The Squaxin Island Tribe is replacing salmon-killing invasive weeds with a streamside forest.

The tribe recently planted an acre of new forest along Skookum Creek. Over the last five years the tribe and Mason County Conservation District effectively controlled invasive knotweed that was rapidly spreading throughout the watershed.

“It is almost impossible to find any knotweed left in the watershed,” said Andy Whitener, natural resources director for the tribe. “We’re replacing it with a forest that can help salmon.”

Knotweed is a fast-spreading and adaptive invasive species mostly found along stream corridors. Controlling it across an entire watershed is a significant accomplishment. “Knotweed is incredibly tough, people have even found it growing on slopes with no apparent water source,” said Sarah Zaniewski, a tribal salmon habitat biologist.

Over the last five years tribal and the conservation district staff tracked knotweed infestations each growing season throughout the watershed using global positioning system technology. Conservation district crews then used that data to treat the infestations with herbicide by either spraying the plants or swabbing the leaves by hand.

The tribe is replanting with native species found to grow well throughout the watershed and that provide shade and nutrients that support healthy stream habitat. “Streamside forests should include the kind of features that salmon evolved to depend on,” Zaniewski said.

Skookum Creek has crucial coho and chum spawning and rearing habitat. For the last decade, the tribe has restored salmon habitat throughout the watershed. The tribe built several logjams that provide critical habitat to juvenile and adult salmon, which included installing spawning gravel beds, and replanted miles of riparian corridor to provide shade to the creek.

Naturally spawning populations of coho are on a gradual decline throughout the region, in part because of declining freshwater habitat. “Coho salmon depend on the health of freshwater habitat because juveniles spend a year to 18 months there before heading out to the ocean,” Zaniewski said.

The riparian planting also will help counter a trend in declining forest cover. Deep South Sound watersheds lost almost 20,000 acres of forests between 2006 and 2011, according to the State of Our Watersheds Report, produced by the treaty tribes in western Washington.

“Forests that grow right up to the edges of creeks matter a great deal to stream health and how well our salmon runs are doing,” Whitener said. “Our treaty rights are directly connected to the health of our watersheds.”