A new approach for assessing winning and losing plant species facing climate change on the GLORIA alpine summits

Climate change in alpine habitats has a direct impact on vascular plant species, and is leading to changes in species abundance and distribution. Alpine plant communities are expected to experience a turnover of species over time, due to the loss of cold-adapted specialists and the upslope migration of more thermophilic taxa. Therefore, assessments of single species changes are important for research and conservation. Here, we propose a new analysis protocol for the GLORIA (GLobal Observation Research Initiative in Alpine environments) network, and potentially, for other monitoring programmes capable of defining winning and losing plant species. The proposed approach involves the non-parametric Cliff's 'Delta' measure of 'effect size', which provides a measure of the intensity of species abundance changes over time and is applicable for vegetation data collected using both re-visitation and long-term monitoring approaches. Compared to other methods, Cliff's 'Delta' was more conservative and efficient in detecting winning/losing taxa, as well as being suitable to analyse data of rare species with few records. To test the effectivity of the Cliff 'Delta' method, we analysed the vegetation data from three Italian GLORIA sites. We investigated 413 vascular plant species and found a total of 41 winning and 24 losing species. Moreover, we used Cliff 'Delta' to assess whether plant assemblages are responding differently among sites and plant growth forms. Our findings showed that alpine plant communities are changing faster on Apennines sites and that growth form types respond differently across the study sites.