US FOREST ECOSYSTEMS ARE CURRENTLY UNDER THREAT FROM THE COMBINED AND INTERACTIVE EFFECTS OF CLIMATE CHANGE AND NON-NATIVE PESTS. DESPITE CREDIBLE FORECASTS OF FOUNDATIONAL TREE DECLINES, WE CANNOT PREDICT HOW THESE LOSSES WILL ALTER FOREST WATER USE, STAND RESILIENCE, OR WATER FLUX TO DOWNSTREAM ECOSYSTEMS. THE GOAL OF THIS PROJECT IS TO ADVANCE FORESTRY AND ECOHYDROLOGY RESEARCH TO IMPROVE PREDICTIONS OF STAND ROOTING RESPONSES TO INSECT INFESTATION AND DROUGHT. WE WILL TRACE PRECIPITATION THROUGH SOILS, GROUNDWATER, AND INTO TREES VIA STABLE ISOTOPES IN WATER (2H, 18O) IN THREE MIXED-SPECIES STANDS THAT EACH INCLUDE ONE TREE SPECIES VULNERABLE TO INSECT INVASIONS (ASH [FRAXINUS AMERICANA], MAPLE [ACER SACCHARUM], AND HEMLOCK [TSUGA CANADENSIS]). WE WILL OBSERVE THE ROOT WATER UPTAKE (RWU) STRATEGIES OF THE THREATENED SPECIES IN EACH STAND AS WELL AS THE THREE MOST ABUNDANT NEIGHBORING SPECIES. IN PROJECT YEAR 2, WE WILL FIELD-SIMULATE AN INSECT INFESTATION OF THE THREATENED TREES AND OBSERVE RWU CHANGES IN BOTH THE INFESTED AND NEIGHBORING TREES, AND CONSEQUENT CHANGES TO SOIL MOISTURE, GROUNDWATER RECHARGE, AND STAND TRANSPIRATION. WE WILL DEVELOP SIMULATION ROUTINES TO ESTIMATE THE RWU RESPONSES TO DISTURBANCE WITHIN A FULLY-DISTRIBUTED PROCESS-BASED ECOHYDROLOGICAL MODEL. OUR RESEARCH WILL FORECAST HOW CHANGES IN THE RWU STRATEGIES OF MIXED-SPECIES STANDS CAUSED BY INFESTATIONS ALTER FOREST VULNERABILITY TO DROUGHT (AND THEREFORE FUTURE INFESTATIONS) AND STREAMFLOW. WE WILL USE THE DATA AND ECOHYDROLOGIC MODELING ADVANCES GENERATED IN THIS SEED EXPERIMENT TO DESIGN AN EXPANDED STUDY ON THE HYDROLOGIC CONSEQUENCES OF PRE- AND POST-INFESTATION SALVAGE HARVESTS OF INFESTED FOUNDATIONAL FOREST TREES.