Riparian vegetation and island formation along the gravel-bed Fiume Tagliamento, Italy

After more than 300 taers of river management, scientific knowledge of European river systems has evolved with limited empirical knowledge of truly natural systems. In particular, little is known of the mechanisms supporting the evolution and maintenance of islands and secondary channels. The dynamic, gravel-bed Fiume Tagliemento, Italy, provides an opportunity to acquire baseline data from a river where the level of direct engineering intervention along the main stem is remarkably small. Againts a background of a strong alpine to mediterrranean climatic and hydrocological gradient, this paper explores relationships between topography, sediment and vegetation at eight sites along the active zone of the Tagliamento. A conceptual model of islands development is proposed which intergrates the interactionsn between large woody debris and vegetation, geomorphic features, sediment calibre and hydrological regime. Islands maybe develop on bare gravel sites be dissected form the floodplain by channel avulsion. Depositional and erosional processes result in different islands types and development stages. Differences in the apparent trajectories of island development are identified for each of the eight study sites along the rive. The management implications of the model and associated observations of the role of riparian vegetation in island development are considered. In particular, the potential impacts of woody debris removal, riparian tree management, regulation of river flow and sediment regimes, and changes in the riparian tree species' distribution are discussed.