Paleoecological reconstruction of the Bridger Range, Montana, USA
Benes, James Victor
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The postglacial vegetation and fire history of the Greater Yellowstone Ecosystem (GYE) is poorly known immediately outside of the Yellowstone and Grand Teton national parks due to the scarcity of pollen and charcoal records. The paleoecological record of the Bridger Range near the northwestern GYE boundary provides new information on the ecological history of the region. A 5-m-long sediment core was taken from Fairy Lake (45°54'16.00"N, 110°57'29.00"W, 2306 m elev) to reconstruct the regional vegetation, fire, and climate history. Pollen analysis reveals shifts in vegetation from tundra-steppe to early Picea with Pinus parkland, and open forest of Pinus, Pseudotsuga, Abies, and Picea and finally closed forest over the last ca. 15,000 years, similar to other regional pollen records in the GYE. Fluctuations in different conifer species are interpreted as a response to regional climate changes. Wetter, cooler periods are associated with expansion of Picea. Warmer periods of time are associated with more open landscapes, and more frequent burning, but with less biomass burnt due to the more open landscape. Changes in the ratio of arboreal pollen to non-arboreal pollen were studied through time from sites spanning a west-to-east transect across the Northern Rocky Mountains (NRM), with Fairy Lake, and other records from the northern GYE in the center. Arboreal pollen is higher in the west, where annual/seasonal rainfall (or available moisture during the growing season) is greater. Charcoal records from the NRM were also compared to Fairy Lake's charcoal record in an effort to distinguish Fairy Lake from other NRM sites. The Fairy Lake fire record is similar to some NRM sites in the late-glacial and late Holocene with increased fire activity along with increases in available biomass. Archeological remains in the Fairy Lake watershed suggest some level of human activity in recent centuries, although the extent of human influence on vegetation change is not easily distinguished from climatic controls.