Influence of Geomorphic Disturbance on Phenotypic Species Plasticity and Vegetation Cover in High-Elevated Belts

The degradation of permafrost and the higher number of heavy rainfall events increase geomorphic disturbance (GMD), affecting the vegetation establishment in high-elevation belts. To evaluate the effect of GMDs on vegetation development, it is essential to understand how species or plant groups respond to disturbances. In this study, we investigated vegetation establishment in undisturbed and disturbed plot pairs along elevational transects in the Austrian and Italian Central Alps. Differences in total vegetation cover, species diversity, the cover of different plant groups and the community weighted means of the Landolt indicator values were analysed using the Kruskal-Wallis test for non-parametric data and paired t-test for parametric data. Generalised additive models combined with a principal component analysis were applied to identify the significant environmental variables (e.g., inclination or precipitation) explaining the differences found. To assess species' plasticity, the three most abundant species (five individuals per plot) per undisturbed-disturbed pairs were collected on-site, and functional traits measured in the laboratory. Disturbed sites exhibited lower total vegetation cover, species number, cover of competitive species, dwarf shrubs, herbs and lichens. The cover of stress-tolerant, cryophilic species and herbs was higher in disturbed sites. The observed variations can be mainly explained by climatic, edaphic and topographic variables. The Stream Power Index as a disturbance proxy had a significant negative influence on the total vegetation cover and herb cover and a positive influence on bryophyte, dwarf shrub, and tree cover. Most collected species showed high trait plasticity, with disturbance primarily reducing plant height and specific leaf area. Synthesis: GMD was the key driver in relation to both vegetation cover and species richness. The cover of most functional plant groups as well as species plasticity was primarily affected by climatic factors, soil conditions and the presence of less acidic debris than by GMD.