Expansion of Canopy-Forming Willows Over the Twentieth Century on Herschel Island, Yukon Territory, Canada
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Canopy-forming shrubs are reported to be increasing at sites around the circumpolar Arctic. Our results indicate expansion in canopy cover and height of willows on Herschel Island located at 70° north on the western Arctic coast of the Yukon Territory. We examined historic photographs, repeated vegetation surveys, and conducted monitoring of long-term plots and found evidence of increases of each of the dominant canopy-forming willow species (Salix richardsonii, Salix glauca and Salix pulchra), during the twentieth century. A simple model of patch initiation indicates that the majority of willow patches for each of these species became established between 1910 and 1960, with stem ages and maximum growth rates indicating that some patches could have established as late as the 1980s. Collectively, these results suggest that willow species are increasing in canopy cover and height on Herschel Island. We did not find evidence that expansion of willow patches is currently limited by herbivory, disease, or growing conditions.
KeywordsArctic Tundra Climate change Willows (Salix spp.) Shrub encroachment Yukon
The authors wish to thank C.R. Burn for reading and providing helpful comments on the manuscript; D. Reid, S. Gilbert, and V. Loewen for field logistical support; and F. Doyle for contributing repeat photographs. The authors also wish to thank Qikiqtaruk–Herschel Island Territorial Park wardens and park management, in particular, Lee John Meyook and Richard Gordon; the 2008 and 2009 ArcticWOLVES Herschel Island field crews, M. Grabowski, C. Henry, and A. Trimble for field assistance; David Neufeld for providing old photographs; and the Aurora Research Institute for theirr logistical support. Support in the form of funds received from the Government of Canada International Polar Year Program, NSERC, the Polar Continental Shelf Program, the Canon National Parks Science Scholars Program, the Alberta Ingenuity, W. Garfield Weston Foundation, the Northern Scientific Training Program INAC, and the C-BAR Grant Program, the Canadian Circumpolar Institute, and the Air North (flight discounts) is gratefully acknowledged. The authors thank the Inuvialuit people for the opportunity to conduct research on their traditional lands.
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