lead to a higher probability of failure. The assumption is that the polygon is 

homogeneous and the probability of failure is equal throughout.

As discussed before, all distributed mechanistic models require calibration and validation against local landslide information in a slide inventory map.

Analysis of Slope Stability Along Roads

Depending on the terrain that is traversed and the style of construction, roads can have 

a variety of effects on slope stability. Cut and fill slopes are normally steeper than local 

undisturbed terrain and are inherently less stable. Cut slopes also frequently intercept 

shallow groundwater and can concentrate this water in places that will cause landslides. 

Normally, groundwater concentrations will occur where road fill is thickest—across the 

corridors of small unchanneled valleys and hollows. Disruption of groundwater flow by 

the overlying fill can cause elevated pore water pressures and fillslope failure. Mountain 

roads are sometimes damaged when they cross landslides that are so large they are relatively unaffected by the road, yet the road is a victim when the slides move.

The stability of a road corridor can be considered at a variety of spatial scales, 

ranging again from individual slides to the general mass stability of an entire road. 

Individual slides are analyzed using methods such as those introduced previously. At 

broader scales of investigation, mapping techniques have been developed that can be 

described as qualitative engineering geomorphology analyses. This method of “reading 

the landscape” from a geomorphic perspective over time scales well beyond human 

experience is described in a series of papers published mostly in the Quarterly Journal 

of Engineering Geology. Perhaps the first of these is the pioneering work by Brunsden 

and others (1975). In this approach, landforms are mapped in detail using a combination 

of air photo interpretation and field work, and then process domains, including those 

of landslides, are interpreted from the morphologic maps. By doing this, a qualitative 

assessment of local or regional landslide hazard can be produced. Future remote sensing will likely incorporate LiDAR capabilities into evaluating road stability (Kwak and 

others 2005).

Quantitative deterministic analyses, most often based on the infinite slope equation, 

can also be done over entire road corridors. A recent example is that of Borga and others 

(2004) who used the SHALSTAB model with an adaptation of the groundwater component to accommodate the interception and rerouting of groundwater by a road network. 

A similar approach is used by Prasad and others (2005) who employ a modified version 

of the SINMAP probabilistic stability analysis as part of the Road Sediment Analysis 

Model (RSAM).

Chapter 13. Tools for Analysis
USDA Forest Service RMRS-GTR-231. 2010. 273

Model Calibration and Validation

Calibration is the process of determining input variables so that the model generates 

satisfactory predictions. Validation is using a calibrated model on a different site or data 

set to see whether reasonable values are still predicted (Conroy and others 2006; Elliot 

and Foltz 2001; Elliot and others 1991). Many models require some form of calibration as part of the application. For example, many of the WEPP vegetation files require 

calibration for local weather conditions to ensure that predicted amounts of canopy and 

ground cover are correct. The SWAT model is generally calibrated for runoff for current 

conditions before evaluating alternative management activities. Many research papers 

have been published on model validation, but it is always a good practice to compare 

predicted runoff and erosion rates and amounts with values observed in the area. Are 

the predicted values reasonable compared to monitoring or research studies that have 

been done in the past for similar conditions? If not, the user may need to consider some 

additional calibration or add some qualifying comments in the report associated with 

the modeling activity. If a given tool does not appear to be performing in a satisfactory manner, it may be useful to contact the group supporting that model to ensure the 

model is being used correctly and to determine if the model is appropriate for the given 

conditions.

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Chapter 14.

Understanding and Evaluating Cumulative 

Watershed Impacts

Leslie M. Reid, Research Geologist, Redwood Sciences Laboratory, Pacific Southwest Research 

Station, USDA Forest Service, Arcata, CA

Introduction

Considerable effort is devoted to evaluating cumulative watershed impacts during 

planning for forestry activities on federally managed lands. With the recently increased 

emphasis on reducing forest fuels, cumulative impact analyses must now evaluate a new 

suite of activities over a broader scale than had generally been considered in the past. It 

is useful to review the concept of cumulative impacts and the variety of methods used 

for impact analysis to identify approaches capable of addressing the new challenges.

This paper first outlines the history and definition of cumulative watershed impacts 

and discusses the types of interactions that complicate their evaluation. Methods used 

for cumulative impact evaluation are then described. Finally, the types of errors found in 

evaluations are identified, and the relevance of such problems is assessed by identifying 

flaws found to be significant by federal courts. A variety of earlier publications can provide additional insight and detail concerning cumulative impact analysis (CEQ 1997; 

MacDonald 2000; Reid 1993, 1998).

History and Definition

Cumulative impacts are nothing new. The importance of cumulative watershed impacts was widely recognized by the mid-1800s when a French economist described the 

increasing incidence of debris flows in the Alps:

“The elements of destruction are increasing in violence...The devastation 

advances in geometrical progression as the higher slopes are bared of their 

wood, and ‘the ruin from above,’ to use the words of a peasant, ‘helps to hasten the desolation below’” (Blanqui 1843, Address to the French Academy 

of Moral and Political Science, quoted by Marsh 1864).

George Marsh observed the problems caused by altered runoff and erosion in Europe 

and the Middle East and noted that analogous conditions were developing in America:

“The rivers which rise in [deforested uplands of the Adirondacks], flow with 

diminished currents in dry seasons, and with augmented volumes of water after heavy rains. They bring down much larger quantities of sediment, 

Cumulative Watershed Effects 

of Fuel Management in the 

Western United States
278 USDA Forest Service RMRS-GTR-231. 2010.

and the increasing obstructions to the navigation of the Hudson, which are 

extending themselves down the channel in proportion as the fields are encroaching upon the forest, give good grounds for the fear of serious injury 

to the commerce of the important towns on the upper waters of that river, unless measures are taken to prevent the expansion of ‘improvements’ 

which have already been carried beyond the demands of a wise economy” 

(Marsh 1864).

The U.S. Congress passed the Forest Reserve Act in 1891 largely in response to the 

increasing concern over downstream impacts arising from rapid upland deforestation. 

This Act authorized the President to set aside selected forestlands, and these reserves 

eventually became the first national forests. The focus on watershed concerns was evident in the 1911 Weeks Law, which authorized purchase of lands for national forests if 

they were in the watersheds of navigable streams. In a sense, the Forest Service exists 

because of early recognition of cumulative watershed impacts.

The term “cumulative impacts” did not become widely used until the Council on 

Environmental Quality (CEQ) produced guidelines for implementing the National 

Environmental Policy Act (NEPA) of 1969. This particular issue arose because NEPA 

planning focused on specific projects or programs. The CEQ realized that a broader 

perspective on problems could be overlooked under these conditions—examination of 

a project in isolation would not reveal the impact levels that would actually be experienced. The CEQ thus specified that the overall, or “cumulative,” impact level also must 

be evaluated, and defined the cumulative impact as:

“...the impact on the environment which results from the incremental impact 

of the action when added to other past, present, and reasonably foreseeable 

future actions regardless of what agency (Federal or non-Federal) or person 

undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period 

of time” (40 CFR § 1508.7).

The term “cumulative effect” is widely used as a synonym for “cumulative impact,” 

and the CEQ defines “effect” to be the same as “impact” in the context of NEPA (40 

C.F.R. 1508.8). The CEQ did not specifically define “watershed impact,” but common 

usage indicates that this refers to any impact that involves water flowing through a 

landscape, either because water-related resources are impacted or because a change in 

watershed processes generates the impact. Cumulative watershed impacts are just one 

variety of cumulative impact, but watershed impacts often are important influences on 

other types of cumulative impacts. Analyses of cumulative impacts on terrestrial wildlife, for example, often need to consider the cumulative influences of watershed impacts 

on riparian habitat.

The notable point about the definition is that there is nothing sophisticated or mysterious about it. “Cumulative” is being used simply as an adjective with thesaurus 

synonyms of “aggregate,” “collective,” “accruing,” and “combined,” rather than as part 

of a name for a new type of impact. The net impact that a resource experiences usually 

represents the combined effects of multiple influences, so evaluation of the cause and 

severity of any impact ordinarily involves assessment of multiple influences and so is, 

in effect, an analysis of the cumulative impact.

Interactions Between Impact-Generating Influences

The overall impact on a resource—the “cumulative” impact—differs from an “individual impact” if the total impact is affected by more than one anthropogenic influence. 

Influences can interact in several ways, contributing to impacts that can accumulate 

through time, space, or both. Impacts can accumulate as a result of repetition of an activity at a site (example: multi-cycle logging in the transitional snow zone periodically 

increases rain-on-snow peakflows, increasing the cumulative cost of excess downstream 

Chapter 14. Understanding and Evaluating Cumulative Watershed Impacts
USDA Forest Service RMRS-GTR-231. 2010. 279

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States

flood damage) or from progression of the activity to new sites (example: additional logging increases the spatial scale of the increased rain-on-snow flooding, also increasing 

the cumulative cost of flood damage), and they can accumulate from different coexisting activities or from different activities occurring sequentially (example: logging, 

housing developments, and fire all increase rain-on-snow flood peaks). Impact severity 

can increase either because one type of change accumulates (example: the cumulative 

cost of increased flood damage accrues through time) or because different influences 

affect the same entity (example: flood damage increases because of both increased flood 

peaks and increased channel aggradation). If influences from a single activity impact 

a resource progressively through time (CEQ 1997) or by way of multiple mechanisms 

(example: logging can contribute to both increased peakflows and increased aggradation, both leading to increased flood damage), the overall impact can also be evaluated 

as a cumulative impact.

