Effective of Climate on Development of Two Sphagnum Bogs in South‐Central Wisconsin

Aquatic pollen, charcoal, sediment, and accumulation—rate changes from radiocarbon—dated cores from two sites in south—central Wisconsin were studied to explore the evolution of local wetlands since deglaciation. Sphagnum bog evolution in south—central Wisconsin appears to have been directly related to the regional climatic changes during the past 6000 yr (the middle and the late Holocene). Although the two sites had different origins and different early histories, both were deep lakes until 6300 BP when they became shallow ponds dominated by the aquatic macrophyte Brasenia. These wetland changes were concurrent with a regional upland vegetational change from mesophytic forest to Quercus savanna and were caused by a regional decrease in annual precipitation and by an increase in temperature. At °3000 BP, in response to a cooler, wetter climate, both wetlands became Sphagnum—Ericaceae bogs, and the upland vegetation changed to a closed Quercus forest. The paleoecological evidence suggests that bog development is a function of climate and that many bogs have developed in the northern Midwest during the past 3000 yr as effective moisture has increased.