United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical

Report RMRS-GTR-105

July 2003

Coarse Woody Debris:

Managing Benefits and

Fire Hazard in the

Recovering Forest

James K. Brown

Elizabeth D. Reinhardt

Kylie A. Kramer
Abstract _____________________________________

Brown, James K.; Reinhardt, Elizabeth D.; Kramer, Kylie A. 2003. Coarse woody debris:

managing benefits and fire hazard in the recovering forest. Gen. Tech. Rep. RMRSGTR-105. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain

Research Station. 16 p.

Management of coarse woody debris following fire requires consideration of its positive and

negative values. The ecological benefits of coarse woody debris and fire hazard considerations are summarized. This paper presents recommendations for desired ranges of coarse

woody debris. Example simulations illustrate changes in debris over time and with varying

management.

Keywords: fuel, salvage, snags, reburn, Fire and Fuels Extension to the Forest Vegetation

Simulator

The Authors

James K. Brown received his B.S. degree from the

University of Minnesota in 1960, his M.S. degree from

Yale in 1961, and his Ph.D. degree from the University of

Michigan in 1968, all in forestry. From 1961 to 1965, he

was a Research Forester with the Lake States Forest

Experiment Station. In 1965 he transferred to the Intermountain Fire Sciences Laboratory, Missoula, MT, where

he continued research on the physical properties, inventory, and prediction of fuels. From 1979 until his retirement in 1995, he was leader of a Prescribed Fire and Fire

Effects Research Work Unit.

Elizabeth Reinhardt is a Research Forester in the

Prescribed Fire and Fire Effects Research Work Unit at

the Fire Sciences Laboratory in Missoula, MT. She has

degrees in English (A.B., Harvard University, 1978) and

forestry (M.S., 1982 and Ph.D., 1991, University of Montana).

Her research has included studies of fuel consumption,

tree mortality, and prescription development.

Kylie A. Kramer worked in fire suppression for 7 years,

then worked at the Fire Sciences Laboratory in Missoula,

MT. Her work there included tree climbing, canopy fuel

analysis, leaf area index analysis, and FFE-FVS fuel

modeling. She has a chemistry degree from the University of Puget Sound and is currently investigating biodegradable polymers at the University of Montana.

Acknowledgments

Thanks to Stu Lovejoy and the Bitterroot National

Forest staff for suggesting the need for this paper and for

providing data for the example simulations.

You may order additional copies of this publication by sending

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USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 1

The Management Concern ________

Large fires in the Inland West during the past

decade and efforts to conduct salvage logging have

intensified public debate on what is the proper harvest

of dead trees. Harvesting fire-killed trees as soon as

possible following fire is often called salvage. The

objectives of salvage can be to provide economic value,

improve forest health by thinning, and reduce fire

hazard by removing fuel (Gorte 1996; SAF 1995). In

this report, harvesting and salvage refer to cutting of

trees for their product value and for reducing fire

hazard. Positive values of salvage harvest are generally perceived as economic benefits from jobs and

forest products, site rehabilitation, fuel hazard reduction, and lessening the buildup of insect pests. Negative values include lost recreational opportunities,

damaged soils through erosion and reduced nutrient

processes, reduced wildlife habitat, and spread of

weeds (McIver and Starr 2001). A quandary faced by

managers is deciding where and how to manage firekilled trees in the new developing forest. Their decisions about taking action come down to two questions:

Where on the landscape should cutting and fuel treatment be undertaken, and how much of what sized

material should be removed?

An important goal in dealing with these concerns is

to manage toward quantities of accumulated downed

woody material such that the risk of damage from a

reburn is acceptable and benefits derived from coarse

woody debris (CWD) can be realized. Considerable

uncertainty exists over the effects of a possible reburn

on soil productivity and vegetation succession. Although repeated fires have occurred as long as vegetation covered the landscape (Pyne 1982), the term

“reburn” has specific meaning. Reburn results when

falldown of the old burned forest contributes significantly to the fire behavior and fire effects of the next

fire.

The purposes of this report are (1) to identify a range

of CWD quantities that provides for positive values

and avoids excessive fire hazard, and (2) to illustrate

how simulation of the effects of various management

alternatives on CWD over long periods can assist in

planning. We examined the knowledge of the ecology

of CWD, its contribution to potential fire behavior,

historical stand structures and large fuel accumulations, and potential reburn severity as a basis for

identifying optimum quantities of CWD. The fires of

2000 on the Bitterroot National Forest served as a case

study to illustrate the way in which simulation modeling can be used in conjunction with these general

concepts to aid in planning. Example simulations use

data from the Bitterroot Forest. The general discussion of coarse woody debris is meant to be broadly

applicable and not limited to a particular forest.

A note on terminology: low soil heating severity or

burn severity as reported in the Bitterroot Post Fire

Assessment (Bitterroot National Forest 2000) and as

used in this paper is typical of understory and mixed

fire regime types. Moderate severity is typical of mixed

and stand-replacement fire regime types, and high

severity is typical of the stand-replacement fire regime type. Fire regime type refers to historical effects

of fire (Brown 2000).

• Understory fire regime—fires are generally nonlethal to the overstory (approximately 80 percent

or more of the dominant vegetation survives).

• Stand-replacement fire regime—fires are lethal

to most aboveground dominant vegetation (approximately 80 percent or more of the dominant

vegetation is killed).

• Mixed severity fire regime—fire severity varies

between understory and stand-replacement

regimes.

Ecology of Coarse Woody

Debris _________________________

Coarse woody debris is typically defined as dead

standing and downed pieces larger than 3 inches in

diameter (Harmon and others 1986), which corresponds to the size class that defines large woody fuel.

Some ecologists include woody material larger than

1 inch in diameter as CWD. Coarse woody debris is an

important component in the structure and functioning

of ecosystems. A dead tree, from the time it dies until

Coarse Woody Debris: Managing

Benefits and Fire Hazard in the

Recovering Forest

James K. Brown

Elizabeth D. Reinhardt

Kylie A. Kramer
2 USDA Forest Service Gen Tech. Rep. RMRS-GTR-105. 2003

it is fully decomposed, contributes to many ecological

processes as a standing snag and fallen woody material lying on and in the soil. Fire, insects, pathogens,

and weather are responsible for the decomposition of

dead organic matter and the recycling of nutrients

(Olson 1963; Stoszek 1988). Fire directly recycles the

carbon of living and dead vegetation. The relative

importance of fire and biological decomposition depends on site and climate (Harvey 1994). In cold or dry

environments, biological decay is limited, which allows accumulation of plant debris. Fire plays a major

role in recycling organic matter in these environments. Without fire in these ecosystems, nutrients

are tied up in dead woody material for a long period.