The most widely recognized subdivision of cumulative impacts is into “additive” and 

“synergistic” impacts. Impact severity for additive impacts can generally be inferred by 

summing the effects of the component impacts. For example, reductions in municipal 

water supply from reservoir aggradation can be estimated by summing sediment input rates from the variety of sediment sources in a watershed. In contrast, synergistic 

impacts require additional knowledge if outcomes are to be predicted. For example, 

increased stream temperature reduces salmonid survival, as does decreased pool habitat. 

However, if salmonids cope with increasing temperatures by taking refuge in deep, cool 

pools (Nielsen and others 1994), the combined effect of increased temperatures and 

infilled pools would have a much greater impact than could be predicted by considering 

each impact separately.

Cumulative increases in impact severity can occur if an existing adverse condition 

increases in magnitude, duration, or frequency. Although these kinds of changes usually 

are associated with one another, it may be useful to consider them separately because 

their influences on an impacted resource may differ. Increased turbidity magnitude, for 

example, usually accompanies an increase in duration of high turbidity periods and an 

increased frequency of high turbidity spikes. If magnitudes are high enough, turbidity 

itself can become lethal to salmonids. At lower turbidity levels, protracted duration can 

result in lengthy periods during which salmonids cannot see and capture prey, while an 

increased frequency of moderate turbidity peaks may lead to cumulative gill damage 

(Newcombe and Jensen 1996). Each type of impact holds different implications for the 

impacted resource and requires a different approach to analysis.

Impacts can also occur because a new condition is created by an activity, as when 

a new chemical or species is introduced. In other cases, impact severity may increase 

because the sensitivity of the resource is altered. Warmer stream temperatures, for 

example, might increase salmonid metabolic rates, thereby increasing the salmonids’ 

susceptibility to impacts from heightened dry-season turbidity caused by recreational 

off-highway vehicle use, mining, and riparian grazing.

Impacts also occur if the mechanisms that moderated impact severity during natural 

shifts in condition are no longer operative. In the past, for example, coho salmon may 

have been able to escape high turbidity events in the mainstem by taking refuge in intermittent clear-water tributaries and seasonal wetlands on floodplains (Peterson 1982). 

That coping strategy is defeated if road culverts block access to the tributaries or development fills the wetlands. The fish then become susceptible to impacts from conditions 

that once could have been tolerated or avoided. At a larger scale, regional depletion 

of populations can reduce a species’ resilience and resistance both to anthropogenic 

changes and to natural disturbances such as major storms and fires.

Impacts like those affected by changes in turbidity represent the combination of 

multiple influences—that is, are “cumulative”—in several senses. First, an increase in 

turbidity is likely to be caused by multiple activities that occurred at different times 

in the watershed, and it is the cumulative influence of these activities that leads to the 

turbidity levels now seen. Second, the impact to the resource accumulates through time 

as altered conditions persist. Third, the impacted resource often exhibits the effects of 

multiple impact mechanisms associated with the changed condition. As a hypothetical 
280 USDA Forest Service RMRS-GTR-231. 2010.

example, chronically high turbidity levels might leave fish weakened to the point that 

they succumb to infection induced by gill abrasion during a high turbidity spike. And 

fourth, altered turbidity is usually just one of many impact mechanisms that combine to 

produce the overall impact on the resource of interest.

Interaction between responses can also lead to moderation of impact levels. For 

example, water releases from the base of a reservoir might reduce downstream temperatures that had been artificially raised by loss of riparian shade. Mitigation strategies 

are based in part on inducing responses that can compensate for, or reduce. undesired 

responses from other management activities.

Linkages Between Land Use Activities and Impacts

The impact mechanisms discussed above are “proximal” mechanisms—the changes 

experienced by the resource of concern that result in impact. In the case of watershed 

impacts, these proximal mechanisms often take effect at some distance downstream from 

the activities that ultimately caused them, and they are often delayed in time. Developing 

an understanding of the ultimate causes for a particular impact can be challenging both 

because of the inherent complexity of process interactions and because of the spatial and 

temporal lags those interactions create.

Off-site impacts can occur only if there is a physical transfer of material or energy 

from the activity site to the impact site. The flow of water provides the transfer medium for watershed impacts. Most land use activities occur on hillsides (figure 1), and 

most activities modify characteristics such as vegetation, topography, and soil conditions. Changes to these characteristics, in turn, influence the magnitude and timing of 

inputs of water, sediment, heat, chemicals, nutrients, and wood to streams. If inputs to the 

stream system are modified, the downstream transport of these watershed products is also 

modified, and downstream conditions change in response to the shift in transport rate 

and capacity. Furthermore, changes in the input and transport of one watershed product 

usually influence the input and transport of others. Decreased wood inputs, for example, 

may result in decreased channel roughness, causing increased flow velocities, which can 

increase bed and bank erosion and thereby increase sediment loads. Or, an increase in 

Figure 1. Relation between 

hillside land use 

activities, on-site, and 

off-site environmental 

impacts.

Land-use activity:

logging agriculture roads

grazing urbanization others

Impact to downstream resources:

salmonids water supply homes

bridges esthetics others

Changes in generation and

transport of watershed products:

water sediment heat

wood organic matter others

Changes in watershed 

characteristics:

soils topography

vegetation others

Impact 

to on-site 

resource

Chapter 14. Understanding and Evaluating Cumulative Watershed Impacts
USDA Forest Service RMRS-GTR-231. 2010. 281

sediment input can aggrade a channel, causing it to shift course and undermine banks, 

thereby increasing wood inputs. The cascade of influences that takes effect after an upstream change depends partly on the location and nature of the change and partly on its 

timing relative both to other changes and to large events such as storms and droughts.

The spatial decoupling of downstream impacts from the upslope activities that triggered them obscures the circumstantial linkages between cause and effect. The locations 

at which an impact becomes evident depend on the distributions of 

1. activities that contribute to the impact, 

2. locales likely to respond to the changes, and 

3. resources that might be impacted by the changes. 

Different sites often respond to the same kind of change in different ways. An increased 

input of fine sediment, for example, may not affect channel form along steep boulder 

reaches but may contribute to aggradation downstream in a low-gradient reach or lake.

Temporal decoupling is also common and obscures evidence of causal linkages. Time 

lags between cause and response can arise for several reasons.

1. A long period of accumulation may be required before impacts become significant 

enough to arouse concern (example: gradual declines in a species’ abundance may not 

be evident for a long time).

2. Different steps in the cascade of influences require different lengths of time to recover, 

so impacts may continue to accumulate downstream long after on-site impacts have 

recovered (example: an initial hydrologic change may destabilize channel banks, 

which continue to produce sediment even after the hydrologic regime is restored).

3. An impact may not become evident until the occurrence of an environmental trigger, 

such as a major drought or storm (example: slopes may appear to have remained 

stable until a landslide-generating storm occurs).

4. The change may not occur until the accumulated effect is great enough to trigger 

another suite of processes (example: accelerated sedimentation in a wetland may not 

be of concern until it has progressed to the point that a particular plant species begins 

to die out).

Interpretation of linkages may also be challenging because different kinds of changes 

can lead to the same response, so the cause for an impact often cannot be inferred from 

observation of the impact alone. The distribution and manifestation of future watershed 

impacts thus depends on the geography, history, and ecology of an area, as well as on the 

nature of contemplated land use activities. For these reasons, and because of the potential 

importance of synergistic interactions, causes and effects of changes must be evaluated in 

the context of specific locales and resources of concern.

Assessing and Managing Cumulative Watershed Impacts

Cumulative impact assessment became a challenge for federal land management 

agencies with the adoption of the CEQ’s regulations for implementing NEPA in 1978 (40 

C.F.R. 1500). The importance of environmental impacts was widely appreciated before 

then, but there was no mandate to consider a project as complicit in causing an impact 

if that project did not by itself create a significant impact. The new regulations indicated 

that if an impact is already significant and a new project adds to the impact, that project 

contributes to a significant impact. Such influences would now need to be disclosed and 

evaluated for projects subject to regulation by NEPA. Subsequently, various states passed 

legislation that requires similar evaluations for state and private projects not subject to 

NEPA oversight.

Before the need for cumulative impact analysis, forest management had tended to focus 

on the forest stand level and was based on identifying an appropriate action for the given 

stand condition. Hydrologists and geomorphologists were necessary for meeting forestry 

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
282 USDA Forest Service RMRS-GTR-231. 2010.

related goals only insofar as those goals concerned infrastructure. After implementation 

of NEPA, however, analysis of off-site cumulative impacts required hydrological and 

geomorphological expertise, but foresters, hydrologists, and geomorphologists within 

forest management agencies did not have a history of working together. Methods for 

cumulative impact analysis had to be developed that would enable the interdisciplinary 

work now needed and could be carried out routinely by existing personnel.

