United States 

Department of 

Agriculture 

Forest 

Service 

Northern

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

Report 04-5 February 2004

FOREST HEALTH ASSESSMENT OF WHITEBARK PINE IN

SELECTED STANDS IN THE SELKIRK MOUNTAINS OF 

NORTHERN IDAHO 2001 

Sandra Kegley, John Schwandt, and Ken Gibson 

 

Introduction 

Whitebark pine stands in the Selkirk Mountains, 

Idaho Panhandle National Forests, have been 

steadily declining for several years due to white 

pine blister rust (BR) and mountain pine beetle 

(MPB). Within the past few years, a MPB 

outbreak has significantly increased the rate and

amount of mortality. Ground surveys conducted 

in three areas in the fall of 2000 documented a 

loss of 45-82% of the whitebark pine primarily 

due to MPB. From 33%-87% of the remaining 

green trees in those areas had blister rust (BR) 

symptoms (Kegley et al. 2001). These results 

prompted a more extensive ground survey in the 

fall of 2001 to determine whitebark pine 

conditions in additional stands. 

Methods 

In August and September 2001, five areas of 

whitebark pine were examined for MPB attack 

and BR infection in the Selkirk Mountains, 

Bonners Ferry Ranger District. These areas 

were Cutoff Peak, Fisher Peak, Trout Lake, 

Farnham Ridge, and East Russell Ridge. 

Two types of surveys were conducted. On 

Farnham Ridge and East Russell Ridge, data 

were recorded from a series of variable radius 

plots. On Cutoff Peak, Fisher Peak, and Trout 

Lake, whitebark pine were examined in random 

strip surveys in addition to variable radius plots 

because variable radius plots did not include a 

large enough sample of white bark pine. 

Data recorded for each tree included: species, 

diameter (d.b.h.), and a description of any bark 

beetle activity or blister rust infection. Bark 

beetle activity was classified as current, last 

year, and older MPB attack, or unknown or 

secondary bark beetle mortality. Partial bole 

attacks (strip attacks) and unsuccessful attacks

(pitchouts) were also recorded. BR data 

included branch cankers, bole cankers, and 

percent top kill. Trees with only dead branches 

were rated as lightly infected; multiple branch 

cankers or less than 30% top kill were rated as 

moderately infected; bole cankers or more than 

30% top kill were rated as severely infected. 

Older dead whitebark pine (snags) were not 

recorded. 
In the summers of 2001 and 2002, five Lindgren 

funnel traps baited with MPB attractants, 

exobrevicomin and trans-verbenol (Pherotech, 

Inc.), were hung near the Trout Creek trailhead. 

Traps were monitored weekly and MPB counted 

to determine flight periodicity. 

Logistic regression was used to explore the 

relationship between MPB mass attack, d.b.h., 

and BR condition by area. Pearson’s chi square

test was used to determine the probability of 

MPB attack on trees with or without severe BR. 

Results 

Stand Characteristics 

Stand characteristics for each area including 

total trees per acre (TPA), basal area (BA), 

quadratic mean diameter (QMD), and numbers 

of plots are shown in table 1. 

Table 1. Stand characteristics as determined by ground surveys, 2001. (TPA = trees per acre, BA= 

basal area, QMD = quadratic mean diameter.) The last number in each column is the standard error or 

variance around the mean (SEM). 

