Evaluation of Silvicultural 

Treatments and Biomass 

Use for Reducing Fire 

Hazard in Western States

Kenneth E. Skog

R. James Barbour

Karen L. Abt

E.M. (Ted) Bilek

Frank Burch

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Paper

FPL–RP–634

Roger D. Fight

Robert J. Hugget

Patrick D. Miles

Elizabeth D. Reinhardt

Wayne D. Sheppard
May 2006

Skog, Kenneth E.; Barbour, R. James; Abt, Karen L.; Bilek, E.M. (Ted); 

Burch, Frank; Fight, Roger D.; Hugget, Robert J.; Miles, Patrick D.; Reinhardt, Elizabeth D.; Shepperd, Wayne D. Evaluation of silvicultural treatments and biomass use for reducing fire hazard in western states. Research 

Paper FPL-RP-634. Madison, WI: U.S. Department of Agriculture, Forest 

Service, Forest Products Laboratory. 29 p.

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Abstract

Several analyses have shown that fire hazard is a concern 

for substantial areas of forestland, shrubland, grassland, 

and range in the western United States. In response, broadscale management strategies, such as the National Fire Plan, 

established actions to reduce the threat of undesirable fire. 

Available budgets are insufficient to pay for vegetative 

management on all acres where fire threat is considered unacceptable. The purpose of this report is to begin to identify 

locations in the west where fire hazard reduction treatments 

have a potential to “pay for themselves” at a scale and over 

a long enough time to make investment in additional forest product processing infrastructure a realistic option. The 

resulting revenues from these activities could presumably 

subsidize treatment for other locations. Accordingly, we 

concentrate on areas where wood removed during fire hazard reduction treatments has the potential to support a forest 

products infrastructure. Areas for treatment were selected by 

the criterion where either torching or crowning is likely during wildfires when wind speeds are below 25 mph. We considered thinning treatments designed to result in either evenaged or uneven-aged stand conditions. If there are ecological limitations on basal area that is allowed to be removed 

and there is a need to obtain a certain amount of merchantable wood volume to help cover costs, then uneven-aged 

treatments appear more likely to achieve one of our hazard 

reduction targets. Thinning to maintain an uneven-aged 

structure could be more controversial because it removes 

larger trees, although the revenue from such treatment covers harvest costs more frequently than does revenue from 

thinning to maintain an even-aged structure. The removal 

of large trees by uneven-aged thinning may be reduced by 

supplementary treatments to increase torching index rather 

than thinning to reach a high crowning index. Treatments 

analyzed would treat 7.2 to 18.0 million acres, including 0.8 

to 1.2 million acres of wildland urban interface area, and 

would provide 169 to 640 million oven-dry tons of woody 

biomass (e.g., main stem, tops, and limbs). About 55% of 

biomass would be from sawlogs. Sixty to 70% of acres to 

be treated are in California, Idaho, and Montana. To prepare 

an example estimate of annual harvest amount for the 12 

selected western states, we assume acres needing treatment 

are divided into two parts of equal area. For half the acres, 

an uneven-aged treatment would be applied if at least 300 

ft3 of merchantable wood is removed; for the other half, an 

even-aged treatment would be applied if at least 300 ft3 of 

merchantable wood is removed. Under this scenario, treatment of 0.5 million acres/year would generate 14.6 million 

oven-dry tons of biomass per year or about 29% of the current level of roundwood removals for the selected states. 

Keywords: hazardous fuel reduction, simulation, FIA data, 

biomass utilization, harvesting costs, western states

SI conversion factors

Inch–pound unit Conversion factor SI unit

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

cubic foot (ft3) 0.0283 cubic meter (m3)

mile 1.61 kilometer (km)

Contents

Page

Introduction..........................................................................1

Methods................................................................................2

 Screens for Determining Plots Eligible for Treatment,

 and Plots Receiving Simulated Treatment.......................2

 Fire Hazard Reduction Objectives and Assumptions.......3

 Silvicultural Objectives and Assumptions.......................6

 Estimation of Harvesting Costs .......................................8

 Estimation of Product Revenue .......................................9

 Computations and the Fuel Treatment Evaluator.............9

Findings................................................................................9

 Areas Treated ...................................................................9

 Fire Hazard Reduction ................................................... 11

 Biomass Removed ......................................................... 12

 Composite Treatment With Thinning Over an 

 Extended Period............................................................. 18

 Treatment Costs and Biomass Revenues....................... 21 

Biomass Removal Maps .................................................... 24

 Results From Thinning Treatments Given Alternate 

 Assumptions................................................................... 26

 Concluding Remarks...................................................... 27

References.......................................................................... 28

Acknowledgments

This study was supported by USDA Forest Service National 

Fire Plan Research Project 02.FPL.C.1, Developing Tools to 

Assess Economic Feasibility of Processing Wood Removed 

in the Course of Hazardous Fuels Reduction. We thank 

Kevin McCullough, Forest Service Northern Research 

Station, for preparing the maps for this publication.
are effective fire hazard reduction treatments that would 

tend to produce more merchantable timber. 

• The existing infrastructure for wood product manufacturing is suited to process the kinds of materials 

removed.

• There is a realistic potential to establish new 

infrastructure.

• The political climate is favorable toward these activities. 

Our analysis is intended to cover aspects of each of these 

criteria. To aid agencies to refine a cohesive strategy for reducing fuels, our assessment is intended to show where and 

by how much mechanical treatments that remove woody 

biomass could potentially cover costs of hazardous fuel 

reduction treatments. This knowledge could help determine 

which treatment strategies should be applied in various locations across the West. 

Our study focuses on evaluating treatments to reduce fire 

hazard on timberland (versus other forest land), covers all 

ownerships, and identifies locations likely to have a higher 

proportion of trees that may be used for higher value products, which may help offset treatment costs. The 12 western 

states assessed in this study (see footnote to Table 1) have 

127 million acres of timberland and 77 million acres of other forest land (Miles 2006). Part of our intent is to identify 

large areas where wood supply could sustain businesses to 

use biomass from thinning. We focus on timberland, where 

the value of products is more likely to cover treatment costs. 

While other forest land has hazardous fuels and wood from 

treatments can provide higher value products, the volume 

and value per acre is very likely to be lower in relation to 

treatment costs than it is for timberland. Treatments of other 

forest land may provide an average 7 oven-dry tons (odt) of 

Timberland is forest land capable of producing in excess of 20 ft3

of wood per acre per year at culmination of mean annual increment 

(age where annual growth is greatest) and is not withdrawn from 

timber utilization by statute or administrative regulation. Other 

forest land is not capable of supporting this level of growth.

Introduction

Fire hazard is unacceptably high on many acres of forest 

land in the U.S. West. For some of these acres, mechanical treatments are a way to reduce fire hazard. A cohesive 

strategy is needed for identifying the long-term options and 

related funding needed to reduce fuels (GAO 2005a). Given 

limited government budgets, one approach is to identify 

places where the use of woody biomass from thinning can 

best help pay for hazardous fuel reduction treatments and 

to use this information to aid in allocating funds for all 

types of hazardous fuel reduction treatments. This allocation process would direct funds available for prescribed fire, 

mastication, hand or machine pile and burn, and thinning 

to where they could accomplish the most in terms of verifiable fire hazard reduction. Ultimately, we want to identify 

areas that are large enough to support commercial-scale 

wood processing options based on an objectively defined 

fire hazard reduction program. This will allow funding for 

other types of treatments to be concentrated in areas where 

the removal and sale of wood is not the most appropriate 

solution to the threat of fire. As a result, this analysis is not 

intended to identify every acre where treatments might “pay 

for themselves,” but rather to provide a strategic insight into 

the scope and scale of the potential to use wood removals to 

finance activities in broad geographic regions. 

We do not attempt to identify all acres where removal of 

woody biomass would improve resilience to undesirable fire 

effects nor did we set out to demonstrate that if this were 

done enormous volumes of wood materials could be collected, which is known to be true. We focus only on areas in 

surface and mixed severity fire regime forests, where treatments are needed to reduce fire hazard. We do not attempt to 

include areas that may need treatment for other reasons, and 

our results should not be taken to include all areas that may 

need thinning treatments.

Our analysis began with several assumptions: 

• Some forest types and geographic locations are better 

suited to our alternate thinning strategies because they 

Evaluation of Silvicultural Treatments and 

Biomass Use for Reducing Fire Hazard in 

Western States

Kenneth E. Skog,1 R. James Barbour,2 Karen L. Abt,3 E.M. (Ted) Bilek,1 Frank Burch,4 Roger D. Fight,2

Robert J. Hugget,3 Patrick D. Miles,5 Elizabeth D. Reinhardt,6 and Wayne D. Shepperd7

1UDSA Forest Service, Forest Products Laboratory, Madison, Wisconsin

2USDA Forest Service, Pacific Northwest Research Station, Portland, Oregon

3USDA Forest Service, Southern Research Station, Research Triangle Park, North Carolina

4USDA Forest Service, Forest Management Staff, Washington, DC 

5USDA Forest Service, North Central Research Station, St. Paul, Minnesota

6USDA Forest Service, Rocky Mountain Research Station, Missoula, Montana

7USDA Forest Service, Rocky Mountain Research Station, Ft. Collins, Colorado
Research Paper FPL–RP–634

2

Methods

The primary data for this assessment were plot-level data 

compiled by the Forest Inventory and Analysis Program 

(FIA) 2 of the USDA Forest Service (Smith and others 

2004), with additional plot information from the National 

Forest System. The design of the FIA plot system is intended to provide an error of no more than ±3% with 95% confidence for estimates of an area of 1 million acres. Estimates 

of larger areas would have a lower percentage of error. Each 

plot represents a forest area of about 3,400 acres. The plot 

data indicate current stand conditions on all timberland in 

the West. In our analysis, the area to be treated and woody 

biomass to be removed were estimated as if the treatments 

were to be done in 1 year. In reality, the area treated and 

amounts removed would occur over many years. 

The methods are divided into the following sections: 

(1) screens for determining plot eligibility for treatment and 

plots actually receiving simulated treatment, (2) fire hazard 

reduction objectives and assumptions, (3) silvicultural objectives and assumptions, (4) estimation of harvesting costs, 

(5) estimation of product revenues and net revenues, and 

(6) computations using the Fuel Treatment Evaluator.

Screens for Determining Plots Eligible for 

Treatment, and Plots Receiving Simulated 

Treatment

Of the 126.7 million acres of timberland in the 12 selected 

western states, 23.9 million acres passed an initial screen 

and were considered eligible for treatment (Table 1). A 

second screen was applied when considering a specific silvicultural treatment, and fewer than 23.9 million acres may 

actually receive simulated treatment. 

Initial Screen

The initial screen was applied to two different groups of forest types: (1) forest types with surface or mixed severity fire 

regimes and (2) forest types with high severity fire regimes. 

Group 2 includes lodgepole pine and spruce–fir forest types. 

Group 1 contains all other forest types. 

Plots excluded from fire severity Group 1: 

• Inventoried roadless areas3

• Counties west of Cascade Mountains in Oregon and 

2The FIA program has been in continuous operation since 1928. It 

collects, analyzes, and reports information on the status and trends 

of America’s forests: how much forest exists, where it exists, who 

owns it, and how it is changing. The latest technologies are used 

to acquire a consistent core set of ecological data about forests 

through remote sensing and field measurements. The data in this 

report are summarized from about 37,000 permanent field plots in 

the western United States.

3For a map of inventoried roadless areas, see www. roadless.fs.fed.

us/maps/usmap2.shtml 

woody biomass per acre (Perlack and others 2005) in the 

12 states considered in our study compared with the 24 to 

34 odt/acre estimated for our timberland thinning treatments. We underestimate the acres that can be treated with 

net positive revenue to the extent that some portion of other 

forest area may, on average, provide biomass value in excess of treatment costs. 

This assessment consists of three phases: 

Phase I—Identify, across the West, locations where hazardous fuel reduction treatments are needed that would 

also generate substantial amounts of woody biomass for 

use that could offset treatment costs. 

Phase II—Select specific localities in the West and evaluate the current market potential for using wood and prospects for expanding specific markets to use additional 

wood material. 

Phase III—Evaluate the social acceptability of establishing and supporting the infrastructure necessary to use 

sales of wood as a means for funding fire hazard reduction within the areas identified in Phases I and II of the 

project.

