Pre-European Settlement Vegetation of McHenry County, Illinois
DescriptionReport to the McHenry County Conservation District, Chicago Wilderness, USDA Forest Service, US Fish & Wildlife Service, and the Illinois Conservation Foundation.
AbstractWe mapped and analyzed the landscape pattern and composition of vegetation described by the U. S. Public Land Survey (PLS) of McHenry County, Illinois, which was conducted between 1833 and 1838. McHenry County was mapped by the PLS as 50 % prairie, 44 % timber, 3 % scattering timber and less than 1 % barrens. Timber was predominantly savanna, averaging about 45 trees/ha, while scattering timber averaged less than 40 trees/ha. Both types of vegetation were dominated by bur oak, with white and black oak as secondary species, and about 70 % cover of woody undergrowth dominated by American hazelnut. Forest and woodland, represented by > 100 trees/ha and 50-100 trees/ha, respectively, were far less common than savanna, representing < 30 % of the areas mapped as timber. Both were also dominated by bur, black and white oaks. However, bur oak, the most fire tolerant oak, was less important in forest than in savanna, while white oak was more abundant in forest than in savanna. In addition, more mesophytic and fire intolerant forest trees including red oak, hickory, Scarlet or Hill’s oak, basswood, ash and ironwood had greater importance in forest and woodland than in savanna. This composition and structure of woody vegetation suggests that fire played a strong role in patterning the vegetation of McHenry County. The lack of extensive forest conditions indicates that landscape firebreaks had a minor impact on vegetation pattern. The structure and composition of woody vegetation in McHenry County indicate that restoration goals should include fire management for oak dominance in most woody vegetation types, with woody vegetation dominated by hazel as an important understory component.