Could plant diversity metrics explain climate-driven vegetation changes on mountain summits of the GLORIA network?

High-elevation habitats host a large number of plant species and are characterized by high biodiversity. The vegetation dynamics in these cold adapted ecosystems are difficult to predict, being affected by global warming, especially in the last decades. With the aim to promote a better understanding of climate-driven changes of alpine vegetation, we investigated the variation in species richness, α-diversity, β-diversity, and total cover of plant functional types over a time lapse of 15 years, relying on multiple re-surveys of mountain summit vegetation in 2001, 2008 and 2015. The study area, included in the long term global observation network GLORIA, was at the boundary between temperate and Mediterranean mountains of S-Europe (northern Apennines, Italy). We identified a trend of loss in biodiversity and signals of biotic homogenization using multiple diversity metrics, despite the overall species richness increment observed in the study area. Cold-adapted and rare species declined while dominant species like graminoids and shrubs increased. Our results highlight that long-term vegetation monitoring activities paired with multiple measures of diversity are required to properly assess biodiversity and to obtain useful indications for future conservation activities in alpine environments. The methods here presented could be applied in all GLORIA sites to quantify biodiversity changes over time, obtaining comparable results for biodiversity monitoring in high-elevation habitats from all over the world.