Seedbank Formation and Initial Recruitment of Riparian Vegetation onto Bare Bar in Sand Bed River

The dynamics of riparian vegetation can not only affect the flood management but also the ecological balance. The first stage for the dynamics of riparian vegetation is the seed transportation by dispersal, and then, deposits into the soil seedbank. The second dispersal, such as hydrochory and wind, has been reported to be the main factor on the formation of soil seedbank, and it may be influenced by the hydrological, the morphological variables, and the condition of ground surface.

The field survey of UAV monitoring and soil sampling were conducted in a sand bed river to understand the distribution of soil seed bank and initial vegetation recruitment on bare bars.

The seed density at the shoreline is tightly related to the change of flow regime, the moderate water level fluctuation seems to be the most favorable condition for the seed dispersal and seed deposition since the seed density was highest. The seeds density after the large flood at shoreline is lowest, this might be caused by the serious erosion of river bed.

The analysis of soil seedbank at dunes was separated from the ordinary analysis (shoreline and flat area of sandbar) since dune on sandbar is a special topography with its elevation difference of the upstream and the downstream side. The seed density at the shoreline is higher than it at the flat area, and the seed density and the rate of fine sediment at the downstream of dune is much higher than it at the upstream. The possible reason is that the shoreline with high frequency of inundation has advantage to accumulate seeds. The elevation difference of dune may also promote seeds deposition.

The field survey results can be summarized that the hydrochory is thought to be the dominant vector for seed dispersal to shoreline, and wind seems the significant dispersal method to the flat area and dunes of sandbar.