Whitebark pine (Pinus albicaulis) is a keystone species of upper subalpine ecosystems (Tomback et al. 2001), and is especially important in the high-elevation ecosystems of the northern Rocky Mountains (Arno and Hoff 1989). Its seeds are an essential food source for the endangered grizzly bear (Ursus arctos horribilis), particularly in the autumn, prior to winter denning (Mattson and Jonkel 1990, Mattson and Reinhart 1990, Mattson et al. 1992). In the Greater Yellowstone Ecosystem (GYE), biologists have concluded that the fate of grizzlies is intrinsically linked to the health of the whitebark pine communities found in and around Yellowstone National Park (YNP) (Mattson and Merrill 2002). Over the past century, however, whitebark pine has severely declined throughout much of its range as a result of an introduced fungus, white pine blister rust (Cronartium ribicola) (Hoff and Hagle 1990, Smith and Hoffman 2000, McDonald and Hoff 2001), native pine beetle (Dendroctonus ponderosae) infestations (Bartos and Gibson 1990, Kendall and Keane 2001), and, perhaps in some locations, successional replacement related to fire exclusion and fire suppression (Amo 2001). The most common historical whitebark pine ftre regimes are "stand-replacement", and "mixed severity" regimes (Morgan et al. 1994, Arno 2000, Arno and Allison-Bunnell2002). In the GYE, mixed-severity ftre regimes have been documented in whitebark pine forests in the Shoshone National forest NW of Cody, WY (Morgan and Bunting 1990), and in NE Yellowstone National Park (Barrett 1994). In Western Montana and Idaho, mixed fire regimes have been documented in whitebark pine communities in the Bob Marshall Wilderness (Keane et al. 1994), Selway-Bitterroot Wilderness (Brown et al. 1994), and the West Bighole Range (Murray et al.1998). Mattson and Reinhart (1990) found a standÂreplacing fire regime on the Mount Washburn Massif, within Yellowstone National Park.
Assessing trends and vulnerabilities in the mutualism between whitebark pine (Pinus albicaulis) and Clark’s nutcracker (Nucifraga columbiana) in national parks of the Sierra-Cascade region
