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Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA / KARENZA PEARSON

Swansea University Author: KARENZA PEARSON

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Abstract

Current wildfire activity in the United States is often described as ‘unprecedented’. To evaluatewhether present-day vegetation and wildfire dynamics fall outside of their historical range ofvariability, palaeoecological records provide a baseline of natural disturbance regimes and forestdynamics. I...

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Published: Swansea 2026
Institution: Swansea University
Degree level: Master of Research
Degree name: MRes
Supervisor: Froyd, C. A.
URI: https://cronfa.swan.ac.uk/Record/cronfa72062
first_indexed 2026-06-11T12:23:57Z
last_indexed 2026-06-12T13:21:37Z
id cronfa72062
recordtype RisThesis
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spelling 2026-06-11T13:23:55.8789129 v2 72062 2026-06-11 Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA d53380a0c1f78a4f8c643401403df563 KARENZA PEARSON KARENZA PEARSON true false 2026-06-11 Current wildfire activity in the United States is often described as ‘unprecedented’. To evaluatewhether present-day vegetation and wildfire dynamics fall outside of their historical range ofvariability, palaeoecological records provide a baseline of natural disturbance regimes and forestdynamics. In the Pacific Northwest, concerns have grown over changes in fire regimes, yet high elevation forests in the Cascade Mountains remain relatively understudied. In the high CascadeMountains, pollen and charcoal preserved in sediment from Little Monon Lake (~2,500 cal yr BP) andPyramid Lake (~6,400 cal yr BP) were analysed to reconstruct vegetation and fire histories. Bothrecords reveal persistent dominance of Pinaceae forests, with only modest compositional shifts linkedto disturbance-associated taxa. Statistically significant differences in pollen assemblages identify twoperiods of distinct vegetation at Little Monon Lake and three at Pyramid Lake, with the most recentperiods at both sites beginning around 700 cal yr BP. Mann-Whitney U tests confirm significantdifferences in fire activity between these pollen zones at both sites, indicating a close link betweenvegetation composition and burning. This transition coincides with a marked decline in fire activity,suggesting a regional shift in disturbance dynamics. This downturn is more plausibly explained byclimatic change, likely linked to the onset of the Little Ice Age, than by anthropogenic suppression.Site differences reflect contrasting ecological contexts: Little Monon Lake shows fewer butpotentially more severe fires, influenced by lodgepole pine-dominated forests, while Pyramid Lakeexhibits frequent fire events, consistent with its diverse conifer assemblage and mid-elevation setting.These records demonstrate that high Cascade forests have been resilient to long-term shifts in fireregimes, with vegetation and wildfire interactions dynamic but not driving major ecological change.However, projected increases in fire frequency, severity, and extent under climate change may test thisresilience beyond the range of variability observed. E-Thesis Swansea Paleoecology, paleobiology, wildfire, vegetation, Pacific Northwest, ecology 30 4 2026 2026-04-30 COLLEGE NANME COLLEGE CODE Swansea University Froyd, C. A. Master of Research MRes 2026-06-11T13:23:55.8789129 2026-06-11T13:10:39.2376658 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Biosciences KARENZA PEARSON 1 72062__36935__8a33a6d1d62f45a6a40dbe39b2588404.pdf 2026_Pearson_K.final.72062.pdf 2026-06-11T13:19:11.1644411 Output 4782869 application/pdf E-Thesis – open access true Copyright: the author, Karenza Pearson, 2026. true eng
title Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA
spellingShingle Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA
KARENZA PEARSON
title_short Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA
title_full Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA
title_fullStr Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA
title_full_unstemmed Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA
title_sort Long-term vegetation and wildfire dynamics in the high Cascade Mountains, Pacific Northwest, USA
author_id_str_mv d53380a0c1f78a4f8c643401403df563
author_id_fullname_str_mv d53380a0c1f78a4f8c643401403df563_***_KARENZA PEARSON
author KARENZA PEARSON
author2 KARENZA PEARSON
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publishDate 2026
institution Swansea University
college_str Faculty of Science and Engineering
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hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Biosciences, Geography and Physics - Biosciences{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Biosciences
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description Current wildfire activity in the United States is often described as ‘unprecedented’. To evaluatewhether present-day vegetation and wildfire dynamics fall outside of their historical range ofvariability, palaeoecological records provide a baseline of natural disturbance regimes and forestdynamics. In the Pacific Northwest, concerns have grown over changes in fire regimes, yet high elevation forests in the Cascade Mountains remain relatively understudied. In the high CascadeMountains, pollen and charcoal preserved in sediment from Little Monon Lake (~2,500 cal yr BP) andPyramid Lake (~6,400 cal yr BP) were analysed to reconstruct vegetation and fire histories. Bothrecords reveal persistent dominance of Pinaceae forests, with only modest compositional shifts linkedto disturbance-associated taxa. Statistically significant differences in pollen assemblages identify twoperiods of distinct vegetation at Little Monon Lake and three at Pyramid Lake, with the most recentperiods at both sites beginning around 700 cal yr BP. Mann-Whitney U tests confirm significantdifferences in fire activity between these pollen zones at both sites, indicating a close link betweenvegetation composition and burning. This transition coincides with a marked decline in fire activity,suggesting a regional shift in disturbance dynamics. This downturn is more plausibly explained byclimatic change, likely linked to the onset of the Little Ice Age, than by anthropogenic suppression.Site differences reflect contrasting ecological contexts: Little Monon Lake shows fewer butpotentially more severe fires, influenced by lodgepole pine-dominated forests, while Pyramid Lakeexhibits frequent fire events, consistent with its diverse conifer assemblage and mid-elevation setting.These records demonstrate that high Cascade forests have been resilient to long-term shifts in fireregimes, with vegetation and wildfire interactions dynamic but not driving major ecological change.However, projected increases in fire frequency, severity, and extent under climate change may test thisresilience beyond the range of variability observed.
published_date 2026-04-30T14:21:37Z
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score 11.10865

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