Agricultural and riparian landscapes
The project’s second thematic area is focused on how dam establishment, reservoir drainage, and, potentially, dam removal change agricultural and riparian landscapes. It is expected that, once the dams are removed, the new hydrological conditions will affect the river’s riparian vegetation, related ecological continuities, and the riparian zones within the broader landscape. Agricultural practices (e.g., crop allocation, hedgerow management) may also shift as a result of changes in river bank vegetation and on farms (e.g., shifts in agricultural systems, field organization). These modifications in agricultural practices may then, in turn, further impact the landscape and riparian vegetation. Consequently, this thematic area is interested in how dam removal may affect interactions and feedback among the riparian vegetation, the broader landscape, and agricultural practices. This work will help identify focal zones where observations should be concentrated to monitor landscape changes after the dams are removed (i.e., second project phase).
Researchers wish to characterize the landscape changes that have taken place between the 1950s and the present using remote sensing data. The goal is to identify areas that display notable spatiotemporal homogeneity or heterogeneity (taking into account forests, crop fields, pastures, and developed areas) and to describe structural connectivity between hedgerows, wooded areas, and/or pastures. Research is being carried out at different temporal and spatial scales, and scientists are looking for emerging patterns in agricultural, urban, or forest dynamics. Particular attention is being paid to recent agricultural shifts. The greater aim is to characterize and thus better understand how farming has influenced landscape patterns within the Sélune River Basin. Analyses are especially focused on how areas near the watercourse have affected regional land management and both past and present agricultural production. Data are being gathered by interviewing farmers and performing observational studies in the field. This information will then be analyzed in tandem with spatial data on landscape changes. To characterize plant diversity across agricultural landscapes, researchers are carrying out quadrat sampling within and around crop fields and pastures. Sampling efforts are focused on lower-elevation areas that are in contact with the riparian zone. These data will be linked with data on agricultural practices, dynamics, and landscape changes to identify the factors driving the observed patterns of biodiversity.
First, researchers are characterizing the colonization potential of different riparian species by studying the seeds found in river sediments (Fig. 1). In this seed bank are seeds that arrive in sediments transported downstream and seeds that rain down from riparian plants.
Second, once the dams are removed, researchers will track the riparian vegetation that develops on the exposed bare sediment. They will use both field sampling and remote sensing techniques (Fig. 2). The studies carried out on the Sélune will also be carried out on its tributaries to more fully grasp the influence of the landscape on riparian plant communities. Consequently, the way in which the landscape and different environmental factors affect the composition and dynamics of the riparian community will be better understood.
Furthermore, permanent study plots have been established to monitor the physiological responses of tree species. Five years after dam removal, dendrochronology (i.e., tree-ring analysis) will be used to quantify growth.