United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical

Report RMRS-GTR-132

July 2004

Postfire Mortality of Ponderosa 

Pine and Douglas-fir:

A Review of Methods to Predict Tree 

Death

James F. Fowler

Carolyn Hull Sieg
Rocky Mountain Research Station

Natural Resources Research Center

2150 Centre Avenue, Building A

Fort Collins, CO 80526

Abstract

Fowler, James F.; Sieg, Carolyn Hull. 2004. Postfire mortality of ponderosa pine and Douglas-fir: a review 

of methods to predict tree death. Gen. Tech. Rep. RMRS-GTR-132. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station. 25 p.

This review focused on the primary literature that described, modeled, or predicted the probability of postfire mortality in ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii). The methods and measurements that were used to predict postfire tree death tended to fall into two general categories: those focusing on 

measuring important aspects of fire behavior, the indirect but ultimate cause of mortality; and those focusing on 

tissue damage due to fire, the direct effect of fire on plant organs. Of the methods reviewed in this paper, crown 

scorch volume was the most effective, easiest to use, and most popular measurement in predicting postfire mortality in both conifer species. In addition to this direct measure of foliage damage, several studies showed the importance and utility of adding a measurement of stem (bole) damage. There is no clear method of choice for this, 

but direct assessment of cambium condition near the tree base is widely used in Douglas-fir. Only two ponderosa pine studies directly measured fine root biomass changes due to fire, but they did not use these measurements to predict postfire mortality. Indirect measures of fire behavior such as ground char classes may be the 

most practical choice for measuring root damage. This review did not find clear postfire survivability differences 

between the two species. The literature also does not show a consistent use of terminology; we propose a standard set of terms and their definitions.

Key words: Pinus ponderosa, Pseudotsuga menziesii, wildfire, prescribed burn, crown scorch, bole char, ground 

char, fire intensity

The Authors

James F. Fowler is an Ecologist with the Rocky Mountain Research Station in Flagstaff, AZ. He completed B.S. 

and M.S. degrees in biology from Southwest Missouri State University and a Ph.D. degree in ecology from the 

University of Wyoming.

Carolyn Hull Sieg is a Research Plant Ecologist with the Rocky Mountain Research Station in Flagstaff, AZ. She 

completed a B.S. degree in wildlife biology and M.S. degree in range science from Colorado State University and 

a Ph.D. degree in range and wildlife management at Texas Tech University.

Acknowledgments

Among the people who helped improve this manuscript are Dr. Thomas Kolb, professor at Northern Arizona 

University; Carol Randall, Forest Entomologist, USDA Forest Service Idaho Panhandle National Forests; Charles 

McHugh, Fire Spatial Analyst, Rocky Mountain Research Station, Missoula, MT; and Rudy M. King, Station 

Biometrician, Rocky Mountain Research Station, Fort Collins, CO. Dr. Kevin Ryan, Project Leader, Fire Effects 

Project, Rocky Mountain Research Station, Missoula, MT, also provided helpful conceptual suggestions that improved this paper. Funding was provided by USDA Forest Service Region 1 Forest Health Protection. Noah 

Barstatis, Biological Technician with the Rocky Mountain Research Station, developed the figures.
Contents

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

Fire Damage Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Foliage/Terminal Buds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Stems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Seasonal Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Species Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Summary by Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Management Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Annotated References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Additional References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Postfire Mortality of Ponderosa Pine 

and Douglas-fir:

A Review of Methods to Predict Tree Death

James F. Fowler

Carolyn Hull Sieg
USDA Forest Service RMRS-GTR-132. 2004. 1

Introduction

From the earliest days of forest management in the 

United States, foresters have been confronted with the 

problem of identifying which trees will survive after fire. Initial commercial interest focused on delayed 

wildfire effects, but as prescribed fire became more popular, its effects on tree mortality also became part of the 

question. Salvage timber harvests were aimed both at 

trees directly killed by wildfire and those that could be 

predicted to die within a few years due to tissue damage 

by fire. Concerns about potential insect outbreaks in fire 

damaged trees, changes in wildlife habitat quality, and 

aesthetic issues developed as management objectives 

changed through time.

Ponderosa pine (Pinus ponderosa) and Douglas-fir 

(Pseudotsuga menziesii) are two commercially and ecologically important tree species in the Western United 

States. Both species occur in forest types subject to periodic wildfires, and both species develop a thick insulating bark as they age. Douglas-fir generally occurs on 

more mesic sites that historically burned less frequently 

than most ponderosa pine-dominated sites; regardless, 

prescribed burning is a common management practice in 

forest types dominated by both species (Pyne and others 

1996). The studies reviewed in this paper (fig. 1) investigated postfire mortality of these species using a variety 

of methods to directly and indirectly measure fire damage to tree tissue. As yet, no consensus has developed on 

which methods are the most accurate or practical in predicting short-term postfire mortality. This lack of consensus is due in part to confounding issues related to the 

studies themselves, such as differences in study sites, 

pre- and postfire environments, varying fire severities 

and seasonality, plus differences in tree sizes and stand 

densities. The purpose of this literature review is to gather information on the methods used to evaluate postfire 

mortality in ponderosa pine and Douglas-fir and to evaluate the accuracy and efficiency of those methods.

Our approach was to focus on empirical papers from 

the primary literature, mostly journal articles and government documents, and to give much less weight to 

management notes, marking guides, reviews, and anecdotal reports. We evaluated the study design, sample 

size, data analysis, and results of each article while disregarding discussion points, conclusions, and recommendations unless they were clearly supported by the 

results. The common practice of including results and 

discussion within the same section of paper made this 

task difficult at times. Note that results and conclusions 

presented by authors that were not clearly supported by 

data were intentionally omitted from the synthesis part 

of this review.

The synthesis part of this review is organized primarily by fire damage to major plant organs: leaves/

foliage, stems/bole, and roots. Within each category, an 

overview of methods is followed by a detailed, somewhat chronological, discussion of each method of fire 

Figure 1—Locations of the 

most often cited postfire 

mortality field studies.
2 USDA Forest Service RMRS-GTR-132. 2004. 

damage measurement, grouped by species when possible. The synthesis is followed by an annotated bibliography in which papers may be annotated separately, as a 

series of papers on the same long-term study, or on a common theme by the same author(s). The annotated bibliography has most of the reports cited in the text. Additional 

related references are listed at the end of this review.

Fire Damage Measurements

As we examined the various fire damage measurements it became apparent that there were two general 

categories. Some workers tried to predict tree mortality indirectly via fire behavior parameters: that is, using the ultimate cause of the damage. Others measured 

tree tissue damage directly in order to predict mortality: 

that is, concentrating on the proximal effect of the fire. 

Ground char, bole char, bole scorch height, and crown 

scorch height are examples of the former; crown scorch 

volume, crown consumption volume, direct observation 

of cambium condition, and fine root kill are examples of 

the latter. Fire behavior variables are obviously important when writing fire prescriptions and predicting mortality before the fire; however, after the fire, more direct 

tissue damage measurements may be more accurate. 

This is apparently the case when crown scorch height is 

compared to crown scorch volume, as discussed in the 

next section.

Most of the studies we reviewed measured tree mortality one or more times during the first 3 years postfire. 

Only two studies measured mortality during the first 3 

years and after a longer period of time, 8 years in this 

case: Lynch (1959) for ponderosa pine and Ryan and 

others (1988) for Douglas-fir. The clearest indication 

of when most postfire mortality occurs is from the latter studies and from Miller and Patterson (1927). These 

three studies show that most postfire mortality occurs by 

the end of the second postfire year.

Foliage/Terminal Buds

All but one of the papers listed in table 1 used some 

measure of foliage/terminal bud damage to investigate 

postfire mortality, and these measures were often the 

most explanatory or had the greatest predictive power for tree death. There seem to be three basic fire effects concepts embodied in these variables: scorching 

and thus killing of foliage, bud kill, and consumption 

of leaves and buds. Table 1 shows a diverse set of variable names. Most papers lack clear definitions of what 

is meant by these variables, other than literal meanings 

and the context in which they are written. Scorch height 

as used in these papers (for example, Bevins 1980; 

Peterson 1985; Ryan and Reinhardt 1988) seems to imply the maximum or mean height of foliage scorch and 

thus leaf kill. Scorch volume would again refer to foliage scorch (for example, Peterson 1985; Weatherby and 

others 1994) but could also include bud kill and consumption if it was present and not clearly separated out 

by definition or by other variables in the same study 

(for example, McHugh and Kolb 2003; Wyant and others 1986). The word “kill,” unless defined (for example, 

Ryan and Reinhardt 1988), could refer to leaf scorch, 

bud kill, and/or consumption of either. In the absence of 

specific data collected in that study for consumption or 

bud kill, crown kill must indicate all of the above. For 

example, Herman (1950, 1954) used a variable called 

“length of crown kill” without definition: in other words, 

there was no mention of terminal buds or separation of 

consumption and scorch. Presumably these concepts 

were lumped together.

Two of the earliest investigations of postfire mortality 

focused on western pine beetle (Dendroctonus brevicomis) induced mortality of ponderosa pine by fire injury 

class (Miller and Patterson 1927; Salman1934). Miller 

and Patterson (1927) explicitly combined scorch and 

consumption of leaves and terminal buds into five clearly defined qualitative damage categories and found that 

ponderosa pine trees with almost complete foliage consumption and terminal bud kill but with live cambium 

(injury class 4) died the first year after fire. In their moderate injury class (3) with most of the foliage scorched, 

no bud kill, and with some cambial damage, tree survival rate was 8 percent the third year postfire with all postfire mortality being attributed to bark beetles. Ponderosa 

pine trees with partial foliage scorch (injury class 2) had 

92 percent survival (Miller and Patterson 1927). Salman 

(1934) presented eight fire damage classes ranked by increasing defoliation and cambium injury with a corresponding increase in susceptibility to insect attack and 

increasing mortality.

Two papers explicitly combined foliage scorch and 

bud kill in Douglas-fir into a quantitative variable called 

“percent of prefire crown volume killed,” but they did 

not mention consumption (Ryan and others 1988; Ryan 

and Reinhardt 1988). Although Ryan and others (1988) 

used the term “crown scorch” without definition, the data 

in that paper were a subset of the larger dataset in Ryan 

and Reinhardt (1988), which used the term “crown volume killed,” with crown clearly referring to buds and foliage. They found that percent crown volume killed was 

a significant variable but ranked below number of dead 

cambium quadrants in logistic regression modeling 
USDA Forest Service RMRS-GTR-132. 2004. 3

Table 1—Measurements as originally used by authors to assess fire damage to foliage and buds, stems, and roots of ponderosa pine 

(Pinus ponderosa) or Douglas-fir (Pseudotsuga menziesii). Note that root damage measurements are indirect.

