Hoh River Riparian Restoration:
Focus on Invasive Plant Species Prevention & Control
The Hoh River on the Olympic Peninsula coast in Washington State is one of the few rivers in the lower 48 states supporting relatively healthy wild salmon populations. In 1998, one clump of invasive knotweed was observed at the edge of the Hoh River. During a storm in the winter of 1999 or 2000, this clump was eroded and swept downstream, and from there the species rapidly established throughout the river. Knotweed is a threat to salmon and wildlife habitat because it outcompetes native riparian species, and establishes a monoculture that does not provide food or habitat for terrestrial and semi-terrestrial aquatic species. Knotweed alters the physical and biological characteristics of native riparian forests and riverine habitats, ranging from excessive shading to replacement of native leaf litter that is the basis of aquatic food webs, and increased bank erosion.
Recognizing this threat to critical habitats, the Hoh Tribe initiated a restoration project in 2002, beginning the annual surveys, control, and effectiveness monitoring activities that continue today as a partnership between the 10,000 Years Institute, Hoh Tribe, The Nature Conservancy, private landowners, Olympic National Park, and the U.S. Forest Service. To date, an estimated 99.5% of the knotweed plants have been eradicated on 30 miles of the river and its floodplain, but deeply buried rhizomes persist and require continued surveys and treatment.
10,000 Years Institute has a leadership role in developing effective survey and treatment protocols, implementing this project, and communicating results to agencies, researchers, and the public. Data collected during the course of the project has been used by researchers at the University of Washington and Olympic National Park working to understand the species and impacts to native riparian and aquatic ecosystem dynamics, and most recently, the Western Integrated Pest Management Center has awarded funding to analyze and synthesize the 20-year dataset for a peer-review journal paper.
As knotweed decreases, other invasive species have increased, and the project continues as a multi-species early detection/rapid response (ED/RR) program, focused on maintaining the capacity of a large migrating river system to continually restart native riparian succession, which is foundational to the ecosystem’s food web and is critical to habitat formation.
Knotweed on the Middle Hoh
10KYI has led knotweed control projects on the Hoh River since 2002.
Click through the slideshow below to see the progression of knotweed spread mapped and treated by 10KYI between river miles 16 and 29 from 2002 to 2021.
Invasive Plant Prevention & Control History, Current Trends, Recommended Strategies in the Hoh River
Scroll through the slides below to learn more about the timeline of invasive species management projects and funding sources in the Hoh River, as well as 10KYI survey, treatment, and prevention strategies.
Past Progress Reports
KNOTWEED CONTROL ON THE HOH RIVER SUMMARY REPORT – 2002 TO 2004
KNOTWEED CONTROL ON THE HOH RIVER:2005 SUMMARY REPORT
KNOTWEED CONTROL ON THE HOH RIVER:2007 SUMMARY REPORT
KNOTWEED CONTROL ON THE HOH RIVER:2008 SUMMARY REPORT
KNOTWEED CONTROL ON THE HOH RIVER:2009 SUMMARY REPORT
Research funded through Western IPM Center
Analysis of Distribution, Expansion and Management of Invasive Knotweed Over Two Decades on an Unregulated River
Project Summary: This project will analyze a comprehensive 20-year monitoring and treatment dataset for invasive knotweed along the Hoh River in western Washington. Survey and treatment records for knotweed have been collected and systematically maintained since an eradication program was initiated by the Hoh Tribe in 2002, four years after the initial detection of knotweed in the river. Because the timing and point of introduction of knotweed is precisely known, and the dataset encompasses information on treatment as well as georeferenced survey data, it represents a unique opportunity for an environmental analysis and synthesis of best practices for researchers and managers working on invasive knotweed and other invasive riparian plants. Results will be shared through multiple channels to ensure broad reach to researchers, land and natural resource managers, invasive species managers, and private landowners, including publications, at conferences and through a half-day workshop.