First Generation: Tactical Manuals

The Forest Service provided a decentralized response to the need for cumulative impact 

analysis, with approaches being designed as needed in different Regions. Most prominent among the early approaches were the Equivalent Clearcut Area method developed 

for Idaho and Montana, the R1/R4 Sediment-Fish Model used in the Idaho Batholith, and 

the Equivalent Roaded Acres method from California. This first generation of analysis 

methods consisted of detailed procedures that lead the user through specific calculations. 

Each approach effectively provides an accounting system for activity level, making it 

possible to manage cumulative impacts by holding a watershed’s activity level below 

that associated with impact generation. The methods differ in assumptions about which 

impact is most important and in the strengths of their technical foundations.

Equivalent Clearcut Area

The Equivalent Clearcut Area approach to cumulative impact analysis was developed in the 1970s for application in northern Idaho and Montana (Galbraith 1975; USFS 

1974). In this area, the impact of most concern was identified to be channel destabilization due to increased peakflows resulting from decreased evapotranspiration after 

logging. Altered evapotranspiration is associated directly with changes in canopy cover, 

so the net influence of an activity—including logging, road construction, burning, and 

other forest management activities—can be assessed by determining its effect on canopy 

cover by calculating the “equivalent clearcut area” (ECA) the activity represents. The 

ECA for the proposed project is then added to that already present in the watershed. If 

the resulting total is above the threshold considered acceptable for the area by experts, 

activities are deferred until the ECA recovers through time or activities are modified to 

produce a smaller increase in ECA.

A major advantage to the ECA approach is that it is relatively simple to implement. 

The analysis requires no specialized expertise and can be carried out from the office. 

Furthermore, anyone carrying out the analysis with the same input data will get the same 

answer.

Disadvantages, however, are significant. First, the method is specific to a particular 

type of impact. If other impacts are of concern in an area, other analyses must be done. It 

might be argued that if the most sensitive impact is screened for, others will be handled 

implicitly. However, if other impacts are caused by unrelated mechanisms, there is no 

reason that screening on the basis of one mechanism would produce results relevant 

to problems caused by another mechanism. For example, screening on the basis of increased peakflows would not identify areas sustaining impacts from acid mine drainage. 

Second, recovery is calculated according to that estimated for hydrologic response and 

does not account for the recovery rate of impacted channels. If channel morphology or 

fish populations require years to recover after hydrologic changes are reversed, impacts 

can continue to accrue from new activities taking place after hydrologic recovery. Testing 

of the method suggests that it may underestimate the magnitude of peakflow changes following logging (Belt 1980; King 1989).

R1/R4 Sediment-Fish Model

In the Idaho Batholith area, declining salmonid populations were a major concern, 

and research suggested that deposition of logging-related fine sediment in streams was 

contributing to salmonid decline. Considerable research was devoted to evaluating the 

Chapter 14. Understanding and Evaluating Cumulative Watershed Impacts
USDA Forest Service RMRS-GTR-231. 2010. 283

link between specific forest management activities and erosion rates, between sediment 

inputs and sedimentation (Cline and others 1981), and between sedimentation and salmonid survival (Stowell and others 1983). The result is a series of models that can be 

used to estimate impacts on salmonid survival from the distribution of forestry related 

activities through time in a watershed. Recovery rates for surface erosion are incorporated, so inputs from old activities are lower than for recent ones.

This approach also is easily implemented, once the initial work is done to quantify 

the necessary relationships. However, the model depends strongly on the considerable 

research done to evaluate linkages between forestry and salmonid survival in the Idaho 

Batholith, so the model cannot be transported to a new area without substantial research. 

As was also the case with the ECA method, the approach is targeted for a particular impact mechanism and type of impact—analysis of other impacts would require different 

approaches.

The R1/R4 model has more recently been combined with a water balance model to 

construct the WATSED model (USDA 1992), now used widely in the area to estimate 

the combined effects of changes in runoff and sediment associated with logging.

Equivalent roaded acres

The approach for evaluating cumulative impacts developed by USFS Region 5 in 

California is similar to the ECA method. The focal concern in California had been identified as an increase in peakflows, and research in Oregon suggested that peakflows 

increase if more than 12 percent of a watershed surface is compacted. On this basis, 

the area compacted by each activity in a watershed is summed to determine whether 

the total “equivalent roaded acres” (ERA) is greater than the threshold considered appropriate for an area (for example, Haskins 1987). Here, too, recovery is assessed on 

the basis of recovery from compaction rather than recovery of the impacted resources. 

It was quickly recognized that impacts other than those from increased peakflow had to 

be considered. Descriptions of the method were soon revised to indicate that the calculation resulted in an index of the activity level in a watershed (USFS 1988). Thresholds 

of concern and weighting factors for various activities are intended to be modified to reflect conditions in each area, such as rock type and topography, and can be calibrated by 

measuring the activity levels associated with observed impacts. More detailed analysis 

is triggered if the calculated ERA approaches a threshold of concern for the watershed.

Advantages of this approach are its reproducibility and relative simplicity in calculation. The method can also be calibrated to apply to specific areas and impact types, as 

long as the thresholds for impact can be associated with particular activity levels.

The ERA approach shares most of the disadvantages of the ECA approach, and it 

also carries the implied responsibility for the user to ensure that it is appropriately calibrated for each application. As was also the case for the ECA and R1-R4 methods, there 

is no assurance that a single screening tool can adequately address multiple, unrelated 

impact mechanisms—an initial impact analysis would be needed to identify the impacts 

of concern and assess their associations with ERAs. The ERA approach has also not 

been independently tested. One study suggests that increased ERAs within 200 m of a 

stream are associated with impaired aquatic invertebrate communities (McGurk and 

Fong 1995), but it is not clear whether ERAs are a more efficient index of buffer-strip 

effectiveness than other metrics.

Second Generation: Strategy Guides

Use of standardized procedures such as the ERA method is very different from the 

approach that had been adopted by most other spheres of activity. For non-forestry 

applications, there did not seem to be a perceived need for a single “cumulative impact analysis tool” to address all cumulative impacts. Instead, it was recognized that 

any activity can influence many types of impacts at a variety of spatial and temporal scales. Each impact needs to be evaluated by analytical methods pertinent to that 

specific impact. A highway construction project, for example, might require analysis 

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
284 USDA Forest Service RMRS-GTR-231. 2010.

of cumulative changes in long-term traffic patterns at a regional scale, of cumulative 

peakflow changes at a small-watershed scale, and of the short-term effects of construction on cumulative siltation in a reservoir far downstream. This problem-based 

strategy is simply an extension of approaches to impact evaluation that have been used 

in the past when particular impacts were of concern. Several forestry applications have 

adopted the problem-based strategy, and the CEQ has provided further guidance on 

appropriate analysis strategies.

CDF checklist

By the early 1990s, forestry related applications began to incorporate a broader 

view of cumulative impacts, as exemplified by the approach eventually adopted by the 

California Department of Forestry and Fire Protection (CDF). Because NEPA does not 

apply to non-Federal jurisdictional issues, the California legislature in 1970 passed the 

California Environmental Quality Act (CEQA), which applies requirements similar to 

those of NEPA to activities under state jurisdiction. At first, CDF responded to the need 

to address cumulative impacts for state and private forestry by applying “best management practices” (BMPs), asserting that if direct impacts are held to a minimum, the 

cumulative impact will be insignificant. This approach was found by the courts to be 

invalid as it did not reflect the legal definition of cumulative impact (Environmental 

Protection Information Center v. Johnson, 170 Cal. App. 3d 604, 1st Dist., 1985). (Note: 

published legal opinions are here cited by volume number [170 for this case], the abbreviated name of the source [California Appellate Reporter], the series number [Third], 

the page number on which the opinion begins [604], the court providing the opinion, 

and the year of the decision; unpublished district-level opinions are cited by case number, court, and year).

In the early 1990s, CDF instituted a checklist (CDF 2009 revised) to guide Registered 

Professional Foresters (RPFs) through the logic trail needed to support a professional 

opinion of whether or not cumulative impacts were likely from a Timber Harvest Plan 

(THP). This kind of open-ended approach has the advantage of flexibility, potentially 

allowing use of appropriate analytical methods for the specific types of impacts relevant 

for an area.

In practice, however, the documentation required is minimal, consisting primarily 

of a checklist and a brief explanation of the conclusion. Although the procedure has 

withstood legal challenges, various commentators have questioned its credibility and 

effectiveness. Dunne and others (2001), for example, noted that members of their review committee had “...been told explicitly by some RPFs that, in preparing a THP, they 

would never conclude that a CWE [cumulative watershed effect] is likely because of the 

unnecessary regulatory burden that such an admission would bring.”

CEQ guidance for cumulative impact evaluation

By the late 1990s it had become clear that an appreciable proportion of the cumulative impact assessments prepared for NEPA documents were inadequate (Burris and 

Canter 1997). In 1997, the CEQ published a manual (CEQ 1997) that outlines an appropriate approach to cumulative impact evaluation under NEPA. The recommended steps 

are similar to those used for more general environmental impact assessments (table 1), 

encompassing identification of the impacts of concern and their spatial and temporal 

scales of expression; description of the baseline conditions, proximal impact mechanisms and tolerance to change; determination of the influence of the project on the 

impact mechanisms; and description of the impact level expected after completion of 

the project.

