Integrated Xylem Water Isotopic Observations and Process-based Ecohydrological Model Simulations Reveal Species-Level Plant Hydraulics

Plant water use in hydrologic, land-surface, and earth system models is frequently estimated by a series of equations reliant on unknown model parameters controlling plant hydraulic function. Estimating these plant hydraulic traits is critical for accurate simulation of terrestrial water storage, flow paths, tree resistance to drought, and ultimately, ecosystem response to climate change. Despite the prevalence of δ_XYLEM observations, few studies have used δ_XYLEM to estimate plant traits numerical ecohydrologic models We calibrated EcH₂O-iso, an isotopic-enabled, fully distributed ecohydrologic model, with δ_XYLEM observations of 30 Eastern Hemlock (Tsuga canadensis) trees across seven months. Calibrated values for maximum stomatal conductance, canopy light interception, and rooting depths were validated with independent datasets of latent heat flux, canopy light interception, and δ_XYLEM from a nearby hemlock stand. Results indicate significant correlations between tree diameter (DBH), topographic position, and the calibrated values of several vegetation traits. Our results demonstrate that δ_XYLEM data can be used to accurately parameterize plant traits; however, the locations and sizes of the sampled trees should be considered when upscaling measured or calibrated plant-traits from individual trees into larger horizontal scales.