United States 

Department of 

Agriculture 

Forest 

Service 

Northern 

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

Numbered Report 06-03 February 2006

Mountain Pine Beetle Conditions in Whitebark Pine Stands in the Greater 

Yellowstone Ecosystem, 2006

Ken Gibson, Entomologist 

USDA Forest Service, Forest Health Protection 

Missoula Field Office 

Introduction 

Mountain pine beetle, Dendroctonus ponderosae

Hopkins, (MPB) populations are currently at 

outbreak status in many parts of the 

intermountain West. More than one million 

acres of host stands are infested to some extent in 

the Northern Region alone. Most infested acres 

are in lodgepole pine stands; however, almost 

143,000 of them are in whitebark pine (WBP). 

In the Northern Region, unusually high amounts 

of MPB-infested WBP stands are found in 

northern Idaho and west-central Montana in 

addition to forests in southwestern Montana, and 

Yellowstone National Park (NP)—the latter a 

part of the Greater Yellowstone Ecosystem 

(GYE). 

In 2005, we recorded the highest level of MPBcaused WPB mortality in any one year for which 

we have data. Unpublished office reports 

indicate a similar series of outbreaks existed in 

the 1930s—another period of unusually warm 

temperatures—in Southeastern Idaho, 

Southwestern Montana and Yellowstone NP; but 

we have no records documenting the extent of 

those outbreaks. By most accounts, those 

outbreaks were probably at least as extensive as 

current ones. So, while present outbreaks are 

devastating and unusual; they are likely not 

unprecedented. 

In the GYE, defined as Yellowstone and Grand 

Teton NPs and surrounding national forests in 

the Northern, Intermountain, and Rocky 

Mountain Regions (Gallatin, Beaverhead, 

Custer, Bridger-Teton, Caribou-Targhee, and 

Shoshone National Forests [NF]), there are 

approximately 1,064,600 acres of WBPdominated forested stands. At present, about 

171,200 (16%) of those acres contain some level 

of MPB-caused mortality, recorded in 2005 

during annual aerial-detection surveys (ADS) 

(Figure 1). Nearly 720,000 WBP were estimated 

as having been killed in 2004, recorded as faders 

in 2005 (Meyer 2006; Halsey and Ross, personal 

communication) (Table 1). 
Figure 1. MPB-infested WBP stands in the GYE, 2005 (ADS data) 

I should note, many WBP sites are in wilderness 

areas or parks not routinely surveyed. The 

following tables show a few administrative units 

for which we have no data (“Not flown”). That 

should not be interpreted as areas in which 

outbreaks do not exist. Rather, they are 

reporting areas not surveyed. 

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Table 1. MPB-Infested WBP, Acres and Trees, GYE; Recorded in 2005 (ADS Data)

Administrative 

Unit 

Acres of 

WBP 

MPB-Infested Acres 

(2005) 

Estimated 

Faders 

Average 

Trees/Acre

Yellowstone NP 218,700 29,215 365,200 12.5 

Grand Teton NP 9,300 Not flown Not flown -- 

Gallatin NF 256,100 20,316 37,500 1.8 

Beaverhead NF 108,800 42,441 136,600 3.2 

Custer NF 68,700 1,087 1,300 1.2 

Bridger-Teton NF 115,000 34,373 131,100 3.8 

Caribou-Targhee NF 56,000 1,982 3,900 1.9 

Shoshone NF 232,000 41,746 43,700 1.0 

Total 1, 064,600 171,160 719,300 4.2 

Recently conducted research and observations 

over the past few years, suggest warmer-thannormal temperatures at high-elevation sites have 

increased MPB-caused impacts by increasing 

beetle survival and in some cases shortening 

their life cycles. Under more typical conditions 

over-wintering survival is reduced and 

population expansion is not as rapid (Nijhuis 

2004). The situation existing in the GYE, 

however, is not limited to that geographic area. 

At present, WBP stands throughout the 

intermountain West are experiencing higherthan-normal levels of MPB activity—supporting 

the contention that recent climatic conditions 

have contributed to current outbreaks. 

ADS data for administrative units in the GYE, 

obtained within the past 5 years, indicates MPB 

populations in WBP stands within that 

geographic area were at generally endemic levels 

as recently as 2000. While not all areas were 

surveyed every year, unusually high MPB 

populations have been recorded in most areas 

only during the past 4-5 years (Table 2). The 

Caribou-Targhee and Shoshone NFs showed 

building populations in 2000. Prior to 2000, for 

at least the preceding ten years, only minor 

amounts of beetle-caused mortality were 

recorded in most of the GYE surveyed 

(Unpublished office reports). 

