Hoh River Invasive Species Prevention and Control

The Hoh River project is a continued ‘restoration for resiliency’ applied program to protect native riparian and floodplain plant communities from non-native invasive plants in the wild Hoh River watershed where - because of mature riparian forests and cold water flowing from melting Olympic glaciers - five species of wild salmon, steelhead, and bull trout still thrive.

Through control and prevention of aggressive invasive plants on the terraces, floodplains, riverbanks, and gravel bars of the river, this project implements near-term restoration and long-term protection of native riparian forest, preventing degradation of the ecosystem services, processes, and functions required by the Hoh watershed’s native salmon, steelhead, cutthroat trout, char, and all other species. The project protects past and future restoration investments in fish passage, riparian forest enhancement, bank stabilization, and sustains resiliency to changing climatic conditions in forests and river valleys, while providing meaningful local employment and skills development.

The project covered the thirty miles of the mainstem Hoh River’s floodplain and channel migration zone (CMZ) on the Olympic Peninsula in west Jefferson County, from the boundary of the Olympic National Park at river mile (RM) 30 downstream to the river’s mouth at the Pacific Ocean. Eight miles of the lower reaches (0.5 to 2 miles) of the ten tributaries crossing the forested floodplain were also included in the project - from upstream to down -Owl, Dismal, Willoughby, Elk, Alder, Winfield, Lost, Nolan, Pins, and Braden creeks.

The current project’s work was conducted in 2019, 2020, and the first quarter of 2021. Details are outlined below.

The 2014 and 2015 PCSRF award dollars were spent within the award period.

2019 Accomplishments and Challenges
2019 work on the Hoh River was conducted between January and December when river conditions were low and weather was conducive to fieldwork. Over 7,200 hours of invasive plant prevention and control conducted by 10KYI’s restoration technicians surveying over 4,200 acres of riverbanks, side-channels, gravel bars, islands, and forested floodplains between river miles 30 and 1.0. The crew ranged between 6 and 14 members, coordinated and supported by senior staff with support from 10KYI’s GIS specialist. Pulling, cutting, seed removal, and treating invasive plants with low-risk herbicide was conducted on property owned and/or managed by Olympic National Park (ONP), Olympic National Forest (ONF), Washington State Department of Natural Resources (WADNR), the Hoh Indian Tribe, The Nature Conservancy (TNC), Jefferson County, and small private agricultural and residential landowners. A significant new project started by partners in the watershed - the Middle Hoh Resiliency Plan (now the Hoh River Resiliency Plan) - #18-2005 - became a platform to share the challenges and successes of this project/program.

Project implementation: During January through March of each year, the crew focused on pulling and treating herb Robert and Scotch broom; in April and May, work on Scotch broom and herb Robert continued, and tansy ragwort, reed canarygrass, and spotted jewelweed were added. Knotweed plants found during surveys for these other species were mapped and flagged for late summer and fall herbicide treatment. Scotch broom cut-stump and herb Robert spray treatments continued through the fall and winter as river flow and weather conditions allowed. Concurrent work on all species was conducted upslope out of the river corridor under WCRRI projects #18-2136 and #20-1416. Effectiveness monitoring was conducted at all treated sites to ascertain treatment and method efficacy and degree of seed bank viability. We were surprised by the high degree of efficacy of winter herb Robert treatment and dismayed by the robust response of Scotch broom to cutting only, then covered by river flows and sediment, and branching out v

The goal remaitns the same - after almost two decades of work on the river - the work continues to act early and often - stopping new species, preventing the production of seeds, and to control plants emerging from googles of seeds and propagules banked in sediments and soil. With increasing disturbance from glacial retreat and heavier rain, flashy flows, bank erosion requiring road protection projects, and new introductions from thousands of visitors, vehicles, and equipment - continued investment in prevention and control is critical to supporting the processes forming habitat and protecting resilient native riparian forests.