Guest Post by Emily Iskin, 2022-2023 Sustainability Leadership Fellow, and Ph.D. Candidate in the Department of Geosciences at Colorado State University

Around the globe, rivers were once full of wood. Where did it go? And why does it matter that it’s gone? Wood was historically removed from rivers for transportation (think the Mississippi River), infrastructure, and safety, but we now know that the removal of wood can significantly alter river corridors.

 Wood provides many benefits and performs many functions in river ecosystems. In relation to flows, wood stores water, sediment, and organic matter behind logjams¹; acts as carbon storage² (Fig. 1); and increases the exchange of water, gases, and nutrients between the stream and the streambed^3–5 and between the stream and the floodplain^6–8. Wood can create habitat for plants^9–11 (Fig. 2) and animals^12–14; and increase overall complexity and heterogeneity of the river corridor^15–18. We also know that wood is stored for a period of time in streams, but that an essential function of wood is movement through river systems at varying rates^19,20 to its final destinations of lakes and oceans²¹.

The fields of fluvial geomorphology, riparian ecology, stream biology, and river restoration have recognized the value of wood in rivers for decades. Barriers that need to be decreased or reversed for successful wood reintroduction include deforestation that reduces the historical source of wood, active removal of wood that naturally falls into rivers, fear of mobile wood damaging infrastructure such as bridges, and hesitancy around the local effects of wood in streams such as local flooding and backwater rise near logjams. Overcoming these barriers will require examples of successful reforestation near streams, a shift in policy and responsibility regarding where wood is put in and where it ends up, and eventual room for rivers to inundate their floodplains and move without restriction.

Restoration of natural sources of wood and reintroduction of wood to rivers is gaining traction with communities large and small, but success will require shifting the negative public perception^22,23. This challenge can be overcome through increasing awareness and education around the benefits of wood in streams, starting with effective signs and displays in national and state parks and local river recreation sites. Shifting the view of what a natural stream looks like and increasing public acceptance of wood’s place in these systems is going to increase the speed of restoration and effectiveness of wood in streams. Without public support, the task of restoring wood to river systems is already dead in the water.

References

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17. Wohl, E. Spatial heterogeneity as a component of river geomorphic complexity. Progress in Physical Geography: Earth and Environment 40, 598–615 (2016).
18. Gurnell, A., Tockner, K., Edwards, P. & Petts, G. Effects of deposited wood on biocomplexity of river corridors. Front Ecol Environ 3, 377–382 (2005).
19. Wohl, E. & Iskin, E. P. The Transience of Channel‐Spanning Logjams in Mountain Streams. Water Resour Res 58, (2022).
20. Wohl, E. et al. Why wood should move in rivers. River Res Appl (2023) doi:10.1002/rra.4114.
21. Wohl, E. & Iskin, E. P. Damming the wood falls. Sci Adv 7, (2021).
22. Le Lay, Y.-F. et al. Variations in cross-cultural perception of riverscapes in relation to in-channel wood. Transactions of the Institute of British Geographers 33, 268–287 (2008).
23. Piégay, H. et al. Public Perception as a Barrier to Introducing Wood in Rivers for Restoration Purposes. Environ Manage 36, 665–674 (2005).