SHIFTS IN NORTH AMERICAN PLANT DIVERSITY OVER THE LAST FIVE MARINE ISOTOPE STAGES

Climate is a key driver in changing plant diversity and ecosystem function. As such, understanding how plant diversity changes in response to shifts in climate are becoming increasingly important. We compiled Late-Quaternary pollen records from North America to examine continental-scale patterns in plant diversity over the past 115 ka and address how plant diversity has changed within select regions between Marine Isotope Stages (MIS). Twenty-five pollen records were older than ~21 ka, with several records approaching ~115 ka. To calculate pollen type diversity, we use Hill numbers to represent different diversity metrics. We use the first three levels of Hill numbers, q=0, 1, and 2, equivalent to the richness, Shannon index (diversity of species), and Simpson index (relative abundance of species present). Records were grouped into 7 regions of North America: Arctic, Pacific Northwest, Inner Mountain West, Great Lakes, Southeast, Mexico, and Yucatan. Our analysis shows that q=0 (richness) trends are distinct from q=1 and 2 (Shannon and Simpson) with major shifts in diversity not being reflected in the richness of a site. We found q=0, overall richness, to be more stable than q=1 and 2 with richness having less significant differences between stages compared to diversity. Overall, our results point to a pattern of high diversity around the Gulf of Mexico and in the Pacific Northwest during the last glacial period 115 to 21 ka. As the climate warms across North America, we expect regional plant diversity to shift. We anticipate regions like the Inner Mountain West, which have had relatively stable diversity over the last ~115 ka, to respond less than sensitive regions like the Great Lakes and Yucatan. These results point to more individual, regional responses by vegetation to their environment, rather than a uniform response based on factors such as latitude or elevation.