Fire, insects, and diseases perform similar roles in

that they both create and consume CWD and smaller

dead woody material.

Importance to Wildlife

Coarse woody debris plays many roles in the forest.

Animal life processes, site productivity, site protection, and fire are probably the ones that managers

most often deliberate. Coarse woody debris contributes to biodiversity by being part of the life cycle of soil

mites, insects, reptiles, amphibians, mammals, and

birds (Brown 2000). Invertebrates such as bark beetles,

wood borers, carpenter ants, and wasps utilize CWD

for food and protection. Mammals, reptiles, and amphibians mostly utilize downed logs for purposes such

as feeding, reproduction, and shelter (Harmon and

others 1986). As more downed CWD accumulates in

the forest, activity of small mammals such as voles

increases (Ucitel 1999). A 15 to 20 percent coverage of

downed CWD was recommended by Carey and Johnson

(1995) for favoring small animal communities. A 15

percent coverage of CWD is equivalent to 32 tons per

acre of 6-inch diameter pieces or 64 tons per acre of 12-

inch pieces, assuming wood densities typical of ponderosa pine and lodgepole pine.

Woody debris incorporated in streams creates habitat diversity that improves rearing habitat for anadromous fish (Everest and Harr 1982) and provides survival cover. Woody debris also provides a source of

nutrients for aquatic life that increases abundance of

macroinvertebrates (Smock and others 1989). However, excessive accumulations can block fish passage,

cover important spawning sites, and damage aquatic

habitat during postfire flood events (Gresswell 1999).

Desirable quantities of CWD to leave following salvage logging for recruitment into streams to benefit

aquatic life are only generally known. However, the

origin of CWD that eventually becomes incorporated

in streams is known. In small streams in Washington

and Oregon, McDade and others (1990) found that 70

percent of debris pieces were rooted within 60 ft of the

streambank, and 50 percent came within a 30-ft wide

strip on each side of the stream. In Alaska, Murphy

and Koski (1989) observed that 95 percent of the

CWD came from within 60 ft of the stream. They also

observed that the larger the stream, the larger the

CWD needed to form a stable accumulation. These

studies suggest that leaving an uncut strip 60 to 100

ft from each streambank would maintain CWD in

aquatic habitat.

A range of desirable snag densities depending on

bird species has been suggested for forests in the

Northern Rocky Mountains. About 25 percent of the

bird species in the Northern Rocky Mountains are

cavity nesters (Bull and others 1997). Cavity nesting

birds and bats mostly utilize standing snags especially

those of large diameters (Fischer and McClelland

1983). Smaller snags can be important for foraging.

Salvage logging can enhance habitat for some species

but diminish it for others, resulting in a shift in

diversity but not in richness (McIver and Starr 2001).

For Pileated Woodpeckers (Dryocopus pileatus), Bull

and Holthausen (1993) showed that viable populations were maintained with an average of four snags

per acre (10-inch and greater diameter at breast height,

d.b.h.). Following high intensity wildfire Saab and

Dudley (1998) found that the Lewis’ Woodpecker

(Melanerpes lewis) and Kestrel (Falco sparverius) preferred salvage logged areas that retained about 25

snags per acre (more than 9-inch d.b.h.). The Blackbacked Woodpecker (Picoides arcticus) and Northern

Flicker (Colaptes auratus) preferred the unlogged areas having about 50 snags per acre (more than 9-inch

d.b.h.). Bull (1994) suggested leaving 40 standing or

fallen snags per acre (preferably more than 15-inch

d.b.h.) to retain as much wildlife as possible in stands

to be salvage logged following fire. The CWD loadings

represented by these snag densities range from about

1 to 25 tons per acre depending on diameter of trees

(table 1, 2).

Although an abundant literature shows the importance of standing and downed CWD to wildlife, few

studies have quantified amounts needed to maintain

specific populations much less whole faunal communities. One difficulty in interpreting and applying research results is that many studies deal with populations on specific sites and report conditions that

enhance or maximize populations on those sites. Maintenance of metapopulations and a diversity of species, however, requires a landscape perspective and a

strategy that provides a diversity of habitat structures (Hutto 1995; Lyon and others 2000; Tobalske

and others 1991).

Importance to Soils

Maintaining soil productivity over the long term

generally requires presence of soil organic material

and fire effects characteristic of the natural fire regime. Most fires characteristic of the historic fire

regime or moderate severity prescribed fires are likely
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 3

Table 1—Loading of standing dead ponderosa pine coarse woody debris (tons per acre) by number

of snags per acre and d.b.h. (inches). Loadings computed from table 2.

d.b.h.

Number 6 8 10 12 14 16 20 24

4 0.2 0.4 0.8 1.3 2.0 2.9 5.3 8.6

6 .3 .6 1.2 2.0 3.1 4.4 8.0 12

8 .4 .9 1.6 2.7 4.1 5.9 11 17

10 .5 1.1 2.0 3.3 5.1 7.4 13 22

15 .7 1.6 2.9 5.0 7.7 11 20 32

20 1.0 2.1 3.9 6.6 10 15 27 43

25 1.2 2.7 4.9 8.3 13 18 33 54

30 1.4 3.2 5.9 10 15 22 40 64

40 1.9 4.3 7.8 13 20 29 53 86

50 2.4 5.4 9.8 17 26 37 67

100 4.8 11 20 33 51 74

200 9.6 21 39 66 102

300 14 32 58 100

400 19 43 78

500 24 54 98

to enhance soil development and fertility over the long

term by periodic release of nutrients. However, extremely severe fires or large severely burned areas

within fires, brought on by either rare natural events

or humans, are likely to be highly detrimental to forest

soils (Harvey and others1989).

Nitrogen is the most limiting nutrient in forest

ecosystems. Its quantity and form in the soil is almost

totally dependent on microbial action by way of two

distinct processes, symbiotic and nonsymbiotic N fixation. Except where N-fixing plants such as alder (Alnus

spp.) and ceanothus (Ceanothus spp.) are in good

supply, most N acquisition in forests comes from

nonsymbiotic fixation that depends on organic matter

for energy (Harvey and others 1989). Another group of

microorganisms that depend on soil organic matter

and is important to a conifer’s ability to acquire

nutrients such as N is the ectomycorrhizal fungi

associated with roots. Using ectomycorrhizae as a

bioindicator of healthy, productive forest soils, Graham and others (1994) developed conservative recommendations for leaving CWD after timber harvesting

to ensure enough organic matter was left to maintain

long-term forest productivity. For Montana habitat

types (Pfister and others 1977) they recommended 5

to 9 tons per acre (Douglas-fir/ninebark), 12 to 24

tons per acre (Douglas-fir/pinegrass), 7 to 14 tons per

acre (grand fir/bear grass), 8 to 18 tons per acre

(subalpine fir/bluehuckleberry, subalpine fir/grouse

Table 2—Total tree bole weight (tons) of wood and bark of

individual trees based on whole tree volume

equationsa, wood density, and bark-to-wood ratios

for ponderosa pine (PP), Douglas-fir (DF), and

lodgepole pine (LP)b

. Data based on trees from

stands of a variety of site indexes and densities.

