How do wintering waterbird communities respond to polder restoration in a Ramsar wetland of the Yangtze River Basin, China? A functional and phylogenetic perspective

Wetland restoration has been increasingly implemented to compensate for the substantial loss of natural wetlands, and consideration of multidimensional biodiversity is essential for evaluating how restoration affects the ecological functioning and evolutionary structure of waterbird communities. We explored the effects of polder restoration on the multidimensional diversity (taxonomic, functional, and phylogenetic diversity) and assembly processes of wintering waterbird communities in restored polders, unrestored polders, and natural wetlands within the Shengjin Lake National Nature Reserve of the Yangtze River Basin, China. Waterbird species were categorized into six guilds and their compositions were compared using the Bray–Curtis distance metric. Waterbird species richness and the total branch lengths of the phylogenetic dendrogram (PD) of communities increased during the middle and late wintering periods, and the total branch distance of the functional dendrogram (FD) increased during the middle wintering period compared to unrestored polders, but did not differ from that of natural wetlands. Waterbird individual numbers in the middle and late periods, and FD and PD in the early period, were higher compared with unrestored polders but remained lower than that in natural wetlands. The guild composition of waterbirds in restored polders did not differ from that of unrestored polders, but differed from that of natural wetlands. The observed mean pairwise distances of functional (funMPD) and phylogenetic (phyMPD) dendrograms were not significantly different from the simulated values, implying the dominant roles of stochastic processes in shaping waterbird community structures in the three wetland types. Overall, our findings demonstrate that polder restoration generally increased taxonomic, functional, and phylogenetic diversity, although restored polders have not yet fully matched the biodiversity levels of natural wetlands. This highlights the importance of simultaneously considering multifaceted diversity when assessing the effects of ecological restoration on waterbird communities and reinforces the need for long-term restoration to support waterbird conservation.