Changes in arctic vegetation on Jan Mayen Island over 19 and 80 years

Questions Can recent vegetation changes on an isolated, grazer-free island be explained by recent climate change? Are observed changes consistent when focusing on two different time scales? Location Jan Mayen, an arctic volcanic island in the North Atlantic Ocean. Methods We re-surveyed two botanical studies conducted 19 and 80 yr earlier to explore changes in species frequency, cover and co-occurrence with other species. The observed changes were statistically evaluated using restricted permutation tests and were compared for the two time scales considered using Pearson correlation tests. Results Total number of species did not significantly change over the two time periods considered. One species (Botrychium lunaria) was found new to the island. The dwarf-shrub Salix herbacea and several graminoids increased in frequency or cover, or both, whereas species linked to snowbeds (e.g. Saxifraga spp., Oxyria digyna, Cerastium cerastoides) decreased. Changes over 19 yr were significantly correlated with 80-yr changes considering species frequency, but not when comparing changes in cover and species co-occurrences. Observed changes were more pronounced in the 80-yr comparison. Conclusions Our findings from the virtually grazer-free island of Jan Mayen are in line with other studies on short- and long-term vegetation changes in the Arctic and confirm that indirect effects of climate change (e.g. longer growing season, altered soil moisture conditions, increased nutrient availability) may be the main driver of the observed changes in arctic vegetation composition. However, whereas our study found the main trend to be similar over both time scales considered, discrepancies in the trends of some species suggest that long-term changes are only partly predictable from short-term studies.