The same document summarizes principles of cumulative impact analysis (table 2). 

Several of these points are particularly important. First, analysis is carried out from the 

perspective of the impacted resource. Each significant impact must be evaluated in its 

own right since each will be influenced by different mechanisms, appear in different 

places, and have different recovery rates. Second, the boundaries of the analysis area 

are determined by the locations of the entities that might be influenced by the activity 

Chapter 14. Understanding and Evaluating Cumulative Watershed Impacts
USDA Forest Service RMRS-GTR-231. 2010. 285

in question, so each issue is likely to require analysis over a different area. This need to 

define the analysis scope from the point of view of the impact also holds for temporal 

boundaries, because rates of impact expression and recovery will differ for each impact 

considered.

Clearly, these analytical issues are not compatible with strict adherence to standardized impact analysis methods such as the ECA, ERA, and R1/R4 approaches, and those 

approaches are now often supplemented by additional information concerning specific 

issues of concern.

The Eastwide strategy

Forest Service Regions in the eastern United States developed an analysis approach 

that incorporates much of the CEQ guidance (Tetra Tech 2002). The Eastwide approach follows the structure suggested by MacDonald (2000), which is based largely 

on the CEQ (1997) approach but differs from it in sequencing of steps, reliance on 

“natural range of variability,” and omission of an evaluation of impact significance. 

Appropriate levels of analysis effort are described for different analytical contexts (a 

highly controversial issue, for example, would require a higher level of effort), and 

options for content and approach are described for each level of effort. The Eastwide 

Technical Guide notes that a variety of landscape- and watershed-scale analyses are 

Table 1. Steps in cumulative effects analysis to be addressed during the components of environmental impact assessment 

(after CEQ 1997).

Assessment component: Scoping

1. Identify the significant cumulative effects issues associated with the proposed action and define the assessment goals.

2. Establish the geographic scope for the analysis.

3. Establish the time frame for the analysis.

4. Identify other actions affecting the resources, ecosystems, and human communities of concern.

Assessment component: Describe affected environment

5. Characterize the entities of concern in terms of their response to change and capacity to withstand stresses.

6. Characterize stresses affecting the entities of concern and their relation to regulatory thresholds

7. Define a baseline condition for the entities of concern.

Assessment component: Determine environmental consequences

8. Identify important cause-and-effect relations between human activities and issues of concern.

9. Determine the magnitude and significance of cumulative effects.

10. Modify or add alternatives to avoid, minimize, or mitigate significant cumulative effects.

Assessment component: Implementation

11. Monitor the cumulative effects of the selected alternative and adapt management.

Table 2. Principles of cumulative effects analysis (after CEQ 1997).

1. Cumulative effects are caused by the aggregate of past, present, and reasonably foreseeable future actions.

2. Cumulative effects are the total effect, including both direct and indirect effects, on a given resource, ecosystem, and 

human community of all actions taken, no matter who (federal, nonfederal, or private) has taken the actions.

3. Cumulative effects need to be analyzed in terms of the specific resource, ecosystem, and human community being 

affected.

4. It is not practical to analyze the cumulative effects of an action on the universe; the list of environmental effects must focus 

on those that are truly meaningful. (The boundaries for evaluating cumulative effects should be expanded to the point at 

which the resource is no longer affected significantly or the effects are no longer of interest to affected parties)

5. Cumulative effects on a given resource, ecosystem, and human community are rarely aligned with political or 

administrative boundaries. (Cumulative effects analysis on natural systems must use natural ecological boundaries and 

analysis of human communities must use actual sociocultural boundaries to ensure including all effects)

6. Cumulative effects may result from the accumulation of similar effects or the synergistic interaction of different effects.

7. Cumulative effects may last for many years beyond the life of the action that caused them.

8. Each affected resource, ecosystem, and human community must be analyzed in terms of the capacity to accommodate 

additional effects, based on its own time and space parameters.

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
286 USDA Forest Service RMRS-GTR-231. 2010.

available for many areas, and that these provide much of the information needed for 

cumulative impact analyses.

The approach outlined by the Guide differs from the other methods designed for 

Forest Service use because it consists of a strategy for problem solving that ensures 

that the appropriate topics will be considered during analysis while allowing the user 

to choose the analysis scales and tools appropriate for the specific issues and conditions present. Some of the issues important for cumulative impact evaluations in these 

Regions—and in all other Forest Service Regions—include impacts of forestry, fire, 

recreation, minerals exploration and mining, oil and gas exploration and mining, and 

rural development; relevant waterbodies include streams, wetlands, lakes, reservoirs, 

and groundwater; and potentially impacted resources include flora, fauna, recreational 

values, domestic and municipal water supplies, recreational and commercial fisheries, 

and many others.

An important advantage to the Eastwide Strategy is that it incorporates most of the 

suggestions provided by CEQ (1997). It allows any impact to be evaluated using the 

specific analytical techniques most appropriate for the issue and for the local conditions; provides for selection of temporal and spatial analysis scales appropriate for the 

problems present; and makes good use of the technical expertise present within the 

agency. A potential weakness, however, is the omission of guidance concerning evaluation of impact significance.

Identifying Shortcomings in Cumulative Impact Assessments

Because the need to modify standardized cumulative impact analysis procedures 

seems likely in view of the suggestions provided by CEQ (1997), it is useful to identify 

the particular aspects of non-standardized cumulative impact analyses that are likely 

to present analytical problems. A series of cumulative impact analyses that did not 

incorporate standardized methods were thus evaluated for technical content. Whether 

the types of problems found would be considered significant to the implementation of 

NEPA depends on how those technical flaws are treated by the courts, so recent legal 

decisions involving cumulative impact analyses were then reviewed to determine how 

federal courts deal with the common problems.

Problems in Cumulative Impact Analysis for Private Lands

Analytical problems were identified in 14 non-standardized cumulative watershed 

impact analyses and supporting documents that had been prepared for logging-related activities on private forestlands in northwest California (Reid 2004). Most of 

these documents were intended at least in part to meet requirements of the California 

Environmental Quality Act.

Each document incorporated analytical flaws that generally fell into four categories. 

First, the legal definition of cumulative impacts was often disregarded. Several analyses progressed without an evaluation of existing impact levels or of the contribution 

from “legacy” impacts, even though the definition of “cumulative impact” focuses on 

the combined influence of exactly these types of impacts. Another analysis argued that 

the cumulative impact of the plan would be beneficial because the preferred alternative 

would have a lower impact than one of the other alternatives. The cumulative impact, 

however, is the impact “on the environment”—if the overall impact is detrimental, it 

cannot be presented as “beneficial” simply by comparing the project’s incremental addition to that of an even more damaging alternative.

The second set of problems involves evaluation of impact significance. Several 

analyses argued that an activity would simply perpetuate the existing level of impact 

instead of increasing its severity, thereby implying that the cumulative impact of the 

new activity is insignificant. However, the severity of an impact is necessarily defined 

by the level of damage to the impacted resource, and the level of damage usually 

Chapter 14. Understanding and Evaluating Cumulative Watershed Impacts
USDA Forest Service RMRS-GTR-231. 2010. 287

increases as an impact persists. Consequently, prolonging an impact generally increases its severity.

In most of the documents examined, impact significance was determined simply 

through professional opinion, without any documentation of how the significance 

thresholds were established. One analysis evaluated the sediment input expected from 

a proposed project and then asserted that the added sediment would result in a negligible risk of significant impact. The analysis neglected to note that the existing impact 

level for sediment in the watershed had already resulted in the stream’s addition to 

the 303d list under the Clean Water Act, so a regulatory threshold of significance had 

already been surpassed.

A third set of problems reflected the projects’ reliance on mitigation plans to reduce expected impact levels to non-significance. Either BMPs or offsetting mitigation 

usually were part of the management strategy, but rarely was evidence provided that 

mitigation would be effective, and the overall effects of the mitigated activities on 

the impacted resources were not evaluated. Instead, analyses simply noted that the 

impact levels would be “reduced” by mitigation. However, few of the planned mitigation measures would be capable of preventing the expected impacts because mitigation 

generally was planned for other sites, was designed to offset different kinds of impacts, 

or would become effective only after the planned impacts had occurred.

The final set of problems involved technical errors in the analyses, and most of these 

could have been corrected by technical review. In this case, too, unsupported assertions 

were common. For example, one document arbitrarily considered bank erosion to be 

half natural and half anthropogenic. No evidence was provided to support this assumption, yet the analysis conclusions depended on it.

Problems in USFS and BLM Cumulative Impact Analysis for 

NEPA Documents

Examination of the private-sector analyses disclosed the general types of analytical 

errors that might be expected in non-standardized cumulative impact analyses, but it 

did not indicate whether such problems are operationally important. The operational test for the effectiveness of an impact analysis procedure is whether the method 

produces results that withstand legal challenges. Operational success does not imply 

technical success. An analysis would be considered technically successful only if its 

predictions are found to be accurate. Little information is available concerning the accuracy of predictions from analyses prepared under NEPA, and technical success is not 

considered in this paper.

