1

Research Note RMRS-RN-42. 2011

Rocky Mountain Research Station

Research Note

Authors:

Signe B. Leirfallom, Forestry Research Technician, USDA Forest 

Service, Rocky Mountain Research Station, Missoula Fire 

Sciences Laboratory, Missoula, Montana.

Robert E. Keane, Research Ecologist, USDA Forest Service, Rocky 

Mountain Research Station, Missoula Fire Sciences Laboratory, 

Missoula, Montana.

Citation:

Leirfallom, Signe B.; Keane, Robert E. 2011. Six-year post-fire 

mortality and health of relict ponderosa pines in the Bob 

Marshall Wilderness Area, Montana. Res. Note RMRS-RN-42. 

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

Rocky Mountain Research Station. 5 p.

United States Department of Agriculture

Forest Service

Rocky Mountain Research Station

Research Note RMRS-RN-42

February 2011

Six-Year Post-Fire Mortality and Health 

of Relict Ponderosa Pines in the 

Bob Marshall Wilderness Area, Montana

Signe B. Leirfallom and Robert E. Keane

Abstract: In 2003, lightning-caused fires burned through relict ponderosa pine (Pinus ponderosa) stands in the Bob Marshall Wilderness, 

Montana, after decades of fire exclusion. Since many trees in these 

stands had Native American bark-peeling scars, concern arose about 

the adverse fire effects on this cultural and ecological resource. In 2004, 

Keane and others (2006) began a post-fire monitoring study of the relict pine stands. In 2009, we completed a six year re-measurement of 

those stands. We found that many of the pines with major fire injury 

had recovered, and tree mortality was not as high as initially estimated. 

A low-intensity surface fire, prescribed or lightning-caused, within the 

next 10 years will help preserve the health of these stands in the future.

Keywords: Bob Marshall Wilderness, wilderness prescribed fire, barkpeeled trees, post-fire mortality, Pinus ponderosa 

Introduction

I

n 2004, Keane and others (2006) began a post-fire health 

and mortality assessment of two rare stands of large-diameter ponderosa pines (Pinus ponderosa) near White River 

Park and Big Prairie in the Bob Marshall Wilderness Area on 

the Spotted Bear Ranger District, Flathead National Forest, 

Montana. The study was conducted to evaluate the impacts 

of the Little Salmon Complex fire, which burned through the 

area in the summer of 2003. White River Park and Big Prairie 

are home to relict stands of ponderosa pine that are between 75 

and 600 years old and have great cultural and ecological significance (Arno and others 2008). The stands are limited in area 

by both climate and elevation (Keane and others 2006), and 

many of the older pines have Native American bark peeling 

scars from historical use by the Salish, Kootenai, and Blackfeet 

tribes (Ostlund and others 2005). Since old-growth ponderosa pine stands in the Inland Northwest are rare because of 

broad-scale historical logging, the Bob Marshall stands present 

a unique opportunity to preserve and improve resilience of this 

cultural and ecological resource in a relatively undisturbed, nonfragmented wilderness landscape (Ostlund and others 2005).

After the 2003 fires, concern arose among land managers 

that trees in these relict stands would suffer high mortality, as 

the area had previously experienced prolonged fire exclusion 

that resulted in heavy fuels accumulation (Keane and others 

2006). In 2004, Keane and others (2006) assessed the health 

status of 455 large-diameter (>20 inches [50.8 cm] diameter 
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Research Note RMRS-RN-42. 2011

at breast height [DBH]) ponderosa pines with a goal of examining fire disturbance impacts to help guide preservation 

management decisions; in 2005, they reassessed those same 

trees.

In August of 2009, we completed a six-year post-fire reassessment of the White River Park and Big Prairie ponderosa 

pines using the same methods as Keane and others (2006). In 

addition to measuring DBH and assessing the health status of 

482 large-diameter pines, we assessed the post-fire mortality 

of 891 smaller-diameter (12 to 20 inches [30.5 to 50.8 cm] 

DBH) ponderosa pines. This report details the changes in mortality and health of the large-diameter pines from 2004 to 2009 

and discusses the status of small-diameter pines in 2009. An 

emphasis was placed on evaluating the survival of culturally 

and fire-scarred trees, and management guidance is offered.

Study Site

The ponderosa pine communities in the South Fork of the Flathead Valley are geographically limited to an 8-mile 

(12.9-km) stretch of riverside terraces near Big Prairie and the 

White River/South Fork of the Flathead confluence (fig. 1). 

