BRS Jia Hu

host: Sean Michaletz

Title talk: Interpreting tree ring records using a plant ecophysiological approach

Abstract: Trees rings record a wealth of information on climate, disturbance, and forest dynamics, and can record these processes from the plot to regional scales. However, extracting plant physiological processes from the tree ring record has proved to be more difficult, as integration of leaf to whole tree processes can often lead to confounding results. My research aims to bring a plant ecophysiological perspective to interpreting the tree ring isotopic record and to ask, what processes are the rings actually recording?

Forests are experiencing increasing climate stressors, including record heatwaves, prolonged droughts, and increasing vapor pressure deficit (VPD). Recent studies have highlighted that increasing VPD poses a greater risk for forest resiliency than even changes in precipitation. To understand how VPD has influenced tree ecophysiological responses over longer time scales, one powerful tool is the use of stable carbon and oxygen isotope analysis, especially cellulose in annual tree rings. Stable oxygen isotope in cellulose (d18Ocellulose) has been widely used to re-construct both source water use in trees and changes in atmospheric VPD. In this talk, I will present two ways in which we have used stable isotopes to examine source water use by trees (short term response across seasons) and how VPD has affected tree resiliency (long term response across decades).

The study focuses on the southwest region of the United States, which experiences a bi-modal precipitation regime, characterized by cool winter precipitation and warm summer monsoon precipitation. This bi-modal presents a unique opportunity to examine conditions in which VPD and soil moisture become decoupled, in which mid-summer monsoon rains lead to decreasing VPD while increasing soil moisture. In this talk, I will present two related studies that address the following questions: 1) how do winter and summer precipitation influence tree water use and 2) what can tree rings inform us about the resiliency of trees to future changes in climate? 

Short biography: I am a Professor at Oregon State University, in the Department of Botany and Plant Pathology and my current primary role is the Associate Dean for Academic Programs in the College of Agricultural Sciences. Prior to joining the College of Ag Scie at OSU, I worked at University of Arizona for eight years, in the School of Natural Resources and the Environment and the Laboratory of Tree Ring Research. I examined carbon and water fluxes at small/large spatial and short/long temporal scales. My research also extended to dendrochronology, where our lab examined the physiological responses recorded in the tree ring record. This allowed us to assess both the historical responses as well as the trajectory that tree populations may be moving towards.