INCREASING DROUGHT STRESS MAY THREATEN THE FUNCTIONALITY, PRODUCTIVITY, BIODIVERSITY AND SUSTAINABILITY OF PRODUCTION FOREST ECOSYSTEMS IN THE UNITED STATES. RECENT HOT DROUGHTS HAVE DRIVEN LARGE-SCALE DECLINES IN FOREST PRODUCTIVITY AND TRIGGERED TREE MORTALITY IN MULTIPLE SPECIES IN THE WESTERN US. HOWEVER, FOREST ECOSYSTEMS WITH HIGHER BIODIVERSITY MAY BE MORE RESILIENT TO EXTREME DROUGHTS. THUS, MANAGING FORESTS TO INCREASE THE BIODIVERSITY, PARTICULARLY THE DIVERSITY IN SPECIES' PHYSIOLOGICAL TRAITS PERTAINING TO DROUGHT RESPONSES, HAS EXCITING POTENTIAL FOR MAINTAINING PRODUCTIVITY AND SUSTAINABILITY OF THESE SYSTEMS IN THE FUTURE. THIS RESEARCH WILL HELP ILLUMINATE KEY STRATEGIES TO MAINTAIN HEALTHY FORESTS IN THE WESTERN US AND THE MYRIAD ECONOMIC BENEFITS AND ECOSYSTEM SERVICES THAT THEY PROVIDE TO AMERICAN COMMUNITIES.IN THIS RESEARCH PROJECT, WE WILL USE A SUITE OF FIELD MEASUREMENTS AND MODEL SIMULATIONS TO A) MEASURE HOW TREES RESPOND TO DROUGHT IN WESTERN US FORESTS, B) QUANTIFY THE DEGREE TO WHICH TREE DIVERSITY OF DROUGHT RESPONSES MEDIATES FOREST ECOSYSTEM SERVICES AND THEIR RESPONSE TO DROUGHT, AND C) ESTIMATE THE POTENTIAL FOR MANAGING FOR FUNCTIONAL DIVERSITY TO IMPROVE PRODUCTION FORESTS PRODUCTIVITY, RESILIENCE, AND SUSTAINABILITY IN FUTURE CONDITIONS.THIS RESEARCH IS IMPORTANT BECAUSE IT DIRECTLY ASSESSES THE EFFECTS OF TREE DIVERSITY TO THE ECOSYSTEM SERVICES OF TIMBER PRODUCTION, CARBON SEQUESTRATION, AND WATER RESOURCE PROVISION OF WESTERN US FOREST ECOSYSTEMS. THE RESEARCH WILL PROVIDE 1) FOUNDATIONAL RESEARCH THAT ADVANCES OUR SCIENTIFIC UNDERSTANDING OF HOW BIODIVERSITY CAN INFLUENCE AGROECOSYSTEM PROCESSES, 2) DEVELOPMENT OF MODELS THAT WILL ENABLE ROBUST FORECASTS OF AND GUIDE MANAGEMENT DECISIONS FOR NATURAL RESOURCES AND ECOSYSTEM SERVICES IN FUTURE CLIMATES, AND 3) WILL FACILITATE IMPROVEMENTS TO IMPAIRED NATURAL RESOURCES AND ECOSYSTEM SERVICES IN WESTERN US FORESTS. BROAD-SCALE SOCIETAL BENEFITS INCLUDE ECONOMIC BENEFITS OFMORE EFFICIENT AND RESILIENT FORESTS THAT CAN WITHSTAND DROUGHT STRESS AND STILL PROVIDE KEY ECOSYSTEM SERVICES, INCLUDING TIMBER PRODUCTION, TOURISM AND RECREATION, AMONG OTHERS, TO LOCAL COMMUNITIES.