Short Communication Vegetation-Permafrost Relations within the Forest-Tundra Ecotone near Old Crow, Northern Yukon, Canada

摘要

Old Crow Flats is a 5600 km~2 glaciolacustrine plain that straddles the forest-tundra ecotone in northern Yukon. Continuous taiga corridors occur in the entrenched river valleys, where annual mean ground temperatures (T_g) at the depth of zero annual amplitude at two locations were -3.1 and -4.0℃ in 2013. On the Flats, the vegetation cover is patchy, and T_g varied between -5.1 and -2.6℃. Annual mean near-surface permafrost temperatures (T_(ps)) measured on the Flats between 2008 and 2011 in patches of taiga, tall shrubs and low shrubs were correlated with local snow depth. Snow depth was controlled by vegetation height if the snow supply was not limited, for example, where low shrubs and large lakes dominate the landscape. In this setting, snow depths and, hence, T_(ps) in taiga patches were higher (-2.6 to - 2.9℃) than in the surrounding shrub vegetation (-3.5 to -5.5℃). Where taiga patches were more extensive, redistributed snow was trapped at the patch edge and T_(ps) in taiga was lower (-4.1 to -4.3℃) than in the surrounding shrub patches (-3.2 to -3.6℃). The permafrost temperature field is heterogeneous under patchy vegetation in the forest-tundra ecotone. Our data suggest that it is governed by both the snow-holding capacity of local vegetation patches and the spatial configuration of vegetation in the surrounding landscape, which controls snow supply.