d.b.h. PP DF LP

4 0.017 0.021 0.026

5 .029 .037 .051

6 .048 .060 .081

7 .074 .088 .118

8 .107 .123 .162

9 .147 .166 .215

10 .196 .218 .275

11 .258 .274 .343

12 .332 .341 .420

13 .416 .416 .504

14 .511 .501 .597

15 .617 .595 .698

16 .736 .699 .807

18 1.009 .938 1.051

20 1.334 1.220 1.328

22 1.714 1.546

24 2.151 1.921

26 2.648 2.344

28 3.208 2.819

30 3.832 3.346

aEquations for 4-inch d.b.h. from Faurot (1977) and for 5- to 30-inch d.b.h. from

Brown and Johnston (1976) and Stage (1973). b Wood density and bark ratios from Brown and others (1977).
4 USDA Forest Service Gen Tech. Rep. RMRS-GTR-105. 2003

whortleberry), and 12 to 24 tons per acre (subalpine

fir/bear grass, subalpine fir/twinflower). For ponderosa pine/fescue and Gambel oak (Quercus gambelii)

habitat types in Arizona, they recommended 5 to 13

tons per acre. These recommendations were based on

studies in undisturbed mature stands where ectomycorrhizae populations were used to determine optimum

amounts of organic material. The upper limit of the

recommended ranges or higher seems appropriate for

stands recovering from high severity wildfire where

much of the partially decomposed CWD and other

forest floor organic matter was consumed.

The role of CWD in site protection can be significant

or minor depending on site conditions. On steep slopes,

CWD helps protect soils from erosion due to surface

runoff. It disrupts flow near the ground, creates shade

for seedlings, and reduces trampling by livestock,

wildlife, and people.

Fire Hazard_____________________

Fire hazard generally refers to the difficulty of

controlling potential wildfire. It is commonly determined by fire behavior characteristics such as rate-ofspread, intensity, torching, crowning, spotting, and

fire persistence, and by resistance-to-control. In this

paper we also consider fire severity to be an element of

fire hazard. Fire severity refers to the effects of fire on

the ecosystem. It depends on fuel consumption and

heat flux into all living components. Downward heat

transfer into the soil is an important determinant of

fire severity (Ryan and Noste 1985). Fire intensity,

largely a measure of upward heat transfer, is not a

reliable indicator of fire severity because it can correlate poorly with downward heat transfer. Small and

large downed woody fuels contribute differently to the

various elements of fire hazard.

Fire Behavior

The influence of small woody fuels (3 inches and less

in diameter) on spread rate and intensity of surface

fires and associated torching and crowning is substantial and can be estimated using widely accepted fire

behavior models (Andrews 1986; Finney 1998;

Rothermel 1983; Scott and Reinhardt 2001). Large

woody fuels have little influence on spread and intensity of the initiating surface fire in current fire behavior models; however, they can contribute to development of large fires and high fire severity. Fire

persistence, resistance-to-control, and burnout time

(which affects soil heating) are significantly influenced by loading, size, and decay state of large woody

fuel. However, methods for estimating and interpreting these fire characteristics are not well established.

Accumulations of large dead woody fuel, especially

containing larger diameter decayed pieces, can hold

smoldering fire on a site for extended periods. When

high winds occur, the sustained burning of persistent

fire can be fanned into fast moving, dangerous fires

(Chandler and others 1983). Historically, this was

probably an important factor in development of large

fires. The probability of a reburn is higher, to an

unknown extent, in heavy accumulations of CWD because of the high fire persistence that characterizes

decayed CWD. However, the probability of wildfire

due to high fire persistence can be mitigated by effective fire detection and suppression actions.

Torching, crowning, and spotting, which contribute

to large fire growth, are greater where large woody

fuels have accumulated under a forest canopy and can

contribute to surface fire heat release. Duration of

flaming and energy release during flaming can be

computed using a burnout model (Albini 1976) to

indicate the potential for extreme fire behavior such as

crowning and long-distance spotting. Compared to

surface fuels with little CWD, Rothermel (1991) showed

that 30 tons per acre of 6-inch sound pieces increases

energy release of surface fuels in the flaming front and

the associated crown fire, but not substantially. However, if the large woody fuel is decayed and broken up,

its contribution is considerably greater, similar to fire

in heavy slash. The contribution of large woody fuel to

surface fire intensity is likely underestimated in fire

behavior models that treat large woody pieces as

smooth cylinders. An assumption of a smooth surface

disregards the finely textured nature of bark-covered

and weathered pieces.

Resistance-to-Control

Resistance-to-control is generally viewed as an estimate of the suppression force required for controlling

a unit of fire perimeter. Ratings may be subjective as

applied in the Photo Guide for Appraising Downed

Woody Fuels in Montana Forests (Fischer 1981). For

example, “high” resistance-to-control means “slow work

for dozers, very difficult for hand crews; hand line

holding will be difficult.” Large woody fuel loadings in

the Photo Guide ranged widely depending on size of

downed pieces and undergrowth. Loading for a medium rating ranged from 14 to 50 tons per acre.

The USDA Forest Service Pacific Southwest Region

(1976) developed a resistance-to-control rating scheme

based on difficulty of hand line construction and an

inventory of downed woody fuel loadings by size classes.

High and extreme resistance-to-control ratings were

reached for the following loadings (tons per acre):

0- to 3-inch diameter 3- to 10-inch diameter

High Extreme

5 25 40

10 15 25

15 5 15
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 5

The above ratings were based on the assumption

that few downed pieces greater than a 10-inch diameter were present. In computing the ratings, the number of large pieces (greater than 10 inch) by length

class is more important than their loading in determining resistance-to-control. If the number of pieces

greater than a 10-inch diameter exceeded 10 to 20 per

acre, depending on length, less 3- to 10-inch diameter

material would be required to reach the high and

extreme resistance-to-control ratings.

Soil Heating

Soil heating is a complicated process that depends

on burnout time of duff and woody material, removal

of the insulating duff layer, and soil properties

(Hungerford and others 1991). Under severe burning

conditions, soil organic matter can be removed or

destructively altered, nutrients volatilized, water-absorbing capacity decreased, and living plant parts and

microorganisms killed. Loss of soil organic matter that

is necessary for sustaining the biological activity of

soils (DeBano and others 1998) is probably the most

serious long-term concern.

