Abstract
Protected areas are among the key elements of global biodiversity conservation strategies and aim to conserve native species, habitats and ecosystems. Globalisation has led to increased introductions of species outside their natural range. In their new environment, some of these non-native species have the potential to affect ecosystems and compete with or threaten native species. The environment in close proximity to protected areas is likely to be the stepping stone for non-native species to become established in protected areas. However, little is known about the role that protected area surroundings play in the permeability of protected areas to non-native species. In this thesis, I focused on protected areas and their surrounding belts to address the issue of permeability to non-native species. Examining protected areas in Norway, I showed that non-native species surrounding protected areas have a qualitative impact on the community of non-native species in protected areas. Moreover, the proportion of invasive species was higher in protected areas (40 %) compared to their belts (12 %). The number of non-native species in the surrounding areas also significantly determined the number of non-native species in protected areas. I have also highlighted the dynamics of colonization from the belts to the protected areas by showing that non-native species were detected in the protected areas on average several years after they were recorded in the belts. In addition, I showed in four European countries that the type of land use and land cover in the proximity and within protected areas plays a central role in the establishment of non-native species in protected areas. Anthropogenic land use and land cover around protected areas promoted the establishment of non-native species inside protected areas, regardless of the land use and land cover present in them. Finally, I investigated the colonization dynamics of Acacia dealbata, an invasive t ree species, in and around protected areas in central Portugal over the last twenty years. I showed that disturbances by fires and the loss of tree cover had a significant positive effect on the presence of the species. This thesis highlights the importance of the protected area surroundings for the colonization of non-native species. This is particularly relevant for future management strategies for non-native species in protected areas.