Report 98-5 December 1998

LIMBER PINE MORTALITY ON THE

LEWIS AND CLARK NATIONAL FOREST, MONTANA

Jane Taylor1, Nancy Sturdevant2

INTRODUCTION

Limber pine (Pinus flexilis James) populations at many locations in Montana have been

showing symptoms of declining health over the past 5 to 6 years. The most significant

damage appears to occur at locations on the Lewis and Clark National Forest (NF) in the

north-central part of the state. Large numbers of trees have very thin crowns and poor

terminal growth, and severe mortality is occurring in some areas. Several limber pine

stands were examined in the summer of 1995, and no single, definitive cause of the

decline was identified. In many of the locations, there was evidence of light defoliation

caused by limber pine needle cast (Lophodermella arcuata (Darker) ???Darker).

However, L. arcuata causes defoliation of only 1-year-old needles (Shaw and Leiphart

1960), and on the majority of the observed trees, 1-year-old needles were present, but

needles 2 years old and older were absent. White pine blister rust (Cronartium ribicola

Fisch.) does occur on the Lewis and Clark, and is known to cause high levels of mortality

in some areas. However, the 1995 observations revealed a low rust incidence in the limber

pine populations of concern, and no mortality could be attributed to the rust. Examinations

for root disease pathogens were negative. The 1995 exams also revealed evidence of

minor damage from an unidentified shoot-feeding insect and various secondary twig beetles. Scattered individual trees were found that had been killed by

the mountain pine beetle (Dendroctonus ponderosae Hopkins). None of the pathogens or

insects identified in 1995 were found to a great enough degree to be considered much of a

factor in the overall tree decline problem, and the decline of the limber pine was attributed

to a combination of factors including defoliation from needle cast, severe climatic events,

plus the inherent harshness of the sites where limber pine grows.

In the summer of 1996, transects were established on the Lewis and Clark NF to record

levels of damaging agents in an attempt to find a cause of the decline, and to monitor and

document the current and future tree mortality. In 1998, a needle blight fungus,

Dothistroma septospora (Dorog.) Morelet, was discovered causing severe defoliation and

mortality of limber pine at various locations in Montana (Taylor and Schwandt 1998),

including the areas of concern on the Lewis and Clark NF. The objectives of this paper are

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to present transect data from 1996-1998 on insect and disease activity and tree mortality

on the Lewis and Clark National Forest, and to discuss the involvement of D. septospora

in the limber pine mortality on the Lewis and Clark NF.

METHODS

Between June and August of 1996, four transects were established to monitor the limber

pine decline on the Lewis and Clark NF (Figure 1). The transects were located in stands

that showed moderate to severe tree damage and mortality. The transects were also chosen

to represent variations in geography, elevation, aspect, habitat type and species

composition. The four transects were established in the Lick Creek, Ettien Ridge, Dry

Wolf Creek and Yogo Creek areas

Transects were established by following the slope through the approximate center of a

stand or stringer of limber pine. Basic site information was recorded: slope, aspect and

habitat type (Pfister et al. 1983). Between 48 and 75 limber pine trees in each stand were

tagged and the following data were recorded: tree class, species, diameter at breast height

(dbh), height, crown ratio, crown class, and insect and disease incidence and severity. Age

was determined by taking increment cores from two limber pine trees in each 2-inch

diameter class in each transect. All tree and site information was taken according to

USDA Forest Service, Northern Region stand exam guidelines (USDA Forest Service

1991). Starting in 1998, trees were also rated for damage by D. septospora. If the tree

showed evidence of D. septospora infection, it was estimated whether greater or less than

50% of the crown was infected.

RESULTS AND DISCUSSION

Site and tree characteristics

The sites ranged in elevation from approximately 6400 - 7330 feet (Table 1). The Yogo

Town and Dry Wolf sites were almost pure limber pine and were classified as a limber

pine/bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith) habitat type.

The Ettien Ridge transect was largely limber pine with a minor Douglas-fir (Pseudotsugae

menziesii (Mirb.) Franco) component, and it was classified as a limber pine/Idaho fescue

(Festuca idahoensis Elmer) habitat type. The Lick Creek transect was a mixed

composition of Douglas-fir and limber pine, and it was classified as a Douglas-fir habitat

type. Dry Wolf, Yogo Town, and Lick Creek transects were all positioned at lower to

mid-slope. Dry Wolf and Yogo Town had southern exposures, and Lick Creek had a

western exposure. The Ettien Ridge transect was positioned along a ridge top with a slight

northwestern exposure.

Tree characteristics were summarized for data taken in 1996 (Table 1). The number of

limber pine per transect ranged from 48 to 75. Average tree height on the transects at time

of establishment ranged from 21.1 - 24.1 feet., and average dbh ranged from 6.4 - 7.3

inches. Thirty-nine percent of all trees were classified as dominant or codominant, 36%

were intermediate, 13% were open-grown, and 12% were suppressed.

