Conservation of biodiversity in floodplain rivers
Large rivers and their riparian zones are hot spots of biodiversity (Ward et al. 1999) and over the last ten years a sound conceptual basis has been developed for understanding their functional processes and their biodiversity, although there are still few detailed studies. It is well understood that the key element for the high levels of biodiversity are flood controlled disturbances and geomorphic processes (Junk et al. 1989; Pickett & White 1985; Naiman & Décamps 1990; Bayley 1995; Ward 1989) which create the characteristic patch dynamics, spatial heterogeneity, and the mosaic structure of densely packed ecotones and array of successions over a range of scales (Naiman et al. 1988; Décamps & Tabacchi 1994; Décamps 1996). In turn, these provide the habitat diversity and the specific habitat conditions for characteristic floodplain species and result in high levels of local species richness (alpha-diversity), habitat diversity and between-habitat differences (beta-diversity) and consequently, overall species richness. Understanding the biodiversity of river-floodplain systems requires a hierarchical, scalar approach (see Ward et al. 1999) because biodiversity levels can be compared across a range of scales, e.g. from whole river systems to river segments, lateral and longitudinal gradients within a floodplain, down to the level of single habitat types. Similarly, the significance of operating factors can be viewed from a catchment scale to local habitat conditions (Noss 1990; Gregory et al. 1991; Townsend 1996; Ward 1998; Ward et al. 1999; Tockner & Ward 1999). Anthropogenic alterations in the catchment, e.g. changed patterns of runoff and sediment transport, nutrient loads and pollution, have strongly effected almost all river ecosystems.