Whether an analysis is litigated involves a variety of considerations, including how 

controversial the activity is, the nature of the population likely to be affected by the 

activity, and the level of legal expertise and funding within that population. An inadequate analysis for a non-controversial plan is thus likely to receive little attention, 

while a carefully prepared analysis for a controversial project appears to be more subject to challenge.

Federal agencies responsible for managing forestlands have received adverse decisions in a variety of recent cases involving cumulative impact analyses under NEPA. 

Earlier studies have examined the Forest Service record in NEPA litigation (for example, Jones and Taylor 1995; Malmsheimer 2004; and Smith 2005) evaluated federal 

agency success in cumulative impact litigation at the appellate level between 1995 and 

2004. Most litigation is resolved at the district court level, however, so district-level 

opinions would also need to be examined to identify the most common operational 

problems with cumulative impact analysis.

Sixty-two federal district and appellate court opinions were examined to identify 

analytical deficiencies that were considered significant by litigants or judges. All cases 

were selected for review that fit the following criteria: 

1. the case resulted in a final decision after January 1, 2000, that had been catalogued by 

LexisNexis as of June 1, 2005, or was accessible on the internet; 

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2. the complaint involved analysis of cumulative impacts; and either 

3. the U.S. Forest Service was a defendant (39 district opinions, 13 appellate; representing 

45 individual cases); or 

4. the case involved forest or rangeland management (exclusive of mineral exploration) 

and the Bureau of Land Management was a defendant (9 district opinions, 2 appellate; 

9 individual cases). 

The USFS and BLM were co-defendants in one case. Of the 47 district-level opinions 

examined, 10 were appealed; 5 additional appellate opinions were reviewed for which 

district-level opinions were not available. Two of the district cases were combined into 

one of the appellate cases.

At the district court level, the Forest Service received adverse decisions regarding 

cumulative impact analysis in 21 of the 45 cases, and in two other cases, the Forest 

Service prevailed on cumulative impact issues but lost on other grounds. At the appellate level, the Forest Service received adverse decisions in six of 13 cases; six of the 

lower court decisions were reversed. Overall, the Forest Service prevailed in 47 percent 

of the final cumulative impact decisions for the 45 original cases. Regions 6 (Oregon 

and Washington; involved in 29 percent of the cases) and 9 (Lake States and Northeast; 

20 percent) together accounted for nearly half of the cases. District courts under the 9th

Circuit Court of Appeals handled 70 percent of the cases.

Twenty-nine of the 53 initial BLM and USFS cases (table 3) involved Environmental 

Assessments (EAs) leading to a “Finding of No Significant Impact” (FONSI). In most 

of these cases, plaintiffs argued that the EA does not adequately demonstrate that a significant impact is not likely because either 

1. the analysis is technically invalid; 

2. it does not consider the appropriate past, present, or foreseeable future actions; or 

3. the finding of insignificance is insufficiently supported (in other words, “conclusory”).

If the EA is found to be inadequate, either it must be revised to correct its deficiencies, 

or, if evidence is compelling that the evaluated impacts may be significant, an EIS 

Table 3. Issues contested in cases involving cumulative impact analysis.

All cases (EA, EIS, or CE)	 EA	 EIS

Number Percent Agency Category Total

of of losses percent percent Number Cases Number Cases

Contested issue casesa casesb (number) lostc lostd of cases lost of cases loss

Technically inadequate analysis 45 82 25 56 45 23 11 21 14

Combined activities disregarded 36 65 23 64 42 21 13 14 10

future activities 29 53 19 66 35 16 10 13 9

present activities 21 38 14 67 25 12 7 8 7

past activities 14 25 12 86 22 7 6 7 6

Conclusory non-significance 27 49 17 63 31 20 11 6 6

Other regulations violated 26 47 15 58 27 13 6 11 8

Data insufficient or out of date 18 33 10 56 18 9 6 9 4

Mitigation inadequately supported 17 31 11 65 20 10 7 7 4

Inappropriate tiering 17 31 15 88 27 9 9 8 6

Inappropriate analysis area 13 24 7 54 13 8 4 5 3

Other views inadequately disclosed 10 18 8 80 15 3 3 7 5

Specific impact not evaluated 10 18 9 90 16 6 5 3 3

Improper segmentation 6 11 4 67 7 2 1 4 3

Overall 55 100 33 60 60 29 16 24 16

a Two cases involving both an EA and an EIS are evaluated separately for each category. 

b Percentage of the cases examined in which the issue was contested.

c

 Calculated from the number of decisions adverse to an agency on a particular issue divided by the number of cases in which the issue was 

contested (e.g., agencies received unfavorable opinions regarding analysis of future activities in 19 of the 29 cases regarding future activities, 

resulting in adverse decisions on that issue in 66 percent of those cases). d Calculated from the number of decisions adverse to an agency on a particular issue divided by the total number of cases examined (e.g., 

agencies received unfavorable opinions regarding analysis of future activities in 19 of the 55 cases, resulting in adverse decisions on that 

issue in 35 percent of the cases). 

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must be prepared—the latter was required in nearly one-third of the adverse decisions. 

Plaintiffs ultimately prevailed on cumulative impact issues in 55 percent of the EA 

cases, five of them after appeal.

Twenty-two of the cases challenged an EIS, and two others challenged both an EA 

and an EIS. Agencies ultimately prevailed on cumulative impact issues for an EIS in 

only 33 percent of these cases. The significance of a prospective impact is not itself a 

central issue in most EIS cases because lack of impact is not a requirement for proceeding with a project. Instead, adequacy of the document is based primarily on whether it 

demonstrates that the agency has the appropriate information to allow an informed decision. However, significance becomes important indirectly because an informed decision 

cannot be made if an impact was omitted from the analysis because it was incorrectly 

determined to be insignificant. Although the commonly alleged deficiencies are similar 

to those raised for EA cases, technical challenges are slightly more prevalent in EIS 

cases. If the EIS is found to be inadequate, it must be revised to correct the deficiencies.

The two remaining cases concern Categorical Exclusions (CE), and these decisions 

focus on whether the planned activity fits the criteria needed to allow the activity to 

proceed without further NEPA documentation. Categorical Exclusions are based on an 

assumption that particular types of activities usually do not generate impacts and so 

usually do not require impact analysis. However, the Forest Service Handbook indicates that in some cases the generalization does not apply (FSH 1909.15 ch. 30.3.3). 

Excluded activities thus must be screened to ensure that the particular application of the 

activity will be as benign as expected, and if this initial evaluation suggests that the specific implementation of the activity may be problematic, additional analysis is required. 

Cumulative impact arguments can become important in such cases if the exclusion is 

being challenged on the basis of potential cumulative impacts.

Overall, the two most common complaints are inadequate technical evaluation and 

inadequate consideration of the impacts of other past, present, or future actions. Even 

though courts generally accord agency experts deference in technical issues, plaintiffs 

prevailed in 56 percent of the cases in which the quality of the technical evaluation 

was in question. The most common technical inadequacies are conclusory assessments 

unsupported by evidence and reliance on models that had not been validated for the 

conditions present. In addition, data were alleged to be insufficient or out of date in 

one-third of the cases, and plaintiffs prevailed in 56 percent of the cases in which data 

sufficiency was challenged.

Plaintiffs also prevailed in 64 percent of the cases in which adequacy of the evaluation of impacts from past, present, or reasonably future activities was at issue. The 

most frequent flaw in this category was the failure to include analysis of specific future 

actions that either (1) would follow logically from the proposed action (such as maintenance activities that necessarily follow if a particular activity is initiated) or (2) were 

already proposed and could have impacts that would overlap with those of the proposed 

activity. Analyses were generally considered flawed if past or future actions were simply listed or if activities on other ownerships were ignored.

The need to evaluate interactions between the effects of the proposed project and 

those of reasonably foreseeable future projects was carefully distinguished from the 

need to avoid improper segmentation of analyses: projects that are themselves “cumulative,” “similar,” or “related” need to be combined under a single NEPA document 

to avoid obscuring potential interactions between impacts. Courts generally provided 

agencies with the discretion to determine which projects should be combined for consideration in a single EA or EIS. However, even when segmentation was found to be 

justifiable, the individual projects needed to be evaluated as reasonably foreseeable 

future projects in each others’ EA or EIS—cumulative impact analysis could not be 

avoided by preparing multiple documents.

The third most common issue of contention was lack of support for determinations of 

non-significance. This issue was most common in EA litigation because a FONSI cannot 

be obtained unless the project will have no significant impact, but an EIS must also demonstrate non-significance for particular impacts if further analysis is not to be provided 

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for those impacts. Findings of non-significance were determined to be inadequately supported for particular impacts in all six EISs for which the issue was raised.

Assessment of the effectiveness of mitigation becomes important in EAs if a potentially significant impact is found that must be mitigated to insignificance in order to 

obtain a FONSI. The effectiveness of mitigation thus was contested in 34 percent of the 

EA cases. Here, too, agency analyses tended to prevail unless no evidence was provided 

for mitigation effectiveness.

