Postglacial Vegetation of the North-Central United States: A Review

Abstract

The dramatic changes in climate and physiography following the retreat of the last glaciers are reflected in the record of forest succession as gleaned from pollen studies made chiefly in the Great Lakes area. Fairly rapid deglaciation began about 8500 B.C. while spruce-fir forests still dominated (Valders Retreat). Soon the pine came in, and spruce-pine forests took over (about 7000 B.C.). At the time of the Terminal Glacial (Cochrane, 6000 B.C.) pine was the dominant forest tree, whereas spruce-fir forests had migrated north. During the following three thousand years, while the climate was warmer and drier, pine forests were dominant. Then broad-leaved trees (oaks) made their appearance. First came an oak stage that extended until about 1000 B.C. It was followed, during the next five hundred years, by an oak-hickory stage. The period from 7000 to 600 B.C. is now known as the "hypsithermal interval" rather than by its former, but less suitable, designations (postglacial climatic optimum, thermal maximum) and as such has been correlated with corresponding stages in the European sequence and postglacial chronology. The various radiocarbon dates based oil different sites and carried out in different laboratories have not yet been completely aligned but show considerable agreement with other sources of evidence. Events during Late Glacial and postglacial times apparently had a more far-reaching effect on present-day distribution patterns of plants and animals than did those of the various Glacial and Interglacial periods. These pronounced postglacial changes in climate and physiography definitely affected the mode of life of various paleo-Indian groups living in this region.