Plant traits across different habitats of the Italian Alps: a comparative analysis between native and alien species

While it is well known that the success of alien plants in new environments greatly depends on their functional traits, to date only a few other studies have tested whether coexisting alien and native species show converging or diverging functional attributes. To our knowledge, no comparative analysis between native and alien species has been carried out in the same mountain habitats. We characterized the main habitats of the Italian Alps on the basis of plant species traits and we then tested for evidence of functional axes of variation among the habitats for native and alien plants. Finally, we tested the 'try-harder' and the 'join-the-locals' hypotheses to understand whether coexisting native and alien plant species showed converging or diverging functional attributes. Ordination analysis showed a distribution of the habitats according to the Grime's CSR strategies, and associated to plant growth form and resource acquisition. Co-inertia analysis showed a significant association between native and alien plant traits at habitat level (RV = 0.73; Monte-Carlo test, p = 0.035). Across all species and habitats, the comparative analysis of individual traits showed that alien species have 25% higher plant height, 250% higher leaf mass, 19% lower leaf dry matter content, 10% higher SLA, and 17% longer flowering duration than native species. Overall, our findings demonstrated that aliens differ in many traits from native species in the Italian Alps, but that many of these differences disappear when one compares aliens and natives that co-occur in the same types of habitats.