| Climate warming is predicted to be most pronounced at high latitudes. Thawing permafrost and the resulting release of large amounts of carbon dioxide and methane by microbial decomposition of previously frozen organic carbon is one of the most significant potential feedbacks from terrestrial ecosystems to the climate system. Changes in tundra vegetation structure and composition may counteract or amplify thawing of permafrost. Denser vegetation may reduce the rate of permafrost thawing. In the long term, however, enlargement and expansion of shrubs may eliminate the insulating moss layer, which would increase thawing rates. Mosses are an important component of northern ecosystems and are known for contributing to stable permafrost conditions. Yet, mosses are generally not represented in vegetation models used with climate models. In this research we will study the effects of mosses, shrubs and grasses on permafrost thawing and nutrient availability, and how that further affects vegetation composition and carbon exchange. The approach will be a combination of field experiments and ecosystem modelling, in Siberian tundra, an understudied area. We will measure heat fluxes, thawing depth, soil moisture and nutrient availability in experimental plots where vegetation composition or thawing depth has been manipulated. By comparing with control plots, the direct effects of changes in vegetation on thawing depth, and vice versa will be quantified. I will include a permafrost module in the ecosystem model NUCOM. Unlike other ecosystem models, NUCOM includes dynamic vegetation in terms of mosses, shrubs and grasses, and carbon-nitrogen-water interactions. This enables analysis of the full feedback loop of vegetation?permafrost interactions and the consequences for the carbon balance in tundra ecosystems. The proposed research will generate increased process understanding of vegetation-permafrost feedbacks which is required to improve predictions of the future of the Arctic?s permafrost and its gigantic carbon stores |
