Study of 91 Stream Restoration Projects Shows
A study of 91 stream restoration projects in the lower Columbia River and Oregon coastal river basins that added wood to increase pool complexity and pool surface area -- better habitat for juvenile coho salmon -- found that after six years most of the projects had increased over-wintering rearing capacity for the salmon.
The restoration projects placed large logs in small to medium sized streams that had been damaged by years of neglect and that had lost much of the natural stream's complexity of pools and gravel. The projects' design was to use wood without cabling to hold them in place in areas that would be expected in a natural stream. After six years of monitoring, biologists saw an increase in the surface area of pools and an increase in gravel.
However, the amount of large wood that had been installed declined over the six years in almost 75 percent of the projects and few sites collected new wood. But even with this decline, wood remained on average 100 percent of the pretreatment levels of wood.
In addition, changes in channel complexity and flood plain connectivity, the more wholistic and desired outcomes of the projects, were not observed.
The biological link is more difficult to establish. The quality and extent of the habitat changes, such as changes in pool complexity and substrate (more gravel) extrapolate to better overwinter rearing for coho salmon. In addition, the study postulates the wood projects may also improve the overwinter survival of steelhead and benefit other species, such as lamprey because the projects can increase the sorting and retention of fine sediments.
Determining how and where to place wood in streams is difficult and natural events, such as floods, can alter or sweep away all good intentions. Fourteen percent of the projects after six years lost more wood than was installed. Thirty-eight percent of the projects experienced increased wood volume, pool area and gravel, with only three percent losing wood pieces, pool area and gravel from pretreatment conditions.
"Stream restoration is not a predictable engineering activity. The streams and rivers in the Northwest are dynamic, the environmental conditions quite variable and occasionally extreme, and the response of fish populations is complex," said Kim Jones, research program leader for the Aquatic Inventories Program, Conservation and Recovery Program of the Fish Division at the Oregon Department of Fish & Wildlife.
The article, "Effectiveness of Instream Wood Treatments to Restore Stream Complexity and Winter Rearing Habitat for Juvenile Coho Salmon," appeared in the March 2014 edition of Transactions of the American Fisheries Society. Authors include Jones and staff of the Aquatic Inventories Program: Kara Anlauf-Dunn, analyst; Paul S. Jacobsen, restoration monitoring biologist; Matt Strickland and Sharon E. Tippery, biologists; and Lora Tennant, restoration monitoring biologist.
The projects are a part of the Oregon Watershed Enhancement Board's 1,100 large wood projects in 1,200 kilometers of streams (still only 10 percent of the available spawning and rearing habitat for Coho salmon). The projects, however, had an earlier genesis in the Coastal Salmon Restoration Initiative in 1995, which is now the Oregon Plan.
The 91 projects studied in this research were implemented by 24 ODFW biologists and monitored in western Oregon (mostly coast and lower Columbia) from 1999 -- 2011. During this time period, the projects experienced a wide range of flow events.
"As a result, the findings presented in the paper are likely representative of large wood placement projects in the Northwest that were implemented by a variety of agencies, watershed councils, private contractors and others across a diverse geographic region," Jones said.
Although the results of the watershed projects are not perfect, at the time of installation each project quickly added structure and rearing habitat to streams that would have taken decades to recover from previous management practices. Pools became more complex, larger and shallower and they maintained that complexity over the six years even though wood levels declined in most sites from the amount installed.
"As much as we all support full watershed scale restoration from landscape to the sea across all land management types, the fact is that streams have been greatly altered over the past 150 years and based on current projections, many decades will pass before riparian areas, large wood recruitment, and stream processes will recover to natural conditions," Jones said.
Although stream habitat conditions have stabilized, he added, they have not begun a natural and "significant upward trend. If we wish to improve stream complexity to benefit productivity of salmonid populations in the near term, some active intervention in the form of instream habitat restoration will be needed."
"In the big picture, I am pleased that we have been able to show stabilization in stream habitat trends through our habitat monitoring program," he said. "The restoration projects may in fact be sustaining the stabilization of large wood amounts (trend neither increasing nor decreasing)."
The challenge is to direct restoration at this stream reach scale within a broader watershed context that recognizes the functions and processes that are naturally sustainable.
"We need to continually remind ourselves that restoring watershed function involves more human entities (individuals, landowners, private companies, and agencies), disciplines, and complexities than site scale in-stream projects," Jones said.
learn more on topics covered in the film
see the video
read the script
learn the songs