CGRG Bibliography of Canadian Geomorphology
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Author : Brown, K.; and Hebda, R.
Date : 1999
Title : Postglacial vegetation, climate and fire history of southern Vancouver Island.
Publication : Program and Abstracts. 42nd Annual Meeting of the Western Division of the Canadian Association of Geographers, Okanagan University College, Kelowna, British Columbia, March 11 to 13, 1999
Issue :
Page(s) :
Abstract
Pollen and microscopic charcoal fragments from five low elevation (Enos, Boomerang, and Pixie lakes, East Sooke Fen, and Whyac Lake bog) and two high elevation (Porphyry and Walker lakes) sediment records were used to reconstruct the vegetation and fire disturbance history on southern Vancouver Island, British Columbia. The basal pollen assemblage at Porphyry Lake is dominated by non-arboreal grasses and sage (Artemisia) and precedes the lodgepole pine (Pinus contorta) biogeochron traditionally viewed as the first vegetation assemblage following deglaciation in coastal British Columbia. The grass-sage biogeochron may represent tundra-like vegetation at or near the time of the glacial maximum. We envision a network of alpine and valley glaciers separated by open tundra expanses as opposed to an icesheet covering this part of the island. Our sites record a lodgepole pine biogeochron immediately following deglaciation. Fires were rare or absent and climate cool and dry. Mixed conifer forests replaced the lodgepole pine biogeochron in the late Pleistocene and persisted until approximately the start of the Holocene (10 000 y BP). Low elevation forests were dominated by pine, spruce (Picea), fir (Abies), and western hemlock (Tsuga heterophylla), whereas high elevation forests consisted of pine, spruce, fir, and mountain hemlock (Tsuga mertensiana). Charcoal records show that fires became more common during this interval even though climate seems to have been cool-cold and moist. Coastal Douglas-fir like forests expanded westward (beyond Pixie Lake) during the warm dry early Holocene (ca. 10 000-7500 yBP). Whyac Lake records coastal western hemlock like forests at this time which suggests this area was relatively moist. High elevation sites record relatively abundant western hemlock and Douglas-fir which implies a warmer and drier climate than present. Fires occurred frequently in forested ecosystems during this interval, although East Sooke Fen records a more open landscape and less fire. The mid and late Holocene was characterized by increasing precipitation and decreasing temperature at 7000 yBP and 4000 y BP respectively. Western hemlock forests became established on southwestern Vancouver Island, mountain hemlock forests at high elevations, and Douglas-fir forests in the drier eastern areas. Fires were infrequent in wet western regions (fire-free intervals spanning approximately 3000 years are recorded) but frequent in drier eastern regions and high elevations. The continuous deposition of charcoal in eastern sites may be partially related to aboriginal landscape management practices at this time. This study is important because it shows how paleoecotones and fire disturbance responded to climate and identifies sites potentially sensitive to future climate change.
Bibliography of Canadian Geomorphology