Honors College Thesis


Effect of Fire Severity on Forest Development in a Mature Douglas-fir Forest in Western Oregon Public Deposited

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  • Wildfires can create alternative pathways for forest development, and wildfires have expanded in size, frequency, intensity, and severity across the western United States. The purpose of this paper is to compare forest development of a mature Douglas-fir forest in western Oregon across fire severities. Postburn field measurements were collected in 2022 in the Hagan Research Natural Area (RNA) that burned in the 2020 Holiday Farm Fire. The field data was used to simulate forest development using an array of starting conditions, including unburned (pre-fire data), low, medium, and high fire severity classes. Immediately post-fire, trees per acre, basal area, cubic volume, stand density index, standard deviation of diameter at breast height, crown competition factor, and downed wood volume decreased with increasing fire severity. One hundred years post-fire, with a stand age of 270 years old, all classes, except for the high severity class, had Old Growth Index values approaching that of an old-growth forest lacking the composition of shade tolerant species. In this case study, moderate fire severity in mature Douglas-fir forests may result in a multi-cohort stand only composed of Douglas-fir and thus, large-scale wildfires may result in future forests with lower tree biodiversity than current old-growth forests.
  • Keywords: Forest Development, Wildfire Ecology, Douglas-fir forests, Pacific Northwest, Fire Severity
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