Observations of Species Migrations from Paleoclimatic Studies

Stratigraphic history from within and outside the Yellowstone region, dating from the late Pleistocene, reveal the contribution of large-scale climatic forcings in shaping vegetation provinces over long time scales (Waddington and Wright 1974, Gennett and Baker 1986, 1989, Wigand and Nowak 1992, Whitlock et al. 1994, Whit-lock and Bartlein 1991, 1997). Glacial retreat, changes in the cycle of solar irradiance, and atmospheric circulation patterns have set the altitudinal boundaries of major biomes from grassland to forest to tundra in the GYE, through governing changes in relative warmth and aridity (Waddington and Wright 1974, Baker 1989, Whitlock 1993). These impacts may be further influenced by the steep relief of the Yellowstone region, which shapes regional precipitation and wind patterns across the landscape (Whitlock 1993, Bartlein et al. 1997).

Such global controls have been found to govern the location of whitebark pine and associated species over the millennia within the GYE. Initial deglaciation in the GYE was soon followed by the establishment of forests of first Picea engelmannii by approximately 11,500 years before present, and then albicaulis and A. lasiocarpa as the region warmed and precipitation increased (Whitlock 1993). Subsequently, as conditions became warmer and drier by mid-Holocene, lodgepole pine entered the region and rose in elevation so that whitebark pine was confined to timberline sites (Baker 1976, Whitlock 1993). These patterns of vegetation distribution were overturned approximately 7000 years before present in the north where drier conditions prevailed, and 5000 years before present in the south where a cooler, moister period was initiated, and vegetation came to resemble its current configuration (Whitlock and Bartlein 1991, Whitlock 1993). Such findings point to the conclusion that if warmer and drier conditions than present again prevail, whitebark pine will be confined to isolated peaks across the region.

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