DESCRIPTION
Knotweed control is the primary component of this restoration plan. The project area is a second priority riparian habitat restoration area. The goal of the project is to accelerate the natural recruitment and re-introduction of native conifers from the Oso slide and downstream by reducing knotweed infestations to a level where knotweed is no longer an environmental threat. The project will control knotweed on 25 river miles per year. Approximately 70 acres per year will be controlled. A total of 140 acres and 50 river miles of knotweed will be controlled between Oso and Arlington. Knotweed control will be followed by conifer planting as needed. Knotweed control will open up understory areas allowing 5 acres to be planted with 2000 conifers. A mix of native conifer species will be planted. Approximately 0.5 rivermiles will be replanted providing a seed source for natural recruitment along with providing shade and large wood. Knotweed control allows fishermen and other recreationists to reach the river. Increased salmon runs of all species since cool water and stream complexity benefits all of the salmonid species. There are 259 cooperators with entry agreements with the SCNWCB. 20 agreements are downstream from Oso. Cooperators are contacted yearly. The goal is to add 40 more cooperators. Knotweed stops juvenile tree development. In 50 to 100 years there will be few trees in riparian areas currently forested by successional hardwoods. And, there will be knotweed.
The knotweed treatment covered the North Fork and the South Fork Stillaguamish River; including the tributaries, Squire Creek and Canyon Creek. The goal was achieved in the South Fork where knotweed infestation was light. Along the North Fork, knotweed was detected upsteam from the Oso Slide. The goal was adapted to include knotweed control upstream of the slide area or close to the source of dispersal.
A total of 265.4 gross acres were treated between 2016-2019. The acreage was a combination of new and retreated areas. 13 river miles were protected along the North Fork Stillaguamish and 26.5 river miles were covered in the South Fork Stillaguamish. 22.6 acres along 1.8 river miles were planted between 2016-2019 with 8500 native trees and plugs. The project exceeded the original goal expectations. Only the North Fork Stillaguamish was planted. The South Fork Stillaguamish have light patches of knotweed, and less planting opportunities. 5 large sites were planted. 2600 tree plugs were planted at three locations, downstream from the Oso slide. 25 new landowner permissions were gathered, less than the original intent. However, the agreements were with key owners owning large tracts of land along the river or have easy access to the river and planting area.
