PhD: Impacts of dynamic, climate-driven water availability on tree water use and stress
PhD grant – 36 months
Impacts of dynamic, climate-driven water availability on tree water use and stress
Contrôle climatique de la disponibilité en eau et du stress hydrique des arbres ripicoles
Forests along rivers are under threat due to climate-driven changes in water availability to trees. When water in the rooting zone is limited, trees undergo physiological changes that affect their overall growth and health through water stress. This problem is particularly acute within forests in river floodplains in regions with warm, dry summers. Such forests provide a range of ecosystem services, but they are limited in area, species diversity, and are challenging to manage under a changing climate. There is currently limited understanding linking regional climate to water availability to water use by riparian trees across forests stands, which limits predictive capability of forest response to drought stress over decadal timescales.
This project aims to build new understanding of the ecohydrological links between water availability and stress by employing an interdisciplinary set of research methods along the Rhône River, France. The project will compare the ecohydrological responses to climate in water availability at forest sites along a strong climatic gradient based on 3 existing field installations with ongoing data collection (upper, middle and lower Rhône).
Using hydroclimate data, alongside isotopes in waters and plants, the PhD student will address three research questions: i) How has groundwater versus surface water availability varied recently as a function of climate?; ii) How is water availability and water stress recorded in tree rings?; iii) Can riparian forest responses to water availability be predicted from hydrometeorological data, isotopes, and remote sensing?
In Year 1, the research will focus on analyzing the existing meteorological, soil moisture, groundwater, and river flow data at each site to understand the relationships between climate and water availability to plants.
In Year 2, the student will collect tree rings and extract cellulose to assess the isotopic signature of water use by the trees (δ18O) and their water use efficiency (δ13C), with interpretations supported by the monthly sampling of water fluxes and water source characterization.
In Year 3, the student will focus on remote sensing of Rhône riparian zone over the last several decades with an emphasis on the last few years (using Sentinel 2), which would enable connection of the dendro-isotopic work to canopy-level responses to water availability. This work will also be supported by some UAV flights to assess variations in canopy ET (from thermal data).
Three types of practical outputs are envisioned from this work in relation with other data provided by EUR community: i) better assess potential climate change effects on riparian vegetation at the corridor scale, considering local conditions (leveraging information from the OSR program), ii) predict and validate potential responses of riparian vegetation from water level variations associated with reach-scale river restoration (e.g., Pierre Benite, Peage de Roussillon), iii) design conservation and restoration programs that incorporate information on tree responses to changes in water availability (groundwater and soil moisture) and expected changes in riparian communities as well as health conditions from remote sensing data and thermal studies (supporting ongoing research done by Florentina Moatar). F. Moatar may provide potential support from INRAE in term of modelling and hydrological simulations (J.B. Faure, F. Granger, RiverLy). Isotope analysis can be done in LEHNA with partnership with Switzerland (WSL) for cellulose extraction.
The project is interdisciplinary in terms of the involvement of hydrology, ecology, and ecophysiology with a forest management perspective. Specifically, the project will involve the use and analysis of different types of data (climate data, water fluxes, dendro-isotopes, remote sensing) to explore plant responses to fluctuations in climatically controlled water availability.
The student will receive instruction in various field and laboratory skills including: tree coring, monitoring climate variables and hydrology, collecting field samples; isotopic analysis; data analysis. He/she will also gain understanding of ecohydrology and how plants respond to water variations in water availability. He/she will also be integrated into the research groups of Caylor (UCSB), Singer (Cardiff), Stella (SUNY-ESF), and Piegay (ENS).
The project is co-funded by the US National Science Foundation and EUR H2O’Lyon. Therefore, it links the prospective PhD student to an established team of American researchers at SUNY-ESF in Syracuse (New York) and UC Santa Barbara in California. There is also a strong budgetary investment from NSF in three well-instrumented sites in France along the Rhone River. The student will be able to take full advantage of the data generated from these sites over the last three years and to analyze in collaboration with this international research team. The student will be supported to travel to international conferences (e.g., EGU, AGU), where he/she will present his/her research, and he/she will also be hosted for a extended stay at UCSB, where he/she will take part and assist in teaching on a field course on ecohydrology. He/she will be supported to go to Switzerland to learn cellulose extraction from tree rings in WSL and the isotopic analysis will be done in the LEHNA.
Hervé Piégay (CNRS – ENS de Lyon), Michael Singer (Univ. Santa Barbara)
Supervisors (above) and Kelly Caylor (UCSB), John Stella (SUNY-ESF), Laurent Simon (LEHNA), Florentina Moatar (INRAE)
EUR H2O’Lyon – Doctoral School of Integrated River Basin Sciences
ED 483, Univ. Lyon
Localisation of the PhD student
ENS of Lyon, but research time to be planned in Switzerland, UK (Cardiff), US (UCSB)
Date of beginning, duration
1st October 2020, 3 years
Masters (ecology, hydrology or earth sciences (geology or geography)
Open-minded to interdisciplinarity, experience in dendrochronology or/and ecohydrology and/or remote sensing and/or isotopic analysis, appreciate field work, ideally fluent in French and English.