Long-distance transport of macroscopic charcoal by an intensive crown fire in the Swiss Alps - implications for fire history reconstruction

Abstract

The correct interpretation of charcoal records in a palaeoecological context requires the understanding of the sources and transport of charcoal particles. Conventionally, it is assumed that macroscopic charcoal particles are not transported far from fires ( c. 200m). Therefore macroscopic charcoal records are used to reconstruct local fire frequencies. However, the general scarcity of empirical and experimental evidence impedes a thorough check of this assumption. In this study we present the first unambiguous evidence of kilometre-scaled macroscopic charcoal transport in Europe. During the hot summer of 2003 an intensive crown fire occurred in Leuk, central Swiss Alps. It affected 300 ha of forest as well as 10 ha of pasture and fallow land. Litter traps and nets had been located approximately 5 km west and east of the burned area. The downwind site in the east (Jeizinen) recorded a strong charcoal fallout at 5.3 km from the fire edge. The observed charcoal influx of fragments with a size up to 1.3 cm reached average values of 0.144 and 0.098 mm2/Cm2 per fire (or yr) in five traps and two nets, respectively. These values are comparable with charcoal accumulations measured at only c. 50 m from large fires, suggesting that macroscopic charcoal transport does not decay rapidly to zero with increasing distance from the fire. We suggest a long-distance dispersal model for transport of macroscopic charcoal during large fire events. Reconstructions of local fire regimes may be affected by long-distance transport of macroscopic charcoal, although this problem is mitigated by the tendency of most macroscopic charcoal particles to be deposited within very short distances (< 50 m) from the fire edge.