United States 

Department of 

Agriculture 

Forest 

Service 

Northern 

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

Forest Health

Protection

Report 03-4 February 2003 

UPDATE ON LIMBER PINE DECLINE AND MORTALITY 

ON THE LEWIS AND CLARK NATIONAL FOREST, MONTANA 

Marcus Jackson and Blakey Lockman 

Plant Pathologists 

INTRODUCTION 

This report updates a study that was undertaken 

to identify causes of limber pine decline and 

mortality in central Montana (Taylor and 

Sturdevant 1998). Taylor and Sturdevant 

determined that 85% of the mortality along 

permanent transects in the Lewis and Clark 

National Forest from 1995 through 1998 was 

associated with defoliation from the needle 

pathogen Dothistroma septospora (Doroguine) 

Morelet. Although 41% of the study trees were 

reportedly infected with the white pine blister 

rust pathogen Cronartium ribicola Fisch, Taylor 

and Sturdevant believed rust-caused mortality 

was low, accounting for only 12% of the total 

mortality. The remaining mortality, 

approximately 3%, was attributed to 

suppression. 

METHODS 

Transect establishment methods are described 

in the earlier report (Taylor and Sturdevant 

1998). Four transects were established in the 

Lewis and Clark National Forest. Trees were 

tagged to allow monitoring over time. From 

1996 to 1998, all tree and site data were taken 

according to USDA Forest Service, Northern 

Region stand exam guidelines. 

Data has been collected three times (1999, 

2000, and 2002) since the first report was 

printed. All four transects were visited in July of 

1999 and 2002. During 2000, Dry Wolf and 

Yogo Town were visited in June and Lick Creek 

and Ettien Ridge were visited in October. 

Beginning in 1999, a standardized form 

documenting percent crown affected by D. 

septospora, blister rust severity level, and 

mortality was used. Needle retention data were 

collected in 2002. 

Precipitation data from five weather stations 

within an approximate radius of 35 miles around 

the transects were included in the analysis of 

disease development and mortality. Data for 

“Neihart 8NNW,” “Millegan 14SE,” “White 

Sulphur Springs 2,” “Raynesford 2NNW,” and 

“Stanford” weather stations were taken from the 

Western Regional Climate Center’s web page at 

www.wrcc.dri.edu/index.html. 

Throughout this report, “severe” means 90% or 

more of the foliage in a given crown is affected 

by D. septospora. “Non-severe” means less 

than 90% of the foliage is affected by D. 

septospora in a given crown. 

RESULTS 

Mortality associated with D. septospora

severity

Trees with severely affected crowns were more 

likely to die in subsequent years than nonseverely affected trees in the same year. Table 

1a shows mortality through 2002 associated with 

defoliation data collected in 1999, while Table 1b 

shows mortality through 2002 associated with 

severe defoliation in both 1999 and 2000. 

Thirty-eight percent of the Dry Wolf trees and 

27% of the Yogo Town trees with severely 
2 

affected crowns in 1999 died by 2002 (Table 1a). 

Forty-three percent of the Dry Wolf and 28% of 

the Yogo Town trees with severely affected 

crowns in both 1999 and 2000 died by 2002 

(Table 1b). No trees with less than 90% of their 

crowns affected at the Dry Wolf and Yogo Town 

transects in 1999 and 2000 died by 2002. Three 

percent of the trees at Lick Creek and 7% of the 

trees at Ettien Ridge with non-severely affected 

crowns in 1999 died by 2002. For those trees 

with severely affected crowns in 1999, 60% and 

56% of them died at Lick Creek and Ettien 

Ridge, respectively. In 2000, there was only one 

tree affected by 90% defoliation at Lick Creek 

and none at Ettien Ridge. Six percent of the 

trees at Lick Creek and 10% of the trees at Ettien 

Ridge with non-severely affected crowns in 1999 

and/or 2000 died by 2002. 

Table 1a. Comparison of 1999 D. septospora Severity to Mortality through 2002 

Transect Non-severely Affected Crown in 1999 Severely Affected Crown in 1999 

Lick Creek 1/311 3% 3/52 60% 

Ettien Ridge 3/42 7% 5/9 56% 

Dry Wolf 0/0 0% 13/34 38% 

Yogo Town 0/6 0% 15/56 27% 

Total 4/79 5% 36/104 35% 

1

Dead trees in 2002/# of live trees with <90% of the crown affected in 1999. 2

Dead trees in 2002/# of live trees with 90 to 100% of the crown affected in 1999. 

