Spatio-temporal changes in functional spectra of plant communities following deglaciation.

Although alpine communities have been extensively described, the mechanisms leading to their diversity are little understood. Growing interest in adaptive gradients acting on plant life evolution is producing working tools for the functional classification of species. This functional approach has been recently applied to glacier foreland (Caccianiga et al. 2006; Erschbamer 2007) and alpine communities (Pierce et al. 2007). Integrating these standardised methods to define functional types and phytosociological data, it is possible to provide a functional explanation of plant communities and of the mechanisms underpinning community processes such as succession. We analysed the principal communities of the alpine belt of Italian Alps (Sieversio-Oxyrietum digynae, Saxifrago bryoidis-Poetum alpinae, Caricetum curvulae s.l., Festucetum halleri, Salicetum herbaceae). Within each community, CSR strategies (Grime 2001) were determined from seven traits, and the functional spectrum was represented by ordinating species within ternary plots representing CSR space. We found a succession of functional spectra between communities, with the number of species and the number of functional types positively correlated throughout. The least diverse community (Oxyrietum) was characterised by ruderal strategies reflecting general physical disturbance. The most diverse community (Festucetum) was characterised by ruderals and stress-tolerators, probably reflecting a more varied mosaic of niches and selection pressures acting at α (within habitat) scales. There were consistently more species than functional types, as more than one species may occupy any particular niche. Thus functional diversity is more fundamental and informative than solely the number of species in the evaluation of community properties and processes.