Sorting of seeds by hydrochory

The species composition of riparian vegetation is determined by a variety of processes, including the dispersal of seeds. The seed types that end up at certain locations are determined by their particular characteristics as well as the prevailing hydrology and the physical characteristics of the river channel. A conceptual model is proposed to identify the hydraulic processes involved in the hydrochory pathway that may lead to differential response of different seed types and hence their sorting. The results of a series of laboratory experiments are presented to demonstrate the sorting between seed types by these processes. The behaviour of non‐buoyant seeds during settling and entrainment is shown to be consistent with that of mineral sediments, and their sorting can therefore be described by existing sediment transport theory. Significant sorting of buoyant seed types takes place during transport under the influence of wind and during ingress into marginal emergent vegetation, trapping by vegetation and stranding during receding flows on sloping channel banks.