PAST AND CURRENT TRENDS OF CHANGE IN A DUNE PRAIRIE OAK SAVANNA RECONSTRUCTED THROUGH A MULTIPLE-SCALE HISTORY

The history of a rapidly changing mosaic of prairie and oak savanna in northern Indiana was reconstructed using several methods emphasizing different time scales ranging from annual to millennial. Vegetation ch ange was monitored for 8 yr using plots and for 30 yr using aerial pho tographs. A 20th century fire history was reconstructed from the stand structure of multiple-stemmed trees and fire scars. General Land Offi ce Survey data were used to reconstruct the forest of A.D. 1834. Fossi l pollen and charcoal records were used to reconstruct the last 4000 y r of vegetation and fire history. Since its deposition along the shore of Lake Michigan about 4000 yr ago, the area has followed a classical primary dune successional sequence, gradually changing from pine fore st to prairie/oak savanna between A.D. 264 and 1007. This successional trend, predicted in the models of Henry Cowles, occurred even though the climate cooled and prairies elsewhere in the region retreated. Sev ere fires in the 19th century reduced most tree species but led to a t emporary increase in Populus tremuloides. During the last few decades, the prairie has been invaded by oaks and other woody species, primari ly because of fire suppression since A.D. 1972. The rapid and complex changes now occurring are a response to the compounded effects of plan t succession, intense burning and logging in the 19th century, recent fire suppression, and possibly increased airborne deposition of nitrat es. The compilation of several historical research techniques emphasiz ing different time scales allows this study of the interactions betwee n multiple disturbance variables.