Relative cover and leaf economic traits for native and non-native plants across five U.S. ecoregions

Are non-native plants abundant because they are non-native, and have advantages over native plants, or because they possess ‘fast’ resource strategies, and have advantages in disturbed environments? This question is central to invasion biology but remains unanswered. We quantified the relative importance of resource strategy and origin in 69,441 plots across the conterminous United States containing 11,280 plant species. Non-native species had faster economic traits than native species in most plant communities (77%, 86%, and 82% of plots for leaf nitrogen concentration, specific leaf area, and leaf dry matter content). Non-native species also had distinct patterns of abundance, but these were not explained by their fast traits. Compared to functionally similar native species, non-native species (1) were more abundant in plains and deserts, indicating the importance of biogeographical origin, and less abundant in forested ecoregions, (2) were more abundant where co-occurring species had fast traits, e.g., due to disturbance, and (3) showed weaker signals of local environmental filtering. These results clarify the nature of plant invasion: Although non-native plants have consistently fast economic traits, other novel characteristics and processes likely explain their abundance and therefore impacts.