Invasive Plants in PNW Ecosystems
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Phalaris arundinacea L.control and riparian restoration within agricultural watercourses in King County, Washington.Lizbeth Seebacher – UW Botanic Gardens, University of Washington Re-establishment of native riparian buffers along the margins of agricultural lands is a significant challenge resulting from the competition of established vegetation, particularly Phalaris arundinacea (reed canary grass (RCG)). Agricultural runoff and the associated nitrogen addition contributes to the increasing colonization and dominance by this invasive. Many studies have successfully utilized a form of carbon to reduce nitrogen trying to give native species an competitive edge on exotics. The use of red cedar hogfuel as a carbon addition was utilized in this study. Additionally, I investigated the efficacy of planting mixed canopy layers. Past research has shown that canopy gaps and single canopy layers increased the invasibility of the site by RCG germination and re-generation. The three treatments included: red cedar hogfuel densely planted with willow stakes; a mat planted with mixed canopy layers; and hogfuel with the same mat. Three sites were chosen within agricultural systems in King County. The RCG re-growth via stem count for each treatment and control plots were counted bi-weekly throughout the growing season for two years. The percent cover of vegetation within each plot was also recorded at the end of the experiment to determine survival and competitive efficacy of the planted native species with the RCG. The data from 2004 & 2005 indicate that the hogfuel/willow and the hogfuel/ mat treatments significantly reduced the RCG regrowth for the first two growing seasons after treatment. The results of a controlled competition study between Phalaris arundinacea and Scirpus microcarpus will also be presented. This study included the use of two soil moisture and nitrogen treatments.
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