This paper presents the results from Phase I. For 12 western 

states, we selected timberland acres eligible for treatment 

(determined in part by fire hazard level), applied several alternate silvicultural treatments to reduce hazard while seeking to maintain ecosystem integrity, and evaluated to what 

extent revenues from the sale of biomass may offset harvest 

costs. We compare the results of our analysis to results from 

a previous Forest Service assessment (Forest Service 2003). 

As in the assessment reported here, the 2003 Assessment estimated potential biomass removals by applying silvicultural 

treatments to plot data. Our analysis is more detailed in selecting and treating plots for fire hazard, in calculating and 

comparing harvest costs to product revenue, and in mapping 

locations of removals. 

The terms “woody biomass” and “biomass” refer to all 

wood in all trees—in the main stem, tops, and branches of 

all sizes of trees. “Merchantable wood” refers to the main 

stem of all live trees with a diameter at breast height 

(dbh) ≥5 in., from 1 ft above ground to a minimum 4-in. 

top diameter outside the bark of the central stem, or to the 

point where the central stem breaks into limbs and does not 

include rotten, missing, and form cull. We assign a higher 

value to merchantable wood ≥7 in. dbh and assign a lower 

(chip) value to merchantable wood in smaller trees and 

all sources of non-merchantable wood. Non-merchantable 

wood refers to all wood not classified as “merchantable.” 

Both merchantable wood and non-merchantable wood can 

be used for products. Note that merchantable wood can be 

used for both higher value products, such as lumber, plywood, oriented strandboard (OSB), and pulp, and for lower 

value products, such as chips for fuel. Non-merchantable 

wood is most likely to be used for low value products, but a 

small amount may be used for higher value products.
3

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

Washington, where forests have a long fire return 

interval4

• Plots with lower fire hazard; both crowning index (CI) 

and torching index (TI) >25 mph or CI alone >40 mph

Plots excluded from Group 2 (lodgepole pine and spruce–fir 

forest types):

• All plots outside wildland urban interface (WUI) areas

• Inventoried roadless areas

• Counties west of Cascade Mountains in Oregon and 

Washington, where forests have a long fire return 

interval 

• Plots with lower fire hazard (both CI and TI >25 mph 

or CI alone >40 mph)

Selected counties west of the Cascades were excluded because treatments in forests there would be designed to meet 

objectives other than fire hazard reduction, and our treatments that are designed to reduce fire hazard may not be 

designed to meet those objectives. Those forests do not tend 

to burn with surface and mixed severity fires and have long 

fire return intervals. For results when treatments are applied 

to timberland in those counties, see the section on results 

with alternate assumptions about thinning treatments.

Of the 126.7 million acres of timberland, 67.5 million acres 

(53%) have lower fire hazard by our criteria (Table 1). Of 

the remaining 59.2 million acres, 21.6 million acres (17% of 

all timberland) are in roadless areas or in excluded counties 

in Oregon and Washington. Of the remaining 37.6 million 

acres, 13.8 million acres (11% of all timberland) are in forest types with high severity fire regimes, which leaves 

23.9 million acres eligible for treatment. In total, our screens 

removed 81% of all timberland and 60% of acres with 

higher fire hazard.

4Oregon counties excluded: Benton, Clackamas, Clatsop, Columbia, Coos, Curry, Lane, Lincoln, Linn, Marion, Multnomah, 

Polk, Tillamook, Washington, and Yamhill. Washington counties 

excluded: Clallam, Clark, Cowlitz, Gray’s Harbor, Island, Jefferson, King, Kitsap, Lewis, Mason, Pacific, Peirce, San Juan, Skagit, 

Snohmish, Thurston, Wahkiakum, and Whatcom.

Second Screen

A second screen was applied when applying a specific silvicultural treatment; it determined which eligible plots actually receive simulated treatment. Plots were excluded (not 

treated) if they would not provide 300 ft3 of merchantable 

wood per acre (about 4 odt). The 300-ft3 removal requirement is to assure that the treatment could provide a minimum amount of revenue from higher value products (pulpwood, sawlogs or veneer logs as opposed to lower value 

products such as chips for fuel from small trees and branches) to meet our objective to identify treatment areas where 

product revenues are more likely to cover treatment costs. 

Previous studies have found that mechanical treatments 

that produce less than 300 ft3 of merchantable wood are 

unlikely to cover costs of the treatment (Barbour and others 

2004, Fight and others 2004). For results when treatments 

are applied to plots that would provide less than 300 ft3 of 

merchantable wood per acre, see the section on results with 

alternate assumptions about thinning treatments. 

It is certainly possible that we may have underestimated (or 

overestimated) the number of acres that could be treated 

with a positive net revenue if various assumptions are incorrect and are changed; for example, some “other” forest land 

may have significant volumes of high value wood; treatment 

is applied to some high severity fire regime forest types; 

treatment is applied to some forests west of the Cascades 

in Oregon and Washington; or prices are higher or lower 

for wood products. We suggest our screens as a reasonable 

starting point for understanding what area may be treatable 

with positive net revenue.

Fire Hazard Reduction Objectives and 

Assumptions

Selection of Plots for Treatment 

Each FIA timberland plot was assessed for fire hazard by 

estimating crowning index and torching index (Scott and 

Reinhardt 2001). Plots were selected for treatment if 

CI < 25 alone or TI < 25 mph and CI < 40 (designated 

1 hereafter as CI<25 and TI<25) (Table 2). Torching index 

Table 1—Timberland areas screened as eligible for treatment in 12 western statesa

Area (106

 acres) 

1 2 3 4 5 6 7

Forest type 

group Timberland 

Lower fire hazard 

acres in col. 1 

removed

Inventoried

roadless area in 

col. 2 removed 

Selected counties in 

Oregon and 

Washington in col. 3 

removed

Non-WUI

portion of 

col. 4 

WUI

portion of 

col. 4 

Acres eligible 

for treatment

Spruce–fir and 

lodgepole pine 

types 

32.5 23.3 15.5 14.9 13.8 1.1 1.1

col. 6 only 

Other forest 

types 94.2 35.8 30.3 22.7 21.9 0.8 22.7

col. 5 + 6 

Total 126.7 59.2 45.8 37.6 35.7 1.9 23.9 

a

Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, South Dakota, Utah, Washington, Wyoming. 
4

Research Paper FPL–RP–634

(TI) is the 20-ft aboveground wind speed at which crown 

fire can initiate in a specified fire environment; CI is the

20-ft wind speed at which active crown fire behavior is possible in that environment. For both indexes, lower values 

indicate more hazardous fuel conditions. In other words, if 

crown fire activity can occur even under low wind conditions, the stand is more vulnerable. The focus on crown fires 

is useful because, while all stands may burn under certain 

conditions, stands that are likely to burn in crown fires present particular suppression problems, and consequences of 

crown fires are more severe than those of surface fires. Plots 

with CI<25 or TI<25 were chosen for treatment because 

fires might commonly be expected to occur at wind speeds 

between 15 and 25 mph. A threshold lower than 25 mph 

would not protect all stands in this common range against 

fires. A higher threshold was not chosen because we felt 

that it unrealistic to try to protect stands against extreme 

wind speeds that seldom occur. Choosing a higher threshold 

would result in more extreme thinning treatments on individual plots. 

Assumptions for Calculating Torching and Crowning 

Indexes

Torching and crowning indexes were calculated for each 

plot based on 

• canopy fuel profile as computed from plot data, 

• slope steepness, 

• selected set of fuel moisture conditions corresponding 

to “summer drought” conditions (Rothermel 1991) 

chosen to represent average wildfire scenario, and 

• use of fire behavior fuel model 9 to represent surface 

fuels (Anderson 1982). 

Fuel model 9 is described as hardwood or long-needle pine 

litter. It was chosen not because we assume that all surface 

fuels are hardwood or long-needle pine litter, but because 

fuel model 9 results in mid-range surface fire behavior between FM 8 and 10 (other timber litter models) and 

FM 2 (timber grass model) (personal communication, Paul 

Langowski, Branch Chief, Fuels and Fire Ecology, USDA 

Forest Service, Rocky Mountain Region, 2004). 

No single fuel model can be expected to adequately represent surface fuels in all timberlands. Surface fuels tend to be 

extremely variable both within and between stands. Surface 

fuels may in fact be heavier (resulting in more extreme fire 

behavior) or lighter (resulting in less extreme fire behavior) 

in any given stand. However, no plot data exist to characterize surface fuels. Using a fuel model that results in more 

extreme fire behavior such as fuel model 10 might lead 

to recommending thinning where none is really needed to 

reduce fuel hazard, while a fuel model such as fuel model 

8 that results in very low intensity surface fires may not 

have the sensitivity to identify stands at risk of crowning. 

Fuel model 9 was used as a compromise that is conservative 

(does not recommend excessive thinning) while still sensitive to the effect of ground fuels on fire hazard. 

We also used fuel model 9 when computing TI and CI after 

thinning; that is, we assumed that the thinning treatment did 

not change the surface fuels enough to bump the fuel model 

into a higher fuel class. Again, this assumption was chosen 

to be conservative. We assume that the treatments will minimally increase surface fuels, and they will be implemented 

in such a way that this is true; for example, with whole tree 

yarding or piling and burning activity fuels.5 We also assume that the fuel treatments do not reduce surface fuels, 

because we do not want to exaggerate the effects of the 

treatments on potential fire behavior. In fact, where necessary and as determined on a project level, surface fuels may 

indeed be reduced in conjunction with the thinning activity, 

resulting in additional hazard reduction. 

Analysis of fuel hazard in this work is thus limited to canopy fuels. Surface fuels are an important component of the 

fuel conditions at any site. This analysis does not include the 

important effects of surface fuels on potential fire behavior 

for two reasons: (1) data were not available and (2) treatment under consideration is thinning, which directly affects 

canopy fuels in a consistent way. We made conservative and 

across-the-board assumptions about surface fuels. If fuel 

treatment projects are implemented in any areas identified 

by this study, detailed prescriptions will need to be developed that look at the existing surface fuels and their potential contribution to crown fire initiation, the possible need 

to treat the existing surface fuels, and the need to treat any 

activity fuels created by thinning (that is, branch material 

and non-merchantable trees). 

5Our analysis assumes minimal increase and does not allow surface 

fuels to increase in that the harvesting systems (and associated 

harvest costs) include removing thinned trees down to 1 in. dbh 

and removing tops and branches of all thinned trees with minimal 

amounts left behind.

2

Table 2—Fire hazard reduction objectives and assumptions 

x Select for treatment each plot where CI<25 or TI<25 and CI<40 

x Hazard reduction targets: Remove trees on each plot until 

o CI>25 and TI>25 or

o CI>40 (but TI<25) 

x Fuel model (ground fuels) is 9 (timberland average) and remains the same after thinning 

x Drought severity assumption: Drought summer (1 h = 4%, 10 h = 5%, 100 h = 7%, live = 78%) (Rothermel 1991) 
5

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

Targets for Crowning and Torching Indexes After 

Treatment 

The fuel hazard reduction objective for each plot was to increase TI and CI to above 25 mph or to increase only CI to 

above 40 mph. These objectives are intended to either keep 

a crown fire from starting or to prevent a crown fire from 

spreading if crowns are ignited. For some plots, data on both 

live and dead trees were used to compute CI and TI. For 

other plots, data were only available for live trees because 

older protocols had been used to collect the data. 

Effect of Treatments on Fire Hazard

Tree thinning increases TI and CI in different ways. The TI 

is increased by increasing canopy base height, so that the 

canopy fuels are further from the surface and less likely to 

be ignited by a surface fire. The CI is increased by reducing 

the canopy bulk density; that is, by making the canopy fuels 

less dense so that crown fire is less likely to “run” from tree 

to tree. 

In some cases, a stand may be very open-grown and have 

low canopy bulk density and associated high CI (low risk 

of crown fire spread), but each crown is long (may reach 

close to the ground), so canopy base height and TI are low 

(high risk of torching). In this case, even an intense level 

of thinning may not accomplish the TI objective. This situation is reflected in a number of stands in the data set. In 

these stands, the CI objective (>25 mph) can easily be met 

by limited thinning, but not the TI objective (>25 mph). For 

this situation, we increased thinning until CI was at least 

40 mph, even though TI might still be less than 25 mph. 

