PLANT MACROFOSSILS AND OTHER PALEOENVIRONMENTAL INDICATORS IN AN ALLEGAN COUNTY, MICHIGAN PEAT BOG

Plant macrofossils were used as a proxy to determine the paleoenvironmental conditions in an Allegan County, Michigan bog on which sand concentrations, organic bulk density (OBD), charcoal abundances, and siliceous microfossil abundances have already been determined. Peat deposits from ~6600 cal YBP have abundant Cyperaceae and Nymphaeaceae seeds and Scirpus tissue suggesting deposition in a deep water environment. A succession of Cyperaceae species suggests a shallowing over time and the development of a fen. Shallowing is further indicated by the disappearance of Scirpus ~4300 cal YBP and the presence of shallower water species Sphagnum papillosum and Thelypteris from ~3200-2900 cal YBP. Sponge spicules are abundant during much of this time, disappearing ~3000 cal YBP. At the same time, ericaceous roots appear, becoming progressively more abundant upwards in the core, Cyperaceae species decrease dramatically, and Sphagnum and Thelypteris disappear. These changes suggest the transition from a fen to an emergent bog. Concurrently, there is an increase in the OBD, beginning ~3040 cal YBP indicating a drier environment over the same time interval. The transition to an emergent bog is accompanied by a decrease in the average concentration of sand in the cores, suggesting a change to predominantly aeolian transport. An interval dominated by charcoal and partially burnt plant fragments suggests a major fire at ~1900 cal YBP. The bog was revegetated by Thelypteris and Cyperaceae and Ericaceae species. Chamaedaphne abundance increases, becoming dominant around 1000 cal YBP and Sphagnum sp. reappear ~900 cal YBP. Today the bog is emergent and vegetated dominantly by Chamaedaphne and Sphagnum sp., with accessory Andromeda glaucophylla and Vaccinium oxycoccos. Over time, the bog has undergone hydroseral succession consistent with the terrestrialization process which appears to be partially in response to climate change. Short term fluctuations in sand concentrations, charcoal abundances, and macrofossil assemblages may reflect shorter climate cycles.