Struggling to maintain native plant diversity in a peri-urban reserve surrounded by a highly anthropogenic matrix

High human density and land use intensity often coincide with biodiversity hotspots making peri-urban reserves a keystone for conserving natural remnants in a highly anthropogenic matrix. Particularly, intense propagule pressure by alien plant species can pose a threat to native biodiversity. However, little is known about the factors that determine invasibility and the role of roads and other human disturbances for such small protected areas. Within a peri-urban reserve close to the city of Concepción, south-central Chile, we investigated the influence of different site and landscape characteristics on the richness of native and alien plant species across different habitat (ruderal, road and forest sites) and forest types (native and alien dominated forests). Compared to other protected areas, alien species were frequently found in this reserve indicating the importance of urban areas as source for alien species. Aliens concentrate around disturbed ruderal and road sites, facilitating their spread into the reserve. Natural forest areas are less invaded until now. Within forests alien plant species richness was, however, positively associated to the proximity to disturbed landscapes. Forests dominated by alien tree species within the reserve are not the source for alien species within natural forests, but they negatively affect native species richness by replacing adequate seed sources. In order to prevent a further spread of alien species into peri-urban reserves, large scale anthropogenic disturbances should be minimized, already invaded sites must be monitored and buffer-zones protecting reserves from surrounding land use activities should be established.