Table 1b. Comparison of Two-Year1 D. septospora Severity to Mortality through 2002 

Transect Mortality2

 Non-Severely Affected Crown Severely Affected Crown 

Lick Creek* 2 2/323 6% 0/14 0% 

Ettien Ridge 3 5/48 10% 0/0 0% 

Dry Wolf* 1 0/4 0% 12/28 43% 

Yogo Town 3 0/16 0% 12/43 28% 

Total 9 7/100 7% 24/72 33% 

1

Crown affects for 1999 and 2000. 

2

Number of trees that died from 1999 to 2000. 

3

Dead trees in 2002/# of live trees with <90% of the crown affected in 1999 and/or 2000. 4

Dead trees in 2002/# of live trees with 90 to 100% of the crown affected in both 1999 and 2000. 

*Lick Creek and Dry Wolf transects were each missing 1 year of data for one tree
3 

 

0

50

100

150

200

250

1993199419951996199719981999200020012002

Year

Percent of Average

June, July, and August

Precipitation

Annual Precipitation

Precipitation 

Precipitation at any time during the growing 

season may provide for D. septospora spore 

dissemination and infection of susceptible 

needles (Taylor and Schwandt 1998). 

Combined data* from the five weather stations 

showed higher average precipitation in June, 

July, and August of 1993 (235% of average), 

1995 (144% of average), 1997 (164% of 

average), 1998 (129% of average), and 2002 

(127% of average) than the average (Figure 

1). Precipitation combined for June, July, and 

August in 1994, 1996, 1999, 2000, and 2001 

remained near or below average. The effect of 

drought-like conditions following defoliation 

may cause greater mortality than defoliation 

alone. Annual precipitation was 12% below 

average at the weather stations when 

precipitation data were combined and 

averaged over the 4-year period from 1998 

through 2001. During the 4-year period from 

1994 through 1997, combined annual 

precipitation at the four weather stations was 

4% above average. 

Figure 1. Average precipitation for growing season compared to average annual 

precipitation, 1993-2002. 

______________________________ 

*The “averages” are the means for the entire reporting period for each weather station (ranging from 19 to 

38 years depending on the weather station). 
4 

Needle retention 

Needle retention data were collected in 2002 

(Table 2). Needle retention displayed an 

inverse relationship to previous D. septospora

infections. While approximately three-fourths 

of the trees at Lick Creek and Ettien Ridge 

retained 3 or 4 years of their needles, 

approximately 3/4 of the trees at Dry Wolf and 

Yogo Town retained only 2 years of their 

needles. All trees, except 1, retained 2 or 

more years of their needles.

Table 2. Needle retention in 2002 

 Years Retained1

Transect 1 2 3 4 5 Median 

Lick Creek 0 (0)2 6 (19%) 15 (47%) 8 (25%) 3 (9%) 3 

Ettien Ridge 0 (0) 8 (19%) 12 (28%) 23 (54%) 0 (0) 4 

Dry Wolf 0 (0) 16 (76%) 5 (24%) 0 (0) 0 (0) 2 

Yogo Town 1 (2%) 38 (81%) 8 (17%) 0 (0) 0 (0) 2 

1

The average age of the oldest needles retained throughout the crown of each tree.

Decreasing damage from D. septospora

The average “percent crown affected” by D. 

septospora for each transect was determined by 

adding together the “percent crown affected” of 

all the live trees in the transect and dividing that 

number by the total number of live trees in the 

transect. Since 1999, there has been a 

substantial and continual decrease in the levels 

of D. septospora on all four transects (Table 3).

Table 3. Percent crown affected by Dothistroma septospora1 

Transect 1999 2000 2002 

Lick Creek 53%2 33% 7% 

Ettien Ridge 51% 12% 0% 

Dry Wolf 98% 94% 24% 

Yogo Town 95% 84% 40% 

Average 75% 56% 18% 

1

All live trees averaged across each transect. 

2

Average percent for all the live crowns at the transect for the given year. 