Area of damage

 Measurement/species Citation

Foliage/buds

Percent crown scorch: volume

 Ponderosa pine Cluck and Smith 2001, Dieterich 19791, McHugh and Kolb 2003, McHugh and others 2003, 

Saveland 1982, Saveland and Neuenschwander 1990, Wallin and others 2003, 

Weatherby and others 1994

 Douglas-fir Lynch 19591, Peterson 1984, 1985, Peterson and Arbaugh 1986, 1989, Ryan and others 1988, 

Spicer 1984, Weatherby and others 1994

Percent crown consumed: volume

 Ponderosa pine McHugh and Kolb 2003, McHugh and others 2003 

Crown consumption

 Ponderosa pine Dieterich 1979

Percent crown consumption: height

 Ponderosa pine and Douglas-fir Wyant and others 1986

Percent crown killed: volume

 Douglas-fir Ryan and Reinhardt 1988

Percent crown scorch: height

 Ponderosa pine Harrington 1993

 Douglas-fir Bevins 1980

Percent crown scorch: length

 Ponderosa pine Harrington and Hawksworth 1990, Wyant and others 1986

 Douglas-fir Wyant and others 1986

Percent of live crown kill: length

 Ponderosa pine Herman 1950, 1954

Scorch height: maximum

 Ponderosa pine Saveland and Neuenschwander 1989, 1990, Saveland 1982, Wyant and others 1986

 Douglas-fir Bevins 1980, Peterson 1984, Ryan and others 1988, Spicer 1982, Wyant and others 1986,

Scorch height: mean

 Douglas-fir Peterson 1985, Peterson and Arbaugh 1986, 1989,

Damage classes

 Ponderosa pine Miller and Patterson 1927, Salman 1934

Length of green crown

 Ponderosa pine Mitchell 1914

Stems

Bole char: height

 Ponderosa pine Herman 1950, 1954, McHugh and Kolb 2003, Regelbrugge and Conard 1993, 

Weatherby and others 1994

 Douglas-fir Weatherby and others 1994

Percent bole char: height

 Ponderosa pine Wyant and others 1986

 Douglas-fir Wyant and others 1986

Bole char severity

 Ponderosa pine McHugh and Kolb 2003

Bole char intensity

 Ponderosa pine Weatherby and others 1994

 Douglas-fir Weatherby and others 1994

Bole char classes

 Ponderosa pine Harrington and Hawksworth 1990

Percent basal scorch/char

 Ponderosa pine Weatherby and others 1994

 Douglas-fir Peterson 1984, Peterson and Arbaugh 1986, 1989, Weatherby and others 1994

Bark char depth

 Douglas-fir Peterson and Arbaugh 1986, 1989
4 USDA Forest Service RMRS-GTR-132. 2004. 

of Douglas-fir mortality (n=166) 8 years postfire in 

Montana (Ryan and others 1988). In a greatly expanded 

dataset with 43 prescribed fires, seven conifer species including Douglas-fir, and 2,356 trees, they found that bark 

thickness and crown kill were the most significant variables in logistic regression models (Ryan and Reinhardt 

1988).

Other workers separated measures of consumption 

and scorch (Dieterich 1979; McHugh and Kolb 2003; 

McHugh and others 2003; Wyant and others 1986). 

Wyant and others (1986) used consumption height whereas the other papers used consumption volume; no one 

has separated consumption of buds and leaves. Dieterich 

(1979) found that four of the seven ponderosa pine trees 

with some crown consumption in his study were dead 

within 3 years after a fall fire in northern Arizona. In a 

larger northern Arizona study, mortality rates by level 

of crown consumption were 67 percent mortality at 30 

percent crown consumption and 100 percent mortality at 

60 percent crown consumption (McHugh and Kolb 

2003, n = 1367). In a separate paper, McHugh and others 

(2003) combined crown consumption and crown scorch 

volume into a variable called total crown damage for 

logistic regression modeling to predict probability of 

mortality 3 years postfire. Total crown damage was 

paired with insect attack rating as a predictive model of 

postfire mortality.

In a Colorado study, crown consumption variables, 

measured by quadrant to indicate asymmetric fire damage, were significant contributors to broad multivariate 

discriminant functions that characterized differences between live and dead ponderosa pine and Douglas-fir trees 

2 years after prescribed fire (Wyant and others 1986). In 

this study, crown consumption variables ranked fourth 

Table 1—Continued.

Area of damage

 Measurement/species Citation

Bark char ratio

 Ponderosa pine Peterson 1984, Peterson and Arbaugh 1986, 1989

Cambium condition

 Douglas-fir Peterson and Arbaugh 1989, Ryan and others 1988

Visible cambium injury

 Ponderosa pine Herman 1950, Miller and Patterson 1927, Salman 1934

Resin flow

 Ponderosa pine Wallin and others 2003

Insect attack

 Ponderosa pine Weatherby and others 1994

 Douglas-fir Weatherby and others 1994

Insect attack rating

 Ponderosa pine McHugh and Kolb 2003, McHugh and others 2003

Insect damage

 Douglas-fir Peterson and Arbaugh 1986, 1989

Insect colonization

 Ponderosa pine Wallin and others 2003

Bark beetle presence

 Ponderosa pine Herman 1950, 1954

Roots

Ground fire severity/ground char

 Ponderosa pine McHugh and Kolb 2003

Fire severity: litter/duff

 Douglas-fir Peterson 1984

Ground fire intensity

 Ponderosa pine Weatherby and others 1994 

 Douglas-fir Weatherby and others 1994 

Burned area under dripline

 Ponderosa pine Weatherby and others 1994 

 Douglas-fir Weatherby and others 1994 

1 Unclear methods: volume or height
USDA Forest Service RMRS-GTR-132. 2004. 5

(out of nine to 10 variables) for both species (percent uphill 

quadrant for ponderosa pine and percent downhill quadrant for Douglas-fir), which was below crown scorch 

variables for ponderosa pine and Douglas-fir as well as 

below bole char variables for ponderosa pine.

Many of the publications in table 1 emphasized some 

variation of the term crown scorch, which probably encompassed consumption and bud kill when present. Of 

the publications that used scorch height measured from 

ground level, most used maximum scorch height (Bevins 

1980; Peterson 1984, 1985; Peterson and Arbaugh 1986, 

1989; Ryan and others 1988; Saveland 1982; Saveland 

and Neuenschwander 1989, 1990; Swezy and Agee 

1991; Wyant and others 1986). Peterson (1985) and 

Peterson and Arbaugh (1986, 1989) also used mean 

scorch height.

Mitchell (1914) measured length of green crown 

after fire, but most investigators have used scorch 

length or heights. Saveland (1982) and Saveland and 

Neuenschwander (1990) (table 1) found that scorch 

height and diameter at breast height (dbh) were good indicators of ponderosa pine mortality (n = 194) in northern Idaho, although the latter paper found that crown 

scorch volume was the best predictor. Several workers 

used length of live crown scorched expressed as percent of original live crown length (Harrington 1993; 

Harrington and Hawksworth 1990; Herman 1950, 1954; 

Spicer 1982). Harrington’s (1993) paper focused on 

season of prescribed burn effects, but also found a distinct threshold for increased mortality above 70 percent crown scorch in ponderosa pine 4 years after fire. 

Harrington and Hawksworth (1990) found that dbh and 

crown scorch length were significant independent variables in a logistic regression postfire mortality model 

and that high dwarf mistletoe (Arceuthobium vaginatum) 

ratings, while not significant at the p = 0.05 level, tended to cause higher scorch levels. Herman (1954) found 

that length of crown kill, dbh, and severity of fire were 

better indications of postfire mortality in ponderosa pine 

than bark beetle presence, height of bark scorch, or presence of nearby burned out stumps. The only Douglas-fir 

paper to use percent crown scorch length (Spicer 1982) 

found it to be a better indicator of mortality than crown 

scorch height or bark scorch height.

Bevins (1980) used maximum scorch height as the 

only fire damage variable but also included tree diameter (dbh) to model probability of Douglas-fir postfire 

survival. However, when scorch height was directly compared with other fire damage variables, it was 

less accurate than crown scorch volume for Douglasfir (Peterson 1984, 1985; Peterson and Arbaugh 1986, 

1989) and was “clearly a poor discriminator” compared 

to 15 other fire damage parameters in ponderosa pine 

(Wyant and others 1986).

Many investigators who used measures of scorch 

height also used crown scorch volume, visually estimating the volume scorch as a percent of original crown 

volume (table 1). Some used crown scorch volume 

(which may include some crown consumption) as their 

only measure of postfire foliage damage (Cluck and 

Smith 2001; McHugh and Kolb 2003; McHugh and others 2003; Wallin and others 2003; Weatherby and others 1994). Most workers who compared the efficacy 

of crown scorch volume to other fire damage variables 

in predicting postfire mortality found that it was the 

most accurate for both ponderosa pine and Douglas-fir 

(McHugh and others 2003; Peterson 1984; Peterson and 

Arbaugh 1986, 1989; Saveland and Neuenschwander 

1990; Weatherby and others 1994). These workers 

also found that some measure of bole char was the second most important measurement, except for two studies which did not measure fire bole damage (McHugh 

and others 2003; Saveland and Neuenschwander 1990). 

The only paper we reviewed that did not rank crown 

scorch volume as the most accurate was Ryan and others (1988) (although the introduction section of Ryan 

and Reinhardt [1988] in citing Ryan and others [1988] 

stated that it was), but, even here, it was better than 

scorch height. Interestingly, Peterson (1985) found that 

Douglas-fir crown scorch volume, calculated from mean 

scorch height and crown shape measurements, was less 

accurate than visual estimates of crown scorch volume.

Stems

As noted in the previous section, two early papers investigating postfire mortality combined crown and cambium injury into qualitative damage classes to analyze 

postfire mortality (Miller and Patterson 1927; Salman 

1934). In ponderosa pine trees with 75 to 100 percent fire 

defoliation, Salman (1934) showed the strong mortality 

influence of cambial injury by an increase in mortality 

from 19.2 percent for trees with “none-to-slight” cambial injury to 72.2 percent with “moderate-to-heavy” cambial injury. However, he provided no raw data on sample 

sizes or criteria for cambium damage classes. Miller 

and Patterson (1927) did provide criteria for fire damage classes in ponderosa pine that combined information 

on bole blackening, cambial damage, foliage scorch, and 

bud kill. However, they did not give fire mortality rates 

due to their emphasis on bark beetle infestation. Herman 

(1950) mentioned collecting data on “extent of visible 

injury to the cambium at stump height” but provided no 

data in this or his followup paper (Herman 1954).
6 USDA Forest Service RMRS-GTR-132. 2004. 

More recent papers on Douglas-fir have used chemical tests for the enzyme perioxidase to indicate live/

dead cambium layers taken from four increment borer samples: upslope, downslope, and both cross-slopes 

(Peterson and Arbaugh 1989; Ryan and others 1988). 

In these studies, either the numbers of live quadrants 

(Peterson and Arbaugh 1989) or the numbers of dead 

quadrants were recorded (Ryan and others 1988). Ryan 

and others (1988) found that number of dead quadrants 

at 1.4 m (4.6 feet) was significantly higher in spring 

prescribed fires compared to fall fires and that number of dead quadrants was the best univariate predictor 

of Douglas-fir tree mortality (n = 166) when compared 

with dbh, crown scorch height, and crown scorch volume. However, cambial damage would be expected to 

be a more important mortality predictor in prescribed 

burns where crown damage may be minimal. Predictive 

ability was also improved in multivariate logistic regression models that added crown scorch volume, season of 

burn and/or dbh to number of dead quadrants (Ryan and 

others 1988). Peterson and Arbaugh (1989) concurred 

with Ryan and others (1988) by presenting a logistic regression mortality model with significant variables for 

number of live cambium quadrants and crown scorch 

volume to predict postwildfire mortality of Douglas-fir 

(n = 294).

