Barrens and the Forest-Prairie Interface in Presettlement Crawford County, Illinois

The extent of forest, savanna, barrens, and prairie vegetation of Crawford County, Illinois, was mapped using the General Land Office survey notes of 1804-1821. Forest vegetation was the most exten- sive, covering 40.8% of the county, followed by prairie (34.2%), savanna (18.2%) and barrens (6.8%). Quercus alba L. (white oak) was the dominant forest species with an importance value (IV) of 60.6, followed by Q. velutina Lam. (black oak), Carya spp. (hickories), Ulmus spp. (elms), and Acer saccharinum L. (silver maple). In the savanna white oak again dominated (IV of 66.2), followed by black oak and hickories. The areas designated as barrens by the surveyors were dominated by white oak (IV of 78.8) followed by hickories, black oak, Acer saccharum Marsh. (sugar maple), and Fagus grandifolia Ehrh. (beech). Density (trees/ha) was 149.7, 18.2 and 29.7 for the forest, savanna and barren areas, respectively. Corylus americana Walt. (hazelnut) had the highest frequency for understory shrubs and was commonly associated with the forest- prairie interface and barrens. Shifts in plant community boundaries occur over extended periods of time, and the knowl- edge of the presettlement vegetation can be very useful in interpreting many of these changes. In particular, a comparison of presettlement vegetation with that existing at the present time allows an estimation of the degree and direction of change during the past 150 years in central Illinois. Many of these presettlement plant communities have been destroyed with the frag- mented remains being highly modified by fire suppression, grazing, the introduction of exotic and weedy species, and in many more subtle ways by acid rain, chemical pollutants, drainage, and species extinction. General Land Office (GLO) survey notes are occasionally used to reconstruct presettle- ment vegetation, and when used with other sources, such as soil maps and early historical accounts, provide a reasonable indication of the vegetation just prior to settlement by Euro- peans (Bourdo 1956, Hutchison 1988). In Illinois, the GLO survey notes were used by Anderson (1970) to determine the extent of presettlement prairies. These notes have also been used to reconstruct the presettlement vegetation of Kane (Kilburn 1959), Lake (Moran 1976), Mason and McLean (Rodgers and Anderson 1979), Douglas (Ebinger 1986), Coles (Ebinger 1987), and Williamson (Anderson and Anderson 1975) counties, and the Mackinaw River Valley (Thomas and Anderson 1990). In the present study, the vegetation of Crawford County, Illinois was determined using GLO survey notes. Located in the Southern Till Plain and the Wabash Border Divisions of east- central Illinois (Schwegman 1973), this county has an area of 438 square miles (1134 kmi2). The Wabash River forms the eastern border while the Embarras River flows through the extreme southwest corner of the county. The first parts of the county surveyed were areas enclosed within Indian boundaries. One of these boundary lines, with a north/south orientation, divides the county roughly in half, the second with an east/west orientation divides the eastern portion into two parts (Figure 1). The first deed was recorded in the county clerk's office in 1816, however, according to Perrin (1883) there was considerable settlement prior to that date.