Theses and Dissertations Collection

I used Forest Service aerial die-off surveys, downscaled PRISM climate data, and GRACE groundwater change data to develop boosted regression tree models identifying key variables and thresholds associated with die-off occurance throughout blue oak (Quercus douglasii) distribution. Precipitation in 2015 below 400mm, spring temperature anomalies, 2013-14 summer-fall temperatures, climate water deficit anomalies, and loss of total water storage below 30cm of baseline were associated with increased die-off probability. Model results indicate blue oak is highly influenced by water availability as precipitation and groundwater, and to a lesser extent, elevated temperatures, and temperature anomalies especially in the southeastern portion of their range. Drought frequency and intensity are projected to increase and may threaten the species’ survival given its restricted range and high habitat fragmentation. Knowledge of the climatic and hydrologic variables linked to blue oak die-off will help prioritize climate change related conservation efforts.