Area # of 

plots 

Stand 

Attribute 

Whitebark 

Pine SEM

Lodgepole 

Pine SEM

Subalpine 

Fir SEM Spruce SEM Total SEM

Cutoff Total TPA 22 17% 7.5 23 17.1 56 15.9 30 11.7 131 17.8 

Peak 

Total BA 23 22% 2.9 23 15 31 9.6 29 7.4 106 16.2 

QMD 16.5 2.3 14.1 4 10.0 0.7 14.4 2.0 12.1 0.4 

Live TPA 8 8% 20 0 47 30 105 7 plots 

Live BA 14 15% 20 29 29 91 

Total TPA 108 78% 26.6 0 24 0 6 0 138 38.3 

Fisher 

Peak 

Total BA 110 94% 24.1 0 3 0 3 0 117 26.5 

QMD 13.8 1.3 0 5.0 0 10 0 13.1 0.9 

Live TPA 89 75% 0 24 6 119 6 plots 

Live BA 87 94% 0 3 3 93 

Total TPA 101 42% 34.3 0 103 42.2 37 17.8 240 42.8 

Trout 

Lake 

Total BA 102 50% 18.1 0 24 9.9 29 9.5 156 15.6 

QMD 15.0 2.0 0 6.9 0.7 13.4 4.9 11.8 0.8 

Live TPA 78 36% 0 103 37 218 9 plots 

Live BA 73 57% 0 24 29 127 

Total TPA 89 42% 24.6 35 16.3 45 15.6 41 16.2 211 37.5 

Farnham 

Ridge 

Total BA 58 50% 11.7 25 311.8 13 4.5 18 5.2 115 14.4 

QMD 13.0 1.1 11.8 4.0 7.7 1.1 10.2 1.4 10.7 0.6 

12 plots Live TPA 13 10% 33 45 41 133 

Live BA 8 13% 23 13 18 63 

Total TPA 106 26% 15.4 26 13.4 249 39.9 22 8.7 404 39.2 

Total BA 92 45% 8.9 20 7.3 74 12.5 17 5.5 203 13.1 

East 

Russell 

Ridge 

QMD 13.3 1.4 13.8 4.9 7.5 0.3 14.1 6.8 10.2 0.3 

Live TPA 8 3% 11 249 20 289 25 plots 

Live BA 6 6% 6 74 16 102 

2
The amount of whitebark pine varied widely 

between the five areas sampled, but was the 

species with the largest average d.b.h. in all 

areas. The whitebark pine stand component 

varied from a high of 94% total BA and 78% total 

TPA at Fisher Peak to a low of 22% total BA and 

17% total TPA at Cutoff Peak. However, amount 

of remaining live whitebark varied from 75% live 

TPA (94% live BA) at Fisher Peak to only 3% 

live TPA (6% live BA) at East Russell Ridge. 

Fisher Peak was the only area of the five 

sampled where whitebark pine was still the 

dominant species. Trout Lake and Russell Ridge

are primarily subalpine fir stands while Farnham 

Ridge and Cuttoff Peak also have major 

components of Engelmann spruce and 

lodgepole pine. 

Individual stand losses varied considerably. 

Whitebark pine was originally about half the total 

BA at Trout Lake, Farnham Ridge and East 

Russell Ridge but these numbers have declined 

dramatically at two of the areas. The worst 

losses occurred on Farnham Ridge where 85% 

of the whitebark TPA and 86% of the whitebark 

BA had died and East Russell Ridge where 

whitebark TPA declined 92% and BA decreased

93%. Lodgepole pine on East Russell Ridge 

had also been attacked by MPB resulting in a 

70% decrease in lodgepole pine BA. 

Whitebark Pine Condition 

Number, average diameter, and percent of all 

healthy whitebark pine, those with current, last 

year, and older MPB attack, unknown or 

secondary bark beetle mortality, and BR 

infection are recorded by area in table 2. 

East Russell Ridge had extreme whitebark pine 

mortality; 94% of the whitebark pine sampled 

were dead. Of those, 63% were killed by MPB 

from 2000-2001. On Farnham Ridge, 83% of 

the whitebark pine sampled were dead but most 

of it was old mortality—only 14% occurred in 

2000-2001. However, the sample size may 

have been too small to adequately represent 

actual conditions. On Cutoff Peak, 42% of the 

whitebark pine sampled were dead with most of 

the mortality occurring in 2000-2001. On Fisher 

Peak, 29% of the whitebark were dead; most 

were killed in 2000-2001. Trout Lake had the 

lowest mortality. There, 17% of the whitebark 

sampled were dead and only 8% had been killed

by MPB in 2000-2001. Unknown or secondary 

bark beetle mortality was recorded on only a few 

trees in each area. Very few trees were found 

with strip attacks or pitchouts. Strip attacks 

were classified as current MPB attack, and 

pitchouts were classified as live trees. 

In all areas, the average d.b.h. of trees killed by 

MPB was significantly higher than unattacked 

trees (table 2), and the probability of successful 

MPB attack increased with increasing tree d.b.h.

(p<.02). 

BR infection varied from 57% on Farnham Ridge

to 81% at Cutoff Peak. However, rust infection 

may have been underestimated since small BR 

infections are very difficult see, especially in 

dense crowns or on dead trees. We were most 

confident in identifying trees with severe rust 

infections, so we were most interested in further 

analyses aimed at describing interactions 

between MPB and severely BR infected trees. 

