Thirty years of ecological research at the Gran Sasso d'Italia LTER site: climate change in action

Since 1986, vegetation monitoring of alpine plant communities has been performed at the Gran Sasso d'Italia LTER site (https://deims.org/c0738b00-854c-418f-8d4f-69b03486e9fd) in the Central Apennines, through phytosociological relevés and abundance and coverage estimation of the vascular flora at fine scale. The monitoring activities for abiotic parameters regard air and soil temperatures, rainfall, snowfall and snow cover persistence. A comparative analysis of changes in species composition, life forms, life strategies and morpho-functional types allowed recognition of dynamical processes (fluctuation and degeneration) and an increase in stress- and drought-tolerant and ruderal species, probably linked to a general process of climate change. A trend of variation forced by increasing drought was recorded in high-mountain plant communities, normally within a dynamic fluctuation process. There has been a 50–80% change in species composition with respect to the total number of species observed over the years. Whereas the total number of species has increased in all communities, in high-mountain mesic grassland 20% of sensitive species have completely disappeared. Early signs of a degeneration process were already discernible after seven years: such signs are more evident in snow-dependent communities, with a quantitative increase in more thermophilic and drought-tolerant species and a parallel decrease in more mesic, cryophilic and competitive species. In particular, the following phenomena have been recorded in high-mountain mesic grassland, in agreement with predicted or observed phenomena in other Alpine or Arctic areas: (a) coverage increase (or appearance) of ruderal and stress- and drought-tolerant species; (b) coverage decrease (or disappearance) of cryophilic, mesic and competitive species. These short-term changes could lead, in the medium- or long-term, to a disgregation process affecting the high elevation plant communities of the Apennines (including the local extinction of most of the cold-adapted species), due to their very low resilience. The phenomena described may be linked to the observed climate change which occurred during the last century (in particular in the last 50 years) in the Apennines, consisting mainly, in the mountains, of a strong reduction in the duration of snow-cover and an increase in mean and minimum annual temperatures