Government Land Office (GLO) survey records were used to
reconstruct the presettlement floodplain landscape at the
confluence of the Illinois and Mississippi rivers.
Presettlement prairie and forest land covers were determined by
digitizing GLO plat maps using a computerized geographic
information system (GIS). A case history of land cover change
was determined by comparing this presettlement map to GIS land
cover maps for 1903, 1935, and 1975. Data from witness trees
and current forest samples were used to compare presettlement
and present forest composition and structure. Results indicate
that approximately 56% of the presettlement floodplain was
forested, while 41% was prairie. The presettlement forests were
generally open (86.8 stems/ha) and consisted of several dominant
tree species. In contrast, the present forest is more dense
(489 stems/ha) and is dominated by silver maple (Acer
saccharinum). Early settlement had little affect on the spatial
distribution of forest cover, but river impoundment in 1938
reduced forests to approximately 35% of the floodplain.
Prairies were converted to agriculture during the middle 1800s
and now occupy only 6% of the floodplain. Overall, the
floodplain landscape and vegetation patterns present today are
very different from their presettlement conditions. The major
activities responsible for these changes were timber harvesting,
agriculture, and river impoundment.
