Influence of habitat on the phylogenetic structure of Robinia pseudoacacia forests in the eastern Loess Plateau, China

Abstract

Robinia pseudoacacia forests are an important component of plantations in the Loess Plateau, China. These forest communities with abundant understory plants have become interesting for ecologists and conservationists. However, most studies on species diversity focus on species richness, while few focus on the phylogenetic dimension of plant communities, especially the influence of habitat on phylogeny. In this study, we explored the species richness, phylogenetic diversity and phylogenetic structure of understory plant communities at different site types in the Caijiachuan watershed of Shanxi, China. Our findings indicated that the floristic composition in this area was variable and differed significantly among different habitats. Moreover, the introduction of R. pseudoacacia forests enhanced the heterogeneity of understory environments and provided migration opportunities for species, which played an important role in maintaining and increasing biodiversity. As expected, species richness was closely correlated with phylogenetic diversity, but species-rich communities did not always have the same high level of phylogenetic diversity. We also found that the highest values of them occurred on semi-sunny and semi-shady downhill slopes respectively, and the phylogenetic structure of these two sites was overdispersed. We suggest that these sites are key protected communities, as they may maximize the evolutionary potential of plant communities to respond to future environmental changes. In addition, our data indicated that light conditions have a significant impact on understory plant communities, which is further intensified by soil moisture constraints. Thus, forest managers should provide suitable environmental conditions for the invasion and settlement of understory plants through appropriate management measures, such as canopy pruning and thinning.