**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** FORAGE PRODUCTION ACROSS US RANGELANDS IS DRIVEN BY WATER RESOURCES DELIVERED THROUGH HIGHLY VARIABLE PRECIPITATION PATTERNS THAT OFTEN INCLUDE EXTREME DROUGHT. ALTHOUGH THE AMOUNT OF FORAGE PRODUCTION IS KNOWN TO DEPEND ON THE TOTAL AMOUNT OF PRECIPITATION EACH YEAR, WE STILL HAVE A LIMITEDUNDERSTANDING OF THE CONNECTION BETWEEN THE TIMING OF PRECIPITATION AND FORAGE PRODUCTION. WE SPECIFICALLY LACK AN UNDERSTANDING OF THE SEASONAL ORIGINS (E.G., PRECIPITATION THAT FALLS DURING WINTER VERSUS SUMMER) OF THE SOIL WATER THAT IS ULTIMATELY USED BY FORAGE.BETTER UNDERSTANDING THE ROLE OF PRECIPITATION TIMING IN FORAGE PRODUCTION IS IMPORTANT BECAUSE IT CAN HELP REDUCE UNCERTAINTY ABOUT THE POTENTIAL IMPACTS OF CONTEMPORARY INCREASES IN WEATHER VARIABILITY AND DROUGHT ON US RANGELANDS. BY EXTENSION, WE CAN BETTER UNDERSTAND WHICH RANGELANDS MAY BE MOST VULNERABLE TO CLIMATE CHANGE.THEREFORE, THE GOAL OF THIS SEED GRANT IS TO INFORM PATTERNS OF RANGELAND VULNERABILITY TO INCREASING WEATHER VARIABILITY BY UNRAVELING THE SEASONAL ORIGIN OF SOIL WATER RESOURCES USED FOR FORAGE PRODUCTION.TO ACHIEVE THIS GOAL, WE WILL CONDUCT FIELD SAMPLING OF FORAGE SPECIES ACROSS MULTIPLE RANGELANDS, FOLLOWED BY LABORATORY ANALYSES, THAT WILL LINK THE ISOTOPIC COMPOSITION OF PRECIPITATION IN DIFFERENT SEASONS TO THE ISOTOPIC COMPOSITION OF WATER IN FORAGE. THIS APPROACH WILL HELP US DETERMINE THE SEASONAL SOURCE OF SOIL WATER USED BY KEY FORAGE SPECIES FOUND IN DIFFERENT RANGELANDS. WE WILL THEN USE THIS INFORMATION TO INFORM PATTERNS OF DROUGHT IMPACTS TO FORAGE PRODUCTION OBSERVED THROUGH SATELLITE IMAGERY. THIS PROJECT WILL ALSO LAY THE FOUNDATION FOR A LONG-TERM MONITORING EFFORT IN COLLABORATION WITH USDA SCIENTISTS AND RANCHERS. OVERALL, THE PROJECT WILL PRODUCE THE FOUNDATIONAL KNOWLEDGE NEEDED TO IMPROVE OUR UNDERSTANDING OF THE MECHANISMS DETERMINING RANGELAND VULNERABILITY TO CLIMATE CHANGE.