More Than One Way to Kill a Spruce Forest: Spatial Fingerprint of Deglacial Temperature Change in Eastern North America

The last deglaciation in eastern North America offers a classic system for studying climate-driven plant range dynamics during large and abrupt climate change. However, detailed understanding is limited by the surprising scarcity of well-dated, multi-proxy records of past climate and fire history. In this talk, I first present new temperature reconstructions from fossil pollen and brGDGT records, showing good agreement at individual sites in the southern Great Lakes. Across eastern North America, the spatial fingerprint of deglacial temperature variations shows regionally antiphased patterns of cooling and warming and latitudinal temperature gradient shallowing. I then focus on the collapse of Picea (spruce) woodlands in the southern Great Lakes, to understand how temperature rises and intensified fire regime interact to drive forest collapse. At two sites, increases in charcoal accumulation rates and fire frequency were positively associated with abrupt spruce declines. At the other three sites, however, there was no relationship among spruce declines and fire activity, with spruce declining gradually over several thousand years. Hence, fire was not necessary to the climate-driven loss of spruce woodlands, but sometimes accelerated the decline of spruce woodlands by clearing the way for thermophilous deciduous hardwood species.

Professor John Williams of the University of Wisconsin, Madison, studies paleoecology, paleoclimatology, vegetation dynamics, global climate change, and quaternary environments. To learn more about Williams, please visit his homepage.

This is event is co-sponsored by the Living Earth Collaborative and the Department of Earth and Planetary Sciences.