Removing additional trees might increase CI to a greater 

extent, but since TI would not increase correspondingly we 

judged that overall stand replacement fire hazard was not 

further reduced. 

Limits on Removal of Basal Area

In some treatment cases, we limited total basal area (BA) 

removal. One objective for limiting BA removal is to keep 

canopy closure as high as practical. Opening the canopy, 

while reducing canopy fuels, can lead to different fuel hazard problems: (1) opening the canopy exposes surface fuels 

to solar radiation and wind, which can alter surface fire 

behavior; (2) opening the canopy can lead to increased herbaceous and shrub growth, which may also change surface 

fire behavior; (3) opening the canopy can enhance conifer 

regeneration, ultimately creating ladder fuels; and (4) decreasing BA/acre in some forest types can increase the risk 

that remaining trees will be blown down by strong winds. 

We elected to use BA to drive the prescription engines used 

in the fuel treatment evaluator because it is a uniformly 

measured metric common to all forest inventory data. While 

canopy closure is more directly applicable to fire behavior, 

it is not uniformly defined and is subject to variation based 

on stem size, stocking, canopy architecture, and the methodology by which it is measured.

We also recognize that limiting removals to a 50% reduction 

in BA may not achieve the complete fuel treatment objective and may also leave some forests susceptible to epidemic 

bark beetle outbreaks. While these levels of thinning may 

reduce the potential for crown fire, they will not likely be 

sufficiently aggressive to prevent significant tree mortality 

in dry forest types during drought. However, we intend these 

treatments to be the first step in a continuing management 

process that can eventually achieve a full suite of management goals, including reducing crown fire and torching. We 

should also point out that the limitations we impose here 

are applied at the landscape and larger scales of FIA inventory data and not at smaller scales—where it is certainly 

acceptable and proper silviculture to remove the majority or 

all stocking to regenerate forests, improve wildlife habitat, 

or even provide fuel breaks. Limiting BA removals to 50% 

at the landscape scale provides ample opportunity to affect 

such changes at smaller scales. However, removing over 

half the stocking from the large forested land areas being 

considered in this effort may be both ecologically and socially ill-advised. Therefore, we feel that the stocking limits 

we have imposed here provide a reasonable estimate of 

initial fuel hazard reduction treatments that can be applied in 

western forest types. To the extent that additional objectives 

call for refinement of our treatments and more removals in 

local areas, we may be underestimating the amount of area 

that may be treated with positive average net revenue.

Long-Term Effect of Treatments on Fire Hazard 

Forest stands are dynamic, as are forest fuels. Fuel hazard 

reduction treatments were chosen to reduce torching and 

crowning indexes in the stands as they currently exist. We 

know, however, that fuel treatment effects change over 

time, and that eventually fuels will need to be retreated. Our 

ultimate goal in treating fuels is to create healthy, resilient 

stands in which fire can play its natural role. In lower elevations and drier forest types, such stands might be expected 

to burn fairly frequently, mostly in surface fires that remove 

the shrubs and excess conifer regeneration and that maintain the stand in an open condition. Canopy fuels in such 

stands will typically be elevated and sparse, and surface fuel 

loadings will be low. Subsequent fuel treatments in these 

stands might be relatively inexpensive, large, low-intensity 

prescribed fires. The necessary frequency of such treatments 

should be analyzed as part of a much more site-specific 

planning process, using tools such as FFE–FVS (Reinhardt 

and Crookston 2003) or fire history studies. 

We acknowledge that the fuel hazard reduction treatments 

described here do not address constraints on land management activities specified in existing land and resource management plans and their potential effects on removals. Nor 

do these scenarios address the importance of maintaining 

forest stocking, ground fuels, and other factors that may 

negatively contribute to CI and TI values on the ecologic 

health and productivity of forests. Clearly, other 
6

Research Paper FPL–RP–634

management objectives will sometimes override the application of fuel hazard reduction treatments. 

This analysis was not meant to be a detailed, site-specific 

fuel treatment plan. If fuel treatments are to be conducted, 

they must be planned and assessed in terms of their specific 

locations, values of adjacent resources, proximity of adjacent fuels, and likely rates-of-spread and weather conditions 

at the time of burn. For example, information on most likely 

wind direction with regard to terrain should be taken into 

account when assessing the potential of a fuel treatment to 

mitigate hazard in a specific planning area. This analysis 

is instead a broad-scale analysis meant to identify general 

regions where fuel hazard appears to be high and enough 

volume is present to make it feasible to think that the treatments would not have to be substantially subsidized.

As a general indicator of fuel hazard we have used the 

torching and crowning indexes. These metrics indicate the 

vulnerability of a stand to crowning: torching index reflects 

vulnerability to crown fire initiation, while crowning index 

reflects vulnerability to sustained crown fire. In using these 

metrics, we implicitly assume that our goal in treating fuels 

is not to reduce fire occurrence, but to reduce crown fire 

occurrence. Crown fires are more difficult to suppress than 

are surface fires, have a far greater rate of spread than do 

surface fires, and result in near total stand mortality; surface 

fires tend to be more acceptable in terms of both fire behavior and fire effects, and they may have a positive effect on 

the stand and on fuel hazard reduction. 

Finney (2001) has suggested that an optimal pattern of fuel 

treatments may result in reduced fire spread across a landscape as a result of fire flanking through untreated areas 

rather than spreading in a forward direction. This largely 

theoretical concept has not been integrated into our analysis 

here. However, if fuel treatment should be scheduled, this 

kind of analysis could be conducted to design the most strategically valuable layout of treatment units and to assess the 

potential of those treatments to reduce landscape-level rate 

of spread. Any treatment that results in surface fire rather 

than crown fire will almost certainly result in reduced rate 

of spread, however, since crown fires are more exposed to 

wind and have much higher intensity than that of surface 

fires burning in similar fuels.

Effects of Treatments on Other Resources 

Surface fuels, including shrubs, conifer regeneration, and 

woody debris, contribute to torching behavior and fire hazard. However, they can be important resources in their own 

right. Shrubs may be important as browse for large mammals. Conifer regeneration cannot be eliminated completely 

without eliminating the future stand. Woody debris is important for nutrient cycling, soil quality, and small animal habitat. Site-specific treatment plans may need to acknowledge 

these resources and allow for their continued presence on a 

site, probably through small-scale variability. 

Silvicultural Objectives and Assumptions

The thinning treatments used in this paper to reduce fire 

hazard have an objective of either (1) moving the stand 

toward an uneven-aged condition or (2) moving the stand 

toward an even-aged condition. In addition, the objective 

of some treatments is to limit the amount of basal area removed; that is, to limit the amount of change in stand structure. For forest types prone to wind throw, there is a further 

restriction on removal of basal area to reduce wind throw 

risk. 

Although some authors 

(Graham and others 

1999) have suggested 

that thinning unevenaged stands does not 

reduce fire hazard in 

some cases, the uneven-aged treatments 

described in this study 

were specifically designed to take enough 

trees to reduce TI, CI, 

and the risk of crown 

fire. The treatments 

remove most of the 

smaller trees (ladder 

fuels) and some larger 

trees as well.

Timberland area was 

divided into forest 

types that tend to have 

(1) high severity fire 

regimes (where severe 

fires are routine under 

natural conditions) and 

(2) surface or mixed 

severity fire regimes. 

spruce–fir and lodgepole pine forest types 

are in the high severity 

category, and all other 

forest types are in the 

surface or mixed severity category. Spruce–fir 

and lodgepole pine 

types also have high 

wind throw risk when 

stands are heavily 

thinned. Treatments 

may also differ between 

wildland urban interface (WUI) areas and 

wildland areas.

Development of 

Prescriptions 

The silvicultural prescriptions used 

in this analysis were developed in 

collaboration with USDA Forest 

Service regional silviculturists 

and fuel specialists. The need 

for this analysis was discussed 

with regional silviculturists at the 

USDA Forest Service National 

Silviculture workshop in Granby, 

Colorado, in 2003. Two regional 

silviculturists, Michael Landrum 

and Barry Bollenbacher, volunteered to work with the authors of 

this paper to develop prescriptions.

In June 2004, the authors held a 

special meeting of silviculturists 

and fuel specialists in Denver, 

which included Landrum, Bollenbacher, regional fuels specialist 

Paul Langowski, and others. Participants discussed both unevenaged and even-aged treatments, 

particularly the validity of uneven-aged management to mimic 

landscape-scale effects. Consensus 

was reached that the prescriptions 

and approach were valid.

The resulting prescriptions and 

screening approach were presented 

to the larger group of silviculturists 

and fuel specialists at the USDA 

Forest Service National Silviculture workshop at Lake Tahoe, 

Nevada, in 2005, along with the 

complete study plan and preliminary results. Preliminary results 

were also reviewed by Langowski 

and Susan Stewart, the leader of 

the USDA Forest Service National 

Program for Fuels Reduction.

This process allowed us to use a 

set of generic prescriptions that 

could be applied broadly across the 

conifer forests of the West and that 

were credible from both silvicultural and fire hazard reduction 

perspectives. 
7

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

Spruce–fir and lodgepole pine forest types are excluded 

from treatments except in WUI areas. The reason for this 

exclusion is that severe fires (crown fires) are routine in 

these forest types under natural conditions, and thinning to 

avoid severe fire does not support normal fire ecology. The 

reason for thinning these types in WUI areas is concern for 

public safety, and thinning is substituted for normal recurring severe fire (Table 3).

These are only potential treatments, and the actual selection 

of fire hazard reduction activities by public or private land 

owners may differ. The selection of treatments will vary 

by location and will be influenced by detailed local land 

management constraints from applicable land and resource 

management plans. Private owners of lodgepole pine or 

spruce–fir stands might, in fact, choose to thin them to reduce fire hazard on their land, although it seems likely that 

when markets are available, these treatments will resemble 

commercial timber harvests more than the prescriptions described here.

Forest health related treatments are another reason why 

both public and private land managers might choose to treat 

these forest types. For example, there is growing evidence 

that the likelihood of unusually large outbreaks of bark 

beetles is becoming more common in the interior West. This 

is believed to be a result of global warming (Logan and 

Bentz 1999, Powell and Logan 2005). Treatment of these 

forest types when they occur over large expanses of mature 

stands will undoubtedly be proposed to alter stand structural 

conditions in an attempt to mitigate the impact of insect outbreaks. Again, it is uncertain how such treatments would be 

designed, because simply thinning the stands might not have 

the desired result. 

Salvage logging to remove dead trees could also add considerably to the potential supply of biomass and merchantable 

timber. However, in recent years, new salvage operations 

have generally been quite contentious when they occur on 

public land, and they tend to focus on larger commercialsized trees. 

Treatments for Forests With Surface and Mixed 

Severity Fire Regimes

Treatments 1A and 1B, uneven-aged, high structural 

diversity—Under these treatments, the number of trees 

remaining in each dbh class after treatment is intended to 

contribute equally toward the residual stand density index 

(SDI) for the stand (Long and Daniel 1990). The final level 

of overall SDI is adjusted downward by simulated removal 

of trees across all dbh classes until TI≥25 and CI≥25, or 

CI≥40. For treatments 1A and 1B, the intent of the SDI calculation method is to remove trees to reduce overall SDI, to 

have trees remaining in each dbh class contribute an equal 

amount to SDI, and to have the overall treatment meet a fire 

hazard target. 

In Scenario 1A, removals are limited to 50% of initial basal 

area; in 1B, there is no limitation. These scenarios result in 

treated forest structures that retain high structural diversity 

while retaining intact understories of small trees. 

Achieving CI targets under this scenario is usually accomplished by removal of some trees from the larger dbh 

classes, which lowers crown bulk density. The TI targets can 

be achieved if the stand does not contain large numbers of 

small trees or the crowns are not low to the ground. When 

removals are restricted to less than 50% of the original basal 

area, we avoid impairing the integrity of the overstory forest under this uneven-aged scenario. This limit is based on 

author experience (W. Shepperd) and published unevenaged silviculture guidelines (Alexander and Edminster 

1977, Burns 1983) and was imposed to ensure that some 

semblance of an uneven-aged forest structure is maintained 

after treatment. 

