Patterns of landscape dynamics and their consequences on ecological communities: An application of GIS and remote sensing in the Seine Valley

Large river floodplains are unique ecosystems whose integrity is maintained by hydrological dynamics and river-floodplain connections. Like many European rivers, the Seine was nearly entirely channelled at the beginning of the century to enhance agricultural use of the rich alluvial soils, secure river navigation and prevent flooding. Today, the flood disturbance regime of the Seine floodplain is no longer maintained, instigating changes in the organisation and diversity of communities. This paper assess the changes at different scales and tries to understand how species coexist in the valley today, by studying two communities: grassland plants and breeding avifauna. From a conceptual point of view, this work makes reference to the concepts of landscape ecology, community ecology, and to the theories of hierarchy and information. From a methodological point of view, this work uses the basic tools for comparative spatial analysis: multivariate analysis, grid techniques, and GIS as well as remote sensing. Results show that the plant communities in the wetlands (which represent what is left of the former floodplain) have reached an equilibrium which is no longer a dynamic equilibrium based on the recurrent disturbance of the floodpulse, but an equilibrium imposed by long term agricultural practices. The Seine landscape shifted from a hydraulic dynamic organisation to a agro-ecological organisation. But a closer appraisal (change of scale) suggests that though the mechanisms underlying species coexistence in the wet grassland community imply equilibrium compared to other grasslands of the Seine landscape, in some patches (prone to intensification or change) species coexistence is explained through non-equilibrium mechanisms. This confirms the idea that the landscape is shifting again from a agro-ecological organisation to another type of organisation.