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.