Invasive species can have negative effects on native ecological communities through their impacts on species diversity, soil properties and ecosystem services that contribute to rural livelihoods. Restoration efforts to re-establish native plant communities have been particularly challenged by continued invasion of undesirable ruderal species that are more likely to establish in highly disturbed areas. Mikania micrantha is a fast-growing, allelopathic vine from Central and South America that is rapidly invading ecosystems of Asia and the Pacific, including sub-tropical Nepal. We asked, how does M. micrantha affect the distribution and abundance of native plant species that are culturally important to local human communities? Using a unique, interdisciplinary design, we surveyed the change in herbaceous vegetation composition over 18 years (1996, 2000, 2007, and 2014) in twenty-one, socio-economically diverse but ecologically similar community forests in the rural buffer zone of Chitwan National Park, Nepal. This region, considered a biodiversity hotspot, is of critical importance for both the livelihoods of local people and the conservation of endangered animal species. We hypothesized that cover of M. micrantha and an additional exotic plant, Chromolaena odorata, will be negatively related to native species diversity and richness, and positively related to the abundance of exotic ruderal species.
Results/Conclusions
Contrary to our hypotheses, M. micrantha abundance is positively related to herbaceous species diversity (Pearson correlation=0.94, p= 0.02) but C. odorata has no effect (Pearson correlation= -0.17, p = 0.77). This correlation implies M. micrantha either establishes in areas with higher diversity or it indirectly increases diversity, perhaps by facilitating the establishment of ruderal species. Herbaceous species diversity in community forests was significantly lower prior to M. micrantha invasion in 1996 (Shannon-Wiener index=1.4 ± .55) compared to 2014 (Shannon-Wiener index=2.65 ± .20), despite the increase in non-native species cover. Evidence of the simultaneous increase in species diversity and non-native species abundance across the community forests supports our hypothesis that invasive species are assisting ruderal species establishment. A better understanding of the underlying ecological drivers assisting species invasion could inform land managers about the challenges associated with future restoration efforts.