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Bowles, Marlin L.
McBride, Jenny

Pre-European Settlement Vegetation of Cook County, Illinois as part of a Report to The Cook County Forest Preserve District, CorLands & The Nature Conservancy


Identifier
3.91094
Type
Article
Date created
2002
Description
Report to The Cook County Forest Preserve District, Corlands & The Nature Conservancy.
Abstract
We mapped and analyzed the landscape pattern and composition of vegetation described by the U. S. Public Land Survey (PLS) of Cook County, Illinois, which was conducted between 1821 and 1840. Vegetation was patterned by fire and landscape fire breaks, as well as by topography and soils. Cook County was 73 % prairie, wet prairie and marsh, with fragments of timber essentially restricted to the eastern sides of watercourses or steep topography, which offered protection from eastward-moving prairie fires driven by prevailing winds. The largest blocks of timber occurred along Spring and Poplar Creeks, the Des Plaines River and its confluence with the Calumet Sag Valley, and east of the North Branch of the Chicago River. Most areas of timber averaged < 50 trees/ha, indicating widespread savanna conditions; however, forest tree densities of > 100 trees/ha predominated in timber along Salt Creek, the North Branch and north of the Cal-Sag Valley. Woodland, represented by > 50-100 trees/ha, was less common than savanna or forest. Oaks dominated almost all tracts of timber, with white oak the most important species in forest and woodland, and bur oak more abundant in savanna. Hickory usually co-occurred with oaks, but with lower importance, and reached its greatest importance in woodland. Elm-ash-soft maple-basswood vegetation was most abundant in wet forest conditions on the Chicago Lake Plain, while black oak and bur oak were dominant in savanna on lake plain sand ridges. Willow, cottonwood and aspen were less abundant but occurred across a range of habitat conditions. Woody understory vegetation was not systematically sampled by the PLS, but the small sample indicates that hazel and oak brush dominated this type of vegetation and that it had greater linear cover at higher tree densities. These findings indicate that restoring fire processes in relation to landscape features, as well as ecologically appropriate species, should be important objectives in developing restoration management for oak forest and savanna in this region.