Indirect measures of cambial damage are more common (table 1) and are variations on the theme of bark 

scorch/char, from both height and circumference perspectives. Ryan (1982a) described the relationship between bark thickness and the duration of fire necessary to 

cause cambial mortality in ponderosa pine and Douglasfir and indicated that bark char alone is a poor indicator of 

cambial damage. Despite the qualitative differences between dictionary definitions of scorch and char, the terms 

have been used somewhat interchangeably. For example, 

Regelbrugge and Conard (1993) define height of stembark char as “distance from groundline to the highest 

point of bole blackening,” which could include a change 

in color or texture associated with a scorch definition 

as well as including the charcoal concept of charring. 

McHugh and Kolb (2003) and probably, although not 

crystal clear, Weatherby and others (1994) used Ryan’s 

(1982b) bole char depth classes, which describe the continuum between no scorch to deeply charred. Harrington 

and Hawksworth (1990) used a similar approach.

Several investigators used maximum bark scorch/

char height or char height as a percentage of tree height to 

measure/predict postfire mortality (table 1). Two papers 

presented no data or analysis of scorch height (Herman 

1950; Weatherby and others 1994). However, Herman’s 

(1954) followup paper stated that height of bark scorch 

did not show a close relationship with survival in ponderosa pine (n = 235). In contrast, four other studies showed 

the significant influence of stem/bole char height on postfire mortality. Significantly higher windward stem/bole 

char heights were found in dead ponderosa pine after 

fire (McHugh and Kolb 2003, n = 1367; Wyant and others 1986, n = 95). McHugh and Kolb (2003) also found 

that leeward bole char was significantly higher in dead 

ponderosa pine. Wyant and others (1986) showed similar results for ponderosa pine (n = 95) for uphill and 

downhill quadrants as well as in Douglas-fir (n = 103) 

for windward, leeward, uphill, and downhill quadrants. 

Regelbrugge and Conard (1993) presented two logistic regression models to predict mortality of ponderosa 

pine trees following burning: the two-variable model included dbh and height of stem/bark char as significant 

variables, and the univariate model (p£0.0001) used relative char height (char height as a percent of tree height). 

Wyant and others (1986) also found that bole char height 

variables were significant components of multivariate 

discriminant functions to separate live and dead Douglasfir and ponderosa pine after prescribed fire, but that their 

discriminating power was less than that for crown scorch 

variables.

Several papers included measures of basal scorch/

char circumference, expressed as a percentage of total 

circumference (Peterson 1984; Peterson and Arbaugh 

1986, 1989; Weatherby and others 1994). Apparently 

no one has combined circumference and height measurements to estimate bole surface area damaged by 

fire. Peterson’s (1984) contingency table analysis of 302 

Douglas-fir trees 1 year after the 1981 wildfire season 

showed that basal scorch in combination with crown 

scorch volume had a “prominent survival threshold” 

at less than 70 to 90 percent crown scorch volume and 

less than 70 percent basal scorch. Peterson and Arbaugh 

(1986) also included basal scorch as a significant parameter in a multivariate discriminant function with and 

without crown scorch volume for Douglas-fir. In contrast, basal scorch was not included as a significant variable in a logistic regression model using the same 302 

Douglas-fir trees from the 1981 fires in a later paper 

(Peterson and Arbaugh 1986) or from an analysis of a 

separate 294 Douglas-fir trees from 1982 fires (Peterson 

and Arbaugh 1989). Weatherby and others (1994) analyzed their percent basal scorch data as part of a bole 

char rating variable (see next paragraph). In an experimental approach to basal scorch, Rigolot and others 

(1994) found that for 36 young, vigorous ponderosa 

pine trees with an average dbh of 18.5 cm (7.3 inches), 

85 to 100 percent girdling by artificial heat was necessary to kill them.
USDA Forest Service RMRS-GTR-132. 2004. 7

Harrington and Hawksworth (1990) showed increasing mortality with increasingly severe bole char ratings 

in ponderosa pine. McHugh and Kolb (2003) found significant differences in bole char severity (depth classes Ryan 1982b) between live and dead ponderosa pine 

trees 3 years postfire. Weatherby and others (1994) did 

not analyze their bole char intensity data directly but 

multiplied it by percent basal scorch (as noted above) to 

get a bole char rating prior to analysis. They showed that 

bole char ratings for fire-killed Douglas-fir and ponderosa pine were significantly higher than for beetle-killed 

as well as for live trees.

Bark char depth and bark char ratio, char depth as 

a proportion of original bark thickness, have also been 

used as variables to predict postfire mortality of Douglasfir (Peterson 1984; Peterson and Arbaugh 1986, 1989)

(table 1). Bark thickness and bark char ratio were found 

to be important variables in all three papers. As crown 

scorch volume level increases from 30 to 90 percent, 

bark char ratio had an increasing effect on Douglas-fir 

mortality (Peterson 1984). These parameters were also 

included as significant variables in multivariate discriminant functions with and without crown scorch volume for Douglas-fir (Peterson and Arbaugh 1986) and 

in predictive logistic regression models (Peterson and 

Arbaugh 1986, 1989).

A long standing concern of forest managers is the potential increase in mortality by insects, primarily species 

of Dendroctonus (bark beetles) and Ips (pine engraver 

beetles), following fire, both on fire-damaged trees and 

nearby undamaged trees (Connaughton 1936; Flanagan 

1996; Fischer 1980; Furniss 1965; Miller and Patterson 

1927; Miller and Keen 1960; Salman 1934; Wagener 

1961). Consequently, many investigators of postfire 

mortality in Douglas-fir and ponderosa pine have included insect damage variables in their studies (table 1). 

While the focus here is on fire mortality per se, not on 

physiological fire-response variables, we found one paper that is directly applicable to secondary fire effect and 

tree resistance to colonizing Dendroctonus. Wallin and 

others (2003) measured the amount of constitutive and 

induced resin flow in response to experimental mechanical injury following prescribed fire in northern Arizona 

ponderosa pine and found that both constitutive and induced resin flow were significantly and inversely related 

to crown scorch volume: in other words, trees with less 

crown scorch volume had higher potential to “pitch out” 

colonizing insects.

Miller and Peterson (1927) investigated western pine 

beetle (D. brevicomis) induced mortality of ponderosa pine trees following fires in California and Oregon. 

However, they synonomized beetle attack with tree death 

and did not evaluate delayed fire mortality in their slight 

and moderate damage classes. An early paper by Herman 

(1950) used the presence/absence of bark beetles as one 

of a set of variables to investigate postfire mortality on 

235 ponderosa pine trees in northern Arizona. On 89 

trees that had more than 50 percent crown length killed, 

he found greater than 75 percent mortality on trees with 

bark beetles at 3 months postfire compared to less than 

50 percent mortality on trees without bark beetles. On the 

other hand, by the end of the study Herman (1954) concluded that “damage to crown and severity of fire provide 

a more reliable index to mortality than does presence or 

absence of beetles.”

McHugh and Kolb (2003) and McHugh and others 

(2003) designed insect attack ratings for postfire ponderosa pine trees in northern Arizona by examining the first 

2 m (6.4 feet) of the bole for strip attacks, mass attacks, 

or no attack. The former two categories were separated 

by less than or greater than 75 percent of the circumference showing evidence of pine bark beetles, measured 

by removing small patches of bark. They found significantly higher insect ratings in dead trees from three 

separate fires (n = 272, 312, 833). McHugh and others 

(2003) presented a logistic regression model with total 

crown damage and insect damage as significant variables. That is, in three fires, trees attacked by beetles had 

greater total crown damage and crown scorch than unattacked trees.

In an experimental approach to the investigation 

of secondary insect damage effects on postprescribed 

fire mortality on 40 ponderosa pine trees in northern 

Arizona, Wallin and others (2003) found that the use of 

a synthetic pheromone lure for western pine beetles increased the number of both successful and unsuccessful 

colonization attempts in all crown scorch volume classes. Specifically, they found that ponderosa pine trees 

with greater than 75 percent crown scorch volume and 

pheromone lures had western pine beetle brood signs 

and were dead by 2 years postfire. However, 25 to 50 

percent crown scorch volume trees with the same lure 

had no western pine beetle brood signs and were still 

alive at the end of year 2. Note that the above results are 

descriptive and were not statistically analyzed.

Peterson and Arbaugh (1986, 1989) measured postfire 

insect damage to Douglas-fir 2 years postfire by the number of successful bark beetle entry holes observed from 

the ground, which were ranked into classes: 0, 1 to 10, 

11 to 50, greater than 50. For their study in the Northern 

Rockies (Peterson and Arbaugh 1986), insect damage 

was included as a significant variable with and without crown scorch volume in multivariate discriminant 

functions that separated dead and live trees. They also 
8 USDA Forest Service RMRS-GTR-132. 2004. 

presented a predictive logistic regression model with 

crown scorch volume and insect damage as significant 

variables, but this model did not fit the data as well as 

models with crown scorch volume alone or crown scorch 

volume combined with bark char ratio. In contrast, 

Peterson and Arbaugh’s (1989) similar study of 294 

postfire Douglas-fir trees in the Cascade Mountains did 

not find insect damage as a significant variable in logistic regression models and suggested that regional climate 

patterns may explain the differences. Another suggestion 

in regard to the variability of postfire insect influences 

is that fires may occur after the flight period for adult 

bark beetles or a population of bark beetles may not be 

close enough to take advantage of the fire-damaged trees 

(DeNitto and others 2000).

A direct, lower-bole-only approach to investigate the 

delayed mortality effects of fire and bark beetle interactions following the 1988 Greater Yellowstone Area 

wildfires was initiated by several workers (Amman 

1991; Amman and Ryan 1991; Rasmussen and others 

1996; Ryan and Amman 1994, 1996). Fire damage to 

the cambium was estimated by visual inspection of the 

cambium and expressed as percent basal girdling. Insect 

attack was detected by boring dust and entrance/exit 

holes; species identification was by removal of small 

patches of bark. These studies used criterion-based definitions of delayed-fire-effect mortality and insect-attack-induced mortality in an attempt to separate these 

often confounding postfire mortality causes. Mortality 

due to complete fire girdling (100 percent basal circumference cambium kill) was attributed to fire, while dead 

trees with less than 100 percent girdling and infested by 

bark beetles or borers were attributed to insect mortality. Using these criteria in a survey of 1,012 Douglas-fir 

in lightly burned-to-unburned areas, they found 19 percent delayed mortality due to fire and 13 percent delayed 

mortality due to insects (primarily Douglas-fir beetles, 

Dendroctonus pseudotsugae) at 4 years postfire. These 

studies along with Wallin and others’ (2003) experimental approach seem to present the clearest evidence on the 

interaction of fire and subsequent insect attack for postfire mortality in ponderosa pine and Douglas-fir.

