UBC Theses and Dissertations
First step restoration techniques in invaded grassland in southern British Columbia Knopp, Angela
Invasive species are considered the second greatest threat to biodiversity (after habitat loss) as they can alter ecosystem functioning, including nutrient cycling. Invasive plant species can be controlled using various methods and restoration is often attempted in degraded areas. Biological control temporarily eliminated diffuse knapweed from a site in Vernon, British Columbia, though the site remained completely dominated by other invasive species. Restoration was attempted using seed addition of native species and late summer and spring vegetation removal of invasive species. Seed addition did not result in increased native species abundance in the plots, likely because of abnormally low April precipitation. Vegetation removal in spring did not prevent the emergence of seedlings, and actually increased emergence of diffuse knapweed and thyme-leaved sandwort. Annual grasses on the other hand were more abundant in plots without vegetation removal. Removal of vegetation in the plots was not evident by biomass harvest in August, though it significantly increased diversity and the percentage of forbs in the total biomass. The plots with no vegetation removed had significantly greater percentage of grass in the total biomass and far greater litter mass. Comparing soil samples from two invaded ecosystems (diffuse knapweed and sulphur cinquefoil dominated) to one with few invasive species (bunchgrass dominated) resulted in finding that almost all nutrient levels measured and moisture were highest in the uninvaded ecosystem. As diffuse knapweed reacts positively to the removal of competition, vegetation removal should not be used as a restoration technique in invaded areas. In areas where there is no knapweed, however, vegetation removal may be beneficial to work against dominance by annual grass species. Soils of invaded ecosystems may also need to be considered, and only vegetation that can withstand drought and low levels of nutrients should be used.
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