| Summary: | Specialization: Forest Biology and Management Degree: Doctor of Philosophy Abstract: As climate changes and disturbance regimes shift, there is a need to better understand and anticipate potential impacts of both natural and anthropogenic disturbance agents on forest ecosystems. Lodgepole pine forests in western Canada are experiencing an unprecedented mountain pine beetle (MPB) outbreak, and the ecosystem-level effects of ongoing expansion of MPB into novel habitats east of the Canadian Rockies are unknown. Another way ecosystems are being disturbed is through management practices that are attempting to enhance timber production by using introduced species in plantations; lodgepole pine has been introduced around the world as an important timber species, but its invasive potential in some areas, such as Sweden, remains unclear. To better understand the ecological impacts of disturbance in lodgepole pine ecosystems I investigated: i) fine-scale patterns in understory plant and microbial communities in mature lodgepole pine forests; ii) effects of simulated MPB attack and salvage harvest on above- and below-ground dynamics of these forests; iii) potential for pine regeneration after MPB attack in newly invaded stands; and iv) effects of the introduction of lodgepole pine to Sweden on forest floor properties and processes. In mature undisturbed lodgepole pine forests I identified four fine-scale plant communities, primarily influenced by below-ground factors; four structural microbial communities, primarily influenced by the understory composition; and four functional microbial communities that were not strongly associated with any environmental factors measured in my study. I found short-term resistance to ecosystem change after simulated MPB attack, compared with more immediate ecosystem changes in response to salvage harvest. Regeneration of lodgepole pine seedlings appears unlikely to occur in the short term after MPB attack without active silvicultural intervention. In northern Sweden, introduced lodgepole ...
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