Although tree dbh is not a fire-damage measurement, 

it is “widely recognized as a factor in resistance to fire 

damage” (Ryan and others 1988), and thus many studies included dbh as a variable in their analysis of postfire 

mortality. Cambial resistance to fire damage is directly proportional to bark thickness (Hare 1961; Martin 

1965), and larger trees with thicker bark are more resistant to fire damage (Peterson and Arbaugh 1989; Ryan 

and others 1988; Saveland 1982). Larger trees also have 

greater mass and therefore greater heat capacity that 

“provide[s] greater resistance to fire injury” (Peterson 

and Arbaugh 1989). Most of the studies we reviewed 

found dbh to be significantly different between live and 

dead trees, or it was a significant component of predictive mortality models in both Douglas-fir and ponderosa 

pine (Bevins 1980; Cluck and Smith 2001; Harrington 

1993; Regelbrugge and Conard 1993; Ryan and others 

1988; Saveland 1982; Saveland and Neuenschwander 

1990; Wyant and others 1986). Most models show decreasing mortality with increasing dbh (Bevins 1980; 

Harrington 1993; Regelbrugge and Conard 1993; Ryan 

and others 1988; Saveland and Neuenschwander 1990; 

Wyant and others 1986). The only dissenting evidence 

on the influence of tree dbh comes from Swezy and 

Agee (1991) who presented data showing no significant 

dbh difference between live and dead ponderosa pine in 

Oregon, from McHugh and Kolb (2003) who showed no 

significant dbh difference on the Bridger-Knoll wildfire 

in Arizona, and from Weatherby and others (1994) who 

showed no significant dbh difference in Douglas-fir 4 

years postfire in Idaho. Note that Weatherby and others 

(1994) did show evidence of a significant difference in 

ponderosa pine.

From another perspective, basal area and stand density index were shown to be significant predictive variables for Douglas-fir postfire mortality and subsequent 

Douglas-fir beetle attack in a Wyoming study (Negron 

and others 1999). These results were part of a study with 

a broader approach to Douglas-fir beetle-induced mortality but may represent an important factor to consider 

in future postfire mortality studies.

Roots

Parameters to measure fire damage to root systems 

were used less frequently in postfire mortality studies 

than stem and foliage fire damage measurements and 

were restricted to aboveground observations (table 1). 

Two ponderosa pine studies directly measured fine root 

biomass changes due to prescribed fire (Grier 1989; 

Swezy and Agee 1991) but did not use these measurements to predict postfire mortality. Ground fire intensity 

(Peterson 1984; Weatherby and others 1994) and ground 

fire severity (McHugh and Kolb 2003) have been used 

as qualitative measures of fire damage to fine roots near 

the soil surface. Peterson’s (1984) ground fire intensity and McHugh and Kolb’s (2003) ground fire severity referred to ground char classes developed by Ryan 

(1982b) that are defined as: unburned – no visible effect on soil, fire did not reside on the area although some 

damage may have occurred to aboveground tissues from 

convective or radiated heat; light burn – litter and duff 
USDA Forest Service RMRS-GTR-132. 2004. 9

layers scorched or charred, but the duff is not altered 

over the entire depth; moderate burn – litter completely 

consumed and duff deeply charred or consumed, but the 

underlying mineral soil not visibly altered; deep burn

– litter and duff completely consumed and the structure 

and color of the mineral soil surface are visibly altered. 

Complete criteria for these classes are in Ryan and Noste 

(1985).

Ground fire severity (ground char) has been found to 

be significantly higher under dead trees than live trees 

following fire in ponderosa pine (Swezy and Agee 1991, 

n = approx. 1200; McHugh and Kolb 2003, n = 1367). 

Weatherby and others (1994) also used a quantitative 

variable, “percent of area under the dripline burned.” 

However, they provided no data or analysis for it or for 

ground fire severity.

Because Douglas-fir trees frequently have roots in 

the layer between duff and mineral soil, compared to 

a deeper rooting habit for ponderosa pine trees (Ryan 

1982a), it may be more susceptible to ground fires that 

consume most or all of the duff. However, Peterson 

(1984) implied that ground fire intensity was not all that 

useful in predicting postfire mortality for 302 Douglasfir trees in that a discriminant analysis of his 11 variable 

dataset, five of which were fire damage variables, indicated that crown scorch volume and bark char were the 

most significant variables. His analysis also found that 

ground fire severity was not one of the top two most discriminant variables for lodgepole pine (Pinus contorta), 

subalpine fir (Abies lasiocarpa), or western red cedar 

(Thuja plicata).

Seasonal Effects

As first noted by Harrington (1993) and confirmed by 

this review, most papers on postfire mortality deal with 

either spring/summer wildfires or fall prescribed burns: 

spring/summer wildfires (Herman 1950, 1954; Lynch 

1959; Peterson 1984, 1985; Peterson and Arbaugh 1986, 

1989; Weatherby and others 1994); fall prescribed burns 

(Saveland 1982; Saveland and Neuenschwander 1989, 

1990; Wyant and others 1986). A few researchers, such 

as McHugh and Kolb (2003), have studied fires in different seasons, but interpretations of their data are confounded by the small number of fires and differences 

among sites, fire severity, and tree dbh, in addition to 

season. In an experimental burn specifically designed to 

determine mortality differences between spring, summer, and fall burns, Harrington (1993) followed postprescribed fire mortality in 526 ponderosa pine trees 

for 10 years. He found little difference between spring 

and summer fire mortality, but these growing-season 

fires had higher mortality than fall (dormant season) 

fires (n = 18 plots). The most striking differences were 

in the smaller diameter classes, but these differences 

disappeared at greater than 30 cm (11.8 inches) dbh. A 

study on prescribed fire effects on ponderosa pine greater than 22 cm (8.7 inches) dbh in Crater Lake National 

Park (Swezy and Agee 1991) corroborates Harrington’s 

(1993) findings showing greater mortality in early season burns. In Douglas-fir, Ryan and others (1988) found 

that season had significance only when combined with 

crown scorch volume and number of dead cambium 

quadrants in predicting mortality after a prescribed burn 

(n = 20 plots) in Montana, but noted that the seasonal effects in that study may have been related to differences 

in fire behavior.

Two marking guides have incorporated season of 

fire differences into their recommendations. Wagener’s 

(1961) marking guide for California made slight adjustments for minimum green canopy for ponderosa pine 

survival between mid- and late-season fires but not in 

Douglas-fir. Dieterich (1979) recommended delaying 

salvage marking of ponderosa pine trees damaged during growing-season fires until the following growing 

season if possible, and if not, then both crown scorch 

and crown consumption standards should be lowered.

Species Comparison

A study on postfire mortality of seven western conifers that included Douglas-fir but not ponderosa pine 

indicated that “crown injury is not strongly species dependent” (Ryan and Reinhardt 1988). Only two studies included adequate samples of both Douglas-fir and 

ponderosa pine (Weatherby and others 1994; Wyant and 

others 1986), and these studies showed little betweenspecies differences in the effectiveness of commonly 

used fire damage variables to predict postfire mortality. 

Douglas-fir and ponderosa pine showed no significant 

differences in crown scorch volume or bole char ratings 

within alive, fire-killed, and beetle-killed categories after the Lowman wildfire complex in Idaho (Weatherby 

and others 1994). Similarly, this study showed no between-species differences in average tree dbh for firekilled trees, but there were apparent between-species 

differences in postfire mean dbh for both alive and beetle-killed categories. Two studies found that following 

wildfire, Douglas-fir beetles apparently selected larger 

dbh trees (Bulaon 2003; Weatherby and others 1994). 

Wyant and others (1986) used 16 fire scorch, consumption, and char variables to compare species by fire-killed 

and surviving tree categories. Fifteen of those showed 

no significant difference between species but clear live/
10 USDA Forest Service RMRS-GTR-132. 2004. 

fire-killed differences. One variable, maximum scorch 

height, showed no clear differences between species or 

between live/fire-killed categories.

Summary by Species

Douglas-fir—There have been few attempts to use 

root damage measurements to explain postfire mortality (table 1). Three indirect measures of root damage on 

Douglas-fir were used by workers in this review: ground 

fire severity and burned area under dripline (Weatherby 

and others 1994) and fire severity as judged by effect on 

litter and duff (Peterson 1984). Peterson (1984) found 

that fire severity effects were not among the top three 

independent variables to predict postfire mortality, and 

apparently Weatherby and others (1994) did not analyze 

their root-damage data.

In contrast, all of the independent stem-damage variables on Douglas-fir in table 1 were found to be significant indicators of postfire mortality in one or more 

studies. Peterson’s studies consistently found bark char 

ratio to be a significant variable, and two of his studies 

found percent basal scorch to be significant while one 

did not (Peterson 1984; Peterson and Arbaugh 1986, 

1989, respectively). Weatherby and others (1994) also 

found percent basal scorch (as a component of bole 

char ratings) to be significantly different between live 

and fire-killed trees. Ryan and Amman (1994, 1996) 

described similar effects. Direct measures of cambium 

condition were also significant when used (Peterson and 

Arbaugh 1989; Ryan and others 1988). Insect damage 

was not consistent; two studies found significant bark 

beetle influence on mortality (Peterson and Arbaugh 

1986; Weatherby and others 1994), but a similar study 

did not (Peterson and Arbaugh 1989). Ryan and Amman 

(1996) attributed 13 percent of delayed mortality to bark 

beetles or wood borers 4 years after the 1988 Greater 

Yellowstone Area fires.

Crown scorch volume was clearly the best crown 

damage measurement to predict postfire mortality of 

Douglas-fir (Peterson 1984, 1985; Peterson and Arbaugh 

1986, 1989; Ryan and others 1988). Studies that did not 

use crown scorch volume (Bevins 1980; Wyant and others 1986) found that crown scorch height/length variables were significantly different between live and dead 

trees. The only study to use crown consumption variables found that consumption also had significant predictive power (Wyant and others 1986). Crown scorch 

volume and either bark char ratio, percent basal scorch, 

or number of quadrants with live/dead cambium appear 

to be the best overall measurements to predict Douglasfir, postfire mortality.

Ponderosa pine—Three studies apparently collected 

data on postfire root damage to ponderosa pine (table 

1), but only one study analyzed its data (McHugh and 

Kolb 2003). This study found significant differences 

in ground char ratings between live and dead trees on 

three fires: two wildfires and one prescribed burn.

The literature shows two strong trends in the use of 

stem damage measurements for predicting postfire ponderosa pine mortality. Bole char height, the most frequently used stem fire-damage variable in ponderosa 

pine (table 1), was found to be significantly different 

between live and dead trees in three out of four studies. Similarly, two of the three studies using bole char 

classes found significant differences between live and 

dead trees (McHugh and Kolb 2003; Weatherby and 

others 1994). Two older studies lumped cambium injury and crown injury into broad damage classes (Miller 

and Patterson 1927; Salman 1934). No one used bark 

char ratio or bark char depth as in several Douglas-fir 

studies.

