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 estimated from pollen slides and by a sieving method. The resulting charcoal series are compared to estimate the suitability of these two methods to provide a local or regional fire history. The replication of five different charcoal series from the sieving method shows that this method is suitable for fire-history reconstruction. In our laminated sediments, 1 cm(3) is representative of the charcoal content of the sediment. The large charcoal fragments above 15600 mum(2) are too scarce, however, to provide a significant charcoal series. Comparison of the sieving charcoal series versus the pollen-slide charcoal-series shows that the two series display a roughly similar pattern. The differences between the two series probably result from the accumulation of small particles that have a regional source area and are transported by air over long distances and from high fragmentation rates due to laboratory treatment. Spectral analysis for the last 2000 years shows that the sieving charcoal series have no significant periodic accumulation rate, whereas the spectral analysis of the pollen-slide charcoal series shows a significant period of about 500 years. Because the charcoal particles from the sieving method are larger than those from the pollen-slide method, which are potentially windborne over long distances, our study suggests that the sieving method series is a proxy of local fire history, whereas the pollen-slide method is more suitable for detecting regional trends in fire history.