Riparian vegetation succession of sandbars and response to inundation under the regulation of the Three Gorges Reservoir

Human activities, especially the regulation of reservoirs, has a significant impact on the succession of riparian vegetation. It is already known that the riparian vegetation and the river hydrology have a coupled relationship, yet comprehensive study is still needed to investigate the variation trend of vegetation in the riparian zone of the Middle Yangtze River and its quantified response to the inundate frequency affected by the operation of the Three Gorges Reservoir (TGR). In this study, we collected multi-source remote sensing images, hydrological and meteorological data of the Middle Yangtze River from 1986 to 2021 to discern the vegetation variation character and the inundation dynamics of two typical sandbars located downstream of TGR. Our results showed that the riparian vegetation of both sandbars had a trend of fluctuating growth during the whole study period, and the growth rate increased significantly after the operation of TGR. Affected by the discharge regulation and water storage of TGR, the vegetation occurrence frequency of sandbars has significantly increased correspondingly, as the inundation frequency has decreased. Further analysis revealed that the critical annual inundation days corresponding to suitable vegetation growth zones significantly decreased, and the vegetation communities underwent a succession toward a direction more suitable for terrestrial growth. These results can help understanding the impact of dam construction on the riparian vegetation succession. • Remote sensing (1986–2021) shows post-dam vegetation increases on sandbars. • Vegetation expands as inundation frequency decreases under reservoir regulation. • Hydrological regulation shifts vegetation growth zones to lower inundation durations. • Riparian vegetation transitions from aquatic to terrestrial dominated communities.