Floodplain forests provide valuable ecosystem services, yet human activity has degraded many of these riverine systems. Previous investigations of floodplain forest composition have frequently focused on flooding without incorporating successional dynamics; however, their restoration requires understanding both. We investigated floodplain forest composition along both flooding and succession gradients. River meandering builds new floodplain land with a variable microtopography and diverse levels of flood exposure. We compared vegetation to floodplain land ages on chronological sequences. Our results suggest that diverse species assemblages in floodplains result at least in part from geomorphic change. Ensuring that flood pulses continue to erode riverbanks and deposit sediments on sandbars and in floodplains is essential to the restoration and conservation of diverse forest assemblages in these ecosystems.