Phalaris arundinacea control and riparian restoration within agricultural watercourses in King County, Washington
Seebacher, Lizbeth Ann
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Phalaris arundinacea (reed canarygrass) is one of the most aggressive and challenging invasive species within wetlands of the Pacific Northwest. This invasive typically dominates a site, producing a monoculture, reducing the biodiversity and microhabitats on the site.Three treatments were tested within agricultural watercourses for reed canarygrass stem reduction. Two of the three treatments were successful in reducing the returning stem count. The densely planted single canopy and hogfuel treatment (HF/willow) and a multi-canopy and hogfuel treatment (referred to as an RCG barrier) reduced the returning reed canarygrass stem counts by 64% and 56% respectively compared to the control plots.A competition experiment was implemented within a controlled setting between Phalaris arundinacea and a native wetland sedge, Scirpus microcarpus. In addition to competition, two other treatments were integrated into this experiment, high vs. low soil moisture and high vs. low nitrogen additions. Although a statistically significant reduction of reed canarygrass biomass was not found when reed canarygrass was grown with small fruited bulrush (Scirpus microcarpus), a trend of reduced RCG biomass was noted within the high soil moisture, high nitrogen, interspecific competition treatments. Copious amounts of carbohydrate reserves in reed canarygrass rhizomes can be problematic as the shoots easily return after control methods from the reserves. The carbohydrate reserve levels within reed canarygrass rhizomes were tested after detaching from the parent clone and placing under an opaque material. A sample of the rhizomes were removed after three, six and nine months and analyzed for fructosan levels. The results from the regression indicate too high a variation within the three-month samples and too few data points within the six and nine-month samples to receive a significant fit of the data to the recession line. However, averaging the data, shows a sustained level of fructosans for the first six months, followed by a significant drop of fructosans at the nine month time frame. Additionally, a considerable reduction in the number and size of the rhizomes found after six and nine months reveal that breaking the rhizomes away from the clones and covering with an opaque material weakens their ability to survive over time. This suggest that tilling, followed by mulching, may be an effective control strategy.
- Forestry