All workers who used crown scorch height, crown 

scorch volume, or crown consumption (table 1) found 

them to be significant variables in predicting postfire mortality in ponderosa pine. Saveland and Neuenschwander 

(1990) were the only investigators who compared the efficacy of scorch height versus scorch volume in ponderosa 

pine, and they found crown scorch volume to be a better 

predictor as measured by receiver operating characteristic (ROC) curves, which is a method for evaluating the accuracy of diagnostic systems (Swets and others 1979).

One study combined crown scorch and consumption 

into a total crown damage variable, which was then coupled with insect attack rating (McHugh and others 2003) 

as the most predictive variables in a logistic regression model. Wyant and others (1986) compared several 

crown and bole fire-damage variables and ranked crown 

scorch variables better than foliage consumption and 

bark char variables as judged by correlation between 

predicted and observed outcomes.

Management Implications

Our recommendations for measurements to assess 

postfire damage to trees and to predict mortality include 

a measurement of tree diameter size, dbh, plus one measure from each of the three plant organs: foliage, stems, 

and roots. Several studies showed the importance and 

utility of measuring both foliage and stem damage 

(McHugh and Kolb 2003; Peterson 1984; Peterson and 

Arbaugh 1989; Ryan and others 1988; Wyant and others 1986). Foliage damage, along with stem damage, is 
USDA Forest Service RMRS-GTR-132. 2004. 11

clearly the easiest, most pragmatic, and most important 

measurement as shown in practically all of the studies 

we reviewed. Fine root damage is the most diffi cult to 

measure, and no suitable technique for direct measurement is available.

Foliage damage is best measured by estimating percent crown scorch volume, which usually includes 

crown consumption. As previously noted, it consistently 

outperforms crown scorch height or length. From this 

literature review and from fi eld experience, visual estimates to the nearest 5 percent are possible with reasonable accuracy. Consensus estimates from two to three 

workers guided by Ryan’s (1982a) cautionary notes 

seems the best approach. If crown damage is the only 

damage measurement used, as some have recommended for salvage-type marking (Cluck and Smith 2001; 

Saveland and Neuenschwander 1990), then percent 

crown scorch volume above 80 to 95 percent for ponderosa pine or above 70 to 95 percent for Douglas-fi r 

would indicate probable tree death (p > 0.80) within 2 to 

3 years. These fi gures would need to be reduced when 

combined with high insect attacks (McHugh and others 

2003) or other obvious damage to stems and roots (see 

Peterson 1984), or with drought conditions.

Direct stem damage measurements are limited to 

techniques that allow observation of cambium tissue 

via increment borer samples or removal of small pieces 

of bark, then judging cambium condition visually or by 

chemical tests. However, these are destructive sampling 

techniques and are thus usually limited to one sample 

from each of four quadrants. These should be analyzed 

as number of live/dead quadrants (categorical data), 

since conversion to percent implies higher accuracy. For 

example, one dead quadrant represents a sampling range 

of 1 to 49 percent bole scorch circumference. The results of studies using this technique show that more than 

three dead quadrants alone imply probable tree death. 

However, this technique is best combined with percent 

crown scorch volume (Peterson and Arbaugh 1989; 

Ryan and others 1988). These cambium samples should 

be taken at dbh or at the root crown.

Because direct measures of fi ne root damage are time 

and labor intensive, we recommend the use of ground 

char classes (Ryan 1982b; Ryan and Noste 1985). 

Further use of these classes will allow researchers to 

determine their predictive utility. In addition, new techniques for large scale, direct measurement of fi ne root 

mass/root damage are needed.

Based on their use in the papers we reviewed, the following are recommended terms for fi re damage measurements. A somewhat conceptual defi nition and/or 

specifi c citation is also shown for each term.

• Percent crown scorch volume: A visual estimate 

to the nearest 5 to 10 percent of the proportion of 

prefi re foliage scorched/killed due to fi re (fi g. 2). It 

conceptually includes foliage consumption, bud kill, 

and bud consumption unless specifi cally excluded in 

the methods section of a study: in other words, separation of scorch and consumption. See Dieterich (1979) 

and Miller and Patterson (1927) for photographs of 

foliage scorch and consumption. Miller and Patterson 

(1927) also have drawings on their fi re injury classes 

that conceptually show unburned, scorched, and consumed foliage.

• Crown scorch height: Maximum height of foliage 

scorch/kill measured from ground level. Maximum 

height is inferred unless mean scorch height is specifi cally mentioned in the methods section of a paper. 

In that case, the term “average crown scorch height” 

should be used.

• Percent crown scorch length: The proportion of the 

original crown height with foliage scorch/kill. This 

would conceptually include foliage consumption, bud 

kill, and bud consumption unless specifi cally excluded in the methods section of a paper.

Figure 2—Conceptual drawing of fi re damage to foliage and 

stems. Scorched (fi re-killed) foliage and consumed foliage 

(and buds) are often combined as percent crown scorch 

volume but may also be separated into separate categories as shown. Figure modifi ed from Miller and Patterson 

(1927)

live

scorched

consumed
12 USDA Forest Service RMRS-GTR-132. 2004. 

• Crown consumption: Percent of crown foliage 

volume (and buds unless separated) consumed by 

fire (fig. 2). Use this term when foliage scorch is 

separated from foliage consumption; see percent 

crown scorch volume.

• Bud kill/consumption: Percent of crown bud volume 

consumed by fire. Use this term when bud consumption is separated from foliage consumption; see percent crown scorch volume. Note that we know of no 

studies that have used this measurement.

• Bole scorch height: Maximum height of a change in 

bark color or texture due to fire. This is occasionally 

expressed as a proportion of tree height, in which case 

the term should be “relative bole scorch height.” This 

fire damage measurement would conceptually include 

bark char (a charcoal concept) in lower portions of the 

same stem unless it is specifically excluded in the 

methods section of a paper.

• Bole char height: Maximum height of charcoal-like 

bark (see above).

• Bole damage classes: See Ryan (1982b) for criteria 

based on scorch and char.

• Percent basal girdling: The proportion of the basal circumference in which cambial tissue is killed. 

This is measured indirectly by bark scorch/char (see 

bole scorch height for conceptual differences) or directly by assessing cambial condition (Peterson and 

Arbaugh 1989; Ryan 1982b; Ryan and Frandsen 1991; 

Ryan and others 1988).

• Bark char ratio: depth of mean bark char as a proportion of original mean bark thickness, which is often 

calculated from standard equations.

• Insect damage to bole: There is no consensus for a 

definition from the fire mortality literature. We suggest the development of a measure conceptually 

based on successful/unsuccessful strip attacks and 

mass attacks (Amman and Cole 1983). This measure 

should be estimated at the peak of bark beetle populations within a burned area, usually the second growing season postfire.

• Ground char: Damage classes based on changes in 

litter, duff, and soil characteristics due to fire intensity. See Ryan (1982b) and Ryan and Noste (1985) for 

detailed criteria.

Research Needs

This review points to two broad areas in need of 

further research to develop accurate measures of postfire mortality: damage to roots and damage to cambium. In both of these areas, direct observation of tissue 

damage is difficult, and indirect measures have been 

developed. Measurement of root damage presents the 

greatest technological challenge and a daunting spatial and temporal sampling problem. Swezy and Agee 

(1991) measured pre- and postfire fine root masses, but 

this is time and labor intensive and only works for prescribed fires. As previously noted, Ryan and Noste’s 

(1985) ground char classes may be the only practical 

solution. Measuring bole and root collar cambium damage, either by fire or insects, is less of a technological 

problem because visual and chemical techniques exist 

for assessing tissue condition (Peterson and Arbaugh 

1989; Ryan 1982b; Ryan and Frandsen 1991; Ryan 

and others 1988). The problem is how to assess nondestructively. For insect damage, we suggest research 

to develop cambial tissue damage measurements conceptually based on successful and unsuccessful postfire 

strip attacks and mass attacks (Amman and Cole 1983). 

For fire damage, we suggest research to test the efficacy of Ryan’s (1982b) suggestion to stratify cambium 

sampling by depth of char classes. Cambial sampling 

with an increment borer at the edge of each depth-ofchar class may allow more accurate measurement of 

percent of circumference girdled by fire. Papers in this 

review that used percent basal scorch/char (table 1) inferred tissue damage from postfire, external bark characteristics. Workers who sampled cambium condition 

(table 1) directly, sampled by quadrant. Ryan’s suggestion would appear to be more accurate and efficient; 

thus it needs further evaluation.

This review also revealed the need for more tightly 

controlled experiments. Differences in the severity of 

fires, site characteristics, drought history, ranges of tree 

diameters, and stand densities were confounding factors in a number of the studies we reviewed. There is 

a need for well-replicated experiments that attempt to 

standardize site, tree, and fire conditions as much as 

possible.
USDA Forest Service RMRS-GTR-132. 2004. 13

Annotated References

Amman, Gene D. 1991. Bark beetle-fire associations in the Greater Yellowstone Area. In: Nodvin, 

Stephen C.; Waldrop, Thomas A., eds. Fire and the environment: ecological and cultural perspectives, 

proceedings of an international symposium; 1990 March 20-24; Knoxville, TN. Gen. Tech. Rep. SE69. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment 

Station: 313-320.

and

Amman, Gene D.; Ryan, Kevin C. 1991. Insect infestation of fire-injured trees in the Greater 

Yellowstone Area. Res. Note INT-398. Ogden, UT: U.S. Department of Agriculture, Forest Service, 

Intermountain Research Station. 9 p.

and

Rasmussen, Lynn A.; Amman, Gene D.; Vandygriff, James C.; Oakes, Robert D.; Munson, 

A. Steven; Gibson, Kenneth E. 1996. Bark beetle and wood borer infestation in the Greater 

Yellowstone Area during four postfire years. Res. Pap. INT-RP-487. Ogden, UT: U.S. Department 

of Agriculture, Forest Service, Intermountain Research Station. 10 p.

and

Ryan, Kevin C.; Amman, Gene D. 1994. Interactions between fire-injured trees and insects in 

the Greater Yellowstone Area. In: Despain, Don G., ed. Plants and their Environments: Proceedings 

of the First Biennial Scientific Conference on the Greater Yellowstone Ecosystem; 1991 September 

16-17; Yellowstone National Park, WY. Denver, CO: U.S. Department of Interior, National Park 

Service: 259-271.

and

Ryan, Kevin C.; Amman, Gene D. 1996. Bark beetle activity and delayed tree mortality in 

the Greater Yellowstone Area following the 1988 fires. In: Greenlee, Jason, ed. The ecological 

Implications of Fire in Greater Yellowstone: Proceedings, Second Biennial Conference on the Greater 

Yellowstone Ecosystem; 1993 September 19-21; Yellowstone National Park, WY. Fairfield, WA: 

International Association of Wildland Fire: 151-158.