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Table 1. Transect characteristics and average characteristics of trees on the four transects

(1996 data).

* sd = standard deviation

Insect and disease activity

Blister rust and Dothistroma needle blight were the only two disease agents found

affecting trees on the transects from 1996-1998. A minor amount of sawfly (Neodiprion

sp.) damage was noted each year, but no major insect activity was recorded. Because D.

septospora was not identified until 1998, and because of inconsistencies in blister rust

data collection, only the 1998 data on blister rust and needle blight severity and incidence

were analyzed.

Dothistroma infection was quite prevalent in 1998. Data was recorded in August, and

although many of the infected 2-year-old needles had been shed, enough needles were

present to see symptoms and fruiting bodies of D. septospora. Symptom development was

also evident on 1-year-old needles. Needle samples were collected on each transect, and

the presence of D. septospora was verified through microscopic examination. Eightyseven percent of all trees were infected with D. septospora (Table 2). Needle blight

incidence on the transects ranged from 57% at Ettien Ridge to 100% at Dry Wolf and

Yogo Town. Not only was the incidence of disease high, but the severity was high as well.

Seventy-six percent of all infected trees had greater than 50% of their crowns affected by

needle blight. On a transect basis, the percentage of infected trees with greater than 50%

of their crowns affected ranged from 20% at Ettien Ridge to 100% at Dry Wolf. It was

apparent that D. septospora had been active in these infected trees for least 2-3 years

previously, as evidenced by absence of needles older than 1 year.

Forty-one percent of all trees were infected with C. ribicola (Table 3). The percent of

Transect

Elevation

(ft.)

Slope

(%) Aspect # Trees

Ave.

tree age

(sd*)

Ave. Tree

Height (ft.)

(sd)

Ave. tree

dbh (in.)

(sd)

Lick

Creek

6500 20 W 48 56

(24)

24.0

(9.3)

7.3

(2.9)

Ettien

Ridge

7330 5 NW 60 72

(18)

21.5

(5.3)

6.4

(3.0)

Dry

Wolf

6400 30 S 65 71

(17)

21.1

(4.5)

6.9

(2.4)

Yogo

Town

6400 30 S 75 96

(24)

24.1

(6.1)

7.2

(2.5)

Total - - - 248 74.62

(24)

22.7

(6.4)

6.9

(2.7)

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trees infected with C. ribicola on each transect ranged from 36% at Ettien Ridge to 57% at

Lick Creek. Although the rust incidence was fairly high, the severity of rust infection on

the transects was quite low. Twenty-seven percent of all live trees (64% of infected trees)

were rated as having branch cankers with no bole infections. Only 7% of all live trees

(18% of infected trees) had some degree of topkill from rust. Although trees were not

rated for amount of crown loss due to rust-caused branch mortality, personal observation

was that the current level of rust-caused dieback overall was low.

Mortality

Cumulative tree mortality on the four transects in 1998 ranged from 12% at Ettien Ridge

to 45% at Dry Wolf with an overall average of 24% (Table 4). The mortality rate was

highest between 1996 - 1997. Eighty-five percent of the total mortality was determined to

be associated with defoliation from D. septospora. The conclusion that D. septospora was

associated with tree mortality was based on the high levels of infection recorded in 1998

combined with personal observations of damage and symptoms between 1995-1997

indicating that D. septospora was active in the study areas prior to its identification in

1998. At Dry Wolf and Yogo town, 100% of the mortality was associated with needle

blight, whereas at Ettien Ridge, no mortality was associated with needle blight. Mortality

associated with needle blight defoliation was highest on the transects on south-facing

slopes. Perhaps trees on these south-facing sites are subjected to higher stresses such as

hot temperatures or droughty soil conditions that make them less able to withstand the

effects of severe defoliation.

Taylor and Schwandt (1998) provided a detailed description of the recognition and

biology of D. septospora in limber pine. In general, mortality from D. septospora

defoliation is uncommon in natural stands (Peterson 1981). The severe damage occurring

on the Lewis and Clark NF may be due to the inherent harshness of the limber pine sites.

Limber pine is found on dry, rocky sites that are typified by extreme winter weather and

droughty summer conditions (Steele 1990). Because these sites are so marginal for tree

growth, severe defoliation from D. septospora for several successive years may be enough

additional stress to cause substantial tree mortality.

