The proposed research focuses on the legacies of droughts on individuals and communities that comprise ecosystems. Leveraging a unique set of instrumentation, the project will monitor the continuous physiological variation and recovery of individuals of different dominant tree species in the southwestern US in response to atmospheric drought and soil moisture deficit. This detailed physiology will be linked to an adjunct inventory of the national Forest Inventory and Analysis program to understand how physiological responses, which may differ among species, shape subsequent growth and mortality following drought across the broader region. Finally, the project will test whether individual tree responses can be scaled to match fluxes at the ecosystem level indicated by eddy covariance measurements, examining key hypotheses of how these physiological responses scale to a community and ecosystem level in order to improve predictive models of future climatic impacts.

Intellectual Merit

Current empirical and conceptual tools employed in predicting the biosphere response to anthropogenic climate change make little use of phenomena like demography and life history that are known to be central to the often non-linear dynamics of populations. This gap is particularly evident when considering the impacts of extreme events on ecosystems, especially drought. Consequently, these approaches to assess ecosystem response to drought at a continental or global scale tend to be correlative, often yielding contradictory results, with little power of inference on how these processes are mediated biologically through the physiology of individuals of different species that comprise the ecosystem. The proposed work aims to resolve a fundamental question about drought impacts: Does a drought leave an ecosystem weaker or stronger in the face of subsequent drought? The project will directly investigate the recovery timescales and limits across dominant species with divergent life-history strategies and assess the opportunities and barriers to scaling individual physiology to ecosystem measurements.

Broader Impacts

This proposal provides an extensive commitment to training of scientists at the undergraduate, graduate, post-doctoral, and early-career levels. The research plan will involve six undergraduate students across three institutions and states in cutting-edge research. Students will test and develop meteorological and physiological sensors, participate in physiological ecology field research, and receive training in data analysis and research methods. The project will also support three graduate students from three institutions, who will be involved in all aspects of the project including field research, data collection, analysis and publication of the results. The project will provide research training for two post-doctoral and two early-career scholars in a highly collaborative and integrated study design. The project’s research will be directly linked with teaching activities by incorporating findings and projects into five undergraduate and two graduate courses across Northern Arizona University, Princeton University, and the University of Nevada, Reno. The project contains a central goal of making easy-to-use physiological, ecological, and flux data accessible to the public for drought research and monitoring. In addition, the project will develop sensor capacity needed for a continuous and physiologically-relevant continent-wide forest drought monitoring network. An algorithm for the calculation of Leaf Area Index from standard photographs taken by a cellular phone and a web- based portal to upload these photos will be developed for citizen science engagement with tree mortality and forest health via the distribution of an iPhone app, also providing an easily- introduced measurement into the national USFS Forest Inventory and Analysis program.