THE ROLE OF FIRE IN THE DEVELOPMENT OF SPHAGNUM-DOMINATED PEATLANDS IN WESTERN BOREAL CANADA

1 The effect of fire on vegetation development and accumulation rates in Sphagnum-dominated peatlands of western boreal Canada was studied through plant macrofossil and physicochemical analyses of two Holocene peat sequences characterized by a large number of macroscopic charcoal layers. 2 Field observations and detailed macrofossil analyses of charcoal horizons indicate that these layers represent local fires that burnt the superficial peat deposit. 3 Peat surface fires do not influence the long-term vegetation development of Sphagnum-dominated boreal peatlands. Vegetation response such as species composition changes in moss cover, if any, is generally limited to a few decades after the fire event. 4 Accumulation rates in Sphagnum-dominated boreal peatlands decrease significantly with increasing fire frequencies. Rates of height of peat accumulation and carbon accumulation would approximate zero with a five- to sevenfold increase in the frequency of peat surface fires, compared to the average frequency of this type of fire during the last 2500 years. 5 The frequency of peat surface fires at 7000 years BP, in the Hypsithermal period, was about twice as high as during the period 0-2500 BP, in the Late Holocene.