HOLOCENE CLIMATE, VEGETATION, AND FIRE LINKAGES IN THE UINTA MOUNTAINS, UTAH

Holocene climate variability has resulted in a dynamic disturbance history in the Uinta Mountains. A 12,000-year lake-sediment record from the south slope provides evidence of large-magnitude events during the Holocene. The modern lake basin catastrophically drained in the early 20^th century, providing a unique opportunity to sample and analyzes sediments from the lake bottom. Pollen evidence suggests an overall decrease in Pinus and gradual increase in Poaceae and Picea during the last 6000 years. This long-term trend suggests mid-Holocene climates were warmer-than-present, followed by gradual cooling, Charcoal-based evidence of fire activity suggests decreasing fire frequency since the mid-Holocene. Fire return intervals range from 200 to 400 years between events, with maximum fire frequency during the middle Holocene. Fires have been decreasing in frequency during the last several millennia and suggest the modern Montane forest of the Uinta Mountains developed with infrequent fire. The mid-Holocene maximum in fire frequency, with events occurring at sub-centennial scales, may provide an analog for future trends of increased fire occurrence at middle- and high-elevation in response to decreasing snowpack and warmer summer temperatures.