Successful management and restoration of coastal vegetation requires a quantitative process-based understanding of thresholds hampering (re-)establishment of pioneer vegetation. We expected scouring to be important in explaining the disappearance of seedlings and/or small propagules of intertidal plant species, and therefore quantified the dependence of scouring on plant traits (flexibility, size) and physical forcing by current velocity. Flume studies with unidirectional flow revealed that scouring around seedlings increased exponentially with current velocity and according to a power relationship with plant size. Basal stem diameter rather than shoot length controlled scouring volume. Flexible shoots caused far less scouring than stiff shoots, provided that the bending occurred near the sediment surface as was the case for Zostera, and not on top of a solid tussock base as we observed for Puccinellia. Therefore, shoot stiffness is likely to strongly affect the chances for initial establishment in hydrodynamically exposed areas. Plant traits such as shoot stiffness are subject to a trade-off between advantages and disadvantages, the outcome of which depends on the physical settings.@en

Biophysical interactions between organisms and hydrodynamic forces are a main determinant of geomorphology of intertidal areas. Especially vascular plants have striking effects on intertidal geomorphology. Seagrasses and salt-marsh plants that inhabit intertidal areas are knownto have strongly contrasting morphologies. Differences in growth strategy by which plants cope with hydrodynamic forces are particularly interesting, as modification of these forces determine if and how species enhance sediment accretion. This raises the question to what extent differences in plant growth strategies directly affect the biogeomorphological development of the estuarine landscape. In this paper we i) provide a concise overview of our recent research on this topic, which has often been published in the more ecological literature, and ii) indicate how we have recently assessed the geomorphological effect of different vegetation types, by combining a series of unidirectional flow studies in flumes and hydrodynamic modeling at the landscape with a mechanistic hydrodynamic model (Delft-3D).@en