The ecohydrology of rewilding: A pressing need for evidence in the restoration of upland Atlantic salmon streams

Recent interest in landscape re-wilding and ecological restoration has resulted in a proliferation of large-scale projects in many countries that have the potential to cause significant ecohydrological change. In Scotland an increasing number of watershed “restoration” schemes are motivated by declining Atlantic salmon populations and the threat of climate change. These usually involve riparian planting to shade salmon streams and re-engineering of river channels to “enhance” salmon habitat. However, the need for, and objectives of, these schemes are often highly uncertain and there is no compelling scientific evidence to suggest that they are likely to be successful in halting salmon declines. Remarkably, these schemes - which affect can affect rivers with the highest conservation designations in protected landscapes - have been subject to limited environmental assessment. In some cases, engineering activities pose significant potential risk to juvenile salmon, and existing high quality salmon habitat may be degraded in the re-engineering of streams. This commentary highlights the urgent need for more evidence-based approaches in the management of complex ecohydrological systems.