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UBC Theses and Dissertations

Understanding plant-soil-management interactions of Reynoutria spp. (knotweeds) to inform ecological restoration Jones, Vanessa L.


The management of knotweed species (Reynoutria spp.), aggressive clonal invasive plants of riparian areas, present unique management challenges, particularly within the province of British Columbia (BC) where a knowledge gap exists between field practitioners who work to control knotweed infestations and academic researchers who study them. Academic research on invasive plant management tends to apply a target-based lens, which limits our knowledge to effectively control invasive plants long-term. The primary objective of this research project was to shift this focus from a target-based approach to other often overlooked important relationships, such as plant-soil-management interactions. These are relationships that may reveal much needed solutions to effective long-term control and subsequent ecological restoration. Accomplishing this required a broad set of research questions: 1. Examining the soil microbial ecology of knotweed infestations and native salmonberry (Rubus spectabilis) dominated sites. We found that knotweed infestation altered the soil bacterial community, decreased arbuscular mycorrhizal fungi (AMF) abundance and increased phosphorus compared to soil from salmonberry; 2. Testing the efficacy of a non-chemical control method that could be used near waterways where herbicide use is restricted, wire mesh girdling. It was determined that wire mesh significantly reduced stem and patch height but did not eradicate knotweed infestations in a field setting after two years; and 3. Attempting to conduct a dose-response assay to test for resistance to glyphosate in knotweed. Invasive Plant Managers have been reporting cases of epinastic knotweed patches in BC for several years that seem unaffected by repeated annual herbicide treatment. Rhizomes were collected from two such epinastic populations in Port Alice and North Vancouver, BC. However, a series of climate events impacted the ability to conduct the necessary experiments, and resistance to glyphosate could not be confirmed. While climate events had a significant impact on investigation of research questions, our primary research objective to focus on plant-soil-management interactions was accomplished and demonstrates that bridging the practitioner-researcher divide is critical to meeting long-term ecological restoration goals. The research also illuminates the importance of further understanding the legacy of knotweed invasion on the soil to inform restoration of native ecosystems in the post-control phase.

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