Treatments 2A and 2B, uneven-aged, limited structural 

diversity—In these scenarios, we attempted to achieve 

TI and CI goals by removing as many small trees as possible while still retaining sufficient numbers of smaller 

trees to ensure a continued uneven-aged structure. Trees 

are removed so that the remaining trees in a large dbh class 

contribute more to the residual stand SDI than do trees in 

a smaller dbh classes. For treatments 2A and 2B, the SDI 

calculation method thins to a disproportional distribution 

of SDI over dbh classes to meet a fire hazard target. We 3

Table 3—Treatment scenarios by silviculture methoda

Treatment by limit on basal area removed

Land area, forest type, and silvicultural method Up to 50% No limit Up to 25% 

All land (all forest types except spruce–fir and lodgepole pine) 

Uneven-aged—Thin all diameters, leaving greater numbers of small trees 1A 1B — 

Uneven-aged—Thin all diameters, leaving fewer small trees, and more large trees 2A 2B — 

Even-aged—Thin from below 3A 3B — 

WUI land only (spruce–fir and lodgepole pine only) 

Even-aged—Thin from below until CI and TI goals are met 4B — 4A 

a

Fuel hazard reduction objectives are to thin until CI>25 and TI>25 or CIt40, subject to specified limits on proportion of basal 

area that may be taken. 
8

Research Paper FPL–RP–634

used a distribution that retains more of the larger trees while 

maintaining a residual distribution of trees where each successively larger dbh class has fewer trees than the preceding 

smaller dbh class. This is different from treatments 1A and 

1B, where each dbh class in the residual stand contributes 

equally toward the SDI. 

The level of overall SDI is adjusted downward by simulated 

removal of trees until the target TI and CI values are reached 

(treatment 2B) or until 50% of the original basal area has 

been removed (treatment 2A). This scenario typically produces stands with open understories that contain some small 

trees, but usually retains a good stocking of trees in the 

largest diameter classes. However, as in treatments 1A and 

1B, CI goals are difficult to achieve when tree crowns are 

low to the ground. These situations illustrate that fire risk 

reduction goals cannot always be achieved by just removing 

trees. Further treatment using either mechanical pruning or 

prescribed fire may be needed to raise live crown height and 

achieve TI goals.

Treatments 3A and 3B, even-aged, thin from below— 

These treatments emulate an intermediate thinning in forests being managed under an even-aged silviculture system 

where the intent is to ultimately harvest and replace the 

existing forest. Small trees are completely removed in successively larger dbh classes until CI and TI goals are met 

(treatment 3B), or until 50% of the original basal area has 

been removed (treatment 3A). Although the 50% BA removal restriction may prevent CI and TI goals from being 

achieved, more drastic thinning fundamentally alters the 

character of the forest and should not be prescribed without 

careful consideration of all potential ecosystem effects. We 

assumed that these even-aged treatments to reduce wildfire risk would be intermediate treatments to control forest 

stocking prior to maturity and not harvest treatments meant 

to regenerate the forest. While heavier removals might be 

justified to reduce crown fire risk, those cases require a full 

analysis of ecosystem trade-offs.

These scenarios best suit forest types subject to surface or 

mixed-severity fire regimes and should not be used with 

tree species subject to wind throw. In some cases, these scenarios fail to achieve TI goals in spite of the complete removal of the smallest dbh classes. This usually occurs when 

stocking consists of long-crowned tree species, or in very 

open-grown conditions with low live-crown heights. This 

again illustrates the need to utilize pruning or prescribed fire 

to reduce wildfire risk.

Treatments for Forests With High Severity Fire 

Regimes 

Treatments 4A and 4 B, even-aged, thin from below 

(spruce–fir and lodgepole pine forest types)—These treatments are similar to treatments 3A and 3B, except BA removals are restricted to 25% of existing stocking (treatment 

4A ) or 50% of existing stocking (treatment 4B). The 25% 

removal restriction is based on published partial cutting 

guidelines and is necessary to avoid wind throw in shallowrooted tree species like spruce, fir, and lodgepole pine 

(Alexander 1986a,b). This restriction further limits the 

achievement of CI and TI goals. The dilemma in these 

cases is finding a means to reduce crown fire risk without 

having the forest unravel from wind throw. In these forest 

types, which are typically subject to stand replacement fire 

regimes, the solution may have to be achieved at the landscape scale rather than within individual stands, and may 

involve patch cutting or type conversion of some stands to 

non-forest to break up the continuity of fuels within 

landscapes. 

Estimation of Harvesting Costs

Harvesting cost, the cost to provide biomass ready for transport at the roadside, was estimated for each plot using the 

Fuel Reduction Cost Simulator (FRCS) calculation routine 

from My Fuel Treatment Planner6 (Biesecker and Fight 

2005, Fight and others 2006). The FRCS estimates harvest 

cost, for up to eight harvesting systems, based on the number and average volume of trees in various size categories 

and the slope of the site. 

Ground-based harvesting systems: 

• Manual-felling log-length system—Trees felled manually and manually cut to log length, then transported to 

landing by tractive vehicles.

• Manual-felling whole-tree (WT) system—Trees felled 

manually and whole trees transported to landing by tractive vehicles.

• Mechanized-felling WT system—Mechanized felling 

and transport of whole trees to landing by tractive vehicles.

• Cut-to-length (CTL) system—Trees felled by mechanized single-grip harvesters; limb and buck trees and 

resulting logs transported to landing by tractive vehicles.

Cable-yarding systems:

• Manual-felling log-length system—Trees felled manually and manually cut to log length, then conveyed to the 

landing by cable yarder. 

• Manual-felling WT system—Trees felled manually and 

whole trees conveyed to the landing by cable yarding.

• Manual-felling WT/log-length system—Trees felled 

manually; trees to be sold as sawlogs bucked, then conveyed; trees to be sold as chips, conveyed as whole trees 

by cable yarder to the landing. 

• CTL system—Trees felled by mechanized single-grip 

harvesters; limb and buck trees and logs conveyed to 

landing by cable yarder. 

For both ground and cable systems, whole trees may be cut 

into logs at the landing; logs to be hauled in log form are 

6See www.fs.fed.us/pnw/data/myftp/myftp_home.htm
9

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

loaded on trucks; and logs, tops, and branches to be chipped 

are processed and blown into chip vans.

The cost for the least expensive system suitable for the site 

was assigned to each site. For our calculations, we assume 

(1) harvest is only a partial cut, (2) tops and branches are 

collected for use when the low-cost system brings whole 

trees to the landing, (3) trees down to 1 in. dbh are removed, 

(4) average distance that logs are moved from stump to 

landing is 1,000 ft, (5) average area treated is 100 acres, 

and (6) distance to move equipment between harvest sites 

is 30 miles. Costs may be reduced if small dbh trees are not 

removed from the site and treated by another method (e.g., 

pile and burn). While it is our intent to estimate costs that 

include removal of branches and tops, we chose to allow 

log-length systems (which do not remove tops and branches) 

to ensure we could assign a harvest cost to almost all plots. 

Where stand conditions permit their use, WT systems will 

tend to be less expensive than CTL systems. To the extent 

that log-length systems are chosen, we may have underestimated actual harvest costs that would include removal and 

chipping of all tops and branches.

Estimation of Product Revenue

We assume the same product values and costs for hauling as 

those used in the 2003 Assessment to allow comparison of 

results:

Delivered sawlogs (vol. from main stem ≥7 in. dbh) 

= $290/103 board feet (mbf)

Delivered chips (vol. from wood and bark <7 in. dbh, 

tops and branches of larger trees) = $30/odt

Haul distance = 100 miles

Haul cost = $0.35/odt/mile

The assumed prices are used only as a means to give a 

rough estimate of the extent to which wood revenue from 

alternate treatments may cover costs. Actual prices vary by 

location and over time. To retain similar prices over time, if 

woody biomass supply is increased, it would be necessary 

to expand the number and/or capacity of businesses to use 

wood.

Computations and the Fuel Treatment 

Evaluator

The Fuel Treatment Evaluator 3.0 (FTE), a web-based tool, 

was used to select areas for treatment, apply treatments 

to FIA plot data, and generate removal information and 

maps.7 The FTE is flexible in changing many but not all 

the features of the analysis. Many different features can be 

varied, including (1) treatment areas by state, county, and 

circle about a point or polygon, (2) forest types to be treated, 

(3) minimum cubic feet of merchantable wood removed, 

7For Fuel Treatment Evaluator 3.0, see http://ncrs2.fs.fed.us/4801/

fiadb/fire_tabler_us/rpa_fuel_reduction_treatment_opp.htm

(4) maximum slope for treated plots, (5) land ownership, 

(6) wildland urban interface (WUI) or non-WUI, and 

(7) silvicultural treatments 1A through 4B. Features that 

cannot be changed include the CI and TI limits for selecting a plot (that is, 25 mph) and CI and TI targets after 

treatments.

Findings

Area Treated

The 2003 Assessment identified 96.9 million acres of timberland for possible thinning in fire regime condition classes 

(FRCCs) 1, 2 and 3, with 28.5 million acres in FRCC 3. 

The 2003 Assessment selected plots for treatment if timber 

density, as measured by SDI, was greater than 30% of the 

maximum SDI for the plot forest type.

Our assessment imposed the following additional or different screens on plots and identified 23.9 million acres for 

thinning. Taken together, these restrictions define the following timberland as “eligible” for treatment:

• Plots with (1) CI<25 or (2) TI<25 and CI<40 are 

 included.

• Wetter counties west of the Cascade Mountains in 

 Oregon and Washington are excluded.

• Inventoried roadless areas are excluded.

• High severity fire regime forest types are excluded

 (lodgepole and spruce–fir), except in WUI areas.

After treatments were applied to these 23.9 million acres, 

we selected only the area that would provide 300 ft3 (about 

4 odt) of merchantable wood per acre. The final number 

of acres to be treated ranges from 7.2 to 18.0 million acres 

depending on the treatment (Table 4). Treatments 3A and 4A 

together would treat 7.2 million acres total and treatments 

1B and 4B together would treat 18.0 million acres total.

Acres receiving simulated treatment come from all FRCCs,8

but more than 85% are from FRCCs 2 and 3 (Table 5).

Of the 21.2 million WUI acres identified in 12 western 

states (Stewart and others 2003), an estimated 4.1 million acres are in timberland based on the number of FIA 

timberland survey plots (and the acres they represent) that 

fall within WUI boundaries in these states. The WUI acres 

included for treatment come from both the high severity 

and surface/mixed severity forest type groups. For the high 

severity types (spruce–fir and lodgepole pine), 0.5 million 

acres of WUI were included for treatment (4A or 4B, 

Table 5). For all other forest types, 0.3 to 0.7 million 

acres of WUI were included as part of treatments 1A to 

3B (Table 5). So, the total WUI area to be treated could be

8Fire regime condition classes (FRCCs) refer to the degree to 

which the current fire regime (fire recurrence, intensity, severity, 

etc.) is different from the historical pattern, with FRCC 3 having 

the most divergence. See definitions at http://ncrs2.fs.fed.us/4801/

fiadb/fire_tabler_us/rpa_fuel_reduction_treatment_opp.htm
10

Research Paper FPL–RP–634

Table 5—Treatable area by fire regime condition class (FRCC)

Area (106

 acres) 

 FRCC 

2003 Assessment treatment scenario 1 2 3 Other Total

WUI

only 

Low and mixed severitya 

Total acres where TI or CI < 25 3.0 9.8 8.7 2.3 23.9 1.0 

1A Uneven-aged high diversity, 50% limit 2.1 7.1 6.5 1.5 17.1 0.7 

1B Uneven-aged high diversity, no limit 2.1 7.2 6.6 1.6 17.5 0.7 

2A Uneven-aged limited diversity, 50% limit 1.9 6.1 5.5 1.4 14.8 0.6 

2B Uneven-aged limited diversity, no limit 1.9 6.2 5.5 1.4 15.1 0.6 

3A Even-aged thin from below, 50% limit 1.0 2.8 2.2 0.6 6.7 0.3 

3B Even-aged thin from below, no limit 1.0 2.9 2.3 0.7 6.8 0.3 

High severity WIU only 

4A Even-aged thin from below, 25% limit 0.0 0.4 0.0 0.0 0.5 0.5 

4B Even-aged thin from below, 50% limit 0.0 0.4 0.1 0.0 0.5 0.5 

4

Table 4—Area treated by State and treatment scenario 

Area treated (106 acres) 

