Subarctic ecosystem resilience under changing disturbance regimes

Brehaut, Lucas D. (2021) Subarctic ecosystem resilience under changing disturbance regimes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Disturbance regimes are changing across the subarctic as a result of continued climate change. At the northern range edge of the boreal forest, changes to disturbance regimes are predicted to result in a shift in successional trajectory of the current plant community, altering the structure and function of the current ecosystem. As these boreal tree and shrub species are already climatically primed for range expansion, changes to disturbance regimes may facilitate increased establishment of boreal tree and shrub species beyond their current range edge. An investigation of how different disturbances influence biotic and abiotic conditions for early life-stages of boreal tree and shrub species was conducted at the Canadian boreal-tundra treeline ecotone to determine whether disturbances disrupt the ecological inertia of the current ecosystem, creating suitable conditions for successional change and northward boreal tree range expansion. Impacts to microsite conditions by wildfire, insect granivory on spruce cones, and anthropogenic wood harvesting were examined. These disturbance regimes were selected because they are anticipated to change in frequency and extent across the subarctic with continued climate change. Results from each investigation indicated that while disturbances did create conditions that could support increased establishment of boreal tree species, disturbance severities were low, often creating additional challenges for seed germination and establishment. Thus, disturbance induced changes to ecosystem structure and function are not anticipated at these research locations. Future research is required to examine disturbances of different severity at the range edge in order to determine whether disturbances of higher severity are likely to occur and whether they can break the ecological inertia of the current ecosystem.

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