Disentangling anthropogenic drivers of climate change impacts on alpine plant species: Alps vs. Mediterranean mountains
Global warming has been strongly accelerating in the last decades. Climate models tell us that this trend will continue in the future, accompanied by a marked decline in precipitation in Southern Europe, whereas the Alps will likely receive more winter and less summer precipitation. Climate factors and additionally nitrogen deposition and land-use changes have been identified as global change factors posing threats on high-mountain biodiversity, ecosystem stability and services. On the other hand, the characteristic micro-topographic variability of high mountain ecosystems may buffer them against global change impacts. Monitoring data from European mountain peaks show that changes in biodiversity patterns are closely related to rising temperatures. However, the effects of climate change on plant biodiversity differ significantly between temperate and Mediterranean biomes with species richness increases synchronously with warming in the former and richness decreases in the latter.
The MediAlps project aimed at disentangling anthropogenic and natural factors underlying differential changes in plant species composition and richness observed on mountain summits in the European Alps and the Mediterranean biome at the local and regional spatial scale. Changes in plant species richness and composition and present land-use impact based on systematic field observations were recorded on long-term monitoring plots on 23 summits. Soil temperature, water potential and local dry nitrogen deposition were measured in situ. Topographic parameters were recorded with photogrammetric methods. At the regional level, climate data and regional nitrogen deposition data from online resources (CHELSA, EMEP) were used and past land-use impact was assessed via guideline-aided semi-structured interviews. (Generalized) linear mixed-effects models and structural equation models (SEM) were employed to assess the impact of these drivers on biodiversity changes. Furthermore, spatio-temporal analyses based on satellite images were conducted.
Climate change is and will probably continue to be the main driver of plant biodiversity, species composition and their changes on mountain summits in both biomes. However, there are biome-specific differences with precipitation playing an important role in the Mediterranean biome in addition to temperature, which clearly is the most important single factor in the temperate biome. These changes will likely lead to a further thermophilisation in both biomes. The upwards movement of species from lower elevations will likely also result in a biotic homogenization of the vegetation, exacerbated by the decline of high-elevation endemic species. Species richness will likely continue to increase in the temperate biome until the “pay-off” of extinction debts or threshold effects of population size on extinction risks set in. With decreasing precipitation species richness in the Mediterranean biome will probably decline in the long run, too.
Nevertheless, other anthropogenic drivers have to be considered as well, although their influence is arguably much smaller than that of climate variables, namely nitrogen deposition with a negative influence on species richness change in the temperate biome and present land-use with a positive one in the Mediterranean biome.
In addition to MediAlps’ main focus on comparing multiple anthropogenic ecological drivers in the Alps with the Mediterranean mountains, the project substantially contributed to a spatially larger scaled long-term observation effort in the frame of the GLORIA (Global Observation Research Initiative in Alpine Environments) program.