Long-term vegetation dynamic in the Northwestern Caucasus: which communities are more affected by upward shifts of plant species?

We studied long-term (25-31 years) dynamics of alpine communities at the Teberda Reserve, NW Caucasus, Russia, to test the following hypotheses: (1) lower altitude species increase and high altitude species decrease their abundance as a consequence of climate warming; (2) such changes in abundance are more significant in communities with short growth season (due to persistent snow cover) compared to exposed communities; (3) species with similar changes in abundance have similar functional traits. Four alpine communities with different positions in relief were considered in order of winter snow cover: alpine lichen heaths (ALH), Festuca varia grasslands (FVG), Geranium-Hedysarum meadows (GHM), and snowbed communities (SBC). The altitudinal distribution of species significantly predicted the direction and degree of changes in species abundance in GHM (p < 0.001), SBC (p < 0.02) and FVG (p < 0.05) with high altitude species decreasing and low altitude species increasing their abundance. Mean altitudes of significantly decreasing species exceeded that of increasing species by ca. 100-130 m in FVG, GHM and SBC. There were no species traits or trait combinations that consistently predicted their changing abundance in ALH, FVG and SBC. In GHM increasing species tended to have leaves with higher SLA (i.e. softer leaves) and lower root nitrogen content. The observed dynamic processes may be caused partly by recent climate warming, although slow recovery from historic grazing pressure may also play a role. Regardless of the causes driving the plant species' upward shift, communities experiencing high snow accumulation (SBC, GHM) seem to be more vulnerable to changes in structure and composition.