OUR OVERARCHING GOAL IS TO IMPROVE OUR UNDERSTANDING OF HOW THE MAJOR OUTPUTS OF THE FOREST HYDROLOGIC CYCLE CHANGE THROUGH STAND DEVELOPMENT AND MANIPULATE THOSE DYNAMICS THROUGH SILVICULTURAL APPROACHES TO INCREASE WATER USE EFFICIENCY (WUE). BY TAKING A SYSTEMS APPROACH TO QUANTIFYING EVAPOTRANSPIRATION AND ITS COMPONENTS (SOIL EVAPORATION AND TRANSPIRATION) IN WOODY FEEDSTOCK (LOBLOLLY PINE AND AMERICAN SWEETGUM) ACROSS ENTIRE HARVEST ROTATIONS, WE WILL CAPTURE DYNAMIC SHIFTS OCCURRING THROUGH STAND DEVELOPMENT AND PROVIDE THE MOST COMPREHENSIVE ASSESSMENT OF WUE TO DATE. WE HYPOTHESIZE THAT INHERENT DIFFERENCES IN LEAF HABIT AND AREA AMONG SPECIES, COUPLED WITH SILVICULTURAL OPTIONS RELATED TO DENSITY AND RESOURCE AVAILABILITY, PROVIDE OPPORTUNITY TO REDUCE SOIL EVAPORATION DURING EARLY STAND DEVELOPMENT, THEREBY INCREASING ROTATION-LENGTH WUE AND REDUCING THE OVERALL ECOLOGICAL FOOTPRINT OF WOODY BIOENERGY PRODUCTION SYSTEMS. OUR EMPIRICAL APPROACH, ASSESSING ROTATION-LENGTH HYDROLOGIC BUDGETS AND GENERATING INTEGRATED MEASURES OF WUE USING A SYSTEMS FRAMEWORK, WILL PROVIDE DATA THAT CAN BE USED DIRECTLY BY LANDOWNERS IN THE SOUTHEAST US AS A DECISION SUPPORT TOOL FOR SELECTING WOODY BIOENERGY CROP SPECIES AND SILVICULTURAL APPROACHES. OUR CONCEPTUAL FRAMEWORK, WHICH RELIES BROADLY ON FUNCTIONAL TRAITS OF POTENTIAL WOODY BIOENERGY CROP SPECIES, FORMULATES A HYPOTHESIS THAT WILL BE TESTED WITH OUR EMPIRICAL DATA AND THUS, GENERALIZED PATTERNS, PROCESSES, AND CONTROLS CAN BE TRANSFERRABLE TO OTHER FORESTRY AND AGRICULTURE PRODUCTION SYSTEMS. THIS PROJECT ADDRESSES THE URGENT NEED FOR QUANTITATIVE INFORMATION REGARDING TRADE-OFFS BETWEEN MAXIMIZING FOREST PRODUCTION AND MAINTAINING SUSTAINABLE WATER YIELDS.