Notorious Knotweed on the Skagit
On Saturday August 3rd and small but dedicated contingent of folks from the Phillips 66 refinery in Ferndale rafted along the Skagit River. The group was hosted by the Skagit Fisheries Enhancement Group and the purpose of the trip was to learn about about the invasive knotweed species (Polygonum spp.) along the Skagit River. This trip was made possible because SFEG received a grant from the National Fish and Wildlife Foundation, to which Phillips 66 had made a donation, with the caveat that it be used near one of their refineries. It just so happens that the nearest refinery to the Skagit is in Ferndale, just north of Bellingham.
At the beginning of this leisurely float down the river Philips 66 volunteers enjoyed the majestic scenery, while learning about how knotweed impacts the local ecosystem.
Knotweed is bad for in riparian areas because it impacts the local biota. Studies have shown that on streams with large knotweed infestation there are up to 40% fewer macro-invertebrates. These little water dwelling critters are the main food source for juvenile salmon; fewer bugs means fewer juvenile salmon. Large knotweed infestations also impact local vegetation. Knotweed grows in the understory and forms a monoculture, excluding native species that local fauna have evolved to depend on. The patches are so dense that no light reaches the ground so nothing grows under a knotweed infestation. Typical stream side trees are alders and cottonwoods, which are relatively short lived. The problem is that once these alders and cottonwoods die of old age there is nothing but knotweed left. Knotweed does not provide the inputs to the stream that salmon depend on. Typically you would have a second generation of trees particularly cedars that would thrive once the alders and cottonwoods die, but they are not able to survive in competition with knotweed.
It was initially hard to impress upon the Phillips 66 folks how knotweed was impacting the local system because we started the rafting trip at Sutter Creek (mile post 100 on highway 20). This area has been under the scope of the Upper Skagit Knotweed Control Program since 2010 so there was no knotweed present. In fact SFEG has been controlling knotweed down to Rockport since 2010, so we saw no evidence of this pesky plant until we floated past Howard Miller Steelhead Park.
Once we floated past the project boundary knotweed began to show up in force. The Phillips 66 volunteers were furiously tapping points into the GPS so that SFEG could import those points onto a map in order to prioritize treatment in the coming years. Even though we were busy working hard there was still time to appreciate the qualities that make the Skagit a designated Wild and Scenic River.
