Climatic factors and anthropogenic pressures drive plant invasions in Natura 2000 habitats in Poland

Invasive plants pose an ecological threat around the world. Their influence can also be observed in protected areas such as the European Ecological Network Natura 2000. Although invasional processes can endanger protected habitats, the specific impact of invasive species in such areas and the factors that determine their spread remain understudied. This study aimed to analyse the level of invasiveness and factors correlated with invasions in five selected habitat types protected under the EU Habitats Directive in Natura 2000 areas, based on State Monitoring of Natura 2000 data. A total of 2,096 sites with balanced distribution across the country were analysed, belonging to mesic broadleaf forests, riverine habitats, dry grasslands, mesic wet grasslands and mires. Our study confirmed the presence of 45 invasive species and two potentially invasive species. The most frequently observed species were Impatiens parviflora, Prunus serotina, Solidago gigantea, Erigeron canadensis, Solidago canadensis , and Bidens frondosa . We then analysed the correlation between the presence of invasive species in Natura 2000 sites and 38 variables relating to habitat type, land use, human pressure, climatic conditions, migration corridors, and the nature protection status of the surrounding area. The most important variables correlated with invasions were habitat type, temperature seasonality, mean monthly precipitation of the coldest quarter, mean daily minimum near-surface air temperature of the coldest month, distance from rivers and main roads, and mean population density within a 5 km radius. This study demonstrated the effectiveness of the State Monitoring Programme in detecting invasive species and analysing invasional processes. It could be used to inform the planning of future invasion management and prevention strategies.