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Whitebark Pine: Ecosystem in Peril


by
Katherine C. Kendall
National Biological Service
Whitebark pine (Pinus albicaulis) is well-suited to harsh conditions and populates high-elevation forests in the northern Rocky Mountain, North Cascade, and Sierra Nevada ranges (Fig. 1a). Whitebark pine seeds are unusually large, highly nutritious, and are a preferred food for grizzly bears (Ursus arctos) and many other animals (Kendall and Arno 1990). These pine trees (Fig. 2) are adapted to cold, dry sites and pioneer burns and other disturbed areas. At timberline, they grow under conditions tolerated by no other tree species, thus playing an important role in snow accumulation and persistence. Because few roads occur in whitebark pine ecosystems and because the tree's wood is of little commercial interest, information on the drastic decline of this picturesque tree has only recently emerged.

Fig. 1. (a) Natural distribution of whitebark pine (Arno and Hoff 1989; Olgilvie 1990) with mortality zones. Mortality level is the proportion of trees dead from all causes since presettlement. (b) White pine blister rust infection rates in whitebark pine. Blister rust is present but infection rates are unknown in Canada and the southern United States.

Threats
Fig. 2. Healthy whitebark pine stand in Yellowstone National Park not yet affected by the introduced disease, white pine blister rust. Courtesy D. Reinhart
Whitebark pine is threatened by an introduced disease and fire suppression. In its northern range, many whitebark pine stands have declined by more than 90% (Fig.1a). The most serious threat to the tree is from white pine blister rust (Cronartium ribicola), a non-native fungus that has defied control. Fewer than one whitebark pine tree in 10,000 is rust-resistant. Mortality has been rapid in areas like western Montana, where 42% of whitebark pine trees have died from the disease in the last 20 years; 89% of the remaining trees are infected with rust (Fig. 3; Keane and Arno 1993). Although drier conditions have slowed the spread of blister rust in whitebark pine's southern range, infection rates there are increasing and large die-offs are eventually expected to occur (Fig. 1b).
Fig. 3. Dead whitebark pine trees in Glacier National Park. Courtesy R. McClelland
Before fire suppression, whitebark pine stands burned every 50-300 years. Under current management, they will burn at 3,000-year intervals. Without fire, seral whitebark pine trees are replaced by shade-tolerant conifers and become more vulnerable to insects and disease.

Repercussions
The alarming loss of whitebark pine has broad repercussions: mast for wildlife is diminished and the number of animals the habitat can support is reduced. Such results hinder grizzly bear recovery and may be catastrophic to Yellowstone grizzlies for whom pine seeds are a critical food. Predicted changes in whitebark pine communities include the absence of reforestation of harsh sites after disturbance and the lowering of treelines. In addition, stream flow and timing will be altered as snowpack changes with vegetation.

Implications
Whitebark pine will be absent as a functional community component until rust-resistant strains evolve. Natural selection could be speeded with a breeding program like that developed for western white pine (P. monticola), which also suffers from rust. In some areas where whitebark pine is regenerating, its competitors should be eliminated. To perpetuate whitebark pine at a landscape scale, fires must be allowed to burn in whitebark pine ecosystems.
Isolated populations may become extinct where mountain pine beetle or other agents kill remaining resistant trees. To prevent loss of genetic diversity, seeds of these pines should be collected throughout the species' range and stored as insurance against catastrophic events. To guide restoration efforts, more information is needed on whitebark pine's historical distribution, trends throughout its range, and rust epidemic dynamics.
For further information:
Katherine C. Kendall
National Biological Service
Glacier Field Station
Glacier National Park
West Glacier, MT 59936
References
Arno, S.F., and R.J. Hoff. 1989. Silvics of whitebark pine (Pinus albicaulis). U.S. Forest Service Gen. Tech. Rep. INT-253. 11 pp.

Keane, R.E., and S.F. Arno. 1993. Rapid decline of whitebark pine in western Montana: evidence from 20-year remeasurements. Western Journal of Applied Forestry 8(2):44-47.

 Kendall, K.C., and S.F. Arno. 1990. Whitebark pine--an important but endangered wildlife resource. Pages 264-273 in U.S. Forest Service Gen. Tech. Rep. INT-270.

Olgilvie, R.T. 1990. Distribution and ecology of whitebark pine in western Canada. Pages 54-60 in U.S. Forest Service Gen. Tech. Rep. INT-270.


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