Effects of local and landscape factors on exotic vegetation in the riparian zone of a regulated river: Implications for reservoir conservation

Riparian zones of regulated rivers are susceptible to species invasion due to a variety of anthropogenic disturbances. Adjacent land use and landscape patterns may be significant drivers in this process in conjunction with direct effects of flow regulation. Understanding different influences on invasion is necessary for regional landscape management. Here we explored the effects of local and adjacent landscape factors on exotic vegetation distribution along the Pengxi River controlled by the Three Gorges Dam. Vegetation data were collected in 5 × 1 m quadrats along transect lines perpendicular to the riverbank between 172 m and 178 m elevation. A total of 21 exotic herbs were found, accounting for 11.3% of all identified taxa. There was greater exotic species richness below 175 m zone directly affected by reservoir flooding. Variation partitioning indicated that landscape structure played a more important role in explaining the degree of invasion than did local variables. As expected, the landscape subgroup "landscape composition" appeared to be more influential than "landscape configuration". Hierarchical partitioning showed that overall invasion increased with increasing adjacent agricultural land uses and flooding presence, but decreased with greater distance to human impacts. Given that re-regulation of the reservoir flow regime is unlikely at this time, we support a landscape approach to riparian vegetation management, where the nature and impacts of the surrounding landscape matrix, and the particular composition and forms of land use and human activity should be considered. Suggestions include establishing buffer reserves, reclaiming abandoned agricultural land, and stricter urban greening regulations.