Species turnover of wetland vegetation in northeastern China: Disentangling the relative effects of geographic distance, climate, and hydro-geomorphology

Species turnover is a central issue in plant ecology and has a high significance in conservation of biodiversity and ecosystem management. Niche differentiation and dispersal limitation are the two main processes controlling species turnover of upland vegetation. However, our understanding of the drivers of plant species turnover in wetlands remains poor. To comprehensively disentangle the influences of niche differentiation and dispersal limitation on the plant species turnover in wetlands of the Great Hing'an Mountain valleys, we not only considered two plant functional groups (herbs and shrubs), but also took hydro-geomorphological variables into account when quantifying the effect of environmental differences on species turnover. We found that species similarity, measured by the Jaccard similarity index, decreased with geographic distance for both herbs and shrubs with a decay rate being -0.39 and -0.49, respectively. We then partitioned the variance of species similarity based on type III sums of squares in partial correlations. Results showed that geographic distance and the joint effect were the most important factor explaining the species turnover of herbs and shrubs respectively when representing environmental constraints with climatic variables only. The total explained variances were improved by 15.93% for herbs and 24.69% for shrubs after including hydro-geomorphologic measurements. Our study showed that both dispersal limitation (represented by geographic distance effects) and niche differentiation (represented by climate and hydro-geomorphology) played important roles in shaping wetland species turnover, but their relative effects differed by plant functional groups. Considering hydro-geomorphological characteristics can better elucidate the role of the environment in shaping species turnover in wetland systems than using climatic variables alone.