Primary succession of vegetation on large river bars affected by floods: Key factors for successful river restoration

Vegetation succession is a fundamental principle of ecological restoration. This study investigated early primary succession on large river bars in a monsoon climate, examining how flood magnitude influences successional processes. Results showed that massive floods altered bed material composition, leading to significant changes in direction of plant community change. Vegetation established on substrates coarser than sandy loam persisted, while finer particles led to vegetation loss. In erosional zones, Salix chaenomeloides communities were maintained through cyclic succession, whereas depositional zones experienced retrogressive succession, with S. chaenomeloides replaced by Phragmites japonica. Under moderate to low flood influence, both species acted as pioneers on coarse, nutrient-poor substrates with low organic matter. These findings highlight that changes in vegetation dynamics are driven by river flood intensity through their influence on substrate composition. On newly formed mid-channel bars, high flood-induced erosion promotes cyclic succession dominated by S. chaenomeloides. In contrast, low-energy depositional zones with sandy loam support regressive succession toward P. japonica. Thus, effective restoration depends on maintaining suitable bed material conditions specific to erosional and depositional environments. Managing substrate characteristics across geomorphic zones is essential for the stable establishment and persistence of vegetation on bare sandbars in large river systems.