Estimates of soil heating can be obtained using

FOFEM (Reinhardt and others 1997). The model predicts a time-temperature profile at specified depths;

depths at which critical temperatures occur can also

be predicted. But to date little experience exists in

interpreting the predicted soil temperature profiles

across a large landscape. In addition to considering

temperature, three other aspects of soil heating need

to be evaluated: depth of undesirable heating, duration of heating (for example, 1 minute) that allows

heat effects to unfold, and proportion of area that is

impacted by undesirable soil temperatures. This last

element is necessary because the model predicts a

time-temperature profile based on an estimated unit

average heat flux that expresses heating uniformly

across a given area. In reality, however, excessive soil

heating is concentrated beneath large woody fuel

pieces particularly in the vicinity of piece intersections. For any predicted temperature it can be assumed that the temperature is considerably higher

where the soil is overlaid with CWD, and elsewhere it

is less than predicted.

To explore the effect of CWD on soil temperatures we

exercised the soil heating model in FOFEM for a range

of fuel loadings (fig.1a). We assumed absence of a duff

layer, typical of a young forest developing after standreplacement fire. One possible criterion for evaluating

undesirable soil heating is the temperature at which

organic matter is destructively distilled. This occurs at

200 to 300 ∞C (Hungerford and others 1991). Figure 1a

indicates that high fuel loads (40 tons per acre) are

necessary to cause soil to be excessively heated (at least

275 ∞C) from the surface to 2 cm depths. Figure 1b can

be used to help with interpretation of soil heating

Figure 1—(a) Simulated soil heating. Curves show maximum temperatures reached at several

soil depths for a range of woody fuel loadings. In these simulations, it was assumed the soils and

fuels were dry, and that there was no duff to insulate the soil. (b) Percent of area covered by woody

fuel for a range of piece diameters and woody fuel loadings, assuming the fuel is evenly spread.

Actual area coverage would be reduced because of piece overlap, but area impacted by heating

might be greater due to heating of soils adjacent to but not immediately below woody fuel.

a

Maximum temperature, degrees C

Woody fuel loading, tons/acre

b

Area covered by coarse woody debris, percent

Tons/acre
6 USDA Forest Service Gen Tech. Rep. RMRS-GTR-105. 2003

results. It shows, for several piece sizes, the coverage

of CWD over a range of fuel loads. Even at high fuel

loads, a small portion of an area is covered with woody

fuel. In areas that have no coverage, minimal soil

heating can be expected.

A practical consideration for minimizing severe soil

heating is to concentrate salvage activities in thickets

of dead trees. If the thickets fall down naturally the

CWD becomes concentrated. Burnout of large woody

fuels is enhanced where the material is concentrated

because of the interaction between adjacent burning

pieces. Thus, salvage can be used to reduce and scatter

the potential fuel concentrations.

Historical Conditions ____________

Stand Structure

On dry sites occupied by ponderosa pine and mixed

ponderosa pine and Douglas-fir, a structural mosaic

probably existed due to variation in tree establishment, fire caused mortality, and other factors (Arno

and others 1995). Research plots on the Bitterroot and

Lolo National Forests showed that ponderosa pine

existed in all-aged and even-aged stands that experienced similar fire histories. Although age-class structures varied substantially, most stands probably appeared open or parklike (Arno and others 1997). Long

periods (50 to 100 years) without new pine establishment occurred presumably because the site was too

stocked to allow recruitment of shade-intolerant species, or most of the regeneration was killed by fire.

After 1900, when occurrence of frequent, low intensity fires was significantly reduced in Western forests,

understories changed with an increase in basal area

and number of trees per acre. A shade-tolerant tree

understory of Douglas-fir developed. We computed the

increase in standing bolewood and crowns for trees up

to an 8-inch diameter that accrued from 1900 to 1991

on the four Bitterroot National Forest study plots

(Arno and others 1995). The increase in bolewood

weight ranged from 1 to 11 tons per acre and crown

weight from 0.5 to 6 tons per acre.

In restoring the dry site forest communities, a range

of alternatives is possible because of the wide range in

stand structures that probably existed historically.

However, control of shade-tolerant species such as

Douglas-fir will probably be necessary either using

mechanical means or prescribed fire repeated periodically. Where prescribed fire is applied, probably after

young pine can tolerate low intensity fire, woody fuels

including CWD will be partially reduced.

Large Woody Fuel

Quantities of downed woody fuel, hence CWD, that

fall within the presettlement era historical range of

variability for the understory and mixed fire regime

types can be inferred from existing inventory data and

knowledge of fire history and fuel consumption. An

indication of large downed woody fuel loadings that

existed historically in the ponderosa pine, Douglas-fir,

and lodgepole pine cover types is the summary of data

gathered by forest inventory (stage I) and stand exams

(stage II) during the 1970s (Brown and See 1981). The

forest inventory was based on randomly located plots

and is representative of forestwide conditions excluding classified wilderness. Stand exams were located

where silvicultural activities were anticipated, such

as timber sales that were often targeted for high risk

stands. Thus, quantities of downed woody material

might tend to be greater than found in the forest

inventory over the whole forest as suggested in table 3.

Results of inventories are summarized for the Bitterroot and Lolo National Forests, which have similar

forests and fire histories (table 3). Considerable variability in quantities of downed woody material probably existed with many stands having little downed

woody material and a few stands having excessive

accumulations.

It seems reasonable to speculate that on average the

quantities in table 3 would be less if understory fire

had been allowed to occur at presettlement frequencies. This is supported by Habeck’s (1976) study in the

White Cap drainage of the Selway-Bitterroot Wilderness. In ponderosa pine stands having less than 0.5

Table 3—Average quantities of large woody fuel (tons per acre) by ponderosa pine

(PP), Douglas-fir (DF), and lodgepole pine (LP) cover types on the

Bitterroot and Lolo National Forests inventoried by the forest survey and

stand exam programs (Brown and See 1981). Number of plots is shown

in parentheses.

Bitterroot Lolo

Program PP DF LP PP DF LP

Forest survey 5.3 9.2 12.2 4.8 11.5 13.3

(218) (1,056) (203) (120) (1,000) (768)

Stand exam 11.3 21.1 25.9 10.4 11.9 15.8

(1,685) (7,158) (1,152) (665) (4,233) (1,591)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 7

inch (1 cm) of duff (averaged 2.4 tons per acre), large

woody fuels averaged less than 1 ton per acre. The

shallow duff indicated a fire history characteristic of

the understory fire regime. In stands having more

than a 0.5 inch of duff (averaged 11 tons per acre),

indicating a long period without fire, large woody fuels

averaged 23 tons per acre.

