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Bowles, Marlin L.
McBride, Jenny

Pre-European Settlement Vegetation of Lake County, Illinois

Date created
Report to the Forest Preserve District of Lake County, Chicago Wilderness, USDA Forest Service, US Fish & Wildlife Service, and the Illinois Conservation Foundation.
We mapped and analyzed the landscape pattern and composition of vegetation described by the U. S. Public Land Survey (PLS) of Lake County, Illinois, which was conducted between 1833 and 1839. Lake County was mapped by the PLS as 29 % prairie, 50 % timber, 13 % scattering timber and less than 1 % barrens. Prairie occurred primarily in the south central part of the county, while scattering timber was most predominant in the north and timber was widespread. Based on measures of tree density, areas mapped by the PLS as timber were over 65 % savanna, averaged less than 60 trees/ha, and were dominated by white oak. Areas mapped as scattering timber were over 90 % savanna, averaged less than 30 trees/ha, and were dominated by bur oak. Black oak, red oak and hickory were important secondary species in both types, with white pine and jack pine also important in scattering timber on the sand plain of Lake Michigan. Forest and woodland, represented by > 100 trees/ha and 50-100 trees/ha, respectively, were far less common than savanna, representing about 30 % of the areas mapped as timber and 10 % of the areas mapped as scattering timber. They were concentrated on the east flank of the DesPlaines River and on morainal bluffs along Lake Michigan. They also differed from savanna by dominance of white oak over bur oak and by greater abundance of mesophytic species, including ash, basswood, Hill’s oak, elm, sugar maple and aspen. The landscape pattern of this vegetation indicates that fire processes played a significant role in shaping the presettlement vegetation pattern of Lake Co.