Aerial survey data indicate that whitebark pine 

mortality due to MPB is expanding and 

intensifying (more trees killed per acre) in the 

Selkirk Mountains (fig. 1). Aerial surveys record 

faded trees that were actually attacked and 

killed the previous year. In 2000, surveys 

recorded 9,273 faded whitebark on 8,634 acres. 

By 2002, tree mortality had increased to 40,798 

faded whitebark on 12,786 acres. In 2003, 

recorded mortality was nearly the same with 

38,732 trees killed on 12,735 acres. 

3
Table 2. Whitebark pine with MPB or BR infection by area. 

Location Cutoff Peak

Fisher

Peak Trout Lake 

Farnham 

Ridge 

East Russell 

Ridge 

# WBP 

examined 202 139 200 35 117

Ave. d.b.h. 16.3 14.2 16.9 12.9 14.3

WBP alive 118 (58%) 99 (71%) 167 (84%) 6 (17%) 7 (6%) 

Year 2001 MPB 

attack 21 (10%) 17 (12%) 11 (6%) 3 (9%) 24 (21%) 

Year 2000 MPB 

attack 32 (16%) 14 (10%) 4 (2%) 2 (6%) 50 (43%) 

Older MPB 

attack 24 (12%) 6 (4%) 13 (7%) 19 (54%) 30 (26%) 

Ave d.b.h. 

with MPB 17.7 14.9 20.0 14.1 14.5

Ave d.b.h. 

no MPB 15.3 13.9 16.4 10.1 12.7

Unknown or

secondary

mortality 

7 (3%) 3 (2%) 5 (3%) 5 (14%) 6 (5%) 

Total Dead 84 (42%) 40 (29%) 33 (17%) 29 (83%) 110 (94%) 

WBP killed by 

MPB in 2000-

2001 

53 (26%) 31 (22%) 15 (8%) 5 (14%) 74 (63%) 

WBP infected 

with BR 164 (81%) 90 (65%) 134 (67%) 20 (57%) 78 (67%) 

Mountain Pine Beetle in Whitebark Pine

Selkirk Mountains, Northern Idaho

Aerial Survey Data

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

Trees

Acres

Figure 1. Whitebark pine mortality due to MPB in the Selkirk Mountains 

from 1992-2002 as recorded by aerial surveys. 

4
Blister Rust and Mountain Pine Beetle 

Interactions 

Since it is difficult to determine uninfected trees 

from lightly or even moderately infected trees, 

we focused our analyses on comparing MPB 

success in trees with severe rust infections to 

trees with moderate, light or no infection 

observed. Our logic was that MPB might detect 

severely infected trees due to slower growth 

rate, but might not detect differences between 

uninfected trees and those with only a few dead 

branches or branch cankers. 

 

When data from all areas are pooled, we found 

MPB preferred trees that were not severely 

infected with blister rust (p<.035) (table 3). Only 

35% of trees with severe BR had successful

MPB attacks while 43% of trees without severe 

blister rust had successful MPB attacks. 

Table 3. Interactions between successful 

mountain pine beetle attacks and severe blister 

rust infections on whitebark pine 

No MPB MPB Total

Severe BR 209 (65%) 111 (35%) 320 

Not Severe BR 214 (57%) 159 (43%) 373 

Total 423 270 693

However, this effect was not uniform across all 

areas. The proportion of whitebark severely 

infected with blister rust varied from 17% at 

Farnham Ridge, which had the lowest total rust

infection to 58% at Cuttoff Peak, which had the 

highest total rust infection (table 4). MPB-caused

mortality in whitebark ranged from 14% at Trout 

Lake to 89% at East Russell Ridge.

At Fisher Peak and Trout Lake, where nearly 

half the whitebark were severely infected with 

BR and MPB populations were the lowest, MPB 

seemed to prefer severely infected trees (33.8% 

vs. 19.7% and 15.6% vs. 12.7% respectively). 

Cuttoff Peak had more severely BR infected 

trees and a higher MPB population, but the most 

successful MPB attacks were on trees that were 

not severely infected with BR (44% vs. 33.9%). 

MPB was also most successful in trees without 

severe BR at Farnham Ridge and Russell 

Ridge, which had the highest proportion of MPB 

attacks and the lowest proportion of severely 

infected BR trees.

