Effects of disturbance and alien plants on the phylogenetic structure of riverine communities

Abstract

Questions: Phylogenetic analyses provide important insights in the study of biological invasions. Previous studies have shown contrasting effects of alien species on the phylogenetic structure of recipient communities. In this study, we focus on two riparian plant communities with contrasting natural disturbance regimes: riparian forests and river bar communities. We ask whether these communities differ in alpha diversity and degree of plant invasion. Further, are the phylogenetic diversity (PD) and structure of these habitats related to the level of plant invasion?. Location: Northern Spain. Methods: We determined level of plant invasion in forest and river bar vegetation plots, and calculated PD using mean pairwise distance (MPD) and mean nearest taxon distance (MNTD). We applied null models to analyse the phylogenetic structure of plots, and we tested whether inclusion of alien plant species was associated with differences in observed phylogenetic structure. Results: River bar plots experienced more invasion than forest plots, but the level of invasion was only related to the PD of native species in forests. Most plots had random phylogenetic structure, with a minority of plots tending to phylogenetic overdispersion in forests and to phylogenetic clustering in river bars. MPD increased with the inclusion of alien plant species in forest plots, suggesting phylogenetic overdispersion, while no such pattern was detected with MNTD. MPD increased slightly with increasing invasion in river bar plots, suggesting reduced clustering, while MNTD values decreased with increasing invasion, suggesting the opposite trend. Conclusions: Invasion by alien plants is differentially associated with phylogenetic structure in riparian habitats with different disturbance levels. Our results contrast with those of previous studies of plant invasion of riparian communities, which suggests geographic and ecological variation in the relationship between invasion and phylogenetic community structure in riparian systems. Research is needed to identify the causal factors underlying this variation. © 2020 International Association for Vegetation Science