Evaluating impacts of plant invasions in mountains

Alpine and montane regions globally hold key biodiversity, yet they are threatened by various human pressures that are projected to increase during the 21st century. Invasive species are considered one of the main drivers of biodiversity loss globally. Nevertheless, until recently, alpine and montane systems were among the few ecosystems where invasive plant pressure remained limited. However, recent assesments and reports suggest that this situation is currently changing, as climate warming, land use change, pollution and higher rates of introductions expand species distributions into previously less disturbed mountain habitats. High-elevation habitats can therefore be used as valuable model systems to study invasion patterns and mechanisms. As a result, mountain ecosystems provide valuable model systems for studying invasion patterns and underlying mechanisms, particularly for plants, whose distributions and dynamics have been extensively monitored across regions, to better understand these species future impacts.
In this study, we assess the magnitude and mechanisms of the negative environmental impacts caused by alien plant species occurring in mountain ecosystems worldwide. Specifically, we compiled a list of 564 species recorded as naturalized in 18 mountain regions based on standardized road surveys along elevational gradients conducted by the Mountain Invasion Research Network (MIREN). We evaluated these species using the Environmental Impact Classification for Alien Taxa (EICAT), an objective and transparent method recognized by the IUCN to classify alien species according to the severity of their impacts on native species populations and the mechanisms driving these impacts. Assessments included impacts occurring in both mountain and non-mountain ecosystems.
Our preliminary results suggest that empirical evidence on the environmental impacts of most alien plant species remains limited or entirely lacking, particularly in mountain environments. For the species with available information, the most frequently reported impact mechanisms include competition with native species, indirect effects mediated through interactions with other organisms, and allelopathic effects, such as disruption of pollinator networks.