THE INFLUENCE OF FIRE UPON VEGETATION AND SEDIMENT DELIVERY TO HIGH ELEVATION PONDS ON VANCOUVER ISLAND, BRITISH COLUMBIA

Timberline elevation is conventionally thought to be primarily controlled by temperature. We present evidence that at high elevations on Vancouver Island disturbance by fire has prehistorically been an important agent in maintaining parkland and alpine ecosystems and was likely a major influence on sediment availability and geomorphic processes. We analysed pond sediments and soil profiles for changes in pollen, macrofossil, charcoal, and rock fragments to evaluate the stability and character of alpine and subalpine ecosystems at several locations on Vancouver Island.

Results suggest that frequent fires controlled the prehistoric parkland and timberline configuration and made sediment available for transport by wind or overland flow. Stand-clearing fire produces major hydrologic changes by removing vegetation and organic surface materials thus influencing the rate and intensity of infiltration and runoff, leading to increased slope erosion and deposition of sediment in ponds. We suspect that cessation of aboriginal burning combined with modern fire suppression resulted in changes in the structure of the timberline and a subalpine-alpine configuration unprecedented in the Holocene. This recent forest infilling and encroachment has led to a reduction in alpine vegetation and may have contributed to declines in high elevation fauna such as the nearly extinct Vancouver Island marmot.