Nurse shrubs to mitigate plant invasion along roads of montane Neotropics

Abstract

Roads are known to be a major factor in the ongoing spread and establishment of invasive plants by modifying habitats and providing movement corridors. Controlling plant invasion or restoring highly-invaded areas along roads is a challenging task in current conservation practice. We aim to investigate the possible facilitative effects of nurse shrubs on native vs. exotic species in order to provide applications for conservation and restoration of highly invaded roadsides areas in megadiverse montane areas of Brazil. We estimated the abundance of each plant species (native and exotic) in paired roadsides with and without pioneer nurse shrubs (Baccharis spp.), and measured whether they were facilitated (i.e., growing underneath native nurse shrubs), using a Facilitation Value metric. We found that the proportion of exotic species was 27% greater in areas without the nurse shrubs. In addition, predicted probability of nurse shrubs as facilitators of native species was 61% greater than that of exotic species. Pioneer nurse shrubs that alleviate the environmental shift generated by the construction and use of roads (e.g., disturbed soils with low nutrient content) may represent an interesting alternative to mitigate exotic plant invasion along roadsides, a current global priority for biodiversity conservation. Decision-makers considering whether to build, improve, and maintain roads should take into account the potential spread of exotic plants and the use of nurse shrubs to prevent or mitigate plant invasiveness.