AN 180-YEAR RECORD OF FIRE AND VEGETATION IN A BOREAL WHITE SPRUCE FOREST

Boreal forest fire and vegetation history was examined using an 840-yr fossil pollen and charcoal record from a site dominated by Picea glau ca in Alberta, Canada. The record tvas created using contiguous 5-yr s amples of annually laminated sediments from a 2.7-ha lake (Rainbow Lak e A in Wood Buffalo National Park). Following a peak in the microscopi c charcoal accumulation rate (CHAR), there is a sequence of peaks in s ediment thickness and in 14 of the 21 common pollen and spore taxa, Th e general pollen sequence is an initial peak in herbs, then shrubs, th en deciduous trees, and finally conifers and ?Sphagnum. The peak value for each taxon differs following individual fires, suggesting that a site does not undergo the same postfire vegetation sequence following all, fires, Based an the CHAR, pollen, and sediment thickness records, at least 12 large, local fires are apparent. The average time interva l between the 12 fires is 69 yr. Significant periodicities in CHAR and in II of the pollen laxa range between 95 and 185 yr. These estimates of the mean fire interval are broadly similar to the 71-142 yr fire c ycle for Picea glauca forests, estimated by dendrochronological analys is of regional forests. The pollen taxa also exhibit long-term changes in relative abundance. An initial dominance by Pic ea cf, glauca is t erminated by a fire around AD 1185 and is replaced by Populus dominanc e between AD 1250 and 1550; the fire is followed by an 800-yr period o f increasing abundance of Picea cf, glauca., Herbs and shrubs generall y exhibit a peak in abundance between AD 1350 and 1750., These long-te rm patterns may reflect climatic change, response to fires with differ ent characteristics, or rearrangement of the forest patches around Rai nbow Lake A.