Portland State University. Department of Geography
Term of Graduation
Date of Publication
Master of Science (M.S.) in Geography
1 online resource (vii, 67 pages)
Climate change is projected to bring more frequent and prolonged droughts, causing widespread forest die-off. Identifying tree mortality over large spatial extents in response to the most recent California drought will help forest managers and conservationists understand where there may be a greater likelihood of future die-offs. In order to find more at-risk areas, this study evaluated how interacting site-specific topographic, climate, substrate, and stand characteristics mediated tree mortality in the Central Sierra Nevada during the 2012-2016 drought. The author used lidar and hyperspectral imagery provided by the National Ecological Observatory Network to identify individual dead trees using the Random Forest classification method and created a Random Forest Regression model to assess site-specific environmental variables that had a greater influence on tree mortality. The results show that the most influential variables were tree height, density, and elevation. Results also found higher mortality rates in pines and oaks, meaning further widespread die-off of these trees could reduce forest productivity, increase fire hazard risk, and drive a shift in community composition over the long-term. This study provides a finer resolution mapping of tree mortality over the research area than was reported by the USFS Aerial Detection Survey. Due to the confounding evidence regarding the relative influence of environmental factors on tree mortality during droughts, these results provide robust information to help maintain these changing forests in a climate-informed manner. Because this study is site-specific, more research is needed to assess how environmental factors mediate drought-induced mortality in other regions also projected to have more intense droughts as a result of climate change.
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Sharwood, Lauren Nicole, "Modeling Environmental Factors Related to Drought-Induced Tree Mortality Based on Lidar and Hyperspectral Imagery" (2021). Dissertations and Theses. Paper 5874.