Arctic alpine vegetation change over 20 years

Recent arctic warming experiments have recorded significant vegetation responses, typically an increase in shrub cover and a loss of species richness. We report similar changes in vegetation along an arctic mountainside in northern Sweden over 20 years. During this time mean annual temperature increased by 2.0 degrees C, and growing season temperature by 2.3 degrees C. Growing season length increased by 28% at the bottom of our study area, in birch forest, and by 175% on the mountaintop. Neither total vegetation cover nor the cover of bare ground changed. One common dwarf shrub, Empetrum hermaphroditum, and two common forbs, Viola biflora and Geranium sylvaticum, increased in abundance over time, but no common species moved up the gradient. Species richness declined significantly over time, with an average loss of two species per 50 cm x 100 cm plot. The richness of herbaceous species at intermediate altitudes decreased significantly with increasing shrub cover. In spite of large changes in temperature, the type and magnitude of vegetation change along this mountainside were relatively modest and consistent with those from wide-spread warming experiments.