The authors found that broad-scale forest recovery combined with targeted forest, road, and stream management under the Northwest Forest Plan have resulted in slow but steady improvements in watershed condition.

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It’s Spring of 1993, just over 30 years ago. Newly elected President Bill Clinton and Vice-President Al Gore are in the Pacific Northwest. Also at the table: half of the Clinton cabinet, the governors of California, Oregon and Washington, representatives from non-profit environmental organizations, loggers, mill owners, scientists, and lawyers. What’s the special occasion? The Northwest Forest Conference is underway in Portland, Oregon. It’s the culmination of a decade-long struggle to find a compromise between saving emblematic species like the northern spotted owl, old growth forest, and the logging jobs and wood products that form the backbone of the local economy.  

In the past, old growth forests were viewed by many as “dead zones,” ecosystems past their prime, full of old, dead wood with little value for humans or wildlife other than for building material. Research eventually made it clear that 1) old growth forests are important, 2) not just for owls, but for many other species of fish and wildlife, and 3) not just for wildlife, but also for people. Forests provide the fresh water and clean air that we all need to survive.

Ecosystem management was emerging as a more broadly accepted strategy. President Clinton was advised by those at the Northwest Forest Conference that any plan designed to save a single species, in this case the northern spotted owl, was destined to fail. It was going to take an ecosystem-wide approach, recognizing how all parts of the forest are connected. 

The result of the conference was the Northwest Forest Plan, enacted in 1994. It allowed logging to continue, but at a quarter of the rate prior to the 1980s and addressed key habitat protection measures.  

New protections for forests and water in the Pacific Northwest 

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The old trees, dead wood, shade, insects, and water storage provided by old forests are also essential for salmon. The ecosystem conservation plan that started with an owl was expanded to protect the fish swimming below.  

Federally managed forests support diverse aquatic ecosystems, and protecting those ecosystems was a core consideration in the design of this new Northwest Forest Plan. Forest streams provide many critical resources, including native fishes and water for ecosystems and people. Shortly after the implementation of the Northwest Forest Plan, distinct populations of five species in the salmon family joined the northern spotted owl on the Threatened or Endangered Species List. These included coho, chum, and Chinook salmon and bull and steelhead trout.  

The Aquatic Conservation Strategy written into the Northwest Forest Plan includes road building restrictions and encourages the removal of old, unused roads. It also requires larger buffers of trees between streams and timber harvest areas, preserving shade and protecting stream banks from erosion. Tasked with evaluating whether the Strategy is successfully improving watersheds are the scientists behind the Aquatic and Riparian Effectiveness Monitoring Program.  

The Aquatic and Riparian Effectiveness Monitoring Program includes scientists from the USGS, U.S. Forest Service, and Oregon State University. Their 25-year report describes trends in watershed characteristics since the Northwest Forest Plan was put in place. National forests and Bureau of Land Management resource areas within this area have taken a wide range of actions designed to improve aquatic ecosystems, including upgrading roads, replacing culverts, and facilitating the growth of larger trees along streams. Some of these actions, like replacing damaged culverts, could immediately lead to improved fish passage. Others, like growing large trees to provide shade and in-stream structure for streams, could take decades to make an impact on stream temperature.

“The opportunity to learn from 25 years of continuous monitoring is invaluable,” said Jason Dunham, USGS Supervisory Research Aquatic Ecologist and lead author of the report. “This monitoring effort is our primary means of accounting for changes to watersheds and streams related to protections implemented by the Northwest Forest Plan and the increasing influences of climate change.” The report pairs trends from repeated instream data with whole watershed aspects such as road and vegetation conditions, and for the first time in the history of the Aquatic and Riparian Effectiveness Monitoring Program, includes the effects of climate change.  

Streamflow 

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It may seem obvious that the amount of water flowing through streams is a key component of watershed condition. However, prior to the Aquatic and Riparian Effectiveness Monitoring Program, there was little scientific information about streamflow in the Pacific Northwest other than from gages placed mostly on larger streams. Specifically, the team looked at annual discharge—the quantity of water moving down a stream or river per year-- drought, and stream width. They observed widespread declines in stream width across the region. Trends in drought and annual discharge were more variable, but there were signs of greater prevalence of drought and declining streamflow towards the southern extent of the study area in Oregon and California. These trends are consistent with those expected to occur in a warming climate, suggesting that over the course of the Northwest Forest Plan, climate change has become a major driver of hydrological conditions across the region. 

