A green future with thawing permafrost mires? : a study of climate-vegetatiojn interactions in European subarctic peatlands

Sammanfattning: Climate projections indicate that Arctic and sub-Arctic regions are facing a significant change in climate during the 21st century. With warmer temperatures precipitation is also expected to increase, and in particular winter precipitation. These changes are likely to have large impacts on the Arctic and subarctic environment, and extensive research has focused on ecosystem-climate interactions in Arctic and sub-Arctic environments, but still the environmental response to such changes is not fully understood. This thesis presents the work and outcomes of my research on climate-vegetation interactions in permafrost (ground that remains frozen for two or more consecutive years) mires in subarctic Fennoscandia. In this region permafrost mires demarks the outer border of lowland permafrost existence, where a combination of climatological and environmental conditions allows for the ground to remain frozen year round, making the permafrost particularly sensitive to changes. By combining field observations of vegetation patterns in permafrost mires throughout the study region with spatial data of the present (2008) and projected future climate in subarctic Fennoscandia the future vegetational patterns of these permafrost mires were modeled. Further, the impact of increased snow cover on plant photosynthesis in these environments was assessed through field experiments on a subarctic permafrost mire, where the snow cover was manipulated during seven winters using snow fences. The results suggest that a rapid transition from dry heath tundra vegetation to moist tussock tundra vegetation is to be expected in these permafrost mires with the warmer climate and increased precipitation projected for the studied region. The snow manipulation experiments suggest that even a moderate increase in snow cover thickness increases plant photosynthesis on the long term. This increase in photosynthesis is attributed to the observed shift in plant species composition where moist tussock vegetation is likely to be favored by increased soil moisture, soil temperature and nutrient availability. However, the increased carbon uptake through higher photosynthesis rates is may be completely offset by increased methane emissions from increased wetness in the thawing peatlands.