SOIL AND SEDIMENTARY CHARCOAL EVIDENCE FOR HOLOCENE FOREST FIRES IN AN INLAND TEMPERATE RAINFOREST, EAST-CENTRAL BRITISH COLUMBIA, CANADA

Abstract

Accelerator radiocarbon dating of 147 charcoal samples recovered from colluvial and alluvial fan deposits at 29 sites was used to reconstruct the Holocene fire history of an inland temperate rainforest watershed in east-central British Columbia (BC), Canada. Radiocarbon dates ranged from 182 to 9558 cal. yr BP, with prominent peaks in the probability distribution of calibrated dates at e. 7100, 3900, 2300, 1600 and 250-1000 cal. yr BP. The inferred median fire return interval (FRI) was 800-1200 cal. yr, depending on the extent of inbuilt age errors resulting from charring of wood pre-dating actual fire ages. This FRI is likely an overestimate, as less severe events may not have created sufficient erosion and slope instability to preserve a record of charcoal in buried soils and slope deposits. Median time since fire was 467 cal. yr based on ages of the uppermost charcoal found at each site, but the severity of heart-rots in the dominant redcedars (Thuja plicata Donn ex D. Don) prevented independent confirmation of stand ages by dendrochronology. Sites with multiple charcoal-containing layers having similar radiocarbon ages can be explained with reference to contemporary post-fire mass-wasting processes. Peaks in fire-related sedimentation probability coincided broadly with periods of higher fire frequency c. 600-1000, 1300-2400 and 3500-4500 cal. yr BP inferred from sedimentary charcoal records at subalpine sites in southwestern BC. Correspondence with fire records from more distant sites in northwestern North America was less clear.