The Jamestown S’Klallam Tribe has worked too hard to let an innocent-looking lilac-scented shrub take over its restoration efforts of the Dungeness River. Much like knotweed, Scotch broom and English ivy, the butterfly bush, also known as Buddleia, has become an invasive species in recent years.
“It’s only recently that we’ve realized the threat invasive species may pose to our long-term restoration goals for the Dungeness River,” said Hilton Turnbull, the tribe’s habitat biologist. “There’s not a lot of research available from our area on this species but we’ve been watching it spreading rapidly since 2004 and are concerned it’s affecting salmon habitat.”
The purple flower-bearing bush starts out small as a backyard shrub, but it can quickly grow to be 18-feet tall and 20-feet wide in less than a decade. It can produce as many as 40,000 seeds per single flower head, which spread by wind and water. With a 30-year lifespan and rapid reproduction cycle, the Asian plant out-competes native trees such as red alder, cottonwood, cedar and other conifers. Native trees provide shade that keeps the river cool and help form prime salmon habitat after they fall into the river, creating pools of water for salmon where they rest, feed and hide from predators. Buddleia can’t achieve the same effect.
Butterfly bush is commonly planted to provide habitat for butterflies. However, the Washington State Noxious Weed Control Board has found that it is rarely used by butterflies as a host plant and may in fact displace the native plants needed by butterflies for reproduction.
“Because it spreads rapidly, it can quickly take over the native species,” Turnbull said. “A healthy functioning river with native plants is critical to the successful restoration of the Dungeness River.”
Turnbull has spent the past three summers mapping the shrubs and eradicating them along 10 miles of the river, from its mouth to the Dungeness River Fish Hatchery. So far, the tribe has treated 83 acres of streamside habitat and selectively replanted native species in place of the Buddleia thickets. The tribe’s natural resources staff cuts the Buddleia at its base and applies an herbicide directly to the stump to kill the root system.
Turnbull is working with other groups and agencies to educate riverfront property owners about the issue and help create “fish-friendly yards.” The main problem he faces is that the plant is sold at local nurseries. Turnbull notes that although the plant has been banned from retail sale in California and Oregon, it is still legal to purchase here, despite being listed as a noxious weed in Washington state.
“We’d like to provide information to retailers advising people not to plant buddleia near a stream or river and we can also recommend native plant alternatives to interested landowners,” he said.
Funding for this project comes from a Bureau of Indian Affairs grant. Support from property owners living on the Dungeness River has also been crucial and beneficial to the effort.