Development of Sphagnum-dominated peatlands in boreal continental Canada

Peat cores from five Sphagnum-dominated peatlands in boreal continental Canada were analyzed for plant macro fossils. Results indicate that peatland development was influenced both by local autogenic and regional climatic factors. The general direction in peatland development from rich fen to poor fen to bog can primarily be ascribed to internal processes, especially peat accumulation. Quantitative paleoenvironmental reconstructions based on fossil moss assemblages indicate that all five peatlands were initially dominated by brown mosses with inferred pHs of approximately 6.0, and a water table at 5–15 cm below the surface of the peatland. Subsequently, Sphagnum-dominated peatlands developed 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 fen and bog (Ph < 5). The two most southerly peatlands are youngest, with basal dates of 4670 BP and 4230 BP. Sphagnum peat accumulation at these sites started at 2620 BP and 1790 BP, respectively. Two sites located at intermediate latitudes have basal dates of > 5140 BP and 5020 BP, while the development of Sphagnum-dominated ecosystems dates back to ≈ 3100 BP and 3710 BP, respectively. The most northerly site has the oldest basal date (> 7870 BP), and the oldest date for the initiation of Sphagnum peat accumulation (≈ 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 that prevented peatland development until after 6000 BP when the climate gradually became cooler and moister. Farther north the climate was cool and moist enough to allow peatland development during the early to middle Holocene. In three southern peatlands, the development into a Sphagnum-dominated ecosystem took > 2000 years, while at the more northerly sites Sphagnum became dominant after < 1500 years. Key words: Sphagnum, peatlands, boreal, Holocene, climate.