VEGETATION ON THE EASTERN GREAT PLAINS, NORTH AMERICA, DURING MID-WISCONSINAN TIME--LATE MIS STAGE 3-EARLY MIS STAGE 2

Little is known about the history of prairies on the central Great Plains. Specific questions involve whether prairies were present during the cool period prior to the last glacial maximum (LGM), and if so, whether they survived in situ or were displaced during the subsequent glacial advances to the north. Pollen and plant macrofossil analyses from several sites on the eastern edge of the central Great Plains, in eastern Nebraska and Kansas and western Iowa, reveal consistent changes in vegetation between ~33,000 and 20,000 14C yr B.P. Between 33,000 and about 27,000 14C yr B.P., upland vegetation was apparently very open, with prairie species and scattered Picea, Populus, and Betula cf. papyrifera. Woody riparian/wetland taxa included Salix spp., Betula glandulosa, and Myrica gale. These taxa suggest a modern analog might be aspen parkland near the boreal-forest border. A rich wetland and aquatic vegetation was abundant at all sites. A Picea forest rapidly became widespread across midwestern United States beginning about 24,000 14C yr B.P., and prairie taxa disappeared. As is commonly the case in Wisconsinan Picea-dominated assemblages, there is little else present but Carex spp. These assemblages suggest an analog in the species-poor boreal forest, and a significant climatic shift toward cooler, moister conditions. Picea forests persisted at some sites until after 20,000 14C yr B.P., but in other settings, the persistence of Picea is unknown, because the fossil record ended earlier when loess accumulation began to fill wetlands with silt. The Mid-Wisconsinan parkland was thus displaced, probably southward and westward, from the eastern edge of the central Great Plains as climate cooled during glacial expansion.