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Vegetation is often classified through phytosociology, which defines floristically and ecologically coherent units identified by diagnostic species. Since species- and community-environment relations are regulated by plant functional traits, it is likely that phytosociology has a strong functional underpinning, although the past and current phytosociology does not explicitly tackle this issue. Here we provide an analysis of functional traits of 221 woody species from Northern Italy, diagnostic of 21 European woody vegetation classes (including alien dominated ones). We assessed whether the functional space occupied by selected species corresponds to the physiognomy and ecology of the vegetation they represent, and whether this could help to evaluate major threats, such as invasion by alien species. For each species we collected from Authors' datasets leaf trait data (leaf area, specific leaf area, leaf dry matter content, carbon to nitrogen ratio, leaf nitrogen content) and whole plant (plant height, seed mass) traits, and calculated Competitor, Stress-tolerant, Ruderal (CSR) scores. We identified the multidimensional functional trait space of diagnostic species and clustered classes according to their scores in the functional space, to check whether their physiognomy was coherently represented and mirrored in the CSR space. Lastly, we tested for differences between native and neophyte species and their overlap with classes. Diagnostic species mirrored the global spectrum of plant form and function, and classes showed a functional pattern coherent with their physiognomy and ecology. Evergreen dominated classes showed a similar convergence toward conservative characteristics and the stress-tolerant strategy, as opposed to deciduous forest classes that showed a tendency toward the competitive strategy. None of the classes showed a marked ruderal strategy, thus abiotic stress and biotic competition are the main ecological drivers affecting woody vegetation. Neophyte woody species exhibited relatively more competitive strategies compared to natives, and their invasion could be facilitated in resource-limited or mildly disturbed environments, should climate warming or increased nutrient availability occur. We demonstrated that plant traits and CSR strategies of woody diagnostic species reliably indicate the structure and functions of the phytosociological classes they represent, opening the way to the development of a "functional phytosociology". [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]