Table 2. Acres MPB-Infested WBP in GYE, 2000-2004 (ADS Data)* 

Adm. Unit 2000 2001 2002 2003 2004 

Yellowstone NP Not flown Not flown 11,814 15,086 Not flown 

Grand Teton NP Not flown Not flown Not flown Not flown Not flown 

Gallatin NF 18 0 Not flown 9,014 47,844 

Beaverhead NF 173 Not flown 30,263 38,891 29,978 

Custer NF 0 0 73 533 1,762 

Bridger-Teton NF 199 1,031 6,466 13,506 17,495 

Caribou-Targhee NF 794 3,808 844 4,960 3,417 

Shoshone NF 2,068 30,529 43,300 42,327 48,158 

* Note: Yearly infestation acreage figures are not additive. Currently fading trees are often 

recorded on many of the same acres in succeeding years. 
4

In support of ADS figures, we occasionally 

obtain ground-based data from a series of 

FINDIT (Bentz 2000) plots in a few selected 

beetle-infested stands. Plot data for most 

forested areas in GYE are not available; 

however, we did obtain some from a series of 

plots in Yellowstone NP and adjacent Gallatin 

NF in 2004. I believe these data are 

representative of MPB-caused mortality 

throughout the area within the past 2-3 years. 

In twenty plots established in Yellowstone NP, 

near Avalanche Peak, WBP killed by MPB 

within the past three years averaged almost 96 

trees per acre. On the Gallatin NF, where we 

established ten plots near Lightning Lake, 

mortality—most also killed within the past three 

years—averaged 162 WBP per acre. In the 

Yellowstone plots, beetle-killed trees represented 

80% of the WBP over 5 inches (diameter at 

breast height) in surveyed stands. In the Gallatin 

plots, 74% of the WBP over 5 inches have been 

killed. In some areas, mortality levels have 

already begun to decline due to host depletion. 

On the Shoshone NF, in 2005, ground-collected 

data in a few MPB-infested WBP stands showed 

beetle-caused mortality ranged from 7 to 41 trees 

per acre, most of which were currently infested 

trees. Total mortality, however; most of which 

has occurred within the past 1-3 years, is much 

higher (Allen, personal communication). 

Atypically warm and dry weather, and stands 

that hadn’t experienced significant disturbances 

(MPB outbreaks or fire) for a half-century or so, 

combined a few years ago to create conditions 

that fostered rapidly expanding beetle outbreaks 

in these highly susceptible habitats. Because 

timbered stands on these sites are rarely 

managed, at least in the silvicultural sense, 

epidemics will likely last as long as suitable 

hosts remain or until environmental conditions 

become less conducive to MPB survival and 

expansion. 

WBP and MPB 

While vulnerable to present conditions, WBP is 

one of the hardiest of the pine species, capable of 

surviving in extremely harsh environments. It 

plays a critical role in the ecology and 

sustenance of other members of their shared 

alpine communities; such as grizzly bears, 

Clark’s nutcrackers, and red squirrels. In fact, 

present distribution of WBP is almost totally 

dependent upon Clark’s nutcrackers—virtually 

the sole agents of seed dispersal, and fire-created 

openings in which seeds are cached (Tomback et 

al, 2001). 

Disturbance is an integral part of these highelevation ecosystems. Disturbances such as fire 

and MPB outbreaks, while not frequent, have 

shaped the landscape in these subalpine zones. 

Now, however, introduced pests, and native ones 

taking advantage of especially favorable 

conditions, are exposing WBP to combinations 

of threats it has never before encountered. Some 

WBP ecosystems have been so seriously 

damaged we question their ability to return to 

pre-settlement conditions. 

While WBP sites were some of the last to be 

affected by human encroachment; a subtle, yet 

significant affect has been fire suppression. On 

some sites, stand composition has changed, 

stands have become overmature and more 

densely stocked, and the likelihood for more 

damaging fires has increased. 

