Improving longitudinal habitat connectivity in major river restoration projects through farmland re-allocation

Abstract

River restoration projects are often accompanied by major land consolidation operations, notably the re-allocation of adjacent farmland, which offers the opportunity to create an extensively-managed buffer zone outside the levees where specific habitat features are installed for endangered terrestrial and semi-aquatic biodiversity. Modern, enrivonmentally-friendly land consolidation operations might thus not only contribute to better integrate the newly restored river into the adjacent landscape, but also to reinstate the longitudinal ecological connectivity that crudely lacks along channelized rivers. Based on a theoretical re-allocation of agricultural land via land consolidation, we simulated the creation of a longitudinal biodiversity-friendly grassland buffer along a stretch of the Rhône River (SW Switzerland) where a major revitalisation project is under development. We selected a series of focal species depending on a palette of complementary habitat features, and combinations thereof, to be created for reaching these biodiversity targets. Estimations of species-specific habitat patch size requirements as well as dispersal abilities were used to analyse what would be an optimal spatial connectivity for these habitat features. Since such a buffer zone will necessarily stretch along the riverbed, which implies different spatial contraints and consequential planning strategies, we tested two scenarios via a metapopulation model: (i) arranging key habitat features longitudinally or (ii) positioning them in an isotropic context. Simulations showed that differences in metapopulation connectivity between scenarios were negligible at the foreseen scale. We conclude that land consolidation via targeted farmland re-allocation could be instrumental to restoring ecological connectivity in major river revitalisation projects. We also provide concrete quantitative values for restoring an optimal ecological buffer along the Rhône that will promote locally endangered biodiversity.