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UBC Theses and Dissertations

The cascading effects of invasive Sitka black-tailed deer (Odocoileus hemionus sitchensis) on the soils, plants and fungal communities of Haida Gwaii Mendenhall, Dylan Thomas


In Haida Gwaii, the invasion of Sitka black-tailed deer (Odocoileus hemionus sitkensis) has decreased the abundance and diversity of plant communities, but little is known about their indirect effects on the activity, abundance, diversity and structure of soil fungal communities. In a natural experiment, I compared the edaphic properties, understory plants and soil fungi of deer-invaded and non-invaded islands. Soils on deer-invaded islands had significantly higher penetration resistance, higher phosphate concentrations and lower pH than soil on non-invaded islands. Understory plants on deer-invaded islands had significantly lower cover-abundance, higher species evenness and significant shifts in community composition, largely driven by differences in the abundances of Gaultheria shallon, Polystichum munitum, Lonicera involucrata and Menziesia ferruginea. Ergosterol, a biomarker of fungal biomass, was similar between deer-invaded and non-invaded islands. Illumina sequencing revealed significant differences in the species evenness and composition of the soil fungal community, but similar relative abundances of arbuscular mycorrhizal fungi, ectomycorrhizal fungi, ericoid mycorrhizal fungi and saprotrophic fungi between non-invaded and deer-invaded islands. Differences in the fungal community were significantly correlated with the cover-abundance of understory plants, the depth of the organic horizons, pH and concentrations of ammonium. In a greenhouse bioassay, Thuja plicata seedlings grown in living soils from deer-invaded islands had significantly lower chlorophyll fluorescence values (Fv/Fm), an indicator of plant stress, than seedlings grown in living soil from non-invaded islands, but there were no significant differences in the biomass, root:shoot ratios or the inoculum potential of arbuscular mycorrhizal fungi and dark septate endophytes in Thuja plicata. There were no significant differences in the biomass, root:shoot ratios, Fv/Fm values or inoculum potential of ectomycorrhizal fungi in Tsuga heterophylla grown in soils from deer-invaded and non-invaded islands. Fluorescence-based enzyme assays reveal significantly higher phosphatase activity, lower β-glucosidase and lower cellobiohydrolase activity in soils from deer-invaded islands. Through changes in the physiochemical soil properties and understory plant abundance, Sitka black-tailed deer initiate a cascade of indirect effects on the activity, diversity and composition of the soil fungal community.

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