Whitebark pine is a keystone species in high elevation systems in the Sierra Nevada. Precipitous declines in this species due to a combination of threats have led to proposals to list whitebark pine as an endangered species. Improved understanding of the broad impacts of climate on whitebark forests may be valuable in creating adaptive management plans for this species that take projected climate change into account. In this study, we describe the impacts of the recent drought in California on whitebark pine physiology and growth. We collected needle samples from over 1000 trees in 24 plots that scanned diverse climatic conditions. Needle samples were dried, measured, and pulverized then sent to the Analytical Lab and Stable Isotope Facility at UC Davis for analysis of δ13C and δ15N. Key questions included, 1) how did the drought shift foliar growth (needle length) and foliar stable isotopes, δ13C and δ15N? 2) where did whitebark respond most positively and/or negatively to climate and drought? and 3) did whitebark experience drought stress?
Results/Conclusions
While the region as a whole experienced drought conditions, whitebark pine showed positive growth responses and increased photosynthetic capacity (decreased δ13C ratios) during the drought. Only two plots contained trees that may have showed signs of drought stress, though the results were inconclusive. These trees occurred on the eastern side of the Sierra Nevada in one of the hottest, driest regions of California’s whitebark pine range. Beyond these eastern Sierra plots, whitebark in the subalpine may be limited more by short growing season length and higher snowpack rather than drought. Plots in areas with high snowpack showed even greater increases in needle growth and photosynthetic capacity relative to low snowpack areas. Future work will continue to improve understanding of how whitebark pines respond to climate variables, providing a foundation for species management and restoration plans.