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Green roofs can mitigate a number of urban environmental problems when green roof plant communities provide ecosystem services. However, this perspective may fail to address ecological aspects of the plant community. In particular, it does not account for the potential for green roofs to facilitate biological invasions. We consider current research in green roof ecology in light of the literature on biological invasions, focusing on plant invasion. We evaluate the role of species composition and novel communities, species interactions, succession, and dispersal on the trajectory of green roof plant communities. Green roofs have the potential to introduce invasive species through initial plantings, to become dominated by invasive species, and to spread invasive species, and we provide recommendations for plant selection and maintenance to reduce the risks of facilitating plant invasions to surrounding communities.