Snowmelt Events In Autumn Can Reduce Or Cancel The Soil Warming Effect Of Snow-Vegetation Interactions In The Arctic

The warming-induced growth of vegetation in the Arctic is responsible for various climate feedbacks. Snow-vegetation interactions are currently thought to increase the snow-insulating capacity in the Arctic and thus to limit soil winter cooling. Here, we focus on autumn and early winter processes to evaluate the impact of the presence of erect shrubs and small trees on soil temperature and freezing. We use snow height and thermal conductivity data monitored near Umiujaq, a low-Arctic site in northern Quebec, Canada (56 degrees N, 76 degrees W), to estimate the snow thermal insulance in different vegetation covers. We furthermore conducted a field campaign in autumn 2015. Results show that the occurrence of melting at the beginning of the snow season counteracted the soil warming effect of snow-vegetation interactions. Refrozen layers on the surface prevented wind drift and the preferential accumulation of snow in shrubs or trees. Snowmelt was more intense in high vegetation covers, where the formation of refrozen layers of high thermal conductivity at the base of the snowpack facilitated the release of soil heat, accelerating its cooling. Consequently, the soil was not necessarily the warmest under high vegetation covers as long as melting events occurred. We conclude that under conditions where melting events become more frequent in autumn, as expected under climate warming, conditions become more favorable to maintain a negative feedback among the growth of erect vegetation, snow, and soil temperature in the Arctic, rather than a positive feedback as described under colder climates.