Biological invasions are widely recognized as an important component of human-induced global environmental change, and invasive alien species (IAS) have been listed among the causes of habitat decline and loss. Vascular plants are one of the most investigated taxonomic groups in the field of invasive biology. However, their patterns and co-occurrence dynamics have only recently come into the spotlight, along with the factors driving alien plant assemblages. The abundance and dominance of alien species seem to have a more relevant influence on plant communities than the number of alien species, and some authors have started to qualify and quantify the role of alien species in different vegetation and habitat types.

However, to date, studies specifically investigating alien-dominated plant communities are limited, while the majority are still mostly focused on natural and semi-natural phytocoenoses with few or no aliens.

This Topical Collection welcomes studies dealing with all aspects of alien plant species occurrence at the community level, such as the description and classification of vegetation types dominated or co-dominated by alien plants, studies on ecological processes involving alien species, investigations into the functional role of alien species in the communities, assessment of the impacts (positive, neutral, or negative) that alien species can have on other components of biodiversity (e.g., pollinators), and contributions analyzing threats from alien species to the conservation of relevant vegetation and habitat types. Furthermore, the first checklist of alien-dominated vegetation in Italy, published in 2020, can be implemented and updated.