Snag densities on pre-European landscapes were

estimated by Harrod and others (1998) as 6 to 14 snags

per acre for dry forests east of the Cascades. This

converts to approximately 4.5 to 7.0 tons per acre

based on the wood density of ponderosa pine. He

assumed stand structure to be open and parklike

(basal area of 60 and 80 sq ft per acre) for forests of

ponderosa pine, Douglas-fir, and dry associations of

grand fir (Abies grandis). Lower densities favored

larger tree diameters, which ranged from 7 to 35

inches. Snags were recruited with a life of up to 45

years under a regime of frequent, low intensity surface

fires that created an uneven-aged structure with

small even-aged groups. In a study of snag abundance in western Montana based on forest inventory

data, Harris (1999) reported an average of 2.5, 9, and

12 snags per acre in uncut stands of the ponderosa

pine, Douglas-fir, and lodgepole pine cover types. This

is equivalent to about 2.2 to 6.0 tons per acre of snags.

The spatial distribution of snags was highly variable,

with many plots having none and some plots having

many. The estimated snag densities from both studies

over their modeled life span (Harrod and others 1998)

seem to relate in a plausible way to the accumulated

downed large woody fuels in table 3.

Optimum Coarse Woody

Debris _________________________

The amount of CWD that provides desirable biological benefits, without creating an unacceptable fire

hazard or potential for high fire severity reburn, is an

optimum quantity that can be useful for guiding management actions. To arrive at this optimum, various

sources of information about the roles of CWD in the

forest and its historical dynamics should be considered. Most sources of technical knowledge about the

benefits of CWD and fire characteristics deal with

individual species or restricted segments of the ecosystem. We integrated the various sources of information

to identify an optimum range of CWD that provides an

acceptable risk of fire hazard while providing benefits

to soil and wildlife (fig. 2). The optimum quantity for

soil and fire considerations refers to downed CWD. For

wildlife the optimum quantity involves both standing

and downed CWD.

Although quantitative information is limited, we

stress it here because it provides a good basis on which

to plan. To summarize the positive values from earlier

discussion, for maintaining soil productivity the upper

limit of the following ranges is recommended: 5 to 10 tons

per acre for warm, dry ponderosa pine and Douglas-fir

types, 10 to 20 tons per acre for cool Douglas-fir types,

and 8 to 24 tons per acre for cool lodgepole pine and

lower subalpine fir types. Interestingly, these quantities coincide with the average amounts of large woody

fuel inventoried by forest survey and stand exams

(table 3) that may represent the high end of

presettlement conditions because occurrence of fire

Figure 2—Optimum ranges of coarse woody debris for providing acceptable risks of fire hazard and

fire severity while providing desirable quantities for soil productivity, soil protection, and wildlife

needs for (a) warm dry forest types and (b) cool and lower subalpine forest types. Dotted lines show

a range that seems to best meet most resource needs: 5 to 20 tons per acre for the warm dry types

and 10 to 30 tons per acre for other types.

b

Coarse woody debris, tons/acre

a

Coarse woody debris, tons/acre
8 USDA Forest Service Gen Tech. Rep. RMRS-GTR-105. 2003

and associated fuel consumption had already been

reduced compared to the historical fire regime. Although fire both creates and consumes fuel (Brown

1985), fuel depletion would tend to be greater than fuel

accretion in high frequency fire regime types such as

the warm, dry ponderosa pine and Douglas-fir types.

For cavity-nesting birds, up to 25 tons per acre may

be desirable depending on species (see tables 1 or 2 for

converting tons per acre to number of snags per acre).

For small mammals, more than 30 tons per acre is

best. Needs of riparian systems for CWD can be met by

leaving all or most of the trees in a 60- to 100-ft wide

strip on each side of streams. A wide range in CWD is

indicated for wildlife (fig. 2) because desirable quantities vary greatly by species. However, insufficient

knowledge exists to define the upper limit of CWD

beneficial to wildlife. To encourage a diversity of wildlife species, a worthy objective may be to manage for a

wide range of CWD across the landscape. There is

considerable latitude within the optimum range for

managing CWD to achieve benefits and avoid excessive wildfire threats.

To summarize the negative values, fire hazard including resistance-to-control and fire behavior reach

high ratings when large fuels exceed about 25 to 30

tons per acre in combination with small woody fuels of

5 tons per acre or less. Excessive soil heating is likely

at approximately 40 tons per acre and higher. Thus,

generally high to extreme fire hazard potential exists

when downed CWD exceeds 30 to 40 tons per acre.

Consideration of these positive and negative aspects

indicates that the optimum quantity of CWD is about

5 to 20 tons per acre for warm dry ponderosa pine and

Douglas-fir types and 10 to 30 tons per acre for cool

Douglas-fir and lodgepole pine types and lower subalpine fir types. The recommended optimum ranges of

CWD quantities (fig. 2) should be modified by consideration of other factors such as quantity of small

woody fuel, diameter of CWD, landscape level needs,

and ecosystem restoration objectives. The CWD optimum quantities for acceptable fire hazard are appropriate when accompanied by small dead fuel loadings

of about 5 tons per acre or less. Acceptable CWD quantities are less at higher small fuel loadings (greater than

8 to 10 tons per acre). Acceptable CWD for fire hazard

(fig.2) is slightly less for the warm, dry sites because

they occur in a more flammable fire environment

where generally less soil organic materials are necessary for maintaining soil productivity.

Higher loadings of CWD are acceptable where larger

piece sizes predominate, for example in accumulated

falldown of old growth trees. Larger piece sizes also

are desirable because, faced with decomposition and

fire, they persist longer to benefit wildlife and soil

productivity. Unfortunately, the relationship between

quantity and size of CWD and the various measures of

fire hazard is largely undefined. Thus, it is a matter of

judgment to consider that the larger the diameter of

downed CWD the greater the loading that could be

allowed without undesirable fire effects. A graph of

CWD surface area by piece diameter and vertical

projection of piece areas by piece diameter (fig. 3) can

provide some guidance for adjusting the optimum

range. The curves flatten at about a 5-inch diameter

for the vertical projection and at an 8-inch diameter for

surface area. This suggests that where CWD comprises predominately 3- to 6-inch material, the optimum quantity is less, perhaps by 5 tons per acre or

more, than for larger sized material. With this in

mind, it seems reasonable to assume that high fire

hazard ratings apply when 25 to 30 tons per acre of

CWD largely comprises 3- to 6-inch material. If quantities of CWD, comprising mostly smaller diameter

pieces (3 to 6 inches), were at the upper end of the

optimum range, adverse soil heating might occur at

low fuel moisture contents, especially if substantial

quantities of small woody fuels were also present (8 to

10 tons per acre or more).