Treatments for forest types other than spruce–fir and lodgepole pine Treatments for spruce–

fir and lodgepole pine

Uneven-aged treatments Even-aged treatments Even-aged treatments 

in WUI area only 

High

structural diversity 

Limited 

structural diversity 

50% BA

removal

limit 

No BA 

removal limit 

50% BA 

removal

limit 

No BA 

removal limit 

50% BA 

removal

limit 

No BA 

removal limit

25% BA 

removal

limit 

50% BA 

removal

limit 

State 1A 1B 2A 2B 3A 3B 4A 4B 

AZ 0.5 0.5 0.4 0.4 0.1 0.1 0 0 

CA 4.4 4.4 3.8 3.8 1.5 1.5 0 0 

CO 1.2 1.3 1.1 1.1 0.4 0.5 0.1 0.1 

ID 2.4 2.5 2.2 2.2 1.1 1.1 0.4 0.4 

MT 2.9 3.0 2.5 2.6 1.5 1.6 0 0 

NV 0 0 0 0 0 0 0 0 

NM 0.9 1.0 0.8 0.8 0.3 0.3 0 0 

OR 2.2 2.2 1.8 1.8 0.9 0.9 0 0 

SD 0.1 0.1 0.1 0.1 0 0 0 0 

UT 0.4 0.4 0.4 0.4 0.2 0.2 0 0 

WA 1.8 1.8 1.5 1.5 0.6 0.6 0 0 

WY 0.3 0.4 0.3 0.3 0.2 0.2 0 0 

Total 17.1 17.5 14.8 15.1 6.7 6.8 0.5 0.5 

Treatments for spruce–

fir and lodgepole pine;

even–aged treatments

Even–aged treatments in WUI area only
11

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

0.8 to 1.2 million acres (0.5 plus 0.3 or 0.7). Our treatments 

would suggest removals on 20% to 30% of the timberland 

WUI acres (0.8 to 1.2 million acres of 4.1 million acres). To 

the extent that communities decide to treat WUI areas larger 

than those defined by Stewart and others (2003), we would 

be underestimating the acres of severe fire regime forest 

types that may be treated with positive average net revenue. 

One factor that influences the expense of thinning is the 

slope of the land to be treated. Treatments on steeper slopes 

tend to be more expensive. About 60% of the acres selected 

for treatments are on <40% slopes (Table 6). Treatment 

1B would thin the largest area—17.5 million acres or about 

14% of all timberland in the 12 western states. The highest 

percentage of timberland to be treated would be in California (33%), followed by New Mexico (24%), Idaho (21%), 

Montana (21%), and Arizona (16%) (Fig. 1).

Fire Hazard Reduction 

Four possible fire hazard reduction outcomes were identified for the 23.9 million acres that are eligible for treatment (acres with CI<25 or TI<25 and meeting other initial 

screens):

1. Treatment is applied; both CI>25 and TI>25. 

2. Treatment is applied; CI>40. 

3. Treatment is applied; 50% BA removal limit is

 achieved before achieving either (1) or (2).

4. No treatment applied; <300 ft3 of merchantable wood 

 could be removed.

Uneven-aged treatments (1A, 1B, 2A, 2B) are able to treat 

more than twice as many eligible acres as the even-aged 

treatments (3A, 3B); that is, 14.6 to 17.5 million acres vs. 

6.7 to 6.8 million acres (Table 4). This is because of the 

requirement that removals include 300 ft3 of merchantable 

wood and because uneven-aged treatments take a higher 

proportion of volume as larger (merchantable) trees. 

Uneven-aged treatments with the 50% BA removal limit 

(treatments 1A and 2A) treat 71% and 61% of eligible acres, 

respectively. These treatments reach the medium or high 

hazard reduction goal for 34% and 38% of eligible acres, respectively (Table 7). When the BA limit for the uneven-aged 

treatments is removed (treatments 1B and 2B), a slightly 

greater percentage of acres is treated (72% and 62%), and 

all these treated acres reach the medium or high hazard 

reduction goal. Moving from treatment 1A to 1B and 

6

Table 6—Treatable area and biomass removal by slope for treatments 2B and 3B in surface and 

mixed severity fire regimes

Treatment scenario d40% slope >40% slope Total 

Area (106

 acres) 

Total acres TI or CI < 25 15.8 8.8 23.9 

2B Uneven-aged limited diversity, no BA limit 9.7 5.3 15.1 

3B Even-aged thin from below, no BA limit 3.9 2.9 6.8 

Biomass (106

 odt)

2B Uneven-aged limited diversity, no BA limit 279.1 165.6 444.7 

3B Even-aged thin from below, no BA limit 99.0 78.5 177.5 

Average biomass removal (odt) per acre 

2B Uneven-aged limited diversity, no BA limit 28.7 31.1 29.5 

3B Even-aged thin from below, no BA limit 25.1 27.2 26.0 

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

CA NM ID MT AZ WA OR CO UT WY SD NV

State

Percentage of timberland to be thinned by treatment 1A 

Timberland (%)

Figure 1—Proportion of timberland acres to be thinned by treatment 1A by state.
12

Research Paper FPL–RP–634

thereby reaching a hazard reduction target on each acre 

treated requires an increase in biomass removal of 25% 

(502 to 627 million odt). To move from treatment 2A to 2B 

requires a 16% increase in removals (Table 8), which includes the biomass from the additional 1% of acres treated.

Even-aged (thin from below) treatment with the 50% BA 

removal limit (treatment 3A) treats 28% of all eligible acres 

(Table 4) but reaches the medium or high hazard 

reduction goal for only 7% of the eligible acres (Table 7). 

When the 50% limit is removed (treatment 3B), 28% of 

acres are treated and all these treated acres reach the medium or high hazard reduction goal. Moving from treatment 

3A to 3B requires a 10% increase in biomass removals, 

which includes the biomass from the additional 1% of acres 

treated.

In general terms, for forest area where there is both the 

need to obtain a minimum level of merchantable wood to 

help yield positive average net revenue and a restriction on 

BA removal, our results suggest that the uneven-aged treatment would more likely achieve one of the hazard reduction 

targets than would an even-aged treatment (Table 7). For 

treatments 1A and 2A, a higher proportion of eligible area 

is treated and reaches a target (44% and 30%, respectively) 

compared with treatment 3A (7% ). 

Figures 2 to 13 show number of acres by CI and TI group 

before and after treatment. Uneven-aged treatments are 

effective in raising CI but not as effective in raising TI. 

Conversely, even-aged treatments are very effective in 

raising both TI and CI to >25 mph. Even-aged treatment 

3B reached CI>25 and TI>25 on 95% of all acres treated. 

Only 5% of acres met the CI>40 target alone. In comparison, uneven-aged treatment 2B reached CI>25 and TI>25 

on 62% of acres, with 24% reaching CI>40. 

If raising TI is a priority, then even-aged treatments are 

more effective than uneven-aged treatments. However, a 

trade-off by doing even-aged treatments is that they are 

less likely to produce 300 ft3 of merchantable wood and, 

as noted below, provide positive net revenue from sale of 

products.

Biomass Removed

The 2003 Assessment identified total possible removal 

of 2.1 billion (109) odt biomass with treatment of all 

94.5 million acres of treatable timberland. Removal from 

66.3 million FRCC -2 and FRCC-3 acres could provide 

1.5 billion odt of biomass. If only 60% of FRCC-3 acres are 

treated, the yield would be 346 million odt of biomass.

In our assessment, we identified 7.2 to 18.0 million acres for 

treatment that would yield 169 to 640 million odt (Table 8). 

Treatments 3A and 4A would provide 169 million odt total 

and treatments 1B and 4B, 640 million tons total. The uneven-aged treatments (1A to 2B) generate more than twice 

as much biomass as the even-aged treatments (3A and 3B), 

because more than twice as many acres would be treated and 

more biomass would be removed per acre (Tables 4 and 8).

The distribution of biomass removed by tree size differs 

greatly between the uneven-aged and even-aged treatments. 

In addition, the distribution for the uneven-aged treatments 

differs substantially from the results of the uneven-aged 

treatment used in the 2003 Assessment. The 2003 

Assessment showed the most biomass removed from the 

10-in. dbh class, with progressively less biomass taken from 

larger dbh classes (Forest Service 2003, Fig. 6). In contrast, 

our uneven-aged treatments provide most biomass in ≥21 in. 

dbh classes (Table 9, Figs. 14 and 15). 

7

Table 7—Fire hazard outcomes: Percentage of treatable acresa

Percentage of treatable acres by goal achieved 

Treatment scenario 

Low

(50% BA 

limit 

reached)b

Medium

CI>40 only 

High

CI>25, TI>25

Total achieving 

medium or high 

target 

Total 

receiving 

some 

treatment

Not treated 

(<300 ft3

 merchantable 

wood/acre) Total

1A Uneven-aged 

High diversity, 50% limit 28 21 22 44 71 29 100 

2A Uneven-aged 

Limited diversity, 50% limit 31 18 12 30 61 39 100 

3A Even-aged 

Thin from below, 50% limit 21 4 3 7 28 72 100 

1B Uneven-aged 

High diversity, no limit 0 23 49 72 72 28 100 

2B Uneven-aged 

Limited diversity, no limit 0 14 48 62 62 38 100 

3B Even-aged 

Thin from below, no limit 0 6 22 28 28 72 100 

a

Total treatable area = 23.9 million acres.

b

Treatment is done but BA limit is reached.
13

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

8

Table 8—Initial standing biomass and biomass removals 

Biomass removed (106 odt) by various treatment scenarios per State 

Treatments for forest types other than spruce–fir and lodgepole pine Treatments for spruce–fir + lodgepole pine 

Uneven-aged treatments Even-aged treatments Even-aged treatments in WUI area only 

High structural diversity Limited structural diversity 

State 

Initial vol. biomass 

on treatable land 

(106 odt)

50% BA

removal limit 

1A

No BA 

removal limit 

1B

50% BA

removal limit 

2A

No BA 

removal limit 

2B

50% BA

removal limit 

3A

No BA 

removal limit 

3B

25% BA

removal limit 

4A

50% BA

removal limit 

4B

AZ 29.5 11.0 13.1 8.9 9.9 2.3 2.6 0.1 0.1 

CA 411.7 172.3 222.4 117.4 145.2 37.4 40.1 0.2 0.3 CO 49.3 20.6 28.4 17.4 21.8 6.0 7.5 0.8 1.4 ID 171.4 68.1 83.1 57.7 63.4 26.6 29.4 6.4 10.5 MT 166.7 66.8 84.4 58.9 69.2 36.5 41.9 0.1 0.2 NV 0.9 0.3 0.3 0.2 0.2 0.1 0.1 0 0 NM 41.9 18.3 24.1 15.0 18.4 5.5 6.3 0 0 OR 214.5 78.3 88.7 55.1 56.2 25.5 26.3 0 0 SD 3.9 1.3 1.4 1.1 1.1 0.3 0.3 0 0 UT 18.2 7.5 9.8 6.9 8.0 2.9 3.2 0 0.1 WA 128.7 50.0 60.9 38.8 42.4 14.9 15.4 0 0.0 WY 17.7 7.5 10.3 7.3 8.9 3.6 4.5 0.1 0.2 Total 1254.4 502.0 626.8 384.6 444.7 161.6 177.5 7.6 12.8 

Treatments for spruce–

fir and lodgepole pine;

even–aged treatments

in WUI area only Even–aged treatments
14

Research Paper FPL–RP–634 9

Table 9—Biomass removed by treatment scenario and tree dbh class 

Biomass removed (odt/acre) by various treatment scenarios per dbh class 

Treatments for forest types other than spruce–fir and lodgepole pine Treatments for spruce–fir and lodgepole pine 

Uneven-aged treatments Even-aged treatments Even-aged treatments in WUI area only 

High structural diversity Limited structural diversity 

Tree

dbh class 

(in.)

