ABSTRACT: Disturbance responses, resiliency, and climate change: a characterization of revegetation patterns related to retrogressive thaw slumps on Herschel Island, Yukon Territory, Canada.

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Abstract

Vegetation is an important factor in understanding northern ecosystems, not only because it determines terrestrial primary productivity, but also because locally it can magnify or reduce the impact of prevailing environmental conditions. Despite its ecological importance, however, there is surprisingly little literature characterizing the revegetation patterns following natural disturbances such as those caused by thermokarst in permafrost environments. Changes in arctic vegetation may have already begun as a result of the recent warming in the Arctic (Chapin et al., 1995; Stow et al., 2004; Tape et al., 2006), but without clear knowledge of the existing species, patternsof revegetation, and the resiliency of tundra communities, large-scale management is impossible. Arctic landscapes underlain by massive ground ice and ice-rich permafrost are inherently unstable and often display evidence of past and present thaw subsidence, or thermokarst. Retrogressive thawslumps are a progressive form of backwasting thermokarst that tend to go through cycles of activity, resulting in dramatic changes to the landscape. The cyclic pattern of disturbance and stabilization related to these thaw slumpsresults in a patchy tundra landscape where there are easily identifiable geomorphic units reflecting the stage of stabilization and the time since disturbance. The established research sites of Herschel Island provide excellent examples of both stabilized and active thaw slumps for which therecent history of activity is known (Lantuit and Pollard, 2008). Preliminary findings from Herschel Island show that there are vegetation and soil characteristics distinctive to sites disturbed by thaw slumps. Specifically, plant diversity, species composition, and percent cover in addition to pH, soil temperature, active layer depth, and organic matter content change progressively with the time since disturbance and therefore represent both the relative age of a thaw slump and the degree of stabilization. By describing thevegetation characteristics of stabilized thaw slumps of varying ages (10 to ~300 years old) and comparing them to one another and to undisturbed sites, we can construct an approximate timeline and pattern of recovery for vegetationdisturbed by thaw slumps. This will provide insights into the resiliency of the tundra ecosystem and its probable response to future instability related to climate change.

Bibliography of Canadian Geomorphology