Flood changed the community composition and increased the importance of stochastic process of vegetation and seed bank in a riparian ecosystem of the Yellow River

Abstract

Changes in riparian plant community composition and species richness are anticipated as a result of future projected increases in the risk of flood disasters in riparian ecosystems, but the extent and direction of these changes remain uncertain. In this study, we established four blocks comprising six plots in each block to investigate communities of vegetation and seed banks before and after flooding the middle and lower reaches of the Yellow River to investigate how flood influenced the indicator species, alpha diversity, community composition, and community assembly process. The study found that Symphyotrichum subulatum and Rumex acetosa were the indicator species for pre- and post-flood vegetation, as well as for the seed bank. Furthermore, there was a significant increase in all three alpha diversity indices (Shannon-wiener Index; H, Simpson diversity index; D, and Species richness; S) for both the vegetation and seed bank following the flood event. Our analysis of community assembly revealed that the flood event had a notable effect on the relative importance of different processes driving vegetation and seed bank dynamics. Specifically, according to the species composition assembly analysis, we observed a significant increase in the relative importance of stochastic process but decreased in determined process in vegetation. However, the results of multiple regression on matrices indicated the environmental filtering can hardly explain the deterministic process which the patterns of pre-flood vegetation composition were largely controlled by biological interactions, particularly competition among species. Therefore, the reduction of competitive pressures accompanied with the uncertainty of upstream seed banks make local riparian ecosystem more vulnerable to ecological invasions (after the recorded flood event, the invasive species Bidens pilosa was observed to successfully establish). This vulnerability highlights the need for effective protection and management strategies to ensure the long-term sustainability of riparian ecosystems in the middle and lower reaches of the Yellow River.