Riparian Vegetation Along Current-Exposure Gradients in Floodplain Wetlands of the River Murray, Australia

(1) This paper develops a simple conceptual model of riparian vegetation applicable to floodplain wetlands of a regulated river. The vegetation was studied with respect to two gradients: current and exposure to wave action. The study area was the Chowilla floodplain on the River Murray in the semi-arid zone of South Australia. (2) Four vegetation types were distinguished by cluster analysis and by separation on three ordination axes. Each was strongly and significantly associated with a particular category of wetland on the floodplain. (3) The first ordination axis represented a gradient in vegetation structure. It separated vegetation types dominated by trees from those dominated by sedges and/or grasses; the former had higher species richness and greater range of growth forms. (4) The second ordination axis was a current-related gradient, having a significant regression on current; the vegetation type with the swiftest currents and steepest banks was riparian grasses. (5) The third axis was a gradient related to exposure to wave action. (6) Application of a simple model to vegetation of the Chowilla floodplain suggested how river regulation might have changed wetland vegetation.