Abstract

Three sediment cores from Pyramid Lake (58°53'N, 129°50'W) were studied to reconstruct the late-Quaternary vegetation and fire history of the Cassiar region of northwestern British Columbia. Reconstructions were based on sedimentology, macrofossil evidence and concentrations of fossil pollen and charcoal. A radiocarbon date of 9500 +/- 65 BP provides a minimum age for deglaciation; however, the extrapolated age of the transition from basal diamicton to lacustrine sediments suggests that alpine ice persisted in the basin until about 10 300 BP. Macrofossil and pollen evidence indicate that subalpine fir (Abies lasiocarpa) was established near the elevation of the lake by ca. 9450 BP, suggesting that treeline during the early Holocene was at least as high as today. Migration of arboreal species from areas beyond the range of Cordilleran ice must have occurred in less than 1000 years, much more rapidly than indicated from previous paleovegetation reconstructions in northern British Columbia.