Long term monitoring of the organization of agricultural landscapes and vegetation communities along the Sélune river (France)

Scheduled to begin in 2016, the removal of two dams on the Sélune River, Manche (France) will be one of the largest dam removal and river restoration projects undertaken in Europe. Expected environmental consequences of dam removal 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. This can be challenging to discern such shifts while natural ecological and physical processes have been suppressed or altered since the installation of dams in the 1920s. Long-term analysis is therefore a valuable tool to provide knowledge on how present conditions came about. Here, we focus on the vegetation response to agricultural landscape trajectories over 30 years, at the watershed scale. Because the Sélune river has influenced agricultural land use patterns for decades, we hypothesize that dam removal will modify these patterns through changes in farmers’ decisions. In turn, it will influence ecological continuity and thus, vegetation communities in agricultural landscapes. Our methodological design consists in vegetation surveys in both crops and semi-natural elements (i.e. field margins). Vegetation surveys belong to 10 1km² landscape samples, contiguous to the Sélune river. Landscapes, distributed from upstream to downstream, are selected to represent a gradient in landscape heterogeneity. Vegetation communities are then compared according to their location from and along the Sélune river. Our approach, combining ecological and agricultural data, provides an innovative way of investigating direct and indirect consequences of dam removal.