Summary1. 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 landuse 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.

Aim  To determine how the distribution and cover of different vegetation types are affected by physical factors and livestock in a mountain range with a long evolutionary history of grazing. Location  Upper vegetation belt of the Córdoba mountains (1700–2800 m a.s.l., 31º34′ S, 64º50′ W) in central Argentina. Methods  Using GIS, we analysed the relationships of plant cover types to physical features (physiography and topography) and indicators of accumulated livestock pressure (distance to human settlements and roads) through multinomial logistic regression. We predicted a present vegetation map which was validated with a real map. We then constructed two maps simulating minimum and maximum values of accumulated livestock pressure for the whole area. Map comparisons allowed evaluation of the possible influence of livestock, both in extension and intensity. Results  Both physical features and livestock pressure influenced the occurrence of vegetation units. The overall accuracy of the predicted map at the pixel level was low (26%) indicating low habitat specificity of the vegetation units. We suggest that some part of the unaccounted for variance was due to livestock pressure patterns that were not fully captured by our indicators. Our models proved adequate for predicting the total percentages of vegetation units at coarser scales. The extrapolations showed that under a history of low livestock pressure, such as in sites far away from human settlements and roads, the area would be dominated by woodlands, tussock grasslands and natural rock outcrops. Under a history of heavy livestock pressure, in turn, rock exposed by erosion, tussock grasslands and natural rock outcrops would dominate. Main conclusions  Vegetation units showed low habitat specificity, and were associated with accumulated livestock pressure, indicating that livestock and its associated activities are important factors structuring the landscape and have important consequences for the integrity of the ecosystem. Results suggest that although this system evolved with large herbivores, it has experienced irreversible degradation processes, and intensification of current domestic livestock pressure is likely to lead to even more land degradation.