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

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 tire. but edaphic factors, the survival of disjunct relicts, and the differential migration rates of some taxa are contributor).. 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. [ABSTRACT FROM AUTHOR]