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

Since the late 1980s and early 1990s, wood reintroduction has been a commonly assessed stream restoration technique. Many of the efforts have focused on shortterm, 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.

Widespread Wood Placement and Regrading Drive Lateral Connectivity and Reworking of the Channel and Floodplain in a Valley Bottom Reset to Stage 0

“…Correspondingly, inchannel edge density also increased (although part of this increase is likely due to avulsion, discussed below; Figure 4C). This indicates the importance of wood rearrangement and jam formation in enabling rearrangement of the channel bed, similar to other systems in which wood has been observed to constrict, plunge, and backwater flow to create pools (Livers & Wohl, 2021;Martens & Devine, 2022;Pess et al, 2022). substantial floodplain inundation and reworking.…”

“…Because pools are often maintained by wood in wood-rich riverscapes (Montgomery et al, 2003;Pess et al, 2022), this lack of wood rearrangement may have led to the lack of channel bed rearrangement and new pool formation. Pool area largely did not change (ranging from 1 -1.4% of the valley bottom for the upstream reach and 0.8 -1% for the downstream reach) during this time, and pools largely did not change positions, indicating a lack of in-channel rearrangement.…”

Fisheries Volume 49 Number 1 January 2024

“…We acknowledge that treating habitat degradation symptoms, such as instream wood loss, by adding wood to streams may be initially important to help accelerate restoration of impaired habitat conditions. Such additions may require multiple treatments over decades due to degraded riparian conditions, as was the case in Deep Creek (Strait of Juan de Fuca IMW), where 23 years of wood additions resulted in gradual aquatic habitat recovery (Pess et al 2023 ). However, this is not a long-term solution because habitat restoration is not the fi nal step; rather, restoration of natural processes and allowing for various habitat outcomes to take hold constitute the best way to recover watersheds and populations (Bellmore et al 2019 ).…”

Managing Expectations from Intensively Monitored Watershed Studies

“…We acknowledge that treating habitat degradation symptoms, such as instream wood loss, by adding wood to streams may be initially important to help accelerate restoration of impaired habitat conditions. Such additions may require multiple treatments over decades due to degraded riparian conditions, as was the case in Deep Creek (Strait of Juan de Fuca IMW), where 23 years of wood additions resulted in gradual aquatic habitat recovery (Pess et al 2023). However, this is not a long-term solution because habitat restoration is not the final step; rather, restoration of natural processes and allowing for various habitat outcomes to take hold constitute the best way to recover watersheds and populations (Bellmore et al 2019).…”

“…Although such activities are likely to confound results, scientists should realize that the ultimate decision on watershed-scale habitat restoration resides with policymakers and they should be prepared to factor unanticipated interventions in control sites into the final analysis of results. Intensively monitored watersheds are typically set up as large-scale, long-term studies because restoration activitieseven just one type-can require years to decades to fully implement and mature (Pess et al 2023). It is unreasonable to that stream and watershed restoration actions can reverse within a few years the degradation that took place over a much longer time period (Allan 2004).…”