Bird species richness and abundance in riparian vegetation invaded by exotic Reynoutria spp.

Impacts of invasive alien plant species are threatening biodiversity worldwide and thus it is important to assess their effects on particular groups of organisms. However, such impacts were studied mostly in case of plant or invertebrate communities and our understanding the response of vertebrate species to plant invasions remains incomplete. To improve our knowledge in this respect, we studied bird communities in riparian vegetation along the rivers with different levels of Reynoutria spp. invasion in the Czech Republic. These findings will be interesting for basic ecology enhancing our knowledge of consequences of plant invasions, as well as for conservation practice. We surveyed understory bird species in 26 vegetation blocks along parts of three rivers running from the Beskydy Mountains in spring 2011. We used principal component analysis to assess vegetation structure of particular blocks and the first axis ordinated the blocks according to the degree of invasion by Reynoutria spp. Using generalized linear mixed-effects models we found that counts of Motacilla cinerea, Cinclus cinclus and Sylvia borin, as well as the total bird species richness, significantly decreased with increasing degree of Reynoutria spp. invasion, while Acrocephalus palustris showed the opposite pattern. These results suggest that Reynoutria spp. impacts negatively on the species strictly bond with river banks and habitats specialists, whereas habitat generalist species like Sylvia atricapilla were not affected. Preference of Acrocephalus palustris for Reynoutria spp. corroborates affinity of this species to large invasive herbs observed also in other studies. Our study showed that Reynoutria spp. invasion can reduce species richness of understory birds in riparian communities. Although the distribution of this plant species is still quite limited in central Europe, our results suggest that its more widespread occurrence could potentially threat some river bank bird species. Therefore, we urge for development of management actions that will act counter the Reynoutria spp. invasion.