How does over two decades of active wood reintroduction result in changes to stream channel features and aquatic habitats of a forested river system?

Abstract

AbstractSince the late 1980s and early 1990s, wood reintroduction has been a commonly assessed stream restoration technique. Many of the efforts have focused on short‐term, localized physical changes and response of salmonids to wood reintroduction. Few have examined how long‐term, spatially extensive increases in wood loadings alter stream channel morphology and the geomorphic processes responsible for these changes. We used before and after photos as well as a wood storage survey with tagged restoration logs in a small, low‐elevation Western Washington watershed to characterize the effects of 23 years of wood additions. In the ~6 km of wood placement we saw an increase in wood loading and channel‐spanning logjams, which contributed to deeper and more frequent pools, a reduction in particle size, increases in sediment storage, reduced stream width, vegetation re‐establishment in the riparian zone, and increased development and maintenance of floodplain channels. The largest geomorphic changes occurred due to restoration wood effectively storing pieces moving downstream. These findings imply that the cumulative habitat restoration actions and associated changes to stream habitat conditions are identifiable through comparison of historical and current photos as well as more quantitative habitat metrics. It also demonstrates that wood placement that simulates the function of large key, stable pieces accelerates habitat recovery within basins subjected to historic logging.