Upper subalpine forests, which make up 6% of the total forested acreage in our focal area, are predisposed to burn infrequently and with mixed severity.
Based on data from 13 fire history studies in this forest type within western Montana and northern Idaho, the average stand has a mean fire return interval of 139 years (Arno 1976, 1981a; Arno et al. 1992; Barrett 1983, 1993a, 1993b, 1995, 1997a, 1997b; Gabriel 1976; Keane et al. 1994; Losensky 1993; Zack and Morgan 1994).
Cold weather, rocky terrain, and widely-spaced vegetation amidst sparse fuels are all effective barriers to the spread of fire in the upper subalpine zone. When fires do carry, they tend to creep through the forest understory and remain small, affecting few trees (Fischer and Bradley 1987). Extensive crown fires are generally restricted to the most continuously forested areas. These stand-replacing events are few and far between, usually occurring at intervals of 200 years or more and involving wind-driven crown fires that spread from the lower subalpine zone up into tinder-dry upper subalpine forests (Fischer and Bradley 1987, Smith and Fischer 1997, Barnes et al. 1998).
While the average fire-free period in a given upper subalpine stand tends to be notably long, the lengths of actual fire return intervals usually vary considerably around that mean. This variation is a critical component of the fire regime of upper subalpine forests (Smith and Fischer 1997). Computer models developed by Keane and others (1990), for example, suggest that whitebark pine is more likely to maintain dominance within a stand experiencing fires at irregular intervals averaging 80 years than in a stand that sees fire every 80 years on the dot.
Arno, S. F. 1976. The historical role of fire in the Bitterroot National Forest. USDA Forest Service, Intermountain Forest and Range Experiment Station, Research Paper INT-187.
Arno, S. F. 1981a. Fire history in the vicinity of Sheep Mountain Bog, Lolo National Forest. Unpublished data on file at USDA Forest Service, Intermountain Forest and Range Experiment Station, Fire Sciences Laboratory, Missoula, Montana, USA.
Arno, S. F., E. D. Reinhardt, and J. H. Scott. 1992. Forest Structure and landscape patterns in the subalpine lodgepole pine type: A procedure for quantifying past and present conditions. USDA Forest Service, Intermountain Forest and Range Experiment Station, General Technical Report, INT-294.
Barnes, B. V., D. R. Zak, S. R. Denton, and S. H. Spurr. 1998. Forest Ecology, 4th ed. John Wiley and Sons, New York, New York, USA.
Barrett, S. W. 1983. Fire history of Glacier National Park: North Fork Flathead River Drainage. Final Report Supplement 2220(?) for USDA Forest Service Intermountain Forest and Range Experiment Station, Fire Sciences Laboratory, Missoula, Montana, USA.
Barrett, S. W. 1993a. Fire history of Tenderfoot Creek Experimental Forest, Lewis and Clark National Forest. Final Report RJVA No. INT-92679 for USDA Forest Service, Intermountain Forest and Range Experiment Station, Forestry Sciences Laboratory, Bozeman, Montana, USA.
Barrett, S. W. 1993b. Fire history of southeastern Glacier National Park. Unpublished data on file at USDI National Park Service, Research Division, Glacier National Park, West Glacier, Montana, USA.
Barrett, S. W. 1995. Fire history assessment for the Lolo Trail, Powell Ranger District, Clearwater National Forest. Unpublished data on file at USDA Forest Service, Clearwater National Forest, Powell, Idaho, USA.
Barrett, S. W. 1997a. Historical fire regimes on the Beaverhead-Deerlodge National Forest, Montana. Unpublished data on file at USDA Forest Service, Beaverhead-Deerlodge National Forest, Wise River Ranger District, Wise River, Montana, USA.
Barrett, S. W. 1997b. Fire history of Glacier National Park: Hudson Bay drainage. Unpublished data on file at USDI Glacier National Park, Research Division, West Glacier Montana, USA.
Fischer, W. C., and A. F. Bradley. 1987. Fire Ecology of western Montana forest habitat types. USDA Forest Service, Intermountain Forest and Range Research Station, General Technical Report, INT-223.
Gabriel, H. W. 1976. Wilderness ecology: the Danaher Creek drainage, Bob Marshall Wilderness, Montana. Dissertation, The University of Montana, Missoula, Montana, USA.
Keane, R.E., S.F. Arno, J.K. Brown, and D.F. Tomback. 1990. Modelling disturbances and conifer succession in whitebark pine forests. In Proceedings of the Symposium on Whitebark Pine Ecosystems: Ecology and Management of a High Mountain Resource, Bozeman, Montana, USA.
Keane, R. E., P. Morgan, and J. P. Menakis. 1994. Landscape assessment of the decline of whitebark pine (Pinus albicaulis) in the Bob Marshall Wilderness Complex, Montana, USA. Northwest Science 68: 213-229.
Losensky, B. J. 1993. Fire history for the Birch Creek drainage, Beaverhead Forest. Unpublished Report on file at, USDA Forest Service, Region 1, Missoula, Montana, USA.
Smith, J. K., and W. C. Fischer. 1997. Fire ecology of the forest habitat types of northern Idaho. USDA Forest Service, Intermountain Research Station, General Technical Report, INT-GTR-363.
Zack, A. C., and P. Morgan. 1994. Fire history on the Idaho Panhandle National Forest. Unpublished data on file at USDA Forest Service, Idaho Panhandle National Forest, Coeur d'Alene, Idaho, USA.