This area receives less rain and snow than areas upstream or 

downstream, which are dominated by Douglas-fir (Pseudotsuga 

menziesii var. glauca), lodgepole pine (Pinus contorta), subalpine 

White River Park

Big Prairie Administrative Site

South Fork Flathead River

White

River

0 5 10

Kilometers

Ponderosa Pine Mortality Study Areas

 in the Bob Marshall Wilderness, MT

Sampled 2004, 2005, and 2009

N

Figure 1—White River 

Park and Big Prairie 

ponderosa pine 

mortality study sites 

on the South Fork of 

the Flathead River; the 

2003 fire perimeter is 

shaded gray.
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Research Note RMRS-RN-42. 2011

fir (Abies lasiocarpa), and some western larch (Larix occidentalis). 

The ponderosa communities near the South Fork are limited 

in regenerative potential by the relatively high elevation (4400 

to 4900 ft or 1350 to 1500 m) and a short, frost-free season, 

which hinders cone production and regeneration (Keane and 

others 2006). Prior to 1930, the area had a mean fire return interval of 20 to 30 years (Arno and others 1997). Observations 

made by Ostlund and others (2005) suggest that many of the 

fires may have been started by Native Americans who occupied the area prior to circa 1850. The fires are thought to have 

maintained ponderosa pine as the dominant tree species in this 

area (Ostlund and others 2005). After 1930, fire was mostly 

excluded from the study area until 2003 when lightning started 

the Little Salmon Complex fire that burned much of the South 

Fork Valley, including more than half of the area occupied by 

the relict ponderosa pine (Keane and others 2006). 

Methods

I

n 2004, 2005, and 2009, all large-diameter (>20 inches 

[50.8 cm] DBH) ponderosa pines were measured in the 

study area boundary. Because the study area was in a designated wilderness area, we did not tag individual trees; therefore, 

there is some variation in sample size from year to year. Trees 

were measured along broad transects (approximately 328 ft or 

100 m wide). For each tree, we recorded health status (healthy, 

minor injury, major injury or dead), DBH, and presence of fire 

or bark-peeling scars. In this 

study, a healthy tree showed 

little or no sign of fire injury or mountain pine beetle 

infestation; a tree with minor injury had some crown 

scorch or other fire injury 

but was expected to fully recover; and a tree with major 

injury had some combination of high crown scorch 

(>40%), mountain pine 

beetle infestation, or other 

fire injury that made the tree 

unlikely to recover. In 2004, 

the probable cause of mortality (for example, fire, beetle, 

or unknown) and percent 

crown scorch were also estimated, and GPS coordinates were 

taken for each tree (Keane and others 2006). In 2009, we also 

measured mortality, DBH, and presence of fire or bark-peeling 

scars for 891 smaller ponderosa pines (>12 inches [30.5 cm] 

DBH). Only small trees that had recently died (based on visual 

examination) were sampled in this study; pine snags that were 

dead before the 2003 fire were not sampled.

Though the study area boundary was approximated as closely as possible year to year, the large size of the study area meant 

that some trees near the boundary were included or excluded 

in one year and not in the next. Attempts to relocate trees in 

2005 based on the 2004 GPS coordinates were made but the 

error in the GPS coordinates was often higher than tree spacing. In 2004, 455 large trees were measured; in 2005, 426 large 

trees were measured; and in 2009, 482 large trees were measured. We did not measure trees that had fallen post-fire, so it 

is possible that some trees fell during the study and were not 

re-measured. Based on observation of the study area over time, 

this effect is minimal.

Results

Tree Mortality

Figure 2 shows the distribution of large-diameter (>20 in [50.8 cm] DBH) ponderosa pines by year and tree status. In 2009, 69% of the measured trees were healthy, 11.5% 

had minor injury, 1% had major injury, and 18.5% were dead. 

By comparison, 26% of the small-diameter trees measured in 

2009 were dead. Combined mortality for large- and small-diameter trees was 24% in 2009 based on a sample size of 482 

large-diameter trees and 891 

small-diameter trees. The 

mortality of 18.5% for large 

trees in 2009 was not a significant increase from 15% 

mortality in 2004 (α = 0.05, 

p = 0.2).

In fig. 3, mortality by 

DBH is detailed by 2-inch 

size classes. Consistent with 

other studies of fire mortality 

(Howard 2003), there was a 

decrease in mortality as DBH 

increased, and trees at or 

above 40 inches (101.6  cm) 

DBH experienced zero mortality from the 2003 fire. 

