The Loire, often qualified as the " last wild river of Europe ", was fitted out from the Antiquity. This river, unlike numerous big rivers, little benefited only from researches in ecology. The alluvial vegetation is an excellent integrator of the physical, biological and human conditions of floodplain ecosystems. The plant communities was characterized by phytosociological methods, completed by a quantification of the abiotic parameters structuring the functioning of floodplain ecosystems (hydrology, energy streams, soil parameters). The study of successions in alluvial forests was the object of a structural approach. These investigations were led on seven sites distributed on 500 km of the middle Loire. The statistical analyses allowed to confirm the correlations which existed between ecological conditions and the associated flora ; they also allowed to put in evidence and to organize into a hierarchy the site factors which structured best the spatial distribution of plant communities. So, flood frequency, texture of the substrate and location with regard to the energy streams are excellent integrating parameters. Acquired knowledge makes it possible to establish ecological and phytosociological typologies and of the vegetation, and an elaboration of diagrams of organization and evolution of plant communities in the time. For alluvial forests, the architectural method demonstrated its efficiency on the Loire in the understanding of sylvigenesis processes. Finally, the confrontation of these results authorizes the implementation of a predictive model of evolution of the vegetation. This model will allow to test various scenarios of management of floodplain ecosystems with a care of dynamic conservation of biodiversity.
