Poa annuais the only flowering plant species that has established a breeding population in the maritime Antarctic, through repeated anthropogenic introduction. The first appearance of this species in the Antarctic was observed in 1953. Annual bluegrass inhabits mainly anthropogenic sites, but recently has entered tundra communities. The functioning ofP. annuain the Antarctic could not have been possible without adaptations that enable the plants to persist in the specific climatic conditions typical for this zone.Poa annuais highly adaptable to environmental stress and unstable habitats: huge phenotypic and genotypic variability, small size, plastic life cycle (life-history types ranging from annual to perennial forms). The spreading ofP. annuain the Antarctic Peninsula region is a classic example of the expansion process following anthropogenic introduction of an invasive species, and illustrates the dangers to Antarctic terrestrial ecosystems that are associated with increasing human traffic.

Biological invasions represent significant economic and conservation challenges, though it is widely acknowledged that their impacts are often poorly documented and difficult to predict. In the Antarctic, one non-native vascular plant species is widespread and studies have shown negative impacts on native flora. Using field “common garden” experiments, we evaluate the competitive impact of the increasingly widespread invasive grass Poa annua on the only two native vascular species of Antarctica, the forb Colobanthus quitensis and the grass Deschampsia antarctica. We focus on interactions between these three plant species under current and a future, wetter, climate scenario, in terms of density of individuals. Our analysis demonstrates Poa annua has the potential to have negative impacts on the survival and growth of the native Antarctic vascular species. Under predicted future wetter conditions, C. quitensis communities will become more resistant to invasion, while those dominated by D. antarctica will become less resistant. Under a recently developed unified scheme for non-native species impacts, P. annua can be considered a species that can cause potentially moderate to major impacts in Antarctica. If current patterns of increased human pressure and regional climate change persist and mitigation action is not taken (i.e. reduction of propagule pressure and eradication or control measures), P. annua is likely to spread in Antarctica, especially in the Antarctic Peninsula region, with significant negative consequences for some of the most remote and pristine ecosystems worldwide. Tighter biosecurity across all operators in the region, improved surveillance for the species, and prompt, effective control actions will reduce these risks.