50% BA

removal limit 

1A

No BA 

removal limit 

1B

50% BA

removal limit 

2A

No BA 

removal limit 

2B

50% BA

removal limit 

3A

No BA 

removal limit 

3B

25% BA 

removal limit 

4A

50% BA

removal limit 

4B

2 0.3 0.5 0.5 0.6 0.8 0.9 0.4 0.5 

4 1.1 1.5 1.5 1.7 2.2 2.4 1.5 2.2 6 2.0 2.4 2.7 3.0 4.9 5.1 4.9 5.4 8 2.7 3.3 3.5 3.8 6.2 6.5 4.8 6.6 

10 3.0 3.6 3.5 3.9 4.4 4.7 3.5 5.8 12 2.8 3.4 3.0 3.3 2.5 2.8 0.7 2.1 14 2.3 2.8 2.1 2.4 1.2 1.4 0.4 0.9 16 1.7 2.2 1.4 1.6 0.6 0.8 0.4 0.8 18 1.3 1.7 0.8 1.0 0.4 0.5 0 0.2 20 0.8 1.2 0.4 0.5 0.3 0.3 0 0 

 22+ 11.4 13.2 7.0 7.7 0.7 0.6 0 0 

Total 29.4 35.8 26.4 29.5 24.2 26.0 16.6 24.5 

Treatments for spruce–

fir and lodgepole pine;

even–aged treatments

in WUI area only Even–aged treatments
15

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

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10

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10

0–10 10–20

Acres (106)

Before thinning After thinning

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10

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Treatment 1A Treatment 1A

Treatment 1B Treatment 1B

mph 20–30 30–40 40–50 50–60 60+

Crowning index

Acres (106) Acres (106

)

Acres (106)

0–10 10–20

Before thinning After thinning

mph 20–30 30–40 40–50 50–60 60+

Crowning index

0–5 5–10

Before thinning After thinning

mph 10–15 15–20 20–25 25–30 30+

Torching index

0–5 5–10

Before thinning After thinning

mph 10–15 15–20 20–25 25–30 30+

Torching index

Figure 2—Acres of timberland by crowning index before and after treatment 1A.

Figure 3—Acres of timberland by torching index before and after treatment 1A.

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0–10 10–20

Acres (106)

Before thinning After thinning

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Treatment 1A Treatment 1A

Treatment 1B Treatment 1B

mph 20–30 30–40 40–50 50–60 60+

Crowning index

Acres (106) Acres (106

)

Acres (106)

0–10 10–20

Before thinning After thinning

mph 20–30 30–40 40–50 50–60 60+

Crowning index

0–5 5–10

Before thinning After thinning

mph 10–15 15–20 20–25 25–30 30+

Torching index

0–5 5–10

Before thinning After thinning

mph 10–15 15–20 20–25 25–30 30+

Torching index

Figure 4—Acres of timberland by crowning index before and after treatment 1B.

Figure 5—Acres of timberland by torching index before and after treatment 1B.
16

Research Paper FPL–RP–634

9876543210

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876543210

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Treatment 2A Treatment 2A

Before thinning After thinning

Crowning index

Treatment 2B Treatment 2B

Before thinning After thinning

Torching index

Before thinning After thinning

Crowning index

Before thinning After thinning

Torching index

Acres (106)

Acres (106)

Acres (106)

Acres (106)

0–10 10–20 mph 20–30 30–40 40–50 50–60 60+

0–10 10–20 mph 20–30 30–40 40–50 50–60 60+

0–5 5–10 mph 10–15 15–20 20–25 25–30 30+

0–5 5–10 mph 10–15 15–20 20–25 25–30 30+

Figure 6—Acres of timberland by crowning index before and after treatment 2A.

Figure 7—Acres of timberland by torching index before and after treatment 2A.

9876543210

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876543210

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Treatment 2A Treatment 2A

Before thinning After thinning

Crowning index

Treatment 2B Treatment 2B

Before thinning After thinning

Torching index

Before thinning After thinning

Crowning index

Before thinning After thinning

Torching index

Acres (106)

Acres (106)

Acres (106)

Acres (106)

0–10 10–20 mph 20–30 30–40 40–50 50–60 60+

0–10 10–20 mph 20–30 30–40 40–50 50–60 60+

0–5 5–10 mph 10–15 15–20 20–25 25–30 30+

0–5 5–10 mph 10–15 15–20 20–25 25–30 30+

Figure 8—Acres of timberland by crowning index before and after treatment 2B.

Figure 9—Acres of timberland by torching index before and after treatment 2B.
17

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States Figure 10—Acres of timberland by crowning index before and after treatment 3A. Figure 11—Acres of timberland by torching index before and after treatment 3A.

Figure 12—Acres of timberland by crowning index before and after treatment 3B.

Figure 13—Acres of timberland by torching index before and after treatment 3B.
18

Research Paper FPL–RP–634

Why do our uneven-aged treatments remove so much more 

volume from the large-diameter trees in comparison to the 

2003 Assessment? Since both studies used the stand density 

index (SDI) to specify uneven-aged treatment removals,9

the difference in biomass removal distribution must be due 

to differences in (1) the plots selected for treatment and/or 

(2) the amount of removals required to reach the TI and CI 

targets. There were no explicit fire hazard reduction targets 

in the 2003 Assessment. Our focus on plots with CI<25 or 

TI<25 and plots that provide at least 300 ft3/acre may or 

may not select plots with a higher density of larger trees. 

However, our uneven-aged treatments definitely remove a 

higher proportion of biomass on plots to achieve the hazard 

reduction targets. The residual SDI for our treated stands 

averages ≤20% of maximum SDI, versus 30% of maximum 

SDI for acres treated in the 2003 Assessment. 

One reason that stands were thinned to an average of 

20% of maximum SDI is the need to thin some stands 

enough to achieve CI>40 when we cannot attain TI>25. 

We found that the primary reason that plots did not attain 

TI>25 was low canopy base height; on many trees, the 

branches reached the ground. 

Given concerns about harvesting large trees, there are at 

least two ways we could reduce harvest of large trees and 

reach CI>25 and TI>25. Essentially, we want to attain 

TI>25 so we do not have to thin enough to reach CI>40. 

We can help attain TI>25 by pruning branches to raise 

canopy base height and by decreasing surface fuels. Further 

study is needed to determine the effect of such changes on 

acres that would be treated and net revenues.

Even though our uneven-aged treatments (1A–2B) provide 

more than 25% of biomass from trees ≥22 in. dbh, they still 

provide 20% to 31% of biomass from trees <9 in. dbh. This 

is similar to the results of the 2003 Assessment, where 28% 

for biomass was derived from trees <9 in. dbh (Table 9). 

Our even-aged treatments provide 57% to 58% of biomass 

from trees <9 in. dbh, with most biomass coming from the 

8-in. dbh class (7.0–8.9 in.) (Table 9, Figs. 16 and 17). 

The proportion of all acres treated and biomass removed 

that comes from National Forest land is about 55% for both 

even-aged and uneven-aged treatments (Tables 10 and 11). 

These proportions increase to about 60% for all Federal 

land. The state of Washington has the highest proportion of 

biomass removals from private land (65%–70%).

Composite Treatment With Thinning Over an 

Extended Period

The estimated total biomass removal would be performed 

over a number of years. To prepare a single estimate of pos9The stand density index (SDI) method specifies how many trees 

will remain after treatment in each dbh class by specifying the 

fraction of total SDI that each dbh class will contribute.

sible removals per year over time, we constructed a composite scenario that combines treatments 1A, 3A, and 4A. Since 

we do not know to what degree even-aged or uneven-aged 

thinning treatments will be used, a composite scenario was 

formed in which half the area needing treatment (low TI or 

CI) (12 million acres) was considered for uneven-aged treatment 1A and the remainder considered for even-aged treatment 3A. For any geographic area, we computed biomass 

yield under this combination of treatments as the simple 

average of their yields. The composite also includes biomass 

removal from uneven-aged treatment 4A—treatment of 

spruce–fir and lodgepole pine forest types in WUI areas. 

This assumption about the application of alternate treatments is for illustration only. The selection of the silvicultural treatment method is ultimately a stand-level decision 

based on the unique characteristics of each site and specific 

management objectives.

Our composite scenario would treat 12.4 of the 23.9 million 

acres identified with CI<25 or TI<25; more than half the 

eligible area does not meet the 300-ft3/acre criterion. The 

12.4 million acres would provide 339 million odt of biomass. If 0.5 million acres were treated per year, then 

13.7 million odt of total biomass would be provided 

per year over a period of 25 years. One-half million acres 

is chosen as a tentative annual treatment area to represent a 

plausible estimate, assuming current budgets and program 

emphasis continue for wood fiber and biomass production. 

Current annual harvest of roundwood in western states is 

3.3 billion ft3 or about 50 million odt/year (Smith and others 

2004). This mix of thinning treatments over 25 years would 

increase annual biomass use by an additional 13.7 million 

odt/year compared to 50 million odt/year, or about 27% over 

the current level. 

If 50% of the biomass were used for higher value products, 

then the remaining 50%, or 6.8 million odt/year, would 

be available for fuel. After 25 years, more area will have 

moved into the higher fire hazard class, and continued thinning would likely be required on at least 0.5 million acres/

year. About half the area would be on National Forest land 

in the 12 selected western states.

The total number of acres treated and the total amount of 

biomass removed could be increased by lowering the 

300-ft3/acre merchantable wood requirement, removing the 

limitation to harvest no more than 50% of basal area, treating more area with the uneven-aged treatment, treating areas 

with less stand replacement fire hazard (higher CI and TI), 

protecting against fire hazard for “severe summer drought” 

conditions (vs. “drought summer” conditions), or requiring 

hazard to be reduced by more than indicated by the current 

CI and TI targets. For example, if the requirement to provide 

at least 300 ft3/acre were eliminated, then 23.9 million acres 

of timberland would be thinned (vs. 12.4 million acres) and 

388 million odt would be removed in the 12 western states 

(vs. 339 million odt).
19

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States 86420141210 2 4 6 8 10 12 14 16 18 20 22+ dbh class (in.) 1A1B 864201210 2 4 6 8 10 12 14 16 18 20 22+ dbh class (in.) 2A2B 864201210 2 4 6 8 10 12 14 16 18 20 22+ dbh class (in.) 3A3B 864201210 2 4 6 8 10 12 14 16 18 20 22+ dbh class (in.) 4A4B Uneven-aged treatments 1A and 1B Even-aged treatments 3A and 3B Uneven-aged treatments 2A and 2B Even-aged treatments 4A and 4B

Biomass removed 

(odt/acre)

Biomass removed 

(odt/acre)

Biomass removed 

(odt/acre)

Biomass removed 

(odt/acre)

21%-22% biomass in trees < 9in. dbh

57%-58% biomass in trees < 9in. dbh

30%-31% biomass intrees < 9in. dbh

60%-70% biomass intrees < 9in. dbh

Figure 14—Biomass removal for uneven-aged treatments 1A and 1B by dbh class.

Figure 15—Biomass removal for uneven-aged treatments 3A and 3B by dbh class.

Figure 16—Biomass removal for even-aged treatments 2A and 2B by dbh class.

Figure 17—Biomass removal for even-aged treatments 4A and 4B by dbh class.
20

Research Paper FPL–RP–634

10

Table 10—Acres to be treated and biomass removal by State and timberland ownership for treatment 2A: Uneven-aged with limited structural diversity and 50% BA removal limit.

