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UBC Theses and Dissertations

Comparative analysis of the floristics, soil chemistry, and vegetation-soil-environment relationships at an ultramafic (serpentine) site in southern British Columbia, Canada Lewis, Gary John


Ultramafic soils present an adverse chemical and physical edaphic environment for plant growth characterized by high metal toxicity, low fertility, and frequently unstable and dry conditions. The associated vegetation tends to be distinct from surrounding areas in species composition and structure and often supports high levels of endemism, speciation, and ecotypic differentiation. The general goals of this thesis were to characterize the influence of ultramafic bedrock on the overlying vegetation in southern British Columbia through a detailed comparison of adjacent ultramafic and non-ultramafic soils and to expand the knowledge of the floristics and ecology of ultramafic sites in the province. Grasshopper Mountain, part of the Tulameen ultramafic complex of southern British Columbia, was selected as the study site since the configuration of adjacent ultramafic and non-ultramafic substrata minimized potential confounding factors. Univariate and multivariate analyses of the soil data revealed three different soil types, each with distinct soil chemistry. The most important factors in distinguishing between soil types were related to soil fertility and metal toxicity. Clear floristic and ecological differences were documented between ultramafic and adjacent non-ultramafic soils. Ultramafic soils supported 28 percent of the local species richness and hosted more rare taxa than non-ultramafic soils. Many species showed patterns of local restriction to or exclusion from ultramafic soil habitats. Patterns of plant family richness and abundance and plant ecological group abundance were distinctly different on ultramafic versus non-ultramafic substrata. Multivariate analyses at the landscape, plant community, and species scales, revealed a widespread influence of ultramafic soils on the vegetation. The landscape scale analysis revealed that the main variation in the vegetation data was related to variation in the measured soil and environmental factors. In the community level analysis four main plant communities were recognized by cluster analysis: 1) ultramafic non-forest, 2) ultramafic forest, 3) non-ultramafic upper elevation forest, and 4) non-ultramafic lower elevation forest. Each of these communities was characterized by multiple significant differences based on ANOVA results of mean soil and environmental factors. Two main soil chemistry gradients were defined using non-metric multidimensional scaling: a primary "toxicity-fertility" gradient and a secondary "alkalinity" gradient which clearly separated the four plant communities within ordination space. The species level analysis revealed clear patterns of species response to ultramafic soils and related factors.

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