White Pine Blister Rust 

From 1998 to 1999, there was a reduction in the 

number of trees reported to be infected with C. 

ribicola at three transects (Table 4a). The 

reduction was likely due to changes in crew, 

monitoring methods, and inconsistencies 

described below for 1999 through 2002 data.
5 

Table 4a. Incidence of C. ribicola (including all Rust Severities) 

Transect 1998 

(%) 

1999 

(%) 

2000 

(%) 

2002 

(%) 

Lick Creek 20/371

(54) 

19/37 

(51) 

31/34 

(91) 

27/32 

(84) 

Ettien Ridge 19/53 

(36) 

26/51 

(51) 

36/48 

(75) 

23/43 

(54) 

Dry Wolf 14/36 

(39) 

0/34 

(0) 

3/33 

(9) 

4/21 

(19) 

Yogo Town 24/63 

(38) 

3/62 

(5) 

19/59 

(32) 

27/47 

(57) 

1

Number of infected trees/total number of live trees at the transect (percent of total live trees infected). 

Rust Severity Classes: 

1. Branch infections located greater than 2 feet from bole 

2. Branch infections located 6 inches to 2 feet from bole 

3. Bole infections or branch infection within 6 inches of bole 

4. Topkill from rust

There are many irregularities in the blister rust 

data from 1999 through 2002. Two cankers 

noted in 1999 were missed in 2000, then again 

noted in 2002. Twenty-one cankers were noted 

in 1999 and/or 2000, but not noted on live trees 

in 2002. Many irregularities appear to originate 

from the identification of rust cankers more than 

2 feet from the bole of the tree (Rust Severity 1). 

When Rust Severity 1 data is removed from the 

incidence data, there appears to be a continued 

increase in the numbers of trees that are 

infected with blister rust at each transect since 

1999 (Table 4b). 

Table 4b. Incidence of C. ribicola1

 (not including Rust Severity 1) 

Transect 1999 

(%) 

2000 

(%) 

2002 

(%) 

Lick Creek 18/372

(49) 

163/34 

(47) 

22/32 

(69) 

Ettien Ridge 11/51 

(22) 

14/48 

(29) 

18/43 

(42) 

Dry Wolf 0/34 

(0) 

1/33 

(3) 

3/21 

(14) 

Yogo Town 3/62 

(5) 

5/59 

(8) 

20/47 

(43) 

Total 32/184 

(17) 

36/174 

(21) 

63/143 

(44) 

1

Rust Severities 2, 3, and 4 are included. Rust Severity 1 data was irregular across the 3 years. 2

Number of infected trees/total number of live trees at the transect (percent of total live trees infected). 3

The decrease in incidence is caused by two blister rust infected trees dying between 1999 and 2000.
6 

Mortality 

Annual mortality (Taylor and Sturdevant 1998) 

decreased in all transects from 1997 to 1998 

(Table 5). Mortality remained under 10% for 

each year through 2002 at Lick Creek and Ettien 

Ridge. There was a considerable increase in 

mortality at Dry Wolf and Yogo Town over the 

last two years. Mortality remained under 10% 

from 1998 through 2000, but averaged 18% at 

Dry Wolf and 10% at Yogo Town annually in 

2001 and 2002 (2-year combined mortality 

equally divided between the 2 years).

Table 5. Summary of mortality 

Annual tree mortality1

Transect 1996 1997 1998 1999 2000 20022

 Total3

Lick Creek 7/48 

(15) 

3/41 

(7) 

1/38 

(3) 

1/37 

(3) 

2/36 

(6) 

2/34 

(6) 

16/48 

(33) 

Ettien Ridge 4/60 

(7) 

3/56 

(5) 

0/53 

(0) 

2/53 

(4) 

3/51 

(6) 

5/48 

(10) 

17/60 

(28) 

Dry Wolf 13/65 

(20) 

14/52 

(27) 

2/38 

(5) 

2/36 

(6) 

1/34 

(3) 

12/33 

(36) 

44/65 

(68) 

Yogo Town 3/75 

(4) 

8/72 

(11) 

1/64 

(2) 

1/63 

(2) 

3/62 

(5) 

12/59 

(20) 

28/75 

(37) 

Total 27/248 

(11) 

28/221 

(13) 

4/193 

(2) 

5/189 

(3) 

10/184 

(5) 

31/174 

(18) 

105/248 

(42) 

1

Number of trees that died since previous visit/number of live trees at previous visit of transect (% of live trees). 2

Percent mortality in 2002 is the accumulated mortality of two years (2001 and 2002). 

3

Cumulative mortality on each transect over entire study period.

