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Bowles, Marlin L.
McBride, Jenny

Historic Landscape Vegetation Pattern, Composition, and Structure of Will County, Illinois, as Recorded by the U.S. Public Land Survey (1821-1838)

Date created
Report to the Forest Preserve District of Will County, Chicago Wilderness, USDA Forest Service & US Fish & Wildlife Service.
We mapped and described the presettlement vegetation pattern and structure of Will Co., Illinois based on tree data from the Government Land Office Public Land Survey (PLS), which was conducted between 1821 and 1838. Vegetative cover was 80% grassland. The predominant woody vegetation was timber, with smaller amounts of scattering timber, barrens, brush, and hazel thickets. The vegetation pattern fit an expected landscape model driven by the interaction between landscape fire and fire breaks. Larger blocks of timber and fire-intolerant tree species persisted in the protection of fire barriers that blocked prairie fires driven by prevailing southwesterly winds. Savanna with fire-tolerant oaks occurred in areas with less fire protection, primarily on the western sides of landscape fire barriers. Most of the woody vegetation described as timber by the PLS averaged < 50 trees/ha, corresponding to a modern savanna analog. On areas of glacial till, this vegetation was dominated by white oak. Bur oak, black oak, scarlet oak, and hickory had secondary dominance. Maple, basswood, ash, and elm were less frequent, but increased in abundance along an increasing tree density gradient associated with greater fire protection. Woody undergrowth, primarily oak, hickory and hazel, averaged less than 20% cover in timber, about 35% in scattering timber, and 45% in areas of brush or barrens. Tree density and tree species richness, as well as richness of woody undergrowth, were lower on sand soils, which occur in the southwestern part of the county. Black oak was the predominant species on sand, while, maple, basswood, ash, and elm were essentially absent.