What direct and indirect consequences of dam removal on flora biodiversity at a landscape level ? Study design
Résumé
Scheduled to begin in 2015, the removal of two dams on the Selune River, Manche (France) will be one of the largest dam removal and river restoration projects undertaken in Europe. Dam removal decisions involve a tradeoff of multiple socioeconomic and ecological costs and benefits. Environmental consequences of dam removal may include benefits from restoring more natural flow and sediment regimes but also impacts on biodiversity and associated ecosystem services due to changes in landscape and agricultural dynamics. The aspect of dam removal examined here is the trajectories of vegetation response on lands exposed by dam removal but also on agricultural lands on each side of the valley, from the river up to the plateaus. One challenge associated with this project is to understand how dam removal will influence the logics of farmers’ decisions and the allocation rules of land covers at the landscape level. Indeed, riparian zones are known to serve as conduits for substantial fluxes of materials, species and energy. In addition, riparian zones are connected to semi-natural habitats such as hedgerows, field margins, permanent grasslands facilitating vegetation proliferation and spread overall the landscape. We hypothesized that dam removal by modifying farmer management practices and land use allocation, could influence ecological continuity and thus, vegetation communities in agricultural landscapes. Our methodological design consists in vegetation surveys along transects that run perpendicular to the river and extended to the plateaus, following structural elements constitutive of the ecological continuity. Transects belong to 1 km * 1km agricultural landscapes centered on the Selune river, from upstream to downstream. The landscapes are selected to represent gradients in landscape heterogeneity and ecological continuity. Vegetation long-term monitoring appears as an innovative and pragmatic way of understanding direct and indirect consequences of dam removal at a range of spatial scales in riparian environments. Funding body: This study was part of the project Seripage (“Sélune: Ecologie et gestion des zones rivulaires, ripariennes et des paysages agricoles”) funded by Agence de l’Eau Seine-Normandie.