Taxonomic and functional diversity of North American vegetation during the last interglacial–glacial cycle

Abstract We synthesized pre-last glacial maximum pollen records to reconstruct North American pollen diversity since ca. 130 ka. Using taxonomic diversity (a measure of the number and abundance of taxa) and functional diversity (a measure of the number and abundance of different phenotypes) we identified temporal and spatial diversity trends for six North American bioregions: Arctic, Intermountain West, Mexico, Pacific Northwest, Southeast, and Yucatán. Reconstructed taxonomic temporal and spatial trends vary among bioregions, with regional diversity patterns captured in the functional metric, suggesting shifts in species composition coincide with shifts in ecosystem function. However, significant shifts in taxonomic pollen diversity differed in frequency, magnitude, and timing from their functional counterparts. Variations in both regional taxonomic and functional diversity response to global and regional temperature trends were evident, suggesting temperature alone does not fully explain changes in species composition. Regional richness estimates exhibited higher stability relative to the weighted diversity estimates indicating low levels of species turnover through Late Quaternary warming–cooling phases. Shifts in regional diversity did not predictably respond to stadial and interstadial transitions. Instead, North American patterns of plant diversity over the last ca. 130 ka differ geographically, likely responding to regional rather than global climate change.