Annotation: This series of papers contain the results of studies on delayed fire effects and insect 

induced mortality on Douglas-fir (P. menziesii), lodgepole pine (Pinus contorta), whitebark pine

(Pinus albicaulis), Engelmann spruce (Picea engelmannii), and subalpine fir (Abies lasiocarpa) after 

the 1988 Greater Yellowstone Area fires. The 1991 and 1994 papers contained preliminary results 

of studies more fully described in Rasmussen and others (1996) and Ryan and Amman (1996). Only 

information on Douglas-fir postfire mortality from the 1996 papers is noted here. Mortality was higher 

for trees with greater than 50 percent crown scorch volume and greater than 75 percent basal girdling. 

Figure 1 (which is actually switched with figure 3 in the paper) in Ryan and Amman (1996) and figures 

12 to 14 in Rasmussen and others (1996) graphically showed increased insect infestation/mortality 

with increased basal girdling by fire. Delayed mortality from fire effects and insect infestation was 

18.5 percent and 12.6 percent (n = 1012 Douglas-fir) respectively in unburned or lightly burned areas of the Greater Yellowstone Area 1988 fire mosaic at 4 years postburn. In these extensive areas, 

insect infestation, primarily by Douglas-fir beetles, in uninjured trees the first year after the fire was 

8 percent, declined to 4 percent by the third year, then increased to 12 percent the fourth year. More 

intensive sampling at the burned/unburned boundary showed higher Douglas-fir mortality (n = 125); 

77 percent were dead due to the combined affects of fire and insects. The major increase in Douglasfir beetle infestations (38 percent of the sample) occurred the second year postfire and dropped to 3 

percent by the fourth year in these boundary areas.
14 USDA Forest Service RMRS-GTR-132. 2004. 

Bevins, Collin, D. 1980. Estimating survival and salvage potential of fire-scarred Douglas-fir.

Res. Not. INT-287. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest 

and Range Experiment Station. 8 p.

Annotation: This clear, brief historical introduction to the issue of postfire mortality compares the 

predictive value of dbh, crown scorch height, and percent crown scorch length (not volume) to predict 

mortality of Douglas-fir 1 year postprescribed fire in west-central Montana. The criterion for determining live/dead was a chemical test for live cambium in four quadrants at dbh, similar to Peterson’s 

protocol (1984). Most papers use live green foliage as the criterion. Both dbh and crown scorch 

height were significant variables in the logistic regression model to predict survivability. The sample 

size (n = 176) is a bit small for predicting mortality in eight dbh classes; otherwise the analysis and 

interpretation are clear. A preliminary salvage marking guide is presented based upon stem dbh and 

crown scorch height.

Dieterich, John H. 1979. Recovery potential of fire-damaged southwestern ponderosa pine. Res. 

Not. RM-379. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Forest and Range Experiment Station. 8 p.

Annotation: The study results were based on a November wildfire in northern Arizona. This study 

had a small sample size (n = 25) and an almost anecdotal approach supplemented with photography. 

All 25 trees selected for the study had greater than 75 percent crown scorch and seven had some crown 

consumption. Three of seven trees with some consumption actually survived; these had less than 90 

percent crown scorch. Most needle drop occurred in the second winter following a fall fire.

Harrington, M. G. 1987. Ponderosa pine mortality from spring, summer, and fall crown scorching. Western Journal of Applied Forestry. 2(1): 14-16.

and

Harrington, M. G. 1993. Predicting Pinus ponderosa mortality from dormant season and growing season fire injury. International Journal of Wildland Fire 3(2): 65-72.

Annotation: This experimental paper was based on an understory prescribed fire in an immature ponderosa pine (P. ponderosa) stand (n = 526) in southwestern Colorado during three seasons: late spring, 

midsummer, and autumn. Tree dbh and foliage damage (percent crown scorch length) were important 

variables in determining ponderosa pine mortality, but note that trees with “boles charred severely 

enough to cause cambium damage” were excluded from this study. Dbh and percent crown scorch 

length results agree with many other studies, but the major importance of the paper is its results on 

seasonal effects based on an experimental, randomized block design. Fall burns had a lower mortality 

than spring and summer burns; at 5 years and at 10 years, mortality was 12 percent for autumn burns 

compared to 26 to 30 percent for spring and summer burns. Spring and summer burns caused high 

mortality in trees less than 10 cm (4 inches) dbh with greater than 50 percent crown scorch length. 

Crown scorch mortality thresholds for trees greater than 18 cm (7 inches) dbh were at 90 percent for 

spring-summer burns and over 90 percent for autumn burns. Mortality for late spring and midsummer 

fires did not differ; therefore spring and summer fire results were grouped into a “growing season” 

variable that was significantly different from fall, “dormant season” mortality.

Harrington, Michael G.; Hawksworth, Frank G. 1990. Interactions of fire and dwarf mistletoe on mortality of southwestern ponderosa pine. In: Effects of Fire Management of Southwestern 

Natural Resources, Proceedings of the Symposium; 1988 November 15-17; Tucson, AZ. Gen. Tech. 

Rep. RM-191. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Forest and Range Experiment Station: 234-240.

Annotation: Crown scorch length (by percent classes) and dbh were significant independent variables 

in logistic regression modeling of ponderosa pine mortality in Grand Canyon National Park 1 year 
USDA Forest Service RMRS-GTR-132. 2004. 15

after an August prescribed burn. Amount of scorch was the dominant factor in first-year mortality. The 

purpose and most interesting part of this study is the focus on dwarf mistletoe interactions with fire 

mortality. Dwarf mistletoe ratings (DMR) were also included in their logistic regression model at p = 

0.07, which indicated that higher mistletoe infection ratings tend to have higher average crown scorch 

length. In the medium scorch classes, tree mortality increased as dwarf mistletoe infection increased. 

Results also suggest that dwarf mistletoe can be managed with prescribed fire.

Herman, F. R. 1950. Survival of fire-damaged ponderosa pine. Res. Not. SWFRES-RN-119. 

Tucson, AZ: U.S. Department of Agriculture, Forest Service, Southwestern Forest and Range 

Experiment Station. 3 p.

and

Herman, F. R. 1954. A guide for marking fire-damaged ponderosa pine in the southwest. Res. 

Not. RM-13. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Forest and Range Experiment Station. 4 p.

Annotation: This study looked at ponderosa pine (Pinus ponderosa) mortality 6 years after a wildfire 

in northern Arizona. The data show: (1) a clear mortality threshold at greater than 60 percent crown 

scorch length; (2) a light surface fire had little effect on mortality but heavy ground fire or ground plus 

crown fire had 50 percent mortality at 50 to 60 percent crown scorch length; (3) tree mortality was 

hastened by red turpentine beetles only during the first year after burning; (4) bark scorch height and 

nearby burned out stumps had no effect on mortality. A progress report on the same study (Herman 

1950) also noted that not all bark beetle infested trees died. Based on these results, the authors offered 

these guidelines for marking trees to remove: (1) trees with more than 60 percent of the length of live 

crown scorched by the fire; and (2) trees with 51 to 60 percent of length of live crown scorch if the fire 

in the vicinity of the tree was a heavy ground or a combination ground and crown fire. Because these 

guidelines cannot be expected to cover every individual condition, the author also had other suggestions. For example, if the bark at the base of the tree is severely scorched, the tree may be heat girdled. 

To check this possibility, a few small cuts may be made through the charred bark. Healthy cambium 

is white and spongy, but heat-destroyed cambium rapidly turns brown and gives off a distinctive sour 

smell. Complete or nearly complete heat girdling will kill the trees. The tree has a good chance of 

surviving if it is only partially girdled. In addition, even relatively light damage to “poor vigor” trees 

may be enough to cause their death. These guidelines correctly identified 95 percent of the trees that 

survived and 86 percent of those that died.

Lynch, Donald W. 1959. Effects of a wildfire on mortality and growth of young ponderosa pine 

trees. Res. Not. No. 66. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain 

Forest and Range Experiment Station. 8 p.

Annotation: A moderate sized study (n = 200) on 5 to 30 cm (2 to 12 inch) dbh ponderosa pine (P. 

ponderosa) in Washington 1 to 2 years postwildfire. Results show that mortality was directly related to 

crown injury with a distinct threshold at 80 percent crown scorch after which mortality jumped from 

20 to 24 percent to 63 to 100 percent. All trees died whose crowns were 90 percent or more burned. 

Second-year mortality was restricted to trees smaller than 6 inches dbh except where crown injury 

had been 80 percent or greater. Virtually all mortality occurred during the first two years. It is not clear 

whether percent crown scorch was measured by volume or by crown length. No criteria were given 

for determining dead/live.

McHugh, Charles W.; Kolb, Thomas E. 2003. Ponderosa pine mortality following fire in 

Northern Arizona. International Journal of Wildland Fire 12:7-22.

and
16 USDA Forest Service RMRS-GTR-132. 2004. 

McHugh, Charles W.; Kolb, Thomas E.; Wilson, Jill L. 2003. Bark beetle attacks on ponderosa 

pine following fire in Northern Arizona. Environmental Entomology 32: 510-522.

Annotation: These studies had a relatively large number of trees (1,367) from three fires (a spring 

wildfire, a summer wildfire, and a fall prescribed fire) and make excellent use of definitions and 

criteria from the published literature on fire damage parameters. The postfire mortality paper found 

significant differences between live and dead ponderosa pine 3 years postfire for the following fire 

damage variables: crown scorch volume, total crown damage, bole char height, bole char severity, 

ground char severity, and insect attack rating. Total crown damage above 70 to 80 percent resulted in 

a sharp increase in mortality rate. This paper also included two logistic regression mortality models, 

but the significance level for variables in the models was p£0.10 rather than the traditionally accepted 

level of p£0.05. The U-shaped dbh-mortality curve showing increased mortality in larger dbh classes 

seems counterintuitive and warrants further investigation. Further analysis of this data set showed that 

both dbh and individual fire characteristics affected mortality in this study (King, McHugh, and Kolb, 

personal communication).

The bark beetle paper presented data that clearly show an increase in mortality with increasing crown 

damage by fire at different levels of insect attack. Distinct mortality thresholds are not apparent. Total 

crown damage and insect attack rating variables were significant components (p£0.05) of a logistic 

regression model that predicted probability of postfire mortality.

Miller, J. M. 1929. Why the western pine beetle follows fire. Forest Worker 5(4): 16-17.

Annotation: This brief description of ponderosa pine mortality after a summer wildfire on the Sierra 

National Forest in California shows results that are similar to Miller and Patterson’s (1927) more 

extensive paper and also attributed almost all postfire mortality to bark beetles. It ignores the possible 

delayed effects of fire in a drought year and implicated bark beetles in spite of a statement that “conditions in the fire-damaged trees...were found to be unfavorable for brood development” of western 

pine beetle. However, Miller’s estimates of beetle killed mortality show the highest percentage in the 

50 to 75 percent crown scorch category, which qualitatively agrees with Wallin and others’ (2003) 

colonization-attempt data.

Miller, J. M.; Patterson, J. E. 1927. Preliminary studies on the relation of fire injury to bark beetle attack in western yellow pine. Journal of Agricultural Research 34(7): 597-613.

