Effects of Climate Change and Forest Governance on Large-scale Insect Outbreaks: A Socio-ecological Systems Case Study of the Mountain Pine Beetle in North America
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Date
2020-02-27
Authors
Chen, Dongmei
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Publisher
University of Oregon
Abstract
The mountain pine beetle (MPB) has devastated trees on more than 1.3 million square kilometers of land in North America, converting these forests from a carbon sink to a carbon source. The beetle population has reached an unprecedented level over the 20th century, quickly expanding its outbreak range to regions historically too cold for it to survive. The range expansion has been widely attributed to climate change, yet the relative contributions of climate change and forest governance to MPB infestations have been largely overlooked. This dissertation studies large-scale MPB outbreaks with a perspective grounded in socio-ecological systems (SES) to illustrate the complex adaptive systems of MPB.
By primarily utilizing predictive models to reveal nonlinear and emergent patterns of MPB eruptions, the dissertation investigates cross-scale biotic and abiotic interactions in the MPB SES to explain both top-down and bottom-up controls on beetle outbreaks. In so doing, the case study makes four interdisciplinary contributions. First, it initially examines the continental-scale MPB range expansion that shows extraordinary patterns emerged from ecological processes at local and regional scales. Second, it provides a SES model of large-scale forest disturbances to advance the understanding of anthropogenic impacts on ecosystems. Third, it extends the application of SES resilience to the relationship between regime shift and resilience. Fourth, it creates transferable data and methods for future landscape ecological research.
The dissertation uses climate space to visualize how the MPB climate niche has changed with its spatial expansion, species distribution modeling to demonstrate how bioclimate has contributed to outbreak probability, and geographically weighted regression to localize the significance of climatic and non-climatic factors in driving MPB outbreaks. The results show that the MPB has expanded to a colder climate space compared with its previous range. The landscape-level MPB eruptions exhibit a strong response to climatic warming. Non-climatic controls are common, especially as long-term fire exclusion causing positive feedback to MPB outbreaks. The complexity of MPB SES presents an archetypical ‘tipping-point’ model triggered by human impacts, in which a shift in the disturbance regime reveals that anthropogenically-amplified MPB outbreaks are transforming forest ecosystems.
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Keywords
climate change, climate space, fire suppression, mountain pine beetle, spatial analysis, species distribution modeling