Postglacial vegetation history of mountainous landscapes on Vancouver Island, British Columbia, Canada.
Date
2010-05-03T23:46:12Z
Authors
Mazzucchi, David
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Abstract
Five lake and one soil sediment record from six mountainous sites on Vancouver Island, British Columbia, Canada, were examined for changes in pollen, macrofossils, charcoal, and mineral clasts to reconstruct late Quaternary history of vegetation, fire and climate. The results provide insights into the history and dynamics of the Mountain Hemlock biogeoclimatic zone and highlight the role of several species and species groups not previously recognized. During the early Holocene, Alnus crispa expanded throughout the region following deglaciation, playing a more important role in these ecosystems than today. Abies lasiocarpa was the dominant Abies species at these sites during the late glacial and early Holocene until it was replaced by A. amabilis between about 10,500 and 7300 calBP, perhaps due to changes in regional atmospheric circulation and greater seasonal variability in insolation than we experience today. A. amabilis increased during the mid Holocene and was later replaced at the sites by increased abundance of T. mertensiana while T. heterophylla became much more abundant at nearby low elevations. Ericaceous-heath communities were established soon after deglaciation at the moister sites but not until about 7000 calBP at drier sites. These drier sites show more variation in vegetation throughout their records than the wetter sites. High charcoal and clast concentrations coincident with rapid vegetation shifts during the early Holocene suggest that these changes were probably the result of large stand-clearing fires that exposed mineral soils. A peak in charcoal at several of the sites occurs at ca. 4000 calBP suggesting more frequent fire at that time. During the late glacial and very early Holocene, P. contorta was an important seral species until A. crispa became well established. In the mid to late Holocene when Ericaceous-heath became established, A. crispa was unable to predominate, possibly because of reduced fire activity or because the heath communities hindered the exposure of fresh mineral soil surfaces. As a consequence, conifer-dominated stands were favoured. Basal sediments from these sites are not as old as they are at lower elevations, suggesting that deglaciation may have happened later at higher elevations.
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Keywords
Geology, Geography, Paleoecology, Palynology, Mountain Hemlock, treeline, charcoal, macrofossils