INVESTIGATING POST-GLACIAL BIOGEOGRAPHY, CANOPY DYNAMICS, AND FLORA-MEGAFAUNA INTERACTIONS USING POLLEN RECORDS FROM ACROSS THE GREAT BASIN (Invited Presentation)

The terrestrial ecosystems of the Western United States have been shaped by a long history of environmental and ecological change since the Last Glacial Maximum. Many of the most dramatic changes occurred from ~16,000 – 9,000 years before present, as warming, deglaciation, and the regression of the pluvial Great Basin lakes triggered major biogeographic changes in the distribution of plants and likely facilitated the extinction of most large (>45 kg) mammals. Our pollen record from Mono Lake, California, documents rapid responses of pine-juniper-sagebrush ecosystems during deglaciation. During the Bølling-Allerød, Younger Dryas, and early Holocene, the Mono Lake record shows rapid changes in Artemisia, Cupressaceae, Pinus, and herbaceous pollen taxa, indicative of canopy reorganizations in the openness of the landscape. Moreover, changes in canopy structure are coeval with declines in the abundance of the dung fungal spore Sporormiella and increased micro-charcoal, suggesting strong relationships between megafauna, plants, fire regimes, and climate change within in the late Pleistocene woodlands of the Mono Basin. Here, we further examine these relationships using modern and sub-fossil pollen records synthesized from the Sierra Nevada and Great Basin. We present new surface sample pollen data from the ecotone of the Sierra Nevada and Great Basin in eastern California to better characterized modern semi-arid vegetation-pollen relationships. We compare the modern and fossil pollen data using multivariate analysis to examine compositional and structural gradients across the synthesized fossil studies. Preliminary results show substantial differences exist between the abundance of Cupressaceae, Artemisia, and Pinus pollen depending on latitude and elevation, and many of the Pleistocene woodlands appear to represent environments with no modern analogues. Several sites including Sporormiella data demonstrate similar trends in interactions between megaherbivores and vegetation. Taken together, the modern-fossil pollen comparisons and synthesized paleoecological network reveal substantial reorganizations in the terrestrial ecosystems of the west-central USA driven by both rapid and gradual climate change.