|Abstract or Summary
- Invasive vegetation control studies traditionally aim to control existing populations as well as limit future spread of the species. However, little additional attention has been dedicated to aiding native communities to recover and reestablish. One prominent example of a studied invasive is Brachypodium sylvaticum (Huds.) P. Beauv. (false brome), a bunchgrass native to Europe, Asia, and North Africa but invasive to North America. B. sylvaticum is capable of forming dense monocultures under forested canopies in North America. Such invasions can detrimentally affect the ecological functions and processes of an inhabited ecosystem. To address the negative ecological effects of this grass' invasion, this study evaluated how herbicide and prescribed burns, singly and in combination, affected B. sylvaticum abundance and the surrounding plant community in western Oregon foothills. The specific objectives of this study were to: 1) determine the most effective treatment in reducing B. sylvaticum abundance or cover in the field, 2) evaluate how different treatments alter total plant community cover, excluding B. sylvaticum, 3) assess residual seed bank following prescribed treatments, and 4) describe compositional changes in the plant communities after one growing season following control treatments.
My study was located in Oregon State University's McDonald Forest under a split-plot design with 12 blocks total and 10 treatments randomly assigned within each block, which included the use of two herbicides and prescribed burning in various combinations, for a total of 9 treatments and a no-treatment control. All treatments that involved application of an aggressive, broad-spectrum, foliar herbicide applied in the summer were most effective in reducing not only the existing B. sylvaticum in the field, but also the residual seed bank one year after application, while maintaining native community seed bank abundance. A prescribed burn following the aforementioned summer herbicide demonstrated no added benefit in controlling B. sylvaticum. Less intense fall prescribed burns without a previous broad-spectrum herbicide treatment may promote B. sylvaticum growth.
All treatments involving the aggressive summer herbicide displayed significant reductions in total native species cover and species richness compared to the controls. Treatments without this herbicide demonstrated richness and diversity similar to the controls, but the remaining species after one growing season were primarily dominant shrubs or non-native weeds. Using multivariate community analysis, I documented a shift in species composition due to treatment in which the strongest effect also associated with summer herbicide application.
This study now serves as a baseline to develop and refine cost-effective techniques for both controlling B. sylvaticum populations in the Oregon Coast Range and restoring invaded native plant communities. Future studies should monitor any responding B. sylvaticum populations and species composition beyond the first growing season, consider incorporating multiple applications of such treatments, and quantify seed recruitment by both B. sylvaticum and native species.