Native and exotic plant species respond differently to ecosystem characteristics at both local and landscape scales

Quantitative integration of factors that potentially affect exotic species richness and abundance at multiple spatial scales is relatively scarce in the literature. Our aim was to address this gap by evaluating the relative importance of the biotic community, abiotic factors, and landscape characteristics on the establishment and spread of native and exotic plant species. We assessed the effect of these factors on exotic and native species richness and abundance, and used regression tree and variation partitioning analyses to evaluate how these predictors interact to favor or limit exotic and/or native species. We found that landscape filters were especially important for the arrival of both native and exotic species, whereas biotic factors seemed to regulate the abundance of plant species once they were present within the system. However, the combined effects of different types of predictors explained the largest fraction of total variation in all models regarding exotic species. Furthermore, significant predictor variables had opposite effects on native versus exotic species at both local and landscape scales, which suggests that some ecosystem properties affect native and exotic species differently. Exotic species richness and abundance were increased by low values of native species cover and diversity, high landscape heterogeneity and edge density, human disturbances (e.g., mowing and soil disruption), land use activities (e.g., developed and agricultural areas), and proximity to transportation systems, especially highways. However, exotic species were less common in areas with low anthropogenic disturbance, where natural disturbances seemed to favor native plant species.