Form Submission: Participation Entry

Ponderosa pine is an ecologically and economically important species in the West. Recently, drought-induced mortality in ponderosa pine has contributed the death of over 100 million trees in California. While we have some insight into how the stems and roots perform during drought, we know much less about the foliage, primarily due to methodological limitations. At four national forests representing a drought-intensity gradient within California, we used two independent methods to determine the pine needles’ vulnerability to desiccation. We also measured anatomical traits with the hypothesis that trees from dry areas would have traits that maintain leaf functioning during drought. Data from the two methods for estimating water flow through needles show that the xylem conduits (i.e. the tracheids) were more resistant than the pathways for water movement outside the xylem (i.e. the transfusion tissue and mesophyll); this pattern was conserved among populations. Significant differences in the proportion and dimensions of anatomical traits that prevent water loss were found solely in the most southern population of ponderosa.These results suggest this species is at uniform risk to hydraulic dysfunction caused by drought and that strategies to survive in arid regions may include plastic control of the tissues outside of the vasculature.