Annotation: This study was based mostly on a fall 1917 wildfire in southern Oregon. Its major 

strengths are twofold: pre- and postwildfire beetle infestation data, and bark beetle performance after 

fire. The authors presented 3 years of prewildfire data for number of trees killed, timber volume lost, 

and western pine beetle (Dendroctonus brevicomis) infestation followed by 3 years of postwildfire 

data. The paper focused mainly on fire injured ponderosa pine (P. ponderosa) greater than 25 cm (10 

inches) dbh killed by western pine beetle. No mortality rates were given, but they could be calculated 

from data presented in tables. No criteria were given to determine beetle killed versus delayed-effect 

fire killed trees, but the strong inference is that if western pine beetles were present, mortality was 

attributed to western pine beetles. For example, postfire timber cruises placed trees in one of five fire 

injury classes with clear damage criteria. The criteria for injury class 4 stated that the foliage was 

burned away, terminal buds were killed, but cambium is still alive. These trees died during the first 

year postfire, yet mortality is attributed to beetles, in spite of injury, which would seem to preclude 

survival of most trees with or without beetles. The authors clearly showed that western pine beetles 

moved (up to 3 miles) from areas surrounding the fire into the burned area during the first postfire year, 

then moved back into the 1 mile zone surrounding the fire during the second postfire year. Mortality 

peaked within the burned area during the first postfire year and within the 1 mile zone surrounding 

the fire during the second postfire year then declined to prefire rates in both areas in subsequent years. 

Beetles were preferentially attracted to trees with light to moderate fire damage during the first year 

after the fire. Western pine beetle brood success was low within the fire area when adult population 
USDA Forest Service RMRS-GTR-132. 2004. 17

size was relatively high; that is, the burn area may have been a population sink. Conversely, brood 

success in the area immediately surrounding the fire was high when the adult population was high the 

second year after the fire.

Peterson, David L. 1985. Crown scorch volume and scorch height: estimates of postfire tree condition. Canadian Journal of Forest Research 15: 596-598.

Annotation: The study compared the efficacy of visual estimates of percent crown scorch volume 

with calculated crown scorch volume based on canopy shape and average scorch height in four common conifer species of the Northern Rocky Mountains (from Peterson 1984). Visual estimates are 

markedly more accurate. Calculated scorch volume consistently overestimated volume by 23 to 38 

percent except for scorch volumes greater than 75 percent (by definition they would be the same at 

100 percent). Peterson recommends the use of crown scorch volume rather than crown scorch height 

when timber managers need to identify trees most likely to die.

Peterson, David L. 1984. Predicting fire-caused mortality in four Northern Rocky Mountain conifers. In: Proceedings of the 1983 Convention of the Society of American Foresters, New Forests 

for Changing World; 1983 October 16-20; Portland, OR. Bethesda, MD: The Society of American 

Foresters: 276-280.

and

Peterson, David L.; Arbaugh, Michael J. 1986. Postfire survival in Douglas-fir and lodgepole 

pine: comparing the effects of crown and bole damage. Canadian Journal of Forest Research 16: 

1175-1179.

Annotation: Peterson (1984) was the first of a series of his papers on Douglas-fir (Pseudotsuga menziesii) postfire mortality. This paper clearly shows the effect of combining two variables in predicting 

survivability. Crown scorch volume is the most predictive variable, alone (survival threshold at greater 

than 90 percent) and with bark char ratio (survival thresholds at greater than 50 percent crown scorch 

and greater than 0.3 bark char ratio) and percent basal scorch circumference (survival thresholds at 

greater than 50 percent crown scorch and greater than 70 percent basal scorch). Discriminant analysis 

was used to choose the most significant predictive variables, then contingency table results with these 

variables were shown graphically. The 1984 paper had results for 1 year postfire; results at 2 years 

postfire are presented in Peterson and Arbaugh (1986). At 2 years postfire, crown scorch volume was 

again the most important discriminant function variable. Bark thickness, basal scorch, bark char ratio, 

and insect damage were also significant discriminant function variables. The authors indicate that the 

best logistic regression model for Douglas-fir, judged by three goodness-of-fit tests, combined crown 

scorch volume with insect damage. Graphical presentation of contingency table analysis of postfire 

survival as a function of crown scorch and insect damage showed a major threshold at 90 percent 

crown scorch regardless of insect damage (according to the authors). We note that the medium-high 

insect damage categories seem to have strong impacts on mortality in the 50 to 70 percent crown 

scorch range. The authors caution that these results apply only to late summer wildfires and that strict 

use of logistic regression models is not recommended. This paper shows judicious use of logistic 

regression models.

Peterson, David L.; Arbaugh, Michael J. 1989. Estimating postfire of Douglas-fir in the Cascade 

Range. Canadian Journal of Forest Research 19: 530-533.

Annotation: This paper describes mortality of Douglas-fir (Pseudotsuga menziesii) using a design 

similar to the authors’ 1986 study, the main differences being geography and season of burn. This 

study was conducted in the Cascade Range in Washington and Oregon after late spring wildfires rather 

than late summer wildfires in the Northern Rockies. The results are similar: crown scorch volume 

was the first variable selected in stepwise logistic regression followed by bark char ratio, site, live 

cambium, and bark thickness. Insect damage was not a significant predictive variable in this study as 
18 USDA Forest Service RMRS-GTR-132. 2004. 

it was in their 1986 study. Two graphs show the predicted survival probabilities for actual live and 

dead trees, demonstrating that the logistic regression model predictions fit quite well for observed live 

trees but not for observed dead trees.

Regelbrugge, Jon C.; Conard, Susan G. 1993. Modeling tree mortality following wildfire in 

Pinus ponderosa forests in the central Sierra Nevada of California. International Journal of 

Wildland Fire 3(3):139-148.

Annotation: This cogent, literate paper is a good review of the pertinent fire and statistical literature. 

Crown injury variables were not used since damage data were collected only at 2 years postfire. However, their logistic regression models based on dbh and char height and on relative char height provide 

accurate predictions (83 to 96 percent) of mortality as judged by chi-square (likelihood ratio statistic) 

and receiver-operating characteristic (ROC) curves. For 1,275 trees in 25 stands, 86 percent of which 

were ponderosa pine, mortality varied directly with increasing height of stem bark char and inversely 

with increasing dbh.

Rigolot, E.; Ducrey, M.; Duhoux, F.; Huc, R.; Ryan, K.C. 1994. Effects of fire injury on the physiology and growth of two pine species. In: Proceedings 2nd International Conference on Forest Fire 

Research, Vol II, D.05.; 1994 November; Coimbra, Portugal: 857-866.

Annotation: A controlled experiment helped determine lethal thresholds of tree injury: crown scorch 

by propane torch and basal circumference cambium injury by narrow heating belt for Aleppo pine 

(Pinus Halepensis) in France or burning wick for ponderosa pine (Pinus ponderosa) in Montana. 

The intended cambium injury was less than actual by 5 percent. For ponderosa pine, cambium injury 

needed to be in the greater than 90 percent range to induce mortality, and foliage damage had no effect 

(n = 36). However, these ponderosa pine were in vigorous condition with a mean dbh of 18.5 cm (7.3 

inches).

Ryan, Kevin C. 1982a. Evaluating potential tree mortality from prescribed burning. In: 

Baumgartner, David M., ed. Site Preparation and Fuels Management on Steep Terrain: Proceedings 

of a Symposium; 1982 February 15-17; Spokane, WA. Pullman, WA: Washington State University: 

167-179.

Annotation: This good review covers types of tissue damage from heat, especially via prescribed fire, 

and contains a good discussion of the rationale of using various fire damage measurements for postfire 

mortality studies based on the author’s experience. Focus is on duration and intensity of heat generated by prescribed fire and how tree species’ characteristics relate to surviving different fire intensities 

and durations in the general context of prescribed fire behavior.

Ryan, Kevin C. 1982b. Techniques for assessing fire damage to trees. In: Lotan, J. E., ed. 

Proceedings of the symposium: Fire–its field effects; 1982 October 19-21; Jackson, WY. Missoula, 

MT: The Intermountain Fire Council; Pierre, SD: The Rocky Mountain Fire Council: 1-11.

and

Ryan, Kevin C.; Noste, Nonan V. 1985. Evaluating prescribed fires. In: Lotan, James E.; Kilgore, 

Bruce M.; Fischer, W. C.; Mutch, R.W., tech. coords. Proceedings – Symposium and workshop on 

wilderness fire; 1983 November 15-18; Missoula, MT. Gen. Tech. Rep. INT-182. Ogden, UT: U.S. 

Department of Agriculture, Forest Service, Intermountain Research Station: 230-238.

Annotation: The 1982 symposium paper discusses the use of several fire damage measurements for 

foliage, bole, and roots. Qualitative, criterion-based fire damage classes are presented for bole char 

and root damage (ground char). The 1985 symposium presentation expanded on this by proposing 

a method for classifying fire severity based on four (now widely used) ground char classes and on 

five flame length categories. This system thus comprises a two-dimensional (4 x 5) matrix. Detailed 
USDA Forest Service RMRS-GTR-132. 2004. 19

criteria are given for the ground char classes. There is also a good discussion of fire severity effects 

on vegetation. Note that Ryan 1982b has been previously cited in many papers as Ryan 1983 and as 

Ryan 1982b, but because the symposium proceedings does not have a publication date, the date of the 

symposium (1982) should be used.

Ryan, Kevin C. 1998. Analysis of the relative value of morphological variables in predicting firecaused tree mortality. In: Viegas, D.X., ed. Proceedings of the 3rd International Conference on Forest 

Fire Research and 14th Conference on Fire and Forest Meteorology; Luso, Coimbra - Portugal. Coimbra, 

Portugal: ADAI - Associacao para o Desenvolvimento da Aerodinamica Industrial: 1511-1526.

Annotation: Postfire mortality is reviewed through a discussion of fire behavior, fire damage measurements, and tree physiological response to fire injury. The author emphasized the shortcomings 

of previous investigative approaches and techniques as well as the need for a generalized model of 

postfire tree mortality.

Ryan, Kevin C.; Frandsen, W. H. 1991. Basal injury from smoldering fires in mature Pinus ponderosa Laws. International Journal of Wildland Fire 1(2): 107-118.

Annotation: The focus is on duff accumulation beneath ponderosa pine (Pinus ponderosa) in a 200-

year-old stand in Glacier National Park, Montana, and the physical/biological effect of consumption 

of the duff under 19 trees following a late summer, low intensity prescribed burn. The emphasis is 

on mortality of cambium samples, not tree mortality. Only four of the 19 trees were killed from basal 

injury. The authors present data and discus two opposing fire effects. Large trees tend to resist fire 

injury/mortality due to thicker bark and larger mass. In contrast, larger trees tend to accumulate more 

duff, which makes the root crown more susceptible to smoldering fire injury. Duff depth increased 

with tree diameter, which ranged from 50 to 114 cm (20 to 45 inches) dbh, and decreased with distance 

from the bole, averaging 18 cm (7 inches) deep at 30 cm (12 inches) from the bole and decreasing to 

an average of 6 cm (2.4 inches) at 210 cm (83 inches) from the bole. Duff accumulation is also related 

to fire return frequency. Although this stand had not burned for 69 years, presettlement return intervals 

ranged from13 to 58 years.

