High-resolution pollen, plant macrofossil, charcoal and pyrogenic Polycyclic Aromatic Hydrocarbon (PAH) records were developed from a 154 cm long sediment core collected from Crater Lake (37.39°N, 106.70°W; 3328 m asl), San Juan Mountains, Colorado. Several studies have explored Holocene paleo-vegetation and fire histories from mixed conifer and subalpine bogs and lakes in the San Juan and southern Rocky Mountains utilizing both palynological and charcoal studies, but most have been at relatively low resolution. In addition to presenting the highest resolution palynological study over the last 1000 years from the southern Rocky Mountains, this thesis also presents the first high-resolution pyrogenic PAH and charcoal paired analysis aimed at understanding both long-term fire history and the unresolved relationship between how each of these proxies depict paleofire events.
Pollen assemblages, pollen ratios, and paleofire activity, indicated by charcoal and pyrogenic PAH records, were used to infer past climatic conditions. Although the ecosystem surrounding Crater Lake has remained a largely spruce (Picea) dominated forest, the proxies developed in this thesis suggest there were two distinct climate intervals between ~1035 to ~1350 CE and ~1350 to ~1850 CE in the southern Rocky Mountains, associated with the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) respectively. The MCA was a period of increased aridity, temperature, and regional fire activity, whereas the LIA was wetter, cooler and experienced decreased regional fire activity. The paired charcoal - pyrogenic PAH record indicates that these paleofire proxies follow similar general trends in regional fire patterns (i.e. indicate increased or decreased fire activity, respectively), but that peak concentrations do not correspond to each other. This suggests that these two paleofire proxies record different paleofire events. The vegetation and fire history inferred from Crater Lake sediments demonstrate that centennial and sub-centennial scale climate variability can be determined from high elevation pollen assemblages, pollen ratios, plant macrofossil, charcoal, and pyrogenic PAH proxies
