Boulder ramps as a restoration measure: Increasing in the resilience of mountain freshwater ecosystems to environmental changes

Mountain environments, as biodiversity hotspots, are subject to numerous anthropological pressures. In mountain areas, a common threat to stream biocenoses is the timber industry. Timber industry increases the fine sediment input into the mountain rivers; furthermore, timber transport requires the construction of low-water crossings across streams. Transversal barriers (weirs/fords/pipe culverts) may cause excessive erosion downstream and the accumulation of fine sediments upstream, thereby decreasing habitat heterogeneity. Moreover, mountain stream communities are sensitive to climate change; for e.g., climate change may result in increasing water temperature and decreasing flows. Boulder ramps are considered effective restoration measure for rivers; benthic macroinvertebrate community composition is an effective indicator of stream health. In this study, we selected two mountain streams catchment with forest management. The control was a stream without any objects in the streambed related to timber transport. The other stream contained weirs and pipe culverts. We considered an extensive study period that covered the stages before (2009) and after restoration (2014, 2017–2018, 2019). We present the hypothesis that boulder ramps can restore in-stream habitats, improve biodiversity, and increase the resilience of benthic macroinvertebrate communities to future environmental changes. Our study demonstrates the effectiveness of boulder ramps for mountain streams restoration. We indicated, that the habitat potential of the restored stream-reach for rheophilic and lithophilic invertebrates increased substantially. Moreover, the restored riffles allowed the streambed to be cleared of fine sediments, offering the microrefugia, which were beneficial for mountain stream invertebrates, thereby increasing the diversity and resilience of the benthic communities.