The fitted regression line 

(R2 = 0.64) might be used to estimate mortality in other Bob 

Marshall Wilderness Area ponderosa pine stands that have had 

Figure 2—Status of ponderosa pines over 20 inches (50.8 cm) 

DBH in 2004, 2005, and 2009 as percent of total largediameter trees.
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Research Note RMRS-RN-42. 2011

decades of fire exclusion. Because many factors might influence post-fire tree mortality on a given site (such as antecedent 

climatic conditions, burn season, bark beetle populations, and 

fuel loadings), this relationship should only be used as a starting point.

Changes in Large-Diameter Tree Health 

Status: 2004-2009

The most notable change in large-diameter tree health 

from 2004 to 2009 was the reduction of trees showing major 

injury. In 2004, it was expected that most trees in this class 

would not recover because of percent crown scorch, possible 

cambial girdling (due to heavy pre-fire duff and litter accumulation), and post-fire insect and disease invasion of the 

weakened trees (Keane and others 2006). Trees with major 

injury accounted for 18% of the total trees measured in 2004 

(fig. 2), which initially led to an estimated total mortality of 

34% within a few years (Keane and others 2006). We found 

that a substantial portion of the large-diameter ponderosa 

pines with major fire injury actually recovered, as shown by 

the significant increase in healthy trees (α = 0.05, p<0.0001) 

and the significant reduction in trees showing signs of major 

injury (α = 0.05, p<0.0001) between 2004 and 2009 (fig. 2). 

While the 2009 mortality of 18.5% for large-diameter ponderosas was lower than expected, it is possible that some, 

but not many, dead trees could have fallen or been blown 

over since 2004 and were not accounted for in the 2009 

measurements.

Status of Scarred Trees

Large Diameter

Of the trees measured in 2009, there was no significant 

difference in mortality between culturally or fire-scarred trees 

and unscarred trees (α = 0.05, p = 0.5). In contrast, scarred 

trees measured in 2004 had a significantly higher mortality 

than unscarred trees (α = 0.05, p = 0.0001) (Keane and others 2006). This suggests that most fire-caused mortality of 

scarred trees occurred in the year immediately following the 

fire, while unscarred trees experienced more delayed mortality. This trend is also shown by the significant increase 

in unscarred tree mortality between 2004 (11%) and 2009 

(19%), where α = 0.05 and p = 0.01.

Small Diameter

Because the small-diameter pines were not measured in 

2004 or 2005, we could not compare mortality over time. 

In 2009, 44% of all small-diameter scarred trees were dead, 

which was significantly higher than the mortality of 26% for 

small-diameter, unscarred trees (α = 0.05, p = 0.02).

Discussion

Heavy duff and litter accumulations (>4 inches or 10  cm deep) and encroaching conifer ladder fuels 

were mostly consumed in the 2003 fire in both the White 

River Park and Big Prairie stands (Keane and others 2006). 

Figure 3—Percent mortality 

of ponderosa pines in 

2009 by DBH (inches).
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Research Note RMRS-RN-42. 2011

In general, this was a desirable effect because few of the 

large pines were killed by severe soil heating from burning 

duff and litter (Keane and others 2006) and fire risk to the 

nearby Big Prairie administrative site was reduced. Postfire forest structure in White River Park is now open and 

park-like with a grass understory and very few ponderosa 

pine seedlings, as reproduction is limited by the relative 

dryness of the site compared to surrounding stands (Keane 

and others 2006). Periodic fire, lightning-caused or prescribed, on a 10 to 30-year interval would be beneficial to 

this site to limit duff and litter accumulations and prevent 

future ponderosa mortality caused by soil heating and cambial girdling.

In 2009, an abundance of lodgepole pine seedlings were 

observed in the burned ponderosa pine stands at or near 

Big Prairie, indicating that the future forest structure, in 

the absence of fire, will again be widely spaced ponderosa pine with a dense developing understory of lodgepole 

pine. This will result in the possibility of higher fire risk 

to these stands and a return of higher fire risk to the Big 

Prairie Administrative Site. A prescribed, low-intensity surface fire within the next 10 years might be warranted to 

reduce lodgepole pine densities to maintain ponderosa pine 

health and to reduce the increasing fire risk. It is critical 

that fire treatment occur before the lodgepole pines develop viable cones, which is usually within 5 to 15 years 

(Anderson 2003). Much of the success in restoration of forest structure as a result of the 2003 fire could be lost if these 

lodgepole seedlings reach maturity. Considering the close 

proximity of these stands to the Big Prairie Administrative 

Site, periodic fire to reduce lodgepole density might also 

prevent the need to use heavy fire suppression tactics in this 

area in the future.

