PELLSTON, Mich. — Different species of trees have different strategies for how they respond to water stresses, from warm, sunny afternoons to extended droughts.
However, most models that predict how ecosystems will respond to climate change have poor representation of the diversity of hydraulic traits that control a plant’s drought response.
A new study published in the Journal of Geophysical Research: Biogeosciences reveals an advanced model that can be used to characterize different types of water-stress responses of tree species in forests.
A team of researchers from Ohio State University, University of Michigan and University of Texas at Austin used long-term data from a forest at the University of Michigan Biological Station (UMBS) in Pellston, Michigan, to develop a tree hydrology model for simulating the flow of water through trees, from the soil through the root, stem and leaves.
They focused on sap flow data and eddy covariance observations — also known as flux data, which show how much gases, energy and water move between the Earth’s surface and the atmosphere above.
Called FETCH4, the model formulation represents the physiological characteristics and state of the tree’s conductive system so that the model resolves the nuanced responses of different tree species to the same environmental conditions — air temperature, humidity, sunlight and rain.
The research was led by Dr. Gil Bohrer, a UMBS researcher and a professor of civil, environmental and geodetic engineering at The Ohio State University.
“Just like any other organisms, trees respond to their dynamic environment — they display a form of behavior,” Bohrer said. “Different tree species display different characteristic behavior in response to water stress, and we can use our understanding of this behavior to better model the flow of water and carbon between the atmosphere and the ecosystem, especially under future climate where water stress will be more common.”
Bohrer also is the instructor of a new field course debuting during the 2025 spring term at UMBS: Observation and Modeling of Climate Change Biology.
Students from universities all over the world can join him at the research and teaching campus in northern Michigan from May 20 through June 19 to learn hands-on techniques to measure the science behind climate change — including surface fluxes, radiation and ecosystem interaction with climate change.
The deadline to apply for spring term classes and scholarships on the UMBS Courses website is April 30.
“Climate change biology is a critical area of research. We are thrilled to offer the opportunity for the next generation of scientists to learn directly from Gil for four weeks at our historic field station,” said Dr. Aimée Classen, UMBS director and a professor of ecology and evolutionary biology at the University of Michigan. “He is a leader in his field. The latest model his team developed resolving tree species-specific water-stress response is a valuable tool for future forest management and conservation.”
The research team leveraged one of the most iconic pieces in the U-M Biological Station catalog: the 150-foot AmeriFlux tower.
AmeriFlux is a network of instrumented eddy covariance sites in North, South and Central America that measure ecosystem carbon dioxide, water and energy fluxes as well as other exchanges between the land surface and atmosphere. UMBS is one of AmeriFlux’s Core Sites where ongoing observations are updated regularly for more than 25 years.
Funded by the U.S. Department of Energy, the tower at UMBS provides one of the highest quality long-term datasets on forest carbon dynamics in the world. And its data is downloaded every day by scientists to understand how ecosystems respond to climate change and improve the performance of models that predict climate change and interpret satellite-borne observations on the state of our ecosystem.
The tree hydrology model, FETCH4, which builds upon previous versions, produces tree‐level (individual), species‐level (functional type), and plot‐level outputs of transpiration, sap flow, stem water content and soil moisture and resolves the intra‐ and inter‐daily dynamics of these variables. Plus, FETCH4 also can resolve emergent hydraulic dynamics, such as hysteresis (delayed response) between transpiration and vapor pressure deficit (VPD, combination of air temperature and humidity) and photosynthetically active radiation (PAR) and stress response and recovery.
Read the full paper, titled “Using a Plant Hydrodynamic Model, FETCH4, to Supplement Measurements and Characterize Hydraulic Traits in a Mixed Temperate Forest,” in the Journal of Geophysical Research: Biogeosciences.
The University of Michigan Biological Station serves as a gathering place to learn from the natural world, advance research and education, and inspire action. We leverage over a century of research and transformative experiences to drive discoveries and solutions to benefit Michigan and beyond.
