Pollen, vascular plant and bryophyte macrofossils from peat and silt deposits that filled an oxbow lake near Nichols, Iowa provide a 2500- year record of wetland succession and of upland habitats. Radiocarbon dates of 2320 ± 90 yr B. P. (BETA 12514) near the base and 1260 ±70 yr B.P. (BETA-12513) midway up one section, and 1050 ±70 (BETA 12515) in another provide chronologic control. The pollen diagram indicates substantial changes in local wetland habitats, but less change in upland vegetation in the last 2500 years. Plant macrofossils record changes from a deep to a shallow oxbow lake during the first few hundred years after the meander was cut off. About 1600 yr B.P. marsh vegetation began to encroach as the lake filled with sediment. A somewhat weedy marsh that existed from about 1400 to 900 yr B. P., developed into a rich mire that persisted until the 1840\u27s, when Europeans began cultivating the upland areas. A rise of ragweed pollen (from 7 to 25%) documents the beginning of cultivation in the area, and is accompanied by a sudden increase in diversity and in numbers and taxa of weedy species on the marsh. The presence of abundant charcoal and macrofossils of such prairie taxa as Amorpha and Petalosteinum imply warmer conditions from about 1400 to 900 B. P.; their absence and the appearance of the bryophyte Meesia suggest cooler conditions during the last thousand years
