Vegetation distribution on a gravel point bar on the Wilson River, NSW: A fluvial disturbance model

Vegetation distribution on a gravel point bar on the Wilson River, on the mid-north coast of New South Wales, is determined by the pattern of geomorphic units that comprise the point bar. Morphodynamic interactions between vegetation and fluvial processes vary for these differing geomorphic units, reflecting a combination of successional and hydrogeomorphic processes. Fluvial reworking by floods has created a mosaic of geomorphic units which support vegetation at differing phases of regeneration and growth. Stands of river oak on channel-marginal ridges promote gravel deposition. These features are separated by a series of unvegetated chute channels at the bar head. A range of mid-lower canopy species and more substantive ground cover are evident at the bar core and on the channel-marginal bench, where the dense vegetation cover promotes deposition of fine sands and silts. The bar core is separated from the bench by a scoured flood channel, which supports a lower diversity of vegetation. An extensive, unvegetated bar platform has developed at the apex of the bend. The primary geomorphic unit at the bar tail is an older bar platform unit which has a dense river oak monoculture. This feature has been buried by up to 1 m of sand. Reworking of materials over the point bar surface, and associated implications for vegetation distribution within the riparian zone, are described within a fluvial disturbance model.