THE PRAIRIE-DECIDUOUS FOREST ECOTONE IN THE UPPER MIDDLE WEST∗

Abstract

ABSTRACT The prairie–deciduous forest ecotone changes from a distinct boundary in northern Minnesota to a fragmented mosaic type in Wisconsin, Iowa, and Illinois. The differences largely can be attributed to topography and fire, but edaphic factors, the survival of disjunct relicts, and the differential migration rates of some taxa are contributory. Fossil pollen spectra from the Driftless Area attest to the persistence of the mosaic character throughout the Holocene. Modern surface spectra illustrate the difficulties of recognizing vegetation changes along and across the ecotone.