Despite the optimistic 2009 results, close to 30% of culturally scarred ponderosa pine were lost to the 2003 fire (Keane 

and others 2006). This number is substantial considering the 

rarity of these intact, undisturbed stands. Historically, fires 

burned through these and most other ponderosa stands on a 

regular basis, keeping fuel accumulation and encroachment 

from other conifer species to a minimum (Arno and others 

2008). If fire is once again excluded for an extended length of 

time, conditions conducive for high ponderosa pine mortality 

will increase, and more culturally and ecologically significant 

trees might be lost.

This study only measured the effects of one fire on two 

relict stands. There are a number of other variables that 

influenced the health and recovery of these trees, including post-fire climatic conditions, bark beetle populations, 

and weather events (for example, wind and snow damage). 

While the results of the 2009 measurement are encouraging in terms of survival of large ponderosa pine trees, 

active management of these stands should still be carefully 

considered due to their cultural and natural significance. 

Taking into consideration the fact that fire use by Native 

Americans likely allowed this stand condition to develop 

and exist for centuries (Ostlund and others 2005), prescribed fire is an appropriate tool to maintain these stands 

while still adhering to wilderness values.

Conclusion

Overall, the large-diameter ponderosa pines in White River Park and Big Prairie are experiencing much better 

survival than expected after the 2003 fire. Many of the trees 

with notable fire injury and that appeared to be dying in 2004 

and 2005 have recovered and delayed mortality has been minor. As expected, the mortality rate for small trees (26%) was 

significantly higher (α = 0.05, p = 0.01) than that of large trees 

(18.5%), which is a desirable trend when considering health 

and vigor of the stand (fig. 3). A high proportion of scarred 

trees were lost immediately post-fire, but that trend appears to 

have stabilized.

Land managers on the Spotted Bear Ranger District in 

the Flathead National Forest have a considerable cultural and 

ecological resource under their jurisdiction. The results of the 

2003 fire provided a first step toward restoration and now present a unique opportunity to preserve this resource well into the 

future through the use of innovative wilderness management. 

In the absence of lightning-caused fire and considering the 

history of Native American fire use in this area, wildland fire 

and manager-ignited fire might be warranted as tools to help 

protect and enhance these relict stands in the Bob Marshall 

Wilderness Area.

Acknowledgments

We thank Wendel Hahn for providing horse and mule pack support; Greg Cohn and Violet Holley of the 

USDA Forest Service, Rocky Mountain Research Station for 

their efforts in the field; Paul Hessburg, Sr. of the USDA Forest 

Service, Pacific Northwest Research Station for his help in the 

field; and Deb Mucklow, Tad Wehunt, and the crew at Big 

Prairie (all of the Flathead National Forest) for hosting us. We 

also thank Mick Harrington, Carol Miller, and Helen Smith of 

the USDA Forest Service, Rocky Mountain Research Station 

for their help in the review process.
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Research Note RMRS-RN-42. 2011

References

Anderson, Michelle D. 2003. Pinus contorta var. latifolia. In: 

Fire effects information system, [Online]. U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research 

Station, Fire Sciences Laboratory. Available: http://www.

fs.fed.us/database/feis/ [2010, April 15].

Arno, S.F., H. Smith, and M. Krebs. 1997. Old growth ponderosa pine and western larch stand structures: influences 

of pre-1900 fires and fire exclusion. Res. Pap. RP-INT-495. 

Ogden, UT: U.S. Department of Agriculture, Forest 

Service, Intermountain Research Station. 20 p.

Arno, S.F., L. Ostlund, and R.E. Keane. 2008. Living artifacts: the ancient ponderosa pines of the west. Montana the 

Magazine of Western History 58:55-62.

Howard, Janet L. 2003. Pinus ponderosa var. scopulorum. In: 

Fire effects information system, [Online]. U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research 

Station, Fire Sciences Laboratory. Available: http://www.

fs.fed.us/database/feis/ [2010, May 21].

Keane, R.E., S. Arno, and L.J. Dickinson. 2006. The complexity of managing fire-dependent ecosystems in wilderness: 

relict ponderosa pine in the Bob Marshall Wilderness. 

Ecological Restoration 24(2):71-78.

Ostlund, L., R.E. Keane, S.F. Arno, and R. Andersson. 2005. 

Culturally scarred trees in the Bob Marshall Wilderness, 

Montana, USA: Interpreting Native American historical land use in a wilderness area. Natural Areas Journal 

25:315-325.
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