Biogeomorphic tipping point in braided rivers: vegetation development at a restored Upper Drava River section (Austria)

Abstract We determined how the interaction between geomorphic processes and vegetation development enables tipping points in braided rivers. We performed vegetation monitoring and succession modelling on the restored Kleblach side channel at the Upper Drava River (Austria) to assess long-term trends in vegetation succession and landform development. Two alpine pioneer plant species, the German Tamarisk ( Myricaria germanica ) and the Dwarf bulrush ( Typha minima ), were used to assess the ecosystem consequences of succession. Vegetation rapidly developed on initially open sites; 14 years after restoration, approximately 60% of the study area was characterized by stable succession phases. Even a major flood event in the near future would not reduce the dense vegetation cover. This indicates that a stable, dense vegetation cover can lead to a permanent transition from a dynamic braided to a stable single-channel river without major morphological changes, which we interpret as “biogeomorphic tipping point”. The result is a significant reduction in the indicator species’ habitats, preventing them from maintaining a resilient population in the long term. Thus, maintaining process regimes with high hydro- and morphodynamics is critical for preserving the valuable braided river ecosystems. The idea of “biogeomorphic tipping points” contributes to the process-based conservation and restoration of braided rivers globally.