Long-term vegetation, climate, and fire history in the eastern Uinta Mountains, Utah, U.S.A

A 2.13 meter-long sediment core from Reader Fen Basin (3205m asl) in the eastern Uinta Mountains provides a 10,250-year-long cal yr BP record of vegetation change and fire history. Few studies have explored the long-term vegetation and disturbance history from the Uinta Mountains. As a result, significant gaps remain in understanding historical processes affecting ecosystem dynamics from this region. The vegetation history at Reader Fen Basin suggests subalpine forest species (e.g., Picea engelmannii and Pinus contorta) expanded in the Uinta Mountains soon after glaciers retreated by 9000 cal yr BP. The charcoal-based fire history reconstruction from Reader Fen Basin suggests fires occurred on average every 470 years during the last 10,000 years. Three major shifts in vegetation composition occurred during the Holocene: 1) the displacement of grass and alpine herbaceous communities as arboreal species colonized the watershed, between 10,250 and 9000 cal yr BP, 2) the replacement of Picea engelmannii by the expansion of Pinus contorta forests into the watershed during the middle Holocene, beginning at 9000 cal yr BP when fire became more prominent in the ecosystem, and 3) a reduction of Cyperaceae as grasses began to dominate the fen during the last 3200 cal yr BP. These three major shifts in vegetation composition are largely the result of changing climate and fire frequency. Understanding the frequency and magnitude of past disturbances is necessary for understanding the catalyst of vegetation change for making informed management decisions on present and future ecological change in the Uinta Mountains.