Twenty-seven percent of the documents were found to be flawed in part because 

they were tiered to other documents that were either outdated, incomplete, or were not 

themselves NEPA documents. “Tiering” under NEPA refers to the common practice of 

incorporating the findings of a more general NEPA document—such as an EIS for a 

Forest Plan—into a project-specific NEPA document to avoid duplication of effort. With 

tiering, the NEPA document can simply state that a particular analysis was carried out 

in an earlier NEPA document that has already undergone review; the earlier analysis is 

then not subject to additional review. However, an EA or EIS cannot tier to a document 

that has not already been reviewed under NEPA. Information from non-NEPA documents, such as watershed analyses and published papers, is expected to be used in an 

EIS or EA, but the NEPA document applies the information to the specific project in 

question. The apparent importance of tiering as a legal issue may in part reflect post hoc

rationalizations for why analyses of particular issues were not included in an EIS or EA.

The area selected for the cumulative impact analysis was at issue in 24 percent of 

the cases. For this issue, too, courts are strongly inclined to defer to agency judgment 

unless the decision is not explained or clearly conflicts with legislative intent. Agencies 

lost on this issue, for example, if the analysis area was shown to exclude a potentially 

significant impact to which the planned activity would contribute.

Courts’ Requirements for Valid Analyses

The most common flaws identified by federal courts in cumulative impact analyses 

prepared by federal land management agencies are similar to those found in privatesector analyses in northwest California In both contexts, misunderstandings of the 

definition of cumulative impacts and inappropriate evaluations of significance and mitigation effectiveness are common, as are technical errors. For many of the problem areas, 

courts have described the standards expected of a valid analysis as they explained why 

particular analyses are inadequate. Such instructions from an appellate court are held 

as precedent-setting by district courts in the same circuit (for example, a California or 

Idaho District Court would apply the standards set by the 9th Circuit Court of Appeals), 

and are also often cited by appellate courts in other circuits (for example, 9th Circuit 

decisions regarding cumulative impact analysis are often cited as a basis for opinions 

in other Circuits where such cases are uncommon). District-level opinions, in contrast, 

do not establish precedent and are rarely cited, but are useful indicators of how the 

precedents set by appellate courts are being applied.

General Standards for Evaluation

Cases concerning documentation required by NEPA are usually evaluated according 

to standards set by the Administrative Procedure Act. The Supreme Court described 

what constitutes a violation of that Act: “Normally, an agency rule would be arbitrary 

and capricious if the agency has relied on factors which Congress has not intended it 

to consider, entirely failed to consider an important aspect of the problem, offered an 

explanation for its decision that runs counter to the evidence before the agency, or is so 

implausible that it could not be ascribed to a difference in view or the product of agency 

expertise” (Motor Vehicle Mfrs. Assn. v. State Farm Mutual, 463 U.S. 29, Supreme 

Court 1983). Courts further indicate that an agency decision is not valid if it “is contrary 

to the governing law” (Lands Council v. Powell, 379 F.3d 738, 9th Cir. 2004), and that 

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agency expertise need not be accorded deference if there is a “clear error of judgment” 

(Kern v. BLM, 284 F.3d, 9th Cir. 2002). In Earth Island Inst. v. USFS (351 F.3d 1291, 9th

Cir. 2003) the 9th Circuit Court of Appeals noted that factual errors, too, may undermine 

agency discretion if it can be shown that an agency “unreasonably relied upon inaccurate data,” because of the requirement that “Agencies shall insure the professional 

integrity, including the scientific integrity, of the discussions and analyses in environmental impact statements” (40 C.F.R. § 1502.24). Barring such conditions, however, 

courts generally defer to agency personnel on technical issues.

The governing laws in most litigation regarding USFS cumulative impact analyses include NEPA, the National Forest Management Act, the Endangered Species Act, 

and occasionally the Clean Water Act. Under NEPA, agencies are required to take a 

“hard look” at the environmental consequences of planned actions to ensure that agency 

decisions are fully informed. Litigation thus commonly focuses on whether agency personnel “abused their discretion” by approving a NEPA document that failed to “take a 

hard look” at environmental impacts.

Overall Analysis

Several appellate opinions discuss the types of information needed in cumulative impact analyses under NEPA. The 9th Circuit Court of Appeals explained, “To ‘consider’ 

cumulative effects, some quantified or detailed information is required. Without such 

information, neither the courts nor the public, in reviewing the Forest Service’s decisions, can be assured that the Forest Service provided the hard look that it is required to 

provide...general statements about ‘possible’ effects and ‘some risk’ do not constitute a 

‘hard look’ absent a justification regarding why more definitive information could not 

be provided” (Neighbors of Cuddy Mountain v. USFS, 137 F.3d 1372, 9th Cir. 1998).

Courts frequently stress the intended utility of the analysis: “The cumulative impact 

analysis must be more than perfunctory; it must provide a ‘useful analysis of the cumulative impacts of past, present, and future projects’ ” (Kern v. United States Bureau 

of Land Mgmt. 284 F.3d 1075, 9th Cir. 2002). And again, “The EIS must analyze the 

combined effects of the actions in sufficient detail to be ‘useful to the decisionmaker in deciding whether, or how, to alter the program to lessen cumulative impacts’ ” 

(Muckleshoot Indian Tribe v. USFS, 177 F.3d 800, 9th Cir. 1999).

The 1985 decision for Fritiofson v. Alexander (772 F.2d 1225, 5th Cir. 1985, reversed on other grounds by Sabine River Auth. v. Dep’t of the Interior, 951 F.2d 669, 

5th Cir. 1992) explained, “Given the CEQ regulations, it seems to us that a meaningful 

cumulative-effects study must identify:

1. the area in which the effects of the proposed project will be felt;

2. the impacts that are expected in that area from the proposed project;

3. other past, present, and reasonably foreseeable actions that have or are expected to 

have impacts in the area;

4. the impacts or expected impacts from these other actions; and

5. the overall impact that can be expected if the individual impacts are allowed to 

accumulate.”

This list was subsequently cited by the DC. Circuit Court of Appeals in Grand 

Canyon Trust v. FAA (290 F.3d 339, DC Cir. 2002) and by district courts in the 1st, 2nd, 

4th, 5th, and 11th Circuits.

Past, Present, and Reasonably Foreseeable Future Actions

Several decisions provide insight into requirements for evaluating the effects of other 

actions. According to the 9th Circuit, for example, “The general rule under NEPA is that, 

in assessing cumulative effects, the Environmental Impact Statement must give a sufficiently detailed catalogue of past, present, and future projects, and provide adequate 

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analysis about how these projects, and differences between the projects, are thought to 

have impacted the environment” (Lands Council v. Powell, 379 F.3d 738, 9th Cir. 2004).

A district court opinion pointed out, in addition, that because the cumulative impact 

is the overall impact, the aggregate impact of past, present, and future actions would 

need to be evaluated (EPIC v. Blackwell, no. C-03-4396 EMC, N. Dist. California 

2004). This comment underscores the central point of cumulative impact analysis: the 

cumulative impact on a resource is the overall anthropogenic impact experienced by the 

impacted resource.

The CEQ has recently provided additional guidance on this issue (Connaughton 

2005), noting that a listing of individual past, present, and future projects is not necessarily required because it is the aggregate effect of projects that is important. However, 

individual projects would still need to be identified “if such information is necessary 

to describe the cumulative effect of all past actions combined.” Courts are explicit in 

indicating that the present condition, representing an existing aggregated impact level, 

cannot be interpreted as the condition against which the cumulative level of impact is to 

be judged (see, for example, Grand Canyon Trust v. FAA, 290 F.3d 339, D.C. Cir. 2002). 

Instead, the current condition would need to be compared to the naturally occurring condition to identify the current and likely future levels of impact: the CEQ specifies that 

a description of the “baseline” condition of the resource of concern “should include a 

description of how conditions have changed over time and how they are likely to change 

in the future without the proposed action” (CEQ 1997). For example, the significance 

of a project’s addition of 50 t yr-1 km-2 of sediment to an existing sediment load of 800 

t yr-1 km-2 can be interpreted only if the naturally occurring sediment load is estimated. 

If the natural load were itself 800 t yr-1 km-2, the cumulative post-project input of 6 percent over the natural background load would not likely be significant. In contrast, if the 

natural load were originally 30 t yr-1 km-2 and other human activities had already raised 

the pre-project load to 800 t yr-1 km-2, the cumulative post-project input of about 2,700 

percent over the natural background load would be highly significant. In the latter case, 

the existing aggregated impact level at the time of the project would already be about 

2,600 percent over naturally occurring levels, and the project would add further to an 

already significant cumulative level of impact.

Information concerning individual past projects also may be needed to allow prediction of a project’s direct and indirect impacts (Connaughton 2005), which then provides 

the basis for analyzing the project’s contribution to the cumulative impact. This is the 

function noted by the 9th Circuit’s opinion in Lands Council v. Powell (379 F.3d 738, 9th

Cir. 2004) regarding the need to “...provide adequate analysis about how these projects, 

and differences between the projects, are thought to have impacted the environment,” 

and by an opinion from a district Court: “While this argument [assessing current aggregated impact levels without identifying activities that contributed to the current levels] 

may have some validity in that current conditions will obviously reflect in some measure the effects of past environmental degradation, it ignores the failure of the Whiskey 

South EA to discuss in sufficient detail the connection between prior activities and 

the current project, which is critical to understanding what alternatives may produce 

the least environmental harm while still meeting project goals” (Idaho Conservation 

League v. Bennett, CV 04-447-S-MHW, District of Idaho, 29 Apr 2005). Unless the 

projects that led to existing impacts are identified and their characteristics are contrasted 

with those of the proposed project, it is difficult to support an argument that the outcome 

from proposed activities will be different than in the past.

