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Date of Award
Master of Science (MS)
Bunn, Andrew Godard
Wallin, David O.
Great Basin bristlecone pine (Pinus longaeva) and foxtail pine (Pinus balfouriana) are valuable paleoclimate resources due to the climatic sensitivity of their annually-resolved rings. Recent treeline research has shown that growing season temperatures limit tree growth at and just below the upper treeline. In the Great Basin, the presence of precisely dated remnant wood above modern treeline shows that this ecotone shifts at centennial timescales tracking long-term changes in climate; in some areas during the Holocene climatic optimum treeline was 100 meters higher than at present. Such phenomena has motivated this analysis; regional treeline position models built exclusively from climate data may identify characteristics specific to Great Basin treelines and inform future physiological studies, and provide a measure of climate sensitivity specific to bristlecone and foxtail pine treelines. This study implements a topoclimatic analysis—using topographic position to explain patterns in surface temperatures across complex mountainous terrain—to model treeline position of three semi-arid bristlecone and/or foxtail pine treelines in the Great Basin as a function of topographically modified climate variables calculated from in situ measurements. Results indicate: (1) the treelines used in this study require a growing season length of between 143 - 152 days and average temperature ranging from 5.5 - 7.6 °C, (2) site-specific treeline position models may be improved through topoclimatic analysis—specifically the inclusion of an integrated measure of climate rather than a growing season isotherm measured in degrees, (3) treeline position in the Great Basin is likely out of equilibrium with the current climate indicating a potential shift in the primary growth-limiting factor at the highest elevations where trees are found.
Western Washington University
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Bruening, Jamis M., "Fine-scale Topoclimate Modeling and Climatic Treeline Prediction of Great Basin Bristlecone Pine (Pinus longaeva) in the American Southwest" (2016). WWU Graduate School Collection. 488.