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

Abstract

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

Comparing traits of native and alien plants: Can we do better?

“…Community approaches that quantify a priori identified traits across nested samples along suitable environmental gradients in order to confront observations against an appropriate null model appear the most powerful tool available (Gross et al., , ). The infrequent application of such approaches (Cross et al., ; Dainese & Bragazza, ) suggests we are still a long‐way from developing robust generalisations about plant invasions. For example, comparisons of trait differences between native and alien species are still undertaken at regional scales (Bezeng, Davies, Yessoufou, Maurin, & Van der Bank, ; Kuester, Conner, Culley, & Baucom, ; Marx, Giblin, Dunwiddie, & Tank, ) even though the relevance of such analyses for understanding the vulnerability of plant communities to plant invasion is debatable.…”

“…Comparisons of the similarity in alien and native species traits have been undertaken at regional (Lambdon & Hulme, ; Lambdon, Lloret, & Hulme, ), national (Knapp & Kuhn, ; Thompson, Hodgson, & Rich, ), landscape (Dainese & Bragazza, ; Tecco et al., ), habitat (Tecco et al., ) and community (Gross, Liancourt, Butters, Duncan, & Hulme, ) scales. However, studies that have been undertaken at multiple spatial scales highlight that the interpretation of trait differences is scale‐dependent (Carboni et al., ; Dainese & Bragazza, ; Davies, Cavender‐Bares, & Deacon, ; Diez, Sullivan, Hulme, Edwards, & Duncan, ; Gross et al., ; Lambdon et al., ). This reflects that the relative strength of competitive interactions and environmental filtering on floristic composition will change across different spatial scales.…”

“…As an alternative to plant strategies, the examination of differences between native and alien species among multiple traits has often involved multivariate techniques, particularly ordination (Cleland et al., ; Dainese & Bragazza, ; Gross et al., ; Tecco et al., , ; Zeballos et al., ). However, ordination may not adequately capture the multidimensionality of the niche and thus alternative approaches, including the estimation of n‐dimensional hypervolumes, have been recommended (Blonder, Lamanna, Violle, & Enquist, ).…”

“…Limiting similarity should lead to trait overdispersion as a result of niche partitioning while environmental filtering would lead to trait underdispersion (Catford et al., ). In contrast to the broader plant community literature, the application of null models in community analysis of native and alien traits is not widespread with analyses often restricted to standard statistical comparisons of differences in weightings along multivariate axes (Cleland et al., ; Dainese & Bragazza, ; Tecco et al., ). Furthermore, the few studies that have used null models often simply use data on native and alien species occurrence with no indication of local abundance (Cross et al., ; Davies et al., ; May, Giladi, Ristow, Ziv, & Jeltsch, ; Schaefer et al., ).…”

A plant strategy approach to understand multidecadal change in community assembly processes in Australian grassy woodlands

“…Thompson, Hodgson & Rich ; Lambdon, Lloret & Hulme ; Pyšek et al . ; Jansen, Ewald & Zerbe ; Dainese & Bragazza ; Radford ).…”