Knotweed Control and Riparian Enhancement

The goal of this project was to identify and treat all knotweed infestations in the Dewatto and Union Rivers.

Need: Compared to native plant species, knotweed shows a decreased ability to control erosion despite having an extensive root system. During flood events, plant fragments are washed downstream where rhizome and stem pieces create new infestations. Increased sediment is a factor in the loss of productive salmonid habitat. Sediment can fill in the spaces between riverbed spawning gravels and fill in pools used for rearing. It negatively affects salmonids by smothering viable eggs, decreasing their feeding success, and damaging gill filaments. Knotweed negatively affects aquatic invertebrates that compose the basis of the aquatic food chain by an alteration of the quality and timing of the leaf litter regime. This alteration changes nutrient inputs and soil composition. Invertebrates are the primary food source of juvenile fish species.
Outcomes: Location, Control, Monitoring of Knotweed infestation, and restoration of riparian corridors. Best science demands a three year control cycle.

The goal of this project was to identify and treat all knotweed infestations in the Dewatto and Union Rivers and begin a three year treatment cycle.