A global analysis of elevational distribution of non-native versus native plants

Aim: Much is known about the elevational diversity patterns of native species and about the mechanisms that drive these patterns. A similar level of understanding is needed for non-native species. Using published data, we examine elevational diversity patterns of non-native plants and compare the resulting patterns with those observed for native plants. Location: Global. Methods: We compiled data from 65 case studies on elevational diversity patterns of non-native plants around the world (including 32 cases in which both non-native and native plants were sampled). We compared the elevational distributions (upper and lower limits, and extents) and diversity patterns of non-native and native species. Results: Compared to native plant species, the elevational diversity patterns of non-native plant species were more negative (47% vs. 13%) and less unimodal (44% vs. 84%). That is, non-native species richness tended to be highest at lower elevations, whereas native species richness peaked at mid-elevations. In cases where species richness for both non-native and native species on the same mountains showed unimodal patterns in relation to elevation, maximum values in species richness occurred at lower elevations for non-native species. Main conclusions: At present levels of invasion, non-native and native species show different patterns in both distribution and diversity along elevational gradients worldwide. However, our observations constitute a snapshot of ongoing, long-term invasion processes. As non-native species typically show strong associations with human activities, future changes in human population (e.g. growth and migration), land use and climate change may promote upward spread of non-native species and may thus increase risks of impact on native species and communities.