Ecosystem changes across a gradient of permafrost degradation in Subarctic Québec (Tasiapik Valley, Nunavik, Canada).

Permafrost thaw, tundra shrubification and changes of snow cover properties are documented impacts of climate warming, particularly in Subarctic regions where discontinuous permafrost is disappearing. In order to obtain some insight on those changes, permafrost, active layer thickness, vegetation, snow cover, ground temperature, soil profiles and carbon content were surveyed in an integrated approach in six field plots along a chronosequence of permafrost thaw on an ice-rich silty soil. Historical air photographs and dendrochronology provided the chronological context. Comparison of the plots reveals a positive feedback effect between thaw settlement, increased snow cover thickness, shrub growth, increase in soil temperature and the process of permafrost decay. By the end of the sequence, permafrost was no longer sustainable. Along the estimated 90 years duration of the chronosequence, the originally centimeter thin pedogenic horizons under mosses and lichens increased to a thickness of nearly 65 cm under shrubs and trees. Snow cover increased from negligible to over 2 m. The thickness of soil organic layers and soil organic matter content increased manyfold, likely a result of the increased productivity in the shrub-dominated landscape. Results of this study strongly suggest that permafrost ecosystems in the Subarctic are being replaced under climate warming by shrub and forest ecosystems enriched in carbon on more evolved soils.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author