Ryan, Kevin C.; Peterson, David L.; Reinhardt, Elizabeth D. 1988. Modeling long-term firecaused mortality of Douglas-fir. Forest Science 34(1): 190-199.

Annotation: This paper follows the fate of 166 Douglas-fir (Pseudotsuga menziesii) for 8 years after 

light surface prescribed burns. Of the total 50 percent mortality, 42 percent had occurred by the end of 

the third year. Logistic regression results show that cambium damage (number of quadrants with dead 

cambium at 1.4 m (4.6 feet) bole height) is the most important factor in determining mortality, which 

would be expected for prescribed burns where fire intensity (and thus crown scorch) were somewhat 

controlled. Crown scorch volume, scorch height, and dbh were also presented in separate logistic 

regression models. However, tree height and season of burn were not. Percent crown scorch volume 

was a better predictor of postfire mortality than scorch height. Fall season fires had slightly higher 

mortality than spring fires, but the authors note that this may be due to fire behavior differences rather 

than season. Except for tree height, which is strongly correlated with dbh, each of the above variables 

was also paired with dbh in four additional logistic regression models. In spite of the heavy reliance 

on analysis by logistic regression, the authors present, for field use, a figure showing the relationship 

between dbh and crown scorch volume at three levels of mortality probability.

Ryan, Kevin C.; Reinhardt, Elizabeth D. 1988. Predicting postfire mortality of seven western conifers. Canadian Journal of Forest Research 18:1291-1297.

Annotation: Data on 2,356 trees from 43 prescribed fires in Idaho, Montana, Oregon, and Washington 

were used to model postfire tree mortality. Data were combined for seven species of conifers to develop 

binary logistic regression models for predicting the probability of mortality. Douglas-fir (Pseudotsuga 
20 USDA Forest Service RMRS-GTR-132. 2004. 

menziesii) trees made up 63 percent of the sample in this study. Bark thickness and percent crown 

scorch were significant factors in logistic regression models; scorch height was not. The authors interpreted model coefficients to indicate that “the contribution of crown injury is not strongly species 

dependent.” No criteria or methods of measurement for crown scorch or bark thickness were given, but 

references to previous papers in the introduction infer that crown scorch means both foliage and buds. 

Because data from 43 fires were pooled, data collection methodology is not completely consistent. We 

would caution that mortality determination was made at 3 years for 1,146 trees and at 7 to 8 years for 

1,210 trees and that Ryan and others (1988) found an additional 8 percent mortality from year 3 to year 

8. In addition, mortality cause may be difficult to determine after the first 2 to 3 years postfire.

Saveland, James M.; Neuenschwander, Leon F. 1990. A signal detection framework to evaluate 

models of tree mortality following fire damage. Forest Science 36(1): 66-76.

Annotation: Reviewing mortality predictions for 194 ponderosa pine (Pinus ponderosa) following 

a fall prescribed fire in Idaho, this study’s results indicate that percent crown scorch volume is better 

than dbh plus scorch height to predict mortality. An excellent presentation on Receiver Operating 

Characteristic (ROC) curves makes clear use of this analysis technique to compare the accuracy of 

percent crown scorch volume versus dbh/scorch height in predicting postfire mortality of ponderosa 

pine. There is also a good discussion on the tradeoffs in using probability of mortality values other 

than 0.50 as the decision criterion to model dead/alive predictions.

Spicer, J. L. 1982. Probability models to predict Douglas-fir seed tree mortality after prescribed 

burning. Boise, ID: University of Idaho. 44 p. Thesis.

Annotation: Presented are two models for estimating interior Douglas-fir (Pseudotsuga menziesii var. 

glauca) tree mortality as a direct result of prescribed, understory fire in northern Idaho. Of the variables examined, tree height and percent crown scorch were the most accurate in predicting mortality. 

The models can be used in conjunction with existing fire behavior models and burning guidelines to 

aid managers in site preparation decisions.

Swezy, D. Michael; Agee, James K. 1991. Prescribed-fire on fine-root and tree mortality in oldgrowth ponderosa pine. Canadian Journal of Forest Research 21(5): 626-634.

and

Thomas, Terri L.; Agee, James K. 1986. Prescribed fire effects on mixed conifer forest structure 

at Crater Lake, Oregon. Canadian Journal of Forest Research 16:1082-1087.

Annotation: This study was based on 10 years of prescribed burns in Crater Lake National Park, Oregon, and corroborates Harrington’s (1987, 1993) findings that early season (June and July) prescribed 

burns have higher mortality rates than late season burns (September). Discriminant analysis showed 

significant differences between live and dead trees for five variables with scorch height and ground 

char ranking the highest for approximately 1,200 trees greater than 22 cm (8.7 inches) dbh. Dbh 

itself was not significant. Interesting data from a small sample (n = 9) of old growth ponderosa pine 

(Pinus ponderosa) are presented on litter and duff profiles before and after burns as well as burn soil 

temperatures and fine root mass changes by depth, root size classes, and total biomass for unburned, 

raked and burned, and burn only (litter/duff) trees. The 1986 paper contains an analysis of the 4 years 

postfire for 117 ponderosa pine in the same area as well as for two other species.

Wallin, Kimberly F.; Kolb, Thomas E.; Skov, Kjerstin R.; Wagner, Michael R. 2003. Effects of 

crown scorch on ponderosa pine resistance to bark beetles. Environmental Entomology 32:652-661.

Annotation: This paper examines the constitutive and induced resin-flow response as well as Ips

and Dendroctonus colonization with and without pheromone attractants on 40 ponderosa pine (Pinus 
USDA Forest Service RMRS-GTR-132. 2004. 21

ponderosa) following a winter/early spring prescribed burn. The trees were in a narrow (25 to 27 

cm, 9.8 to 10.6 inch) dbh class and were categorized into four equal crown scorch volume classes. 

Constitutive (baseline) resin flow was significantly higher in the 0 to 50 percent crown scorch classes, 

followed by the 50 to 75 percent and then 75 to 100 percent classes. Induced resin flow (in response to 

mechanical injury) was highest in the 0 to 25 percent crown scorch class, lower in the 25 to 75 percent 

classes, and highly variable in the 75 to 100 percent class. Only trees with greater than 50 percent 

crown scorch had colonization attempts by Ips and Dendroctonus. Colonization was highest in the 

50 to 75 percent crown scorch category and tended to increase from June to September. Pheromone 

attractants increased the number of successful and unsuccessful colonization attempts in all scorch 

categories. All trees with greater than 75 percent crown scorch with pheromone attractants had bark 

beetle (Dendroctonus) brood signs and were dead at the end of year 2. The 25 to 50 percent crown 

scorch class trees had no brood signs and were still alive at the end of year 2.

Weatherby, Julie C.; Mocettini, Phil.; Gardner, Brain R. 1994. A biological evaluation of tree 

survivorship within the Lowman fire boundary, 1989 - 1993. Unpublished report R4-94-06 on file 

at: U.S. Forest Service, Intermountain Region, Forest Pest Management, Boise, ID. 9 p.

Annotation: This paper is distinctive in separating beetle killed (criterion based) and fire killed 

ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) for both graphic and 

descriptive analysis. The results are based on a study of 435 trees within the boundaries of the late 

summer 1989 Lowman Fire complex in Idaho. The literature review section has good insight into 

beetle-fire interactions in a mortality context. Although no statistical tests were performed, graphic 

presentation of descriptive statistics show that beetle-killed Douglas-fir had much less crown scorch 

(40 percent) than fire-killed Douglas-fir (74 percent), while the difference for ponderosa pine was less 

and had overlapping 95 percent confidence intervals. In a similar comparison, bark char ratings were 

higher for both species in fire killed versus beetle killed and in fire killed versus alive trees. The test of 

Reinhardt and Ryan’s (1988) logistic model showed 83 percent accuracy with most of the 17 percent 

error attributable to species-specific insect affects. Tree dbh was vastly different between fire-killed 

and beetle-killed Douglas-fir but not so for ponderosa pine. This was due to an apparent selection by 

Douglas-fir beetles (Dendroctonus pseudotsugae) for larger trees that were expected to survive based 

on Reinhardt and Ryan’s (1988) model. For ponderosa pine, western pine beetle (Dendroctonus brevicomis) tended to attack the same size class that the model predicted would die.

Wyant, James G.; Omi, Philip N.; Laven, Richard D. 1986. Fire induced tree mortality in a 

Colorado ponderosa pine/Douglas-fir stand. Forest Science 32(1): 49-59.

Annotation: This excellent prescribed fire paper focuses on fall fires in ponderosa pine-Douglas-fir 

(Pinus ponderosa-Pseudotsuga menziesii) forests in Colorado, where the authors used ANOVA results 

on 19 independent variables to determine entrance into multivariate discriminant function analysis 

models. Two functions were produced to predict tree mortality the second growing season after fire 

for both ponderosa pine and Douglas-fir. Function 2—which included crown scorch volume, stem 

damage on the least impacted quadrant, and dbh—was chosen as the most pragmatic for each species. 

Scorch height (maximum) was not significant for mortality predictions. Lower bole damage quadrants 

(downhill and windward) were second ranked predictors behind crown scorch volume quadrants (uphill and windward) for ponderosa pine and Douglas-fir, respectively. The authors note that there was 

little between-species difference in levels of mortality-inducing injury to stems and foliage. This paper 

also has a good discussion on the relevance of tree dbh to fire damage resistance.
22 USDA Forest Service RMRS-GTR-132. 2004. 

Additional References

Albini, Frank A. 1976. Estimating wildfire behavior and effects. Gen. Tech. Rep. INT-30. Ogden, UT: U.S. 

Department of Agriculture, Forest Service, Intermountain Forest Range Experiment Station. 8 p.

Alonso, M.; Rozados, M. J.; Vega, J. A.; Perez-Gorostiaga, P.; Cuinas, P.; Fonturbel, M. T.; Fernandez, C. 2001. 

Biochemical responses of Pinus pinaster trees to fire-induced trunk girdling and crown scorch: secondary 

metabolites and pigments as needle chemical indicators. Journal of Chemical Ecology 28(4): 689-701.

Amman, Gene D.; Cole, Walter E. 1983. Mountain pine beetle dynamics in lodgepole pine forests part II: 

population dynamics. Gen. Tech. Rep. INT-145. Ogden, UT: U.S. Department of Agriculture, Forest Service, 

Intermountain Forest Range Experiment Station. 6 p.

Arno, Stephen F.; Harrington, Michael G. 1988. The interior west: managing fire-dependent forests by simulating 

natural disturbance regimes. In: Forest Management into the Next Century: What Will Make It Work? 1997 

November 19-21; Spokane, WA. Madison, WI: Forest Products Society: 53-62.

Baker, William L.; Ehle, Donna. 2001. Uncertainty in surface-fire history: the case of ponderosa pine forests in 

the Western United States. Canadian Journal of Forest Research 31(7): 1205-1226.

Bedard, W. D. 1950. The Douglas-fir beetle. Circular 817. Washington, DC: U.S. Department of Agriculture. 

10 p.

Beese, W. J. 1992. Third-year assessment of prescribed burning on forest productivity of some coastal British 

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