Abstract
The Yellowstone region has been divided into geovegetation regions based on characteristics of the vegetation, climate, and geology (Despain, 1990). The Northern Range or Yellowstone-Lamar valleys features open Douglas-fir parkland, summerÂwet conditions, and substrates composed of glacial debris and sedimentary and granitic material. The Central Plateau is an area of lodgepole forest, relatively dry summers, and infertile rhyolite soils. The Absaroka region consists of mixed conifer forest, relatively dry summers, and andesitic and sedimentary rock types. The environmental history of the geovegetation regions, as revealed from a network of pollen and charcoal records, has been equally distinctive (Whitlock, 1993; Whitlock and Bartlein, 1993; Whitlock et al., 1994, 1995). The Northern Range experienced wetter-than-present summers in the early Holocene between 10 and 7 ka (ka = 1000 14C years before present) as a result of intensified monsoonal circulation. The development of Douglas-fir parkland there has occurred with drying in the late Holocene. The paleoecologic record shows few fires in the early Holocene and increased burning in the last 7000 years as the climate became drier (Millspaugh, in prep.). In the Central Plateau, areas of rhyolite supported lodgepole-pine forest for the last 10,000 years with little change. Charcoal data from this region indicate that fires were most frequent in the early Holocene between 10 and 7 ka, when southern and central Yellowstone National Park (YNP) and Grand Teton National Park (GTNP) were warmer and drier than at present. Fire frequency has decreased in the last few millennia with the onset of present-day cool conditions (Millspaugh, in prep.; Whitlock and Millspaugh, in press). Despite these changes in Holocene climate and fire regime the vegetation of the Central Plateau remained a lodgepole pine forest, presumably because of the infertile soils.