**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** TREE SEEDLINGS ARE PLANTED ON OVER 2 MILLION ACRES OF LAND EACH YEAR IN THE UNITED STATES. SEEDLINGS ARE PLANTED FOLLOWING HARVESTING FOR TIMBER, TO RAPIDLY INTRODUCE TREES INTO AREA AFFECTED BY CATASTROPHIC WILDFIRE, TO AFFOREST LANDS PREVIOUSLY IN AGRICULTURE, AND TO RESTORE DEGRADED ECOSYSTEM. LARGE-SCALE PRIVATE AND PUBLIC FOREST NURSERIES PRODUCE CONTAINERIZED SEEDLINGS TO MEET THESE DEMANDS, BUT THEIR CURRENT GROWING REGIMES FOCUS ON PRODUCING SEEDLINGS FOR CURRENT GROWING CONDITIONS IN THE FIELD. ESPECIALLY IN THE INLAND NORTHWEST AND MIDWEST, VARIABILITY IN WEATHER CONDITIONS ARE EXPECTED TO INCREASE DROUGHT FREQUENCY AND EXTENT. IN ORDER TO SUSTAIN THE FOREST NURSERY INDUSTRY AND IMPROVE LONG-TERM SUCCESS OF PLANTED SEEDLINGS, WE NEED TO BETTER UNDERSTAND HOW TO ACCLIMATE TREE SEEDLINGS TO DROUGHT CONDITIONS WITHIN THE NURSERY. ROOT SYSTEM ARCHITECTURE (I.E., SHAPE AND PHYSICAL SPACE OF ROOTS) PLAYS A KEY ROLE IN THE ABILITY FOR PLANTED SEEDLINGS TO ACCLIMATE TO PLANTING-SITE CONDITIONS AND FOR FUTURE SURVIVAL AND GROWTH. MUCH IS STILL UNKNOWN ABOUT HOW GENETICS CONTROLS RSA AND HOW DROUGHT ACCLIMATION IN THE NURSERY INFLUENCES THE EXPRESSION OF RSA. OUR ULTIMATE GOALS IS TO UNDERSTAND HOW NURSERY-INDUCED DROUGHT ACCLIMATION INFLUENCES TO THE RSA OF TWO HIGHLY COMMERCIAL TREE SPECIES: WESTERN LARCH IN THE INLAND NORTHWEST AND BLACK WALNUT IN THE MIDWEST, AND HOW THIS RESPONSE VARIES BY GEOGRAPHIC SOURCE OF THE SEED. THE SPECIFIC OBJECTIVES OF THE STUDY ARE TO: (1) CHARACTERIZE THE RSA OF DIVERSE WESTERN LARCH AND BLACK WALNUT GEOGRAPHIC SOURCES GROWN WITH DIFFERENT DROUGHT ACCLIMATION REGIMES TO DIRECT CHANGES IN NURSERY CULTURE AND IMPROVE PLANT QUALITY, (2) EXAMINE RSA WITHIN CONTAINER-DEVELOPED ROOT PLUGS AND ROOTS GROWING OUTSIDE THE PLUG IN THE FIELD TO ASSIST IN THE DEVELOPMENT OF A RAPID RSA ASSESSMENT PROTOCOL FOR WESTERN LARCH AND BLACK WALNUT, AND (3) ASSESS THE EFFECTS OF DROUGHT ACCLIMATION BY GENETIC SOURCE ON RSA AND HOW THE RSA AFFECTS SEEDLING SURVIVAL AND GROWTH. THIS NOVEL ASSESSMENT SPANS NURSEY CULTURE, CONTROLLED LABORATORY ASSESSMENT TO DETERMINE MAXIMUM RSA UNDER OPTIMAL CONDITIONS, AND RSA EXPRESSION ON COMMON PLANTING SITES FOR EACH SPECIES. THE KNOWLEDGE GENERATED FROM THE PROJECT WILL BE USED TO BETTER UNDERSTAND HOW NURSERY PRACTICES CAN BE MODIFIED TO PRODUCE SEEDLING WITH DIFFERENT TARGET SPECIFICATIONS FOR SUCCESS FOLLOWING PLANTING NOW AND IN THE FUTURE. WE ARE UNIQUELY QUALIFIED TO PERFORM THIS PROJECT: BOTH INSTITUTIONS HAVE ESTABLISHED FOREST NURSERY RESEARCH PROGRAMS AND FACILITIES TO CONDUCT THE RESEARCH, OPERATIONALLY SCALE THE RESULTS, COMMUNICATE THE RESULTS TO SEEDLING PRODUCERS AND SEEDLING BUYERS IN OUR RESPECTIVE REGIONS, AND INTEGRATE THE RESULTS INTO OPERATIONAL PRACTICE THAT PROVIDES HANDS-ON EDUCATION FOR STUDENTS TO TRANSITION INTO THE NURSERY WORKFORCE.