Analysis of the government land office surveys for three counties in west-central Illinois

Background/Question/Methods The Government Land Office (GLO) records are a valuable resource to reconstruct pre-settlement communities. These records can be a valuable benchmark in the reclamation of disturbed communities throughout the USA but first we need to understand how to interpret the surveyor’s notes.  We used the GLO survey data to map the distribution of tree species and prairie in three west central Illinois (Greene, Jersey and Macoupin) and compared their distribution with modern SCS soils maps using GIS. The three counties are bounded on the west by the Illinois River and on the south by the Mississippi river. Bearing and witness trees from the GLO survey notebooks were located using the GIS.  Maps were prepared of tree distributions and prairies.  Distributions were compared with topographic and soils maps.

Results/Conclusions

The topographic maps show a gradient from floodplain in the west through sharply dissected loess-covered bluffs to flat uplands in the East.  This topographic variation was reflected by a strong vegetation gradient in the GLO data.  Salix spp., Populus deltoides, Ulmus spp, Celtis occidentalis, Fraxinus spp. and Platanus occidentalis   were common on the floodplains.   Upland forests adjacent to the floodplain contain Quercus alba, Q. velutina and Carya spp.  Forests in the eastern part of the counties bordering the prairies contain Q. palustris and Q. stellata, and Q. marilandica. Other investigators have called this prairie border forest the “Illinois Flatwoods”.    Large areas of the study area were classified by the GLO surveyors as “barrens” -- areas of stunted, shrubby vegetation on the edges of prairie. Except for floodplains, the soils in the study site formed in late-Wisconsinan loess that varies in thickness from approximately 8m on the Illinois River bluffs to 1 m on the eastern border of the study site.  In the GLO record forests dominated on hapludalf soils in areas of uneven topography.  Prairies were dominant on argiudoll and argiaquoll soils on flat uplands. Both prairie soil types have argillic (clay) horizons and low permeability to water.  The likely factor controlling the distribution of both the vegetation and soil types is fire frequency.