RANGELANDS ARE ECONOMICALLY AND ECOLOGICALLY IMPORTANT SYSTEMS OCCUPYING ALMOST 50% OF THE GLOBAL LAND SURFACE (&GT;30% IN THE U.S.). THE FUNCTIONS (E.G. PRODUCTION OF FORAGE FOR LIVESTOCK) OF THESE AGROECOSYSTEMS ARE PRIMARILY CONTROLLED BY WATER AVAILABILITY.RAINFALL VARIABILITY IS PREDICTED TO INCREASE AS A RESULT OF MORE FREQUENT EXTREME LARGE RAIN EVENTS (EPES, EXTREME PRECIPITATION EVENTS) AND MORE FREQUENT AND INTENSE DROUGHTS. ALTERED RAINFALL VARIABILITY MAY IMPACT CRITICAL RANGELAND FUNCTIONS AND MAKE SUSTAINABLE MANAGEMENT OF RANGELAND SERVICES MORE CHALLENGING. WE DON'T CURRENTLY KNOW HOW ALTERED RAINFALL VARIABILITY MAY AFFECT THE RELATIONSHIP BETWEEN RAINFALL AND PRODUCTIVITY. SPECIFICALLY, WE DON'T KNOW WHETHER EPES WILL AMELIORATE OR EXACERBATE THE IMPACTS OF DROUGHT. MY GOAL IS TO ASSESS THE EFFECTS OF COMBINED EPES AND DROUGHTS ON RANGELAND PRODUCTIVITY AND MORE SPECIFICALLY TO TEST THE HYPOTHESIS THAT, UNDER SOME CONDITIONS, EPES CAN SUSTAIN PRODUCTIVITY DURING DROUGHT. I WILL EXPERIMENTALLY IMPOSE CONCURRENT EPES AND MILD TO EXTREME DROUGHTS AT A SEMI-ARID RANGELAND RESEARCH SITE IN COLORADO AND QUANTIFY HOW THESE CHANGES AFFECT PRODUCTIVITY. TO EXTEND THE INFERENCE OF THIS EXPERIMENT, I WILL ALSO ASSESS HOW EPE-DROUGHT INTERACTIONS VARY AMONG RANGELANDS BY ANALYZING LONG-TERM OBSERVATIONAL DATASETS OF RAINFALL AND PRODUCTIVITY FROM NUMEROUS GRASSLAND ECOSYSTEMS ACROSS THE UNITED STATES. I EXPECT THAT EPES WILL ONLY SUSTAIN PRODUCTIVITY DURING MILD TO MODERATE DROUGHTS AT THE EXPERIMENT SITE. COMPARING ACROSS GRASSLANDS, I EXPECT THAT LARGE RAINFALL EVENTS WILL SUSTAIN PRODUCTION AT HIGHER LEVELS DURING DROUGHTS IN DRIER SYSTEMS THAN IN WETTER SYSTEMS. THE NEW KNOWLEDGE THAT IS GENERATED BY THIS PROJECT WILL BE SHARED WITH SCIENTISTS, RANGELAND MANAGERS AND PRODUCERS, AND THE GENERAL PUBLIC THROUGH PUBLICATION AND PRESENTATION OF RESULTS ONLINE, IN SCIENTIFIC JOURNALS, AND AT MEETINGS AND CONFERENCES.SUSTAINING RANGELAND NATURAL RESOURCES INTO THE FUTURE WILL REQUIRE MANAGEMENT THAT IS GROUNDED IN A THOROUGH KNOWLEDGE OF THE RELATIONSHIP BETWEEN PRODUCTIVITY AND RAINFALL.UNDERSTANDING HOW RANGELANDS WILL RESPOND TO ALTERED ENVIRONMENTAL VARIABILITY (DUE TO MORE FREQUENT DROUGHTS AND EPES) WILL BE ESSENTIAL FOR ASSESSING RISK AND SUSTAINABLY MANAGING PRODUCTIVITY AND NATURAL RESOURCES INTO THE FUTURE. THIS PROJECT WILL IMPROVE OUR ABILITY TO MANAGE RANGELAND FUNCTIONS (E.G. SUSTAIN HIGH FORAGE AND LIVESTOCK PRODUCTION LEVELS) UNDER CHANGING ENVIRONMENTAL CONDITIONS BY IMPROVING OUR UNDERSTANDING OF HOW RAINFALL VARIABILITY AFFECTS PRODUCTIVITY.