Testing the assumptions of fire history studies: An examination of modern charcoal accumulation in Yellowstone National Park, USA

The interpretation of sedimentary charcoal in lakes rests on several assumptions that concern the source area of charcoal, the timing of charcoal introduction, and the patterns of charcoal accumulation within a lake following fire. To examine empirically such assumptions. eight small lakes were sampled over a five-year period to discern the patterns of charcoal accumulation following the 1988 fires in Yellowstone National Park. Five lakes have watersheds that were burned in 1988, and three lakes lie outside the burned area. Transects from shallow to deep water revealed that different size ranges of macroscopic charcoal produced similar patterns of accumulation. Multiple samples at the same locations in one lake provided an estimate of the analytical error in the data. The analytical error was considerably less than the spatial and temporal variations along the transects. The initial sampling in 1989 indicated that both burned and unburned sites received charcoal during and shortly after the fire, and much of this material was blown from off-shore to the littoral zone. In subsequent years, charcoal abundances increased in deepwater sediments as a result of resuspension and redeposition of littoral and sublittoral charcoal and the inwash of material from burned slopes. By 1993, the amount of sedimentary charcoal in the deepwater sediments of burned sites exceeded that of unburned sites. These results suggest that charcoal accumulation in deepwater sediments may lag several years behind the actual fire event, and the abundance may vary with lake and watershed characteristics. This depositional Lag can obscure efforts to correlate charcoal directly with characteristics of the fire, such as fire size or intensity.