Undergraduate Honors Theses

Thesis Defended

Spring 2013

Document Type




First Advisor

Dr. Holly R. Barnard


As models of future climate project increasing frequency and severity of drought, understanding how trees, which provide valuable ecosystem services and store large amounts of carbon, respond to drought events, is of utmost important. This study examines how tree response to drought varies between species and across topography in a montane headwater catchment. Foliar δ13C was compared between a wet and dry year to characterize changes in water use efficiency (WUE) in the area’s two dominant tree species: ponderosa and lodgepole pine. Lodgepole pine had a significant increase in δ13C in the dry year, indicating that trees were forced to tolerate drought stress by increasing WUE. Ponderosa pine did not significantly change from the wet to dry year, indicating that it was likely able to avoid drought stress through various physiological mechanisms hat allow it to obtain enough water even in drought conditions. Topographically-derived GIS surfaces for incoming solar radiation and topographic wetness index were used to model spatial variability in drought response. While these surfaces were generally not predictive of δ13C in response to drought, improved models could better predict topographical influence on drought sensitivity. The stark contrast in the WUE response of ponderosa and lodgepole pine highlights the importance of understanding variation at the individual catchment scale to effectively model and predict regional and global tree drought response under changing future climate conditions.