Road verges facilitate exotic species’ expansion into undisturbed natural montane grasslands

Abstract

Questions How has exotic plant species richness and composition changed in and adjacent to a montane road verge over a 10‐year period? Are montane road verges conduits of exotic species’ dispersal into adjacent, undisturbed hinterland? Location Montane grassland, Maloti‐Drakensberg Transfrontier Conservation Area, South Africa. Methods We surveyed road verge and adjacent hinterland transects (25 × 2 m; N = 80) across an elevational gradient of 1,500–2,874 m a.s.l. in 2007 and 2017. In each transect, we estimated the cover of each exotic plant species and the total cover of indigenous species. Generalised Linear Models were fitted to test if exotic species’ richness and cover had changed over time. A Canonical Correspondence Analysis was used to determine if exotic species’ composition had changed over time. Results Ten years onwards, exotic species richness had increased significantly across the entire elevational gradient, predominantly in the low‐ to mid‐elevational range. Road verge and adjacent hinterland transects differed in species composition in 2007, but no longer in 2017. Conclusion Exotic species richness and composition displayed a high spatiotemporal rate of change. Over time, exotic species increasingly moved into the hinterland from the verges as a result of human‐mediated colonisation pressure. These results indicate that montane road verges are far better conduits for the dispersal of exotic species than previously assumed, and that further colonisation of the hinterland by exotics can be expected.

Abiotic and biotic contexts shape the effect of disturbance on non‐native plant invasion

“…Disturbance may also influence the abundance of non‐native species in nearby non‐disturbed communities, and this influence may also be modulated by the environmental context. Once established in disturbed areas, non‐native species may invade nearby non‐disturbed communities, which are typically dominated by native species (McDougall et al 2018, Speziale et al 2018, Turner et al 2021). If non‐natives move from disturbed communities into the adjacent non‐disturbed vegetation, then non‐native abundance may decline with increasing distance from disturbed communities.…”

Road Impact on Plant Colonization in the Arid Timanfaya National Park

“…Both roads and trails can alter local environmental conditions, promoting the establishment of native and non-native plants adapted to disturbance [16]. Compared to roads, trails are less susceptible to invasions due to lower propagule pressure and impact severity [17,18]. Additionally, roads create unique environmental conditions, including microclimates and soil characteristics, which make them attractive to native and non-native species [19,20].…”