Exploring abiotic and anthropogenic drivers of alien plant species distribution in the Alps: bioclimatic origin matters!

Plant invasions into mountain ecosystems are influenced by interacting abiotic and biotic processes. In order to establish and spread in a new area, alien plants must be able to tolerate the prevailing climatic conditions, i.e., the greater the degree of climate matching between the invaded region and the species' native region, the higher is the likelihood of establishment. In this study, we assess the role of abiotic and anthropogenic variables driving both alien plant species richness and composition in mountain regions. In addition, we assess whether the climatic pre-adaptation of alien plant species determine different responses to environmental processes. The two questions are examined using the alien flora of the European Alps. Area was the most important predictor of alien plants distribution, followed by anthropogenic disturbance. Climatic conditions had a smaller direct effect on species richness, while temperature appeared as a key driver in determining community differentiation. Considering the bioclimatic origin, both temperature and urban elements showed a significant interaction with bioclimatic origin. Only Holarctic species show a significant negative relationship with temperature, while the effect of human pressure was strongest for tropical species. Our results show that abiotic and anthropogenic processes affect the distribution of alien plants in mountain ecosystems, but differently for species of different bioclimatic origin. In particular, we showed that the climatic pre-adaptation of Holarctic species in association with anthropogenic disturbance can increase the level of invasion of alien plants in mountain areas. Our results also reveal a strong influence of human pressure on tropical species, despite their low adaptability to urban conditions.