Vegetation and soil-snow interactions in themokarst slumps in the western Arctic

Changes in the structure of northern vegetation will likely drive important feedbacks to global climate. Therefore, the relative effects of temperature and disturbance on arctic plant communities may be critically linked to understanding global change. In the last thirty years the rate of thermokarst slumping has doubled in parts of western arctic, likely due to increasing air temperatures. Since these disturbances make areas of ion-rich mineral substrates available for colonization, the response of vegetation in these areas to warming temperatures should be different than in undisturbed terrain. Across a latitudinal temperature gradient, we tested the hypothesis that plant community composition, green alder (Alnus viridis subsp. fruticosa) autecology, and abiotic variables differed on active slumps, stabilized slumps, and undisturbed terrain. Increases in productivity, catkin production, seed viability, height and density of green alder were found at disturbed sites, as compared to undisturbed tundra, likely due to elevated snow pack, increased nutrient availability, warmer ground temperatures, and a thicker active layer found at slumps. Canonical Correspondence Analysis suggests abiotic variables (such as snow pack, active layer depth and nutrient supply rates) are important drivers of plant community structure, which also differs markedly on thermokarst slumps compared with undisturbed terrain. As the frequency of thermokarst slumping increases with continued warming, the effects of these disturbances may magnify the direct effects of temperature on northern ecosystems.