Abstract:  Alien plant species are a growing concern in protected areas, yet little information is available on the role of roads as corridors for alien species and the effects of elevation, land use, and landscape context in these invasions. These concerns are of particular interest in temperate zones of South America, where protected areas have high concentrations of endemic species. We studied roadside alien plant communities and forest‐road edges in Villarrica and Huerquehue national parks in the Andean portion of south‐central Chile. We sampled alien species and their abundance along 21 km of roads inside parks and 22 km outside parks, using 500‐m roadside transects. We also sampled plant species and recorded their abundance in 15 transects located perpendicular to forest‐road edges in four forest types. Of the 66 alien species encountered along roadsides, 61 were present outside parks and 39 inside parks. Elevation and alien species richness along roadsides were significantly and negatively correlated ( R 2 =− 0.56 , p < 0.001). Elevation, land use, and their interaction explained 74% of the variation in alien species richness along roadsides ( p < 0.001). Transects located in pasture or disturbed secondary forests had significantly more alien species. We found no significant edge effect on native and alien species richness in any forest type. Few alien species have percolated into forest interiors. Native and alien diversity in edge plots were not related. Almost half the alien species belonged to three families and 85% were native to Eurasia. Our results suggest that alien species are moving into parks along road corridors and that elevation and land use of the matrix influence these invasion processes. Our findings corroborate the importance of early detection and control of invasive species in protected areas and highlight the importance of considering surrounding matrix land use in developing conservation strategies for reserves.