Investigating biotic drivers of Quaternary landscape change: Late glacial no-analog vegetation communities and the North American megafaunal extinction in northeastern Indiana

In eastern North America, late-glacial and early Holocene pollen assemblages are often characterized by combinations of taxa that lack a modern analog (so-called “no analog” assemblages). Climate change has been evoked to explain these associations. However, this interval is also characterized by the arrival of the first modern humans to the continent and the extinction of 35 genera of megafauna (mammals >100kg). The regional disappearance of the no-analog vegetation approximately coincides with the fossil-inferred timing of the megafaunal decline, but stratigraphic and dating uncertainties have prevented conclusive determination of local lead-lag relationships. This study investigates the impacts of ancient megaherbivores on vegetation, through the maintenance of herbivory and disturbance regimes not present on the modern landscape. An 11.7m sediment core was taken from Appleman Lake in LaGrange County, Indiana, and fossil pollen and charcoal records were constructed for the interval of the megafaunal decline. Fossil spores of the dung fungus Sporormiella are used as a proxy for megafaunal presence and decline. The Appleman record, which spans the Younger Dryas, deglaciation, and vegetation reorganization, shows that Sporormiella abundances sharply declined during the megafaunal extinction. The local megafaunal disappearance is compared to changes in vegetation and fire at the site, including a decline in grasses and the establishment of an oak-beech-elm complex.