Paper No. 32
Presentation Time: 8:00 AM-6:00 PM
COMPARISON OF HOLOCENE DROUGHT, FIRE, AND VEGETATION HISTORY IN THE EASTERN SAWATCH RANGE, CENTRAL COLORADO
CARTER, Grace E., Geology and Geophysics, Ecology, University of Wyoming, 1000 University Ave, Laramie, WY 82071, POWERS, Kristine, Limnological Research Center, University of Minnesota, Minneapolis, MN 55455 and SHUMAN, Bryan N., Geology and Geophysics, University of Wyoming, 1000 University Ave, Laramie, WY 82071, gcarter6@uwyo.edu
Paleoenvironmental histories of Rocky Mountain watersheds, particularly those near ecotones, provide important information about how vegetation responds to various disturbances as well as changes in climate regimes. This study focuses on Emerald Lake, located 14 kilometers southwest of Leadville, CO at 3050 meters above sea level. Emerald Lake is a small, hydrologically isolated lake on the flank of a lateral moraine. This study aims to reconstruct the lake level of Emerald Lake, and the vegetation and fire history of the surrounding landscape. Using palynological, charcoal, and geochemical analyses in conjunction with ground penetrating radar, bulk density, and loss-on-ignition data, we will endeavor to answer the following questions: 1) How do the vegetation responses to disturbances such as drought and fire register in the pollen record? 2) What correlation is evident among the lake level (drought), vegetation and fire histories? 3) Have disturbances pushed the vegetation around Emerald Lake outside of its historic range of variability? 4) What is the relationship of fuel load, climate, and fire through the Holocene?
Preliminary data from ground penetrating radar, bulk density and loss-on-ignition analyses demonstrate that local conditions were drier than present prior to approximately 3200 cal yr BP, and that the subsequent wet conditions have been punctuated by two multi-century drought episodes. Comparison of preliminary Emerald Lake data with other Holocene lake level studies in the western United States demonstrate some synchronicity in lake level fluctuations across a wide area, including low water levels after ca. 900 cal yr BP. Preliminary palynological evidence, including changes in the percentages of Pinus (pine), Picea (spruce), Pseudotsuga (fir), and Artemisia (sagebrush) pollen, suggests that a shift from a forested environment to an open, sagebrush-dominated landscape occurred during a period of lower lake levels before ca. 3200 cal yr BP. Variations in fire activity appear to represent both the effects of climate and changes in vegetation type (fuel loads). As observed in some modern ecological studies, fire may have also played an important role in clearing lodgepole-dominated ecosystems to make way for the succession of more open landscapes during the onset of prolonged dry conditions.
