| Description |
The future of the American southwest is of interest to those concerned with water availability, forest ecology, and industry. In order to model future changes to an environment, it is important to assess the past and the present states. Range Creek Canyon, located in the northern section of the Colorado Plateau, near the moisture boundary of Pacific and Gulf of Mexico-derived precipitation, provided a site to assess the current ecology of an archaeologically important site. Natural seeps in the canyon also provided a chance to analyze the past 3,300 years of ecological change. Sediment cores were extracted from North Gate Bog (NGB), and Cherry Meadows (CHM), two natural seeps within the canyon, to reconstruct past climate and fire regimes using a multiproxy approach. A baseline of modern vegetation was established by systematically sampling the modern pollen assemblages (Chapter 2) and comparing them to existing vegetation surveys. Surveys were carried out at 10 m, 100 m, and 200-1000 m circumference for each of the two sites. The percent of taxa type was determined with ARCGIS using polygon data. The vegetation was then compared to surface pollen surrounding the cores at varying distances. Results of Chapter 2 found that surface pollen represented either local or regional vegetation based on the site's elevation. The study showed that the local pollen signal of vegetation within 200 m is faithfully represented in the surface pollen assemblages. In deep canyon topography, a comparison of the surface pollen to the modern vegetation should be done as a preliminary analysis to understand ABSTRACT iv the reliability of local and regional vegetation and secondary climate conclusions. Sedimentary pollen and charcoal were used to examine climate (Chapter 3) and fire regime changes (Chapter 4) within the last 3,000 years. Chapter 3 utilized the pollen ratios of taxa with opposite moisture requirements, coupled with X-Ray Fluorescence, to distinguish changes in the availability of seasonal moisture and multiyear climate variability. Coniss cluster analysis derived four distinct pollen zones that capture vegetation change. Dry adapted taxa such as Amaranthaceae, Sarcobataceae, Cupressaceae, and Poaceae were used to detect arid times. Summer wet taxa such as Pinus edulis and Ambrosia and winter precipitation taxa such as Artemisia were analyzed to determine seasonal moisture variations. An overall dry climate with moisture delivered during the winter months was dominant in the first vegetations zones from 3300 to 2750 cal yr BP. Lower fire activity is noted around 2300 when a shift to a summer wet regime occurred as inferred from the increase of Pinus edulis. During Zone 3 (1600 to 750 cal yr BP) pre and post Fremont, a summer wet environment is evident. Lastly, Zone 4 (750 to 0 cal yr BP) captured increased aridity time post Fremont to a summer wet climate with low fire activity during European settlement to present. |