Table 4. Interactions between successful mountain pine beetle attacks and severe blister rust 

infections on Whitebark pine (WBP) sampled in each area 

Location Cutoff Peak

Fisher

Peak Trout Lake

Farnham 

Ridge 

East Russell 

Ridge 

# WBP 

examined 202 139 200 35 117

Severe BR 

No MPB 78 45 76 4 6

Severe BR 

+ MPB 40 23 14 2 32

% MPB in 

 Severe BR 33.9% 33.8% 15.6% 33.3% 84.2%

MPB + not 

severe BR 37 14 14 22 72

No MPB +

Not Sev. BR 47 57 96 7 7

% MPB in not

Severe BR 44% 19.7% 12.7% 75.9% 91.1%

Total Sev BR 118 (58%) 68 (49%) 90 (45%) 6 (17%) 38 (32%) 

Total MPB 77 (38%) 37 (27%) 28 (14%) 24 (68%) 104 (89%) 

5
Flight Monitoring 

In 2001, flight-monitoring traps were placed near

beetle-infested whitebark pine stands on May 30

and monitored weekly except for a period of 2 

weeks in August. We observed new attacks in 

whitebark pine trees on May 29 that had been 

strip attacked the previous year. We caught 

MPB on June 9, the first time trap catches were 

collected, through September 18 when traps 

were removed. There appeared to be two peaks 

during the MPB summer flight—one occurring in 

early July, the other sometime in August (fig. 2). 

In 2002, we placed flight-monitoring traps in the 

same location on June 6. Beetles were caught 

from then through September 20. Traps were 

removed September 25. Once again, there 

appeared to be two peaks in the flight—one in 

late June to mid-July, the other in mid- to late 

August (fig. 3). The troughs between the peaks 

were periods of cool, or cool and wet weather. 

MPB Trap Catches in Whitebark Pine

Northern Idaho 2001

0

2000

4000

6000

8000

10000

12000

14000

9-Jun

16-Jun

23-Jun

30-Jun

7-Jul

14-Jul

21-Jul

28-Jul

4-Aug

11-Aug

18-Aug

25-Aug

1-Sep

8-Sep

15-Sep

Traps placed May 30

Figure 2. MPB flight period in whitebark pine, summer 

2001. Trap catches were not collected August 11 or 18, 

therefore beetles collected August 25 were averaged 

over the 3-week period. 

MPB Trap Catches in Whitebark Pine

Northern Idaho 2002

0

1000

2000

3000

4000

5000

6000

14-Jun

21-Jun

28-Jun

5-Jul

12-Jul

19-Jul

26-Jul

2-Aug

9-Aug

16-Aug

23-Aug

30-Aug

6-Sep

13-Sep

20-Sep

Traps placed June 6

cool

cool & wet

Figure 3. Mountain pine beetle flight period 

in whitebark pine, summer 2002. 

6
Discussion 

To date, MPB populations are still active in the 

Selkirk Mountains of northern Idaho. In some 

areas, few live mature whitebark pines remain. 

In other areas, MPB populations are not as high

and beetle-caused mortality has not been as 

extreme. However, we expect mortality due to 

MPB to continue for the next few years. Walkthrough examinations of trees near Trout Lake in 

October 2002 discovered many green trees had 

been attacked by MPB. Those were recorded 

as faders in 2003. 

Flight period of MPB in whitebark pine appears 

to be longer than in lodgepole pine. In 

lodgepole pine, the major flight generally occurs 

in July and August (Amman & Cole 1983). 

Normally, MPB could take 2 years to complete 

their development at the high elevations where 

whitebark pine occurs (Amman & Cole 1983). 

Because we have had warm, dry weather well 

into the fall for the past few years, it is possible 

that the life cycle has been shortened to 

something less than 2 years. Our winters have 

also been relatively mild for the past few years, 

which may have allowed MPB life stages not 

normally cold-hardy to survive the winter. 

Population sampling in the fall revealed eggs, 

larvae, pupae and adults under the bark of dying 

trees. Normally, and in most MPB hosts, only 

larvae survive the winter (Amman & Cole 1983). 

The two peaks in the flight period both years 

could be two univoltine populations emerging at 

different times. It is also possible the first peak 

is the major flight and the second peak is adults 

re-emerging from initially attacked trees to attack 

additional trees. This is known to occur in 

lodgepole pine (Barbara Bentz, personal 

communication). Additional studies are needed 

to determine the life cycle of MPB in whitebark 

pine. Many more beetles were caught in 2001 

than in 2002. This may have been because few 

live host trees were left in the vicinity of the traps 

in 2002. 

