USDA Forest Service R6-NR-FHP-2007-01

Ecology of Whitebark Pine in the Pacific Northwest

Gregory J. Ettl

College of Forest Resources, University of Washington Box 352100 Seattle, WA 98195

Whitebark pine (Pinus albicaulis) is found in the subalpine zone throughout the Coastal, Olympic, Cascade, and Klamath Mountains, extending well into California at high elevations along the Sierra Nevada. Precipitation is > 300 cm/yr on the western slopes of the Coastal Mountains in British Columbia and the Olympics & Washington Cascades (Franklin and Dyrness 1988). Precipitation generally decreases along the Oregon Cascades moving south, with 50-100 cm/yr common in southern Oregon. The coastal mountain ranges in southern Oregon and Northern California, including the Siskiyou, Trinity, and Klamath Mountain ranges also receive precipitation upwards of 300 cm/yr, decreasing to 150-200 cm/yr throughout much of the California Cascades and northern Sierra Nevada (Schoenherr 1992).

In the coastal ranges and Cascade ranges of British Columbia, Washington, and northern Oregon heavy precipitation leads to persistent snowpack, and therefore whitebark pine is often restricted to exposed ridges of the subalpine zone or drier sites in the rain shadow of these ranges where it commonly grows in association with subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), and lodgepole pine (Pinus contorta). Whitebark pine is also a minor component of moister subalpine sites, or in mixed subalpine forests at lower elevations. Moister subalpine sites west of the Cascade crest in the southern Washington and northern Oregon Cascades have mountain hemlock (Tsuga mertensiana) and whitebark pine in association on some of the highest and most exposed slopes (Diaz et al. 1997). Whitebark pine typically loses dominance in the lower subalpine zone, and its dominance being restricted to drier sites may be related to drought tolerance. However, whitebark pine is also considered a seral species with lower shade tolerance than most Pacific subalpine conifers. High elevation whitebark pine populations are typically isolated on mountain peaks, as whitebark pine is outcompeted by other subalpine tree species at lower elevations, therefore forming a metapopulation structure.

The southern Oregon Cascades show a decrease in subalpine fir and Engelmann spruce, and an increase in mountain hemlock, lodgepole pine and Shasta red fir (Abies magnifica var. shastensis) growing in association with whitebark pine. Westside, wetter slopes and lower subalpine slopes are often dominated by Shasta red fir and mountain hemlock with whitebark pine increasing in abundance on ridges. Mountain hemlock is often the dominant subalpine species in both the number of trees/ha and in basal area on mesic sites, with lodgepole pine and Shasta red fir typically more abundant than whitebark pine; western white pine (Pinus monticola) is also present (Goheen et al. 2002). Whitebark pine is common on high elevation ridges in this region, and drier soils lead to greater dominance by whitebark pine on these sites, occasionally forming pure stands in areas east of the Cascade crest. The subalpine zone of the eastern side of the southern Cascades are often more open with

20 Proceedings of the Conference Whitebark Pine: A Pacific Coast Perspective

lodgepole pine increasing in importance (Hopkins 1979). Whitebark pine is also common near treeline in the Sierra Nevada, Oregon and California Cascades and coastal mountains, with increasing importance of additional 5-needle pines including Pinus flexilis, Pinus balfouriana, and Pinus longaeva (Schoenherr 1992).

White pine blister rust (Cronartium ribicola) is common throughout the Pacific Northwest, generally decreasing toward eastern WA and south through OR and CA; lower infection levels may be related to lower transmission rates on drier sites and/or to a more recent arrival of white pine blister rust on these sites. The spread of blister rust south and east, particularly in California and the Great Basin region, will require additional attention and resources to be allocated to all high-elevation 5-needle pines. There is considerable variability in blister rust infection at finer scales, for example across mountain ranges, and this variability may be related to local variation in the alternate host Ribes, microclimate, and/or variation in blister rust resistance among hosts.

Field data used to create a spatially explicit metapopulation model for whitebark pine for Mt. Rainier National Park using RAMAS GIS predicts a rapid decline in whitebark pine in the park, with the population falling below 100 individuals in 148 years (Ettl and Cottone 2004). The proportion of blister rust resistant whitebark pine is unknown, but incorporating resistance into the model only moderately slows population decline (Cottone 2001). Infected trees show relatively low cone production (DelPrato 1999) and therefore even resistant trees, with presumed slow disease progression, are likely to have limited reproduction. The fire return interval is variable in whitebark pine stands across the Pacific Northwest (range ~30- 300 years) with wetter sites showing longer return intervals. Furthermore, low fuel availability in open grown high-elevation ecosystems typically leads to poor fire transmission across the landscape. Modeling a fire return interval of 50 years, projects a faster decline for whitebark pine in Mt. Rainier than in the absence of fire (Cottone 2001). It seems likely that mixed species whitebark pine stands would benefit from reduced competition provided by prescribed fire, but it is unclear whether the loss of whitebark pine from fire-related mortality could be compensated for by increased whitebark pine seedling establishment in recently burned areas. Natural progression of white pine blister rust throughout whitebark pine communities puts the species at risk of local extinction without human assistance, although whitebark pine may persist through chance, patchy host distribution, or natural selection. Propagation and planting of resistant whitebark pine hold the best prospects for maintaining whitebark pine in the Pacific Northwest. The spread of blister rust suggests a similar fate for all 5-needle high-elevation pines, and gaps in our knowledge of these systems should be addressed in preparation for the arrival of blister rust.

References. Cottone, N. 2001. Modeling whitebark pine infected with blister rust in Mt. Rainier National Park. M.S. Thesis. St. Joseph’s University, Philadelphia, PA.

DelPrato, P.R. 1999. Response of whitebark pine (Pinus albicaulis) to white pine blister rust (Cronartium ribicola) in Mount Rainier National Park. M.S. Thesis. St. Joseph’s University, Philadelphia, PA.

21 USDA Forest Service R6-NR-FHP-2007-01

Diaz, N.M., C.T. High, T.K. Mellen, D.E. Smith, and C. Topik. 1997. Plant associations and management guide for the mountain hemlock zone. Gifford Pinchot and Mt. Hood National Forests. USDA Forest Service, Pacific Northwest Region. R6-MTH-GP- TP-08-95. 111 pp.

Ettl, G.J., and N. Cottone. 2004. Whitebark pine Pinus albicaulis in Mt. Rainier National Park, USA: Response to blister rust infection. In H. R. Akçakaya, M. A. Burgman, O.Kindvall, C. C. Wood. P. Sjögren-Gulve, J. S. Hatfield, and M. A. McCarthy (Eds), Species Conservation and Management: Case Studies, Pp. 36-47. Oxford University Press, New York, N.Y.

Franklin, Jerry F. and C.T. Dyrness. 1988. Natural Vegetation of Oregon and Washington. Oregon State University Press. Corvallis, OR. 452 pp.

Goheen, E.M., D.J. Goheen, K. Marshall, R.S. Danchok, J.A. Petrick, and D.E. White. 2002. The status of whitebark pine along the Pacific Crest National Scenic Trail on the Umpqua National Forest. USDA Forest Service, Pacific Northwest Research Station. General Technical Report PNW-GTR-530. 22 pp.

Hopkins, W.E. 1979. Plant associations of the Freemont National Forest. USDA Forest Service, Pacific Northwest Region. R6 ECOL-79-004. 106 pp.

Schoenherr, A.A. 1992. A Natural History of California. University of California Press. Berkeley, CA. 772 pp.

22