Table 2. Summary of D. septospora infection data on the four transects.*

trees infected with

D. septospora

infected trees with

<50% crown

affected

infected trees with

>50% crown affected

Transect # % of total

live tress

# % of

total

infected

# % of total

infected

Lick Creek 36 97 10 28 26 72

Ettien

Ridge

30 57 24 80 6 20

Dry Wolf 36 100 0 0 36 100

Yogo

Town

63 100 5 8 58 92

Total 165 87 39 24 126 76

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* 1998 data

Table 3. Summary of C. ribicola infection data on the four transects.*

* 1998 data

**rust severity class:

1 - branch infections located > 2 feet from bole

2 - branch infections located 6 inches - 2 feet from bole

3 - bole infection or branch infection within 6 inches of bole

4 - topkill from rust

Table 4. Summary of tree mortality on the four transects.

Trees infected with

C. ribicola

# of infected trees by rust severity class**

(% of live trees)

#

% of live

trees 1 2 3 4

Lick Creek

21 57

6

(16)

3

(8)

6

(16)

6

(16)

Ettien Ridge

19 36

7

(13)

3

(6)

4

(8)

5

(9)

Dry Wolf

14 39

9

(25)

2

(6)

2

(6)

1

(3)

Yogo Town

24 38

13

(21)

7

(11)

2

(3)

2

(3)

Total

78 41

35

(19)

15

(8)

14

(7)

13

(7)

Transect Cumulative tree mortality by year

(% of total trees)

% mortality

attributed to

D.

septospora

% mortality

attributed

to C.

ribicola

- 1996 1997 1998 - -

Lick

Creek

7

(15)

10

(21)

11

(23)

73* 18*

Ettien

Ridge

4

(7)

7

(12)

7

(12)

0 71*

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* balance of mortality was attributed to suppression

Only seven trees on all four transects were found to have been killed by C. ribicola; this

accounted for 12% of the total mortality on all four transects (Table 4). Mortality from

blister rust was highest on the Ettien Ridge transect. At Dry Wolf and Yogo Town, no

mortality was attributed to blister rust.

Future mortality trends

Infection by D. septospora is quite cyclical in nature, and is closely associated with

summer moisture events (Funk 1985). Therefore, it is difficult to speculate what the

needle blight situation will be in the future. However, given the severe defoliation that has

occurred during the past 3 years on the Lick Creek, Dry Wolf, and Yogo Town transects,

it is likely that additional mortality will occur in the next few years as a result of D.

septospora defoliation. The level of mortality will depend on many factors, including the

needle blight disease level and the number and severity of stressful weather events.

Although mortality from blister rust on the study transects is currently low, the disease is active in these areas. Over

time, mortality from blister rust will probably increase.

The presence of D. septospora as a serious disease agent in limber pine, a species already

facing the threat of blister rust, may have serious implications. During severe needle

blight outbreaks, a substantial number of trees may be killed, and the survival of new

seedlings may be severely limited by rust and needle blight.

Future monitoring

The transects on the Lewis and Clark NF will be monitored annually for mortality and

insect and disease activity, with an emphasis on needle blight defoliation and blister rust

damage. Additional transects have been established at various locations in Montana to

further evaluate the effects of D. septospora defoliation on the decline of limber pine

(Taylor and Schwandt 1998).

LITERATURE CITED

Funk, A. 1985. Foliar fungi of western trees. Can. For. Serv., Victoria, B.C. 159p.

Peterson, G.W. 1981. Research in the United States on Dothistroma needle blight of pines.

In: Current research on conifer needle diseases. Proceedings: Conference of the IUFRO

Dry

Wolf

13

(20)

27

(42)

29

(45)

100 0

Yogo

Town

3

(4)

11

(15)

12

(16)

100 0

Total 27

(11)

55

(22)

59

(24)

85* 12*

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working party on needle diseases. September 15-19, 1980. Sarajevo, Bosnia, Yugoslavia.

113p.

Pfister, R.D.; B.L. Kovalchik; S.F. Arno; R.C. Presby. 1983. Forest habitat types of

Montana. USDA For. Serv. Gen. Tech. Rpt. INT-34. Int. For. and Range Exp. Sta. Ogden,

UT. 174p.

Shaw, C.G. and C.D Leiphart. 1960. Two serious foliage diseases of western white pine in

the Inland Empire. Plant Disease Reptr. 44: 655-659.

Steele, R.S. 1990. Pinus flexilis James. Limber pine. In: Silvics of North America.

Volume 1. Conifers. R.M. Burns and B.H. Honkala eds. USDA For. Serv. Ag. Hndbk

654. Washington, D.C. 675p.

Steele, R.S. 1990. Pinus flexilis James. Limber pine. In: Silvics of North America.

Volume 1. Conifers. R.M. Burns and B.H. Honkala eds. USDA For. Serv. Ag. Hndbk

654. Washington, D.C. 675p.

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.

USDA Forest Service. 1991. Stand Examination field instructions: Region one. Timber

management data handbook. FSH 2409.21h. R1. Chapter 400. USDA For. Serv.,

Missoula, MT. 220p.

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