Vegetation and climate history of southeast Vancouver Island, British Columbia
Date
1995
Authors
Allen, Gregory Bruce
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Abstract
The vegetation and climate history of southeast Vancouver Island was reconstructed by palynologically analyzing 50 modern surface sample analogues and 2 lake sediment cores (Rhamnus and Heal Lakes). Results indicate that a series of vegetation and climatic changes have occurred in this region from the close of the Fraser Glaciation to the present. An initial phase of cool to cold and dry climate was present on southeast Vancouver Island approximately 13,000 BP to 11,800 BP. The vegetation consisted of mainly P. contorta in the lowlands and mixed forests of lodgepole pine and alder with significant subalpine vegetation in the highlands. From 11,800 BP to 10,000 BP coniferous species such as spruce, true fir and western hemlock invaded the region under a moist and cool climate. The forest structure closed decreasing non-arboreal species. The start of the Holocene (10,000 BP) was marked by the appearance of Douglas-fir in the regional forest. Decreased precipitation and increased temperatures during an initial xerothermic interval (10,000-7,000 years BP) caused Douglas-fir to expand into the region and lake levels to fall. Both highland and lowland forests took on modern Coastal Douglas-Fir like characteristics. An increase in precipitation and/or a modest decrease in temperature, 7,000-8,000 years BP, caused an increase in western hemlock and western red cedar in upland communities, whereas Douglas-fir forests with significant stands of Garry oak (a sensitive xerothermic indicator) occupied the coastal lowlands. The highland Rhamnus Lake region took on more Coastal Western Hemlock like characteristics while the lowland Heal Lake remained similar to the CDF. A moderate climate, approaching modern values, began to develop after 3,000 BP. Modern dry CWH and CDF conditions began to develop at both the Rhamnus and Heal Lake sites respectively at this time.
Comparison with previous reconstruction's from Vancouver Island and coastal British Columbia reveals a good correspondence between pollen zones and timing of climatic and vegetation events. Applications of these results include forest management of potentially sensitive areas to future climate changes.