Holocene vegetation dynamics, fire history, lake level and climate change in the Kootenay Valley, southeastern British Columbia, Canada

摘要

The environmental history of the Kootenay Valley in the southern Canadian Rockies was reconstructed using lake sediment from Dog Lake, British Columbia, and compared to other paleoenvironmental studies in the region to understand how vegetation dynamics and fire regimes responded to climate change during the Holocene. A pollen-based vegetation reconstruction indicates five periods of vegetation change. At 10,300 cal yr B.P. Pinus-Juniperus parkland colonized the valley and by 7600 cal yr B.P. was replaced by mixed stands of Pinus, Picea and Pseudotsuga/Larix. Fire frequencies increased to their Holocene maximums during the 8200-4000 cal yr B.P. period. From 5500-4500 cal yr B.P. Pseudotsuga/Larix reached its maximum extent in the Kootenay Valley under a more frequent fire regime. At 5000 cal yr B.P. Picea and Abies began to expand in the area and by 4500 cal yr B.P. the forest shifted to a closed montane spruce forest type with dramatically reduced fire frequency. The shift to less frequent forest fires after 4500 cal yr B.P., along with a moisterPicea - dominated closed forest, corresponds to Neoglacial advances in the Canadian Rockies and Coast Mountains. Fire intervals after 4000 cal yr B.P. are significantly longer than the shorter fire intervals of the early to mid Holocene. A return to drier, more open forest condition occurs between 2400-1200 cal yr B.P. with a slight increase in fire activity and summer drought events. Lower lake levels inferred by charophyte accumulation rates during the 2400-1200 cal yr B.P. interval support this moisture regime shift. An abrupt shift toPicea dominated forest occurred from 1200-1000 cal yr B.P. and a final period of wet-closed forest cover reaches its maximum extent from 700-150 cal yr B.P. that appears to be a response to Little Ice Age cooling. Present forests are within their natural range of variability but are predicted to shift again to a drier more open structure with increased Pseudotsuga/Larix cover. More frequent stand replacing fires and increased area burned likely will accompany this change due to continued global warming.