Forest Cover and Stream Temperature 

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Stream temperature influences many aquatic ecological processes, most notably the survival

and growth of cold-water fish species such as salmon and trout, a major focus of the Northwest Forest Plan. Stream temperature is mainly a function of the amount of shade provided by trees along its banks, which is strongly influenced by timber harvest and other disturbances like wildfires. Monitoring data show little change in overall canopy cover. There were large declines in canopy cover in specific areas, such as those impacted by wildfire. There were also large gains in canopy cover in areas where forests have expanded. Stream temperatures were relatively cool overall, and within the ranges suitable for cold-water fishes.

In-stream Large Wood 

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When a tree dies, or is knocked over by wind or fire, it may end up in a stream. In-stream wood can benefit streams in many ways that may not be obvious at first glance. It can cool water temperature, provide shelter for fish, and act as food for the insects and microorganisms that fish feed on. Before the Northwest Forest Plan, it was common practice to remove dead wood from streams, which resulted in a lack of in-stream wood. The life cycle of a tree can take hundreds of years, from germination to death and the eventual placement in a stream.

Because of this time frame, researchers didn’t expect to see huge changes in the amount of in-stream wood in only 25 years. To account for potential future delivery of wood from forests to streams, they used satellite images of forest vegetation to predict how many old growth trees may become in-stream wood in the future. Localized losses and gains were variable across the region, some some large gains in areas that were historically logged but have been left to recover, and losses in areas with recent wildfires.  But overall,the team estimates a 4% increase in large trees across the extent of the Northwest Forest Plan area. In the Washington-Oregon Coast area, gains of large trees were even higher.  

Forest Roads and Stream Sediment 

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Roads are a major source of sediment inputs into streams. When a logging truck rumbles down an unpaved forest road, it can cause dirt to tumble down into streams. Some fine sediment in streams is good and can benefit species such as native lamprey. But too much sediment can clog the gravel that salmon need for spawning and reduce the survival of salmon eggs and fry. So how about those rules restricting forest roads? Did they result in more stable streambanks and clearer water? Road decommissioning has reduced the estimated length of roads near streams by about 7%. In-stream data suggest declines in fine sediment across habitats in 90% of sampled watersheds. Road management appears to be having the desired effects of decreasing fine sediment on stream beds.  

Impacts on Fish and their Food Sources 

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The conservation of fish species was a major emphasis of the Northwest Forest Plan, but directly monitoring fish species on over 24 million acres? Not very practical. Instead, macroinvertebrates were the target creatures of the monitoring program. Macroinvertebrates are animals like insects, mollusks, and other small life forms that fish eat. They can indicate stream water quality and food web condition. Overall, trends in macroinvertebrates suggest food webs are functioning with little evidence of lasting impacts from past disturbances.  

Another important factor influencing fish is “connectivity.” Although salmon and trout undergo well-known migrations through streams, they encounter many physical barriers along the way. The 25-year report includes the most detailed inventory of stream culverts on federal land to date. Culverts allow streams to flow under roads, but can restrict fish passage if they’re old, damaged, or not designed properly. Of the 3,193 culverts surveyed, 2,420 were determined to be barriers to fish passage, that’s 76%. These stream culvert barriers currently block access to over 3,400 miles of fish habitat. Since adoption of the Northwest Forest Plan, many have been repaired or replaced to allow fish to pass, but there’s still a lot of work to be done. Additional surveys are needed to better map where culverts exist on the landscape, and to determine their current condition.  

What does the future hold? 

This report provides the foundation for the future of monitoring aquatic ecosystems on federal lands across the Pacific Northwest. Crews working for the Aquatic and Riparian Effectiveness Monitoring Program are continuing to collect data each year. Ongoing collaborations between USGS, the Forest Service, Bureau of Land Management, and other federal and university partners are continuing. These collaborations will update trends in in-stream conditions as new data come in. Although forest management was the initial emphasis of the Northwest Forest Plan, it is clear these changes are interacting with the effects of climate change, including droughts, floods, wildfires, heatwaves, and other disturbances. From an aquatic perspective, this translates into major impacts on water resources, from the watersheds and streams that drain them, and the availability of water for fish, wildlife, and people. The future of the Pacific Northwest is intimately tied to forests and water. Continued monitoring of all aspects of these critical resources is essential for understanding how society can adapt to changes that would have been impossible to imagine just 25 years ago.