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 Sphagnumdominated 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 fiveto 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.