Charcoal accumulation following a recent fire in the Cascade Range, northwestern USA, and its relevance for fire-history studies

Abstract

Stratigraphic records of macroscopic charcoal particles (>125 μm in diameter) are widely used as a means of reconstructing past fire events, yet fire-history studies rest on assumptions about the processes by which charcoal is transported and deposited in lake sediments. In order to clarify the interpretation of charcoal data, charcoal abundance in sediment cores was examined from 36 lakes within and near the 1996 Charlton Burn, a large stand-replacing fire in the central Cascade Range of Oregon. Stratigraphic variations in charcoal abundance provided strong evidence that macroscopic charcoal recorded a signal of local fire and that prevailing winds affected charcoal transportation, increasing charcoal abundance in lakes downwind of the fire. Charcoal abundance in the uppermost sediments (0–2 cm depth) was related primarily to whether or not a site had burned and secondarily to the surface area of the lake. At the Charlton Burn area, other variables that may influence the transportation of charcoal after a fire, such as relative position of unburned lakes, distance of the lake from the centre of the fire, maximum adjacent slope, and width of riparian vegetation, were not statistically significant. These results support the assumption in charcoal analysis that there is a relationship between the occurrence of local fire and peaks in macroscopic charcoal. Confirming this relationship strengthens the interpretation of long-term fire-history records.