Comparison of pollen-slide and sieving methods in lacustrine charcoal analyses for local and regional fire history

The charcoal content from laminated lake sediments in Quebec, Canada, was e stimated from pollen slides and by a sieving method. The resulting charcoal series are compared to estimate the suitability of these two methods to pr ovide a local or regional fire history. The replication of five different c harcoal series from the sieving method shows that this method is suitable f or fire-history reconstruction. In our laminated sediments, 1 cm(3) is repr esentative of the charcoal content of the sediment. The large charcoal frag ments above 15600 mum(2) are too scarce, however, to provide a significant charcoal series. Comparison of the sieving charcoal series versus the polle n-slide charcoal-series shows that the two series display a roughly similar pattern. The differences between the two series probably result from the a ccumulation of small particles that have a regional source area and are tra nsported by air over long distances and from high fragmentation rates due t o laboratory treatment. Spectral analysis for the last 2000 years shows tha t the sieving charcoal series have no significant periodic accumulation rat e, whereas the spectral analysis of the pollen-slide charcoal series shows a significant period of about 500 years. Because the charcoal particles fro m the sieving method are larger than those from the pollen-slide method, wh ich are potentially windborne over long distances, our study suggests that the sieving method series is a proxy of local fire history, whereas the pol len-slide method is more suitable for detecting regional trends in fire his tory.