Non-native Plants Threaten Gales Creek
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The Gales Creek watershed is one of the many large rural sub-basins of the Tualatin River. Over the last 100 years the landscape of the watershed has changed dramatically. Where there were once Oregon oak and Douglas fir there is now pastureland, vineyards, Christmas tree farms, and orchards. Where there were once flood plains there are now agricultural crops. Disturbances on the land have allowed non-native plants to take hold and threaten the health of Gales Creek.
Japanese knotweed which thrives on stream banks may be the most threatening of these intruders. Japanese knotweed has bright green heart-shaped leaves and hollow reddish colored stems. It grows extremely rapidly and establishes extensive root systems. It is shade tolerant and reproduces from small stem or root fragments. The combination of these traits makes it a serious threat to Oregon’s native plant communities.
Once established, knotweed can form dense patches 10 feet high that exclude native vegetation, including willows and cottonwoods. As it takes over it can cause changes to the stream. Knotweed does not hold the soil well, causing stream banks to erode and sediment to enter the streams. It offers less shade than a native canopy, causing water temperature to increase. And large wood in the stream may become more scarce, a key component of Pacific Northwest river systems. Finally, a monoculture of knotweed is not able to provide habitat for wildlife or support the aquatic food chain.
Three Rivers is helping to address the problem of Japanese knotweed in Gales Creek. In partnership with the Tualatin River Basin Watershed Council and the Bureau of Reclamation, a crew surveyed three miles of Gales Creek to locate and document the extent of knotweed coverage. The survey found that 23 acres of the 97 mapped have some level of infestation. Within the infested 23 acres, approximately 11 acres are covered in 70% density. These facts will be used to recommend treatment methods and strategies and to locate sources of funding for removal and control.
Please click here to read the Lower Gales Creek Report and here to visit our Lower Gales Creek project page.