Improving the representation of plant hydraulic behavior in vegetation and land-surface models is critical for improving our predictions of the impacts of drought stress on ecosystem carbon and water fluxes. Species-specific hydraulic traits play an important role in determining the response of ecosystem carbon and water fluxes to water stress. Here, we use a newly developed tree hydrodynamic model, the Finite-difference Ecosystem-scale Tree Crown Hydrodynamics model version 3 (FETCH3), to investigate the influence of species-specific hydraulic traits on stomatal response to water stress. FETCH3 simulates water transport through the soil, roots, and xylem as flow through porous media. The model resolves water potentials along the vertical dimension, and stomatal response is linked to xylem water potential. The tree-level model is scaled to the plot scale based on the species composition and canopy structure of the plot, allowing the model to be parameterized using ET observations at both the tree level (sap flux) and plot level (eddy covariance).
We demonstrate how ET observations at both the tree and plot scale can be used in conjunction with this new modeling framework and a multi-objective Bayesian optimization approach to provide insights about species-specific hydraulic traits. Here, we parameterized the model using both sap flow and eddy covariance measurements from a mixed forest at the University of Michigan Biological Station (UMBS). This approach allows us to resolve information about species-specific hydraulic parameters, and provides insights about the interactions among water stress, species-specific hydraulic strategies, and stomatal regulation.