Since the study began, mortality has been 33%, 

28%, 68%, and 37%; respectively, for Lick 

Creek, Ettien Ridge, Dry Wolf, and Yogo Town 

(Figure 2). At the Dry Wolf and Yogo Town 

transects, all mortality from 1999 through 2002 

was associated with greater than 90% of each 

 crown affected by D. septospora. Three of the 

four trees that died at Lick Creek during this 

period were associated with severe crown 

effects. Two of the eight trees that died at Ettien 

Ridge were also associated with high levels of 

D. septospora. 

0

10

20

30

40

50

60

70

Percent 

Mortality

Lick Creek Ettien

Ridge

 Dry Wolf Yogo

Tow n

Transect

2002

2000

1999

1998

1997

1996

Figure 2. Percent mortality for each transect for each measurement year. 
7 

DISCUSSION 

Needle Cast (Dothistroma septospora)

Taylor and Sturdevant (1998) attributed 85% of 

the mortality along the transects to D. 

septospora, 12% to C. ribicola, and 3% to 

suppression. Our results support their findings, 

as we have shown that 80% of the mortality was 

associated with D. septospora since 1999. This 

study shows greater subsequent mortality when 

90% or more of a tree’s crown was affected by 

D. septospora than trees with less than 90% of 

their crowns affected. Increased precipitation 

during the growing season of 1993, 1995, 1997, 

and 1998 may have contributed to D. 

septospora dissemination, germination, and 

infection from 1996 through 2000. 

Taylor and Sturdevant (1998) suggested that 

limber pine may be less able to withstand 

defoliation because of the hot, droughty 

conditions on south-facing slopes. There was 

more mortality on the transects of the southfacing slopes (Dry Wolf, Yogo Town) than the 

transects on the west and northwest-facing 

slopes (Lick Creek, Ettien Ridge). However, the 

south-facing slopes also had more defoliation 

associated with D. septospora than the west and 

northwest-facing slopes. This suggests that the 

conditions on the south-facing slopes in this 

study may have been more conducive to 

infection or the trees on these slopes may have 

been more susceptible to infection by D. 

septospora. 

Even though the levels of D. septospora

declined since 1999, mortality has increased on 

the Yogo Town and Dry Wolf transects. 

Inadequate soil moisture may have prevented 

many of the previously heavily defoliated trees 

from recovering. 

Retention of 2 or more years of needles and 

declining rates of defoliation suggest the effects 

of D. septospora infections may be waning on 

the transects. However, since much remains 

unknown about the biology of this fungus in 

limber pine, we cannot reliably predict the future 

effects this fungus will have on these stands. 

White Pine Blister Rust (Cronartium ribicola) 

Limber pine are more likely to have multiple 

leaders than some other 5-needled pines. Due 

to the presence of several stems, individual 

stem infections are less likely to be lethal. This 

is one reason that the white pine blister rust 

rating system does not perform well for limber 

pine. 

This study shows the difficulty in identifying 

white pine blister rust on limber pine. Some 

year-to-year variability could have been caused 

by differences in observers’ abilities to see and 

properly identify blister rust cankers. The high 

number of missed cankers and/or previously 

misidentified cankers suggests there may be 

another canker fungus or other biotic or abiotic 

problem causing symptoms similar to early 

blister rust infections. Another possible 

explanation is that some of these cankers were 

produced on trees that responded to the cankers 

with “bark resistance reactions” as has been 

seen on other 5-needled pines, but this is 

unlikely due to the low level of resistance 

observed in natural populations of western white 

pine (Bingham 1983). 

Although there were many inconsistencies in 

rating white pine blister rust, the data support 

the conclusion that C. ribicola was a minor factor 

in the overall mortality on the transects from 

1999 through 2002. However, the incidence of 

blister rust appears to have continually 

increased since 1999 and may be an 

increasingly important factor contributing to 

mortality in the future. 

LITERATURE CITED 

Bingham, R.T. 1983. Blister rust resistant 

western white pine for the Inland Empire: The 

story of the first 25 years of the research and 

development program. USDA For. Serv. GTR 

INT-146. Ogden, UT. 45p. 
8 

Taylor, J.E. and N. Sturdevant. 1998. Limber 

pine mortality on the Lewis and Clark National 

Forest, Montana. USDA For. Serv. Forest Health 

Protection Rpt. 98-5. Missoula, MT. 7p. 

Taylor, J.E. and J.W. Schwandt. 1998. 

Dothistroma needle blight of limber pine in 

Montana. USDA For. Serv. Forest Health 

Protection Rpt. 98-4. Missoula, MT. 7p. 

ACKNOWLEDGEMENTS 

The authors thank Brennan Ferguson and John 

Schwandt for their review and constructive 

comments regarding this report. We also thank 

Gregg DeNitto and Beverly Bulaon for their field 

support of this project.