DEVELOPMENT OF SPHAGNUM-DOMINATED PEATLANDS IN BOREAL CONTINENTAL CANADA

Peat cores from five Sphagnum-dominated peatlands in boreal continenta l Canada were analyzed for plant macrofossils. Results indicate that p eatland development was influenced both by local autogenic and regiona l climatic factors. The general direction in peatland development from rich fen to poor fen to bog can primarily be ascribed to internal pro cesses, especially peat accumulation. Quantitative paleoenvironmental reconstructions based on fossil moss assemblages indicate that all fiv e peatlands were initially dominated by brown mosses with inferred pHs of approximately 6.0, and a water table at 5 - 15 cm below the surfac e of the peatland. Subsequently, Sphagnum-dominated peatlands develope d with pHs of 4.0-4.5 and a water table at 15-30 cm of depth. Chemical factors triggered a rapid transition from rich fen (pH > 6) to poor f en and bog (pH < 5). The two most southerly peatlands are youngest, wi th basal dates of 4670 BP and 4230 BP. Sphagnum peat accumulation at t hese sites started at 2620 BP and 1790 BP, respectively. Two sites loc ated at intermediate latitudes have basal dates of > 5140 BP and 5020 BP, while the development of Sphagnum-dominated ecosystems dates back to almost-equal-to 3100 BP and 3710 BP, respectively. The most norther ly site has the oldest basal date (> 7870 BP), and the oldest date for the initiation of Sphagnum peat accumulation (almost-equal-to 7000 BP ). The younger age of the peat deposits in the four southern sites is due to warm and dry climatic conditions during the middle Holocene tha t prevented peatland development until after 6000 BP when the climate gradually became cooler and moister. Farther north the climate was coo l and moist enough to allow peatland development during the early to m iddle Holocene. In three southern peatlands, the development into a Sp hagnum-dominated ecosystem took > 2000 years, while at the more northe rly sites Sphagnum became dominant after < 1500 years.