Severity of Reburn ______________

A question often asked by managers is if a reburn

occurs, what fire effects can be expected? The interest

is primarily in recovery of vegetation and possible

impairment to soil productivity. The purpose of this

section is to suggest in general terms how burn severity and postfire succession might be affected by recurrence of fire at varying periods following the previous

fire. The probability of a reburn occurrence, which is

small for a particular site but high over a large area

such as a Ranger District, is not dealt with here.

Figure 3—Surface area and vertical

projection per ton of woody material as they

vary by size class. Square feet/ton

Piece diameter
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 9

Vegetative succession following forest fire including

reburns depends on a number of interacting factors

including fire severity, prefire vegetation, species adaptations to fire, environmental conditions, and chance

(Brown 2000; Lyon and Stickney 1976; Miller 2000;

Morgan and Neuenschwander 1988). Although succession depends on many variables, the following

principles can provide a general description of plant

community development after a reburn.

1. The course of succession is set by the prefire

composition of species that survive fire onsite by protected sprouting plant parts and seeds (Stickney 1990).

In Northern Rocky Mountain wildfires, which are

mostly of moderate to high severity, there is a tendency to get back most of the species that were present

before fire (Lyon and Stickney 1976).

2. Many herb and shrub species have sprouting

parts such as rhizomes, bulbs, and root crowns that

are buried in mineral soil to varying depths.

3. The more severe the fire the higher the mortality

and the less the survivor component in both species

and number of plants (Stickney 1990). Only deeply

buried sprouting parts survive. Resilient species such

as pinegrass (Calamagrostis rubescens) and Douglas

spirea (Spiraea betulifolia) usually retain surviving

plant components. Further additions must come from

offsite plants. Offsite colonizers that have light, easily

wind-disseminated seeds are favored. Thus, both desired native plant and weed species fitting this category are favored.

4. The pattern of burn severity within a fire relates

to the pattern of fuel consumption (Miller 2000). Duration of fire over uninsulated soil largely determines

severity.

5. A future influence of unknown consequences on

postfire succession is global warming, which may

affect fire severity and plant establishment, growth,

and mortality (Ryan 2000).

With these principles in mind, some general statements about the effects of a reburn during high to

extreme burning conditions with low fuel moistures

can be made:

0 to 10 Years After First Fire—High severity fire

is unlikely because duff and downed woody fuels that

support prolonged burning would be absent. Large

woody fuels would still be accumulating through

falldown, and they would not have decayed enough to

support smoldering combustion, which can extend the

period of downward heating. If salvage operations

leave concentrations of small woody fuels, high severity

burning could occur where the fuels are concentrated.

This situation would be aggravated where standreplacement fire did not consume foliage, thus allowing a layer of scorched needles to accumulate as

surface fuel. Surviving onsite herbs and shrubs should

dominate the recovering vegetation. Newly established trees that regenerate by producing seeds could

be lost. Even seedlings of species having sprouting

capability could die if their root systems are not well

established.

10 to 30 Years After First Fire—Downed CWD

would exhibit some decay and support a longer period

of burning. A duff layer, however, would not be well

established and would be unable to contribute to soil

heating. Thus, high burn severity would primarily

occur where large woody material was lying on or near

the soil surface. High severity fire could be substantial

where a large proportion of the soil surface was directly overlain by large woody material, which could

accumulate from falldown of a large amount of tree

basal area. A limited amount of conifer regeneration

might be possible from young cone-bearing trees established onsite after the previous fire. Onsite herbs

and shrubs would dominate the recovery vegetation

except where burnout of large woody pieces caused

deep soil heating, which would occur particularly in

the near vicinity of overlapping pieces.

30 to 60 Years After First Fire—Large woody

pieces would probably exhibit considerable decay, and

a forest floor of litter and duff would be established to

a variable extent depending on the density of overstory conifers. Burnout of large woody pieces and duff

is assisted by the interaction of these two components

(Brown and others 1991). Higher severity burning

than would typically occur during earlier periods is

possible depending on extent of soil coverage by large

woody pieces. If a conifer overstory exists, crowning

coupled with burnout of duff could amplify the burn

severity. Offsite colonizers would be an important

component of the recovery in the more severely burned

locations. Prescribed fire during this period could

greatly reduce the severity of a reburn wildfire. However, a reburn involving optimum quantities of CWD

should not lead to unusually severe fire effects. Historically, fires probably often occurred in the understory and mixed fire regime types when large downed

woody fuels were in the optimum range.

To predict succession more specifically following a

reburn, managers would need an inventory of plant

species onsite and offsite and an inventory of fuels.

Planning Retention of Coarse

Woody Debris __________________

The environmental effects of postfire salvage and

fuel treatment activities may be due to the activity of

removing trees or due to the altered stand structure

(McIver and Starr 2001). Deciding whether to remove

fire-killed or damaged trees and how much CWD

should be retained on various sites could be viewed as

passing through a series of decision gates or addressing questions that evaluate the environmental effects.

For example, consider the following questions:
10 USDA Forest Service Gen Tech. Rep. RMRS-GTR-105. 2003

1. Where will salvage activities cause unacceptable

soil compaction, erosion, and sedimentation? Roads

have the greatest potential for exacerbating erosion.

Also consider the need for site rehabilitation and that

a reburn in heavy accumulations of CWD could encourage erosion.

2. Where will expected falldown of fire-killed trees

together with existing downed woody fuels exceed the

optimum CWD? Consider mortality to surviving trees

that may die during the next 5 to 10 years due to fire

injury, insects, and windfall.

3. Where should landscape scale considerations influence retention of CWD? For example, salvage may

be desirable in the wildland-urban interface zone and

elsewhere to break up large blocks of high fuel loadings and create areas having low to moderate fire

behavior potential and resistance-to-control. Salvage

may be undesirable where large diameter snags needed

by wildlife are in short supply in adjoining areas.

The Bitterroot National Forest: An

Example _______________________

Following the wildfires of 2000 on the Bitterroot

National Forest, managers were particularly concerned

with:

1. Potential for large, severe fires in the future that

are of high risk to firefighters and public safety

2. Creating a fire-defensible wildland-urban interface

3. Recovery of the dry site forest types to fit with the

historical fire regime

4. Effects of a possible reburn on soil productivity

and vegetation succession

5. Providing wildlife values and forest products

6. Avoiding soil erosion and sedimentation and invasion of weeds

Of primary concern were three ecosystems identified as vegetation response units (VRU) in the Bitterroot Fires 2000 Assessment of Post-fire Conditions

with Recovery Recommendations (Bitterroot National

Forest 2000):

1. VRU 2—warm, dry ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii var.

glauca) habitat types

2. VRU 3—cool, dry, and moist Douglas-fir habitat

types

3. VRU 4—cool lodgepole pine (Pinus contorta) and

lower subalpine fir (Abies lasiocarpa) habitat types.