Acres treated Biomass to be removed (odt) 

State 

Acres eligible 

for treatment Total 

 National 

 Forest 

 Other 

 Federal

 State and 

 local gov. Private Total 

 National 

 Forest 

 Other 

 Federal 

 State and 

 local gov. Private 

AZ 844,451 413,222 316,982 0 0 96,240 8,901,267 6,867,401 0 0 2,033,866

CA 5,467,486 3,478,730 1,766,799 20,323 16,269 1,675,339 117,381,106 65,070,309 588,359 1,737,615 49,984,823CO 1,945,105 1,054,944 482,649 157,398 12,542 402,355 17,398,116 8,943,541 2,351,401 211,267 5,891,907

ID 3,004,862 2,182,848 1,343,161 135,434 202,480 501,773 57,689,068 35,658,467 3,539,846 5,327,192 13,163,563

MT 4,440,812 2,540,589 1,505,048 149,000 138,483 748,058 58,892,268 38,243,579 3,243,330 2,636,406 14,768,953

NV 25,232 9,304 1,092 0 0 8,212 192,926 20,144 0 0 172,782

NM 1,404,418 787,752 512,827 0 54,071 220,854 14,997,999 10,664,842 0 1,051,653 3,281,504

OR 3,112,455 1,789,192 806,719 284,183 52,430 645,860 55,089,353 28,254,642 8,399,877 2,137,529 16,297,305

SD 223,963 80,251 80,251 0 0 0 1,062,287 1,062,287 0 0 0

UT 523,600 353,186 200,433 30,689 39,798 82,266 6,934,122 3,906,055 321,374 1,133,697 1,572,996

WA 2,264,744 1,534,488 686,527 36,119 216,675 595,167 38,766,200 18,400,940 1,095,845 6,430,970 12,838,445

WY 621,160 338,519 113,335 94,639 9,121 121,424 7,280,875 3,066,847 1,809,850 147,305 2,256,873

Total 23,878,288 14,563,025 7,815,823 907,785 741,869 5,097,548 384,585,587 220,159,054 21,349,882 20,813,634 122,263,017

Table 11—Acres to be treated and biomass removal by State and timberland ownership for treatment 3A: Even-aged with 50% BA removal limit 

Acres treated Biomass to be removed (odt) 

State 

Acres

eligible for 

treatment Total 

 National 

 Forest 

 Other 

 Federal

 State and  local gov. Private Total 

 National 

 Forest 

 Other 

 Federal 

 State and 

 local gov. Private 

AZ 844,451 70,231 53,333 0 0 16,898 2,300,432 1,882,860 0 0 417,572

CA 5,467,486 1,455,312 803,633 2,247 15,575 633,857 37,423,559 19,151,946 47,758 1,149,565 17,074,290CO 1,945,105 429,960 217,922 67,048 8,171 136,819 5,956,266 2,818,756 1,048,046 105,005 1,984,459

ID 3,004,862 1,105,848 642,028 90,900 110,619 262,301 26,649,934 14,295,157 2,224,638 2,664,724 7,465,415

MT 4,440,812 1,536,571 999,233 77,359 67,275 392,704 36,497,740 25,363,725 1,803,451 1,278,766 8,051,798

NV 25,232 9,304 1,092 0 0 8,212 142,687 14,990 0 0 127,697

NM 1,404,418 293,242 188,486 0 22,511 82,245 5,466,340 3,553,175 0 573,497 1,339,668

OR 2,137,653 857,370 275,806 148,508 44,611 388,445 25,486,043 8,467,099 3,399,133 1,773,572 11,846,239

SD 223,963 21,271 21,271 0 0 0 272,654 272,654 0 0 0

UT 523,600 167,257 84,645 16,043 9,087 57,482 2,868,301 1,473,863 200,898 214,992 978,548

WA 2,287,432 569,146 278,986 5,649 118,078 166,433 14,913,636 7,262,337 121,295 3,578,001 3,952,003WY 621,160 162,644 85,293 44,401 0 32,950 3,612,843 2,180,780 902,466 0 529,597

Total 22,926,174 6,678,156 3,651,728 452,155 395,927 2,178,346 161,590,435 86,737,342 9,747,685 11,338,122 53,767,286
21

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

Treatment Costs and Biomass Revenues

Average treatment costs per acre for even-aged treatments 

are about the same as that for uneven-aged treatments for 

the acres selected for each treatment (Tables 12 and 13), 

though fewer acres are selected for even-aged treatments, 

because fewer acres are able to provide the needed 

300 ft3/acre with the even-aged treatment. 

Average per acre biomass gross revenues are significantly 

higher from the uneven-aged treatments, primarily because 

uneven-aged treatments average 67% of volume in the 

form of higher value sawlogs compared with 50% for evenaged treatments (Table 14). In either case, it is interesting 

that effective treatments tend to remove some commercial 

timber, and this could become a major bone of contention 

with environmental groups who recognize the need for fire 

hazard reduction treatments but do not advocate commercial 

timber harvest (Brown 2002). Average net revenues per acre 

are positive without subsidy for all treatments on gentle 

slopes and for uneven-aged treatments 1A, 1B, and 2B on 

steep slopes (Table 13). When average revenues exceed 

average treatment costs across the selected treatment area, 

this means that positive net revenues on some acres would 

more than cover net costs on other acres. With a $20/green 

ton subsidy for chips, average net revenues per acre are 

also positive for uneven-aged treatments 2A and 2B and for 

even-aged treatment 3B on steep slopes. Even with a subsidy, even-aged treatment 3A on steep slopes incurs a net 

cost per acre. The positive average net revenues for all 

treatments on gentle slopes indicate we could relax the 

300-ft3 merchantable wood requirement (and still have 

positive average net revenue over all acres) and treat more 

acres with gentle slopes.

Treatment Costs

The estimated cost to harvest and move biomass to the 

roadside is less than $1,000/acre for about 50% of acres 

treated for all treatments except treatment 4A. For selected 

forest types in WUI areas, treatment 4A limits removal to no 

more than 25% of basal area and at the same time requires 

removal of 300 ft3/acre. This combination appears to select 

timberland area with relatively low harvest costs per acre 

(Table 14). Acres on gentle slopes (≤40%) tend to cost less 

than $1,000/acre and acres on steep slopes (>40%) more 

than $1,000/acre (Figs. 18 and 19). The average cost for 

treatments on gentle slopes is $692 to $986/acre, while costs 

on steep slopes average $1,811 to $1,975/acre (Table 13). 

Even though the even-aged treatments call for more trees 

to be harvested per acre on average (Table 12), their harvesting cost per acre is lower than or about the same as the 

cost for uneven-aged treatments, which harvest fewer trees. 

This may be explained in part by the fact that we selected 

the lowest cost harvesting system for each plot analyzed; it 

is possible that when trees are smaller, a more automated 

(less expensive) harvesting system may be selected on average than when there are several large trees to be harvested. 

Costs for even-aged treatments would also be kept low by 

the requirement to provide a certain volume in larger trees 

to provide at least 300 ft3/acre, thus limiting the proportion 

of small trees. 

Biomass Revenues

Using biomass values from the 2003 Assessment, we estimate that the delivered value of biomass per acre varies 

from $1,600 to $,2600, excluding treatments 4A and 4B, 

if the main stem volume of trees ≥7 in. dbh goes to higher 

value products and the remainder is delivered as fuel chips 

(Table 14). If all volume goes for chips, the delivered value 

varies from $430 to $640/acre. 

For uneven-aged treatments 1A and 1B, about 67% of 

biomass is merchantable wood from trees ≥7 in. dbh. For 

even-aged treatments 3A and 3B, about 50% of biomass is 

merchantable wood. Also, the tonnage of biomass removed 

per acre is somewhat greater for treatments 1A and 1B compared with treatments 3A and 3B. As a result, if merchantable wood goes to higher value products, the revenue from 

the uneven-aged treatments 1A and 1B is $800 to $1,200/

acre more than for the even-aged treatments 3A and 3B. If 

all wood goes for chips, treatments 1A and 1B provide only 

$50 to $100 more per acre than do treatments 3A and 3B 

(Table 13).

Net Revenue (Costs) From Treatments

Average net revenue from uneven-aged treatments (1A, 1B, 

2A, 2B) is positive for gentle slopes ($278 to $690/acre) and 

negative for steep slopes (−$9 to −$490/acre). Average net 

revenue for even-aged treatments (3A, 3B) is $400 to $700 

less than that for uneven-aged treatments in the same slope 

category (Table 13). Net revenues for treatments on steep 

slopes are least negative for uneven-aged treatments 1B and 

2B (−$9 and −$120/acre, respectively).

In comparison to the uneven-aged treatment analyzed in the 

2003 Assessment, our uneven-aged treatments (1A, 1B, 2A, 

2B) are estimated to provide about the same net revenue 

per acre for sites with gentle slopes ($350 to $700/acre). 

For steep slopes, however, our net revenue per acre is about 

$700 less and negative whereas the estimates from the 2003 

Assessment are positive. This difference could be due to the 

difference in plots selected—only plots with higher hazard 

and resulting in less removal per acre to meet target, and/or 

higher harvest costs per acre.

If a subsidy of $20/green ton is provided for chips delivered 

to a mill, then the net revenue is positive for all treatments 

on gentle slopes and uneven-aged treatments 1A, 1B, and 

2B (Table 13). If merchantable wood is sold as chips rather 

than sawlogs, then all treatments, on both gentle and steep 

slopes, incur a net cost (Table 13).

For the product values and haul costs assumed, we could 

relax the requirement for 300 ft3/acre for uneven-aged treatment for sites with gentle slope (resulting in more acres 

treated) and still have average positive net revenue per acre. 
22

Research Paper FPL–RP–634 12

Table 12—Cumulative percentage of acres treated by harvest cost per acre for each treatment scenario 

Cumulative percentage of acres treated by harvest cost per acre 

Treatment scenarioa

Total 

acres 

(106) $0 to 199 $200 to 399 $400 to 599 $600 to 799 $800 to 999 $1,000 to 1,199 $1,200 to 1,399 $1,400 to 1,599 $1,600 to 1,799 $1,800 to 1,999 $2,000 to 2,199 $2,200 to 2,399 $2,400 to 2,399

1A Uneven-aged 17.1 1 10 25 37 47 55 61 66 73 82 89 96 100 

2A Uneven-aged pine 14.8 0 9 25 39 48 56 62 66 74 84 91 98 100 3A Even-aged 6.7 0 4 21 33 42 48 52 55 66 79 89 100 100 4A Even-aged pine, SF, WUI 0.5 0 13 36 58 72 76 80 82 90 95 98 100 100 1B Uneven-aged 17.5 1 10 23 34 43 50 56 62 69 77 84 91 100 2B Uneven-aged pine 15.1 0 9 24 38 47 55 60 65 72 81 88 94 100 3B Even-aged 6.8 0 4 20 31 39 46 50 54 64 77 86 96 100 4B Even-aged pine, SF, WUI 0.5 0 9 27 40 55 62 71 77 82 84 90 96 100 aPine is lodgepole pine; SF, spruce–fir. 

Table 13—Estimated gross operational costs to cut and move wood biomass to roadside 

Biomass removed Average treatment cost ($/acre)

Treatment trees/acre odt/acre Slope d40% Slope >40% 

1A 223 29 847 1,759 

2A 300 26 819 1,825 3A 446 24 854 1,966 4A 285 17 692 1,811 

1B 301 36 986 1,839 2B 348 30 882 1,864 3B 477 26 902 1,975 4B 381 25 952 1,822 
23

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

14

Table 14—Estimated revenues minus fuel treatment costs and transport costsa,b

Total merchantable wood from main 

stem of trees t7 in. dbh 

 mbf/acre odt/acre 

Other biomass: 

trees <7 in. dbh; 

tree tops + branches 

t7 in. dbh (odt/acre)

Net revenue (cost) 

with merchantable 

wood used for higher 

value products 

($/acre) 

Net revenue (cost) with 

merchantable wood 

used for chips ($/acre)

Net revenue (cost) with 

merchantable wood for 

higher value products 

and chips ($/acre) given 

$20/green ton subsidy

Gross revenue with 

merchantable wood for 

higher value products 

($/acre) 

Gross revenue with 

merchantable 

wood for chips 

($/acre) 

Treatment d40% slope >40% slope d40% slope >40% slope d40% slope >40% slope d40% slope >40% slope d40% slope >40% slope d40% slope >40% slope d40% slope >40% slope d40% slope >40% slope

1A 7.3 7.6 19.5 20.3 9.5 9.9 $533 ($319) ($992) ($1,910) $912 $79 $2,393 $2,500 $503 $526 

2A 6.0 6.5 16.0 17.5 9.8 10.1 278 (490) (971) (1,862) 669 (87) 2,022 2,200 472 498 3A 4.1 5.0 11.0 13.4 12.6 11.6 (112) (833) (973) (1,882) 391 (368) 1,568 1,800 501 499 

4A 3.0 3.9 7.9 10.5 8.7 6.2 (144) (726) (766) (1,550) 202 (478) 1,120 1,325 349 304 

1B 8.8 9.1 23.6 24.4 11.8 12.2 686 (9) (1,161) (1,917) 1,159 479 2,910 3,006 619 639 

2B 6.6 8.5 17.6 22.9 11.0 5.8 356 (120) (1,023) (1,909) 798 114 2,240 2,650 528 431 

3B 4.5 5.4 12.0 14.4 13.2 12.7 (86) (762) (1,024) (1,892) 441 (255) 1,692 1,944 530 542 

4B 5.0 6.4 13.5 17.3 11.0 7.5 (18) (266) (1,073) (1,615) 421 36 1,789 2,093 480 420 

aAssumptions: Delivered sawlog value = $290/mbf; delivered chip value = $30/odt; transport cost = $0.35/odt; haul distance = 100 miles. bMerchantable wood: Main tree stem t7 in. dbh.
24

But for treatments 3A and 3B on gentle slopes and for all 

treatments on steep slopes, we would need to require more 

than 300 ft3 of merchantable wood per acre to attain positive 

average net revenue per acre.