Incorporation of Professional Opinion

Courts do not consider simple reliance on professional judgment to be adequate—

decisions based on expert opinion are considered “conclusory” unless some supporting 

evidence is provided. The 9th Circuit explained the limitations of professional judgment: 

“...allowing the Forest Service to rely on expert opinion without hard data either vitiates a plaintiff’s ability to challenge an agency action or results in the courts second 

guessing an agency’s scientific conclusions. As both of these results are unacceptable, 

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we conclude that NEPA requires that the public receive the underlying environmental 

data from which a Forest Service expert derived her opinion. In so finding, we note 

that NEPA’s implementing regulations require agencies to “identify any methodologies 

used and ... make explicit reference by footnote to the scientific and other sources relied 

upon for conclusions” used in any EIS statement. 40 C.F.R. § 1502.24.” (Idaho Sporting 

Congress v. Thomas, 137 F.3d 1146, 9th Cir. 1998; internal citations omitted). In contrast, when the basis for the expert opinion is documented and supporting evidence is 

provided, courts routinely defer to the opinions of agency experts on technical matters 

(for example, Shenandoah Ecosystems Defense Group v. USFS, 144 F. Supp. 2d 242, 

W. Dist. Virginia, Harrisonburg Div., 2001).

Courts have also indicated the importance of disclosing and discussing reasonable 

opposing opinions or alternative interpretations: “...the court should ‘ensure that the 

statement contains sufficient discussion of the relevant issues and opposing viewpoints 

to enable the decisionmaker to take a ‘hard look’ at environmental factors, and to make 

a reasoned decision’” (Natural Resources Defense Council v. Hodel, 865 F.2d 288, D.C. 

Cir. 1988; and Izaak Walton League of America v. Marsh, 655 F.2d 346, D.C. Cir. 1981).

Reliance on Modeling

Courts often find expert opinion to be inadequately supported if the experts have relied on modeling tools that have not been validated for the particular areas or conditions 

to which they were applied. In a recent case, the 9th Circuit noted, “The Forest Service, 

granted appropriate deference, still does not demonstrate the required reliability of 

the spreadsheet model. We are asked to trust the Forest Service’s internal conclusions 

of the reliability of the spreadsheet model when the Forest Service did not verify the 

predictions of the spreadsheet model. Under the circumstances of this case, the Forest 

Service’s basic scientific methodology, to be reliable, required that the hypothesis and 

prediction of the model be verified with observation” (Lands Council v. Powell, 379 

F.3d 738, 9th Cir. 2004).

The same decision explained that “NEPA requires that the Environmental Impact 

Statement contain high-quality information and accurate scientific analysis. 40 C.F.R. § 

1500.1(b). If there is incomplete or unavailable relevant data, the Environmental Impact 

Statement must disclose this fact. 40 C.F.R. § 1502.22.” On this basis, the court also 

found the use of a model relating hydrologic change to increased sedimentation to be 

inappropriate: “The Forest Service’s heavy reliance on the WATSED model in this case 

does not meet the regulatory requirements because there was inadequate disclosure that 

the model’s consideration of relevant variables is incomplete. Moreover, the Forest 

Service knew that WATSED had shortcomings, and yet did not disclose these shortcomings until the agency’s decision was challenged on the administrative appeal. We hold 

that this withholding of information violated NEPA, which requires up-front disclosures 

of relevant shortcomings in the data or models.”

Assessing Impact Significance

Conclusory statements are particularly prevalent in findings that impacts will not be 

significant. Accordingly, the 9th Circuit stressed that “An agency’s decision not to prepare an EIS will be considered unreasonable if the agency fails to supply a convincing 

statement of reasons why potential effects are insignificant” (Save the Yaak Committee 

v. Block, 840 F.2d 714, 9th Cir. 1988).

In assessments of significance, courts frequently refer explicitly or implicitly to the 

CEQ definition of cumulative impact to determine whether the intent of the regulation 

is being met. For example, a district court in Ohio found that a Forest Service analysis of significance did not actually address cumulative impacts: “...The Forest Service 

considers the following statement to be cumulative impact analysis: ‘If the 150 bats 

wintering on the Forest were to be lost for any reason, over 99.9 percent of the total population would remain unaffected.’ This is not cumulative impact analysis. The Forest 

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Service fails to acknowledge whether all of the other federal agencies with populations 

of Indiana bats present take such a cavalier attitude toward the preservation and recovery of the species. If each National Forest, National Refuge, National Park, and other 

federal lands does take such an attitude, then the effects are truly significant and, in layman’s terms, catastrophic... ” (Buckeye Forest Council v. United States Forest Service, 

No. 1:04-Cv-259, S. Dist. Ohio, W. Div., 2004). The Forest Service analysis was clearly 

inconsistent with the CEQ definition: “...Cumulative impacts can result from individually minor but collectively significant actions....”

Legal opinions provide additional guidance concerning the standards against which 

significance is to be assessed. For example, the Forest Service had argued in an EA that 

sediment inputs from salvage logging following a wildfire would be insignificant because they would be small compared to those caused by the fire. The Court responded, 

“Whether the increased erosion from logging and roadbuilding is smaller or larger than 

that produced by the fire is irrelevant. The proper evaluation should identify the impact 

of the increased sediment from the logging and roadbuilding on the fisheries habitat 

in light of the documented increases that already have resulted from the fire” (Blue 

Mountains v. Blackwood, 161 F.3d 1208, 9th Cir. 1998).

Similarly, defendants in a case not included in the present survey argued that the 

relevant standard against which to evaluate the significance of an impact is the current 

condition, the “no-action alternative.” By doing so, they found that the proposed project 

would not provide a significant increase in impact over existing levels. The court, however, held the argument untenable, reaffirming that significance is to be evaluated for 

the overall impact and not for the incremental addition caused by the project: “Because 

there is no analysis of cumulative noise impact on the Park against which the additional 

noise impact of the replacement airport can be evaluated, the FAA’s error in ignoring 

cumulative impact of man-made noise is not harmless...for the FAA has impermissibly 

taken ‘a foreshortened view of the impacts which could result from the act’ of constructing the replacement airport” (Grand Canyon Trust v. FAA, 290 F.3d 339, D.C. Cir. 

2002).

Once the overall impact level is evaluated, assessment of the significance of that 

impact level must then take into account both the context of the impact and its intensity, 

and regulations identify particular aspects of intensity that should be considered (40 

CFR 1508.27). As noted by the regulations (table 4), other governing legislation may establish specific criteria for significance. For example, if a waterway is listed as impaired 

Table 4. Factors to consider for evaluating impact “significance” under NEPA (40 CFR 1508.27).

(a) Context. This means that the significance of an action must be analyzed in several contexts, such as society as a whole (human, 

national), the affected region, the affected interests, and the locality. Significance varies with the setting of the proposed action. For 

instance, in the case of a site-specific action, significance would usually depend upon the effects in the locale rather than in the world 

as a whole. Both short- and long-term effects are relevant.

(b) Intensity. This refers to the severity of impact. Responsible officials must bear in mind that more than one agency may make decisions 

about partial aspects of a major action. The following should be considered in evaluating intensity

(1) Impacts that may be both beneficial and adverse. A significant effect may exist even if the Federal agency believes that on balance 

the effect will be beneficial.

(2) The degree to which the proposed action affects public health or safety.

(3) Unique characteristics of the geographic area such as proximity to historic or cultural resources, park lands, prime farmlands, 

wetlands, wild and scenic rivers, or ecologically critical areas.

(4) The degree to which the effects on the quality of the human environment are likely to be highly controversial.

(5) The degree to which the possible effects on the human environment are highly uncertain or involve unique or unknown risks.

(6) The degree to which the action may establish a precedent for future actions with significant effects or represents a decision in 

principle about a future consideration.

(7) Whether the action is related to other actions with individually insignificant but cumulatively significant impacts. Significance exists 

if it is reasonable to anticipate a cumulatively significant impact on the environment. Significance cannot be avoided by terming an 

action temporary or by breaking it down into small component parts.

(8) The degree to which the action may adversely affect districts, sites, highways, structures, or objects listed in or eligible for listing in 

the National Register of Historic Places or may cause loss or destruction of significant scientific, cultural, or historical resources.

(9) The degree to which the action may adversely affect an endangered or threatened species or its habitat that has been determined to 

be critical under the Endangered Species Act of 1973.

(10) Whether the action threatens a violation of Federal, State, or local law or requirements imposed for the protection of the 

environment.

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under section 303(d) of the Clean Water Act, the impact level is already deemed significant by regulatory agencies.

Effectiveness of Mitigation

If an impact being evaluated in an EA is potentially significant, plans often include a 

mitigation program to reduce the overall impact to insignificant levels, and this practice 

creates additional analytical challenges because the document must then evaluate the effectiveness of mitigation (FSH 1909.15, Ch.10.15). Courts then may need to determine 

whether the mitigation plans are indeed adequate to ensure that impacts will be insignificant: “In evaluating the sufficiency of mitigation measures, we consider whether 

they constitute an adequate buffer against the negative impacts that may result from the 

authorized activity. Specifically, we examine whether the mitigation measures will render such impacts so minor as to not warrant an EIS” (National Parks and Conservation 

Association v. Babbitt, 241 F.3d 722, 9th Cir. 2001).

