Habitat determines plant community responses to climate change in the High Arctic

Plant climate responses may depend on site-specific environmental context. Using fences and open-top chambers, we enhanced snow depth (creating Ambient, Medium, and Deep regimes) over an 11-year period and increased temperatures for two summers in dry heath and mesic meadow habitats on Svalbard, Norway. Comparison of plant growth form abundance and diversity responses in these two habitats showed that the response was more limited in the dry heath than in the mesic meadow. Common to both habitats was a decrease in shrub abundance and vascular plant species richness in the Deep snow regimes. Bryophyte abundance increased with enhanced snow cover in both habitats, but only up to a certain extent of snow depth in the meadow. However, for many growth forms, the effects of snow enhancement were habitat specific. In the mesic meadow, the abundance of forbs and bryophytes increased with snow enhancement, but the effect was stronger when combined with summer warming. The “bryofication” — that is, an increased abundance of bryophytes in response to snow enhancement and summer warming — also influenced overall plant diversity in the mesic meadow. Bryophytes are species-rich taxa and may respond differently than vascular plants to environmental change. We show that the inclusion of even the most common bryophytes in measures of diversity may determine overall plant diversity responses to environmental change in the Arctic.