Search

We performed a comprehensive comparative study of functional traits in coexisting alien and native woody species in order to examine the strategies related to resource use and dispersion underlying alien success in mountain Chaco woodlands of central Argentina. Our approach integrated seemingly contrasting pieces of evidence in the region. We specifically assessed whether (i) the 'functional acquisitive trend' previously observed along a broad environmental gradient accounts for woody alien naturalization when considering a single mesic ecosystem; or (ii) more than one trait syndrome is important among alien species, which would be more in line with the context-dependent nature of biological invasions at a local scale. Fifteen vegetative and regenerative traits were measured on the most common 14 native and 11 alien woody species. We compared the attributes of (i) native and alien species and (ii) between native species and two contrasting groups of alien species identified in the previous analysis. The overall trait comparison (i) showed that, in terms of vegetative attributes, woody alien species tend to be on average more acquisitive than native species. However, (ii) two contrasting syndromes were revealed among alien species: a group of seven deciduous species with acquisitive attributes; and a group of four evergreen species showing markedly more conservative attributes than the first group. The functional attributes of 'conservative aliens' completely overlapped with the range observed for native species, except for an exclusive dispersal phenology and a stronger tendency to clonal spread. Acquisitive aliens, in turn, proved to be beyond the range of attributes of native species, at the acquisitive extreme, as they did in previous comparisons. Despite their importance, general trends in plant functional attributes across regions and ecosystems can sometimes obscure trends at more local scales that are nevertheless important for the understanding and management of particular systems. Our study concurs with previous general trends when looking at the overall comparison between native and alien species, but unveils contrasting functional strategies among alien species when examining their attributes more closely, even within the same ecosystem. [ABSTRACT FROM AUTHOR]

1 Two main views have been put forward to explain whether coexisting alien and resident plant species should show converging or diverging functional attributes. According to the ‘try-harder’ hypothesis, successful aliens should differ from resident species with traits that allow them to deal better with the local conditions than resident species. On the other hand, the ‘join-the-locals’ hypothesis stresses the importance of filtering by environmental factors and predicts strong functional trait similarities between alien and native species, especially among the dominants. 2 On the basis of a functional trait comparison between native and alien species of central-western Argentina across five contrasting ecosystems and four land-use regimes, we tested these hypotheses over a broad range of habitats. We built a data set with common measurement methods and biogeographical factors but strongly varying environmental conditions, ranging from mesic to extremely dry, and from nearly pristine to heavily disturbed. 3 When considering all species together, the main trend of variation in trait syndromes was between acquisitive (tender, large leaves, with high specific area) and conservative (tough, small leaves, with low specific area and low nutrient content). Although both native and alien species appeared to be well spread across the whole range of trait variation, woody alien species showed a significantly more acquisitive set of attributes (higher specific leaf area, larger and thinner leaves, lower wood density) than native species. No significant difference was detected between herbaceous alien and native species. These general trends were maintained under contrasting climatic and land-use conditions. 4 Synthesis. The patterns detected for herbaceous species were in line with the ‘join-the-locals’ hypothesis. In contrast, those found for woody species, with woody alien species showing more acquisitive attributes than native species in more resource-rich habitats, provide partial support for the ‘try-harder’ hypothesis. Overall, our findings reinforce the idea that a universal suit of attributes is unlikely to explain alien plant distribution. They also stress the need for caution when mixing major life-forms in comparative plant trait analysis. [ABSTRACT FROM AUTHOR]