Approximately 126,000 acres in VRU 2 and VRU 3

were burned with 60 percent of VRU 2 and 49 percent

of VRU 3 experiencing moderate to high soil heating

severity (Bitterroot National Forest 2000). Understory and mixed fire regime types characterize VRU 2

and VRU 3. Management direction for these vegetation

response units was to keep wildfire hazard in the

wildland-urban interface at acceptable levels by reducing fuels and to return the vegetation and fuels to

conditions falling within the historical range of variability (Brown 2000) for these fire regime types. Approximately 86,000 acres burned in VRU 4, with 51

percent of the area experiencing moderate and high

soil heating severity, which fits with the mixed and

stand-replacement fire regime types that characterize VRU 4. In all, 356,000 acres were burned on the

Bitterroot National Forest and adjacent State and

private lands.

Modeling Predictions

Management of CWD should consider how much of

it is desired onsite in the future. This requires predictions of falldown of fire-killed trees, continued tree

mortality and falldown, and loss of dead woody material through deterioration and decay. The time interval chosen for predicting CWD should be long enough

for a new immature or mature forest to develop. Keep

in mind that the further in time the projection, the

more uncertainty exists about the predicted values.

Reasonable predictions of CWD can probably be provided over a period of 50 to 100 years.

To project future trends of CWD we used The Fire

and Fuels Extension (FFE) (Beukema and others

2000) to the Forest Vegetation Simulator (FVS) (Stage

1973) to simulate the effects of alternative management strategies on future quantities of CWD and

small woody fuels. The FVS simulates tree growth,

tree mortality and regeneration, and the impacts of a

wide range of silvicultural treatments. The FFE simulates additions to fuel pools from stand dynamics and

management activities, and the removal of fuels

through decay, mechanical treatments, and prescribed

or wildfires. Various types of fuels are represented,

including canopy fuels and surface fuels by diameter

classes. Fire behavior of the propagating fire front and

fire effects, such as fuel consumption, tree mortality,

and smoke production, are modeled. Model outputs

include fuel characteristics, stand structure, snag density, and potential fire behavior that provide a basis

for comparing proposed stand and fuel treatments.

We selected three stands representing different vegetation types on the Bitterroot National Forest to

illustrate how FVS and FFE could be used to simulate

the effects of no treatment, salvage, and fuel treatment on CWD. The selected stands were considered

typical of forest conditions occurring commonly on the

Bitterroot National Forest (table 4). The VRU 2 stand

contained a few old growth ponderosa pine and Douglas-fir trees with a dense understory of Douglas-fir, a

condition that has developed extensively in the absence of repeated low intensity fire. The VRU 3 stand

is a pure Douglas-fir stand with trees mostly ranging
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 11

from 4 to 20 inches d.b.h. The VRU 4 stand consisted

of a dominant lodgepole pine overstory with a dense

understory of small subalpine fir and Englemann

spruce (Picea engelmannii). The salvage treatment

called for removing merchantable quality dead trees

greater than 12 inches d.b.h. Approximately the same

proportion of trees in each size class was removed.

Fuel treatment called for removing dead trees 6 inches

and less in d.b.h. by slashing, piling, and burning.

Figure 4a shows an untreated stand typical of VRU 2

following high severity fire, while figure 4b shows a

similar stand following partial salvage and surface

fuel treatment. Figure 4c shows a VRU 2 stand following low severity fire, partial salvage, and surface fuel

treatment.

For the simulation of high fire severity (100 percent

tree mortality) in VRU 2, untreated CWD accumulated well beyond the optimum range for the next 100

years (fig. 5). The large quantity of CWD together

with 8 to 10 tons per acre of small woody fuel (fig. 6)

presented a high fire hazard over many years. Salvage

of 50 percent or more of the merchantable dead trees

accompanied by treatment of fuel left an acceptable

quantity of CWD (fig. 7). The number of snags greater

than 12 inches d.b.h. per acre (snags per acre, SPA)

initially ranged from 4 for the 100 percent salvage

treatment to 17 for 50 percent salvage (table 5). After

20 years SPA falls to 0.8 for 100 percent salvage and

1.5 for 50 percent salvage. Many years elapse in high

fire severity burns before newly grown large diameter

snags can replace the fallen snags, so leaving an ample

density of snags following fire can help maintain a

minimal snag resource during the 20 to 40 year postfire

period when many snags have already fallen. Leaving

a high density of snags would require constraints on

harvesting.

Living stand structure and CWD varied considerably

between simulations of low and high fire severity (fig.

5). Under low severity fire (80 percent tree mortality),

Table 4—Number of trees per acre by d.b.h. class (inches) for

the representative vegetation response unit stands

used in the FFE simulation of postfire recovery.

VRU2 VRU 3 VRU 4

d.b.h. DF PP DF LP ES AF

0–1 409 112 191 464 5345

1–4 436 0 27 246

4–8 142 153 130 16

8–12 56 141 108 13

12–16 18 50 12 2

16–20 10 1 13

20–24 1 2

24–28 2

28–32 3

32+ 2

a

Figure 4—(a) Untreated stand following high

severity fire, Bitterroot National Forest, 2002.

(b) Treated stand following high severity fire,

Bitterroot National Forest, 2002. Note the

reduced density of standing dead trees and the

presence of coarse woody debris on the forest

floor. (c) Treated stand following low severity

fire, Bitterroot National Forest, 2002. Note

the standing live and dead trees, as well as

the residual coarse woody debris.

b

c
12 USDA Forest Service Gen Tech. Rep. RMRS-GTR-105. 2003

Figure 5—Simulated quantities of standing and surface coarse woody debris and live 3+

inch biomass for vegetation response unit 2 with no salvage and no fuel treatments under

(a) low (80 percent tree mortality) and (b) high (100 percent tree mortality) fire severity

conditions. Shaded bands indicate desired ranges.

untreated CWD peaked at 24 tons per acre but remained slightly higher than the 20-tons per acre upper

limit of optimum for next the 100 or more years due to

contributions from growth and mortality of the surviving forest. Fuel treatment without salvage removed

about 4 tons per acre of CWD and 2 tons per acre of

small woody fuel. This kept CWD within the optimum

range and lowered fire hazard.

For the VRU 3 stand, assuming high fire severity,

untreated CWD peaked at 53 tons per acre and remained greater than the 30-tons per acre upper limit

of optimum for the next 100 years (fig. 8). Salvage

accompanied by fuel treatment lowered CWD into the

optimum range (fig. 9). The simulations for salvage of

all dead merchantable trees without fuel treatment

and 50 percent salvage accompanied by fuel treatment

produced nearly the same amount of CWD over the

Figure 6—Simulated quantities of surface small woody fuel (0- to 3-inch diameter) for

vegetation response unit 2 for combinations of 100 percent salvage, 50 percent salvage and

no salvage with treated and untreated fuels under (a) low (80 percent tree mortality) and

(b) high (100 percent tree mortality) fire severity conditions.

a

a

Tons/acre

Year

b

Tons/acre

Year

b
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 13

Figure 7—Simulated quantities of surface

coarse woody debris for vegetation

response unit 2 for high severity-100

percent salvage-treat fuels, high severity50 percent salvage-treat fuels and low

severity-no salvage-treat fuels.

