AN OVERVIEW OF FACTORS THAT INFLUENCE THE DEVELOPMENT OF CANADIAN PEATLANDS

Canadian peatlands can be classified into ombrotrophic bogs and minero trophic fens, the latter subdivided into poor, moderate-rich, and extr eme-rich fens, each with distinctive indicator species, acidity, alkal inity, and base cation content. If hydrology is considered the most im portant factor in peatland classification then the primary division mu st be between ombrotrophic bogs and minerotrophic fens; however both c hemical and vegetational differences strongly indicate that the primar y division of peatlands should be between acidic, Sphagnum-dominated b ogs and poor fens on the one hand, and alkaline, brown-moss-dominated rich fens on the other. Although some metals such as sulphur and alumi num also vary along this gradient, nutrient contents of the surface wa ters do not. Bogs and fens are oligotrophic to mesotrophic wetlands th at should be distinguished from eutrophic, non-peat-forming wetlands s uch as marshes and swamps by the presence in the former of a well-deve loped ground layer of bryophytes associated with relatively little sea sonal water level fluctuation. Oligotrophy is probably maintained in b ogs and poor fens by reduced water flow, whereas rich fens maintain me sotrophy by having larger water through-puts; however this is not well documented. Sphagnum appears to have real ecological significance, bo th in the initial stages of acidification and in controlling surface w ater temperature. Seasonal variation in surface water chemistry in all peatland types is relatively small, however precipitation events lead ing to changes in water levels do affect some chemical components. Alt hough both autogenic and allogenic factors affect peatland development , initiation of peat formation and early development of peatlands duri ng the Early and Mid Holocene were considerably influenced by regional climatic change. Later developmental patterns during the late Holocen e and those seen at the present time appear to be more influenced by a utogenic factors.