Wood entrance, deposition, transfer and effects on fluvial forms and processes: Problem statements and challenging issues

Throughout the world before the 1970s, in-channel large wood (hereafter LW), was generally considered a nuisance or a hazard to be avoided because of the hydraulic effects and consequential associated risks that it could produce. LW was systematically removed from channels for a perceived benefit to human activities. Over the last four decades, LW has received an increasing interest among scientists who recognise it as a significant structural and functional component of aquatic ecosystems. Research in geomorphology has addressed LW characters and its effects on flow hydraulics, on channel and valley forms and their evolution, on the storage and transfer of sediment and organic matter, as well as on associated habitats for aquatic communities. After considering the space-time framework within which the wood dynamics can be studied, we highlight the LW effects on channel morphology and fluvial processes, the ecological and societal consequences of wood in rivers and implications in terms of river management and restoration. After centuries of wood removal, LW is now introduced in rivers for ecological improvement in some areas of North America, Europe, Australia, and Japan