Flooding and land use drive variation in phylogenetic structure and taxonomic diversity of plant communities in urban riparian zones of a regulated river

Abstract

Riparian zones in urban areas have been persistently affected by human-mediated disturbances such as dam construction and urbanization. However, the driving patterns of variation in the phylogenetic diversity (PD) and taxonomic diversity (TD) of urban riparian plants remain unclear due to the complexity of the urban riparian environment. Therefore, 15 sample sites along rivers affected by the Three Gorges Dam in the urban areas of Chongqing, Southwest China, were selected to investigate the variations in TD and PD and their driving factors in riparian plant communities subjected to multiple disturbances. The middle position of the riparian zone had the highest plant TD compared with that in the upper and lower positions, while the upper position had the highest plant PD. Flood duration and the proportion of urban green space within a 500 m radius (PGS) adversely affected riparian plant TD. However, invasive plant TD was positively affected by the flood duration, suggesting that invasive plant species have a greater ability to occupy ecological niches under flood stress than native plant species. Fragmented, heterogeneous surrounding landscapes drive plant invasions. Phylogenetic structure was aggregated, indicating an environmental filtering strategy of the riparian plant community. Plant PD was positively related to riparian position and soil pH. It was also negatively affected by PGS probably due to fragmentation in nearby urban green spaces. Flood duration and PGS significantly influenced the composition of riparian plant communities. A majority of invasive species were flood tolerant, which may threaten the stability of riparian ecosystems. The implications for maintaining riparian plant diversity in the riparian zones along the watersheds heavily disturbed by dam construction and urbanization were explored. Our research contributes to sustainable planning and ecological restoration strategies that support the resilience and functionality of urban riparian zones in reservoir-regulated basins worldwide.