There was a strong relationship between MPB 

attacks and tree d.b.h. in all areas. Average 

d.b.h. of MPB attacked trees was higher than 

unattacked trees and probability of attack 

increased with increasing d.b.h. This relationship

has been well documented in lodgepole pine 

(Cole and Amman 1980, Safranyik et al. 1982) 

but only suspected in whitebark pine. 

Results from these surveys seem to indicate 

MPB generally favor trees that are not severely 

infected with blister rust (p< .035), although this 

pattern was not consistent across all five areas. 

Cutoff Peak, Farnham Ridge, and East Russell 

Ridge where the MPB populations were the 

highest followed this pattern. In a previous 

survey at nearby Pyramid Lake where MPB 

populations were high, we found MPB attacking

more trees without obvious BR signs than with 

some level of BR (Kegley et al. 2003). Although 

analyses in this area were not restricted to 

severely infected trees, MPB seemed to prefer 

trees without BR. 

However, results from Fisher Peak and Trout 

Lake, which had the lowest MPB populations, 

indicated MPB preferred severely BR infected 

trees. This agrees with surveys at two sites in 

Montana, where low MPB populations preferred 

whitebark pine with higher BR infection levels 

(Adams and Six 2002). Therefore, it appears 

that at low population levels, MPB may select 

BR weakened trees but as MPB populations 

increase, attacks become more random. 

The mixed results from all these studies may be 

due partially to the difficulty in accurately 

assessing BR infection levels on mature trees. 

Therefore, perhaps we should focus our analysis 

on severely infected trees. It seems unlikely 

MPB could detect differences between trees 

with light BR infections and those without any 

infection anyway. We also believed severely 

infected trees would more likely affect MPB 

behavior, and we are much more confident in 

accurately diagnosing trees with severe BR 

infections. 

Sample sizes of MPB-infested trees and ones 

severely infected with BR were fairly small in this 

study. Larger samples might help clarify 

relationships between MPB and BR. Because 

d.b.h. is an important factor in MPB attack, it 

must be taken into account in statistical 

analyses to prevent clouding possible 

relationships with severity of rust infection. 

We plan to continue monitoring Fisher Peak and 

Trout Lake stands that had low MPB activity. 

We hope to document any apparent changes in 

the BR/MPB relationship as MPB populations 

increase. 

7
Acknowledgements 

Gary Kempton, Doug Wulff, and Brandon 

Mastrude helped with surveys on Cutoff Peak, 

Fisher Peak, Trout Lake, and Farnham Ridge. 

Doug Nishek collected beetles from traps. 

Michael Marsden conducted the statistical 

analysis. 

Literature Cited 

Adams, J. and D. Six. 2002. Effect of white pine

blister rust infection on mountain pine beetle 

preference in whitebark pine. Poster

presented at NSF-Train Program, Univ. of 

Montana, Missoula, MT, Sept. 12, 2002. 

Amman, G.D. and W.E Cole. 1983. Mountain 

Pine Beetle Dynamics in Lodgepole Pine 

Forests Part II: Population Dynamics. 

USDA For. Serv. Intermountain Forest & 

Range Exp. Sta. Ogden, UT 84401, Gen. 

Tech. Rpt. INT-145. 

Bentz, Barbara, Intermountain Forest and 

Range Experiment Station, personal 

communication. 

Cole, W.E and G.D. Amman. 1980. Mountain 

pine beetle dynamics in lodgepole pine 

forests Part I: Course of an infestation. 

USDA Forest Service, Gen. Tech. Rpt. INT89. 56 p. 

Kegley, S., J. Schwandt, and K. Gibson. 2001. 

Forest health assessment of whitebark pine 

on Pyramid Pass, Russell Mountain, and 

Burton Ridge in the Selkirk Mountains on the 

Idaho Panhandle National Forests. USDA 

For. Serv. Northern Region FHP rpt. 01-8. 

11 p. 

Kegley, S., K. Gibson, J. Schwandt, and M. 

Marsden. 2003. A test of verbenone to 

protect individual whitebark pine from

mountain pine beetle attack. USDA For. 

Serv. Northern Region FHP rpt. 03-9. 6 p. 

Safranyik, L,. D.M. Shrimpton, and H.S. 

Whitney. 1982. Management of lodgepole 

pine to reduce losses from the mountain pine 

beetle. Canadian Forestry Service, Forestry 

Technical Report 1. 24 p. 

8