UBC Theses and Dissertations
The effects of introduced Sitka black-tailed deer (Odocoileus hemionus sitchensis) on plant and soil microbial communities on Haida Gwaii and silvicultural tools to improve western redcedar survival Catomeris, Catriona
Soils support vast microbial biodiversity, which control nutrient cycling and can form symbioses with plants; however, overabundant herbivores directly and indirectly affect soils. Introduced Sitka black-tailed deer (Odocoileus hemionus sitchensis) have dramatically altered plant communities on Haida Gwaii, BC, but their effects on soils are unknown. As such, I compared soil physicochemical properties and microbial communities on deer-free and deer-inhabited islands within the archipelago. I additionally assessed the ability of deer repellents and arbuscular mycorrhizal fungal inoculum (AMF) to reduce western redcedar (Thuja plicata) browse damage and increase growth. Distinct plant and bryophyte communities on deer-free and deer-inhabited islands were influenced by Gaultheria shallon, Polystichum munitum, Rhytidiadelphus triquetrus, Hylocomium splendens, Kindbergia oregana, and Scapania bolanderi. Phospholipid fatty acid profiling revealed soils on deer-inhabited islands contained lower fungal and bacterial biomass (NS) than deer-free islands. Gram-negative bacteria were more ¹³C-depleted, likely due to the higher bryophyte cover or soil moisture, on deer-inhabited islands. Plant Root Simulator® probe-measured supply rates of NH₄⁺, Fe³⁺, and A¹³⁺ were higher (NS), while PO₄-, K⁺, and Mn²⁺ were lower (NS), on deer-inhabited islands. Soil pH was lower, while penetration resistance was higher on deer-inhabited islands. In the greenhouse, differences in chemical properties rather than AMF inoculum were likely responsible for the greater redcedar biomass when grown in soil from: a deer-inhabited island versus a deer-free island; and, a redcedar cutblock versus a cedar-free cutblock. Seedling growth did not differ between seedlings inoculated with a commercial AMF inoculum (RootGrow™) and non-inoculated seedlings in the field. A commercial deer repellent (Plantskydd®) reduced browse damage on redcedar seedlings and increased the proportion of time a seedling remained unbrowsed. Commercial inoculum did not promote seedling growth, but browse frequency was lowest on redcedar that received both deer repellent and inoculum. Browse frequency of redcedar boughs was almost a third lower in experimental plots treated with wolf urine than those treated with water. Introduced deer dramatically altered plant and soil communities, which may slow decomposition and nutrient cycling. Deer did not reduce AMF inoculum potential, but browse frequency was high, suggesting fear-inducing deer repellents are a better strategy for redcedar protection.
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