Community-level variation in plant functional traits and ecological strategies shapes habitat structure along succession gradients in alpine environment

Plant traits and ecological strategies elucidate various aspects of ecosystem functioning and services. However, the well-recognized trade-offs evident at the species level are not always expected to mirror community-level variation. Here, we investigated, at the regional scale, the community-level trade-offs of three key plant traits representing economics and size spectra (LA—leaf area, LDMC—leaf dry matter content and SLA—specific leaf area) and Grime’s CSR (competitive, stress tolerant, ruderal) plant strategies. We compared six siliceous alpine plant communities, also representative of Habitat types of EU Community interest (Habitats Directive, 92/43/EEC), distributed along a succession gradient, using a wide range of phytosociological relevés for which we calculated community weighted mean (CWM) trait values and C-, S- and R-scores. Our aims were to: (1) determine the validity of the plant community global spectrum of trait variation within alpine habitats; (2) investigate the discriminating capacity of plant traits and strategies to identify functional niches of dominance, stress and disturbance along the succession gradient; (3) quantify the variation in community structure (species richness and total species cover) through such functional niches. We observed a clear pattern of community-level trait variation that reflected the plant economics spectrum: from acquisitive and fast-growing characteristics in pioneer succession stages, to conservative and stress-tolerant features toward the succession climax, while the productive niche typical of C-selected strategies was scarce. Species richness and total species cover were both greater at intermediate levels of S- and R-selection gradients, indicating high niche differentiation in habitats characterized by exposure to stress or disturbance. Overall, this study demonstrates that trait trade-offs between communities identified at the global scale can undergo adaptation at the regional scale caused by local environmental conditions and also confirms the applicability of CSR strategies to investigate community-level variation of alpine vegetation.