Homogenization and differentiation of Andean ecoregion floras driven by non-native plants: the role of political and environmental factors

• Non-native plants drive both floristic homogenization and differentiation between Andean ecoregions. • Floristic similarity declined with geographic and climatic distances and political dissimilarity. • Geographic distance and political dissimilarity more strongly affect non-native similarity. Non-native plants can drive either homogenization or differentiation of plant communities; however, studies examining these effects at regional scale remain limited. Here, we assessed whether non-native plant introductions contribute to increasing or decreasing floristic similarity between 34 Andean ecoregions and evaluated the role of geographic, climatic, and political factors associated with these patterns. We compiled ecoregion plant composition from the GBIF and GRIIS databases, distinguishing native and non-native plant species. For each pair of ecoregions, we calculated the Jaccard similarity index separately for native and non-native plants and derived a homogenization index for 496 ecoregion pairs. We then regressed the Jaccard indices of native and non-native plants against geographic and climatic distances and political dissimilarity (the proportion of non-shared countries between ecoregion pairs). Both homogenization (37.7% of cases) and differentiation (34.7%) processes were found. Both native and non-native floristic similarity declined with geographic and climatic distances and political dissimilarity. The effect of political dissimilarity on non-native plants was the strongest, but it varies with the geographic distance. These interactions between biogeographic and sociopolitical factors contribute to a better understanding of ongoing floristic change across complex transnational mountain regions.