Biomass Removal Maps 

Figures 20 to 25 indicate locations where biomass removal 

from thinning on timberland are most likely to provide net 

revenues per acre for large areas needing treatment to 

reduce fire hazard based on the CI and TI criteria used here. 

These areas include northern California, northern and 

central Idaho, western Montana, central and northern Oregon, and Washington. Smaller acreages include central to 

southern Colorado, central/east Arizona, and northern New 

Mexico. The timberland in WUI areas that needs treatment 

and would provide at least 300 ft3 per acre is found primarily in northern California, northern Idaho, western Montana, 

western Washington, and central Colorado (Fig. 24).

The maps do not imply that these are the only places where 

fire hazard is high. That was not the intent of our analysis. 

Our intent was to find the places where fire hazard is high 

and treatments to reduce it would provide a substantial and 

sustainable supply of wood that could offset treatment costs. 

Figure 18—Timberland treated by treatment 2B by harvest cost category and slope.

Figure 19—Timberland treated by treatment 3B by harvest cost category and slope.

Research Paper FPL–RP–634
25

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

Figure 20—Total biomass removed per 160,000-acre 

area for uneven-aged treatment 1A.

Figure 21—Average biomass removed per acre for uneven-aged treatment 1A.

Figure 22—Total biomass removed per 160,000-acre 

area for even-aged treatment 3A.

Figure 23—Average biomass removed per acre for 

even-aged treatment 3A.
26

Research Paper FPL–RP–634

The importance of a commercial timber component in 

financing fire hazard reduction treatments has been shown 

in several previous analyses (Barbour and others 2004, Fight 

and others 2004, Fried and others 2004). 

As also shown here, without this commercial component, 

the treatments are frequently not effective and would not 

pay for themselves. 

Our analysis suggests that the easiest places to implement 

large-scale operations that meet objective criteria (CI and 

TI thresholds) for fire hazard reduction and have a chance 

of paying for themselves are northern California, northern 

and central Idaho, western Montana, central and northern 

Oregon, and Washington. Our analysis does not suggest that 

these are the only places where fire hazard reduction opportunities exist or even where selected stand-level operations 

could pay for themselves. On the contrary, we found that 

only 10 %to 30 % of the area that meets our criteria for high 

fire hazard appears in the areas identified on these maps. In 

addition, the current analysis does not address the other two 

components of our analytical framework; i.e., the places 

where there is a reasonable business opportunity and the 

places where such large-scale operations would be socially 

acceptable. Consideration of those two components will be 

covered in future analyses.

The important point to take away from these maps is that 

the areas where the most wood could become available 

from fire hazard reduction treatments is concentrated in 

the northern half of the West. This is not really a surprising 

result because that is the most heavily forested part of the 

West. It is also where most of the remaining forest products 

industry is concentrated. An existing industry will undoubtedly make it easier to implement treatments where many 

small trees with little commercial value need to be processed. The manufacturing facilities needed to process this 

currently non-merchantable material are easier to establish 

near existing wood products facilities, because the critical 

mass of other mill residues and human expertise needed to 

support activities such as wood-fired electrical generation 

or other manufacturing processes that could use this material are already available. The presence of an existing wood 

residue stream will be important in creating confidence that 

sufficient raw materials will be available over the long run. 

In general, manufacturing processes that use these materials, 

e.g., electrical generation from wood residues, wood composites, pulp and paper, mulching, etc., are not stand-alone 

operations but are integrated with more traditional solid 

wood product operations.

Results From Thinning Treatments Given 

Alternate Assumptions

Treatments 2B and 3B were applied under the following 

alternate assumptions: 

Figure 24—Total biomass removed per 160,000-acre 

area for uneven-aged treatment 1B in WUI areas 

only.

Figure 25—Total biomass removed per 160,000-acre 

area for even-aged treatment 4A (spruce–fir and 

lodgepole pine) in WUI areas.
27

Evaluation of Silvicultural Treatments and Biomass Use for Reducing Fire Hazard in Western States

1. Only treat Oregon and Washington counties previously 

 excluded from analysis.

2. Only treat plots that provide <300 ft3 of merchantable 

 wood per acre. 

3. Assume delivered sawlog value as $175/mbf and deliv-

 ered chip value as $15/odt. 

Results for the treatment 2B and 3B base cases, where no 

assumptions were changed, are shown in Table 15. Results 

under alternate assumptions show (1) there is substantial 

acreage in Oregon and Washington that, if treated, may 

provide positive average net revenue, (2) acres that provide 

<300 ft3 of merchantable wood per acre yield small tonnage 

per acre, on average, with higher costs per acre, and (3) with 

lower product prices, average net revenue could be negative 

for all treatments on both gentle and steep slopes. 

Thinning treatments 2B and 3B for previously excluded Oregon and Washington counties would treat 4.9 and 3.7 million acres, respectively, for a respective increase of 34% 

and 54% over acres treated in the respective base cases. 

The average amount of biomass removed per acre would 

be notably higher than the averages for the base cases: 

45 vs. 30 odt/acre for treatment 2B, and 39 vs. 26 odt/acre 

for treatment 3B. The net revenues would be $650 to 

$750 odt/acre more than those for the base case, where 

merchantable wood is used for higher value products. 

The average amount of biomass removed for acres providing <300 ft3 is 4.3 and 3.5 tons/acre for treatments 2B and 

3B, respectively, or 13% to 15% of the average removal per 

acre for the respective base cases. It would cost an average 

$120 to $1350 more per acre in net cost (depending on treatment and slope) to treat these acres than to treat the acres 

providing ≥ 300 ft3/acre (Table 15).

With hypothetical lower sawlog and chip values, thinning 

treatments 2B and 3B provide negative average net revenue 

for both gentle and steep slope sites (−$566 to −$1573/acre), 

which is lower than base case net revenues by $700 to 

$1,100/acre.

Concluding Remarks

Of a total timberland area of 127 million acres, this study 

identified 59.2 million acres of timberland in 12 western 

states with a high risk for stand replacement fire (CI or 

TI < 25 mph). After excluding roadless areas, selected 

counties in Oregon and Washington, and high severity fire 

regime forest types in non-wildland–urban interface (WUI) 

areas, we identified 23.9 million acres eligible for treatment.

The proportion of eligible acres that can be thinned and 

provide positive net revenue from the sale of biomass 

products varies substantially, depending on whether an 

even- or uneven-aged silvicultural treatment is used. The 

proportion of treated acres that will attain a given hazard 

reduction will also depend on whether removals are limited 

or not limited to taking 50% of initial basal area.

Under our assumptions, uneven-aged treatments 1A, 2A, 

1B, and 2B will be able to treat a higher proportion of acres 

with resulting positive net revenue than will even-aged 

treatments 3A and 3B. Moreover, for treated acres, if there is 

a 50% limit on basal area removed, then uneven-aged treatments are more likely to attain one of our hazard reduction 

targets (CI>25 and TI>25, or TI>40) than are the even-aged 

treatments.

If sawlogs are sold for higher value products and if smaller 

trees, tops, and branches are sold for chips, then we estimate 

the following net revenues for uneven- and even-aged treatments 1B and 3B. 

• Uneven-aged treatment 1B is able to treat the greatest 

number of eligible acres (72% or 17.2 million acres), 

meet the hazard reduction target on those acres, and 

provide average net revenues (costs) of $686 and 

−$9/acre on gentle and steep slopes, respectively. Given 

these positive net revenues, the proportion of acres that 

could be treated could be higher than 72% and still result in positive average net revenue; that is, lower the 

300 ft3/acre merchantable wood requirement. 

• Even-aged treatment 3B is able to treat 28% or 6.7 million eligible acres, meet the hazard reduction target on 

those acres, and provide average net revenues of −$86 

and −$762, on gentle and steep slopes, respectively. The 

proportion of steep slope acres treated would need to be 

reduced to attain positive average net revenue; that is, 

raise the 300 ft3/acre merchantable wood requirement.

Both uneven-aged and even-aged treatments are able to 

meet hazard reduction targets on all acres if we remove 

the BA removal limits and the requirement to provide 

300 ft3/acre of merchantable wood. But the hazard reduction 

benefit of removing the BA limit may be limited or offset by 

the effect of a more open canopy and more greatly altered 

stand structure. The data on costs and revenues suggest that 

if uneven-aged treatments are used everywhere, revenues 

could cover a notably higher proportion of costs than if 

even-aged treatments were used everywhere.

If we assume a $20/green ton subsidy for chips, average 

revenue is positive for all treatments on gentle slopes 

and increases the most for even-aged treatments (about 

$500/acre) because they provide the most chips. Revenue 

for uneven-aged treatments increases about $410/acre. 

However, net revenue for the even-aged treatments remains 

negative for steep slopes. 

The eligible acres and treated acres are predominately in 

California, Idaho, and Montana, which include 65% to 70% 

of the treated acres for both uneven-aged and even-aged 

treatments. There are an estimated 21.2 million acres of 

WUI area in the 12 western states studied, of which an estimated 4.1 million acres is timberland. Treatments would 

cover 20% to 30% of this timberland—treatments 

1A through 3B would cover 0.3 to 0.7 million acres and 
treatments 4A and 4B, an additional 0.5 million acres. Harvest costs may be higher in WUI areas, so our net revenue 

estimates may be too high (as found in the Lake Tahoe 

Basin and Jackson Hole/Yellowstone regions). The WUI 

average net revenue is highest for treatment 4B on gentle 

slopes (−$18/acre).

Given the concern about removing large trees by unevenaged thinning, it may be possible to reduce large tree harvest 

with supplementary treatments to increase torching index 

rather than thinning to reach a high crowning index. 

Supplementary treatments could include pruning and 

reducing surface fuels. These changes to the uneven-aged 

thinning would decrease biomass yield, number of acres 

providing 300 ft3/acre, and gross revenue per acre. They 

are also likely to increase harvest costs and decrease net 

revenue per acre. Further study is needed to evaluate these 

possible changes.

Our estimates of acreage to be treated, biomass yield, and 

net revenues are sensitive to a range assumptions. In particular, if timberland in the western counties of Oregon and 

Washington were treated, biomass removal could increase 

up to 50% from our base case treatments. Also, the net revenue per acre from treatment will vary by location and over 

time with changing market conditions, and it could be lower 

or higher than our estimated average amounts.

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15

Table 15—Results under alternate thinning treatment assumptionsa

Average net revenue ($/acre)

Assumptionb Treatment 

Area treated 

(106 acres) 

Biomass 

removed

(106 odt) 

Biomass removed

per acre (odt) d40% slope >40% slope

Base case (no change) 2B 15.1 444.7 29.5 356 (120) 

Include only Oregon and Washingtonc 2B 4.9 223.1 45.1 1,108 642 

Include only plots providing <300 ft3

merchantable wood per acre 2B 8.8 38.1 4.3 (151) (1,231)

Lower product prices 2B 15.1 444.7 29.5 (566) (1,189)

 

Base case (no change) 3B 6.8 177.5 26.0 (86) (762) 

Include only Oregon and Washingtonc 3B 3.7 145.3 38.7 562 (100)

Include only plots providing <300 ft3

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Lower product prices 3B 15.1 444.7 29.5 (798) (1,573) a

Lower product price assumptions: Delivered sawlog value =$175/mbf; delivered chip value = $15/odt; transport cost = $0.35odt. b

Other assumptions for treatment case remain the same. 

c

Previously excluded. 

Research Paper FPL–RP–634

28
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