Large climate change, large effect? Vegetation changes over the past century in the European High Arctic

Questions: Terrestrial vegetation is assumed to be highly vulnerable to climate change in the Arctic, which has experienced the highest rates of temperature increase globally over the past decades. However, long-term studies at the community scale are rare, particularly for the European High Arctic. We ask: (1) has Arctic vegetation changed over the past century; (2) can observed changes be related to recent climate change; and (3) do observed changes in vegetation prevail for specific species or species functional groups? Location: The Svalbard Archipelago, High Arctic Norway. Methods: In 2009 we resurveyed three plant sociological studies up to 85 yrs after the first surveys. Vegetation data were recorded from 1-m(2) non-permanently marked plots, and soil pH was measured. We applied restricted permutation tests to evaluate whether observed changes in vegetation (species richness, occurrence frequency, coverage) and in soil pH were significant and independent of plant community type. We compared species co-occurrences over time to study changes in species composition and to identify the species most likely causing these changes. Results: Total number of species and average number of species per plot has not changed, and are 75 and nine, respectively. Occurrence frequency changed significantly for 34% of the 64 species tested (11 species increased, 11 decreased). Species cover decreased significantly for 27% of the species and increased for one species. Observed changes in frequency and cover are not significantly related to species' functional groups or species affiliated to moist or dry habitats. Polygonum viviparum, Saxifraga cernua and Alopecurus borealis have changed most in co-occurring with other species. Soil pH increased significantly from 6.4 to 6.8. Conclusions: Our results suggest that the strong climatic warming in the High Arctic over the past decades has contributed to significant changes in the vegetation studied on Svalbard over the past 85 yrs. Internal community restructuring and the overall stability in species richness may be explained by time-delayed responses of well-established communities, and/ or by a limited size of the species pool in the area.