RAPID: Woody Plant Responses to Extreme Drought in California: Characterizing Species-Level Drought Survival and Mortality Mechanisms

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The current California drought is in its fourth year and represents the driest three-year record in California History, with 46% of the state currently in the category of exceptional drought. The drought is causing mass mortality of trees and shrubs throughout the state so quickly that scientists are scrambling to document the impacts to forests and watersheds. This research project provides an opportunity to study trees and shrubs where the California chaparral shrublands meet the Mojave Desert - an area with rapid changes in vegetation. The physiological and ecological characteristics that promote survival during this extreme drought will be identified and used to predict how continued drought is likely to further affect California ecosystems. The work will support the mission of NSF by promoting the progress of science towards the health of forests and watersheds, and will specifically promote progress in research on plant drought resistance, climate change, and natural resource management. The research will be overseen by the principal investigator, and will utilize undergraduate and graduate students at a minority serving institution, training these students in scientific approaches, analyses, and dissemination of results. The goal of the project is to associate species-specific mortality and survival with physiological mechanisms so that further responses to the current extreme drought in California can be approached with predictive power. The study will be conducted in a series of permanent plots at the intersection of two major North American biomes, the California Floristic Province and the Mojave Desert, where there is great potential for changes in species composition due to climate change. The biogeographical origin, drought resistance, and hydraulic traits of all of the woody species at the sites have already been characterized. Based on the current physiological knowledge of this community, the link between mortality and actual physiological processes can be measured in real time. The project will also allow evaluations of the role of biogeographic origin of study species to understand the nature of local extinction and range contractions within the research system. Mortality rates from the 2007 drought at the primary research location in Morongo Valley in southern California exist, and in 2009 three 0.125 ha circular plots were established, with all woody species identified and marked. Long-term permanent plots will be re-censused, and two additional sites at higher altitudes will be established to monitor future changes. Dendrometer bands will be installed on stems within the research plots for finer scale measurements of growth in response to climate. Finally, measurement of stable isotopic composition of plant xylem water and soil water will be used to monitor changes in the depth of water uptake and changes in water sources. The research will be supervised by the principal investigator and will be conducted with the help of undergraduate and graduate students at a minority serving institution, stimulating student interest in local ecosystems. The study area is highly biodiverse, with large numbers of endemic species. The expected outcome of the project is to increase the ability to predict how species with contrasting drought response strategies will fare as climate change-type drought continues or intensifies in Mediterranean-type ecosystems in the future, and provide opportunities for students to work with critical ecological issues that can be linked to global processes.