Table 5—Number of dead snags per acre in vegetation response

unit 2 simulated by FFE for varying treatments and

periods following fire.

Years following fire

 Treatments 3 20 40 60 80

All snags (>0 inch d.b.h.)

80% M, no S, no Ta 482 26 32 39 39

100% M, no S, no T 532 14 11 18 26

100% M, 50% S, yes T 154 3.9 28 34 45

100% M, 100% S, yes T 140 3.1 28 34 45

Snags >12 inch d.b.h.

80% M, no S, no T 22 8.2 3.2 3.0 3.4

100% M, no S, no T 34 11 1.7 .1 .7

100% M, 50% S, yes T 17 1.5 .3 .2 2.3

100% M, 100% S, yes T 3.7 .8 .1 .2 2.3

a M is mortality, S is salvage of dead merchantable trees, T is slash, pile, and

burn trees < 6 inches d.b.h.

simulation period. The CWD exceeded the 30-tons per

acre upper limit of optimum for 18 years, making these

treatments marginally acceptable. Regardless of the

level of salvage prescribed, fuel treatment was necessary to keep CWD within the optimum range. Immediately after fire, SPA were 33 for 50 percent salvage

and 7 for complete salvage. Most snags fell within

about 20 years. After that the difference in SPA between salvage treatments was slight. However, for

Year

Tons/acre

Figure 8—Simulated quantities of standing

and surface coarse woody debris and live

3+ inch biomass for vegetation response

unit 3 with no salvage and no fuel treatments

under high (100 percent tree mortality) fire

severity conditions. The shaded band

indicates desired ranges.

about 20 years in this simulation, the level of salvage

affected snag density significantly. Depending on species and d.b.h., the time snags remain standing generally ranges from 15 to 40 or more years. In planning for

retention of a given amount of CWD, treatment of fuel

that reduces small-sized CWD (trees up to 6 inches

d.b.h.) makes it possible to retain more large-diameter

dead snags.

For the VRU 4 lodgepole pine stand, the salvage

prescription had little effect on CWD (fig. 10) because

few merchantable trees were present. Without salvage or fuel treatment, the CWD exceeded the optimum range by 1 to 5 tons per acre for about 20 years

then fell within the optimum range. This simulation

suggests that fuel treatment and salvage would be

unnecessary unless landscape considerations such as

maintaining low fire hazard in the wildland interface

zone or in a strategically placed fuel break are important.

In stand-replacement fires, the CWD from the firekilled trees is all that exists for a long time, until the new

forest undergoes mortality and falldown. Some allowance

for decay should be considered in the planning. For

example, if 20 tons per acre was considered desirable

in the 40 to 60 year old immature forest, 25 tons per

acre or possibly more should be retained from the firekilled trees. In low severity fire where an overstory

survived, recruitment of CWD will probably occur

regularly over time as trees continue to die from

various causes such as insects, blowdown, and fire

injury. Meeting a target of 20 tons per acre in 40 years
14 USDA Forest Service Gen Tech. Rep. RMRS-GTR-105. 2003

Year

a

Figure 9—Simulated quantities of (a) small woody fuel and (b) coarse woody debris for

vegetation response unit 3 for 100 percent salvage-no fuel treatment, 100 percent salvage-treat

fuel and 50 percent salvage-treat fuel under high (100 percent tree mortality) fire severity

conditions. The shaded band indicates desired ranges.

Year

a

Year

b

Figure 10—Simulated quantities of (a) small woody fuel and (b) coarse woody debris for

vegetation response unit 4 for no salvage-no fuel treatment, 100 percent salvage-treat fuel and

100 percent salvage-no fuel treatment under high (100 percent tree mortality) fire severity

conditions. The shaded band indicates desired ranges.

may only require 15 tons per acre from falldown of the

trees directly killed by fire.

In VRU 2 where applying prescribed fire in the future

might be necessary to maintain desired conditions,

leaving excessive CWD, especially in the 3- to 6-inch

diameter class, could hamper prescribed fire efforts.

But also consider that prescribed fire will reduce the

CWD loadings. On sites where most of the CWD

loading comprises large pieces (greater than 12 inches),

which would offer less of a hindrance to prescribed

burning, consider retaining CWD loadings at the high

end of the optimum range.

Conclusion_____________________

Management of CWD following fire requires consideration of its positive and negative values. The lower

b

Year
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-105. 2003 15

limit of the optimum range is determined by the

ecological benefits of CWD, including wildlife habitat

and site productivity, and the upper limit by excessive

fire hazard. A wide range of CWD is acceptable depending on many individual site and landscape considerations including severity of burn, desired future

stand conditions, restoration objectives, and desired

structural diversity.

Because CWD amounts at a given site can be expected to change over time with or without management, simulation modeling can help with planning

and designing treatments. Predicted quantities of

CWD over time vary considerably with fire severity

and postfire treatment, but they also depend on prefire

stand structure. Site-specific analysis can strengthen

decisionmaking by allowing managers to tailor

postfire treatments to best achieve desired CWD

quantities over time. Simulating snag recruitment,

falldown, and subsequent decay allows decisions on

fuel treatment (salvage harvest and/or surface fuel

treatment) to be made in the context of expected future

conditions as well as current conditions.

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The Rocky Mountain Research Station develops scientific information and technology to improve management, protection, and use of

the forests and rangelands. Research is designed to meet the needs

of National Forest managers, Federal and State agencies, public and

private organizations, academic institutions, industry, and individuals.

Studies accelerate solutions to problems involving ecosystems,

range, forests, water, recreation, fire, resource inventory, land reclamation, community sustainability, forest engineering technology,

multiple use economics, wildlife and fish habitat, and forest insects

and diseases. Studies are conducted cooperatively, and applications

may be found worldwide.

Research Locations

Flagstaff, Arizona Reno, Nevada

Fort Collins, Colorado* Albuquerque, New Mexico

Boise, Idaho Rapid City, South Dakota

Moscow, Idaho Logan, Utah

Bozeman, Montana Ogden, Utah

Missoula, Montana Provo, Utah

Lincoln, Nebraska Laramie, Wyoming

*Station Headquarters, 240 West Prospect Road, Fort Collins, CO 80526

ROCKY MOUNTAIN RESEARCH STATION

RMRS