A District Court opinion further indicates the kind of analysis considered appropriate: “BLM...relied entirely upon future permits and mitigation plans in determining that 

these impacts would not be significant.... The mitigation measures must be ‘developed 

to a reasonable degree,’ however, and neither a ‘perfunctory description’ nor a ‘mere 

listing’ of measures, in the absence of ‘supporting analytical data,’ is sufficient to sustain a finding of no significant impact” (Western Land Exchange Project v. BLM, 315 

F. Supp. 2d 1068, Dist. Nevada 2004; internal citations omitted). The same opinion also 

notes that BLM intended to institute a monitoring program to determine the nature of 

likely impacts and plan future mitigation efforts, but “Where research is necessary to 

determine the extent of an unknown and possibly significant environmental risk, an EIS 

should be prepared so that the research can be done and the decision made in reliance 

on that information, rather than the other way around....BLM’s reliance on an unwritten, 

untested, and unsupported monitoring plan in the face of unknown and possibly significant environmental impacts does not excuse its decision to forego an EIS” (internal 

citations omitted).

Courts also have noted that the timing of mitigation is important if impacts are to be 

reduced to insignificance. In Klamath-Siskiyou Wildlands Center v. USFS (no. Civ. S 

03-1334 FCD DAD, N. Dist. California 2004), mitigation work was scheduled after the 

planned logging, so the near-term impacts of logging on runoff would not be offset by 

mitigation: “The fact remains, however, that short term impacts to the watershed will 

occur, and those impacts appear significant and highly uncertain. Neither the net long 

term benefits of the program, nor the risk associated with not implementing the project, 

relieve the Forest Service of its duty to conduct an EIS when the project will have significant environmental impacts. 40 C.F.R. §1508.27(a).”

Conclusions

As federal courts repeatedly note, the role of NEPA documents is to demonstrate that 

there has been a “hard look” taken at the potential impacts of a project and that those impacts are understood well enough that surprises are unlikely. It is then the responsibility 

of agency personnel to decide how to use the resulting information: “NEPA merely prohibits uninformed—rather than unwise—agency action” (Robertson v. Methow Valley 

Citizens Council, 490 U.S. 332, Supreme Court 1989). Given the guidance provided 

by the CEQ and the federal courts, it is clear that the preparation of a useful cumulative 

impact analysis is not unduly complicated or onerous (“NEPA does not require the government to do the impractical” Inland Empire Public Lands Council v. USFS, 88 F.3d 

754, 9th Cir. 1996).

Much of the confusion surrounding analysis of cumulative watershed impacts for forest management applications appears to arise from misunderstandings of the nature of 

cumulative impacts. In this context, “cumulative” simply means “total” or “combined”; 

Leslie M. Reid Cumulative Watershed Effects of Fuel Management in the Western United States
296 USDA Forest Service RMRS-GTR-231. 2010.

a directive to evaluate the cumulative impact on a resource simply means that the overall 

impact on that resource is to be assessed. The influence of an individual project is then 

evaluated as the extent to which that project will augment or diminish the overall impact 

level for the resource. Such an analysis would take into account potential interactions between environmental changes caused by the project and by past, present, and reasonably 

foreseeable future projects. Spatial and temporal scales for analysis would be determined 

by the spatial and temporal scales at which potential impacts would be expressed, and 

would vary by impact. Similarly, the level of quantitative rigor employed would be selected to be appropriate for the context and issues present.

Such an approach might be facilitated by rephrasing the underlying question from 

“What are the cumulative impacts of the project?” to “What are the impacts of concern 

in the area, and how might the proposed project influence those impacts?” With this reformulation, the focus is shifted to specific impacts, those impacts are defined from the 

perspective of the impacted resources, and the problem becomes recognizable as one that 

agency resource specialists already know how to address.

Most of the problems encountered with the private-sector and agency analyses that 

were examined would have been avoided had the analyses been subject to rigorous technical review and had the procedure outlined by CEQ (1997) been followed. The analysis 

steps required for such an evaluation have already been carried out to some extent if a 

watershed analysis is available for the area in question. Such analyses should already 

outline the impacts of concern and their severity, distribution, and causal mechanisms. 

Watershed analysis carried out under the Northwest Forest Plan (REO 1995), for example, accomplishes steps 1, 2, 3, 4, 6, 7, and 8 of the CEQ procedure outlined in table 1. 

Although a project-based NEPA document cannot simply state that cumulative impacts 

have already been analyzed through watershed analysis (in other words, it cannot “tier” 

to a watershed analysis), it can take advantage of the analytical work already done by 

watershed analysis in the same way that it makes use of other scientific literature, as long 

as the “...study is reasonably available to the interested public” (Connaughton 2005). The 

increment added by the NEPA document would then evaluate how the particular project 

influences the mechanisms and impacts already evaluated by the watershed analysis. This 

approach has the added advantage of efficiency: a single watershed analysis can provide 

the background information necessary for analyzing the cumulative watershed impacts 

of any number of projects occurring within the watershed. The most useful route to development of effective cumulative impact assessments for federally managed forestlands 

may be through adaptation of the watershed analysis procedure to more consistently 

provide the information that will be needed by future cumulative impact analyses.

Whatever procedure is used for analysis, three issues remain that are of particular 

importance. First, more guidance would be useful for assessing the significance of impacts. The CEQ has provided a list of factors to be considered to assess significance 

(table 4) and calls for evaluating the capacity of a resource to withstand additional 

change, but the ultimate determination of significance is often a value-based decision. 

Development of a defensible procedure for making such determinations would simplify 

future analyses. Second, the information needed to determine whether past analyses 

provided accurate predictions is not available. A study to compare on-the-ground outcomes with predicted impact levels would be useful, as would a program to monitor the 

accuracy of future analyses. Only through such work can analytical procedures, mitigation, and management practices be improved. Finally, and perhaps most importantly, the 

quality of any analysis ultimately depends on the expertise and technical knowledge of 

those preparing the analysis.

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Connaughton, J.L. 2005. Guidance on the consideration of past actions in cumulative effects 

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Workshop Participants and 

First Round Reviewers (2006)

Name Title Affiliation

Adams, Paul Extension Watershed Specialist Oregon State University

Audin, Lisa Stewardship Coordinator University of Idaho

Bailey, Robert Geographer WO

Condrat, Charlie Hydrologist R4

Conroy, Bill Hydrologist WSU

Contreras, Glen Fisheries Research Scientist WO

Curran, Mike Research Soil Scientist BC Ministry of Forestry

Decker, Lynn Director US Fire Learning Network The Nature Conservancy

DeHart, Sharon Soil Scientist R1

Dumroese, Debbie Project Leader RMRS

Dwire, Kate Research Riparian Ecologist RMRS

Elder, Kelly Research Hydrologist RMRS

Elliot, Bill Project Leader RMRS

Entwistle, Deb Forest Hydrologist R2

Flood, Paul Soil Scientist R4

Foltz, Randy Research Engineer RMRS

Furniss, Mike Hydrologist PNW Station

Graham, Russ Research Forester RMRS

Hyde, Kevin Hydrologist RMRS

Jain, Terrie Research Forester RMRS

Jurgenson, Marty Professor Michigan Tech University

Kershner, Jeff Center Director USGS

Knopp, Chris Forest Supervisor R3

LaFayette, Russell Regional Hydrologist R9

Lewis, Lisa A. Soil Scientist WO, National Riparian Service Team

Link, Tim Academic Faculty University of Idaho

Luce, Charlie Research Hydrologist RMRS

Matthews, Susan Forest Supervisor R8

MacDonald, Lee Professor Colorado State University

McCammon, Bruce Regional Hydrologist R6

McCormick, Frank AWAE Program Manager RMRS, AWAE

McKean, Jim Research Geomorphologist RMRS

Neary, Dan Project Leader RMRS

Nelson, Rodger Fisheries Biologist R4

Potyondy, John Program Manager RMRS, StreamTeam

Reid, Leslie Research Geologist PSW

Rhodes, Chuck Research Biochemist AWAE

Rieman, Bruce Project Leader RMRS

Robichaud, Pete Research Engineer RMRS

Rosenberger, Amanda Fisheries Biologist RMRS

Rummer, Robert Project Leader SRS

Ryan, Doug Program Manager PNW Station

Stednick, John Professor Colorado State University

Trettin, Carl Project Leader SRS

Troendle, Chuck Research Hydrologist SI International (RMRS Retired)

Young, Mike Research Fisheries Biologist AWAE
Rocky

 Mountain

 Research Station

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and technology to improve management, protection, and use of the 

forests and rangelands. Research is designed to meet the needs of 

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forests, water, recreation, fire, resource inventory, land reclamation, 

community sustainability, forest engineering technology, multiple use 

economics, wildlife and fish habitat, and forest insects and diseases. 

Studies are conducted cooperatively, and applications may be found 

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