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Paleoecology of postglacial sediments in the Fraser lowland region of British Columbia Mathewes, Rolf Walter

Abstract

The postglacial vegetation history of the University of British Columbia Research Forest and the Yale area in the Fraser Lowland region was investigated using percentage and absolute pollen analysis, macrofossil analysis, and radiocarbon dating. A marine clay deposit from the U.B.C. Forest records the oldest (12,690 ± 190 B.P.) assemblage of terrestrial plant remains so far recovered from the postglacial of south-coastal British Columbia. Lodgepole pine dominated this early vegetation, although some fir, spruce, alder and herbs were also present. Four lakes were also studied paleoecologically. The oldest is Marion L., where a previously undescribed pollen assemblage of Pinus aontortat Salixt and Shepherdia is recorded in clay older than 12,350 ± 190 B.P. By at least 11,000 B.P., the three other lakes were also accumulating pollen-rich deposits, dominated in the early-stages by Pinus eontortat Abiest Piaea and Alnus, The first evidence of cedar (Thuja and perhaps Chamaecyparis) history in southwestern British Columbia is presented from pollen and macrofossil analyses. Pollen of Douglas-fir began a rapid increase about 10,500 B.P. at all four lakes, probably in response to a climatic amelioration. Between approximately 10,000 B.P. and 8,000 B.P. in the Yale area, pollen assemblages suggest that the climate was relatively warm and dry, although natural succession, topography, and fires might account for the increase of non-arboreal vegetation observed in the interval. At Marion and Surprise lakes nearer the coast, palynological evidence of a similar xerothermic interval is slight, probably reflecting an ameliorating oceanic influence. Evidence of warm and dry conditions is restricted to this period between 10,000 B.P. and 8,000 B.P., in contrast to the classical concept of a Hypsithermal interval between 8,500 and 3,000 B.P. in the Pacific Northwest.

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