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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
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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Swansea
2026
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| Institution: | Swansea University |
| Degree level: | Master of Research |
| Degree name: | MRes |
| Supervisor: | Froyd, C. A. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa72062 |
| 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. 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. |
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| Keywords: |
Paleoecology, paleobiology, wildfire, vegetation, Pacific Northwest, ecology |
| College: |
Faculty of Science and Engineering |