A much more drastic affect of human 

intervention than fire exclusion in many forested 

ecosystems has been the introduction of nonnative pests. In WBP habitats, none have been 

more threatening to the long-term survivability 

of WBP than white pine blister rust. The 

development of WBP breeding programs to 

promote rust resistance hold some hope for 

future generations of WBP. They are described 

in more detail by Tomback and others (2001). 
A more serious threat to WBP, however; at least 

in the short term, is a native pest—MPB. MPB 

outbreaks occasionally reach levels sufficient to 

kill millions of mature trees before running their 

course. And local climatic conditions may 

exacerbate an already bad situation. A few years 

of warmer- and drier-than-normal conditions 

enable beetles to kill WBP in unusually high 

numbers in a remarkably short period of time. 

MPB outbreaks in the early part of the twentieth 

century were mostly recorded in hosts other than 

WBP. We often concluded MPB outbreaks in 

WBP were the result of outbreaks developing 

first in LPP stands at lower elevations, and more 

hospitable climates, then moving into WBP 

stands as LPP resources were exhausted. We 

know such phenomena did occur during MPB 

outbreaks in the 1970s (Parker 1973) and 1980s 

(personal observations). 

Now, however, we believe some 1930s 

outbreaks may have developed in WBP; then 

moved down into LPP stands. We find that to be 

the case at many WBP sites today (Unpublished 

office reports). Similarities between historic and 

recent MPB outbreaks in WBP suggest a 

commonality is unusually warm yearly 

temperatures. United States’ weather records 

show warmer temperatures for the 1930s than 

any other decade in the twentieth century—and 

very close to extremes we have experienced in 

the past 3-5 years (Anonymous 2006). It is 

reasonable to assume similar conditions in 

natural ecosystems, then and now. 

As a result, MPB outbreaks today in WBP stands 

are at levels not previously quantified. Still, we 

know 1930s outbreaks were extreme. Furniss 

and Renkin (2003) quoted a 1934 report for 

Yellowstone NP, which stated: “The mountain 

pine beetle epidemic is threatening all of the 

white bark and lodgepole pine stands in 

Yellowstone Park. Practically every stand of 

white bark pine is heavily infested...and will be 

swept clean in a few years. If the insects spread 

from the white bark pine to the lodgepole stands, 

it seems inevitable that much of the park will be 

denuded.” 

Conclusion 

Over the past few decades, we have learned 

much in not only coping with MPB, but in 

developing means to reduce beetle-caused 

mortality in some stands and situations. We 

know we can, in some host species, 

silviculturally create stand conditions less 

impacted by beetles (McGregor, et al 1987; 

Bartos and Amman, 1989). And we have 

learned to use beetle-produced pheromones to 

our advantage. Female-produced attractant 

pheromones have been used to manipulate beetle 

populations (Borden, et al 1983). Verbenone, 

the primary anti-aggregant pheromone produced 

mostly by male beetles, has been used 

successfully to protect high-value trees from 

beetle attack (Bentz, et al 2005; Kegley, et al 

2003; Kegley and Gibson, 2004). 

However, we have much yet to learn relative to 

silvicultural manipulations of WBP stands to 

reduce MPB-caused mortality. Some 

management alternatives may advantageously 

include the use of prescribed fire (Tomback, et al 

2001). In the meantime, we have had good 

success in preventing attacks using preventive 

sprays of insecticides; and to a lesser, but stillvaluable extent, verbenone has been useful. 

As restoration projects are developed and 

implemented, it will be important to preserve 

mature cone-bearing trees from MPB 

depredations while beetle populations remain 

high. Plant pathologists and geneticists are 

developing breeding programs, similar to 

successful ones for western white pine, to 

forestall affects of white pine blister rust. Cone 

collections from trees resistant to blister rust, but 

susceptible to MPB, will be critical to the 

success of these programs. Combined efforts of 

entomologists, plant pathologists, silviculturists, 

and other resource specialists will be required if 

WBP is to be successfully preserved and restored 

to critical, high-elevation sites throughout its 

historic range. 

5
References 

Allen, K.K. 2006. Entomologist, USDA Forest 

Service, Forest Health Management, 

Rapid City, SD. Personal 

communication. 

Anonymous. 2006. Climate of 2005—Annual 

review, U.S. summary. National Climate 

Data Center, National Oceanic and 

Atmospheric Administration. Asheville, 

N.C. 

Bartos, D.L.; Amman, G.D. 1989. 

Microclimate: an alternative to tree vigor 

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Research Paper INT-400. 10p. 

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