Stable water isotopes are useful tracers of physical hydrologic processes since phase changes preferentially partition molecules with the heavy isotopes of water (18O and 2H or D) into the liquid phase and molecules with the light isotopes of water (16O and 1H) into the vapor phase. In this way, the isotopic composition of water contains a record of water transport through time. We use stable water isotopes to study hydraulic traits along the soil-plant-atmosphere continuum to understand how different trees use water. Specifically, we measure the isotopic composition of ambient and transpired vapor as well as soil, stem, and leaf waters from the dominant trees at the AmeriFlux and FASET eddy covariance sites. This work will help characterize species-specific hydraulic traits and give insight into how forest hydrology will change in the future.